,transcriber's ,notes ,small capitals have been transcribed as ,,all ,,capitals2 text in italics has been transcribed between underscores1 as text4 ,the symbol is used to represent an upside-down ,u4 ,more ,transcriber's ,notes may be found at the end of this text4 ,published by the ,mc,graw-,hill ,book ,company ,new ,york ,successors to the ,book ,departments of the ,mc,graw ,publishing ,company ,hill ,publishing ,company ,publishers of ,books for ,electrical ,world ,the ,engineering and ,mining ,journal ,the ,engineering ,record ,power and ,the ,engineer ,electric ,railway ,journal ,american ,machinist ,,electric ,,transmission ,,of ,,water ,,power ,by ,,alton ,d4 ,,adams1 ,a4,m4 ,,member ,,american ,,institute ,,of ,,electrical ,,engineers ,,new ,,york ,,mcgraw-,,hill ,,book ,,co4 #aijf ,copyrighted1 #aijf1 by the ,mc,g,r,a,w ,,publishing ,,company ,,new ,,york ,,table ,,of ,,contents ,,chapter ,,page ,i4 ,,water-,,power ,,in ,,electrical ,,supply #a ,,ii4 ,,utility ,,of ,,water-,,power ,,in ,,electrical ,,supply #aj ,,iii4 ,,cost ,,of ,,conductors ,,for ,,electric-,,power ,,transmission #ai ,,iv4 ,,advantages ,,of ,,the ,,continuous ,,and ,,alternating ,,current #ca ,v4 ,,the ,,physical ,,limits ,,of ,,electric-,,power ,,transmission #dd ,,vi4 ,,development ,,of ,,water-,,power ,,for ,,electric ,,stations #ea ,,vii4 ,,the ,,location ,,of ,,electric ,,water-,,power ,,stations #fd ,,viii4 ,,design ,,of ,,electric ,,water-,,power ,,stations #hc ,,ix4 ,,alternators ,,for ,,electrical ,,transmission #ajc ,x4 ,,transformers ,,in ,,transmission ,,systems #abb ,,xi4 ,,switches1 ,,fuses1 ,,and ,,circuit-,,breakers #ace ,,xii4 ,,regulation ,,of ,,transmitted ,,power #aee ,,xiii4 ,,guard ,,wires ,,and ,,lightning ,,arresters #afh ,,xiv4 ,,electrical ,,transmission ,,under ,,land ,,and ,,water #ahg ,,xv4 ,,materials ,,for ,,line ,,conductors #bjj ,,xvi4 ,,voltage ,,and ,,losses ,,on ,,transmission ,,lines #bae ,,xvii4 ,,selection ,,of ,,transmission ,,circuits #bcc ,,xviii4 ,,pole ,,lines ,,for ,,power ,,transmission #bdf ,,xix4 ,,entries ,,for ,,electric ,,transmission ,,lines #bfa ,,xx4 ,,insulator ,,pins #bgj ,,xxi4 ,,insulators ,,for ,,transmission ,,lines #bhg ,,xxii4 ,,design ,,of ,,insulator ,,pins ,,for ,,transmission ,,lines #bih ,,xxiii4 ,,steel ,,towers #cjf ,,index #cbg ,,electric ,,transmission ,,of ,,water-,,power4 ,,chapter ,i4 ,,water-,,power ,,in ,,electrical ,,supply4 ,electrical supply from transmitted water-power is now distributed in more than fifty cities of ,north ,america4 ,these include ,mexico ,city1 with a population of #djb1jjj2 ,buffalo and ,san ,francisco1 with #ceb1chg and #cdb1ghb respectively2 ,montreal1 with #bff1hbf1 and ,los ,angeles1 ,st4 ,paul1 and ,minneapolis1 with populations that range between #ajj1jjj and #bjj1jjj each4 ,north and south these cities extend from ,quebec to ,anderson1 and from ,seattle to ,mexico ,city4 ,east and west the chain of cities includes ,portland1 ,springfield1 ,albany1 ,buffalo1 ,hamilton1 ,toronto1 ,st4 ,paul1 ,butte1 ,salt ,lake ,city1 and ,san ,francisco4 ,to reach these cities the water-power is electrically transmitted1 in many cases dozens1 in a number of cases scores1 and in one case more than two hundred miles4 ,in the ,east1 ,canada is the site of the longest transmission1 that from ,shawinigan ,falls to ,montreal1 a distance of eighty-five miles4 ,from ,spier ,falls to ,albany the electric line is forty miles in length4 ,hamilton is thirty-seven miles from that point on the ,niagara escarpment1 where its electric power is developed4 ,between ,st4 ,paul and its electric water-power station1 on ,apple ,river1 the transmission line is twenty-five miles long4 ,the falls of the ,missouri ,river at ,caon ,ferry are the source of the electrical energy distributed in ,butte1 sixty-five miles away4 ,los ,angeles draws electrical energy from a plant eighty-three miles distant on the ,santa ,ana ,river4 ,from ,colgate power-house1 on the ,yuba1 to ,san ,francisco1 by way of ,mission ,san ,jos1 the transmission line has a length of #bbj miles4 ,between ,electra generating station in the ,sierra ,nevada ,mountains and ,san ,francisco is #aed miles by the electric line4 ,illustration3 ,,fig4 #a4--,spier ,falls ,transmission ,lines4 ,these transmissions involve large powers as well as long distances4 ,the new plant on the ,androscoggin is designed to deliver #aj1jjj horse-power for electrical supply in ,lewiston1 ,me4 ,at ,spier ,falls1 on the ,hudson1 whence energy goes to ,albany and other cities1 the electric generators will have a capacity of #cb1jjj horse-power4 ,from the two water-power stations at ,niagara ,falls1 with their twenty-one electric generators of #e1jjj horse-power each1 a total of #aje1jjj1 more than #cj1jjj horse-power is regularly transmitted to ,buffalo alone2 the greater part of the capacity being devoted to local industries4 ,electrical supply in ,st4 ,paul is drawn from a water-power plant of #d1jjj and in ,minneapolis from a like plant of #g1djj horse-power capacity4 ,the ,caon ,ferry station1 on the ,missouri1 that supplies electrical energy in both ,helena and ,butte1 has a capacity of #aj1jjj horse-power4 ,both ,seattle and ,tacoma draw electrical supply from the #h1jjj horse-power plant at ,snoqualmie ,falls4 ,the ,colgate power-house1 which develops energy for ,san ,francisco and a number of smaller places1 has electric generators of #ae1jjj horse-power aggregate capacity4 ,at the ,electra generating station1 where energy is also transmitted to ,san ,francisco and other cities on the way1 the capacity is #ac1ccj horse-power4 ,electrical supply in ,los ,angeles is drawn from the generating station of #d1jjj horse-power1 on the ,santa ,ana ,river1 and from two stations1 on ,mill ,creek1 with an aggregate of #d1fjj1 making a total capacity of not less than #h1fjj horse-power4 ,five water-power stations1 scattered within a radius of ten miles and with #d1bjj horse-power total capacity1 are the source of electrical supply in ,mexico ,city4 ,the foregoing are simply a part of the more striking illustrations of that development by which falling water is generating hundreds of thousands of horse-power for electrical supply to millions of population4 ,this application of great water powers to the industrial wants of distant cities is hardly more than a decade old4 ,ten years ago ,shawinigan ,falls was an almost unheard-of point in the wilds of ,canada4 ,spier ,falls was merely a place of scenic interest2 the ,missouri at ,caon ,ferry was not lighting a lamp or displacing a pound of coal2 that falling water in the ,sierra ,nevada ,mountains should light the streets and operate electric cars in ,san ,francisco seemed impossible1 and that diversion of ,niagara1 which seems destined to develop more than a million horse-power and leave dry the precipices over which the waters now plunge1 had not yet begun4 ,in some few instances where water-power was located in towns or cities1 it has been applied to electrical supply since the early days of the industry4 ,in the main1 however1 the supply of electrical energy from water-power has been made possible only by long-distance transmission4 ,the extending radius of electrical transmission for water-powers has formed the greatest incentive to their development4 ,this development in turn has reacted on the conditions that limit electrical supply and has materially extended the field of its application4 ,transmitted water-power has reduced the rates for electric service4 ,it may not be easy to prove this reduction by quoting figures for net rates1 because these are not generally published1 but there are other means of reaching the conclusion4 ,illustration3 ,,fig4 #b4--,snoqualmie ,falls ,transmission ,lines4 ,in the field of illumination electricity competes directly with gas1 and in the field of motive power with coal4 ,during the past decade it is well known that the price of gas has materially declined and the price of coal1 barring the recent strike period1 has certainly not increased4 ,in spite of these reductions electrical supply from water-power has displaced both gas and coal in many instances4 ,moreover1 the expansion of electric water-power systems has been decidedly greater1 as a rule1 than that of electrical supply from steam-driven stations4 ,an example of the fact last stated may be seen in ,portland1 ,me4 ,in the spring of #ahii1 a company was formed to transmit and distribute electrical energy in that city from a water-power about thirteen miles distant4 ,for some years1 prior to and since the date just named1 an extensive electric system with steam-power equipment has existed in ,portland4 ,in spite of this1 the system using water-power1 on ,january #ast1 #aijc1 had a connected load of #ceb enclosed arcs and #bj1jjj incandescent lamps1 besides #hce horse-power in motors4 ,comparing the expansion of electric water-power systems with those operated by steam1 when located in different cities1 ,hartford and ,springfield may be taken on the one hand and ,fall ,river and ,new ,bedford on the other4 ,the use of water-power in electrical supply at ,hartford began in ,november1 #ahia1 and has since continued to an increasing extent4 ,throughout the same period electrical supply in ,fall ,river has been derived exclusively from steam4 ,in #ahij the population of ,hartford was #ec1bcj1 and in #aijj it stood at #gi1hej1 an increase of #ej per cent4 ,at the beginning of the decade ,fall ,river had a population of #gd1cih1 and at its close the figures were #ajd1hfc1 a rise of #dj4i per cent4 ,in #ahib the connected load of the electric supply system at ,fall ,river included #dea arc and #g1hjj incandescent lamps1 and motors aggregating #adj horse-power4 ,by #aija this load had increased to #a1aaa arcs1 #bd1bed incandescent lamps1 and #fjj horse-power in motors4 ,the electric supply system at ,hartford in #ahib was serving #hjj arcs1 #b1jjj incandescent lamps1 and no motors4 ,after the use of transmitted water-power during nine years the connected load of the ,hartford system had come to include #a1fgi arcs1 #fh1gbe incandescent lamps1 and #c1dgf horse-power of motor capacity in #aija4 ,at the beginning of the decade ,hartford was far behind ,fall ,river in both incandescent lamps and motors1 but at the end ,hartford had nearly three times as many incandescent lamps and nearly six times as great a capacity in connected motors4 ,as ,fall ,river had a population in #aijj that was greater by thirty-one per cent4 than the population of ,hartford1 and the percentage of increase during the decade was only #i4a lower in the former city1 water-power seems to have been the most potent factor in the rise of electric loads in the latter4 ,electric gains at ,hartford could not have been due to the absence of competition by gas1 for the price of gas there in #aija was #a per #a1jjj cubic feet1 while the price in ,fall ,river was #a4aj for an equal amount4 ,water-power began to be used in electrical supply at ,springfield during the latter half of #ahig4 ,in that year the connected load of the ,springfield electric system included #a1jjf arcs1 #bd1ggh incandescent lamps1 and motors with a capacity of #fdg horse-power4 ,five years later1 in #aijb1 this connected load had risen to #a1cii arc lamps1 #de1gce incandescent lamps1 and a capacity of #a1jbe horse-power in electric motors4 ,at ,new ,bedford1 in #ahig1 the electric system was supplying #djf arc and #bb1abb incandescent lamps besides motors rated at #bih horse-power4 ,this load1 in #aijb1 had changed to #dhh arcs1 #ah1jee incandescent lamps1 and #dcb horse-power in capacity of electric motors4 ,from the foregoing figures it appears that while #hb arc lamps were added in ,new ,bedford1 #cic such lamps were added in ,springfield4 ,while the electric load at ,new ,bedford was increased by #acd horse-power of motors1 the like increase at ,springfield was #cgh horse-power1 and while the former city lost #d1jfg from its load of incandescent lamps1 the latter gained #bj1ieg of these lamps4 ,during all these changes electrical supply in ,springfield has come mostly from water-power1 and that in ,new ,bedford has been the product of steam4 ,population at ,springfield numbered #dd1agi in #ahij and #fb1jei in #aijj1 an increase of #dj4e per cent4 ,in the earlier of these years ,new ,bedford had a population of #dj1gcc1 and in the later #fb1ddb1 an increase of #ec4c per cent4 ,in #aijb the average price obtained for gas at ,springfield was #a4jd and at ,new ,bedford #a4ah per #a1jjj cubic feet4 ,springfield contains a prosperous gas system1 and the gross income there from the sale of gas was thirty-one per cent greater in #aijb than in #ahig4 ,during this same period of five years the gross income from sales of electrical energy1 developed in large part by water-power1 increased forty-seven per cent4 ,for the five years of general depression1 ending in #ahig gross annual income of gas sales in ,springfield rose only five per cent1 and the like electric income nine per cent4 ,in the five years last named the electrical supply system was operated with coal4 ,the application of transmitted water-power in electrical supply has displaced steam as a motive power in many large industrial plants that never would have been operated from steam-driven electric stations4 ,an example of this sort exists at ,portland1 where one of the motors operated by the electric water-power system1 in an industrial plant1 has a capacity of #cjj horse-power4 ,every pound of coal burned in ,concord1 ,n4 ,h41 is hauled by the single steam railway system entering that city1 which railway operates large car and repair shops there4 ,some years ago the railway installed a complete plant of engines1 dynamos1 and motors for electric-driving throughout these shops4 ,these engines and dynamos now stand idle and the motor equipment1 with an aggregate capacity of #eij horse-power1 is operated with energy purchased from the local electrical supply system and drawn from water-power4 ,another striking example of the ability of electric water-power systems to make power rates that are attractive to large manufacturers may be seen at ,manchester1 ,n4 ,h4 ,one of the largest manufacturing plants in that city purchases energy for the operation of the equivalent of more than #g1jjj incandescent lamps1 and of motors rated at #igf horse-power1 from the electrical supply system there1 whose generating stations are driven mainly by water-power4 ,the ,manchester electrical supply system also furnishes energy1 through a sub-station of #hjj-;horse-power capacity1 to operate an electric railway connecting ,manchester and ,concord4 ,this electric line is owned and operated in common with the only steam railway system of ,new ,hampshire1 so that the only inducement to purchase energy from the water-power system seems to be one of price4 ,in ,buffalo the electric transmission system from ,niagara ,falls supplies large motors of about #bj1jjj horse-power capacity in manufacturing and industrial works1 and #g1jjj horse-power to the street railway system1 besides another #d1jjj horse-power for general service in lighting and small motors4 ,few large cities in the ,united ,states have cheaper coal than ,buffalo1 and in ,portland1 ,concord1 and ,manchester coal prices are moderate4 ,in the ,rocky ,mountain region1 where coal is more expensive1 the greater part of the loads of some electric water-power systems is made up of large industrial works4 ,in ,salt ,lake ,city the electrical supply system1 which draws its energy almost exclusively from water-powers1 had a connected load of motors aggregating #b1fjj horse-power as far back as #aija1 and also furnished energy to operate the local electric railway1 and several smelters six miles south of the city1 besides all the local lighting service4 ,as good lump coal sells in ,salt ,lake for #d4ej per ton1 slack at less than one-half this figure1 and the population there by the late census was only #ec1eca1 the figures for the load of motors are especially notable4 ,at ,helena energy from the #aj1jjj horse-power station at ,caon ,ferry operates the local lighting and power systems1 two smelting and a mining plant4 ,,cities ,,with ,,electrical ,,supply ,,from ,,water-,,power4 ---------------------------------------- -------------------- ,miles from ,water-,horse-,power of ,city4 ,power to ,city4 ,water-,driven ,population4 ,stations4 ---------------------------------------- -------------------- ,mexico ,city #aj to #ae #d1bjj #djb1jjj ,buffalo #bc ,a#cj1jjj #ceb1chg ,montreal #he -- #bff1hbf ,san ,francisco #adg #ac1ccj #cdb1ghb ,minneapolis #aj #g1djj #bjb1gah ,st4 ,paul #be #d1jjj #afc1jfe ,los ,angeles #hc #h1fjj #ajb1dgi ,albany #dj #cb1jjj #id1aea ,portland1 ,ore4 -- -- #ij1dbf ,hartford #aa #c1fjj #gi1hej ,springfield1 ,mass4 #f #c1ghj #fb1jei ,manchester1 ,n4 ,h4 #ac4e #e1cgj #ei1ihg ,salt ,lake ,city #cf4e #aj1jjj #ec1eca ,portland1 ,me4 #ac #b1ffj #ej1ade ,seattle -- #h1jjj #hj1fga ,butte #fe #aj1jjj #cj1dgj ,oakland #adb #ae1jjj #ff1ijj ,lewiston1 ,me4 #c #c1jjj #bc1gfa ,concord1 ,n4 ,h4 #d #a1jjj #ai1fcb ,helena1 ,mont4 #bj -- #aj1ggj ,hamilton1 ,ont4 #ce #h1jjj ,quebec #g #c1jjj ,dales1 ,ore4 #bg #a1ccj ---------------------------------------- -------------------- ,a ,power received4 ,in ,butte1 energy from the station just named operates the works of five smelting and mining companies1 driving motors that range from #a to #hjj horse-power in individual capacity4 ,the capacity of the ,butte sub-station is #g1fjj horse-power4 ,the great electric water power system marked by the ,santa ,ana station at one end and the city of ,los ,angeles at the other1 eighty-three miles distant1 includes more than #afj miles of transmission lines1 several hundred miles of distribution circuits1 and supplies light and power in twelve cities and towns4 ,among the customers of this system are an electric railway1 a number of irrigation plants1 and a cement works4 ,these works contain motors that range from #aj to #bjj horse-power each in capacity4 ,motors of fifty horse-power or less are used at pumping stations in the irrigation systems4 ,applications of water-power in electrical supply during the past decade have prepared the way for a much greater movement in this direction4 ,work is now under way for the electric transmission of water-power1 either for the first time or in larger amounts1 to ,albany1 ,toronto1 ,chicago1 ,duluth1 ,portland1 ,oregon1 ,san ,francisco1 ,los ,angeles1 and dozens of other cities that might be named4 ,another ten years will see the greater part of electrical supply on the ,american continent drawn from water-power4 ,only the largest city supplied from each water-power is named above4 ,thus the same transmission system enters ,albany1 ,troy1 ,schenectady1 ,saratoga1 and a number of smaller places4 ,,chapter ,,ii4 ,,utility ,,of ,,water-,,power ,,in ,,electrical ,,supply4 ,in comparatively few systems is the available water-power sufficient to carry the entire load at all hours of the day1 and during all months of the year1 so that the question of how much fuel can be saved is an uncertain one for many plants4 ,again1 the development of water-power often involves a large investment1 and may bring a burden of fixed charges greater than the value of the fuel saved4 ,in spite of these conflicting opinions and factors1 the application of water-power in electrical systems is now going on faster than ever before4 ,if a saving of fuel1 measured by the available flow of water during those hours when it can be devoted directly to electrical supply1 were its only advantage1 the number of cases in which this power could be utilized at a profit would be relatively small4 ,if1 on the other hand1 all of the water that passes down a stream could be made to do electrical work1 and if the utilization of this water had other advantages nearly or quite as great as the reduction of expense for coal1 then many water-powers would await only development to bring profit to their owners4 ,no part of the problem is more uncertain than the first cost and subsequent fixed charges connected with the development of water-power4 ,to bring out the real conditions1 the detailed facts as to one or more plants may be of greater value than mere general statements covering a wide range of cases4 ,on a certain small river the entire water privilege at a point where a fall of fourteen feet could be made available was obtained several years ago4 ,at this point a substantial stone and concrete dam was built1 and also a stone and brick power-house with concrete floor and steel truss roof4 ,in this power-house were installed electric generators of #hjj kilowatts total capacity1 direct-connected to horizontal turbine wheels4 ,the entire cost of the real estate necessary to secure the water-power privilege plus the cost of all the improvements was about #acj1jjj4 ,more than enough water-power to drive the #hjj-kilowatt generators at full load was estimated to be available1 except at times of exceptionally low water4 ,at this plant the investment for the water-power site1 development1 and complete equipment was thus #afb per kilowatt capacity of generators installed4 ,allowing #fe days of low water1 these generators of #hjj kilowatts capacity may be operated #cjj days per year4 ,if the running time averages ten hours daily at full load1 the energy delivered per year is #b1djj1jjj kilowatt hours4 ,ten per cent of the total investment should be ample to cover interest and depreciation charges1 and this amounts to #ac1jjj yearly4 ,it follows that the items of interest and depreciation on the original investment represent a charge of #j4ed cent per kilowatt hour on the assumed energy output at this plant4 ,this energy is transmitted a few miles and used in the electrical supply system of a large city4 ,on another river the entire water privilege was secured about four years ago at a point where a fall of more than #bj feet between ledges of rock could be obtained and more than #b1jjj horse-power could be developed4 ,at this point a masonry dam and brick power-house were built1 and horizontal turbine wheels were installed1 direct-connected to electric generators of #a1ejj kilowatts total capacity4 ,the entire cost of real estate1 water rights1 dam1 building1 and equipment in this case was about #bej1jjj4 ,assuming1 as before1 that generators may be operated at full capacity for #aj hours per day during #cjj days per year1 the energy delivered by this plant amounts to #d1ejj1jjj kilowatt hours yearly4 ,the allowance of #aj per cent on the entire investment for interest and depreciation is represented by #be1jjj yearly in this case1 or #j4ef cent per kilowatt hour of probable output4 ,energy from this plant is transmitted and used in a large system of electrical supply4 ,if1 through lack of water or inability to store water or energy at times when it is not wanted1 generators cannot be operated at full capacity during the average number of hours assumed above1 the item of interest and depreciation per unit of delivered energy must be higher than that computed4 ,with the possible figure for this item at less than six-tenths of a cent per kilowatt hour1 there is opportunity for some increase before it becomes prohibitive4 ,at the plant last named the entire investment amounted to #aff per kilowatt capacity of connected generators1 compared with #afb in the former case1 and these figures may be taken as fairly representative for the development of water-power in a first-class manner on small rivers1 under favorable conditions4 ,in both of these instances the power-houses are quite close to the dams4 ,if long canals or pipe lines must be built to convey the water1 the expense of development may be greatly increased4 ,one advantage of water- over steam-power is the smaller cost of the building with the former for a given capacity of plant4 ,the building for direct-connected electric generators1 driven by water-wheels1 is relatively small and simple4 ,space for fuel1 boilers1 economizers1 feed-water heaters1 condensers1 steam piping1 and pumps is not required where water-power is used4 ,no chimney or apparatus for mechanical draught is needed4 ,the model electric station operated by water-power usually consists of a single room with no basement under it4 ,one such station has floor dimensions #bg by #eb feet1 giving an area of #a1djd square feet1 and contains generators of #hjj kilowatts capacity4 ,this gives #a4ge square feet of floor space per kilowatt of generators4 ,in this station there is ample room for all purposes1 including erection or removal of machinery4 ,next to the saving of fuel1 the greatest advantage of water-power is due to the relatively small requirements for labor at generating stations where it is used4 ,this is well illustrated by an example from actual practice4 ,in a modern water-power station that contributes to electrical supply in a large city the generator capacity is #a1bjj kilowatts4 ,all of the labor connected with the operation of this station during nearly twenty-four hours per day is done by two attendants working alternate shifts4 ,these attendants live close to the station in a house owned by the electric company1 and receive #fj each per month in addition to house rent4 ,considering the location1 #ab per month is probably ample allowance for the rent4 ,this brings the total expense of operation at this station for labor up to #acb per month1 or #a1ehd per year1 a sum corresponding to #a4cb yearly per kilowatt of generator capacity4 ,at steam-power stations of about the above capacity1 operating twenty-four hours daily1 #f is an approximate yearly cost of labor per kilowatt of generators in use4 ,it thus appears that water-power plants may be operated at less than one-fourth of the labor expense necessary at steam stations per unit of capacity4 ,on an average1 the combined cost of fuel and labor at electric stations driven by steam-power is a little more than #gf per cent of their total cost of operation4 ,of this total1 labor represents about #bh1 and fuel about #dh per cent4 ,water-power1 by dispensing with fuel and with three-fourths of the labor charge1 reduces the expense of operation at electric stations by fully #fi per cent4 ,but this great saving in the operating expenses of electric stations can be made only where water entirely displaces coal4 ,if part water-power and part coal are used1 the result depends on the proportion of each1 and is obviously much affected by the variations of water-power capacity4 ,in such a mixed system the saving effected by water-power must also depend on the extent to which its energy can be absorbed at all hours the day4 ,by far the greater number of electric stations using water-power are obliged also to employ steam during either some months in the year or some hours in the day1 or both4 ,illustration3 ,,energy ,,curves ,,from ,,water ,,power ,,electric ,,stations4 ,,fig4 #c4 ,it is highly important1 therefore1 to determine1 as nearly as may be1 the answers to three questions3 ,first1 what variations are to be expected in the capacity of a water-power during the several months of a year8 ,second1 if the daily flow of water is equal in capacity to the daily output of electrical energy1 how far can the water-power be devoted to the development of that energy8 ,third1 with a water-power sufficient to carry all electrical loads at times of moderately high water1 what percentage of the yearly output of energy in a general supply system can be derived from the water8 ,to the first of these questions experience alone can furnish an answer4 ,variations in the discharge of rivers during the different months of a year are very great4 ,in a plant laid out with good engineering skill some provision will be made for the storage of water1 and the capacity of generating equipment will correspond to some point between the highest and lowest rates of discharge4 ,curve ,no4 #a in the diagram on the opposite page represents the energy output at an electric station driven entirely by water-power from a small stream during the twelve months of #aija1 the entire flow of the stream being utilized4 ,during ,december1 #aija1 the output of this station was #ebg1gjj kilowatts1 and was greater than that in any other month of the year4 ,taking this output at #ajj per cent1 the curve is platted to show the percentage attained by the delivered energy in each of the other months4 ,at the lowest point on the curve1 corresponding to the month of ,february1 the output of energy was only slightly over #cc per cent of that in ,december4 ,during nine other months of the year the proportion of energy output to that in ,december was over #fj and in three months over #hj per cent4 ,for the twelve months the average delivery of energy per month was #gc4g per cent of that during ,december4 ,,percentages ,,of ,,energy ,,delivered ,,in ,,different ,,months1 #aija4 ,january #fh4j ,february #cc4a ,march #hj4e ,april #ha4g ,may #gg4i ,june #eh4f ,july #fg4g ,august #ge4h ,september #gi4c ,october #fe4i ,november #ie4h ,december #ajj4j ,at a somewhat small water-power station on another river with a watershed less precipitous than that of the stream just considered1 the following results were obtained during the twelve months ending ,june #cjth1 #aijj4 ,for this plant the largest monthly output of energy was in ,november1 and this output is taken at #ajj per cent4 ,the smallest delivery of energy was in ,october1 when the percentage was #ec4a of the amount for ,november4 ,in each of seven other months of the year the output of energy was above #hj per cent of that in ,november4 ,during ,march1 ,april1 ,may1 and ,june the water-power yielded all of the energy required in the electrical supply system with which it was connected1 and could1 no doubt1 have done more work if necessary4 ,for the twelve months the average delivery of energy per month was #hj4f per cent of that in ,november1 the month of greatest output4 ,,percentages ,,of ,,energy ,,delivered ,,in ,,different ,,months1 #ahii ,,and #aijj4 ,july #fh4f ,august #fi4a ,september #gc4c ,october #ec4a ,november #ajj4j ,december #hg4j ,january #hd4i ,february #ia4c ,march #ih4e ,april #he4g ,may #hj4h ,june #gd4i ,the gentler slopes and better storage facilities of this second river show their effect in an average monthly delivery of energy #f4i per cent higher as to the output in a month when it was greatest than the like percentage for the water-power first considered4 ,these two water-power illustrate what can be done with only very moderate storage capacities on the rivers involved4 ,at both stations much water escapes over the dams during several months of each year4 ,with enough storage space to retain all waters of these rivers until wanted the energy outputs could be largely increased4 ,as may be seen by inspection of curve ,no4 #b1 the second water-power has smaller fluctuations of capacity1 as well as a higher average percentage of the maximum output than the water-power illustrated by curve ,no4 #a4 ,if the discharge of a stream during each twenty-four hours is just sufficient to develop the electrical energy required in a supply system during that time1 the water may be made to do all of the electrical work in one of two ways4 ,if the water-power has enough storage capacity behind it to hold the excess of water during some hours of the day1 then it is only necessary to install enough water-wheels and electric generators to carry the maximum load4 ,should the storage capacity for water be lacking1 or the equipment of generating apparatus be insufficient to work at the maximum rate demanded by the electrical system1 then an electric storage battery must be employed if all of the water is to be utilized and made to do the electrical work4 ,the greatest fluctuations between maximum and minimum daily loads at electric lighting stations usually occur in ,december and ,january4 ,the extent of these fluctuations is illustrated by curve ,no4 #c1 which represents the total load on a large electrical supply system during a typical week-day of ,january1 #aija4 ,on this day the maximum load was #b1gbj and the minimum load #fab kilowatts1 or #bb4e per cent of the highest rate of output4 ,during the day in question the total delivery of energy for the twenty-four hours was #cj1bdi kilowatt hours1 so that the average load per hour was #a1bfj kilowatts4 ,this average is #df per cent of the maximum load4 ,computation of the area included by curve ,no4 #c above the average load line of #a1bfj kilowatts shows that about #ag4h per cent of the total output of energy for the day was delivered above the average load1 that is1 in addition to an output at average load4 ,it further appears by inspection of this load curve that this delivery of energy above the average load line took place during #ab4c hours of the day1 so that its average rate of delivery per hour was #dch kilowatts4 ,if a water-power competent to carry a load of #a1bfj kilowatts twenty-four hours per day be applied to the system illustrated by curve ,no4 #c1 then about #ag4h per cent of the energy of the water for the entire day must be stored during #aa4g hours and liberated in the remaining #ab4c hours4 ,this percentage of the total daily energy of the water amounts to #cf per cent of its energy during the hours that storage takes place4 ,if all of the storage is done with water1 the electric generators must be able to work at the rate of #b1gbj kilowatts1 the maximum load4 ,if all of the storage is done in electric batteries1 the use of water may be uniform throughout the day1 and the generator capacity must be enough above #a1bfj kilowatts to make up for losses in the batteries4 ,where batteries are employed the amount of water will be somewhat greater than that necessary to operate the load directly with generators1 because of the battery losses4 ,in spite of the large fluctuations of electrical loads throughout each twenty-four hours1 it is thus comparatively easy to operate them with water-powers that are little1 if any1 above the requirements of the average loads4 ,perhaps the most important question relating to the use of water-power in electrical supply is what percentage of the yearly output of energy can be derived from water where this power is sufficient to carry the entire load during a part of the year4 ,with storage area for all surplus water in any season1 the amount of work that could be done by a stream might be calculated directly from the records of its annual discharge of water4 ,as such storage areas for surplus water have seldom1 or never1 been made available in connection with electrical systems1 the best assurance as to the percentage of yearly output that may be derived from water-power is found in the experience of existing plants4 ,the question now to be considered differs materially from that involving merely the variations of water-power in the several months1 or even the possible yearly output from water-power4 ,the ratio of output from water-power to the total yearly output of an electrical system includes the result of load fluctuations in every twenty-four hours and the variable demands for electrical energy in different months1 as well as changes in the amount of water-power available through the seasons4 ,in order to show the combined result of these three important factors curve ,no4 #d has been constructed4 ,this indicates the percentages of total semi-yearly outputs of electrical energy derived from water-power in two supply systems4 ,each half-year extends either from ,january to ,june1 inclusive1 or from ,july to ,december1 inclusive1 and thus covers a wet and dry season4 ,each half-year also includes a period of maximum and one of minimum demand for electrical energy in lighting4 ,the period of largest water supply usually nearly coincides with that of heaviest lighting load1 but this is not always true4 ,electrical systems have purposely been selected in which the water-power in at least one month of each half-year was nearly or quite sufficient to carry the entire electrical load4 ,the percentage of energy from water-power to the total energy delivered by the system is presented for each of five half-years4 ,three of the half-years each run from ,july to ,december1 and two extend from ,january to ,june1 respectively4 ,the half years that show percentages of #ff4h1 #hj4b1 and #ie4f1 respectively1 for the relation of energy from water-power to the total electrical output relate to one system1 and the half years that show percentages of #ha4ig and #id4c for the energy from water-power relate to another system4 ,for the half-year when #ff4h per cent4 of the output of the electrical system was derived from water-power1 the total output of the system was #c1iff1jbf kilowatt hours4 ,during the month of ,december in this half-year more than #ih per cent of the electrical energy delivered by the system was from water-power1 though the average for the six months was only #ff4h per cent from water4 ,in the following six months1 from ,january to ,june1 the electrical supply system delivered #d1afa1ged kilowatt hours1 and of this amount the water-power furnished #hj4b per cent4 ,for the six months just named1 one month1 ,may1 saw #ii per cent of all the delivered energy derived from water-power4 ,the same system during the next half-year1 from ,july to ,december1 without any addition to its water-power development or equipment1 got #ie4f per cent of its entire energy output from water-power1 and this output amounted to #d1dae1ide kilowatt hours4 ,in one month of the half-year just named only #j4b per cent of the output was generated with steam-power4 ,these three successive half years illustrate the fluctuations of the ratio between water-power outputs and the demands for energy on a single system of electrical supply4 ,the percentage of #ha4i for energy derived from water-power during the half-year from ,july to ,december represents the ratio of output from water to the total for an electrical supply system where water generated #id per cent of all the energy delivered in one month4 ,in the same system during the following six months1 with exactly the same water-power equipment1 the percentage of output from water-power was #id4c of the total kilowatt-hours delivered by the system4 ,this result was reached in spite of the fact that the total outputs of the system in the two half-years were equal to within less than one per cent4 ,the lesson from the record of these five half-years is that comparatively large variations are to be expected in the percentage of energy developed by water-power to the total output of electrical supply systems in different half-years4 ,but1 in spite of these variations1 the portion of electrical loads that may be carried by water-power is sufficient to warrant its rapidly extending application to lighting and power in cities and towns4 ,,chapter ,,iii4 ,,cost ,,of ,,conductors ,,for ,,electric-,,power ,,transmission4 ,electrical transmission of energy involves problems quite distinct from its development4 ,a great water-power1 or a location where fuel is cheap1 may offer opportunity to generate electrical energy at an exceptionally low cost4 ,this energy may be used so close to the point of its development that the cost of transmission is too small for separate consideration4 ,an example of conditions where the important problems of transmission are absent exists in the numerous factories grouped about the great water-power plants at ,niagara and drawing electrical energy from it4 ,in such a case energy flows directly from the dynamos1 driven by water-power1 to the lamps1 motors1 chemical vats1 and electric heaters of consumers through the medium1 perhaps1 of local transformers4 ,here the costs and losses of transmitting or distributing equipments are minor matters1 compared with the development of the energy4 ,if1 now1 energy from the water-power is to be transmitted over a distance of many miles1 a new set of costs is to be met4 ,in the first place1 it will be necessary to raise the voltage of the transmitted energy much above the pressure at the dynamos in order to save in the weight and cost of conductors for the transmission line4 ,this increase of voltage requires transformers with capacity equal to the maximum rate at which energy is to be delivered to the line4 ,these transformers will add to the cost of the energy that they deliver in two ways3 by the absorption of some energy to form heat1 and by the sum of annual interest1 maintenance1 and depreciation charges on the price paid for them4 ,other additions to the cost of energy delivered by the transmission line must be made to cover the annual interest1 maintenance1 and depreciation charges on the amount of the line investment1 and to pay for the energy changed to heat in the line4 ,near the points where the energy is to be used1 the transmission line must end in transformers to reduce the voltage to a safe figure for local distribution4 ,this second set of transformers will further add to the cost of the delivered energy in the same ways as the former set4 ,from these facts it is evident that1 to warrant an electrical transmission1 the value of energy at the point of distribution should at least equal the value at the generating plant plus the cost of the transmission4 ,knowing the cost of energy at one end of the transmission line and its value at the other1 the difference between these two represents the maximum cost at which the transmission will pay4 ,three main factors are concerned in the cost of electric power transmission1 namely1 the transformers1 the pole line1 and the wire or conductors4 ,these factors enter into the cost of transmitted energy in very different degrees1 according to the circumstances of each case4 ,the maximum and average rates of energy transmission1 the total voltage1 the percentage of line loss1 and the length of the line mainly determine the relative importance of the transformers1 pole line1 and conductors in the total cost of delivered energy4 ,first cost of transformers varies directly with the maximum rate of transmission1 and is nearly independent of the voltage1 the length of the transmission1 and the percentage of line loss4 ,a pole line changes in first cost with the length of the transmission1 but is nearly independent of the other factors4 ,line conductors1 for a fixed maximum percentage of loss1 vary in first cost directly with the square of the length of the transmission and with the rate of the transmission2 but their first cost decreases as the percentage of line loss increases and as the square of the voltage of transmission increases4 ,if a given amount of power is to be transmitted1 at a certain percentage of loss in the line and at a fixed voltage1 over distances of #ej1 #ajj1 and #bjj miles1 respectively1 the foregoing principles lead to the following conclusions3 ,the capacity of transformers1 being fixed by the rate of transmission1 will be the same for either distance1 and their cost is therefore constant4 ,transformer losses1 interest1 depreciation1 and repairs are also constant4 ,the cost of pole line1 depending on its length1 will be twice as great at #ajj and four times as great at #bjj as at #ej miles4 ,interest1 depreciation1 and repairs will also go up directly with the length of the pole lines4 ,line conductors will cost four times as much for the #ajj- as for the #ej-mile transmission1 because their weight will be four times as great1 and the annual interest and depreciation will go up at the same rate4 ,for the transmission of #bjj miles the cost of line conductors and their weight will be sixteen times as great as the cost at #ej miles4 ,it follows that interest1 depreciation1 and maintenance will be increased sixteen times with the #bjj-mile transmission over what they were at #ej miles1 if voltage and line loss are constant4 ,a concrete example of the cost of electric power transmission over a given distance will illustrate the practical application of these principles4 ,let the problem be to deliver electrical energy in a city distant #ajj miles from the generating plant4 ,transformers with approximately twice the capacity corresponding to the maximum rate of transmission must be provided1 because one set is required at the generating and another at the delivery station4 ,the cost of these transformers will be approximately #g4ej per horse-power for any large capacity4 ,reliability is of the utmost importance in a great power transmission1 and this requires a pole line of the most substantial construction4 ,such a line in a locality where wooden poles can be had at a moderate price will cost1 with conductors in position1 about #gjj per mile1 exclusive of the cost of the conductors themselves or of the right of way but including the cost of erecting the conductors4 ,the #ajj miles of pole line in the present case should1 therefore1 be set down at a cost of #gj1jjj4 ,a large delivery of power must be made to warrant the construction of so long and expensive a line1 and #aj1jjj horse-power may be taken as the maximum rate of delivery4 ,on the basis of two horse-power of transformer capacity for each horse-power of the maximum delivery rate1 transformers with a capacity of #bj1jjj horse-power are necessary for the present transmission4 ,at #g4ej per horse-power capacity1 the first cost of these transformers is #aej1jjj4 ,before the weight and cost of line conductors can be determined1 the voltage at which the transmission shall be carried out and the percentage of the energy to be lost in the conductors at periods of maximum load must be decided on4 ,the voltage to be used is a matter of engineering judgment1 based in large part on experience1 and cannot be determined by calculation4 ,in a transmission of #ajj miles the cost of conductors is certain to be a very heavy item1 and1 as this cost decreases as the square of the voltage goes up1 it is desirable to push the voltage as high as the requirements for reliable service permit4 ,a transmission line #adb miles long1 from the mountains to ,oakland1 ,cal41 has been in constant and successful use for several years with #dj1jjj volts pressure4 ,this line passes through wet as well as dry climate4 ,it seems safer to conclude1 therefore1 that #dj1jjj volts may be used in most places with good results4 ,having decided on the amount of power and the voltage and length of the transmission1 the required weight of conductors will vary inversely as the percentage of energy lost as heat in the line4 ,the best percentage of loss depends on the number of factors1 some of which1 such as the cost of energy at the generating plant1 are peculiar to each case4 ,as a provisional figure1 based in part on the practice elsewhere1 the loss on the line here considered may be taken at #aj per cent4 when transmitting the full load of #aj1jjj horse-power4 ,if the line is constructed on this basis the percentage of loss will be proportionately less for any smaller load4 ,thus1 when the line is transmitting only #e1jjj horse-power1 the loss will amount to #e per cent4 ,during the greater portion of each day the demand for power is certain to be less than the maximum figure1 so that a maximum loss of #aj per cent will correspond to an average loss on all the power delivered to the line of probably less than #g per cent4 ,in order to deliver #aj1jjj horse-power by the transformers at a receiving station from a generating plant #ajj miles distant where the pressure is #dj1jjj volts1 the copper conductors must have a weight of about #a1ejj1jjj pounds1 if the loss of energy in them is #aj per cent of the energy delivered to the line4 ,taking these conductors at a medium price of #ae cents per pound1 their cost amounts to #bbe1jjj4 ,the combined cost of the transformers1 pole line1 and line conductors1 as now estimated1 amounts to #dde1jjj4 ,no account is taken of the right-of-way for the pole line1 because in many cases this would cost nothing1 the public roads being used for the purpose2 in other cases the cost might vary greatly with local conditions4 ,the efficiency of the transmission is measured by the ratio of the energy delivered by the transformers at the receiving station for local distribution to the energy delivered by the generating plant to the transformers that supply energy to the line for transmission4 ,if worked at full capacity the large transformers here considered would have an efficiency of nearly #ih per cent2 but as they must work1 to some extent1 on partial loads1 the actual efficiency will hardly exceed #if per cent4 ,the efficiency of the line conductors rises on partial loads1 and may be safely taken at #ic per cent for all of the energy transmitted1 though it is only #ij per cent on the maximum load4 ,the combined efficiencies of the two sets of transformers and the line give the efficiency of the transmission1 which equals the product of #j4if #j4ic #j4if1 or almost exactly #he4g per cent4 ,in other words1 the transformers at the water-power station absorb #a4ag times as much energy as the transformers at the receiving station deliver to distribution lines in the place of use4 ,interest1 maintenance1 and depreciation of this complete transmission system are sufficiently provided for by an allowance of #ae per cent yearly on its entire first cost4 ,as the total first cost of the transmission system was found to be #dde1jjj1 the annual expense of interest1 depreciation1 and repairs at #ae per cent of this sum amounts to #ff1gej4 ,in order to find the bearings of this annual charge on the cost of power transmission the total amount of energy transmitted annually must be determined4 ,the #aj1jjj horse-power delivered by the system at the sub-station is simply the maximum rate at which energy may be supplied1 and the element of time must be introduced in order to compute the amount of transmitted energy4 ,if the system could be kept at work during twenty-four hours a day at full capacity1 the delivered energy would be represented by the product of the numbers which stand for the capacity and for the total number of hours yearly4 ,unfortunately1 however1 the demands for electric light and power vary through a wide range in the course of each twenty-four hours1 and the period of maximum demand extends over only a small part of each day4 ,the problem is1 therefore1 to find what relation the average load that may be had during the twenty-four hours bears to the capacity required to carry this maximum load4 ,as the answer to this question depends on the power requirements of various classes of consumers1 it can be obtained only by experience4 ,it has been found that some electric stations1 working twenty-four hours daily on mixed loads of lamps and stationary motors1 can deliver energy to an amount represented by the necessary maximum capacity during about #c1jjj hours per year4 ,applying this rule to the present case1 the transformers at the sub-station1 if loaded to their maximum capacity of #aj1jjj horse-power by the heaviest demands of consumers1 may be expected to deliver energy to the amount of #c1jjj #aj1jjj #cj1jjj1jjj horse-power hours yearly4 ,the total cost of operation for this transmission system was found above to be #ff1gej per annum1 exclusive of the cost of energy at the generating plant4 ,this sum1 divided by #cj1jjj1jjj1 shows the cost of energy transmission to be #j4bbb cent per horse-power hour1 exclusive of the first cost of the energy4 ,to obtain the total cost of transmission1 the figures just given must be increased by the value of the energy lost in transformers and in the line conductors4 ,in order to find this value1 the cost of energy at the generating plant must be known4 ,the cost of electrical energy at the switchboard in a water-power station is subject to wide variations1 owing to the different investments necessary in the hydraulic work per unit of power developed4 ,with large powers1 such as are here considered1 a horse-power hour of electrical energy may be developed for materially less than #j4e cent in some plants4 ,as the average efficiency of the present transmission has been found to be #he4g per cent of the energy delivered by the generators1 it is evident that #a4ag horse-power hours must be drawn from the generators for every horse-power hour supplied by the transformers at the sub-station for distribution4 ,in other words1 #j4ag horse-power hour is wasted for each horse-power hour delivered4 ,the cost of #j4ag of a horse-power hour1 or say not more than #j4e #j4ag #j4jhe cent1 must thus be added to the figures for transmission cost already found1 that is1 #j4bbb cent per horse-power hour1 to obtain the total cost of transmission4 ,the sum of these two items of cost amounts to #j4cjg cent per horse-power hour1 as the entire transmission expense4 ,it may now be asked how the cost of transmission just found will increase if the distance be extended4 ,as an illustration1 assume the length of the transmission to be #aej instead of #ajj miles4 ,let the amount of energy delivered by the sub-station1 the loss in line conductors1 and the energy drawn from the generating plant remain the same as before4 ,evidently the cost of the pole line will be increased #ej per cent1 that is1 from #gj1jjj to #aje1jjj4 ,transformers1 having the same capacity1 will not be changed from the previous estimate of #aej1jjj4 ,if the voltage of the transmission remain constant1 as well as the line loss at maximum load1 the weight and cost of copper conductors must increase with the square of the distances of transmission4 ,for #aej miles the weight of copper will thus be #b4be times the weight required for the #ajj-mile transmission4 ,instead of an increase in the weight of conductors a higher voltage may be adopted4 ,the transformers for the two great transmission systems that extend over a distance of about #aej miles1 from the ,sierra ,nevada ,mountains to ,san ,francisco ,bay1 in ,california1 are designed to deliver energy to the line at either #dj1jjj or #fj1jjj volts1 as desired4 ,though the regular operation at first was at the lower pressure1 the voltage has been raised to #fj1jjj4 ,the lower valleys of the ,sacramento and the ,san ,joaquin rivers1 which are crossed by these ,california systems1 as well as the shores of ,san ,francisco ,bay1 have as much annual precipitation and as moist an atmosphere as most parts of the ,united ,states and ,canada4 ,therefore there seems to be no good reason to prevent the use of #fj1jjj volts elsewhere4 ,the distance over which energy may be transmitted at a given rate1 with a fixed percentage of loss and a constant weight of copper1 goes up directly with the voltage employed4 ,this rule follows because1 while the weight of conductors to transmit energy at a given rate1 with a certain percentage of loss and constant voltage1 increases as the square of the distance1 the weight of conductors decreases as the square of the voltage when all the other factors are constant4 ,applying these principles to the #aej-mile transmission1 it is evident that an increase of the voltage to #fj1jjj will allow the weight of conductors to remain exactly where it was for the transmission of #ajj miles1 the rate of working and the line loss being equal for the two cases4 ,the only additional item of expense in the #aej-mile transmission1 on the basis of #fj1jjj volts1 is the #ce1jjj for pole line4 ,allowing #ae per cent on the #ce1jjj to cover interest1 depreciation1 and maintenance1 as before1 makes a total yearly increase in the costs of transmission of #e1bej over that found for the transmission of #ajj miles4 ,this last sum amounts to #j4jage cent per horse-power hour of the delivered energy4 ,the cost of transmission is thus raised to #j4cjg #j4jage #j4cbd cent per horse-power hour of delivered energy on the #aej-mile system with #fj1jjj volts4 ,existing transmission lines not only illustrate the relations of the factors named above to the cost and weight of conductors1 but also show marked variations of practice1 corresponding to the opinions of different engineers4 ,in order to bring out the facts on these points1 the data of a number of transmission lines are here presented4 ,on these lines the distance of transmission varies between #e and #adb miles1 the voltage from #e1jjj to #ej1jjj1 and the maximum rate of work from a few hundred to some thousands of horse-power4 ,for each transmission the single length and total weight of conductors1 the voltage1 and the capacity of the generating equipment that supplies the line is recorded4 ,from these data the volts per mile of line1 weight and cost of conductors per kilowatt capacity of generating equipment1 and the weight of conductors per mile for each kilowatt of capacity in the generating equipment are calculated4 ,in each case the length of line given is the distance from the generating to the receiving station4 ,the capacity given for generating equipment in each case is that of the main dynamos1 where their entire output goes to the transmission line in question1 but where the dynamos supply energy for other purposes also1 the rating of the transformers that feed only the particular transmission line is given as the capacity of generating equipment4 ,,distance ,,and ,,voltage ,,of ,,electrical ,,transmission4 ---------------------------------------- ------------------------ ,distance in ,volts4 ,volts per ,miles4 ,mile4 ---------------------------------------- ------------------------ ,colgate to ,oakland1 ,cal4 #adb #fj1jjj #dbb ,caon ,ferry to ,butte1 ,mont4 #fe #ej1jjj #gfi ,santa ,ana ,river to ,los ,angeles #hc #cc1jjj #cig ,ogden to ,salt ,lake ,city1 ,utah #cf4e #af1jjj #dch ,madrid to ,bland1 ,n4 ,m4 #cb #bj1jjj #fbe ,welland ,canal to ,hamilton1 ,can4 #ce #bb1ejj #fdc #cg ,san ,gabriel ,caon to ,los ,angeles #bc #af1jjj #fie ,caon ,city to ,cripple ,creek1 ,colo4 #bc4e #bj1jjj #hea ,apple ,river to ,st4 ,paul1 ,minn4 #be #be1jjj #a1jjj ,yadkin ,river to ,salem1 ,n4 ,c4 #ad4e #ab1jjj #hbg ,into ,victor1 ,colo4 #h #ab1fjj #a1ege ,montmorency ,falls to ,quebec #g #e1ejj #ghe ,farmington ,river to ,hartford #aa #aj1jjj #iji ,sewall's ,falls to ,r4,r4 shops ,concord #e4e #aj1jjj #a1hah ,wilbraham to ,ludlow ,mills #d4e #aa1ejj #b1eee ,to ,dales1 ,ore4 #bg #bb1jjj #had ---------------------------------------- ------------------------ ,the transmission systems here considered have been selected because it was possible to obtain the desired data as to each1 and it may be presumed that they fairly illustrate present practice4 ,it may be noted at once that in general the line voltage is increased with the length of the transmission4 ,thus1 the transmission for the ,ludlow ,mills over a distance of #d4e miles is carried out at #aa1ejj volts4 ,on the other hand1 the transmission between ,caon ,ferry and ,butte1 a distance of #fe miles1 employs #ej1jjj volts and represents recent practice4 ,the system from ,colgate to ,oakland1 a distance of #adb miles1 the longest here considered1 now has #fj1jjj volts on its lines4 ,in spite of the general resort to high pressures with greater distances of transmission1 the rise in voltage has not kept pace with the increasing length of line4 ,for the ,wilbraham-,ludlow transmission the total pressure amounts to #b1eee volts per mile1 while the line from ,colgate to ,oakland with #ca4e times the length of the former operates at an average of only #dbb volts per mile4 ,of the fifteen transmissions considered1 six are over distances of less than #ae miles1 and for four of the six the voltage is more than #ijj per mile4 ,eight transmissions range from #bc to #hc miles in length1 with voltages that average between #a1jjj volts per mile at #be miles and only #cig per mile on the #hc-mile line4 ,the volts per mile are #f times as great in the ,ludlow as in the ,oakland transmission4 ,,capacity ,,of ,,generating ,,stations ,,and ,,weight ,,of ,,conductors4 ---------------------------------------- ---------------------------- ,kilowatt ,total ,weight ,pounds of ,capacity at of ,conductors ,location of ,transmission4 ,generators4,conductors4 per ,kilowatt ,capacity4 ---------------------------------------- ---------------------------- ,wilbraham to ,ludlow #d1fjj #ag1hbj #c4g;,a ,sewall's ,falls to railroad shops #ej #f1iad #ae ,into ,victor1 ,colo4 #a1fjj #ae1ifj #aj ,to ,dales1 ,ore4 #a1jjj #cc1ici #cd ,apple ,river to ,st4 ,paul #c1jjj #aei1fjj #ec ,farmington ,river to ,hartford #a1ejj #ed1jed #cf ,caon ,city to ,cripple ,creek #a1ejj #ei1jgi #ci ,yadkin ,river to ,salem #a1ejj #eh1jgc #ci ,montmorency ,falls to ,quebec #b1djj #ahi1jef #gi ,caon ,ferry to ,butte #e1gjj #feh1cbj #aae ,san ,gabriel ,caon to ,los ,angeles #a1bjj #gc1jjb #fa ,welland ,canal to ,hamilton #f1jjj #cgf1did #fc ,madrid to ,bland1 ,n4 ,m4 #fjj #abg1fhj #bab ,ogden to ,salt ,lake ,city #b1bej #bib1cfe #abi ,santa ,ana ,river to ,los ,angeles #b1bej #ffd1hcj #bie ,colgate to ,oakland #aa1bej #ijf1ied #ha #ddf1fbg #dj;,a ---------------------------------------- ---------------------------- ,a ,aluminum4 ,these wide variations in the volts per mile on transmission lines and in length of lines lead to different weights of conductors per kilowatt of generator capacity4 ,all other factors remaining constant1 the weight of conductors per kilowatt of generator capacity would be the same whatever the length of the transmission1 provided that the volts per mile were uniform for all cases4 ,one important factor1 the percentage of loss for which the line conductors are designed at full load1 is sure to vary in different cases1 and lead to corresponding variations in the weights of conductors per kilowatt of generator capacity4 ,in conductors of equal length one pound of aluminum has nearly the same electrical resistance as two pounds of copper1 and this ratio must be allowed for when copper and aluminum lines are compared4 ,from the table it may be seen that the weight of conductors per kilowatt of generator capacity for the transmission from ,santa ,ana ,river is #bi4e times as great as the like weight for the line into ,victor4 ,but the volts per mile are four times as great on the ,victor as they are on the ,santa ,ana ,river line4 ,the extreme range of the cases presented is that between the ,ludlow plant1 with the equivalent of #g4d pounds1 and the ,santa ,ana ,river system with #bie pounds of copper conductors per kilowatt of generator capacity4 ,three transmissions with #a1ege to #b1eee volts per mile have the equivalent of #g4d to #ae pounds of copper each1 per kilowatt of generator capacity4 ,,weight ,,and ,,cost ,,of ,,conductors4 ---------------------------------------- ------------- ,pounds per,dollars per ,kilowatt ,generator ,mile4 ,kilowatt4 ---------------------------------------- ------------- ,wilbraham to ,ludlow #j4hf;,a #a4aa ,sewall's ,falls to railroad shops #b4g #b4be ,into ,victor1 ,colo4 #j4i #a4ej ,to ,dales1 ,ore4 #a4b #e4aj ,apple ,river to ,st4 ,paul #b4a #g4ie ,farmington ,river to ,hartford #c4b #aj4hj ,caon ,city to ,cripple ,creek #a4f #e4he ,yadkin ,river to ,salem #b4f #e4he ,montmorency ,falls to ,quebec #aa4b #aa4he ,caon ,ferry to ,butte #a4g #ag4be ,san ,gabriel ,caon to ,los ,angeles #b4f #i4he ,welland ,canal to ,hamilton #a4g #i4de ,madrid to ,bland1 ,n4 ,m4 #f4f #ca4hj ,ogden to ,salt ,lake ,city #c4e #ai4ce ,santa ,ana ,river to ,los ,angeles #c4e #dd4be ,colgate to ,oakland 4#ef #bd4ae 4#bg;,a ---------------------------------------- ------------- ,a ,aluminum4 ,of the seven transmissions using between #cf and #gi pounds of copper for each kilowatt of generator capacity1 four have voltages ranging from #hbg to #a1jjj per mile1 and on only one is the pressure as low as #fdc volts per mile4 ,five transmission lines vary between #aae and #bie pounds of copper1 or its equivalent1 per kilowatt of generator capacity1 and their voltages per mile are as high as #gfi in one case and down to #bha in another4 ,allowing for some variations in the percentages of loss in transmission lines at full load1 the fifteen plants plainly illustrate the advantage of a high voltage per mile1 as to the weight of conductors4 ,this advantage is especially clear if the differences due to the lengths of the transmissions are eliminated by dividing the weight of conductors per kilowatt of generator capacity in each case by the length of the transmission in miles4 ,this division gives the weight of conductors per kilowatt of generators for each mile of the line1 which may be called the weight per kilowatt mile4 ,for the ,ludlow transmission this weight is only #j4hf pound of aluminum1 the equivalent of #a4gb pounds of copper1 while the like weight for the line into ,quebec is #aa4b pounds of copper1 or #f4e times that for the former line4 ,but the voltage per mile on the ,ludlow is #c4b times as great as the like voltage on the ,quebec line4 ,the weight of conductor per kilowatt mile in the ,victor line is only #j4i pound1 and the like weight for the line between ,madrid and ,bland is #f4f pounds1 or #g4c times as great4 ,on the ,victor line the voltage per mile is #b4e times as great as the voltage for each mile of the ,bland line4 ,comparing systems with nearly equal voltages per mile1 it appears in most cases that only such difference exists in their pounds of conductors per kilowatt mile as may readily be accounted for by designs for various percentages of loss at full load4 ,though the transmission line into ,butte is nearly twice as long as the one entering ,hamilton1 the weight of conductors for each is #a4g pounds per kilowatt mile4 ,the line from ,santa ,ana ,river is more than twice as long as the one entering ,salt ,lake ,city1 but its voltage per mile is only nine per cent less1 and there are #c4e pounds of copper in each line per kilowatt mile4 ,the final1 practical questions as to conductors in electrical transmission relate to their cost per kilowatt of maximum working capacity1 and per kilowatt hour of delivered energy4 ,if the cost of conductors per kilowatt of generator capacity is greater than that of all the remaining equipment1 it is doubtful whether the transmission will pay4 ,if fixed charges on the conductors more than offset the difference in the cost of energy per kilowatt hour at the points of development and delivery1 it is certain that the generating plant should be located where the power is wanted4 ,the great cost of conductors is often put forward as a most serious impediment to long-distance transmission1 and the examples here cited will indicate the weight of this argument4 ,in order to find the approximate cost of conductors per kilowatt of generator capacity for each of the transmission lines here considered1 the price of bare copper wire is taken at #ae cents1 and the price of bare aluminum wire at #cj cents per pound4 ,in each case the weight of copper or aluminum conductor per kilowatt of generator capacity is used to determine their costs per kilowatt of this capacity at the prices just named4 ,this process when carried out for the #ae transmission lines shows that their cost of conductors per kilowatt of generator capacity varies between #a4aa for the #d4e mile line into ,ludlow and #dd4be for the line of #hc miles from the ,santa ,ana ,river4 ,it should be noted that the former of these lines operates at #b1eee and the latter at #cig volts per mile4 ,the line into ,madrid shows an investment in conductors of #ca4hj per kilowatt of generator capacity with #fbe volts per mile4 ,that a long transmission does not necessarily require a large investment in conductors per kilowatt of generator capacity is shown by the line #fe miles long into ,butte1 for which the cost is #ag4be per kilowatt1 with #gfi volts per mile4 ,for the transmission to ,st4 ,paul1 a distance of #be miles1 at #a1jjj volts per mile1 the cost of conductors is #g4ie per kilowatt of generator capacity4 ,the seven-mile line into ,quebec shows an investment of #aa4he per kilowatt of generator capacity4 ,,chapter ,,iv4 ,,advantages ,,of ,,the ,,continuous ,,and ,,alternating ,,current4 ,electrical transmissions over long distances in ,america have been mainly carried out with alternating current4 ,in ,europe1 on the other hand1 continuous current is widely used on long transmissions at high voltages4 ,so radical a difference in practice seems to indicate that neither system is lacking in points of superiority4 ,a fundamental feature of long transmissions is the high voltage necessary for economy in conductors1 and this voltage is attained by entirely different methods with continuous and alternating currents4 ,in dynamos of several hundred or more kilowatts capacity the pressure of continuous current has not thus far been pushed above #d1jjj volts1 because of the danger of sparking and flashing at the commutator4 ,where #aj1jjj or more volts are required on a transmission line with continuous current a number of dynamos are connected in series so that the voltage of each is added to that of the others4 ,in this way the voltage of each dynamo may be as low as is thought desirable without limiting the total line voltage4 ,there is no apparent limit to the number of continuous-current dynamos that may be operated in series or to the voltage that may be thus obtained4 ,in the recently completed transmission from ,st4 ,maurice to ,lausanne1 ,switzerland1 with continuous current1 ten dynamos are connected in series to secure the line voltage of #bc1jjj4 ,when occasion requires twenty or thirty or more dynamos to be operated in series1 giving #ej1jjj or #ge1jjj volts on the line1 machines exactly like those in the transmission just named1 may be used4 ,no matter how many of these dynamos are operated in series the electric strain on the insulation of the windings of each dynamo remains practically constant1 because the iron frame of each dynamo is insulated in a most substantial manner from the ground4 ,the electric strain on the insulation of the windings of each dynamo in the series is thus limited to the voltage generated by that dynamo4 ,there is no practical limit to the thickness or strength of the insulation that may be interposed between the frame of each dynamo and the ground1 and hence no limit to line voltage as far as dynamo insulation is concerned4 ,it is impracticable to operate alternating dynamos in series so as to add their voltages1 and the pressure available in transmission with alternating current must be that of a single dynamo or must be obtained by the use of transformers4 ,the voltage of an alternating may be carried much higher than that of a continuous-current dynamo of very large capacity1 and in many cases pressures of #ac1bjj volts are now supplied to transmission lines by alternating dynamos4 ,just how high the voltage of single alternating dynamos will be carried no one can say1 but it seems probable that the practical limit will prove to be much less than the voltages now employed in some transmissions4 ,as the voltage of alternating dynamos is carried higher the thickness of insulation on their armature coils and consequently the size or number of slots in their armature cores and the size of these cores increase rapidly4 ,the dimensions and weight of an alternating dynamo per unit of its capacity thus go up with the voltage1 and at some undetermined point the cost of the high-voltage dynamo is greater than that of a low-voltage dynamo of equal capacity with raising transformers4 ,to the voltage that may be supplied by transformers there is no practical limit now in sight4 ,lines have been in regular operation from one to several years on which transformers supply #dj1jjj to #ej1jjj volts2 some large transformers have been built for commercial use at #fj1jjj volts1 and other transformers for experimental and testing purposes have been employed in a number of cases for pressures of #ajj1jjj volts and more4 ,available voltages for continuous- and alternating-current transmissions are thus on a practically equal footing as to their upper limit4 ,the amount of power that may be generated and delivered with either the alternating- or continuous-current system of transmission is practically unlimited4 ,single alternating dynamos may be had of #e1jjj or even #h1jjj kilowatts capacity if desired1 but it is seldom that these very large units are employed1 because the capacity of a generating station should be divided up among a number of machines4 ,it is perhaps impracticable to build single continuous-current dynamos with capacities equal to those of the largest alternators1 but as any number of the continuous-current machines may be operated either in series or multiple1 the power that may be applied to a transmission circuit is unlimited4 ,at the plant or plants where the power transmitted by continuous current is received1 a number of motors must be connected in series to operate at the high-line voltage4 ,these motors may all be located in a single room1 may be connected to machinery in different parts of a building1 or may be in use at points miles apart4 ,the vital requirement is that the motors must be in series with each other so that the line voltage divides between them4 ,if simply mechanical power is wanted at the places where the motors are located1 they complete the transmission system and no further electrical apparatus is required4 ,where1 however1 as at ,lausanne1 the transmitted power is to be used in a system of general electrical supply1 the motors that receive the current at the line voltage must drive dynamos that will deliver energy of the required sorts4 ,in the station at ,lausanne four of the motors to which the transmission line is connected each drives a #c1jjj-volt three-phase alternator for the distribution of light and power4 ,the fifth motor at this station drives a #fjj-volt dynamo which delivers continuous current to a street railway4 ,a sixth motor in the same series drives a cement factory some distance from the station4 ,neglecting minor changes in capacity due to losses in the line and motors1 this continuous-current system must thus include three kilowatts in motors and dynamos for each kilowatt delivered for general electrical distribution at the receiving station4 ,in a case in which only mechanical power is wanted at the receiving station1 the dynamos and motors concerned in the transmission must have a combined capacity of two horse-power for each horse-power delivered at the motor shaft4 ,in contrast with these figures1 the electrical equipment in a transmission with alternating current for mechanical power alone includes two kilowatts capacity in generators and motors1 besides two kilowatts capacity in transformers for each corresponding unit of power delivered at the motor shaft unless generators and motors operate at the full line voltage4 ,if a general electrical supply is to be operated by the alternating system of transmission1 either motors and dynamos or rotary converters must be added to transformers where continuous current is required4 ,an alternating transmission may thus include as little as one kilowatt in dynamos and one in transformers1 or as much as two kilowatts capacity in dynamos1 two in transformers1 and one in motors for each kilowatt delivered to distribution lines at the receiving station4 ,line construction from the continuous-current transmission is of the most simple character apart from the necessity of high insulation4 ,only two wires are necessary and they may be of any desired cross-section1 strung on a single pole line and need not be transposed4 ,on these wires the maximum voltage for which insulation must be provided is the nominal voltage of the system4 ,it is possible under these conditions to build a single transmission line with two conductors of such size and strength and at such a distance apart that a high degree of reliability is attained against breaks in the wires or arcing between them4 ,in a transmission of power by two- or three-phase alternating current at least three wires are necessary and six or more are often employed4 ,if six or more wires carrying current at the high voltages required by long transmissions are mounted on a single line of poles1 it is not practicable to obtain such distances between the wires as are desirable4 ,the repair of one set of wires while the other set is in operation is a dangerous task1 and an arc originating between one set of the wires is apt to be communicated to another set4 ,for these reasons two pole lines are frequently provided for a transmission with alternating current1 and three or more wires are then erected on each line4 ,compared with a continuous-current transmission1 one with alternating current often requires more poles and is quite certain to require more cross-arms1 pins1 insulators1 and labor of erection4 ,for a given effective voltage of transmission it is harder to insulate an alternating- than a continuous-current line4 ,in the first place the maximum voltage of the alternating line with even a true sine curve of pressure is #a4d times the nominal effective voltage1 but the insulation must withstand the maximum pressure4 ,then comes the matter of resonance1 which may carry the maximum voltage of an alternating circuit up to several times its normal amount1 if the period of electrical vibration for that particular circuit should correspond to the frequency of the dynamos that operate it4 ,even where the vibration period of a transmission circuit and the frequency of its dynamos do not correspond1 and good construction should always be planned for this lack of agreement1 resonance may and often does increase the normal voltage of an alternating transmission by a large percentage4 ,the alternating system of transmission must work at practically constant voltage whatever the state of its load1 so that the normal stress on the insulation is always at its maximum4 ,in a transmission with continuous current on the other hand1 if the prevailing practice of a constant current and varying pressure on the line is followed1 the insulation is subject to the highest voltage only at times of maximum load on the system4 ,lightning is a very real and pressing danger to machinery connected to long transmission lines1 and this danger is much harder to guard against in an alternating system than in a system with continuous constant current4 ,the large degree of exemption from damage by lightning enjoyed by series arc dynamos is well known1 the magnet windings of such machines acting as an inductance that tends to keep lightning out of them4 ,moreover1 with any continuous-current machines lightning arresters having large self-induction may be connected in circuit and form a most effective safeguard against lightning1 but this plan is not practicable on alternating lines4 ,in the matter of switches1 controlling apparatus1 and switchboards1 an alternating transmission requires much more equipment than a system using continuous1 constant current4 ,the ten dynamos in the generating station at ,st4 ,maurice1 with a capacity of #c1dej kilowatts at #bc1jjj volts1 are each connected and disconnected with the transmission by a switch in a small circular column of cast-iron that stands hardly breast high4 ,an amperemetre and voltmetre are mounted on each dynamo4 ,the alternating generators in a station of equal capacity and voltage would require a large switchboard fitted with bus-bars1 oil switches1 and automatic circuit-breakers4 ,relative efficiencies for the continuous-current and the alternating-transmission systems vary with the kind of service required at receiving stations and with the extent to which transformers are used in the alternating system1 other factors being constant4 ,for purposes of comparison the efficiency at full load of both alternating- and continuous-current dynamos and motors1 also of rotary converters1 may be fairly taken at #ib per cent1 and the efficiency of transformers at #if per cent4 ,for the line an efficiency of #id per cent may be assumed at full load1 this being the actual figure in one of the ,swiss transmissions of #b1afj kilowatts at #ad1djj volts to a distance of #cb miles4 ,where the continuous current system must simply deliver mechanical power at the receiving stations1 its efficiency under full load amounts to #ib 4#id 4#ib #gi4fe per cent from dynamo shaft to motor shaft4 ,an alternating system delivering mechanical power will have an efficiency of #ib 4#id 4#if 4#ib #gf4df per cent between dynamo shaft and motor shaft1 if the line voltage is generated in the armature coils of the dynamo and the line loss is #f per cent4 ,if step-up transformers are employed to secure the line voltage the efficiency of the alternating transmission delivering mechanical power drops to the figure of #ib 4#if 4#id 4#if 4#ib #gc4dj per cent4 ,it thus appears that for the simple delivery of mechanical power the continuous current transmission has an advantage over the alternating of three to six per cent in efficiency1 depending on whether step-up transformers are employed4 ,when the receiving station must deliver a supply of either continuous or alternating current for general distribution1 the efficiency of the continuous-current transmission amounts to #ib 4#id 4#ib 4#ib #gc4bg per cent4 ,the alternating-transmission system in a case in which no step-up transformers are employed will deliver alternating current of the same frequency as that on the transmission line at any desired pressure for general distribution at an efficiency of #ib 4#id 4#if #hc4jb per cent1 if step-down transformers are used1 but the efficiency drops to #hc4jb 4#if #gi4gj per cent4 when step-up transformers are introduced4 ,if the alternating transmission uses no step-up transformers and delivers either alternating or continuous current by means of motor generators1 its efficiency at full load is #hc4jb 4#ib 4#ib #gj4bf per cent1 but with step-up transformers added the efficiency drops to #gj4bf 4#if #fg4dc per cent4 ,in a transmission where electrical energy must be delivered for general distribution1 the full-load efficiency of an alternating system ranges either higher or lower than that of a continuous-current system depending on whether the current from the transmission line must be converted or not4 ,line loss is the same whatever the load in a constant-current transmission1 so that line efficiency falls rather rapidly with the load4 ,on the other hand1 at constant pressure the percentage of energy loss on the line varies directly with the load1 but the actual rate of energy loss with the square of the load4 ,on partial loads the line efficiency is thus much higher with alternating than with continuous constant current4 ,efficiency of electrical machinery is generally low at partial loads1 so that in cases in which the number or capacity of alternating dynamos1 transformers1 motors1 or rotary converters for a transmission would be greater per unit of delivered power than the corresponding number or capacity of machines for a transmission by continuous current1 the latter would probably have the advantage in the combined efficiency of machinery at partial loads4 ,in this way the lower-line efficiency of one system might offset the lower efficiency of machinery in the other4 ,energy is usually very cheap at the generating station of a transmission system4 ,for this reason small differences in the efficiencies of different systems should be given only moderate weight in comparison with the items of first cost1 reliability1 and expense of operation4 ,in the matter of first cost at least the continuous-current system seems to have a distinct advantage over the alternating4 ,without going into a detailed estimate1 it is instructive to consider the figures given by a body of five engineers selected to report on the cost of continuous- and alternating-current equipments for the ,st4 ,maurice and ,lausanne transmission4 ,according to the report of these engineers1 a three-phase transmission system would have cost #adj1jjj more than the continuous-current system actually installed1 all other factors remaining constant4 ,it should be noted that the conditions of this transmission are favorable to three-phase working and unfavorable to continuous-current equipment1 because all of the energy except that going to the #djj horse-power motor at the cement mill must be delivered at the receiving station for general distribution4 ,moreover1 four out of the five motors at ,lausanne drive three-phase generators1 and only one drives a continuous-current dynamo for the electric railway1 so that a three-phase transmission would have required only one rotary converter4 ,had the transmission been concerned merely with the delivery of mechanical power1 as at the cement mill1 the advantage of the continuous- over the alternating-current system in the matter of first cost would have been much greater than it was4 ,long-distance transmission with three-phase current began at ,frankfort1 in #ahia1 when #eh kilowatts were received over a #be1jjj-volt line from ,lauffen1 #aji miles away4 ,shortly after this historic experiment1 three-phase transmission in the ,united ,states began on a commercial scale1 and plants of this sort have multiplied rapidly here4 ,meantime very little has been done in ,america with continuous currents in long transmissions4 ,in ,europe1 the birthplace of the three-phase system1 it has failed to displace continuous current for transmission work4 ,about a score of these continuous-current transmissions are already at work there4 ,if the opinion of ,european engineers as to the lower cost of the continuous-current system1 all other factors being equal1 is confirmed by experience1 this current will yet find important applications to long transmissions in the ,united ,states4 ,systems of transmission with continuous-current may operate at constant voltage and variable current1 at constant current and variable voltage1 or with variations of both volts and amperes to correspond with changes of load4 ,dynamos of several thousand kilowatts capacity each can readily be had at voltages of #ejj to #fjj1 but the attempt to construct dynamos to deliver more than two or three hundred kilowatts each at several thousand volts has encountered serious sparking at the commutator4 ,thus far1 dynamos that yield between #cjj and #djj kilowatts each have been made to give satisfactory results at pressures as high as #b1ejj volts4 ,another one of the ,swiss transmissions takes place over a distance of thirty-two miles at #ad1djj volts1 the capacity being #b1afj kilowatts4 ,to give this voltage and capacity1 eight dynamos are connected in series at the generating station1 each dynamo having an output of #aej amperes at #a1hjj volts1 or #baf kilowatts4 ,continuous-current motors are1 of course1 subject to the same limitations as dynamos in the matter of capacity at high voltage1 so that a series of motors must be employed to receive the high-pressure energy from the line4 ,the number of these motors may just equal1 or may be less or greater than the number of dynamos1 but the total working voltage of all the motors in operation at one time must equal the total voltage of the dynamos in operation at that time minus the volts of drop in the line4 ,each constant-current motor may have any desired capacity up to the practicable maximum1 but it must be designed for the current of the system4 ,the voltage at the terminals of each motor varies with its load1 being greatest when the motor is doing the most work4 ,constant speed is usually attained at each motor by means of a variable resistance connected across the terminals of the magnet coils4 ,the amount of this resistance is regulated by a centrifugal governor1 driven by the motor shaft4 ,this governor also shifts the position of the brushes on the commutator to prevent sparking as the current flowing through the magnet coils is changed4 ,for a constant-current transmission the magnet and armature windings of both dynamos and motors are usually connected in series with each other and the line so that the same current passes through every element of the circuit1 except that each motor may have some current shunted out of its magnet coil for the purpose of speed regulation4 ,in some cases1 however1 the magnet coils of the dynamos are connected in multiple with each other and receive their current from a separate dynamo designed for the purpose4 ,with this separate excitation of the magnet coils1 the dynamo armatures are still connected in series with each other and the line4 ,the total voltage at the generating station and on the line of a constant-current system varies with the rate at which energy is delivered1 and has its maximum value only at times of full load4 ,to obtain this variation of voltage1 it is the general practice to change the speed of the dynamos by means of an automatic regulator which is actuated by the line current4 ,any increase of the line current actuates the regulator and reduces the speed of the dynamos1 while a decrease of the line current raises the dynamo speed4 ,with a good regulator the variations of the line current are only slight4 ,under this method of regulation the dynamos in operation have a substantially constant current in both armature and magnet coils at all times1 so that there is no reason to shift the position of the brushes on the commutator4 ,generating stations of constant current transmission systems are generally driven by water-power and the speed regulator operates to change the amount of water admitted to each wheel4 ,each turbine wheel usually drives a pair of dynamos1 but one or any number of dynamos might be driven by a single wheel4 ,the two dynamos driven by a single wheel are generally connected in series at all times1 and are cut in or out of the main circuit together4 ,when the load on a constant-current generating station is such that the voltage can be developed by less than all the dynamos1 one or more dynamos may be stopped and taken out of the circuit4 ,to do this the dynamo or pair of dynamos to be put out of service may be stopped1 their magnet coils having first been short-circuited1 and then a switch across the connections of their armatures to the lines closed1 after which the connections of the armatures to the line are opened4 ,by a reverse process1 any dynamo or pair of dynamos may be cut into the operating circuit4 ,at the terminals of each dynamo in the series1 while in operation1 the voltage is simply that developed in its armature1 so that the insulation between the several windings is subject to only a corresponding stress4 ,the entire voltage of the line1 however1 tends to force a current from the coils of the dynamo at one end of the series into its frame1 thence to any substance on which that frame rests1 and so on to the frame and coils of the dynamo at the other end of the series4 ,to protect the insulation of the dynamo coils from the line voltage1 thick blocks of porcelain are placed beneath the dynamo frames1 and the armature shafts are connected to those of the turbines by insulating couplings4 ,besides the switches1 already mentioned1 a voltmeter and ammeter should be provided for each dynamo and also for the entire series of machines4 ,this completes the switchboard equipment1 which is1 therefore1 very simple4 ,as the line loss of a constant-current system is the same whatever the load that is being operated1 this loss may be a large percentage of the total output when the load is light4 ,if1 for illustration1 five per cent of the maximum voltage of the station is required to force the constant current through the line1 the percentage of line loss will rise to ten when the station voltage is one-half the maximum1 and to twenty when the station is delivering only one-quarter of its full capacity4 ,in view of this property of constant-current working1 the line loss should be made quite small in its ratio to the maximum load1 as most stations must work on partial loads much of the time4 ,five per cent of maximum station voltage is a fair general figure for the line loss in a constant-current transmission1 but the circumstances of a particular case may dictate a higher or a lower percentage4 ,on the #cb-mile transmission1 above named1 the loss in the line is six per cent of the station output at full load4 ,if a transmission with continuous current is to be carried out at constant pressure the limitation as to the capacity and voltage of each dynamo is about the same as with constant current4 ,probably more energy is now transmitted by continuous current at constant pressure than by any other method1 the greater part being devoted to electric railway work at #ejj to #fjj volts4 ,dynamos for about these voltages can readily be had in capacities up to several thousand kilowatts each1 but the length of transmission that can be economically carried out at this pressure is comparatively small4 ,for each kilowatt delivered to a line at #ejj volts and to be transmitted to a distance of five miles at a ten per cent loss in the line1 the weight of copper conductors must be #cgb pounds1 costing #ef4hj at #ae cents per pound4 ,this sum is twice to four times the cost of good continuous-current dynamos per kilowatt of capacity4 ,if the distance of transmission is ten miles and the voltage and line loss remain as before1 the weight of copper conductor must be increased to #a1dhh pounds per kilowatt delivered to the line1 costing #bbg4bj4 ,experience has shown that in sizes of not more than #djj kilowatts1 continuous-current dynamos may safely have a voltage of #b1jjj each1 and any number of such dynamos may be operated in multiple1 giving whatever capacity is desired4 ,at #b1jjj volts and a loss of #aj per cent in the line the weight of copper conductors per kilowatt would be #ic pounds1 costing #ac4ie1 for each kilowatt delivered to the line on a #aj-mile transmission4 ,with #b1jjj volts on a #bj-mile transmission the weight of conductors per kilowatt would be the same as their weight on a #e-mile transmission at #ejj volts1 the percentage of loss being equal in the two cases4 ,large continuous-current motors of1 say1 #ej kilowatts or more can be had for a pressure of #b1jjj volts1 so that any number of such motors might be operated from a #b1jjj-volt1 constant-pressure line entirely independent of each other4 ,from these figures it is evident that a transmission of #aj miles may be carried out with continuous-current at constant pressure from a single dynamo with good efficiency and a moderate investment in conductors4 ,when the distance is such that much more than #b1jjj volts are required for the constant-pressure transmission1 with continuous current1 resort must be had to the connection of dynamos and motors in series4 ,any number of dynamos may be so connected as in the case of constant-current work4 ,the combined voltages of the series of motors connected to the constant-pressure transmission line must equal the voltage of that line1 so that the number of motors in any one series must be constant4 ,if the voltage of transmission is so high that more than two or three motors must be connected in each series1 there comes the objection that motors must be operated at light loads during much of the time4 ,moreover1 each series of motors must be mechanically connected to the same work1 as that of driving a single dynamo or other machine1 because if the loads on the motors of a series vary differently1 these motors will not operate at constant speed4 ,continuous-current transmission at constant pressure with motors in series thus lacks the flexibility of transmission at constant current where any motor may be started and stopped without regard to the others in the series1 the line voltage being automatically regulated at the generating station according to the number of motors in use at any time and to the work they are doing4 ,in the efficiency of its dynamos1 motors and line1 a constant-pressure system of transmission is substantially equal to one with constant current at full load4 ,at partial loads the constant-pressure line has the advantage because the loss of energy in it varies with the square of the load4 ,thus at constant pressure the line loss in energy per hour at half-load is only one-fourth as great as the loss at full load4 ,on the other hand1 the energy loss in the constant-current line is the same at all stages of load4 ,because of these facts it is good practice to allow1 say1 a ten-per-cent loss in a constant-pressure line and only five per cent in a constant-current line at full load4 ,in a generating station at #b1jjj volts or more constant pressure1 it is desirable to have the magnet coils of the main dynamos connected in multiple and separately excited by a small dynamo at constant pressure4 ,this plan is especially desirable when the armatures of several dynamos are connected in series to obtain the line voltage4 ,separately excited magnet coils make it easier to control the operation of the several dynamos1 coils of low-voltage are cheaper to make than coils of high voltage1 and the low voltage windings are less liable to burn out4 ,if a series of constant-pressure motors is in use at one point1 it may be cheaper and safer to excite its magnet coils from a special dynamo than from the line4 ,in a transmission carried out with series-wound dynamos and motors1 the speed of the motors may be constant at all loads without any special regulating mechanism4 ,to attain this result it is necessary that all the motors be coupled so as to form a single unit mechanically and that the dynamos be driven at constant speed4 ,a transmission system of this sort may include a single dynamo and a single motor1 or two or more dynamos1 and two or more motors may be used in series4 ,when the dynamos of such a system are driven at constant speed and a variable load is applied to the single motor1 or to the mechanically connected motors1 both the voltage of the system and the amperes flowing in all its parts change together so that practically constant speed is maintained at the motors1 provided that the design of both the dynamos and motors is suitable for the purpose4 ,with the maximum load on the motors the volts and amperes of the system have their greatest values1 and these values both decline with smaller loads4 ,the chief disadvantage of this system lies in the fact that where more than one motor is employed all the motors must be mechanically joined together so as to work on the same load4 ,compared with the constant-current system1 this combination of series dynamos with mechanically connected series motors has the distinct advantage that neither the dynamos nor motors require any sort of regulators in order to maintain constant motor speed4 ,it is only necessary that the dynamos be driven at constant speed and that both the dynamos and motors be designed for the transmission4 ,in comparison with a constant-pressure system1 the one under consideration has the advantage that neither its dynamos nor motors require magnet coils with a high voltage at their terminals and composed of fine wire or separate excitation by a special dynamo4 ,these features of the system with series dynamos and motors1 the latter being joined as a mechanical unit1 make it cheaper to install and easier to operate than either of the other two4 ,this system is especially adapted for the delivery of mechanical power in rather large units4 ,the voltage available may be anything desired1 but is subject to the practical limitations that all the motors must deliver their power as a mechanical unit1 so that unless the power is quite large the number of motors in the series and1 therefore1 the voltage is limited4 ,an interesting illustration of the system of transmission just described exists between a point on the ,river ,suze1 near ,bienne1 ,switzerland1 and the ,biberest paper mills4 ,at the river a #djj horse-power turbine water-wheel drives a pair of series-wound dynamos1 each rated at #acj kilowatts and #c1cjj volts4 ,these dynamos are connected in series1 giving a total capacity of #bfj kilowatts and a pressure of #f1fjj volts4 ,at the ,biberest mills are located two series-wound motors1 mechanically coupled and connected in series with each other and with the two-wire transmission line1 which extends from the two dynamos at the ,river ,suze4 ,each of these motors has a capacity and voltage equal to that of either of the dynamos previously mentioned4 ,the coupled motors operate at the constant speed of #bjj revolutions per minute at all loads and deliver over #cjj horse-power when doing maximum work4 ,between the generating plant at the river and the ,biberest mills the distance is about #ai miles1 and the two line wires are each of copper1 #bge mils1 or a little more than one-fourth inch in diameter4 ,the dynamos and motors of this system are mounted on thick porcelain blocks in order to protect the insulation of their windings from the strain of the full-line voltage4 ,either of the three systems of transmission by continuous-current that have been considered requires a smaller total capacity of electrical apparatus for a given rate of mechanical power delivery than any system using alternating current except that where both the dynamos and motors operate at line voltage4 ,,chapter ,v4 ,,the ,,physical ,,limits ,,of ,,electric-,,power ,,transmission4 ,electrical energy may be transmitted around the world if the line voltage is unlimited4 ,this follows from the law that a given power may be transmitted to any distance with constant efficiency and a fixed weight of conductors1 provided the voltage is increased directly with the distance4 ,the physical limits of electric-power transmission are thus fixed by the practicable voltage that may be employed4 ,the effects of the voltage of transmission must be met in the apparatus at generating and receiving stations on the one hand1 and along the line on the other4 ,in both situations experience is the main guide1 and theory has little that is reliable to offer as to the limit beyond which the voltage will prove unworkable4 ,electric generators are the points in a transmission system where the limit of practical voltage is first reached4 ,in almost all high-voltage transmissions of the present day in the ,united ,states alternating generators are employed4 ,very few if any continuous-current dynamos with capacities in the hundreds of kilowatts and voltages above #d1jjj have been built in ,europe1 and probably none in the ,united ,states4 ,where a transmission at high voltage is to be accomplished with continuous current1 two or more dynamos are usually joined in series at the generating station1 and a similar arrangement with motors is made at the receiving station1 so that the desired voltage is available at the line though not present at any one machine4 ,alternating dynamos that deliver current at about #f1jjj volts have been in regular use for some years1 in capacities of hundreds of kilowatts each1 and may readily be had of several thousand kilowatts capacity4 ,but even #f1jjj volts is not an economical pressure for transmissions over fifteen to fifty miles1 such as are now quite common2 consequently in such transmissions it has been the rule to employ alternators that operate at less than #c1jjj volts1 and to raise this voltage to the desired line pressure by step-up transformers at the generating station4 ,more recently1 however1 the voltage of alternating generators has been pushed as high as #ac1jjj in the revolving-magnet type where all the armature windings are stationary4 ,this voltage makes it practicable to dispense with the use of step-up transformers for transmissions up to or even beyond #cj miles in some cases4 ,this voltage of #ac1jjj in the armature coils is attained only by constructions involving some difficulty because of the relatively large amount of room necessary for the insulating materials on coils that develop this pressure4 ,the tendency of this construction is to give alternators unusually large dimensions per given capacity4 ,it seems probable1 moreover1 that the pressures developed in the armature coils of alternating generators must reach their higher limits at a point much below the #ej1jjj and #fj1jjj volts in actual use on present transmission lines4 ,in the longest transmissions with alternating current there is1 therefore1 little prospect that step-up transformers at the generating stations and step-down transformers at receiving stations can be dispensed with4 ,the highest voltage that may be received or delivered at these stations is simply the highest that it is practicable to develop by transformers and to transmit by the line4 ,a very high degree of insulation is much more easy to attain in transformers than in generator armatures1 because the space that can be readily made available for insulating materials is far greater in the transformers1 and further because their construction permits the complete immersion of their coils in petroleum4 ,this oil offers a much greater resistance than air to the passage of electric sparks1 which tend to set up arcs between coils at very high voltages and thus destroy the insulation4 ,danger to insulation from the effect known as creeping between coils at widely different pressures is largely avoided by immersion of the coils in oil4 ,for several years groups of transformers have been worked regularly at #dj1jjj to #fj1jjj volts1 and in no instance is there any indication that the upper limit of practicable voltage has been reached4 ,on the contrary1 transformers have repeatedly been worked experimentally up to and above #ajj1jjj volts4 ,from all these facts1 and others of similar import1 it is fair to conclude that the physical limit to the voltages that it is practicable to obtain with transformers is much above the #ej1jjj or #fj1jjj volts now in practical use on transmission systems4 ,so far as present practice is concerned1 the limit to the use of high voltages must be sought beyond the transformers and outside of generating and receiving stations4 ,as now constructed1 the line is that part of the transmission system where a physical limit to the use of higher voltages will first be reached4 ,the factors that tend most directly to this limit are two3 temporary arcing between the several wires on a pole1 and the less imposing but constant passage of energy from one wire to another4 ,on lines of very high voltage arcing is occasionally set up by one of several causes4 ,at a point where one or more of the insulators on which the wires are mounted become broken or defective1 the current is apt to flow from one wire to another along a wet cross-arm1 until the wood grows carbonized and an arc is formed that ends by burning up the cross-arm or even the pole4 ,where lines are exposed to heavy sea fog1 the salt is in some cases deposited on the insulators and cross-arms to an extent that starts an arc between the wires1 and ends often in the destruction of the cross-arm4 ,in some instances the glass and porcelain insulators supporting wires used with high voltages are punctured by sparks that pass right through the material of the insulator to the pin on which it is mounted1 thus burning the pin and ultimately the cross-arm4 ,this trouble is easily met1 however1 by the adoption of a better grade of porcelain or of an insulator with a greater thickness of glass or porcelain between the wires and the supporting pin4 ,arcs between lines at high voltages usually start by sparks that jump from the lower edges of insulators1 when they are wet or covered with salt deposit1 to the cross-arm4 ,as the lower edges of insulators are only a few inches from their cross-arms1 the sparks find a path of comparatively low resistance by passing from insulator to cross-arm and thence to the other insulator and wire4 ,the wood of a wet cross-arm is a far better conductor than the air4 ,where wires are several feet or more apart1 sparks probably never jump directly through the air from one to the other4 ,large birds flying close to such wires1 however1 have in some instances started momentary arcs between them4 ,the treatment of cross-arms with oil or paraffine reduces the number of arcs that occur on a line of high voltage1 but does not do away with them4 ,as the voltages of long transmissions have gone up1 the distance through the air between wires and the distances between the lower wet edges of insulators and the cross-arms have been much increased4 ,most of the earlier transmission lines for high voltages were erected on insulators spaced from one to two feet apart4 ,in contrast with this practice1 the three wires of the transmission line in operation at #ej1jjj volts between ,caon ,ferry and ,butte are arranged at the corners of a triangle seventy-eight inches apart1 one wire at the top of each pole and the other two at opposite ends of the cross-arm4 ,a voltage that would just start an arc along a wet cross-arm between wires eighteen inches apart would be quite powerless to do so over seventy-eight inches of cross-arm1 the lower wet edges of insulators being equidistant from cross-arms in the two cases4 ,to reach the cross-arm1 the electric current passes down over the wet or dirty outside surface of the insulator to its lower edge4 ,in the older types of insulators the lower wet edge often came within two inches of the cross-arm4 ,for the #ej1jjj-volt line just mentioned the insulators 7see illus47 are mounted with their lower wet edges about eight inches above the cross-arms4 ,at its lower edge each insulator has a diameter of nine inches1 and a small glass sleeve extends several inches below this edge and close to the wooden pin1 to prevent sparking from the lower wet edge of the insulator to the pin4 ,these increased distances between wires in a direct line through the air1 and also the greater distances between the lower wet edges of insulators and their pins and cross-arms1 are proving fairly effective to prevent serious arcing under good climatic conditions1 for the maximum pressures of #ej1jjj to #fj1jjj volts now in use4 ,if these voltages are to be greatly exceeded it is practically certain that the distance between wires1 and from the lower wet edges of insulators to the wood of poles or cross-arms1 must be still further increased to avoid destructive arcing4 ,the nearest approach to an absolute physical limit of voltage with present line construction is met in the constant current of energy through the air from wire to wire of a circuit4 ,a paper in vol4 ,,xv41 ,transactions ,american ,institute ,electrical ,engineers1 gives the tests made at ,telluride1 ,col41 to determine the rates at which energy is lost by passing through the air from one wire to another of the same circuit4 ,the tests at ,telluride were made with two-wire circuits strung on a pole line #aa1gbj feet in length1 at first with iron wires of #j4afe inch diameter and then with copper wires of #j4afb inch diameter4 ,measurements were made of the energy escaping from wire to wire at different voltages on the line1 and also with the two wires at various distances apart4 ,it was found that the loss of energy over the surfaces of insulators was very slight1 and that the loss incident to the passage of energy directly through the air is the main one to be considered4 ,this leakage through the air varies with the length of the line1 as might be expected4 ,tests were made with pairs of wires running the entire length of the pole line and at distances of #ae1 #bb1 #ce1 and #eb inches apart respectively4 ,losses with wires #bb or #ce inches apart were intermediate to the losses when wires were #ae and #eb inches apart respectively4 ,results given in the original paper for the pair of wires that were #ae inches apart and for the pair that were #eb inches apart are here reduced to approximate watts per mile of two-wire line4 ,at #dj1jjj volts the loss between the two wires that were #ae inches apart was about #aej watts per mile1 and between the two wires that were #eb inches apart the loss was #hd watts per mile4 ,the two wires #ae inches apart showed a leakage of approximately #dac watts per mile when the voltage was up to #dd1jjj1 but the wires #eb inches apart were subject to a leakage of only #id watts per mile at the same voltage4 ,at #dg1cjj volts1 the highest pressure recorded for the two wires #ae inches apart1 the leakage between them was about #a1bae watts per mile1 while an equal voltage on the two wires #eb inches apart caused a leakage of only #abb watts per mile1 or one-tenth of that between the wires that were #ae inches apart4 ,when about #ej1jjj volts were reached on the two wires #eb inches apart1 the leakage between them amounted to #adj watts per mile2 but beyond this voltage the loss went up rapidly1 and was #bbe watts per mile at about #ed1fjj volts4 ,for higher pressures the loss between these two wires still more rapidly increased1 and amounted to #a1cfh watts per mile with about #ei1cjj volts1 the highest pressure recorded4 ,with a loss of about #a1bae watts per mile between the two wires #eb inches apart1 the voltage on them was #eh1hjj1 in contrast with the #dg1cjj volts producing the same leakage on the two wires #ae inches apart4 ,evidently1 however1 at even #eb inches between line wires the limit of high voltage is not far away4 ,when the voltage on the #eb-;inch line was raised from #ed1fjj to #ei1cjj1 the leakage loss between the two wires increased about #a1adc watts per mile4 ,if the leakage increases at least in like proportion1 as seems probable1 for still higher pressures1 the loss between the two wires would amount to #f1cba watts per mile with #hj1jjj volts on the line4 ,on a line #bjj miles long this loss by leakage between the two wires would amount to #a1bfd1bjj watts4 ,any such leakage as this obviously sets an absolute1 physical limit to the voltage1 and consequently the length of transmission4 ,fortunately for the future delivery of energy at great distances from its source1 the means to avoid the limit just discussed are not difficult4 ,other experiments have shown that with a given voltage and distance between conductors the loss of energy from wire to wire decreases rapidly as their diameters increase4 ,the electrical resistance of air1 like that of any other substance1 increases with the length of the circuit through it4 ,the leakage described is a flow of electrical energy through the air from one wire to another of the same circuit4 ,to reduce this leakage it is simply necessary to give the path from wire to wire through the air greater electrical resistance by increasing its length1 that is1 by placing the wires at greater distances apart4 ,the fact demonstrated at ,telluride1 that with #dg1cjj volts on each line the leakage per mile between the two wires #ae inches apart was ten times as great as the leakage between the two wires #eb inches apart1 is full of meaning4 ,evidently1 leakage through the air may be reduced to any desired extent by suitable increase of distance between the wires of the same circuit4 ,but to carry this increase of distance between wires very far involves radical changes in line construction4 ,thus far it has been the uniform practice to carry the two or three wires of a transmission circuit on a single line of poles1 and in many cases several such circuits are mounted on the same pole line4 ,for the #fe mile transmission into ,butte1 ,mont41 only the three wires of a single circuit are mounted on one pole line1 and this represents the best present practice4 ,the cross-arms on this line are each #h feet long1 and one is attached to each pole4 ,the poles are not less than #ce feet long and have #h-;inch tops4 ,one wire is mounted at the top of each pole1 and the other two wires near the ends of the cross-arm1 so that the three wires are equidistant and #gh inches apart4 ,by the use of still heavier poles the length of cross-arms may be increased to #ab or #ad feet1 for which their section should be not less than #d by #f inches4 ,placing one wire at the pole top1 the #ab-;foot cross-arm would permit the three wires of a circuit to be spaced about #aj4e feet apart4 ,the cost of extra large poles goes up rapidly and there are alternative constructions that seem better suited to the case4 ,moreover1 a few tens of thousands of volts above present practice would bring us again to a point where even #aj4e feet between wires would not prevent a prohibitive leakage4 ,two poles might be set #bj feet apart1 with a cross-piece between them1 extending out #e feet beyond each pole and having a total length of #cj feet4 ,this would permit three wires to be mounted along the cross-piece at points about #ad feet apart4 ,if the present transmission pressures of #ej1jjj to #fj1jjj volts are to be greatly exceeded1 the line structure may involve the use of a separate pole for each wire of a circuit1 each wire to be mounted at the top of its pole4 ,this construction calls for three lines of poles to carry the three wires of a three-phase transmission4 ,each of these poles may be of only moderate dimensions1 say #cj feet long with #f- or #g-;inch top4 ,the cost of three of these poles will exceed by only a moderate percentage that of a #ce- or #dj-;foot pole with an #h- to #aj-;inch top1 such as would be necessary with #ab-;foot cross-arms4 ,the distance between these poles at right angles to the line may be anything desired1 so that leakage from wire to wire through the air will be reduced to a trifling matter at any voltage4 ,extra long pins and insulators at the pole tops will easily give a distance of two feet or more between the lower wet edge of each insulator and the wood of pin or pole4 ,such line construction would probably safely carry two or three times the maximum voltage of present practice1 and might force the physical limit of electrical transmission back to the highest pressure at which transformers could be operated4 ,with not more than #fj1jjj volts on the line the size of conductors is great enough in many cases to keep the loss of energy between them within moderate limits when they are six feet apart1 but with a large increase of voltage the size of conductors must go up or the distances between them must increase4 ,,chapter ,,vi4 ,,development ,,of ,,water-,,power ,,for ,,electric ,,stations4 ,electrical transmission has reduced the cost of water-power development4 ,without transmission the power must be developed at a number of different points in order that there may be room enough for the buildings in which it is to be utilized4 ,this condition necessitates relatively long canals to conduct the water to the several points where power is to be developed1 and also a relatively large area of land with canal and river frontage4 ,with electrical transmission the power1 however great1 may well be developed at a single spot and on a very limited area of land4 ,the canal in this case may be merely a short passageway from one end of a dam to a near-by power-house1 or may disappear entirely when the power-house itself forms the dam1 as is sometimes the case4 ,these differences between the distribution of water for power purposes and the development by water of electrical energy for transmission may be illustrated by many examples4 ,a typical case of the distribution of water to the points where power is wanted may be seen in the hydraulic development of the ,amoskeag ,manufacturing ,company at ,manchester1 ,n4 ,h4 ,this development includes a dam across the ,merrimac ,river1 and two parallel canals that follow one of its banks for about #c1djj feet down stream4 ,by means of a stone dam and a natural fall a little beyond its toe a water head of about forty-eight feet is obtained at the upper end of the high-level canal4 ,below this point there is little drop in the bed of the river through that part of its course that is paralleled by the two canals4 ,all of the power might be thus developed within a few rods of one end of the dam1 if means were provided for its distribution to the points where it must be used4 ,years ago1 when this water-power was developed1 the electrical transmission or distribution of energy was unheard of1 and distribution of the water itself had therefore to be adopted4 ,for this purpose the two canals already mentioned were constructed along the high bank of the river at two different levels4 ,illustration3 ,,fig4 #d4--;,hydraulic ,development on the ,merrimac ,river4 ,the high-level canal1 so called1 was designed to take water directly from the basin or forebay a little below one end of the dam1 so that between this canal and the river there is a full water head of about forty-eight feet4 ,over nearly its entire course the nearer side of this high-level canal runs between #dej and #gej feet from the edge of the river wall1 and thus includes between it and the river a large area on which factories to be driven by water-wheels may be located4 ,it was thought1 however1 that this strip of land between the high-level canal and the river was too wide for a single row of mill sites1 and the lower level canal was therefore constructed parallel with that on the higher level1 but with about twenty-one feet less elevation4 ,between these two canals a strip of land about #bej feet wide was left for the location of mills4 ,by this arrangement of canals it is possible to supply wheels located between the high and the low levels with water under a head of about twenty-one feet1 and to supply wheels between the lower canal and the river with water under a head of about twenty-nine feet4 ,the entire area of land between the high canal and the river is thus made readily available for factory buildings4 ,water for the lower canal is drawn mainly from the high canal through the wheels in buildings that are located between the two canals4 ,it is desirable in a case of this sort to have as much water flow through the wheels between the high and low canal as flows through the wheels between the low canal and the river1 but this is not always possible4 ,a gate is therefore provided at the forebay where the two canals start1 by which water may pass from the forebay directly into the low canal when necessary1 but the head of twenty-one feet between the forebay and the low canal is lost as to this water4 ,between the high and low canal1 and between the low canal and the river twenty-three turbine wheels or pairs of wheels have been connected1 and these wheels have a combined rating of #i1ejj horse-power4 ,to carry out this hydraulic development it thus appears that about #a4c miles of canal have been constructed2 one-half this length of river-front has been required1 and about one-sixth square mile of territory has been occupied4 ,contrast with this result what might have been done if electrical transmission of power had been available at the time when this water-power was developed4 ,all but a few rods in length of the existing #a4c miles of canal might have been omitted1 and an electric generating station with wheels to take the entire flow of the river might have been located not far from one end of the dam4 ,factories utilizing the electric power thus developed might have been located at any convenient points along the river-front or elsewhere1 and no space would have been made unavailable because of the necessity of head- and tail-water connections to scattered sets of wheels4 ,compare with the foregoing hydraulic development that at ,caon ,ferry on the ,missouri ,river1 in ,montana1 where #aj1jjj horse-power is developed under a water-head of #cb feet4 ,at ,caon ,ferry the power-house is #bbe feet by #ej feet at the floor level inside1 contains turbine wheels direct-connected to ten main generators of #g1ejj kilowatts1 or #aj1jjj horse-power combined capacity1 and is built on the river bank close to one end of the #ejj-;foot dam4 ,the canal which runs along the land side of the power-house1 and takes water at the up-stream side of the abutment1 is about twice the length of the power-house itself4 ,the saving in the cost of canal construction alone1 to say nothing of the saving as to the required area of land1 is evidently a large item in favor of the electrical development and transmission4 ,in its small area and short canal the ,caon ,ferry plant is not an exception1 but is rather typical of a large class of electric water-power plants that operate under moderate heads4 ,a like case may be seen in the plant at ,red ,bridge1 on the ,chicopee ,river1 in ,massachusetts1 where a canal #cdj feet long1 together with penstocks #ajj feet long1 convey water from one end of the dam and deliver it to wheels in the electric station with a head of #di feet4 ,this station contains electric generators with a combined capacity of #d1hjj kilowatts or #f1djj horse-power1 and its floor area is #ada by #eg feet4 ,illustration3 ,,fig4 #e4--;,canal at ,red ,bridge on ,chicopee ,river4 ,so1 again1 at ,great ,falls1 on the ,presumpscot ,river1 in ,north ,gorham1 ,me4 7see cut71 the electric station sets about #dj feet in front of the forebay wall1 which adjoins one abutment of the dam1 and there is no canal whatever1 as short penstocks bring water to the wheels with a head of #ce feet4 ,in ground area this station is #fg4e by #ee feet1 and its capacity in main generators is #b1jjj kilowatts or #b1gjj horse-power4 ,a striking illustration of the extent to which electrical transmission reduces the cost of water-power development may be seen at ,gregg's ,falls on the ,piscataquog ,river1 in ,new ,hampshire1 where an electric station of #a1bjj kilowatts capacity has been built close to one end of the dam1 and receives water for its wheels under a head of #ea feet through a short penstock1 #aj feet in diameter1 that pierces one of the abutments4 ,illustration3 ,,fig4 #f4 ,perhaps the greatest electric water-power station anywhere that rests close to the dam that provides the head for its wheels is that at ,spier ,falls 7see cut71 on the upper ,hudson4 ,one end of this station is formed by the high wall section of the dam1 and from this wall the length of the station down-stream is #cib feet1 while its width is #gj feet #aj inches1 both dimensions being taken inside4 ,the canal or forebay in this case1 like that at ,caon ,ferry1 lies on the bank side of the power-station1 and is about equal to it in length4 ,from this canal ten short penstocks1 each #ab feet in diameter1 will convey water under a head of #hj feet to as many sets of turbine wheels in the station4 ,these wheels will drive ten generators with an aggregate capacity of #bd1jjj kilowatts or #cb1jjj horse-power4 ,sometimes the slope in the bed of a river is so gradual or so divided up between the number of small falls1 or the volume of water is so small1 that no very large power can be developed at any one point without the construction of a long canal4 ,in a case of this sort electrical transmission is again available to reduce the expense of construction that will make it possible to concentrate all the power from a long stretch of the river at a single point4 ,this is done by locating electric generating stations at as many points as may be thought desirable along the river whose energy is to be utilized1 and then transmitting power from all of these stations to the single point where it is wanted4 ,a case in point is that of ,garvins ,falls and ,hooksett ,falls on the ,merrimac ,river and four miles apart4 ,at the former of these two falls the head of water is twenty-eight feet1 and at the latter it is sixteen feet4 ,to unite the power of both these falls in a single water-driven station would obviously require a canal four miles long whose expense might well be prohibitive4 ,energy from both these falls is made available at a single sub-station in ,manchester1 ,n4 ,h41 by a generating plant at both points and transmission lines thence to that city4 ,at ,hooksett the present capacity of the electric station is #a1jjj horse-power1 and at ,garvins ,falls the capacity is #a1gjj horse-power4 ,the river is capable of developing larger powers at both of these falls1 however1 and construction is now under way at ,garvins that will raise its station capacity to #e1jjj horse-power4 ,a similar result in the combination of water-powers without the aid of a long canal is reached in the case of ,gregg's ,falls and ,kelley's ,falls1 which are three miles apart on the ,piscataquog ,river4 ,at the former of these two falls the electric generating capacity is #a1fjj horse-power1 as previously noted1 and at the latter fall the capacity is #a1jjj horse-power4 ,in each case the station is close to its dam1 and no canal is required4 ,electrical transmission unites these two powers in the same sub-station at ,manchester that receives the energy from the two stations above named on the ,merrimac ,river4 ,instead of transmitting power from two or more waterfalls to some point distant from each of them1 the power developed at one or more falls may be transmitted to the site of another and there used4 ,this is1 in fact1 done at the extensive ,ludlow twine mills on the ,chicopee ,river1 in ,massachusetts4 ,these mills are located at a point on the river where its fall makes about #b1ejj horse-power available1 and this fall has been developed to its full capacity4 ,after a capacity of #b1djj horse-power in steam-engines had been added1 more water-power was sought1 and a new dam was located on the same river at a point about #d4e miles up-stream from the mills4 ,the entire flow of the river was available at this new dam1 and a canal #d4e miles long might have been employed to carry the water down to wheels at the mills in ,ludlow4 ,such a canal would have meant a large investment1 not only for land and construction1 but also1 possibly1 for damages to estates bordering on the river1 if all of its water was diverted4 ,instead of such a canal1 an electric generating station was located close to the new dam with a capacity of #f1djj horse-power1 and this power is transmitted to motors in the mills at ,ludlow4 ,even where the power is to be utilized at some point distant from each of several waterfalls1 it may be convenient to combine the power of all at one of them before transmitting it to the place of use4 ,this is actually done in the case of two electric stations located respectively at ,indian ,orchard and ,birchem ,bend on the ,chicopee ,river1 whose energy is delivered to the sub-station of the electrical supply system in ,springfield1 ,mass4 ,at the ,indian ,orchard station the head of water is #cf feet1 and at ,birchem ,bend it is #ad feet1 while the two stations are about #b miles apart4 ,a canal of this length might have been built to give a head of #ej feet at the site of the ,birchem ,bend dam1 but instead of this an electric station was located near each fall1 and a transmission line was built between the two stations4 ,each generating station was also connected with the sub-station in ,springfield by an independent line1 and power is now transmitted from one generating plant to the other1 as desired1 and the power of both may go to the sub-station over either line4 ,in the ,indian ,orchard station the dynamo capacity is about #b1jjj kilowatts1 and at ,birchem ,bend it is #hjj kilowatts4 ,another case showing the union of two water-powers by electrical transmission1 where the construction of an expensive canal was avoided1 is that of the electrical supply system of ,hartford1 ,conn4 ,this system draws a large part of its energy from two electric plants on the ,farmington ,river1 at points that are about #c miles apart in the towns of ,windsor and ,east ,granby1 respectively4 ,at one of these plants the head of water is #cb feet1 and at the other it is #bc feet1 so that head of #ee feet might have been obtained by building a canal #c miles long4 ,each of these stations is located near its dam1 and the generator capacity at one station is #a1bjj and at the other #a1ejj kilowatts4 ,transmission lines deliver power from both of these plants to the same sub-station in ,hartford4 ,sometimes two or more water-powers on the same river that are to be united are so far apart that any attempt to construct a canal between them would be impracticable4 ,this is illustrated by the ,spier and ,mechanicsville ,falls on the ,hudson ,river1 which are #be miles apart in a direct line and at a greater distance by the course of the stream4 ,at ,spier ,falls the head is #hj feet1 and at ,mechanicsville it is #ah feet4 ,union of the power of these two falls is thus out of the question for physical reasons alone4 ,electrical transmission1 however1 brings energy from both of these water-powers to the same sub-stations in ,schenectady1 ,albany1 and ,troy4 ,in another class of cases electrical transmission does what could not be done by any system of canals1 however expensive2 that is1 unites the water-powers of distinct and distant rivers at any desired point4 ,thus power from both the ,merrimac and the ,piscataquog rivers is distributed over the same wires in ,manchester2 the ,yuba and the ,mokelumne contribute to electrical supply along the streets of ,san ,francisco2 and the ,monte ,alto and ,tlalnepantla yield energy in the ,city of ,mexico4 ,it does not follow from the foregoing that it is always more economical to develop two or more smaller water-powers at different points along a river for transmission to some common centre than it is to concentrate the water at a single larger station by more elaborate hydraulic construction1 and then deliver all of the energy over a single transmission line4 ,the single larger hydraulic and electric plant will usually have a first cost larger than that of the several smaller ones1 because of the required canals or pipe lines4 ,a partial offset to this larger hydraulic investment is the difference in cost between one and several transmission lines1 or at least the cost of the lines that would be necessary between the several smaller stations in order to combine their energy output before its transmission over a single line to the point of use4 ,against the total excess of cost for the single larger hydraulic and electrical plant there should be set the greater expense of operation at several smaller and separate plants4 ,even a small water-driven electric station that can be operated by a single attendant at any one time must have two attendants if it is to deliver energy during the greater part or all of every twenty-four hours4 ,but a single attendant can care for a water-power plant of #b1jjj horse-power or more capacity1 so that two plants of #gej horse-power each will require double the operating force of one plant of #a1ejj horse-power4 ,if two such plants are constructed instead of one that has their combined capacity1 the monthly wages of the two additional operators will amount to at least one hundred dollars4 ,if money is worth six per cent yearly1 it follows that an additional investment of #a1bjj #j4jf #bj1jjj might be made in hydraulic work to concentrate the power at one point before the annual interest charge would equal the increase of wages made necessary by two plants4 ,reliability of operation is one of the most important requirements in an electric water-power plant1 and its construction should be carried out with this in view4 ,anchor ice is a serious menace to the regular operation of water-wheels in cold climates1 because it clogs up the openings in the racks and in the wheel passages4 ,anchor ice is formed in small particles in the water of shallow and fast-flowing streams1 and tends to form into masses on solid substances with which the water comes in contact4 ,at the entrance to penstocks or wheel chambers1 steel racks with long1 narrow openings1 say one and one-quarter inches wide1 are regularly placed to keep all floating objects away from the wheels4 ,when water bearing fine anchor or frazil ice comes in contact with these racks1 it rapidly clogs up the narrow openings between the bars1 unless men are kept at work raking off the ice as it forms4 ,at the ,niagara ,falls electric station1 in some instances1 when the racks become clogged1 they have been lifted1 and the anchor ice allowed to pass down through the wheels4 ,this is said to have proved an effective remedy1 but it would obviously be of no avail in a case where the ice clogged the passages of the wheels themselves4 ,the best safeguard against anchor ice is a large1 deep forebay next to the racks1 where the water1 being comparatively quiet1 will soon freeze over after cold weather commences4 ,the anchor ice coming down to this forebay and losing most of its forward motion1 soon rises to the surface or to the under side of the top coating of solid ice1 and the warmer water sinks to the bottom4 ,good construction puts the entrance ends of penstocks well below the surface of water in the forebay1 so that they may receive the warmer water that contains little or no anchor ice4 ,illustration3 ,,fig4 #g4--;,cross ,section of ,dike on ,chicopee ,river at ,red ,bridge4 ,illustrations of practice along these lines1 as to size1 depth of forebay1 and location of penstocks may be seen in many well-designed plants4 ,one instance is that at ,garvins ,falls1 on the ,merrimac ,river1 where the new hydraulic development for #e1jjj horse-power is now under way4 ,water from the river in this case comes down to the power-station through a canal #ejj feet long1 and of #fh feet average width midway between the bottom and the normal flow line4 ,in depth up to his flow line the canal is #ab feet at its upper and #ac feet at its lower end1 just before it widens into the forebay4 ,in this forebay the depth increases to #ag feet1 and the width at the rack is double that of the canal4 ,the steel penstocks1 each #ab feet in diameter1 terminate in the forebay wall at an average distance of #g feet behind the rack1 and each penstock has its centre #aj4f feet below the water level in the forebay4 ,as there is a large pond created by the dam in this case1 and as the flow of water in the canal is deep rather than swift1 enough opportunity is probably afforded for any anchor ice to rise to the surface before it reaches the forebay in this case4 ,penstocks for the electric station at ,great ,falls1 on the ,presumpscot ,river1 whence energy is drawn for lighting and power in ,portland1 ,me41 are each #h feet in diameter1 and pierce the forebay wall behind the rack with their centres #ae feet below the normal water level in the forebay4 ,in front of the forebay wall the water stands #bg feet deep1 and the pond formed by the dam1 of which the forebay wall forms one section1 is #a1jjj feet wide and very quiet4 ,though the ,maine climate is very cold in winter and the ,presumpscot is a turbulent stream above the dam and pond1 there has never been any trouble with anchor ice at the ,great ,falls plant4 ,an excellent illustration is thus presented of the fact that deep1 still water in the forebay is a remedy for troubles with ice of this sort4 ,maximum loads on electrical supply systems are usually from twice to four times as great as the average loads during each twenty-four hours4 ,a pure lighting service tends toward the larger ratio between the average and maximum load1 while a larger motor capacity along with the lamps1 tends to reduce the ratio4 ,furthermore1 by far the greater part of the energy output of an electrical supply system during each twenty-four hours must be delivered between noon and midnight4 ,for these reasons there must be enough water stored1 that can flow to the station as wanted1 to carry a large share of the load during each day1 unless storage batteries are employed to absorb energy at times of light load1 if the entire normal flow of the river is to be utilized4 ,it is usually much cheaper to store water than electrical energy for the daily fluctuations of load1 and the only practicable place for this storage is most commonly behind the dam that maintains the head for the power-station4 ,this storage space should be so large that the drain upon it during the hours of heavy load will lower the head of water on the wheels but little1 else it may be hard to maintain the standard speed of revolution for the wheels and generators1 and consequently the transmission voltage4 ,illustration3 ,,fig4 #h4--,valley ,flooded above ,spier ,falls on the ,hudson ,river4 ,at the ,great ,falls plant1 water storage to provide for the fluctuations of load in different parts of the day takes place back of the dam1 and for about one mile up-stream4 ,this dam is #dej feet long in its main part1 and a retaining wall increases the total length to about #a1jjj feet4 ,for half a mile up-stream from this dike and dam the average width of the pond is #a1jjj feet1 and its greatest depth is not less than #bg feet4 ,as the station capacity is #b1gjj horse-power in main generators1 with a head of #ce feet at the wheels the storage capacity is more than ample for all changes of load at different times of day4 ,the dam at ,spier ,falls1 on the ,hudson ,river1 is #a1hbj feet long between banks1 #aee feet high above bedrock in its deepest section1 and raises the river #ej feet above its former level4 ,behind the dam a lake is formed one-third of a mile wide and #e miles long4 ,water from this storage reservoir passes down through the turbines with a head of #hj feet1 and is to develop #cb1jjj horse-power4 ,as a little calculation will show1 this lake is ample to maintain the head under any fluctuation in the daily load4 ,at ,caon ,ferry1 where electrical energy for ,butte and ,helena1 ,mont41 is developed1 the dam1 which is #dhj feet long1 crosses the river in a narrow canyon that extends up-stream for about half a mile4 ,above this canyon the river valley widens out1 and the dam1 which maintains a head of #cj feet at the power-station1 sets back the water in this valley1 and thus forms a lake between two and three miles wide and about seven miles long4 ,at the station the generator equipment has a total rating of #aj1jjj horse-power4 ,from these figures it may be seen that the storage lake would be able to maintain nearly the normal head of water for some hours1 when the station was operating under full load1 however small the flow of the river above4 ,illustration3 ,,fig4 #i4--;,canal at ,bulls ,bridge on ,housatonic ,river4 ,,chapter ,,vii4 ,,the ,,location ,,of ,,electric ,,water-,,power ,,stations4 ,cost of water-power development depends1 in large measure1 on the location of the electric station that is to be operated4 ,the form of such a station1 its cost1 and the type of generating apparatus to be employed are also much influenced by the site selected for it4 ,this site may be exactly at1 or far removed from1 the point where water that is to pass through the wheels is diverted from its natural course4 ,a unique example of a location of the former kind is to be found near ,burlington1 ,vt41 where the electric station is itself a dam1 being built entirely across the natural bed of one arm of the ,winooski ,river at a point where an island near its centre divides the stream into two parts4 ,the river at this point has cut its way down through solid rock1 leaving perpendicular walls on either side4 ,up from the ledge that forms the bed of the stream1 and into the rocky walls1 the power-station1 about #aaj feet long1 is built4 ,the up-stream wall of this station is built after the fashion of a dam1 and is renforced by the down-stream wall1 and the water flows directly through the power-station by way of the wheels4 ,a construction of this sort is all that could well be attained in the way of economy1 there being neither canal nor long penstocks1 and only one wall of a power-house apart from the dam4 ,on the other hand1 the location of a station directly across the bed of a river in this way makes it impossible to protect the machinery if the up-stream wall1 which acts as the dam1 should ever give way4 ,the peculiar natural conditions favorable to the construction just considered are seldom found4 ,illustration3 ,,fig4 #aj4--,power-house on the ,winooski ,river1 near ,burlington1 ,vt4 ,one of the most common locations for an electric water-power station is at one side of a river1 directly in front of one end of the dam and close to the foot of the falls4 ,a location of this kind was adopted for the station at ,gregg's ,falls1 one of the water-powers included in the electric system of ,manchester1 ,n4 ,h41 where the spray of the fall rises over the roof of the station4 ,two short steel penstocks1 each ten feet in diameter1 convey the water from the forebay section of the dam to wheels in the station with a head of fifty-one feet4 ,illustration3 ,,fig4 #aa4--;,canal and ,power-house on ,st4 ,joseph ,river1 ,buchanan1 ,mich4 ,a similar location was selected for the station at ,great ,falls1 on the ,presumpscot ,river 7see cuts71 whence electrical energy is delivered in ,portland1 ,me4 ,four steel penstocks1 a few feet long and each eight feet in diameter1 bring the water in this case from the forebay section of the dam to the wheel cases in the power-house4 ,illustration3 ,,fig4 #ab4--,power-house on ,hudson ,river at ,mechanicsville4 ,where the power-station is located at the foot of the dam1 as just described1 that part which serves as a forebay wall usually carries a head gate for each penstock4 ,the overfall section of a dam may give way in cases like the two just noted without necessarily destroying the power-station1 but in times of freshet or very high water the station may be flooded and its operation stopped4 ,the risk of any such flooding will vary greatly on different rivers1 and in particular cases may be very slight4 ,location of the generating station close to the foot of the dam at one end obviously avoids all expense for a canal and cuts the cost of penstocks down to a very low figure4 ,such locations for stations are not limited to falls of any particular height1 and the short penstocks usually enter the dam nearer its base than its top and pass to the station at only a slight inclination from the horizontal4 ,at ,great ,falls1 above mentioned1 the head of water is thirty-seven feet4 ,a short canal is constructed in some cases from one end of a dam to a little distance down-stream1 terminating at a favorable site for the electric station4 ,construction of this sort was adopted at the ,birchem ,bend ,falls of the ,chicopee ,river1 whence energy is supplied to ,springfield1 ,mass4 ,these falls furnish a head of fourteen feet1 and the water-wheels are located on the floor of the open canal at its end4 ,the power-station is on the shore side of this canal1 and the shafts of the water-wheels extend through bushings in the canal wall1 which forms the lower part of one side of the station1 to connect with the electric generators inside4 ,this rather unusual location of water-wheels has at least the obvious advantage that they require no room inside of the station4 ,furthermore1 as the canal is between the station and the river1 any break in the canal is not apt to flood the station4 ,illustration3 ,,fig4 #ac4--,york ,haven ,power-house1 on ,susquehanna ,river1 ,pennsylvania4 ,an illustration of the use of a very short canal to convey water from one end of a dam to a power-station exists in the #aj1jjj horse-power plant at ,caon ,ferry1 ,mont41 where the head of water is thirty feet4 ,in this case the masonry canal is but little longer than the power-house1 and this latter sits squarely between the canal and the river1 virtually at the foot of the falls4 ,other examples of the location of generating stations between short canals and the river may be seen at ,concord1 ,n4 ,h41 where the head of water is sixteen feet2 at ,lewiston1 ,me41 where the head is thirty-two feet2 and at ,spier ,falls1 on the ,hudson ,river1 ,new ,york1 where there is a head of eighty feet4 ,there is some gain in security in many cases by locating the power-station several hundred feet from the dam and a little to one side of the main river channel4 ,for such cases a canal may be cheaper than steel penstocks when the items of depreciation and repairs are taken into account4 ,aside from the question of greater security for the station in the event of a break in the dam1 it is necessary in many cases to convey the water a large fraction of a mile1 or even a number of miles1 from the point where it leaves its natural course to that where the power-station should be located4 ,an example in point exists at ,springfield1 ,mass41 where one of the electric water-power stations is located about #a1djj feet down-stream from a fall of thirty-six feet in the ,chicopee ,river1 because land close to the falls was all occupied at the time the electric station was built4 ,illustration3 ,,fig4 #ad4--,power-house at ,caon ,ferry on the ,missouri ,river4 ,illustration3 ,,fig4 #ae4--,shawinigan ,falls ,power-plant4 ,the ,shawinigan ,falls of the ,st4 ,maurice ,river in ,canada occur at two points a short distance apart1 the fall at one point being about #ej and at the other #ajj feet high4 ,a canal #a1jjj feet long takes water from the river above the upper of these falls and delivers it near to the electric power-house on the river bank below the lower falls4 ,in this way a head of #abe feet is obtained at the power-house4 ,the canal in this case ends on high ground #acj feet from the power-house1 and the water passes down to the wheels through steel penstocks #i feet in diameter4 ,illustration3 ,,fig4 #af4--,power-house on ,white ,river1 ,oregon4 ,another interesting example of conditions that require a power-house to be located some distance from the point where water is diverted from its natural course may be seen at the falls on the ,apple ,river1 whence energy is transmitted to ,st4 ,paul1 ,minn4 ,by means of a natural fall of #cj feet1 a dam #dg feet high some distance up-stream1 and some rapids in the river1 it was there possible to obtain a total fall of #hb feet4 ,to utilize this entire fall a timber flume1 #a1eej feet in length1 was built from the dam to a point near the power-house on the river bank and below the falls and rapids4 ,the flume was connected with the wheels1 #hb feet below1 by a steel penstock #cac feet long and #ab feet in diameter4 ,as the ,st4 ,mary's ,river leaves ,lake ,superior it passes over a series of rapids about half a mile in length1 falling twenty feet in that distance4 ,to make the power of this great volume of water available1 a canal #ac1jjj feet long was excavated from the lake to a point on the river bank below the rapids4 ,between the end of the canal and the river sits the power-station1 acting as a dam1 and the water passes down through it and the wheels under a head of twenty feet4 ,illustration3 ,,fig4 #ag4--,power-house ,across ,canal at ,sault ,ste4 ,marie1 ,mich4 ,by means of a canal #af1bjj feet long from the ,st4 ,lawrence ,river a head of water amounting to fifty feet has been made available at a point on the bank of ,grass ,river near ,massena1 ,n4 ,y4 ,there again the power-station acts as a dam1 and the canal water passes down through it to reach the river4 ,illustration3 ,,fig4 #ah4--;,canal and ,station on ,payette ,river1 ,idaho4 ,from these illustrations it may be seen that in many cases1 in comparatively level country1 a water-power can be fully developed only by means of canals or pipe lines1 and the generating stations cannot be located at the points where the water is diverted4 ,thus far the cases considered have been only those with moderate heads and rather large volumes of water4 ,in mountainous country1 where rivers are comparatively small and their courses are marked by numerous falls and rapids1 it is generally necessary to utilize the fall of a stream through some miles of its length in order to effect a satisfactory development of power4 ,to reach this result1 rather long canals1 flumes1 or pipe lines must be utilized to convey the water to power-stations and deliver it at high pressures4 ,in cases of this kind the cost of the canal or pipe line may be the largest item in the power development1 and it may be an important question whether this cost should be reduced or avoided by the erection of several small generating plants instead of one large one4 ,california offers numerous examples of electric-power development with water that has been carried several miles through artificial channels4 ,an illustration of this class of work exists at the ,electra power-house on the bank of the ,mokelumne ,river1 in the ,sierra ,nevada ,mountains4 ,water is supplied to the wheels in this station under a head of #a1dej feet through pipes #c1fjj feet long leading to the top of a near-by hill4 ,to reach this hill the water1 after its diversion from the ,mokelumne ,river at the dam1 flows twenty miles through a canal or ditch and then through #c1jjj feet of wooden stave pipe4 ,another example of the same sort may be seen in the power-house at ,colgate1 on the ,north ,yuba ,river1 in the chain of mountains above named4 ,water taken from this river passes through a wooden flume nearly eight miles long to the side of a hill #gjj feet above the power-house1 and thence down to the wheels through steel and cast-iron pipes1 five in number and thirty inches each in diameter4 ,even with long flumes1 canals1 and pipe lines1 it may be necessary to locate a number of generating stations along a single river of the class now under consideration in order to utilize its entire power4 ,thus on the ,kern ,river1 which rises in the ,sierra ,nevada ,mountains and empties into ,tulare ,lake1 two electric power-stations are under construction1 and surveys are being made for three more4 ,of these stations1 the one at the lowest level will operate under an #hgb-;foot head of water1 and this water1 after its diversion from the river1 will pass through twenty-one tunnels1 with an aggregate length of about ten miles1 and through six flumes mounted on trestles and having a total length of #a1gjc feet4 ,next up-stream is a station near the point where water is diverted for the plant just named4 ,this second station will work under a head of #cag feet1 and water for it will come from a point farther up-stream by canals1 tunnels1 and flumes1 with an aggregate length of eleven and one-half miles4 ,at three points still higher up on this river it is the intention to locate three other power-stations by conducting the water in artificial channels1 about twelve and one-half1 fifteen1 and twenty miles in length respectively4 ,farther south in ,california1 on the ,santa ,ana ,river and ,mill ,creek1 extensive power developments on the lines just indicated have been carried out4 ,on ,mill ,creek1 about six miles from the city of ,redlands1 is an electric station operating under a head of #ecj feet1 with water in part diverted from the stream a little less than two miles above and brought down through a steel pipe #aj1bej feet long and thirty inches in diameter4 ,this pipe line also takes water from the tail race of another generating plant at its upper end4 ,with some additions and modifications1 the station just described is the famous ,redlands plant1 built in #ahic1 and believed to be the first for three-phase transmission in the ,united ,states4 ,illustration3 ,,fig4 #ai4--;,canal and ,power-station on ,neversink ,river1 ,new ,york4 ,at the upper end of the pipe line just named the second station operates1 in part1 with water drawn from ,mill ,creek through a combination of tunnels1 flumes1 and cement and steel pipes1 with a combined length of about three miles1 and delivered to some of the wheels with a head of #fbg feet4 ,the other wheels at this plant receive water drawn from the same creek by a pipe line about six miles long4 ,a large part of this line is composed of #ca-;inch cement pipe1 laid in trenches and tunnels4 ,the water in the #h1jjj feet of pipe next to the power-house has a fall of #a1ifj feet1 and this pipe is of steel and #bd and #bf inches in diameter4 ,the head of #a1ifj feet1 minus friction losses in the steel pipes1 is delivered at the wheels4 ,from the foregoing it appears that in a space of eight miles along ,mill ,creek there is a fall of more than #b1dij feet4 ,to utilize this fall1 water is diverted from the creek at three points within a distance of six miles and delivered in two power-stations under three different heads4 ,as the stream gathers in volume between the upper and the lower intakes1 an equal amount of power could have been developed in a single station only by taking the three separate conduits or pipe lines to it and delivering their water there at three heads4 ,whether the expense of extending conduits and pipe lines to a single generating station will more than offset the advantages to be gained thereby is a question that should be decided on a number of factors varying with each case4 ,in general1 it may be said that the smaller the volume of water to be handled and the greater its head1 the more advantageous is it to concentrate the generating machinery in the smallest practicable number of stations4 ,on the ,santa ,ana ,river1 into which ,mill ,creek flows1 the ,santa ,ana plant1 whence energy is transmitted to ,los ,angeles1 is located4 ,water reaches this plant through a conduit of tunnels1 flumes1 and pipes1 with a total length of about three miles from the point where the flow of the river is diverted4 ,the #b1baj feet of this conduit nearest the power-plant are composed of #cj-;inch steel pipe1 with a fall of #gbh feet4 ,within fifteen miles of ,mexico ,city are five water-power stations that supply energy for its electrical system4 ,two of these stations are on the ,monte ,alto and three are on the ,tlalnepantla ,river1 the two former stations being about three miles1 and the more distant of the three latter stations five miles1 apart4 ,at a distance of several miles above the highest station on each river the water is diverted by a canal1 and the water of each of these canals1 after passing through the wheels of the highest station1 goes on to the remaining station1 or stations1 on the same river by a continuation of the canal4 ,illustration3 ,,fig4 #bj4--,wood ,pipe ,line to ,pike's ,peak ,power-house4 ,by placing the stations so short a distance apart the head of water at each station is reduced4 ,on one stream these heads are #dib and #eid feet respectively1 and at two of the stations on the other stream they are #edg and #bie feet respectively4 ,this division of the total head of water afforded by each river results in a rather small capacity for each station1 the total at the five plants being only #d1bbe kilowatts4 ,in contrast with this figure the already mentioned ,electra plant has generators of #aj1jjj1 the ,santa ,ana plant generators of #c1jjj1 and the larger of the two ,mill ,creek plants generators of #c1ejj kilowatts capacity4 ,it should be noted that the cost of operation1 as well as that of original construction1 will vary materially between one large and several smaller stations of equal total capacity1 the advantage as to operative cost being obviously with the one large plant4 ,illustration3 ,,fig4 #ba4--,power-house at ,great ,falls1 ,presumpscot ,river4 ,all of the power-stations here considered have been equipped with water-wheels and generators operating on horizontal shafts1 and this is the general practice4 ,this arrangement brings the generators and the floor of the power-station within a few feet of the level of the tail-water4 ,by the general use of draught tubes with turbine wheels the floors of stations are often kept twenty feet or more above the tail-water level4 ,where the total available head of water is quite small1 as is often the case with rivers where the volume of water is great1 it is generally necessary to bring the level of the station floor down to within a few feet of the tail-water4 ,the ,birchem ,bend station of the ,springfield1 ,mass41 electric system affords a good example of this sort1 the floor of this station being only #b4f feet above the ordinary level of the tail-water4 ,at this station the difference of level between the head- and tail-water is only fourteen feet1 and even with the low floor level named the top sides of the horizontal turbine wheels are covered only by #d4e feet of water4 ,at the ,garvin's ,falls station of the ,manchester1 ,n4 ,h41 electric system the level of the floor of the generator room is thirteen feet above the ordinary level of the ,merrimac ,river1 on the bank of which this station is located2 but in this case the total head of water is about twenty-eight feet4 ,the high water of the ,merrimac in #ahif1 before the ,garvin's ,falls station was built1 reached a point #e4bd feet above its present floor level1 and #ah4bd feet above the ordinary level of the river at the point where the station is located4 ,under the ,red ,bridge electric station of the ,ludlow ,manufacturing ,company1 on the ,chicopee ,river1 in ,massachusetts1 the tail-water is twenty feet below the level of the floor and twenty-four feet below the centres of the water-wheel and generator shafts4 ,the difference between wheel-shaft and tail-water levels at this station is near the maximum that can be attained with horizontal pressure turbines1 because a draught tube much longer than twenty-five feet does not give good results4 ,in a pressure turbine the guides and wheel must be completely filled with water1 as must also the draught tube1 for efficient operation4 ,if draught tubes are much more than twenty-five feet long1 it is hard to keep a solid column of water from turbine to tail-water in each1 and if this is not done a part of the head of water becomes ineffective4 ,as pressure turbines are employed almost exclusively at electric stations with low heads of water1 it is frequently impossible to locate such stations above the possible level of tail-water in times of flood if horizontal wheels direct-connected to generators are employed4 ,illustration3 ,,fig4 #bb4--,power-house at ,garvin's ,falls on the ,merrimac ,river4 ,if turbines with vertical shafts are to be used1 a power-station may be so located or constructed that all the electrical equipment will be above the highest known water-mark4 ,with vertical shafts1 connecting wheels1 and generators1 the main floor of an electric station may be located above the crest of the falls where the power is developed instead of at or near their base4 ,illustration3 ,,fig4 #bc4--,power-house ,no4 #b at ,niagara ,falls4 ,by far the most important examples of electric stations laid out on this plan are those at ,niagara ,falls1 where there are four such plants4 ,two of these generating plants1 with an aggregate capacity of #aje1jjj horse-power1 stand a mile above the falls1 and are supplied with water through a short canal from ,niagara ,river4 ,beneath each of these two stations a long1 narrow wheel pit has been excavated through rock to a depth of #agb feet below the level of water in the canal4 ,both wheel pits terminate in a tunnel #g1jjj feet long that opens into the river below the falls4 ,in this wheel pit the tail-water level is #afa feet below that of the water in the canal1 and #aff feet below the floor of the power-station4 ,water passes from the canal down the wheel pits to the wheels near the bottom through steel penstocks1 each seven feet in diameter1 and a vertical shaft extends from each wheel case to a generator in the station above4 ,locations like that at ,niagara give great security against high water and washouts1 but are seldom adopted because of the large first cost of plant construction4 ,with heads of water from several hundred to #b1jjj feet the loss of a few feet of head reduces the available power to only a very slight extent1 and impulse wheels are usually employed4 ,draught tubes are not available to increase the heads at such wheels1 and any fall of the water after it leaves the wheels does no useful work4 ,illustration3 ,,fig4 #bd4--;,colgate ,power-house4 ,electric stations driven by impulse wheels under great heads1 like those at ,colgate1 ,electra1 ,kern ,river1 ,santa ,ana ,river1 and ,mill ,creek1 may be located far enough above the beds of their water-courses to avoid dangers from freshets1 without serious loss of available power4 ,,chapter ,,viii4 ,,design ,,of ,,electric ,,water-,,power ,,stations4 ,illustration3 ,,fig4 #be4--;,cross ,section of ,columbus1 ,ga41 ,power-station4 ,water-wheels must be located at some elevation between that of head- and tail-water4 ,with horizontal shafts and direct-connected wheels and generators the main floor of the station is brought below the level of the wheel centres4 ,this is much the most general type of construction1 and was followed in the ,massena1 ,sault ,ste4 ,marie1 ,caon ,ferry1 ,colgate1 ,electra1 ,santa ,ana1 and many other well-known water-power stations4 ,if horizontal shafts are employed for wheels and generators with belt or rope connections between them the floor of the generator room may be elevated a number of feet above the wheels4 ,this difference of elevation is usually provided for either by upper and lower parts of the same room1 or by separate rooms one above the other and a floor between them4 ,a two-story construction of this latter sort was frequently adopted in the older water-power stations1 and good examples of it may be seen in connection with the electrical supply system at ,burlington1 ,vt41 and the ,indian ,orchard station in the ,springfield1 ,mass41 system4 ,vertical wheel shafts make the elevation of the main or generator floor of a station independent of that of the wheels1 and thus give the highest degree of security against high water4 ,after the vertical wheel shaft reaches the generator room1 it may be geared to a horizontal shaft that has one or more dynamos directly mounted on it1 or drives dynamos through belts or ropes4 ,belt-driving in this way1 from horizontal shafts connected by bevel gears with vertical wheel shafts1 is not uncommon in the older class of water-power stations4 ,generators mounted singly or in pairs on horizontal shafts that are driven by gearing on vertical wheel shafts have been adopted at the ,lachine ,rapids and ,south ,bend plants1 and it seems to offer a desirable method of connection in cases where vertical wheels are necessary and the cost of generators must be kept at a low figure4 ,with this method of driving the generators can be designed for any economical speed and step bearings avoided4 ,illustration3 ,,fig4 #bf4--;,cross ,section of ,combined ,steam- and ,water-power ,station at ,richmond1 ,va4 ,illustration3 ,,fig4 #bg4--;,cross ,section of ,wheel ,house at ,buchanan1 ,mich4 ,the most desirable method of driving generators with vertical wheels1 where the expense is not too great1 is the direct mounting of each generator on the upper end of a wheel shaft 7see cut74 ,this method of connection not only requires a special type of generator1 but may put serious limits on its speed4 ,in general1 the peripheral speed of a pressure turbine should be about #ge per cent of the theoretical velocity of water issuing under a head equal to that at which the wheel operates1 in order to give the best efficiency4 ,the rotative speeds of turbines1 operating under any given head1 should thus increase as their capacities and diameters decrease4 ,because of these principles it is the common practice1 with horizontal wheels1 to mount two or more on each shaft to which a generator is direct-connected in order to obtain a greater speed of rotation than could be obtained with a single wheel of their combined power4 ,thus1 at ,sault ,ste4 ,marie the horizontal shaft on which each #djj-kilowatt generator is mounted is driven at #ahj revolutions per minute by four turbines under a head of about #bj feet4 ,at ,massena the head of water is #ej feet1 and each #e1jjj horse-power generator is driven at #aej revolutions per minute by six turbines on a horizontal shaft4 ,vertical turbines are sometimes mounted singly on their shafts1 as was done in the hydroelectric plant at ,oregon ,city on the ,willamette ,river1 and this practice gives speeds that are too low for direct-connected dynamos of moderate cost1 unless the head of water is unusually great4 ,at the ,oregon ,city plant the head of water is only #dj feet1 and yet a single #db-;inch turbine was mounted on the vertical shaft that drives each generator4 ,illustration3 ,,fig4 #bh4--,longitudinal ,section of ,buchanan1 ,mich41 ,power-house4 ,the most notable examples of direct-connected generators and vertical turbines is that at ,niagara ,falls1 where twenty-one generators of #e1jjj horse-power each are mounted at the tops of as many vertical wheel shafts in two of the four stations4 ,each vertical shaft in the ,niagara stations is driven at #bej revolutions per minute by a pair of turbines1 one above the other4 ,the maximum head between the water in the ,niagara canal and that in the tunnel which forms the tail-race is #afa feet4 ,on ten shafts the centres of the wheel cases are #acf feet below the level of water in the canal1 and no draft tubes are used4 ,illustration3 ,,fig4 #bi4--,section of ,power-house ,no4 #b at ,niagara ,falls4 ,the eleven pairs of wheels at the second ,niagara power-house have their centre line #abh4be feet below the canal level and a draft tube for each pair of wheels extends to a point below the tail-water level4 ,it is entirely practicable to use more than a single pair of turbines on the same vertical shaft1 as is shown at the ,hagneck station on the ,jura1 in ,switzerland1 where the head of water is about twenty-one feet and four turbines are mounted on each vertical shaft4 ,the combined capacity of these four wheels on each shaft is #a1ejj horse-power and its speed is #ajj revolutions per minute4 ,at the top of each shaft an #h1jjj-volt generator1 with external1 revolving magnet frame1 is mounted4 ,the use of four wheels per vertical shaft presents no great difficulty and should be resorted to more frequently in the future4 ,illustration3 ,,fig4 #cj4--;,interior of ,power-house1 ,buchanan1 ,mich4 ,for horizontal1 direct-connected turbine wheels and generators the nearly uniform practice is to locate the generators in a single row from one end of a station to the other1 and this brings the turbines into a parallel row4 ,on this plan the shaft of each connected generator and its group of turbines sets at right angles to the longer sides of a station and approximately parallel with the direction in which water flows to the wheels4 ,the typical water-power station with direct-connected units is thus a rather long1 narrow building into which water enters on one side through penstocks and leaves on the other through tail-races4 ,such stations usually set with one of the longer sides parallel to the river into which the tail-water passes and between this river and the canal or pipe line4 ,at ,massena the electric station occupies the position of a dam between the end of the power canal and the ,grass ,river1 being about #aej feet wide and #eej feet long4 ,canal water entering this station passes through its wheels to the river under a head of about #ej feet4 ,a similar construction was followed at ,sault ,ste4 ,marie1 where the power-station separates the end of the canal from the ,st4 ,mary's ,river4 ,this station is #ajj feet wide1 #a1cfh feet long1 and is to contain #hj sets of horizontal wheels1 each set being connected to its own generator1 and through these wheels the canal water passes under a head of approximately #bj feet4 ,ten generators are placed in line at the ,caon ,ferry station which is #bbe by #ej feet inside1 and each generator is driven by a pair of horizontal wheels under a head of #cj feet4 ,this station sets between a short canal and the ,missouri ,river1 near one end of the dam4 ,passing from water-heads of less than #ej to those of several hundred or even more than #a1jjj feet1 the general type of station building remains about the same1 but there is an important change in the arrangement of direct-connected wheels and generators4 ,with these high heads of water1 wheels of the impulse type1 to which the water is supplied in the form of jets from nozzles1 are employed4 ,these jets pass to the wheels in planes at right angles to their shafts1 instead of flowing in lines parallel to these shafts like water to pressure turbines4 ,the shafts of impulse wheels and their direct-connected generators are consequently arranged parallel with the longer instead of the shorter sides of their stations4 ,this plan results in long1 narrow stations with water entering at one and leaving at the other of the longer sides1 just as in the case of direct-connected turbines under moderate heads4 ,stations with direct-connected impulse wheels are even longer for a given number and capacity of units than are stations with pressure turbines4 ,colgate power-house1 on the ,north ,yuba ,river1 contains seven generators1 each direct-connected to an impulse wheel and shafts all parallel to its longer sides4 ,this station is #bge feet long by #dj feet wide1 and the water which enters one side by five iron pipes1 #cj inches each in diameter1 under a head of about #gjj feet1 is discharged from the other side into the river4 ,illustration3 ,,fig4 #ca4--,plan of ,generating ,station near ,cedar ,lake for ,city of ,seattle1 ,wash4 ,illustration3 ,,fig4 #cb4--;,foundation of ,power-station at ,spier ,falls4 ,illustration3 ,,fig4 #cc4--,plan of ,power-station at ,great ,falls4 ,at ,electra station on the ,mokelumne ,river five pairs of impulse wheels are direct-connected to five generators1 each unit having its shaft diagonal with the walls of the building1 and pipes deliver water to the wheels under a head of #a1dej feet4 ,the ground plan of the generator room at this plant is #dj by #bjh feet4 ,the power-station on ,santa ,ana ,river1 whence energy is transmitted #hc miles to ,los ,angeles1 measures #abg feet long and #cf feet wide inside1 and contains four generating units in line1 each of which consists of a direct-connected dynamo and impulse wheel1 with shafts parallel to the longer sides of the station4 ,jets driving the wheels in this station are delivered under a head of #gbh feet minus the loss by friction in a penstock #b1baj feet long4 ,illustration3 ,,fig4 #cd4--,power-house at ,red ,bridge on ,chicopee ,river4 ,both of the first ,niagara plants1 with vertical wheels far below the stations in the pits1 are long and narrow and have their generators in a single row4 ,the later of these two stations has a ground area of approximately #gb by #dif feet outside1 and contains eleven generators all in line4 ,from these examples it may be seen that the prevailing type of electric water-power station1 whether designed for horizontal or vertical wheels of either the pressure or impulse type1 is wide enough for only a single row of generators and wheels1 and has sufficient length to accommodate the required number of units4 ,a few modern stations that depart from this general plan will be found1 as that at ,great ,falls1 on the ,presumpscot ,river1 whence electrical supply for ,portland1 ,me41 is drawn4 ,this station sets about forty feet in front of the forebay end of the dam1 and two penstocks enter the rear wall1 while the other two enter one each through two of the remaining opposite sides4 ,of the four generators1 with their direct-connected wheels1 two are arranged with parallel shafts1 while the other two have their shafts in line and at right angles to the lines of the former two4 ,the station containing these generating sets has a floor area of #ee by #fg4e feet4 ,illustration3 ,,fig4 #ce4--,plan and ,elevation of ,red ,bridge ,station on the ,chicopee ,river4 ,modern electric stations driven by water-power are usually but one story in height and are clear inside from floor to roof1 save for cranes and roof trusses4 ,this construction may be seen in the ,niagara1 ,spier ,falls1 ,caon ,ferry1 ,colgate1 ,electra1 ,santa ,ana ,river and many other notable plants4 ,in spite of this one-story style of construction1 the electric stations reach fair elevations because of the necessity for head room to operate cranes in placing and removing generators4 ,at ,garvin's ,falls1 on the ,merrimac ,river1 the electric station contains generators of #fej kilowatts each and the distance from floor to the lower cords of roof trusses is #bg feet4 ,in the station at ,red ,bridge1 on the ,chicopee ,river1 where generators are of #a1jjj kilowatts capacity each1 the distance between floor and the under side of roof beams is #cj4ff feet4 ,between the floor and roof trusses at the ,birchem ,bend station1 on the river last named1 the distance is #bf4be feet1 but each generator is rated at only #djj kilowatts4 ,in the ,caon ,ferry plant1 with its generators of #gej kilowatts each1 the distance from floor to roof trusses is #bh feet4 ,at the plant on ,santa ,ana ,river1 the #gej-kilowatt generators1 being connected to impulse-wheels1 operate at #cjj revolutions per minute1 have relatively small diameters and are mounted over pits in the floor so that their shaft centres are only about two feet above it4 ,by these means the distance from floor to roof trusses was reduced to #ah4be feet4 ,all these examples of elevations between floors and roof supports are for stations with direct-connected generators and horizontal wheels4 ,in the new ,niagara station1 where generators of #c1gej kilowatts each are mounted on vertical wheel shafts that rise from the floor1 the distance between the floor and roof trusses is #ci4e feet4 ,electric stations driven by water-power are now constructed almost entirely of materials that will not burn--that is1 stone1 brick1 tile1 concrete1 cement1 iron1 and steel4 ,stone masonry laid with cement mortar or concrete masonry is very generally employed for all those parts of the foundations that come in contact with the tail-water4 ,for sub-foundations bedrock is very desirable1 but where this cannot be reached piles are driven closely and their tops covered with several feet of cement concrete as a bedding for the stone foundation4 ,where stone is plenty or bricks hard to obtain1 the entire walls of a water-power station are frequently laid entirely with stone in concrete mortar4 ,if bricks can readily be had they are more commonly used than stone for station walls above the foundations4 ,concrete formed into a monolithic mass is a favorite type of construction for the foundations1 walls and floors of water-power plants in ,southern ,california4 ,cement and concrete are much used for station floors in all parts of the country1 and these floors are supported by masonry arches in cases where the tail-water flows underneath the station after leaving the wheels4 ,station roofs are usually supported by steel trusses or ,i-beams1 and slate and iron are favorite roof materials4 ,with iron roof-plates an interior lining of wood1 asbestos1 or some other poor conductor of heat is much used to prevent the condensation of water on the under side of the roof in cold weather4 ,walls of water-power stations are usually given sufficient thickness of masonry to support all loads that come upon them without the aid of steel columns4 ,in some cases where cranes do not extend entirely across their stations1 one end of each crane is supported by one of the station walls and the other end by a row of iron or steel columns rising from the floor4 ,where the generator-room of a station has its floor level below high-water mark especial care should be taken to make the walls water-proof to an elevation above this mark4 ,as the travelling-crane and the loads which it carries in erecting wheels and generators form a large part of the weight on the station walls1 these walls are often reduced as much as one-half in thickness at the level of the crane1 thus forming benches on which the ends of the cranes rest4 ,illustration3 ,,fig4 #cf4--,steel ,penstocks at ,chamblay ,power-house4 ,the ,garvin's ,falls station1 on the ,merrimac ,river1 rests on arches of stone masonry through which the tail-water passes1 and the brick walls are water-proofed to an elevation eight feet above the floor4 ,at twenty feet above the floor the twenty-four-inch brick walls on the two longer sides are reduced to eight inches in thickness1 thus forming benches each sixteen inches wide on which the crane travels4 ,arches of stone masonry support the twenty-four-inch brick walls of the station at ,red ,bridge1 on the ,chicopee ,river1 and these walls on the two longer sides decrease in thickness to twelve inches at an elevation of twenty-one feet above the floor1 thus forming benches twelve inches wide for the ends of the crane4 ,one concrete wall of the ,santa ,ana station is #b4e feet thick to a distance of #ac4e feet above the floor1 and then shrinks to a thickness of #a4e feet1 corresponding to that of the opposite wall1 thus forming a bench twelve inches wide for one end of the crane4 ,the other end of the crane in this case is supported by an ,i-beam on a row of iron columns4 ,it is not uncommon to locate horizontal turbines in a room separate from that occupied by the generators to which they are direct-connected1 in order to protect the latter from water in the event of a break in penstocks or wheel cases4 ,in cases of this sort the shafts connecting wheels and generators pass through the wall between them4 ,the horizontal turbines may be located at the bottom of a canal whose water presses against the wall through which the wheel shafts pass1 or they may be contained in iron cases at the ends of penstocks4 ,in this latter case an extension of the station is often provided for a wheel room to contain these cases4 ,such wheel rooms are long1 narrow1 low-roofed and parallel to the generator rooms of their stations4 ,the floors of these wheel rooms are at nearly the same levels as the floors of generator rooms1 but elevations of their roofs above the floors are much less than like elevations in the main parts of the stations4 ,the ,garvin's ,falls1 ,red ,bridge1 and ,apple ,river stations have wheel rooms of the type just described4 ,with impulse-wheels to which water passes in planes at right angles to their shafts it is desirable1 in order to avoid changes in the direction of water pipes1 that direct-connected wheels and generators occupy the same room1 and this is the arrangement at the ,colgate1 ,electra1 ,santa ,ana1 ,mill ,creek1 and many other power-houses using such equipments4 ,the area of a wheel room may frequently be reduced at stations operating direct-connected horizontal-pressure turbines under low heads by placing the wheels at the bottom of the canal which has one side of the station or generator room for a retaining wall4 ,this plan was adopted at the ,birchem ,bend plant with a head of fourteen feet1 and at the ,sault ,ste4 ,marie station where the head of water is about twenty feet4 ,vertical wheels direct-connected to generators must be directly underneath the main room of their station1 and may be in a canal over which the station is built1 in a wheel room that forms its lower part1 or in a wheel pit and supplied with water through penstocks1 as at the ,niagara ,falls plants4 ,step-up transformers developing very high voltages are not an element of safety in a generator room1 and the better practice is to locate them in a separate apartment by themselves1 if not in a separate building4 ,for the ,niagara ,falls plant1 the transformers that deliver three-phase current at #bb1jjj volts are located in a building across the canal from the generating plant4 ,at ,caon ,ferry the transformers operating at #ej1jjj volts1 three-phase1 are located in a steel and iron addition to the power-house4 ,transformers at ,electra station1 which are intended to work ultimately at #fj1jjj volts1 are located in an extension of the main building and are separated from the generator-room by a wall4 ,at the ,santa ,ana plant the #cc1jjj-volt transformers are grouped in one corner of the generator room1 but no partition separates their space from the remainder of the room4 ,in the ,colgate plant the transformers1 working at #dj1jjj volts1 are spaced along one of the longer sides of the station opposite to and only a few feet from the row of generators4 ,one end of the main room in the ,apple ,river plant is devoted exclusively to the #be1jjj-volt transformers1 and there is a distance of about twenty-seven feet between them and the nearest generator4 ,the highest degree of safety for transformers at these great voltages seems to require that they be located in a separate room where the floor1 walls1 and roof are made entirely of incombustible material4 ,illustration3 ,,fig4 #cg4--,one of the ,turbine ,wheels at ,spier ,falls on the ,hudson ,river4 ,water supplied to horizontal turbine wheels under moderate heads usually enters the station by penstocks on one side and leaves it by the tail-race on the other1 but this is not true in every case4 ,at the ,birchem ,bend plant1 the canal in which the wheels are located being between the station and the river1 water never enters or passes under the station1 which has a continuous foundation4 ,so again at the ,apple ,river plant the single supply pipe1 twelve feet in diameter and delivering water under a head of eighty-two feet1 lies parallel with the greater length of the station and between it and the river4 ,short penstocks pass from this supply pipe into the wheel section of the power-house1 and the water after passing through the wheels flows out to the river between the masonry piers that support the twelve-foot pipe4 ,the generator section of this station has thus no water flowing under it4 ,an interesting distinction may be noted between the conditions as to the tail-water about the foundations of stations working under low and those under great water heads4 ,in cases of the former sort the volumes of water are relatively great and the foundations of stations are usually submerged1 and much reduced in area to make room for the tail-races4 ,thus1 the foundations of the station at ,red ,bridge1 where there is #di feet head1 have nearly all of their footings under water1 and of a total length of #ade feet at the top of these foundations the six tail-races underneath cut out #ib feet4 ,these tail-races extend underneath both the wheel and generator rooms4 ,where power is derived from water delivered under great head from pipe nozzles to impulse-wheels1 stations are usually well above the water levels of streams into which they discharge1 and passages for tail-water underneath the station shrink to small tunnels through their foundations4 ,seven of these tunnels have a total width of less than #be feet at the ,santa ,ana ,river station1 which is #abg feet long1 and where the head of water is #gbh feet4 ,at the ,colgate plant1 with its head of #gjj feet1 the water1 at times of light load1 instead of flowing out of its passages underneath the station1 shoots from the pipe nozzles clear across the ,north ,yuba ,river on the bank of which the station stands4 ,illustration3 ,,fig4 #ch4--,power ,plant of ,ludlow ,manufacturing ,company4 ,in a comparison of floor areas per kilowatt of main generator capacities in electric stations using water- and those using steam-power1 the matter of space for transformers may be entirely omitted1 because the extent of this space is independent of the type or location of water-wheels1 or the difference of water and steam as motive powers4 ,where water-wheels and their connected generators occupy separate rooms1 as is often the case with turbines under low pressures1 the wheel room has a little less length1 and is generally narrower than the generator room4 ,thus1 at the ,red ,bridge station the generator room is #ada feet long and the wheel room about #abg feet1 while the former is #cc4cc feet and the latter #bd feet wide4 ,so again at ,apple ,river ,falls the generator room is #adj by #cj feet and the wheel room #ajf by #bb feet1 the generator room in this case containing also transformers4 ,it follows that if wheels can be located outside of the station1 as in a canal1 quite a reduction in its total floor area can be made1 which may easily range from #bj to #dj per cent4 ,the kilowatt capacity per square foot of floor area in both wheel and generator rooms combined tends to increase with the individual capacity of the generating units4 ,generators on vertical shafts seem to require about as much floor space per unit of capacity as do generators on horizontal shafts4 ,in the ,red ,bridge station the total capacity is #d1hjj kilowatts of main generators in six horizontal units1 and the area of the generator room alone is #j4if square foot per kilowatt of this capacity4 ,the second station with vertical units at ,niagara ,falls has a capacity of #da1bej kilowatts in eleven generators on vertical shafts1 and its floor area amounts to #j4hf square foot per kilowatt2 narrow impulse-wheels of large diameter tend to economy of floor space1 as in ,electra station1 where the room containing wheels and generators has an area of only #j4hc square foot per unit of its #aj1jjj kilowatts capacity4 ,at the ,colgate plant1 where the total rating of generators is #aa1bej kilowatts1 the floor area under wheels and generators is almost exactly one square foot per kilowatt4 ,the ,santa ,ana station1 with a total capacity of #c1jjj kilowatts1 has #a4eb square feet of floor area for each unit of capacity4 ,this last figure may be compared with the #a4gb square feet per kilowatt of generator rating for the #d1hjj-kilowatt station at ,red ,bridge and the #a4ge square feet per unit of capacity in the #hjj-kilowatt plant at ,birchem ,bend4 ,illustration3 ,,fig4 #ci4--,power-house on ,payette ,river1 ,idaho4 ,all types of water-power stations with direct-connected wheels and generators have much smaller floor areas per unit capacity than do steam-power stations with direct-connected horizontal units4 ,thus1 the modern steam-driven station at ,portsmouth1 ,n4 ,h41 has a plan area in engine- and boiler-rooms of #af1hga square feet1 and its total capacity in four direct-connected units is #d1djj kilowatts1 so that the area amounts to #c4hb square feet per kilowatt rating of its generators4 ,of this area about #df per cent is in the boiler-room4 ,,floor ,,dimensions ,,for ,,direct-,,connected1 ,,horizontal ,,water-,,wheels ,,and ,,generators ,,at ,,electric ,,stations4 ---------------------------------------- ------------------- ,number ,total ,station4 ,feet ,long4 ,feet ,wide4 of ,kilowatt ,generators4,capacity4 ---------------------------------------- ------------------- ,a,niagara1 ,no4 #b #dif #gb #aa #da1bej ,sault ,ste4 ,marie #a1cfh #ajj #hj #cb1jjj ,colgate #bge #dj #g #aa1bej ,electra #bjh #dj #e #aj1jjj ,caon ,ferry #bbe #ej #aj #g1ejj ,red ,bridge #ada #eg #f #d1hjj ,apple ,river #adj #cj #d #c1jjj #ajf #bb ,santa ,ana ,river #abg #cf #d #c1jjj ,great ,falls #fg4e #ee #d #b1jjj ,garvin's ,falls #fb #cj #b #a1cjj #ej #bc ,birchem ,bend #ef4f #bf4g #b #hjj ,portsmouth #ad4d #aai4ff 7steam-driven7inside1 but minus #cfj #e #d1djj square feet4 ---------------------------------------- ------------------- ,a ,vertical wheel shafts4 ,some of these dimensions apply to the inside and some to the outside of stations4 ,some small projections are not included4 ,,chapter ,,ix4 ,,alternators ,,for ,,electrical ,,transmission4 ,dynamos in the generating station of an electric transmission system should be so numerous that if one of them is disabled the others can carry the maximum load4 ,if only two generators are installed1 it is thus desirable that each be large enough to supply the entire output1 so that the dynamo capacity exceeds the greatest demand on the station by #ajj per cent4 ,to avoid so great excess of dynamo capacity it is common practice to install more than two generators4 ,other considerations also tend to increase the number of dynamos in the generating station of a transmission system4 ,thus one transmission line may be devoted exclusively to lighting1 another to stationary motors1 and a third to electric railway service2 and it may be desirable that each line be supplied by an independent dynamo to avoid any effect of fluctuations of railway or motor load on the lighting system4 ,at the generating station of the transmission system that supplies electric light and power in ,portland1 ,me41 the idea of independent units has been carried out with four #ejj-kilowatt dynamos1 each driven by a pair of wheels fed with water through a separate penstock from the dam4 ,each of these dynamos operates one of the four independent transmission circuits4 ,where a number of water-power stations feed into a single sub-station the requirement that each generating station have its capacity divided up among quite a number of dynamos may not exist1 since one station may be entirely shut down for repairs and the load carried meantime by the other stations4 ,a good illustration of this point may be seen at ,manchester1 where a single sub-station receives energy transmitted from four water-power plants4 ,at one of these plants the entire capacity of #a1bjj kilowatts is in a single generator4 ,the foregoing considerations as to the number of dynamos apply with equal force to both steam- and water-driven stations1 but other factors tend to increase the number of dynamos in water-power plants where the head of water is comparatively small4 ,this tendency is due to the fact that the peripheral speeds of pressure turbine water-wheels should be about twenty-five per cent less than the velocity at which water would issue from an opening under the head of water at which these wheels operate in order to secure high efficiency4 ,this velocity of water and therefore the peripheral speed of pressure turbine wheels varies with the square root of the head of water4 ,illustration3 ,,fig4 #dj4--;,generators at ,sault ,ste4 ,marie ,power ,plant4 ,since the peripheral speed of turbines is thus determined by the heads of water under which they operate1 and since the diameters of turbines must increase with their capacities1 the rate of revolution for pressure turbines under any given head decreases as the power goes up4 ,for this reason it is often desirable to use a larger number of dynamos in a water-power plant than would otherwise be required in order to avoid very low speeds of revolution on the direct-connection to the turbines4 ,a notable illustration of this practice exists in the great water-power plant of the ,michigan-,lake ,superior ,power ,company1 at ,sault ,ste4 ,marie1 ,mich41 where a generating capacity of #cb1jjj kilowatts is divided up between #hj dynamos of #djj kilowatts each4 ,the head of water available at the pressure turbines in this plant is about #af feet1 and their speed is #ahj revolutions per minute4 ,in order to obtain even this moderate speed under the head of #af feet it was necessary to select turbines of only #adj horse-power each4 ,four of these turbines are mounted on each shaft that drives a #djj-kilowatt dynamo1 direct-connected1 so that there are #cbj wheels in all4 ,had a smaller number of wheels been employed to yield the total power their speed and that of direct-connected dynamos must have been less than #ahj revolutions per minute4 ,as the cost of dynamos increases with very low speeds it is often cheaper to install a larger number of dynamos at a higher speed than a smaller number at a lower speed for a given total capacity4 ,the use of a larger number of units than would otherwise be necessary in order to avoid a very low speed is further illustrated by the #g1ejj-kilowatt plant of the ,missouri ,river ,power ,company1 at ,caon ,ferry1 ,mont4 ,this capacity is made up of ten generators1 each rated at #gej kilowatts and direct-connected to a pair of pressure turbine wheels operating at #aeg revolutions per minute1 under a head of about #cb feet4 ,under comparatively high heads of water pressure turbines operate at speeds that are ample for direct-connection to even the largest dynamos4 ,illustration3 ,,fig4 #da4--;,interior of ,power-house ,no4 #b1 ,niagara ,falls4 ,thus in the ,niagara ,falls plant1 where the head of water is #acf feet1 each pair of turbines drives a direct-connected dynamo of #c1gej kilowatts at #bej revolutions per minute4 ,in the rare case where the power to be developed is so great that the number of generators necessary to give security and reliability to the service leaves each generator with a capacity larger than is desirable for structural reasons1 the number must be increased simply to reduce the size of each generator4 ,such a state of facts existed at ,niagara ,falls1 where the first station contains ten dynamos of #c1gej kilowatts each1 and the second station contains eleven units of like capacity4 ,in the greater number of transmission systems the generators are direct-connected to either steam-engines or water-wheels1 and their speeds of rotation are largely determined by the requirements of these prime movers4 ,steam-engines can be designed with some regard to the desirable speeds for direct-connection to dynamos1 but water-wheels are less flexible in this particular4 ,each type of wheel has its peripheral speed mainly determined by the head of water under which it may be required to operate1 and variation from this speed means serious loss of efficiency4 ,illustration3 ,,fig4 #db4--aj1jjj ,h4 ,p4 #ab1jjj ,volt ,generator in ,canadian ,power-house at ,niagara ,falls4 ,under heads of much more than #ajj feet pressure turbines operate at rather high speeds in all except very large sizes4 ,it is much the more common to see water-wheels at a lower speed belted to dynamos at a higher speed2 but in some instances1 as at the lighting plant of ,spokane1 ,wash41 wheels of a higher speed are belted to dynamos of a lower speed4 ,another plan by which moderate dynamo speeds are obtained with water-wheels under rather high heads mounts a dynamo at each end of the shaft of a large turbine or pair of turbines4 ,this plan is followed at the plant of the ,royal ,aluminum ,company1 ,shawinigan ,falls1 ,quebec1 where there are two pairs of horizontal turbine wheels1 each pair developing #c1bjj horse-power under a head of #abe feet1 and driving a dynamo direct-coupled on each end of its shaft4 ,where vertical wheels are employed it is sometimes more desirable to drive some standard type of dynamo with horizontal shaft by means of bevel gears than to design a special dynamo to mount directly on the vertical shaft4 ,this latter plan is warranted in very large work like that at two of the ,niagara ,falls generating stations1 where the twenty-one #c1gej-kilowatt dynamos are direct-connected1 each on the vertical shaft of a turbine4 ,this type of connection is not one that will be frequently followed1 but at one other point--,portland1 ,ore4--each dynamo is mounted directly on the shaft of its vertical turbine wheel4 ,where water-wheels must operate under heads of several hundred feet1 it is usually necessary to abandon pressure turbines and to adopt one of the types of impulse-wheels4 ,in this class of wheels the peripheral speed of highest efficiency is only one-half the spouting velocity of the water under any particular head4 ,this gives the impulse-wheels about two-thirds the peripheral speed of pressure turbines of equal diameter and consequently about two-thirds as many revolutions per minute4 ,but as the water may be applied at one or more points on the circumference of an impulse-wheel1 as desired1 such wheels may have much greater diameters than pressure turbines for equal power under a given head4 ,illustration3 ,,fig4 #dc4--;,generators in ,power-station at ,mechanicsville on the ,hudson ,river4 ,illustration3 ,,fig4 #dd4--;,generators at ,chamblay1 ,quebec1 ,power-house4 ,these properties of low peripheral speed1 as to head and great diameter1 as to power developed1 fit impulse-wheels for direct-connection to dynamos where great heads of water must be employed1 and they are generally used in such cases4 ,this is particularly true for the ,pacific coast1 where water-powers depend more on great heads than on large volumes4 ,in the generating plant of the ,bay ,counties' ,power ,company1 at ,colgate1 ,cal41 the dynamos are direct-connected to impulse-wheels that operate under a head of #gjj feet4 ,the three #b1bej-kilowatt dynamos in this plant are each mounted on a wheel shaft operating at #bhe revolutions per minute1 and each of the four #a1abe-kilowatt dynamos is direct-driven by an impulse-wheel at #djj revolutions per minute4 ,at the ,electra1 ,cal41 plant of the ,standard ,electric ,company the impulse-wheels operate at #bdj revolutions per minute under a head of #a1dej feet4 ,each of the five pairs of these wheels drives a #b1jjj-kilowatt generator1 direct-connected4 ,as the head of water at these wheels is #a1dej feet1 its spouting velocity is about #cjj feet per second1 or #ah1jjj feet per minute4 ,each wheel is eleven feet in diameter1 so that a speed of #bdj revolutions per minute gives the periphery a little less than #i1jjj feet per minute1 or about one-half of the spouting velocity of the water4 ,these two great plants are excellent illustrations of the way in which impulse-wheels1 under great heads1 may be given speeds that are suitable for direct-connected dynamos4 ,illustration3 ,,fig4 #ea;a4 ,plan and ,elevation of ,water ,wheels and ,generators at ,power ,station on ,burrard ,inlet1 near ,vancouver1 ,b4 ,c4 ,three types of alternators1 the revolving armature1 the revolving magnet1 and the inductor1 are used in the generating plants of electric transmission systems4 ,revolving armatures are used in the dynamos of comparatively few transmission systems and hardly at all in those of recent date4 ,the prevailing type of alternator for transmission work is that with internal revolving magnets and external stationary armature4 ,this type is employed in the great water-power plants at ,caon ,ferry1 ,mont42 ,sault ,ste4 ,marie1 ,mich41 and for all of the generators installed in the later ,niagara ,falls plants4 ,for the sixteen earlier vertical generators at ,niagara ,falls the revolving magnets are external to the stationary armatures1 but this construction has the disadvantage of high first cost and inaccessibility of the internal armature1 and is not likely to be often adopted elsewhere4 ,illustration3 ,,fig4 #df4--;,elevations of ,water-wheels and ,generators at ,power-station on ,burrard ,inlet1 near ,vancouver1 ,b4 ,c4 ,inductor alternators are those in which both the armature and magnet coils are stationary and only a suitable structure of iron revolves2 they are employed in a comparatively small number of transmission systems1 but this number includes some of the largest plants4 ,the seven alternators in the ,colgate1 ,cal41 plant aggregating #aa1bej kilowatts capacity1 and the five alternators in the plant at ,electra in the same ,state1 with a capacity of #aj1jjj kilowatts1 are all of the inductor type4 ,as more commonly constructed the magnet winding of the inductor alternator consists of only one or two very large coils1 which are in some cases as much as ten feet in diameter4 ,the repair of these large magnet coils seems to present a more serious problem1 in case of accident1 than the repair of the small coils used on interval1 revolving magnets4 ,as far as satisfactory operating qualities are concerned1 inductor alternators and those with revolving magnets seem to be on an equality1 but for structural reasons inductor alternators will probably be built less freely in the future than in the past4 ,nearly all long transmissions are now carried out with either two- or three-phase current4 ,the most notable two-phase installation is that at ,niagara ,falls1 where the original ten generators1 as well as the eleven dynamos later added in two of the large plants1 are all of the two-phase type4 ,at ,caon ,ferry1 ,mont41 the first four of the #gej-kilowatt generators were two-phase1 but the six machines of like capacity installed later are three-phase4 ,in the latest plants of large capacity or involving very long transmissions three-phase machines have been generally employed4 ,this is true of the ,colgate and ,electra plants in ,california1 and of that at ,sault ,ste4 ,marie1 ,mich4 ,illustration3 ,,fig4 #dg4--;,interior of ,power-house at ,garvin's ,falls on the ,merrimac ,river4 ,illustration3 ,,fig4 #dh4--ejj-,kilowatt ,generator in ,station at ,great ,falls on the ,presumpscot ,river4 ,as to frequency1 existing practice extends all the way from #acc cycles per second on the lines at ,marysville1 ,cal41 down to only #ae cycles on the transmission for the ,washington ,baltimore ,electric ,railway4 ,more common practice ranges between #be and #fj cycles4 ,niagara ,falls saw the first great plant installed for #be cycles1 but others of that frequency are now engaged in the supply of light and power for general distribution4 ,for transmission to electric railway lines a frequency of #be cycles has been and is being widely used1 prominent examples of which may be seen in the ,new ,hampshire traction1 the ,berkshire1 and the ,albany ,hudson systems4 ,illustration3 ,,fig4 #di4--;,columbus1 ,ga41 ,water-power ,station4 ,the strong feature of a system at #be cycles is that it is well suited to the supply of continuous currents through rotary converters with reasonable numbers of poles1 armature slots1 and commutator bars4 ,illustration3 ,,fig4 #ej4--ajfe-,kilowatt1 #bcjj volt ,generator ,connected to ,motor in ,shawinigan ,sub-station at ,montreal4 ,on the other hand1 the cost of transformers is greater with current at #be cycles per second than with a higher frequency1 and this current is only just bearable for incandescent lighting and quite unsuited for arc lamps1 because of the fluctuating character of the light produced4 ,at #ae cycles per second a current can be employed for incandescent lighting with satisfactory results only by means of some special devices1 as lamps with very thick filaments1 to avoid the flicker4 ,very low fluctuations cut down undesirable effects in the way of inductance and resonance1 but these effects can be avoided to a large degree in other ways4 ,where power is the most important element in the service of an electric water-power and transmission system there is a decided tendency to adopt a rather small number of periods for the system1 even at some disadvantage as to lighting facilities4 ,this is illustrated by the transmission from ,st4 ,anthony's ,falls1 ,minn41 at #ce cycles1 from ,caon ,city to ,cripple ,creek1 ,col41 at #cj cycles1 by the ,sault ,ste4 ,marie plant of #cb1jjj kilowatts at #cj cycles1 as well as by the two ,niagara ,falls plants of #gh1gej kilowatts at #be cycles4 ,where the main purpose of a transmission system is the supply of light and power for general distribution1 sixty periods per second are adopted as the standard in many cases4 ,this number of periods in comparison with a smaller one tends to increase the cost of rotary converters but decreases the cost of transformers1 and is suitable for both incandescent and arc lighting4 ,illustration3 ,,fig4 #ea4--;,efficiency ,curves for ,motor ,generators at ,montreal ,sub-station of the ,shawinigan ,transmission ,line4 ,few1 if any1 transmission systems have recently been installed for frequencies above sixty cycles1 and the older plants that worked at higher figures have in most cases been remodelled4 ,during the past decade the voltages of alternators have been greatly increased1 but have not caught up with the demand for high pressures on long-transmission lines4 ,ten years ago when the first long transmissions were going into operation #b1jjj volts was considered high for an alternator4 ,as this voltage is too low for economy of conductors longer than three or four miles1 the important early transmissions were all carried out with the aid of step-up transformers at generating stations4 ,the practice then was1 and to a large extent still is1 to design the alternators for a transmission with a voltage well suited to their economical construction1 and then give the step-up transformers any ratio necessary to attain the required line voltage4 ,,alternators ,,in ,,transmission ,,systems4 ---------------------------------------- ---------------------------- ,number at ,plant4 ,kilowatts ,each4 ,alternator ,voltage4 ,phase4 ,cycles4 ,r4 ,p4 ,m4 ,type of ,location of ,system4 ,magnet4 ,method of ,connec- tions4 ---------------------------------------- --------------------- ,niagara ,falls,a #afc1gej #b1cjjbbe #bej ,external ,direct revolving ,niagara ,falls,a #ec1gej #b1cjjbbe #bej ,internal ,colgate to ,oakland #cb1bej #b1djjcfj #bhe ,inductor ,colgate to ,oakland #da1abe #b1djjcfj #djj ,electra to ,s4,francisco #eb1jjj 4444#cfj #bdj ,portsmouth to ,pelh'm #ab1jjjac1bjjcbe #hc4c;,internal ,portsmouth to ,pelh'm #ba1jjjac1bjjcbe #id ,virginia ,city #b #gej #ejjcfj #djj ,external ,ogden ,salt ,lake #e #gej #b1cjjcfj #cjj ,internal ,chaudire ,falls #b #gejaj1ejjcff4fdjj ,yadkin ,river ,falls #b #gejab1jjjcff #aff ,lewiston1 ,me4 #c #gejaj1jjjcfj #ahj ,farmington ,river to #b #gej #ejjcfj 444 ,hartford1 ,conn4 #b #fjj #ejjbfj 444 ,caon ,ferry to ,butte #aj #gej #ejjcfj #aeg ,apple ,riv4 to ,st4 ,paul #d #gej #hjjcfj #cjj ,edison ,co41 ,l4 ,angeles #d #gjj #gejcej 444 ,madrid to ,bland #b #fjj #fjecfj #ij ,caon ,city to ,cripple ,creek #c #dej #ejjccj 444 44444 ,sault ,ste4 ,marie #hj #djj #b1djjccj #ahj ,st4 ,hyacinthe1 ,que4 #c #ahj #b1ejjcfj #fjj ,great ,falls to ,portland1 ,me4 #d #ejjaj1jjjcfj #bbe ---------------------------------------- --------------------- ,a ,niagara ,falls ,power ,company4 ,thus in the two water-power plants connected with the electrical supply system of ,hartford1 ,conn41 the alternators operate at #ejj volts with transformers that put the line voltage up to #aj1jjj4 ,in the station on ,apple ,river that supplies the lighting system of ,st4 ,paul1 ,minn41 the alternators operate at #hjj volts1 and this is raised to #be1jjj volts for the line4 ,at ,caon ,ferry the alternator voltage of #ejj is multiplied by #ajj in the transformers giving #ej1jjj on the line4 ,illustration3 ,,fig4 #eb4--,transmission ,line of ,new ,hampshire ,traction ,company4 ,where the generating station of a transmission system is located close to a part of its load the alternators are given a voltage suitable for distribution1 say about #b1djj1 and any desired pressure on the line is then obtained by means of step-up transformers4 ,two of the ,niagara ,falls plants are an illustration of this practice1 the voltage of all the alternators there being #b1bjj1 which is raised to #bb1jjj for the transmission of a part of the energy to ,buffalo4 ,a similar practice is followed in the water-power plant at ,ogden1 where the generators furnish current at #b1cjj volts for local distribution1 and transformers raise the pressure to #bf1jjj volts for the transmission to ,salt ,lake ,city4 ,in the #cb1jjj-kilowatt plant at ,sault ,ste4 ,marie1 ,mich41 the alternators operate at #b1djj volts and a large part of their load is local1 but this voltage will no doubt be raised by transformers when transmission lines are operated4 ,for generating stations that carry little or no local loads the cost of transformers can be saved if the generators develop the voltage required on the transmission lines4 ,this possible saving has led to the development of alternators that generate voltages as high as #ae1jjj in their armature coils4 ,such alternators have stationary armatures in all cases and are of either the revolving magnet or inductor type4 ,at the present time many transmission systems in the ,united ,states operating at #aj1jjj or more volts develop these pressures in the armature coils of their alternators1 and the number of such systems is rapidly increasing4 ,it is now the rule rather than the exception to dispense with step-up transformers on new work where the line voltage is anything under #ae1jjj4 ,perhaps the longest transmission line now in regular operation with current from the armature coils of an alternator is that at #ac1bjj volts between the generating station at ,portsmouth and one of the sub-stations of the ,new ,hampshire ,traction system at ,pelham1 a distance of forty-two miles4 ,in at least one transmission system now under construction1 that of the ,washington1 ,baltimore ,annapolis ,electric ,railway1 the voltage of generators to supply the line without the intervention of step-up transformers will be #ae1jjj4 ,the company making these alternators is said to be ready to supply others that generate #bj1jjj volts in the armature coils whenever the demand for them is made4 ,in quite a number of cases alternators of about #ac1jjj volts have been installed for transmissions along electric railway lines4 ,alternator ,systems ,using ,high-voltage ,alternators4 ,voltages4 ,electrical ,development ,co4 of ,ontario1 ,niagara ,falls #ab1jjj ,lighting and ,street ,railway1 ,manchester1 ,n4 ,h4 #aj1jjj ,lighting and ,street ,railway1 ,manchester1 ,n4 ,h4 #ab1ejj ,lighting and ,power1 ,portland1 ,me4 #aj1jjj ,lighting and ,power1 ,north ,gorham1 ,me4 #aj1jjj ,mallison ,power ,co41 ,westbrook1 ,me4 #aj1jjj ,lighting and ,power1 ,lewiston1 ,me4 #aj1jjj ,electric ,railway1 ,portsmouth1 ,n4 ,h4 #ac1bjj ,electric ,railway1 ,pittsfield1 ,mass4 #ab1ejj ,ludlow ,mills1 ,ludlow1 ,mass4 #ac1bjj ,electric ,railway1 ,boston to ,worcester1 ,mass4 #ac1bjj ,electric ,railway1 ,albany ,hudson1 ,n4 ,y4 #ab1jjj ,empire ,state ,power ,co41 ,amsterdam1 ,n4 ,y4 #ab1jjj ,lehigh ,power ,co41 ,easton1 ,pa4 #ab1jjj ,hudson ,river ,power ,co41 ,mechanicsville1 ,n4 ,y4 #ab1jjj ,light and ,power1 ,anderson1 ,s4 ,c4 #aa1jjj ,fries ,mfg4 ,co41 ,salem1 ,n4 ,c4 #ab1jjj ,light and ,power1 ,ouray1 ,col4 #ab1jjj ,washington ,baltimore ,electric ,railway #ae1jjj ,canadian ,niagara ,power ,co41 ,niagara ,falls #ab1jjj ,ontario ,power ,co41 ,niagara ,falls #ab1jjj ,this list of high-voltage alternators is not intended to be exhaustive1 but serves to indicate their wide application4 ,if such alternators can be purchased at a lower price per unit of capacity than alternators of low voltage plus step-up transformers1 there is an apparent advantage for transmission systems in the high-voltage machines4 ,this advantage may rest in part on a higher efficiency in the alternators that yield the line voltage than in the combination of low-voltage alternators plus step-up transformers4 ,it is not certain1 however1 that depreciation and repairs on the generators of high voltage will not be materially greater than the like charges on generators of low voltage1 and some advantage in price should be required to cover this contingency4 ,just how far up the voltage of alternators can be pushed for practical purposes is uncertain1 but it seems that the limit must be much below that for transformers where there is ample room for solid insulation and the coils can be immersed in oil4 ,the use of generators at #aj1jjj volts and above tends to lower the volts per mile on transmission lines1 because it seems better in some cases to increase the weight of line conductors rather than to add step-up transformers1 as in the #db-mile transmission from ,portsmouth to ,pelham4 ,,chapter ,x4 ,,transformers ,,in ,,transmission ,,systems4 ,transformers are almost always necessary in long electric systems of transmission1 because the line voltage is greater than that of generators1 or at least that of distribution4 ,as transformers at either generating or receiving stations represent an increase of investment without corresponding increase of working capacity1 and also an additional loss in operation1 it is desirable to avoid their use as far as is practicable4 ,in short transmissions over distances of less than fifteen miles it is generally better to avoid the use of transformers at generating stations1 and in some of these cases1 where the transmission is only two or three miles1 it is even more economical to omit transformers at the sub-stations4 ,thus1 where energy is to be transmitted two miles and then applied to large motors in a factory1 or distributed at #b1ejj volts1 the cost of bare copper conductors for the three-phase transmission line will be only about #f per kilowatt of line capacity at #b1ejj volts1 with copper at #ae cents per pound1 and a loss of #e per cent at full load4 ,the average loss in such a line will probably be as small as that in one set of transformers and a line of higher voltage4 ,furthermore1 the first cost of the #b1ejj-volt generators and line without transformers will be less than that of generators and line of higher voltage with step-down transformers at the sub-station4 ,as generators up to #ac1ejj volts are now regularly manufactured1 it is quite common to omit step-up transformers at the main stations of rather short transmission systems4 ,this practice was followed in the #ac1ejj-volt transmission to ,manchester1 ,n4 ,h41 the #aj1jjj-volt transmission to ,lewiston1 ,me41 and the #ab1jjj-volt transmission to ,salem1 ,n4 ,c4 ,in most transmission over distances of twenty-five miles or more1 step-up transformers at generating stations as well as step-down transformers at sub-stations are employed4 ,as yet the highest voltages that have been put into practical use on transmission lines 7that is1 #ej1jjj to #fj1jjj7 are much below the pressures that have been yielded by transformers in experimental work4 ,these latter voltages have in a number of instances gone above #ajj1jjj4 ,the numbers and capacities of transformers used at main stations vary much in their relation to the numbers and individual capacities of generators there4 ,in some cases there are three times as many transformers as three-phase generators1 and the capacity of each transformer is either equal to or somewhat greater than one-third of the capacity of each generator4 ,illustration3 ,,fig4 #ec4--,transformers at ,central ,sub-station1 ,montreal4 ,thus in the station at ,spier ,falls on the ,hudson1 whence power is transmitted to ,albany and other cities1 the number of step-up transformers will be thirty and their aggregate capacity will be #bd1jad kilowatts1 while the total number of three-phase generators will be ten1 with a combined capacity of #bd1jjj kilowatts4 ,another practice is to give each transformer a capacity greater than one-third of that of the three-phase generator with which it is to be connected1 and make the total number of transformers less than three times as great as the number of generators4 ,an example of this sort exists in the station on ,apple ,river1 whence power is transmitted to ,st4 ,paul4 ,this station contains four three-phase generators of #gej kilowatts each1 and six transformers of #ejj kilowatts each1 these latter being connected in two sets of three each4 ,the use of three transformers for each three-phase generator instead of three transformers for each two or three generators1 tends to keep transformers fully loaded when in use1 and therefore to increase their efficiency4 ,on the other hand1 efficiency increases a little with the size of transformers1 and the first cost per unit capacity is apt to be less the greater the size of each4 ,another solution of the problem is to provide one transformer for each three-phase generator1 each transformer being wound with three sets of coils1 so that the entire output of a generator can be sent into it4 ,this practice is followed at the ,hochfelden water-power station1 whence power is transmitted to ,oerlikon1 ,switzerland1 also in the water-power station at ,grenoble1 ,france1 whence energy at #bf1jjj volts is transmitted to a number of factories4 ,with three-phase transformers each generator and its transformer may form an independent unit that can be connected with the line at pleasure1 thus tending to keep transformers at full load4 ,though three-phase transformers are much used in ,europe1 they have thus far had little application in the ,united ,states4 ,single-phase transformers may1 of course1 be limited in number to that of the three-phase generators with which they are used1 but such transformers must regularly be connected to the generators and line in groups of two or three4 ,such an equipment was provided in part at the #g1ejj-kilowatt station on the ,missouri ,river at ,caon ,ferry1 which contains ten three-phase generators of #gej kilowatts each4 ,the transformers at this station include twelve of #cbe kilowatts each1 connected in four groups of three each1 also six transformers of #iej kilowatts each which are also connected in groups of three4 ,three of these larger transformers have a capacity of #b1hej kilowatts1 or nearly equal to that of four generators4 ,with two-phase generators single-phase transformers must be connected in pairs1 and it is common to provide two transformers for each generator4 ,thus1 in the ,rainbow station on the ,farmington ,river1 whence energy is transmitted to ,hartford1 there are two generators of the two-phase type and rated at #fjj kilowatts each1 also four transformers rated at #cjj kilowatts each4 ,as the regulation of transformers on overloads is not as good as that of generators1 it seems good practice to give each group of transformers a somewhat greater capacity than that of the generator or generators whose energy is to pass through it4 ,this plan was apparently followed at the ,caon ,ferry station1 where the total generator capacity is #g1ejj kilowatts and the total capacity of step-up transformers is #i1fjj kilowatts4 ,each group of the #cbe-kilowatt transformers there has a capacity of #ige kilowatts1 while each generator is only of #gej kilowatts4 ,usually the number of groups of transformers at a two-phase or three-phase generating station is made greater than the number of transmission circuits supplied by the station1 for some of the reasons just considered4 ,when this is not the case it is commonly desirable in any event to have as many groups of step-up transformers as there are transmission circuits1 so that each circuit may be operated with transformers that are independent of the other circuits4 ,at sub-stations it is desirable to have a group of transformers for each transmission circuit1 and it may be necessary to subdivide the transformer capacity still further in order to keep transformers in operation at nearly full load1 or to provide a group of transformers for each sort of service or for each distribution circuit4 ,all of the transformers at a sub-station should have a total capacity at least equal to that of the generators whose energy they are to receive1 minus the losses in step-up transformers and the line4 ,transformers at sub-stations do not necessarily correspond in number or individual capacity with those at generating stations1 and the number of sub-station transformers bears no necessary relation to the number of generators by which they are fed4 ,two transmission circuits extend from ,caon ,ferry to a sub-station at ,butte1 and in that sub-station there are six transformers divided into two groups for three-phase operation1 each transformer being rated at #iej kilowatts4 ,this sub-station equipment thus corresponds to only the six #iej-kilowatt transformers in the generating station1 because the four groups of smaller transformers there are used to supply the transmission line to ,helena4 ,in the sub-station at ,st4 ,paul that receives the entire output of the plant on ,apple ,river1 where the six transformers of #ejj kilowatts each are located1 ten transformers receive energy from two three-phase transmission circuits4 ,six of these transformers are rated at #cjj kilowatts each4 ,the #cjj-kilowatt transformers are connected in two groups of three each1 and the #bjj-kilowatt in two groups of two each1 transforming current from three-phase to two-phase4 ,the aggregate capacity of the sub-station transformers is thus #b1fjj kilowatts1 while that of transformers at the generating station is #c1jjj kilowatts4 ,with four generators at the water-power plant there are ten transformers at the sub-station1 where all the energy1 minus losses1 is delivered4 ,at ,watervliet1 where one of the several sub-stations of the system with its larger generating plant at ,spier ,falls is located1 the capacity of each transformer is #a1jjj kilowatts1 though each transformer at ,spier ,falls has a rating below this figure4 ,in the sub-station at ,manchester1 ,n4 ,h41 that receives nearly all of the energy from four water-power plants1 containing eight generators with an aggregate capacity of #d1jcj kilowatts1 there are located twenty-one step-down transformers that have a total rating of #d1bjj kilowatts4 ,these twenty-one transformers are fed by six circuits1 of which five are three-phase and one is two-phase4 ,a part of the transformers supply current to motor-generators1 developing #ejj-volt current for a street railway1 and the remaining transformers feed circuits that distribute alternating current4 ,from these examples it may be seen that in practice either one or more groups of transformers are employed in sub-stations for each transmission circuit1 that the total number of these transformers may be just equal to or several times that of the generators from which they receive energy1 and that the individual capacities of the transformers range from less than one-third to more than that of a single generator4 ,groups of transformers at a main station must correspond in voltage with that of the generators in the primary and that of the transmission line in the secondary windings4 ,sub-station transformers receive current at the line voltage and deliver it at any of the pressures desired for local distribution4 ,where step-up transformers are employed the generator pressure in nearly all cases is at some point between #ejj and #b1ejj volts4 ,at the ,caon ,ferry station the voltage of transformers is #eej in in the primary and #ej1jjj in the secondary windings4 ,in the ,colgate power-house1 whence energy is transmitted to ,oakland1 the generator pressure of #b1djj volts is raised to #dj1jjj volts by transformers4 ,generator voltage in the power-house on ,apple ,river is #hjj and transformers put the pressure up to #be1jjj for the line to ,st4 ,paul4 ,transformers at the ,niagara ,falls station raise the voltage from #b1bjj to #bb1jjj for the transmission to ,buffalo4 ,as transformers can be wound for any desired ratio of voltages in their primary and secondary coils1 a generator pressure that will allow the most economical construction can be selected where step-up transformers are employed4 ,in general it may be said that the greater the capacity of each generator1 the higher should be its voltage and that of the primary coils of step-up transformers1 for economical construction4 ,at sub-stations the requirements of distribution must obviously fix the secondary voltages of transformers4 ,weight and cost of transformers depend in part on the frequency of the alternating current employed1 transformers being lighter and cheaper the higher the number of cycles completed per second by their current1 other factors remaining constant4 ,in spite of this fact the tendency during some years has been toward lower frequencies1 because the lower frequencies present marked advantages as to inductive effects in transmission systems1 the distribution of power through induction motors1 the construction and operation of rotary converters1 and the construction of generators4 ,instead of the #acc cycles per second that were common in alternating systems when long transmissions first became important1 sixty cycles per second is now the most general rate of current changes in such transmission systems4 ,but practice is constantly extending to still lower frequencies4 ,the first ,niagara ,falls plant with its twenty-five cycles per second reached the lower limit for general distribution1 because incandescent lighting is barely satisfactory and arc lighting decidedly undesirable at this figure4 ,in contrast with the great transmissions from ,caon ,ferry to ,butte1 ,colgate to ,oakland1 and ,electra to ,san ,francisco1 which operate at sixty cycles1 the system between ,caon ,city and ,cripple ,creek1 in ,colorado1 as well as the great plant at ,sault ,ste4 ,marie1 employs thirty-cycle current1 and the lines from ,spier ,falls to ,schenectady1 ,albany1 and ,troy are intended for current at forty cycles per second4 ,from these examples it may be seen that the bulk and cost of transformers is not the controlling factor in the selection of current frequency in a transmission system4 ,illustration3 ,,fig4 #ed4--;,first ,floor of ,saratoga ,sub-station4 ,transformers used at either generating or sub-stations are cooled by special means in many cases4 ,the advantages of so-called artificial cooling are smaller weight and first cost in transformers1 and perhaps longer life for the insulation of windings4 ,for these advantages a small increase in the cost of operation must be paid4 ,station transformers are usually cooled either by forcing air through their cases under pressure1 or else by passing water through pipes in the oil with which the transformer cases are filled4 ,if cooling with air-blast is adopted1 a blower1 with electric motor or some other source of power to operate it1 must be provided4 ,where transformers are oil-insulated and cooled with water there must be some pressure to maintain the circulation4 ,if free water under a suitable head can be had for the cooling of transformers1 as in most water-power plants1 the cost is very slight4 ,where water must be purchased and pumped through the transformers its cost will usually be greater than that of cooling with air-blast4 ,one manufacturer gives the following as approximate figures for the rate at which water at the temperature of #ae centigrade must be forced through his transformers to prevent a rise of more than #ce centigrade in their temperature1 probably when operating under full loads4 ,transformers--,kilowatts4 ,gallons per minute4 #aej #j4e #djj 4#ge #djj #a4jj #a1jjj #a4e #ge 4#cg ,an air-blast to cool transformers at main or sub-stations may be provided in either of two ways4 ,one plan is to construct an air-tight compartment1 locate the transformers over openings in its top1 and maintain a pressure in the compartment by means of blower-fans that draw cool air from outside4 ,such an arrangement has been carried out at the sub-station in ,manchester1 ,n4 ,h4 ,the basement underneath this sub-station is air-tight1 and in the concrete floor over it there are twenty-seven rectangular openings1 each twenty-five by thirty inches1 and intended for the location of a #bjj-kilowatt transformer4 ,aggregate transformer capacity over these openings will thus be #e1djj kilowatts4 ,pressure in this basement is maintained by drawing outside air through a metal duct that terminates in a hood on the outside of the sub-station about nine feet above the ground4 ,in the roof of this sub-station there are ample skylight openings to permit the exit of hot air that has been forced through the transformers4 ,in the air-tight basement are two electric motors of ten horse-power each1 connected to the blower that maintains the pressure4 ,it may be noted that in this case there is less than one-horse power of motor capacity for each #bjj kilowatts capacity in transformers4 ,where there are not more than six or nine transformers to be cooled1 it is common practice to provide a separate motor and blower for each group of three transformers1 and lead the air directly from each blower to its group of transformers by a metal duct1 thus avoiding the necessity for an air-chamber4 ,in such cases a blower giving a three-eighth-ounce air pressure per square inch and a motor of one horse-power capacity are generally provided for each group of three transformers rated at #ajj to #aej kilowatts each4 ,where cooling with air-blast is adopted1 oil-insulation cannot be carried out because the air must come into intimate contact with the transformer coils and core4 ,both oil-insulation with water cooling and dry insulation with cooling by air-blast have been widely used in transmission systems of large capacity and high voltage4 ,in the ,colgate plant1 where the line pressure is #dj1jjj volts1 the #gjj-kilowatt transformers are oil-insulated and water-cooled1 and this is also true of the #iej-kilowatt transformers in the #ej1jjj-volt transmission between ,caon ,ferry and ,butte4 ,on the other hand1 the transmission system between ,spier ,falls1 ,schenectady1 and ,albany1 carried out at #bf1ejj volts1 includes transformers that range from several hundred to #a1jjj kilowatts each in capacity and are all air-cooled4 ,either a water-cooled transformer or one cooled by air-blast may be safely overloaded to some extent1 if the circulation of air or water is so increased that the overload does not cause heating beyond the allowable temperature4 ,the circulation of air or water through a transformer should never be forced to an extent that cools the transformer below the temperature of the air in the room where it is located1 as this will cause the condensation of water on its parts4 ,in some cases it is desirable that means for the regulation of transformer voltages through a range of ten per cent or more each way from the normal be provided4 ,this result is reached by the connection of a number of sections at one end of the transformer winding to a terminal board1 where they may be cut in or out of action at will4 ,regulation is usually desired1 if at all1 in a secondary winding of comparatively low voltage1 and the regulating sections generally form a part of such winding1 but these sections may be located in the primary winding4 ,in order to keep the number of transformers smaller and the capacity of each larger than it would otherwise be1 it is practicable to divide the low-voltage secondary winding of each transformer into two or more parts that have no electrical connection with each other4 ,these different parts of the winding may then be connected to distinct distribution lines or other services4 ,an example of this sort exists in the ,hooksett sub-station of the ,manchester1 ,n4 ,h41 transmission system4 ,three-phase current at about #aa1jjj volts enters the primary windings of three transformers at this sub-station4 ,each of these transformers has a single primary1 but two distinct secondary windings4 ,three of these secondaries1 one on each transformer1 are connected together and feed a rotary converter at about #chj volts1 three-phase4 ,the other three secondary windings are connected in like manner to a second rotary converter4 ,each of these transformers is rated at #bej kilowatts1 and each rotary is rated at #cjj kilowatts1 so that the transformer capacity amounts to #gej kilowatts and that of the converters to #fjj kilowatts1 giving a desirable margin of transformer capacity for railway service4 ,with the ordinary method of connection and windings1 six transformers of #abe kilowatts each would have been required in this sub-station4 ,high voltage for transmission lines may be obtained by the combination of two or more transformers with their secondary coils in series4 ,this method was followed in some of the early transmissions1 as in that at #aj1jjj volts to ,san ,bernardino and ,pomona1 begun in #ahia1 where twenty transformers1 giving #ejj volts each1 were used with their high-voltage coils in series4 ,some disadvantages of such an arrangement are its high cost per unit of transformer capacity and its low efficiency4 ,in a single-phase system the maximum line pressure must be developed or received in the coils of each transformer1 unless two or more are connected in series4 ,this is also true as to either phase of a two-phase system with independent circuits4 ,in three-phase circuits the coils of a transformer connected between either two wires obviously operate at the full line pressure4 ,the same result is reached when the three transformers of a group are joined to the line in mesh or -fashion4 ,if the three transformers of a group are joined in star or ,y-fashion1 the coils of each transformer are subject to fifty-eight per cent of the voltage between any two wires of the three-phase line on which the group is connected4 ,it is no longer the practice to connect two or more transformers in series either between two wires of a two-phase or between two wires of a three-phase circuit1 because it is cheaper and more efficient to use a single transformer in each of these positions4 ,where very high voltage must be developed or received with a three-phase system1 the star or ,y-connection of each group of three transformers has the advantage of a lower strain on the insulation of each transformer than that with the mesh or -grouping4 ,thus if the -grouping is used1 the line pressure equals that of each transformer coil1 but if the ,y-grouping is used the line voltage is #a4gc times that of each transformer coil4 ,at the ,colgate power-house1 the #gjj-kilowatt transformers are designed for a maximum pressure of #fj1jjj volts on the three-phase line when ,y-connected1 so that the corresponding voltage is #cd1fge in their secondary coils4 ,the primary coils of these same transformers are connected in mesh or -form and each coil operates at #b1cjj volts1 the generator pressure4 ,transformers are in some cases provided with several sets of connections to their coils so that they may be operated at widely different pressures4 ,thus1 in the ,colgate plant1 each transformer has taps brought out from its secondary coils so that it can be operated at either #bc1age1 #bh1ibe1 or #cd1fge1 with #b1cjj volts at its primary coil4 ,corresponding to the three voltages named in each secondary coil are voltages of #dj1jjj1 #ej1jjj1 and #fj1jjj on a three-phase line connected with three of these transformers in ,y-fashion4 ,the mesh or -connection is used between the coils of transformers on some transmission lines of very high voltage4 ,the #iej kilowatt transformers in the system between ,caon ,ferry and ,butte illustrate this practice1 being connected -fashion to the #ej1jjj-volt line4 ,when transformers that will operate at the desired line voltage on -connection can be obtained at slight advance over the cost of transformers requiring ,y-connections1 it is often better practice to select the former1 because this will enable an increase of seventy-three per cent in the voltage of transmission to be made at any future time by simply changing to ,y-connections4 ,such an increase of voltage may become desirable because of growing loads or extension of transmission lines4 ,an example of this sort came up some time ago in connection with the transmission between ,ogden and ,salt ,lake ,city1 which was operating at #af1jjj volts1 three-phase1 with the high-pressure coils of transformers connected in -form4 ,by changing to ,y-connections the line voltage was raised seventy-three per cent without increasing the strain on transformer insulation4 ,in some cases it is desirable to change alternating current from two-phase to three-phase1 or vice versa1 for purposes of transmission or distribution1 and this can readily be done by means of static transformers4 ,one method often employed to effect this result includes the use of two transformers connected to opposite phases of the two-phase circuit4 ,the three-phase coil of one of these transformers should be designed for the desired three-phase voltage1 and should have a tap brought out from its central point4 ,the three-phase coil of the other transformer should be designed for #hg per cent of the desired three-phase voltage4 ,one end of the coil designed for #hg per cent of the three-phase voltage should be connected to the centre tap of the three-phase coil in the other transformer4 ,the other end of the #hg per cent coil goes to one wire of the three-phase circuit4 ,the other two wires of this circuit should be connected1 respectively1 to the outside end of the coil that has the central tap4 ,as a matter of illustration it may be required to transform #ejj-volt1 two-phase current from generators1 to #bj1jjj-volt1 three-phase current for transmission4 ,two transformers designed for #ejj volts in their primary coils are necessary for this work4 ,one of these transformers should have a secondary coil designed for #bj1jjj volts1 so that the ratio of transformation is #bj1jjj #ejj or #dj to #a1 and a tap should be brought out from the centre of this coil4 ,the other transformer should have a secondary voltage of #j4hg #bj1jjj #ag1djj1 so that its ratio of transformation is #cd4h to #a4 ,these two transformers1 with the connections above indicated1 will change the #ejj-volt1 two-phase current to #bj1jjj volts1 three-phase4 ,at one of the water-power stations supplying energy for use in ,hartford1 four transformers of #cjj kilowatts each change #ejj-volt1 two-phase current from the generators to #aj1jjj-volt1 three-phase1 for the transmission line4 ,in the ,niagara water-power station the generators deliver two-phase current at #b1bjj volts1 and #ige-kilowatt transformers are connected in pairs to change the pressure to #bb1jjj volts1 three-phase1 for transmission to ,buffalo4 ,a transformer is used in some cases to raise the voltage and compensate for the loss in a transmission line4 ,for this purpose the secondary of a transformer giving the number of volts by which the line pressure is to be increased is connected in series with the line4 ,the primary winding of this transformer may be supplied from the line boosted or from another source4 ,transformers ranging in capacity from #ajj to #a1jjj kilowatts each1 such as are commonly used for transmission work1 have efficiencies of #if to #ih per cent at full loads1 when of first-class construction4 ,efficiency increases slowly with transformer capacity within the limits named1 and #ih per cent can be fairly expected in only the larger sizes4 ,in any given transformer the efficiency may be expected to fall a little1 say one or two per cent1 between full load and half load1 and another one per cent between half load and quarter load4 ,these figures for efficiencies at partial loads vary somewhat with the design and make of transformers4 ,in general1 it may be said that step-up or step-down transformers will cost approximately #g4ej per kilowatt capacity1 or about one-half of the like cost of low-voltage dynamos4 ,if dynamos of voltage sufficiently high for the transmission line can be had at a figure below the combined cost of low-volt dynamos and raising transformers1 it will usually pay to avoid the latter and develop the line voltage in the armature coils4 ,this plan avoids the loss in one set of transformers4 ,,transformers ,,in ,,transmission ,,systems4 ---------------------------------------- ------------------- ,trans- ,trans- ,genera- formers formers tors at at ,power- at ,sub- ,power- ,transmission ,system4 stations4 stations4stations4 ------------------------- ,no4 ,kw4 ,no4 ,kw4 ,no4 ,kw4 ,each4 ,each4 ,each4 ---------------------------------------- ---------------- ,caon ,ferry to ,butte #ab #cbe ,a ,a 444 444 #f #iej #f #iej #aj #gej ,apple ,river to ,st4 ,paul 444 444 #f #cjj 444 444 #f #ejj #d #bjj #d #gej ,white ,river to ,dales #c #djj #c #cge #b #ejj ,farmington ,river to ,hartford #d #cjj 444 444 #b #fjj ,ogden to ,salt ,lake ,b#i #bej 444 444 #e #gej ,colgate to ,oakland 444 #gjj 444 444 #caabe #dbbej ,presumpscot ,river to ,portland 444 444 #f #bjj 444 444 #c #aej #d #ejj #a #ahj #c #cjj ,four water-powers to ,manchester 444 444 #ba #bjj #a #dej #d #fej #aabjj ---------------------------------------- ---------------- ,a ,other transformers at ,helena sub-stations4 ,b ,part of energy distributed directly from generators4 ,,chapter ,,xi4 ,,switches1 ,,fuses1 ,,and ,,circuit-,,breakers4 ,electrical transmission has worked a revolution in the art of switching4 ,as long as the distances to be covered by distribution lines required pressures of only a few hundred volts1 the switch contacts for generators and feeders could well be exposed in a row on the surface of vertical marble slabs and separated from each other by distances of only a few inches4 ,these switches were capable of manual operation even at times of heavy overload without danger of personal injury to the operator or of destructive arcing between the parts of a single switch or from one switch to another near-by4 ,on the back of these marble slabs one or more sets of bare bus-bars could be located without much probability that an accidental contact between them would start an arc capable of destroying the entire switchboard structure and shutting down the station4 ,the rise of electric pressures to thousands and tens of thousands of volts in distribution and transmission systems has vastly increased the difficulty of safe and effective control with open-air switches4 ,the higher the voltage of the circuit to be operated under load the greater must be the distance between the contact parts of each switch and also between adjacent switches4 ,such switches must also be farther removed from the operators as the voltages of their circuits go up1 as a person cannot safely stand very close to an electric arc of several feet or even yards in length4 ,in the ,west1 where long transmissions are most common1 long break-stick switches have been much used with high voltages4 ,these switches depend on the length of the break to open the circuit and on the length of the stick that moves the switch-jaw or plug to insure the safety of the operator4 ,where switches of this sort are used it is highly important to have ample distances between the contact points of each switch and also between the several switches4 ,on circuits of not more than #aj1jjj volts an arc as much as a yard long will in some cases follow the opening switch blade and hold on for several seconds4 ,on the #cc1jjj-volt transmission line at ,los ,angeles a peculiar form of switch is used which makes a break between a pair of curved wire horns that are ten inches apart at their nearest points4 ,when the contact between these horns is broken the arc travels up between portions of the horns that curve apart and is thus finally ruptured4 ,besides the very large space required for open switches on circuits of #e1jjj to #aj1jjj volts or more1 there is a further objection that the arcs developed by opening such switches under heavy loads rapidly destroy the contact parts and produce large quantities of metallic vapor that is objectionable in a central station4 ,in some experiments performed at ,kalamazoo 7,a4 ,i4 ,e4 ,e41 vol4 xviii41 p4 #djg7 with open-air switches the voltages ranged from #be1jjj to #dj1jjj4 ,the loads on circuits broken by the switches were highly inductive and mounted from #a1bjj to #a1cjj kilovolt-amperes4 ,at #be1jjj volts the arc produced by the open-air switch held on for several seconds4 ,at #dj1jjj volts the arc following the opening of this switch was over thirty feet long1 and being out of doors near the pole line the arc struck the line wires and short-circuited the system4 ,it has been shown that the oscillations of voltage occurring when a circuit under heavy load is opened by an open-air switch may be very dangerous to insulation 7,a4 ,i4 ,e4 ,e41 vol4 xviii41 p4 #chc74 ,in the ,kalamazoo test the oscillations of this sort were reported to have reached two or three times the normal voltage of the system when the open-air switch was used4 ,illustration3 ,,fig4 #ee4--;,connections between ,power-houses #a and #b at ,niagara ,falls4 ,facts of the nature just outlined have led to the development of oil switches4 ,the general characteristic of oil switches is that the contact parts are immersed in1 and the break between these contacts takes place under1 oil4 ,two types of the oil switch are made1 one having all of its contact parts in the same bath of oil and the other having a separate oil-bath for each contact4 ,compared with those of the open-air type1 oil switches effect a great saving of space1 develop no exposed arcs or metallic vapors1 cause little if any oscillation or rise of voltage in an alternating circuit1 and can be depended on to open circuits of any voltage and capacity now in use4 ,in the tests above mentioned at ,kalamazoo1 a three-phase oil switch making two breaks in each phase and with all the six contacts in a single oil-bath was used to open circuits of #be1jjj volts and #a1bjj to #a1cjj kilovolt-arcs with satisfactory results4 ,at #dj1jjj volts1 however1 this type of switch spat fire and emitted smoke1 indicating that it was working near its ultimate capacity4 ,a three-phase switch with each of its six contacts in a separate cylindrical oil-chamber was used to open the #dj1jjj-volt #a1cjj kilovolt-arc circuit at ,kalamazoo with perfect success even under conditions of short-circuit and without the appearance of fire or smoke at the switch4 ,the three-phase switch used in the tests at ,kalamazoo and having each of its contacts in a separate oil-chamber was similar in construction to the switches used in the ,metropolitan and ,manhattan railway stations in ,new ,york ,city4 ,in each of these switches the two leads of each phase terminate in two upright brass cylinders4 ,these cylinders have fibre linings to prevent side-jumping of the arcs when the switch is opened1 and each cylinder is filled with oil4 ,into the two brass cylinders of each phase dips a -shaped contact piece through insulating bushings1 and the ends of this contact piece fit into terminals at the bottom of the oil pots4 ,a wooden rod joins the centre or upper part of the -contact piece1 and the three rods of a three-phase switch pass up through the switch compartment to the operating mechanism outside4 ,the six brass cylinders and their three -contact pieces are usually mounted on a switch cell built entirely of brickwork and stone slabs4 ,for a three-phase switch the brick and stone cell has three entirely separate compartments1 and each compartment contains the two brass cylinders that form the terminals of a single phase4 ,on top of and outside the cell the mechanism for moving the wooden switch rods is mounted4 ,in the ,metropolitan station1 where the voltage is #f1jjj1 the vertical movement of the -shaped contact piece with its rod is twelve inches4 ,at the ,manhattan station1 where the operating voltage is #ab1jjj1 the vertical movement of the -contacts in opening a switch is seventeen inches4 ,the total break in each phase in a switch at the ,metropolitan station is thus twenty-four inches1 or four inches per #a1jjj volts1 and the total break per phase in switches at the ,manhattan station is thirty-four inches1 or #b4ff inches per #a1jjj volts total pressure4 ,oil switches are now very generally employed on alternating circuits that operate at #b1jjj volts or more for purposes of general distribution4 ,on circuits of moderate voltage like that just named1 and even higher1 it is common practice to use oil switches that have only a single reservoir of oil each1 the entire six contacts in the case of a three-phase switch being immersed in this single reservoir4 ,such switches are usually operated directly by hand and are located on the backs of or close to the slate or marble boards on which the handles that actuate the switch mechanism are located4 ,a good example of this sort of work may be seen at the sub-station in ,manchester1 ,n4 ,h41 where energy from four water-power stations is delivered over seven transmission lines and then distributed by an even larger number of local circuits at #b1jjj volts three-phase4 ,at the ,garvin's ,falls station1 one of the water-power plants that delivers energy to the sub-station in ,manchester1 the generators operate at #ab1jjj volts three-phase1 and these generators connect directly with the bus-bars through hand-operated oil switches on the back of the marble switchboard4 ,these last-named switches1 like those at the ,manchester sub-station1 have all the contacts of each in a single reservoir of oil4 ,with very high voltages1 where only a few hundred kilowatts are concerned1 and also with powers running into thousands of kilowatts at as low a pressure as #b1jjj volts1 it is very desirable to remove even oil switches from the switchboard and the vicinity of the bus-bars4 ,great powers as well as very high voltages not only increase the element of personal danger to an attendant who must stand close to a switch while operating it1 but also render the damage to other apparatus that may result from any failure of or short-circuit in a switch much more serious4 ,illustration3 ,,fig4 #ef4--,wire-room ,back of ,switchboard in ,power-station on ,french ,broad ,river1 ,north ,carolina4 ,as soon as the switches are removed to a distance from the operating board the necessity for some method of power control becomes evident1 since the operator at the switchboard should be able to make or break connections of any part of the apparatus quickly4 ,the necessity for the removal of switches for very large powers to a distance from the operating boards and for the application of mechanical power to make and break connections was met before the development of oil switches4 ,thus at the first ,niagara 7,a4 ,i4 ,e4 ,e41 vol4 xviii41 p4 #dhi7 power-house1 in #ahic1 the switches for the #c1gej-kilowatt1 #b1bjj-volt generators1 though of the open-air type1 were located in a special switch compartment erected in the generator room and over a cable subway at some distance from the operating board4 ,these switches were actuated through compressed-air cylinders into which air was admitted by the movement of levers near the switchboard4 ,evidently a switch of this capacity--#a1jjj amperes per pole and #b1bjj volts1 two-phase--could not well be operated by hand-power wherever located1 because of the large effort required4 ,in the second generating station at ,niagara ,falls oil switches similar to those used at the ,manhattan ,elevated ,railway plant in ,new ,york1 but two-phase1 were employed4 ,each of these oil switches at ,niagara ,falls has a capacity of #e1jjj horse-power1 like the previous open-air switches1 and is electrically actuated4 ,illustration3 ,,fig4 #eg4--,section through ,cable ,subway under ,oil ,switches in ,niagara ,power-house ,no4 #b4 ,in these electrically operated oil switches a small motor is located on top of the brick cell that contains the contact parts1 and this motor releases and compresses springs that open and close the switch4 ,while it is not desirable to employ open-air switches to open circuits of several thousand or even hundreds of kilowatts at voltages of #b1jjj or more1 it is nevertheless possible to do so4 ,this is shown by the experience of the first ,niagara ,falls station1 where the #b1bjj-volt two-phase switches are reported to have opened repeatedly currents of more than #fjj amperes per phase without injurious sparking4 ,the great rise of voltage that was shown by the experiments at ,kalamazoo to follow the opening of a simple open-air switch was avoided at the first ,niagara switches by a simple expedient4 ,in these #e1jjj horse-power open-air switches a shunt of high resistance was so connected between each pair of contacts that the blades and jaws that carried the main body of the current never completely opened the circuit4 ,when the main jaws of one of these switches were opened the shunt resistance continued in circuit until subsequently broken at auxiliary terminals4 ,that no excessive rise of voltage took place when one of these switches was open was shown by connecting two sharp terminals in parallel with the switch and by adjusting these terminals to a certain distance apart4 ,had the voltage risen on opening the switch above the predetermined amount there would have been an arc formed by a spark jumping the distance between the pointed terminals4 ,illustration3 ,,fig4 #eh4--,schenectady ,switch-house on ,spier ,falls ,line4 ,illustration3 ,,fig4 #ei4--,second-floor ,plan of ,saratoga ,switch-house on ,spier ,falls ,line4 ,safety and reliability of operation at high voltages1 say of #e1jjj or more1 require that each element of the equipment be so isolated as well as insulated from every other element that the failure or even destruction of one element will not seriously endanger the others4 ,with this end in view the cables from each generator to its switch should be laid in a conduit of brick or concrete that contains no other cables4 ,the brick or stone compartment for each phase of each switch should be so substantial that the contacts of that phase may arc to destruction without injury to the contacts of another phase4 ,bus-bars1 like switches1 should be removed from the operating switchboard1 because an arc between them might destroy other apparatus thereon1 and even the board itself4 ,it is not enough to remove bus-bars from the switchboard where very high voltages are to be controlled1 but each bar should be located in a separate brick compartment so that an arc cannot be started by accidental contact between two or more of the bars4 ,it is convenient to have the brick and stone compartments for bus-bars built horizontally one above the other4 ,the top and bottom of each compartment may conveniently be formed of stone slabs with brick piers on one side and a continuous brick wall on the other to hold the stone slabs in position4 ,connections to the bus-bars should pass through the continuous brick wall that forms what may be termed the back of the compartments4 ,to close the openings between the brick piers at the front of the compartments movable slabs of stone may be used4 ,feeders passing away from the bus-bars1 like dynamo cables running to these bars1 should not be grouped close together in a single compartment1 but each cable or circuit should be laid in a separate fireproof conduit to the point where it passes out of the station4 ,illustration3 ,,fig4 #fj4--;,ground ,floor of ,saratoga ,switch-house4 ,the folly of grouping a large number of feeders that transmit great powers together in a single combustible compartment was well illustrated by the accident that destroyed the cables that connected the first ,niagara power-station with the transformer-house on ,january #bith1 #aijc4 ,on the evening of that day lightning short-circuited one of the cables in the short bridge that connects ,no4 #a station with the transformer-house1 and all the cables in this bridge1 supplying local consumers as well as railways and lighting in ,buffalo1 were destroyed4 ,this bridge contained probably more than thirty-six cables1 as that number of new cables was put in position within twenty-four hours after the accident1 and these cables1 covered with inflammable insulation1 were close together4 ,the result was not only the loss of the cables1 but also the damage to power users4 ,if these cables had been located in separate fire-proof conduits1 it is highly probable that only the one directly affected by lightning would have been destroyed4 ,the brick and stone compartments for bus-bars may be located in the basement underneath the switchboard1 as at the ,portsmouth station of the ,new ,hampshire ,traction ,company1 or at any other place in a station where they are sufficiently removed from the other apparatus4 ,in power-house ,no4 #b at ,niagara ,falls a cable subway beneath the floor level runs the entire length1 parallel with the row of generators 7,a4 ,i4 ,e4 ,e41 vol4 xix41 p4 #ecg74 ,in this subway1 which is thirteen feet nine and three-quarter inches wide and ten feet six inches high1 the two structures for bus-bar compartments are located4 ,each of these structures measures about #f4f feet high and #a4h feet wide1 and contains four bus-bar compartments4 ,in each compartment is a single bar1 and the four bars form two sets for two-phase working4 ,above the bus-bar compartments and rising from the floor level are the oil switches4 ,a space over the cable subway midway of its length and between the two groups of oil switches is occupied by the switchboard gallery which is raised to some elevation above the floor and carries eleven generator1 twenty-two feeder1 two interconnecting1 and one exciter panels4 ,in power-house ,no4 #a the bus-bars are located in a common space above the #e1jjj horse-power open-air switches already mentioned1 and each bar has an insulation of vulcanized rubber covered with braid and outside of this a wrapping of twine4 ,of course2 an insulation of this sort would amount to nothing if by any accident an arc were started between the bars4 ,where each bus-bar is located in a separate fireproof compartment1 as at ,niagara power-house ,no4 #b1 the application of insulation directly to each bar is neither necessary nor desirable4 ,consequently the general practice where each bar has its own fireproof compartment is to construct the bars of bare copper rods4 ,with main switches for generators and feeders removed from the operating board and actuated by electric motors or magnets1 the small switches at the board with which the operator is directly concerned must of course control these magnets or motors4 ,the small switches at the operating board are called relay switches1 and the current in the circuits opened and closed by these switches and used to operate the magnets or motors of the oil switches may be conveniently obtained from a storage battery or from one of the exciting dynamos4 ,probably the best arrangement of the relay switches is in connection with dummy bus-bars on the face of the switchboard1 so that the connections on the face of the board constitute at all times a diagram of the actual connections of the generator and feeder circuits4 ,it is also desirable for quick and correct changes in the connections of the main apparatus that all the relay switches and instruments necessary for the control of any one generator or any one feeder be brought together on a single panel of the switchboard4 ,if this plan is followed1 the operator at any time will have before him on a single panel all of the switches and instruments involved in the connections then to be made1 and the chance for mistakes is thus reduced to a minimum4 ,the plan just outlined was that adopted at the ,niagara power plant ,no4 #b1 where a separate panel is provided for each of eleven generators and each of twenty-two feeders4 ,on each of the eleven generator panels there are two selector relay switches1 one generator relay switch1 and one relay generator field switch4 ,on each of the twenty-two feeder panels there are two relay selector switches4 ,the relay switches on the two interconnecting panels serve to make connections between the two groups of five and six generators respectively in power-house ,no4 #b and the ten generators of power-house ,no4 #a4 ,on each panel there are relay indicators to show whether the oil switches that carry the main current respond to the movements of their relay switches4 ,where the electric generators operate at the maximum voltage of the system1 as at ,garvin's ,falls and in the power-house of the ,manhattan ,elevated ,railway1 there may be said to be only one general plan of connections possible4 ,that is1 the generators must connect directly with the main bus-bars at the voltage of the system1 and the feeders or transmission lines must also connect to these same bars4 ,of course there may be several sets of bus-bars for different circuits or classes of work1 but this does not change the general plan of through connections from generators to lines4 ,so1 too1 the arrangement of switches is subject to variations1 as by placing two switches in series with each other in each dynamo or feeder cable1 or by connecting a group of feeders through their several switches to a particular set of bus-bars and then supplying this set of bars from the generator bus-bars through a single switch4 ,illustration3 ,,fig4 #fa4--,switchboard ,wiring1 ,glens ,falls ,sub-station on ,spier ,falls ,line4 ,where the voltage of transmission is obtained by the use of step-up transformers1 the connections of these transformers may be such as to require nearly all switching to be done on either the high- or low-tension circuits4 ,the more general practice was formerly to do all switching in the generator circuits and on the low-tension side of transformers1 except in the connection and disconnection of transformers and transmission lines with the high-tension bus-bars1 when not in operation4 ,where generators operate at the maximum voltage of the system only two main groups of switches are necessary1 one group connecting generators to bus-bars1 and the other group connecting bus-bars to the transmission lines4 ,as soon as step-up transformers are introduced the number of switch groups must be increased to four if the usual method of connection is followed1 and there must be both a high voltage and a low voltage set of bus-bars4 ,that is1 one set of switches must connect generators with low-tension bus-bars1 another group must connect low-tension bars with the primary coils of transformers1 a third group joins the secondary coils of transformers with the high-tension bars1 and the fourth group of switches joins the transmission lines to the high-tension bus-bars4 ,switches connecting the secondary coils of step-up transformers to the high-tension bus-bars1 and also the transmission lines to these same bars1 have often been of the simple open-air type with short knife-blade construction4 ,these switches have been used to disconnect the secondary coils of transformers and also the transmission lines from the high-tension bus-bars when no current was flowing1 and switches of the simple knife-blade construction with short breaks could of course be used for no other purpose4 ,with switches of this sort on the high-tension side of apparatus the practice is to do all switching of line circuits on the low-tension side4 ,it is possible to avoid some of this multiplication of switches if each generator with its transformers is treated for switching purposes as a unit and the switching for this unit is done on the secondary or high-voltage side of the step-up transformers4 ,the adoption of this plan1 of course1 implies the use of switches that are competent to break the secondary circuit of any group of transformers under overload conditions and at the maximum voltage of the system1 but oil switches as now made are competent to meet this requirement4 ,when all switching of live circuits is confined to those of high voltage there is also the incidental advantage that heavy contact parts carrying very large currents are avoided in the operating switches4 ,where each generator is connected directly to its own group of transformers the secondary coils of these transformers will pass through oil switches to high-tension bus-bars1 and the use of low-tension bus-bars may be avoided4 ,from these high-tension bus-bars the transmission lines will pass through oil switches1 so that on this plan there are only two sets of oil switches1 namely1 those connecting the secondary coils of transformers to the high-tension bus-bars1 and those connecting the transmission lines to the same bars4 ,each group of two or three transformers1 according as two or three are used with each generator1 should be connected to its generator through short-break1 open-air knife switches for convenience in disconnecting and changing transformers that are not in operation1 but these switches are not intended or required to open the circuit of the generators and primary coils when in operation4 ,illustration3 ,,fig4 #fb4--;,distributing ,switchboard1 ,central ,sub-station1 ,montreal4 ,a plan similar to that just outlined was followed at the station of the ,independent ,electric ,light and ,power ,company1 ,san ,francisco1 where each of the #eej-volt generators is ordinarily connected directly to the primary coils of two transformers that change the current from two-phase to three-phase and then deliver it through oil switches to the high-tension bus-bars at #aa1jjj volts4 ,to these bus-bars the #aa1jjj-volt feeders for five sub-stations are connected through switches4 ,at this station there is a set of #eej-volt bus-bars to which any of the generators may be connected1 but to which no generator is connected in ordinary operation4 ,the generators alone have switches connecting with these bars4 ,when it is desirable to operate any particular generator on some pair of transformers other than its own1 that generator is disconnected from its own transformers and connected to the #eej-volt bus-bars4 ,the generator whose transformers are to be operated by the generator before mentioned next has its switch connected to the #eej-volt bus-bars1 while the brushes of the contact rings of the former generator are raised4 ,as the leads from each generator to its two switches are permanently joined1 the switching operations just named connect the transformers of one generator with the other generator that has its switch closed on the #eej-volt bars4 ,illustration3 ,,fig4 #fc4--,switchboard at ,chambly ,power-station4 ,where it is desired that a single reserve transformer may be readily substituted for any one of a number of transformers in regular use1 the connections to each of these latter transformers may be provided with double-pole double-throw knife switches on both the primary and secondary sides1 so that when these switches are thrown one way at any transformer in regular use the reserve transformer will be connected in its place4 ,fuses and automatic circuit-breakers alike are intended to break connections without the intervention of human agency under certain predetermined conditions4 ,in the fuse the heat generated by a certain current is sufficient to melt or vaporize a short length of special conductor4 ,in the circuit-breaker a certain current gives a magnet or motor sufficient strength to overcome the pressure of a spring1 and contact pieces through which the current is passing are pulled apart4 ,the primary object of both the fuse and the circuit-breaker is thus to open connections and stop the flow of energy when more than a certain current passes4 ,when any current passes through a circuit in the reverse of its regular direction the circuit-breaker can be arranged to break the connections1 though the fuse cannot4 ,a fuse must carry the current at which it is designed to melt during some seconds before enough heat is developed to destroy it1 and the exact number of seconds for any particular case is made a little uncertain by the possibility of loose connections at the fuse tips which develop additional heat and also by the heat-conducting power of its connecting terminals4 ,a circuit-breaker may be set so as to open its connections in one or more seconds after a certain current begins to flow4 ,when connections are broken by a fuse the molten or vaporized metal forms a path that an arc may easily follow4 ,a circuit-breaker with its contacts under oil offers a much smaller opportunity than a fuse for the maintenance of an arc4 ,these qualities of fuses and circuit-breakers form the basis of their general availability and comparative advantages in transmission circuits4 ,much variation exists in practice as to the use of fuses and circuit-breakers on transmission circuits4 ,one view often followed is that fuses and circuit-breakers should be entirely omitted from the generator and transmission lines4 ,the argument in favor of this practice is that temporary short circuits due to birds that fly against the lines or to sticks and loose wires that are thrown onto them will interrupt all or a large part of the transmission service if fuses or circuit-breakers that operate instantly are employed4 ,on the other hand1 it may be said that if fuses and circuit-breakers are omitted from the generator and transmission circuits a lasting short circuit will make it necessary to shut down an entire plant in some cases until it can be removed4 ,electric transmission at high voltages became important before magnetic circuit-breakers competent to open overloaded circuits at such voltages were developed4 ,consequently the early question was whether a transmission line and the generators that fed it should be provided with fuses or be solidly connected from generators to the distribution circuits of sub-stations4 ,the original tendency was strong to use fuses in accord with the practice at low voltages4 ,the great importance of continuous service from transmission systems and the many interruptions caused by temporary short circuits where fuses were used led to their abandonment in some cases4 ,an example of this sort may be seen at the first ,niagara station4 ,in #ahic1 when this station was equipped1 no magnetic circuit-breaker was available for circuits of either #aa1jjj or #b1bjj volts1 carrying currents of several thousand horse-power1 and fuses were employed in lines at both these pressures 7,a4 ,i4 ,e4 ,e41 vol4 xviii41 pp4 #die1 #dig74 ,the fuses adopted in this case were the same for both the #b1bjj and the #aa1jjj-volt lines and were of the explosive type4 ,each complete fuse consisted of two lignum-vit blocks that were hinged together at one end and were secured when closed at the other4 ,in these blocks three parallel grooves for fuses were cut and in each groove a strip of aluminum was laid and connected to suitable terminals at each end4 ,vents were provided for the grooves in which the aluminum strips were placed so that the expanding gas when a fuse was blown would escape4 ,when these fuse blocks were new and the blocks of lignum vit made tight joints the metallic vapor produced when a fuse was blown was forced out at the vents and the connections of the line were thus broken4 ,after a time1 however1 when the joints between the blocks were no longer tight because of shrinkage1 the expanding gas of the fuse would reach the terminals and an arc would continue after the fuse had blown4 ,these aluminum fuses1 which were adopted about #ahic1 were abandoned at the ,niagara plant in #ahih4 ,since this later date the #b1bjj-volt feeders from the ,no4 #a power-house to the local consumers have had no fuses at the power-house1 nor have circuit-breakers been installed there in the place of the fuses that were removed4 ,at the large manufacturing plants supplied through these local ,niagara feeders1 the feeders formerly terminated in fuses1 but these have since been displaced by circuit-breakers4 ,in the second ,niagara power-station1 completed in #aijb1 the local #b1bjj-volt feeders are provided with circuit-breakers1 but no fuses4 ,between the generators and bus-bars of the first ,niagara plant the circuits were provided with neither fuses nor automatic circuit-breakers1 and this practice continues there to the present time4 ,besides the aluminum fuses in the #aa1jjj-volt transmission line at the first ,niagara station1 there were lead fuses in the #b1bjj-volt primary circuits of the step-up transformers that supplied these lines4 ,at the other end of these lines1 in the ,buffalo sub-station1 another set of aluminum fuses was inserted before connection was made with the step-down transformers4 ,between the secondary coils of these transformers and the #eej-volt converters there were no fuses1 but these converters were connected to the railway bus-bars through direct current circuit-breakers4 ,these lead fuses1 which contained much more metal than those of aluminum1 when blown set up arcs that lasted until power was cut off by opening a switch1 and usually destroyed their terminals4 ,an effort was made to so adjust the sizes of the fuses in this transmission system that in case of a short circuit in distribution lines at ,buffalo only the fuses in the sub-station would be blown1 leaving those at ,niagara entire4 ,this plan did not prove effective1 however1 and a severe overload on the distribution lines in ,buffalo would blow out fuses clear back to the generator bus-bars at the ,niagara station4 ,in order to accomplish the opening of overloaded circuits with greater certainty1 to delay such opening where the overload might be of only a momentary nature1 and to confine the open circuit to the lines where the overload existed1 automatic circuit-breakers were substituted for the fuses named in the ,niagara and ,buffalo transmission system4 ,this system was also changed from #aa1jjj to #bb1jjj volts on the transmission lines1 thus rendering the requirements as to circuit-opening devices more severe4 ,these circuit-breakers were fitted with time-limit attachments so that any breaker could be set to open at the end of any number of seconds after the current flowing through it reached a certain amount4 ,a circuit-breaker with such a time-limit attachment will not open until the time for which it is set1 after the amperes flowing through it reach a certain figure1 has elapsed1 no matter how great the current may be4 ,moreover1 if the overload is removed from a line before the number of seconds for which its time-limit circuit-breaker is set have elapsed1 the circuit-breaker resets itself automatically and does not open the connections4 ,if a circuit-breaker is set to open a line after an interval of say three seconds from the time when its current reaches the limit1 the line will not be opened by a mere momentary overload such as would blow out a fuse4 ,by setting the time-limit relays of circuit-breakers in transmission lines to actuate the opening mechanism after three seconds from the time that an overload comes on1 and then leaving the breakers on distribution lines to operate without a time-limit1 it seems that the opening of breakers on the distribution lines should free the system from an overload there before the breakers on the transmission lines have time to act4 ,such a result is very desirable in order that the entire service of a transmission system may not be interrupted every time there is a fault or short circuit on one of its distribution lines4 ,this plan was followed in the ,niagara and ,buffalo system4 ,in the #bb1jjj-volt lines at the ,niagara station the time relays were set to actuate the breakers after three seconds1 at the terminal house in ,buffalo1 where the transformers step down from #bb1jjj to #aa1jjj volts1 the circuit-breakers in the #aa1jjj volt lines to sub-stations had their relays set to open in one second4 ,finally the circuit-breakers in the distribution lines from the several sub-stations were left to operate without any time limit4 ,by these means it was expected that a short circuit in one of the distribution circuits from a sub-station would not cause the connections of the underground cable between that sub-station and the terminal house to be broken1 because of the instant action of the circuit-breaker at the sub-station4 ,furthermore1 it was expected that a short circuit in one of the underground cables between the terminal house and a sub-station would be disconnected from the transmission line at that house and would not cause the circuit-breakers at the ,niagara station to operate4 ,it is reported that the foregoing arrangement of circuit-breakers with time relays failed of its object because the breakers did not clear their circuits quick enough and that the time-limit attachments on the #bb1jjj and #aa1jjj volt lines are no longer in use 7,a4 ,i4 ,e4 ,e41 vol4 xviii41 p4 #ejj74 ,as the circuits under consideration convey thousands of horse-power at #aa1jjj and #bb1jjj volts it may be that time-limit devices with circuit-breakers would give good results under less exacting conditions4 ,time-limit relays are perhaps an important aid toward reliable operation of transmission systems1 but they are subject to the objection that no matter how great the overload they will not open the circuit until the time for which they are set has run4 ,in the case of a short circuit the time-limit relay may lead to a prolonged drop in voltage throughout the system1 which is very undesirable for the lighting service and also allows all synchronous apparatus to fall out of step4 ,with a mere momentary drop in voltage the inertia of the rotating parts of synchronous apparatus will keep them in step4 ,for these reasons it is desirable to have circuit-breakers that will act immediately to open a line on which there is a short circuit or very great overload1 but will open the line only after an interval of one or more seconds when the overload is not of a very extreme nature4 ,this action on the part of circuit-breakers at the second ,niagara power-station was obtained by the attachment of a dash-pot to the tripping plunger of each circuit-breaker 7,a4 ,i4 ,e4 ,e41 vol4 xviii41 p4 #edc74 ,with moderate overloads of a very temporary nature this dash-pot so retards the action of a tripping plunger that the circuit-breaker does not open4 ,when a short circuit or great overload comes onto a line the pull on the tripping plunger or the circuit-breaker on that line is so great that the resistance of the dash-pot to the movement is overcome at once and the line is disconnected from the remainder of the system4 ,the fact that a circuit-breaker may be designed to open the line which it connects1 whenever the direction from which the flow of energy takes place is reversed1 is taken advantage of at some sub-stations to guard against a flow of energy from a sub-station back toward the generating station4 ,by this means a flow of energy from a sub-station to a short circuit in one of the lines or cables connecting it with the generating plant is prevented4 ,,chapter ,,xii4 ,,regulation ,,of ,,transmitted ,,power4 ,regulation of voltage at incandescent lamps is a serious problem in the distribution of electrically transmitted energy4 ,good regulation should not allow the pressure at incandescent lamps rated at #aaj to #abj volts to vary more than one volt above or below the normal4 ,electric motor service is much less exacting as to constancy of voltage1 and the pressure at motor terminals may sometimes be varied as much as ten per cent without material objection on the part of users4 ,a mixed service to these three classes of apparatus must often be provided where transmitted energy is used1 and the limitations as to variations at incandescent lamps are thus the ones that must control the regulation of pressure4 ,transmission systems may be broadly divided into those that have no sub-stations and must therefore do all regulation at the generating plant1 and those that do have one or more sub-stations so that regulation of voltage may be carried out at both ends of the transmission line4 ,illustration3 ,,fig4 #fd4--;,arc-lighting ,switchboard at ,central ,sub-station1 ,montreal4 ,as a rule1 a sub-station with an operator in attendance is highly desirable between transmission and distribution lines1 and this is the plan generally followed at important centres of electrical supply1 even though the transmission is a short one4 ,one example of this sort may be noted at ,springfield1 ,mass41 where energy for electrical supply is transmitted from two water-power plants on the ,chicopee ,river only about four and a half and six miles1 respectively1 from the sub-station in the business centre of the city4 ,the voltage of transmission for two-phase current in this case is #f1jjj1 and is reduced to about #b1djj volts at the sub-station for the general distribution of light and power4 ,a similar instance may be seen at ,concord1 ,n4 ,h41 where electrical energy at both #b1ejj and #aj1jjj volts is delivered to a sub-station in the business section from a water-power plant at ,sewall's ,falls1 on the ,merrimac ,river1 four and one-half miles distant4 ,from this sub-station the current is distributed at about #b1ejj volts for the supply of lamps and motors4 ,a sub-station was found desirable at ,concord for purposes of regulation before the voltage of transmission was raised above that of distribution4 ,subsequently1 when the load increased1 the voltage of #aj1jjj was adopted on a part of the transmission circuit in order to avoid an increase in the size of their conductors4 ,illustration3 ,,fig4 #fe4--;,area of ,electrical ,distribution at ,montreal4 ,illustration3 ,,fig4 #ff4 ,illustration3 ,,fig4 #fg4 ,illustration3 ,,fig4 #fh4 ,in some instances1 however1 transmission and distribution lines are joined without the intervention of a sub-station1 where regulation of voltage can be accomplished1 though this practice has little to recommend it aside from the savings in first cost of installation and subsequent cost of operation4 ,these savings are more apparent than real if fairly constant pressure is to be maintained at the lamps1 because what is gained by the omission of sub-stations will be offset1 in part at least1 by additional outlays on the lines if good regulation is to be maintained4 ,this fact may be illustrated by reference to ,figs4 #ff1 #fg1 and #fh1 in each of which ,d represents a generating station and ,a1 ,b1 and ,c towns or cities where energy from the station is to be distributed4 ,in the case of each figure it is assumed that the distance between the generating station and each of the cities or towns is such that distributing lines with a loss of1 say1 not more than two per cent in voltage at full load cannot be provided between the generating station and each city or town because of the cost of conductors4 ,this being so1 one or more centres of distribution must be located in each town1 and the transmission lines must join the distribution lines at these centres either on poles or in sub-stations4 ,if several of these towns are in the same general direction from the generating plant so as to be reached by the same transmission line1 as ,a1 ,b1 and ,c in ,fig4 #ff1 this one line will be all that is necessary with a sub-station in each town4 ,where sub-stations are not employed a separate transmission circuit must be provided between the generating plant and each town for reasons that will appear presently4 ,the percentage of voltage variation in a transmission line under changing loads will be frequently from five to ten1 and is thus far beyond the allowable variations at incandescent lamps4 ,to give good lighting service the centre of distribution1 where the transmission line joins the distribution circuits1 must be maintained at very nearly constant voltage if no sub-station is located there4 ,regulation at a generating station will compensate for the changing loss of pressure in a line under varying loads so as to maintain a nearly constant voltage at any one point thereon4 ,no plan of station regulation1 however1 can maintain constant voltages at several points on the same transmission line when there is a varying load at each4 ,the result is that even though the several towns served are in the same general direction from the generating station1 as in ,fig4 #fg1 yet each town should have its separate transmission line where no sub-stations in the towns are provided4 ,in the case illustrated by ,fig4 #fh1 where the towns served are in very different directions from the generating station1 there should be a separate transmission line to each1 regardless of whether there is a sub-station or only a centre of distribution there4 ,even in the case illustrated by ,fig4 #fh1 as in each of the others1 there is a large saving effected in the cost of distribution lines by the employment of a sub-station at the point where these lines join the transmission circuit1 provided that the variation of pressure at lamp terminals is to be kept within one volt either way from the standard4 ,with the variations of loads the loss of pressure in the distribution lines will range from zero to its maximum amount and the connected lamps will be subjected to the change of voltage represented by this total loss1 unless the distribution start from a sub-station where the loss in distribution lines can be compensated for by regulation4 ,to give good service the distribution lines should be limited to a loss of one per cent at full load if there is no sub-station where they join transmission lines4 ,with opportunity for regulation at a sub-station the maximum loss in distribution lines may easily be doubled1 thus reducing their weight by one-half in comparison with that required where there is no sub-station4 ,another advantage of connecting transmission and distribution lines in a sub-station1 where regulation of voltage can be had1 lies in the fact that it is practically impossible to maintain an absolutely constant pressure miles from a generating plant at the end of a transmission line that is carrying a mixed and varying load4 ,a result is that without the intervention of regulation at a sub-station it is almost impossible to give good lighting service over a long transmission line4 ,furthermore1 the labor of regulation at a generating station is much increased where there are no sub-stations1 because it must be much more frequent and accurate4 ,the absence of sub-stations from a transmission system thus implies more transmission circuits1 heavier distribution circuits1 more labor at the generating plant1 and a poor quality of lighting service4 ,where stationary motors form the great bulk of the load on a transmission system1 and good lighting service is of small importance1 it may be well to omit sub-stations at some centres of distribution4 ,this is a condition that sometimes exists in the ,rocky ,mountain region where the main consumers of power along a transmission line may be mines or works for the reduction of ores4 ,an example of this sort exists in the system of the ,telluride ,power ,transmission ,company1 in ,utah1 which extends from ,provo ,caon1 on the river of the same name1 entirely around ,utah ,lake by way of ,mercur1 ,eureka1 and ,provo1 and back to the power-house in ,provo ,caon1 a continuous circuit of #aje miles4 ,the transmission voltage on this line is #dj1jjj1 and at intervals where there are distributing points the voltage is reduced to about #e1jjj by transformers on poles1 and without the aid of regulation at sub-stations in some cases4 ,the power thus transmitted is largely used in mines and smelters for the operation of motors1 but also for some commercial lighting4 ,regulation at generating stations of the voltage on transmission lines may be accomplished by the same methods whether there are sub-stations at centres of distribution or not4 ,in any such regulation the aim is to maintain a certain voltage at some particular point on the transmission line1 usually its end1 where the distribution circuits are connected4 ,if more than one point of distribution exists on the same transmission line1 the regulation at the generating plant must be designed to maintain the desired pressure at only one of these points1 leaving regulation at the others to be accomplished by local means4 ,one method of regulation consists in the overcompounding of each generator so that the voltage at its terminals will rise at a certain rate as its load increases4 ,if a generator and transmission line are so designed that the rise of voltage at the generator terminals just corresponds with the loss of voltage on the line when the output of that generator alone passes over it to some particular point1 then the pressure at that point may be held nearly constant for all loads if no energy is drawn from the line elsewhere4 ,these several conditions necessary to make regulation by the compounding of generators effective can seldom be met in practice4 ,if a varying number of generators must work on the same transmission line1 or if varying loads must be supplied at different points along the line1 no compound winding of generators will suffice to maintain a constant voltage at any point on the line that is distant from the power-station4 ,for these reasons the compound winding of generators is of minor importance so far as the regulation of voltage on transmission lines is concerned1 and on large alternators is not generally attempted4 ,an example may be noted on the #c1gej-kilowatt generators at ,niagara ,falls1 where the single magnet winding receives current from the exciters only4 ,a much more effective and generally adopted method of regulation of voltage at the generating plants of transmission systems is based on the action of an attendant who varies the current in the magnet coils of each generator so as to raise or lower its voltage as desired4 ,the regulation must be for some one point on the transmission line1 and the attendant at the generating plant may know the voltage at that point either by means of a pair of pressure wires run back from that point to a voltmeter at the generating plant1 by a meter that indicates the voltage at the point in question according to the current on the line1 or by telephone connection with a sub-station at the point where the constant voltage is to be maintained4 ,pressure wires are a reliable means of indicating in the generating station the voltage at a point of distribution on the line1 but the erection of these wires is quite an expense in a long transmission1 and in such cases they are only occasionally used4 ,owing to inductive effects and to variable power-factors the amperes indicated on a line carrying alternating current are far from a certain guide as to the drop in voltage between the generating station and the distant point4 ,in long transmissions1 telephone communication between the generating plant and the sub-stations is the most general way in which necessary changes to maintain constant voltage at sub-stations are brought to the attention of the attendant in the generating plant4 ,few1 if any1 extensive transmission systems now operate without telephone connection between a generating plant and all of its sub-stations1 or between a single sub-station and the several generating plants that may feed into it4 ,thus1 the generating plant at ,spier ,falls1 on the ,hudson ,river1 will be connected by telephone with sub-stations at ,schenectady1 ,albany1 ,troy1 and some half-dozen smaller places4 ,on the other hand1 the single sub-station in ,manchester1 ,n4 ,h41 that receives the energy from four water-power plants has a direct telephone line to each4 ,where two or more transmission lines from the same power-station are operated from the same set of bus-bars the voltage at a distant point on each line cannot be held constant by changes of pressure on these bus-bars4 ,one generator only may be connected to each transmission line and be regulated for the loss on that line1 but this loses the advantages of multiple operation4 ,another plan is to connect a regulator in each transmission line before it goes from the generating plant4 ,one type of regulator for this purpose consists of a transformer with its secondary coil divided into a number of sections and the ends of these sections brought out to a series of contact segments4 ,the primary coil of this transformer may be supplied with current from the bus-bars and the secondary coil is then connected in series with the line to be regulated1 so that the secondary voltage is added to or subtracted from that of the main circuit4 ,a movable contact arm on the segments to which the sections of the secondary coil are connected makes it possible to vary the secondary voltage by changing the number of these sections in circuit4 ,in another transformer used for regulating purposes the primary coil is connected to the bus-bars as before and the movable secondary coil is put in series with the line to be regulated4 ,the regulation is accomplished in this case by changing the position of the secondary relative to that of the primary coil and thus raising or lowering the secondary voltage4 ,both of these regulators require hand adjustment1 and the attendant may employ the telephone1 pressure wires1 or the compensating voltmeter above mentioned1 to determine the voltage at the centre of distribution4 ,the voltage indicated by this so-called 8compensator0 is that at the generating station minus a certain amount which varies with the current flowing in the line to be regulated4 ,the voltmeter coil of the compensator is connected in series with the secondary coils of two transformers1 which coils work against each other4 ,one transformer has its secondary coil arranged to indicate the full station voltage1 and the other secondary coil is actuated by a primary coil that carries the full current of the regulated line4 ,by a series of contacts the effect of this last-named coil can be varied to correspond with the number of volts that are to be lost at full load between the generating station and the point on the transmission line at which the voltage is to be held constant4 ,if there is no inductive drop on the transmission line1 or if this drop is of known and constant amount1 the compensator may give the actual voltage at the point for which the regulation is designed4 ,automatic regulators are used in some generating stations to maintain a constant voltage either at the generating terminals or at some distant distributing point on a line operated by a single generator4 ,these regulators may operate rheostats that are in series with the magnet windings of the generators to be regulated1 and raise or lower the generator voltage by varying the exciting current in these windings4 ,these regulators are much more effective to maintain constant voltage at generating stations than at the distributing end of long transmission lines with variable power-factors4 ,in spite of the compound winding of generators1 of automatic regulators for the exciting currents in their magnet coils1 and of regulating transformers in the transmission circuits1 hand-adjustment of rheostats in series with the magnet coils of generators remains the most generally used at the generating stations of long transmission systems4 ,automatic regulators at the ends of transmission lines in sub-stations are now being introduced1 and may prove very desirable4 ,illustration3 ,,fig4 #fi4--,motor-generators in ,shawinigan ,sub-station at ,montreal4 ,the more exacting and final work of regulation in transmission systems is usually done at the sub-stations4 ,after a nearly constant voltage is delivered at the high-pressure coils of step-down transformers in a sub-station1 there remains the varying losses in these transformers1 in motor-generators or converters1 in distribution lines and in service transformers1 to be compensated for4 ,in general1 three or four sorts of loads must be provided for1 namely1 arc or incandescent lamps for street lighting on series circuits1 usually of #d1jjj to #aj1jjj volts4 ,arc and incandescent lamps on constant-pressure circuits of #b1jjj to #b1ejj volts for commercial lighting1 direct-current stationary motors on constant-pressure circuits of about #ejj volts1 and alternating motors which may be served at either #b1ejj or #ejj volts according to their sizes and locations4 ,to these loads may be added that of street-car motors of #ejj volts1 direct current4 ,both the stationary and the street-car motors1 but more especially the latter1 by their changes of load give rise to large and rapid fluctuations of voltage on the distribution lines to which they are connected4 ,the problem of regulation with combined lamp and motor loads is not1 therefore1 so much to maintain a nearly constant voltage at the motors as to protect the lamps from the fluctuations of voltage which the motors set up4 ,illustration3 ,,fig4 #gj4--,one of the #a1jfe-kilowatt ,motor-generators in the ,shawinigan ,sub-station at ,montreal4 ,for street-car motors using direct current at about #ejj volts1 the sub-station equipment includes either step-down transformers and converters or motor-generators with or without transformers4 ,it is the practice in some cases where both lighting and street-railway service are drawn from the same transmission system to keep these two kinds of service entirely separate1 devoting independent generators and transmission lines1 as well as independent transformers and converters or motor-generators1 to the street-car work4 ,this is done in the transmission system centring at ,manchester1 ,n4 ,h41 in which each one of the four water-power plants1 as well as the sub-station1 has a double set of bus-bars on the switchboard2 and from each water-power plant to the sub-station there are two transmission circuits4 ,in operation1 one set of generators1 bus-bars1 transmission circuits1 and transformers supply converters or motor-generators for the street-car motors2 and another set of generators1 bus-bars1 transmission circuits1 and transformers are devoted to lighting and stationary motors in this system4 ,where street-car motors draw their energy from the same generators and transmission lines that supply commercial incandescent lamps1 some means must be adopted to protect the lighting circuits from the fluctuations of voltage set up by the varying street-car loads4 ,one way to accomplish this purpose is to operate the lighting circuits with generators driven by synchronous motors in the sub-stations4 ,these generators may1 of course1 be of either direct or alternating type and of any desired voltage4 ,the synchronous motors driving these generators take their current from the transmission line either with or without the intervention of step-down transformers4 ,by this use of synchronous motors the lighting circuits escape fluctuations of voltage corresponding to those on the transmission line1 because synchronous motors maintain constant speeds independently of the voltage of the circuits to which they are connected4 ,this plan was followed at ,buffalo1 where the street-car system and the lighting service are operated with energy from the ,niagara ,falls stations over the same transmission line4 ,in one of the sub-stations at ,buffalo1 both #b1bjj-volt1 two-phase alternators1 and #aej-volt continuous-current generators for lighting service1 are driven by synchronous motors connected to the ,niagara transmission line through transformers4 ,at other sub-stations in ,buffalo1 the #ejj-volt continuous current for street-car motors is obtained from the same transmission system through transformers and converters4 ,another solution of the problem of voltage regulation where street-railway and commercial lighting service are to be drawn from the same transmission line is found in the operation of #ejj-volt continuous-current generators in the sub-stations by synchronous motors fed from the line either directly or through transformers4 ,this plan has been adopted in the transmission system of the ,boston ,edison ,company1 which extends to a number of cities and towns within a radius of twenty-five miles4 ,the sub-stations at ,natick and ,woburn in this system1 where there are street-railway as well as lighting loads1 contain #ejj-volt continuous-current generators driven by synchronous motors connected directly to the three-phase transmission lines4 ,in a case like this the synchronous motors maintain their speed irrespective of the voltage on the line and thus tend to hold that voltage steady in spite of the variable losses due to fluctuating loads4 ,stationary motors should not as a rule be operated from the same distribution lines that supply incandescent lamps1 especially in sizes above one horse-power1 and this is the better practice4 ,motor circuits of about #b1djj volts and two- or three-phase1 alternating1 or #ejj volts1 alternating or direct current1 may be supplied at a sub-station either by transformers alone in the first case or by transformers and converters in the second4 ,in either case no especial provision is usually necessary for the regulation of constant pressure on the motor circuits4 ,illustration3 ,,fig4 #ga4--a1ajj-kilowatt1 #b1cjj-volt1 ,three-phase1 #cj-;cycle1 ,synchronous ,motor at ,sub-station of ,shawinigan ,line in ,montreal4 ,in some transmission systems the distribution circuits for stationary motors are not fed by the same transmission lines that carry the lighting load1 but draw their energy from lines that do no other work4 ,this practice is certainly desirable1 as it frees the lighting circuits from all fluctuations of voltage due to line losses with changing motor loads4 ,examples of this sort may be seen at ,springfield1 ,mass41 and ,portland and ,lewiston1 ,me41 in each of which the load of stationary motors is operated over independent transmission as well as distribution lines4 ,in transmission systems series arc and incandescent lamps for street lighting are commonly operated either by direct-current arc dynamos or by constant-current transformers or constant-pressure transformers with automatic regulators at the sub-stations4 ,the arc dynamos are driven by either induction or synchronous motors supplied directly from the transmission line or through transformers4 ,as the arc dynamos regulate automatically for constant current no further regulation is required4 ,if the series arc and incandescent lamps are to be supplied with alternating current1 the constant-current transformer or the constant-current regulator come into use4 ,this type of transformer and regulator alike depend for their regulating effect on the movement of a secondary coil on a transformer core in such a way that the current in this coil1 which is in series with the lamps1 is held nearly constant4 ,such constant-current transformers and regulators are usually supplied from the transmission line through regular constant-pressure transformers1 and they hold their currents sufficiently constant for the purposes of their use4 ,the main problem of regulating thus comes back to the #bej- or #b1bjj-volt1 constant-pressure circuits for incandescent lighting1 supplied from transmission lines through transformers or motor generators or both at the sub-station4 ,for this regulation one of the most reliable instruments is the hand of a skilful attendant1 guided by voltmeters connected with pressure wires from minor centres of distribution1 and adjusting the regulating transformers above mentioned1 or other regulating devices4 ,,chapter ,,xiii4 ,,guard ,,wires ,,and ,,lightning ,,arresters4 ,lightning in its various forms is the greatest danger to which transmission systems are exposed1 and it attacks their most vulnerable point1 that is1 insulation4 ,the lesser danger as to lightning is that it will puncture the line insulators and shatter or set fire to the poles4 ,the greater danger is that the lightning discharge will pass along the transmission wires to stations and sub-stations and will there break down the insulation of generators1 motors1 or transformers4 ,damage by lightning may be prevented in either of two ways1 that is1 by shielding the transmission line so completely that no form of lightning charge or discharge can reach it1 or by providing so easy a path from line conductors to earth that lightning reaching these conductors will follow the intended path instead of any other4 ,in practice the shielding effect is sought by grounded guard wires1 and the easy path for discharge takes the form of lightning arresters1 but neither of these devices is entirely effective4 ,aerial transmission lines are exposed to direct discharges of lightning1 to electromagnetic charges due to lightning discharges near by1 and to electrostatic charges that are brought about by contact with or induction from electrically charged bodies of air4 ,it is evidently impracticable to provide a shield that will free overhead lines from all these influences4 ,to cut off both electrostatic and electromagnetic induction from a wire and also to free it from a possible direct discharge of lightning1 it seems that it would at least be necessary completely to incase the wire with a thick body of conducting material4 ,this condition is approximated when an electric circuit is entirely beneath the surface of the ground1 but would be hard to maintain with bare overhead wires4 ,it seems1 however1 that grounded guard wires near to and parallel with long aerial circuits should tend to discharge any high electrostatic pressures existing in the surrounding air1 and materially to reduce the probability that a direct discharge of lightning will choose the highly insulated circuits for its path to earth4 ,lightning arresters may conduct induced and direct lightning discharges to earth1 without damage to transmission lines1 so that both arresters and guard wires may logically be used in the same system4 ,wide differences of opinion exist as to the general desirability of grounded guard wires on transmission lines1 both because of their undoubted disadvantages and because the degree of protection that they afford is uncertain4 ,it seems1 however1 that the defects of guard wires depend in large degree on the kind of wire used for the purpose1 and the method of its erection4 ,galvanized iron wire with barbs every few inches has been more generally used for guard wires along transmission lines than any other sort4 ,sometimes a single guard wire of this sort has been run on a pole line carrying transmission circuits1 and the more common location of this single wire is on the tops of the poles4 ,in other cases two guard wires have been used on the same pole line1 one of these wires being located at each end of the highest cross-arm and outside of the power wires4 ,besides these guard wires at the ends of the top cross-arms of a pole line1 a third wire has in some systems been added to the tops of the poles4 ,these guard wires have sometimes been secured to the poles and cross-arms by iron staples driven over the wire and into the wood1 and in other cases the guard wires are mounted on small glass insulators4 ,much variation in practice also exists as to the ground connections of guard wires1 such connections being made at every pole in some systems1 and much less frequently in some others4 ,with all these differences in the practical application of guard wires it is not strange that opinions as to their utility do not agree4 ,further reason for differences of opinion as to the practical value of guard wires exists in the fact that in some parts of the country the dangers from lightning are largely those of the static and inductive sort1 that are most effectively provided for by lightning arresters1 while in other parts of the country direct lightning strokes are the greatest menace to transmission systems4 ,at the present time1 knowledge of the laws governing the various manifestations of energy that are known under the general head of lightning is imperfect1 and the most reliable rules for the use of guard wires along transmission lines are those derived from practical experience4 ,a case where a guard wire did not prove effective as a protection against lightning is that of the ,san ,miguel ,consolidated ,gold ,mining ,company1 of ,telluride1 ,col41 whose three transmission lines ran from the water-power plant to points from three to ten miles distant1 as described in ,a4 ,i4 ,e4 ,e41 vol4 xi41 p4 #ccg1 and following pages4 ,this transmission operated at #c1jjj volts1 single-phase1 alternating1 and the pole lines ran over the mountains at elevations of #h1hjj to #ab1jjj feet above sea-level1 passing across bare ridges and tracts of magnetic material4 ,it was stated that the country over which the circuits ran is so dry and rocky that it was practically impossible to secure good ground connections along the line1 and no mention was made of the way in which the ground wire was grounded1 or of the number of its ground connections4 ,furthermore1 it does not appear that there was more than one guard wire on each pole line4 ,under these circumstances1 and with a certain make of lightning arresters in use at the station1 lightning was a frequent cause of damage to the connected apparatus4 ,the insulation of some of the machinery is described as honeycombed with perforations which led to continual leakage1 grounds1 and short-circuits1 which seems to indicate that the damage was being done by static and inductive discharges rather than by direct lightning strokes1 one of which would have disabled a machine at once4 ,the type of lightning arrester in use on this system was changed1 and thorough ground connections were provided for the new arresters1 after which the damage by lightning came to an end4 ,it is not stated1 however1 that the guard wires were removed4 ,this case has been referred to as one in which guard wires failed to give protection1 but1 as may be seen from the above facts1 such a statement is hardly fair4 ,in the first place1 it does not appear that the single guard wire on each pole line was effectively grounded anywhere4 ,again1 a large part of the damage to apparatus appears to have been the result of static or inductive discharges that could not in the nature of things have been prevented by a guard wire4 ,finally1 as the guard wire was not removed after the new lightning arresters were erected1 it is possible that this wire prevented some direct discharges over the transmission wires that would have been destructive4 ,on page #cha of the volume of ,a4 ,i4 ,e4 ,e4 above cited1 it is stated that the frequency and violence of lightning discharges that entered a certain electric station on ,staten ,island were much less after guard wires had been erected along the connected circuits than they were before the guard wires were put up4 ,it is also stated on page #che of the same volume that examination of statistics of a number of stations in this country and ,europe had shown that in every case where an overhead guard wire had been erected over power circuits1 or where these circuits ran for their entire distance beneath telegraph wires1 lightning had given no trouble on the circuits so protected4 ,unfortunately1 the speaker who made this statement did not tell us where the interesting statistics mentioned could be consulted4 ,on the first pole line erected for power transmission from ,niagara ,falls to ,buffalo1 two guard wires were strung at opposite ends of the top cross-arm on guard irons there located4 ,this cross-arm also carried parts of two power circuits1 and the nearest wires of these circuits were distant about thirteen inches from the guard irons4 ,these guard wires were barbed1 and grounded at every fifth pole1 according to an account given in ,a4 ,i4 ,e4 ,e41 vol4 xviii41 at #ead and following pages4 ,the character of the ground connections is not stated4 ,much trouble in the way of grounds and short circuits on the transmission lines was caused by these guard wires at times when they were broken by the weight of ice coatings and wind pressure4 ,as a result of these troubles the guard wires were removed in #ahih4 ,since that date it appears that the transmission lines between ,niagara ,falls and ,buffalo have been without guard wires4 ,up to #aija1 according to page #ecg in the volume just cited1 twenty per cent of the interruptions in operation at the ,niagara plant were caused by lightning1 and it seems probable that this record applies to the period after #ahih1 when the guard wires were removed4 ,it is also stated that during a single storm the line was struck five times1 and that five poles with their cross-arms were destroyed4 ,if these direct lightning strokes occurred while there were no guard wires along the line1 as seems to have been the fact1 it is a fair question whether such wires well grounded would not have carried off the discharges without damage4 ,in ,california1 the country of long transmissions1 the use of guard wires along the pole lines is quite general4 ,many of these lines run east and west across the ,state1 and a single line may thus have elevations in its different parts all the way from that of tide-water up to several thousand feet above sea-level4 ,unless guard wires are strung with these lines there is much manifestation of induced or static electricity1 according to an account at page #ech1 in vol4 xviii41 ,a4 ,i4 ,e4 ,e41 where it is said that in the absence of guard wires a person will be knocked off his feet every time he touches a transmission wire that is entirely disconnected from the source of power4 ,it is also said that this static charge on idle power lines is sufficient1 in time1 to puncture the insulation of the connected apparatus4 ,on the other hand1 where the grounded and barbed guard wires are strung over the entire lengths of these long power lines1 these lines may be handled with impunity when they are idle4 ,ground connections to the guard wire are said to be made at about every fourth pole1 and to consist of a wire stapled down the face of the pole and joined to an iron plate beneath its butt4 ,the barbed guard wire itself1 of which each pole line appears to have but one1 is regularly stapled to the tops of the poles4 ,at the reference just named it is related that on a certain transmission line running east and west across the ,state for a distance of forty-six miles1 and protected by a guard wire1 no trouble was experienced during a severe storm that swept north and south over the line4 ,meantime the damage on other lines in the same neighborhood1 and presumably not protected by guard wires1 was large4 ,illustration3 ,,fig4 #gb4--,transposition of ,wires on ,chambly ,montreal ,line4 ,between the electric plant at ,chambly1 on the ,richelieu ,river1 and ,montreal1 ,quebec1 a distance of #af4f miles1 a transmission line of three circuits on two pole lines1 with guard wires1 was operated from some time in #ahih to ,december #ast1 #aijb1 or somewhat more than four years4 ,on the date last named the dam that maintained the head of water at the ,chambly station gave way1 and the plant was shut down during nearly a year for repairs4 ,for as much as three years this line was operated at #ab1jjj volts1 sixty-six cycles per second1 two-phase4 ,during the remainder of the period up to the failure of the dam the line was operated at #be1jjj volts1 sixty-three cycles1 three-phase4 ,in each transmission two pole lines were employed with two cross-arms per pole4 ,one two-phase1 four-wire circuit was carried on each of three of these cross-arms4 ,at each end of the upper cross-arm on each pole1 and at a distance of fifteen inches from the nearest power wire1 a guard wire was mounted on a glass insulator4 ,a third guard wire was mounted on a glass insulator at the top of each pole1 and this third guard wire was about twenty inches from the nearest power wire4 ,each of these guard wires was made up of two ,no4 #ab ,b4 ,w4 ,g4 galvanized iron wires twisted together1 with a four-point barb every five inches of length4 ,poles carrying these lines were ninety feet apart1 and at each pole all three of the guard wires were connected by soldered joints to a ground wire that was stapled down the side of the pole1 passed through an iron pipe eight feet long1 and was then twisted several times about the butt of the pole before it was set in the ground4 ,at three points along the line the conductors consisted of single-conductor underground or submarine cables that had an aggregate length of about twenty-five miles4 ,no lightning arresters were employed at the points where the overhead transmission wires joined the underground cables4 ,these two-phase1 #ab1jjj-volt circuits were operated from some time in #ahih to some time in #aijb1 and during that time there was no damage done by lightning either at the ,chambly plant1 on the overhead line or the underground cable1 or at the ,montreal sub-station4 ,this record is not due to lack of thunder-storms1 for in the territory where the line is located these storms are frequent and severe4 ,one very severe storm during the period in question resulted in serious damage on distribution lines at ,chambly and ,montreal1 where the guard wires were not in use1 but the transmission line and its connected apparatus escaped unharmed4 ,the path of this storm was in the direction of the transmission line from ,montreal to ,chambly1 and several trees were struck on the way4 ,at the time of this storm and during an entire summer there were no lightning arresters in the power-house at ,chambly4 ,in #aijb1 when the transmission line just considered was changed from two-phase to three-phase1 and its voltage raised from #ab1jjj to #be1jjj1 the method of protection by grounded1 barbed guard wires1 as above described1 was retained4 ,two three-phase circuits were arranged on each of the two pole lines1 with one wire of each circuit on an upper cross-arm and two wires of each circuit on a lower cross-arm1 so that the nearest power wire on the upper cross-arm is thirty-two inches from the guard wire1 and the nearest power wire on the lower cross-arm is about thirty inches from the guard wire at each end of the upper cross-arm4 ,the guard wire at the tops of the poles is about thirty-three inches from each of the power wires on the upper cross-arm4 ,in this three-phase line there is about #a1ddj feet of three-conductor underground cable1 and this cable lies between the end of the overhead line and the sub-station in ,montreal4 ,at the juncture of the overhead line and the cables there is a terminal house containing lightning arresters1 and there are also arresters at the ,chambly plant and the ,montreal sub-station4 ,no lightning arresters are connected to this line save those at the generating plant1 the terminal house and the sub-station4 ,during that part of the year #aijb in which the new #be1jjj-volt line was in operation--that is1 after the change and up to the time of the failure of the dam--this line and its connected apparatus were not damaged in any way by lightning1 and the same is true for the period in which the line was idle pending repairs on the dam4 ,the experience on this ,montreal and ,chambly transmission is probably among the best evidence to be found anywhere as to the degree of protection from lightning that may be had by the use of guard wires4 ,in spite of cases like that just considered1 where guard wires appear to have given a large degree of protection to transmission systems1 many important transmissions are operated without them4 ,an example of this sort may be seen in the transmission line between the #aj1jjj-;horse-power plant at ,electra1 in the ,sierra ,nevada ,mountains of ,california1 and ,san ,francisco1 a distance of #aed miles1 where it seems that no guard wires are in use4 ,another important transmission line that appears to get along without guard wires is that between the #aj1jjj-;horse-power plant at ,caon ,ferry1 on the ,missouri ,river1 and ,butte1 ,mont41 sixty-five miles away4 ,on the transmission line between the power-station on ,apple ,river1 in ,wisconsin1 and the sub-station at ,st4 ,paul1 ,minn41 about twenty-seven miles long1 there are no guard wires for lightning protection4 ,further east1 on the large1 new transmission system that stretches from ,spier ,falls and ,glens ,falls on the north to ,albany on the south1 a distance in a direct line of forty miles1 no guard wires are employed4 ,on its way the transmission system just named touches ,saratoga1 ,schenectady1 ,mechanicsville1 ,troy1 and a number of smaller places1 thus forming a network with several hundred miles of overhead wire4 ,examples of this sort might be multiplied1 but those already named are sufficient to show that it is entirely practicable to operate long transmission systems without guard wires as a protection against lightning4 ,with these examples of transmission systems both with and without guard wires1 the expediency of their use on any particular line should be determined by weighing their supposed advantages against their known disadvantages1 under the existing conditions4 ,it seems fairly certain from all the evidence at hand that if guard wires are to offer any large degree of protection to transmission systems such wires must be frequently and effectively grounded4 ,there is certainly some reason to think that the failures of guard wires to protect transmission systems in some instances may have been due to the lack of numerous and effective ground connections4 ,such1 for example1 may have been the case above mentioned1 at ,telluride1 ,col4 ,on the other hand1 it seems reasonable to believe that the apparently high degree of protection afforded by the guard wires on the ,chambly and ,montreal line is due to the fact that these wires are connected through soldered joints at every pole with a ground wire that is wound about its base4 ,the nearer the guard wires are located to the power wires on a line the greater is the danger that a guard wire will come into contact with a power wire by breaking or otherwise4 ,it is probable that the protection given by a guard wire does not increase nearly as fast as the distance between it and a power wire is diminished4 ,even if one guard wire on a line is thought to be desirable1 it does not follow that two or more such wires should be used1 for the additional protection given by two or three guard wires beyond that given by one wire may be trifling1 while the cost of erection and the danger of crosses with the power circuits increase directly with the number of guard wires4 ,at one time it was thought very desirable to have barbs on guard wires1 but now the better opinion seems to be that1 as barbs tend to weaken the wire1 they lead to breaks and cause more trouble than they are worth4 ,the point where the barbs are located seems to rust more quickly than do other parts of the wire4 ,in some cases barbed guard wires that have given trouble by breaking have been taken down and smooth wires put up instead4 ,if a guard wire is well grounded at least as often as every other pole1 its size may be determined largely on considerations of mechanical strength and lasting qualities4 ,for ordinary spans a ,no4 #d ,b4 ,s4 ,g4 galvanized soft iron wire seems to be about right for guarding purposes4 ,iron seems to be the most desirable material for guard wires because it gives the required mechanical strength and sufficient conductivity at a less cost than copper1 aluminum1 or bronze1 and is easier to handle and less liable to break than steel4 ,it was formerly the practice to staple guard wires to the tops of poles or to the ends of cross-arms1 but it was found that the wire was more apt to rust and break at the staple than elsewhere1 and in the better class of work such wires are now mounted on small insulators4 ,this practice1 as stated above1 was followed on the ,montreal and ,chambly line4 ,in all cases the connection between the guard wire and each of its ground wires should be soldered1 and the ground wire should have a large surface in contact with damp earth1 either through a soldered joint with a ground plate1 by winding a number of turns about the butt of the pole1 or by other means4 ,it is thought by some telegraph engineers that the use of a separate ground wire running to the top of each pole is quite as effective as a protection against lightning as is a guard wire that runs to all of the poles and is frequently connected to the ground4 ,this practice is mentioned at page #bf of 8,culley's ,handbook of ,practical ,telegraphy40 ,such ground wires are free from most of the objections to the ordinary guard wires4 ,it seems quite certain that a guard wire along an alternating-current line1 and grounded at frequent intervals1 must act as a secondary circuit of a transformer by reason of its ground connections1 and thus absorb some energy from the power circuits4 ,no experimental data are yet available1 however1 to show how large this loss may be in an ordinary case4 ,it is fairly evident that there must be some electrostatic effects between the working conductors and a guard wire1 but here again data are lacking as to the amount of any such effect4 ,on most1 if not all1 transmission lines the guard wire or wires1 if used at all1 are placed either above or on a level with the highest power conductors4 ,with one conductor of a three-phase circuit mounted on a pin set in the top of a pole1 and the two remaining conductors on a two-pin cross-arm beneath1 in the method most frequently adopted for transmission lines of very high voltage1 it is obviously impracticable to put guard wires either above or on a level with the power circuits4 ,in the latest transmissions there is a strong tendency to omit guard wires entirely and rely on lightning arresters for protection4 ,lightning arresters are wrongfully named1 for their true purpose is not to arrest or stop lightning1 but to offer it so easy a path to the ground that it will not force its way through the insulation of the line or of machinery connected to the system4 ,the requirements of a lightning arrester are in a degree conflicting1 because the resistance of the path it offers must be so low as to allow discharges of atmospheric electricity to earth and so high as to prevent any flow of current between the transmission lines4 ,in other words1 the insulation of the line conductors must be maintained at a high standard in spite of the connection of lightning arresters between each conductor and the earth2 but the resistance to the arrester must not be so high that lightning will pierce the insulation of the line or machinery at some other point4 ,when a lightning discharge takes place through an arrester the resistance which the arrester offers to a flow of current is for the moment greatly reduced by the arcs which the lightning sets up in jumping the air-gaps of the arrester4 ,each wire of a transmission circuit must be connected alike to arresters1 and the paths of low resistance through arcs in these arresters to the earth would obviously short-circuit the connected generators unless some construction were adopted to prevent this result4 ,in some early types of lightning arresters magnetic or mechanical devices were resorted to in order to break arcs formed by the discharge of lightning4 ,the type of lightning arrester now in common use on transmission lines with alternating current includes a row of short1 parallel1 brass cylinders mounted on a porcelain block and with air-gaps of one-thirty-second to one-sixteenth of an inch between their parallel sides4 ,the cylinder at one end of the row is connected to a line wire and the cylinder at the other end to the earth1 when a #b1jjj or #b1ejj-volt circuit is to be protected4 ,for higher voltages a number of these single arresters are connected in series with each other and with the free ends of the series to a line wire and to the earth1 respectively4 ,thus1 for a #aj1jjj-volt line1 four or1 better1 five single arresters are connected in series to form a composite arrester for each line conductor4 ,for any given line voltage the number of single arresters going to make up the composite arrester should be so chosen that the regular working voltage will not jump the series of air-gaps between the little brass cylinders1 but yet so that any large rise of voltage will be sufficient to force sparks across these gaps4 ,a variation of this practice by one large manufacturing company is to mount the group of single arresters on a marble board in series with each other and with an adjustable air-gap4 ,this gap is intended to be so adjusted that any large increase of voltage on the lines will be relieved by a spark discharge4 ,an arrester made up entirely of the brass cylinders and air-gaps has the disadvantage that an arc once started between all the cylinders by a lightning discharge so lowers the resistance between each line wire and the earth that the generating equipment is short-circuited and the arcs may not cease with the escape of atmospheric electricity4 ,to avoid this difficulty it is the practice to connect a conductor of rather large ohmic resistance such as a rod of carborundum in series with the brass cylinders and air-gaps of lightning arresters4 ,this resistance should be non-inductive so as not to offer a serious obstacle to lightning discharge1 and its resistance should be great enough to prevent a flow of current from the generators that will be large enough to maintain the arcs started in the arrester by the lightning discharge4 ,accurate data are lacking as to the amount of this resistance that should be employed with arresters for any given voltage4 ,as a rough1 approximate rule it may be said that in some cases good results will be obtained with a resistance in ohms in series with a group of lightning arresters that represents one per cent of the numerical value of the line voltage4 ,that is1 for a #aj1jjj-volt line the group of arresters for each wire may be connected to earth through a resistance of1 say1 #ajj ohms1 so that if the generator current follows the arc of a lightning discharge through the arresters it must pass through a fixed resistance of #bjj ohms in going from one line wire to another4 ,this rule is given merely as an illustration of the resistance that will work well in some cases1 and should not be taken to have a general application4 ,if the resistance connected in series with lightning arresters is high1 the tendency is a little greater for lightning to go to earth at some point in the apparatus where the insulation is low4 ,if only a small resistance is employed to connect lightning arresters with the earth1 the danger is that arcs formed by lightning discharges will be followed and maintained by the dynamo currents4 ,in one make of lightning arrester the row of little brass cylinders is connected at the ends to carbon rods which form a resistance for the purpose just mentioned4 ,two of these carbon rods are contained in each arrester for #b1jjj or #b1ejj volts1 and the resistance of each rod may be anywhere from several score to several hundred ohms as desired4 ,this form of arrester may be connected directly from line to earth without the intervention of any outside resistance1 since the carbon rods may easily be given all the resistance that is desirable4 ,one of the most important features in the erection of a lightning arrester is its connection to earth4 ,if this connection is poor it may render the arrester useless so far as protection from lightning is concerned4 ,it need hardly be said that ground connections formed by driving long iron spikes into the walls of buildings or into dry earth are of slight value as far as protection from lightning is concerned4 ,a good ground connection for lightning arresters may be formed with a copper or galvanized iron plate1 which need not be over one-sixteenth of an inch thick1 but should have an area of1 say1 ten to twenty square feet4 ,this plate may be conveniently made up into the form of a cylinder and should have a number of half-inch holes punched in a row down one side into which one or more copper wires with an aggregate area equal to that of a ,no4 #d or ,no4 #b wire1 ,b4 ,s4 gauge1 should be threaded and then soldered4 ,this plate or cylinder should be placed deep enough in the ground to insure that the earth about it will be constantly moist1 and the connected copper wire should extend to the lightning arresters4 ,it is a good plan to surround this cylinder with a layer of coke or charcoal4 ,a good earth connection for lightning arresters may be made through large water-pipes1 but to do this it is not enough simply to wrap the wire from the lightning arresters about the pipe4 ,a suitable contact with such a pipe may be made by tapping one or two large bolts into it and then soldering the wires from lightning arresters into holes drilled in the heads of these bolts4 ,a metal plate laid in the bed of a stream makes a good ground4 ,with some of the older types of lightning arresters it was the custom to insert a fuse between the line wire and the ground1 but this practice defeats the purpose for which the arrester is erected because the fuse melts and leaves the arrester disconnected and the circuit unprotected with the first lightning discharge4 ,the modern arresters for alternating-current circuits are made up of a series of metal cylinders and short air-gaps and are connected solidly without fuse between line and earth4 ,illustration3 ,,fig4 #gc4--;,entry of ,lines at the ,power-house on ,neversink ,river4 ,it was once the practice to locate lightning arresters almost entirely in the stations1 but this has been modified by experience and consideration of the fact that as the line acts as a collector of atmospheric electricity1 paths for its escape should be provided along the line4 ,consideration fails to reveal any good reason why lightning that reaches a transmission line some miles from a station should be forced to travel to the station1 where it may do great damage before it finds an easy path to earth4 ,it is1 therefore1 present practice to connect lightning arresters to each wire at intervals along some lines as well as at stations and sub-stations4 ,the main purpose of arresters is to offer so easy a path to earth that lightning discharges along the lines will not flow to points of low insulation in generators1 transformers1 or even the line itself4 ,practice is far from uniform as to the distance between lightning arresters on transmission lines1 the distances varying from less than one to a large number of miles apart4 ,in general the lines should be provided with lightning arresters at least where they run over hilltops and at any points where lightning strokes are unusually frequent4 ,where a long overhead line joins an underground cable arresters should always be connected1 and the same is true as to transformers located on the transmission line4 ,the multiplication of arresters along pole lines should be avoided as far as is consistent with suitable protection1 because every bank of arresters may develop a permanent ground or short-circuit1 unless frequently inspected and kept clean and in good condition4 ,arresters1 besides those connected along the lines1 should be located either in or just outside of stations and sub-stations4 ,if the buildings are of wood1 the arresters had better be outside in weather-proof cases1 but in brick or stone buildings the arresters may be properly located near an interior wall and well removed from all other station equipment4 ,transmission lines1 on entering a station or sub-station1 should pass to the arresters at once and before connecting with any of the operating machinery4 ,to increase the degree of protection afforded by lightning arresters choke-coils are frequently used with them4 ,a choke-coil for this purpose usually consists of a flat coil of copper wire or strip containing twenty to thirty or more turns and mounted with terminals in a wooden frame4 ,this coil is connected in series with the line wire between the point where the tap for the lightning arrester is made and the station apparatus4 ,lightning discharges are known to be of a highly oscillatory character1 their frequency being much greater than that of the alternating currents developed in transmission systems4 ,the self-induction of a lightning discharge in passing through one of these choke-coils is great1 and the consequent tendency is to keep the discharge from passing through the choke-coil and into the station apparatus and thus to force the discharge to pass to earth through the lightning arrester4 ,the alternating current employed in transmission has such a comparatively low frequency that its self-induction in a choke-coil is small4 ,increased protection against lightning is given by the connection of several groups of lightning arresters one after another on the same line wire at an electric station4 ,this gives any lightning discharge that may come along the wire several paths to earth through the different groups of arresters1 and a discharge that passes the first group will probably go to earth over the second or third group4 ,in some cases a choke-coil is connected into a line wire between each two groups of lightning arresters as well as between the station apparatus and the group of arresters nearest thereto4 ,an electric transmission plant at ,telluride1 ,col41 where thunder-storms are very frequent and severe1 was equipped with arresters and choke-coils of the type described1 and the results were carefully noted 7vol4 xi41 ,a4 ,i4 ,e4 ,e41 p4 #cdf74 ,a small house for arresters and choke-coils was built close to the generating station of this system and they were mounted therein on wooden frames4 ,four choke-coils were connected in series with each line wire1 and between these choke-coils three lightning arresters were connected1 while a fourth arrester was connected to the line before it reached any of the choke-coils4 ,these arresters were watched during an entire lightning season to see which bank of arresters on each wire discharged the most lightning to earth4 ,it was found that1 beginning on the side that the line came to the series of arresters1 the first bank of arresters was traversed by only a few discharges of lightning1 the second bank by more discharges than any other1 the third bank by quite a large number of discharges1 and the fourth bank seldom showed any sign of lightning discharge4 ,over the second bank of arresters the lightning discharges would often follow each other with great rapidity and loud noise4 ,the obvious conclusion from these observations seems to be that three or four banks of lightning arresters connected in succession on a line at a station together with choke-coils form a much better protection from lightning than a single bank4 ,at the plant in question1 that of the ,san ,miguel ,consolidated ,gold ,mining ,company1 the entire lightning season after the erection of the arresters in question was passed without damage by lightning to any of the equipment4 ,during the two lightning seasons previous to that just named the damage by lightning to the generating machinery at the plant had been frequent and extensive4 ,a good illustration of the high degree of security against lightning discharges that may be attained with lightning arresters and choke-coils exists at the ,niagara ,falls plants and the terminal house in ,buffalo1 where the step-up and step-down transformers have never been damaged by lightning though the transmission line has been struck repeatedly and poles and cross-arms shattered 7vol4 xviii41 ,a4 ,i4 ,e4 ,e41 p4 #ebg74 ,this example bears out the general experience that lightning arresters1 though not an absolute protection1 afford a high degree of security to the apparatus at electric stations4 ,lightning arresters are in some cases connected across high-voltage circuits from wire to wire so that the full line pressure tends to force a current across the air-gaps4 ,the object of this practice is to guard against excessive voltages on the circuit such as might be due to resonance4 ,in such a case1 as in that where arresters are connected from line wire to earth as a protection against lightning1 the number of air-gaps should be such that the normal line voltage will not force sparks across the air-gaps and thus start arcs between the cylinders4 ,the number and total length of air-gaps in a bank of arresters necessary to prevent the formation of arcs by the regular line voltage depends on a number of factors besides the amount of that voltage4 ,according to the report of the ,committee on ,standardization of the ,american ,institute of ,electrical ,engineers1 the sparking distances in air between opposed sharp needle points for various effective sinusoidal voltages are as follows 7vol4 xix41 ,a4 ,i4 ,e4 ,e41 p4 #ajia73 ----------------------------------- ,kilovolt ,square ,inches ,sparking ,root of ,mean ,square4 ,distance4 ----------------------------------- #e #j4bbe #aj 4#dg #ae 4#gbe #bj #a4j #be #a4c #cj #a4fbe #ce #b4j #dj #b4de #de #b4ie #ej #c4ee #fj #d4fe #gj #e4he #hj #g4a #ij #h4ce #ajj #i4f #aaj #aj4ge #abj #aa4he #acj #ab4ie #adj #ac4ie #aej #ae4j ----------------------------------- ,it may be noted at once from this table that the sparking distance between the needle points increases much faster than the voltage between them4 ,thus1 #bj1jjj volts will jump an air-gap of only an inch between the points1 but seven times this pressure1 or #adj1jjj volts1 will force a spark across an air-gap of #ac4ie inches4 ,two cylinders or other blunt bodies show smaller sparking distances between them at a given voltage than do two needle points1 but when a number of cylinders are placed in a row with short air-gaps between them the aggregate length of these gaps that will just prevent the passage of sparks at a given voltage may be materially greater or less than the sparking distance of that voltage between needle points4 ,it has been found by experiment that the numbers one-thirty-second-inch spark-gaps between cylinders of non-arcing alloy necessary to prevent the passage of sparks with the voltages named and a sine wave of electromotive force are as follows 7vol4 xix41 ,a4 ,i4 ,e4 ,e41 p4 #ajbf73 ------------------- ,number of ,normal #a_/cb-;,inch ,voltage ,air-,gaps ,withheld4 in ,series4 ------------------- #e #f1hjj #aj #aj1jjj #ae #ab1ejj #bj #ad1ejj #be #af1djj #cj #ah1bjj #ce #ai1cjj #dj #bj1ejj #de #ba1gjj #ej #bb1fjj #ee #bc1ijj #fj #be1jjj #fe #bf1jjj #gj #bg1jjj #ge #bh1jjj #hj #bi1jjj ------------------- ,according to these data1 only ten air-gaps of one-thirty-second of an inch each and #j4cabe inch combined length are required between cylinders to prevent a discharge at #aj1jjj volts1 though opposed needle points may be #j4dg inch apart when a spark is obtained with this voltage4 ,on the other hand1 eighty air-gaps of one-thirty-second of an inch each between cylinders of non-arcing metal1 or a total gap of #b4e inches1 are necessary to prevent a discharge at #bi1jjj volts1 though #cj1jjj volts can force a spark across a single gap of only #a4fbe inches between opposed needle points4 ,under the conditions that existed in the test just recorded the pressure at which the aggregate length of one-thirty-second of an inch air-gaps that just prevents a discharge equals the single sparking distance between needle points seems to be about #ah1jjj volts4 ,the object of dividing the total air-gap in a lightning arrester for lines that carry alternating current up into a number of short gaps is to prevent the continuance of an arc by the regular generator or line current after the arc has been started by a lightning discharge4 ,as soon as an electric spark leaps through air from metal to metal1 a path of low electrical resistance is formed by the intensely heated air and metallic vapor4 ,if the arc thus formed is1 say1 two inches long it will cool a certain amount as the passing current grows small and drops to zero4 ,if1 however1 this total arc of two inches is divided into sixty-four parts by pieces of metal1 the process of cooling as the current decreases will go on much more rapidly than with the single arc of two inches because of the great conducting power of the pieces of metal4 ,as an alternating current comes to zero twice in each period1 the many short arcs formed in an arrester by a lightning discharge are so far cooled during the small values of the following line current that the resistance quickly rises to a point where the regular line voltage cannot continue to maintain them1 if the arrester is properly designed for the system to which it is connected4 ,in this way the many-gap arrester destroys the many small arcs started by lightning discharges that would continue and short-circuit the line if they were combined into a single long arc4 ,when an electric arc passes between certain metals like iron and copper a small bead is raised on their surfaces4 ,if these metals were used for the cylinders of arresters the beads on their surface would quickly bridge the short air-gaps4 ,certain other metals1 like zinc1 bismuth1 and antimony1 are pitted by the passage of arcs between their surfaces4 ,by suitable mixture of metals from these two classes1 an alloy is obtained for the cylinders of lightning arresters that pits only slightly and is thus but little injured by lightning discharges4 ,after long use and many discharges an arrester of the class here considered gradually loses its power to destroy electric arcs4 ,this may be due to the burning out of the zinc and leaving a surface of copper on the cylinders4 ,aside from the structure of an arrester and the normal voltage of the circuit to which it is connected1 its power to destroy arcs set up by lightning discharges depends on the capacity of the connected generators to deliver current on a short-circuit through the gaps1 and upon the inductance of the circuit4 ,the greater the capacity of the generators connected to a system the more trying are the conditions under which arresters must break an arc because the current to be broken is greater4 ,so1 too1 an increase of inductance in a circuit adds to the work of an arrester in breaking an arc4 ,an arc started by lightning discharge at that period of a voltage phase when it is at or near zero is easily destroyed by the arrester1 but an arc started at the instant when the regular line voltage has its maximum value is much harder to break because of the greater amount of heat generated by the greater current sent through the arrester4 ,for this reason the arcs at arresters will hold on longer in some cases than in others1 according to the portion of the voltage phase in which they are started by the lightning discharge4 ,lightning discharges1 of course1 may occur at any phase of the line voltage1 and for this reason a number of discharges must take place before it can be certain from observation that a particular arrester will always break the resulting arc4 ,between twenty-five and sixty cycles per second there is a small difference in favor of the latter in the power of a given arrester to break an arc1 due probably to the fact that more heat in the arcs is developed per phase with the lower than with the higher frequency4 ,it will now be seen that while increase of the regular line voltage requires a lengthening of the aggregate air-gap in lightning arresters to prevent the formation of arcs by this voltage alone1 the increase of generating capacity requires more subdivisions of the total air-gap in order that the arcs maintained by the larger currents may be cooled with sufficient rapidity4 ,these two requirements are to some extent conflicting1 because the subdivision of the total air-gaps renders it less effective to prevent discharges due to the normal line voltage1 as has already been shown4 ,the result is that the more an air-gap is subdivided in order to cool and destroy arcs that have been started by lightning1 the longer must be the aggregate air-gap in order to prevent the development of arcs directly by the normal line voltage4 ,furthermore1 the practical limit of subdivision of the air-gap is soon reached because of the difficulty of keeping very short gaps clean and of nearly constant length4 ,as a resistance in series with an arrester cuts down the generator current that can follow a lightning discharge1 such a resistance also decreases the number of air-gaps necessary to give an arrester power to destroy arcs on a particular circuit4 ,the increase of resistance in series with a lightning arrester as well as the increase in the aggregate length of its air-gaps subjects the insulation of connected apparatus to greater strains at times of lightning discharge4 ,on systems of large capacity the number and aggregate length of air-gaps in arresters necessary to destroy arcs must be greater than the number or length of these air-gaps necessary to prevent the development of arcs by the normal line voltage1 unless a relatively large resistance is connected in series with each arrester4 ,to reduce the strains produced on the insulation of line and connected apparatus under these conditions by lightning discharges1 a resistance is connected in shunt with a part of the air-gaps in one make of lightning arrester4 ,the net advantage claimed for this type of arrester is that a lower resistance may be used in series with all the air-gaps than would otherwise be necessary4 ,one-half of the total number of air-gaps in this arrester are shunted by the shunt resistance and the series and shunt resistance are in series with each other4 ,only the series air-gaps or those that are not shunted must be jumped in the first instance by the lightning discharge1 which thus passes to earth through these air-gaps and the shunt and series resistance in series4 ,an arc is next started in the shunted air-gaps1 and this arc is in turn destroyed because the shunt weakens the current in these gaps4 ,this throws the entire current of the arc through the series air-gaps and the shunt and series resistance all in series with each other4 ,as the shunt resistance is comparatively large1 the current maintaining the arc in the series air-gaps is next so reduced that this arc is broken4 ,taking the claims of its makers just as they stand1 the advantages of the shunted air-gaps are not very clear4 ,the series air-gaps alone must evidently be such that the normal line voltage will not start an arc over them1 and these same series gaps must be able to break the arcs of line current flowing through them and the shunt and series resistance all in series4 ,evidently the greatest strain on the insulation of the line and apparatus occurs at the instant when the lightning discharge takes place through the series gaps and the shunt and series resistances all in series with each other4 ,why develop subsequent arcs in the shunted air-gaps8 ,why not throw the shunted air-gaps away and combine the shunt and series resistances8 ,,chapter ,,xiv4 ,,electrical ,,transmission ,,under ,,land ,,and ,,water4 ,energy transmitted over long distances must sometimes pass through conductors that are underground or beneath water4 ,in some other cases it is a question of relative advantages merely1 whether portions of a transmission line go under water or overhead4 ,where the transmitted energy must enter a sub-station in the heart of a large city1 it not infrequently must go by way of underground conductors without regard to the voltage employed4 ,in some cities the transmission lines may be carried overhead1 provided that their voltage is within some moderate figure1 but not otherwise4 ,here it becomes a question whether transmission lines at high voltage shall be carried underground1 or whether transforming stations shall be established outside of the restricted area and then low-pressure lines brought into the business section overhead or underground1 as desired4 ,where a transmission line must cross a steam railway track it may be required to be underground1 whether the voltage is reduced or not4 ,the distance across a body of water in the path of a transmission line may be so great that a span is impossible and a cable under the water therefore necessary4 ,such a cable may work at the regular line voltage1 or a transformer station may be established on one side or on each side of the body of water4 ,even where it is possible to span a body of water with a transmission line1 the cost of the span and of its supports may be so great that a submarine cable is more desirable4 ,a moderate increase in the length of a transmission line in order to avoid the use of a submarine cable is almost always advisable1 but where rivers are in the path of the line it is generally impossible to avoid crossing them either overhead or underneath4 ,thus1 ,st4 ,paul could only be reached with the #be1jjj-volt line from the falls on ,apple ,river by crossing the ,st4 ,croix ,river1 one-half mile wide1 on the way4 ,in order to carry out the #dj1jjj-volt transmission between ,colgate and ,oakland1 the ,carquinez ,straits1 which intervened with nearly a mile of clear water1 were crossed4 ,sometimes1 as in the former of the two cases just named1 an existing bridge may be utilized to support a transmission line1 but more frequently the choice lies between an overhead span from bank to bank of a river and a submarine cable between the same points4 ,the prime advantage of an overhead line at high voltage is its comparatively small first cost1 which is only a fraction of that of an underground or submarine cable in the great majority of instances4 ,at very high voltages1 like #dj1jjj to #ej1jjj or more1 the overhead line must also be given first place on the score of reliability1 since the lasting qualities of underground and submarine cables at such pressures is as yet an unknown quantity4 ,on the other hand1 at voltages in which cable insulation has been shown by experience to be thoroughly effective1 underground or submarine cables may be more reliable than overhead lines because of the greater freedom from mechanical disturbances which these cables enjoy4 ,in the business portion of many cities a transmission line must go underground1 whether its voltage is high or low4 ,under these conditions1 it may be desired either to transmit energy to a sub-station for distribution within the area where conductors must be underground1 or to transmit energy from a generating station there located to outside points4 ,if the transmitted energy is reduced in pressure before reaching such a sub-station1 a transforming station must be provided1 and this will allow the underground cables to operate at a moderate voltage4 ,for such a case the advantages as to insulation at the lower voltage should be compared with the additional weight of conductors in the cable and the cost of the transforming apparatus and station4 ,if the voltage at which current is delivered from the transforming station does not correspond with the required voltage of distribution at the sub-station1 the necessary equipment of step-down transformers is doubled in capacity by lowering the voltage of the transmitted energy where it passes from the overhead line to the underground cables4 ,conditions of just this sort exist at ,buffalo in connection with the delivery of energy from the power-stations at ,niagara ,falls4 ,this transmission was first carried out at #aa1jjj volts1 and a terminal station was located at the ,buffalo city limits where the overhead lines joined underground cables that continued the transmission at the same voltage to several sub-stations in different parts of the city4 ,later the voltage of the overhead transmission line was raised to #bb1jjj1 and it not being thought advisable to subject the insulation of the underground cables to this higher pressure1 transformers were installed at the terminal station to lower the line voltage to #aa1jjj for the underground cables4 ,as the sub-stations in this case also have transformers1 there are two kilowatts of capacity in step-down transformers for each kilowatt of delivery capacity at the sub-stations4 ,illustration3 ,,fig4 #gd4--;,cable ,terminal ,house for the #be1jjj-volt ,chambly ,line at ,montreal4 ,the saving effected in capacity of transformers and in the weight of cables by continuing the full transmission voltage right up to the sub-stations whence distribution takes place furnishes a strong motive to work underground cables at the pressure of the overhead transmission line of which they form a continuation4 ,thus1 at ,hartford1 the #aj1jjj-volt overhead lines that bring energy from water-power stations to the outskirts of the city connect directly in terminal houses there with underground cables that complete the transmission to the sub-station at the full line voltage4 ,in ,springfield1 ,mass41 the overhead transmission lines from water-power stations connect directly with underground cables at a distance of nearly two miles from the sub-station1 and these cables are thus subject to the full line pressure of #f1jjj volts4 ,the overhead line that brings energy at #be1jjj volts from ,apple ,river falls to ,st4 ,paul terminates about three miles from the sub-station there1 and the transmission is completed by underground cables that carry current at the #be1jjj-volt pressure4 ,in these and similar cases the relative advantages of underground cables at the full voltage of transmission and of overhead lines at a much lower pressure1 in the central portions of cities1 must be compared4 ,the overhead lines at moderate voltage will no doubt cost less in almost every case than underground cables of equal length and at the full transmission voltage4 ,as an offset to the lower cost of overhead city lines at moderate voltage1 where they are permitted by local regulations1 comes the increase in weight of conductors due to the low pressure on the overhead lines1 and also the cost of additional transformer capacity1 unless the lines that complete the transmission operate at the voltage of distribution4 ,the #aj1jjj-volt lines that transmit energy from ,great ,falls to ,portland1 ,me41 terminate in two transformer houses that are distant about #j4e mile and #b4e miles1 respectively1 from the sub-station there4 ,in these transformer houses the voltage is reduced to #b1ejj1 and the transmission is then continued at this pressure to the sub-station whence distribution takes place without further transformation4 ,where a river or other body of water must be crossed by a transmission line1 either of three plans may be followed4 ,the overhead line may be continued as such across the water1 either by a single span or by two or more spans supported by one or more piers built for that purpose in the water4 ,the overhead line may connect directly with a submarine cable1 this cable being thus exposed to the full voltage of the transmission4 ,as a third expedient1 a submarine cable may be laid and connected with step-down transformers on one bank and with step-up transformers on the other bank of the river or other body of water to be crossed4 ,the overhead lines connecting with these transformers can obviously be operated at any desired voltage1 and this is also true of the cable4 ,even though the distance across a body of water is not so great that a transmission line can not be carried over it in a single span1 the cost of such a span may be large4 ,a case in point is that of the ,colgate and ,oakland line1 where it crosses the ,carquinez ,straits by a span of #d1dbg feet4 ,these straits are about #c1bjj feet wide where the transmission line crosses1 and overhead lines were required to be not less than #bjj feet above high water so as not to impede navigation4 ,in order to gain in ground elevation and thus reduce the necessary height of towers1 two points #d1dbg feet apart on opposite sides of the straits were selected for their location4 ,under these circumstances two steel towers1 one sixty-five feet and the other #bbe feet high1 were required to support the four steel cables that act as conductors across the straits4 ,to take the strain of these four cables1 each with a clear span nearly three times as great as that of the ,brooklyn ,bridge1 eight anchors with housed strain insulators were constructed1 four on the land side of each tower4 ,on each of these anchors the strain is said to be #bd1jjj pounds4 ,at each end of the cables making this span is a switch-house where either of the two three-phase transmission lines may be connected to any three of the four steel cables1 thus leaving one cable free for repairs4 ,it is not possible to state here the relative cost of these steel towers and cables in comparison with that of submarine cables for the same work1 but at first glance the question appears to be an open one4 ,the voltage of #dj1jjj1 at which this transmission is carried out1 is probably higher than that on any submarine cable in use1 but it is possible that a suitable cable can be operated at this voltage4 ,whatever the limitations of voltage as applied to submarine cables1 it would1 of course1 have been practicable to use step-up and step-down transformers at the switch-houses and thus operate a submarine cable at any voltage desired4 ,in another case1 on a transmission between ,portsmouth and ,dover1 ,n4 ,h41 it was necessary to cross an arm of the sea on a line #d1haa feet long with a three-phase circuit operating at #ac1ejj volts4 ,it was decided to avoid the use of either a great span or of raising and lowering transformers at this crossing1 and to complete the line through a submarine cable operating at the full voltage of transmission4 ,to this end a brick terminal house six by eight feet inside1 and with an elevation of thirteen feet from the concrete floor to the tile roof1 was erected on each bank of the bay at the point where the submarine cable came out of the water4 ,the lead-covered cable pierced the foundation of each of these terminal houses at a point four feet below the floor level and rose thence on one wall to an elevation eleven feet above the floor to a point where connection was made with the ends of the overhead lines4 ,from this connection on each of the three conductors a tap was carried to a switch and series of lightning arresters4 ,a single lead-covered cable containing three conductors makes connection between these two terminal houses4 ,at each end of this cable the lead sheath joins a terminal bell one foot long and #b4e inches in outside diameter1 increasing to four inches at the end where the three conductors pass out4 ,this terminal bell is filled nearly to the flaring upper end with an insulating compound4 ,in the instance just named it is possible that the cost of the submarine cable was less than would have been the outlay for shore supports and a span nearly a mile long across this body of water4 ,underground and submarine cables have been operated at voltages suitable for transmission during periods sufficiently long to demonstrate their general reliability4 ,the ,ferranti underground cables between ,deptford and ,london have regularly carried current at #aa1jjj volts since a date prior to #ahij4 ,during about five years cables with an aggregate length of sixteen miles have transmitted power from ,st4 ,anthony's ,falls to ,minneapolis4 ,at ,buffalo1 some thirty miles of rubber-insulated cables have been in use for underground work at #aa1jjj volts since #ahig1 and eighteen miles of paper-insulated cable since the first part of #aija4 ,these examples are enough to show that transmission through underground cables at #aa1jjj to #ab1jjj volts is entirely practicable4 ,at ,reading1 ,pa41 an underground cable one mile long has carried three-phase current at #af1jjj volts for the ,oley ,valley ,railway since some time in #aijb4 ,the cables in the transmission from ,apple ,river to ,st4 ,paul1 which carry three-phase current at #be1jjj volts1 have a total length of three miles1 and have been in use since #aijj4 ,this voltage of #be1jjj is probably the highest in regular use on any underground or submarine cable conveying energy for light or power4 ,from the experience thus far gained there is much reason to think that the voltages applied to underground cables may be very materially increased before a prohibitive cost of insulation is reached4 ,on submarine cables the voltage of #ac1jjj in the ,portsmouth and ,dover transmission1 above mentioned1 is perhaps as great as any in use4 ,it does not appear1 however1 that any material difference exists1 as to the strain on its insulation at a given voltage1 between a cable when laid in an underground conduit and when laid under water4 ,in either case the entire stress of the voltage employed operates on the insulation between the several conductors in the cable and between each conductor and the metallic sheath4 ,underground conduits have little or no value as insulators of high voltages1 because it is practically impossible to keep them water-tight and prevent absorption or condensation of moisture therein4 ,for these reasons a cable that gives good results at #be1jjj volts in an underground conduit should be available for use at an equal voltage under water4 ,the standard structure of high-voltage cables for either underground or submarine work includes a continuous metallic sheath outside of each conductor or of each group of conductors that goes to make up a circuit4 ,as most transmissions are now carried out with three-phase current1 the three conductors corresponding to a three-phase circuit are usually contained in a single cable and covered by a single sheath4 ,the cables used in transmission systems at ,portsmouth1 ,buffalo1 and ,st4 ,paul are of this type4 ,if single-phase or two-phase current is transmitted1 each cable should contain the two conductors that go to make up a circuit4 ,in work with alternating currents the use of only one conductor per cable should be avoided because of the loss of energy that results from the currents induced in the metallic sheath of such a cable4 ,illustration3 ,,fig4 #ge4--;,cable ,terminal ,house at ,piscataqua ,river ,crossing4 ,where the two1 three1 or more conductors that form a complete circuit for alternating current are included in a single metallic sheath1 the inductive effects of currents in the several conductors tend to neutralize each other and the waste of energy in the sheath is in large part avoided4 ,to neutralize more completely the tendency to local currents in their metal sheath1 the several insulated conductors of an alternating circuit are sometimes twisted together1 after being separately insulated1 before the sheath is put on4 ,distribution of power at ,niagara ,falls was at first carried out through single-conductor1 lead-covered cables with two-phase current at #b1bjj volts4 ,one objection to this plan was the loss of energy by induced currents in the lead coverings of the cables4 ,it was later decided to adopt three-phase distribution at #aj1jjj volts for points distant more than two miles from the power-station4 ,each three-phase circuit for this purpose was made up of three conductors separately insulated and then covered with a single lead sheath1 so as to avoid losses through induced currents in the latter4 ,underground and submarine cables for operation at high voltages are generally covered with a continuous lead sheath and sometimes with a spiral layer of galvanized iron wire4 ,for high-voltage work underground the lead covering is generally preferred without iron wire1 but in submarine work coverings of both sorts are employed4 ,the lead sheath of a cable being continuous completely protects the insulation from contact with gases or liquids4 ,as ducts of either tile1 wood1 or iron form a good mechanical protection for a cable1 the rather small strength of a lead sheath is not a serious objection in conduit work4 ,submarine cables1 on the other hand1 depend on their own outer coverings for mechanical protection1 and may be exposed to forces that would rapidly cut through a lead sheath4 ,cables for operation under water should usually be covered1 therefore1 with a layer of galvanized iron wires outside of the lead sheath4 ,these wires are laid closely about the cable in spiral form and are usually between #j4ab and #j4be inch in diameter each1 depending on the size of the cable and its location4 ,underground conduits cannot be relied on to exclude moisture and acids of the soil from the cables which they contain1 and either of these agents may lead to destructive results4 ,if cables insulated with rubber1 but without a protecting covering outside of it1 are laid in underground conduits1 the rubber is apt to be rapidly destroyed by fluids and gases that find their way into the conduit4 ,if a plain lead-covered cable is employed the acids of the soil attack it1 and if stray electric currents from an electric railway find the lead a convenient conductor it is rapidly eaten away where they flow out of it4 ,to avoid both of these results the underground cable should have a lead sheath1 and this sheath may be protected by an outside layer of hemp or jute treated with asphaltum4 ,rubber1 paper1 and cotton are extensively used as insulation for underground and submarine cables1 but the three are not usually employed together4 ,as a rule1 the insulation is applied separately to each conductor1 and then an additional layer of insulation may be located about the group of conductors that go to make up the cable4 ,where rubber insulation is employed1 a lead sheath may or may not be added1 but where insulation depends on cotton or paper the outer covering of lead is absolutely necessary to keep out moisture4 ,the radial thickness of insulation on each conductor and of that about the group of conductors in a cable should vary according to the voltage of operation4 ,cables employed between the generating and sub-stations of the ,manhattan ,elevated ,railway1 to distribute three-phase current at #aa1jjj volts1 are of the three-conductor type1 rubber insulated1 lead covered1 and laid in tile conduits4 ,each cable contains three ,no4 #jjj stranded conductors1 and each conductor has its own insulation of rubber4 ,jute is laid on to give the group of conductors an outer circular form1 and outside of the group a layer of insulation and then a lead sheath is placed4 ,outside diameter of this cable is nearly three inches1 and the weight nine pounds per linear foot4 ,the #aa1jjj-volt1 three-phase current from ,niagara ,falls is distributed from the terminal house to seven sub-stations in ,buffalo through about #cj miles of rubber-insulated and #ah miles of paper-insulated1 three-conductor1 lead-covered cables1 all in tile conduits4 ,in each cable the three ,no4 #jjj stranded conductors are separately insulated and then twisted into a rope with jute yarn laid in to give an even round surface for the lead sheath to rest on4 ,a part of the rubber-insulated cables have each conductor covered with #i_/cb-;inch of #cj per cent pure rubber compound1 and the remaining rubber cables have #h_/cb-;inch covering on each conductor of #dj per cent pure rubber compound4 ,the paper-insulated cable has #ac_/fd-;inch of paper around each conductor1 and also another #ac_/fd-;inch of paper covering about the group of three conductors and next to the lead sheath4 ,in outside diameter the rubber-insulated cable is #b-c_/h inches1 and of the paper-insulated cable #b-e_/h inches1 the radial thickness of the lead sheath being #a_/h-;inch in each case4 ,it is reported that the cables insulated with #i_/cb-;inch of the mixture1 said to be #cj per cent pure rubber1 have proved to be more reliable than the cables insulated with #h_/cb-;inch of a mixture said to be #dj per cent pure rubber4 ,vol4 xviii41 ,a4 ,i4 ,e4 ,e41 #acf1 #hcf4 ,the six miles of underground cables that carry three-phase1 #be1jjj-volt current in ,st4 ,paul are of the three-conductor type1 lead covered1 and laid in a tile conduit4 ,one of the two three-mile cables is insulated with rubber and the other with paper4 ,in the former cable each conductor is separately insulated with a compound containing about #ce per cent of pure rubber and having a radial thickness of #g_/cb-;inch4 ,the three conductors after being insulated are laid up with jute to give a round surface1 tape being used to hold them together1 and then a rubber cover #e_/cb-;inch thick is placed about the group1 after which comes the lead sheath over all4 ,in the three miles of paper-insulated cable each conductor is separately covered with paper to a thickness of #i_/cb-;inch1 then the three conductors are laid together with jute and taped1 and next a layer of paper #d_/cb-;inch thick is put on over the group4 ,outside of all comes the lead sheath1 which has an outer coating of tin4 ,the paper insulation in these cables was saturated with a secret insulating compound4 ,the lead sheath on both the rubber and paper insulated cables is #a_/h-;inch thick and the sheath of the former contains #c per cent of tin4 ,each of the three conductors in each cable consists of #g copper strands and has an area of #ff1jjj circular mils4 ,outside of the lead sheath each of these cables has a diameter of about #b-a_/d inches4 ,by the manufacturer's contract these cables were tested up to #dj1jjj volts before shipment1 and might be tested up to #cj1jjj volts in their conduits during any time within five years from their purchase4 ,in first cost the cable with rubber insulation was said to be about #ej per cent more expensive than the cable in which paper was used4 ,vol4 xvii41 ,a4 ,i4 ,e4 ,e41 #fej4 ,underground cables in which the separate conductors are covered with cotton braid treated with an insulating compound1 and then the group of conductors going to make up the cable enclosed in a lead sheath1 are extensively used in ,austria and ,germany4 ,for cables that operate at #aj1jjj to #ab1jjj volts the radial thickness of cotton insulation on each conductor is said to be within #c_/af-;inch1 and these cables are tested up to #be1jjj volts by placing all of the cable except its ends in water1 and then connecting one end of the #be1jjj-volt circuit to the water and the other end to the conductors of the cable4 ,a test on the paper-insulated cable at ,st4 ,paul showed its charging current to be #a4a amperes at #be1jjj volts for each mile of its length4 ,for the cable with rubber insulation the charging current per mile of length was found to be about twice as great as the like current for the paper-insulated cable4 ,each of the two overhead transmission lines connected with these cables consisted of three solid copper wires with an area of #ff1jjj circular mils each1 and all three so mounted on the poles as to form the corners of an equilateral triangle twenty-four inches apart4 ,the charging current of one of these three-wire1 overhead circuits was found to be about #j4ajc ampere per mile1 at #be1jjj volts1 or a little less than one-tenth of the like current for the paper cable4 ,these tests were made with three-phase current of sixty cycles per second4 ,where overhead transmission lines join underground or submarine cables1 either with or without the intervention of transformers1 lightning arresters should be provided to intercept discharges of this sort that come over the overhead wires4 ,lightning arresters were provided in the terminal house at ,buffalo1 where the #bb1jjj-volt overhead lines feed the #aa1jjj-volt cables through transformers1 also at the terminal house in ,st4 ,paul1 where the #be1jjj-volt overhead lines are electrically connected to the underground cables4 ,if an underground or submarine cable connects two portions of an overhead line1 as in the ,portsmouth and ,dover transmission above mentioned1 lightning arresters should be provided at each end of the cable1 as was done in that case4 ,one advantage of a high rather than a low voltage on underground cables1 where power is to be transmitted at any given rate1 lies in the fact that the amperes flowing at a fault in the cable determine the destructive effect there1 rather than the voltage of the transmission4 ,it is reported that a fault or short-circuit in one of the #aa1jjj-volt cables at ,buffalo usually melts off but little lead at the sheath and does not have enough explosive force to injure the cable or its duct4 ,ozone seems to destroy the insulating properties of rubber very rapidly1 and as it is well known that the silent electric discharge from conductors at high voltages develops ozone1 care should be taken to protect rubber insulation from its action4 ,this is especially true at the ends of cables where connections are made with switches or other apparatus1 and the rubber insulation is exposed4 ,to protect the rubber at such points it is the practice to solder a brass cable head or terminal bell to the lead sheath near its end1 this head having a diameter perhaps twice as great as that of the sheath1 and then to fill the space about the cable conductors in this head with an insulating compound4 ,heads of this sort were used on the #aa1jjj-volt cables at ,buffalo as well as on the #ac1ejj-volt cable in the ,portsmouth and ,dover transmission4 ,as insulating materials1 whether rubber1 cotton1 or paper1 may be impaired or destroyed by heat1 it is necessary that the temperature of underground cables under full load be kept within safe limits4 ,rubber insulation can probably be raised to #abe or #aej ,fahrenheit without injury1 and paper and cotton may go a little higher4 ,for a given size and make of leaded cable the rise of temperature in its conductors above that of the surrounding air1 for a given loss in watts per foot of the cable1 may be determined by computation or experiment4 ,the next step is to find out how much the temperature of the air in the conduits where the cable is to be used will rise above the temperature of the earth in which the conduits are laid1 with the given watt loss per foot of cable4 ,on this point there are but little experimental data4 ,obviously1 the material of which ducts are made1 the number of ducts grouped together with cables operating at the same time1 and the extent to which ducts are ventilated must have an important bearing on this question4 ,at ,niagara ,falls some tests were made to show the rise of air temperature in a section of thirty-six-duct conduit lying between two manholes about #adj feet apart4 ,for the purpose of this test twenty-four of the thirty-six ducts in the conduit had one ,no4 #f drawing-in wire passed through each of them4 ,these twenty-four wires were connected into three groups of eight wires each1 so that one group was all in ducts next to the surrounding earth1 another group was one-half in ducts next to the earth and the other half in ducts separated from the earth by at least one duct1 while the third group of wires was entirely in ducts separated from the earth by at least one duct4 ,it was found that when enough current was sent through these wires to represent a loss of #e4e watts per foot of ducts in which they were located1 the rise of temperature in the air of the ducts next to the earth was about #ajh ,fahrenheit above that of the earth4 ,for the ducts separated from the earth by at least one other duct the rise in temperature of contained air was #add ,fahrenheit above the earth4 ,if the earth about the ducts reached #gj in hot weather1 the temperature of air in the inner ducts1 with a loss of #e4e watts per duct foot1 would thus be #bad4 ,this temperature is too high for either rubber1 cotton1 or paper insulation1 to say nothing of the amount by which the temperature of the conductors and insulation of a cable in operation must exceed that of the surrounding air in its duct4 ,the cables actually installed in the ducts just considered were designed for a loss of #b4cd watts per foot4 ,as the ,no4 #f wire used in the test did not nearly fill each duct as a cable would do1 it would be very interesting to know how much ventilation took place while the test was going on4 ,unfortunately1 this point was not reported4 ,vol4 xviii41 ,a4 ,i4 ,e4 ,e41 #ejh4 ,,chapter ,,xv4 ,,materials ,,for ,,line ,,conductors4 ,copper1 aluminum1 iron1 and bronze are all used for conductors in long-distance electric transmissions1 but copper is the standard metal for the purpose4 ,an ideal conductor for transmission lines should combine the best electrical conductivity1 great tensile strength1 a high melting point1 low coefficient of expansion1 hardness1 and great resistance to oxidation4 ,no one of the metals named possesses all of these properties in the highest degree1 and the problem is to select the material best suited to each case4 ,aluminum suffers very slightly by exposure to the weather1 copper and bronze suffer a little more1 while iron and steel wire are attacked seriously by rust4 ,iron1 copper1 and bronze are all so hard that little or no trouble has occurred from wires of these metals cutting or wearing away at the points of attachment to insulators4 ,aluminum1 on the other hand1 is so soft that swaying of the wire may1 in time1 cause material wear at the supports1 or it may be cut by tie wires4 ,but lines of aluminum wire have not been in use long enough to determine how much trouble is to be expected from its lack of hardness4 ,a small coefficient of expansion is desirable in transmission wires1 because the strain on the wire itself and on its supports varies rapidly with the amount of vertical deflection of each span1 becoming greater as the deflection decreases4 ,taking the expansion of copper as unity1 that of aluminum is #a4d2 of bronze1 #a4a2 and of iron and steel1 #j4g4 ,from these figures it follows that iron and steel wires show the least variation in the amount of sag between supports1 and aluminum wire shows the most4 ,wrought iron melts at about #b1hjj1 steel at #b1gjj1 copper at #a1ibi1 bronze at about the same point as copper1 and aluminum at #a1aeg ,fahrenheit4 ,this low melting point of aluminum may prove a source of trouble by opening a line of that material where some foreign wire falls on it4 ,this1 according to a report1 was illustrated at a sub-station on a #cj1jjj-volt transmission line where a destructive arc was started at the switchboard4 ,not being able to extinguish the arc in any other way1 a lineman threw an iron wire across the aluminum lines just outside of the sub-station1 and these lines were immediately melted through by the iron wire1 thus opening the circuit4 ,the trouble may have warranted so desperate a remedy in this case2 but1 as a rule1 it does not pay to cut a transmission line in order to get rid of a short circuit4 ,in the ordinary construction of transmission lines on land the tensile strength of wire is secondary in importance to its electrical conductivity1 because supports can be spaced according to the strength of the conductor used4 ,when large bodies of water must be crossed1 tensile strength is a prime requirement4 ,thus a #adb-mile line from ,colgate to ,oakland1 in ,california1 crosses the ,straits of ,carquinez in the form of steel cables1 each seven-eighths of an inch in diameter and #d1dbg feet long4 ,steel wire was selected for this long span1 probably because it can be given a greater tensile strength than that of any other metal4 ,annealed iron wire has a tensile strength between #ej1jjj and #fj1jjj pounds per square inch4 ,steel wires vary all the way from #ej1jjj to more than #cej1jjj pounds per square inch in strength1 but mild steel wire with a strength ranging from #hj1jjj to #ajj1jjj pounds per square inch is readily obtained4 ,soft copper shows a tensile strength between #cb1jjj and #cf1jjj pounds per square inch1 and hard-drawn copper between #de1jjj and #gj1jjj pounds1 depending on the degree of hardness4 ,silicon-bronze wires vary in strength from less than #fj1jjj to more than #ajj1jjj pounds per square inch1 and phosphor-bronze has a tensile strength of about #ajj1jjj pounds4 ,bronze wires1 like those of most alloys1 show a much wider range of strength than those of iron or copper4 ,in silicon-bronze wire the electrical conductivity decreases as the tensile strength increases4 ,the tensile strength of aluminum wire is lower than that of any other used in transmission lines1 being only about #cj1jjj pounds per square inch4 ,solid aluminum wires of large size have given trouble by breaking under strains well within their nominal strength1 due probably to imperfections or twists4 ,this trouble is now generally avoided by the use of aluminum cables4 ,in that most necessary property of a transmission line--conductivity--copper excels all other metals except silver4 ,taking the conductivity of soft copper wire at #ajj1 the conductivity of hard-drawn copper is #ih2 that of silicon-bronze ranges from #df to #ih2 that of aluminum is #fj2 of phosphor-bronze1 #bf2 of annealed iron wire1 #ad2 and of steel wire of #ajj1jjj pounds tensile strength per square inch1 #aa4 ,copper wire1 both soft and hard1 as regularly made1 does not vary more than one per cent from the standard1 and aluminum and annealed iron wires also show high uniformity as to resistance4 ,silicon-bronze and steel wires1 on the other hand1 fluctuate much in electrical conductivity4 ,for any particular transmission line the resistance is usually determined by considerations apart from the metal to be used as a conductor1 so that a line of given resistance or conductivity must be constructed of that material which best conforms to the requirements as to size of wire1 weight1 strength1 and cost4 ,allowing the weight of any definite mass of copper to represent unity1 the weight of an equal mass of wrought iron is #j4hg2 of steel1 #j4hi2 of aluminum1 #j4cj2 while that of bronze is very nearly equal to that of the copper4 ,the smallest line wire that can be used for a given length and resistance is one of pure1 soft copper4 ,next in cross-sectional area come hard-drawn copper and some silicon-bronze1 either of which need be only two per cent larger than the soft copper for an equal resistance4 ,some other silicon-bronze wire of greater tensile strength per square inch would require a sectional area of #b4ag times that of the soft copper4 ,aluminum wire with #fj per cent of the conductivity of copper requires #a4ff of its section for wires of equal resistance4 ,as phosphor-bronze has only #bf per cent of the conductivity of copper1 the section of the bronze must be #c4hd times that of the copper wire if their lengths and resistance are to be equal4 ,an annealed iron wire is equal in resistance to a copper wire of the same length when the iron has #g4ad times the section of the copper4 ,steel1 with #aa per cent of the conductivity of copper1 must have #i4ji times the copper section in order that wires of the same length may have equal resistances4 ,it is not desirable to use a copper wire smaller than ,no4 #d ,b4 ,s4 gauge for transmission lines1 because of the lack of tensile strength in smaller sizes4 ,when the conductivity of a copper wire smaller than ,no4 #d is ample1 an iron wire will give the required conductivity1 with a strength far greater than that of the copper4 ,for a line of given length and conductivity of any other metal the weight compared with that of a copper line is represented by the product of the figures for relative section of the two lines and of the weight of unit mass of the metal in question compared with that of copper4 ,thus1 for the same conductivity the weight of a certain length of iron wire is #j4hg #g4ad #f4ba times the weight of a copper wire4 ,for the steel wire above named the weight is #j4hi #i4ji #h4ji times that of a copper line of equal conductivity4 ,phosphor-bronze in a line of given length and resistance has #c4hd times the weight of soft copper4 ,silicon-bronze for a transmission line must weigh from #a4jb to #b4ag times as much as soft copper for a given length and conductivity4 ,aluminum for a line of fixed length and conductivity will weigh #a4ff #j4c #j4e times as much as copper4 ,for a line of fixed length and resistance1 hard-drawn copper will weigh about two per cent more than soft copper4 ,taking the tensile strength of soft copper at #cd1jjj pounds per square inch1 hard-drawn copper at #de1jjj to #gj1jjj1 silicon-bronze at #fj1jjj to #ajj1jjj1 phosphor-bronze at #ajj1jjj1 iron at #ee1jjj1 steel at #ajj1jjj1 and aluminum at #cj1jjj pounds1 the relative strengths of wires with equal sectional areas compared with the soft copper are1 for hard-drawn copper1 #a4cb to #b4jf2 silicon-bronze1 #a4gf to #b4id2 phosphor-bronze1 #b4id2 iron1 #a4fb2 steel1 #b4id2 and for aluminum1 #j4hh4 ,comparing wires on the basis of equal resistances for equal lengths1 with soft copper again the standard1 the tensile strength of each as to it is as follows3 ,a hard-drawn copper line has #a4jb #a4cb #a4cd to #a4jb #b4jf #b4aj times the strength of a line of soft copper4 ,with silicon-bronze the strength of line wire would range between #a4jb #a4gf #a4gi and #b4ag #b4id #f4ch times that of copper4 ,iron would give the line a strength as to soft copper represented by #g4ad #a4fb #aa4ef4 ,steel of #ajj1jjj pounds tensile strength per square inch will give a line #i4ji #b4id #bf4gj times as strong as it would be if composed of soft copper4 ,with aluminum the strength of the line would be #a4ff #j4hh #a4df times that of copper4 ,for phosphor-bronze the figures are #c4hd #b4id #aa4bi4 ,from the foregoing it may be shown how many times the price of soft copper per pound may be paid for each of the other metals to form a line of given length and resistance at a cost equal to that of a soft copper line4 ,these prices per pound for the several metals relative to that of soft copper are as follows3 ,taking the price of soft copper as one1 the price for hard-drawn copper must be #a #a4jb #j4ih4 ,for silicon-bronze the price may be as high as #a #a4jb #j4ih1 or as low as #a #b4ag #j4df of the price of soft copper wire4 ,phosphor-bronze may have a price represented by only #a #c4hd #j4bf that of copper4 ,the price of iron wire should be #a #f4ba #j4af of that of copper1 and for steel wire of the quality stated the price can only be #a #h4ja #j4ab4 ,aluminum wire alone may have a higher price per pound than soft copper for the same resistance and cost of line1 the figure for the relative cost of this metal being #a #j4e #b4 ,from the foregoing it appears that for a line of given cost1 length1 and resistance1 soft copper has the least cross-section and tensile strength2 steel1 the greatest cross-section1 weight1 tensile strength1 and lowest permissible price per pound2 and aluminum1 the least weight and highest price per pound4 ,,relative ,,properties ,,of ,,wires ,,having ,,equal ,,lengths ,,and ,,resistances4 ---------------------------------------- ----------------- ,relative ,relative ,relative ,relative ,metal in ,wire4 ,cross ,weights4 ,tensile ,prices per ,sections4 ,strengths4,pound for ,same ,total ,cost4 ---------------------------------------- ----------------- ,soft ,copper #a4jj #a4jj #a4 #a4jj ,hard ,copper #a4jb #a4jd #a4cd 4#ih ,very ,hard ,copper #a4jb #a4jb #b4aj 4#ih ,no4 #a ,silicon-,bronze #a4jb #a4jb #a4gi 4#ih ,no4 #b ,silicon-,bronze #b4ag #b4ag #f4ch 4#df ,aluminum #a4ff 4#ej #a4df #b4jj ,phosphor-,bronze #c4hd #c4hd #aa4bi 4#bf ,annealed ,iron #g4ad #f4ba #aa4ef 4#af ,mild ,steel #i4ji #h4ji #bf4gj 4#ab ---------------------------------------- ----------------- ,the relative cross sections and weights of both iron and steel wires are so great as to prevent their general use because of the labor and cost of their erection4 ,so far as the first cost of the wire alone is concerned1 iron may be approximately equal to copper in some metal markets4 ,the only practical place for an iron wire1 however1 is one where copper would be too small or not strong enough4 ,steel wire finds a place1 in spite of its high resistance1 in those exceptional cases where a single span of several thousand feet must be made1 requiring high tensile strength4 ,in such cases it is usually better to give the steel span a greater resistance than an equal length of the main portion of the line1 so as to avoid excessive size and weight of the span4 ,even when this is done the resistance of the steel span would be very small compared with that of a long transmission line4 ,phosphor-bronze finds little use as conductors in transmission systems because of its relatively high electrical resistance4 ,if great tensile strength is wanted1 iron or steel will supply it at a fraction of the cost of phosphor-bronze4 ,as a conductor simply1 phosphor-bronze is worth only #j4bf as much per pound as soft copper1 while its actual market price is greater than that of copper4 ,silicon-bronze of relatively high resistance1 requiring #b4ag times the section and weight of copper for equal conductivity1 is entitled to little or no consideration as a transmission line material4 ,this alloy1 in order to give equal conductivity at equal cost with copper1 must sell at only #j4df of the price of copper per pound4 ,but the price of silicon-bronze is equal to1 or greater than1 the price of copper1 so that the cost of the high-resistance silicon-bronze for a line of given resistance will be more than twice that of copper4 ,for this more than double cost the bronze gives #f4ch times the tensile strength of a soft copper line of equal conductivity4 ,taking the market price of steel at one-fifth that of copper1 which is amply high for the steel1 as a rule1 a steel wire of equal conductivity with the copper will cost only #a4f times as much and will have #bf4g times the tensile strength of the copper1 or four times the tensile strength of a wire of equal conductivity made from the high-resistance silicon-bronze4 ,from this it is clear that steel offers a cheaper combination of conductivity and strength than does silicon-bronze of high resistance4 ,that grade of silicon-bronze having the lowest resistance may cost #j4ih as much per pound as soft copper1 and will have #a4gi times the strength of the copper for equal conductivity4 ,this bronze actually costs more per pound than copper1 so that it cannot give equal conductivity at equal cost4 ,very hard-drawn copper has a conductivity equal to that of the best silicon-bronze1 and the tensile strength of this copper is seventeen per cent greater than that of the bronze4 ,silicon-bronze costs more per pound than hard copper1 but even with equal prices the hard copper gives equal conductivity and higher strength at the same cost4 ,furthermore1 the conductivity of silicon-bronze is much more liable to serious variations than that of hard copper4 ,between hard-drawn copper and steel there is very little apparent place for any grade of bronze in electric transmission lines4 ,the hardest copper wire is very stiff1 and is more liable to crack when twisted or bent than is wire of only medium hardness4 ,such medium-hard copper has a tensile strength of thirty-four per cent greater than soft copper of equal conductivity1 and is much used on long transmission lines4 ,aluminum is the only metal which1 for given conductivity in a transmission line1 combines a smaller weight1 a greater tensile strength1 and a higher permissible price than soft copper for the same total cost4 ,for equal conductivity an aluminum wire has a greater tensile strength than one of medium-hard copper1 and costs less than copper of any grade when the price per pound of the aluminum is less than twice that of copper1 which is usually the case4 ,these properties make aluminum by far the most important competitor of copper in electric transmission and have led to its use in a number of cases1 notably for the two longest lines in the world1 namely1 between ,colgate and ,oakland and between ,electra and ,san ,francisco1 in ,california4 ,it has not been found practicable to solder joints in aluminum wires because of the resulting electrolytic action when aluminum is in contact with other metals4 ,joints of aluminum wires are usually made by slipping the ends past each other in an oval aluminum sleeve and then giving the sleeve and wires two or three complete twists1 or by a process of cold welding with a sleeve joint4 ,long transmission lines are in nearly all cases run with bare wire supported by poles4 ,where very high voltages are employed no insulation that can be put on the wire will make it safe to handle1 and the cost of such insulation would add materially to that of the entire line4 ,it is1 therefore1 the practice to run transmission lines above all other wires and to rely entirely on the supports for insulation4 ,the considerations thus far noted apply alike to wires carrying continuous and alternating currents1 but there are some other factors that apply solely to alternating lines4 ,owing to the inductive effects of alternating currents in long1 parallel wires1 such wires should be transposed between their supports at frequent intervals4 ,the induction between wires increases with the frequency of the current carried1 and decreases with the distance between the wires4 ,according to these conditions1 wires should be transposed as often as every eighth of a mile in some cases1 and at intervals of one mile or more in others4 ,an alternating current when passing along a line tends to concentrate itself in the outer layers of the wire1 leaving the centre idle4 ,this unequal current distribution increases with the frequency of the current and with the area of the cross section of the wire4 ,the practical effect of this unequal distribution is to make the resistance of a wire a little higher for alternating than for continuous currents4 ,in existing transmission lines the increase of resistance due to this cause seldom amounts to one per cent4 ,when an alternating current passes through a circuit1 the action termed self-induction sets up an electromotive force in the circuit that opposes the flow of current1 as does the resistance of the wire1 and this is called the inductance of the circuit4 ,the ratio of this inductance to the resistance of a circuit increases with the number of periods per second of the alternating current used and with the sectional area of the wires composing the circuit4 ,for a circuit of ,no4 #f ,b4 ,s4 gauge wire the inductance amounts to only five per cent of the line resistance1 but for a circuit of ,no4 #jjj wire the inductance consumes as much of the applied voltage as does the resistance1 with #fj-;cycle current4 ,both the unequal distribution of alternating current over the cross-section of a conductor and the inductance of circuits make it desirable to keep the diameters of transmission wires as small as other considerations permit4 ,as soft copper has greater conductivity per unit of area than any of the other available metals1 it clearly has an advantage over all of them as to inductance and increase of resistance with alternating current4 ,at very high voltages there is an important leakage of energy between the conductors of a circuit1 and this loss varies inversely with the distance between these conductors4 ,thus it happens that inductance makes it desirable to bring the parallel wires of a circuit close together1 while the leakage of energy from wire to wire makes it desirable to carry them far apart4 ,to provide greater security from interruption1 the conductors for important transmissions are in some cases carried on two independent pole lines4 ,even where all the conductors are on a single line of poles it is frequent practice to divide them up into a number of comparatively small wires1 and this decreases inductance4 ,data of a number of transmission lines presented in the appended table illustrate the practice in some of the more recent and important cases as to the materials1 size1 number1 and arrangement of the wires4 ,the plants of which particulars are given include the greatest power capacities1 the longest distances1 and the highest voltages now involved in electrical transmissions4 ,each of the lines named is worked with alternating current of two- or three-phase4 ,each three-phase line must have at least three wires1 and each two-phase line usually has four wires4 ,on ten of the lines the number of wires is greater than three or four1 thus reducing the necessary size of each wire for a given conductivity of the line4 ,the ,butte1 ,oakland1 and ,hamilton lines are run on two sets of poles for greater security1 and a second pole line has been added to the ,niagara and ,buffalo system to carry additional wires4 ,the largest wire used in any of these lines is the aluminum cable of #ejj1jjj circular mils between ,niagara ,falls and ,buffalo4 ,this cable has #a4ff times the area in cross section of a copper cable of equal conductivity4 ,,sizes ,,and ,,materials ,,of ,,wires ,,on ,,some ,,american ,,transmission ,,lines4 ---------------------------------------- ----------------------- ,length ,number ,size of of ,location of ,transmission4 ,line,wires4 ,each ,wire,metal in,trans- - -- ,b4 ,s4 ,wire4 mis- ,volt- ,gauge4 sion4 age4 ,miles4 ---------------------------------------- ----------------------- ,caon ,ferry to ,butte #ej1jjjf #j ,copper #fe ,colgate to ,oakland #dj1jjjc #jj ,copper #adb #c #jjj ,aluminum#adb ,electra to ,san ,francisco #dj1jjjcdga1jcd ,c4 ,m4 #adg ,santa ,ana ,r4 to ,los ,angeles #cc1jjjf #a ,copper #hc ,apple ,river to ,st4 ,paul #be1jjjf #b #be ,welland ,canal to ,hamilton #bb1ejjc #a #ce #c #jj #cg ,caon ,city to ,cripple ,creek #bj1jjjc #c #bc-a_/b ,madrid to ,bland #bj1jjjf #d #cb ,white ,river to ,dales #bb1jjjc #f #bg ,ogden to ,salt ,lake ,city #af1jjjf #a #cf-a_/b ,san ,gabriel ,caon to ,los ,angeles #af1jjjf #e #bc ,to ,victor1 ,col #ab1fjjc #d #h ,niagara ,falls to ,buffalo #bb1jjjfcej1jjj ,c4 ,m4 #bc #bb1jjjcejj1jjj ,c4 ,m4,aluminum #bj ,yadkin ,river to ,salem #ab1jjjc #a ,copper #ad4e ,farmington ,riv'r to ,hartford#aj1jjjcccf1dbj ,c4 ,m4,aluminum #aa ,wilbraham to ,ludlow ,mills #aa1ejjface1bdg ,c4 ,m4 #d4e ,niagara ,falls to ,toronto #fj1jjjfaij1jjj ,c4 ,m4 ,copper #ge ---------------------------------------- ----------------------- ,aluminum lines are now employed for the three longest electrical transmissions in ,north ,america4 ,in the longest single line1 that from ,electra power-house to ,san ,francisco1 a distance of #adg miles1 aluminum is the conductor used4 ,the #adb-mile transmission between ,colgate and ,oakland is carried out with three aluminum and three copper line wires4 ,for the third transmission in point of length1 that from ,shawinigan ,falls to ,montreal1 a distance of #he miles1 three aluminum conductors are employed4 ,the three transmissions just named have unusually large capacities as well as superlative lengths1 the generators in the ,electra plant being rated at #aj1jjj1 in the ,colgate plant at #aa1bej1 and in the ,shawinigan plant at #g1ejj kilowatts4 ,weight and cost of such lines are very large4 ,for the three ,no4 #jjjj aluminum conductors1 #adb miles each in length1 between ,colgate and ,oakland1 the total weight must be about #ddj1jfg pounds1 costing #acb1jbj at #cj cents per pound4 ,between ,electra and ,mission ,san ,jos1 where the line branches1 is #ajj miles of the #adg-mile transmission from ,electra to ,san ,francisco4 ,on the ,electra and ,mission ,san ,jos section the aluminum conductors comprise three stranded cables of #dga1jcd circular mils each in sectional area and with a total weight of about #gba1bjj pounds4 ,this section alone of the line in question would have cost #baf1cfj at #cj cents per pound4 ,the #he-mile aluminum line from ,shawinigan ,falls to ,montreal is made up of three-stranded conductors each with a sectional area of #ahc1gjh circular mils4 ,all three conductors have a combined weight of about #bbe1cjj pounds1 and at #cj cents per pound would have cost #fg1eij4 ,aluminum lines are not confined to new transmissions1 but are also found in additions to those where copper conductors were at first used4 ,thus1 the third transmission circuit between the power-house at ,niagara ,falls and the terminal house in ,buffalo1 a distance of #bj miles by the new pole line1 was formed of three aluminum cables each with an area of #ejj1jjj circular mils1 though the six conductors of the two previous circuits were each #cej1jjj circular mils copper4 ,from these examples it may be seen that copper has lost its former place as the only conductor to be seriously considered for transmission circuits4 ,aluminum has not only disputed this claim for copper1 but has actually gained the most conspicuous place in long transmission lines4 ,this victory of aluminum has been won in hard competition4 ,the decisive factor has been that of cost for a circuit of given length and resistance4 ,from the standpoint of cross-sectional area aluminum is inferior to copper as an electrical conductor4 ,comparing wires of equal sizes and lengths1 the aluminum have only sixty per cent of the conductivity of the copper1 so that an aluminum wire must have #a4ff times the sectional area of a copper wire of the same length in order to offer an equal electrical resistance4 ,as round wires vary in sectional areas with the squares of their diameters1 an aluminum wire must have a diameter #a4bh times that of a copper wire of equal length in order to offer the same conductivity4 ,the inferiority of aluminum as an electrical conductor in terms of sectional area is more than offset by its superiority over copper in terms of weight4 ,one pound of aluminum drawn into a wire of any length will have a sectional area #c4cc times as great as one pound of copper in a wire of equal length4 ,this follows from the fact that the weight of copper is #eee pounds while that of aluminum is only #afg pounds per cubic foot1 so that for equal weights the bulk of the latter is #c4cc times that of the former metal4 ,as the aluminum wire has equal length with and #c4cc times the sectional area of the copper wire of the same weight1 the electrical conductivity of the former is #c4cc #a4ff #b times that of the latter4 ,hence1 for equal resistances1 the weight of an aluminum is only one-half as great as that of a copper wire of the same length4 ,from this fact it is evident that when the price per pound of aluminum is anything less than twice the price of copper1 the former is the cheaper metal for a transmission line of any required length and electrical resistance4 ,the tensile strength of both soft copper and of aluminum wire is about #cc1jjj pounds per square inch of section4 ,for wires of equal length and resistance the aluminum is therefore sixty-six per cent stronger because its area is sixty-six per cent greater than that of a soft copper wire4 ,medium hard-drawn copper wire such as is most commonly used for transmission lines has a tensile strength of about #de1jjj pounds per square inch1 but even compared with this grade of copper the aluminum wire of equal length and resistance has the advantage in tensile strength4 ,while the aluminum line is thus stronger than an equivalent one of copper1 the weight of the former is only one-half that of the latter1 so that the distance between poles may be increased1 or the sizes of poles1 cross-arms1 and pins decreased with aluminum wires4 ,in one respect the strain on poles that carry aluminum may be greater than that on poles with equivalent copper lines1 namely1 in that of wind pressure4 ,a wind that blows in a direction other than parallel with a transmission line tends to break the poles at the ground and prostrate the line in a direction at right angles to its course4 ,the total wind pressure in any case is obviously proportional to the extent of the surface on which it acts1 and this surface is measured by one-half of the external area of all the poles and wires in a given length of line4 ,as the aluminum wire must have a diameter twenty-eight per cent greater than that of copper wire of equal length1 one-half of the total wire surface will also be twenty-eight per cent greater for the former metal4 ,this carries with it an increase of twenty-eight per cent in that portion of the wind pressure due to wire surface4 ,in good practice the number of transmission wires per pole line is often only three1 and seldom more than six1 so that the surface areas of these wires may be no greater than that of the poles4 ,it follows that the increase of twenty-eight per cent in the surface of wires may correspond to a much smaller percentage of increase for the entire area exposed to wind pressure4 ,such small difference as exists between the total wind pressures on aluminum and copper lines of equal conductivity is of slight importance in view of the general practice by which some straight as well as the curved portions of transmission lines are now secured by guys or struts at right angles to the direction of the wires4 ,vibration of transmission lines and the consequent tendency of cross-arms1 pins1 insulators1 and of the wires to work loose is less with aluminum than with copper conductors as ordinarily strung1 because of the greater sag between poles given the former and also probably because of their smaller weight4 ,an illustration of this sort may be seen on the old and new transmission lines between ,niagara ,falls and ,buffalo4 ,the two old copper circuits consist of six cables of #cej1jjj circular mils section each on one line of poles1 and are strung with only a moderate sag4 ,in a strong wind these copper conductors swing and vibrate in such a way that their poles1 pins1 and cross-arms are thrown into a vibration that tend to work all attachments loose4 ,the new circuit consists of three #ejj1jjj circular mil aluminum conductors on a separate pole line strung with a large sag between poles1 and these conductors take positions in planes at large angles with the vertical in a strong wind1 but cause little or no vibration of their supports4 ,one reason for the greater sag of the aluminum over that of the copper conductors in this case is the fact that the poles carrying the former are #adj feet apart while the distance between the poles for the latter is only seventy feet1 on straight sections of the line4 ,the necessity for greater sag in aluminum than in copper conductors1 even where the span lengths are equal1 arises from the greater coefficient of expansion possessed by the former metal4 ,between #cb and #bab ,fahrenheit aluminum expands about #j4jjbb1 and copper #j4jjaf of its length1 so that the change in length is #dj per cent greater in the former than in the latter metal4 ,the conductors in any case must have enough sag between poles to provide for contraction in the coldest weather1 and it follows that the necessary sag of aluminum wires will be greater than that of copper at ordinary temperature4 ,in pure air aluminum is even more free from oxidation than copper1 but where exposed to the fumes of chemical works1 to chlorine compounds1 or to fatty acids the metal is rapidly attacked4 ,for this reason aluminum conductors should have a water-proof covering where exposed to any of these chemicals4 ,the aluminum line between ,niagara ,falls and ,buffalo is bare for most of its length1 but in the vicinity of the large chemical works at the former place the wires are covered with a braid treated with asphaltum4 ,aluminum alloyed with sodium1 its most common impurity1 is quickly corroded in moist air1 and should be carefully avoided4 ,all of the properties of aluminum here mentioned relate to the pure metal unless otherwise stated1 and its alloys should not1 as a rule1 be considered for transmission lines4 ,as aluminum is electropositive to most other metals the soldering of its joints is quite sure to result in electrolytic corrosion1 unless the joints are thoroughly protected from moisture1 a result that is hard to attain with bare wires4 ,the regular practice is to avoid the use of solder and rely on mechanical joints4 ,a good joint may be made by slipping the roughened ends of wires to be connected through an aluminum tube of oval section1 so that one wire sticks out at each end1 then twisting the tube and wires and giving each of the latter a turn about the other4 ,aluminum may be welded electrically and also by hammering at a certain temperature1 but these processes are not convenient for line construction4 ,especial care is necessary to avoid scarring or cutting into aluminum wires1 as may be done when they are tied to their insulators4 ,aluminum tie wires should be used exclusively4 ,to avoid the greater danger of damage to solid wires and also to obtain greater strength and flexibility1 aluminum conductors are most frequently used in the form of cables4 ,the sizes of wires that go to make up these cables commonly range from ,no4 #f to #i ,b4 ,s4 gauge for widely different cable sections4 ,thus the #ahc1gjh circular mil aluminum cable between ,shawinigan ,falls and ,montreal is made up of seven ,no4 #f wires1 and the #dga1jcd circular mil cable between ,electra and ,mission ,san ,jos contains thirty-seven ,no4 #i wires4 ,from the ,farmington ,river to ,hartford each #ccf1dbj circular mils cable has exceptionally large strands of approximately ,no4 #c wire4 ,it appears from the description of a #dc-mile line in ,california 7vol4 xvii41 ,a4 ,i4 ,e4 ,e41 p4 #cde7 that a solid aluminum wire of #bid mils diameter1 or ,no4 #a ,b4 ,s4 gauge1 can be used without trouble from breaks4 ,this wire was tested and its properties reported as follows3 ,diameter1 #bic4i mils4 ,pounds per mile1 #dai4d4 ,resistance per mil foot1 #ag4f ohms at #be ,c4 ,resistance per mile at #be ,c41 #a4jjggc ohms4 ,conductivity as to copper of same size1 #ei4i per cent4 ,number of twists in six inches for fracture1 #ag4i4 ,tensile strength per square inch1 #cb1hih pounds4 ,this wire also stood the test of wrapping six times about its own diameter and then unwrapping and wrapping again4 ,it was found in tests for tensile strength that the wire in question took a permanent set at very small loads1 but that at points between #ad1jjj and #ag1jjj pounds per square inch the permanent set began to increase very rapidly4 ,from this it appears that aluminum wires and cables should be given enough sag between poles so that in the coldest weather the strains on them shall not exceed about #ae1jjj pounds per square inch4 ,this rather low safe working load is a disadvantage that aluminum shares with copper4 ,from the figures just given it is evident that the strains on aluminum conductors during their erection should not exceed one-half of the ultimate strength in any case1 lest their sectional areas be reduced4 ,,aluminum ,,cables ,,in ,,transmission ,,systems4 ---------------------------------------- ------------------------- ,size of ,number,miles,circular,strands ,strands4 ,locations4 of of ,mils of per ,b4 ,s4 ,g4 ,cables4,each4 ,each4 ,cable4 ,approx- imate4 ---------------------------------------- ------------------------- ,niagara ,falls to ,buffalo #c #bj #ejj1jjj 44 44 ,shawinigan ,falls to ,montreal #c #he #ahc1gjh #g #f ,electra to ,mission ,san ,jos #c #ajj #dga1jcd #cg #i ,colgate to ,oakland #c #add #baa1jjj #g #e-f ,farmington ,river to ,hartford #c #aa #ccf1dbj #g #c ,lewiston1 ,me4 #c #c4e #add1fhh #g #h ,ludlow1 ,mass4 #f #d4e #ace1bdg #g #g ---------------------------------------- ------------------------- ,this table of transmission systems using aluminum conductors is far from exhaustive4 ,aluminum is also being used to distribute energy to the sub-stations of long electric railways1 as on the ,aurora and ,chicago which connects cities about forty miles apart4 ,the lower cost of aluminum conductors is also leading to their adoption instead of copper in city distribution of light and power4 ,thus at ,manchester1 ,n4 ,h41 the local electric lines include about four miles each of #ejj1jjj and #gej1jjj circular mil aluminum cable with weather-proof insulation4 ,the larger of these cables contains thirty-seven strands of about ,no4 #g wire4 ,as may be seen from the foregoing facts1 the choice of copper or aluminum for a transmission line should turn mainly on the cost of conductors of the required length and resistance in each metal4 ,so nearly balanced are the mechanical and electrical properties of the two metals that not more than a very small premium should be paid for the privilege of using copper4 ,as already pointed out1 the costs of aluminum and copper conductors of given length and resistance are equal when the price per pound of aluminum wire is twice that of copper4 ,during most of the time for several years the price of aluminum has been well below double the copper figures1 and the advantage has been with aluminum conductors4 ,with the two metals at the same price per pound aluminum would cost only one-half as much as equivalent copper conductors4 ,when the price of aluminum is fifty per cent greater per pound than that of copper1 the use of the former metal effects a saving of twenty-five per cent4 ,for the new ,niagara and ,buffalo line1 completed early in #aija1 aluminum was selected because it effected a saving of about twelve per cent over the cost of copper4 ,all of the aluminum lines here mentioned1 except the short one near ,hartford1 were completed during or since #aijj4 ,most of the facts here stated as to the line between ,niagara ,falls and ,buffalo are drawn from vol4 xviii41 ,a4 ,i4 ,e4 ,e41 at pages #ebj and #eba4 ,the greater diameter of aluminum over equivalent copper conductors has advantages in transmission with alternating current at very high voltages4 ,at high voltages1 say of #dj1jjj or more1 the constant silent loss of energy from one conductor to another of the same circuit through the air tends to become large and even prohibitive in amount4 ,this loss is greater1 other factors being constant1 the smaller the diameter of the conductors in the line4 ,it follows that this loss is more serious the smaller the power to be transmitted1 because the smaller the diameter of the line wires4 ,the silent passage of energy from wire to wire increases directly with the length of line and thus operates as a limit to long transmissions4 ,,chapter ,,xvi4 ,,voltage ,,and ,,losses ,,on ,,transmission ,,lines4 ,the voltage on a transmission line may be anything up to at least #fj1jjj1 and the weight of conductors varies inversely with the square of the figures selected1 the power1 length and loss being constant4 ,whatever the total line pressure1 the weight of conductors varies inversely with the percentage of loss therein4 ,the case of maximum loss and minimum weight of conductors is that in which all of the transmitted energy is expended in heating the line wires4 ,such a case would never occur in practice1 because the object of power transmission is to perform some useful work4 ,minimum loss is theoretically zero1 and the corresponding weight of conductors is infinite1 but these conditions obviously cannot be attained in practice4 ,between these extremes of minimum and of infinite weights of conductors comes every practical transmission with a line loss greater than zero and less than #ajj per cent4 ,to determine the weight and allowable cost of conductors1 the cost of the energy that will be annually lost in them enters as one of the factors4 ,at this point the distinction between the percentage of power lost at maximum load and the percentage of total energy lost should come into view4 ,line loss ordinarily refers to the percentage of total power consumed in the conductors at maximum load4 ,this percentage would correspond with that of total energy lost if the line current and voltage were constant during all periods of operation1 but this is far from the case4 ,a system of transmission may operate with either constant volts or constant amperes on the line conductors1 but in a practical case constancy of both these factors is seldom or never to be had4 ,this is because the product of the line volts and amperes represents accurately in a continuous-current system1 and approximately in an alternating-current system1 the amount of power transmitted4 ,in an actual transmission system1 the load--that is1 the demand for power--is subject to more or less variation at different times of the day1 and the line volts or amperes1 or both1 must vary with it4 ,if the transmission system is devoted to the operation of one or more factories the required power may not vary more than twenty-five per cent during the hours of daily use2 but if a system of general electrical supply is to be operated1 the maximum load will usually be somewhere between twice and four times as great as the average load for each twenty-four hours4 ,such fluctuating loads imply corresponding changes in the volts or amperes of the transmission line4 ,a number of rather long transmissions is carried out in ,europe with continuous1 constant current1 and in such systems the line voltage varies directly with the load4 ,as the loss of power in an electrical conductor depends entirely on its ohms of resistance1 which are constant at any given temperature1 and on the amperes of current passing through it1 the line loss in a constant-current system does not change during the period of operation1 no matter how great may be its changes of load4 ,for this reason the percentage of power loss in the line at maximum load is usually smaller than the percentage of energy loss for an entire day4 ,if1 for example1 the constant-current transmission line is designed to convert into heat #e per cent of the maximum amount of energy that will be delivered to it per second--that is1 to lose #e per cent of its power at maximum load--then1 when the power which the line receives drops to one-half of its maximum1 the percentage of loss will rise to #aj1 because #j4je #j4e #j4a4 ,so again1 when the power sent through the line falls to one-quarter of the full amount1 the line loss will rise to #j4je #j4be #j4b1 or #bj per cent4 ,from these facts it is clear that a fair all-day efficiency for a constant-current transmission line can be obtained only in conjunction with a high efficiency at maximum load1 if widely varying loads are to be operated4 ,it does not necessarily follow from these facts as to losses in constant-current lines that such losses should always be small at maximum loads1 for if a large loss may be permitted at full load a still greater percentage of loss at partial loads may not imply bad engineering4 ,in a large percentage of electric water-power plants some water goes over the dam during those hours of the day when loads are light1 the storage capacity above the dam not being sufficient to hold all of the surplus water during most seasons of the year4 ,if1 therefore1 the line loss in a constant-current transmission1 where all of the daily flow of water cannot be used1 is not great enough to reduce the maximum load that would otherwise be carried1 then the fact that the percentage of line loss at small loads is still larger is not very important4 ,obviously1 it makes little difference whether water goes over a dam or through wheels to make up for a loss in the line4 ,in a case where all the water can be stored during small loads and used during heavy loads1 it is clearly desirable to keep the loss in a constant-current line down to a rather low figure1 say not more than five per cent1 at maximum load4 ,much the greater number of electrical transmissions are carried out with nearly constant line voltage1 mostly alternating1 and the line current in such cases varies directly with the power transmitted1 except as to certain results of inductance on alternating lines4 ,as line resistance is constant1 save for slight variations due to temperature1 the rate of energy loss on a constant-pressure line varies with the square of the number of amperes flowing1 and the percentage of loss with any load varies directly as the number of amperes4 ,these relations between line losses and the amperes carried follow from the law that the power1 or rate of work1 is represented by the product of the number of volts by the number of amperes1 and the law that the power actually lost in the line is represented by the product of the number of ohms of line resistance and the square of the number of amperes flowing in it4 ,in each of these cases the power delivered to the line is1 of course1 measured in watts1 each of which is #a_/gdf of a horse-power4 ,applying these laws1 it appears that if the loss of a certain constant-pressure transmission line is #aj per cent of the power delivered to it at full load1 then1 when the power1 and consequently the amperes1 on the line is reduced one-half1 the watts lost in the line as heat will be 7#a_/b7 #a_/d of the watts lost at full load1 because the number of amperes flowing has been divided by #b4 ,but the amount of power delivered to the line at full load having been reduced by #ej per cent1 while the power lost on the line dropped to one-fourth of #aj per cent1 or to #b4e per cent of the full line load1 it follows that the power lost on the line at half-load is represented by #j4jbe #j4e #j4je1 or #e per cent of the power then delivered to it4 ,this rise in the efficiency of a constant-pressure transmission line as the power delivered to it decreases1 together with the fact that maximum loads on such lines continue during hardly more than one to two hours daily1 tends to raise the allowable percentage of line loss at maximum loads4 ,this is so because a loss of fifteen per cent at maximum load may easily drop to an average loss of somewhere between five and ten per cent for the entire amount of energy delivered to a line during each day under ordinary conditions in electrical supply4 ,in the practical design of transmission lines1 therefore1 the sizes of conductors are influenced by the relation of the largest load to be operated to the greatest amount of power available for its operation1 and by questions of regulation1 as well as by considerations of all-day efficiency4 ,if the maximum load that must be carried by a transmission system during a single hour per day requires nearly as much power as can be delivered to the line conductors1 either because of lack of water storage or of water itself1 even if it is stored1 it may be desirable to design these conductors for a small loss at maximum load1 rather than to install a steam plant4 ,so again1 as the fluctuation in voltage at the delivery end of a transmission line between no load and full load will amount to the entire drop of volts in the line at full load1 if the pressure at the generating end is constant1 the requirements of pressure regulation on distribution circuits limit the drop of pressure in the transmission conductors4 ,for good lighting service with incandescent lamps at about #aaj volts1 the usual pressure1 it is necessary that variations be held within one volt either way of the pressure of the lamps--that is1 between #aji and #aaa volts4 ,every long-transmission system for general electrical supply necessarily includes one or more sub-stations where the distribution lines join the transmission circuits1 and where the voltage for lighting service is regulated4 ,as the limits of voltage variations on lighting circuits are so narrow1 it is necessary to keep the changes of pressure on the transmission lines themselves within moderate limits1 or such as can be compensated for at sub-stations4 ,this is particularly true in cases where energy transmitted over a single circuit is distributed for both incandescent lamps and large electric motors1 because the starting and operation of such motors causes large fluctuations of amperes and terminal voltage on the transmission circuits4 ,to hold such fluctuations within limits which a sub-station can readily compensate for1 it is necessary that the loss in the transmission line be moderate1 say often within ten per cent of the total voltage delivered to it at maximum load4 ,capacity and cost of equipment at generating stations go up with the percentage of line loss1 and thus serve to limit its economical amount4 ,for every horse-power delivered to a transmission line at a water-power station there must be somewhat more than one horse-power of capacity in water-wheels1 at least one horse-power in generators1 and frequently a further capacity of one horse-power in step-up transformers4 ,every additional horse-power lost in the line at maximum load1 if the generating plant is to be worked up to its full capacity1 implies an addition of somewhat more than one horse-power capacity in water-wheels1 one horse-power in generators1 and one horse-power in transformers4 ,since the cost of a generating station is thus increased as the maximum line loss is raised1 a point may be reached where any further saving in the cost of the line is more than offset by the corresponding addition to the cost of the station and of its operation4 ,just where this point1 as indicated by a percentage of line loss1 is to be found depends on the factors of each case1 important among which is the length of the transmission line4 ,much effort has been made to fix some exact relation for maximum economy between the first cost of conductors for a transmission line and the amount of energy annually lost as heat therein4 ,the best-known statement applying to this case is that of ,lord ,kelvin1 made in a paper read before the ,british ,association in #ahha4 ,according to the rule there laid down1 the most economical size for the conductors of a transmission line is that for which the annual interest on first cost equals the cost of the energy annually wasted in them4 ,if transmission systems were designed for the sole purpose of wasting energy in their line conductors this rule would exactly apply1 for it simply shows how the cost of energy wasted1 plus the interest on the cost of the conductor in which it is wasted1 may be brought to a minimum4 ,as a matter of fact1 transmission systems are primarily intended to deliver energy rather than to waste it2 but of the proportions of the entire energy to be delivered and wasted 7which is exactly what we want to know71 the rule of ,kelvin takes no account4 ,according to his rule1 the cheaper the cost of power where it is developed1 the less should be paid for conductors to bring it to market4 ,the obvious truth is that the less the cost of power development at a particular point1 the more may be invested in a line to bring it to market4 ,if power cost nothing whatever at its source it would not be worth while to build any transmission line at all if this rule is correct4 ,a modification of ,lord ,kelvin's rule has been proposed by which it is said that the interest on the cost of the conductors and the annual value of the energy lost in them should be equal1 value here meaning what the energy can be sold for4 ,this rule would make an investment in line conductors too large4 ,the entire cost of production and transmission for the delivered energy should not be greater than the cost of a like amount of energy developed at the point where the delivery is made4 ,in this entire cost of production and transmission1 interest on the investment in line conductors is only one item4 ,it is perhaps impossible to state any exact rule for the most economical relation between the cost of conductors and the loss of energy therein that will apply to every transmission4 ,a maximum limit to the weight of conductors may1 however1 be set for most cases4 ,this limit should not allow the annual interest and depreciation charges on the investment in line conductors1 plus all other costs of development and transmission1 to raise the total cost of the transmitted energy above the cost of development for an equal amount of energy at the point where the transmitted energy is delivered4 ,while the maximum investment in transmission conductors may be properly limited in the way just stated1 it by no means follows that this maximum limit should be reached in every case4 ,in the varying requirements of actual cases1 the problem may be to deliver a fixed amount of power at the least possible cost1 or to deliver the largest possible amount of power at a cost per unit under that of development at the point of use4 ,frequently a transmission system has a possible capacity in excess of present requirements1 and a line that would not be too heavy for future business might put an unreasonable burden of interest charges on present earnings4 ,the foregoing considerations apply to the design of conductors for a transmission line after the voltage at which it is to operate has been decided on4 ,quite a different set of facts should influence the selection of this voltage4 ,a transmission that would be entirely impracticable with any percentage of line loss that might be selected1 if carried out at some one voltage1 might represent a paying business at some higher voltage and any one of several sizes of line conductors4 ,the power that could be delivered by a line of practicable cost1 operated at one voltage1 might be too small for the purpose in hand1 while the available power at a higher voltage might be ample4 ,if any given power is to be transmitted with a given percentage of maximum loss in line conductors1 the weight of these conductors will increase as the square of their length1 and decrease as the square of the full voltage of operation in every case4 ,thus1 if the length of this transmission is doubled1 the weight of the conductors must be multiplied by four1 the voltage remaining the same2 but if the voltage is doubled and the line length remains unchanged1 the weight of conductors must be divided by four4 ,with the length of line and the voltage of transmission either lowered or raised together1 the weight of the conductors remains fixed1 for constant power and loss4 ,an illustration of this last rule may be drawn from the case of lines designed to transmit any given power a distance of ten miles at #aj1jjj volts1 and a distance of fifty miles at #ej1jjj volts1 in which the total weight of conductors would be the same for each line if the percentage of loss was constant4 ,this statement of the rule as to proportionate increase of voltage and distance presents the advantages of high voltages in their most favorable light4 ,though a uniform ratio between the voltage of operation and the length of line allows a constant weight of conductors to be employed for the transmission of a given power with unchanging efficiency of conductors1 yet other considerations soon limit the advantage thus obtained4 ,important among these considerations may be mentioned the mechanical strength of line conductors1 difficulties of line insulation1 losses between conductors through the air1 limits of generator voltages1 and the cost of transformers4 ,if the ten-mile transmission at #aj1jjj volts1 above mentioned1 requires a circuit of two ,no4 #a_/j copper wires1 the total weight of these wires will be represented by 7#e1ejj #aj #b #cbj7 #a1jjj #ce1bjj pounds1 allowing #e1ejj feet of wire per mile of single conductor to provide something for sag between poles1 and #cbj pounds being the weight of bare ,no4 #a_/j copper wire per #a1jjj feet4 ,when the length of line is raised to #ej miles1 the two-wire circuit will contain #e1ejj #ej #b #eej1jjj feet of single conductor1 and since the voltage is raised to #ej1jjj at the same time1 the total weight of conductors will be #ce1bjj pounds as before4 ,the weight of single conductor per #a1jjj feet is therefore only #fd pounds in the #ej-mile line4 ,a ,no4 #g copper wire1 ,b4 ,s4 gauge1 has a weight of #fc pounds per #a1jjj feet1 and is the nearest regular size to that required for the #ej-mile line as just found4 ,it would be poor policy to string a wire of this size for a transmission line1 because it is so weak mechanically that breaks would probably be frequent in stormy weather4 ,the element of unreliability introduced by the use of this small wire on a #ej-mile line would cost far more in the end than a larger conductor4 ,as a rule1 ,no4 #d ,b4 ,s4 gauge wire is the smallest that should be used on a long transmission line in order to give fair mechanical strength1 and this size has just twice the weight of a ,no4 #g wire of equal length4 ,here1 then1 is one of the practical limits to the advantages that may be gained by increasing the voltage with the length of line4 ,as line voltage goes up1 the strain on line insulation increases rapidly1 and the insulators for a circuit operated at #ej1jjj volts must be larger and of a much more expensive character than those for a #aj1jjj-volt circuit4 ,in this way a part of the saving in conductors effected by the use of very high voltages on long lines is offset by the increased cost of insulation4 ,another disadvantage that attends the operation of transmission lines at very high voltages is the continuous loss of energy by the silent passage of current through the air between wires of a circuit4 ,this loss increases at a rapid rate after a pressure between #dj1jjj and #ej1jjj volts is reached with ordinary distances between the wires of each circuit4 ,to keep losses of this sort within moderate limits1 and also to lessen the probability of arcs on a circuit at very high voltage1 the distance of eighteen inches or two feet between conductors that carry current at #aj1jjj volts should be increased to six feet or more on circuits that operate at #ej1jjj volts4 ,such an increase in the distance between conductors makes the cost of poles and cross-arms greater1 either by requiring them to be larger than would otherwise be necessary or by limiting the number of wires to two or three per pole and thus increasing the number of pole lines4 ,these added expenses form another part of the penalty that must be paid for the use of very high voltages and the attendant saving in the cost of conductors4 ,apparatus grows more expensive as the voltage at which it is to operate increases1 because of the cost of insulating materials and the room which they take up1 thereby adding to the size and weight of the iron parts4 ,generators for alternating current can be had that develop as much as #ac1ejj volts1 but such generators cost more than others of equal power that operate at between #b1jjj and #b1ejj volts4 ,these latter voltages are as high as it is usually thought desirable to operate distribution circuits and service transformers in cities and towns1 so that if more than #b1ejj volts are employed on the transmission line1 step-down transformers are required at a sub-station4 ,for a transmission of more than ten miles the saving in line conductors by operation at #aj1jjj to #ab1jjj volts will usually more than offset the additional cost of generators designed for this pressure and of step-down transformers4 ,if the voltage of transmission is to exceed that of distribution1 it will generally be found desirable to carry the former voltage up to #aj1jjj or #ab1jjj1 at least4 ,as the cost of generators designed for the voltage last named is less than that of lower voltage generators plus transformers1 step-up transformers should usually be omitted in systems where these pressures are not exceeded4 ,for alternating pressures above #ac1jjj to #ae1jjj volts1 step-up transformers must generally be employed4 ,in order that the saving in the weight of line conductors may more than offset the additional cost of transformers when the voltage of transmission is carried above #ae1jjj1 this voltage should be pushed on up to as much as #be1jjj in most cases4 ,power transmission with continuous current has the advantage that the cost of generators remains nearly the same whatever the line voltage1 and that no transformers are required4 ,such transmissions are common in ,europe1 but have hardly a footing as yet in the ,united ,states4 ,the reason for the uniform cost of continuous-current generators is found in the fact that they are connected in series to give the desired line voltage1 and the voltage of each machine is kept under #c1jjj or #d1jjj4 ,as a partial offset to the low cost of the continuous-current generators and to the absence of transformers1 there is the necessity for motor-generators in a sub-station when current for lighting as well as power is to be distributed4 ,in spite of the various additions to the cost of transmission systems made necessary by the adoption of very high voltages1 these additions are much more than offset by the saving in the cost of conductors on lines #cj1 #ej1 or #ajj miles in length4 ,in fact1 it is only by means of voltages ranging from #be1jjj to #ej1jjj that the greatest of these distances1 and others up to more than #adj miles1 have been successfully covered by transmission lines4 ,above #fj1jjj volts there has been but slight practical experience in the operation of transmission lines4 ,calculations to determine the sizes of conductors for electric transmission lines are all based on the fundamental law discovered by ,ohm1 which is that the electric current flowing in a circuit at any instant equals the electric pressure that causes the current divided by the electric resistance of the circuit itself1 or current pressure resistance4 ,substituting in this formula the units that have been selected because of their convenient sizes for practical use1 it becomes1 amperes volts ohms1 in which the ohm is simply the electrical resistance1 taken as unity1 of a certain standard copper bar with fixed dimensions4 ,the ampere is the unit flow of current that is maintained with the unit pressure of one volt between the terminals of a one-ohm conductor4 ,when this formula is applied to the computation of transmission lines the volts represent the electrical pressure that is required to force the desired amperes of current through the ohms of resistance in any particular line1 and these volts have no necessary or fixed relation to the total voltage at which the line may operate4 ,thus1 if the total voltage of a transmission system is #aj1jjj1 it may be desirable to use #ejj1 #a1jjj1 or even #b1jjj volts to force current through the line1 so that one of these numbers will represent the actual drop or loss of volts in the line conductors when the number of amperes that represent full load is flowing4 ,as it is a law of every electric circuit that the rate of transformation of electric energy to heat or work in each of its several parts is directly proportional to the drop of voltage therein1 it follows that a drop of #ejj or #a1jjj or #b1jjj volts in the conductors of a #aj1jjj-volt transmission line at full load would correspond to a power loss of five to ten or twenty per cent respectively4 ,any other part of #aj1jjj volts might be selected in this case as the pressure to be lost in the line4 ,evidently no formula can give the number of volts that should be lost in line conductors at full load for a given power transmission1 but this number must be decided on by consideration of the items of line efficiency1 regulation1 and the ratio of the available power to the required load4 ,having decided on the maximum loss of volts in the line conductors1 and knowing the full voltage of operation1 the power and consequently the number of amperes delivered to the line at maximum load1 the resistance of the conductors may then be calculated by the formula1 amperes volts ohms4 ,thus1 if the proposition is to deliver #b1jjj1jjj watts or #b1jjj kilowatts to a two-wire transmission line with a voltage of #bj1jjj1 the amperes in each wire must be represented by #b1jjj1jjj #bj1jjj #ajj4 ,with a drop of ten per cent or #b1jjj volts in the two line conductors1 their combined resistance must be found from #ajj #b1jjj ohms1 and the ohms are therefore twenty4 ,if the combined length of the two conductors is #bjj1jjj feet1 corresponding to a transmission line of a little under twenty miles1 the resistance of these conductors must be #bj #bjj #j4a ohm per #a1jjj feet4 ,from a wire table it may be seen that a ,no4 #a_/j wire of copper1 ,b4 ,s4 gauge1 with a diameter of #j4cbdi inch1 has a resistance of #j4ajja ohm per #a1jjj feet at the temperature of #ij ,fahrenheit1 a little less at lower temperatures1 and is thus the required size4 ,obviously1 the resistance of twenty ohms is entirely independent of the length of the line1 all the other factors being constant1 and wires of various sizes will be required for other distances of transmission4 ,it is often convenient to find the area of cross section for the desired transmission conductor instead of finding its resistance4 ,this can be done by substituting in the formula1 amperes volts ohms1 the expression for the number of ohms in any conductor1 and then solving as before4 ,electrical resistance in every conductor varies directly with its length1 inversely with its area of cross section1 and also has a constant factor that depends on the material of which the conductor is composed4 ,this constant factor is always the same for any given material1 as pure iron1 copper1 or aluminum1 and is usually taken as the resistance in ohms of a round wire one foot long and #j4jja inch in diameter1 of the material to be used for conductors4 ,such a wire is said to have an area in cross section of one circular mil1 because the square of its diameter taken as unity is still unity1 that is1 #a #a #a4 ,in like manner1 for the convenient designation of wires by their areas of cross-section1 each round wire of any size is said to have an area in circular mils equal to the square of its diameter measured in units of #j4jja inch each4 ,thus1 a round wire of #j4a inch diameter has an area of #ajj #ajj #aj1jjj circular mils1 and a round wire one inch in diameter has an area of #a1jjj #ajjj #a1jjj1jjj circular mils4 ,the circular mils of a wire do not express its area of cross section in terms of square inches1 but this is not necessary since the resistance of a wire of one circular mil is taken as unity4 ,obviously1 the areas of all round wires are to each other as are their circular mils4 ,from the foregoing it may be seen that the resistance of any round conductor is represented by the formula1 ohms l s circular mils1 in which l represents the length of the conductor in feet1 s is the resistance in ohms of a wire of the same material as the conductor but with an area of one circular mil and a length of one foot1 and the circular mils are those of the required conductor4 ,substituting the quantity1 l s circular mils1 for ohms in the formula1 amperes volts ohms1 the equation1 amperes volts 7l s circular mils71 is obtained1 and this reduces to circular mils amperes l s volts4 ,for any proposed transmission all of the quantities in this formula are known1 except the desired circular mils of the line conductors4 ,the constant quantity s is about #aj4h for copper1 but is conveniently used as eleven in calculation1 and this allows a trifle for the effects of impurities that may exist in the line wire4 ,the case above mentioned1 where #b1jjj kilowatts were to be delivered to a transmission line at #bj1jjj volts1 and a loss of #b1jjj volts at full load was allowed in the line conductors1 may now be solved by the formula for circular mils4 ,taking the resistance of a round copper wire #j4jja inch in diameter and one foot long as eleven ohms1 and substituting the #ajj amperes1 #b1jjj volts1 and #bjj1jjj feet of the present case in the formula1 gives circular mils 7#ajj #bjj1jjj #aa7 #b1jjj #aaj1jjj4 ,the square root of this #aaj1jjj will give the diameter of a copper wire that will exactly meet the conditions of the case1 or the more practical course of consulting a table of standard sizes of wire will show that a ,no4 #a-j ,b4 ,s4 gauge1 with a diameter of #j4cbdi inch1 has a cross section of #aje1ejj circular mils1 or about five per cent less than the calculated number1 and is the size nearest to that wanted4 ,as this ,no4 #a-j wire will give a line loss at full load of about #aj4e per cent1 or only one-half of one per cent more than the loss at first selected1 it should be adopted for the line in this case4 ,the formula just made use of is perfectly general in its application1 and may be applied to the calculation of lines of aluminum or iron or any other metal just as well as to lines of copper4 ,in order to use the formula for any desired metal1 it is necessary that the resistance in ohms of a round wire of that metal one foot long and #j4jja inch in diameter be known and substituted for s in the formula4 ,this resistance of a wire one foot long and #j4jja inch in diameter is called the specific resistance of the substance of which the wire is composed4 ,for pure aluminum this specific resistance is about #ag4g1 for soft iron about sixty1 and for hard steel about eighty ohms4 ,the use of these values for s in the formula will therefore give the areas in circular mils for wires of these three substances1 respectively1 for any proposed transmission line4 ,in the same way the specific resistance of any other metal or alloy1 when known1 may be applied in the formula4 ,the foregoing calculations apply accurately to all two-wire circuits that carry continuous currents1 whether these circuits operate with constant current1 constant pressure1 or with pressure and current both variable4 ,where circuits are to carry alternating currents1 certain other factors may require consideration4 ,almost all transmissions with alternating currents are carried out with three-phase three-wire1 or two-phase four-wire1 or single-phase two-wire circuits4 ,of the entire number of such transmissions1 those with the three-phase three-wire circuits are in the majority1 next in point of number come the two-phase transmissions1 and lastly a few transmissions are carried out with single-phase currents4 ,the voltage of a continuous-current circuit1 by which the power of the transmission is computed and on which the percentage of line loss is based1 is the maximum voltage operating there2 but this is not true for circuits carrying alternating currents4 ,both the volts and amperes in an alternating circuit are constantly varying between maximum values in opposite directions along the wires4 ,it follows from this fact that both the volts and amperes drop to zero as often as they rise to a maximum4 ,it is fully demonstrated in books on the theory of alternating currents1 that with certain ideal constructions in alternating generators1 and certain conditions in the circuits to which they are connected1 the equivalent or1 as they are called1 the virtual values of the constantly changing volts and amperes in these circuits are #j4gjg of their respective maximum values4 ,or1 to state the reverse of this proposition1 the maximum volts and amperes respectively in these circuits rise to #a4dad times their equivalent or virtual values4 ,these relations between maximum and virtual volts and amperes are subject to some variations with actual circuits and generators1 but the virtual values of these factors1 as measured by suitable volt- and amperemeters1 are important in the design of transmission circuits1 rather than their maximum values4 ,when the volts or amperes of an alternating circuit are mentioned1 the virtual values of these factors are usually meant unless some other value is specified4 ,thus1 as commonly stated1 the voltage of a single-phase circuit is the number of virtual volts between its two conductors1 the voltage of a two-phase circuit is the number of virtual volts between each pair of its four conductors1 and the voltage of a three-phase circuit is the number of virtual volts between either two of its three conductors4 ,several factors not present with continuous currents tend to affect the losses in conductors where alternating currents are flowing1 and the importance of such effects will be noted later4 ,in spite of such effects1 the formula above discussed should be applied to the calculation of transmission lines for alternating currents1 and then the proper corrections of the results1 if any are necessary1 should be made4 ,with this proviso as to corrections1 the virtual volts and amperes of circuits carrying alternating currents may be used in the formula in the same way as the actual volts and amperes of continuous current circuits4 ,thus1 reverting to the above example1 where #b1jjj kilowatts was to be delivered at #bj1jjj volts to a transmission line in which the loss was to be #b1jjj volts1 the kilowatts should be taken as the actual rate of work represented by the alternating current1 and the volts named as the virtual volts on the line4 ,the virtual amperes will now be #ajj1 as were the actual amperes of continuous current1 and the size of line conductor for a single-phase alternating transmission will therefore be #a-j1 the same as for the continuous-current line4 ,if the transmission is to be carried out on the two-phase four-wire system1 the virtual amperes in each of these wires will be fifty instead of #ajj1 as the power will be divided equally between the two pairs of conductors1 and each of these four wires should have a cross-section in circular mils just one-half as great as that of the ,no4 #a-j wire4 ,the required wire will thus be a ,no4 #c ,b4 ,s4 gauge1 of #eb1fcj circular mils1 this being the nearest standard size4 ,in weight the two ,no4 #a-j wires and the four ,no4 #c wires are almost equal1 and they should be exactly equal to give the same loss in the single-phase and the two-phase lines4 ,for a three-phase circuit to make the transmission above considered1 each of the three conductors should have an area just one-half as great as that of each of the two conductors for a single phase circuit1 the loss remaining as before1 and the nearest standard size of wire is again ,no4 #c1 as it was for the two-phase line4 ,this is not a self-evident proposition1 but the proof can be found in books devoted to the theory of the subject4 ,from the foregoing it is evident that while the single-phase and two-phase lines require equal weights of conductors1 all other factors being the same1 the weight of conductors in the three-phase line is only seventy-five per cent of that in either of the other two4 ,neglecting the special factors that tend to raise the size and weight of alternating-current circuits1 the single-phase and two-phase lines require the same weight of conductors as does a continuous-current transmission of equal power1 voltage1 and line loss4 ,it should be noted that in each of these cases the factor l in the formula for circular mils denotes the entire length of the pair of conductors for a continuous-current line1 or double the distance of the transmission with either of the alternating-current lines4 ,having found the circular mils of any desired conductor1 its weight per #a1jjj feet can be found readily in a wire table4 ,in some cases it is desirable to calculate the weight of the conductors for a transmission line without finding the circular mils of each1 and this can be done by a modification of the above formula4 ,a copper wire of #a1jjj1jjj circular mils weighs nearly #c4jc pounds per foot of its length1 and the weight of any copper wire may therefore be found from the formula1 pounds 7circular mils #c4jc l7 #a1jjj1jjj1 in which pounds indicates the total weight of the conductor1 l1 its total length1 and the circular mils are those of its cross-section4 ,this formula reduces to the form1 circular mils 7#a1jjj1jjj pounds7 7#c4jc l7 and if this value for circular mils is substituted in the formula above given for the cross-section of any wire1 the result is 7#a1jjj1jjj pounds7 7#c4jc l7 7l amperes #aa7 volts4 ,transposition of the factors in this last equation brings it to the form1 pounds 7#c4jc l amperes #aa7 7#a1jjj1jjj volts71 which is the general formula for the total weight of copper conductors when l1 the length of one pair1 the total amperes flowing1 and the volts lost in the conductors are known for either a continuous-current1 a single-phase1 or a two-phase four-wire line4 ,if the value of l1 #bjj1jjj1 of amperes1 #ajj1 and of volts1 #b1jjj1 for the transmission above considered are substituted in the formula for total weight1 just found1 the result is pounds 7#c4jc 7#bjj1jjj7 #ajj #aa7 7#a1jjj1jjj #b1jjj71 which reduced to pounds #ff1ffj1 the weight of copper wire necessary for the transmission with either continuous1 single-phase or two-phase current4 ,with three-phase current the weight of copper in the line for this transmission will be #ge per cent of the #ff1ffj pounds just found4 ,one or more two-wire circuits may be employed for the continuous current or for the single-phase transmission1 and if one such circuit is used the weight for each of the two wires is obviously #cc1ffj pounds4 ,for a two-phase transmission two or more circuits of two wires each will be used1 and in the case of two circuits1 if all four of the wires are of equal cross section1 as would usually be the case1 the total weight of each is #af1hcj pounds4 ,if the transmission is made with one three-phase circuit1 the weight of each of the three wires is #af1hcj pounds1 and their combined weight1 #ej1dij pounds of copper4 ,in each of these transmission lines the length of a single conductor in one direction is #ajj1jjj feet1 or one-half of the length of the wires in a single two-wire circuit4 ,for the two-wire line the calculated weight of each conductor amounts to #ff1ffj #bjj #ccc4c pounds per #a1jjj feet4 ,for a two-phase four-wire line and also for a three-phase three-wire line1 the weight of each conductor is #af1hcj #ajj #afh4c pounds per #a1jjj feet4 ,on inspection of a table of weights for bare copper wires it may be seen that a ,no4 #a-j ,b4 ,s4 gauge wire has a weight of #cbj pounds per #a1jjj feet1 and being much the nearest size to the calculated weight of #ccc pounds should be selected for the two-wire circuit4 ,it may also be seen that a ,no4 #c wire1 with a weight of #aei pounds per #a1jjj feet1 is the size that comes nearest to the calculated weight of #afh pounds1 and should therefore be employed in the three-wire and the four-wire circuits1 for two- and three-phase transmissions4 ,either a continuous-current1 single-phase1 two-phase1 or three-phase transmission line may of course be split up into as many circuits as desired1 and these circuits may or may not be designed to carry equal portions of the entire power4 ,in either case the combined weights of the several circuits should equal those above found1 the conditions as to power1 loss1 and length of line remaining constant4 ,it will be noted that the formul for the calculation of the circular mils and for the weight of the conductors in the transmission line lead to the selection of the same sizes of wires1 as they obviously should do4 ,several laws governing the relations of volts lost1 length and weight of line conductors1 may be readily deduced from the above formul4 ,evidently the circular mils and weight of line conductors vary inversely with the number of volts lost in them when carrying a given current1 so that doubling this number of volts reduces the circular mils and weight of conductors by one-half4 ,if the length of the line changes1 the circular mils of the required conductors change directly with it1 but the weight of these conductors varies as the square of their length4 ,thus1 if the length of the line conductors is doubled1 the cross-section in circular mils of each conductor is also doubled1 and each conductor is therefore four times as heavy as before for the same current and loss in volts4 ,should the length of the conductors and also the number of volts lost in them be varied at the same rate1 the circular mils of each conductor remain constant1 and its weight increases directly with the distance of transmission4 ,thus1 with the same size of line wire1 both the number of volts lost and the total weight are twice as great for a #ajj- as for a fifty-mile transmission4 ,if the total weight of conductors is to be held constant1 then the number of volts lost therein must vary as the square of their length1 and their circular mils must vary inversely as the length4 ,so that if the length of a transmission line is doubled1 the circular mils for conductors of constant weight are divided by two1 and the volts lost are four times as great as before4 ,each of these rules assumes that the watts and percentage of loss in the line are constant4 ,the above principles and formul apply to the design of transmission lines for either continuous or alternating currents1 but where the alternating current is employed certain additional factors should be considered4 ,one of these factors is inductance1 by which is meant the counter-electromotive force that is always present and opposed to the regular voltage in an alternating current circuit4 ,one effect of inductance is to cut down the voltage at that end of the line where the power is delivered to a sub-station1 just as is also done by the ohmic resistance of the line conductors4 ,between the loss of voltage due to line resistance and the loss due to inductance there is the very important difference that the former represents an actual conversion of electrical energy into heat1 while the latter is simply the loss of pressure without any material decrease in the amount of energy4 ,while the loss of energy in a transmission line depends directly on its resistance1 the loss of pressure due to inductance depends on the diameter of conductors without regard to their resistance1 on the length of the circuit1 the distance between the conductors1 and on the frequency or number of cycles per second through which the current passes4 ,as a result of these facts1 it is not desirable or even practicable to use inductance as a factor in the calculation of the resistance or weight of a transmission line4 ,on transmission lines1 as ordinarily constructed1 the loss of voltage due to inductance generally ranges between #be and #ajj per cent of the number of volts lost at full load because of the resistance of the conductors4 ,this loss through inductance may be lowered by reducing the diameter of individual wires1 though the resistance of all the circuits concerned in the transmission remains the same1 by bringing the wires nearer together and by adopting smaller frequencies4 ,in practice the volts lost through inductance are compensated for by operating generators or transformers in the power-plant at a voltage that insures the delivery of energy in the receiving-station at the required pressure4 ,thus1 in a certain case1 it may be desirable to transmit energy with a maximum loss of ten per cent in the line at full load1 due to the resistance of the conductors1 when the effective voltage at the generator end of the line is #aj1jjj1 so that the pressure at the receiving-station will be #i1jjj volts4 ,if it appears that the loss of pressure due to inductance on this line will be #a1jjj volts1 then the generators should be operated at #aa1jjj volts1 which will provide for the loss of #a1jjj volts by inductance1 leave an effective voltage of #aj1jjj on the line1 and allow the delivery of energy at the sub-station with a pressure of #i1jjj volts1 when there is a ten-percent loss of power due to the line resistance4 ,inductance not only sets up a counter-electromotive force in the line1 which reduces the voltage delivered to it by generators or transformers1 but also causes a larger current to flow in the line than is indicated by the division of the number of watts delivered to it by the virtual voltage of delivery4 ,the amount of current increase depends on both the inductance of the line itself and also on the character of its connected apparatus4 ,in a system with a mixed load of lamps and motors there is quite certain to be some inductance1 but it is very hard to predetermine its exact amount4 ,experience with such systems shows1 however1 that the increase of line current due to inductance is often not above five and usually less than ten per cent of the current that would flow if there were no inductance4 ,to provide for the flow of this additional current1 due to inductance1 without an increase of the loss in volts because of ohmic resistance1 the cross section of the line conductors must be enlarged by a percentage equal to that of the additional current4 ,this means that in an ordinary case of a transmission with either single1 two1 or three-phase alternating current1 the circular mils of each line wire1 as computed with the formul above given1 should be increased by five to ten per cent4 ,such increase in the cross section of wires of course carries with it a like rise in the total weight of the conductors for the transmission4 ,if wire of the cross section computed with the formul is employed for the alternating current transmission1 inductance in an ordinary case will raise the assumed line loss of power by five to ten per cent of what it would be if no inductance existed4 ,thus1 with conductors calculated by the formul for a power loss of ten per cent at full load1 inductance in an ordinary case would raise this loss to somewhere between #aj4e and eleven per cent4 ,as a rule it may therefore be said that inductance will seldom increase the weight of line conductors1 or the loss of power therein1 by more than ten per cent4 ,when an alternating current flows along a conductor its density is not uniform in all parts of each cross section1 but the current density is least at the centre of the conductor and increases toward the outside surface4 ,this unequal distribution of the alternating current over each cross section of a conductor through which it is passing increases with the diameter or thickness of the conductor and with the frequency of the alternating current4 ,by reason of this action the ohmic resistance of any conductor is somewhat greater for an alternating than for a continuous current1 because the full cross section of the conductor cannot be utilized with the former current4 ,fortunately1 the practical importance of this unequal distribution of alternating current over each cross section of its conductor is usually slight1 so far as the sizes of wires for transmission lines are concerned1 because the usual frequencies of current and diameters of conductors concerned are not great enough to give the effect mentioned a large numerical value4 ,thus1 sixty cycles per second is the highest frequency commonly employed for the current on transmission lines4 ,with a #d-j wire1 and the current frequency named1 the increase in the ohmic resistance for alternating over that for continuous current does not reach one-half of one per cent4 ,having calculated the circular mils of weight of a transmission line by the foregoing formul1 it appears that the only material increase of this weight required by the use of alternating current is that due to inductance4 ,this increase cannot be calculated exactly beforehand because of the uncertain elements in future loads1 but experience shows that it is seldom more than ten per cent of the calculated size or weight of conductors4 ,,chapter ,,xvii4 ,,selection ,,of ,,transmission ,,circuits4 ,maximum power1 voltage1 loss1 and weight of conductors having been fixed for a transmission line1 the number of circuits that shall make up the line1 and the relations of these circuits to each other1 remain to be determined4 ,in practice wide differences exist as to the number and relations of circuits on a single transmission line between two points4 ,cases illustrating this fact are the #adg-mile transmission from ,electra power-house to ,san ,francisco and the #fe-mile transmission between ,caon ,ferry1 on the ,missouri ,river and ,butte1 ,mont4 ,at the ,electra plant the generator capacity is #aj1jjj kilowatts1 and the transmission to ,san ,francisco is carried out over a single pole line that carries one circuit composed of three aluminum conductors1 each with an area in cross section of #dga1jjj circular mils4 ,from the generators at ,caon ,ferry1 which have an aggregate capacity of #g1ejj kilowatts1 a part of the energy goes to ,helena over a separate line1 and the transmission to ,butte goes over two pole lines that are #dj feet apart4 ,each of these two pole lines carries a single circuit composed of three copper conductors1 and each conductor has a cross section of #aje1fjj circular mils4 ,the difference in practice illustrated by these two plants is further brought out by the fact that their voltages are not far apart1 as the ,caon ,ferry and ,butte line operates at #ej1jjj1 and the ,electra and ,san ,francisco line at #fj1jjj volts4 ,economy in the construction of a transmission line points strongly to the use of a single circuit1 because this means only one line of poles1 usually but one cross-arm for the power wires per pole1 the least possible number of pins and insulators1 and the smallest amount of labor for the erection of the conductors4 ,in favor of a single circuit there is also the argument of greatest mechanical strength in each conductor1 since the single circuit is to have the same weight as that of all the circuits that may be adopted in its place4 ,where each conductor of the single circuit would have a cross section of less than #hc1fij circular mils1 if of copper1 corresponding to a ,no4 #a ,b4 ,s4 gauge wire1 the argument as to mechanical strength is of especial force1 since two equal circuits instead of one1 in the case where one circuit of ,no4 #a wires would have the required weight1 reduce the size of each conductor to ,no4 #d wire1 of #da1gdj circular mils cross section1 and this is the smallest wire that it is practicable to use on long lines for mechanical reasons4 ,opposed to these arguments for a single circuit are those based on the supposed greater reliability of two or more circuits1 their greater ease of repair1 their more effective means of regulation1 and the influence on inductance of a reduction in the size of conductors4 ,in spite of the consequent reduction in the size of each conductor1 the use of two or more separate circuits for the same transmission is sometimes thought to increase its reliability1 because in case of a break or short-circuit on one of the circuits the other will still be available4 ,breaks in transmission conductors are due either to mechanical strains alone1 as wind pressure1 the falling of trees1 or the accumulation of ice1 or else to an arc between the conductors that tends to melt them at some point4 ,as a smaller conductor breaks or melts more readily than a large one1 the use of two or more circuits instead of a single circuit tends to increase troubles of this sort4 ,it thus seems that while two or more circuits give a greater chance of continued operation after a break in a conductor actually occurs1 the use of a single circuit with larger conductors makes any break less probable4 ,when repairs must be made on a transmission line1 as in replacing a broken insulator or setting a pole in the place of one that has burned1 it is certainly convenient to have two or more circuits so that one may be out of use while the repairs on it are made4 ,it is practicable1 however1 to make such repairs on any high-voltage circuit1 even when it is in use1 provided the conductors are spaced so far apart that there is no chance of making a contact or starting an arc between them4 ,to get such distance between conductors there should be only one circuit per pole1 and even then more room should be provided for that circuit than is common in this type of construction4 ,on each of the two pole lines between ,caon ,ferry and ,butte there is a single circuit of three conductors arranged in triangular form1 two at the opposite ends of a cross-arm and one at the top of the pole1 and the distance from each conductor of a circuit to either of the other two is #f4e feet4 ,this distance between conductors is perhaps as great as that on any transmission circuit now in use1 but it seems too small to make repairs on the circuit reasonably safe when it is in operation at a pressure of #ej1jjj volts4 ,there seems to be no good reason why the distance between the conductors of a single circuit to which a pole line is devoted might not be increased to as much as ten feet1 at the slightly greater expense of longer cross-arms4 ,with as much as ten feet between conductors1 and special tools with long wooden handles to grasp these conductors1 there should be no serious danger about the repair of even #fj1jjj-volt lines when in operation4 ,as the #fj1jjj-volt line between ,electra and ,san ,francisco consists of only one circuit1 it seems that repairs on it must be contemplated during operation4 ,another example of a high-voltage transmission carried out with a single circuit is that between ,shawinigan ,falls and ,montreal1 a distance of eighty-five miles4 ,in this case the circuit is made up of three aluminum conductors1 each of which has an area in cross section of #ahc1gej circular mils1 and these conductors are located five feet apart1 one at the top of each pole1 and two at the ends of a cross-arm below4 ,this single circuit is in regular operation at #ej1jjj volts for the supply of light and power in ,montreal1 and it is hard to see how repairs while there is current on the line are to be avoided4 ,inductance varies with the ratio between the diameter of the wires in any circuit and the distance between these wires1 but as inductance simply raises the voltage that must be delivered by generators or transformers1 and does not represent a loss of energy1 it may generally be given but little weight in selecting the number of circuits1 the distance between conductors1 and the size of each conductor4 ,if two or more circuits with smaller conductors have a combined resistance in multiple equal to that of a single circuit with larger conductors1 the loss of voltage due to inductance may be greater on the single circuit than the corresponding loss on the multiple circuits1 but the advantages due to the single circuit may more than compensate for the higher pressure at generators or transformers4 ,that such advantages have been thought to exist in actual construction may be seen from the fact that the #adg-mile line from ,electra power-house to ,san ,francisco1 and the #hc-mile line from ,shawinigan ,falls to ,montreal1 are composed of one circuit each4 ,as inductance increases directly with the length of circuits1 these very long lines are especially subject to its influence1 yet it was thought that the advantages of a single circuit more than offset its disadvantages in each case4 ,where several sub-stations1 widely separated1 are to be supplied with energy by the same transmission line1 another argument exists for the division of the line conductors into more than one circuit1 so that there may be an independent circuit to each sub-station4 ,as the pressure for local distribution lines must be regulated at each sub-station1 it is quite an advantage to have a separate transmission circuit between each sub-station and the power plant1 so that the voltage on each circuit at the power-house may be adjusted as nearly as possible to the requirements of its sub-station4 ,an interesting illustration of this practice may be noted in the design of transmission circuits for the line between ,spier ,falls on the ,hudson ,river and the cities of ,schenectady1 ,troy1 and ,albany1 located between thirty and forty miles to the south1 which passes through ,saratoga and ,ballston on the way4 ,when this transmission line is completed1 four three-phase circuits1 one of ,no4 #j and three of ,no4 #jjj copper wire1 will run to the ,saratoga switch-house from the generating plant at the ,falls1 a distance of some eight miles4 ,from this switch-house two circuits of ,no4 #j conductors go to the ,saratoga sub-station1 a little more than one mile away1 two circuits of ,no4 #jjj wires run to the ,watervliet sub-station1 across the river from ,troy and thirty-five miles from the generating station1 and one circuit of ,no4 #j and one circuit of ,no4 #jjj wires are carried to ,schenectady1 thirty miles from ,spier ,falls1 passing through and supplying the ,ballston sub-station on the way4 ,other circuits connect the sub-station at ,watervliet with that at ,schenectady and with the water-power station at ,mechanicsville4 ,from the ,watervliet sub-station secondary lines run to sub-stations that control the local distribution of light and power in ,albany and ,troy4 ,this network of transmission circuits was made desirable by the conditions of this case1 which include the general supply of light and power in three large and several smaller cities1 the operation of three large electric railway systems1 and the delivery of thousands of horse-power for the motors in a great manufacturing plant4 ,in not every transmission system with different and widely scattered loads it is thought desirable to provide more than one main circuit4 ,thus1 the single circuit eighty-three miles long that transmits energy from ,shawinigan ,falls to ,montreal is designed to supply power also in some smaller places on the way4 ,so again1 the #adg-mile circuit from ,electra power-house to ,san ,francisco passes through a dozen or more smaller places1 including ,stockton1 and is tapped with side lines that run to ,oakland and ,san ,jos4 ,in cases like this1 where very long lines run through large numbers of cities and towns that sooner or later require service1 it is obviously impracticable to provide a separate circuit for each centre of local distribution4 ,it may well be in such a case that a single main transmission circuit connected to a long line of sub-stations will represent the best possible solution of the problem4 ,at the power-house end of such a circuit the voltage will naturally be regulated to suit that sub-station where the load is the most important or exacting1 and each of the other sub-stations will be left to do all of the regulating for its own load4 ,illustration3 ,,fig4 #gf4--;,connections at ,watervliet ,sub-station on ,spier ,falls ,line4 ,the greater the total loss of voltage on a transmission line supplying sub-stations that are scattered along much of its length1 the larger will be the fluctuations of voltage that must be compensated for at all of the sub-stations save one1 under changing loads1 if only one circuit is employed between the power-plant and these sub-stations4 ,suppose1 for example1 that a transmission line #ajj miles long is composed of a single circuit1 and supplies two sub-stations1 one located #ej miles and the other #ajj miles from the power-plant4 ,assume at first that there is no load whatever at the intermediate sub-station4 ,if the single transmission circuit operates with #ej1jjj volts at the power-plant1 and #de1jjj volts at the sub-station #ajj miles away when there is a full load there1 corresponding to a loss of ten per cent1 then the pressure at the intermediate sub-station will be #dg1ejj volts4 ,if1 now1 the load at the sub-station #ajj miles from the power-house drops to a point where the entire line loss is only #a1jjj volts1 and the pressure at the generating plant is lowered to #df1jjj volts so as to maintain #de1jjj volts at the more distant sub-station1 then the pressure at the intermediate sub-station will be #de1ejj volts1 or #b1jjj volts less than it was before4 ,if the loss on the entire line at full load were only five per cent1 making the voltage at the sub-station #ajj miles away #dg1ejj when that at the generating station is #ej1jjj1 then the pressure at the intermediate sub-station will be #dh1gej volts4 ,upon a reduction of the loss on the entire length of line to one-fifth of its maximum amount1 or to #ejj volts1 the pressure at the generating station must be reduced to #dh1jjj volts1 if that at the more distant sub-station is to be held constant at #dg1ejj4 ,at the intermediate sub-station the pressure will then be #dg1gej volts1 or #a1jjj volts less than it was at full load4 ,from these two examples it may be seen that the extent of pressure variation at the intermediate sub-station will depend directly on the maximum line loss1 if the regulation at the generating station is such as to maintain a constant voltage at the sub-station #ajj miles away4 ,illustration3 ,,fig4 #gg4--,sections of ,switch-house on ,new ,hampshire ,traction ,system4 ,all the foregoing has assumed no load to be connected at the intermediate sub-station1 and with a load there the fluctuations of pressure will of course depend on its amount as well as on the load at the more distant sub-station4 ,one of the strongest reasons for the use of two or more circuits in the same transmission line arises from the rapid fluctuations of load where large stationary motors or an electric railway system is operated4 ,when a transmission line must carry a load of stationary or railway motors1 it is a common practice to divide the line into at least two circuits1 and to devote one circuit exclusively to railway or motor work and another to lighting1 at any one time4 ,in some cases this division of the transmission system into two parts1 one devoted to the lighting and the other to the motor load1 is carried out not only as to the sub-station apparatus and the line1 but also as to the transformers1 generators1 water-wheels1 and even the penstocks at the power-plant4 ,it is possible even to carry this division of the transmission system still further1 and to separate either the motor or the lighting load1 or both1 into sections1 and then to devote a distinct transmission circuit1 group of transformers1 generator1 and water-wheel to the operation of each section4 ,an example of the complete division of generating and transmitting apparatus into independent units may be noted in the case of the system that supplies light and power in ,portland1 ,me41 from a generating plant on the ,presumpscot ,river1 thirteen miles away4 ,at this station four steel penstocks1 each provided with a separate gate at the forebay wall1 bring water to as many pairs of wheels1 and each pair of wheels drives a direct-connected generator4 ,four three-phase circuits connect the generating plant with the sub-station at ,portland1 and each circuit between the generating plant and a transformer-house outside the business section of the city is made up of ,no4 #b solid soft-drawn copper wires4 ,each of these four sets of apparatus1 from head-gate to sub-station1 is usually operated independently of the others1 and supplies either the motor load or a part of the electric lighting4 ,in this way changes in the amount of one section of the load cause no fluctuation of the voltage on the other sections4 ,at ,manchester1 ,n4 ,h41 the sub-station receives energy from four water-power plants1 and is provided with two sets of low-tension1 #b1cjj-volt1 three-phase bus-bars1 one set of these bus-bars being devoted to the operation of the local electric railway system1 and the other set to the supply of lamps and stationary motors4 ,each set of these bus-bars is divided into a number of sections1 and by means of these sections different transmission circuits are devoted to different portions of the lighting and motor loads4 ,as three of the four water-power plants are connected to the sub-station by two circuits each1 the division of loads in this case is often carried clear back to the generators1 one generator in a power-house being operated1 for instance1 on railway work and another on a lighting load at the same time4 ,this plan has the obvious advantage that much of the regulation for the several parts of the entire load may be done at the generators1 thus reducing the amount of regulation necessary at the sub-station1 and that fluctuating motor loads do not affect the lamps4 ,in this case the conductors of the several transmission circuits are all of moderate size1 and the division of the lines was evidently adopted for purposes of regulation1 rather than to reduce the amount of inductance4 ,thus the line between ,gregg's ,falls and the sub-station1 a distance of six miles1 is made up of one three-phase circuit of ,no4 #d and one circuit of ,no4 #f bare copper wires4 ,the fourteen-mile line between the plant at ,garvin's ,falls and the sub-station1 the longest of the four transmissions1 is made up of two three-phase circuits1 each composed of ,no4 #j bare copper wires4 ,in the case of the ,gregg's ,falls plant the subdivision of the line has gone further than that of the generating equipment1 for the station there contains only a single generator1 the rating being #a1bjj kilowatts1 while two circuits run thence to the sub-station4 ,another instance showing extensive subdivision of a line into separate circuits may be noted in the seven-mile transmission from ,montmorency ,falls to ,quebec1 ,canada1 where sixteen conductors1 each ,no4 #j copper wire1 make up four two-phase circuits that connect a plant of #b1djj kilowatts capacity with its sub-station4 ,such multiplication of transmission circuits has some advantages from the standpoint of regulation1 but there are good reasons for limiting it to rather short lines1 where it is1 in fact1 almost exclusively found4 ,on very long lines the use of numerous circuits composed of rather small conductors would obviously increase the constant expense of inspection and repairs and add materially to uncertainty of the service4 ,very few1 if any1 transmission lines of as much as twenty-five miles in length are divided into more than two circuits1 and in several instances lines of superlative length have only a single circuit each4 ,the greatest single power transmission in the world1 that between ,niagara ,falls and ,buffalo1 is carried out with two pole lines1 one of which is about twenty and the other about twenty-three miles long4 ,the longer pole line1 which is also the older1 carries two three-phase circuits1 each of which is made up of three #cej1jjj circular mil copper conductors4 ,the shorter pole line carries a single three-phase circuit composed of aluminum conductors1 each of which has an area in cross section of #ejj1jjj circular mils4 ,in electrical conductivity the aluminum circuit is intended to be equal to each of the two that are composed of copper4 ,according to the description of the ,niagara ,falls and ,buffalo transmission system in vol4 xviii41 ,a4 ,i4 ,e4 ,e41 pages #eah to #ebg1 each of these three circuits is designed to transmit about #g1ejj kilowatts1 and the maximum power transmitted up to ,august1 #aija1 was #ae1fjj kilowatts1 or about the calculated capacity of two of the circuits4 ,according to the description just mentioned1 the transmission circuits used to supply energy for use at ,buffalo are regularly operated in parallel1 and this is also true of the generators and the step-down transformers1 though the uses to which this energy is applied include lighting1 large stationary motors1 and the electric railway system4 ,apparatus in the generating station at ,niagara ,falls and in the terminal-house near the city limits of ,buffalo is so arranged1 however1 that two of the #c1gej kilowatt generators and eight step-up transformers at the power-house1 together with one transmission circuit and three step-down transformers in the terminal-house at ,buffalo1 may be operated independently of all the other apparatus4 ,as already pointed out1 the use of separate circuits for each sub-station1 and for lighting and power loads at each sub-station in very long transmission systems1 is often impracticable4 ,even in comparatively short transmissions the multiplication of circuits and the use of rather small and mechanically weak conductors increased the first cost of installation and the subsequent expense of inspection and repairs4 ,an objection to operation with a single circuit in a transmission line that supplies widely separated sub-stations with lighting1 power1 and railway loads is the consequent difficulty of pressure regulation on the distribution lines at each sub-station4 ,such a transmission line necessarily delivers energy at different and fluctuating voltages at the several sub-stations1 and these fluctuations are of course reproduced on the secondary side of the step-down transformers4 ,fortunately1 however1 the use of synchronous motor generators1 either in place of or in connection with static transformers1 goes far to solve the problem of pressure regulation for distribution circuits supplied with energy from transmission lines4 ,this is due to the well-known fact that with constant frequency the speed of rotation for a synchronous motor is constant without regard to fluctuations in the applied voltage or changes in its load4 ,with a constant speed at the motor and its connected generator it is of course easy to deliver current at constant voltage to the distribution lines4 ,this constancy of speed makes the synchronous motor generator a favorite in large transmission systems with both power and lighting loads4 ,the satisfactory lighting service in ,buffalo1 operated with energy transmitted from ,niagara ,falls1 seems to be due in some measure to the use of synchronous motor generators at the sub-station in ,buffalo1 whence lighting circuits are supplied4 ,as above stated1 the three circuits that make up the transmission line between ,niagara ,falls and ,buffalo are operated in multiple1 and in the latter place there is a large load of both railway and stationary motors4 ,as the three circuits are operated in multiple1 they of course amount to only a single circuit so far as fluctuations of voltage due to changes in these several sorts of loads are concerned4 ,according to vol4 xviii41 ,a4 ,i4 ,e4 ,e41 pages #abe and following1 the load on the transmission system at ,buffalo in #aija was made up of about #g1jjj horse-power in railway motors1 #d1jjj horse-power in induction motors1 and #d1jjj horse-power divided up between series arc lamps1 constant pressure incandescent lamps1 and continuous current motors4 ,the railway load is operated through step-down transformers and rotary converters4 ,the induction motors are connected either to the #b1jjj-volt secondary circuits of the step-down transformers or to service transformers supplied by these circuits4 ,on these railway and stationary motor loads there is of course no necessity for close pressure regulation4 ,series arc lamps are operated through step-down transformers and synchronous motors direct-connected to constant continuous current dynamos4 ,continuous current stationary motors draw power from the transmission lines through step-down transformers and rotary converters1 like the railway load4 ,for the #b1bjj volt circuits that supply service transformers for commercial arc and incandescent lighting the transmitted energy passes through step-down transformers and synchronous motor-generators4 ,these motor-generators raise the frequency from twenty-five to sixty cycles per second4 ,finally the continuous current three-wire system for incandescent lighting at about #bej volts between outside wires is operated through step-down transformers and synchronous motors direct-connected to continuous current generators4 ,for this last-named service rotary converters were at first tried1 but were found to be impracticable because voltage fluctuations on the transmission line 7due largely to the railway and motor loads7 were reproduced on the continuous-current circuits by the rotary converters4 ,since the adoption of motor-generators this fluctuation of the service voltage is no longer present4 ,another case in which synchronous motor-generators deliver power from a transmission line that carries both a lighting and a motor load is that of the ,shawinigan sub-station in ,montreal4 ,at this sub-station the #he-mile transmission line from the generating plant at ,shawinigan ,falls terminates4 ,as already pointed out1 this line is composed of a single three-phase circuit of aluminum conductors1 each of which has a cross section of #ahc1gej circular mils4 ,in the ,montreal sub-station the thirty-cycle1 three-phase current from ,shawinigan ,falls is delivered to transformers that lower the voltage to #b1cjj4 ,the current then goes to five synchronous motor-generators of #a1bjj horse-power capacity each1 and is there converted to sixty-three cycles per second1 two-phase1 at the same voltage4 ,this converted current passes onto the distribution lines of the local electrical supply system in ,montreal1 which also draws energy from two other water-power plants1 and is devoted to lighting1 stationary motors1 or to the street railway work1 as may be required4 ,though separate local distribution circuits are devoted to these several loads1 the fluctuations in the stationary and railway motor work necessarily react on the voltage of the transmission line and transformers at the sub-station4 ,by the use of the synchronous motor-generators the lighting circuits are protected from these pressure variations4 ,as the numbers of sub-stations at different points on long transmission lines increase1 and stationary motor and railway loads at each become more common1 it is to be expected that the use of synchronous motor-generators for lighting service will be much more frequent than at present4 ,with such use there will disappear one of the reasons for the multiplication of transmission circuits4 ,illustration3 ,,fig4 #gh4--,transfer ,switches at ,saratoga ,switch-house on ,spier ,falls ,line4 ,where several transmission circuits connect a generating plant with a single sub-station1 or with several sub-stations in the same general direction1 it is desirable to have switches so arranged that two or more circuits may be combined as one1 or so that any circuit that ordinarily operates a certain load or sub-station may be devoted to another when occasion requires4 ,for this purpose transfer switches on each circuit are necessary at generating plants1 sub-stations1 and often at switch-houses4 ,these transfer switches will ordinarily be of the knife type1 and intended for manual operation when the circuits to which they are connected are not in use4 ,as such switches are exposed to the full voltage of transmission1 the insulation of their conducting parts should be very high4 ,in the extensive transmission system between the power-plants at ,spier ,falls and ,mechanicsville and the sub-stations at ,troy1 ,albany1 and ,schenectady1 ,n4 ,y41 a transfer switch of highly insulated construction has been much used4 ,the two blades of this switch move independently of each other1 but both are mounted between the same metal clips4 ,each blade is of two by one-quarter inch drawn copper rod1 and the clips supporting the two blades are mounted on top of a circular metal cap four and three-quarter inches in outside diameter and two inches high1 that is cemented over the top of a large1 double petticoat1 porcelain line insulator4 ,illustration3 ,,fig4 #gi4--;,cross ,section of ,schenectady ,switch-house on ,spier ,falls ,line4 ,clips into which these copper blades are swung in closing the switch are also mounted in caps carried by insulators in the way just described4 ,each of these insulators is mounted on a large wooden pin1 and these pins are secured in timbers at the points where the switches are wanted4 ,this construction of switches gives ample insulation for the line voltage of #cj1jjj in this system4 ,by means of the transfer switches just described1 either of the transmission circuits leaving the ,spier ,falls power-plant may be connected to any one of the ten generators and ten groups of transformers there4 ,at the ,saratoga switch-house1 any one of the twelve conductors1 making up the four three-phase circuits from ,spier ,falls may be connected to any one of the eighteen conductors making up the six three-phase circuits that go south to ,saratoga1 ,watervliet1 and ,schenectady sub-stations1 in the way indicated by the drawing4 ,so again at the ,watervliet sub-station1 where energy at #bf1ejj volts is received from ,spier ,falls and energy at #aj1hjj volts from ,mechanicsville1 any single conductor from either of these water-power plants may be connected1 either directly or through a transformer1 with either conductor running to the railway and lighting sub-stations about ,albany and ,troy4 ,where several transmission circuits are employed1 this complete flexibility of connection evidently adds materially to the convenience and reliability of operation4 ,,circuits ,,in ,,transmission ,,lines4 ---------------------------------------- ------------------------ ,cycles ,length,number,number ,circular per ,location of ,lines4 in of of ,mils ,second ,miles4,cir- ,pole per of cuits4,lines4 ,wire4 ,current4 ---------------------------------------- ------------------------ ,electra to ,san ,francisco #adg #a #a ,a#dga1jcd #fj ,colgate to ,oakland1 ,cal4 #adb #b #b #acc1ajj #fj ,a#baa1jjj ,santa ,ana ,river to ,los ,angeles #hc #b #a #hc1fij #fj ,shawinigan ,falls to ,montreal #he #a #a ,a#ahc1gej #cj ,caon ,ferry to ,butte #fe #b #b #ajf1ejj #fj ,welland ,canal to ,hamilton #ce #a #a #hc1fij #fj ,welland ,canal to ,hamilton #cg #a #a #acc1ajj #fj ,spier ,falls to ,schenectady #cj #b #a #aje1fjj #dj #afg1hjj ,spier ,falls to ,watervliet1 ,n4 ,y4 #ce #b #a #afg1hjj #dj ,ogden to ,salt ,lake ,city #cf #b #a #hc1fij #fj ,apple ,river ,falls to ,st4 ,paul #bg #b #a #ff1cgj #fj ,niagara ,falls to ,buffalo #bc #b #a #cej1jjj #be ,niagara ,falls to ,buffalo #bj #a #a ,a#ejj1jjj #be ,farmington ,river to ,hartford #aa #a #a ,a#cfd1dbj #fj ,niagara ,falls to ,toronto #ge #b #a;,b #aij1jjj #be ---------------------------------------- ------------------------ ,a ,aluminum conductor4 ,b ,steel towers4 ,,chapter ,,xviii4 ,,pole ,,lines ,,for ,,power ,,transmission4 ,long transmission lines should follow the most direct routes between generating and sub-stations as far as practicable4 ,the number of poles1 cross-arms1 and insulators increases directly with the length of line1 and the weight of conductors with the square of that length1 other factors remaining equal4 ,every material deviation from a straight line must therefore be paid for at a rather high rate4 ,distribution lines necessarily follow the public streets in order to reach consumers1 but the saving of the cost of a private right of way and ease of access are the main considerations which tend to keep transmission lines on streets and highways4 ,except in very rough or swampy country1 the difficulty of access to a pole line on a private right of way is not a serious matter and should be given but little weight4 ,the cost of a private right of way may be more important1 and should be compared with the additional cost of the pole line and conductors if erected on the public highway4 ,in this additional cost should be included any items for paving about the poles1 extra pins1 insulators1 and guys made necessary by frequent turns in the highway1 and the sums that may be required to secure the necessary franchises4 ,there is also the possible contingency of future legislation as to the voltage that may be maintained on wires located over public streets4 ,these considerations taken together give a strong tendency to the location of long transmission lines on private rights of way1 especially where the amount of power involved is great and the voltage very high4 ,a transmission line #hj4c miles in length recently erected between ,rochester and ,pelham1 ,n4 ,h41 by way of ,portsmouth1 where the generating station is located1 to feed an electric railway system1 operates at #ac1bjj volts and is mainly located on private rights of way4 ,deeds conveying the easements for this right of way provide that all trees or branches within one rod on either side of the line may be cut away4 ,the transmission line between ,niagara ,falls and ,buffalo1 about twenty-three miles long and operating at #bb1jjj volts1 is largely on a private way thirty feet wide4 ,illustration3 ,,fig4 #hj4--,transmission ,line of ,new ,hampshire ,traction ,company over ,hampton ,river ,bridge1 #d1fbc ,feet ,long4 ,for the transmission between ,caon ,ferry and ,butte the line is mainly located on a private way4 ,between ,colgate and ,oakland the transmission line is mostly on private way1 and this is also true of the greater part of some other high-pressure lines in ,california4 ,these private rights of way range from fifty to several hundred feet wide1 it being necessary in forests to cut down all trees that are tall enough to fall onto the wires4 ,in some cases of transmission at very high voltage two independent pole lines are erected and one or more circuits are then run on each set of poles4 ,this construction has been followed on the transmission line between ,niagara ,falls and ,buffalo1 ,caon ,ferry and ,butte1 ,welland ,canal and ,hamilton1 and between ,colgate and ,oakland4 ,such double pole lines are more usually located on the same right of way1 this being true of the ,caon ,ferry and ,colgate systems1 but this is not always the case4 ,in the ,hamilton system the two lines of poles1 one thirty-five miles and the other thirty-seven miles in length1 are located several miles apart4 ,the two sets of poles on a part of the ,buffalo line are less than thirty feet1 on the ,colgate line are twenty-five feet1 and on the ,caon ,ferry line are forty feet apart4 ,the main reasons for the use of two pole lines instead of one are the probability that an arc started on one circuit will be communicated to another on the same poles1 and the greater ease and safety of repairs when each circuit is on a separate line of poles4 ,on each pole line of the ,caon ,ferry transmission1 and also on each pole line of the ,colgate transmission1 there is only one three-wire circuit4 ,on the ,caon ,ferry line each wire of the two circuits has a cross-section of only #ajf1ejj circular mils1 and on the ,colgate line one circuit is of #acc1bbe circular mils wire and the other circuit is of #baa1fjj circular mils cable4 ,in contrast with these figures the line of the ,standard ,electric ,company between ,electra and ,mission ,san ,jos1 a distance of ninety-nine miles1 is made up of only three conductors1 each being an aluminum cable of #dga1jcd circular mils section4 ,inductance increases with the frequency of the current in a conductor1 and in each of the three systems just considered the frequency is sixty cycles per second4 ,the use of one circuit of larger wire instead of two circuits of smaller wire has the obvious advantage of greater mechanical strength in each conductor1 saves the cost of one pole line and of the erection of the second circuit4 ,with voltages above #dj1jjj to #ej1jjj on long transmission lines there is a large loss of energy by leakage directly through the air from wire to wire4 ,to keep this loss within desirable limits it may be necessary to give each wire of a circuit a greater distance from the others of the same circuit than can readily be had if all the wires of each circuit are mounted on one line of poles4 ,if there is only one three-wire circuit to be provided for1 three lines of poles or two lines with a long crosspiece between them may be set with any desired distance between the lines so that the leakage through the air with one wire on each pole will be reduced to a small quantity4 ,on a line built in this way it would be practically impossible for an arc to start between the wires by any of the usual means4 ,distances from pole to pole in the same line vary somewhat with the number1 size1 and material of the conductors to be carried4 ,on ordinary construction in a straight line poles are often spaced from #ajj to #aaj feet apart--that is1 about fifty poles per mile4 ,on curves and near corners the spacing of poles should be shorter4 ,poles for the #hj4c miles1 mentioned in ,new ,hampshire1 are regularly located #ajj feet apart4 ,of the two pole lines between ,niagara ,falls and ,buffalo1 the older was designed to carry twelve copper cables of #cej1jjj circular mils each1 and its poles were spaced only #gj feet apart4 ,the newer line is designed to carry six aluminum cables of #ejj1jjj circular mils each and its poles are #adj feet apart4 ,poles in each of the lines between ,caon ,ferry and ,butte are regularly spaced #aaj feet apart and each pole carries three copper cables of #ajf1ejj circular mils4 ,illustration3 ,,fig4 #ha4--;,chambly-,montreal ,line ,crossing the ,chambly ,canal4 ,illustration3 ,,fig4 #hb4--,special ,wooden ,structures on ,line ,between ,spier ,falls and ,schenectady4 ,the two #adb-mile lines between ,colgate and ,oakland are each made up of poles #acb feet apart1 and one line of poles carries the three copper conductors and the other line of poles the aluminum conductors already named4 ,as aluminum wire has only one-half the weight of copper wire of equal conductivity1 the length of span between poles carrying aluminum wire may be greater than that where copper is used4 ,only a part of the strain on poles is due to the weight of wires carried1 however4 ,where a body of water must be crossed1 a very long span1 with special supports for the wires at each side1 may be necessary4 ,a case of this sort was met where the ,colgate and ,oakland line crosses the ,carquinez ,straits at a point where the waterway is #c1bjj feet wide4 ,it was necessary to have the lowest part of the cables across these straits at least #bjj feet above the surface of the water so that vessels with the tallest masts could pass underneath4 ,to secure the necessary elevation for the cables a steel tower was built on each bank of the straits at such a point that the distance between the points for cable support on the two towers is #d1dbg feet apart4 ,as the banks rise rapidly from the water level1 one steel tower was given a height of only #fe feet1 while the height of the other was made #bbe feet4 ,between these two towers four steel cables were suspended1 each cable being made up of nineteen strands of galvanized steel wire1 having an outside diameter of seven-eighths inch and weighing #g1jhj pounds for the span4 ,the breaking strain of each cable is #ih1jjj pounds1 and it has the electrical conductivity of a ,no4 #b copper wire4 ,the cables are simply supported on the towers by steel rollers1 and the pull of each cable1 amounting to twelve tons1 is taken by an anchorage some distance behind each tower1 where the cable terminates4 ,each anchorage consists of a large block of cement deeply embedded in the ground1 and with anchor bolts running through it4 ,each cable is secured to its anchorage through a series of strain insulators1 and the regular line cables of copper and aluminum are connected with the steel cables just outside of the shelter built over the strain insulators of each anchor4 ,steel cables were used for the long span across the straits because of the great tensile strength that could be had in that metal4 ,this span is1 no doubt1 the longest and highest that has ever been erected for electrical transmission at high voltage4 ,illustration3 ,,fig4 #hc4--,special ,structure on ,line ,between ,spier ,falls and ,schenectady4 ,it has been suggested in one instance that steel towers ninety feet high and #a1jjj feet apart be substituted for pole lines and the wires strung from tower to tower4 ,such construction would increase the difficulty of insulation and would cost more at the start than a line of wooden poles4 ,the question is whether a lower maintenance and depreciation rate for the steel towers would offset their disadvantages compared with poles4 ,pole lines should be staked out with a transit1 and the same instrument can be used to give a perpendicular position to each pole and bring it into line4 ,wooden poles are used in most cases of high-voltage transmission lines4 ,iron poles would make it unsafe to work on any circuit carried by them when it was transmitting current at high voltage4 ,with iron poles a defective insulator might lead to the destruction of the conductors at that point through continuous arcing on to the iron4 ,illustration3 ,,fig4 #hd4--;,crossing of ,delaware and ,hudson ,railway ,tracks by #cj1jjj-volt ,line at ,saratoga1 ,n4 ,y4 ,the kinds of wood used for poles vary in different sections of the country4 ,in ,new ,england1 chestnut poles are a favorite and were used on the #hj4c miles of transmission line mentioned in ,new ,hampshire4 ,cedar poles are used to some extent in nearly all parts of the country1 including ,canada4 ,spruce and pine poles are employed to some extent1 especially in lengths of more than fifty feet4 ,in the ,rocky ,mountain region and in ,california round cedar poles from the forests of ,oregon1 ,washington1 and ,idaho are much used4 ,sawed redwood poles from the trunks of large trees were erected on the #adg-mile line between ,electra power-house and ,san ,francisco4 ,for the ,colgate and ,oakland line ,oregon cedar poles were selected1 and the transmission between ,caon ,ferry and ,butte was carried out with cedar poles from ,idaho4 ,for transmission circuits it is far more important at most points to have poles very strong rather than very long4 ,where wires or obstructions must be crossed by the high-voltage circuits the poles should be long enough to carry these circuits well above everything else4 ,in the open country1 where no obstructions are to be avoided1 it does not pay to use poles with a length greater than thirty-five feet4 ,illustration3 ,,fig4 #he4--,pole ,line from ,spier ,falls over ,mount ,mc,gregor4 ,short poles offer less surface to the wind1 the length of the lever through which wind pressure acts to break the pole at the ground decreases with the length of pole1 and the shorter the poles the smaller is the strain on struts and guy wires4 ,if poles are only thirty or thirty-five feet long1 they may be large in diameter without excessive cost4 ,as a rule1 no pole should be used with a top less than seven inches in diameter1 and a pole with this top should not be required to carry more than three wires4 ,a pole with seven- or eight-inch top and thirty feet long should measure not less than twelve inches in diameter at the butt4 ,for longer poles the diameters at the butt should increase up to at least eighteen inches for a round pole sixty feet long4 ,in the ,new ,hampshire transmission above named the standard length of poles is thirty-five feet4 ,on the line between ,caon ,ferry and ,butte the poles range from thirty-five to ninety feet in length4 ,the round cedar poles used in the ,colgate and ,oakland line range from twenty-five to sixty feet in length1 from eight to twelve inches diameter at the top1 and from twelve to eighteen inches diameter at the butt4 ,on the line between ,electra and ,san ,francisco the square-sawed redwood poles are reported to have the following dimensions1 in a paper read at the annual convention of ,edison ,illuminating ,companies in #aijb4 --------------------------------------- ,height1 ,top1 ,butt1 ,depth ,feet4 ,inches4 ,inches4 in ,ground4 --------------------------------------- #ce #g #g #ab #ab #e4e #dj #h #h #ac-a_/b #ac-a_/b #f #de #i #i #ae #ae #f4e #ej #aj #ajaf #af #g #fj #aa #aaag #ag #h --------------------------------------- ,the relative dimensions of these poles are of interest because1 being sawed from the trunks of large trees1 they could have any desired measurements at the tops and butts4 ,these poles1 over the greater part of the line1 carried the three aluminum cables of #dga1jcd circular mils each1 previously mentioned4 ,depth to which poles are set in the ground ranges from about five feet for twenty-five- or thirty-foot poles to eight feet for poles sixty feet long4 ,in locations where the soil is very soft or where poles must resist heavy strains the stability of each pole may be much increased by digging the hole two feet or more larger in diameter than the butt of the pole1 and then filling in cement concrete--one part1 by measure1 of ,portland cement1 three of sand and five of broken stone--all around the butt of the pole after it is in the hole4 ,the butts of poles up to a point one foot or more above the ground line are frequently treated with hot tar1 pitch1 asphalt1 or carbolineum before the poles are erected1 and in ,salt ,lake ,city salt is said to be used around pole butts after they are in the hole4 ,in some cases the poles of transmission lines are painted over their entire length4 ,pole tops should always be pointed or wedge-shaped1 to shed water1 and paint or tar should be applied to these tops4 ,in some cases poles are filled with crude petroleum or other preservative compound in iron retorts1 where moisture is withdrawn from the pole by exhausting the air1 and then1 after treatment with dry steam1 the poles have the compound forced into them by hydraulic pressure4 ,in favorable soils cedar poles may remain fairly sound for twenty years1 chestnut poles more than one-half of that time1 and spruce and pine about five years4 ,poles up to forty feet in length may be readily set with pike poles1 but when they are much longer than this a derrick will save time and labor4 ,a derrick should have a little more than one-half the length of the poles to be set4 ,illustration3 ,,fig4 #hf4--;,chambly-,montreal ,line ,crossing the ,richelieu ,river4 ,poles should be guyed or braced at all points where there are material changes in the direction of the line1 and on long straight stretches about every fifth pole should be guyed or braced in both directions to prevent the poles setting back when the line wire is cut or broken at any point4 ,where there is room for wooden struts1 as on a private right of way1 they should be used instead of guys because of their more substantial character and the higher security of insulation thus obtained4 ,ordinary strain insulators cannot be relied on with lines that operate at very high voltages1 and where guys must be used a timber four by six inches and ten to twenty feet long may have the guy twisted about each end of it and be used as a strain insulator4 ,a guy or strut should come well up under the lower cross-arm on a pole to avoid breaking of the pole at the point of attachment4 ,where poles have heavy circuits and several cross-arms each it is sometimes desirable to attach a guy or strut beneath the lowest arm and also a guy close to the pole top4 ,galvanized iron or steel wire is the material best suited for guys1 and the cable form has greater strength and is more flexible than solid wire4 ,illustration3 ,,fig4 #hg4--;,cross-arms and ,insulators on the ,line ,between the ,chambly ,plant and ,montreal4 ,on the transmission line between ,electra and ,san ,francisco1 which is intended to operate at #fj1jjj volts1 the use of guys has been mostly avoided and struts employed instead4 ,where a guy had to be used1 a strain insulator of wood six by six inches and twenty feet long was inserted in it4 ,the number and spacing of cross-arms on the poles of transmission lines are regulated by the number of circuits that each pole must carry and by the desired distance apart of the wires4 ,formerly it was common to carry two or more circuits on a single line of poles1 but now a frequent practice is to give each pole line only one circuit and each pole only one cross-arm1 except that a small cross-arm for a telephone circuit is placed some feet below the power wires4 ,with only one transmission circuit per pole line1 one wire is usually placed at the top of the pole and the other two wires at opposite ends of the single cross-arm4 ,the older pole line for the transmission between ,niagara ,falls and ,buffalo carried two cross-arms per pole for the power wires1 these cross-arms being two feet apart4 ,each cross-arm was of yellow pine1 twelve feet long1 four by six inches in section1 and intended to carry four three-wire circuits1 but only two circuits have been erected on these two cross-arms4 ,on the later pole line for this same transmission each pole carries two cross-arms1 the upper intended for four and the lower cross-arm for two wires1 so that one three-wire circuit may be strung on each side of the poles1 two wires on the upper and one on the lower arm in the form of an equilateral triangle4 ,the pole lines between ,caon ,ferry and ,butte1 ,colgate and ,oakland1 and ,electra and ,san ,francisco all have only one cross-arm for power wires per pole1 and the third wire of the circuit in each case is mounted at the top of the pole so that the three conductors are at the corners of an equilateral triangle4 ,this relative position of the conductors makes it easy to transpose them as often as desired4 ,on the line from ,caon ,ferry to ,butte the cross-arms are each eight feet long with two holes for pins seventy-eight inches apart1 and are attached to the pole five feet ten and one-half inches from the top4 ,gains for cross-arms should be cut from one to two inches deep in poles before they are raised1 and one hole for three-quarters or seven-eighths-inch bolt should be bored through the centre of the cross-arm and of the pole at the gain4 ,each cross-arm should be attached to the pole by a single bolt passing entirely through the pole and cross-arm with a washer about three inches in diameter next to the cross-arm4 ,one large through bolt weakens the pole and arm less than two smaller bolts or lag-screws1 and the arm can be more easily replaced if there is only one bolt to remove4 ,alternate poles in a line should have their cross-arms bolted on opposite sides1 and at corners double arms should be used4 ,yellow pine is a favorite wood for cross-arms1 though other varieties are also used4 ,the large1 long pins necessary on high voltage lines tend to increase the sectional area of cross-arms1 and a section less than five and one-half by four and one-half inches is seldom desirable4 ,on the line between ,electra and ,san ,francisco1 which carries the three aluminum cables of #dga1jcd circular mils each1 the cross-arms of ,oregon pine have a section of six by six inches each4 ,standard dimensions of some smaller cross-arms are four and three-quarters by three and three-quarters inches1 but it may be doubted whether these arms are strong enough for long transmission work4 ,cross-arms should be surfaced all over and crowned one-quarter to one-half inch on top so as to shed water4 ,after being kiln dried1 cross-arms should be boiled in asphaltum or linseed oil to preserve the wood and give it higher insulating properties4 ,cross-arms longer than five feet should be secured by braces starting at the pole some distance below each arm and extending to points on the arm about half-way between the pole and each end of the arm4 ,illustration3 ,,fig4 #hh4--,tail ,race and ,pole ,line at ,chambly1 ,quebec ,power-station4 ,each brace may be of flat bar iron about one and one-half by one-quarter inch in section1 or the brace for both ends of an arm may be made of a single piece of angle-iron bent into the proper shape4 ,for high-voltage lines it is undesirable to employ iron braces of any sort1 since these braces form a path of low resistance that comes much too close to the pins on which the insulators and wires are mounted4 ,braces formed of hard wood are much better as to insulation1 and such braces of maple are in use on the line between ,butte and ,caon ,ferry where the voltage is #ej1jjj4 ,each brace on that line is thirty-six inches long and three inches wide1 with one end bolted to the centre of its pole and the other end to the cross-arm twenty-three inches from the pole centre4 ,the line from ,electra has hard-wood braces secured with wood pins4 ,wood is the most common material for pins on which to mount the insulators of high-voltage transmission circuits4 ,iron has been used for pins to some extent1 and its use is on the increase4 ,oak and locust pins are generally used1 the latter being stronger and more lasting4 ,in ,california1 pins of eucalyptus wood are much used and are said to be stronger than locust4 ,all wooden pins should be boiled several hours in linseed oil after being well dried4 ,this increases the insulating and lasting properties of the pins4 ,high-voltage lines require long pins to hold the lower edges of insulators well above the cross-arms1 and these pins must be much stronger than those used on ordinary lines1 because of the increased leverage of each wire4 ,a pin twelve inches long over all and having a diameter of one and one-half inches in the part that enters the cross-arm has been much used for transmission circuits1 but is much too short and weak for high voltages4 ,on the #ej1jjj-volt line between ,caon ,ferry and ,butte the pins are seasoned oak boiled in paraffin4 ,each of these pins is seventeen and one-half inches long1 two and one-half inches in diameter for a length of four and one-half inches in the middle part1 two inches in diameter for a length of five and one-half inches that fits into the cross-arm or pole top1 and one and one-half inches in diameter at the top of the thread inside of the insulator4 ,these pins hold the outside edges of the insulators nine inches above the tops of cross-arms4 ,each of these pins is held in its socket by a three-eighths-inch bolt that passes entirely through the pin and the cross-arm or pole top4 ,on the line between ,electra and ,san ,francisco the pins are each sixteen and seven-eighths inches long1 two and three-quarters inches in diameter at the largest central part1 and two and one-quarter inches in diameter in the lower part1 five inches long1 that fits into the cross-arm or pole top4 ,one of these pins broke at the shoulder with a pull of #b1bjj pounds at the threaded part4 ,carriage bolts one-half inch in diameter pass through the cross-arm and pin two inches from the top of the arm1 and one bolt three inches from the pin on each side4 ,without these bolts the arms split on test with a pull of #a1bjj pounds on the pin1 but with the bolts the pin broke as above4 ,,chapter ,,xix4 ,,entries ,,for ,,electric ,,transmission ,,lines4 ,the entrance of transmission lines into generating plants and sub-stations presents special problems in construction and insulation4 ,one of these problems has to do with the mechanical security of each conductor at the point where it passes through the side or roof of the station4 ,conductors are sometimes attached to the station so that the strain of the line is borne by the side wall where they enter and tends to pull it out of line4 ,this practice has but little to commend it1 aside from convenience1 for unless the conductors are rather small1 or the wall of the station is unusually heavy1 the pull of the former is apt to bulge the latter in the course of time4 ,for any heavy line the end strain is ultimately most suitably taken by an anchor securely fixed4 ,as special insulators must be used where a conductor is secured directly to such an anchor1 it is usually more convenient to set one or more heavy poles with double cross-arms at the end of a line1 and then to make these poles secure by large struts1 or by guys attached to anchors4 ,extra heavy cross-arms on these end poles should be provided with iron pins for the line insulators2 two or more of the insulators mounted in this way within a few feet of each other1 for each wire1 will stand up against the end strain on almost any line4 ,insulators that are to take the end strain of a line in this way should allow attachment of the wire at the side1 so that the force exerted by each conductor tends to press the insulator against the side of its pin1 rather than to pull off the top of the insulator4 ,the end strain of the line having been taken on poles close to the station1 the conductors may be attached to insulators on the wall1 the latter thus being subjected to very little mechanical strain4 ,overhead lines usually enter a station through one of its side walls1 but an entry may be made in the roof4 ,it is desirable to have a side entry on the gable end of a building rather than on a side below the eaves where there will be much dripping of water4 ,if an entry must be made below the eaves1 a shelter should be provided above the entry1 and the roof of this shelter should have a gutter that will carry water away from the wires4 ,entrance of each conductor into a station must be effected in such a way that ample insulation of the circuit will be maintained1 and in some cases so that rain1 snow1 and wind will be excluded4 ,the line voltage and the climate where the station is located thus have an important bearing on the form of entry that is suitable in any particular case4 ,the simplest form of entry for a high-voltage line is a clear opening1 usually circular in form1 through the wall of the station for each wire4 ,insulators for each wire should be provided both inside and outside of the wall to hold the wire at the centre of this opening4 ,such insulators are usually most conveniently supported by fixtures attached to both sides of the wall1 and insulators on the outside should of course be kept in an upright position1 unless completely protected from rain and snow4 ,the diameter of the openings through the wall should be great enough to prevent any visible discharge of current between the wire and wall under the worst conditions of snow1 rain1 fog1 or dust4 ,such an opening must1 therefore1 increase in diameter with the voltage of the line4 ,the larger these openings for the line wires1 the greater is the opportunity for rain1 snow1 dust1 and cold air to enter the station through them4 ,openings may be so protected as to keep out snow and rain by means of shelters on the outside of the wall on which they are placed1 but such shelters cannot keep out the cold air4 ,if the openings for the entrance of wires are located in the wall of a room that contains air-blast transformers1 the area of openings for circuits of very high voltage may be no greater than is necessary to allow the escape of heated air from the transformers4 ,the milder the climate1 other factors being the same1 the higher the voltage of circuits which may enter a station through openings that are free for the movement of air4 ,with circuits of only moderate voltage1 say less than #ae1jjj1 it is quite practicable to admit wires to a station through perfectly free openings1 in the coldest parts of the ,united ,states4 ,with voltages of #bj1jjj to #fj1jjj it is often necessary1 in the colder parts of the country1 to close the opening in the wall through which each wire enters with a disc of insulating material4 ,in order to keep the current leakage over these discs within proper limits1 the diameters of the discs must increase with the voltage of the circuit4 ,this increase of disc diameter obviously lengthens the path of leakage current over the disc surface4 ,where the openings in a wall for the entrance of high-voltage circuits are closed by insulating discs about the wires1 these discs may make actual contact with bare wires1 or the wire at each entry may have some special insulation4 ,in the side wall of the sub-station at ,manchester1 ,n4 ,h41 the entrance of transmission lines from four water-power plants is provided for by circular openings in slate slabs that are built into the brickwork4 ,the transmission circuits from three of the water-power plants operate at #aj1jjj to #ab1jjj volts1 and the circuit from the fourth plant at about #f1jjj volts4 ,circular openings in the slate slabs are each five inches in diameter1 and they are spaced twelve to fifteen inches between centres4 ,a single wire enters through each of these openings and is held at the centre by insulators both inside and outside of the wall4 ,each wire is bare where it passes through the slate slab1 and the circular openings are not closed in any way4 ,the largest wires passing through these five-inch circular openings in the slate slabs are of solid copper1 ,no4 #j1 of #j4cbe-;inch diameter each4 ,before passing through the opening in the slate slabs the wires of these transmission circuits are tied to regular line insulators supported by cross-arms secured to the outside of the brick wall by iron brackets4 ,the point of attachment of each wire to its insulator is about nine inches below the centre of the circular hole by which it enters the sub-station4 ,this ,manchester sub-station is equipped with air-blast transformers from which the hot air is discharged into the same room that the transmission lines enter4 ,along one side of the sub-station there are twenty-seven of these five-inch circular openings in the slate slabs for entrance of the high-voltage lines1 and on another side of the sub-station there are a greater number of smaller openings for the distribution circuits4 ,were it not for the air-blast transformers1 all of these openings would probably admit more air than would be desirable in a climate as cold as that at ,manchester4 ,another example of openings in the walls of a station for the entrance of transmission circuits1 where there is free movement of the air between the inside and outside of the building1 is that of the #cc1jjj-volt line between ,santa ,ana ,river and ,los ,angeles1 ,cal4 ,in this case a sewer pipe twelve inches in diameter is built into the wall of the station for each wire of the line1 so that there is a free opening of this size from inside to outside4 ,each wire of the #cc1jjj-volt circuit enters the station through the centre of one of these twelve-inch pipes1 and is thus surrounded by six inches of air on every side4 ,as the temperature near ,los ,angeles seldom or never goes down to zero1 these large openings do not admit enough air to be objectionable4 ,besides this mild climate1 air-blast transformers add to the favorable features in the stations having the twelve-inch openings4 ,in another case1 however1 where the openings for the entrance of wires of very high voltage allow free movement of air between the inside and outside of the station1 the climate is cold and the winter temperatures go down to #cj or more below zero4 ,this condition exists on the #be1jjj-volt line between ,apple ,river ,falls and ,st4 ,paul1 where six ,no4 #b wires enter the generating station through plain circular openings in the brick side wall of a small extension where the lightning arresters are located4 ,air-blast transformers are located in the end of the station next to this lightning-arrester house1 but it is not certain that the hot air from them escapes through the openings for the wires4 ,in another case where the climate is about as cold as that just named1 a gallery is built along one side of the exterior of the station at some distance above the ground1 and two openings are provided for each wire of the high-tension line4 ,one of these two openings is in the horizontal floor of the gallery and allows the entrance of the wire from the outside1 and the other opening is in the side wall of the station against which the gallery is built4 ,the two openings for each wire being thus at right angles to each other1 and the opening to the outside air being protected from the wind by its horizontal position1 no more than a permissible amount of cold air1 it is said1 finds its way into the station4 ,in some cases with lines of moderate voltage1 say #aj1jjj to #ae1jjj1 and in probably the majority of cases with lines of #be1jjj volts or more1 the entry for the high-tension wires is entirely closed4 ,an example of this practice may be seen at the various sub-stations of the ,new ,hampshire ,traction ,company1 which are located along their #ab1jjj-volt line between ,portsmouth and ,pelham1 in that ,state4 ,for the entry of each wire on these lines a sixteen-inch square opening is made in the brick wall of the sub-station4 ,on the outside of this wall a box is built about a group of three or more of these openings located side by side4 ,the top or roof of this box is formed by a slab of bluestone three inches thick1 which is set into the wall and extends twenty-six inches from the face of the wall1 with a slight slope from the horizontal4 ,the ends1 the bottom1 and the outer side of this box are formed by slabs of slate one inch thick1 so that the enclosed space has an area in vertical cross section at right angles to this building #ae4e inches high and twenty-two inches wide4 ,illustration3 ,,fig4 #hi4--;,cable ,entering ,building4 ,in the bottom of this box there is a circular opening for each wire1 and into this opening fits a heavy glass or porcelain bushing through which the wire passes4 ,after reaching the inside of the box the wire turns at right angles and passes through the sixteen-inch square opening into the sub-station4 ,beneath the box a special insulator is secured by an iron bracket to the outside of the brick wall for each line wire1 and this insulator takes the strain of the wire before it is carried up through the bushing in the bottom of the box4 ,this form of entry is permissible where the desire is to exclude cold air from the station1 and where the voltage is not high enough to cause serious leakage over the surface of the bushing and the slate forming the bottom of the box4 ,in all of the cases above mentioned the wires used to enter the stations were the regular line conductors and were bare4 ,another type of entry in sub-stations is that employed on the extensive transmission system between ,spier ,falls1 ,schenectady1 and ,albany1 ,n4 ,y4 ,the maximum voltage on this system is #cj1jjj1 and the lines usually enter each sub-station through the brick wall at one of its gable ends4 ,outside of and about the entry of each circuit or group of circuits a wooden shelter is built on the brick wall of the sub-station4 ,each shelter has a slanting roof that starts from the brick wall at some distance above the openings for the entrance of the line1 and terminates in a gutter4 ,the front of each shelter is carried down three feet below the centre of the openings in the brick wall1 and the ends go still lower4 ,the front of each shelter is four feet in height1 is four feet from the face of the brick wall1 and has a circular opening of #aj-;inch diameter for each wire of the transmission line4 ,in line with each circular opening in the wooden shield there is an opening of #ae-;inch diameter in the brick wall of the sub-station1 and into this opening in the brickwork fits a ring of wood with #ae-;inch outside and #aa-;inch inside diameter4 ,to this wooden ring a #ae-;inch disc of hard fibre #a_/h-;inch thick is secured1 and a porcelain tube #bd inches long and of #b-;inch inside diameter passes through a hole in the centre of this disc4 ,within the wooden shield and in line with each circular opening in it and with the corresponding porcelain tube through the fibre disc a line insulator is secured4 ,within the sub-station and in line with each tube there is also an insulator1 and the two insulators near opposite ends of each tube hold the line wire that passes through it in position4 ,each wire of the transmission lines1 of which the largest is ,no4 #jjj solid of #j4daj-;inch diameter1 terminates at one of the insulators within the wooden shield1 and is there connected to a special insulated wire that passes through one of the porcelain tubes into the sub-station4 ,a copper trolley sleeve #ab inches long is used to make the soldered connection between the bare line wire and the insulated conductor that passes through the porcelain tube4 ,each of these entry cables1 whatever its size1 is insulated first with a layer of rubber #i_/cb-;inch thick1 then with varnished cambric wound on to a thickness of #i_/cb-;inch1 and lastly with two layers of weather-proof braid outside of the cambric4 ,this form of closed entry for the transmission lines obviously excludes snow1 rain1 cold air1 and dust from the station4 ,whether the fibre discs and wooden rings1 together with the insulation on the entry cables1 are as desirable as a glass disc at the entry is another question4 ,another instance where the entry for a high-tension line is closed with the aid of combustible material is that of the #be1jjj-volt transmission between the water-power plant at ,chambly1 on the ,richelieu ,river1 and the sub-station in ,montreal4 ,the four three-phase circuits of this line are made up of ,no4 #jj wires of #j4cfe-;inch diameter each1 which enter the power-station at ,chambly and the terminal-house in ,montreal bare1 as they are outside4 ,at each end of the line the wires are secured to insulators on a horizontal arm with their centres twenty-two inches outside of an end wall of the station or terminal building4 ,the insulators are mounted with their centres thirty inches apart1 and a few inches above the tops of these insulators a corresponding row of wooden bushings pass through the wall with an outward slant4 ,at the ,chambly end of the line each of these bushings is of oak1 boiled in stearin1 four inches in diameter and twelve inches long4 ,at the ,montreal end the wall bushings are of boxwood1 and each is four inches square and twelve inches long4 ,each of the wooden bushings carries a glass tube1 and is itself held in position by the concrete of the wall in which it is located4 ,entrance to the station by each of the bare ,no4 #jj wires is gained through one of these glass tubes1 and cold air is excluded4 ,quite a different type of closed entry for the wires of a transmission line is in use on that between ,shawinigan ,falls and ,montreal1 which operates at #ej1jjj volts4 ,for the entry of each of the three aluminum cables that make up this line1 each cable being composed of seven ,no4 #f ,b4 ,s4 gauge wires1 a tile pipe of twenty-four-inches diameter was set into the station wall4 ,the end of each tile pipe is closed by a glass plate1 with a small hole at its centre1 through which the cable passes4 ,as the cable is thus held twelve inches from the terra cotta pipe all the way around1 any leakage of current must pass over this length of glass surface at each cable or through the air4 ,a heavy coating of frost sometimes collects on these plates1 and this increases the amount of current leakage over them4 ,surface leakage in a case of this sort1 of course1 varies with the size of the glass plate1 and if a tile pipe is used the limit of size is soon reached4 ,there seems to be no good reason1 however1 why a glass plate of any desired dimensions should not be set directly into the brick wall of a station for each line wire and the tile pipes entirely omitted4 ,this plan is followed on the system of the ,utah ,light ,power ,company1 which extends to ,salt ,lake ,city1 ,ogden1 ,provo1 and a number of other points in that ,state4 ,on the #dj1jjj-volt line of that system an entry for each wire is provided by setting two plates of glass into the brick wall1 one plate being flush with the inner surface and the other with the outer surface of the wall4 ,in the centre of each plate there is a hole of about #b4e-;inch diameter1 into which a glass or porcelain tube fits4 ,the line wire enters the station through this tube1 and it does not appear that any shelter for the glass plates is located outside of the building4 ,an entry of this type for the #dj1jjj-volt line with glass plates in a brick wall at a gable end of the ,murphy mill is said to have given satisfactory results during four years1 though that wall faces the southwest1 from which direction most of the storms come4 ,at this entry each glass plate is not more than eighteen inches in diameter1 and the wires are about four feet apart4 ,on a #af1jjj-volt line of the same company1 a glass plate twelve inches square with a three-quarter-inch hole at its centre1 and the bare wire passing through without a tube1 has given results that were entirely satisfactory4 ,two quite different types of entry to stations are used on the #ej1jjj-volt line between ,caon ,ferry and ,butte1 ,mont4 ,one type1 employed at the side wall of a corrugated iron building1 consists of a thick bushing of paraffined wood carrying a glass tube two inches in diameter1 four feet long1 with a side wall of five-eighths to three-quarter-inch1 through which the line conductor passes4 ,on the roof of the power-station at ,caon ,ferry a vertical entry is made with the #ej1jjj-volt circuit4 ,for this purpose each line wire is brought to a dead end on three insulators carried by a timber fixture on the roof4 ,a vertical tap drops from each line wire and passes through the roof and into the station4 ,this roof is of wood1 covered with tin outside and lined with asbestos inside4 ,each tap is an insulated wire1 and elaborate methods are adopted in the way of further insulation1 and to prevent water from following the wire down through the roof4 ,over the point of entrance sits a large block of paraffined wood with a central hole1 and down through this hole passes a long cylinder of paper that extends some distance above the block4 ,into the top end of this cylinder fits a wood bushing1 and a length of the tap wire that has been served with a thick layer of rubber is tightly enclosed by this bushing4 ,the rubber-covered portion of the tap wire also extends above the bushing1 and has taped to it a paper cone that comes down over the top of the paper cylinder to keep out the water4 ,on the outside of this paper cylinder1 at a lower point1 a still larger paper cone is attached to prevent water from following the cylinder down through the wooden block4 ,at the lower end of the paper cylinder1 within the station1 there is another bushing of wood1 and between this and the wooden bushing at the top of the cylinder and inside of the paper cylinder there is a long glass tube4 ,down through this tube and into the station the insulated tap wire passes4 ,from the experience thus far gained with high-voltage lines1 it seems that their entrance into stations should always be at a side wall1 unless there is some imperative reason for coming down through the roof4 ,if climatic conditions permit1 no form of entry can be more reliable than a plain1 ample opening through the wall with a large air-space about each wire4 ,if the opening must be closed1 it had better be done with one or more large plates of thick glass set directly into the brickwork of the wall4 ,some additional insulation is obtained by placing a long glass or porcelain tube over each wire where it passes through the central hole in the glass plates4 ,each conductor should be bare at the entry1 as it is on the line4 ,some of the above examples of existing practice in entries for transmission lines are taken from ,vol4 xxii41 ,a4 ,i4 ,e4 ,e4 ,,chapter ,,xx4 ,,insulator ,,pins4 ,wooden insulator pins are among the weakest elements in electric transmission systems4 ,as line voltages have gone up it has been necessary to increase the distances between the outside petticoats of insulators and their cross-arms and to lengthen the insulators themselves in order to keep the leakage of current between the conductors within permissible limits4 ,to reduce the leakage1 the wires on most lines are located at the tops instead of in the old position at the sides of their insulators4 ,all this has tended to a large increase of the mechanical strains that operate to break insulator pins at the point where they enter the cross-arm1 because the strain on each line wire acts with a longer leverage4 ,again1 it is sometimes necessary that transmission lines make long spans across rivers or elsewhere1 and a very unusual strain may be put on the insulator pins at these places4 ,as long as each electric system was confined to a single city or town a broken insulator pin could be quickly replaced1 and any material interruption of service from such a cause was improbable4 ,where the light and power supply of a city1 however1 depends on a long transmission line1 as is now the case in many instances1 and where the line voltage is so great that contact between a wire and a cross-arm will result in the speedy destruction of the latter by burning1 a broken pin may easily lead to a serious interruption of the service4 ,besides the increase of mechanical strains on insulator pins1 there is the danger of destruction of wooden pins by charring1 burning1 and other forms of disintegration due to leakage of current over the insulators4 ,this danger was entirely absent in the great majority of cases so long as lines were local and operated at only moderate voltages4 ,these several factors combined are bringing about marked changes in design4 ,on straight portions of a transmission line the insulator pins are subject to strains of two principal kinds4 ,one of these is due directly to the weight of the insulators and line wire1 and acts vertically to crush the pins by forcing them down onto the cross-arm4 ,the other is due to the horizontal pull of the line wire1 which is often much increased by coatings of ice and by wind pressure1 tending to break the pins by bending--most frequently at the point where they enter the cross-arm4 ,a strain of minor importance on pins is that encountered where a short pole has been set between two higher ones1 and the line at the short pole tends to lift each insulator from its pin1 and each pin from the cross-arm4 ,where the line changes its direction1 as on curves and at corners1 the side strain on pins is greatly increased1 and such places give by far the largest amount of trouble through the breaking of pins4 ,the latter seldom fail by crushing through the weight of the lines they support1 because the size of pin necessary to withstand the bending strain has a large factor of safety as to crushing strength4 ,insulators are sometimes lifted from wooden pins1 and the threads of these pins stripped where a short pole is used1 as already noted2 but failure of this kind is not common4 ,iron pins are either screwed or cemented into their insulators1 but the cemented joint is much more desirable1 because where a screw joint is made the unequal expansion of the iron and the glass or porcelain is apt to result in breakage of the insulator4 ,where cement is used1 both the pins and insulators should be threaded or provided with shoulders of some sort1 so that1 although the shoulders of threads do not come into contact with each other1 they will1 nevertheless1 help to secure a better hold4 ,pure ,portland cement1 mixed with water to a thick liquid1 has been used with success1 the insulator being placed upside down and the pin held in a central position in the hole of the insulator while the cement is poured in4 ,another cement that has been used for the same purpose is a mixture of litharge and glycerin4 ,melted sulphur is also available4 ,the same forces that tend to lift an insulator from its pin tend also to pull the pin from its socket in the cross-arm or pole top4 ,with wooden pins the time-honored custom has been to drive a nail into the side of the cross-arm so that it enters the shank of the pin in its socket4 ,this plan is good enough so far as immediate mechanical strength is concerned1 but is not desirable1 because it is hard to remove a nail when a pin is to be removed1 and also because the rust of the nail rots the wood4 ,a better plan is to have a small hole entirely through each cross-arm and insulator pin at right angles to the shank of that pin in its socket1 and then to drive a small wooden pin entirely through from side to side4 ,some of the important factors affecting the strains on insulator pins vary much on different transmission lines1 as may be seen from the following table of lines on which wooden pins are used4 ,on the older line between ,niagara ,falls and ,buffalo1 the regular length of span is #gj feet1 and each copper conductor of #cej1jjj circular mils is attached to its insulator #g4e inches above the cross-arm4 ,on the new line the length of span is #adj feet1 and each aluminum conductor of #ejj1jjj circular mils is attached to its insulator #aj inches above the cross-arm4 ,,table ,i4--,,data ,,of ,,lines ,,on ,,wooden ,,pins4 ---------------------------------------- ------------------------- ,circular ,mils,feet ,length ,inches from ,location of the ,lines4 of ,each of ,span ,wire to ,conductor4 ,between ,shank of ,pin4 ,poles4 ---------------------------------------- ------------------------- ,colgate to ,oakland ,b#acc1ajj 444 #ac ,electra to ,san ,francisco ,a#dga1jcd #acj #ae ,caon ,ferry to ,butte ,b#aje1fjj #aaj #ac-a_/b ,shawinigan ,falls to ,montreal ,a#ahc1gej #ajj #af-a_/d ,niagara ,falls to ,buffalo ,b#cej1jjj #gj #g-a_/b ,niagara ,falls to ,buffalo ,a#ejj1jjj #adj #aj ,chambly to ,montreal ,b#acc1ajj #ij #h-a_/b ,colgate to ,oakland ,a#baa1fjj 444 #ac ---------------------------------------- ------------------------- ,a ,aluminum conductors4 ,b ,copper conductors4 ,,table ,,ii4--,,dimensions ,,of ,,wooden ,,pins ,,in ,,inches4 ---------------------------------------- ----------------------- ,length,length,diam- ,diam-,diameter ,length ,location of ,lines4 of of eter eter of of ,stem4 ,shank4 of of ,threaded,threaded ,shank4,shoul- ,end4 ,part4 der4 ---------------------------------------- ----------------------- ,colgate to ,oakland #aj-c_/h #e-c_/h #b-a_/h #b-a_/b #a-c_/h #b ,electra to ,san ,francisco #ab #d-g_/h #b-a_/d #b-c_/d #a-c_/h #b ,caon ,ferry to ,butte #ab-a_/b #e-a_/h #b #b-a_/b #a-a_/h #c ,shawinigan ,falls to ,montreal #ac-a_/b #e #b-c_/d #c #a 44 ,niagara ,falls to ,buffalo,a #e-a_/d #f #b #b-c_/d #g_/h #a-a_/b ,niagara ,falls to ,buffalo,b #g-c_/d #f #b-a_/d #b-c_/d #a-a_/b #b-a_/b ,chambly to ,montreal,c #g #e #a-a_/b #a-g_/h 44 44 ,caon ,ferry to ,butte,d#ab-c_/h #g-g_/h #b-a_/h #b-a_/b #a-a_/h #c ---------------------------------------- ----------------------- ,a ,pins on old line4 ,b ,pins on new line4 ,c ,approximate dimensions4 ,d ,pole top pins4 ,to compensate for the greater strains introduced by doubling the length of span and using pins of longer stem1 the diameter of the shank of the new pins was increased to two inches4 ,one line between ,colgate and ,oakland is of copper1 and the other is of aluminum conductors1 but the same pins appear to be used for each4 ,on the line between ,caon ,ferry and ,butte1 ,mont41 the pin used in pole tops has a shank #b-c_/d inches longer and #a_/h-;inch greater in diameter than the pin used in cross-arms4 ,the weakest pin included in the table seems to be that in use on the line between ,chambly and ,montreal1 which is of hickory wood1 about #a-a_/b inches in diameter at the shank1 and carries its ,no4 #jj copper wire #h-a_/b inches above the cross-arm4 ,the following dimensions for standard wooden insulator pins to be used on all transmission lines are proposed in vol4 xxi41 page #bce1 of the ,transactions of the ,american ,institute of ,electrical ,engineers4 ,these pins are designed to resist a uniform pull at the smaller end and at right angles to the axis in each case4 ,the length of each pin1 in inches between the shoulder and the threaded end1 is represented by ,l1 and the diameter of each pin at its shank by ,d4 ,l4 ,d4 #a #j4hg #b #a4aj #c #a4bf #d #a4ci #e #a4ej #f #a4ei #g #a4fg #h #a4ge #i #a4hb #aj #a4hh #aa #a4ie #ac #b4jf #ae #b4ag #ag #b4be #ai #b4cd #ba #b4db ,the two strongest pins in ,table ,,ii4 appear to be those in use on the line between ,shawinigan ,falls and ,montreal and on the line from ,niagara ,falls to ,buffalo4 ,the former have a diameter of #b-c_/d inches at the shank1 and the wire is carried #af-a_/d inches above the shoulder of the pin4 ,on the new ,niagara line the shank diameter of each pin is only #b-a_/d inches1 but the line wire is only #aj inches above the shoulder4 ,it was found by tests that a strain of #b1ajj pounds at the top of the insulator and at right angles to the axis of this ,niagara pin was necessary to break it at the shank4 ,this strain is about six times as great as the calculated maximum strain that will occur in service on the line4 ,some of the pins here noted are much stronger than those proposed in the above specifications for standard pins4 ,the pins on the old ,niagara line have a shank diameter of #b inches1 with a stem only #e-a_/d inches long1 while the proposed pin of #b inches diameter at the shank has a stem #aa inches long4 ,on the ,colgate and ,oakland line a shank diameter of #b-a_/h inches goes with a length of #aj-c_/h inches in the stem1 but the proposed pin with this size of shank has a stem #ac inches long4 ,for a shank of #b-a_/d inches diameter the proposed pin has a stem #ae inches long1 but the pins with this diameter of shank on the ,electra line are only #ab inches long in the stem4 ,the #b-a_/d-;inch diameter of shank in the pins on the new ,niagara line goes with a length of only #g-c_/d inches in the stem4 ,the new ,niagara pin is thus almost exactly twice as strong as the proposed pin1 since the strength of a pin where the shank joins the stem varies inversely as the length of the stem1 all other factors being the same4 ,pins on the ,shawinigan ,falls line have a shank #b-c_/d inches in diameter1 with a length of #ac-a_/b inches in the stem2 but the largest of the proposed pins1 that with a stem #ai inches long1 has a diameter of only #b-a_/b inches in the shank4 ,it is hardly too much to say in the interest of good engineering that the wooden pin of about #e inches length of stem and #a-a_/b inches diameter of shank1 as well as all longer pins of no greater strength1 should be discarded for long transmission lines of high voltage4 ,these pins have done good service on telegraph and telephone lines1 and on local lighting circuits of ,no4 #f ,b4 ,s4 gauge wire or smaller1 and they may well be left for such work4 ,to meet the conditions of transmission work a change in both the shape and size of pins is necessary4 ,in the first place1 the shoulder on pins where the shank and stem meet1 that relic of telegraph practice1 should be entirely discarded4 ,this change will save considerable lumber on pins of a given diameter at the shank1 and will increase the strength of the pin by avoiding the sharp corner at the junction of the shank and stem4 ,another change of design should leave an excess of strength in the stem of the pin1 to provide for deterioration of the wood1 and particularly for charring by current breakage4 ,this increase of diameter and strength near the top of the pin will cost nothing in lumber1 for the wood is necessarily there unless it is turned off4 ,the shank of each pin should be proportionately shorter than in the older type1 and the pin hole should be bored only part way through the cross-arm4 ,a saving in lumber for pins and for cross-arms will thus be made1 since the size of the cross-arm may be less for a given resistance to splitting4 ,with these changes in general design the pin is a simple cylinder in the shank1 with a gentle taper from the shank to form the stem4 ,an example of this design1 which might well serve as a basis for a line of standard pins1 would be a pin #b inches in diameter and #c-a_/b inches long in the shank1 and tapering for a length of #e inches from the shank to form the stem1 with a diameter of #a-a_/b inches at the top4 ,the hole in a cross-arm for this pin should be #c-a_/b inches deep1 and this1 in an arm #d-c_/d inches deep1 would leave #a-a_/d inches of wood below the pin4 ,from the lower end of the pin hole1 a hole #a_/d-;inch in diameter should run to the bottom of the cross-arm to drain off water4 ,a line of longer pins designed to resist the same line pull as this short one would be strong enough for small conductors1 say up to ,no4 #a ,b4 ,s4 gauge wire4 ,for larger wires1 long spans and sharp angles in a line1 a pin #b-a_/d inches in diameter and #d-a_/b inches long in the shank1 tapering for #e inches to a diameter of #a-c_/d inches at the top1 or longer pins of equal strength1 should be used4 ,where the pin holes do not extend through the cross-arm there is no need of a shoulder on the pin to sustain the weight of the line wire4 ,in the cross-arm on the new ,niagara ,falls line each pin hole is bored to a depth of #e inches1 leaving #a inch of wood below the hole4 ,on the line from ,electra to ,san ,francisco the depth of each pin hole is again #e inches1 and the depth of the cross-arm #f inches4 ,the pins for use on the ,electra line were kept for several hours in a vat of linseed oil at a temperature of #baj ,f4 ,the pins for the ,shawinigan line were boiled in stearic acid4 ,all wooden pins should be treated chemically1 but the object of this treatment should be to prevent decay rather than to give them any particular insulating value4 ,the lack of strength in wooden pins and their destruction in some cases by current leakage are leading to the use of iron and steel pins4 ,such a pin1 in use on the lines of the ,washington ,power ,company1 of ,spokane1 ,wash41 is made up of a mild steel bar #ag-a_/b inches long and #a-a_/h inches in diameter1 cast into a shank at one end1 so that the total length is #ah inches4 ,the cast-iron shank has a diameter of #b-a_/af inches1 with a shoulder of #b-a_/b inches diameter at its upper end4 ,to prevent the pin from lifting out of its hole a small screw enters the top of the cross-arm and bears on the top end of the shank4 ,above the cast-iron shank the length of the steel rod is #ab inches1 and starting #c_/d inch down from its top a portion of the rod #c_/d inch long is turned to a diameter of one inch4 ,it is said that this pin begins to bend with a pull of #a1jjj pounds at its top1 but that it will support the insulator safely even when badly bent4 ,insulators may resist puncture and prevent surface arcing from wire to pin1 but still allow a large though silent flow of energy over the pins and cross-arms between the conductors of a transmission circuit4 ,the rate at which current flows from one wire of a transmission circuit to another in this way depends on the total resistance of each path over insulator surfaces and through air to the pins and cross-arm1 and then over these parts4 ,if the pins and cross-arm are entirely of iron1 the total resistance of the path through them from wire to wire is practically that of the insulator surfaces4 ,if the pins and cross-arm are of wood which is dry1 they may offer an appreciable part of the total resistance of the path through them between the wires of a circuit2 but if the wood be wet1 its resistance is very much reduced4 ,the resistance of wooden pins and cross-arm may be so small compared with that of the air and insulator surfaces that complete the path through them from wire to wire of a circuit1 that the effect of these wooden parts in checking the flow of current between conductors is relatively unimportant1 and yet the resistances of these pins and the cross-arm may affect their lasting qualities4 ,the current that flows over the pins and cross-arms from one wire to another of a high-tension circuit may be so small as not to injure these wooden parts when evenly distributed over them1 and yet this same current may char or burn the wood if confined to a narrow path4 ,such a leakage current will naturally cease to be evenly distributed over pins and their cross-arms when certain portions of their surfaces are of much lower resistance than others1 because an electric current divides and follows several possible paths in the inverse ratio of their resistances4 ,these narrow paths of relatively low resistance along wooden pins and cross-arms are heated and charred by the very current that they attract1 so that the conductivity of the path and the heat developed therein react mutually to increase each other1 and tend toward the destruction of the wood4 ,among causes that tend to make some parts of pins and cross-arms better conductors than others1 there may be mentioned cracks in the wood1 where dirt and moisture collect1 dust1 with a mixture of salt deposited on the wood by the winds at certain places1 and sea fogs that are often blown only against one side of the pins and arms and deposit salt4 ,to make matters worse1 the same cause that creates a path of relatively good conductivity along wooden pins and cross-arms often materially lowers the resistance offered to the leakage of current by the insulator surfaces4 ,thus an increase of the rate at which energy passes from wire to wire of a circuit1 and the concentration of this energy in certain parts of the wooden path1 are sometimes brought about at the same time4 ,where the line insulators employed are so designed that the resistance of the dry wooden pins and cross-arms forms a material part of the total resistance between the wires of a circuit1 a rain or heavy fog may cause a very large increase in the rate at which energy passes over these wooden parts between the conductors4 ,as long as only moderate voltages were carried on line conductors1 the charring and burning of their pins and cross-arms was a very unusual matter2 but with the application of very high pressures on long circuits the destruction of these wooden parts by the heat of leakage currents has become a serious menace to transmission systems4 ,even with low voltages there may be charring and burning of pins and cross-arms if the line insulators are very poor or if the conditions as to weather and flying dust are sufficiently severe4 ,in vol4 xx4 of the ,transactions of the ,american ,institute of ,electrical ,engineers1 pages #dce to #ddb and #dga to #dgi1 an account of the charring and burning of pins on several transmission lines is given1 from which some of the following examples are taken4 ,in one case a line that ran near a certain chemical factory was said to be much troubled by the burning of its pins1 though the voltage employed was only #ddj1 and the insulators were designed for circuits of #aj1jjj volts4 ,in rainy weather1 when insulators1 pins1 and cross-arms were washed clear of the chemical deposits1 there was no pin burning4 ,similar trouble has been met with on sections of the #dj1jjj-volt ,provo line1 in ,utah1 where dust1 mixed with salt1 is deposited on the insulators1 pins1 and cross-arms4 ,on page #gjh a #b1jjj-volt line is mentioned on which fog1 dust1 and rain caused much burning of pins4 ,when circuits are operated at voltages of #dj1jjj to #fj1jjj1 no very severe climatic conditions are necessary to develop serious trouble in the wooden pins by leakage currents1 even where the transmission lines are supported in insulators of the largest and best types yet developed4 ,striking examples along this line may be seen in the transmission systems between ,colgate and ,oakland1 ,cal41 and between ,electra and ,san ,francisco4 ,both of these systems were designed to transmit energy at #fj1jjj volts1 but the actual pressure of operation seems to have been limited to about #dj1jjj volts during much of their period of service4 ,insulators of a single type and size are used on both of these transmission lines1 and are among the largest ever put into service on long circuits4 ,each of these insulators is #aa inches in diameter1 and #aa-a_/d inches high from the lower edge to the top1 the line wire being carried in a central top groove4 ,the wooden pins used on the two lines vary a little in size1 so that on the ,electra line each pin stands #aa-a_/b inches above its cross-arm1 while on the ,colgate line the corresponding distance is #ab inches4 ,as the insulators are of the same size in each case1 the length of the pin between the lower edge of each insulator and the top of the cross-arm is #d inches on the ,colgate line and #c-a_/b inches on the ,electra line4 ,on the latter line a porcelain sleeve1 entirely separate from and making no contact with the insulator1 covers each pin from the top of its cross-arm to a point above the lower edge of the insulator4 ,on the ,colgate line each insulator makes contact with its pin for a length of #b-a_/b inches down from the top of its thread1 and on the ,electra line the contact of each insulator with its pin runs down #c-a_/b inches below the top of the thread4 ,this leaves #i inches in the length of the pin between the insulator contact and the top of each cross-arm on the ,colgate line1 and a corresponding length of pin amounting to #h-a_/b inches on the ,electra line4 ,of this #h-a_/b inches of pin surface1 about #f inches is covered by the porcelain insulating sleeve used on each pin of the ,electra line1 so that only about #b-a_/b inches of the length of each pin on that line is exposed to the leakage of current from the insulator directly through the air4 ,both the sizes of pins just mentioned were made of eucalyptus wood1 boiled in linseed oil4 ,each one of three pins taken from a pole1 between ,north ,tomer and ,cordelia1 on the ,colgate line1 was badly charred and burned on its side that faced the damp ocean winds4 ,this charring extended all the way down each pin from the point where the insulator made contact with it1 a little under the threads1 to the top of the cross-arm nine inches below4 ,two of these pins were located at the opposite ends of a cross-arm1 and the third was fixed in the top of the pole4 ,this cross-arm was charred or burnt1 as well as the pin1 but no defects could be detected in the insulators that the pins supported4 ,as to these three pins1 the most reasonable explanation seems to be that enough current leaked over both the outside and inside surfaces of each insulator and through the air to char the pin and cross-arm4 ,in flowing down each pin1 the current was naturally concentrated on the side exposed to the damp winds of the ocean1 because the deposit of moisture by these winds lowered the resistance on that side4 ,when these winds were not blowing1 and before a pin became charred on one side1 its resistance was probably about the same all the way around1 and the leakage current1 being distributed over the pin1 was not sufficient to char it4 ,the damp wind would1 of course1 lower the surface resistance of each insulator1 and this1 with the deposit of moisture on the pins and cross-arm1 many have made a very material reduction in the total resistance from wire to wire4 ,the insulators used on these pins each had two petticoats1 an upper one1 #aa inches in diameter1 and a lower one1 #f-a_/b inches in diameter1 the lower edge of the smaller petticoat being #g-a_/b inches beneath the lower outside edge of the larger petticoat4 ,as the inner surface of the larger petticoat was much nearer to a horizontal plane than the inner surface of the smaller petticoat1 moisture would have been more readily retained on it1 and the greater part of the surface resistance of the insulator during wet weather must therefore have been on the inside of the smaller petticoat4 ,at its lower edge the smaller petticoat was distant radially about #a-c_/d inches from the pin1 and the distance between the pin and the inside surface of the smaller petticoat gradually decreased to actual contact at a point #e-a_/b inches above this lower edge4 ,the path of the current from the line wire to the pin in this case seems to have been first over the entire insulator surface to the lower edge of the smaller petticoat and then partly up over the inner surface of this petticoat and partly from that surface through the air4 ,on each of these three pins the charring was quite as bad just below the thread as it was further down1 so that a large part of the leakage current seems to have gone up over the interior surface of the smaller petticoat4 ,the charred portion of these pins extended but little1 if at all1 into the threads near the tops or into the part of the pin fitting into the cross-arm4 ,the preservation of the part of each pin that entered the cross-arm seems to have been due to the increase of surface and decrease of resistance of the cross-arm in comparison with the pin4 ,preservation of the threaded part of each pin seems to have been due to its protection from moisture and its high resistance1 so that little or no current passed over it4 ,another pin taken from the same line as the three just considered was badly burned at a point about #a4ge inches below the threads1 but on sawing it completely across at two points below the charred spot the entire section was found to be perfectly sound and free from any sign of burning4 ,the explanation of the condition of this pin is1 perhaps1 that the resistance of the burned part1 owing to its additional protection and dryness1 was high compared with that of the lower part of the pin1 and thus developed most of the heat on the passage of current4 ,it is not clear1 however1 why this pin should burn only just below the thread1 while other pins of the same kind on the same line were charred all the way down from the thread to the cross-arm4 ,another curious result noticed in some pins on this same line is the softening of the threads so that they can be rubbed off with the fingers4 ,,relation ,,of ,,pins ,,and ,,insulators4 ---------------------------------------- -------------------------- ,voltage,diameter ,height ,length of ,pin ,location of ,line4 of of of ,covered by ,line4 ,insula- ,insula- ,insulator4 tor4 tor4 ---------------------------------------- -------------------------- ,inches4 ,inches4 ,inches4 ,electra to ,san ,francisco #fj1jjj #aa #aa-a_/d #ab ,colgate to ,oakland #fj1jjj #aa #aa-a_/d #h ,caon ,ferry to ,butte #ej1jjj #i #ab #aj-a_/b ,shawinigan ,falls to ,montreal #ej1jjj #aj #ac #aj-a_/d ,santa ,ana ,river to ,los ,angeles #cc1jjj #f-c_/d #d-g_/h #b-a_/b ,provo around ,utah ,lake #dj1jjj #g #e-c_/d #d-c_/d ,spier ,falls to ,schenectady #cj1jjj #h-a_/b #f-c_/d #e-a_/d ,niagara ,falls to ,buffalo #bb1jjj #g-a_/b #g #e ---------------------------------------- -------------------------- ,the softened wood of the threads is not charred1 but is said to have a sour taste and to resemble digested wood pulp4 ,while the threads of a wooden pin are destroyed in this way the remainder of the pin may still remain perfect and show no charring4 ,,relations ,,of ,,pins ,,and ,,insulators4 ---------------------------------------- --------------------- ,length of ,distance ,distance ,pin from ,outerfrom ,lowest ,location of ,line4 ,between ,petticoat ,petticoat ,insula- to ,pin to ,pin tor and ,through ,through ,cross-arm4 ,air4 ,air4 ---------------------------------------- --------------------- ,inches4 ,inches4 ,inches4 ,electra to ,san ,francisco #j #aj-a_/b #c-a_/b ,colgate to ,oakland #c-a_/b #aj #b-a_/b ,caon ,ferry to ,butte #a-a_/b #j #a-a_/b ,shawinigan ,falls to ,montreal #c-a_/d #i-a_/b #a ,santa ,ana ,river to ,los ,angeles #c-a_/b #b-c_/d 44 ,provo around ,utah ,lake #c-a_/b #b-a_/b 44 ,spier ,falls to ,schenectady #d #d #e_/h ,niagara ,falls to ,buffalo #c #d-a_/b #b ---------------------------------------- --------------------- ,in explanation of this disintegration of the threads of wooden pins it was stated that a number of these pins1 the tops of which were reduced to a white powder1 had been taken from the line between ,niagara ,falls and ,buffalo1 on which the voltage is #bb1jjj1 and that this powder proved on analysis to be a nitrate salt4 ,this salt was thought to be the result of the action of nitric acid on the wood1 it being supposed that the acid was formed by a static discharge acting on the oxygen and nitrogen of the air between the threads of the insulator and pin4 ,in support of this view it was stated that an experimental line of galvanized-iron wire at ,niagara ,falls1 which was operated at #ge1jjj volts continuously during nearly four months1 turned black over its entire length of about two miles4 ,this surface disintegration was not due to the normal action of the air1 for similar wire at the same place remained bright when not used as an electrical conductor4 ,these facts seemed to indicate that the brush discharge from the wires carrying the #ge1jjj-volt current developed nitric acid from the oxygen and nitrogen of the air1 and that this acid attacked the wire4 ,one of the above-mentioned pins used on the ,electra line was much charred and burned away at a point a little below the threads4 ,the charred path of the current could also be traced down the side of the pin to the cross-arm1 but this path was not as badly burned as the spot near the top of the pin4 ,a composite pin from a #cc1jjj-volt line1 probably a part of the transmission system between the ,santa ,ana ,river and ,los ,angeles1 was burned through its wooden threads to the central iron bolt1 along a narrow strip at one side4 ,every pin burned on this line was said to show the effects of the current in the way just described1 but no cross-arms were burned and very few insulators punctured4 ,the composite pin was made up of a central iron bolt #aj-e_/h inches long1 #a_/b-;inch in diameter1 and with a thin head above the wooden threads1 a sleeve of wood #b-e_/h inches long and #a inch in diameter in its threaded portion1 and a sleeve of porcelain #c-a_/h inches long and #a-a_/d inches in diameter at its upper and #b-aa_/af inches at its lower end4 ,the sleeves of wood and porcelain were slipped over the central iron bolt so that the portions of the pin above the cross-arm measured #e-g_/h inches4 ,in this case the path of the leakage current seems to have been over both the exterior and interior surface of the insulator and then through the wooden sleeve to the central bolt and the cross-arm4 ,the facts just outlined certainly indicate a serious menace to the permanence and reliability of long1 high-voltage transmission lines supported by insulators on wooden pins4 ,if such results have been encountered on the lines above named1 where some of the largest and best designs of insulators are employed1 it is only fair to assume that similar destructive effects of leakage currents are taking place on many other lines that operate at high voltages4 ,it seems at least doubtful whether any enlargement or improvement of the insulators themselves will entirely avoid the destruction of their wooden pins in one of the ways mentioned4 ,it is probable1 but not certain1 that further extension of distances through air and over insulator surfaces1 both exterior and interior1 between line wires and wooden pins1 will prevent charring and burning of the latter by leakage currents4 ,much has already been done in the way of covering most of the pin above its cross-arm with the insulator parts1 but even those portions of the pin that are best protected in this way are not free from burning4 ,thus1 on the ,colgate line1 eight inches of each pin is protected by the interior surface of its insulator1 but these pins were charred quite as badly where best protected1 up close to the thread1 as they were down near the cross-arm4 ,the same is true of the ,electra line1 where a porcelain sleeve runs up about the pin from the cross-arm to a point above the inner petticoat of each insulator1 so that the entire length of the pin above the cross-arm is protected4 ,on the ,caon ,ferry line1 a glass sleeve that virtually forms a part of each insulator1 though mechanically separate from it1 protects the pin from its threaded portion to within #a4e inches of the cross-arm4 ,insulators on the line from ,shawinigan ,falls to ,montreal are each #ac inches long and extend down over the pin to within #a4e inches of the cross-arm4 ,the burned portion of each pin from the ,santa ,ana line was that carrying the threads1 and thus in actual contact with that part of the insulator which was separated by the greatest surface distance from the line wire4 ,aside from the burning of pins is the destruction of their threaded parts by some chemical agency that is developed inside of the tops of the insulators1 as shown in the cases of the ,colgate and ,niagara lines4 ,it does not appear that any improvement of insulators will necessarily prevent chemical action4 ,though it may not be practicable to so increase the surface resistance of each insulator that the burning of wooden pins by leakage current will be prevented1 the substitution of a conducting for an insulating pin may remedy the trouble4 ,as the insulators1 pins1 and cross-arm form a path for the leakage current from wire to wire1 the wooden pins by their resistance1 especially when dry1 must develop heat4 ,in pins of steel or iron this heat would be trifling and would do no damage4 ,with pins of good conducting material1 like iron1 the amount of leakage from wire to wire1 with a given design of insulator1 would1 no doubt1 be somewhat greater than the leakage with wooden pins4 ,it will be cheaper1 however1 to increase the resistance of new insulators up to the combined resistance of present insulators and their wooden pins than it will be to replace these pins when they are burned4 ,from all the evidence at hand1 it seems that insulators which reduce the leakage of current over their surfaces to permissible limits as far as mere loss of energy is concerned1 even with iron pins1 will not prevent the charring and destruction of wooden pins4 ,illustration3 ,,fig4 #ij4--;,glass ,insulator and ,sleeve on #ej1jjj-volt ,line ,between ,caon ,ferry and ,butte1 ,mont4 ,when any suitable insulator is dry and clean it offers all necessary resistance to the leakage of current over its surface1 and any resistance in the pin that carries the insulator is of small importance4 ,if the resistance of an insulator needs to be reinforced by that of its pin in any case1 it is when the surface of the insulator is wet or dirty4 ,unfortunately1 however1 the same weather conditions that deposit dirt or moisture on an insulator make similar deposits on its pin1 and the resistance of the pin is lowered much more than that of the insulator by such deposits4 ,the increase of current leakage over the surface of an insulator during rains and fogs usually does no damage to the insulator itself1 but such leakage over the wet pin soon develops a surface layer of carbon that continues to act as a good conductor after the moisture that temporarily lowered the resistance has gone4 ,reasons like these have led some engineers to prefer iron pins with insulators that offer all of the resistance necessary for the voltage employed on the line4 ,it may be suggested that the use of iron pins will transfer the charring and burning to the wooden cross-arms1 but this does not seem to be a necessary result4 ,the comparative freedom of cross-arms from charring and burning where wooden pins are used seems to be due to the larger surface and lower resistance of the cross-arms4 ,with iron pins having a shank of small diameter1 so that the area of contact surface between the pin and the wooden cross-arm is relatively small1 there may be some charring of the wood at this contact surface4 ,should it be thought desirable to guard against any trouble of this sort1 the surface of the iron pin in contact with the cross-arm may be made ample by the use of large washers1 or by giving each pin a greater diameter at the shank than elsewhere4 ,it may be noted that the pins with a central iron bolt only half an inch in diameter1 that were used on the #cc1jjj-volt ,santa ,ana line1 were said to have caused no burning of their cross-arms in those cases in which the wooden threads about the top of the central bolt were burned through4 ,another possible trouble with iron pins is that they1 by their greater rate of expansion than glass or porcelain1 will break their insulators4 ,such results can readily be avoided by cementing each iron pin into its insulator1 instead of screwing the insulator onto the pin4 ,iron pins will1 no doubt1 cost somewhat more than those of wood1 but this cost will in any event be only a small percentage of the total investment in a transmission line4 ,considering the cost of the renewals of wooden pins1 there seems little doubt that on a line where the voltage and other conditions are such as to result in frequent burning1 iron pins would be cheaper in the end4 ,iron pins have already been adopted on a number of high-voltage lines4 ,not only iron pins1 but even iron cross-arms and iron poles are in use on a number of transmission lines4 ,on a long line now under construction in ,mexico1 iron towers1 placed as much as #djj feet apart1 are used instead of wooden poles1 and both the pins and cross-arms are also of iron4 ,the #ge-mile line from ,niagara ,falls to ,toronto is carried entirely on steel towers4 ,the ,vancouver ,power ,company1 ,vancouver1 ,british ,columbia1 use a pin that consists of a steel bolt about #ab inches long fitted with a sleeve of cast iron #d-a_/b inches long to enter the cross-arm1 and a lead thread to screw into the insulator4 ,on the #aaa-mile line of the ,washington ,power ,company1 of ,spokane1 which was designed to operate at #fj1jjj volts and runs to the ,standard and ,hecla mines1 a pin consisting of a steel bar #a-a_/h inches in diameter1 with a cast-iron shank #b-a_/af inches in diameter to enter the cross-arm1 and with the lead threads for the insulator1 is used4 ,illustration3 ,,fig4 #ib4--;,iron ,pins on ,spier ,falls ,line4 ,on the network of transmission lines between ,spier ,falls1 ,schenectady1 ,albany1 and ,troy1 in the ,state of ,new ,york1 the insulators are supported on iron pins of two types4 ,one of these pins1 used at corners and where the strain on the wire line is exceptionally heavy1 is made up of a wrought-iron bolt #c_/d-;inch in diameter and #af-a_/b inches long over the head1 and of a malleable iron casting #h-c_/d inches long4 ,this casting has a flange of #e by #c-c_/d inches at its lower end that rests on the top of the cross-arm1 and the bolt passes from the top of the casting down through it and the cross-arm4 ,threads are cut on the lower end of the bolt1 and a nut and washer secure it in the cross-arm4 ,the total height of this pin above the cross-arm is #i-a_/d inches4 ,for straight work on this line a pin with stem entirely of malleable iron1 and a bolt that comes up through the cross-arm and enters the base of the casting1 is used4 ,the cast top of this pin has four vertical webs1 and its rectangular base1 which rests on the top of the cross-arm1 is #c-a_/b by #d inches4 ,the bolt that comes up through the cross-arm and taps into the base of the casting is #c_/d-;inch in diameter4 ,the cast part of this pin has such a length that the top of its insulator is carried #aj-c_/d inches above the cross-arm4 ,for the casting the length is #i-a_/d inches4 ,both of the types of iron pins in use on the ,spier ,falls lines are secured to their insulators with ,portland cement poured into the pin hole while liquid when the insulator is upside down and the pin is held centrally in its hole4 ,the top of each casting is smaller in diameter than the hole in the insulator1 and is grooved so as to hold the cement4 ,illustration3 ,,fig4 #ic4--,standard ,pin1 ,toronto and ,niagara ,line4 ,on a long line designed for #fj1jjj volts1 and recently completed in ,california1 wooden pins are used with porcelain insulators1 each #ad inches in diameter and #ab-a_/b inches high4 ,each of these pins is entirely covered with sheet zinc from the cross-arm to the threaded end1 and it is expected that this metal covering will protect the wood of the pin from injury by the leakage current4 ,,chapter ,,xxi4 ,,insulators ,,for ,,transmission ,,lines4 ,line insulators1 pins1 and cross-arms all go to make up paths of more or less conductivity between the wires of a transmission circuit4 ,the amount of current flowing along these paths from one conductor to another in any case will depend on the combined resistance of the insulators1 pins1 and cross-arm at each pole4 ,as a general rule1 the wires of high-voltage transmission circuits are used bare because continuous coverings would add materially to the cost with only a trifling increase in effective insulation against high voltages4 ,in some instances the wires of high-pressure transmission lines have individual coverings for short distances where they enter cities1 but often this is not the case4 ,at ,manchester1 ,n4 ,h41 bare conductors from water-power plants enter the sub-station1 well within the city limits1 at #ab1jjj volts4 ,from the water-power at ,chambly the bare #be1jjj-volt circuits1 after crossing the ,st4 ,lawrence ,river over the great ,victoria bridge1 pass overhead to a terminal-house near the water-front in ,montreal4 ,in order to reach the ,general ,electric ,works1 the #cj1jjj-volt circuits from ,spier ,falls enter the city limits of ,schenectady1 ,n4 ,y41 with bare overhead conductors4 ,where transmission lines pass over a territory exposed to corrosive gases1 it is sometimes desirable to give each wire a weather-proof covering4 ,an instance of this sort occurs near ,niagara ,falls where the aluminum conductors forming one of the circuits to ,buffalo are covered with a braid that is saturated with asphaltum for some distance4 ,each path1 formed by the surface of the insulators of a line and the pins and cross-arm by which they are supported1 not only wastes the energy represented by the leakage current passing over it1 but may lead to the charring and burning of the pins and cross-arm by this current4 ,to prevent such burning1 the main reliance is to be placed in the surface resistance of the insulators rather than that of pins and cross-arms4 ,these insulators should be made of glass or porcelain1 and should be used dry--that is1 without oil4 ,in some of the early transmission lines1 insulators were used on which the lower edges were turned inward and upward so that a circular trough was formed beneath the body of the insulator1 and this trough was filled with heavy petroleum4 ,it was found1 however1 that this trough of oil served to collect dirt and thus tended to lower the insulation between wire and cross-arm1 so that the practice was soon abandoned4 ,glass and porcelain insulators are rivals for use on high-tension lines1 and each has advantages of its own4 ,porcelain insulators are much stronger mechanically than are those of glass1 and are not liable to crack because of unequal internal expansion1 a result sometimes met with where glass insulators are exposed to a hot morning sun4 ,in favor of glass insulators it may be said that their insulating properties are quite uniform1 and that1 unlike porcelain1 their internal defects are often apparent on inspection4 ,in order to avoid internal defects in large porcelain insulators1 it has been found necessary to manufacture some designs in several parts and then cement the parts of each insulator together4 ,defective insulators may be divided into two classes--those that the line voltage will puncture and break and those that permit an excessive amount of current to pass over their surfaces to the pins and cross-arms4 ,where an insulator is punctured and broken1 the pin1 cross-arm1 and pole to which it is attached are liable to be burned up4 ,if the leakage of current over the surface of an insulator is large1 not only may the loss of energy on the line where the insulator is used be serious1 but this energy follows the pins and cross-arm in its path from wire to wire1 and gradually chars the former1 or both1 so that they are ultimately set on fire or break through lack of mechanical strength4 ,the discharge over the surface of an insulator may be so large in amount as to have a disruptive character1 and thus to be readily visible4 ,more frequently this surface leakage of current over insulators is of the invisible and silent sort that nevertheless may be sufficient in amount to char1 weaken1 and even ultimately set fire to pins and cross-arms4 ,all insulators1 whether made of glass or porcelain1 should be tested electrically to determine their ability to resist puncture1 and to hold back the surface leakage of current1 before they are put into practical use on high-tension lines4 ,experience has shown that inspection alone cannot be depended on to detect defective glass insulators4 ,electrical testing of insulators serves well to determine the voltage to which they may be subjected in practical service with little danger of puncture by the disruptive passage of current through their substance4 ,it is also possible to determine the voltage that will cause a disruptive discharge of current over the surface of an insulator1 when the outer part of this surface is either wet or dry4 ,this is as far as electrical tests are usually carried1 but it seems desirable that such tests should also determine the amount of silent1 invisible leakage over the surface of insulators both when they are wet and when they are dry1 at the voltage which their circuits are intended to carry4 ,such a test of silent leakage is important because this sort of leakage chars and weakens insulator pins1 and sets fire to them and cross-arms1 besides representing a waste of energy4 ,the voltage employed to test insulators should vary in amount according to the purpose for which any particular test is made4 ,glass and porcelain1 like many other solid insulators1 will withstand a voltage during a few minutes that will cause a puncture if continued indefinitely4 ,in this respect these insulators are unlike air1 which allows a disruptive discharge at once when the voltage to which it is exposed reaches an amount that the air cannot permanently withstand4 ,because of this property of glass and porcelain insulators1 it is necessary in making a puncture test to employ a voltage much higher than that to which they are to be permanently exposed4 ,in good practice it is thought desirable to test insulators for puncture with at least twice the voltage of the circuits which they will be required to permanently support on transmission lines4 ,for the first transmission line from ,niagara ,falls to ,buffalo1 which was designed to operate at #aa1jjj volts1 the porcelain insulators were tested for puncture with a voltage of #dj1jjj1 or nearly four times that of the circuits they were to support4 ,porcelain insulators for the second line between ,niagara ,falls and ,buffalo1 after the voltage of transmission had been raised to #bb1jjj1 were given a puncture test at #fj1jjj volts4 ,of these insulators tested at #fj1jjj volts only about three per cent proved to be defective4 ,these puncture tests were carried out by placing each insulator upside down in an open pan containing salt water to a depth of two inches1 partly filling the pin hole of the insulator with salt water1 and then connecting one terminal of the testing circuit with a rod of metal in the pin hole1 and the other terminal with the pan4 ,alternating current was employed in these tests1 as is usually the case 7,volume xviii41 ,transactions ,a4 ,i4 ,e4 ,e41 pp4 #ead to #ebj74 ,for the transmission lines between ,spier ,falls1 ,schenectady1 ,albany1 and ,troy1 where the voltage is #cj1jjj1 the insulators were required to withstand a puncturing test with #ge1jjj volts for a period of five minutes after they had been soaked in water for twenty-four hours4 ,there is some difference of opinion as to the proper duration of a puncturing test1 the practice in some cases being to continue the test for only one minute on each insulator1 while in other cases the time runs up to five minutes or more4 ,as a rule1 the higher the testing voltage compared with that under which the insulators will be regularly used1 the shorter should be the period of test4 ,instead of being tested in salt water as above described1 an insulator may be screwed onto an iron pin of a size that fits its threads1 and then one side of the testing circuit put in contact with the pin and the other side connected with the wire groove of the insulator4 ,care should be taken where an iron pin is used either in testing or for regular line work1 that the pin is not screwed hard up against the top of the insulator1 as this tends to crack off the top1 especially when the pin and insulator are raised in temperature4 ,iron expands at a much higher rate than glass or porcelain1 and it is desirable to cement iron pins into insulators rather than to screw them in4 ,there seems to be some reason to think that an insulator will puncture more readily when it is exposed to severe mechanical stress by the expansion of the iron pin on which it is mounted4 ,tests of insulators are usually made with alternating current1 and the form of the voltage curve is important1 especially where the test is made to determine what voltage will arc over the surface of the insulator from the line wire to the pin4 ,the square root of the mean square for two curves of alternating voltage or mean effective voltage1 as read by a voltmeter1 may be the same though the maximum voltages of the two curves differ widely4 ,in tests for the puncture of insulators1 the average alternating voltage applied is more important than the maximum voltage shown by the highest points of the pressure curve1 because of the influence of the time element with glass and porcelain4 ,on the other hand1 when the test is to determine the voltage at which current will arc over the insulator surface from the line wire to the pin1 the maximum value of the pressure curve should be taken into consideration because air has no time element1 but permits a disruptive discharge under a merely instantaneous voltage4 ,alternators used in transmission systems usually conform approximately to a sine curve in the instantaneous values of the pressures they develop1 and it is therefore desirable that tests on line insulators be made with voltages whose values follow the sine curve4 ,either a single transformer or several transformers in series may be employed to step up to the required voltage1 but a single transformer will usually give better regulation and greater accuracy4 ,an air-gap between needle points is not a very satisfactory means by which to determine the average voltage on a testing circuit1 because1 as already pointed out1 the sparking distance between the needle points depends mainly on the maximum instantaneous values of the voltage1 which may vary with the load on the generator1 and the saturation of its magnets4 ,for accurate results a step-down voltmeter transformer should be used on the testing circuit4 ,an insulator that resists a puncture test may fail badly when subjected to a test as to the voltage that will arc over its surface from line wire to pin4 ,this arc-over test should be made with the outer surface of the insulator both wet and dry4 ,for the purpose of this test the insulator should be screwed onto an iron pin1 or onto a wooden pin that has been covered with tinfoil4 ,one wire of the testing circuit should then be secured in the groove of the insulator1 and the other wire should be connected to the iron or tin foil of the pin4 ,the voltage that will arc over the surface of an insulator from the line wire to the pin depends on the conditions of that surface and of the air4 ,in light air1 such as is found at great elevations1 an arc will jump a greater distance than in dry air near the sea-level4 ,a fog increases the distance that a given voltage will jump between a line wire and its insulator pin1 and a heavy rain lengthens the distance still further4 ,the heavier the downpour of rain the greater is the distance over the outside surface of an insulator that a given voltage will arc over4 ,the angle at which the falling water strikes the insulator surface also has an influence on the voltage required to arc over that surface1 a deviation from a downpour perpendicular to the plane of the lower edge of the petticoat of the insulator seeming to increase the arcing distance for a given voltage4 ,an insulator should be given an arc-over test under conditions that are approximately the most severe to be met in practice4 ,these conditions can perhaps be fairly represented by a downpour of water that amounts to a depth of one inch in five minutes for each square inch of the plane included by the edge of the largest petticoat of the insulator1 when the direction of the falling water makes an angle of forty-five degrees with that plane4 ,a precipitation of one inch in depth on a horizontal plane during five minutes seems to be a little greater than any recorded by the ,united ,states ,weather ,bureau4 ,under the severe conditions just named1 the voltage required to arc over the insulator surface from line wire to pin should be somewhat greater at least than the normal voltage of the circuit where the insulator is to be used4 ,for the transmission line between ,spier ,falls and ,schenectady1 on which the maximum voltage is #cj1jjj1 the insulators were required to stand a test of #db1jjj volts when wet1 without arcing over from line wire to pin4 ,in these wet tests the water should be sprayed evenly onto the insulator surface like rain1 and the quantity of water that strikes the insulator in a given time should be measured4 ,when the outside of an insulator is wet with rain1 it is evident that most of the resistance between the line wire and the insulator pin must be offered by the inside surface of the petticoat of the insulator4 ,for this reason an insulator that is to withstand a very high voltage so that no arc will be formed over its wet outside surface must have a wide1 dry surface under its petticoat4 ,in some tests of line insulators reported in ,volume xxi41 ,transactions ,a4 ,i4 ,e4 ,e41 p4 #cad1 the results show that the voltage required to arc over from line wire to pin depends on the shortest distance between them1 rather than on the distance over the insulator surface4 ,three insulators1 numbered #d1 #e1 and #g in the trial1 were in each case tested by a gradual increase of voltage until a discharge took place between the wire and pin4 ,the pins were coated with tinfoil1 and the testing voltage was applied to the tie wire on each insulator and to the tinfoil of its pin4 ,insulators #d1 #e1 and #g permitted arcs from wire to pin when exposed to #gc1hjj1 #gd1gjj1 and #gd1gjj volts respectively1 the surfaces of all being dry and clean4 ,the shortest distances between wires and pins over insulator surface and through air were #f-e_/h1 #f-a_/d1 and #g-g_/h inches respectively for the three insulators1 so that the arcing voltages amounted to #aa1adj1 #aa1ieb1 and #i1dgi per inch of these distances4 ,measured along their surfaces1 the distances between wires and pins on these three insulators were #h1 #aa-a_/d1 and #ae-a_/b inches respectively1 so that the three arcing voltages1 which were nearly equal1 amounted to #i1bbe1 #f1fdj1 and #d1hai per inch of these distances4 ,these figures make it plain that the arcing voltage for each insulator depends on the shortest distance over its surface and through the air1 from wire to pin4 ,it might be expected that the voltage in any case would arc equal distances over clean1 dry insulator surface or through the air1 and the experiments just named indicate that this view is approximately correct4 ,the sparking distance through air between needle points1 which is greater than that between smooth surfaces1 is #e4he inches with #gj1jjj volts1 and #g4a inches with #hj1jjj volts according to the report in ,volume xix41 ,a4 ,i4 ,e4 ,e41 p4 #gba4 ,comparing these distances with the shortest distances between wires and pins in the tests of insulators numbered #d1 #e1 and #g1 which broke down at #gc1hjj to #gd1gjj volts when dry1 it seems that a given voltage will arc somewhat further over clean1 dry insulator surface than it will through air4 ,this view finds support from the fact that only a part of each of the shortest distances between wire and pin was over insulator surface1 the remainder being through air alone4 ,the fact that the dry part of the surface of an insulator and the air between its lower wet edge and the pin or cross-arm offer most of the resistance between the line wire and the pin and cross-arm is plainly brought out by the results of the tests above mentioned1 in the cases of insulators numbered #d and #g4 ,while #gc1hjj volts were required to arc from line-wire to pin when the entire insulator was dry and clean1 the arc was formed at only #ec1djj volts during a moderate rain-storm1 in the case of ,no4 #d insulator4 ,with insulator ,no4 #g the arcing voltage was #gd1gjj when the entire surface was clean and dry1 but the arc from wire to pin was started at #eb1hjj volts during a moderate rain4 ,no4 #e insulator seems to present an erratic result1 for when dry and clean the arc jumped from wire to pin at #gd1gjj volts1 and yet during a moderate rain no arc was formed until a voltage of #gj1djj was reached4 ,for each of the seven insulators on which tests are reported as above1 the voltage required to arc from line wire to pin was nearly or quite as great during a dry snow-storm as when the insulator surface was clean and dry4 ,when the insulators were covered with wet snow their surface insulation broke down at voltages that were within ten per cent above or below the arcing voltages during a moderate rain in five cases4 ,with two insulators the arcing voltages1 when they were covered with wet snow1 were only about sixty per cent of the voltages necessary to break down the surface insulation between wire and pin during a moderate rain4 ,when the outside surface of an insulator is wet1 as during a moderate rain1 it seems that the under surface of the insulator1 and the distance through air from the lower wet edge of the insulator to the pin or cross-arm1 make up most of the insulation that prevents arcing over from the wire to the pin or cross-arm4 ,it further appears that it is useless to extend the distance across the dry under surface of the insulator indefinitely without a corresponding increase of the direct distance through air from the lower wet edge of the insulator to the wood of cross-arm or pin4 ,insulator ,no4 #g in the tests under consideration had a diameter at the lower edge of its outer petticoat of seven inches1 and was mounted on a standard wooden pin4 ,the diameter of this pin in the plane of the lower edge of the insulator was probably about #a-a_/d inches1 so that the radial distance through air from this edge to the pin must have been #b-g_/h inches approximately4 ,during a moderate rain the surface insulation of this insulator broke down and an arc was formed from wire to pin with #eb1hjj volts4 ,the sparking distance between needle points at #ej1jjj volts is #c4ee inches1 according to ,volume xix41 ,a4 ,i4 ,e4 ,e41 p4 #gba1 and must be shorter between smooth surfaces1 such as the wire and pin in question1 so that nearly all of the #eb1hjj volts in this case must have been required to jump the #b-g_/h inches of air1 leaving very little to overcome the slight resistance of the wet outside surface of the insulator4 ,on this insulator the surface distance from wire to pin was #ae-a_/b inches1 while the shortest breaking distance was only #g-g_/h inches1 so that the distance across the dry under surface of the insulator must have been #ae-a_/b - 7#g-g_/h - #b-g_/h7 #aj-a_/b inches approximately4 ,it is evidently futile to put a path #aj-a_/b inches long across dry insulator surface in parallel with a path only #b-g_/h inches long in air1 as an arc will certainly jump this shorter path long before one will be formed over the longer4 ,the same line of reasoning applies to ,no4 #c insulator in this test1 which had a diameter of #f-c_/d inches1 a surface distance from wire to pin of #ac inches1 and a minimum distance of #g-a_/d inches1 and whose surface insulation broke down at #dh1fjj volts during a moderate rain4 ,the necessity of increasing the distance between the lower wet edges of insulators and the pins and cross-arm1 as well as the distance across the dry under surfaces of insulators1 led to the adoption of the so-called umbrella type for some high-voltage lines4 ,in this type of insulator the main or outer petticoat is given a relatively great diameter1 and instead of being bell-shaped is only moderately concave on its under side4 ,with an insulator of this type mounted on a large1 long pin1 the lower edge of the umbrella-like petticoat may be far removed from the pin and cross-arm4 ,beneath the large petticoat of such insulators for high voltages there are usually one or more smaller petticoats or sleeves that run down the pin1 and increase the distance between it and the lower edge of the largest petticoat4 ,,insulators ,,on ,,transmission ,,lines4 ---------------------------------------- ------------------------- ,material ,inches ,inches ,voltage of ,diameter,height ,location of ,line4 of ,insula- of of ,line4 tor4 ,insula- ,insula- tor4 tor4 ---------------------------------------- ------------------------- ,electra to ,san ,francisco #fj1jjj,porcelain #aa #aa-a_/d ,colgate to ,oakland #fj1jjj,porcelain #aa #aa-a_/d ,caon ,ferry to ,butte #ej1jjj;,glass #i #ab ,shawinigan ,falls to ,montreal #ej1jjj,porcelain #aj #ac-a_/b ,provo around ,utah ,lake #dj1jjj;,glass #g #e-c_/d ,santa ,ana ,river to ,los ,angeles #cc1jjj,porcelain #f-c_/d #d-g_/h ,spier ,falls to ,schenectady #cj1jjj,porcelain #h-a_/b #f-c_/d ,apple ,river ,falls to ,st ,paul #be1jjj;,glass #g #e-c_/d ,chambly to ,montreal #be1jjj,porcelain #e-a_/b #f-a_/b ,niagara ,falls to ,buffalo #bb1jjj,porcelain #g-a_/b #g ,portsmouth to ,pelham1 ,n4 ,h4 #ac1jjj,porcelain #e-a_/d #c-c_/d ,garvins ,falls to ,manchester1 ,n4 ,h4 #ab1jjj;,glass #e #d-c_/d ---------------------------------------- ------------------------- ,the inner petticoat or sleeve that runs down over the pin and sometimes reaches nearly to the cross-arm1 of course becomes wet on its outside surface and at its lower edge during a rain2 but between this lower wet part of the inner petticoat1 or sleeve1 and the lower wet edge of the larger outside petticoat1 there is a wide1 dry strip of insulator surface4 ,a result is that an arc over the surface of the outside petticoat can reach the wet edge of the sleeve only by crossing the strip of dry under surface or jumping through the air4 ,the same type of insulator is used on the #fj1jjj-volt lines between ,electra and ,san ,francisco and between ,colgate and ,oakland1 each insulator having an outer petticoat #aa inches in diameter and one inner petticoat or sleeve #f-a_/b inches in diameter4 ,this inner petticoat runs down the pin for a distance of #g-a_/b inches below the outer petticoat4 ,slightly different pins are used for mounting the insulators on the two transmission lines just named1 so that on the former the distance through air from the lower edge of the outer petticoat to the cross-arm is #aa inches1 and on the latter the corresponding distance is #aa-a_/b inches4 ,on the ,electra line the lower edge of the inner petticoat of each insulator is about #c-a_/b inches1 and on the ,colgate line about #d inches above the cross-arm4 ,,insulators ,,on ,,transmission ,,lines4 ---------------------------------------- --------------------------- ,inches ,inches ,inches ,inches from from from from ,top of ,outside ,lowest ,edge of ,location of ,line4 ,insulator,petticoat,petticoat ,outside to to to to ,edge ,cross- ,cross- ,cross- of ,lowest arm4 arm4 arm4 ,petticoat4 ---------------------------------------- --------------------------- ,electra to ,san ,francisco #ad-a_/b #aa #c-a_/b #g-a_/b ,colgate to ,oakland #ae #aa-a_/b #d #g-a_/b ,caon ,ferry to ,butte #ac-a_/b #g-c_/d #a-a_/b #f-a_/d ,shawinigan ,falls to ,montreal #af-a_/d #aa-c_/d #c-a_/d #h-a_/b ,santa ,ana ,river to ,los ,angeles #h-e_/h #c-c_/d #c-c_/d #j ,spier ,falls to ,schenectady #aj-c_/d #g-c_/h #d-a_/d #c-c_/h ,niagara ,falls to ,buffalo #aj #e-a_/b #c #b-a_/b ,chambly to ,montreal #h-a_/b #d-a_/b #b #b-a_/b ---------------------------------------- --------------------------- ,on each of the lines named in this table the wires are strung on the tops of their insulators4 ,the ,caon ,ferry line is carried on insulators each of which has three short petticoats and a long separate sleeve that runs down over the pin to within #a-a_/b inches of the cross-arm4 ,this sleeve makes contact with its insulator near the pin hole4 ,the outside petticoat of each insulator on this line is #g-c_/d inches above the cross-arm and #f-a_/d inches above the lower end of the sleeve4 ,both the main insulator and the sleeve1 in this case1 are of glass4 ,white porcelain insulators are used to support the #ej1jjj-volt ,shawinigan line1 and are of a recent design4 ,each of these insulators has three petticoats ranged about a central stem so that their lower edges are #d-a_/b inches1 #i inches1 and #ac inches respectively1 below the top4 ,the highest petticoat is #aj inches1 the intermediate #i-c_/d inches1 and the lowest #d-a_/d inches in diameter4 ,the height of this insulator is #ac inches1 compared with #aa-a_/d inches for those used on the ,electra and ,colgate lines and #ab inches for the combined insulator and sleeve used on the ,caon ,ferry line4 ,when mounted on its pin1 this insulator on the ,shawinigan line holds its wire #af-a_/d inches above the cross-arm1 compared with a corresponding distance of #ad-a_/b inches on the ,electra1 #ae inches on the ,colgate1 and #ac-a_/b inches on the ,caon ,ferry line4 ,the two upper petticoats on each of these insulators are much less concave than the lowest one1 and the edges of all three stand respectively #aa-c_/d1 #g-a_/d1 and #c-a_/d inches above the cross-arm4 ,from the edge of the top to the edge of the bottom petticoat the direct distance is #h-a_/b inches4 ,of the three transmission lines above named that operate at #ej1jjj to #fj1jjj volts1 that between ,shawinigan ,falls and ,montreal leads as to distances between the line wire and insulator petticoats and the cross-arm4 ,on the ,santa ,ana line1 where the voltage is #cc1jjj1 the insulator is of a more ordinary type1 being of porcelain1 #f-c_/d inches in diameter1 #d-g_/h inches high1 and having the lower edges of its three petticoats in the same plane4 ,each of these insulators holds its wire #h-e_/h inches above the cross-arm1 and has all of its petticoats #c-a_/b inches above the cross-arm4 ,unlike the three insulators just described1 which are mounted on wooden pins1 this ,santa ,ana insulator has a pin with an iron core1 wooden threads1 and porcelain base4 ,this base extends up from the cross-arm a distance of #c-a_/h inches1 and the wooden sleeve1 in which the threads for the insulator are cut1 runs down over the central bolt of the pin to the top of the porcelain base1 which is #e_/h-;inch below the petticoats4 ,the #cj1jjj-volt lines from ,spier ,falls are carried #aj-c_/d inches above their cross-arms by triple petticoat porcelain insulators4 ,each of these insulators is #h-a_/b inches in diameter1 #f-c_/d inches high1 and is built up of three parts cemented together4 ,a malleable-iron pin cemented into each insulator with pure ,portland cement carries the outside petticoat #g-a_/b inches and its lowest petticoat #d-a_/d inches above the cross-arm4 ,when the voltage on the ,spier ,falls lines was raised from about #ac1jjj to #cj1jjj1 the circuits being carried in part by one-piece porcelain insulators1 a number of these insulators were punctured at the higher pressures1 and some cross-arms and poles were burned as a result4 ,no failures resulted on those parts of these lines where the three-part insulators were in use4 ,the second pole line between ,niagara ,falls and ,buffalo was designed to carry circuits at #bb1jjj volts1 or twice that for which the first line was built4 ,porcelain insulators were employed on both of these lines1 but while the #aa1jjj-volt line was carried on three-petticoat insulators1 each with a diameter of #g inches and a height of #e-a_/b inches1 the #bb1jjj-volt line was mounted on insulators each #g-a_/b inches in diameter and #g inches high1 with only two petticoats4 ,the older insulator has its petticoats #b inches above the cross-arm1 and the lower petticoat of the new insulator is #c inches above the arm4 ,these two insulators illustrate the tendency to lengthen out along the insulator axis as the voltage of the circuits to be carried increases4 ,illustration3 ,,fig4 #ic;,a4--,the ,old and ,new ,insulators on the ,niagara ,falls-,buffalo ,line4 ,for future work at still higher voltages1 the advantage as to both first cost and insulating qualities seems to lie with insulators that are very long in an axial direction1 and which have their petticoats arranged one below the other and all of about the same diameter1 rather than with insulators of the umbrella type1 like those on the ,electra and ,colgate lines4 ,,chapter ,,xxii4 ,,design ,,of ,,insulator ,,pins ,,for ,,transmission ,,lines4 ,bending strains due to the weights1 degree of tension1 and the directions of line wires1 plus those resulting from wind-pressure1 are the chief causes that lead to the mechanical failure of insulator pins4 ,considering the unbalanced component of these forces at right angles to the axis of the pin1 which alone produce bending1 each pin may be considered as a beam of circular cross section secured at one end and loaded at the other4 ,for this purpose the secured end of the beam is to be taken as the point where the pin enters its cross-arm1 and the loaded end of the beam is the point where the line wire is attached to the insulator4 ,the distance between these two points is the length of the beam4 ,the maximum strain in the outside fibres of a pin measured in pounds per square inch of its cross section1 represented by ,s1 may be found from the formula1 ,p ,x ,s ------- 4#jihb ,d where ,p is the pull of the wire in pounds1 ,d is the diameter of the pin at any point1 and ,x is the distance in inches of that point from the wire4 ,inspection of this formula shows that ,s1 the maximum strain at any point in the fibres of a pin1 when the pull of the line-wire1 ,p1 is constant1 increases directly with the distance1 ,x1 from the wire to the point where the strain1 ,s1 takes place4 ,this strain1 ,s1 with a constant pull of the line wire1 decreases as the cube of the diameter1 ,d1 at the point on the pin where ,s occurs increases4 ,that cross section of a pin just at the top of its hole in the cross-arm is thus subject to the greatest strain1 if the pin is of uniform diameter1 because this cross section is more distant from the line wire than any other that is exposed to the bending strain4 ,for this reason it is not necessary to give a pin a uniform diameter above its cross-arm1 and in practice it is always tapered toward its top4 ,notwithstanding this taper1 the weakest point in pins as usually made is just at the top of the cross-arm1 and it is at this cross section where pins usually break4 ,this break comes just below the shoulder that is turned on each pin to prevent its slipping down through the hole in its cross-arm4 ,if the shoulder on a pin made a tight fit all around down onto the cross-arm1 the strength of the pin to resist bending would be thereby increased1 but it is hard to be sure of making such fits1 and they should not be relied on to increase the strength of pins4 ,by giving a pin a suitable taper from its shoulder at the cross-arm to its top1 the strain per square inch1 ,s1 in the outside fibres of the pin may be made constant for every cross section throughout its length above the cross-arm1 whatever that length may be4 ,the formula above given may be used to determine the diameters of a pin at various cross sections that will make the maximum stress1 ,s1 at each of these cross sections constant4 ,by transposition the formula becomes ,p ,d ------- ,x4 4#jihb ,s ,where the pin is tapered so that ,s is constant for all cross sections1 then for any pull1 ,p1 of the line wire on the pin the quantity 7,p_/4#jihb ,s7 must be constant at every diameter1 ,d1 distant any number of inches1 ,x1 from the point where the wire is attached4 ,if the constant1 7,p_/4#jihb ,s7 is found for any one cross section of a pin1 therefore1 the diameter at each other cross section with the same maximum stress1 ,s1 may be readily found by substituting the value of this constant in the formula4 ,the so-called 8standard0 wooden pin that has been very generally used for ordinary distribution lines1 and to some extent even on high-voltage transmission lines1 has a diameter of nearly #a4e inches just below the shoulder4 ,the distance of the line wire above this shoulder varies between about #d4e and #f inches1 according to the type of insulator used1 and to whether the wire is tied at the side or top of the insulator4 ,if the line wire is tied to the insulator #e inches above the shoulder of one of the standard pins1 then ,x becomes #e1 and ,d becomes #a4e in the formula last given4 ,from that formula by transposition and substitution ,p ,d 7#a4e7 ------- --- ------ #j4fge4 4#jihb ,s ,x #e ,substituting #j4fge for the quantity 7,p_/#j4jihb ,s7 in the formula ,d 7,p_/#j4jihb ,s7 ,x gives the formula ,d #j4fge ,x1 from which the diameters at all cross sections of a tapered pin above its shoulder1 that will give it a strength just equal to that of a section of #a4e inches diameter and #e inches from the line wire1 may be found4 ,to use the formula for this purpose it is only necessary to substitute any desired values of ,x therein and then solve in each case for the corresponding values of ,d4 ,let it be required1 for instance1 to determine what diameter a pin should have at a cross section one inch below the line wire in order that the maximum strain at that cross section may equal the corresponding strain at a cross section five inches below the line wire and of #a4e inch diameter4 ,substituting one as the value of ,x1 the last-named formula becomes ,d #j4fge1 and from this1 ,d #j4hgg1 which shows that the diameter of the pin one inch below the line wire should be #j4hgg-;inch4 ,a similar calculation will show that if a pin is long enough so that a cross section above the cross-arm is #ab inches below the line wire1 the diameter of this cross section should be equal to the cube root of #j4fge #ab #h4a1 which is #b4jjh1 or practically two inches4 ,it should be observed that the calculations just made have nothing to do with the ability of a pin to resist any particular pull of its line wire4 ,these calculations simply show what diameters a pin should have at different distances below its line wire in order that the maximum stress at each of its cross sections may equal that at a cross section #e inches below the wire where the diameter is #a4e inches4 ,in ,vol4 xx41 ,a4 ,i4 ,e4 ,e41 pp4 #dae to #dai1 specifications are proposed for standard insulator pins based on calculations like those just made4 ,as a result of such calculations1 the following table for the corresponding values of ,x and ,d1 as used in the above formula1 are there presented1 each expressed in inches4 ---------- ,x ,d ---------- #a #j4hgg #b #a4ajf #c #a4bfc #d #a4cie #e #a4ejj #f #a4eib #g #a4fgh #h #a4ged #i #a4hbe #aj #a4hhh #aa #a4ie #ac #b4jf #ae #b4ag #ag #b4be #ai #b4cd #ba #b4db ---------- ,a pin twenty-one inches long between the line wire and the cross-arm will have a uniform strength to resist the pull of the wire if it has the diameter given in this table at the corresponding distances below the line wire4 ,from this it follows that a pin of any length between wire and cross-arm corresponding to ,x in the table will be equally strong to resist a pull of the line wire as a standard #a4e-;inch diameter pin with its wire five inches above the cross-arm4 ,in other words1 if a pin that is twenty-one inches long between the line wire and the cross-arm has the diameters given in the table at the corresponding distances below the wire1 then a pin of equal strength to resist bending1 and of any shorter length1 would correspond in the part above the cross-arm to an equal length cut from the top end of the longer pin4 ,designating that part of a pin that is above the cross-arm as the 8stem10 and that part in the cross-arm as the 8shank10 each pin in the specifications under consideration is named by the length of its stem1 as a #e-1 #g- or #aa-;inch pin4 ,it is proposed that each pin of whatever length be threaded for a distance of #b4e inches at the top of its stem with four threads per inch1 the sides of each thread being at an angle of ninety degrees with each other4 ,each thread is to cut into the pin about #c_/cb inch1 come to a sharp angle at the bottom1 and be about #a_/af inch wide on top4 ,at the end of the pin the proposed diameter over the thread is one inch in all cases1 and at the lower end of the threaded portion the outside diameter is #a4be inches4 ,near the end of the pin the diameter at the bottom of the thread is thus only #ac_/af inch1 and the corresponding diameter at the lower end of the threaded portion is about #a-a_/af inches on all pins4 ,each pin is to have a square shoulder to rest on the cross-arm1 and the diameter of this shoulder is to be #c_/h inch greater than the nominal diameter of the shank of the pin4 ,the proposed length of this shoulder on all pins is #a_/d inch before the taper begins4 ,the actual diameter of the shank of each pin just below its shoulder is to be #a_/cb inch less than the nominal diameter1 and the actual diameter of the lower end of each shank is to be #a_/af inch less than the nominal diameter4 ,with these explanations the proposed sizes of pins have dimensions as follows in inches3 ----------------------------- ,nominal ,length of,length of,diameter of ,stem4 ,shank4 ,shank4 ----------------------------- #e #d-a_/d #a-a_/b #g #d-a_/d #a-c_/d #i #d-a_/d #a-g_/h #aa #d-c_/d #b #ac #d-c_/d #b-a_/h #ae #d-c_/d #b-a_/d #ag #e-c_/d #b-c_/h #ai #e-c_/d #b-a_/b ----------------------------- ,in order rightly to appreciate the utility of this table of proposed standard pins1 it is necessary to have in mind the fact that all the dimensions are based on the assumption that a wooden pin with a shank of one and one-half inches diameter1 and with its line wire attached five inches above the cross-arm1 is strong enough for general use on transmission lines4 ,such an assumption covers a wide range of practice1 but its truth may well be doubted for many cases4 ,that this assumption does form the basis of the entire table is clearly shown by the fact that the calculated diameter at the shank of each pin is made to depend on a uniform pull1 ,p1 of the line wire1 giving a uniform maximum stress1 ,s1 in the outer fibres of the wood just where the shank joins the stem4 ,in other words1 every pin in the table is designed to break with a uniform pull of the line wire1 provided that the point on the insulator where the wire is attached is just on a level with the top of its pin in each case4 ,it will at once occur to practical men that while a five-inch pin with one and one-half inch shank1 or a larger pin of equal ability to resist the pull of a line wire1 may be strong enough for the conductors of some transmission lines1 this same pin may be entirely too weak for the longer spans1 sharper angles1 and heavier conductors of other lines4 ,thus1 on the sixty-five-mile line between ,caon ,ferry and ,butte1 ,mont41 each conductor is of copper and has a cross section of #ajf1ejj cm41 while on the older line between ,niagara ,falls and ,buffalo each copper conductor has a cross section of #cej1jjj cm4 ,evidently with equal conditions as to length of span1 amount of sag1 and sharpness of angles on these two lines1 pins ample in strength for the smaller wire might be much too weak for the larger wire4 ,a little consideration will show that it is neither rational nor desirable to adopt pins of uniform strength for all transmission lines1 but that several degrees of strength are necessary to correspond with the range in sizes of conductors in regular use4 ,the size of pins for use on any transmission line1 when the maximum bending strain exerted by the conductors has been determined1 should be found by calculation and experiment1 or by experiment alone4 ,according to ,trautwine1 the average compressive strength of yellow locust is #i1hjj pounds1 of hickory #h1jjj pounds1 and of white oak #g1jjj pounds per square inch in the direction of the grain4 ,these compressive strengths are less than the tensile strengths of the same woods1 and should therefore be employed in calculation1 since the fibres on one side of a bending pin are compressed while the fibres on the other side are elongated4 ,substituting #a1jjj for the value of ,s in the formula1 ,s 7,p ,x_/74#jihb ,d771 and also #e for the value of ,x1 and #a-a_/b for the value of ,d1 the resulting value of ,p is found to be #gcf4e pounds4 ,this result shows that with a locust pin of #a-a_/b inches diameter at the shank1 and with its line wire attached five inches above the shoulder1 the unbalanced side pull of the wire that will break the pin by bending is #gcf pounds1 provided that the wood of the pin has a strength of #a1jjj pounds per square inch in compression4 ,as all of the proposed standard pins in the above table are designed for uniform strength to resist the same pull of a line wire attached on a level with the top of the pin in each case1 it follows that the pull of #gcf pounds by the wire will break any one of these pins under the conditions stated4 ,the calculation just made takes no account of the fact that the actual diameter of the shank of each pin just below the shoulder is #a_/cb inch less than the nominal diameter1 but this of course reduces the strength somewhat4 ,trautwine states that the figures above given for the compressive strengths of wood are only averages and are subject to much variation4 ,of course no pin should be knowingly loaded in regular practice to the breaking point1 and to provide against variations in the strength of wood1 and for unexpected strains1 a liberal factor of safety1 say four1 should be adopted in fixing the maximum strains on insulator pins4 ,applying this factor to the calculations just made1 it appears that the maximum pull of the line wire at the top of any one of the above proposed standard pins should not exceed #gcf #d #ahd pounds in regular work4 ,a little calculation will readily show that the side pull of some of the larger conductors now in use on transmission lines will greatly exceed #ahd pounds under conditions1 as to sag1 angles and wind pressure1 that are frequently met in practice4 ,on page #ddh1 ,vol4 xx41 ,a4 ,i4 ,e4 ,e41 some tests are reported on six locust wood pins with shank diameters of #a-g_/af to #a-a_/b inches4 ,each of these pins was tested by inserting its shank in a hole of #a-a_/b inches diameter in a block of hard wood1 and then applying a strain at about right angles to the pin and about #d-a_/b inches from the block by means of a ,seller's machine4 ,the pull on each pin was applied gradually1 and in most of the pins the fibres of the wood began to part when the side pull reached #gjj to #gej pounds1 though the maximum loads sustained were about ten per cent above these figures4 ,the average calculated value of ,s1 the compressive strength of the wood in these pins1 was #aa1acj pounds per square inch on the basis of the loads at which the fibres of the wood began to break1 and #ac1fbc pounds per square inch for the loads at which the pins gave way4 ,on pages #fej to #fec of the volume last cited1 results are reported of tests on twenty-two pins of eucalyptus wood1 which is generally used for this purpose in ,california4 ,twelve of these pins were of a size much used in ,california on lines where the voltage is not above #cj1jjj4 ,each of the twelve pins was #f-g_/h inches long in the stem1 #d-e_/h inches long in the shank1 #a-a_/b inches in diameter at the shank1 #b inches in diameter at the square shoulder where the shank joins the stem1 and #a-c_/h inches in diameter at the top of the thread4 ,the pins were tested by mounting each of them in a cross-arm1 securing the cross-arm in a testing machine so that the pin was horizontal1 placing an insulator on the pin1 and exerting the strain on a cable wrapped around the side groove of the insulator4 ,this cable varied a little from right angles to the axis of each pin1 but the component of the strain at right angles to this axis was calculated and the breaking load here mentioned is that component4 ,nearly all of these twelve pins broke square off at the cross-arm4 ,for a single pin1 the lowest breaking strain was #gje pounds1 the largest #a1cfj pounds1 and the average for the twelve pins was #a1jhe pounds4 ,unfortunately1 the exact distance of the cable from the cross-arm is not stated1 but as the cable was wound about the side groove of the insulator it was probably either in line with or a little below the top of the pin4 ,it seems probable also that the diameter of these pins at the shoulder--that is1 two inches--may have increased the breaking strain somewhat by giving the shoulder a good bearing on the cross-arm4 ,the ten other pins were of the size in use on the #fj1jjj-volt line between ,colgate power-house and ,oakland1 ,cal4 ,each of these pins had a length of #e-c_/h inches and a maximum diameter of #b-a_/h inches in the shank1 and a length of #aj-c_/h inches in the stem1 with a diameter of #b-a_/b inches at the shoulder4 ,this shoulder was not square1 but its surface formed an angle of forty-five degrees with the axis of the pin1 and this bevel shoulder took up #a_/d inch of the length just given for the stem of the pin4 ,at #b-a_/b inches from its threaded end the stem of the pin had a diameter of #a-ae_/af inches1 and the diameter slopes to #a-c_/h inches at two inches from the end4 ,the two inches of length at the top of the stem has the uniform diameter of #a-c_/h inches1 and is threaded with four threads per inch for the insulator4 ,each of these ten pins was tested1 as already described1 until it broke1 but the break in this case started as a split at the lower end of the threaded portion and ran down the stem to the shoulder in a line nearly parallel with the axis of the pin4 ,the pull on the cable at right angles to the axis of each pin had a maximum value of #a1dge pounds in one case1 and a corresponding value of #c1aij pounds in another1 while the average breaking strain for the ten pins was #b1caj pounds4 ,unfortunately1 the report of this test above named does not distinctly state just how far the testing cable was attached above the shank of each of these large pins2 but it seems probable that the same insulator was used with the larger as with the smaller pins1 and if this was so the testing cable was attached near the end of each pin1 as this cable was wound about the side groove of the insulator used on the smaller pins4 ,with the types of insulator in actual use on the ,colgate and ,oakland line the wire is carried at the top groove and its centre is about two and a half inches above the top of the pin4 ,it is therefore probable that these pins would not withstand as great strains on the lines as they did in these tests4 ,the bevel shoulder on each of these larger pins no doubt increases its ability to resist a bending strain1 because the bevel surface fits tightly down into a counterbore in the cross-arm4 ,where the pin has a shoulder at right angles with the axis1 as is more usually the case1 and the top of the cross-arm is a little rounding1 the square shoulder does not have a firm seat and is of slight importance as far as the strength of the pin to resist a bending strain is concerned4 ,evidently the weakest point in the ten larger pins of this test was at the lower end of the threaded portion1 since in each case the break was in the form of a long split starting where the thread ended4 ,there seems to be no sufficient reason for the reduction of the diameter of a pin intended for a heavy line wire to a diameter as small as one inch at the threaded end1 or for limiting the length of the threaded portion to #b4e inches1 as proposed in the specifications for standard pins4 ,it is certain that the cost of the pin would be no more if its diameter at the threaded end were #a-a_/d or #a-c_/h inches with a uniform taper from the end of the pin down to the shoulder and with the thread cut down the stem for three or four inches4 ,furthermore1 any increase in the cost of insulators for these larger threaded ends of pins would no doubt be a small matter4 ,some excess of strength in the stem of a pin over that of its shank is to be desired1 for the stem is more exposed to the weather and to charring by leakage currents over the surface of the insulator4 ,on high-voltage lines1 this charring is usually worse at that part of each pin just below its thread1 and the commonest breaks of pins on these lines leave the insulators with the threaded portions of their pins hanging on the wire1 while the remainder of each pin remains on the cross-arm4 ,from the tests just noted it is evidently poor design to give the threaded portion of a pin a short length of uniform diameter1 and then to increase the diameter at once by a shoulder1 as was done with the pins on the ,colgate and ,oakland line4 ,this design evidently leads to failure of pins by splitting from the lower end of the threads4 ,the better design is the more common one which gives the stem of the pin a uniform taper from the shoulder to the top4 ,where the line wire is secured to the top of its insulator1 anywhere from one to three inches above the top of the pin1 there is a strong tendency for the insulator to tip on its pin1 and this tendency is more effectively met the longer the joint between the pin and insulator4 ,,chapter ,,xxiii4 ,,steel ,,towers4 ,steel towers are rapidly coming into use for the support of electric transmission lines that deliver large units of energy at high voltages to long distances from water-powers4 ,one case of this sort is the seventy-five-mile transmission of #bd1jjj horse-power at #fj1jjj volts from ,niagara ,falls to ,toronto4 ,another example may be seen in the seventy-five-mile line of steel towers which carries transmission circuits of #fj1jjj volts to ,winnipeg4 ,guanajuato1 ,mexico1 which is said to have produced more silver than any other city in the world1 receives some #c1cjj electric horse-power over a #fj1jjj-volt transmission line one hundred miles long on steel towers4 ,between ,niagara ,falls and ,lockport the electric circuits now being erected are supported on steel towers4 ,on a transmission line eighty miles long in northern ,new ,york1 for which plans are now being made1 steel towers are to support electric conductors that carry current at #fj1jjj volts4 ,for the elevations above ground at which it is common to support the conductors of transmission lines--that is1 from twenty-five to fifty feet--a steel tower will cost from five to twenty times as much as a wooden pole in various parts of the ,united ,states and ,canada4 ,it follows at once from this fact that there must be cogent reasons1 apart from the matter of first cost1 if the general substitution of steel towers for wooden poles on transmission lines is to be justified on economic grounds4 ,during fifteen years the electric transmission of energy from distant water-powers to important centres of population has grown from the most humble beginnings to the delivery of hundreds of thousands of horse-power in the service of millions of people1 and the lines for this work are supported1 with very few exceptions1 on wooden poles4 ,among the transmissions of large powers over long distances at very high voltages that have been in successful operation during at least several years with wooden pole lines are the following3 the #fj1jjj-volt circuit that transmits some #ac1jjj horse-power from ,electra station across the ,state of ,california to ,san ,francisco1 a distance of #adg miles1 is supported by wooden poles4 ,in the same ,state1 the transmission line #adb miles long between ,colgate power-house and ,oakland1 at #fj1jjj volts1 and with a capacity of about #ae1jjj horse-power1 hangs on wooden poles1 save at the span nearly a mile long over the ,straits of ,carquinez4 ,wood is used to carry the two #ee1jjj-volt circuits that run sixty-five miles from the #aj1jjj-;horse-power station at ,caon ,ferry on the ,missouri ,river to ,butte4 ,between ,shawinigan ,falls and ,montreal1 a distance of eighty-three miles1 the conductors that operate at about #ej1jjj volts are carried on wooden poles4 ,electrical supply in ,buffalo to the amount of #cj1jjj horse-power depends entirely on circuits from ,niagara ,falls that operate at #bb1jjj volts and are supported on lines of wooden poles4 ,in the operation of these and many other high-voltage transmissions during various parts of the past decade some difficulties have been met with1 but they have not been so serious as to prevent satisfactory service4 ,nevertheless1 it is now being urged that certain impediments that are met in the operation of transmission systems would be much reduced by the substitution of steel towers for wooden poles1 and it is even suggested that perhaps the first cost1 and probably the last cost1 of a transmission line would be less with steel than with wood for supports4 ,the argument for steel in the matter of costs is that while a tower requires a larger investment than a pole1 yet the smaller number of towers as compared with that of poles may reduce the entire outlay for the former to about that for the latter4 ,more than this1 it is said that the lower depreciation and maintenance charges on steel supports will make their final cost no greater than that of wooden poles4 ,in the present state of the market1 steel towers can be had at from three to three and one-half cents per pound1 and the cost of a steel tower or pole will vary nearly as its weight4 ,during the first half of #aijd the quotations on tubular steel poles to the ,southside ,suburban ,railway ,company1 of ,chicago1 were between the limits just stated4 ,that company ordered some poles built up of steel sections about that time at a trifle less than three cents per pound4 ,each of these poles was thirty feet long and weighed #faf pounds1 so that its cost was about eighteen dollars 7xxi1 ,a4 ,i4 ,e4 ,e41 #ged74 ,for a forty-five-foot steel pole to carry a pair of #aa1jjj-volt1 three-phase circuits along the ,new ,york ,central electric road the estimated cost was eighty dollars in the year last named 7xxi1 ,a4 ,i4 ,e4 ,e41 #gec74 ,on the #ajj-mile line to ,guanajuato1 ,mexico1 above mentioned1 the steel towers were built up of #c #c #c_/af angles for legs1 and were stayed with smaller angle sections and rods4 ,each of these towers has four legs that come together near the top1 is forty feet high1 weighs about #a1ejj pounds1 and carries a single circuit composed of three ,no4 #a ,b4 ,s4 gauge hard-drawn copper cables4 ,the weight of each of these cables is #a1cdj pounds per mile1 and the forty-foot towers are spaced #ddj feet apart1 or twelve per mile1 over nearly the entire length of line4 ,at three cents per pound1 the lowest figure at which these towers could probably be secured for use in the ,united ,states1 the approximate cost of each would be forty-five dollars4 ,between ,niagara ,falls and ,lockport each of the steel towers that is to carry a single three-phase transmission circuit has three legs built up of tubing that tapers from two and one-half inches to smaller sizes and is braced at frequent intervals4 ,the height of these towers is forty-nine feet1 and the weight of each is #b1hjj pounds4 ,at three cents per pound the cost of each tower amounts to eighty-four dollars4 ,for a long transmission line in northern ,new ,york bids were recently had on towers forty-five feet high to carry six wires1 and the resulting prices were #ajj to #abe each for a tower weighing about #c1jjj pounds4 ,on the line between ,niagara ,falls and ,toronto the standard tower holds the lowest cables #dj feet above ground at the insulators1 has a weight of #b1cfj pounds1 and would cost #gj4hj at #c cents per pound4 ,in ,january1 #aijb1 four steel towers were purchased to support transmission circuits for two spans of #acb feet each over the ,chambly ,canal1 near ,chambly ,canton1 ,quebec4 ,each pair of these towers was required to support eleven ,no4 #b-j ,b4 ,s4 gauge bare copper wires with the span of #acb feet between them4 ,the vertical height of each of these four towers is #add feet above the foundation1 and they were designed for a maximum stress in any member of not more than one-fourth of its ultimate strength1 with wires coated to a diameter of one inch with ice and under wind pressure4 ,for these four steel towers erected on foundations supplied by the purchasers the price was #d1fgj1 and the contract called for a weight in the four towers of not less than #aba1jjj pounds4 ,on the basis of this weight the cost of the towers erected on foundations was #c4hf cents per pound4 ,with these examples of the cost of steel towers a fair idea may be gotten of the relative cost of wooden poles4 ,for poles of cedar or other desirable wood thirty-five feet long and with eight-inch tops fitted with either one or two cross-arms an estimated cost of five dollars each is ample to cover delivery at railway points over a great part of the ,united ,states and ,canada4 ,this size of pole has been much used on the long1 high-voltage transmission systems that involve large power units and use heavy conductors4 ,examples of lines where such poles are used may be seen between ,niagara ,falls and ,buffalo1 between ,colgate power-house and ,oakland1 and between ,caon ,ferry and ,butte4 ,of course some longer poles were used in special locations1 like the crossing of steam railways1 but it is also true that on the lines supported by steel towers such locations make exceptionally high towers necessary4 ,the thirty-five-foot poles will hold the electric lines about as high above the ground level as the forty-nine-foot towers on the ,niagara ,falls and ,toronto transmission1 because the former will be set so much closer together4 ,on the line just named the regular minimum distance of the electric cables above the ground level at the centres of spans is twenty-five feet4 ,the standard towers on this line carry the lower electric cables forty feet above the ground at the insulators1 and it was thought desirable to allow a sag of fifteen feet at the centres of the regular spans of four hundred feet each4 ,on these towers the conductors that form each three-phase circuit are six feet apart1 and lines drawn between the three cables form the sides of an equilateral triangle4 ,with a pin fourteen and three-fourths inches long like that used on these steel towers1 and one conductor at the top of a thirty-five-foot pole1 where the other two are supported by a cross-arm five feet three inches below1 giving six feet between cables1 the lower cables are held by their insulators twenty-six feet above the ground1 when the poles are set five feet deep4 ,between thirty-five-foot poles one hundred feet is a very moderate span1 and one that is exceeded in a number of instances4 ,thus on the #adb-mile line from ,colgate power-house to ,oakland the thirty-five-foot poles are #acb feet apart1 and one line of these poles carries three conductors of #acc1jjj-;circular-mil copper1 while the other pole line has three aluminum cables of #afh1jjj circular mils4 ,on the later transmission line from ,niagara ,falls to ,buffalo1 which was designed for three-phase circuits of #ejj1jjj-;circular-mil cable1 the regular distance between the thirty-five-foot poles is #adj feet4 ,a maximum sag of twenty-four inches between poles #ajj feet apart under the conditions named above brings the lowest points of the wire twenty-four feet above the ground4 ,the steel towers on the line to ,guanajuato being only forty feet in length1 and spaced #ddj feet apart1 it seems that the distance of conductors from the ground at the centres of spans is probably no greater than that just named4 ,particular attention is called to this point because it has been suggested that the use of steel towers would carry cables so high that wires and sticks could not be thrown onto them4 ,it thus appears that thirty-five-foot wooden poles set one hundred feet apart will allow as much distance between conductors1 and still keep their lowest points as far above the ground1 as will forty- to forty-nine-foot towers placed four hundred feet or more apart4 ,the two lines that have their conductors further apart perhaps than any others in the world are the one from ,caon ,ferry to ,butte1 on thirty-five-foot wooden poles1 and the one to ,guanajuato1 on steel towers4 ,in each of these cases the cables are seventy-eight inches apart at the corners of an equilateral triangle4 ,with steel towers four hundred feet or wooden poles one hundred feet apart1 four of the latter must be used to one of the former4 ,at #e per pole this requires an investment of #bj in poles as compared with at least #de for a tower like those on the ,guanajuato line1 #hd for a tower like those on the line from ,niagara ,falls to ,lockport1 or #gj for one of the towers on the ,niagara and ,toronto line4 ,each of the towers on the line to ,toronto carries two three-phase circuits1 and the least distance between cables is six feet4 ,to reach the same result as to the distance between conductors with the two circuits on poles1 it would be desirable to have two pole lines1 so that #dj would represent the investment in the poles to displace one tower for two circuits4 ,the older pole line between ,niagara ,falls and ,buffalo carries two three-phase circuits on two cross-arms1 and the #cej1jjj-;circular-mil copper cables of each circuit are at the angles of an equilateral triangle whose sides are each three feet long4 ,in this case1 however1 the electric pressure is only #bb1jjj volts4 ,the costs above named for poles and towers include nothing for erection4 ,each tower has at least three legs and more commonly four1 and owing to the heights of towers and to the long spans they support it is the usual practice to give each leg a footing of cement concrete4 ,it thus seems that the number of holes to be dug for a line of towers is nearly or quite as great as that for a line of poles1 and considering the concrete footings the cost of erecting the towers is probably greater than that for the poles4 ,with wooden poles about four times as many pins and insulators are required as with steel towers1 or say twelve pins and insulators on poles instead of three on a tower4 ,for circuits of #ej1jjj to #fj1jjj volts the approximate cost of each insulator with a steel pin may be taken at #a4ej1 so that the saving per tower reaches not more than #ac4ej in this respect4 ,in the labor of erecting circuits there may be a small advantage in favor of the towers1 but the weight of the long spans probably offsets to a large extent any grain of time due to fewer points of support4 ,an approximate conclusion from the above facts seems to be that a line of steel towers will probably cost from #a4e to twice as much as a line or lines of wooden poles to support the same number of conductors the same distance apart1 even when the saving of pins and insulators is credited to the towers4 ,this conclusion applies to construction over a large part of the ,united ,states and ,canada4 ,it is known that wooden poles of good quality retain enough strength to make them reliable as supports during ten or fifteen years1 and it is doubtful whether steel towers will show enough longer life to more than offset their greater first cost4 ,it may be noted here that any saving in the cost of insulators or other advantage that there may be in spans four hundred feet or more long can be as readily secured with wooden as with steel supports4 ,with these long spans the requirements are greater height and strength in the line supports1 and these can readily be obtained in structures each of which is formed of three or four poles with cross-braces4 ,such wooden structures have long been in use at certain points on transmission lines where special long spans were necessary or where there were large angular changes of direction4 ,in those special cases where structures #ge to #aej or more feet in height are necessary to carry a span across a waterway1 as at the ,chambly ,canal above mentioned1 steel is generally more desirable than wood because poles of such lengths are not readily obtainable4 ,neither present proposals nor practice1 however1 contemplates the use of steel towers having a length of more than forty to fifty feet on regular spans4 ,much the strongest argument in favor of steel towers for transmission lines is that these towers give a greater reliability of operation than do wooden poles4 ,it is said that towers will act as lightning-rods and thus protect line conductors and station apparatus4 ,as to static and inductive influences from lightning1 it is evident that steel towers can give no protection4 ,if each tower has an especial ground connection it will probably protect the line to some extent against direct lightning strokes1 but there is no reason to think that this protection will be any greater than that given by well-grounded guard wires1 or even by a wire run from a ground plate to the top of each pole or wooden tower4 ,if a direct lightning stroke passes from the line conductors to a wooden support it frequently breaks the insulator on that support1 and the pole is often shattered or burned4 ,such a result does not necessarily interrupt the transmission service1 however1 as the near-by poles can usually carry the additional strain of the line until a new pole can be set4 ,quite a different result might be reached if lightning or some other cause broke an insulator on a steel tower1 and thus allowed one of the electric cables to come into contact with the metal structure1 as the conductor would then probably be burned in two4 ,to repair a heavy cable thus severed where the spans were as much as #djj feet long would certainly require some little time4 ,where a conductor in circuits operating at #bj1jjj to #ce1jjj volts has in many cases dropped onto a wooden cross-arm1 it has often remained there without damage until discovered by the line inspector1 but no such result could be expected with steel towers and cross-arms 7xxi1 ,a4 ,i4 ,e4 ,e41 #gfj74 ,where steel towers are employed it would seem to be safer to use wooden cross-arms1 for the reasons just stated4 ,this is1 in fact1 the practice on the steel towers before named that support #be1jjj-volt circuits over the ,chambly ,canal1 and also on the steel towers that carry the #fj1jjj-volt circuits from ,colgate power-house over the mile-wide ,straits of ,carquinez4 ,on the #dj1jjj-volt transmission line between ,gromo and ,nembro1 ,italy1 where timber is scarce and steel is cheap1 both the poles and cross-arms are of wood4 ,it is thought that the comparatively small number of insulators used where a line is supported at points about four hundred feet apart should contribute to reliability in operation1 but insulators now give no more trouble than other parts of the line1 and the leakage of energy over their surfaces is very small in amount1 as was shown in the ,telluride tests4 ,whatever benefits are to be had from long spans are as available with wooden as with steel supports1 and at less cost4 ,one advantage of steel towers over wooden poles or structures is that the former will not burn and are probably not subject to destruction by lightning4 ,where a long line passes over a territory where there is much brush1 timber or long grass1 the fact that steel towers will not burn may make their choice desirable4 ,in tropical countries where insects rapidly destroy wooden poles the use of steel towers may be highly desirable even at much greater cost1 and such a case was perhaps presented on the line to ,guanajuato1 ,mexico4 ,mechanical failures of wooden insulator pins have been far more common than those of poles1 both as a direct result of the line strains and because such pins are often charred and weakened by the leakage of energy from the conductors4 ,for these reasons the general use of iron or steel pins for the insulators of long lines operating at high voltages seems desirable4 ,such pins are now used to support the insulators on a number of lines with wooden poles and cross-arms1 among which may be mentioned the forty-mile1 #cj1jjj-volt transmission between ,spier ,falls and ,albany and the forty-five-mile #bh1jjj-volt line from ,bear ,river to ,ogden1 ,utah4 ,iron or steel pins add very little to the cost of a line1 and materially increase its reliability4 ,one of the cheapest and best forms of steel pins is that swaged from a steel pipe and having a straight shank and tapering stem with no shoulder4 ,a pin of this sort for the #djj-;foot spans of #aij1jjj-;circular-mil copper cable on the line from ,niagara ,falls to ,toronto measures three and one-quarter inches long in the shank1 eleven and one-half inches in the taper1 and has diameters of two and three-eighths inches at the larger and one and one-eighth inches at the smaller end4 ,on spans under #aej feet between wooden poles pins of this type but with a much smaller diameter could be used to advantage4 ,on long transmission lines where the amount of power involved is very large the additional reliability to be had with steel towers is probably great enough to justify their use4 ,for the great majority of power transmissions1 however1 it seems probable that wooden poles or structures will long continue to be much the cheaper and more practicable form of support4 ,the line of steel towers on a private right of way seventy-five miles long1 carrying two circuits for the transmission of #bd1jjj horse-power at #fj1jjj volts from ,niagara ,falls to ,toronto1 is one of the most prominent examples of this type of construction4 ,eventually there will be two rows of steel towers along the entire length of the line4 ,on the straight portions of the line the steel towers are regularly erected #djj feet apart1 but on curves the distances are less between towers1 so that their total number is about #a1djj for each line4 ,standard curving along the line requires towers placed #ej feet apart1 and a change in the direction of not more than ten degrees at each tower1 except at the beginning and end of the curve1 where the change in direction is three degrees4 ,when the change in the direction of the line is not more than six degrees1 the corresponding spans allowed with each change are as follows3 ,degrees ,feet of change4 span4 #a_/b #cjj #a #bhf #a-a_/b #bgc #b #bei #b-a_/b #bdf #c #bcb #c-a_/b #bai #d #bje #d-a_/b #aib #e #agh #e-a_/b #afe #f #aea ,at some points along the line conditions require a span between towers of more than #djj feet1 the regular distance for straight work4 ,one example of this sort occurs at ,twelve-,mile ,creek1 where the stream has cut a wide1 deep gorge in the ,erie plateau4 ,at this point the lines make a span of #fbe feet between towers4 ,illustration3 ,,fig4 #id4--,transposition ,tower 7,second ,tower74 ,illustration3 ,,fig4 #ie4--;,elevations and ,plan of ,tower4 ,the regular steel tower used in this transmission measures #df feet in vertical height from its foot to the tops of the lower insulators1 and #ea feet #c inches to the tops of the higher insulators4 ,the lower six feet of this tower are embedded in the ground1 so that the tops of the insulators measure about #dj feet and #de feet #c inches respectively above the earth4 ,at the ground the tower measures #ad feet at right angles to the transmission line and #ab feet parallel with it4 ,the width of each tower at the top is #ab feet at right angles to the line1 and the two sides having this width come together at points about #dj feet above the ground4 ,between the two ,l bars thus brought nearly together1 at each side of a tower a piece of extra heavy #c-;inch steel pipe is bolted so as to stand in a vertical position4 ,each piece of this pipe is about #c-a_/b feet long and carries a steel insulator pin at its upper end4 ,the two pieces of pipe thus fixed on opposite sides of the top of a tower carry the two highest insulators4 ,for the other four insulators of each tower1 pins are fixed on a piece of standard #d-;inch pipe that serves as a cross-arm1 and is bolted in a horizontal position between the two nearly rectangular sides of each tower1 at a point two feet below the bolts that hold the vertical #c-;inch pipes1 already named1 in position4 ,save for the two short vertical and one horizontal pipe1 and the pins they support1 each tower is made up of ,l-shaped angle-bars bolted together4 ,each of the two nearly rectangular sides of a tower consists of two ,l bars at its two edges1 three ,l bars for cross-braces at right angles to the edges1 and four diagonal braces also formed of ,l bars4 ,the lower halves of the ,l bars at the edges of each side of a tower have sections of #c #c #a_/d1 and the upper halves have sections of #c #c #c_/af4 ,this last-named cross-brace and the other two cross-braces have a common section of #b #a-a_/b #a_/h4 ,for the lower set of diagonal braces the common section is #b-a_/b #b #a_/h1 and the upper set has a section of #b #a-a_/b #a_/h in each member4 ,at the level of the lowest cross-braces the two rectangular sides of a tower are tied together by one member of #b #a-a_/b #a_/h of ,l section and at right angles to the sides1 and by two diagonal braces of #e_/h round rod between the corners of the tower4 ,on each of its two triangular sides a tower has four horizontal braces and three sets of diagonal braces4 ,the two upper horizontal braces are of #b #a-a_/b #a_/h ,l section1 and the lowest is the same1 but the remaining horizontal brace has a section of #b-a_/b #b #a_/h4 ,bars of #b #a-a_/b #a_/h ,l section are used for the two upper sets of diagonal braces1 and bars of #b-a_/b #b #a_/h for the lower set4 ,in addition to the cross-braces named1 each triangular side of a tower near the top of the corner bars has two short cross-pieces with the common ,l section of #c-a_/b #c-a_/b #e_/h1 one just above and the other just below the cross-arm of #d-;inch pipe to hold it in place4 ,at the bottom of each of the four corner bars of a tower a foot is formed by riveting a piece of #c #a_/d ,l section and #ae inches long at right angles to the corner bar4 ,on one corner bar of each tower there are two rows of steel studs for steps1 one row being located in each flange of the ,l section4 ,on the same flange these steps are two feet apart1 but taking both flanges they are only one foot apart4 ,every part of each steel tower is heavily galvanized4 ,illustration3 ,,figs4 #if1 #ig1 #ih4--,raising ,towers on ,niagara ,transmission ,line4 ,illustration3 ,,fig4 #ii4--,one of the ,towers in ,position4 ,the labor of erecting these steel towers was reduced to a low figure by the method employed1 as shown in the accompanying illustration4 ,each tower was brought to the place where it was to stand with its parts unassembled4 ,for erecting the towers a four-wheel wagon with a timber body about thirty feet long was used4 ,when it was desired to raise a tower1 two of the wheels1 with their axle1 were detached from the timber body of the wagon1 and this body was then stood on end to serve as a sort of derrick4 ,this derrick was guyed at its top on the side away from the tower1 and a set of blocks and tackle was then connected to the top of the derrick and to the tower at a point about one-fourth of the distance from its top4 ,a rope from this set of blocks ran through a single block fixed to the base of the derrick and then to a team of horses4 ,on driving these horses away from the derrick the steel tower was gradually raised on the two legs of one of its rectangular sides until it came to a vertical position4 ,the next operation was to bring the legs of the tower into contact with the extension pieces that were fixed in the earth and then bolt them together4 ,illustration3 ,,fig4 #ajj4--,steel ,tower for ,transmission ,line4 ,the tops of the three pins that carry the insulators for each three-phase circuit are at the corners of an equilateral triangle 7,fig4 #ajj71 each of whose sides measures six feet4 ,the six steel insulator pins used on each tower are exactly alike1 and each is swaged from extra heavy pipe4 ,each finished pin is #b-c_/h inches in diameter for a length of #c-a_/d inches1 and then tapers uniformly to a diameter of #a-a_/h inch at the top through a length of #aa-a_/b inches4 ,this gives the pin a total length of #ad-c_/d inches4 ,in the larger part there are two #i_/af-;inch holes from side to side1 and within two inches of the top there are three circular grooves each #c_/af inch wide and #a_/af inch deep4 ,forged steel sockets of two types are employed to attach the steel pins with the pipes4 ,each socket is made in halves1 and these halves are secured to both the pipe and the pin by through bolts4 ,like all other parts of the towers1 these steel pins and sockets are heavily galvanized4 ,on each of the four corner bars of a tower the lower six feet of its length is secured to the upper part by bolts or rivets4 ,this lower six feet of each corner bar is embedded in the earth1 and the construction just named makes it easy to replace the bars in the earth when corrosion makes it necessary4 ,footings for each tower are provided by digging four nearly square holes with their sides at approximately #de degrees with the direction of the transmission line1 and the shortest side of each hole at least two feet long4 ,centres of these holes are #ad feet #c inches apart in a direction at right angles to the line1 and #ac feet #i inches apart parallel with the line4 ,in hard-pan each one of the holes was filled to within #b feet #f inches of the top with stones1 after the leg of the tower was in position1 and then the remainder of the hole was filled with cement grouting mixed four to one4 ,at the bottom of each hole in marsh land a wooden footing #c feet #f inches #bd inches was laid flat beneath the leg of the tower1 and then the hole was filled to within #b-a_/b feet of the surface with the excavated material4 ,next above this filling comes a galvanized iron gutter-pipe1 four inches in diameter1 and filled with cement about the leg of the tower for a length of two feet4 ,outside of this pipe the hole is made rounding full of cement grouting4 ,illustration3 ,,fig4 #aja4--,transmission ,line at ,welland ,canal4 ,at some points along the transmission line exceptionally high towers are necessary1 a notable instance being found at the crossing over the ,welland ,canal1 where the lowest part of each span must not be less than #aej feet above the water4 ,for this crossing two towers #ace feet high above ground are used1 as seen in ,fig4 #aja4 ,each of these towers is designed to carry all four of the three-phase power circuits that are eventually to be erected between ,niagara ,falls and ,toronto4 ,for this purpose there was used a special design of tower with a width of about #dh feet at right angles to the direction of the line below the top truss1 and a width of about #fh4e feet at that truss where the two lower conductors of each circuit are attached4 ,with all spans longer than #djj feet1 a tower of heavier construction than the standard type is used1 and this tower provides three insulators for the support of each conductor4 ,a tower of this type that supports the lowest conductors about #dj feet above the ground level has its corner bars made up of #d #d #c_/h and #d #d #e_/af ,l sections1 has three cross-arms of extra heavy #d-;inch pipe1 and a #f-;inch vertical standard pipe to support each group of three insulators for the highest conductor of each circuit4 ,each of the lower conductors of a circuit on this tower is supported by an insulator on each of the three parallel cross-arms4 ,on some of these towers1 for long spans1 the two outside insulators for the support of each conductor are set a little lower than the insulator between them4 ,illustration3 ,,fig4 #ajb4--;,heavy ,tower at ,credit ,river4 ,illustration3 ,,fig4 #ajc4--;,angle ,tower ,near ,bronte4 ,angle towers1 used where the line makes a large change in direction at a single point1 have three legs on each rectangular side1 a width of #bj feet on each of these sides for some distance above the ground1 and a width of #bg feet #b inches at the top4 ,in these towers the two legs on the triangular side that is in compression are each made up of four #c #c #a_/d ,l sections joined by #a-a_/b #a_/d lattices and rivets4 ,towers of this sort are used near the ,toronto terminal-station1 where the line changes #ce degrees at a single point1 and near the crossing of ,twelve-,mile ,creek1 where the angular change of the line on a tower is #de degrees4 ,close to each terminal-station and division-house the transmission line is supported by terminal towers4 ,these towers differ from the others in that each carries insulators for only three conductors1 and these insulators are all at the same level4 ,each terminal tower has nine insulators1 arranged in three parallel rows of three each for the conductors of a single circuit1 and each conductor thus has its strain distributed between three pins4 ,all three wires of a circuit are held #dj feet above the ground by a terminal tower1 and pass to their entries in the wall of a station at the same level4 ,as these terminal towers must resist the end strain of the line1 they are made extra heavy1 the four legs each being made up of #d #d #e_/af and #d #d #c_/h ,l sections4 ,for the three cross-arms on one of these towers three pieces of #d-;inch pipe1 each #ae feet #i inches long1 are secured at its top with their parallel centre lines #cj inches apart in the same plane4 ,each of these pipes carries three insulator pins with their centres #g feet #d-a_/b inches apart4 ,on the bottom of each leg of a terminal tower there is a foot1 formed by riveting on bent plates1 that measure #ae and #ah inches1 respectively1 on the two longer sides4 ,each foot of this tower is set in a block of concrete #e feet square that extends from #c4e feet to #g4e feet below the ground level4 ,insulators for the transmission line1 which are illustrated in ,fig4 #ajd1 are of brown1 glazed porcelain1 made in three parts1 and cemented together4 ,the three parts consist of three petticoats or thimbles1 each of which slips over or into one of the others1 so that there are three outside surfaces and three interior or protected surfaces between the top of an insulator and its pin4 ,from top to bottom the height of each insulator is #ad inches1 and this is also the diameter of the highest and largest petticoat4 ,the next or middle petticoat has a maximum diameter of #aj inches and the lowest petticoat one of #h inches4 ,cement holds the lowest petticoat of the insulator on one of the steel pins previously described1 and in this position the edge of the lowest petticoat is about #b-a_/b inches from the steel support4 ,at the top of each insulator the transmission conductor is secured1 and the shortest distance from this conductor to any of the steel parts through the air is about #ag inches4 ,from the step-up transformer house at ,niagara ,falls to the terminal-station at ,toronto1 a distance of seventy-five miles1 each three-phase1 #fj1jjj-volt1 #be-;cycle circuit on the steel towers is made up of three hard-drawn copper cables with a cross section of #aij1jjj circular mils each1 and is designed to deliver #ab1jjj electric horse-power with a loss of ten per cent1 on a basis of #ajj per cent power factor4 ,six equal strands of copper make up each cable1 and this wire has been specially drawn with an elastic limit of more than #ce1jjj pounds and a tensile strength of over #ee1jjj pounds per square inch4 ,this cable is made in uniform lengths of #c1jjj feet1 and these lengths are joined by twisting their ends together in copper sleeves1 and no solder is used4 ,no insulation is used on these cables4 ,illustration3 ,,fig4 #ajd4--;,insulators4 ,instead of a tie-wire1 a novel clamp is employed to secure the copper cable on each insulator4 ,this complete clamp is made up of two separate clamps that grasp the cable at opposite sides of each insulator and of two half-circles of hard-drawn copper wire of #j4ahg inch diameter4 ,each half-circle of this wire joins one-half of each of the opposite clamps1 and fits about the neck of the insulator just below its head4 ,two bronze castings1 one of which has a bolt extension that passes through the other1 and a nut1 make up each separate clamp4 ,when the combined clamp is to be applied1 the sides are separated by removing the nut that holds them together1 the half-circles are brought around the neck of the insulator1 and each of the side clamps is then tightened on to the cable by turning the nut that draws its halves together4 ,this complete clamp can be applied as quickly as a tie-wire1 is very strong1 and does not cut into the cable4 ,each of the regular steel towers is designed to withstand safely a side strain of #aj1jjj pounds at the insulators1 or an average of #a1fff pounds per cable4 ,with the #aij1jjj-mil cable coated to a depth of #a_/b inch with ice and exposed to a wind blowing #ajj miles per hour1 the estimated strains on each steel pin for different spans and angular changes in the direction of the line are given in the accompanying table3 ,,pounds ,,strain ,,on ,,pins1 #a_/b-;,,inch ,,sleet1 #ajj ,,miles ,,wind4 ,degrees and ,minutes4 ,span1---------------------------------- - feet4 #j #j4cj #a #a4cj #b #b4cj #c ---------------------------------------- #j #j #ce #fi #ajd #ach #agc #bjg #ajj #bef #bia #cbe #cfj #cid #dbi #dfc #bjj #eab #edg #eha #faf #fej #fhe #gai #cjj #gfh #hjc #hcg #hgb #ijf #ida #ige #djja1jbda1jeia1jica1abha1afba1aiga1bca #ejja1bhja1caea1cdia1chda1daha1deca1dhg #fjja1ecfa1egaa1fjea1fdja1fgda1gjia1gdc #gjja1giba1hbga1hfaa1hifa1icja1ifea1iii #hjjb1jdhb1jhcb1aagb1aebb1ahfb1bbab1bee #ijjb1cjdb1ccib1cgcb1djhb1ddbb1dggb1eaa #a1jjjb1efjb1eieb1fbib1ffdb1fihb1gccb1gf g ---------------------------------------- ,degrees and ,minutes4 ,span1------------------------------ feet4 #c4cj #d #d4cj #e #e4cj #f ----------------------------------- #j #bdb #bgf #caa #cde #chj #dad #ajj #dih #ecb #efg #fja #fcf #fgj #bjj #ged #ghh #hbc #heg #hib #ibf #cjja1jaja1jdda1jgia1aaca1adha1ahb #djja1bffa1cjja1ccea1cfia1djda1dch #ejja1ebba1eefa1eiaa1fbea1ffja1fid #fjja1ggha1haba1hdga1hhaa1iafa1iej #gjjb1jcdb1jfhb1ajcb1acgb1agbb1bjf #hjjb1bijb1cbdb1ceib1cicb1dbhb1dfb #ijjb1edfb1ehjb1faeb1fdib1fhdb1gah #a1jjjb1hjbb1hcfb1hgab1ijeb1idjb1igd ----------------------------------- ,the copper cables were so strung as to have a minimum distance from the ground of #be feet at the lowest points of the spans4 ,in order to do this the standard steel towers that hold the lower cables #dj feet above the ground level at the insulators are spaced at varying distances apart1 according to the nature of the ground between them4 ,at each tower the upper cable of each circuit is #e feet #c inches higher than the two lower cables1 and this distance between the elevations of the upper and the lower cables is maintained whatever the amount of sag at the centre of each span4 ,if there is a depression between two standard towers on a straight portion of the line1 the sag in the centre of a span #djj feet long may be as much as #ah feet4 ,where a rise and fall in the ground between towers make it necessary to limit the sag to #ad feet in order to keep the lowest cables #be feet above the highest point of earth1 the length of span is limited to #cej feet4 ,if the rise and fall of ground level between towers allow a sag of only #aa feet with the lowest cable #be feet above the earth1 the length of span with #dj-;foot towers is reduced to #cjj feet2 and if for a like reason the sag is limited to #h feet1 the span may only be #bej feet4 ,illustration3 ,,fig4 #aje4--,take-up ,arrangement on ,terminal ,tower4 ,at each terminal tower1 where the cables are secured before they pass into a terminal-station1 the three insulators for each cable are in a straight line with their centres1 #cj inches apart4 ,when a line cable reaches the first insulator of the three to which it is to be attached on one of these towers1 it is passed around the neck of this insulator and then secured on itself by means of two clamps that are tightened with bolts and nuts4 ,see ,fig4 #aje4 ,the cable thus secured turns up and back over the tops of the three insulators and goes to the terminal-station4 ,around the neck of the insulator to which the line cable has been secured in the way just outlined a short detached length of the regular copper cable with the parts of a turnbuckle at each end is passed1 and this same piece of cable also passes around the neck of the next insulator in the series of three4 ,by joining the ends of the turnbuckle and tightening it1 a part of the strain of the line cable in question is transferred from the first to the second insulator of the series4 ,in the same way a part of the strain of this same line cable is transferred from the second insulator of the series to the third1 or one nearest to the terminal-station4 ,,index4 ,air-blast cooled transformers1 #abi ,air-gap data1 #ahc ,air gaps1 number in series to stand given voltage1 #ahc ,albany-,hudson ,ry4 ,plant1 #aba ,alternating currents1 #bbg ,alternator voltage1 #aah ,alternators1 #ajc data1 #aah for high voltage1 #abj inductor1 #aab types of1 #aaa ,aluminum as a conductor1 #bjj1 #bji cables in use1 #bac conductor joints1 #bjf conductors1 #bg1 #bh corrosion of1 #baa properties of1 #bab soldered joints1 #bjf vs4 copper1 #bji wire1 cost of1 #bi ,amoskeag ,mfg4 ,co4 plant1 #ea1 #eb ,amsterdam 7,n4 ,y47 plant1 #aba ,anchor ice1 #ei ,anderson 7,s4 ,c47 plant1 #aba ,apple ,river 7,minn47 plant1 #a1 #bf1 #bg1 #bh1 #ga1 #ig1 #ih1 #ii1 #ajb1 #aah1 #aai1 #abd1 #abf1 #abg1 #acd1 #agd1 #ahg1 #aij1 #aib1 #bjh1 #bde1 #bfd1 #bid ,arc lighting1 #afg ,arcing1 #df ,automatic regulators1 #afb ,barbed wire1 #afi1 #age ,belt drive1 #hc1 #ajg ,bienne plant 7,switzerland71 #db ,birchem ,bend1 #eg1 #fg1 #gi1 #ie1 #ig1 #ih1 #ajb ,blower capacity necessary to cool transformers1 #acj ,boosters1 #acc ,boston-,worcester ,ry4 plants1 #aba ,braces for cross-arms1 #bei ,bronze conductors1 #bjj ,brush discharge1 #bha ,buchanan 7,mich47 plant1 #hh ,building materials1 #ie ,bulls ,bridge plant1 #fc ,burrard ,inlet 7,b4 ,c47 plant1 #aaa1 #aab ,bus-bars1 #adb1 #adg dummy1 #ade ,cable insulation1 #aie sheaths1 #aid ways1 #adj ,cables1 aluminum1 #bab aluminum1 in use1 #bac charging current1 #aig cost of1 #ahh1 #aif for alternating current1 #aid high-voltage1 #aia paper insulated1 #aif protection against electrolysis1 #aie rubber-covered1 #aie submarine1 #aib temperature of1 #aih voltage in1 #aij1 #aif ,canadian-,niagara ,falls ,power ,co41 #aba ,canals1 #ea1 #ec long1 #fh ,caon ,city plant1 #bf1 #bg1 #bh1 #aag1 #aah1 #abg1 #bjh ,caon ,ferry plant1 #a1 #c1 #bf1 #bg1 #bh1 #df1 #di1 #ec1 #fb1 #fh1 #fi1 #hc1 #hi1 #id1 #ie1 #ig1 #ajb1 #aje1 #aab1 #aac1 #aah1 #aai1 #abd1 #abe1 #abf1 #abg1 #acj1 #acb1 #acd1 #agd1 #bjh1 #bcc1 #bcd1 #bde1 #bdf1 #bdi1 #bed1 #beg1 #bei1 #bfh1 #bgb1 #bhj1 #bhb1 #bid1 #bie1 #cjb ,cedar ,lake plant1 #ij ,chambly plant1 #if1 #aaj1 #adi1 #aef1 #agb1 #ahi1 #bdi1 #bee1 #bef1 #beg1 #bfg1 #bgb1 #bhg1 #bid1 #bie1 #caa1 #cab ,charging current for cable1 #aig ,charring of pins1 #bgf1 #bgh ,chaudire ,falls plant1 #aah ,choke-coil used with lightning arresters1 #ahj ,circuit breakers1 #ace1 #aej breakers1 time limit1 #aeb ,circuits1 selection of1 #bcc ,coal1 price of1 in ,salt ,lake ,city1 #h ,colgate plant1 #a1 #c1 #bf1 #bg1 #bh1 #gd1 #hb1 #hc1 #ij1 #id1 #ig1 #ih1 #ii1 #aja1 #ajb1 #ajh1 #aab1 #aac1 #aah1 #abg1 #acj1 #acb1 #acd1 #ahg1 #aij1 #bja1 #bjf1 #bjh1 #bac1 #bde1 #bdf1 #bej1 #bed1 #beg1 #bgb1 #bgg1 #bhj1 #bhb1 #bid1 #bie1 #cjd1 #cji ,columbus 7,ga47 plant1 #hc1 #aae ,compounding1 #afj ,compressive strength of woods1 #cjb ,conductivity of the conductor metals1 #bja ,conductors1 #bjj aluminum1 #bg1 #bh1 #bjf aluminum1 properties of1 #bab coefficients of expansion1 #bjj corrosion of1 #baa cost of1 #bb1 #bi1 #bjc1 #bjd1 #bje cost of aluminum1 #bi cost of per k4 w41 #bh cost of copper1 #bi data1 #bjd data from representative transmission plants1 #bjh expansion of aluminum and copper1 #baa melting points1 #bjj minimum size for transmission line1 #bjb properties of ideal1 #bjj relative conductivity1 #bja relative cost of1 #bj relative properties for equal lengths and resistances1 #bjd relative strengths for given area1 #bjc relative weight for given conductivity1 #bjb relative weight of1 #bjb relative weights of three-phase1 two-phase1 and single-phase lines1 #bbj resistance of1 #bbe skin effect1 #bjf1 #bcc weight per k4 w41 #bg ,conduits1 #aie radiation loss in1 #aih temperature rise in1 #aih ,constant current regulator1 #afg transformer1 #afg ,control equipment for d4 c4 and a4 c4 plants1 #ce ,copper conductors1 #bjj cost of1 #bb vs4 aluminum1 #bji wire1 cost of1 #bi ,corrosion of conductors1 #baa ,cross-arm braces1 #beh iron1 #bhd location of1 #beg material1 #beh ,cross-arms1 #di1 #bef ,crossings1 #ahg ,dales plant 7,white ,river71 #bf1 #bg1 #bh1 #ga1 #acd1 #bjh ,dams1 #fb ,delta connection1 #aca ,depreciation1 #aa ,design of power-plant1 #hc ,dike1 #fj ,direct connection1 #hd ,discharge1 static1 #agj ,distribution system1 #aeh ,draught tubes1 #gi ,dummy bus-bars1 #ade ,easton 7,pa47 plant1 #aba ,edison ,co4 7,los ,angeles7 plant1 #aah ,efficiency constant-current transmission1 #baf curves1 motor-generator set1 #aag of constant-voltage transmission1 #bag of transformers1 #acc relative1 of a4 c4 and d4 c4 transmission1 #ce ,electra plant1 #a1 #c1 #gd1 #hb1 #hc1 #ib1 #id1 #ig1 #ih1 #aja1 #ajb1 #ajh1 #aab1 #aac1 #aah1 #abg1 #agd1 #bjf1 #bjh1 #bab1 #bac1 #bcc1 #bce1 #bcf1 #bde1 #bdh1 #bec1 #bed1 #bef1 #bei1 #bgb1 #bge1 #bgg1 #bhj1 #bha1 #bhb1 #bid1 #bie ,electric power1 market for1 #g ,electrical ,development ,co41 ,niagara plant1 #abj ,electricity vs4 gas1 #f ,electrolysis1 #aie ,energy curves of hydro-electric stations1 #ac electrical1 cost of at switchboard1 #bc ,entrance end strain1 #bfa1 #cbe insulating discs1 #bfb into buildings1 #agi of lines1 #agi1 #bfa1 #bfe through roof1 #bfi wall openings1 #bfb ,entries for transmission lines1 #bfa ,expansion1 coefficient of1 for copper and aluminum1 #baa coefficients of1 for various conductor metals1 #bjj ,farmington ,river 7,conn47 plant1 #bf1 #bg1 #bh1 #eh1 #aah1 #abe1 #acd1 #bjh1 #bab1 #bac1 #bde ,feeders1 #adc ,ferranti cables1 #aib ,fire-proofing1 #ie ,floor1 distance from roof to1 #ie location of1 #gi space1 #ab1 #aja1 #ajb space per k4 w4 of generators1 #ab ,floors1 #ie ,fog1 #df1 #bgg ,fore-bay1 #ei1 #fj ,foundations1 #ie ,frequency1 #aac1 #abg effect on transformer cost1 #aaf ,fuel1 price of1 in ,salt ,lake ,city1 #h ,fuses1 #ace1 #aej ,garvins ,falls plant1 #ef1 #fj1 #gi1 #hj1 #id1 #if1 #ig1 #ajb1 #aac1 #ade1 #bdj1 #bid ,gas vs4 electricity1 #f ,gears1 #hd1 #ajh ,generators 7a4 c471 #ajc d4 c4 vs4 a4 c41 #ca ,generators1 belt-driven1 #ajg capacity of1 #cb compounding of1 #afj cost of1 #dj 7a4 c47 cost1 #cb 7a4 c47 data1 #aah direct-connected to horizontal turbines1 #hi to impulse wheels1 #ij connection to vertical shafts1 #hd 7d4 c47 field excitation of1 #da floor space1 #aja per k4 w41 #ab gear-driven1 #ajh 7a4 c47 high-voltage1 #abj 7d4 c47 in series1 #ca 7d4 c47 installation of1 #da insulation of1 #ci1 #de lightning protection1 #cd limiting voltage of1 #dd 7a4 c47 limiting voltage of1 #cb 7d4 c47 limiting voltage of1 #ca overload capacity1 #ajc relation between voltage and capacity1 #abg revolving armatures1 #aab fields1 #aab series-wound1 #da speed regulation1 #ch ,glass vs4 porcelain insulators1 #bhh ,great ,falls plant1 #ed1 #fj1 #fa1 #fd1 #fg1 #gh1 #ib1 #ic1 #ajb1 #aad1 #aah ,greggs ,falls plant1 #ed1 #ef1 #fd1 #bdj ,ground connections1 #agh for guard wires1 #aga1 #agb ,grounded guard wires1 #afh ,guard wires1 #afh installation of1 #age ,guying of poles1 #bee ,hagneck 7,switzerland7 plant1 #hf ,hooksett ,falls plant1 #ef1 #aca ,hydro-electric plants1 #a built at the dam1 #fd-fg canals1 long1 #fh-gc long and short1 #eh short1 #ec-ef capacity and weight of conductors per k4 w4 for various plants1 #bg 7#hjj k4 w47 cost of1 #aj 7#aejj k4 w47 cost of1 #aa cost of labor1 #ab cost of operation1 #ab1 #gg design of1 #hc floor1 #gi space per k4 w41 #aja interest and depreciation1 #aa linked together1 #ef-eh load factors1 #ad1 #ae location of1 #fd model design1 #ab operation1 #ei vs4 steam plant1 #e1 #ab with pipe-lines1 #gc-gg with steam auxiliary1 #hd ,ice1 #ei ,impulse wheel speed1 #ajh wheels1 #hb1 #ij location of1 #ii ,indian ,orchard plant1 #eg1 #hd ,inductance1 #bjf1 #bcj ,induction1 electro-magnetic1 electrostatic1 #afh on lines1 #bjf regulator1 #afb ,inductor alternators1 #aab ,insulation1 as affected by ozone1 #aig cost of paper vs4 rubber1 #aif of a4 c4 and d4 c4 lines1 #cd of apparatus1 #adb of cables1 #aie of electrical machines1 #de of generators1 #ci protection against ozone1 #aih ,insulator arc-over test1 #bia -pins1 #bgj 7see ,pins7 ,insulators1 #bgg1 #bhb1 #bhg1 #cbb and pins1 data from various plants1 #bhj defective1 #bhh glass vs4 porcelain1 #bhh in snow1 #bic method of fastening to iron pins1 #bga novel clamp1 #cbc on various transmission lines1 #bid petticoats1 #bid testing of1 #bhh tests1 #bij test voltage1 #bhi with oil1 #bhg ,iron conductors1 #bjj ,kelley's ,falls plant1 #ef ,kelvin's law1 #bai ,labor1 cost of1 #ab in hydro-electric stations1 #ab ,leakage1 #bge1 #bhg line1 #bjg1 #bad ,lewiston 7,me47 plant1 #aah1 #abj1 #abb1 #afg1 #bac ,lighting1 incandescent1 minimum frequency1 #aaf series distribution1 #afg ,lightning arrester1 effect of series resistance1 #ahe arresters1 #afh1 #agf ground connection1 #agh multiple air-gap1 #agf1 #ahc non-arcing metals in1 #ahd series connection of1 #ahj shunted air-gaps1 #ahe with choke coil1 #ahj protection1 #cd ,line calculations1 #bba-bcb charging current1 #aig conductors1 #bjj conductors1 cost of1 #bb weight of1 #ba construction1 #bbb cost1 #caj cross-arms1 #di spacing of wires1 #df 7a4 c47 transmission1 #cd 7d4 c47 transmission1 #cc end strain1 #cbe leakage1 #dg loss1 #ci losses due to grounded guard wires1 #agf ,lines1 sag1 #cji transposition of1 #cad ,line voltages1 #de ,load factors1 #ad1 #ae lighting1 #fa maximum1 #fj motor1 #afj railway1 #afd ,loss in conduits1 #aih relation to weight of conductors1 #bae ,losses due to grounded guard wire1 #agf on transmission lines1 #bae ,ludlow ,mills plant1 #bf1 #bg1 #bh1 #eg1 #gi1 #ajj1 #aba1 #bjh1 #bac ,madrid 7,n4 ,m47 plant1 #bf1 #bg1 #bh1 #aah1 #bjh ,manchester 7,n4 ,h47 plants1 #abj ,market for electric power1 #g ,materials1 building1 #ie for line-conductors1 #bjj ,mechanicsville plant1 #eh1 #fg1 #aji1 #aba1 #agd ,melting points of conductor metals1 #bjj ,montmorency ,falls plant1 #bf1 #bg1 #bh1 #bdj ,motor load1 #afj ,motor-generator set efficiency curve1 #aag ,motors1 series-wound1 #da 7d4 c47 speed regulation1 #ch synchronous1 #bda ,multiple air-gap arrester1 #agf ,needle-point spark-gap for measuring pressure1 #bij ,neversink ,river plant1 #ge1 #agi ,niagara ,falls ,power ,co41 #c1 #ei1 #ha1 #hf1 #hg1 #ic1 #id1 #ie1 #ig1 #aja1 #ajb1 #aje1 #ajf1 #ajg1 #ajh1 #aab1 #aac1 #aag1 #aah1 #aai1 #abg1 #acc1 #acg1 #adj1 #adc1 #ade1 #aea1 #aec1 #afa1 #afe1 #agj1 #aha1 #ahh1 #aid1 #aie1 #bjh1 #baa1 #bdj1 #bde1 #bdf1 #beg1 #bgb1 #bgc1 #bge1 #bhj1 #bhg1 #bhi1 #bid1 #bie1 #big ,nitric acid from air1 #bha ,non-arcing metals1 #ahd ,north ,gorham 7,me47 plant1 #abj ,ogden 7,utah7 plant1 #bf1 #bg1 #bh1 #aah1 #abj1 #acb1 #acd1 #bjh1 #bde ,ohm's law1 #bbc ,oil switches1 #acf ,ontario ,power ,co41 #aba ,operating expenses1 #ei ,operation1 cost of1 #ab1 #gg ,operations1 reliability of1 #caa ,ouray 7,col47 plant1 #aba ,overhead line connection to underground1 #aig ,overload capacity of generators1 #ajc ,ozone1 #aig ,painting of poles1 #bee ,paper insulated cables1 #aif vs4 rubber insulation1 #aif ,payette ,river 7,idaho7 plant1 #gc1 #aja ,penstocks1 #ei1 #ih ,phase1 #aac ,pike's ,peak plant1 #gg ,pilot wires1 #afa ,pins1 #bei1 #bgj and insulators1 data from various plants1 #bhj burning of1 #bgj1 #bgf1 #bgh charring of1 #bgf1 #bgh composite1 #bha compressive strength of woods1 #cjb design of1 #bih dimensions of1 #cja formula for diameter of1 #bii iron1 #bge1 #bhe1 #bhf expansion of1 #bij method of fastening insulators1 #bga method of fastening to cross-arms1 #bga metal1 #bga1 #bge1 #bhb1 #bhe1 #bhf of uniform strength1 #cjj1 #cjb proportions1 #cja relative cost of metal and wooden1 #bhd shank1 #bgd shoulder1 #bge1 #bii1 #cje softening of threads1 #bhj steel1 #bge1 #cab strain with #a_/b-;inch sleet and #ajj-mile wind for different spans1 #cbd strains on1 #bgj1 #bih strength of1 #cjc table of standard1 #cja treatment of1 #bei1 #bge weakest point1 #bih wooden1 data from various plants1 #bgb dimensions of1 #bgb dimensions of standard1 #bgc ,pipe-lines1 #gc ,pittsfield 7,mass47 plant1 #aba ,pole line1 cost of1 #ba lightning arresters1 #agi relative cost of1 #bj lines1 #bdf ,poles1 cost1 #caj depth in ground1 #bed diameter of1 #bed dimensions of1 #bed guying of1 #bee iron1 #bhd length of1 #bec1 #cji life of1 #bee setting of1 #beb spacing of1 #bdi steel1 cost of1 #cjg treatment of1 #bee woods for1 #beb ,porcelain vs4 glass insulators1 #bhh ,portland 7,me47 plant1 #abj1 #aff1 #bci ,portsmouth1 ,n4 ,h4 plant 7steam71 #ajb1 #aah1 #aai1 #abj1 #aba1 #add1 #aid1 #bfd1 #bid ,power plant1 relative cost of a4 c4 and d4 c41 #cf transmitted1 total cost of1 #bd ,radiation loss in conduits1 #aih ,railway crossing1 #ahg1 #beb service1 #afd ,red ,bridge plant1 #ec1 #fj1 #gi1 #ic1 #id1 #if1 #ig1 #ii1 #aja1 #ajb ,regulation1 #aee1 #bci as effected by synchronous motors1 #afe at receiving end1 #afb hand1 #afa ,regulator1 automatic1 #afb constant-current1 #afg induction1 #afb ,relay-switches1 #ade ,resistance1 #bbe in series with lightning arrester1 #ahe ,revolving armature alternators1 #aab field alternator1 #aab ,river crossings1 #ahg1 #aij1 #bdi ,roof1 distance from floor1 #ie ,roofs1 #ie ,rope-drive1 #hc ,rotaries1 cost of1 #aag suitable frequency for1 #aae ,rubber-covered cables1 #aie maximum temperature1 #aih protection against ozone1 #aih ,sag in lines1 #cji ,st4 ,hyacinthe 7,que47 plant1 #aah ,st4 ,joseph plant1 #ff ,st4 ,maurice plant 7,switzerland71 #ca ,salem 7,n4 ,c47 plant1 #aba1 #abb ,san ,gabriel ,caon plant1 #bf1 #bg1 #bh1 #bjh ,santa ,ana plant1 #a1 #bf1 #bg1 #bh1 #gd1 #gf1 #hb1 #hc1 #ib1 #id1 #ie1 #if1 #ig1 #ih1 #ii1 #aja1 #ajb1 #bjh1 #bde1 #bfc1 #bhj1 #bha1 #bid1 #bie1 #bif ,sault ,ste4 ,marie plant1 #gb1 #hc1 #he1 #hi1 #ig1 #ajb1 #ajd1 #aje1 #aab1 #aac1 #aag1 #aah1 #abj1 #abg ,scott system1 #acb ,series distribution1 #afg machines1 #da ,sewall's ,falls plant1 #bf1 #bg1 #bh1 #aee ,shawinigan ,falls plant1 #a1 #gj1 #ga1 #ajg1 #aaf1 #aag1 #afc1 #afd1 #aff1 #bji1 #bab1 #bac1 #bce1 #bcf1 #bdb1 #bde1 #bfg1 #bgb1 #bgc1 #bhj1 #bhb1 #bid1 #bie1 #bif ,sheaths for cables1 #aid ,shunted air-gaps1 #ahe ,skin effect1 #bjf1 #bcb ,snoqualmie ,falls plant1 #c1 #d map of transmission lines1 #d ,snow1 #bic ,soldered joints1 #bjf ,spacing of poles1 #bdi of wire1 #bcd ,spans1 long1 #aij1 #bej strains for different lengths1 #cbd ,sparking distances1 #ahb voltages1 #ahb ,speed1 peripheral1 of impulse wheels1 #ajh peripheral of turbines1 #he1 #ajc regulation1 #ch1 #db d4 c4 motors1 #ch ,spier ,falls plant1 #a1 #b1 #c1 #ed1 #eh1 #fa1 #fb1 #fh1 #ia1 #id1 #ih1 #abd1 #abf1 #abg1 #acj1 #ada1 #adb1 #adf1 #afa1 #agd1 #bcf1 #bcg1 #bdc1 #bdd1 #bde1 #bej1 #bec1 #bff1 #bhj1 #bhe1 #bhg1 #bhi1 #bia1 #bid1 #bie1 #bif1 #cab ,star connection1 #aca ,static discharges1 #agj ,steam and water-power station combined1 #hd electric plant1 cost of labor1 #ab cost of operation1 #ab floor area per k4 w41 #ajb vs4 water-power1 #e ,steel towers1 #cjf ,storage capacity1 #ae ,strains on insulation as affected by resistance in series with arrester1 #ahe ,stray currents1 protection against1 #aie ,submarine cables1 #ahg1 #aib1 #aid ,sub-station1 arrangement of apparatus1 #abh ,sub-stations1 #aeg1 #bcg ,surges1 #acf ,switchboard1 #aef wiring1 #adf1 #adh1 #adi ,switches1 #ace1 #bdd arcing of1 #ace electrically operated1 #adj long break1 #ace oil1 #acf open-air1 #acf pneumatically operated1 #adj power operated1 #ach relay1 #ade ,switch-houses1 #ada1 #adb1 #bch1 #bdd ,switching1 #adf high-tension1 #adg ,synchronous converters1 #aae cost1 #aag motors1 #afe1 #bda ,tail-race1 #if ,telephone1 #afa ,telluride plant1 #dg1 #afj1 #afi1 #aha ,temperature of cables1 #aih rise in conduits1 #aih ,tensile strength of conductor metals1 #bja ,time-limit circuit-breaker1 #aeb ,time relays1 #aeb1 #aec ,towers1 #bej1 #cjf angle1 #cbj cost1 #caj dimensions1 #cad erection of1 #caf-cai heavy1 #cbj reliability of operation1 #caa spans1 #cac steel1 cost1 #cjg1 #cjh steel pins1 #cab strain on1 #cbd ,transformers1 #abb air-blast vs4 water-cooled1 #abi artificially cooled1 #abi at sub-stations1 #abe blower capacity necessary to cool1 #acj constant-current1 #afg cooling1 quantity of water necessary1 #abi cost1 #ba1 #aaf1 #abd1 #acd cost of operation1 #abi cost of1 relative1 #bj delta and star connections1 #aca efficiency1 #acc frequency1 effect of1 #aaf insulation1 #de in transmission systems1 #acd limiting voltage for1 #cb location of1 #ig polyphase1 #abd regulation1 #abe reserve1 #adi secondary1 in series1 #aca single-phase1 #abd two- to three-phase1 #acb used to compensate drop1 #acc used to regulate voltage1 #afb voltages1 #de when to use1 #abb ,transmission1 constant-current1 #ch1 #baf constant-voltage1 #dj1 #bag continuous-current1 #ca1 #cb control equipment1 #ce cost of1 #ai1 #dj1 #bbb 7d4 c47 cost of1 #dj efficiency1 #ce1 #da first long line1 #cg frequency1 #aac generator end1 #ajc lightning protection1 #cd limiting voltage1 #dd lines1 arcing1 #df calculation of1 #bba-bcb charging current1 #aig construction1 #bbb cost1 #caj cross-arms1 #di1 #bef crossings1 #ahg1 #aij data from various plants1 #bde effect of length on cost1 #bj effect of length on cost of power1 #bd efficiency1 #bb1 #bd end strain at entries1 #cbe entrance to buildings1 #agi1 #bfa inductance1 #bjf induction1 #afh insulation1 #cd insulators 7see ,insulators71 #bhg insulator-pins 7see ,pins71 #bgj interest1 maintenance and depreciation1 #bb leakage1 #dg1 #bjg1 #bad length of1 capacity of1 population supplied1 #h lightning arresters 7see ,lightning ,arresters71 #agi lightning protection1 #aah long spans1 #aij loss1 #bb1 #ci losses1 #bae maximum investment in1 #bbj method of fastening conductors to insulators1 #cbc operation1 #caa pole spacing1 #bdi regulation with synchronous motors1 #bda relative weights of three-phase1 two-phase1 and single-phase1 #bbh right-of-way1 #bdf sag in1 #cji spacing of wire1 #bcd steel towers 7see ,towers71 #cjf switch-houses1 #bch switches1 fuses1 and circuit-breakers1 #ace take up1 arrangement for1 #cbe total cost of1 #bb total cost of operation1 #bc transposition of wires1 #bjf1 #cad voltage1 #ba1 #bae in cables1 #aij regulation1 #acj wind pressure1 #baj long line1 #bba minimum-sized wire1 #bjb physical limits of1 #dd a4 c4 pole line construction1 #cd d4 c4 pole line construction1 #cc pole lines1 #bdf problems1 #ai regulation1 #aee1 #bci selection of circuits1 #bcc single vs4 parallel circuits1 #bda spacing of conductors1 #df submarine1 #ahg three-phase1 #aac three-phase and two-phase1 #bbh two-phase1 #aac underground1 #ahg without step-up transformers1 #abj ,transposition of wires1 #bjf ,turbines1 high-speed1 #ajg horizontal1 #gi1 #hc1 #hi1 #ig impulse1 #hb1 #ij1 #ii speed of1 #ajh low-head good speed1 #aje peripheral1 speed of1 #he1 #ajc pressure1 #gi several on same shaft1 #he1 #aje vertical1 #gi1 #hd1 #he1 #hf1 #ig ,underground cable connected to overhead line1 #aig cables1 #ahg ,victor 7,colo47 plant1 #bf1 #bg1 #bh1 #bjh ,virginia ,city plant1 #aah ,voltage drop compensation1 #acc fluctuations1 #bah high1 alternators1 #abj measurements1 #bij in cables1 #aij1 #aif limiting1 #dd for a4 c4 machines1 #cb for d4 c4 machines1 #ca of transmission lines1 #ba1 #bae regulation1 #acj1 #aee sparking1 #ahb test for insulators1 #bhi ,volts per mile1 #bf ,wages paid attendants1 #ab ,walls1 #ie ,washington ,baltimore ,ry41 #aba ,washouts1 #ha ,water-cooled transformers1 #abi ,water-power1 development of1 #ea high head1 #gd-gg low head1 #ea-gd per cent4 of energy available1 #af pure hydraulic development1 #ea stations 7see ,hydro-electric ,stations7 storage capacity1 #ae1 #fa utilization of1 #aj vs4 steam1 #e ,water1 storage of1 #ae1 #fa ,weight of the conductor metals1 #bjb ,welland ,canal plant1 #a1 #bf1 #bg1 #bh1 #bjh1 #bde1 #bdh ,westbrook 7,me47 plant1 #abj ,white ,river to ,dales plant1 #bf1 #bg1 #bh1 #ga1 #acd ,wind1 #cbd pressure on lines1 #baj ,winooski ,river plant1 #fd ,wire room1 #aci ,wood1 compressive strength of1 #cjb ,woods for poles1 #beb ,yadkin ,river 7,n4 ,c47 plant1 #bf1 #bg1 #bh1 #aah1 #bjh ,transcriber's ,notes ,this transcription uses the text of the original work4 ,inconsistencies 7e4g41 per cent4 and per cent2 ,chambly and ,chamblay2 ,garvin's and ,garvins ,falls2 #a-j and #a_/j ,b4 ,s4 gauge2 hyphenation2 capitalisation2 use of italics1 etc47 have been retained1 except as mentioned below4 ,some of the calculations in the book give different results to the ones provided2 these have not been corrected4 ,in this book1 8cm40 stands for circular mils1 not for centimeters4 ,page #gf1 ,fig4 #af3 the text in the centre of the illustration probably reads #abjj feet ,pipe ,line4 ,page #aaa3 between figures #dd and #df the original book has figure #ea;a2 the numbering has not been changed4 ,changes made3 ,obvious minor typographical and punctuation errors have been corrected silently4 ,fractions have been standardised to x_/y2 all occurrences of vs4 have been italicised4 ,in-line multi-line formulas have been changed to single-line formulas4 ,table of ,contents3 the ,index has been added4 page #ae3 table header changed to small caps as others page #ca3 ,electrical transmission changed to ,electrical transmissions page #ef3 ,canon changed to ,caon page #gg3 ,tlaluepantla changed to ,tlalnepantla page #cab3 ,teluride changed to ,telluride page #ccb3 ,canon changed to ,caon4