,,the ,,thought ,,is ,,in ,,the ,,question ,,the ,,information ,,is ,,in ,,the ,,answer ,illustration3 ,,hawkins ,,electrical ,,guide ,,number ,,seven ,,questions ,,answers ,,illustrations ,a ,,progressive ,,course ,,of ,,study ,,for ,,engineers1 ,,electricians1 ,,students ,,and ,,those ,,desiring ,,to ,,acquire ,a ,,working ,,knowledge ,,of ,,electricity ,,and ,,its ,,applications ,a ,,practical ,,treatise by ,,hawkins ,,and ,,staff ,illustration3 ,,theo4 ,,audel ,,co4 #gb ,,fifth ,,ave4 ,,new ,,york4 ,,copyrighted1 #aiae1 ,,by ,,theo4 ,,audel ,,co41 ,,new ,,york4 ,printed in the ,united ,states4 ,,table ,,of ,,contents ,,guide ,,no4 #g4 ,,alternating ,,current ,,systems #a1eca to #a1ehf ,advantages of the alternating current--classification of systems--vector summation2 examples--forms of circuit3 series1 parallel1 parallel series1 series parallel--transformer systems3 individual transformers2 transformation at distribution centers--single phase system2 two wire transmission and three wire distribution2 objections to single phase systems2 advantages--monocyclic system--two phase systems3 adaptation2 ordinary voltages used2 two phase three wire system2 two phase five wire system--three phase systems3 six wire2 four wire2 three wire2 connections3 star1 delta1 star delta1 delta star2 evolution of three wire system2 pressure and current relations2 connection of transformers2 open delta connection--change of frequency--,schaghticoke-,schenectady transmission line--transformation of phases3 three to one1 three to two1 two to six1 and three to six phase--,scott connection for transforming from three to two phase--three to two phase with three star connected transformers--economy of a4c4 systems--relative weights of copper required for polyphase systems--aermotor towers of ,southern ,power ,co4--choice of voltage--usual transmission voltages--diagram of three phase distribution--mixed current systems2 usual d4c4 pressure on traction lines2 use of mixed systems4 ,,auxiliary ,,apparatus #a1ehg to #a1ehh ,classification of auxiliary devices3 switching devices1 types--current or pressure limiting devices1 types--lightning protection devices1 types--regulating devices1 types--synchronous condensers1 types--indicating devices4 ,,switching ,,devices #a1ehi to #a1fab ,definition of a switch--behaviour of the current when the circuit is broken--points on design--installation of single throw and double throw switches--plug switches--forms of break3 open1 enclosed1 fuse1 horn1 oil--disconnecting switches--pole top switches--horn break switches--motor starting switch--oil switches2 nature of an oil break--remote control oil switches--motor operated switches--rupturing capacity of oil switches--float switches4 ,,current ,,and ,,pressure ,,limiting ,,devices #a1fac to #a1fgf ,necessity for these devices2 steam analogy--fuses3 advantages and disadvantages2 types3 plug1 cut out1 expulsion1 no arc1 magnetic blow out1 quick break fuse1 etc4--metal used--current limiting inductances3 construction1 location--circuit breakers3 progressive breaking of the circuit2 carbon contacts--automatic features3 overload trip1 underload trip1 low voltage trip1 auxiliary circuit trip--relays3 adaptation2 classification3 protective1 regulative1 communicative1 a4c4 and d4c41 circuit opening1 circuit closing1 primary1 secondary1 overload1 underload1 over voltage1 low voltage1 reverse energy1 reverse phase1 instantaneous1 time limit1 inverse time limit1 differential--how to select relays4 ,,lightning ,,protection ,,devices #a1fgg to #a1gad ,essential parts3 air gaps1 resistances1 inductances1 arc suppressing devices--requirements--air gap arresters--multi-gap arresters2 difference between spark and arc2 distribution of stress2 sparking at the gaps2 how the arc is extinguished2 effect of frequency2 graded shunt resistances2 the cumulative or breaking back effect--arresters for grounded ,y and non-grounded neutral systems--multiplex connection--horn gap arresters3 operation2 objection to the horn gap--electrolytic arresters3 critical voltage1 temporary and permanent2 determination of number of cell2 putting cell in commission2 nature of the film2 horn gaps on electrolytic arresters2 charging of electrolytic arresters2 charging arresters for non-grounded circuits--grounded and non-grounded neutral circuits--ground connections--choke coils3 principal objects2 principal electrical conditions to be avoided2 why choke coils are made in the form of an hour glass2 cooling--static interrupters2 how to connect condenser and choke coil2 effect of condenser4 ,,regulating ,,devices #a1gae to #a1gfb ,regulation of alternators--a4c4 feeder regulation--application of induction type regulators2 types3 induction1 and variable ratio transformer regulators2 operation of induction regulators2 neutral position2 regulator capacity--polyphase induction regulators3 construction1 operation2 automatic control2 why two relays are used2 difficulties encountered in operation of relays2 vibration or chattering of the contacts2 poor contact of primary relay--variable ratio transformer voltage regulators3 types3 drum1 and dial2 dial type for high voltage--small feeder voltage regulators3 construction and operation2 adjustment--automatic voltage regulators for alternators3 method of regulation--line drop compensators3 essential parts2 connections2 construction and operation2 diagram of automatic voltage regulator using a line drop compensator--starting compensators3 necessity for2 construction and operation--star delta switches4 ,,synchronous ,,condensers #a1gfc to #a1ggf ,characteristics--effect of fully loaded and lightly loaded induction motors on the power factor--synchronous motor used as condenser--effects of low lagging power factors2 example--cost of synchronous condenser vs4 cost of copper--location of condenser--synchronous condenser calculations and diagram for same4 ,,indicating ,,devices #a1ggg to #a1hch ,virtual value of an alternating current or pressure--the word effective erroneously used for virtual3 steam engine analogy illustrating this error--classification of instruments3 electromagnetic or moving wire1 hot wire1 induction1 dynamometer--electromagnetic or moving iron instruments3 types3 plunger1 inclined coil1 magnetic vane2 character of scale2 objections and precautions--inclined coil instruments--magnetic vane instruments--hot wire instruments--induction instruments3 types3 shielded pole1 rotary field2 operation of both types--dynamometers3 construction and operation2 how arranged to measure watts--watthour meters3 types3 commutator1 induction1 ,faraday disc2 essential parts2 object of the motor2 object of generator2 objection to commutator meter--principles of induction watthour meters3 essential parts2 strength of rotating field2 moving element2 retarding element2 registering element2 frame and bearings2 friction compensator2 power factor adjustment2 frequency adjustment--,faraday disc1 or mercury motor ampere hour meter3 construction and operation--frequency indicators3 types3 synchronous motor1 resonance1 induction2 synchronous motor as frequency indicator--resonance frequency indicators3 adaptation--induction frequency meter3 construction and operation--synchronism indicators3 types3 lamp or voltmeter1 resonance or vibrating reed1 rotating field--power factor indicators3 wattmeter type2 disc1 or rotating field type--ground detectors4 ,,chapter ,,lv ,,alternating ,,current ,,systems ,the facility with which alternating current can be transformed from one voltage to another1 thus permitting high pressure transmission of electric energy to long distances through small wires1 and low pressure distribution for the operation of lighting systems and motors1 gives a far greater variety of systems of transmission and distribution than is possible with direct current4 ,furthermore1 when the fact that two phase current can be readily transformed into three phase current1 and these converted into direct current1 and vice versa1 by means of rotary converters and rectifiers1 is added to the advantages derived by the use of high tension systems1 it is apparent that the opportunity for elaboration becomes almost unlimited4 ,these conditions have naturally tended toward the development of a great variety of systems1 employing more or less complicated circuits and apparatus1 and although alternating current practice is still much less definite than direct current work1 certain polyphase systems are now being generally accepted as representing the highest standards of power generation1 transmission and distribution4 ,a classification of the various alternating current systems1 to be comprehensive1 should be made according to several points of view1 as follows3 #a4 ,with respect to the arrangement of the circuit1 as a4 ,series2 b4 ,parallel2 c4 ,series parallel2 d4 ,parallel series4 #b4 ,with respect to transformation1 as ,transformer2 #c4 ,with respect to the mode of transmitting the energy1 as a4 ,constant pressure2 b4 ,constant current4 #d4 ,with respect to the kind of current1 as a4 ,single phase two wire2 three wire2 b4 ,monocyclic four wire2 c4 ,two phase three wire2 five wire2 six wire2 three wire2 four wire2 d4 ,three phase star connection2 delta connection2 star delta connection2 delta star connection2 e4 ,multi-phase of more than three phases2 #e4 ,with respect to transmission and distribution1 as a4 ,frequency changing2 b4 ,phase changing2 c4 ,converter2 d4 ,rectifier4 ,in order to comprehend the relative advantages of the various alternating current systems1 it is first necessary to understand the principle of vector summation4 ,vector ,summation4--,this is a simple geometrical process for ascertaining the pressure at the free terminals of alternating current circuits4 ,the following laws should be carefully noted3 #a4 ,if two alternating pressures which agree in phase are connected together in series1 the voltage at the free terminals of the circuit will be equal to their arithmetical sum1 as in the case of direct currents4 ,illustration3 ,,fig4 #b1abc4--,vectors4 ,a vector is defined as3 a line1 conceived to have both a fixed length and a fixed direction in space1 but no fixed position4 ,thus ,a and ,b are lines1 each having a fixed length1 but no fixed direction4 ,by adding an arrow head the direction is fixed and the line becomes a vector1 as for example vector ,c4 ,the fixed length is usually taken to represent a definite force1 thus the fixed length of vector ,c is #d4g which may be used to represent #d4g lbs41 #d4g tons1 etc41 as may be arbitrarily assumed4 ,when there is phase difference between the two alternating pressures1 connected in series1 the following relation holds3 #b4 ,the value of the terminal voltage will differ from their arithmetical sum1 depending on the amount of their phase difference4 ,when there is phase difference1 the value of the resultant is conveniently obtained as explained below4 ,ques4 ,how are vector diagrams constructed for obtaining resultant electric pressure8 ,ans4 ,on the principle of the parallelogram of forces4 ,ques4 ,what is understood by the parallelogram of forces8 ,ans4 ,it is a graphical method of finding the resultant of two forces1 according to the following law3 ,if two forces acting on a point be represented in direction and intensity by adjacent sides of a parallelogram1 their resultant will be represented by the diagonal of the parallelogram which passes through the point4 ,illustration3 ,,fig4 #b1abd4--,parallelogram of forces4 ,,oc is the resultant of the two forces ,,oa and ,,ob4 ,the length and direction of the lines represent the intensity and direction of the respective forces1 the construction being explained in the accompanying text4 ,thus in fig4 #b1abd1 let ,,oa and ,,ob represent the intensity and direction of two forces acting at the point ,o1 ,draw ,,ac and ,,bc1 respectively parallel to ,,ob and ,,oa1 completing the parallelogram1 then will ,,oc1 the diagonal from the point at which the forces act1 represent the intensity and direction of the resultant1 that is1 of a force equivalent to the combined action of the forces ,,oa and ,,ob1 these forces being called the components of the force ,,oc4 ,ques4 ,upon what does the magnitude of the resultant of two forces depend8 ,ans4 ,upon the difference in directions in which they act1 as shown in figs #b1abe to #b1abh4 ,ques4 ,is the parallelogram of forces applied when the difference in direction or phase difference of two forces is #ij degrees8 ,ans4 ,it is sometimes more conveniently done by calculation according to the law of the right angle triangle4 ,illustration3 ,,figs4 #b1abe to #b1abh4--,parallelograms of forces showing increase in magnitude of the resultant of two forces1 as their difference of direction1 or electrically speaking1 their phase difference is diminished4 ,the diagrams show the growth of the resultant of the two equal forces ,,oa and ,,ob as the phase difference is reduced from #afe successively to #abj1 #fj1 and #ae degrees4 ,according to this principle1 if two alternating pressures have a phase difference of #ij degrees they may be represented in magnitude and direction by the two sides of a right angle triangle as ,,oa and ,,ob in fig4 #b1abi2 then will the hypotenuse ,,ab represent the magnitude and direction of the resultant pressure4 ,that is to say1 the resultant pressure ,,ab 77,,oa7 7,,ob77 7#a7 ,,example4--,a two phase alternator is wound for #cjj volts on one phase and #bjj volts on the other phase1 the phase difference being #ij4 ,if one end of each winding were joined so as to form a single winding around the armature1 what would be the resultant pressure8 ,by calculation1 substituting the given values in equation 7#a71 ,resultant pressure 7#cjj #bjj7 7#acj1jjj7 #cfj4f volts4 ,this is easily done graphically as in fig4 #b1abi by taking a scale1 say1 #a #ajj volts and laying off ,,oa #c #cjj volts1 and at right angles ,,ob #b #bjj volts1 then by measurement ,,ab #c4fjf #cfj4f volts4 ,illustration3 ,,fig4 #b1abi4--,method of obtaining the resultant of two component pressures acting at right angles by solution of right angle triangle4 ,the equation of the right angle triangle is explained at length in ,guide ,no4 #e1 page #a1jgj4 ,ques4 ,when the two pressures are equal and the phase difference is #ij1 is it necessary to use equation 7#a7 to obtain the resultant8 ,ans4 ,no4 ,the resultant is obtained by simply multiplying one of the pressures by #a4da4 ,this is evident from fig4 #b1acj4 ,here the two pressures ,,oa and ,,ob are equal as indicated by the dotted arc4 ,since they act at right angles1 ,,ob is drawn at #ij to ,,oa4 ,according to the equation of the right angle triangle1 the resultant ,,ab 7#a #a7 #b #a4dadb which ordinarily is taken as #a4da4 ,this value will always represent the ratio between the magnitude of the resultant and the two component forces1 when the latter are equal1 and have a phase difference of #ij degrees4 ,forms of ,circuit4--,alternating current systems of distribution may be classed1 with respect to the kind of circuit used1 in a manner similar to direct current systems1 that is1 they may be called series1 parallel1 series parallel1 or parallel series systems1 as shown in figs4 #b1aca to #b1acd4 ,illustration3 ,,fig4 #b1acj4--;,diagram for obtaining the resultant of two equal component pressures acting at right angles4 ,series ,circuits4--,these are used in arc lighting1 and series incandescent lighting1 a constant current being maintained2 also for constant current motors and generators supplying secondary circuits4 ,illustration3 ,,figs4 #b1aca to #b1acd4--,various forms of circuit4 ,these well known forms of circuit are used in both alternating and direct current systems4 ,the simple series circuit1 fig4 #b1aca1 is suitable for constant current arc lighting4 ,fig4 #b1acb1 shows the parallel constant pressure circuit2 this form of circuit is largely used but is seldom connected direct to the alternator terminals1 but to a step down transformer1 on account of the low pressure generally required4 ,fig4 #b1acc illustrates a parallel series circuit1 and #b1acd1 a series parallel circuit4 ,several forms of constant current alternator1 analogous to the ,thompson-,houston and ,brush series arc dynamos1 have been introduced4 ,in the design of such alternators self-induction and armature reaction are purposely exaggerated2 so that the current does not increase very much1 even when the machine is short circuited4 ,with this provision1 no regulating device is required4 ,illustration3 ,,fig4 #b1ace4--,typical ,american overhead #f1fjj volt single phase interurban trolley line1 ,baltimore and ,annapolis short line1 ,annapolis1 ,md4 ,an objectionable feature is that the voltage of a constant current alternator will rise very high if the circuit be opened1 because it is then relieved of inductance drop and armature reaction4 ,to guard against a dangerous rise of voltage1 a film cut out or equivalent device is connected to the terminal of each machine so that it will short circuit the latter if the voltage rise too high4 ,ques4 ,what advantage have constant current alternators over constant current dynamos8 ,ans4 ,the high pressure current is delivered to the external circuit without a commutator1 hence there is no sparking difficulty4 ,the above relates to the revolving field type of alternator4 ,there are1 however1 alternators in which the armature revolves1 the current being delivered to the external circuit through collector rings and brushes4 ,this type of alternator1 it should be noted1 is for moderate pressures1 and moreover there is no interruption to the flow of the current such as would be occasioned by a tangential brush on a dynamo in passing from one commutator segment to the next4 ,in the revolving field machine1 though the armature current be of very high pressure1 the field current which passes through the brushes and slip rings is of low pressure and accordingly presents no transmission difficulties4 ,illustration3 ,,fig4 #b1acf4--;,diagram of parallel circuit4 ,it is a constant pressure circuit and is very widely used for lighting and power4 ,if each lamp takes say ampere1 the current flowing in the circuit will vary with the number of lamps in operation2 in the above circuit with all lamps on1 the current is #e #b amperes4 ,ques4 ,state a disadvantage4 ,ans4 ,some source of direct current for field excitation is required4 ,ques4 ,in a constant current series system1 upon what does the voltage at the alternator depend8 ,ans4 ,the number of devices connected in the circuit1 the volts required for each1 and the line drop4 ,parallel ,circuits4--,these are used for constant pressure operation4 ,such arrangement provides a separate circuit for each unit making them independent so that they may vary in size and each one can be started or stopped without interfering with the others4 ,parallel circuits are largely used for incandescent lighting1 and since low pressure current is commonly used on such circuits they are usually connected to step down transformers1 instead of direct to the alternators4 ,illustration3 ,,fig4 #b1acg4--;,diagram of parallel series circuit1 showing fall of pressure between units4 ,this system is very rarely used2 it has the disadvantage that if a lamp filament breaks1 the resistance of the circuit is altered and the strength of the current changed4 ,the voltmeter shows the fall of pressure along the line4 ,it should be noted that1 although the meter across ,,ab is shown as registering zero pressure1 there is1 strictly speaking1 a slight pressure across ,,ab1 in amount1 being that required to overcome the resistance of the conductor between ,a and ,b4 ,parallel ,series ,circuits4--,fig4 #b1acg shows the arrangement of a parallel series circuit and the pressure conditions in same4 ,such a circuit consists of groups of two or more lamps or other devices connected in parallel and these groups connected in series4 ,such a circuit1 when used for lighting1 obviously has the disadvantage that if a lamp filament breaks1 the resistance of the group is increased1 thus reducing the current and decreasing the brilliancy of the lamps4 ,this arrangement accordingly does not admit of turning off any of the lights4 ,series ,parallel ,circuits4--,the arrangement of circuits of this kind is shown in fig4 #b1acd2 they are used to economize in copper since by joining groups of low pressure lamps in series they may be supplied by current at correspondingly higher pressure4 ,thus1 if in fig4 #b1acd1 #aaj volt1 ampere lamps be used1 the pressure on the mains1 that is1 between any two points as ,a and ,b would be #aaj #c #ccj volts4 ,each group would require ampere and the five groups #e #b amperes4 ,illustration3 ,,fig4 #b1ach4--dd1jjj volt lines entering the ,gastonia sub-station of the ,southern ,power ,co4 ,the poles used are of the twin circuit two arm type1 built of structural steel1 their height varying from #de to #hj feet1 the latter weighing #i1jjj pounds each4 ,these poles have their bases weighted with concrete4 ,transformer ,systems4--,nearly all alternating current systems are transformer systems1 since the chief feature of alternating current is the ease with which it may be transformed from one pressure to another4 ,accordingly1 considerable economy in copper may be effected by transmitting the current at high pressure1 especially if the distance be great1 and1 by means of step down transformers1 reducing the voltage at points where the current is used or distributed4 ,ordinarily and for lines of moderate length1 current is sent out direct from the alternator to the line and transformed by step down transformers at the points of application4 ,with respect to the step down transformers1 there are two arrangements3 #a4 ,individual transformers2 #b4 ,one transformer for several customers4 ,illustration3 ,,fig4 #b1aci4--;,diagram of transformer system with individual transformers4 ,the efficiency is low1 but such method of distribution is necessary in sparsely settled or rural districts4 ,individual transformers1 that is1 a separate transformer for each customer is necessary in rural districts where the intervening distances are great as shown in fig4 #b1aci4 ,ques4 ,what are the objections to this method of distribution8 ,ans4 ,it requires the use of small transformers which are necessarily less efficient and more expensive per kilowatt than large transformers4 ,the transformer must be built to carry1 within its overload capacity1 all the lamps installed by the customer since all may be used occasionally4 ,usually1 however1 only a small part of the lamps are in use1 and those only for a small part of the day1 so that the average load on the transformer is a very small part of its capacity4 ,since the core loss continues whether the transformer be loaded or not1 but is not paid for by the customer1 the economy of the arrangement is very low4 ,in the second case1 where one large transformer may be placed at a distribution center1 to supply several customers1 as in fig4 #b1adj1 the efficiency of the system is improved4 ,ques4 ,why is this arrangement more efficient than when individual transformers are used8 ,illustration3 ,,fig4 #b1adj4--;,diagram of transformer system with one transformer located at a distribution center and supplying several customers as ,a1 ,b1 and ,c4 ,such arrangement is considerably more efficient than that shown in fig4 #b1aci1 as explained in the accompanying text4 ,ans4 ,less transformer capacity is required than with individual transformers4 ,ques4 ,why is this8 ,ans4 ,with several customers supplied from one transformer it is extremely improbable that all the customers will burn all their lamps at the same time4 ,it is therefore unnecessary to install a transformer capable of operating the full load1 as is necessary with individual transformers4 ,ques4 ,does the difference in transformer capacity represent all the saving8 ,ans4 ,no2 one large transformer is more efficient than a number of small transformers4 ,ques4 ,why8 ,ans4 ,the core loss is less4 ,for instance1 if four customers having #bj lamps each were supplied from a single transformer1 the average load would be about #h lamps1 and at most not over #aj or #ae lamps1 and a transformer carrying #cj to #ce lamps at over load would probably be sufficient4 ,a #a1ejj watt transformer would therefore be larger than necessary4 ,at #c per cent4 core loss1 this gives a constant loss of #de watts1 while the average load of #h lamps for #c hours per day gives a useful output of #fj watts1 or an all year efficiency of nearly #fj per cent41 while a #a1jjj watt transformer would give an all year efficiency of #fg per cent4 ,for long distance transmission lines1 the voltage at the alternator is increased by passing the current through a step up transformer1 thus transmitting it at very high pressure1 and reducing the voltage at the points of distribution by step down transformers as in fig4 #b1ada4 ,illustration3 ,,fig4 #b1ada4--;,diagram illustrating the use of step up and step down transformers on long distance transmission lines4 ,the saving in copper is considerable by employing extra high voltages on lines of moderate or great length as indicated by the relative sizes of wire4 ,ques4 ,in practice1 would such a system as shown in fig4 #b1ada be used8 ,ans4 ,if the greatest economy in copper were aimed at1 a three phase system would be used4 ,the purpose of fig4 #b1ada is to show the importance of the transformer in giving a flexibility of voltage1 by which the cost of the line is reduced to a minimum4 ,ques4 ,does the saving indicated in fig4 #b1ada represent a net gain8 ,ans4 ,no4 ,the reduction in cost of the transmission is partly offset by the cost of the transformers as well as by transformer losses and the higher insulation requirements4 ,illustration3 ,,fig4 #b1adb4--,single and twin circuit poles 7,southern ,power ,co474 ,the twin circuit pole at the right is used for #aa1jjj volt circuits1 while the single circuit poles at the left carry #dd1jjj volt conductors1 being used on another division for #ajj1jjj volt line4 ,every case of electric transmission presents its own problem1 and needs thorough engineering study to intelligently choose the system best adapted for the particular case4 ,single ,phase ,systems4--,there are various arrangements for transmission and distribution classed as single phase systems4 ,thus1 single phase current may be conveyed to the various receiving units by the well known circuit arrangements known as series1 parallel1 series parallel1 parallel series1 connections previously described and illustrated in figs4 #b1aca to #b1acd4 ,again single phase current may be transmitted by two wires and distributed by three wires4 ,this is done in several ways1 the simplest being shown in fig4 #b1adc4 ,illustration3 ,,fig4 #b1adc4--;,diagram illustrating single phase two wire transmission and three wire distribution4 ,the simplified three wire arrangement at ,a1 is not permissible except in cases of very little unbalancing4 ,where the difference between loads on each side of the neutral may be great some form of balancing as an auto-transformer or equivalent should be used1 as at ,b4 ,ques4 ,under what conditions is the arrangement shown in fig4 #b1adc desirable8 ,ans4 ,this method of treating the neutral wire is only permissible where there is very little unbalancing1 that is1 where the load is kept practically the same on both sides of the neutral4 ,ques4 ,what advantage is obtained by three wire distribution8 ,ans4 ,the pressure at the alternator can be doubled1 which means1 for a given number of lamps1 that the current is reduced to half1 the permissible drop may be doubled1 the resistance of the wires quadrupled1 and their cost reduced nearly #ge per cent4 ,illustration3 ,,fig4 #b1add4--ajj1jjj volt ,milliken towers with one circuit strung 7,southern ,power ,co474 ,these towers are mounted on metal stubs sunk #f feet in the ground4 ,where the angle of the line is over #ae degrees1 however1 these stubs are weighted with rock and concrete1 and where an angle of over #cj degrees occurs1 two and sometimes three towers are used for making the turn4 ,the weight of the standard ,milliken tower is #c1jhj lbs41 and its height from the ground to peak is #ea feet4 ,the towers are spaced to average eight to a mile and a strain tower weighing #d1bej lbs4 is used every mile4 ,for particularly long spans a special heavy tower weighing #f1jjj lbs4 is used4 ,the circuits are transposed every #cj miles4 ,multiple disc insulators are used1 four discs being used to suspend each conductor from standard towers and ten discs to each conductor on strain towers4 ,the standard span is #fjj feet1 sag #aa ft at #ej ,fahr4 ,ques4 ,what modification of circuit ,a 7fig4 #b1adc71 should be made to allow for unbalancing in the three wire circuit8 ,ans4 ,an auto-transformer or balance coil as it is sometimes called should be used as at ,b4 ,this is a very desirable method of balancing when the ratio of transformation is not too large4 ,ques4 ,for what service would the system shown in fig4 #b1adc be suitable8 ,ans4 ,for short distance transmission1 as for instance1 in the case of an isolated plant because of the low pressure at which the current is generated4 ,the standard voltages of low pressure alternators are #djj1 #dhj1 and #fjj volts4 ,illustration3 ,,fig4 #b1ade4--,view of a typical isolated plant4 ,the illustration represents an electric lighting plant on a farm showing the lighting of the dwelling1 barn1 tool house and pump house4 ,the installation consists of a low voltage dynamo with gas engine drive and storage battery together with the necessary auxiliary apparatus4 ,ques4 ,in practice are single phase alternators used as indicated in fig4 #b1adc8 ,ans4 ,alternators are wound for one1 two or three phases4 ,three phase machines are more commonly supplied and in many cases it will pay to install them in preference to single phase1 even if they be operated single phase temporarily4 ,for a given output1 three phase machines are smaller than single phase and the single phase load can usually be approximately balanced between the three phases4 ,moreover1 if a three phase machine be installed1 polyphase current will be available in case it may be necessary to operate polyphase motors at some future time4 ,standard three phase alternators will carry about #gj per cent4 of their rated kilowatt output when operated single phase1 with the same temperature rise4 ,ques4 ,how are three phase alternators used for single phase circuits8 ,ans4 ,the single phase circuit is connected to any two of the three phase terminal leads4 ,illustration3 ,,fig4 #b1adf4--;,diagram showing arrangement of single phase system for two wire transmission and three wire distribution1 where the transmission distance is considerable4 ,in order to reduce the cost of the transmission line1 the current must be transmitted at high pressure2 this necessitates the use of a step down transformer at the distributing center as shown in the illustration4 ,ques4 ,what form of single phase system should be used where the transmission distance is considerable8 ,ans4 ,the current should be transmitted at high pressure1 a step down transformer being placed at each distribution center to reduce the pressure to the proper voltage to suit the service requirements as shown in fig4 #b1adf4 ,thus1 if #aaj volt lamps be used on the three wire circuit1 the pressure between the two outer wires would be #bbj volts4 ,a transformation ratio of say #aj3a would give #b1bbj volts for the primary circuit4 ,the current required for the primary with this ratio being only 4#a that used in the secondary1 a considerable saving is effected in the cost of the transmission line as must be evident4 ,with the high pressure alternator only one transformation of the current is needed1 as shown at the distribution end4 ,in place of the high pressure alternator1 a low pressure alternator could be used in connection with a step up transformer as shown in fig4 #b1adg1 but there would be an extra loss due to the additional transformer1 rendering the system less efficient than the one shown in fig4 #b1adf4 ,such an arrangement as shown in the fig4 #b1adg might be justified in the case of a station having a low pressure alternator already in use and it should be desired to transmit a portion of the energy a considerable distance4 ,ques4 ,how could the system shown in fig4 #b1adg be made more efficient than that of fig4 #b1adf8 ,ans4 ,by using a high pressure alternator in order to considerably increase the transmission voltage4 ,thus1 a #b1bjj volt alternator and #a3aj step up transformer would give a line pressure of #bb1jjj volts1 which at the distribution end could be reduced1 to #bbj volts for the three wire circuit1 using a #ajj3a step down transformation4 ,illustration3 ,,fig4 #b1adg4--;,diagram illustrating how electricity can be economically transmitted a considerable distance with low pressure alternator already in use4 ,ques4 ,would this be the best arrangement8 ,ans4 ,no4 ,ques4 ,what system would be used in practice for maximum economy8 ,ans4 ,three phase four wire4 ,ques4 ,what are the objections to single phase generation and transmission8 ,ans4 ,it does not permit of the use of synchronous converters1 self-starting synchronous motors1 or induction motor starting under load4 ,it is poorly adapted to general power distribution1 hence it is open to grave objections of a commercial nature where there exists any possibility of selling power or in any way utilizing it for general converter and motor work4 ,illustration3 ,,fig4 #b1adh4--;,angle tower showing ,general ,electric strain insulators4 ,the tower being subject to great torsional strains is erected on a massive concrete foundation4 ,the construction is similar to the standard tower but of heavier material1 and having the same vertical dimensions but with bases #bj ft4 square4 ,ques4 ,for what service is it desirable8 ,ans4 ,for alternating current railway operation4 ,there are advantages of simplicity in the entire generating1 primary1 and secondary distribution systems for single phase roads4 ,these advantages are so great that they justify considerable expense1 looked at from the railway point of view only1 the single phase system throughout may be considered as offering the most advantage4 ,ques4 ,what are the objectionable features of single phase alternators8 ,ans4 ,this type of alternator has an unbalanced armature reaction which is the cause of considerable flux variation in the field pole tips and in fact throughout the field structure4 ,in order to minimize eddy currents1 such alternators must accordingly be built with thinner laminations and frequently poorer mechanical construction1 resulting in increased cost of the machine4 ,the large armature reaction results in a much poorer regulation than that obtained with three phase alternators1 and an increased amount of field copper is required1 also larger exciting units4 ,these items augment the cost so that the single phase machine is considerably more expensive than the three phase1 of the same output and heating4 ,illustration3 ,,fig4 #b1adi4--;,elementary alternator developing one volt at frequencies of #fj and #be1 showing the effect of reducing the frequency4 ,since for the same number of pole1 the ,r4,p4,m4 have to be decreased to decrease the frequency1 increased flux is required to develop the same voltage4 ,hence in construction1 low frequency machines require larger magnets1 increased number of turns in series on the armature coils1 larger exciting units as compared with machines built for higher frequency4 ,ques4 ,what factor increases the difficulties of single phase alternator construction8 ,ans4 ,the difficulties appear to increase with a decrease in frequency4 ,the adoption of any lower frequency than #be cycles may result in serious difficulties in construction for a complete line of machine1 especially those of the two or four pole turbine driven type where the field flux is very large per pole4 ,monocyclic ,system4--,in this system1 which is due to ,steinmetz1 the alternator is of a special type4 ,in construction1 there is a main single phase winding an auxiliary or teaser winding connected to the central point of the main winding in quadrature therewith4 ,the teaser coil generates a voltage equal to about #be per cent4 of that of the main coil so that the pressure between the terminals of the main coil and the free end of the teaser is the resultant of the pressure of the two coils4 ,illustration3 ,,fig4 #b1aej4--;,diagram of monocyclic system1 showing lighting and power circuits4 ,by various transformer connections it is possible to obtain a practically correct three phase relationship so that polyphase motors may be employed4 ,in this system1 two wires leading from the ends of the single phase winding in the alternator supply single phase current to the lighting load1 a third wire connected to the end of the teaser being run to points where the polyphase motors are installed as shown in fig4 #b1aej4 ,the monocyclic system is described at length in the chapter on alternators1 ,guide ,no4 #e1 pages1 #a1aef to #a1aei4 ,two ,phase ,systems4--,a two phase circuit is equivalent to two single phase circuits4 ,either four or three wire may be employed in transmitting two phase current1 and even in the latter instance the conditions are practically the same as for single phase transmission1 excepting the unequal current distribution in the three wires4 ,fig4 #b1aea shows a two phase four wire system4 ,illustration3 ,,fig4 #b1aea4--;,diagram of two phase four wire system4 ,it is desirable for supplying current for lighting and power4 ,the arrangement here shown should be used only for lines of short or moderate length1 because of the low voltage4 ,motors should be connected to a circuit separate from the lighting circuit to avoid drop on the latter while starting a motor4 ,ques4 ,for what service is the system shown in fig4 #b1aea desirable8 ,ans4 ,it is adapted to supplying current for lighting and power at moderate or short distances4 ,either #aaj or #bbj volts are ordinarily used which is suitable for incandescent lighting and for constant pressure arc lamps1 the lamps being connected singly or two in pairs4 ,ques4 ,where current for both power and light are obtained from the same source how should the circuits be arranged8 ,ans4 ,a separate circuit should be employed for each1 in order to avoid the objectionable drop and consequent dimming of the lights due to the sudden rush of current during the starting of a motor4 ,illustration3 ,,fig4 #b1aeb4--;,diagram of two phase three wire system4 ,a wire is connected to one end of each phase winding as at ,a and ,b1 and a third wire ,c1 to the other end of both phases as shown4 ,disagreeable fluctuation of the lights are always met with when motors are connected to a lighting circuit and the effect is more marked with alternating current than with direct current1 because most types of alternating current motor require a heavy current usually lagging considerably when starting4 ,this not only causes a large drop on the line1 but also reacts injuriously upon the regulation of transformers and alternators1 their voltage falling much more than with an equal non-inductive load4 ,ques4 ,what voltages are ordinarily used on two phase lines of more than moderate length8 ,ans4 ,for transmission distances of more than two or three miles1 pressures of from #a1jjj to #b1jjj volts or more are employed to economize in copper4 ,for long distance transmission of over fifty miles1 from #cj1jjj to #ajj1jjj volts and over are used4 ,ques4 ,for long distance transmission at #cj1jjj to #dj1jjj volts1 what additional apparatus is necessary8 ,ans4 ,step up and step down transformers4 ,illustration3 ,,fig4 #b1aec4--;,diagram illustrating two phase three wire transmission4 ,the third wire ,c is attached to the connector between one end of phase ,a1 and phase ,b windings4 ,ques4 ,explain the method of transmitting two phase current with three wires4 ,ans4 ,the connections at the alternator are very simple as shown in fig4 #b1aeb4 ,one end of each phase winding is connected by the brushes a and b'1 to one of the circuit wires1 that is to ,a and ,b respectively4 ,the other end of each phase winding is connected by a lead across brushes a' and b1 to which the third wire ,c is joined4 ,the current and pressure conditions of this system are represented diagrammatically in fig4 #b1aec4 ,the letters correspond to those in fig4 #b1aeb1 with which it should be compared4 ,as shown in the figure each coil is carrying #ajj amperes at #a1jjj volts pressure4 ,since the phase difference between the two coils is #ij1 the voltage between ,a and ,b is #b #a4dad times that between either ,a or ,b and the common return wire ,c4 ,the current in ,c is #b #a4dad times that in either outside wire ,a or ,b1 as indicated4 ,ques4 ,how should the load on the two phase three wire system be distributed8 ,ans4 ,the load on the two phases must be carefully balanced4 ,illustration3 ,,fig4 #b1aed4--;,diagram of two phase three wire system and connections for motors and lighting circuits4 ,ques4 ,why should the power factor be kept high8 ,ans4 ,a high power factor should be maintained in order to keep the voltage on the phases nearly the same at the receiving ends4 ,ques4 ,how should single phase motors be connected and what precaution should be taken8 ,ans4 ,single phase motors may be connected to either or both phases1 but in such cases1 no load should be connected between the outer wires otherwise the voltages on the different phases will be badly unbalanced4 ,fig4 #b1aed shows a two phase three wire system1 with two wire and three wire distribution circuits1 illustrating the connection for lighting and for one and two phase motors4 ,illustration3 ,,fig4 #b1aee4--;,diagram of two phase system with four wire transmission and three wire distribution4 ,in the three wire circuits the relative pressures between conductors are as indicated2 that is1 the pressure between the two outer wires ,a and ,b is #ada volts1 when the pressure between each outer wire and the central is #ajj volts4 ,ques4 ,describe another method of transmission and distribution with two phase current4 ,ans4 ,the current may be transmitted on a four wire circuit and distributed on three wire circuit as in fig4 #b1aee4 ,the four wire transmission circuit is evidently equivalent to two independent single phase circuits4 ,in changing from four to three wires1 it is just as well to connect the two outside wires ,a and ,b together 7fig4 #b1aeb71 as it is to connect a and b4 ,it makes no difference which two secondary wires are joined together1 so long as the other wires of each transformer are connected to the outside wires of the secondary system4 ,ques4 ,for what service is the two phase three wire system adapted8 ,ans4 ,it is desirable for supplying current of minimum pressure to apparatus in the vicinity of transformers4 ,it is more frequently used in connection with motors operating from the secondaries of the transformers4 ,ques4 ,how should the third or common return wire be proportioned8 ,ans4 ,since the current in the common return wire is #da4d per cent4 higher than that in either of the other wires it must be of correspondingly larger cross section1 to keep the loss equal4 ,illustration3 ,,figs4 #b1aef and #b1aeg4--;,conventional diagrams illustrating star and delta connected three phase alternator armatures4 ,ques4 ,what is the effect of an inductive load on the two phase three wire system and why8 ,ans4 ,it causes an unbalancing of both sides of the system even though the energy load be equally divided4 ,the self-induction pressure in one side of the system is in phase with the virtual pressure in the other side1 thus distorting the current distribution in both circuits4 ,ques4 ,describe the two phase five wire system4 ,ans4 ,a two phase circuit may be changed from four to five wires by arranging the transformer connections as in fig4 #b1aeh4 ,as shown1 the secondaries of the transformers are joined in series and leads brought out from the middle point of each secondary winding and at the connection of the two windings1 giving five wires4 ,with #a1jjj volts in the primary windings and a step down ratio of #aj3a1 the pressure between ,a and ,c and ,c and ,e will be #ajj volts and between the points and the connections ,b or ,d at the middle of the secondary coils1 #ej volts4 ,the pressure across the two outer wires ,a and ,e is1 as in the three wire system1 #b or #a4da times that from either outer wire to the middle wire ,c1 that is #ada volts4 ,the pressure across the two wires connected to the middle of the coils1 that is1 across ,b and ,d1 is #ej #b #gj4e volts4 ,illustration3 ,fig4 #b1aeh4--,two phase four wire transmission and five wire distribution system4 ,the relative pressures between the various conductors are indicated in the diagram4 ,three ,phase ,systems4--,there are various ways of arranging the circuit for three phase current giving numerous three phase systems4 #a4 ,with respect to the number of wires used they may be classified as a4 ,six wire2 b4 ,four wire2 c4 ,three wire4 ,illustration3 ,,fig4 #b1aei4--,line connections of three phase three wire long distance transmission1 and distribution system4 ,the three phase alternator ,a1 is driven by the water wheel ,b1 and furnishes current at say #b1bjj volts plus sufficient pressure to compensate for line drop4 ,with #a3aj step up transformers ,c1 this would give a transmission pressure of #bb1jjj volts plus line drop4 ,it is this transformation that secures the copper economy of the system4 ,at the distribution end are the step down transformers2 one set reducing the voltage down to #b1bjj volts1 and supplying current direct to the synchronous motor1 and through another set of other step down transformers1 as ,l and ,k1 to lighting and power circuits at #bbj volts4 ,another set of step down transformers ,m reduce the pressure directly to #abj volts for power and lighting1 the pressure being regulated by the regulators ,g4 ,arc lamps with individual transformers further reducing the pressure to #ej volts are connected to this circuit as shown4 #b4 ,with respect to the connections1 as a4 ,star2 b4 ,delta2 c4 ,star delta2 d4 ,delta star4 ,the six wire system is shown in fig4 #b1afj4 ,it is equivalent to three independent single phase circuits4 ,such arrangement would only be used in very rare instances4 ,illustration3 ,,fig4 #b1afj4--,three phase six wire system4 ,it is equivalent to three independent single phase circuits and would be used only in very rare cases4 ,ques4 ,how can three phase current be transmitted by three conductors8 ,ans4 ,the arrangement shown in fig4 #b1afj may be resolved into three single circuits with a common or grounded return4 ,when the circuits are balanced the sum of the current being zero no current will flow in the return conductor1 and it may be dispensed with1 thus giving the ordinary star or ,y connected three wire circuit1 as shown in fig4 #b1afc4 ,the transformation from six to three wires being shown in figs4 #b1afa to #b1afc4 ,illustration3 ,,figs4 #b1afa to #b1afc4--;,evolution of the three phase three wire system4 ,fig4 #b1afa is a conventional diagram of the three phase six wire system shown in fig4 #b1afj4 ,a wire is connected to both ends of each phase winding1 giving six conductors1 or three independent two wire circuits4 ,in place of the wires running from ,a1 ,b1 and ,c1 they may be removed and each circuit provided with a ground return as shown in fig4 #b1afb4 ,the sum of the three currents being zero1 or nearly zero1 according to the degree of unbalancing1 the ground return may be eliminated and the ends ,a1 ,b1 and ,c of the three phase winding connected1 as in fig4 #b1afc1 giving the so called star point4 ,fig4 #b1aff is a view of an elementary three phase three wire star connected alternator4 ,ques4 ,what are the pressure and current relations of the star connected three wire system8 ,illustration3 ,,figs4 #b1afd and #b1afe4--,three phase four wire star connected alternator and conventional diagram showing pressure and current relations4 ,illustration3 ,,figs4 #b1aff and #b1afg4--,three phase star connected alternator1 and conventional diagram showing pressure relations4 ,ans4 ,these are shown in the diagram1 fig4 #b1aff and #b1afg4 ,assuming #ajj amperes and #a1jjj volts in each phase winding1 the pressure between any two conductors is equal to the pressure in one winding multiplied by #c1 that is #a1jjj #a4gcb #a1gcb volts4 ,the current in each conductor is equal to the current in the winding1 or #ajj amperes4 ,ques4 ,describe the delta connection4 ,ans4 ,in the delta connection1 the three phase coils are connected together forming an endless winding1 leads being brought out from these points4 ,fig4 #b1afh shows a delta connected three phase alternator1 the pressure and current relation being given in fig4 #b1afi4 ,illustration3 ,,figs4 #b1afh and #b1afi4--,three phase delta connected alternator and conventional diagram showing pressure and current relations4 ,ques4 ,what are the pressure and current relations of the delta connected three wire system8 ,ans4 ,they are as shown in fig4 #b1afi4 ,assuming #ajj amperes and #a1jjj volts in each phase winding1 the pressure between any two conductors is the same as the pressure in the winding1 and the current in any conductor is equal to the current in the winding multiplied by #c1 that is #ajj #a4gcb #agc4b amperes1 that is1 disregarding the fraction1 #agc amperes4 ,ques4 ,what are the relative merits of the star and delta connections8 ,ans4 ,the power output of each is the same1 but the star connection gives a higher line voltage1 hence smaller conductors may be used4 ,illustration3 ,,fig4 #b1agj4--,t connection of transformers in which three phase current is transformed with two transformers4 ,the connections are clearly shown in the illustration4 ,the voltage across one transformer is only #hf4f of that across the other1 so that if each transformer be designed especially for its work one will have a rating of 4#hff ,,ei and the other ,,ei4 ,the combined rates will then be #a4hff as compared with #a4gcb ,,ei for three single phase transformers connected either star or delta4 ,when it is remembered that the cost of copper conductors is inversely as the square of the voltage1 the advantage of the ,y connected system can be seen at once4 ,assuming that three transformers are used for a three phase system of given voltage1 each transformer1 star connected1 would be wound for #a #c #eh of the given voltage1 and for full current4 ,for delta connection1 the winding of each transformer is for #eh of the current4 ,accordingly the turns required for star connection are only #eh of those required for delta connection4 ,ques4 ,what is the objection to the star connection for three phase work8 ,ans4 ,it requires the use of three transformers1 and if anything happen to one1 the entire set is disabled4 ,ques4 ,does this defect exist with the delta connection8 ,ans4 ,no4 ,one transformer may be cut out and the other two operated at full capacity1 that is at the capacity of the three4 ,ques4 ,describe the ,t connection4 ,ans4 ,in this method two transformers are used for transforming three phase current4 ,it consists in connecting one end of both windings of one transformer to the middle point of like windings of the other transformer as in fig4 #b1agj4 ,illustration3 ,,fig4 #b1aga4--,open delta connection or method of connecting two transformers in delta for three phase transformation4 ,it is used when one of the three single phase delta connected transformers becomes disabled4 ,ques4 ,what is the open delta connection8 ,ans4 ,it is a method of arranging the connections of a bank of three delta connected transformers when one becomes disabled as in fig4 #b1aga4 ,change of ,frequency4--,there are numerous instances where it is desirable to change from one frequency to another1 as for instance to join two systems of different frequency which may supply the same or adjacent territory1 or1 in the case of a low frequency installation1 in order to operate incandescent lights satisfactorily it would be desirable to increase the frequency for such circuits4 ,this is done by motor generator sets1 the motor taking its current from the low frequency circuit4 ,synchronous motors are generally used for such service as the frequency is not disturbed by load changes2 it also makes it possible to use the set in the reverse order1 that is1 taking power from the high frequency mains and delivering energy at low frequency4 ,illustration3 ,,fig4 #b1agb4--;,course of the ,schaghticoke-,schenectady transmission line of the ,schenectady ,power ,co4 ,this transmission line carries practically the entire output of the ,schaghticoke power house to ,schenectady1 ,n4 ,y41 a distance of approximately #ba miles4 ,the line consists of two separate three phase1 #dj cycle1 #cb1jjj volt circuits1 each of #f1jjj kw4 normal capacity4 ,these circuits start from opposite ends of the power house1 and1 after crossing the ,hoosic ,river1 are transferred by means of two terminal towers1 fig4 #b1agc1 to a single line of transmission towers4 ,the two circuits are carried on these on opposite ends of the cross arms1 the three phases being superimposed4 ,the power house ends of the line are held by six short quadrangular steel lattice work anchor poles with their bases firmly embedded in concrete1 the cables being dead ended by ,general ,electric disc strain insulators4 ,this equipment1 together with the lightning arrester horn gaps and the heavy line outlet insulators mounted on the roof of the power house1 is shown in fig4 #b1agd4 ,while each circuit carries only #f1jjj kw4 under normal conditions1 either is capable of carrying the entire output of the station2 in this case1 however1 the line losses are necessarily augmented4 ,this feature prevents any interruption of the service from the failure of one of the circuits4 ,there are altogether #aig transmission towers1 comprising several distinct types4 ,ques4 ,in the parallel operations of frequency changing sets what is necessary to secure equal division of the load8 ,ans4 ,the relative angular position of the rotating elements of motor and generator must be the same respectively in each set4 ,illustration3 ,,fig4 #b1agc4--;,beginning of ,schaghticoke-,schenectady transmission line2 view showing transfer towers with power house in background4 ,ques4 ,how is this obtained8 ,ans4 ,because of the mechanical difficulty of accurately locating the parts1 the equivalent result is secured by arranging the stationary element in one of the two machines so that it can be given a small angular shift4 ,transformation of ,phases4--,in alternating current circuits it is frequently desirable to change from one number of phases to another4 ,for instance1 in the case of a converter1 it is less expensive and more efficient to use one built for six phases than for either two or three phases4 ,illustration3 ,,fig4 #b1agd4--,view from roof of power house of the ,schaghticoke-,schenectady transmission line1 showing anchor poles1 strain insulators1 lightning arrester horn gap and line entrance bushings4 ,the numerous conditions met with necessitate various phase transformations1 as #a4 ,three phase to one phase2 #b4 ,three phase to two phase2 #c4 ,two phase to six phase2 #d4 ,three phase to six phase4 ,these transformations are accomplished by the numerous arrangements and combinations of the transformers4 ,illustration3 ,,fig4 #b1age4--,three phase to one phase transformation with two transformers4 ,the diagram shows the necessary connections and the relative pressures obtained4 ,three ,phase to ,one ,phase4--,this transformation may be accomplished by the use of two transformers connected as in fig4 #b1age in which one end of one primary winding is connected to the middle of the other primary winding and the second end of the first primary winding at a point giving #hf4f per cent4 of that winding as shown4 ,the two secondary windings are joined in series4 ,three ,phase to ,two ,phase4--,the three phase system is universally used for long distance transmission1 because it requires less copper than either the single or two phase systems4 ,for distribution1 however1 the two phase system presents certain advantages1 thus1 it becomes desirable at the distribution centers to change from three phase to two phase4 ,this may be done in several ways4 ,ques4 ,describe the ,scott connection4 ,illustration3 ,,fig4 #b1agf4--,the ,scott connection for transforming from three phase to two phase4 ,in this method one of the primary wires ,b of the 4#hff ratio transformer is connected to the middle of the other primary as at ,c1 the ends of which are connected to two of the three phase wires4 ,the other phase wire is connected at ,d1 the point giving the 4#hff ratio4 ,the secondary wires are connected as shown4 ,ans4 ,two transformers are used1 one having a #aj3a ratio1 and the other1 a #c3a1 that is1 an #h4ff3a ratio4 ,the connections are arranged as in fig4 #b1agf4 ,it is customary to employ standard transformers having the ratios #aj3a1 and #i3a4 ,ques4 ,what names are given to the two transformers8 ,ans4 ,the one having the #aj3a ratio is called the main transformer1 and the other with the #h4ff3a ratio1 the teaser transformer4 ,in construction1 the transformers may be made exactly alike so that either may be used as main or teaser4 ,in order that the connections may be properly and conveniently made1 the primary windings should be provided with #ej and #hf4f taps4 ,illustration3 ,,fig4 #b1agg4--,three phase to two phase transformation with three star connected transformers4 ,two of the secondary windings are tapped at points corresponding to #eg4g of full voltage2 these two windings are connected in series to form one secondary phase of voltage equal to that obtained by the other full secondary winding4 ,ques4 ,describe another way of transforming from three to two phases4 ,ans4 ,the transformation may be made by three star connected transformers1 proportioning the windings as in fig4 #b1agg1 from which it will be seen that two of the secondary windings are tapped at points corresponding to #eg4g per cent4 of full voltage4 ,three ,phase to ,six ,phase4--,this transformation is usually made for use with rotary converters and may be accomplished in several ways4 ,as these methods have been illustrated in the chapter on ,converters 7page #a1dfb71 it is unnecessary to again discuss them here4 ,fig4 #b1agh1 below shows the diametrical connection for transforming three phase to six phase4 ,illustration3 ,,fig4 #b1agh4--;,diagram of diametrical connection1 three phase to six phase4 ,it is obtained by bringing both ends of each secondary winding to opposite points on the rotary converter winding1 utilizing the converter winding to give the six phases4 ,this transformation of phases may also be obtained with transformers having two secondary windings4 ,alternating ,current ,systems4--,the saving in the cost of transmission obtained by using alternating instead of direct current is not due to any difference in the characteristics of the currents themselves1 but to the fact that in the case of alternating current very high pressures may be employed1 thus permitting a given amount of energy to be transmitted with a relatively small current4 ,in the case of direct current systems1 commutator troubles limit the transmission pressure to about #a1jjj volts1 whereas with alternating current it may be commercially generated at pressures up to about #ac1jjj and by means of step up transformers1 transmitted at #aaj1jjj volts or more4 ,illustration3 ,,fig4 #b1agi4--;,end of ,schaghticoke-,schenectady transmission line at ,schenectady2 view showing entrance bushings and lightning arrester horn gaps4 ,relative ,weights of ,copper ,required by ,polyphase ,systems4--,a comparison between the weights of copper required by the different alternating current systems is rendered quite difficult by the fact that the voltage ordinarily measured is not the maximum voltage1 and as the insulation has to withstand the strain of the maximum voltage1 the relative value of copper obtained by calculation depends upon the basis of comparison adopted4 ,as a general rule1 the highest voltage practicable is used for long distance transmission1 and a lower voltage for local distribution4 ,furthermore1 some polyphase systems give a multiplicity of voltages1 and the question arises as to which of these voltages shall be considered the transmission voltage4 ,if the transmission voltage be taken to represent that of the distribution circuit1 and the polyphase system has as many independent circuits as there are phases1 the system would represent a group of several single phase systems1 and there would be no saving of copper4 ,under these conditions1 if the voltage at the distant end be taken as the transmission voltage1 and the copper required by a single phase two wire system as shown in fig4 #b1ahj1 be taken as the basis of comparison1 the relative weights of copper required by the various polyphase systems is given in figs4 #b1aha to #b1ahh4 ,illustration3 ,,fig4 #b1ahj4--,single phase line1 used as basis of comparison in obtaining the relative weights of copper required by polyphase systems1 as indicated in figs4 #b1aha to #b1ahh4 ,in the case represented in fig4 #b1ahj1 if the total drop on the line be #ajj volts1 the generated voltage must be #a1ajj volts1 and the resistance of each line must be #ej #a1jjj 4#je ohms4 ,calculated on this basis1 a two phase four wire system is equivalent to two single phase systems and gives no economy of copper in power transmission over the ordinary single phase two wire system4 ,this is the case also with any of the other two phase systems1 except the two phase three wire system4 ,illustration3 ,,figs4 #b1aha to #b1ahh4--;,circuit diagrams showing relative copper economy of various alternating current systems4 ,in this system two of the four wires of the four wire two phase system are replaced by one of full cross section4 ,the amount of copper required1 when compared with the single phase system1 will differ considerably according as the comparison is based on the highest voltage permissible for any given distribution1 or on the minimum voltage for low pressure service4 ,if ,e be the greatest voltage that can be used on account of the insulation strain1 or for any other reason1 the pressure between the other conductors of the two phase three wire system must be reduced to ,e #b4 ,the weight of copper required under this condition is #ade4g that of the single phase copper4 ,on the basis of minimum voltage1 the relative amount of copper required is #gb4i that of the single phase system4 ,illustration3 ,,fig4 #b1ahi4--,twin circuit aermotor towers carrying #dd1jjj volt conductors 7,southern ,power ,co474 ,these towers vary in height from #ce to #ej feet1 and the circuits are transposed every #aj miles4 ,the towers are assembled on the ground and erected by means of gin poles4 ,they are normally spaced #ejj feet apart with a sag of #e feet #h inches4 ,the minimum distance between towers is #cjj feet and the maximum #gjj feet4 ,figs4 #b1ahg and #b1ahh are two examples of three phase four wire systems4 ,the relative amount of copper required as compared with the single phase system depends on the cross section of the fourth wire4 ,the arrangement shown in fig4 #b1ahh1 where the fourth wire is only half size1 is used only for secondary distribution systems4 ,illustration3 ,,fig4 #b1aij4--;,general ,electric standard tower for high tension three phase transmission line4 ,illustration3 ,,fig4 #b1aia4--;,general ,electric transposition tower for high tension three phase transmission line4 ,choice of ,voltage4--,in order to properly determine the voltage for a transmission system there are a number of conditions which must be considered in order that the economy of the entire installation shall be a maximum4 ,the nature of the diversely various factors which affect the problem makes a mathematical expression difficult and unsatisfactory4 ,ques4 ,what is the relation between the cross sectional area of the conductors and the voltage8 ,ans4 ,for a given circuit1 the cross sectional area of the conductors1 or weight varies inversely as the voltage4 ,illustration3 ,,fig4 #b1aib4--;,general ,electric standard tower under construction4 ,ques4 ,would the highest possible voltage then be used for a transmission line8 ,ans4 ,the most economical voltage depends on the length of the line and the cost of apparatus4 ,for instance1 alternators1 transformers1 insulation and circuit control and lightning protection devices become expensive when manufactured for very high pressures4 ,hence if a very high pressure were used1 it would involve that the transmission distance be great enough so that the extra cost of the high pressure apparatus would be offset by the saving in copper effected by using the high pressure4 ,in the case of the longest lines1 from about #ajj miles up1 the saving in copper with the highest practicable voltage is so great that the increase in other expenses is rendered comparatively small4 ,in the shorter lines as those ranging in length from about one mile to #ej or #ge miles1 the most suitable voltage must be determined in each individual case by a careful consideration of all the conditions involved4 ,no fixed rule can be established for proper voltage based on the length1 but the following table will serve as a guide3 ,illustration3 ,,fig4 #b1aic4--,line of the ,schenectady ,power ,company crossing the tracks of the ,boston and ,maine ,railroad near ,schaghticoke4 ,usual ,transmission ,voltages ---------------------------------------- ,length of line ,voltage in miles --------------------------------------- #a #ejj to #a1jjj #a to #b #a1jjj to #b1cjj #b to #c #b1cjj to #f1fjj #c to #aj #f1fjj to #ac1bjj #aj to #ae #ac1bjj to #bb1jjj #ae to #bj #bb1jjj to #dd1jjj #bj to #dj #dd1jjj to #ff1jjj #dj to #fj #ff1jjj to #hh1jjj #fj to #ajj #hh1jjj to #aaj1jjj --------------------------------------- ,ques4 ,what are the standard voltages for alternating current transmission circuits8 ,ans4 #f1fjj1 #aa1jjj1 #bb1jjj1 #cc1jjj1 #dd1jjj1 #ff1jjj1 #hh1jjj4 ,the amount of power to be transmitted determines1 in a measure1 the limit of line voltage4 ,if the most economical voltage considered from the point of view of the line alone1 be somewhere in excess of #ac1bjj1 step up transformers must be employed1 since the highest voltage for which standard alternators are manufactured is #ac1bjj4 ,in a given case1 the saving in conductor by using the higher voltage may be more than offset by the increased cost of transformers1 and the question must be determined for each case4 ,illustration3 ,,fig4 #b1aid4--,view of a three phase1 #b1cjj volt1 #fj cycle line at ,chazy1 ,n4 ,y4 ,the current is transmitted at the alternator voltage #b miles over the single circuit pole line4 ,the poles are of cedar with fir cross arms1 and are fitted with pin insulators4 ,they are from #ce to #dj feet high and are spaced at an average of about #abj feet4 ,the conductors are bare copper wire ,no4 #jj ,b4 ,s4 ,the alternators consist of one #ej kw41 and one #ajj kw4 ,general ,electric machines4 ,ques4 ,what are the standard transformer ratios8 ,ans4 ,multiples of #e or #aj4 ,illustration3 ,,figs4 #b1aie to #b1aig4--;,diagram showing electric railway system4 ,three phase current is generated at the main station where it passes to step up transformers to increase the pressure a suitable amount for economical transmission4 ,at various points along the railway line are sub-stations1 where the three phase current is reduced in pressure to #ejj or #fjj volts by step down transformers1 and converted into direct current by rotary converters4 ,the relatively low pressure direct current is then conveyed by feeders to the rails1 this resulting in a considerable saving in copper4 ,mixed ,current ,systems4--,it is often desirable to transmit electrical energy in the form of alternating current1 and distribute it as direct current or vice versa4 ,such systems may be classed as mixed current systems4 ,the usual conversion is from alternating current to direct current because of the saving in copper secured by the use of alternating current in transmission1 especially in the case of long distance lines4 ,such conversion involves the use of a rotary converter1 motor generator set1 or rectifier1 according to the conditions of service4 ,illustration3 ,,fig4 #b1aih4--;,example of converter sub-station1 showing the ,brooklyn ,edison ,co4 ,madison sub-station4 ,the transformers are seen on the left1 the converter shown at the right is a ,westinghouse synchronous booster rotary converter1 consisting of a standard rotary converter in combination with a revolving armature alternator mounted on the same shaft with the converter and having the same number of poles4 ,the function of the machine is to convert and regulate the pressure4 ,by varying the field excitation of the alternator1 the ,a4 ,c4 voltage impressed on the rotary converter proper can be increased or decreased as desired4 ,thus1 the ,d4 ,c4 voltage delivered by the converter is varied accordingly4 ,this type of converter is well adapted for any application for which a relatively wide variation1 either automatic or non-automatic1 in direct current voltage is necessary4 ,also especially for serving incandescent lighting systems where considerable voltage variation is required for the compensation of drop in long feeders1 for operation in parallel with storage batteries and for electrolytic work where extreme variations in voltage are required by changes in the resistance of the electrolytic cells4 ,the suburban trolley forms a good example of a mixed system1 in which alternating current is generated at the central station and transmitted to sub-stations1 where it is transformed to low pressure1 and converted into direct current for use on the line4 ,fig4 #b1aie shows the interior of a sub-station of this kind4 ,ques4 ,what direct current pressure is usually employed on traction lines8 ,ans4 #ejj volts4 ,ques4 ,mention another important service performed by a mixed system4 ,ans4 ,if the generator furnish alternating current it must be converted into direct current in order to charge storage batteries4 ,,chapter ,,lvi ,,auxiliary ,,apparatus ,for the proper control of the alternating current in any of the numerous systems described in the previous chapter1 various devices1 which might be classed as auxiliary apparatus1 are required4 ,these may be grouped into several divisions1 according to the nature of the duty which they perform1 as #a4 ,switching devices2 a4 ,ordinary switches2 b4 ,oil break switches2 c4 ,remote control switches4 #b4 ,current or pressure limiting devices2 a4 ,fuses2 b4 ,reactances2 c4 ,circuit breakers2 d4 ,relays4 #c4 ,lightning protection devices2 a4 ,air gap arresters2 b4 ,multi-gap arresters2 c4 ,horn gap arresters2 d4 ,electrolytic arresters2 e4 ,vacuum tube arresters2 f4 ,choke coils2 g4 ,static interrupters4 #d4 ,regulating devices2 a4 ,induction voltage regulators2 b4 ,variable ratio transformer regulators drum type2 dial type2 c4 ,compensation shunts2 d4 ,pole type regulators2 e4 ,small feeder voltage regulators2 f4 ,automatic voltage regulators2 g4 ,line drop compensators2 h4 ,starting compensators2 i4 ,star delta switches4 #e4 ,power factor regulating devices2 a4 ,condensers2 b4 ,synchronous condensers4 #f4 ,indicating devices2 plunger type2 a4 ,moving iron instruments inclined coil type2 magnetic vane type2 b4 ,hot wire instruments2 c4 ,induction instruments shielded pole type2 repulsion type2 d4 ,dynamometers2 e4 ,instrument transformers2 commutator type2 f4 ,watthour meters induction type2 ,faraday disc type2 synchronous motor type2 g4 ,frequency indicators resonance type2 induction type2 lamp type2 h4 ,synchronism indicators voltmeter type2 resonance type2 rotating field type2 i4 ,power factor indicators wattmeter type2 rotating field type2 j4 ,ground detectors2 k4 ,earth leakage cut outs2 l4 ,oscillographs4 ,,chapter ,,lvii ,,switching ,,devices ,a switch is a piece of apparatus for making1 breaking1 or changing the connections in an electric circuit4 ,the particular form and construction of any switch is governed by the electrical conditions under which it must operate4 ,since the electric current cannot be stopped instantly when the circuit in which it is flowing1 is broken1 an arc is formed as the switch contacts separate2 this tends to burn the contacts1 and to short circuit1 the severity of such action depending on the voltage and the proximity of the switch terminals4 ,accordingly in switch design1 provision must be made to counteract these tendencies4 ,thus1 #a4 ,the contacts should separate along their entire length1 rather than at a point2 #b4 ,the terminals should be far enough apart and properly protected to prevent short circuiting of the arcs2 #c4 ,the break should be quick2 #d4 ,the gap should be surrounded by the proper medium 7air or oil7 to meet the requirements of the electrical conditions4 ,a great variety of switches have been introduced to suit the different requirements4 ,knife switches are used for low pressure service1 the multiple break form being used where it is desired to reduce the arcing distance4 ,ques4 ,how should single throw switches be installed8 ,ans4 ,they should open downward so gravity will keep them open4 ,illustration3 ,,figs4 #b1aii and #b1bjj4--;,general ,electric triple pole solenoid operated1 single throw remote control switch1 and push button switch for operating same4 ,switch is a self-contained unit with two sets of contacts1 main laminated copper brushes1 and carbon auxiliary contacts to take the arc on breaking the circuit4 ,the main brushes are so made that each lamination makes an end on contact with the switch blade without any tendency to force the laminations apart4 ,a wiping effect1 given to the contacts every time the switch is closed1 keeps the contact surfaces clean and insures good contact at all times4 ,the carbon auxiliary contacts are made of blocks of carbon fastened without screws4 ,in operation1 the switch is actuated by a double coil solenoid1 one coil for closing and one for opening1 controlled by the single pole double throw push button switch shown in fig4 #b1bjj1 which is normally in the open position and remains closed only when held by the operator4 ,one of these switches is furnished with each control switch and must always be used1 as the solenoid coils are not intended for continuous service4 ,the power required to operate the remote control switch is small1 being approximately #a4f amperes at #aaj volts1 #j4ha amperes at #bbj volts direct current1 and #aj amperes at #aaj volts1 and #f amperes at #bbj volts alternating current #fj cycles4 ,the main switch can be closed and opened by hand1 and the push button located at any point4 ,ques4 ,how should double throw switches be installed8 ,ans4 ,horizontally4 ,illustration3 ,,figs4 #b1bja and #b1bjb4--,palmer service switch and fuse box1 for either plug1 cartridge or open link fuses4 ,fig4 #b1bja illustrates the box in open position for the inspection of fuses1 etc4 ,the cover is held open by a simple lock so that the switch cannot fall closed by gravity1 the box may be mounted so that the service wires lead directly into a sealed terminal chamber from any direction1 and all current carrying parts made accessible by the opening of the switch are dead4 ,fig4 #b1bjb illustrates the device with side of box and cover cut away to show interior and the normally sealed cover of terminal chamber removed4 ,the switch contacts do not enter their contact clips until the flanged cover of the box has closed the switch opening1 no current connections being made to line or load until the box is completely closed1 and in consequence there is no opportunity to make improper connections to any live parts of switch1 when conduit connections are used to the service and meter wires4 ,ques4 ,what is a plug switch8 ,ans4 ,a switch in which the current is ruptured in a tube enclosed at one end1 thereby confining the arc and limiting the supply of air4 ,they are used on high pressure circuits of from #aj1jjj to #bj1jjj volts1 for transferring live circuits and for voltmeter and synchronizing circuits where there is very little energy4 ,the usual current capacity is from #d to #g amperes4 ,illustration3 ,,fig4 #b1bjc and #b1bjd4--;,bus transfer plug switch4 ,the method of supporting the contact farthest from the panel consists of a porcelain pillar of the same height as the receptacle1 clamped to a brass connecting or bus bar which in turn is fastened to the receptacle4 ,illustration3 ,,fig4 #b1bje4--;,ammeter jack4 ,this plug switch is insulated for high pressure and consists of two parts3 the ammeter jack1 and the ammeter jack plug1 cable1 and bushing4 ,the receptacle1 which is simple in construction1 consists of a brass bushing well insulated from the panel and protected on the front of the panel by a porcelain bushing4 ,on the end of this tube and insulated from it1 is a phosphor bronze spring which1 when the plug is out1 rests on the brass tube and keeps the circuit closed4 ,the plug consists of a brass rod well insulated and set in a brass tube1 both being fastened in a handle which is stained black and polished4 ,inside the handle is run a twin conductor cable1 one side being soldered in the brass tube and the other to the brass rod4 ,the other end of the cable is run through a bushing set in the panel and thence to the ammeter or current transformer4 ,where it is desired to remove the plug and cable from the board1 or to plug both ends of the cable in different receptacles1 a plug instead of a bushing should be used4 ,in this case a cable should be provided with a plug on each end4 ,forms of ,break4--,on high pressure circuits there are several types of switch3 they are classified with respect to the break1 that is to say1 according as the break takes place1 #a4 ,in open air2 #b4 ,in an enclosed air space2 #c4 ,aided by a metal fuse2 #d4 ,aided by a horn2 #e4 ,in oil4 ,illustration3 ,,fig4 #b1bjf4--,westinghouse fused starting switch for squirrel cage motors4 ,it is arranged for ,national ,electric ,code fuses on one end only and has springs on the other end to open the switch automatically if left closed at this end4 ,the corresponding terminals at both ends of the switch are connected in grooves in the back of the slate base so that the wiring need be connected to one set of these terminals only1 thus decreasing the number of connections necessary1 as shown in fig4 #b1bjg4 ,in starting an induction motor1 the switch is thrown to the end that is not fused and held there until the motor is up to running speed2 then it is quickly thrown to the fused position1 thus protecting the circuit under running conditions4 ,illustration3 ,,fig4 #b1bjg4--;,diagram of connections of ,westinghouse fused starting switch for squirrel cage motors4 ,the starting current of induction motors is several times the normal running current and1 when the controlling switch is fused to carry the running load only1 the fuses are apt to blow when the motor is started4 ,the fuses must be of a capacity to prevent overloads under running conditions4 ,these switches are designed to meet this difficulty and are used without auto-starters to control motors up to #e horse power rating4 ,ques4 ,what is the objection to open air break8 ,ans4 ,the relatively long gap required to extinguish the arc1 limiting this form of switch to low or moderate pressure circuits4 ,the open air arc may cause very high voltage oscillations when the circuit contains inductance and capacity unless the break occur at zero value4 ,illustration3 ,,fig4 #b1bjh4--,westinghouse single pole disconnecting switch4 ,disconnecting switches are used primarily for isolating apparatus from the circuit for purposes of inspection and repair2 also for sectionalizing feeders4 ,they are not designed for opening under load1 and therefore no attempt should be made to open them with current in the circuit4 ,in connection with lightning arrester installations1 disconnecting switches are particularly useful1 providing a simple and effective means for isolating the arresters while cleaning and inspecting4 ,the switch is opened and closed with a hook on the end of a wooden pole1 which hook engages in a hole provided in the switch blade4 ,this type of disconnecting switch is intended for wall mounting4 ,the live parts are mounted on porcelain insulators carried on a cast iron yoke or base1 forming a simple and substantial construction4 ,ques4 ,what are disconnecting switches8 ,ans4 ,knife switches in series with other switches so that the apparatus controlled by the latter may be repaired in safety by entirely disconnecting it from the bus bars or live circuit4 ,such switches are not intended to rupture the load current4 ,illustration3 ,,figs4 #b1bji and #b1baj4--,westinghouse disconnecting switches for pressures over #c1cjj volts4 ,illustration3 ,,figs4 #b1baa and #b1bab4--,westinghouse selector type disconnecting switch4 ,fig4 #b1baa1 view showing both sides closed2 fig4 #b1bab1 view with one side open4 ,the selector type of disconnecting switch is a transfer switch which does not require the circuit to be interrupted while making the change4 ,it can also be used to connect two independent circuits in parallel4 ,in construction1 it is in effect two single throw1 single pole disconnecting switches with the hinge jaws connected together and mounted on the same insulator4 ,the hinge jaw is also provided with dummy jaws to hold either blade of the switch in the open position4 ,except for these differences in the hinge jaws1 the construction is similar to the switch shown in fig4 #b1bji4 ,it should not be used to open the circuit when loaded4 ,illustration3 ,,fig4 #b1bac4--;,hook stick for operating a disconnecting switch4 ,ques4 ,what are the features of the enclosed air break8 ,ans4 ,the switch is more compact than the open air break type1 but pressure oscillations are caused on opening the circuit the same as with the open air break1 and it is not desirable for heavy current4 ,illustration3 ,,fig4 #b1bad4--;,baum #ce1jjj volt1 #bjj ampere1 double break pole type switch4 ,while designed for disconnecting purposes only1 it can break considerable amperage4 ,the levers and couplings are fastened with tape pins4 ,the control shaft coupling is adjustable to any angle1 and the switch can be locked in the open or closed position4 ,a removable wooden handle is supplied and the switch can be handled in any weather4 ,the arms can be extended to hold fuse fittings1 or dead end insulators in the event of a heavy strain1 but it is preferable to have fuses on another structure as a precaution against coming in contact with the energized portion of the switch1 and it is also preferable to take the strain of the line on a pole a few feet from the switch1 rather than on the switch structure1 particularly in the larger sizes4 ,an insulating wood section in the control shaft separates the control handle from the remainder of the switch4 ,discharging horns can be fitted to this type of switch and when so equipped they have been found capable of breaking considerable loads4 ,ques4 ,how is the fuse arranged in the metal fuse break type of switch8 ,ans4 ,it is placed in a tube fitted with powdered carbonate of lime or some other insulating powder4 ,illustration3 ,,fig4 #b1bae4--,pacific swivel type blade for ,baum pole top switches4 ,the twist type of blade1 here shown1 is especially adapted to switches operating in freezing or sleety weather4 ,it will be seen that the first few degrees through which the rotating insulator is moved have the effect of twisting the blade between the shoes of the contact1 which breaks any seal through freezing1 or corrosion4 ,illustration3 ,,fig4 #b1baf4--,pacific #bb1jjj volt1 #ajj ampere1 pole top switch equipped with fuse tubes2 designed to meet the need for a small group controlled disconnecting switch1 having several features making it suitable for use with service transformer installations and line branches4 ,the switch is made with clamped pipe arms permitting adjustment4 ,it is equipped with fuse tubes and fittings1 but should the fuses be not desired1 the arm may be shortened4 ,provision is made for fitting insulator pins to the top of the arms1 when the switch is mounted vertically1 which will hold insulators at right angles to the switch1 making it possible to end a line on the top of these arms and then drop down through the switch to the bank of transformers4 ,the switch is so constructed that gravity tends to hold it in either the open or the closed position4 ,provision can be made for locking4 ,illustration3 ,,fig4 #b1bag4--;,horn break switch4 ,in operation1 the arc formed at break1 will travel toward the extremities of the horns because of the fact that a circuit will tend to move so as to embrace the largest possible number of lines of force set up by it4 ,hence1 the arc that starts between the horns where they are near together rises between them until it becomes so attenuated that it is extinguished4 ,illustration3 ,,fig4 #b1bah4--,westinghouse rear connected motor starting switch1 for pressures up to #fjj volts4 ,it is used for starting rotary converters and direct current motors of large capacity having starting torque small enough to permit cutting out the starting resistance in few steps4 ,the clips can be connected to any type of resistor1 the steps of which are successively short circuited as the switch closes2 the amount of resistance in the armature circuit is thus gradually reduced4 ,a pause should be made after each step of resistance is thrown in to allow the motor speed to accelerate4 ,if the starting switch do not have to carry the full load current and can be short circuited by another switch1 a starting switch of smaller capacity equivalent to #ej per cent of running current of the machine can be used4 ,the switch is of the single pole1 single throw1 rear connected1 four point1 knife blade type4 ,ques4 ,describe its operation4 ,ans4 ,the moving arm of the switch draws the fuse through the tube1 thus opening the circuit without much disturbance4 ,illustration3 ,,fig4 #b1bai4--;,baum disconnecting switch with horns and auxiliary contacts 7,pacific ,mfg4 ,co474 ,this switch is for use on systems operating at #ajj1jjj volts or over4 ,it has a spacing of five feet between outer insulators1 is equipped with auxiliary shoes that break the circuit between the horns1 diverting it from the current carrying contacts so that they are not attacked by the arc4 ,ques4 ,what is the objection to the metal fuse switch8 ,ans4 ,the powder is set flying by the explosion of the arc1 which1 as it settles1 gets into the bearings of any machine that may be in the vicinity4 ,ques4 ,what is a horn break switch8 ,ans4 ,one provided with horn shaped extensions to the contacts1 as shown in fig4 #b1bai4 ,the arc formed on breaking the circuit1 as it travels toward the extremities of the horns1 becomes attenuated and is finally ruptured4 ,illustration3 ,,fig4 #b1bbj4--,kelman switching mechanism4 ,the pantograph arrangement of the contact blades gives a double horizontal break deep down in the oil4 ,this gives over the break a heavy head of oil which immediately closes in around the thin blades as they leave the contacts in opening1 thus effectually extinguishing the arc4 ,the opening spring acts within the pantograph itself without any intervening mechanism1 and the light weight of the few moving parts enables the spring to accelerate the blades rapidly1 thus obtaining a quick break4 ,the contacts are of the return bend type1 which makes a flexible contact1 to obtain alignment with the blades at all times4 ,the pantograph and contacts are supported on corrugated porcelain insulators on a hardwood base or insulator board4 ,the insulators are fitted with iron ends for securing the different parts4 ,at each end of the insulator board is an upright or lifting board which serves to lift the switching mechanism out of the tank4 ,the leads are heavily insulated4 ,ques4 ,what are the objections to this type of switch8 ,ans4 ,the considerable space required for the horns and arcs1 and the line surges caused by the arc4 ,horn switches were used extensively for high pressure alternating current circuits before the introduction of oil switches4 ,illustration3 ,,fig4 #b1bba4--,sectional view of ,pacific weatherproof oil switch for use in places exposed to the weather4 ,all moving and contact parts are supported from the cast iron top and are readily removable for inspection or repair4 ,oil ,switches4--,the extensive use of high pressure currents and alternating current motors and other devices introducing inductance make it necessary to use switches radically different from the ordinary air break types4 ,illustration3 ,,fig4 #b1bbb4--;,general ,electric central station triple pole single throw oil switch2 view of switch in tank4 ,this type is for pressures up to #aaj1jjj volts1 being adapted for stations employing open wiring1 since the connections are made at the top of the switch and its construction obviates the need for isolating it in a cell4 ,one tank with two breaks in series are used for each phase4 ,the opening of circuits of considerable current value with inductive loads is not possible with old style switches which were quite adequate for the service for which they were designed4 ,these circuits are controlled with ease and certainty by the oil switch4 ,illustration3 ,,figs4 #b1bbc to #b1bbf4--,westinghouse indoor1 two pole double throw oil switch for pressures not over #f1fjj volts4 ,fig4 #b1bbc1 open position2 fig4 #b1bbe1 closed position4 ,this type of switch is suited for a wide range of application1 being made in both switchboard and wall mounting styles2 also for remote mechanical control by the use of bell cranks and connecting rods4 ,the wall mounting style is adaptable to motor installations on account of the facility with which it may be mounted on any support1 convenient to the motor operator4 ,the lever and handle extend outward over the oil tank1 so that the switch may readily be mounted against a wall1 post or any vertical support4 ,the characteristic features of this type of switch are3 knife blade contacts submerged in oil2 live parts carried on a porcelain base affording a permanent insulation between adjacent poles1 and between the frame and live parts2 compactness and accessibility2 enclosure of all live metal parts2 and low first cost4 ,each contact jaw has attached to it an arcing piece which takes the final break1 thus preventing any burning of the jaws4 ,these arcing pieces are inexpensive and readily replaced when worn or burnt away4 ,the contact making parts are enclosed in a sheet metal oil tank which has an insulating lining4 ,the leads are brought out at the top4 ,connections to the outside circuit are made inside the switch and a porcelain insulator is slipped over the joint1 thus providing a straight continuous connection from the line with maximum insulation4 ,on the #f1fjj volt switch1 insulation is obtained by the use of porcelain bases for supporting the live parts4 ,in the #c1cjj volt switch specially treated wooden bases are used1 suitable barriers being provided between the poles where necessary to prevent arcs communicating4 ,ques4 ,what is an oil switch8 ,ans4 ,one in which the contact is broken under oil4 ,this type of switch is the one almost universally used on high pressure alternating current circuits1 because of the fact that the oil tends to cause the current to break when at its zero value1 thus preventing the heavy arcing which would occur with an air break switch1 and the consequent surges in the line which are so often the cause of breakdown of the insulation of the system4 ,illustration3 ,,fig4 #b1bbg4--,kelman electric control unit for oil switch4 ,it consists of an iron frame which contains the opening and closing coils and the bearings for the operating bell crank4 ,a small switch on the frame automatically opens the coil circuit at the end of the stroke in either direction and operates signal lamps to indicate the open or closed position4 ,the automatic overload release opens the switch by closing the opening coil circuit4 ,this electrical operating unit gives satisfactory service through a wide variation of voltage4 ,it requires a momentary expenditure of energy of from #a1ejj to #d1jjj watts1 depending on the size4 ,ques4 ,what is the nature of an oil break8 ,ans4 ,it is not a quick break4 ,oscillograph records show that the effect of the oil is to allow the arc to continue during several cycles and then to break the current1 usually at the zero point of the wave4 ,remote ,control ,oil ,switches4--,it is desirable in the case of switches on high pressure circuits to locate the parts which carry the high pressure current at some distance from the switchboard in order that they may be operated with safety4 ,with respect to the manner in which the switches are operated they may be classed1 as #a4 ,hand operated2 #b4 ,power operated4 ,illustration3 ,,figs4 #b1bbh and #b1bbi4--,views showing mechanism of hand operated remote control switches4 ,fig4 #b1bbh1 straight mechanism2 fig4 #b1bbi1 angular mechanism4 ,ques4 ,what kind of power is used8 ,ans4 ,electricity is used in most cases2 in some installations1 switches are operated by compressed air4 ,ques4 ,for what pressures should remote control switches be used8 ,ans4 ,for pressures above #a1ajj volts4 ,ques4 ,describe the operating mechanism of a remote control1 hand1 and electrically operated switch4 ,ans4 ,for hand operation1 the mechanism between the operating lever and switch proper1 consists simply of a system of links and bell cranks4 ,various shapes of bell crank are used1 to permit change in direction or position of the force applied to operate the switch4 ,illustration3 ,,fig4 #b1bcj4--,pacific oil switch with solenoid control1 designed for #fj1jjj and #gj1jjj volt installations2 it is capable of handling a #be1jjj kw4 generating station4 ,the break is horizontal1 made by the rotation of a flat member edgewise through the oil4 ,the solenoid1 at its extreme outer position1 has a free start before commencing to move the control parts of the switch4 ,as it approaches the extreme inner position1 where the opening spring and the contacts begin to offer the greatest resistance1 the magnetic action is1 of course1 most powerful1 and the leverage by which it is applied moves to an increasing radius1 by means of rollers working in the curved slots of the control shaft levers4 ,these curved slots and rollers have the additional advantage of making the opening action very free and smooth4 ,the tripping coil does not act on the latch directly1 but gives a hammer blow that is positive4 ,the latch proper is a roller having a powerful hold and easy release4 ,current can not be left on either the closing or opening coils1 as they are automatically cut out by the movement of the switch4 ,ques4 ,name two classes of electrically operated remote control switch4 ,ans4 ,those operated by solenoids1 and those operated by motors4 ,the solenoid type are closed by the action of a plunger solenoid1 and opened either by another solenoid called a tripping coil or by gravity4 ,some examples of remote control are shown in the accompanying illustrations4 ,ques4 ,what indicating devices are used with electrically operated switches8 ,ans4 ,red and green lamps2 red for closed and green for open as shown in fig4 #b1bca4 ,illustration3 ,,fig4 #b1bca4--;,diagram of connections of motor operated remote control switch4 ,the motor which operates the switch is controlled by a small lever generally mounted on the panel with the instruments which are in the circuit controlled by the switch4 ,the standard pressure for operating the motors is #abe volts4 ,ques4 ,for what service are motor operated switches used8 ,ans4 ,for exceptionally heavy work where the kilowatt rupturing capacity is greater than that for which the other types are suitable4 ,illustration3 ,,fig4 #b1bcb4--;,general ,electric motor operated three phase oil switch4 ,the operation of the oil switch is accomplished by a small hand controlling switch1 generally mounted on the panel1 with the instruments which are in the circuit controlled by the oil switch4 ,the standard pressure for the operating motor is #abe volts4 ,the switch has six breaks1 each break being a separate tank4 ,in addition to this isolation of the breaks1 each phase is enclosed in a fireproof brick compartment1 making it impossible for trouble in one phase to be communicated to another4 ,the cells are constructed of brick with top and bottom slabs of slate4 ,the capacities of such switches1 range from #b1ejj to #fj1jjj volts1 and from #ajj to #a1jjj amperes4 ,rupturing ,capacity of ,oil ,switches4--,while an oil switch may be designed for a given pressure and to carry a definite amount of current1 it should not be understood that the switch will necessarily rupture the amount of normal energy equivalent to its volt ampere rating4 ,illustration3 ,,figs4 #b1bcc to #b1bce4--;,diagrams showing connections for ,general ,electric single1 double1 and triple pole1 solenoid operated remote control switches4 ,the operating coils are shown connected to main switch circuit1 but may be connected to an entirely separate control circuit4 ,connections are the same for either alternating or direct current4 ,oil switches are often used on systems with generator capacity of many thousand kilowatts4 ,it is therefore essential that the switches shall be able to break not only their normal current1 but also greatly increased current that would flow if a short circuit or partial short circuit occur4 ,illustration3 ,,fig4 #b1bcf4--,westinghouse three pole hand operated remote control oil switch1 adapted for the control of alternating current circuits of small and moderate capacities1 the pressures of which do not exceed #be1jjj volts4 ,each unit is installed in a separate masonry compartment4 ,the open position of contacts is maintained by gravity4 ,up to and including the #fjj ampere capacity1 the contacts are cone shaped with an arcing tip1 as shown for capacities in excess of #fjj amperes1 brush contacts are furnished with auxiliary arcing contacts of the butt type4 ,each pole has two sets of contacts1 thus providing a double break in each line4 ,with both types of contact1 the final break of the arc is taken and the main contacts protected by auxiliary arcing contacts which are inexpensive and readily renewable4 ,the upper or stationary contacts are mounted on porcelain insulators secured in the soapstone base4 ,the lower or movable contacts are carried by a wooden rod connected to and moved vertically by the operating mechanism4 ,the operating mechanism of the hand operated breaker consists of a simple system of levers1 bell cranks1 and rods4 ,the necessary energy for making a positive contact is small owing to the use of a toggle mechanism4 ,the leads are brought out of the top of the breaker through heavy porcelain insulators4 ,on breakers above #c1ejj volts1 the connections to the line wires are made by means of a union which can be tightened with a socket wrench fitting inside the insulator4 ,as the leads coming into the switch are necessarily insulated wire or cable1 this arrangement eliminates all exposed live parts and is well adapted to making connections readily to bus bars located above or in the rear of the circuit breakers4 ,illustration3 ,,fig4 #b1bcg4--;,cutler-,hammer enclosed float switch1 designed for the automatic control of alternating current motors operating pumps used to fill or empty tanks1 sumps or other reservoirs4 ,the switch is operated by the rise and fall of a copper float which is connected to the switch lever by a brass rod or copper chain4 ,as the water level rises and falls1 the float moves up and down4 ,this movement is transmitted to the switch lever and the switch 7if the movement be sufficient7 is tripped to make or break the motor circuit4 ,to insure the best operation it is necessary that the float rod be provided with a guide so that the float will move up or down in a vertical line1 as shown4 ,the minimum difference in water level at which the switch will operate is approximately #aj to #ab inches4 ,when the float is placed in a closed tank1 the minimum height inside from the bottom of the tank to the top should be at least #f inches greater than the difference in water level to provide sufficient clearance for the float4 ,when this type switch is used as a tank switch1 the contacts are closed when the water level is low1 putting the motor1 driving the pump1 in motion4 ,when the water in the tank reaches a predetermined high level the float arm opens the switch contacts1 and the motor is disconnected from the line4 ,for sump pump purposes1 the contacts open on low level and close on high level1 the lever being reversed for this purpose4 ,two pole1 three pole and four pole switches of this type are made1 all arranged to completely disconnect single phase1 two phase and three phase motors from their circuits4 ,when used with small motors which may be thrown across the line to start1 the switch may be used without a self starter if desired4 ,under short circuit conditions alternators develop instantaneously many times their normal load current1 while the sustained short circuit current is approximately two and a half to three times normal1 or even higher with turbine alternators4 ,hence1 circuit breakers of the so called instantaneous type must be capable of rupturing the circuit when the current is at a maximum1 whereas1 non-automatic switches1 or circuit breakers with time limit relays will be required to interrupt only the sustained short current circuit4 ,the reason is evident1 since the delay in opening the switch allows the current to approach the sustained short circuit conditions4 ,,chapter ,,lviii ,,current ,,and ,,pressure ,,limiting ,,devices ,in any electric installation there must be provided a number of automatic devices to secure proper control4 ,the great multiplicity of devices designed for this purpose may be divided into two general classes1 as #a4 ,current limiting2 #b4 ,pressure limiting4 ,because of the heating effect of the current which increases in proportion to the square of the strength of the current1 it is necessary to protect circuits with devices which do not allow the current to exceed a predetermined value4 ,accordingly fuses1 circuit breakers1 reactances1 etc41 are used1 each possessing certain characteristics1 which render it suitable for particular conditions of service4 ,for instance1 just as in analogy1 steam boilers must be protected against abnormal pressures by safety valves1 electric circuits must be guarded against excessive voltages by pressure limiting devices1 otherwise much damage would occur1 such as the burning out of incandescent lamps1 grounding of cables1 etc4 ,the control of steam is simple as compared to the electric current1 the latter being the more difficult to manage because of its peculiar behaviour in certain respects1 especially in the case of alternating current which necessitates numerous devices of more or less delicate construction for safety both to the apparatus and the operator4 ,fuses4--,a fuse is an electrical safety valve1 or more specifically1 the actual wire or strip of metal in a cut out1 which may be fused by an excessive current1 that is to say1 by a current which exceeds a predetermined value4 ,a fuse1 thus serves to protect a circuit from any harm resulting from an undue overload4 ,fuses have been treated at such length in ,guide ,no4 #b1 ,chapter ,,xxv1 that very little can be said here1 without repetition4 ,illustration3 ,,fig4 #b1bch4--,sectional view of ,noark #bej volt1 #djj ampere enclosed fuse4 ,the fusible element is divided into strips ,a1 ,b1 ,c1 and ,d4 ,this parallel link construction results1 upon the operation of the fuse1 in the formation of a number of small arcs1 thus facilitating the absorption of the metal vapor formed when the fuse blows4 ,the fusible strips1 of which there are two or four in number1 according to the ampere capacity of the fuse1 are entirely surrounded by a granular material which is chemically inactive with respect to the fusible link and whose function is to absorb the metallic vapor formed upon the blowing of the fuse4 ,the contact blades ,t and ,l are made of round edge copper1 the round edges facilitating the insertion of the fuses in the circuit terminals4 ,r and ,s are the end ferrules1 attached to cover ,e1 by the pin ,m4 ,ques4 ,what effect have the terminals on a fuse8 ,ans4 ,the current at which a fuse melts may be greatly changed by the size and shape of the terminals4 ,if near together and large1 they may conduct considerable heat from the fuse thus increasing the current required to blow the fuse4 ,ques4 ,what is the objection to large fuses8 ,ans4 ,the discharge of molten metal when the fuse blows is a source of danger4 ,ques4 ,what should be used in place of large fuses8 ,ans4 ,circuit breakers4 ,ques4 ,what are the objections to fuses in general8 ,ans4 ,the uncertainty as to the current required to blow them2 the constant expansion and contraction is liable to loosen the terminal screws when screws are used4 ,ques4 ,what is the advantage of fuses8 ,ans4 ,they form an inexpensive means of protecting small circuits4 ,illustration3 ,,fig4 #b1bci4--;,cross section through plug fuse4 ,with this type of fuse it is impossible to place any except the correct size of plug in the socket4 ,ques4 ,describe a plug fuse4 ,ans4 ,it is constructed as shown in fig4 #b1bci1 the fuse wire being visible and stretching between the two metal portions of the plug4 ,ques4 ,what is a cut out fuse8 ,ans4 ,one similar to a simple fuse1 but provided with clip contacts as used for knife switch contacts4 ,the fuse wire is usually contained in a china or porcelain tube1 which also serves the purpose of a handle for withdrawing the fuse4 ,ques4 ,what is an expulsion fuse8 ,ans4 ,one in which the fuse is placed in an enclosed chamber with a vent hole4 ,in operation1 when the fuse blows1 the hot air and molten metal are expelled through the vent4 ,ques4 ,what is a no arc fuse8 ,ans4 ,a cartridge type fuse1 in which the space surrounding the fuse wire is filled with powdered material4 ,illustration3 ,,fig4 #b1bdj4--;,inside view of end ferrule of ,noark enclosed fuse4 ,two prongs ,o and ,v1 which are a part of the knife blade ,k1 pass through the square holes in the ends of the ferrule ,r1 and are riveted to the anchor plate ,t4 ,the object of this plate is to stiffen the structure and to increase the current carrying capacity of the metal between the holes1 also to permit of proper alignment of the plates4 ,in each ferrule is placed a vent screen1 composed of reticulate material1 such as cheese cloth4 ,the fuzz between the threads of the cheese cloth prevents the escape of the granular material through the vent holes ,a1 but when the fuse operates1 allows free egress of the air1 thereby permitting the vapor formed upon the operation of the fusible element to quickly and freely pass through the interstices of the filling material and become cooled1 eliminating any possibility of flame issuing from the ends of the tube4 ,the object of the powdered material is to assist in extinguishing the arc formed when the fuse blows4 ,ques4 ,what is a magnetic blow out fuse8 ,ans4 ,an enclosed fuse which is subject to the action of a magnetic field produced by the current1 the magnetic field tending to blow out the arc when fusing occurs4 ,ques4 ,what is a quick break fuse8 ,ans4 ,one having a weight suspended from its center1 or springs attached to its ends so that the arc formed at fusing is quickly attenuated and extinguished4 ,ques4 ,what is the disadvantage of a fuse as compared to an oil switch circuit breaker8 ,ans4 ,when a fuse blows1 the arc causes oscillations in the line1 which cause excessive rise of pressure under certain capacity conditions1 whereas this disturbance is reduced to a minimum with an oil switch4 ,illustration3 ,,fig4 #b1bda4--,quick break fuse4 ,the fuse wire is connected between the fixed terminal ,a and the movable arm ,b1 and is held under tension by the spring which exerts pressure on the movable arm in a direction tending to separate ,a and ,b4 ,in operation1 when the fuse blows1 the movable arm quickly moves to the position ,b1 thus attenuating the arc and accelerating its extinguishment4 ,ques4 ,what metal is used for fuse wires8 ,ans4 ,various metals4 ,ordinary fuse wire is made of lead or an alloy of lead and tin4 ,ques4 ,what is the objection to aluminum8 ,ans4 ,it becomes coated with oxide or sulphide1 which acts as a tube tending to retain the metal inside and prevent rupture4 ,ques4 ,what is the objection to copper8 ,ans4 ,its high fusing point4 ,current ,limiting ,inductances4--,the great increase in capacity of power stations1 for supplying the demands of densely populated centers and large manufacturing districts1 together with the decrease in the reactance of modern alternators and transformers due to improvement in design to obtain better regulation1 has presented a problem in apparatus protection not contemplated in the earlier days of alternating current distribution4 ,this problem is entirely separate and distinct from that of eliminating the tendency toward short circuit1 incident to the high voltages now common in transmission lines4 ,it accepts that all short circuits must occasionally occur and considers only the protection of the connected apparatus against the mechanical forces due to the magnetic stresses of such enormous currents4 ,illustration3 ,,fig4 #b1bdb4--,notched end fuse4 ,this is a simple form of fuse consisting of a strip of metal 7or wire7 fixed between two end pieces to fit around the terminals4 ,this type is often proportioned so that it is only possible to place the correct size of fuse in the terminals4 ,sometimes1 in place of the end pieces as shown1 the fuse metal is fixed between two clamping screws4 ,ques4 ,what means are employed to limit the value of a short circuit current8 ,ans4 ,a current limiting inductance coil 7called a reactance7 is placed in series with the alternators or transformers4 ,illustration3 ,,fig4 #b1bdc4--;,general ,electric current limiting reactance2 view showing details of construction4 ,the core consists of a hollow concrete cylinder1 alloy anchor plates or sockets being embedded in the core near the ends to receive the radial brass bolts4 ,an extension at each end of the core provides for clamping and bracing the reactance in installation4 ,the supports for the winding are made of resin treated maple and are located upon the core by radial brass studs screwed into the alloy sockets1 and insulated by mica tubes4 ,the nuts by which the structure is tightened1 rest upon heavy fibre washers4 ,wooden barriers fitted and shellacked into the supports add to the creepage surface between layers of the winding and between the winding and the core4 ,the supports of the layer next to the core are separated from the core by strips of treated pressboard4 ,the coil consists of bare stranded cable in several layers1 usually three in number4 ,it is wound into grooves in the treated wood supports1 which are protected from contact with the cable by heat shields of asbestos shellacked into the grooves4 ,the winding is usually in the form of two back turn sections1 thereby allowing the terminals of the coil to be brought out at the ends of the outside layer4 ,this assures accessibility and ease of connection1 and the removal of the leads from proximity to the core4 ,two turns at each end of the winding are given extra spacing for the purpose of additional insulation4 ,the final turn at each end of the coil is securely held in place by alloy clamps bolted to the supports4 ,the wood is protected from contact with the clamps by shields of asbestos4 ,the ends of the cable between the two sections are welded by the oxyacetylene process4 ,ques4 ,what are its essential features of construction8 ,ans4 ,it consists of bare stranded cable wound around a concrete core and held in place by wooden supports as shown in fig4 #b1bdc4 ,in order to avoid the prohibitive expense of high voltage insulation1 the reactance coil is designed for the low tension circuit4 ,this requirement prohibits the use of a magnetic core which1 if economically designed for normal operation1 would become saturated at higher densities1 or1 if designed large enough to avoid saturation at short circuit conditions1 would become prohibitive in cost and dimensions4 ,the elimination of all magnetic material from the construction of the concrete core reactance permits of no saturation1 and assures a straight line voltage characteristic at all current loads4 ,illustration3 ,,fig4 #b1bdd4--,westinghouse magnetic blow out circuit breaker1 designed for the protection of street railway and electric locomotive equipments2 it serves the combined purpose of fuse block and canopy switch4 ,the contact tips are surrounded by a moulded arc chute which confines and directs the arc until the magnetic blow out extinguishes it4 ,the current carrying contacts consist of copper strips separated by air spaces4 ,an auxiliary contact or arcing tip at the end of the switch lever takes the burning of the arc when the breaker opens1 and thus confines the burning to a very small piece which can be easily removed and replaced at small cost4 ,the hand tripping lever and the resetting lever have insulated handles1 so that they can be safely handled1 even in the dark4 ,ques4 ,where is the proper location for a current limiting reactance8 ,ans4 ,as near the alternator as possible4 ,ques4 ,why8 ,ans4 ,to lessen the possibility of a short circuit occurring between the reactance and the alternator4 ,ques4 ,beside limiting the current1 what other service is performed by the reactance8 ,ans4 ,it protects the alternator from high frequency surges coming in from the outside1 and limits the current from other machines on the same bus4 ,illustration3 ,,fig4 #b1bde4--;,general ,electric magnetic blow out circuit breaker4 ,this type may be used in air or water tight boxes and is peculiarly adapted for service where the arc must be confined4 ,circuit ,breakers4--,the importance of circuit protective devices1 commonly called circuit breakers1 is fully recognized4 ,the duty of a circuit breaker is to protect the apparatus in an electrical circuit from undesirable effects arising from abnormal conditions1 by automatically breaking the circuit4 ,accordingly a circuit breaker must comprise a switch in combination with electrical control devices designed to act under abnormal conditions in the circuit4 ,a circuit breaker is a device which automatically opens the circuit in event of abnormal conditions1 in the circuit4 ,illustration3 ,,fig4 #b1bdf4--,magnetic blow out circuit breaker4 ,this is a direct current breaker in which the final break occurs in a magnetic field4 ,it is a principle in electromagnetics that a conductor carrying a current in a magnetic field will tend to move in a direction at right angles to the field4 ,the arc set up on breaking a circuit constitutes a conductor1 and in magnetic blow out circuit breakers1 as generally manufactured1 there is an electromagnet1 energized by the current to be broken1 which produces a field in the neighborhood of the arc1 with the result that the arc moves outward1 and so becomes attenuated and is finally extinguished4 ,the form shown in the figure is used on cars equipped with heavy motors4 ,when so used1 it is in many cases mounted in a box with the handle ,h projecting at one end4 ,a and ,k are the terminals of the breaker and ,b is the tripping coil1 which also serves to set up the magnetic field necessary for blowing out the arc4 ,x is the armature of coil ,b and is pulled down against the action of the spring ,s whenever the current exceeds that for which the breaker is set4 ,the tripping current is adjusted by means of nut ,t4 ,the iron plate ,p and a similar one back of it are magnetized by the current in coil ,b1 and as the break takes place between these two poles1 the arc is promptly extinguished by the field that exists there4 ,in operation1 ,a and ,k are the terminals1 ,d ,d is a contact that is forced up against ,f1 ,f when the breaker is set4 ,the current then takes the path ,a-,b-,f-,d ,d-,f-,k4 ,when the breaker trips1 the contact piece ,d ,d flies down and the tendency is for an arc to form between ,f1 ,f2 the magnetic field blows the arc upwards1 and whatever burning takes place is on the contacts ,e1 ,e1 which are so constructed that they may be readily renewed4 ,to trip the breaker by hand1 the knob ,n is pressed4 ,in the design of circuit breakers1 there are several methods used to effect the rupturing of the arc between contacts when opened on heavy overload1 such as3 #a4 ,magnetic blow out2 #b4 ,thermal break2 #c4 ,carbon break4 ,in the magnetic blow out type1 the arc is extinguished between auxiliary contacts confined by a chute in which the arc is rapidly blown out due to a powerful magnetic field from one or more electromagnets4 ,this type may be used in air or watertight boxes and is peculiarly adapted for service where the arc must be confined4 ,illustration3 ,,fig4 #b1bdg4--,thermal overload circuit breaker4 ,in construction two contact blocks are fixed rigidly to1 but insulated from1 the switch arm4 ,they are connected electrically by two parallel strips of suitable metal1 each fitted with a steel catch piece4 ,when the switch is closed the strips are sprung apart over a fixed catch1 and the full rated current does not release the catch4 ,overload causes the strips to move apart1 and the circuit breaker flies off under the action of a spring4 ,in a carbon break type1 the arc is finally ruptured between carbon break contacts4 ,the breaking of the circuit is accomplished progressively1 that is to say1 it is done in three stages1 by several sets of contact1 known respectively as #a4 ,the main contacts2 #b4 ,the intermediate contacts2 #c4 ,the carbon contacts4 ,in operation1 as the circuit breaker acts to break the circuit1 first the main contacts1 separate1 then the intermediate contacts1 and finally the carbon contacts between which the arc is ruptured4 ,ques4 ,what is the object of the intermediate contacts8 ,ans4 ,to prevent the forming of an arc on the main contacts4 ,illustration3 ,,fig4 #b1bdh4--;,carbon break discs of ,condit circuit breaker4 ,the two pairs of similar discs which slide past each other are so arranged that these surfaces coincide at the instant the intermediate contacts separate after which1 as the contact arm opens further1 they gradually disengage4 ,ques4 ,what is the object of the carbon contacts8 ,ans4 ,first to protect the intermediate contacts by providing a path for the current after the intermediate contacts separate1 and #b1 to slow down the current by means of the considerable resistance of the carbon1 thus reducing to a minimum the arc which is formed when the carbon contacts separate4 ,ques4 ,how is the automatic operation of a circuit breaker usually accomplished8 ,ans4 ,usually through the medium of a solenoid1 or electromagnet energized by current from the circuit controlled by the breaker4 ,illustration3 ,,fig4 #b1bdi4--,mechanically connected insulated latches used on ,condit circuit breakers to produce inter-locking tripping4 ,the essential features of construction and operation of a circuit breaker is shown in the elementary diagrams1 figs4 #b1bej to #b1bec4 ,in construction as shown in fig4 #b1bej it consists essentially of three sets of contacts1 a swinging contact arm which is set in the closed position by the handle operating through the toggle joint1 the movement of which is limited in the closing direction by the stop4 ,the latter is made adjustable by an eccentric pin or equivalent4 ,connected to the toggle is the plunger of the solenoid whose winding is energized by current from the circuit which the circuit breaker is to control4 ,illustration3 ,,figs4 #b1bej to #b1bec4--;,elementary diagrams illustrating the operation of a carbon circuit breaker of the overload type1 showing the progressive opening of such device4 ,fig4 #b1bej1 closed position2 fig4 #b1bea1 main contacts open2 fig4 #b1beb1 intermediate contacts open2 fig4 #b1bec1 carbon contacts open1 circuit broken4 ,in operation1 the circuit is closed by hand by turning the handle downward to the position shown in fig4 #b1bej1 that is as far as it will go4 ,since the toggle has passed the center line the arm will be held normally in this position because of the spring action of the contacts4 ,now1 if the current rise above a predetermined limit1 the pull exerted by the solenoid will overbalance the tendency of the toggle to remain in the closed position1 and pull the two toggle links downward below the center line1 drawing the contact arm back and breaking the circuit4 ,illustration3 ,,fig4 #b1bed4--;,i-,t-,e overload circuit breaker4 ,in operation3 the current from one side of the circuit enters the circuit breaker at ,a1 passing through the laminated bridge ,b to contact block ,c1 thence through coil ,d and terminal ,e to the motor4 ,the coil ,d surrounds a magnetic core1 having pole pieces ,f and ,g and armature ,h4 ,the effect of the current in the coil is to energize the magnet1 thus tending to lift the armature against the force of gravitation4 ,the volume of current required to trip the circuit breaker is determined by the position of the armature1 which is subject to ready adjustment1 and is indicated on the calibration plate ,p4 ,from the opposite side of the line1 the current enters at ,i1 passing downward through the laminated bridge member ,j1 into terminal ,k1 whence it passes out to the motor4 ,when the current passing through the circuit breaker attains sufficient volume1 the force generated by the magnetic coil overcomes the weight of the armature ,h2 and the latter is drawn upward toward the pole pieces with constantly increasing force1 until the insulated projections ,l and ,m strike against the respective restraining latches ,n and ,o1 thereby releasing the two switch members1 which at once open in response to the force supplied by the spring of the contact members and auxiliary springs provided for the purpose4 ,positiveness in opening is further assured by the blow of the armature1 which is added to the other opening forces2 hence1 the heavier the overload1 the more violent the blow and the quicker the circuit breaker opens2 or the greater the current the more promptly it is interrupted4 ,this is the ,i-,t-,e or ,inverse ,time ,element principle4 ,illustration3 ,,fig4 #b1bee4--;,condit #fjj volt1 #a1bjj ampere1 single pole1 type ,k1 circuit breaker with pull down handle4 ,illustration3 ,,fig4 #b1bef4--;,condit #fjj volt1 #f1jjj ampere1 single pole1 switch board mounting1 circuit breaker1 with pull down handle4 ,illustration3 ,,fig4 #b1beg4--;,general ,electric triple pole1 overload1 circuit breaker1 with two overload coils1 capacity #cjj amperes1 #dhj volts4 ,the progressive action which takes place during this operation is shown in figs4 #b1bej to #b1bec in which the main contacts separate first1 then the intermediate1 and finally the carbon contacts as mentioned before4 ,ques4 ,what name is given to this type of circuit breaker8 ,ans4 ,it is called an overload circuit breaker4 ,illustration3 ,,fig4 #b1beh4--,parts of ,general ,electric #b1jjj ampere #fej volt circuit breaker4 ,a1 cover for secondary contact bracket2 ,b1 spring washer for ,ea42 ,c1 pin for links and ,g2 ,d1 spring for carbon support2 ,e1 plate for ,f2 ,f1 carbon support2 ,g1 secondary contact bracket2 ,h1 contact plate2 ,i1 screw for ,h2 ,j1 nut for ,k and ,w2 ,k1 contact stud1 upper2 ,l1 laminated brush1 complete with support2 ,m1 leather buffer for ,l2 ,n1 main link2 ,o1 pin for ,na and ,la left hand and ,cb and ,na right and left hand2 ,p1 screw for ,n and magnet frame shaft2 ,q1 washer for ,n and magnet frame shaft2 ,r1 screw for ,s and ,v2 ,s1 index plate2 ,t1 plate for ,gb2 ,u1 screw for ,t2 ,v1 magnet frame2 ,w1 contact stud1 lower2 ,x1 pin for ,cb1 ,na and ,v2 ,y1 washer for ,x and ,o2 ,z1 calibrating screw with thumb nut2 ,aa1 armature with contact plate2 ,ba1 catch lever complete with catch ,ca1 button handle for ,ba2 ,da1 spring cotter for ,ea2 ,ea1 pin for ,f and ,fa2 ,fa1 operating link for ,g2 ,ga1 pin for ,d2 ,ha1 carbon holder with copper and carbon contacts2 ,ia1 flexible connections for ,g and ,f2 ,ja1 screw for ,g and flexible connection plate2 ,ka1 screw for ,na and ,ha2 ,la1 copper secondary contact2 ,ma1 screw for ,la2 ,na1 secondary contact lever2 ,oa1 cross bar for ,na2 ,pa1 screw for ,l and ,m2 ,qa1 secondary toggle link 7left hand72 ,ra1 spring cotter for ,wa and ,o2 ,sa1 brush lever2 ,ta1 buffer for ,cb and ,sa2 ,ua1 secondary toggle link 7right hand72 ,va1 washer for ,wa2 ,wa1 pin for ,cb1 ,qa1 ,ua and ,n2 ,xa1 pin for ,sa and ,cv2 ,ya1 spring cotter for all pins1 except ,wa1 catch lever pin and buffer2 ,za1 secondary contact link2 ,ab1 washer for ,fb2 ,bb1 guard for ,fb2 ,cb1 handle lever2 ,db1 catch for ,cb2 ,eb1 screw for ,db2 ,fb1 handle with stud2 ,gb1 secondary connection4 ,automatic ,features4--,there are three methods of connecting the winding of the solenoid1 or trip coil as it is called3 ,illustration3 ,,figs4 #b1bei to #b1bfb4--;,elementary diagrams illustrating the various methods of electromagnetic control for circuit breakers4 ,fig4 #b1bei1 overload trip2 fig4 #b1bfj1 underload trip1 fig4 #b1bfa1 low voltage trip2 fig4 #b1bfb1 control from auxiliary circuit by means of a relay4 #a4 ,in series with the main circuit2 #b4 ,in shunt with the main circuit2 #c4 ,in shunt with an auxiliary circuit4 ,illustration3 ,,fig4 #b1bfc4--;,diagram of ,general ,electric low voltage trip with tripping switch normally open4 ,the automatic controls arising from these connections give various kinds of protection to the circuit and are known as #a4 ,overload trip2 #b4 ,underload trip2 #c4 ,low voltage trip2 #d4 ,auxiliary circuit trip4 ,illustration3 ,,fig4 #b1bfd4--;,diagram of ,general ,electric low voltage trip1 with tripping switch normally closed4 ,ques4 ,what is the object of the overload trip8 ,ans4 ,it is intended to open the circuit when the current exceeds a predetermined value4 ,ques4 ,what modifications are made in the mechanism shown in the elementary diagrams8 ,ans4 ,sometimes a latch is used in place of the toggle and a magnet in place of the solenoid as in figs4 #b1bfe and #b1bff4 ,ques4 ,why is a magnet used in combination with a latch8 ,ans4 ,because with this arrangement very little movement is required to trip the breaker1 and for such conditions1 a magnet is more efficient than a solenoid4 ,illustration3 ,,figs4 #b1bfe and #b1bff4--;,circuit breaker with automatic control mechanism consisting of magnet and latch2 views showing breaker in open and closed positions1 and essential features4 ,the toggle is used to obtain sufficient leverage to easily close switch against the pressure of the brush contacts but not to lock switch1 this being done by the latch as shown1 the latter closing by the action of a spring1 there being a roller ,r at the end which engages the arm to reduce friction4 ,in operation1 when the current exceeds a predetermined limit the magnet attracts the latch and releases the contact arm4 ,the brush contacts which are exerting pressure against the contact arm1 rapidly push it away1 and assisted by gravity1 the arm flies open to the position shown in fig4 #b1bff4 ,ques4 ,how does the latch arrangement work8 ,ans4 ,when the proper current is reached1 the magnet pulls open the latch and the contact arm of the breaker moves by the force of gravity or other means and opens the circuit4 ,ques4 ,how does the underload trip operate8 ,ans4 ,the same as the overload type except that they operate on a diminution of current instead of an excess4 ,illustration3 ,,figs4 #b1bfg and #b1bfh4--,positions in circuit of current and pressure coils of circuit breakers4 ,ques4 ,describe the no voltage trip4 ,ans4 ,the energy for the trip of this breaker is derived from a high resistance or fine wire coil which is arranged to be placed directly across the line1 in operation1 when the current flowing through the circuit falls below a predetermined value1 the energy of the coil is insufficient to counteract the force of a spring1 which then trips the breaker4 ,illustration3 ,,fig4 #b1bfi4--;,diagram of ,general ,electric shunt trip with coil connected beyond breaker and thrown out of circuit after tripping4 ,ques4 ,describe the auxiliary circuit trip4 ,ans4 ,a pressure coil is used which is energized by current from an auxiliary circuit4 ,the coil is only momentarily energized1 by push button1 relay or other control1 as distinguished from the preceding types1 in which the coil is constantly energized4 ,illustration3 ,,fig4 #b1bgj4--;,diagram of ,general ,electric shunt trip with auxiliary circuit opening switch to throw coil out of circuit after tripping4 ,illustration3 ,,fig4 #b1bga4--;,general ,electric shunt trip attachment4 ,the shunt trip attachment has been designed to provide for conditions under which the low voltage attachment cannot be successfully applied4 ,it resembles the low voltage attachment in construction1 but differs in that it trips the circuit breaker when energized4 ,the shunt trip should be allowed to remain only momentarily in circuit2 hence it should be so connected that the opening of the circuit breaker immediately disconnects it from the circuit4 ,whenever it is impossible to connect the shunt trip in this manner1 the circuit opening auxiliary switch should be used in connection with it4 ,illustration3 ,,fig4 #b1bgb4--;,general ,electric low voltage attachment for circuit breakers4 ,this low voltage trip is designed to operate the circuit breaker when the line voltage drops to approximately #ej per cent or less of the normal voltage4 ,it should be noted that the coil is always in circuit1 as is the case with the overload and underload coils1 and that it operates with the releasing of its armature4 ,it is always necessary to use a fixed amount of resistance 7depending upon the voltage of the system7 in series with the low voltage release4 ,the low voltage release performs the functions of a shunt trip coil when used in conjunction with a push button1 auxiliary switch or speed limiting device1 and is generally preferred to the shunt trip attachment4 ,illustration3 ,,fig4 #b1bgc4--;,general ,electric circuit opening auxiliary switch4 ,this switch opens an auxiliary circuit when the circuit breaker opens1 and is intended to be used in connection with a shunt trip attachment to insure the immediate disconnection of the shunt coil from the circuit4 ,it may also be employed to serve other purposes1 such as tripping another circuit breaker having a low voltage attachment1 and permitting another circuit breaker to remain closed only when the circuit breaker equipped with the auxiliary switch is open4 ,ques4 ,what other name is given to the auxiliary circuit trip8 ,ans4 ,it is sometimes called the shunt trip1 though ill advisedly so4 ,illustration3 ,,fig4 #b1bgd4--;,general ,electric circuit closing auxiliary switch4 ,this switch closes when the circuit breaker opens1 and may be used to announce the automatic opening of the circuit breaker through the means of an indicating lamp or an alarm bell4 ,it is often necessary to arrange one circuit breaker so that1 in opening1 it will trip others4 ,this may be accomplished by using a circuit closing auxiliary switch in connection with a low voltage or shunt trip attachment on the circuit breakers to be tripped4 ,the construction of this type of switch is such that it may be opened by hand after the circuit breaker opens1 but it is automatically reset when the circuit breaker is closed4 ,relays4--,oil break switches and carbon break circuit breakers are commonly used to open electrical circuits at some given overload and on short circuit4 ,to secure additional protection under a variety of abnormal conditions or to provide for a certain predetermined operation or sequence of operations1 relays may be employed4 ,illustration3 ,,fig4 #b1bge4--;,general ,electric type ,c circuit breaker4 ,specially adapted to motor driven machine tool applications4 ,for use in mills1 machine shops1 factories1 foundries and office buildings4 ,for general motor work1 automobile charging outfits1 storage batteries1 rectifier sets1 cranes1 etc4 ,list of parts3 ,a1 calibrating post2 ,b1 laminated contact2 ,c1 secondary contact spring2 ,d1 contact blade2 ,e1 cotter pin for ,g2 ,f1 toggle link2 ,g1 pin for ,d and ,f2 ,h1 stop for ,aa2 ,i1 hinge frame2 ,j1 operating lever2 ,k1 pin for ,i and ,j2 ,l1 toggle link2 ,m1 connection2 ,n1 screw for ,m1 ,o and ,p2 ,o1 nut for ,n and ,p2 ,p1 terminal2 ,q1 tripping coil2 ,r1 calibrating screw2 ,s1 laminated contact2 ,t1 calibrating scale2 ,u1 calibrating spring2 ,v1 connection post2 ,w1 knob2 ,x1 washer for ,y2 ,y1 handle2 ,z1 buffer2 ,aa1 armature2 ,ba1 laminated connection2 ,ca1 connection2 ,da1 base4 ,a relay is defined as3 ,a device which opens or closes an auxiliary circuit under predetermined electrical conditions in the main circuit4 ,the object of a relay is generally to act as a sort of electrical multiplier1 that is to say1 it enables a comparatively weak current to bring into operation a much stronger current4 ,illustration3 ,,fig4 #b1bgf4--;,diagram of connections of ,general ,electric shunt trip coil with and without circuit opening auxiliary switch4 ,ques4 ,for what service are relays largely used8 ,ans4 ,they are employed in connection with high voltage switches where the small amount of energy derived from an ordinary instrument transformer is insufficient for tripping4 ,the connections between relays and circuit opening devices are usually electrical4 ,combinations of this nature are extremely flexible since they permit the use of a number of devices1 each having a different function1 with a single circuit breaker or oil switch as well as with two or more switches1 to secure the desired operation and protection4 ,selection4--,in all electrical installations protection of apparatus is important1 but in some large central stations this is secondary to continuity of service4 ,to combine maximum protection without interruptions of service is not always possible1 but these requirements can be approximated very closely by the use of reliable and simple controlling or protecting devices if proper care be taken to select the relays suited to the special conditions of the installation4 ,to do this intelligently1 a knowledge of the various types of relay is necessary4 ,illustration3 ,,fig4 #c1jgc4--;,diagram of connections of ,general ,electric low voltage release coil when used with speed limiting device on rotary converter4 ,there is a multiplicity of types and a classification to be comprehensive1 should1 as in numerous other cases1 be made from several points of view4 ,accordingly relays may be classified3 #a4 ,with respect to the nature of the service performed1 as a4 ,protective2 b4 ,regulative2 c4 ,communicative4 #b4 ,with respect to the operating current1 as a4 ,alternating current2 b4 ,direct current4 #c4 ,with respect to the manner of performing their function1 as a4 ,circuit opening2 b4 ,circuit closing4 #d4 ,with respect to the operating current circuit1 as a4 ,primary2 b4 ,secondary4 #e4 ,with respect to the abnormal conditions which caused them to operate1 as a4 ,overload2 b4 ,underload2 c4 ,over voltage2 d4 ,low voltage2 e4 ,reverse energy2 f4 ,reverse phase4 #f4 ,with respect to the time consumed in performing their function1 as a4 ,instantaneous 7so called72 b4 ,definite time limit2 c4 ,inverse time limit4 #g4 ,with respect to the character of its action1 as a4 ,selective2 b4 ,differential4 #h4 ,with respect to whether it acts directly or indirectly on the circuit breaker1 as a4 ,main2 b4 ,auxiliary4 ,illustration3 ,,fig4 #b1bgh4--;,general ,electric overload and low voltage type ,c circuit breaker for #fjj volts or less4 ,it has one overload1 and one low voltage coil as shown4 ,screens are provided between contacts4 ,protective ,relays4--,these are used to protect circuits from abnormal conditions of voltage1 or current1 which would be undesirable or dangerous to the circuit and apparatus contained therein4 ,ques4 ,how do protective relays operate8 ,ans4 ,they act in combination with automatic circuit breakers1 operating when their predetermined setting has been reached1 energizing the trip coil of the circuit breaker and opening the circuit4 ,fig4 #b1bgi shows the principles of relay operation4 ,when the current or pressure in the main circuit reaches the predetermined value at which the protective system should operate1 the relay magnet attracts the pivoted contact arm and closes the auxiliary circuit2 this permits current to flow from the current source in that circuit and energize the trip coil thus opening the main circuit4 ,illustration3 ,,fig4 #b1bgi4--;,diagram illustrating the operation of a circuit closing relay4 ,when the predetermined abnormal condition is reached in the main circuit1 the relay closes the auxiliary circuit1 thus energizing the trip coil and opening the breaker4 ,regulative ,relays4--,this class of relay is used to control the condition of a main circuit through control devices operated by a secondary circuit4 ,ques4 ,for what service are relays of this class employed8 ,ans4 ,they are used as feeder circuit or generator regulators4 ,ques4 ,how do they differ from protective relays8 ,ans4 ,they have differentially arranged contacts1 that is to say1 arranged for contact on either side of a central or normal position4 ,illustration3 ,,fig4 #b1bhj4--;,diagram showing a railway synchronous converter protected by a single pole overload circuit breaker with low voltage release attachment and bell alarm switch4 ,the low voltage attachment trips the breaker on failure of direct current voltage also when speed limit device closes4 ,internal troubles are taken care of by the alternating current automatic devices 7not shown74 ,communicative ,relays4--,these are used for signalling in a great variety of ways for indicating the position of switching apparatus or predetermining the condition of electric circuits4 ,a4 ,c4 and ,d4 ,c4 ,relays4--,as here used1 the classification refers to the kind of current used on the auxiliary circuit4 ,in some cases direct current is used to energize the trip gear of the circuit breaker or oil switch1 and in others1 alternating current4 ,illustration3 ,,fig4 #b1bha4--;,diagram showing three phase motors protected by triple pole overload circuit breakers1 with two overload coils1 also one overload coil and low voltage release coil4 ,the use of the low voltage release allows the breaker to be tripped from a distance by means of a short circuiting switch or push button4 ,a4 ,c4 and ,d4 ,c4 relays are respectively known as circuit opening and circuit closing relays1 being later fully described4 ,circuit ,opening ,relays4--,the duty of a circuit opening relay is to open the auxiliary circuit1 usually alternating current1 nd thereby cause the oil switch or circuit breaker to be opened by the use of a trip coil in the secondary of a current transformer1 or by low voltage release coil4 ,the trip coil of the breaker is generally shunted by the relay contacts and when the moving contact of the relay disengages from the stationary contact1 the current from the transformer which supplies the relay1 flows through the trip coil thus opening the breaker4 ,these features of operation are shown in fig4 #b1bhb4 ,illustration3 ,,fig4 #b1bhb4--;,diagram illustrating the operation of a circuit opening relay4 ,when the relay contacts are in the normal closed position1 as shown1 the coil is short circuited4 ,when the predetermined abnormal condition is reached in the main circuit1 the relay contacts are opened with a quick break1 sending the current through the trip coil momentarily1 and opening the breaker4 ,ques4 ,where are circuit opening relays chiefly employed8 ,ans4 ,in places where direct current is not available for energizing the trip coil4 ,ques4 ,what is the objection to alternating current trip coils8 ,ans4 ,they have relatively high impedance and impose a heavy volt ampere load on the transformers4 ,circuit ,closing ,relays4--,the duty of a circuit closing relay is to close the auxiliary circuit at the time when the predetermined abnormal condition is reached in the primary circuit4 ,the closing of the auxiliary circuit energizes the trip coil and opens the breaker4 ,illustration3 ,,figs4 #b1bhc to #b1bia4--;,general ,electric instantaneous overload circuit opening relays1 covers removed4 ,circuit opening relays are used chiefly in those cases where direct current for the tripping circuit is not available4 ,alternating current trip coils have relatively high impedance and impose a heavy volt ampere load on the current transformers4 ,to reduce this load during normal operation the circuit opening relay is frequently used and is usually necessary where instruments and meters are to be operated on the same current transformers as the trip coils if the greatest accuracy be required4 ,the relay contacts in the normal1 closed position1 short circuits the trip coil4 ,when the relay operates on overload or other abnormal condition the contacts are opened with a quick break1 sending the current through the trip coil circuit momentarily and tripping the switch4 ,with circuit opening relays1 the trip coils of the oil switch must be set to trip somewhat lower than the setting of the relay4 ,in construction the relay consists of a solenoid with iron frame forming the support for the relay2 a central plunger or armature of special construction which is picked up or released by the magnetic action of the solenoid2 a plunger rod which actuates the relay contacts1 which are mounted on an insulated base usually above the solenoid2 a tube or plate for the calibration marking and adjustment2 covers of glass or metal to keep out dust2 terminal boards with points corresponding to tagged leads from relay coils and external wiring diagrams4 ,the relay contacts are of two kinds1 circuit opening1 as shown above1 and circuit closing1 as shown in figs4 #b1bib to #b1cjj4 ,ques4 ,what kind of current is generally used for the auxiliary circuit of a circuit closing relay8 ,ans4 ,direct current4 ,ques4 ,at what pressure8 ,ans4 ,from #abe to #bej volts4 ,ques4 ,where is this current usually obtained8 ,ans4 ,from a storage battery1 or from the exciter4 ,ques4 ,for what current are the contacts ordinarily designed8 ,ans4 ,about #aj amperes4 ,illustration3 ,,figs4 #b1bib to #b1cjj4--;,general ,electric alternating current1 instantaneous overload circuit closing relays1 covers removed4 ,the function of a circuit closing relay is to close an electrical circuit1 usually direct current1 through a trip coil on an oil switch or circuit breaker1 or it may short circuit a low voltage release coil1 and thereby open the oil switch or circuit breaker on occurrence of the condition upon which the relay is designed to operate4 ,direct current at #abe or #bej volts taken from exciter bus bars or storage battery system is generally used for the tripping circuit4 ,circuit closing contacts have a cone shaped central element of carbon or metal which makes contact with flexible contact fingers symmetrically arranged above the cone4 ,these contacts will make and break a circuit of #aj amperes at #abe volts without the use of auxiliary circuit opening switches4 ,relays are made with two or three contacts for connecting one side of a direct current circuit through one or two separate circuits1 or trip coils respectively1 to the side of opposite polarity4 ,usually only two contacts are required4 ,where two or more trip coils are used1 which may not be connected permanently in parallel1 the three contact relays are selected and in some cases four contacts furnished4 ,primary and ,secondary ,relays4--,primary relays are sometimes called series relays as they have the current coils connected directly in series with the line1 both on high and low tension circuits4 ,secondary relays receive their current supply from the secondary circuits of current transformers4 ,alternating current relays connected to secondary of pressure transformers and relays with both current and pressure windings are included in this class4 ,ques4 ,what is the usual winding of the coils8 ,ans4 ,the current coils are usually wound for #e amperes and the pressure coils for #aaj volts4 ,illustration3 ,,fig4 #b1cja4--;,alternating current low voltage circuit closing low voltage relay1 for #fjj volts or less4 ,the contacts are similar to those of the circuit closing overload type except that they are inverted4 ,as long as the pressure is normal the contact cone is held above the contacts4 ,when the pressure falls below one half normal1 the cone and plunger rod drop and close the contact4 ,this relay does not pick up its own plunger4 ,the plunger rod is pushed up by hand after the pressure circuit is established4 ,low voltage relays are generally used in connection with a low voltage release or shunt trip coil on an oil switch or a circuit breaker4 ,they are used in connection with motor booster sets to prevent a disastrous speed of the booster which might result from the loss of alternating current power4 ,they are also sometimes used for indicating purposes4 ,ques4 ,what refinement is made in the design of relays and why8 ,ans4 ,care is exercised to reduce to a minimum the volt ampere load imposed by the relay on the current transformer to permit the use of un-stranded meters and relays upon the same transformer4 ,the use of circuit opening relays to cut out the trip coil of an oil switch during normal operation1 has been described1 and in the short time that the trip coil is in circuit1 it does not affect the accuracy of the instrument readings4 ,this practice1 however1 does not apply in the case of curve drawing meters1 voltage compensators or other devices which have in themselves sufficient load for separate current transformers4 ,in this connection it should be noted that to obtain accurate instrument and meter readings2 the current transformers should not be loaded beyond certain limits which depend upon the volt ampere load and power factor of each of the connected devices4 ,illustration3 ,,fig4 #b1cjb4--;,condit type ,k circuit breaker with shunt trip and no voltage attachment4 ,the shunt trip is usually applied as an auxiliary to other types of trip4 ,it consists of a fine wire coil which is mounted as a self-contained part of the breaker and which when energized1 trips the circuit breaker4 ,it is used to open the breaker from some distant point1 and the coil is arranged to be connected across the line4 ,the coils are so arranged that the circuit breakers will operate on a voltage #be above or #be below normal4 ,the shunt trip coil is not intended to remain across the line and should be only momentarily energized4 ,the no voltage trip1 receives energy from a high resistance or fine wire coil which is arranged to be placed directly across the line1 but in contradistinction to the shunt trip type1 in which the coil is momentarily energized to trip the breaker1 the no voltage coil is constantly energized and a decrease or failure of pressure trips the breaker4 ,it can be used as a remote control device the same as the shunt trip4 ,its general use1 however1 is to cause the circuit breaker to open when the voltage of the line fails from any cause4 ,its use is recommended on all motor circuits1 as it affords an additional protection against accidents1 for if the voltage should fail1 the breaker immediately opens1 and before the machine can start again the attendant must close the breaker4 ,it will not work for the protection of storage batteries or of motor generator sets charging storage batteries1 as1 when the voltage of the generator fails1 the voltage of the battery still maintains its full value4 ,the action of the coil is independent of the direction of flow of current2 it simply allows the breaker to stay closed as long as the voltage is on the line and opens the breaker when the voltage on the line ceases4 ,no voltage circuit breakers are normally so adjusted that they will not release until the voltage approaches #ej of normal4 ,so great is the variety of combination used and the variations of these factors in their several combinations at different loads and settings1 that special consideration of each arrangement is advisable4 ,illustration3 ,,fig4 #b1cjc4--;,general ,electric alternating current high pressure series overload relays controlling #de1jjj volt oil switches4 ,these relays are connected in series with the line4 ,if current transformers are to be used on the same circuit for other purposes1 and have sufficient capacity to supply energy for operating relay coils1 then secondary relays would be more economical1 otherwise the series relays are much less expensive4 ,by means of a specially treated wooden rod1 the relay operates a tripping switch1 closing a separate tripping circuit1 usually #abe or #bej volts direct current4 ,relays and switches are for mounting on flat surfaces4 ,series relays are essentially the same as secondary relays except in the coil winding and insulation4 ,the corrugated horizontal arms which carry the relays1 as shown1 are insulated posts1 insulating the relays from the ground4 ,the wood rod from each relay is connected directly to a tripping shaft on the oil switch which buckles an auxiliary toggle1 thereby opening the main toggle and tripping the oil switch4 ,overload ,relays4--,series relays are connected directly in series with the line and are chiefly used with high pressure oil break switches for overload protection4 ,if current transformers are to be used on the same circuits for other purposes1 and have sufficient capacity to admit of adding a relay coil1 secondary relays would be more economical2 otherwise1 the series relays are less expensive4 ,by means of a specially treated wooden rod1 the relay operates a tripping switch1 closing a separate tripping circuit1 usually #abe or #bej volts direct current4 ,series relays are essentially the same as secondary relays except in the coil winding and insulation4 ,underload ,relays4--,these are similar in construction to low voltage relays but have current instead of pressure windings4 ,over ,voltage ,relays4--,these are usually of the circuit closing type and are similar to secondary overload relays1 but have pressure instead of current windings4 ,low ,voltage ,relays4--,relays of this class are in most cases used ,illustration3 ,,fig4 #b1cjd4--;,condit #fjj volt1 #a1ejj ampere single pole back connected type ,k circuit breaker1 motor operated4 ,the mechanical and electrical features of the circuit breakers are no different than when hand operated1 the only difference being that the motor is used for the operating means4 ,this motor is so arranged that even should it over travel1 due to an accident to the controlling circuit1 it cannot produce more than a predetermined strain on the circuit breaker4 ,in other words1 after the motor has closed the circuit breaker1 further travel of the motor will not result in putting a strain on the operating parts4 ,suitable motors are supplied for this service1 the type of motor varying in accordance with the character of the operating current supplied4 ,the advantage of this type of electrical operation is that it puts very little strain on the switch mechanism1 takes very little operating current1 allows the use of standard parts1 and makes an extremely substantial and flexible structure4 ,its disadvantage is that it closes slowly1 and it must not1 therefore1 be used in places where quick closing is essential4 for the protection of motors in the event of a temporary weakening or failure of the pressure4 ,they are also used in connection with a low voltage release or shunt trip coil on an oil switch or a circuit breaker4 ,reverse ,energy ,relays4--,the chief object of this species of relay is to protect the generator4 ,when so used1 the overload adjustment is set at the maximum value to give overload protection only at the maximum carrying capacity of the generator and a sensitive reverse protection to prevent a return of energy from the line4 ,illustration3 ,,fig4 #b1cje4--;,general ,electric direct current solenoid control relay4 ,solenoids for operating large switches1 etc41 frequently require comparatively large operating currents in the closing coils4 ,this necessitates the use of relatively heavy leads between the control switch and the solenoid and is the cause of severe arcing at the control switch1 especially with solenoids of high inductance4 ,these objectionable features can best be eliminated by the use of a suitable control relay located near the solenoids4 ,the control relay consists of a solenoid plunger and switch1 the latter insulated from the frame of the relay4 ,it operates satisfactorily on one-half the rated voltage and requires only a very small operating current4 ,the terminals of the switch and the relay coils are independent4 ,the relay can be wound for operation on #abe1 #bej1 or #fjj volt circuits4 ,reverse ,phase ,relays4--,this type of relay is used chiefly to prevent damage in case of reversal of leads in reconnecting wiring to two or three phase motors4 ,time ,element4--,it is often inconvenient that a circuit breaker should be opened immediately on the occurrence of what may prove to be merely a momentary overload1 so that time lag attachments are frequently provided1 particularly with relays4 ,these devices1 which may form part of the relay or may be quite distinct from it1 retard its action until the overload has lasted for a predetermined time--several seconds or more4 ,illustration3 ,,fig4 #b1cjf4--;,alternating current series reverse phase single pole1 circuit closing1 two contact relay for #fjj volts or less4 ,this type of relay is used chiefly to open motor circuits for elevators to prevent damage in case of reversal of leads in reconnecting wiring to two or three phase motors4 ,the relay is provided with a dust proof metal cover4 ,ques4 ,what should preferably govern the time lag8 ,ans4 ,it should depend on the extent to which the overload is reduced as the time elapses4 ,instantaneous ,relays4--,the so called instantaneous relays operate almost instantly on the occurrence of the abnormal condition that they are to control4 ,there is of course a slight time element comparable with that of an overload circuit breaker1 but for practical purposes1 the operation may be considered as instantaneous4 ,illustration3 ,,fig4 #b1cjg4--;,electric circuits of ,condit type ,a relay4 ,the construction is described in fig4 #b1cji4 ,as here shown1 the relay is not in operation1 but should the current passing through the coil be of sufficient value to cause the lower movable half of the magnetic circuit to approach the upper stationary half of the circuit1 the relay will be transformed from an ordinary electromagnet into a repulsion motor4 ,the contact will short circuit the brushes of the armature and thus cause it to revolve1 the speed of rotation being dependent on the amount of current flowing to a predetermined point1 and thereafter the speed of rotation of the motor remains constant irrespective of the current value4 ,time adjustment3 ,this is obtained by varying the distance through which the contact travels1 provision being made whereby adjustment can be made as close as 4#a of a second4 ,current adjustment3 ,this is obtained by means of a calibrated spring4 ,standard relays are calibrated at #f1 #h1 #aj1 and #ab amperes1 the coils being designed to carry five amperes continuously1 with a temperature rise not exceeding #hf ,fahr4 ,power to operate relay3 ,the relay requires twenty volt amperes for its operation at full load2 the influence of this type of relay on the ratio and phase angle of current transformers is small4 ,time ,limit ,relays4--,under this classification there are two sub-divisions4 #a4 ,definite time limit2 #b4 ,inverse time limit4 ,illustration3 ,,fig4 #b1cjh4--;,characteristic curves of ,condit type ,a selective relay4 ,curves #a1 #b1 #c1 and #d show the time variation of this relay with different settings at the various current values4 ,the relay may be adjusted to trip the switch at any point represented between curves #a and #d4 ,this relay is a combination of an inverse time limit relay and a definite time limit relay4 ,the combination of the characteristics of the two types are seen in the curve1 the first part of which is inverse1 and the latter part definite from a point of three or four times full load current4 ,this combination of features being desirable as1 for instance1 in transmission work1 particularly where it is necessary to use circuit breakers set selectively1 as1 due to the inverse feature of the curve1 the relays can be set so that on a moderate overload1 they will require the proper length of time to operate1 and at the same time will operate quickly enough on heavy short circuits to prevent damage to the distribution system or its apparatus4 ,due to the definite feature of the latter part of the curve1 the relays of the varying circuit breakers when once set to operate at different time values will never operate simultaneously irrespective of the value of the short circuit current1 thus tending toward continuity of service4 ,ques4 ,describe the time mechanism of a definite time limit relay4 ,ans4 ,it consists of an air dash pot1 and an air diaphragm or equivalent retarding device connected to the contact mechanism4 ,ques4 ,how does it operate8 ,ans4 ,in some designs1 when the contacts are released1 they descend by gravity against the action of the retarding device thereby making contact a definite interval after the occurrence of the abnormal condition4 ,illustration3 ,,fig4 #b1cji4--;,condit type ,a selective relay1 designed for use with circuit breakers where selective or discriminating action is required4 ,the circuits and connections of this relay are illustrated in fig4 #b1cjg1 and its characteristics in fig4 #b1cjh4 ,in construction1 the relay consists of a special motor with a short circuited armature and a split field4 ,under normal conditions1 the fields are separated from each other and the motor armature does not revolve4 ,the force tending to pull the two faces of the field together is opposed by a spring1 the compression of which determines the number of amperes necessary to cause the relay to begin operation4 ,the motor structure performs the whole work and the motor itself un-meshes and meshes the gears without the aid of any external device4 ,ques4 ,how does the inverse time limit type operate8 ,ans4 ,the actuating and contact mechanism is attached directly to an air bellows and in operation tends to compress the bellows against the action of a specially constructed escape valve in the latter4 ,illustration3 ,,fig4 #b1caj4--;,condit type ,b time limit attachment1 designed to give sufficient time to allow an induction motor to start without opening the circuit breaker1 and not have the circuit breaker trip on the momentary rush of current4 ,its action is inverse2 that is1 the greater the current the less time it takes to operate and is so arranged that four to five times full load current or a short circuit will trip the circuit breaker instantly4 ,the time limit attachment is applied directly to the armature which trips the circuit breaker and is adapted for the so called primary trip4 ,it consists of an air vacuum dash pot with a graphite piston1 the dash pot being fastened to the stationary calibrating ring of the trip coil and the moving outside cylinder is fastened to the armature of the circuit breaker4 ,when the current reaches a point where it overcomes the weight of the armature and lifts the same1 the magnetic force tending to raise the armature is opposed by the vacuum created in the interior of the cylinder4 ,as the magnetic force continues the vacuum is overcome due to the leakage of air past the plunger and the armature gradually moves up until it reaches the point where it trips the circuit breaker4 ,if at any point of the armature travel1 the current drop back to normal1 the armature immediately resets itself by means of a ball valve in the top of the brass cylinder4 ,ques4 ,why is the arrangement called inverse time limit8 ,ans4 ,because the retardation varies inversely with the pressure on the bellows1 and therefore inversely with the magnitude of the abnormal condition4 ,ques4 ,what other device may be used to retard the operation8 ,ans4 ,a damping magnet is sometimes used which acts on a disc or drum and which may be adjustable4 ,illustration3 ,,figs4 #b1caa and #b1cab4--;,general ,electric alternating current low pressure series overload relays4 ,fig4 #b1caa1 instantaneous time limit relay2 fig4 #b1cab1 inverse time limit relay4 ,these relays have carbon contacts and will make or break a direct current circuit of #aj amperes at #abe volts without auxiliary circuit opening switch4 ,they are used where several circuits are controlled by one automatic oil break switch or one shunt trip1 overload and shunt trip or low voltage release carbon break circuit breaker4 ,these relays may be used for signal purposes2 they are back connected1 the connections can be seen in the illustrations4 ,ques4 ,how is the inverse time element introduced by this arrangement8 ,ans4 ,the retardation is due to eddy currents induced by moving the disc or drum through the magnetic field4 ,the reaction thus induced varies inversely with the magnitude of the force with which the disc or drum is urged through the field and hence inversely with the abnormal condition4 ,ques4 ,what are the ordinary limits of adjustment for inverse time limit relays8 ,ans4 ,from one-half second to #cj seconds1 depending upon the time setting and magnitude of the overload current4 ,illustration3 ,,figs4 #b1cac to #b1cba4--;,general ,electric time limit overload circuit opening relays with covers removed4 ,the construction of this relay is similar to that of the inverse time limit relay1 except that it has a compression spring interposed between the plunger and diaphragm4 ,the plunger compresses the spring and further motion is prevented by a stop1 making the relay practically independent of the amount of the overload1 only the stored energy of the spring1 if the overload continue1 applies power1 dependent on its own mechanical strength1 to the diaphragm4 ,the time limit therefore becomes practically a constant for any given setting under ordinary conditions of overload or short circuit4 ,if1 however1 the overload come on slowly so that the spring is not fully compressed at once1 the time limit will vary slightly4 ,if the scheme of selective operation make it necessary to take care of a creeping load of this character1 two relays may be used and definite time limit positively secured4 ,in this case1 an instantaneous circuit closing1 overload relay would be used and a definite time limit relay1 provided with a direct current coil in circuit with the closing contacts of the first relay4 ,the time limit relay would be of the circuit closing type and control a direct current trip coil on the oil switch4 ,a setting of from two to six seconds is ordinarily used1 depending upon the requirements4 ,where selective operation is desired a minimum setting of two seconds is recommended4 ,differential ,relays4--,in this type of relay there are two electromagnets4 ,in normal working these oppose and neutralize each other4 ,should1 however1 either winding become stronger or weaker than the other1 the balance is upset1 the magnet energized1 and the relay comes into operation4 ,illustration3 ,,fig4 #b1cbb4--;,differential relay transformer and reverse current circuit breaker discriminating device4 ,a differential relay is one whose electromagnet has two windings4 ,in normal working these oppose and neutralize one another4 ,should however1 either winding become stronger or weaker than the other1 the balance is upset1 the magnet is energized1 and the relay comes into operation4 ,a modification of such a relay for alternating current is here shown1 from which it will be seen that when the currents are as indicated1 the circuit ,a has the larger pressure induced in it1 whereas1 should the main current reverse with reference to the shunt current1 the circuit ,b would have the larger induced pressure4 ,a modification of such a relay for alternating current is shown in fig4 #b1cbb1 from which it will be seen that when the currents are as indicated1 the circuit ,a has the larger pressure induced in it1 whereas1 should the main current reverse with reference to the shunt current1 the circuit ,b would have the larger induced pressure4 ,illustration3 ,,fig4 #b1cbc4--;,diagram of modern power house wiring and busses showing location of relays4 #a;,how to ,select ,relays4--,the following general information on relays1 together with reference to the one line diagram1 fig4 #b1cbc1 will be of interest and assistance in making a selection from the various relays previously described to meet the requirements of modern power house and sub-station layouts4 #a ,,note4--,as suggested by the ,general ,electric ,co4 ,single pole relays are used on single phase and on balanced three phase circuits4 ,double pole relays are used on ungrounded three phase and on quarter phase4 ,illustration3 ,,fig4 #b1cbd to #b1cbi4--;,general ,electric inverse time limit overload circuit closing relays4 ,in this type of relay its mechanism is so designed that a delay or lapse of time in opening the circuit breaker after a predetermined condition of the circuit has been reached1 depends on the flow of current1 that is1 if the current be great1 the time will be small1 and if the current be of a moderate value1 the time will be correspondingly longer4 ,triple pole relays are used on three phase grounded neutral and interconnected quarter-phase4 ,circuit closing relays are recommended in all cases where a constant source of direct current is available for operating trip coils4 ,the conditions for which relays have been designed for power circuits may perhaps be best described1 by considering a one line diagram from the generator end to the sub-station auxiliary machines and feeders4 ,considering first alternating current circuits1 the prevailing practice is to make the circuit breakers by which the alternators are connected to the low tension bus non-automatic1 in order to insure minimum interruption of alternator service4 ,the chance of trouble in this part of the circuit is remote1 but should it occur1 the station attendant could generally open the circuit breaker before the machines would be injured4 ,reverse current relays of instantaneous or time limit types are often connected to the secondaries of current and of pressure transformers to indicate by lamp or bell any trouble that may occur in the generator circuit4 ,these relays operate with a low current reversal at full pressure and conversely with a proportionally greater current at voltages less than normal4 ,at zero pressure1 the relay would act as an overload one1 set for high overload4 ,at zero current1 a voltage considerably in excess of normal would be required to operate it4 ,illustration3 ,,fig4 #b1ccj4--;,diagram showing two phase motor or feeder circuit protected by double pole double coil1 overload circuit breaker 7or two single pole breakers interlocked7 with bell alarm switch4 ,specifications sometimes call for automatic generator circuit breakers3 in this case definite time limit overload relays are used4 ,they are connected in the secondaries of current transformers and are designed to give the same time delay for all trouble conditions2 they allow the defective circuit to be opened1 if possible1 at a point more remote from the generator than the generator circuit breaker4 ,when the total generator capacity exceeds the rated rupturing capacity of the circuit breakers1 one or more sectionalizing circuit breakers are placed in each bus4 ,if operating conditions admit1 these devices are made non-automatic and are left disconnected except in case of emergency2 but if it be necessary for them to be continually in service1 they may be made automatic by means of instantaneous overload relays connected to current transformers in the low voltage bus2 the relays being adjusted to trip the circuit breaker under short circuit conditions1 confining the trouble to one section and preventing the circuit breakers rupturing more than their rated capacity4 ,installations with but one bank of power transformers1 and without high voltage bus1 are provided with automatic circuit breakers operated by an inverse time limit relay4 ,the relay is connected to the secondaries of current transformers1 which in turn are connected in the low voltage side of the power transformer4 ,stations with more than one bank of power transformers1 a high voltage bus1 and high and low voltage circuit breakers1 may have both circuit breakers arranged to trip at the same time or one after the other4 ,as in the former case1 they are operated from the inverse time limit relay connected in the low voltage side4 ,illustration3 ,,fig4 #b1cca4--;,condit #fjj volt1 #a1ejj ampere1 single pole type ,k circuit breaker pneumatically operated4 ,it is the same as the electrically operated circuit breaker1 except that a pneumatic cylinder mechanism is supplied in place of either the electromagnet or the motor4 ,this cylinder mechanism is so arranged that the air pressure is only on the cylinder at the instant of operation4 ,at all other times the air pressure is shut off by means of a control valve4 ,the kind of remote control to be used depends on local conditions4 ,in general1 the hand operated remote control device is preferable where conditions are such that it can be used1 and where it is necessary to use electrically operated1 the motor operated type is recommended if conditions be such that slow closing is not objectionable4 ,illustration3 ,,figs4 #b1ccb and #b1ccc4--;,diagram showing two phase four wire no voltage connections for ,i-,t-,e circuit breaker4 ,the two no voltage coils for two phase four wire circuits are connected respectively to binding posts ,b1 ,c and ,a1 ,d on the face of the base4 ,b and ,d are connected to lower spring contacts #b and #a respectively1 of the small disconnecting switch4 7,in instruments supplied on individual bases1 these connections are made in the factory1 let into channels in back of base and covered with wax47 ,each of the upper contacts a and b of the disconnecting switch is connected respectively through resistance ,r#b and ,r#a to one main in each phase at aa and bb4 ,c and ,a are respectively connected to the other main in each phase at #c and #d4 ,thus each of the no voltage coils operates across one phase independent of the other4 ,the terminals #c1 aa1 bb and #d1 must1 in all cases1 be so connected that they will be subject to the full voltage of the circuit1 irrespective of the position of the starting switch4 ,illustration3 ,,figs4 #b1ccd and #b1cce4--;,diagram showing two phase three wire no voltage connections for ,i-,t-,e circuit breaker4 ,the two no voltage coils for two phase1 three wire circuits are connected respectively to binding posts ,b1 ,c and ,a ,d on the face of the base1 and from ,a and ,c connections are made to lower contacts #b and #a respectively of the disconnecting switch4 ,binding posts ,b and ,d are connected together on the back of the board4 7,in instruments supplied on individual bases1 these connections are made in the factory1 let into channels in back of base and covered with wax47 ,each of the upper contacts a and b is connected respectively through resistance ,r#b and ,r#a to one of the mains at aa and bb as shown4 ,d is connected through resistance ,r#c to the common wire of both phases at #c ,b and ,d being connected as aforesaid1 thus forming a common connection for both no voltage coils4 ,terminals aa and bb of the resistances must be connected to the outside main across the two phases1 terminal #c to the main common to both phases1 the connections being so made that these terminals will be subject to the full voltage of the circuit irrespective of the position of the starting switch4 ,illustration3 ,,fig4 #b1ccf and #b1ccg4--;,diagram showing three phase no voltage connections for ,i-,t-,e circuit breaker4 ,the no voltage coils for three phase circuits are connected in by means of binding posts ,a1 ,b1 ,c and ,d on the face of the base1 and from the ,a and ,b of the no voltage coils1 connections are made respectively to spring contacts #a and #b of the small disconnecting switch4 ,each of the contacts a and b of the disconnecting switch is connected respectively through resistance ,r#b and ,r#a to one of the mains at aa and bb4 ,the terminal ,c is connected through resistance ,r#c on the back of the board to the middle main as shown at point #c4 ,the terminal ,d is linked on the back of the board to terminal ,b to complete the ,greek3 ,d connection4 ,the terminals aa1 bb and #c of the circuit breaker must1 in all cases1 be so connected that they will be subject to full voltage of the circuit irrespective of the position of the starting switch4 ,each no voltage coil is supplied with two terminal wires1 one covered with green and one with black insulation4 ,in replacing these coils particular care should be taken to see that the terminal wires connected to any one binding post are of unlike color4 ,in plants in which two or more banks of transformers are operated in parallel between high and low voltage busses1 it is desirable to have for each transformer bank1 an automatic circuit breaker equipment which will act selectively and disconnect only the bank in which trouble may occur4 ,with a circuit breaker on each side of transformer bank1 selective action may be secured in two ways as follows3 #a4 ,by means of an instantaneous differential relay connected in the secondaries of current transformers installed on both the high and low voltage sides of each transformer bank4 ,the relay operates on a low current1 reversal on either side of the bank4 #b4 ,by means of one inverse time limit1 secondary or series relay installed on that side of the transformer bank which is opposite the source of power1 the relay being arranged to trip both the high and low voltage circuit breakers4 ,the first method has the disadvantage of high first cost due to the high voltage current transformers required1 but is more positive than the second method and is independent of the number of transformer banks in parallel4 ,the second method is the less expensive of the two and protects against overloads as well as short circuits in the transformers1 but it is less positive and introduces delay in the disconnection of the transformer when trouble occurs4 ,furthermore1 it is not selective when less than three banks are operating in parallel4 ,the automatic circuit breakers in the outgoing line may be operated from inverse time limit relays connected in the secondaries of current transformers2 or in case transformers are not necessary for use with instruments1 series high voltage inverse time limit relays connected directly in the line may be used4 ,whether to select current transformers with relays insulated for low voltage1 or to choose series relays1 is a question of first cost and adaptability to service conditions4 ,below #cc1jjj volts1 the commercial advantages in favor of the series relay are slight1 and since it is somewhat difficult to design this device for the large current capacities met with at the lower voltage1 it is generally the practice to use the relay with current transformer1 because of its operating advantage4 ,this practice1 however1 is not entirely followed1 since some service conditions 7described later7 make the use of series relays very desirable and practical4 ,illustration3 ,,figs4 #b1cch and #b1cci4--;,general ,electric instantaneous direct current reverse current or discriminating relays4 ,fig4 #b1bch1 for #ejj amperes2 fig4 #b1cci for #b1jjj amperes4 ,these relays are designed for mounting directly on circuit breaker studs4 ,these relays consist of a horseshoe magnet with a shunt wound armature pivoted between its poles4 ,the magnet is mounted on the current carrying stud of the circuit breaker between the back of the panel and the first contact or supporting nut1 and is placed in a vertical position4 ,the contacts are insulated from the magnet permitting the use of an auxiliary circuit for the tripping device1 independent of the circuit controlled by the circuit breaker4 ,the magnet is excited by the current flowing through the stud1 and the armature is connected across the line in series with suitable resistance4 ,rotation of the armature in the normal direction is prevented by a stop4 ,reversal of the current flowing through the stud changes the direction in which the armature tends to rotate1 causing it to move away from the stop and close the circuit through an auxiliary trip coil and trip the circuit breaker4 ,these relays are used to protect dynamos1 storage batteries1 or main station busses from damage on reversal of current due to short circuit1 or from the grounding of machines or connection4 ,relay contacts must not be used to open the shunt trip coil circuits4 ,an auxiliary switch should be provided for this purpose in all cases where the opening of the circuit breaker does not disconnect the trip coil from the source of supply4 ,inverse time limit relays are satisfactory for one1 or more than two outgoing lines in parallel as they act selectively to disconnect the defective line only1 but installations with only two outgoing lines in parallel have the same load conditions in both lines and selective tripping of the circuit breakers in the defective line is obtained by means of a selective relay acting instantaneously under short circuit conditions only4 ,illustration3 ,,fig4 #b1cdj4--;,general ,electric direct current1 reverse current relay1 used to protect dynamos1 storage batteries1 or main station busses from damage on reversal of current due to short circuits or from the grounding of machine or connections4 ,it is mounted on vertical bus bars as in the case of cables1 on the side wall1 or other flat surface1 and the cables threaded through the frame4 ,when used to trip a circuit breaker1 the breaker is provided with a shunt trip connected across the circuit1 the tripping circuit being closed through the relay contacts on the occurrence of sufficient reverse current to lift the relay armature4 ,the relay is either instantaneous or time limit as desired4 ,in the time limit relay1 the time interval is obtained by the leather bellows shown in the illustration4 ,the time setting can be varied within certain limits by means of a valve on the bellows outlet4 ,the operation of the relay depends on the relative value and direction of magnetic flux set up by a pressure coil1 shown in the illustration1 and the current in the vertical bars4 ,under normal conditions these fluxes are in the same direction and circulate around a closed magnetic circuit4 ,when the current in the bars reverses1 the two fluxes oppose each other and force flux through the normally open leg of the magnetic circuit4 ,when the reversal of current is of predetermined value1 the relay armature is lifted and the purpose of the relay accomplished4 ,the relay design and action is similar to the reverse current relay previously mentioned1 and is connected to the secondaries of current transformers in each high voltage line and pressure transformers in the low voltage bus4 ,in the sub-station1 the conditions are the reverse of those in the main station1 the incoming lines becoming the source of power4 ,if there be only one incoming line and no high voltage bus1 the line circuit breaker is generally non-automatic4 ,with one incoming line and high voltage bus1 the circuits from the service side of the bus are equipped with automatic circuit breakers and relays4 ,these relays and those used for other arrangements of two or more incoming lines in parallel1 as well as high and low voltage circuit breakers1 are of the same design and are applied in the same manner as for the generating station4 ,regarding the relay equipments for auxiliary machines1 the same practice is recommended with the generator end of alternating current motor generator sets as with the main generators1 the outgoing feeder circuit breakers being tripped from inverse time limit or instantaneous relays4 ,illustration3 ,,fig4 #b1cda4--;,general ,electric direct current differential relay for balancer set2 instantaneous1 #ejj 7or less7 volt type for mounting on panel4 ,in many power plants direct current1 three wire1 power service is furnished by high voltage two wire dynamos operating in connection with balancer sets consisting of two low voltage machines on a common shaft4 ,with this combination of machine1 a short circuit or heavy overload on one side of the system will shift the neutral considerably1 and the lamps on the opposite side may burn out4 ,to protect the lamps1 a differential relay operating on #ae volts unbalancing1 is commonly used2 it is connected to trip either the dynamo's circuit breakers 7or a circuit breaker connected in the bus between the balancer set and the other dynamos74 ,with several synchronous machines in parallel1 the relays are arranged to operate with the least time delay with which it is possible to get selective action1 in order to prevent the machines being thrown out of step in event of trouble conditions causing a decrease of voltage4 ,the various types of induction motor and various conditions under which they are employed1 have brought about the development of several types of relay to protect the motors and the apparatus with which they are used4 ,it is desirable to disconnect a large motor in case of voltage failure1 and with conditions requiring either a motor operated1 or a solenoid operated circuit breaker1 a low voltage relay is used to close the tripping circuit whenever the voltage decreases to1 approximately1 #ej per cent4 below normal4 ,illustration3 ,,fig4 #b1cdb4--;,condit time limit relay1 designed primarily for use in connection with feeder circuits1 where close selection or discrimination of circuit breakers is not required4 ,it may be used satisfactorily on lighting and power circuits and also where there are sudden1 momentary fluctuations of current4 ,this relay is used in connection with series transformers4 ,the contact arrangements are provided so that the relays may be used as circuit closing or circuit opening relays4 ,the delayed action is produced by an air vacuum dash pot with a graphite piston4 ,the piston of the dash pot is connected to an arm arranged to be moved by the armature4 ,when the current reaches a point where it overcomes the weight of the armature and lifts the same1 the magnetic force tending to lift the armature is opposed by the pull of the vacuum created in the interior of the shell into which fits the graphite piston4 ,as the magnetic pull continues the vacuum is overcome due to the leakage of air past the piston1 and the armature gradually moves until it reaches a point where it causes the circuit breaker to trip1 either by closing the contacts in the circuit closing type1 or by opening the contacts in the circuit opening type4 ,if1 at any portion of its travel1 the current drop to normal1 the armature immediately resets4 ,the time adjustment consists of an arrangement whereby the distance through which the armature moves before tripping the breaker1 may be changed1 thus altering the time of tripping4 ,the current adjustment is made by changing the effective turns of the actuating coil1 the travel of the armature and the force exerted by it being the same for all current adjustment4 ,the winding is designed to carry #e amperes continuously with a temperature rise not exceeding #fh ,fahr4 standard calibration is provided so that the relay will start to operate at #e1 #f1 #h and #ab amperes4 ,up to #eej volts1 these relays may be connected across the line1 but for higher voltages they are connected to secondaries of pressure transformers4 ,smaller motors with which hand operated circuit breakers are used1 are generally provided with low voltage release attachments that perform the same function as the relay4 ,induction motors are sometimes subjected to high voltage conditions and to protect them from injury1 high or excess voltage relays are employed to trip the automatic circuit breaker4 ,these relays are of similar design and wired in the same manner as the low voltage relays4 ,illustration3 ,,fig4 #b1cdc4--;,characteristic curves of ,condit time limit relay as illustrated in fig4 #b1cdb4 ,settings3 curve ,a1 #e amperes2 curve ,b1 #f amperes2 curve ,c1 #h amperes2 curve ,d1 #ab amperes4 ,reverse phase relays have been developed for operating conditions under which a reversal of phase would cause trouble1 as for example1 in the case of elevator motors4 ,these are so designed that any phase reversal that would reverse an induction motor1 would operate the relay and disconnect the automatic circuit breaker4 ,the design is based on the principle of the induction motor1 and in the case of low voltage motors of limited capacity1 the relay may be connected in series in the motor leads4 ,if the voltage or capacity of the motor make this arrangement inexpedient1 the relay may be placed in the secondaries of current or pressure transformers connected in the motor leads4 ,underload relays are often used to trip the automatic circuit breaker that is placed in the primaries of arc lighting circuits to prevent an abnormal rise of secondary voltage in case of a break in the secondary circuit4 ,illustration3 ,,fig4 #b1cdd4--;,diagram showing storage battery and charging dynamo protected by double pole single coil underload circuit breaker4 ,in operation1 the circuit breaker disconnects the battery when fully charged1 and protects the dynamo from reverse current4 ,the underload relay is similar in design to the low voltage relay excepting that it acts on a decrease of current4 ,the problem of protecting induction motors1 from injury1 that may result from running on single phase1 or from an overload1 and at the same time permit the motor to be started with the necessarily high starting current that may be greatly in excess of the overload current1 has caused the development of the series relay4 ,illustration3 ,,fig4 #b1cde4--;,diagram showing direct current motors protected by overload circuit breakers with bell alarm switches3 a1 double pole single coil breaker no switch required4 ,low voltage device is on the starting rheostat2 b1 single pole breaker in series with lever switch4 ,low voltage attachment on the breaker4 ,illustration3 ,,fig4 #b1cdf4--;,diagram showing two wire dynamo1 protected by a single pole overload circuit breaker with bell alarm switch4 ,breakers must be on opposite side from the series field4 ,illustration3 ,,fig4 #b1cdg4--;,diagram showing dynamo protected by a single pole overload circuit breaker with reverse current relay and combined circuit opening and bell alarm switch4 ,this device may be connected in series with the motor leads for voltages up to #b1ejj2 it is designed with an inverse time limit device which may be adjusted to give the desired protection4 ,the field for relays is more extensive for alternating current than for direct current power circuits1 the latter being generally confined to much smaller and simpler systems and areas of distribution1 and generally sufficient selective action can be obtained by the use of fuses or circuit breakers arranged with instantaneous trip4 ,illustration3 ,,fig4 #b1cdh4--;,diagram showing three wire dynamo protected by double pole double coil overload circuit breaker 7or two single pole breakers with interlock7 with bell alarm switches4 ,complete protection is secured as breaker is connected between armature and series field4 ,operating conditions sometimes make it advisable for the generator circuit breakers to open only after the auxiliary and feeder circuit breakers have failed to isolate the trouble4 ,this is accomplished by using direct current series inverse time limit relays to trip the generator circuit breakers4 ,instantaneous reverse current relays are used to trip the machine circuit breaker of battery charging sets1 rotaries and motor generator sets to prevent their running as a motor on the charging or direct current end4 ,these relays can act only in case of current reversal4 ,to prevent serious unbalancing of voltages in ,edison three-wire systems causing trouble1 differential balance relays are used to trip the circuit breakers on a small percentage of unbalancing4 ,,chapter ,,lix ,,lightning ,,protection ,,devices ,lightning protection devices1 or lightning arresters1 are devices for providing a path by which lightning disturbances or other static discharges may pass to the earth4 ,lightning arresters1 designed for the protection of transmission lines1 must perform this function with a minimum impairment of the insulation of the lines4 ,in general the construction of lightning arresters comprise #a4 ,air gaps2 #b4 ,resistances2 #c4 ,inductances2 #d4 ,arc suppressing devices4 ,ques4 ,what are the causes of static charges8 ,ans4 ,they may be caused by sandstorms in dry climates1 or may be due to grounds on the high pressure side of a system4 ,ques4 ,what causes high frequency oscillations8 ,ans4 ,they are usually due to lightning discharges in the vicinity of the line4 ,ques4 ,what are the requirements of lightning protection devices8 ,ans4 ,they must prevent excessive pressure differences between line and ground1 line and line1 and between conductor turns in the electrical apparatus4 ,air ,gap ,arresters4--method of relieving any abnormal pressure condition is to connect a discharge air gap between some point on an electric conductor and the ground4 ,the resistance thus interposed between the ground and the conductor is such that any voltage very much in excess of the maximum normal will cause a discharge to ground1 whereas at other times the conductor is ungrounded because of the air gap4 ,this forms the principle of air gap arresters4 ,illustration3 ,,fig4 #b1cdi4--,non-arcing multi-gap arrester4 ,based on the principle of employing for the terminals across which the arc is formed1 such metals as are least capable of maintaining an alternating arc between them4 ,this so called non-arcing property of certain metals was discovered by ,alexander ,wurtz4 ,the action is such that the line current which follows the lightning discharge follows as an arc1 but is stopped at the end of one alternation because of the property of the non-arcing metals to carry an arc in one direction1 but requiring an extremely high voltage to start a reverse arc4 ,the non-arcing metals ordinarily employed are alloys of zinc and copper4 ,plain multi-gap arresters as here shown operate satisfactorily with the smaller machines and on circuits of limited power1 but for large machines of close regulation1 and therefore of very large momentary overload capacity1 especially when a number of such are operated in parallel1 such arresters were found insufficient1 the line current following the lightning discharge frequently was so enormous that the circuit did not open at the end of the half wave1 that is the arrester held the arc and was destroyed4 ,the introduction of synchronous motors made it necessary that the arc should be extinguished immediately1 otherwise the synchronous motors and converters would drop out of step1 and the system would in this way be shut down4 ,to insure the breaking of the arc1 resistance was introduced in the arrester1 the modified device being known as the low equivalent arrester as shown in fig4 #b1cej4 ,the single gap while adequate for telegraph line protection1 was found insufficient for electric light and power circuits1 because since the current in such circuits is considerable and usually at high pressure it would follow the lightning discharge across the gap4 ,thus the problem arose to devise means for short circuiting the line current resulting in various modifications of gap arrester4 ,multi-gap ,arresters4--,the essential elements of an arrester of this type are a number of cylinders spaced with a small air gap between them and placed between the line to be protected and the ground1 or between line and line4 ,in operation1 the multi-gap arrester discharges at a much lower voltage than would a single gap having a length equal to the sum of the small gaps4 ,in explaining the action of multi-gaps1 there are three things to consider3 ,illustration3 ,,fig4 #b1cej4--,low equivalent arrester4 ,this is a modification of the multi-gap arrester shown in fig4 #b1cdi4 ,about half of the total number of gaps are shunted by a resistance1 and another resistance inserted between the cylinders and the earth4 ,with this arrangement the middle point is at ground pressure1 and there are between line and ground only one half of the total number of gaps4 ,this is sufficient to prevent a bridging of the gaps under normal conditions4 #a4 ,the transmission of the static stress along the line of the cylinders2 #b4 ,the sparking at the gaps2 #c4 ,the action and duration of the current which follows the spark1 and the extinguishment of the arc4 ,ques4 ,what is a spark8 ,ans4 ,the conduction of electricity by air4 ,ques4 ,what is an arc4 ,ans4 ,the conduction of electricity by vapor of the electrode4 ,distribution of ,static ,stress4--,the cylinders of the multi-gap arrester act like plates of condensers in series4 ,this condenser function is the essential feature of its operation4 ,when a static stress is applied to a series of cylinders between line and ground1 the stress is immediately carried from end to end4 ,if the top cylinder be positive it will attract a negative charge on the face of the adjacent cylinder and repel an equal positive charge to the opposite face and so on down the entire row4 ,the second cylinder has a definite capacity relative to the third cylinder and also to the ground2 consequently the charge induced on the third cylinder will be less than on the second cylinder1 due to the fact that only part of the positive charge on the second cylinder induces negative electricity on the third1 while the rest of the charge induces negative electricity to the ground4 ,each successive cylinder1 counting from the top of the arrester1 will have a slightly smaller charge of electricity than the preceding one4 ,illustration3 ,,fig4 #b1cea4--;,general ,electric #b1bjj volt multi-gap arrester for station installation4 ,it consists of fourteen knurled cylinders and two shunt resistance rods mounted on a porcelain base4 ,one of these rods has a low resistance1 and shunts nine gaps2 the other rod has a high resistance1 and shunts eleven gaps4 ,the effect of the shunt resistance in extinguishing the line current arc is the same1 therefore1 as that of an equal series resistance but is without the objectionable features of the latter4 ,series resistance limits the discharge current to such an extent that an arrester with series resistance fails to protect against destructive rises of voltage when the conditions are severest4 ,graded shunt resistance responds to all frequencies and opens a discharge path for excessive voltage when the frequencies are high as well as when they are low4 ,its further effect in withholding the line current from the gaps after the relieving discharge has occurred1 is to aid the non-arcing quality of the metal cylinders in quickly suppressing the arc that follows a discharge4 ,the arc is extinguished at the end of the half cycle of line current in which the discharge takes place4 ,sparking at the ,gaps4--,the quantity of electricity induced on the second cylinder is greater than on any lower cylinder and its gap has a greater pressure strain across it as shown in fig4 #b1ceg4 ,when the voltage across the first gap is sufficient to spark1 the second cylinder is charged to line voltage and the second gap receives the static strain and breaks down4 ,the successive action is similar to overturning a row of ten-pins by pushing the first pin against the second4 ,this phenomenon explains why a given length of air gap concentrated in one gap requires more voltage to spark across it than the same total length made up of a row of multi-gaps4 ,illustration3 ,,fig4 #b1ceb4--;,general ,electric #b1bjj volt arrester in the act of discharging1 and shunting the line current4 ,the figure shows an actual discharge taking place4 ,it will be seen that the heavy line current passes across only four of the gaps1 and then goes through the resistance rods2 while the static discharge passes straight across the entire series of thirteen gaps4 ,when the gaps of an arrester are shunted by even a low resistance1 discharges of very high frequency find it relatively difficult to pass through the resistance rods1 owing to the impedance of the rods1 but comparatively easy to pass across all the gaps1 owing to the capacity effect in breaking down the gaps4 ,the higher the frequency1 the more pronounced is this effect1 hence the discharges select different paths through gaps and resistances depending upon the frequency4 ,by frequency is meant1 not the frequency of the line current but the lightning frequency1 which may run into hundreds of thousands1 or into millions of cycles4 ,the equivalent needle gap for this arrester is shown by tests to be nearly the same for all frequencies and quantities of discharge2 that is1 the arrester is equally responsive to all frequencies4 ,illustration3 ,,figs4 #b1cec to #b1cee4--,oscillograph record of the phenomena that take place in the different circuits or selective paths of a multi-gap arrester during a discharge such as shown in fig4 #b1ceb4 ,as the spark crosses each successive gap1 the voltage gradient along the remainder readjusts itself4 ,how the ,arc is ,extinguished4--,when the sparks extend across all the gaps the line current will follow if1 at that instant1 the line pressure be sufficient4 ,on account of the relatively greater line current1 the distribution of pressure along the gaps becomes equal1 and has the value necessary to maintain the line current arc on a gap4 ,the line current continues to flow until the voltage of the generator passes through zero to the next half cycle1 when the arc extinguishing quality of the metal cylinders comes into action4 ,illustration3 ,,figs4 #b1cef and #b1ceg4--;,diagram showing condenser action of cylinders and pressure gradient for static stress4 ,the alloy contains a metal of low boiling point which prevents the reversal of the line current4 ,it is a rectifying effect1 and before the pressure again reverses1 the arc vapor in the gaps has cooled to a non-conducting state4 ,effect of ,frequency4--,the higher the frequency of the lightning oscillation1 the more readily will the multi-gap respond to the pressure4 ,briefly stated1 the problem is to properly limit the line current so that the arc may be extinguished2 to arrange a shunt circuit so that the series resistance will be automatically cut out if safety demand it on account of a heavy lightning stroke and1 while retaining these properties1 to make the arrester sensitive to a wide range of frequency4 ,it should be noted that series resistance limits the rate of discharge of the lightning as well as of the line current4 ,the greater the value of the line current1 the greater the number of gaps required to extinguish the arcs4 ,graded ,shunt ,resistances4--,any arc is unstable and can be extinguished by placing a properly proportioned resistance in parallel with it4 ,all the minor discharges then pass over the resistances and the unshunted spark gaps1 the resistance assisting in opening the line current after the discharge4 ,very heavy discharges pass over all the spark gaps1 as a path without resistance1 but those spark gaps which are shunted by the resistance1 open after the discharge4 ,the line current1 after the first discharge is accordingly deflected over the resistances1 and limited thereby1 the circuit being finally opened by the unshunted spark gaps4 ,the arrangement of shunted resistances is shown in fig4 #b1ceh4 ,illustration3 ,,fig4 #b1ceh4--;,arrangement of graded resistances on multi-gap arrester4 ,the ,cumulative or ,breaking ,back ,effect4--,the graded shunt resistance gives a valuable effect1 where the arrester is considered as four separate arresters4 ,this is the cumulative or breaking back action4 ,when a lightning strain between line and ground takes place1 the pressure is carried down the high resistance ,h 7figs4 #b1cfe and #b1cff71 to the series gaps ,,gs1 and the series gaps spark over4 ,although it may require several thousand volts to spark across an air gap1 it requires relatively only a few volts to maintain the arc which follows the spark4 ,in consequence1 when the gaps ,,gs spark over1 the lower end of the high resistance is reduced practically to ground pressure4 ,if the high resistance can carry the discharge current without giving an ohmic drop sufficient to break down the shunted gaps ,,gh1 nothing further occurs--the arc goes out4 ,if1 on the contrary1 the lightning stroke be too heavy for this1 the pressure strain is thrown across the shunted gaps1 ,,gh1 equal in number to the previous set4 ,in other words1 the same voltage breaks down both of the groups of gaps1 ,,gs and ,,gh1 in succession4 ,the lightning discharge current is now limited only by the medium resistance ,m1 and the pressure is concentrated across the gaps1 ,,gm4 ,if the medium resistance cannot discharge the lightning1 the gap ,,gm spark1 and the discharge is limited only by the low resistance4 ,the low resistance should take care of most cases but with extraordinarily heavy strokes and high frequencies1 the discharge can break back far enough to cut out all resistance4 ,in the last steps1 the resistance is relatively low in proportion to the number of shunt gaps1 ,,gl1 and is designed to cut out the line current immediately from the gap1 ,,gl4 ,this breaking back effect is valuable in discharging lightning of low frequency4 ,illustration3 ,,figs4 #b1cei to #b1cfd4--,westinghouse safety spark gaps4 ,fig4 #b1cei1 indoor type2 figs4 #b1cfj to #b1cfd1 outdoor type4 ,it is well known that with transformers1 operating on high voltage lines and having large ratios of transformation1 there may occur1 on the low tension side1 momentary voltages to ground greatly in excess of the normal4 ,these momentary increases in voltage between the low tension circuits and ground are commonly called static disturbances4 ,in general they are the result of a change in the static balance of the high tension side and its connecting circuits4 ,unless certain precautions are taken1 such a static disturbance on the low tension side may cause serious stresses in the secondary insulation of a transformer with a high ratio of transformation4 ,this induced static voltage is independent of the ratio of transformation4 ,the static stresses are more serious in a high ratio transformer simply because the insulation of its secondary is less able to withstand them4 ,a method of relieving this disturbance is to connect a discharge spark gap between some point of the low tension side of the transformer to be protected 7a middle or neutral point1 if one be available7 and the ground4 ,the spark gap opening is such that any voltage very much in excess of the maximum normal will cause a discharge to ground1 and thus the low tension side is practically tied to ground during such disturbance1 while at other times it is ungrounded4 ,the ,underwriters recommend the grounding of the neutral point of low tension circuits when the conditions are such that the maximum normal voltage between the point connected and ground will not exceed #bej volts4 ,the rule allows one side of a #bej volt circuit or the middle point of a #eej volt circuit to be grounded4 ,the spark gaps shown above are designed for use on transformer secondary circuits and for protecting individual series arc lamps4 ,these spark gaps are single pole1 and consist of two cylinders of non-arcing metal with an air gap between4 ,one of the cylinders is connected to the ground1 the other to the line4 ,illustration3 ,,figs4 #b1cfe and #b1cff4--;,graded shunt resistance arrester connections4 ,fig4 #b1cfe1 connections for #cc1jjj volt ,y system with grounded neutral2 fig4 #b1cff1 connections for #cc1jjj volt delta or ungrounded ,y systems4 ,the type of arrester shown above may be considered as four arresters in one4 ,first1 for small discharges there are a few gaps in series with a high shunt resistance4 ,this part of the arrester will safely discharge accumulated static and also all disruptive discharges of small ampere capacity4 ,this path is shown through ,h 7resistance7 and ,,gs 7gaps74 ,second1 there are a number of gaps in series with a medium shunt resistance which will discharge disruptive strokes of medium ampere capacity4 ,this path is shown through ,m 7resistance7 and ,,gh plus ,,gs 7gaps74 ,third1 there are a greater number of gaps in series with a low shunt resistance which will discharge heavy disruptive strokes4 ,this path is shown through ,l 7resistance7 and ,,gm plus ,,gh plus ,,gs 7gaps74 ,fourth1 the total number of gaps has no series resistance1 thus enabling the arrester to freely discharge the heaviest induced strokes4 ,this path is shown through zero resistance and ,,gh plus ,,gm plus ,,gh plus ,,gs 7gaps74 ,in each of the above circuits the number of gaps and the resistance are so proportioned as to extinguish the line arc at the end of the half cycle in which the lightning discharge takes place4 ,illustration3 ,,fig4 #b1cfg4--;,installation of a ,general ,electric #ab1ejj volt1 three phase1 multi-gap lightning arrester in the ,garfield ,park sub-station of the ,west ,chicago park common4 ,the ,v unit multi-gap arrester1 which is plainly seen in the illustration1 is made up of ,v units consisting of gaps between knurled cylinders and connected together at their ends by short metal strips4 ,the base is of porcelain1 which thoroughly insulates each cylinder1 and insures the proper functioning of the multi-gaps4 ,the cylinders are made of an alloy that contains metal of low boiling point which gives the rectifying effect1 and metals of high boiling point which cannot vaporize in the presence of the one of low boiling point4 ,the cylinders are heavily knurled4 ,as the arc plays on the point of a knurl it gradually burns back and when the metal of low boiling temperature is used up1 the gap is increased at that point4 ,the knurling1 thus1 insures longer life to the cylinder by forcing successive arcs to shift to a new point4 ,when worn along the entire face1 the cylinder should be slightly turned4 ,the low resistance section of the graded shunt is composed of rods of a metallic alloy4 ,these rods have large current carrying capacity1 and practically zero temperature coefficient up to red heat4 ,the medium and high resistance rods are of the same standard composition previously used4 ,the contacts are metal caps shrunk on the ends2 the resistances are permanent in value and the inductance is reduced to a minimum4 ,the rods are glazed to prevent absorption of moisture and surface arcing4 ,after the spark passes1 the arcs are extinguished in the reversed order4 ,the low resistance1 ,l1 is proportioned so as to draw the arcs immediately from the gaps1 ,,gl4 ,the line current continues in the next group of gaps1 ,,gm1 until the end of the half cycle of the generator wave4 ,illustration3 ,,figs4 #b1cfh to #b1cgj4--,multi-gap or low equivalent lightning arrester4 ,it consists of3 #a1 a number of gap units in series2 #b1 a number of gap units in shunt with a resistance2 and #c1 a series resistance4 ,all resistances are wire wound and the series resistance is non-inductive4 ,the shunt resistance and gap units are mounted on marble4 ,when a discharge occurs1 the series gaps are broken down1 and if the discharge be heavy enough1 it will meet opposition in the shunt resistance and pass over the shunted gaps1 through the series resistance to the ground4 ,the arc which tends to follow the discharge is then withdrawn from the shunted gaps by the shunt resistance1 and aided by both resistances is suppressed by the series gaps4 ,the pressure of discharge is determined by the number of series gaps as sufficient number is used to withstand the normal voltage and yet give a proper factor of safety for the severest service4 ,at this instant the medium resistance1 ,m1 aids the rectifying quality of the gaps1 ,,gm1 by shunting out the low frequency current of the alternator4 ,on account of this shunting effect the current dies out sooner in the gaps1 ,,gm1 than it otherwise would4 ,in the same manner1 but to a less degree1 the high resistance1 ,h1 draws the line current from the gaps1 ,,gh4 ,this current now being limited by the high resistance1 the arc is easily extinguished at the end of the first one-half cycle of the alternator wave4 ,ques4 ,what is the difference between arrester for grounded ,y and non-grounded neutral systems8 ,ans4 ,the connections are shown in figs4 #b1cfe and #b1cff4 ,the difference in design lies in the use of a fourth arrester leg between the multiplex connection and ground or ungrounded system4 ,ques4 ,why is the fourth leg introduced8 ,ans4 ,the arrester is designed to have two legs between line and line4 ,if one line become accidentally grounded1 the full line voltage would be thrown across one leg if the fourth or ground leg were not present4 ,illustration3 ,,fig4 #b1cga4--,westinghouse three pole or four pole arrester in weather proof wooden case which protects the arrester units from rain and snow when they are installed in exposed locations1 as on poles or buildings4 ,on a ,y system with a grounded neutral1 the accidentally grounded phase causes a short circuit of the phase and the arrester is relieved of the strain by the tripping of the circuit breaker4 ,briefly stated1 the fourth or ground leg of the arrester is used when1 for any reason1 the system could be operated1 even for a short time with one phase grounded4 ,ques4 ,describe the multiplex connection4 ,ans4 ,it consists of a common connection between the phase legs of the arrester above the earth connection and provides an arrester better adapted to relieve high pressure surges between lines than would otherwise be possible4 ,its use also economizes in space and material for delta and partially grounded or non-grounded ,y systems4 ,illustration3 ,,figs4 #b1cgb and #b1cgc4--,westinghouse multi-gap lightning arrester and views showing parts4 ,in construction1 a series of gaps1 between non-arcing metal cylinders arranged in a row1 is connected between line and ground in series with a composition stick resistor having a resistance of something between #hj and #abj ohms4 ,in operation1 if an excessive pressure be developed on a line1 electric discharge arcs form between the metal cylinders1 and the charge of electricity flows to ground1 relieving the excessive stress4 ,the resistance of the stick resistor limits the flow so that an excessive power current cannot pass through the arrester4 ,the tendency for a destructive power arc to follow the discharge arc is thus counteracted4 ,the composition resistors and the gap cylinders are mounted in pairs on a porcelain base1 and complete units are arranged within weather proof wooden boxes as indicated4 ,for two pole arresters1 one unit is mounted on the back of the box4 ,for three pole and four pole arresters1 two units are used2 one is secured on each side of the box4 ,illustration3 ,,figs4 #b1cgd to #b1cgf4--;,connections for ,westinghouse multi-gap 7type ,g7 arresters4 ,these arresters may be installed outside on poles or buildings1 or indoors on station walls4 ,the weather proof wooden case 7as shown in fig4 #b1cga7 protects the arrester units from rain and snow when installed in exposed places4 ,fig4 #b1cgd shows single phase installation1 fig4 #b1cge1 two phase installation1 and fig4 #b1cgf1 three phase installation4 ,on a two pole circuit one line wire is connected to the top of each of the composition resistors of each arrester unit1 as shown in fig4 #b1cgd1 and the ground wire is connected to the middle point of the gap series4 ,on four pole circuits1 fig4 #b1cge1 the same scheme of connections is used1 but two arrester units are necessary and the connections of both are the same4 ,on three pole circuits1 two arrester units are used1 with the same connections as for four pole circuits1 except that there are but three line connections instead of four as in fig4 #b1cgf4 ,horn ,gap ,arresters4--,a horn gap arrester consists essentially of two horn shaped terminals forming an air gap of variable length1 one horn being connected to the line to be protected and the other to the ground usually through series resistance as shown in fig4 #b1cgh4 ,ques4 ,how does the horn gap arrester operate8 ,ans4 ,the arc due to the line current which follows a discharge1 rises between the diverging horn and becoming more and more attenuated is finally extinguished4 ,illustration3 ,,fig4 #b1cgg4--;,horn gap arrester1 diagram showing arrester and connections between line and ground4 ,the horn type arrester was invented by ,oelschlaeger for the ,allgemeine ,electricitaets ,gesellschaft1 and like the ,thomson arc circuit arrester1 its operation is based on the fact that a short circuit once started at the base1 the heat generated by the arc will cause it to travel upward until it becomes so attenuated that it is ruptured4 ,on circuits of high voltage this rupture sometimes takes a second or two1 but seems to act with little disturbance of the line4 ,sometimes a water resistance is used1 a choke coil being inserted in the circuit in series4 ,in one installation for a #dj1jjj volt line1 the horns were made of ,no4 #j1jjj copper wire with gap knees #b to #c or #c inches4 ,the capacity of the water resistance receptacle was #ae gallons4 ,users differ as to whether the water should contain salt4 ,the choke coil can be made of about #ah turns of iron wire wound on a #f inch cylinder4 ,ques4 ,what is the objection to the horn gap on alternating current circuits8 ,ans4 ,the arc lasts too long for synchronous apparatus to remain in step4 ,ques4 ,what provision was made to shorten the duration of the arc8 ,ans4 ,a series resistance was inserted in the arrester circuit as shown in fig4 #b1cgg4 ,ques4 ,what difficulty was caused by the series resistance8 ,ans4 ,with sufficient series resistance to prevent loss of synchronism1 the arrester failed to protect the system under severe conditions4 ,ques4 ,with these objections what use was found for the horn gap arrester8 ,ans4 ,it is used as an emergency arrester on some overhead lines1 to operate only when a shut down is unavoidable1 also for series lighting circuits4 ,illustration3 ,,fig4 #b1cgh4--;,general ,electric horn gap with charging resistance for cable system4 ,arresters for cable systems differ from arresters for overhead circuits only in the construction of the horn gaps4 ,the necessity for this difference is due to the fact that a cable system has a very much higher electrostatic capacity and much less inductance than an overhead system4 ,in consequence1 the currents which flow into the arrester during charging are somewhat higher4 ,it is desirable to avoid these heavier currents1 especially during the time of breaking the arc at the horn gap4 ,this is accomplished by using a special horn gap and resistance4 ,this consists of an auxiliary horn mounted above and insulated from the regular horn in such a manner as to intercept the arc if it rise on the regular horns4 ,enough resistance is connected in series with this auxiliary horn so that the current flow and arc across this gap are always limited to a moderate value4 ,such a device has several advantages4 ,since the mechanism is so arranged that the charging is always done through the auxiliary horn the current rush is limited during the charging and thus troubles from carelessness or ignorance are avoided4 ,it also gives a nearer uniform charging current4 ,in the use of this auxiliary horn gap and resistance there are three successive stages1 as follows3 #a1 light discharges will pass across the smaller gaps to the auxiliary horn and through the series resistance to the cells2 #b1 if the discharge be heavy1 the resistance offers sufficient impedance to cause the spark to pass to the main horn4 ,this is accomplished with only a slight increase in pressure because the gap is already ionized4 ,if the cells be in normal condition1 the spark at the gap is immediately extinguished1 without any flow of line current2 #c1 if the cells be in poor form1 the line current may follow the discharge across the main gap and the arc will rise to the safety horn and be extinguished through a resistance4 ,for mixed overhead and cable systems the choice of arrester will be a matter of judgment4 ,if there be a comparatively short length of cable1 the usual practice for overhead systems may be adopted4 ,for direct connection to busbars1 arresters with charging resistance should be used4 ,illustration3 ,,figs4 #b1cgi and #b1chj4--;,diagram showing connections of horn type lightning arresters on series circuits4 ,the necessity of service requires that series lightning systems be fully equipped against damage by lightning and similar trouble4 ,the most common disturbances occurring on series circuits are the surges set up by the sudden opening of the loaded circuit4 ,these disturbances are especially severe where circuits are accidentally grounded1 due to contact of the wires where they pass through other circuits4 ,ques4 ,how are the spark gaps adjusted8 ,ans4 ,they are set to give a low spark pressure relative to the voltage of the line4 ,illustration3 ,,fig4 #b1cha4--;,general ,electric horn type arrester1 mounted for #ae light series arc circuit4 ,the horn type arrester consists of a horn gap with series resistance between each line and ground4 ,the resistances and horn gaps are mounted on porcelain bases and the latter on insulating wooden supports4 ,the supports have asbestos barriers 7except for lowest voltages71 and backs to eliminate liability of damage from the arc which forms in the horn gap at the time of the discharge4 ,the spark gaps are adjusted to give a low spark pressure relative to the voltage of the circuit4 ,the number and ohmic value of the resistance rods used in the various arresters depend upon the voltage and current of the circuit4 ,ques4 ,why are horn arresters well suited to protect series lighting circuits against surges8 ,ans4 ,because the surges are damped out before the arc which forms across the horn gaps is interrupted4 ,these arcs last for several cycles1 since the length of the time of action of the arrester depends upon the lengthening of the arc between the horn gaps1 limited by the series resistance4 ,since practically all disturbances on lighting circuits are of low frequency1 the series resistance can be used with good results2 it aids the horn in extinguishing the arc1 limits the size of the arc and prevents short circuits occurring during the period of discharge4 ,illustration3 ,,fig4 #b1chb4--;,general ,electric horn arrester for pole installation4 ,quite frequently series circuits are run underground in cables for some distance from the generating station4 ,in order to protect the cables it is advisable to place horn arresters at the points where the cable joins the overhead wires4 ,the resistance units are mounted in the wooden box4 ,this design is used to economize space1 since if the horn gaps be placed in the box the latter would have to be made very large to accommodate the asbestos barriers and backs4 ,in installing this type of arrester it is advisable to place it as near as possible to the top of the pole so that the arc may rise unobstructed and thus avoid the likelihood of live wires coming in contact with the horns which1 during the operation of the series current1 are alive4 ,electrolytic ,arresters4--,arresters of this class are sometimes called aluminum arresters because of the property of aluminum on which their action depends2 that is1 it depends on the phenomenon that a non-conducting film is formed on the surface of aluminum when immersed in certain electrolytes4 ,if however1 the film be exposed to a higher pressure1 it may be punctured by many minute holes1 thus so reducing its resistance that a large current may pass4 ,when the pressure is again reduced the holes become resealed and the film again effective4 ,illustration3 ,,figs4 #b1chc and #b1chd4--;,elevation and plan of ,general ,electric horn gaps and operating stand for high voltage arresters4 ,in construction1 the aluminum arrester consists essentially of a system of nested aluminum cup shaped trays1 supported on porcelain and secured in frames of heated wood1 arranged in a steel tank4 ,the system of trays is connected between the line and ground1 and between line and line1 a horn gap being inserted in the arrester circuit which prevents the arrester being subjected to the line voltage except when in action4 ,the electrolyte is poured into the cones and partly fills the space between the adjacent ones4 ,the stack of cones with the electrolyte between them is then immersed in a tank of oil4 ,the electrolyte between adjacent cones forms an insulation4 ,the oil improves this insulation and prevents the evaporation of the solution4 ,illustration3 ,,fig4 #b1che4--;,cross section of ,general ,electric aluminum 7electrolytic7 lightning arrester4 ,a cylinder of insulating material concentric with the cone stack is placed between the latter and the steel tank1 the object being to improve the circulation of the oil and increase the insulation between the tank and the cone stack4 ,the arrester1 as just described consists of a number of cells connected in series4 ,ques4 ,of what does a single cell consist and what are its characteristics8 ,ans4 ,it consists of two of the cone shaped aluminium trays or plates and an electrolyte1 which forms a condenser that will stand about #cej volts before breaking down4 ,when this voltage is exceeded the cell becomes a fairly good conductor of electricity1 but as soon as the voltage drops its resistance again resumes a very high value4 ,ques4 ,what is the critical voltage8 ,ans4 ,the voltage at which the current begins to flow freely4 ,illustration3 ,,fig4 #b1chf to #b1cij4--,parts of ,general ,electric #ae1jjj volt aluminum lightning arrester1 not including horn gaps1 etc4 ,up to a certain voltage the cell allows an exceedingly low current to flow1 but at a higher voltage the current flow is limited only by the internal resistance of the cell1 which is very low4 ,a close analogy to this action is found in the well known safety valve of the steam boiler1 by which the steam is confined until the pressure rises above a given value1 when it is released4 ,on the aluminum plates there are myriads of minute safety valves1 so that1 if the electric pressure rise above the critical voltage1 the discharge takes place equally over the entire surface4 ,it is important to distinguish between the valve action of this hydroxide film and the failure of any dielectric substance4 ,ques4 ,when a cell is connected permanently to the circuit what two conditions are involved8 ,ans4 ,the temporary critical voltage and the permanent critical voltage4 ,for instance1 if the cell have #cjj volts applied to it constantly1 and the pressure be suddenly increased to1 say #cbe volts1 there will be a considerable rush of current until the film thickness has been increased to withstand the extra #be volts2 this usually requires several seconds4 ,in this case #cbe volts is the temporary critical voltage of the cell4 ,similar action will occur at any pressure up to about the permanent critical voltage1 or the voltage at which the film cannot further thicken1 and therefore allows a free flow of current4 ,if the voltage be again reduced to #cjj the excess thickness of film will be gradually dissolved1 and if it vary periodically between two values1 each of which is less than the permanent critical value1 the temporary critical voltage will be the higher value4 ,this feature is of great importance as it provides a means of discharging abnormal surges1 the instant the pressure rises above the impressed value4 ,illustration3 ,,fig4 #b1cia4--,volt ampere characteristic curve of a ,general ,electric aluminum 7electrolytic7 cell on alternating current4 ,the permanent critical voltage is between #cce and #cfj volts4 ,with alternating current1 the cell acts as a fairly good condenser1 and there is not only the leakage through the film1 but also a capacity current flowing into the cell4 ,the phase of this current1 then1 is nearly #ij degrees ahead of the pressure and represents a very low energy factor4 ,ques4 ,how is the number of cells required for a given circuit determined8 ,ans4 ,the number required for a given operating voltage is determined by allowing about #bej to #cjj volts per cell4 ,ques4 ,in putting cells in commission how is the electrolyte introduced8 ,ans4 ,it is poured into the aluminum trays and the overflow drawn off at the bottom of the tank4 ,ques4 ,describe the further operations in putting cells in commission4 ,ans4 ,after putting in the electrolyte it is allowed to stand for a few days until part has evaporated1 then the oil is poured over the surface to prevent further evaporation4 ,illustration3 ,,fig4 #b1cib4--,westinghouse electrolytic lightning arrester1 for three phase ungrounded neutral service1 #be1jjj maximum voltage4 ,these arresters are designed for the protection of alternating current circuits from all kinds of static disturbances4 ,they have been standardized for installation on three phase circuits of voltages of #b1bjj to #aaj1jjj4 ,they cannot be used for voltages of less than #ac1ejj4 ,for voltages below this the horn gaps cannot1 with safety1 be set close enough together1 out of doors1 to take advantage of the freedom of discharge of the electrolytic element4 ,if the horn gaps be set too close together they may be short circuited by rain4 ,a shelter should be built for arresters of #ac1ejj volts and below for their protection when installed outside4 ,ques4 ,what action takes place when the trays stand in the electrolyte and cell is disconnected from the circuit8 ,ans4 ,part of the film deteriorates4 ,ques4 ,what is the nature of the film8 ,ans4 ,the film is composed of two parts1 one of which is hard and insoluble1 and apparently acts as a skeleton to hold the more soluble part4 ,the action of the cell seems to indicate that the soluble part of the film is composed of gases in a liquid form4 ,ques4 ,what action takes place when a cell which has stood for some time disconnected1 is reconnected to the circuit8 ,illustration3 ,,figs4 #b1cic and #b1cid4--;,aluminum trays for ,westinghouse electrolytic lightning arresters4 ,ans4 ,there is a momentary rush of current which reforms the part of the film which has dissolved4 ,this current rush will have increasing values as the intervals of rest of the cell are made greater4 ,many electrolytes have been studied1 but none has been found which does not show this dissolution effect to a greater or lesser extent4 ,if the cell has stood disconnected from the circuit for some time1 especially in a warm climate1 there is a possibility that the initial current rush will be sufficient to open the circuit breakers or oil switches4 ,this current rush also raises the temperature of the cell1 and if the temperature rise be great1 it is objectionable4 ,when the cells do not stand for more than a day1 however1 the film dissolution and initial current rush are negligible4 ,ques4 ,what is the object of using horn gaps on electrolytic arresters8 ,ans4 ,the use is threefold3 #a1 it prevents the arrester being subjected continually to the line voltage2 #b1 acts as a disconnecting switch to disconnect the arrester from the line for repairs1 etc41 and #c1 acts as a connecting switch for charging4 ,illustration3 ,,fig4 #b1cie4--;,horn gaps and transfer device of ,general ,electric aluminium lightning arrester for #ab1ejj volt non-grounded neutral circuit4 ,the object of the transfer device is to provide a means for interchanging the ground stacks with one of the line stacks of cones during the charging operation so that the films of all the cells will be formed to the same value4 ,the transfer device consists of a rotating switch which may be turned #ahj degrees1 thus interchanging the connections of the ground stack and one of the line stacks4 ,for arresters up to #bg1jjj volts the device is mounted with three insulators on the pipe frame work1 and is operated by a hand wheel2 for arresters of higher voltage1 the transfer device is mounted directly over the tanks and is operated by bevel gears and hand wheel4 ,charging of ,electrolytic ,arresters4--,in electrolytic arresters all electrolytes dissolve the film when the arrester is on open circuit1 the extent of the dissolution depending upon the length of time the film is in the electrolyte1 and upon its temperature4 ,it is therefore necessary to charge the cells from time to time and thus prevent the dissolution and consequent rush of current which would otherwise occur when the arrester discharges4 ,ques4 ,describe the charging operation for arresters with grounded circuits4 ,ans4 ,it consists in simply closing simultaneously the three horn gaps so that the full pressure across the cells causes a small charging current to flow and form the films to their normal condition4 ,illustration3 ,,fig4 #b1cif4--,sectional view of ,general ,electric vacuum tube arrester for railway signal circuits4 ,the arrester is essentially a gap in a vacuum4 ,in construction1 the gap is formed between the inner wall of a drawn metal shell and a disc electrode mounted concentric with it4 ,the electrode is supported on a brass rod which serves as the lead in connection1 and has ample current carrying capacity4 ,the electrode system is insulated from the tube and rigidly supported in position by a bushing made of vitreous material4 ,the bushing does not form the vacuum seal1 that being made by a special compound4 ,the open end of the tube is finally closed by a porcelain bushing4 ,the tube is exhausted in a special machine which solders a small hole in the end after the vacuum has been established4 ,the possibility of solder entering the active part of the vacuum space is prevented by a diaphragm punching1 and both the electrode and the lining of the tube are of non-arcing metal4 ,the arrester has a spark pressure of from #cej to #fjj volts direct current1 and an equivalent needle gap of about 4#jje inch4 ,the arrester will not stand a continuous flow of current due to excessive heating1 hence if there be a possibility of this due to high pressure crosses1 fuses should be used4 ,r4,r4,s4,a4 standard terminals are used4 ,ques4 ,describe the charging operation for arresters for non-grounded circuits4 ,ans4 ,first1 the horn gaps are closed for five seconds and opened again to normal position1 thus charging the cells of the three line stacks4 ,second1 with the horn gaps still in normal position1 the position of the transfer device is reversed and the horn gaps are again closed for five seconds and returned to the normal position4 ,the complete charging operation takes but a few moments and should be performed daily4 ,the operation is valuable1 not only in keeping the films in good condition1 but also in giving the operator some idea of the condition of the arrester by enabling him to observe the size and color of the charging spark4 ,illustration3 ,,fig4 #b1cig4--;,highland ,park sub-station1 ,charlotte1 ,n4,c41 showing old lightning arrester tower on the left and ,general ,electric aluminum 7electrolytic7 cell lightning arrester and horn gaps in foreground4 ,grounded and ,non-grounded ,neutral ,circuits4--,it is important to avoid the mistake of choosing an arrester for a thoroughly grounded neutral when the neutral is only partially grounded1 that is1 grounded through an appreciable resistance4 ,careful consideration of this condition will make the above statement clear4 ,in an arrester for a grounded neutral circuit1 each stack of cones normally receives the neutral pressure when the arrester discharges1 but if a phase become accidentally grounded1 the line voltage is thrown across each of the other stacks of cones until the circuit breaker opens the circuit4 ,the line voltage is #agc per cent4 of the neutral or normal operating voltage of the cells and therefore about #aej per cent4 of the permanent critical voltage of each cell4 ,this means that when a grounded phase occurs1 this #ej per cent4 excess pressure is short circuited through the cells until the circuit breaker opens4 ,illustration3 ,,fig4 #b1cih4--,westinghouse electrolytic station lightning arrester for direct current up to #a1ejj volts consists of a tank of oil in which are placed1 on properly insulated supports1 a nest of cup shaped aluminum trays4 ,the spaces between the trays are filled with electrolyte1 a sufficient quantity for one charge being furnished with each arrester4 ,the top tray is connected with the line through a #fj ampere fuse1 and the bottom tray is connected to the tank which is thoroughly grounded by means of a lug4 ,the fuse is of the enclosed type and mounted on the cover of the arrester4 ,a small charging current flows through the trays continuously and keeps the films on the trays built up1 so that no charging is required4 ,this charging current is not1 however1 of sufficient value to raise the temperature appreciably4 ,the immersed area of each tray is #ajj square inches4 ,the shape and the arrangement of the trays is such that any gases generated by the discharge can pass out readily without disturbing the electrolyte between the trays4 ,the amount of energy to be dissipated in the arrester depends upon the kilowatt capacity of the generator1 the internal resistance of the cells1 and the time required to operate the circuit breakers4 ,it is evident that the greater the amount of resistance in the neutral1 the longer will be the time required for the circuit breakers to operate4 ,therefore1 in cases where the earthing resistance in the neutral is great enough to prevent the automatic circuit breakers opening practically instantaneously1 an arrester for a non-grounded neutral system should be installed4 ,illustration3 ,,figs4 #b1cii to #b1dja4--,westinghouse ground fittings4 ,fig4 #b1cii1 ground plate2 fig4 #b1djj1 ground point2 fig4 #b1dja1 cap4 ,the ground plate consists of a circular piece of cast iron1 #ab inches in diameter1 #a inches thick with a inch pipe tap in center to connection to arrester4 ,the surface is increased by means of corrugations1 as shown in the accompanying illustrations1 to #dfa square inches1 affording ample contact with the earth and enabling it to take care of all discharges through the arrester4 ,the plate should preferably be buried at the foot of the pole so that the ground wire runs to it in a straight line from the arrester4 ,care should1 of course1 be taken to see that the earth in which the plate is buried is damp4 ,if the ground wire be placed within the pipe leading to the ground plate it should be soldered to a cap at the top of the pipe to eliminate the inductive effect due to the wire being surrounded by iron4 ,a simple and effective method of securing a good ground is by means of an iron pipe with a malleable iron point having a dipped galvanized finish1 and a brass cap with a lug for soldering the ground wire4 ,the pipe may be driven into the earth1 or if it be too hard to permit driving1 a hole may be dug and the pipe placed therein4 ,it should extend from eight to ten feet above and below the earth to secure1 respectively1 a good ground and prevent any tampering with the ground wire4 ,should it be desired to make use of a longer pipe which would be inconvenient to drive into the earth1 two pieces can be used and connected together by a coupling4 ,the brass cap and malleable iron point are tapped for use with inch pipe4 ,ground ,connections4--,in all lightning arrester installations it is of the utmost importance to make proper ground connections1 as many lightning arrester troubles can be traced to bad grounds4 ,it has been customary to ground a lightning arrester by means of a large metal plate buried in a bed of charcoal at a depth of six or eight feet in the earth4 ,a more satisfactory method of making a ground is to drive a number of one inch iron pipes six or eight feet into the earth surrounding the station1 connecting all these pipes together by means of a copper wire or1 preferably1 by a thin copper strip4 ,a quantity of salt should be placed around each pipe at the surface of the ground and the ground should be thoroughly moistened with water4 ,it is advisable to connect these pipes to the iron framework of the station1 and also to any water mains1 metal flumes1 or trolley rails which are available4 ,illustration3 ,,figs4 #b1djb to #b1djd4--;,general ,electric magnetic blow out arrester for use on railways4 ,it consists of an adjustable spark gap in series with a resistance4 ,part of the resistance is in shunt with a blow out coil1 between the poles of which is the spark gap4 ,the parts are mounted in a strong1 porcelain box1 which1 for car and pole use1 is in turn mounted in a substantial asbestos lined1 wooden box4 ,in operation1 when the lighting pressure comes on the line1 it causes the spark gap to break down and a discharge occurs through the gap and the resistance rod to ground4 ,part of the current shunts through the blow out coil producing a strong magnetic field across the spark gap4 ,the magnetic field blows out the discharge arc and restores normal conditions4 ,the resistance is only #fj ohms 7for #ejj volt rating work71 and the spark gap only one-fortieth of an inch 74#jbe in474 ,the following suggestions are made for the usual size station4 #a4 ,place three pipes equally spaced near each outside wall1 making twelve altogether1 and place three extra pipes spaced about six feet apart at a point nearest the arrester4 #b4 ,where plates are placed in streams of running water1 they should be buried in the mud along the bank in preference to being laid in the stream4 ,streams with rocky bottoms are to be avoided4 #c4 ,whenever plates are placed at any distance from the arrester1 it is necessary also to drive a pipe into the earth directly beneath the arrester1 thus making the ground connection as short as possible4 ,earth plates at a distance cannot be depended upon4 ,long ground wires in a station cannot be depended upon unless a lead is carried to the parallel grounding pipes installed as described above4 #d4 ,as it is advisable occasionally to examine the underground connections to see that they are in proper condition1 it is well to keep on file exact plans of the location of ground plates1 ground wires and pipes1 with a brief description1 so that the data can be readily referred to4 ,illustration3 ,,fig4 #b1dje4--;,general ,electric magnetic blow out arrester for line use4 ,it consists essentially of a small spark gap which is in series with a resistance1 and between the poles of a magnet4 ,the operation is similar to that of the arrester shown in figs4 #b1djb to #b1djd1 but the magnet is a permanent magnet instead of an electromagnet4 ,the spark gap and the magnet are mounted within porcelain blocks in such a way that the discharge arc is blown by the magnet through an arc chute and a cooling grid which is also held by the porcelain4 ,the cooling grid in the arc chute materially assists the magnet in extinguishing the discharge arc1 giving the arrester a high arc rupturing quality4 ,the series rod is carborundum and is connected externally to the other portion of the arrester4 ,the arrester is self-contained4 #e4 ,from time to time the resistance of these ground connections should be measured to determine their condition4 ,the resistance of a single pipe ground in good condition has an average value of about #ae ohms4 ,a simple and satisfactory method of keeping account of the condition of the earth connections is to divide the grounding pipes into two groups and connect each group to the #aaj volt lighting circuit with an ammeter in series4 ,choke ,coils4--,a lightning discharge is of an oscillatory character and possesses the property of self-induction1 accordingly it passes with difficulty through coils of wire4 ,moreover1 the frequency of oscillation of a lightning discharge being much greater than that of commercial alternating currents1 a coil can readily be constructed which will offer a relatively high resistance to the passage of lightning and at the same time allow free passage to all ordinary electric currents4 ,opinions on the design of choke coils for use with lightning arresters vary considerably4 ,some engineers recommend the use of very large choke coils1 but while large choke coils of high inductance do choke back the high frequency currents better than smaller coils of less inductance1 they cost more1 and under many conditions they are a menace to the insulation unless the lightning arresters be installed on both sides of them4 ,illustration3 ,,fig4 #b1djf4--,westinghouse line suspension choke coil4 ,it is so designed that it can be inserted directly in the transmission line wire or in the station wiring and held in position therein by the tension of the line or station wires4 ,because of the fact that no insulators are required1 solely to support this choke coil1 and that it can be installed in either a vertical or a horizontal position it can often be utilized effectively in power and sub-station layouts4 ,terminals1 each having a inch round hole1 to accommodate the conductors are provided at each end of the coil4 ,three square headed binding screws are supplied which clamp the conductors in position4 ,the coil is provided with a strain insulator1 so arranged within the coil at its axis1 that it assumes any mechanical tension transmitted from the conductors4 ,no mechanical tension reaches the turns of the choke coil proper4 ,in construction1 the choke coil is made in but one size having a current carrying capacity of #bjj amperes and is suitable for a voltage of #b1jjj to #bb1jjj4 ,for higher voltages than #bb1jjj1 several choke coils are connected in series4 ,one coil is used for each #bb1jjj volts or fraction thereof1 of the pressure between the wires of the circuit4 ,application3 ,this type of choke coil may be used for alternating current service for the entire range from #bb1jjj to #aaj1jjj volts4 ,it may be used on transformers1 but is not recommended for the protection of generators4 ,part of the functions of the choke coil are performed by the end turns of a transformer and extra insulation is invariably installed in all power transformers built in recent years4 ,the choice of choke coils must be influenced by the condition of insulation in the transformers as well as by the cost1 pressure regulation1 and nature of the lightning protection required4 ,ques4 ,what are the primary objects of a choke coil8 ,ans4 ,to hold back the lighting disturbance from the circuit apparatus during discharge1 and to lower the frequency of the oscillation so that whatever charge gets through the choke coil will be of a frequency too low to cause serious pressure drop around the first turns of the end coil in either alternator or transformer4 ,illustration3 ,,figs4 #b1djg to #b1dji4--;,general ,electric choke coils4 ,fig4 #b1djg1 hour glass choke coil1 #de1jjj volts2 fig4 #b1djh1 low voltage choke coil1 #f1fjj volts2 fig4 #b1dji1 low voltage choke coil1 #d1fjj volts4 ,if there be no arrester1 the choke coil cannot perform the first function1 accordingly a choke coil is best considered as an auxiliary to an arrester4 ,ques4 ,what is the principal electrical condition to be avoided with a choke coil8 ,ans4 ,resonance4 ,the coil should be so arranged that if continual surges be set up in the circuit1 a resonant voltage due to the presence of the choke coil cannot build up at the transformer or generator terminals4 ,this factor is a menace to the insulation4 ,another way of stating the condition is as follows3 ,so arrange the choke coil as not to prevent surges1 originating in a transformer1 passing to the arrester4 ,ques4 ,what is another electrical condition to be avoided and why8 ,ans4 ,internal static capacity between adjacent turns ,illustration3 ,,fig4 #b1daj4--,westinghouse choke coil for high pressure transmission circuits1 #b1bjj to #be1jjj volts4 ,choke coils of this type are wound without iron cores on circular or elliptical center blocks4 ,they have a large number of layers and few turns per layer 7except those made for small currents1 they usually have one turn per layer71 which give the best condition for insulating and cooling4 ,they are air cooled1 heavily insulated and have a line lead at the top1 as shown4 ,choke coils are designed to prevent the short circuits sometimes caused by the local concentration of pressure such as may be produced by a lightning discharge4 ,they limit1 to some extent1 an abnormal rise of pressure on the apparatus by delaying the advance of a static wave from the line and thus give the arrester more time to act4 ,the disturbance caused by a lightning flash passes along the line in the form of a surge or tidal wave4 ,if this wave pass a choke coil1 it is flattened out1 and if the coil be of sufficient power1 becomes practically harmless4 ,it is evident1 however1 that the choke coil receives the full force of the wave1 and that1 consequently1 it must be heavily insulated2 moreover1 the choke coil must not overheat under load1 nor introduce into the circuit excessive inductive resistance4 of the choke coil1 because this lowers the effectiveness of the coil4 ,ques4 ,what is the object of making choke coils in the form of an hour glass8 ,ans4 ,to prevent sagging between the supports4 ,illustration3 ,,fig4 #b1daa4--,westinghouse air cooled choke coil particularly suitable for outdoor use4 ,the method of mounting is such that insulation for any desired voltage is readily obtained with the same type of porcelain1 and mounting in any position is possible4 ,the coil is a helix of aluminum rod1 about #ae inches in diameter and containing about #cj turns4 ,bracing clamps are provided to give mechanical strength to the helix1 and the rod used is of sufficient diameter to carry #bjj amperes4 ,the coil is supported on two insulating columns made up of porcelain insulators1 which1 except for the end pieces1 are interchangeable4 ,the number of insulators used in the columns depends on the voltage of the circuit in which the coil is to be used4 ,the apparatus can be mounted in any position convenient for the wiring1 on floor1 wall1 or ceiling4 ,it is intended principally for the protection of transformers4 ,where greater reactance than is afforded by a single coil is desired on the higher voltage circuits1 it is recommended that two or more coils be connected in series1 one coil being used for each #bb1jjj line voltage4 ,this coil should not be used for generators4 ,the insulating columns are supported on substantial cast iron blocks on wooden bases4 ,ques4 ,how are choke coils cooled8 ,ans4 ,by air1 or by oil4 ,ques4 ,for what service are oil cooled choke coils used8 ,ans4 ,on circuits of pressures above #be1jjj volts1 choke coils immersed in oil1 as are transformer coils1 have advantages in that the coil is amply insulated not only from the ground but against side flash1 and that copper of comparatively small section may be used without undue heating4 ,illustration3 ,,fig4 #b1dab4--,westinghouse air cooled choke coil1 for voltages of from #b1bjj to #aaj1jjj4 ,in construction1 the coils are made of aluminum rod wound into a helix of about #ae inches in diameter and having #bj turns4 ,the helix is supported on two insulators4 ,for mechanical reasons it is necessary to have the aluminum rod of sufficient size to secure rigidity1 consequently every coil has a capacity of #bjj amperes and may be used on any circuit up to that capacity4 ,the coils are insulated according to the standard practice for disconnecting switches1 the insulators being mounted on wooden pins supported by a wooden base4 ,this apparatus can be mounted in any position4 ,the wiring of a station or sub-station is facilitated because the protection may be placed so as to simply form part of the wiring4 ,the coils are symmetrical so that it is immaterial which end is connected to the line or to the apparatus4 ,static ,interrupters4--,a static interrupter is a combination of a choke coil and a condenser1 the two being mounted together and placed in a tank and oil insulated4 ,it is used on high pressure circuits and its function is to so delay the erroneously called static wave in its entry into the transformer coil1 that a considerable portion of the latter will become charged before the terminal will have reached full pressure4 ,a choke coil alone sufficiently powerful to accomplish this would be too large and costly on very high pressure and would interfere with the operation of the system4 ,ques4 ,how is the condenser and choke coil connected8 ,ans4 ,the condenser is connected between the line and ground behind the choke coil near the apparatus to be protected as shown in fig4 #b1dac4 ,illustration3 ,,fig4 #b1dac4--;,diagram showing connections of static interrupter for protecting a transformer4 ,ques4 ,what is the effect of the condenser8 ,ans4 ,the condenser1 which has a very small electrostatic capacity1 has no appreciable effect upon the normal operation1 but a very powerful effect upon the static wave on account of its extremely high frequency4 ,,chapter ,,lx ,,regulating ,,devices ,regulation of ,alternators4--,practically all the methods employed for regulating the voltage of direct current dynamos and circuits1 are applicable to alternators and alternating current circuits4 ,for example3 in order that they shall automatically maintain a constant or rising voltage with increase of load1 alternators are provided with composite winding similar to the compound winding of direct current dynamos1 but since the alternating current cannot be used directly for exciting the field magnets1 an accessory apparatus is required to rectify it or change it into direct current before it is used for that purpose4 ,it is a fact1 however1 that composite wound alternators do not regulate properly for inductive as well as non-inductive loads4 ,in order to overcome this defect compensated field alternators have been designed which automatically adjust the voltage for all variations of load and lag4 ,these machines have already been described4 ,alternating ,current ,feeder ,regulation4--,with slight modification1 the various methods of feeder regulation employed with direct current1 may be applied to alternating current distribution circuits4 ,for instance1 if a non-inductive resistance be introduced in any electric circuit1 the consequent drop in voltage will be equal to the current multiplied by the resistance4 ,therefore1 feeder regulation by means of rheostats is practically the same in the case of alternating current as in that of direct current4 ,in the case of the former1 however1 the effect of self-induction may also be utilized to produce a drop in voltage4 ,in practice1 this is accomplished by the use of self-induction coils which are commonly known as reactance coils4 ,illustration3 ,,fig4 #b1dad4--;,diagram illustrating the principle of induction voltage regulators4 ,the primary coil ,p1 consisting of many turns of fine wire1 is connected across the main conductors ,c and ,d1 coming from the alternator4 ,the secondary coil ,s1 consisting of a few turns of heavy wire1 is connected in series with the conductor ,d4 ,the laminated iron core ,e1 mounted within the coils1 is capable of being turned into the position shown by the dotted lines4 ,when the core is vertical1 the magnetic lines of force produced in it by the primary coil1 induces a pressure in the secondary coil which aids the voltage2 when turned to the position indicated by the dotted lines1 the direction of the magnetic lines of force are reversed with respect to the secondary coil and an opposing pressure will be produced therein4 ,thus1 by turning the core1 the pressure difference between the line wires ,g and ,h1 can be varied so as to be higher or lower than that of the main conductors ,c and ,d4 ,regulators operating on this principle may be used for theatre dimmers1 as controllers for series lighting1 and also to adjust the voltage or the branches of unbalanced three wire single phase and polyphase systems4 ,application of ,induction ,type ,regulators4--,in supplying lighting systems1 where the load and consequently the pressure drop in the line increases or decreases1 it becomes necessary to raise or lower the voltage of an alternating current1 in order to regulate the voltage delivered at the distant ends of the system4 ,this is usually accomplished by means of alternating current regulators or induction regulators4 ,a device of this kind is essentially a transformer1 the primary of which is excited by being connected directly across the circuit1 while the secondary is in series with the circuit as shown in fig4 #b1dad4 ,by this method the circuit receives the voltage generated in the secondary4 ,illustration3 ,,fig4 #b1dae4--;,diagram of induction regulator raising the voltage #aj4 ,in the diagram an alternator is supplying #ajj amperes at #b1bjj volts4 ,the regulator raises the feeder pressure to #b1dbj volts1 the current being correspondingly reduced to #ia amperes1 the other #i amperes flowing from the alternator through the primary of the regulator1 back to the alternator4 ,illustration3 ,,fig4 #b1daf4--;,diagram of induction regulator lowering the voltage #aj4 ,the diagram shows the regulator lowering the feeder pressure to #a1ihj volts with an increase of the secondary current to #aaa amperes1 the additional #aa amperes flowing from the feeder1 through the primary back to the feeder4 ,ques4 ,name two types of pressure regulator4 ,ans4 ,the induction regulator1 and the variable ratio transformer regulator4 ,ques4 ,of what does an induction regulator consist8 ,ans4 ,it consists of a primary winding or exciting coil1 a secondary winding which carries the entire load current4 ,illustration3 ,,fig4 #b1dag4--,moving element or primary of ,westinghouse motor operated single phase induction regulator4 ,it consists of a core of punchings built up directly on the primary shaft and carrying the primary winding1 which is divided into four coils4 ,the primary coils are machine wound and the layers of the winding are separated from each other by heavy insulating material in addition to the cotton covering of the inductors4 ,the complete coils are insulated and impregnated with insulating compound before being placed in the slots4 ,the coils are held in position by fibre wedges4 ,the primary is wound for the full transmission voltage1 and is connected across the line1 while the secondary is connected in series with the line4 ,ques4 ,what is its principle of operation8 ,ans4 ,when the primary coil is turned to various positions the magnetic flux sent through the secondary coil varies in value1 thereby causing corresponding variation in the secondary voltage1 the character of which depends upon the value and direction of the flux4 ,ques4 ,what is the effect of turning the secondary coil to a position at right angles with the primary coil8 ,ans4 ,the primary will not induce any voltage in the secondary1 and accordingly it has no effect on the feeder voltage4 ,ques4 ,what is this position called8 ,ans4 ,the neutral position4 ,ques4 ,what are the effects of revolving the primary coil from the neutral position first in one direction then in the other8 ,ans4 ,turning the primary in one direction increases the voltage induced in the secondary1 thus increasing the feeder voltage like the action of a booster on a direct current circuit while turning the primary in the opposite direction from the neutral position1 correspondingly decreases the feeder voltage4 ,illustration3 ,,fig4 #b1dah4--,moving element or primary of ,westinghouse motor operated polyphase induction regulator4 ,ques4 ,it was stated that for neutral position the primary had no effect on the secondary2 does the secondary have any effect on the feeder voltage8 ,ans4 ,the secondary tends to create a magnetic field of its own self-induction1 and has the effect of a choke coil4 ,ques4 ,how is this tendency overcome8 ,ans4 ,the primary is provided with a short circuited winding1 placed at right angles to the exciting winding4 ,in the neutral position of the regulator1 this short circuited winding acts like the short circuited secondary of a series transformer1 thus preventing a choking effect in the secondary of the regulator4 ,ques4 ,what would be the effect if the short circuited winding were not employed8 ,illustration3 ,,fig4 #b1dai4--,top end of stationary element or secondary of ,westinghouse polyphase induction regulator2 view showing leads4 ,the secondary is built up in a short skeleton frame with brackets for the rotor bearings bolted to the frame and the top cover bolted to the top brackets4 ,in assembling the secondary1 the punchings are stacked loosely in the skeleton frame and an expanding building mandrel placed inside the punchings and expanded1 thereby truing up the latter before they are finally compressed and the end plates keyed in position4 ,then1 prior to removing the mandrel a finishing cut is taken on the surface of the frame to which the bearing brackets are attached1 and as the top cover and brackets are also accurately machined the alignment of the primary with the secondary is almost perfect1 thus reducing to a minimum the tendency to develop vibration and noise4 ,ans4 ,the voltage required to face the full load current through the secondary would increase as the primary is turned away from either the position of maximum or minimum regulation1 reaching its highest value at the neutral position4 ,the short circuited winding so cuts down this voltage of self-induction that the voltage necessary to force the full load current through the secondary when the regulator is in the neutral position is very little more than that necessary to overcome the ohmic resistance of the secondary4 ,ques4 ,what effect is noticeable in the operation of a single phase induction regulator8 ,ans4 ,it has a tendency to vibrate similar to that of a single phase magnet or transformer4 ,illustration3 ,,fig4 #b1dbj4--;,bottom end of stationary element or secondary of ,westinghouse polyphase induction regulator4 ,ques4 ,why8 ,ans4 ,it is due to the action of the magnetizing field varying in strength from zero to maximum value with each alteration of the exciting current1 thus causing a pulsating force to act across the air gap1 which tends to cause vibration when the moving part is not in perfect alignment4 ,ques4 ,explain the effect produced by bad alignment8 ,ans4 ,if the bearings of the primary be not in perfect alignment with the bore of the secondary1 thereby making the air gap on one side smaller than that on the other1 the crowding over of the flux to the smaller air gap will cause an intermittent pull in that direction1 which will develop vibration unless the primary bearings are tight and the shaft sufficiently stiff to withstand the pull4 ,ques4 ,upon what does the regulator capacity for any given service depend8 ,illustration3 ,,fig4 #b1dba4--,westinghouse two kw41 hand operated1 air cooled induction regulator for testing purposes4 ,ans4 ,it depends upon the range of regulation required and the total load on the feeder4 ,ques4 ,how is the capacity stated8 ,ans4 ,in percentage of the full load of the feeder4 ,for instance1 on a #ajj kilowatt circuit1 a #aj kw4 regulator will give #aj per cent4 regulation1 and a #e kw4 regulator1 #e per cent4 regulation4 ,polyphase ,induction ,regulators4--,the polyphase induction regulator is similar to the single phase regulator except that both the primary and secondary elements are wound with as many sets of coil as there are phases in the circuit4 ,in construction these windings are distributed throughout the complete circumference of the stationary and moving elements and closely resemble the windings of an induction motor4 ,illustration3 ,,fig4 #b1dbb4--,westinghouse polyphase motor operated induction regulator showing operating mechanism4 ,the primary shaft is turned by means of a bronze worm wheel engaging a forged steel worm1 provided with a ball bearing end thrust4 ,this worm gear is housed in a separate casting bolted to the cover4 ,the casting is made separate in order to permit close adjustment between the worm wheel and the worm to aid in counteracting the tendency to vibration4 ,finished surfaces on the worm gear casting are provided for mounting the motor and the brake4 ,on the automatic regulator1 the worm shaft is connected to the motor through a spur gear and pinion1 which constitutes a compact driving device having very little friction4 ,provision is made for either alternating current or direct current motor drive4 ,when a motor driven regulator is operated by hand1 the brake must be held in the release position1 otherwise it will be impossible to operate the regulator4 ,in the hand operated regulator the spur gear is replaced by a hand wheel and the regulator is driven directly from the worm shaft4 ,polyphase regulators have but little tendency to vibrate because the field across the air gap is the resultant of two or more single phase fields and is of a constant value at all times4 ,this field rotates at a rate depending upon the number of poles and the frequency of the circuit4 ,this produces a mechanical pull of constant value which rotates with the magnetic field varying its position from instant to instant4 ,it is evident that this pull is of an entirely different character from that produced by the single phase field and that there is no tendency to set up the vibration that the mechanical pull of the single phase regulator tends to establish4 ,illustration3 ,,fig4 #b1dbc4--;,general ,electric adjustable compensation shunt4 ,it is used as the compensating shunt for direct current voltage regulators4 ,in operation1 the shunt may be adjusted so as to compensate for any desired line drop up to #ae per cent4 ,it is preferably placed in the principal lighting feeder but may be connected to the bus bars so that it will take the total current4 ,the latter method is sometimes undesirable1 as large fluctuating power loads on separate feeders might disturb the regulation of the lighting feeders4 ,adjustment is made by sliding the movable contact shown at the center of the shunt4 ,this contact may be clamped at any desired point and it determines the pressure across the compensating winding of the regulator's control magnet4 ,where pressure wires are run back to the central station from the center of distribution1 they may be connected directly to the pressure winding of the main control magnet1 and it is unnecessary to use the compensating shunt4 ,there is1 however1 considerable torque developed1 and the device for revolving the moving element must be liberally designed so as to withstand the excess torque caused by temporary overloads or short circuits4 ,ques4 ,in what respects do polyphase induction regulators differ in principle from single phase regulators8 ,ans4 ,the induced voltage in the secondary has a constant value1 and the regulation is effected by varying the phase relation between the line voltage and the regulator voltage4 ,ques4 ,how is the primary wound8 ,ans4 ,it is wound with as many separate windings as there are phases in the circuit1 and these primary or shunt windings are connected to the corresponding phases of the feeder4 ,illustration3 ,,fig4 #b1dbd4--;,general ,electric direct current 7form ,s7 voltage regulator4 ,it consists of a main control magnet1 relay1 condenser and reversing switch1 as shown in the diagram fig4 #b1dbh4 ,this regulator cannot be used for compensation of line drop as the current coil is omitted2 it is not a switchboard instrument1 but is designed for inexpensive installations such as for regulating the voltage of motor generator sets when the current is taken from a trolley line or some other fluctuating source4 ,the regulating outfit comprises1 besides the regulator1 one or more condenser sections according to field discharge1 set of iron brackets when regulator cannot be mounted on front of switchboard1 one compensating shunt1 when it is desired to compensate for line drop4 ,field rheostats having sufficient resistance to reduce the voltage the proper amount must be used with voltage regulator installations4 ,to prevent undue decay at the relay contacts1 allow one section for each #ae kw4 capacity of dynamo with laminated poles1 and one for each #bb kw4 capacity with solid steel poles4 ,ques4 ,what kind of magnetizing flux is produced by the primary windings8 ,ans4 ,a practically constant flux which varies in direction4 ,ques4 ,how is the secondary wound8 ,ans4 ,there is a separate winding for each phase4 ,ques4 ,why is the voltage induced in the secondary constant8 ,ans4 ,because of the constant magnetizing flux4 ,ques4 ,how is the line voltage varied by a polyphase regulator8 ,ans4 ,when the regulator is in the position of maximum boost1 the line ,,ab1 fig4 #b1dbe represents the normal busbar voltage1 ,,bc the regulator voltage1 and ,,ac the resultant feeder voltage4 ,when the regulator voltage is displaced #ahj degrees from this position1 the regulator is in the position to deliver minimum voltage to the feeder1 the regulator voltage being then represented by ,,bd1 and the resultant feeder voltage by ,,ad4 ,when the regulator voltage is displaced angularly in the direction ,,bf1 so that the resultant feeder voltage ,,af becomes equal to the normal busbar voltage ,,ab1 the regulator is in the neutral position4 ,intermediate resultant voltages for compensating the voltage variations in the feeders may be obtained by rotating the moving element or primary in either direction from the neutral position4 ,for example1 by rotating the primary through the angle ,,fbe1 the resultant voltage may be made equal to ,,ae or ,,aj1 thereby increasing the feeder voltage by an amount ,,bj2 or by rotating it in the opposite direction through the angle ,,fbg1 the feeder voltage may be reduced by an amount ,,bh4 ,illustration3 ,,fig4 #b1dbe4--;,diagram illustrating operation of polyphase induction regulator4 ,ques4 ,how are induction regulators operated8 ,ans4 ,by hand or automatically4 ,ques4 ,how is automatic operation secured8 ,ans4 ,by means of a small motor1 controlled by voltage regulating relays4 ,ques4 ,how is the control apparatus arranged8 ,ans4 ,two relays are employed with each regulator1 a primary relay connected to the feeder circuit and operating under changes of voltage therein1 and a secondary relay connected between the primary relay and the motor1 and operated by the contacts of the former1 for starting1 stopping and reversing the motor in accordance with changes in the feeder voltage1 thereby causing the regulator to maintain that voltage at its predetermined normal value4 ,illustration3 ,,fig4 #b1dbf4--,westinghouse voltage regulating primary relay2 view of mechanism with case removed4 ,this relay is practically a voltmeter arranged for making and breaking contacts with fluctuations of voltage4 ,as shown in the figure1 it consists essentially of a solenoid and a balance beam carrying two movable contact points on one end and attached to the solenoid core at the other4 ,the oscillation of the core causes the contact carrying end of the beam to move between two stationary contact points connected to the auxiliary or secondary relay circuit4 ,the stationary contact points are fitted with adjusting screws for either increasing or decreasing the distance between them1 to the amount of change in the voltage required for making or breaking contact2 in other words1 for varying the sensitiveness of the relay4 ,means for varying the normal voltage which it is desired to maintain are provided in the spring attached to the balance beam and controlled by the micrometer adjusting screw4 ,increasing the tension of the spring results in lowering the normal voltage position4 ,the relay is wound for a normal voltage of #aaj volts1 and has a range of adjustment from #ij to #acj volts4 ,the total energy required for its operation is about #ej watts at normal voltage4 ,voltage transformers having at least #ej watts capacity are1 therefore1 required4 ,the parts are3 ,a1 solenoid2 ,b1 solenoid core2 ,c1 end of balance beam2 ,d1 pivots1 bearings2 ,e1 movable contact arm2 ,f1 upper stationary contact point2 ,g1 lower stationary contact point2 ,h1 adjusting screw2 ,k1 adjusting spring2 ,l1 feeder binding posts2 ,m1 auxiliary circuit and secondary relay binding posts4 ,illustration3 ,,fig4 #b1dbg4--,westinghouse voltage regulating secondary relay2 view showing relay removed from oil tank4 ,the secondary relay is practically a motor starting switch of the double pole double throw type1 electrically operated through the contacts of the primary relay4 ,it is provided with contact points of one-half inch rod4 ,the relay is suitably connected for starting1 stopping and reversing the motor and for properly operating the motor brake4 ,the parts are3 ,a1 solenoid2 ,b1 laminated field2 ,c1 movable contact arm2 ,d1 stationary contact arms2 ,e1 removable brass contact points2 ,f1 terminal block2 ,g1 terminals4 ,ques4 ,why are two relays used8 ,ans4 ,for the reason that a primary relay1 of sufficient accuracy and freedom from errors due to temperature and frequency variations1 could not be made sufficiently powerful to carry the relatively large current required for operating the motor4 ,ques4 ,what names are given to the relays8 ,ans4 ,primary and secondary4 ,ques4 ,what difficulties were encountered in the operation of relays8 ,illustration3 ,,fig4 #b1dbh4--;,diagram of connections of ,general ,electric direct current 7form ,s7 voltage regulator1 for #abe1 #bej1 and #eej volts4 ,the range of voltage is given in the following table3 ----------------------------------- ,regulator,range of voltage ------------------------ #af #ag #ah #ai #bj ----------------------------------- #abe #aje #aaj #aae #abj #abe #bej #baj #bbj #bcj #bdj #bej #eej #eej ----------------------------------- ,ans4 ,vibration or chattering at the contacts of both relays and tendency of the movable contact arm of the primary relay to hug closer to one of the stationary contact points than to the other1 thereby operating too often4 ,ques4 ,what causes vibration or chattering at the contacts8 ,ans4 ,this is due to the voltage frequently approximating the value required for closing a contact1 thereby causing the contact points to barely touch and make several poor contacts in succession4 ,ques4 ,what objectionable action is produced by vibration at the contacts8 ,ans4 ,arcing1 burning and pitting of the contacts1 even when alloys of the rarer metals are used1 such as those of the platinum group1 having extreme hardness and high melting points4 ,illustration3 ,,fig4 #b1dbi4--;,diagram of connections of automatic induction regulator and auxiliary apparatus on single phase circuit4 ,ques4 ,what effect is produced by poor contact of the primary relay8 ,ans4 ,it causes chattering in the secondary relay2 which burns out and wears away its contact points1 increasing the heating of the motor1 creating objectionable noise and entailing wear and tear on the whole outfit4 ,ques4 ,why does the movable contact arm of the primary relay tend to remain nearer one of the stationary contact points than the other8 ,ans4 ,this is due to the tendency of the relay to open the contact whenever the voltage equals that at which the contact closes4 ,illustration3 ,,fig4 #b1dcj4--;,diagram of connections of automatic induction regulator and accessory apparatus on three phase feeder circuit4 ,ques4 ,what provision is made in the primary relay to prevent vibration or chattering8 ,ans4 ,two auxiliary windings are provided3 one in series with each of the stationary contact points and so arranged as to assist in making the contact by increasing the pressure on the contact points at the instant of closure4 ,the best effect of the compounding action of the auxiliary coils is obtainable when arranged for per cent4 of the torque of the main coil4 ,illustration3 ,,fig4 #b1dca4--,westinghouse drum type variable transformer voltage regulator4 ,it consists of a drum and finger type switch4 ,a preventive resistance is used between the different contacts1 making it unnecessary to open the circuit when moving from one tap of the regulating transformer to the next tap4 ,a spring actuated1 quick moving1 central stopping mechanism is used to prevent burning the resistances4 ,the regulator is arranged to give #dj points of regulation4 ,in many cases this large number of points is not absolutely necessary1 but it is desirable to use them because the voltage per step is thus reduced to a small value1 and a corresponding increase in the life of the contacts results because of the reduced sparking at the lower voltage4 ,two drums are employed4 ,the first drum has ten contacts and a corresponding number of fingers1 the latter being mounted upon an insulated bar4 ,these fingers are connected to the floating coils of the regulating transformer1 and as the drum is rotated1 the finger connected to the line is brought into contact successively with each of the ten taps4 ,the second drum is of similar construction and consists of a changing and reversing switch4 ,it connects the two floating coils to the various taps on the main secondary coil of the regulating transformer at the proper time1 and also reverses the transformer so that the total winding can be used for either raising or lowering the voltage4 ,all the points of regulation are obtained by a continuous motion of the handle1 the various connections produced in the manner are shown in the diagram1 fig4 #b1dcc4 ,the top and base of the regulator are made of cast iron and the top is supported by steel bars1 two of which are insulated1 and used to support the metallic bases finger to which the cable leads are attached4 ,the drums consist of metal castings mounted upon insulated shafts4 ,the first drum1 which is the only one upon which arcing can take place1 is provided with removable copper contact tips4 ,the main castings are made of aluminum to secure low inertia of the drum4 ,a sheet iron cover is used to enclose the regulator1 and the leads are brought out through the bottom of the controller4 ,a non-inductive resistance placed in parallel with each coil of the secondary relay1 takes current approximately in phase with the current in the main coil of the primary relay1 and of proper strength to make the number of ampere turns in the auxiliary coil three-fourths per cent4 of the number in the main coil4 ,the resistances have the additional effect of absorbing the discharge from the main coils of the secondary relay when the contacts are broken1 thereby obviating sparking at the primary contact points4 ,illustration3 ,,fig4 #b1dcb4--;,diagram showing connections of the ,stillwell regulator4 ,illustration3 ,,fig4 #b1dcc4--;,diagram showing position of the floating coil on different steps of ,westinghouse drum type variable ratio transformer regulator4 ,the upper half of the diagram shows the connections of the various coils for each position of the regulator handle4 ,this arrangement applies to a regulator used in connection with an independent regulating transformer4 ,when regulators are used in connection with large power transformers1 the regulating transformer can be omitted and auxiliary coils can be placed on the main transformer to provide the necessary taps for regulating purposes4 ,the lower half of the diagram shows the connections used when auxiliary coils are added to a large transformer4 ,the diagram shows connections for a single phase regulator4 ,where polyphase regulators are required1 the connections consist essentially of two sets of single phase connection1 and the controller is extended in length so as to contain double sets of drum and contact4 ,variable ,ratio ,transformer ,voltage ,regulators4--,the principle of operation of this class of regulator is virtually the same as that of the induction type regulator2 that is to say1 both consist of regulating transformers1 but in the variable ratio method the primary or series coil is divided into a number of sections which may be successively cut in or out of the circuit to be regulated1 instead of varying the flux through the entire coil1 as in the induction type4 ,there are two distinct mechanical forms of variable ratio regulator3 #a4 ,drum type2 #b4 ,dial type4 ,drum ,type ,regulators4--,this form of variable ratio transformer consists essentially of a drum and finger type switch1 similar to a railway controller4 ,there are many contacts1 giving a large number of points of regulation1 obtained by the use of changing switches and floating coils4 ,the floating coil is a part of the secondary winding of the regulating transformer which is insulated from the main portion of the winding1 and is sub-divided by taps into a number of equal sections4 ,the sub-divisions of the main secondary winding are much larger1 each one being equivalent to the whole of the floating coil4 ,illustration3 ,,fig4 #b1dcd4--;,diagram of connections of ,general ,electric high voltage cut out relay 7form ,a7 for voltage regulators4 ,its use in connection with the regulator protects the system from any sudden rise in voltage due to some accident to the regulator which might cause the relay contacts to stick1 thus producing full field on the exciter4 ,in construction1 the control magnet is connected in series with the alternating current control magnet on the regulator and the contacts are connected in series with the rheostat shunt circuit4 ,then1 should the voltage rise beyond a certain value1 predetermined by the setting of the thumb screw supporting the plunger of the control magnet1 the contacts of the relay are tripped open which1 by inserting all the resistance in the exciter field1 reduces the exciter voltage which in turn reduces the alternating current voltage4 ,this relay has to be reset by hand4 ,ques4 ,describe the operation of a drum regulator4 ,ans4 ,the floating coil and main windings are first connected in series with each other and with the line to be regulated4 ,the floating coil is then cut out of the circuit step by step4 ,when entirely cut out it is transferred to the next lower tap on the main winding1 after which it is again cut out step by step and then transferred again4 ,by continuing this process a large number of steps are provided with but comparatively few actual taps on the transformer4 ,ques4 ,how many floating coils are used and why8 ,ans4 ,two floating coils are included in each regulator so that one can be transferred while the other is supplying the current to the line4 ,dial ,type ,regulators4--,this form of variable ratio transformer regulator consists of a regulating transformer and a dial type switch as shown in the accompanying illustrations4 ,the regulating transformer is similar to a standard transformer except that the secondary winding is provided with a number of taps leading to the contact of the dial switch as shown in the diagram fig4 #b1dcg4 ,illustration3 ,,fig4 #b1dce4--;,dial of ,westinghouse dial type variable ratio voltage regulator4 ,the dial consists of a marble slab1 upon which the contacts are mounted in a circle as shown4 ,the contact arm is arranged to move from contact to contact4 ,the alternate small contacts are dummies1 serving to prevent the contact arm springing down between contacts when moving from one to another4 ,the panel contains a changing switch which makes it possible to double the range of a regulator1 since the transformer connections can be changed to both raise and lower to an extent equal to the full range of the transformer4 ,the total range in voltage from a certain per cent4 below to a certain per cent4 above the line voltage can be obtained in a number of steps equal to twice the number of divisions into which the secondary winding of the transformer is divided4 ,ques4 ,what modification is made to adapt dial regulators for heavy current8 ,ans4 ,a dial with a series transformer1 and a shunt or auto-transformer are employed as shown in fig4 #b1dcf4 ,ques4 ,why is such modification desirable8 ,ans4 ,because1 the additional cost of a series transformer is small in comparison with the cost of building a dial with a large current carrying capacity1 and the cost of bringing out a number of heavy leads from a small transformer4 ,illustration3 ,,fig4 #b1dcf4--;,diagram of connections for ,westinghouse #aa point dial1 series transformer and auto-transformer4 ,the auto-transformer has a number of taps connected across the line1 the series transformer is placed in series with one side of the line1 and connected to a dial1 as shown4 ,ques4 ,how are dial regulators modified for high voltage8 ,ans4 ,standard dials may be used with series and shunt transformers similar to the method used for heavy current circuits4 ,ques4 ,describe the connections4 ,ans4 ,the primary of the shunt transformer is connected across the line and the secondary has a number of taps which are connected to contacts on the dial4 ,the primary of the series transformer is connected in series with the line and two leads from the secondary winding are connected to the dial4 ,the connections are similar to those shown in fig4 #b1dcg1 except that shunt transformers are used instead of auto-transformers4 ,illustration3 ,,fig4 #b1dcg4--;,diagram of connections for ,westinghouse dial type variable ratio voltage transformer4 ,in construction the secondary winding of the transformer is divided into #aj1 #ad1 or #bj parts giving #aa1 #ae1 or #ba taps which are brought out from the secondary winding and connected to the various points of the dial4 ,the diagram shows connections for an #aa point dial and regulating transformer4 ,since there is a difference of voltage between adjacent contacts1 the contact arm must not touch the contact toward which it is moving until after it has left the contact upon which it was resting4 ,moreover1 it is undesirable to open the circuit each time in moving from one contact to the next4 ,these conflicting requirements are met by the use of arcing tips which are placed on the contact arm so that a very close adjustment can be obtained1 and so arranged that the contacts are not short circuited but always have a gap of from one-sixteenth to one-eighth inch in the circuit during the time of changing from one contact to the next4 ,the air gaps form a preventive resistance4 ,a quick moving mechanism is used to accelerate the movement from one contact to the next1 a very quick movement being necessary to avoid undue arcing4 ,the capacity of the regulator is #bjj amperes at #b1bjj volts1 being arranged to give a maximum increase in voltage of #djj volts4 ,the maximum pressure between contacts is #be volts4 ,illustration3 ,,fig4 #b1dch4--;,diagram of connections of ,general ,electric pole type regulator4 ,the operation of the regulator is obtained by means of a small single phase motor which is in continuous operation1 and which by mechanical means may be connected to the regulator shaft4 ,the control of the mechanism is obtained by means of a voltage relay4 ,the operating motor1 which is of the drawn shell type1 is provided with a starting clutch and will consequently start up with full load4 ,under actual operating conditions it will1 of course1 be comparatively seldom that the motor will be called upon to start up4 ,a non-inductive resistance1 made up from standard units1 is connected in series with the relay winding and several taps are provided1 so that the relay can be adjusted for any voltage from #aj per cent4 below normal4 ,in order to readily dissipate the heat developed in the resistance1 it has been mounted in a pocket on the back of the tank1 openings being provided for natural air ventilation4 ,the relay plunger is hinged to one end of a balance arm1 which arm is provided with two trip pins to control the mechanism4 ,an adjustable helical spring is attached to the other end of the arm to assist the magnetic pull of the coil in balancing the plunger and also for adjustment4 ,the relay is not provided with series winding for line drop compensation1 but it may be used with a standard line drop compensator1 which then has to be installed outside of the regulator4 ,the voltage relay must be connected to the feeder side of the regulator1 the necessary low voltage to be obtained from a distributing transformer1 or if this should not be available in the immediate vicinity1 a #bjj watt step down transformer will be satisfactory4 ,the motor is designed to operate in parallel with the relay1 the normal connections being as shown4 ,the speed of the motor and the ratio of the gearing is such that it requires about #ij seconds to operate the regulator from limit to limit1 but1 as this regulator is not intended to take care of sudden voltage fluctuations1 the comparatively long time of operation will not be objectionable4 ,illustration3 ,,figs4 #b1dci to #b1ddc4--;,general ,electric pole type regulator removed from tank4 ,it consists essentially of a primary and secondary coil1 operating motor1 and voltage relay mechanism4 ,the regulator and mechanism is suspended in a cast iron tank1 the lower part1 containing the regulator core and coils1 being filled with oil4 ,the leads for the regulator are brought out at the upper part of the tank4 ,the outgoing leads are compressed into bushings and connected to the leads of the regulator by means of terminals1 the arrangements being such that the regulator with mechanism can be removed from the tank without difficulty4 ,besides the cover1 the tank is also provided with a hinged door on the front side so as to give access to the mechanism4 ,the door is provided with a gasket and the construction is practically rain and dust proof4 ,however as there is always danger of the door not being clamped down perfectly1 thus making it possible for water to enter the tank1 a pocket has been provided inside the tank and underneath the door to collect the water4 ,capacity up to #b4c kw41 to control #b1cjj volts1 #fj cycle1 #aj ampere feeders1 and for a voltage range of #aj per cent4 above or below normal1 the operating motor and relay being designed for #aaj or #bbj volts4 ,no provision is made for line drop compensation1 although this can be obtained by installing a current transformer and a line drop compensator externally to the regulator4 ,it will be seen that the circuit comprising the dial1 the secondary of the shunt1 transformer and the secondary of the series transformer form a circuit which is not electrically connected to the main circuit4 ,it can therefore be grounded without disturbing the main circuit as a safeguard to render it impossible for the pressure of the dial to be higher above the ground than the secondary voltage of the shunt transformer4 ,illustration3 ,,figs4 #b1ddd to #b1ddf4--,sectional views of ,general ,electric pole type regulator winding and core4 ,the secondary core has only two slots containing a single coil1 while the rotor or primary core has four slots4 ,two of these slots are occupied by a single primary coil1 and the two circular slots in quadrature thereto contain the compensating or short circuit winding4 ,this winding also serves to hold the primary punchings together1 and it consists of two copper rods riveted to the two cast brass flanges4 ,the secondary coil is form wound1 while the primary coil is wound directly on the core4 ,the rotor flanges1 both top and bottom1 are provided with discs which are turned in alignment with the punchings1 and these discs bear against the top and bottom flanges between which the secondary punchings are clamped4 ,these secondary flanges are also turned in alignment with the secondary punchings1 so that an even air gap between the primary and the secondary is assured4 ,the secondary coil is wound with an opening in the upper horizontal part which affords passage for the operating shaft of the rotor4 ,a bearing for this shaft is provided in the table which supports the mechanism and from which the regulator is suspended4 ,flexible leads are brought out from the rotor and twisted around the shaft as in standard regulator practice4 ,the regulator being two pole1 the rotor is turned through an angle of #ahj deg4 to obtain the full range of the regulator4 ,small ,feeder ,voltage ,regulators4--,in some generating stations the voltage is maintained constant at the busbars and the line drop compensated by automatically operated regulators connected in the main feeders4 ,it is possible in this way to obtain constant voltage at all loads at the various distribution centers1 that is1 at those points on the feeders where the lines of the majority of consumers are connected as shown in fig4 #b1ddg4 ,illustration3 ,,figs4 #b1ddg and #b1ddh4--,systems of distribution illustrating use of small feeder or pole type voltage regulators4 ,it is evident1 however1 that1 while the voltage at the center of distribution can be maintained constant1 no account can be taken of the drop in the lines between this center and the consumers4 ,this drop is generally negligible1 except in some particularly long lines1 as1 for example1 consumer ,b in fig4 #b1ddg4 ,in order to obtain perfect regulation at ,b1 it would be necessary to install a separate regulator in that line1 this regulator to be installed either at the center ,c or preferably at ,b4 ,in a great many cases the power distribution is not as ideal as indicated in fig4 #b1ddg1 but rather as shown in fig4 #b1ddh1 that is1 the consumers are connected all along the feeder4 ,in this case there is no definite center of distribution1 and the automatic regulator installed in the station can be adjusted to give only approximately constant voltage at an imaginary center of distribution ,c2 that is1 the voltage cannot be held constant at any definite point during changes of load distribution4 ,illustration3 ,,fig4 #b1ddi4--;,general ,electric pole type regulator in service2 its construction is shown in fig4 #b1dej4 ,the majority of the consumers may1 however1 obtain sufficiently good voltage while a few may have reason for criticism4 ,to overcome this difficulty it is necessary either to increase the copper in the feeder or else to install small automatic regulators4 ,there are also cases where a small amount of power is transmitted a long distance through a feeder direct from the station4 ,the amount of copper required to reduce the line drop is usually too great to be considered and the cost of the ordinary automatic regulator is also comparatively high4 ,in such cases small pole type regulators as shown in fig4 #b1ddi are desirable4 ,ques4 ,describe the operation of the regulator mechanism shown in fig4 #b1dej4 ,ans4 ,assuming the voltage to be normal1 the balance arm of the relay will be held horizontal1 the trips ,f will not engage with the triggers ,e1 and no movement is therefore transmitted to the ratchet wheel ,c4 ,if the voltage drops below normal1 the left hand trip will descend until it finally gets in the way of the left hand trigger just before it reaches the limit of its counterclockwise travel4 ,this trigger will therefore release the left pawl ,d1 which will engage with the ratchet wheel and will consequently turn it clockwise until the rocker arm reaches its right hand limit4 ,before the rocker arm reaches the left hand limit1 the released pawl must be locked by its trigger1 so that if the voltage has reached its normal value1 further movement of the ratchet wheel will not take place1 whereas if the voltage be still too low1 the trigger will again release the pawl by striking the trip of the relay4 ,illustration3 ,,fig4 #b1dej4--,mechanism of ,general ,electric pole type regulator4 ,the operating motor 7described in fig4 #b1dch7 is direct connected to a worm and gear1 the shaft of which is provided with a bell crank4 ,a rod ,a1 connects the crank with the rocker arm ,b1 which thus may be caused to oscillate over a ratchet wheel ,c4 ,the rocker arm is provided with two pawls ,d1 which can engage with the teeth of the ratchet wheel1 so that this wheel can be rotated one way or the other4 ,the ratchet wheel is mounted on the same shaft as a worm1 which engages with the gear segment carried by the regulator shaft1 so that the movement of the ratchet wheel is directly transmitted to the regulator4 ,besides the two large pawls ,d1 the rocker arm also carries two smaller ones ,e1 called the triggers4 ,these triggers usually hold the pawls locked in such positions as not to engage with the ratchet wheel1 but the pawls will be released when the triggers strike the trips ,f of the relay arm4 ,a limiting device for the movement of the ratchet wheel and the regulator segment is provided1 as shown4 ,this device consists of two cams ,k1 mounted on a common arm1 which can turn on the shaft of the ratchet wheel4 ,normally these cams are not within reach of the pawls1 but through a lever arrangement1 controlled by the regulator segment1 the arm holding the cams may be rotated so that1 if the trigger has been raised1 so as to release the pawl1 the tip of the pawl will bear on the cam of the limiting device1 and before the pawl can engage with the ratchet wheel it has already been locked by its trigger4 ,a further movement of the ratchet wheel in that particular direction is therefore impossible1 while it is free to be moved the other way4 ,a positive stop for the gear segment is also provided4 ,the motor is provided with oil ring bearings1 and the gear for the motor worm runs in oil1 the supporting casting forming a well therefor4 ,illustration3 ,,fig4 #b1dea4--;,diagram of connections of ,general ,electric direct current voltage regulator 7form ,t7 with two dynamos and one exciter4 ,in cases where several shunt or compound wound direct current machines are operating in parallel1 either on two wire or three wire systems1 a good arrangement for voltage regulation and line drop compensation is obtained by using this regulator and a separate exciter4 ,the compensating shunt as well as pressure wires can be used to maintain a constant pressure at the center of distribution4 ,ques4 ,how is this automatic locking of the pawl obtained8 ,ans4 ,by having a lip ,g on the under side of the pawl strike a finger ,h fastened to the bearings in front of the ratchet wheel4 ,the pawl is thus raised just before it reaches the limit of its clockwise travel sufficient to be locked by its trigger4 ,illustration3 ,,fig4 #b1deb4--;,condenser sections and method of assembling same with tripod4 ,the tripod bolts are made of extra length to accommodate the addition of extra condenser sections if necessary4 ,the illustration shows three sections in position4 ,ques4 ,how does the mechanism operate when the voltage rises above normal8 ,ans4 ,as described above1 with the exception that the right hand trip causes a rotation of the regulator in the opposite direction4 ,ques4 ,how is adjustment made for various voltages8 ,ans4 ,taps are provided on the resistance in series with the relay1 and finer adjustment can be obtained by means of the helical spring on the right hand end of the balance arm4 ,in order to adjust the sensitiveness of regulation1 the bearing for the balance arm can be raised or lowered by means of a stud ,j1 fig4 #b1dej1 connecting this bearing with the bearing of the operating shaft1 and the regulator can be made to maintain the voltage within #a per cent4 above or below normal4 ,illustration3 ,,fig4 #b1dec4--,westinghouse unit switch type pressure regulator1 designed for handling heavy currents where a variable ratio transformer type of regulator is desired4 ,the regulator consists of a number of electrically operated switches controlled from a master switch4 ,these switches are arranged to perform practically the same cycle of operation as previously described for the drum type regulators4 ,the transformer windings are divided into sections1 and two floating coils are provided which are connected to various taps on the main auto-transformer4 ,these floating coils have intermediate steps1 and the successive operation of the switches connects the floating coils in proper sequence to the main auto-transformer1 and transfers the line connection from one point of the floating coil to the next4 ,in this way a #bc point regulator with sixteen switches1 and a #ga point regulator with #ba switches may be supplied4 ,the master switches are arranged with an automatic lock to prevent their being operated too rapidly4 ,the magnet switches themselves are so interlocked that the proper sequence of operation is insured4 ,the electrically operated switches may be of the open type1 mounted on a slate or marble switchboard1 when the whole control outfit is placed in a room which is comparatively free from dust or dirt of any kind1 and where there is no danger of employees coming in contact with the switches4 ,the other type of switch is entirely enclosed1 the main contacts being oil immersed4 ,the frames of these switches are grounded and the whole design is arranged to operate under ordinary dirty conditions4 ,all of these switches1 however1 should receive the necessary inspection and attention4 ,the contacts have a long life and are easily renewed4 ,regulators of this type are adapted for metallurgical purposes where the regulation is effected in the primary circuit and the secondary circuit is of very low voltage but large current capacity and is used for supplying power to the furnaces4 ,these regulators have been built in capacities up to #hjj amperes at #c1cjj volts4 ,ques4 ,what provision is made for convenient inspection8 ,ans4 ,a snap switch is provided by means of which the power to the motor and relay can be disconnected4 ,illustration3 ,,figs4 #b1ded and #b1dee4--;,front and rear views of ,general ,electric automatic voltage regulator4 ,the regulator has a direct current control magnet1 an alternating current control magnet1 and a relay4 ,the direct current control magnet is connected to the exciter bus bars4 ,this magnet has a fixed stop core in the bottom and a movable core in the top which is attached to a pivoted lever having at the opposite end a flexible contact pulled downward by four spiral springs4 ,for clearness1 however1 only one spring is shown in the figure4 ,opposite the direct current control magnet is the alternating current control magnet which has a pressure winding connected by means of a pressure transformer to the alternator or bus bars4 ,there is an adjustable compensating winding on the alternating current magnet connected through a current transformer to the principal lighting feeder4 ,the object of this winding is to raise the voltage of the alternating current bus bars as the load increases4 ,the alternating current control magnet has a movable core and a lever and contacts similar to those of the direct current control magnet1 and the two combined produce what is known as the floating main contacts4 ,the relay consists of a ,u shaped magnet core having a differential winding and a pivoted armature controlling the contacts which open and close the shunt circuit across the exciter field rheostat4 ,one of the differential windings of the relay is permanently connected across the exciter bus bars and tends to keep the contacts open2 the other winding is connected to the exciter bus bars through the floating main contacts and when the latter are closed1 neutralizes the effect of the first winding and allows the relay contacts to short circuit the exciter field rheostat4 ,condensers are connected across the relay contacts to prevent severe arcing and possible injury4 ,automatic ,voltage ,regulators for ,alternators4--,the accurate regulation of voltage on any alternating current system is of importance4 ,the desired voltage may be maintained constant at the alternator terminals by rapidly opening and closing a shunt circuit across the exciter field rheostat4 ,illustration3 ,,fig4 #b1def4--;,diagram of connections of ,general ,electric contact making ammeter for operating on alternating current circuits4 ,the instrument is designed to indicate with the aid of a current transformer1 certain values of current in an alternating current system4 ,this value depends upon the setting of the regulating rheostat in parallel with the pressure coil of the ammeter4 ,it is also possible with this instrument1 together with the necessary control apparatus1 to hold certain values of current4 ,by using a different magnet coil this meter may be connected to a shunt instead of a current transformer and used on a direct current system4 ,ques4 ,describe in more detail this method of regulation4 ,ans4 ,the rheostat is first turned in until the exciter voltage is greatly reduced and the regulator circuit is then closed4 ,this short circuits the rheostat through contacts in the regulator and the voltage of the exciter and alternator immediately rise4 ,at a predetermined point1 the regulator contacts are automatically opened and the field current of the exciter must again pass through the rheostat4 ,the resulting reduction in voltage is arrested at once by the closing of the regulator contacts which continue to vibrate in this manner and keep the generator voltage within the desired limits4 ,the connections are shown in fig4 #b1deg4 ,illustration3 ,,fig4 #b1deg4--;,diagram of ,general ,electric automatic voltage regulator connections with alternator and exciter4 ,in operation1 the circuit shunting the exciter field rheostat through the relay contacts is opened by means of a single pole switch at the bottom of the regulator panel and the rheostat turned in until the alternating current voltage is reduced #fe per cent4 below normal4 ,this weakens both of the control magnets and the floating main contacts are closed4 ,this closes the relay circuit and demagnetizes the relay magnet1 releasing the relay armature1 and the spring closes the relay contacts4 ,the single pole switch is then closed and as the exciter field rheostat is short circuited1 the exciter voltage will at once rise and bring up the voltage of the alternator4 ,this will strengthen the alternating current and direct current control magnets1 and at the voltage for which the counterweight has been previously adjusted1 the main contacts will open4 ,the relay magnet will then attract its armature and by opening the shunt circuit at the relay contacts will throw the full resistance into the exciter field circuit tending to lower the exciter and alternator voltage4 ,the main contacts will then be again closed1 the exciter field rheostat short circuited through the relay contacts and the cycle repeated4 ,this operation is continued at a high rate of vibration due to the sensitiveness of the control magnets and maintains a steady exciter voltage4 ,line ,drop ,compensators4--,in order that the actual voltage at a distant point on a distribution system may be read at the station some provision must be made to compensate for the line drop1 that is to say1 for the difference in voltage between the alternator and the center of distribution4 ,in order to do this a device which is known as a line drop compensator is placed in the voltmeter circuit as shown in the diagram1 fig4 #b1deh4 ,ques4 ,what are the essential parts of a line drop compensator8 ,ans4 ,the elements of a line drop compensator are a variable resistance1 and a variable inductance4 ,ques4 ,describe the connections4 ,ans4 ,the secondary of a pressure transformer is connected in series with the compensator inductance and resistance1 and the secondary of a current transformer as shown in the diagram1 fig4 #b1deh4 ,illustration3 ,,fig4 #b1deh--;,diagram showing essential parts and connections for a line drop compensator4 ,the compensator corrects the voltmeter indication at the supply end of a feeder for the ohmic and inductive drop in pressure between that point and the point of consumption1 so that the reading of the station voltmeter corresponds with the actual voltage at the point of consumption1 independent of the power factor and current4 ,it is especially useful for adjusting pressure regulators4 ,ques4 ,how are the inductance and resistance wound8 ,ans4 ,they are wound so that any proportion of the winding of either can be put in or out of the voltmeter circuit4 ,illustration3 ,,fig4 #b1dei4--;,general ,electric line drop compensator4 ,it has two dial switches with many taps to the resistance and reactance in the box so that it can be adjusted to compensate accurately for line losses with loads of varying power factor4 ,dial ,r changes resistance1 and dial ,x1 reactance4 ,illustration3 ,,fig4 #b1dfj4--;,general ,electric line drop compensator4 ,this compensator contains besides resistance and inductance1 a current transformer1 the secondary of the transformer being connected in series with the resistance and inductance2 the primary of the contained current transformer is connected to an external current transformer4 ,the reactance and resistance are both so wound that any proportion of the winding can be cut in or out of the voltmeter circuit4 ,both elements have #ab points of adjustment of one volt each1 giving a total combined drop at maximum setting of about #ag volts4 ,ques4 ,how can the voltmeter indicate the pressure at the center of distribution8 ,ans4 ,if the amount of inductance and resistance be properly adjusted1 there will be produced a local circuit corresponding exactly in all its characteristics to the main circuit4 ,hence1 any change in the main circuit produces a corresponding change in the local circuit1 and causes the voltmeter to always indicate the pressure at the end of the line or center of distribution or at any point for which the adjustment is made4 ,illustration3 ,,fig4 #b1dfa4--,westinghouse line drop compensator4 ,for single phase circuits1 one compensator and one series transformer1 that is the instrument as listed with transformers1 will give correct indications for a single phase circuit4 ,the same voltage transformer serves for both voltmeter and compensator4 ,for balanced two phase circuits one compensator and one transformer connected in one of the phases is sufficient4 ,two single phase compensators should be used for unbalanced two phase circuits4 ,for three phase circuits the compensator should be connected by means of two series transformers4 ,ques4 ,how should the adjustment be made8 ,ans4 ,it is advisable to calculate the ohmic drop for full load and set the resistance arm at the point which will give the required compensation and then adjust the inductance arm until the voltmeter reading corresponds to the voltage at the point on the line selected for normal voltage4 ,illustration3 ,,fig4 #b1dfb4--;,diagram of automatic voltage regulator1 using line drop compensator4 ,for ordinary installations the compensating winding on the alternating current control magnet is connected to a current transformer in the main feeder4 ,a dial switch is provided by which the strength of the alternating current control magnet can be varied and the regulator made to compensate for any desired line drop up to #ae per cent4 according to the line requirements4 ,where the power factor of the load has a wide range of variation1 a special line drop compensator1 such as shown in fig4 #b1dei1 adapted to the regulator would be desirable4 ,the connections are readily understood by the diagram4 ,the number of condenser sections which will prevent undue arcing at the relay contacts depends on the characteristics of the exciter4 ,they may be roughly estimated by allowing one section for each #ae kw4 capacity for exciters with laminated poles1 and one for each #bb kw4 capacity for exciters with solid steel poles4 ,it is necessary though to have one condenser section for each pair of relay contacts1 and at times it becomes necessary to apply a double section for each pair of contacts4 ,in the lower part of the figure the line drop compensation and connections is reproduced in more detail on a larger scale4#b #b ,,note4--,it is desirable1 in any system of distribution1 to read the active voltage at the point of distribution1 by means of the voltmeters in the station4 ,a compensator proper consists of a variable resistance and a variable inductance1 and sometimes a current transformer4 ,in wiring1 the voltmeter1 instead of being connected directly across the secondaries of a pressure transformer1 has inserted in series with it1 portions of the resistance and inductance of the compensator4 ,these are so connected that the drop in pressure across them will be combined with that of the pressure transformer1 so that the voltmeter reading indicates the pressure at the center of distribution or end of the line4 ,starting ,compensators4--,these are used for starting induction motors and consist of inductive windings 7one for each phase7 with a number of taps connecting with switch contacts as shown in fig4 #b1dfc4 ,a starting compensator is similar to a rheostat except that inductive windings are used in place of the resistance grids4 ,illustration3 ,,fig4 #b1dfc4--;,diagram of connections of ,general ,electric two phase starting compensator with no voltage release and fuses4 ,ques4 ,describe the inductive windings4 ,ans4 ,the compensator winding consists of an inductive coil in each phase with each coil placed on a separate leg of a laminated iron core4 ,each coil is provided with several taps so located that a number of sub-voltages may be obtained4 ,ques4 ,are starting compensators necessary for small motors8 ,why8 ,ans4 ,no1 because the full voltage starting current taken1 although equal to several times the load current1 is nevertheless so small1 compared with the capacity of the station alternators or feeders1 that it does not materially affect the regulation of the circuit4 ,illustration3 ,,fig4 #b1dfd4--;,diagram of connections of ,general ,electric three phase starting compensator with low voltage release and fuses4 ,illustration3 ,,fig4 #b1dfe4--;,diagram of connections of ,general ,electric two phase starting compensator with no voltage release and overload relays for #a1jdj to #b1ejj volt circuits4 ,motors larger than about #g horse power cause an objectionably heavy rush of current if thrown directly on the line4 ,starting compensators obviate such sudden variations of line load and are accordingly recommended for motors above #g horse power except in cases where voltage variations and excessive starting currents are not objectionable4 ,illustration3 ,,figs4 #b1dff and #b1dfg4--;,general ,electric three phase hand operated starting compensator4 ,fig4 #b1dff1 compensator in case2 fig4 #b1dfg1 compensator with case removed4 ,the compensator consists of a core and windings1 a cable clamp1 and a switch1 assembled in a substantial metal case with external operating handle and release lever4 ,the windings consist of coils wound on separate legs of a laminated core1 and tapped at several points1 the connections terminating at the switch contacts4 ,the shaft of the switch extends through the sides of the compensator case1 and is operated by a lever at the right1 being held in the running position by a lever at the left4 ,it is provided with wiping contacts4 ,the switch is immersed in oil1 and is intended to be used as a line switch as well as for starting the motor4 ,the lever has three positions3 off1 starting1 and running4 ,in the off position1 both compensator and motor windings are disconnected from the line4 ,in the starting position1 the switch connects the line to the ends and the motor to the taps of the compensator winding without overload relays or fuses in circuit4 ,in the running position1 the compensation winding is cut out and the motor is connected to the line through suitable fuses or overload relays mounted directly above the compensator4 ,to prevent the attendant throwing the motor directly on the line1 and thereby causing a rush of current which it is the object of the compensator to avoid1 an automatic latch is provided and so arranged that the lever at off position can be thrown only into the starting position 7backward72 and can be thrown thence into the running position 7forward7 only by a quick throw of the lever1 whereby any appreciable drop in speed and consequent increase in current in passing from the starting into the running position is avoided4 ,ques4 ,what should be noted with respect to the compensator winding taps8 ,ans4 ,the choice of a tap giving so low a voltage as to require over one minute for starting should be avoided so as to prevent the overheating to which starting compensators1 in common with other motor starting devices1 are liable if left in circuit unnecessarily long1 or if the motor be started several times in rapid succession4 ,illustration3 ,,fig4 #b1dfh4--;,diagram of connections of ,general ,electric three phase starting compensator with no voltage release and overload relays4 ,it should also be noted that the starting current diminishes rapidly as full speed is approached4 ,it is1 therefore1 important that the switch be kept in the starting position until the motor has finished accelerating to prevent any unnecessary rush of current when the switch is thrown to the running position4 ,illustration3 ,,fig4 #b1dfi4--;,general ,electric starting compensator with low voltage release and overload relays4 ,on the switch shaft there are mounted two levers1 held together with a strong spring which operates in either direction and prevents the switch being left on the starting position4 ,on the running side it is held by the external low voltage release lever until released either by hand or by the action of a low voltage relay4 ,the low voltage release consists of a cast iron frame open at the bottom and totally enclosing the coil4 ,a laminated plunger is used to hold the tripping lever1 the latter engaging with the lever mounted on the switch shaft4 ,the compensator cannot be thrown into the running position without first going to the starting position and it cannot be left on the starting position4 ,ques4 ,what is the usual arrangement of starting compensators for large motors8 ,ans4 ,starting compensators may be wound for any voltage or current for which it is practicable to build motors4 ,for very large motors the switching device is generally separate from1 the compensator itself and consists of triple and four pole switches for three phase and two phase motors respectively4 ,one double throw switch or two interlocked single throw switches are required for the motor and a single throw switch for energizing the compensator1 the running side of the motor circuit being provided with fuses or automatic circuit breakers1 or the switches provided with low voltage and overload release attachments4 ,star ,delta ,switches4--,these are starting switches1 designed for use with small three phase squirrel cage motors having their windings so arranged that they may be connected in star for starting and in delta for running4 ,ques4 ,describe the operation of a star delta switch4 ,ans4 ,in starting the motor1 the drum lever is thrown in the starting direction which connects the field windings of the motor in star4 ,when the motor has accelerated and has come partially up to speed the starting lever is quickly thrown to the running position in which position the field windings are connected in delta4 ,the effect of connecting the field winding in star at starting is to reduce the voltage applied to each phase winding1 while in the running position each phase of the field winding has full line voltage impressed upon it4 ,illustration3 ,,figs4 #b1dgj to #b1dgd4--;,general ,electric time limit overload relay for starting compensator4 ,in case of overload1 the relay armature is raised and at the end of its travel1 opens the small switch at the top which in turn opens the circuit of the low voltage release coil causing the compensator switch to return to the off position4 ,the oil dash pot provides a certain time element and can be adjusted to operate immediately upon overload or at any interval up to five minutes4 ,each relay has five calibrating points1 the lowest being the normal full load current of the motor1 the highest #cjj per cent4 full load current4 ,the scale on the calibration tube reads direct and shows various values of current at which the relay may be set to operate4 ,to change overload setting3 #a1 loosen set screw2 #b1 turn relay plunger on piston rod until white mark comes opposite required value of current2 #c1 tighten set screw4 ,time element adjustment3 ,removing oil dash pot by turning to the left will expose the cup shaped piston1 made of which are two concentric discs 7,b and ,c7 held together by a milled lock nut1 ,a4 ,there is a hole in each disc through which the oil must pass when the plunger of the relay is raised4 ,the time element may be varied by changing the size of the opening between these discs1 that is1 to have the relays operate in a shorter period of time1 increase the size of the opening and vice-versa4 ,to change the time setting3 #a1 remove the oil dash pot2 #b1 raise the discs ,b and ,c on the piston rod2 #c1 loosen the lock nut ,a2 #d1 change the opening between ,b and ,c1 giving a larger opening for shorter time of operation1 and a smaller opening for longer time2 #e1 tighten lock nut ,a2 #f1 replace discs in piston ,d2 #g1 replace oil dash pot4 ,illustration3 ,,figs4 #b1dge1 and #b1dgf4--;,front and side views 7oil tank removed7 of ,cutler-,hammer star delta switch for starting small three phase squirrel cage motors4 ,in construction1 the switch consists of one set of stationary fingers and a rotating wooden cylinder1 carrying two sets of contacts4 ,these parts are supported from the switch frame casting and are enclosed in a steel tank which contains an insulating oil4 ,flexible oil proof cable leads are brought out through insulated bushings in the top of the switch and tagged for convenience in connecting to the lines and motor4 ,to prevent seepage of oil1 the leads are sealed into the top of the cover with an oil proof sealing wax4 ,the lever of the star delta switch is arranged with an interlock which prevents its being thrown directly into the running position from the off position4 ,it is necessary to throw the lever first into the starting position and then with an uninterrupted movement to the running position4 ,the circuit of the motor is broken only for an instant in changing from star to delta and no heavy inrush current occurs4 ,no voltage release protection is provided by a latching solenoid which holds the spring centered drum cylinder in the running position4 ,the no voltage release coil is mounted in the lower part of the starting switch1 immersed in the oil tank1 and is protected against mechanical injury and grounding4 ,the coil is in circuit during the running period only and requires not more than #h to #ae watts to hold the switch in the running position4 ,the operation of this protective device is such that on failure of voltage the star delta switch will immediately be returned to the off position4 ,overload release protection consists of two relays on a small slate panel1 which is mounted directly on the side of the star delta switch4 ,the switch contacts of the overload release are connected in series with the connections to the no voltage release coil so that when an overload occurs the overload relay operates to open the circuit to the no voltage release coil1 thus permitting the switch lever to return to the off position4 ,the overload relays do not afford overload protection during the starting period1 and when such protection is desired starting fuses should be installed4 ,these fuses1 if used1 should have a capacity of #bej to #cjj per cent4 of the normal full load current of the motor4 ,illustration3 ,,fig4 #b1dgg4--;,diagram of connections of ,general ,electric three phase starting compensator with low voltage release and overload relays for #a1jdj-b1ejj volt circuits4 ,,chapter ,,lxi ,,synchronous ,,condensers ,synchronous ,condensers4--,a synchronous motor when sufficiently excited will produce a leading current1 that is1 when over excited it acts like a great condenser1 and when thus operated on circuits containing induction motors and similar apparatus for the purpose of improving the power factor it is called a synchronous condenser4 ,although the motor performs the duty of a condenser it possesses almost none of the properties of a stationary condenser other than producing a leading current1 and is free from many of the inherent defects of a stationary condenser4 ,the relation of power factor to the size and efficiency of prime movers1 generators1 conductors1 etc41 and the value of synchronous condensers for improving the power factor is generally recognized4 ,induction motors and other inductive apparatus take a component of current which lags behind the line pressure1 and thereby lowers the power factor of the system1 while a non-inductive load1 such as incandescent lamps1 takes only current in phase with the voltage and operates at unity power factor4 ,since transformers require the magnetizing current1 they may seriously affect the power factor when unloaded or partially loaded1 but when operating at full load their effect is practically negligible4 ,the relative effect of fully loaded and lightly loaded induction motors on the power factor is indicated by the diagram1 fig4 #b1dgh4 ,the magnetizing current is nearly constant at all loads and is wattless1 lagging #ij degrees behind the impressed pressure1 or at right angles to the current which is utilized for power4 ,in the figure1 ,,ab is the magnetizing component1 which is always wattless1 and ,,cb the power component4 ,the angle ,,acb gives the phase relation between voltage and current2 the cosine of this angle ,,cb ,,ac is the power factor4 ,illustration3 ,,fig4 #b1dgh4--;,diagram showing relative effect of fully loaded and lightly loaded induction motors on power factor4 ,it is evident from the diagram that if the load be reduced1 the side ,,cb is shortened1 and as ,,ab is practically constant1 the angle of lag ,,acb is increased4 ,it therefore follows that the cosine of this angle1 or the power factor is reduced4 ,the figure clearly shows the reason for the low power factor of induction motors on fractional loads and also shows that since the magnetizing current is practically constant in value1 the induction motor can never operate at unity power factor4 ,with no load1 the side ,,cb 7real power7 is just sufficient to supply the friction and windage4 ,if this be represented by ,,db1 since ,,ab remains constant1 the power factor is reduced to #aj or #ae per cent4 and the motor takes from the line about #cj per cent4 of full load current4 ,it therefore follows that a group of lightly loaded induction motors can take from the system a large current at exceedingly low power factor4 ,the synchronous motor when used as a condenser1 as before stated1 has the property of altering the phase relation between pressure and current1 the direction and extent of the displacement being dependent on the field excitation of the condenser4 ,it can be run at unity power factor and minimum current input1 or it can be over excited and thereby deliver leading current which compensates for the inductive load on other parts of the system4 ,the synchronous condenser1 therefore1 can supply magnetizing current to the load on a system while the power component is supplied by the generators4 ,illustration3 ,,fig4 #b1dgi4--;,general ,electric #djj kw41 #eej volt1 #fjj ,r4,p4,m41 synchronous condenser with direct connected exciter installed in sub-station ,no4 #a of the ,colorado ,light ,power ,co41 ,cripple ,creek1 ,colo4 ,the machine is designed for alternating current starting by means of a compensator4 ,the field is provided with a standard synchronous motor winding1 and1 in addition1 an amortisseur winding which assists in starting and serves as a damping device to minimize hunting4 ,illustration3 ,,fig4 #b1dhj4--;,diagram showing relative location of alternators and synchronous motors in plant of ,witherbee ,sherman ,co41 ,mineville ,n4 ,y4 ,the distribution system of the ,company is provided with three synchronous motors1 as shown4 ,the system includes two hydro-electric1 one turbine driven1 and one engine driven generator plants2 from three of these1 current is transmitted to the fourth1 which is located in ,mineville1 at the point ,a1 the current being distributed to the motor circuits from the points ,a and ,b4 ,the transmission to the central station at ,mineville is over three phase circuits at #f1fjj volts4 ,for operating the mine at ,cheever1 current is transmitted direct from the generating station at ,port ,henry4 ,the distribution from ,a and ,b is all at #c1cjj volts1 being stepped down to #ddj volts for the operation of the motors1 which have a total rated capacity of #d1gfb horse power4 ,excepting three synchronous motors1 the load is practically all inductive1 there being less than #aj kw4 required for lighting4 ,the actual power demand ranges from #fj to #fe per cent4 of the rated motor capacity1 and prior to the installation of the synchronous motors1 the power factor was approximately #fh per cent41 the condenser effect of these motors making it possible to maintain an average of about #ij per cent4 power factor in spite of the fact that a considerable portion of the induction motor load is very widely distributed4 ,the three synchronous motors are partially loaded1 each motor driving an air compressor through belting4 ,the #ahj kva4 motor at ,cheever takes about #aej kw4 for the operation of a #a1bej cubic foot compressor1 while the two #cfj kva4 machines take about #cjj kw4 each1 for the operation of two #b1ejj cu4 ft4 sets4 ,the operation of these compressors affords a method of utilizing a portion of the motor capacity mechanically1 inasmuch as the load on the motors is practically constant during the time the mines are in operation1 and thereby permit the motors to be run at approximately #hj per cent4 power factor4 ,effects of ,low ,lagging ,power ,factors4--,transformers are rated in kva4 output2 that is1 a #ajj kva4 transformer is supposed to deliver #ajj kw4 at unity power factor at normal voltage and at normal temperatures2 but1 if the power factor should be1 say 4#f lagging1 the rated energy output of the transformer would be only #fj kw4 and yet the current and1 consequently1 the heating would be approximately the same as when delivering #ajj kw4 at unity power factor4 ,illustration3 ,,fig4 #b1dha4--;,field of a synchronous condenser4 ,note the amortisseur winding1 erroneously called squirrel cage winding1 consisting of two end rings which serve to short circuit spokes passing through the pole tips as shown4 ,the amortisseur winding assists in starting and serves also as a damping device to minimize hunting4 ,the regulation of transformers is inherently good1 being for small lighting transformers about #a to #b per cent4 for a load of unity power factor1 and about #d to #e per cent4 at 4#g power factor4 ,larger transformers with a regulation of #a per cent4 or better at a unity power factor load1 would have about #c per cent4 regulation at 4#g power factor4 ,alternators also are rated in kva4 output1 usually at any value of power factor between unity and 4#h4 ,the deleterious effects of low power factor loads on alternators are even more marked than on transformers4 ,these are1 decreased kw4 capacity1 the necessity for increased exciter capacity1 decreased efficiency1 and impaired regulation4 ,assume the case of a #ajj kva4 4#f power factor1 #fj kw4 output4 ,it is probable that normal voltage could be obtained only with difficulty1 unless the alternator was especially designed for low power factor service4 ,the lagging power factor current in the armature sets up a flux which opposes the flux set up by the fields1 and in consequence tends to demagnetize them1 resulting in low armature voltage4 ,it is often impracticable1 without the installation of new exciters1 to raise the alternator voltage by a further increase of the exciting voltage and current4 ,the field losses1 and therefore the field heating of the alternator1 when it is delivering rated voltage and current1 are greater at lagging power factor than at unity4 ,increased energy input and decreased energy output both cause a reduction in efficiency4 ,illustration3 ,,fig4 #b1dhb4--;,diagram of a section of the ,northern ,california ,power ,co4's transmission system1 showing relative location of alternators and synchronous condenser4 ,the synchronous condenser is installed at ,kennett1 which is served by generating stations at ,kilarc and ,volta1 located respectively #bh and #ch miles from the point at which the condenser is operated4 ,the local demand amounts to about #f1ejj kw41 and before the installation of the synchronous condenser1 the power factor was about #gi per cent4 and after installing1 about #if per cent4 while the voltage at the point where the synchronous condenser is installed is raised approximately #aj per cent4 during the change from no load to full load4 ,in order to obtain close voltage regulation1 a regulator is used in connection with the synchronous condenser and holds the voltage1 at the center of distribution1 within #b per cent4 ,the regulator is mounted on the side of the control panel and connected in the field of the synchronous condenser to automatically change the excitation and compensate for voltage variations4 ,a graphic demonstration of the improvement in voltage regulation1 which has been secured in this case1 is given by the curve drawing voltmeter records reproduced in fig4 #b1dhc4 ,the regulation at unity power factor of modern alternators capable of carrying #be per cent4 overload1 is usually about #h per cent4 ,their regulation at 4#g power factor lagging is about #be per cent4 ,the effect of low power factor on the lines can best be shown by the following example3 ,,example4--,assuming a distance of five miles and a load of #a1jjj kw4 and desiring to deliver this load at a pressure of about #f1jjj volts1 three phase1 with an energy loss of #aj per cent41 each conductor at unity power factor would have to be #gi1bjj c4m41 at 4#i power factor1 #ig1ecc c4m41 and at 4#f power factor1 #bah1jjj c4m4 ,in other words1 at the lower power factor of 4#f1 the investment in copper alone would be #b4h times as much4 ,illustration3 ,,fig4 #b1dhc4--;,curve drawing voltmeter records at ,kennett1 ,cal4 ,the upper curve shows voltage regulation with synchronous condenser out of service1 and the lower curve1 with synchronous condenser in operation4 ,if the same size of wire were used at both unity and 4#f power factor lagging1 the energy loss would be about #b4h times the loss at unity power factor1 or about #bh per cent4 ,low lagging power factor on a system1 therefore1 will generally mean limited output of prime movers2 greatly reduced kilowatt capacity of generator1 transformer and line2 and increased energy losses4 ,the regulation of the entire system will also be poor4 ,cost of ,synchronous ,condenser vs4 ,cost of ,copper4--,referring to the example given in the preceding paragraph1 and calculating the necessary extra investment in copper with the 4#f power factor load1 and copper at #ag cents per pound1 the result is that #bi1bib pounds more copper is required than with the power factor of 4#i which means a total extra investment in copper alone of #e1jjj 7#bi1bib 4#ag74 ,a synchronous condenser of sufficient capacity to accomplish the same result would cost about the same amount4 ,it would therefore cost less to install the condenser because at the same time a considerably increased capacity would be obtained from the alternators1 transformers1 etc4 ,illustration3 ,,fig4 #b1dhd4--;,diagram showing the field current taken by a synchronous motor of normal design when operating at normal kva4 input at various power factors4 ,it will be noted that a slight departure from unity power factor necessitates a considerable change in field current4 ,as the field curves increase with the square of the current1 there is a rapid increase in temperature with leading current4 ,this action of leading or lagging current serves automatically to keep the flux constant in the armature with changes in field excitation4 ,when the motor is running at unity power factor1 an increase in field excitation causes a leading current to flow1 and at the same time this leading current demagnetizes the field until the density of the armature is restored to its normal value4 ,if the field be decreased a lagging current flows which in turn magnetizes the field bringing the density back to its original value4 ,therefore1 with a constant line voltage1 the iron losses in a synchronous motor are approximately constant irrespective of the field excitations with the exception that the internal voltage will vary slightly due to the armature ,i ,r drop1 the density being a trifle lower at full load than at no load4 ,synchronous ,condenser ,calculations4--,in figuring on the installation of a condenser for correcting power factor troubles1 a careful survey of the conditions should be made with a view of determining just what these troubles are and to what extent they can be remedied by the presence of a leading current in the system4 ,illustration3 ,,fig4 #b1dhe4--;,diagram showing a set of phase characteristic curves taken from a ,general ,electric synchronous motor4 ,these curves show the current input to the motor at various loads with constant voltage and varying field excitation4 ,there is a certain field current at each load that causes a minimum current4 ,any increase or decrease of field from the value increases the current and causes it to lead or lag with respect to the line voltage4 ,by referring to the minimum input curve1 it will be noted that if the machine be running at full load minimum input current and load is taken off1 the current will be leading or vice versa4 ,in each case the phase characteristic curve was run back on the lagging side to the break down point4 ,at no load and one quarter load the motor still ran in step when the field was reduced to zero and even taken off altogether1 and it was necessary to reverse the field current in order to back down the motor4 ,the motor runs without slip1 as a synchronous motor1 in this condition1 obtaining its excitation from the lagging current and running as a reaction machine4 ,the amount of load a machine will carry without field varies with the design1 the average being about #dj of full load4 ,it will be noted from the limit of stability curve that the lighter the load on the machine when it breaks down from lack of sufficient excitation1 the greater the current input at this point4 ,the no load characteristic rises sharply on each side with slight change in field current1 while it flattens out with increase in load until at overload the current input is practically the same throughout a large range of field current4 ,illustration3 ,,fig4 #b1dhf4--;,comparison of the speed current curves and speed power factor curves of a typical synchronous1 and induction motor4 ,it will be noted that the power factor of the synchronous motor at start is higher than that of the induction motor owing to the higher resistance of the squirrel cage winding4 ,as the machine approaches synchronism1 however1 the magnetizing current of the induction motor drops to a very much lower value than in the synchronous motor and the power factor is consequently much higher4 ,the magnetizing current of the induction motor at full speed is usually #be per cent4 of full load current while that of the synchronous motor is from #bjj to #bej per cent4 of full current1 or even higher when running full speed and normal voltage4 ,this of course is due to the large air gap on the synchronous machine4 ,the current at start with full voltage applied is usually higher in an induction motor owing to the fact that the total impedance of the stator and rotor are less due to the greater distribution of the windings and the lower resistance of the squirrel cage4 ,the high magnetizing current of a synchronous motor should not be lost sight of as it is a very important consideration in starting the machine4 ,even though the motor can be brought practically to synchronous speed while still on the compensator1 if line voltage be thrown on1 there will be a very heavy rush of current4 ,the obvious thing to do is to get the field on the motor while still on the compensator1 whenever possible1 to avoid the high magnetizing current4 ,this magnetizing current is obviously equal to the circuit current of the machine at no load field4 ,in some cases additional torque near synchronism can be obtained by short circuiting the field winding through the field rheostat4 ,this has the effect of reducing the resistance of the rotor winding to some extent and causing the motor to have less slip with a given load4 ,the gain from this source is small1 however1 in most cases1 as the self-inductance of the field winding is so high as to allow very little current to flow even if the field be short circuited so that the total effective resistance of the rotor winding is not materially reduced4 ,in some cases where the torque is nearly sufficient1 however1 enough gain may be obtained to take care of the conditions4 ,if the field be short circuited before the motor is started there will be a reduction in starting torque and an increase in current from the line1 hence if this method be resorted to1 arrangements must be made to short circuit the field after the motor has come to constant speed4 ,it is necessary to possess a thorough knowledge of the system1 covering the generating capacity in energy and kva41 average and maximum load1 and power factor on the alternators1 average and maximum load1 and power factor on the feeders1 system of distribution1 etc4 ,illustration3 ,,fig4 #b1dhg4--;,curves showing amount of wattless component required to raise the power factor of a given kw4 load to required higher value4 ,the wattless components are expressed as percentages of the original kw4 load4 ,the numbers at the right which indicate the points of tangency of the power factor curves to the #ajj per cent4 line1 show the amount of wattless component required to raise a given kw4 load of given lagging power factor to unity power factor4 ,obviously the addition of further wattless component in a given case would result in a leading power factor less than unity4 ,the desirable location of a condenser is1 of course1 nearest the inductive load in order to avoid the transmission of the wattless current1 but it often happens that a system is so interconnected that one large condenser cannot economically meet the conditions1 in which case it may be better to install two or more smaller ones4 ,the question of suitable attendance should also be considered and1 for this reason1 it may be necessary to compromise on the location4 ,when the location of the condenser has been decided upon and the load and power factor within its zone determined1 the proper size of condenser to raise the power factor to a given value can be found as follows3 ,the method of procedure can best be explained by reference to a concrete case4 ,assume a load of #dej kw4 at 4#fe power factor4 ,it is desired to raise the power factor to 4#i4 ,what will be the rating of the condenser8 ,illustration3 ,,fig4 #b1dhh4--;,diagram for synchronous condenser calculations4 ,referring to the diagram1 fig4 #b1dhh1 it is necessary to start with #dej kw4 ,at 4#fe power factor1 or #fib kva41 this has a wattless lagging component of 7#fib - #dej7 #ebe kva4 ,with the load unchanged and the power factor raised to 4#i1 there will be #ejj apparent kva41 which will have a wattless component of 7#ejj - #dej7 #bah kva4 ,it is obvious that the condenser must supply the difference between #ebe kva4 and #bah kva41 or #cjg kva4 ,a #cjj kva4 condenser would1 therefore1 meet the requirements4 ,if it be desired to drive some energy load with the condenser and still bring the total power factor to 4#i1 proceed as indicated in fig4 #b1dhi4 ,assume a total load of #aej kw4 on the motor4 ,as before1 #dej kw4 at 4#fe power factor1 or #fib kva41 with a wattless component of #ebe kva4 ,the energy load will be increased from #dej to #fjj kw4 as indicated1 and with the power factor raised to 4#i there will be a kva4 of #ffg with a wattless component of 7#ffg - #fjj7 #bia4 ,there must be supplied #ebe - #bia #bcd in leading kva4 ,the synchronous motor then must supply #aej kw4 energy and #bcd kva4 wattless1 which would give it a rating of 7#aej #bcd7 #bgh kva4 at 4#fh power factor4 ,illustration3 ,,fig4 #b1dhi4--;,diagram for synchronous condenser calculation for cases where it is desired to drive some energy load with the condenser and still bring the total power factor to 4#i4 ,the standard #cjj kva4 condenser would evidently raise the power factor slightly above 4#i power factor leading4 ,by reference to the chart1 fig4 #b1dij1 the size of the required condenser can be obtained direct without the use of the above calculation4 ,the method of using this curve is as follows3 ,assume a load of say #c1jjj kw4 at 4#g power factor and that it be desired to raise the power factor to 4#i4 ,run up the vertical line at #c1jjj kw4 to the 4#g power factor line1 and from there along the horizontal line to the margin and find a wattless component at this power factor of #c1jjj kva41 approximately4 ,again run up the #c1jjj kw4 vertical line to the 4#i power factor line and from there along the horizontal line to the margin and find a wattless component of #a1ejj kva4 ,the rating of the condenser will then be #c1jjj kva4 - #a1ejj kva4 #a1ejj kva4 ,this table of course can be used for hundreds of kilowatts as well4 ,illustration3 ,,fig4 #b1dij4--;,curve showing the relation of energy load to apparent load and wattless components at different power factors4 ,for determining the rating of a synchronous motor to drive an energy load this curve is not so valuable1 although it can be used in determining the wattless component direct in all cases where the energy component and power factor are known4 ,knowing this energy component and power factor or wattless component1 the energy load can obviously be found by referring to the curved lines on the diagrams1 the curve that crosses the junction of the vertical energy line and the power factor or wattless component line giving the total apparent kva4 ,,chapter ,,lxii ,,indicating ,,devices ,alternating current ammeters or voltmeters indicate the virtual values of the current or pressure respectively1 that is to say1 they indicate1 the square root of the mean square of a variable quantity4 ,illustration3 ,,fig4 #b1dia4--,line curve of alternating current1 illustrating various current or pressure values4 ,the virtual value1 or 4#gjg maximum value1 is the value indicated by an ammeter or voltmeter4 ,thus1 if the maximum value of the current be #ajj volts1 the virtual value as indicated by an ammeter is #ajj 4#gjg #gj4g amperes4 ,the virtual value of an alternating current or pressure is equivalent to that of a direct current or pressure which would produce the same effect4 ,for instance an alternating current of #aj virtual amperes will produce the same heating effect as #aj amperes direct current4 ,the relation of the virtual value of an alternating current to the other values is shown in fig4 #b1dia4 ,when the current follows the sine law1 the square root of the mean square1 value of the sine functions is obtained by multiplying their maximum value by #a #b or 4#gjg4 ,illustration3 ,,fig4 #b1dib4--,wagner tubular aluminum pointer4 ,the word effective is commonly used erroneously for virtual1 even among the best writers and the practice cannot be too strongly condemned#c4d ,the difference between the two is illustrated in ,guide ,no4 #e1 page #a1jac1 fig4 #a1bcg1 the mechanical analogy here given may make the distinction more marked4 #c ,,note4--,i adhere to the term virtual1 as it was in use before the term efficace which was recommended in #ahhi by the ,paris ,congress to denote the square root of mean square value4 ,the corresponding ,english adjective is efficacious1 but some engineers mistranslate it with the word effective4 ,i adhere to the term virtual mainly because effective is required in its usual meaning in kinematics to represent the resolved part of a force which acts obliquely to the line of motion1 the effective force being the whole force multiplied by the cosine of the angle at which it acts with respect to the direction of motion4--,s4 ,p4 ,thompson4 #d ,,note4--,the author adheres to the term virtual because in mechanics the adjective effective is used to denote the difference of two opposing forces2 for instance1 at any instant in the operation of a steam engine1 effective pressure forward pressure - back pressure1 hence1 to be consistent in nomenclature1 the term effective cannot be used for the forward or virtual pressure1 that is1 the pressure impressed on an electric circuit4 ,in the operation of a steam engine1 there are two pressures acting on the piston3 #a4 ,the forward pressure2 #b4 ,the back pressure4 ,the forward pressure on one side of the piston is that due to the live steam from the boiler1 and the back pressure1 on the other side1 that due to the resistance or opposition encountered by the steam as it exhausts from the cylinder4 ,in order that the engine may run and do external work1 it is evident that the forward pressure must be greater than the back pressure1 and it follows that the pressure available to run the engine is the difference between these two pressures1 this pressure difference being known as the effective pressure1 that is to say effective pressure forward pressure - back pressure ,thus1 electrically speaking1 the effective voltage is that voltage which is available for driving electricity around the circuit1 that is1 effective volts virtual volts - back volts virtual pressure - 7virtual pressure - drop7 ,in the case of the steam engine1 the forward pressure absolute1 that is1 measured from a perfect vacuum is the virtual pressure 7not considering the source74 ,the back pressure may vary widely for different conditions of operation as illustrated in figs4 #b1dic and #b1did4 ,illustration3 ,,figs4 #b1dic and #b1did4--,steam engine indicator cards1 illustrating in mechanical analogy1 the misuse of the term effective as applied to the pressure of an alternating current4 ,the card fig4 #b1dic1 represents the performance of a steam engine taking steam at #fj lbs4 7gauge7 pressure and exhausting into the atmosphere4 ,the exhaust line being above the atmospheric line shows that the friction encountered by the steam in flowing through the exhaust pipe produces a back pressure of two lbs4 ,hence at the instant represented by the ordinate y1 the effective pressure is #fj - #b #eh lbs41 or using absolute pressures1 #gd4g - #af4g #eh lbs41 the virtual pressure being #fj lbs4 gauge1 or #gd4g lbs4 absolute4 ,now1 the back pressure may be considerably reduced by exhausting into a condenser as represented by the card1 fig4 #b1did4 ,here1 most of the pressure of the atmosphere is removed from the exhaust1 and at the instant y1 the back pressure is only #f lbs41 and the effective pressure #gd4g - #f #fh4g lbs4 ,thus1 in the two cases for the same virtual pressure of #fj lbs4 gauge or #gd4g lbs4 absolute1 the effective pressures are #eh lbs4 and #fh4g lbs4 respectively4 ,in the measurement of alternating current1 it is not the average1 or maximum value of the current wave that defines the current commercially1 but the square root of the mean square value1 because this gives the equivalent heating effect referred to direct current4 ,there are several types of instrument for measuring alternating current1 and they may be classified as #a4 ,electromagnetic 7moving iron72 #b4 ,hot wire2 #c4 ,induction2 #d4 ,dynamometer4 ,electromagnetic or ,moving ,iron ,instruments4--,this type of instrument depends for its action upon the pull of flux in endeavoring to reduce the reluctance of its path4 ,this pull is proportional to the product of the flux and the current1 and so long as no part of the magnetic circuit becomes saturated1 the flux is proportional to the current1 hence the pull is proportional to the square of the current to be measured4 ,illustration3 ,,fig4 #b1die4--;,a calibrated scale4 ,this means that printed scales are not employed1 but each instrument has its scale divisions plotted by actual comparison with standards1 after which the division lines are inked in by a draughtsman4 ,there are makes of direct current instruments employing printed scales in which the scale deflections are fairly accurate1 even though the scales are printed1 but printed scales should not be used on alternating current instruments4 ,ques4 ,what are some objections to moving iron instruments8 ,ans4 ,instruments of this type are not independent of the frequency1 wave form1 or temperature and external magnetic fields may affect the readings temporarily4 ,illustration3 ,,fig4 #b1dig4--,plunger form of electromagnetic or moving iron type of ammeter4 ,there are several forms of moving iron ammeters1 which may be classified as #a4 ,plunger2 #b4 ,inclined coil2 #c4 ,magnetic vane4 ,ques4 ,describe the plunger type4 ,ans4 ,this type of ammeter consists of a series coil and a soft iron plunger forming a solenoid1 the plunger is so suspended that the magnetic pull due to the current flowing through the coil is balanced by gravity1 as shown in fig4 #b1dig4 ,ques4 ,how should the plunger be constructed to adapt it to alternating current1 and why8 ,ans4 ,it should be laminated to avoid eddy currents4 ,illustration3 ,,fig4 #b1dig4--,one form of plunger instrument as made by ,siemens4 ,it has gravity control1 is dead beat1 and is shielded from external magnetic influence4 ,the moving system consists of a thin soft iron pear shaped plate ,i pivoted on a horizontal spindle ,s running in jewelled centers4 ,to this spindle ,s is also attached a light pointer ,p and a light wire ,w1 bent as shown1 and carrying a light piston ,d1 which works in a curved air tube ,t4 ,this tube ,t is closed at the end ,b but fully open at the other ,a1 and constitutes the air damping device for making the instrument dead beat4 ,ques4 ,what is the character of the scale and how should it be constructed8 ,ans4 ,the scale is not uniform and should be hand made and calibrated under the conditions which it is to be used4 ,ques4 ,what is the objection to moving iron ammeters8 ,ans4 ,since the coil carries the entire current they are large and expensive4 ,ques4 ,what precaution should be taken in installing moving iron ammeters8 ,ans4 ,since gravity is the controlling force1 the instrument should be carefully levelled4 ,ques4 ,describe an inclined coil instrument4 ,ans4 ,it consists of a coil mounted at an angle to a shaft carrying the vane and pointer1 as shown in fig4 #b1dih4 ,a spring forms the controlling force and holds the pointer at zero when no current is flowing4 ,illustration3 ,,fig4 #b1dih4--;,inclined coil form of electromagnetic or moving iron instrument4 ,ques4 ,what is the principle of operation of the inclined coil instrument8 ,ans4 ,when a current is passed through the coil1 the iron tends to take up a position with its longest sides parallel to the lines of force1 which results in the shaft being rotated and the pointer moved on the dial1 the amount of movement depending upon the strength of the current in the coil4 ,ques4 ,describe a magnetic vane instrument4 ,ans4 ,it consists of a small piece of soft iron or vane mounted ,illustration3 ,,fig4 #b1dii4--,magnetic vane form of electromagnetic or moving iron instrument4 ,illustration3 ,,fig4 #b1ejj4--,magnetic vane movement of a ,wagner instrument2 it is used both for voltmeters and ammeters4 ,this type differs from the dynamometer movement in that a vane of very soft iron replaces the moving coil4 ,the magnetic vane movement makes use of its controlling spring only for the purpose of resisting the pull on the vane and the returning of the needle to zero4 ,the spring does not carry any current4 on a shaft that is pivoted a little off the center of a coil as shown in fig4 #b1dii1 and carrying a pointer which moves over a scale4 ,ques4 ,how does it work8 ,ans4 ,its principle of operation is that a piece of soft iron placed in a magnetic field and free to move1 will move into such position as to conduct the maximum number of lines of force4 ,the current to be measured is passed around the coil1 producing a magnetic field through the center of the coil4 ,the magnetic field inside the coil is strongest near the inner edge1 hence1 the vane will move against the restraining force of a spring so that the distance between it and the inner edge of the coil will be as small as possible4 ,illustration3 ,,fig4 #b1eja4--,solenoid and plunger illustrating the operation of moving iron instruments4 ,when a current flows through the coil1 a field is set up as indicated by the dotted lines of force4 ,the current flowing in the direction indicated by the arrow induces a north pole at ,n1 which in turn induces a south pole in the plunger at ,s1 thus attracting the plunger4 ,the effect of the field upon the plunger may also be stated by saying that it tends to cause the plunger to move in a direction so as to conduct the maximum number of lines of force1 that is1 toward the solenoid4 ,thus if ,,abcd be the initial position of the plunger only five lines of force pass through it3 should it move to the position ,a,b,c,d1 the number of lines passing through it will then be #i1 assuming the field to remain unchanged4 ,the operation of moving iron instruments of the plunger type may be explained by saying that the current flowing in the coil produces a pole at its end and induces an unlike pole at the end of the plunger nearest the coil1 thus attracting the plunger1 as illustrated in fig1 #b1eja above4 ,illustration3 ,figs1 #b1ejb and #b1ejc4--,wagner series transformers4 ,fig4 #b1ejb1 wound primary series transformer2 fig4 #b1ejc1 open primary transformer4 ,wagner series transformers are made in three general types3 ,one for switchboard mounting with wound primary2 one for switchboard mounting with open primary1 and one with open primary suitable for slipping over bus bars or switch stud4 ,these transformers have #e ampere secondary winding1 and are intended for use in connection with instrument of scale capacity #j-e1 although the scale should be calibrated to indicate the primary current4 ,the capacities are from #b watts to #ej watts1 being suitable for operation on circuits of #gej to #ff1jjj volts4 ,hot ,wire ,instruments4--,instruments of this class depend for their operation on the expansion and contraction of a fine wire carrying either the current to be measured or a definite proportion of that current4 ,the expansion or contraction of the wire is caused by temperature changes1 which in turn are due to the heating effect of the current flowing through the wire4 ,since the variations in the length of the wire are extremely small1 considerable magnification is necessary4 ,pulleys or levers are sometimes used to multiply the motion1 and sometimes the double sag arrangement shown in fig4 #b1ejd4 ,as shown here1 ,a is the active wire carrying the current to be measured and stretched between the terminals ,t and ,t4 ,it is pulled taut at its middle point by another wire ,c1 which carries no current1 and is1 in its turn1 kept tight by a thread passing round the pulley ,d attached to the pointer spindle1 the whole system being kept in tension by the spring ,e4 ,hot wire instruments are equally accurate with alternating or direct current1 but have cramped scales 7since the deflection is proportional to the square of the current71 and are liable to creep owing to unequal expansion of the parts4 ,there is also the danger that they may be burnt out with even comparatively small overloads4 ,they are not affected by magnetic fields but consume more current than the other types1 these readings are inaccurate near either end of the scale4 ,illustration3 ,,fig4 #b1ejd4--;,diagram illustrating the principle of hot wire instruments4 ,the essential parts are the active wire ,a1 stretched between terminals ,t and ,t1 tension wire ,c1 thread ,e1 and pulley ,d to which is attached the pointer4 ,induction ,instruments4--,these were invented by ,ferraris1 and are sometimes called after him4 ,they are for alternating current only1 and there are two forms3 #a4 ,shielded pole type2 #b4 ,rotary field type4 ,ques4 ,describe the shielded pole type of induction instrument4 ,ans4 ,as shown in figs4 #b1eje1 and #b1ejf it consists1 essentially of a disc ,a1 or sometimes a drum and a laminated magnet ,b4 ,covering some two-thirds of the pole faces are two copper plates or shields ,c1 and a permanent magnet ,d4 ,illustration3 ,,figs4 #b1eje and #b1ejf4--,plan and elevation of shielded pole type of induction instrument4 ,ques4 ,how does it work8 ,ans4 ,eddy currents are induced in the two copper plates or shields ,c1 which attract those in the disc1 producing in consequence a torque in the direction shown by the arrow1 against the opposing action of a spring4 ,magnet ,d damps the oscillations4 ,illustration3 ,,fig4 #b1ejg4--;,diagram showing construction and operation of ,hoskins instrument4 ,it is of the modified induction type in which the torque is produced from the direct repulsion between a primary and a secondary1 or induced current4 ,as shown in the diagram1 the instrument embodies the principle of a short circuited transformer1 consisting of a primary or exciting coil ,a1 a secondary or closed coil ,b1 linked in inductive relation to the primary by a laminated iron core ,c1 constructed to give a completely closed magnetic circuit1 that is1 without air gap4 ,the secondary is so mounted with respect to the primary as to have a movement under the influence of their mutual repulsion when the primary is traversed by an alternating current4 ,this movement of the secondary ,b is opposed by a spiral spring1 so that the extent of movement will be dependent upon and will indicate the strength of the primary current4 ,to increase the sensitiveness of the instrument and also to adjust the contour of the scale1 an adjustable secondary ,d1 which has an attraction effect upon the coil ,b1 is provided upon the core4 ,the effect of this coil is inversely proportional to its distance from the end of the swing of the coil ,b4 ,the vane1 ,e1 which is a part of the stamping ,b1 is adjusted to swing freely and with a large amount of clearance1 between the poles of a permanent magnet ,f1 which acts as a damper on the oscillation of the moving element1 but does not cause any friction or affect the accuracy of the calibration4 ,the primary1 like that of a transformer1 is an independent electrical circuit and may be highly insulated4 ,this meter will withstand several hundred per cent4 overload for some time because of the very high value of the self-induction and the fact that the controlling spring is not in the circuit and therefore cannot burn off4 ,illustration3 ,,figs4 #b1ejh to #b1eaa4--;,hoskins instruments4 ,fig4 #b1ejh1 voltmeter1 small pattern2 fig4 #b1eji1 ammeter1 large pattern2 fig4 #b1eaj1 voltmeter1 horizontal edgewise pattern2 fig4 #b1eaa1 illuminated dial voltmeter4 ,ques4 ,describe the rotary field type of induction instrument4 ,ans4 ,the parts are arranged similar to those of wattmeters1 the necessary split phase being produced by dividing the current into two circuits1 one inductive and the other non-inductive4 ,illustration3 ,,fig4 #b1eab4--;,hoskins instrument with case removed4 ,it has a very short magnetic circuit which is composed of silicon steel1 permitting low magnetic densities to be used4 ,dynamometers4--,this type of instrument is used to measure volts1 amperes1 or watts1 and its operation depends on the reaction between two coils when the current to be measured is passed through them4 ,one of the coils is fixed and the other movable4 ,illustration3 ,,fig4 #b1eac4--;,diagram of ,siemens' dynamometer4 ,it consists of two coils on a common axis but set in planes at right angles to each other in such a way that a torque is produced between the two coils which measures the product of their currents4 ,this torque is measured by twisting a spiral spring through a measured angle of such degree that the coils shall resume their original relative positions4 ,when constructed as a voltmeter1 both coils are wound with a large number of turns of fine wire1 making the instrument sensitive to small currents4 ,then by connecting a high resistance in series with the instrument it can be connected across the terminals of a circuit whose voltage is to be measured4 ,when constructed as a wattmeter1 one coil is wound so as to carry the main current and the other made with many turns of fine wire of high resistance suitable for connecting across the circuit4 ,illustration3 ,,fig4 #b1ead4--,wagner dynamometer movement4 ,in this type of instrument the deflection is proportional to the square of the current1 producing a constantly decreasing sensitiveness as the pressure applied is decreased4 ,the dynamometer movement is1 for any indication1 more accurate than the magnetic vane1 but cannot readily be employed for the indication of current1 as required in ammeters4 ,ques4 ,describe the construction of a dynamometer4 ,ans4 ,it consists1 as shown in fig4 #b1eac1 of a fixed coil1 composed of a number of turns of wire1 and fastened to a vertical support4 ,the fixed coil is surrounded by a movable coil composed of a few number of turns or often of only one turn of wire4 ,the movable coil is suspended by a thread and a spiral spring attached to a tortive head which passes through the center of a dial4 ,the ends of the movable coil dip into mercury cups1 which act as pivots and electrical contacts1 making connection with one end of the fixed coil and one terminal of the instrument as shown4 ,the tortion head can be turned so as to place the planes of the coils at right angles to each other and to apply tortion to the spring to oppose the deflection of the movable coil for this position when a current is passed through the coils4 ,a pointer attached to the movable coil indicates its position on the graduated dial between the two stops4 ,another pointer attached to the tortion head performs a similar function4 ,illustration3 ,,fig4 #b1eae4--;,armature of ,wagner dynanometer movement4 ,greater accuracy is claimed for this movement than the magnetic vane1 but it cannot readily be employed for the indication of current flow1 as required in ammeters4 ,the magnetic vane movement is used on the ,a4 ,c4 ammeter1 and can be used also in the ,a4 ,c4 voltmeters2 it makes use of its controlling spring only for the purpose of resisting the pull on the vane and the returning of the pointer to zero4 ,the dynanometer movement is recommended for voltmeters4 ,illustration3 ,,fig4 #b1eaf4--,wagner #be watt pressure transformer for use with various alternating current instruments1 such as voltmeters1 wattmeters1 etc4 ,they are made in capacities #be1 #ej1 #ajj1 and #bjj watts1 and are built for pressures of #gej to #fj1jjj volts4 ,ques4 ,how does the dynamometer operate8 ,ans4 ,when current is passed through both coils1 the movable coil is deflected against one of the stop pins1 then the tortion head is turned to oppose the movement until the deflection has been overcome and the coil brought back to its original position4 ,illustration3 ,,fig4 #b1eag4--,moving element of ,keystone dynamometer instrument4 ,the illustration shows the movable coil1 pointer1 aluminum air vane for damping the oscillations1 controlling springs1 and counter weights4 ,illustration3 ,,fig4 #b1eah4--,keystone dynamometer movement4 ,since the law governing this type of instrument is the law of current squares1 it follows that in the case of voltmeters1 equally divided scales cannot be obtained4 ,in the case of wattmeters1 the scale is approximately equally divided1 due to the fact that the movement of the moving coil is proportional to the product of the current in the fixed and moving coils4 ,the moving parts have been made as light in weight as is consistent with mechanical strength1 and the entire moving system is supported on jeweled bearings4 ,the motion of the pointer is rendered aperiodic by the use of an aluminum air vane moving in a partially enclosed air chamber4 ,this method of damping the oscillations of the moving parts renders unnecessary the use of mechanical brakes or other frictional devices1 which tend to impair the accuracy of the instrument4 ,the illustration shows a voltmeter1 which1 however1 differs but little from a wattmeter4 ,in the case of a wattmeter the fixed coils are connected in series with the line1 either directly or through a current transformer1 while the moving coil is connected in shunt to the line4 ,the angle through which the tortion head was turned1 being proportional to the square root of the angle of tortion1 the current strength in amperes is equal to the square root of the angle of tortion multiplied by a calculated constant1 furnished by the maker of the instrument4 ,ques4 ,how is the dynamometer arranged to measure watts8 ,ans4 ,when measuring watts1 the instrument should be so arranged that one coil carries the main current1 and the other a small current which is proportional to the pressure4 ,illustration3 ,,fig4 #b1eai4--,leeds and ,northrup electro-dynamometer4 ,it is a reliable instrument for the measurement of alternating currents of commercial frequencies4 ,when wound with fine wire and used in connection with properly wound resistances1 it is equally useful for measuring alternating pressures1 and may thus be employed to calibrate alternating current voltmeters as well as ammeters4 ,to give accurate results the instruments must be carefully constructed and designed with a view to avoiding the eddy currents always set up by alternating currents in masses of metal near1 or in the circuits4 ,the constant of a dynamometer may be obtained with a potentiometer1 but this is usually done with precision by the manufacturer and a certificate giving the value of the constant is furnished with the instrument4 ,the size and cost of dynamometers rapidly increase with the maximum currents which they are designed to carry1 and when more than #ejj amperes are to be measured1 the use of other instruments and methods is recommended4 ,ques4 ,in the construction of a dynamometer what material should not be used and why8 ,ans4 ,no iron or other magnetic material should be employed because of the hysteresis losses occasioned thereby4 ,the frame should be of non-conducting material so as to avoid eddy currents4 ,illustration3 ,,figs4 #b1ebj to #b1ebf4--,various types of ,wagner instruments4 ,fig4 #b1ebj1 small round type2 fig4 #b1eba1 horizontal edgewise type2 fig4 #b1ebb1 smallest switchboard type2 fig4 #b1ebc1 portable type2 fig4 #b1ebd1 combination voltmeter and ammeter in one case2 fig4 #b1ebe1 vertical type2 fig4 #b1ebf1 polyphase type4 ,watt ,hour ,meters4--,a watt hour meter is a watt meter that will register the watt hours expended during an interval of time4 ,watt hour meters are often erroneously called recording or integrating watt meters4 ,there are several types of the electromotor form of watt hour meter1 which may be classified as #a4 ,commutator type2 #b4 ,induction type2 #c4 ,faraday disc type4 ,illustration3 ,,fig4 #b1ebg--;,interior ,weston single phase wattmeter4 ,the general appearance of the dynamometer movement and the relative positions of the various parts are clearly shown4 ,the parts are assembled on one base1 the whole movement being removable by unfastening two bolts4 ,the fixed winding is made up of two coils1 which together produce the field of the wattmeter4 ,the movable coil is wound to gauge with silk covered wire and treated with cement4 ,while winding1 the coil is spread at diametrical points to allow the insertion of the staff1 which is centered by means of two curved plates cemented to the inside surface of the coil and forming a part thereof4 ,the coil is held in a definite position by two tiny pins which pass through the staff and engage with ears on the curved plates4 ,illustration3 ,,fig4 #b1ebh4--,westinghouse single phase induction type watt hour meter removed from case4 ,the friction compensation1 or light load adjustment1 is accomplished by slightly unbalancing the two legs of the shunt magnetic circuit4 ,to do this a short circuited loop is placed in each air gap1 and means are provided for adjusting the position of the loops so that one loop will enclose and choke back more of the flux than the other loop1 and thus produce a slight torque4 ,it will be noted1 that this torque depends on voltage alone1 which is practically constant1 and is entirely independent of the load4 ,adjustment is accomplished by means of either of two screws which makes micrometer adjustment possible4 ,it is clamped when adjusted by means of a set screw1 which prevents change4 ,this method makes possible an accuracy of adjustment which effectively prevents creeping4 ,the power factor adjustment consists of an adjustable compensating coil placed around the shunt pole tip4 ,this is adjusted at the factory by twisting together the leads of the compensating coil1 thus altering its resistance until the desired lagging effect is had4 ,frequency adjustment4 #acc cycle meters are first calibrated on #fj cycles and the leads then untwisted to make them correct on #acc cycles4 ,to change such a meter for use on #fj cycles it is necessary only to retwist these leads to the point shown by the condition of the wire4 ,ques4 ,what are the essential parts of a watt hour meter8 ,ans4 ,a motor1 generator1 and counting mechanism4 ,illustration3 ,,fig4 #b1ebi4--,pointer and movable system of ,weston wattmeter4 ,the coil is described in fig4 #b1ebg4 ,the pointer consists of a triangular truss with tubular members1 an index tip of very thin metal being mounted at its extremity4 ,the index tip is reinforced by a rib stamped into the metal4 ,the pointer is permanently joined to a balance cross1 consisting of a flat center web1 provided with two short arms and one long arm1 each arm carrying a nut by means of which the balance of the system may be adjusted4 ,the longest arm1 which is opposite the pointer1 carries a balance nut1 consisting of a thin walled sleeve provided with a relatively large flange at its outer end4 ,the sleeve is tapped with #bgb threads to the inch1 the internal diameter of the sleeve being made slightly smaller than the outside diameter of the screw1 and the sleeve is split lengthwise2 therefore when sprung into place and properly adjusted it will remain permanently in position4 ,a sleeve which is forced over the end of the staff carries the pointer firmly clamped between a flanged shoulder and a nut4 ,by perforating the web plate of the balance cross with a hole having two flat sides that fit snugly over a similarly shaped portion of the sleeve1 the pointer is given a definite and permanently fixed angular position4 ,the air damperconsists of two very light symmetrically disposed vanes1 which are enclosed in chambers made as nearly air tight as possible4 ,these vanes are formed of very thin metal stiffened by ribs1 stamped into them and by the edges1 which are bent over to conform to the surface of the side walls of the chambers4 ,they are attached by metal eyelets to a cross bar carried on a sleeve similar in construction to the one at the upper end of the staff4 ,this cross bar is held in place by a nut1 and is provided at the center with a hole having two flat sides1 being similar in shape to the one in the balance cross4 ,this hole likewise fits over a sleeve and definitely locates the vanes with reference to the other parts of the system4 ,the damper box is cast in one piece to form the base that carries the field coils and the movable system4 ,ques4 ,what is the function of the motor8 ,ans4 ,since the motor runs at a speed proportional to the energy passing through the circuit1 it drives the counting mechanism at the proper speed to indicate the amount of energy consumed4 ,ques4 ,what is the object of the generator8 ,ans4 ,it furnishes a suitable counter torque or load for the motor4 ,illustration3 ,,fig4 #b1ecj4--,westinghouse polyphase induction type watt hour meter1 covers removed4 ,this type is made for two phase three wire and four wire1 and three phase three wire and four wire circuits4 ,meters for circuits of more than #cjj amperes or #ejj volts require transformers1 but1 like the self-contained meters1 are calibrated to read directly in kilowatt hours on the dial1 without a multiplying constant4 ,ques4 ,is there any other resistance to be overcome by the motor8 ,ans4 ,it must overcome the friction of all the moving parts4 ,ques4 ,is the friction constant8 ,ans4 ,no4 ,illustration3 ,,figs4 #b1eca to #b1ecc4--;,diagram of electromagnetic circuit of ,westinghouse induction type watt hour meter1 and diagram showing rotation of field4 ,the dotted lines show the main paths of the magnetic flux produced by the two windings1 the directions1 however1 are constantly reversing owing to the alternations of the current in the coils4 ,denoting the shunt and series pole tips by the letters as shown1 a clear statement of the relation of the fields for each quarter period may be given4 ,the signs and - represent the instantaneous values of the poles indicated4 ,thus1 at one instant the shunt pole tips ,a1 ,c1 and ,a are maximum 1 -1 and 1 respectively because the instantaneous value of the current is maximum1 while the value of the series flux is zero4 ,at period later the shunt current is zero1 giving zero magnetic pressure at the pole tips1 while the series current has reached a maximum value1 giving maximum-and at the pole tips ,b and ,d4 ,at the next period the shunt current is again maximum1 but in a direction opposite to what it was at the beginning1 making the pole tips ,a1 ,c1 and ,a 1 -1 and 1 respectively1 while the series current again is zero1 etc41 the values for the complete cycle being given in fig4 #b1ecc4 ,it will be observed from the table that both the and - signs move constantly in the direction from ,a to ,a1 indicating a shifting of the field in this direction1 the process being repeated during each cycle4 ,ques4 ,what provision is made to correct the error due to friction8 ,ans4 ,the meter is compensated by exciting an adjustable auxiliary field from the shunt or pressure circuit4 ,ques4 ,what is the construction of the generator8 ,ans4 ,in nearly all meters it consists of a copper or aluminum disc carried on the same shaft with the motor and rotated in a magnetic field of constant value4 ,ques4 ,how is the counter torque produced8 ,ans4 ,when the disc is rotated in the magnetic field1 eddy currents are induced in the disc in a direction to oppose the motion which produces them4 ,ques4 ,for what services is the commutator type meter used8 ,ans4 ,it is used on both direct and alternating current circuits4 ,illustration3 ,,figs4 #b1ecd and #b1ece4--;,cross section of bearings of ,westinghouse induction type watt hour meter4 ,the lower bearing consists of a very highly polished and hardened steel ball resting between two sapphire cup jewels1 one fixed in the end of the bearing screw and the other mounted in a removable sleeve on the end of the shaft4 ,owing to the minute gyrations of the shaft the ball has a rolling action1 which not only makes a lower friction coefficient than the usual rubbing action1 but presents constantly new bearing surfaces and thus produces long life4 ,the upper bearing is only a guide bearing to keep the shaft in a vertical position1 and is subject to virtually no pressure1 and consequently little friction4 ,it consists of a steel pin fastened to a removable screw and projecting down into a bushing in a recess drilled in the shaft4 ,the bottom of this recess is filled with billiard cloth saturated with watch oil4 ,a film of oil is maintained around the pin by capillary action4 ,ques4 ,what is the objection to the commutator meter8 ,ans4 ,the complication of commutator and brushes1 and the fact that the friction of the brushes is likely to affect the accuracy of the meter4 ,illustration3 ,,fig4 #b1ecf4--;,diagram of ,fort ,wayne1 induction watt hour meter4 ,it is designed to register the energy of alternating current circuits regardless of the power factor1 and embodies the usual induction motor1 eddy current generator and registering mechanism4 ,the electrical arrangement of the meter consists of a current circuit composed of two coils connected in series with each other and in series with the line to be measured1 and a pressure circuit consisting of a reactance coil and a pressure coil connected in series with each other and across the line to be measured4 ,in addition1 the pressure circuit contains a light load coil wound over a laminated sheet steel member1 adjustably arranged in the core of the pressure coil and connected across a small number of turns of the reactance coil so as to give a field substantially in phase with the impressed pressure4 ,the light load winding is further provided with a series adjustable resistance furnished for the purpose of regulating the current flowing in the light load winding1 thereby providing a means of lagging the meter on high frequencies1 such as #abe or #adj cycle circuits4 ,the pressure circuit also comprises a lag coil wound over the upper limb of the core of the pressure circuit and provided with an adjustable resistance for obtaining a held component in quadrature with the shunt field4 ,ques4 ,what are its characteristics8 ,ans4 ,it is independent of power factor1 wave form1 and frequency when no iron is used in the motor4 ,ques4 ,what meter is chiefly used on ,a4 ,c4 circuits8 ,ans4 ,the induction meter4 ,illustration3 ,,fig4 #b1ecg4--;,fort ,wayne multiphase induction watt hour meter4 ,the construction of the mechanism is essentially two single phase motor elements1 one at the bottom of the meter in a suitable position1 the other inverted and placed at the top of the meter4 ,each element acts on a separate cup1 but both cups are mounted on a single shaft so that the registration is due to the resultant torque of the two elements4 ,the meter is provided with three supporting lugs1 the one at the top being keyholed and one of the bottom two1 slotted to facilitate leveling4 ,the registering mechanism is mounted on a cast iron bracket at the middle of the meter between the two motor elements4 ,the supporting bracket is attached to the meter base by two screws and aligned by two dowel pins4 ,the register is of the four dial type1 reading in kilowatt hours4 ,each division of the right hand circle1 or that passed over by the most rapidly moving pointer1 equals one kilowatt hour in meters without a dial constant4 ,in meters of larger capacities1 dial constants of #aj1 #ajj and #a1jjj are used1 in which case it is only necessary to add one1 two or three ciphers to the observed reading4 ,principles of ,induction ,watt ,hour ,meters4--,every commercial meter of this type is made up of a number of elements1 described below4 ,each of these elements and parts has certain functions1 and each is therefore necessary to the successful operation of the meter2 moreover1 each element1 unless correctly designed1 may introduce a source of inaccuracy4 ,these elements are3 #a4 ,the field producing element2 #b4 ,the moving element2 #c4 ,the retarding element2 #d4 ,the registering element2 #e4 ,the mounting frame and bearings2 #f4 ,the friction compensator2 #g4 ,the power factor adjustment2 #h4 ,frequency adjustment2 #i4 ,the case and cover4 ,illustration3 ,,figs4 #b1ecc to #b1eda4--;,connections of ,fort ,wayne multiphase watt hour meters 7type k--forms ,,mab and ,,mak71 for #ajj-fbe volt circuits1 #e-aej amperes4 ,fig4 #b1ech two and three phase1 three wire circuit1 #be-cf cycles2 fig4 #b1eci two and three phase1 #c wire circuit1 #cf cycles and above2 fig4 #b1edj1 two phase #d wire circuit1 #be-cf cycles2 fig4 #b1eda two phase1 #d wire circuit #cf cycles and above4 ,illustration3 ,,fig4 #b1edb4--;,fort ,wayne single phase induction watthour meter with cover removed4 ,the rotating parts consist of an aluminum disc mounted on a short shaft of small diameter4 ,the lower end has inserted in it a hardened steel pivot which rests in a cup shaped jewel bearing4 ,the top of the meter shaft is drilled and provided with a small washer having the central hole of very small diameter4 ,into this hole there extends a steel pin around which the shaft turns4 ,two micrometer screws are provided for load adjustment--one for the full load and the other for the light load adjustment4 ,the adjustment for accuracy on full load is secured by varying the position of the permanent magnets1 sliding them either in or out from the center of the rotating disc of the meter depending on whether it is desired to increase or decrease the speed of the disc4 ,the micrometer screw shown in the figure serves to vary the position of the permanent magnets1 causing the shoe in which the two magnets are firmly clamped to slide on the milled magnet support which is cast as an integral part of the meter frame4 ,when the proper position of the magnets has been accurately determined by adjustment and test1 the shoe which holds the two magnets is clamped firmly to the milled magnet support by two screws1 one of which is shown in the figure4 ,the adjustment for accuracy on light load is secured by varying the position of a metal punching1 known as the starting plate1 laterally under the pressure pole in the path of the pressure flux4 ,this lateral movement is accomplished by means of the micrometer screw4 ,when the proper position of this punching has been accurately determined by adjustment and test1 it is secured in place by tightening the two brass screws which serve to clamp it to the meter frame4 #a4 ,the ,field ,producing ,element4--,this consists of the electromagnetic circuit and the measuring coils4 ,one of these coils1 connected in series with the circuit to be metered1 is wound of few turns and is therefore of low inductance4 ,the current through it is in phase with the current in the metered circuit4 ,the other coil1 connected across the circuit1 is highly inductive1 and therefore the current in it is nearly #ij degrees out of phase with1 and proportional to the voltage of the metered circuit across its terminals4 ,therefore1 when the current in the circuit is in phase with the voltage 7#ajj per cent4 power factor7 the currents in the meter coils are displaced almost #ij degrees with respect to each other4 ,ques4 ,how is this angle made exactly #ij degrees8 ,ans4 ,by means of the power factor adjustment4 ,illustration3 ,,fig4 #b1edc4--,rear view of ,fort ,wayne single phase induction watthour meter with back cover plate removed4 ,the pressure and current coils and their respective cores lie behind the main frame of the meter4 ,this complete electromagnetic unit can be removed as a whole from its mounting in the case4 ,the pressure coil is wound from enameled wire1 the number of turns being very high4 ,the current coils have but few turns each and are wound from cotton covered wire4 ,all coils are treated with insulating compound before assembling in the meters4 ,the laminated iron cores placed within these coils are built up from magnetic steel4 ,the magnetic circuits formed by the cores of the pressure and current coils are so arranged that they exert a high torque upon the disc of the rotating element in order that minute variations in the friction of the moving parts1 which are likely to occur will not cause any appreciable error in the registration of the meter4 ,the iron case surrounding the electrical elements protect that part of the meter from the effects of external stray fields1 while the astatic arrangement of the permanent magnets tends to prevent any influence on the damping system4 ,the fact that the iron frame of the meter lies between the permanent magnets and the current coils protects the magnets from the effects of short circuits which create a strong magnetic field within the meter itself4 ,ques4 ,how are the coils mounted8 ,ans4 ,they are so mounted on the core that the currents in them produce a rotating or shifting field in the air gap1 in somewhat the same manner that the currents in the primary windings of an induction motor produce a rotating field4 ,illustration3 ,,fig4 #b1edd4--;,fort ,wayne single phase induction watthour meter with cover register and permanent magnets removed to show solid meter frame4 ,a heavy steel back plate held in place by two screws inserted from the front of the central casting encloses the back part of the completely assembled meter4 ,a felt gasket lying on a suitable ledge seals the joint against the entrance of dust or moisture when the back plate is drawn down firmly by the screws4 ,the cover which encloses the back part of the meter is a non-magnetic metallic stamping4 ,it is held in place by wing nuts on the two light brass studs extending forward from the meter frame4 ,this joint between the main frame and the cover is also sealed against the entrance of dust and moisture by the use of a suitable felt gasket4 ,two glass windows are provided in this cover1 one to permit the reading of the register dials1 the other to permit observation of the disc's rotation4 ,the cover is sealed in place in the usual way by passing a sealing wire through a hole drilled in the cover sealing stud and thence through a hole provided in the wing of the seal nut4 ,the terminal chamber is an extension of the casting which supports all the inner parts of the meter4 ,the heavy brass terminals used for connecting the meter in circuit are held permanently by a non-combustible insulating compound which is moulded in place around them4 ,this construction gives excellent insulation and is a safeguard against accidental short circuits across terminals4 ,a punched terminal cover which fits over the terminal chamber is hinged at the upper left hand corner so that it will of its own accord swing out of the way when the terminal cover sealing screw is removed4 ,this hinged style of cover will be found convenient when installing and connecting the meter in circuit4 ,when this cover is swung back into closed position it is fastened in place by passing a seal right through the seal screw and through a lug provided on the cover4 ,ques4 ,what is the strength of the rotating field with #ij degrees phase difference between the currents8 ,ans4 ,it is proportional to the product of the currents in the two coils and therefore proportional to the product of current and voltage in the metered circuit4 ,at any other power factor the field is proportional to this product multiplied by the sine of the angle of phase difference between the two meter currents4 ,if the current in the voltage coil be in quadrature with the voltage of the metered circuit1 at any power factor the sine of the angle of phase difference between the currents in the meter circuits will be equal to the cosine of the angular displacement between the current and voltage in the metered circuit4 ,under these conditions therefore the strength of the shifting field is proportional also to the power factor of the circuit4 ,in other words1 the strength of the rotating field is proportional to the product of the volts1 amperes and power factor and is therefore a measure of the actual power4 ,illustration3 ,,fig4 #b1ede4--,sangamo single phase induction watt hour meter2 view with cover removed showing mechanism4 ,ques4 ,in what part of the meter is energy consumed8 ,ans4 ,in the field producing element4 ,illustration3 ,,fig4 #b1edf4--,main grid or supporting frame of ,sangamo single phase induction watt hour meter4 ,the grid is of cast iron and its design is such that the weight of the permanent magnets1 series laminated element and return plate are carried on the main portion1 the smaller projecting brackets carrying no weight except that of the moving system4 ,the supporting grid is removed by taking out the three screws locating and holding it in position1 to the iron base1 also removing at the same time the screws connecting the leads of the series coils to the binding posts at the bottom4 ,the meters are all built with four binding posts so that they may be connected either with two series leads and a tap for the pressure connection or with both sides of the circuit carried through the meter4 ,the wire meters employ a #bbj volt shunt coil1 connected across the binding posts within the meter1 one series coil being in each of the outer lines of the three wire system4 ,this renders unnecessary the use of a pressure tap4 ,it is upon the design of this element that the losses in the meter depend4 ,current is flowing through the shunt coil continuously1 even when no energy is being taken1 and the higher the inductance of this coil1 the smaller will be the energy component of the constant flow4 ,the series coil causes a loss of energy proportional to the square of the current flowing4 ,it also causes a drop in voltage1 both inductive and resistive1 hence1 the resistance and inductance of the series coil of the meter should be as low as possible4 ,ques4 ,how should the magnetic circuit be designed8 ,ans4 ,the design should be such that the increase of magnetic flux with high voltage or high current will not have a retarding action but will act only to increase the torque4 ,if the retarding effect be not prevented1 the meter will1 of course1 run slow at overloads4 ,a comparative test of meters at varying load and at varying voltage will reveal the characteristics of the magnetic circuit4 #b4 ,the ,moving ,element4--,this usually consists of a light metal disc revolving through the air gap in which the rotating field is produced4 ,illustration3 ,,fig4 #b1edg4--,moving element of ,sangamo single phase induction watt hour meter4 ,it consists of a light aluminum disc mounted on a hard brass shaft1 the entire system weighing #ae4f grams4 ,the disc is swaged under heavy pressure1 to render it stiff4 ,the arrangement of the disc1 shaft1 and bearings is shown in fig4 #b1edh4 ,by unscrewing the upper and lower bearings the disc and shaft can be removed without disturbing the magnets or adjustments4 ,ques4 ,what is the action of the disc8 ,ans4 ,it acts like the squirrel cage armature of an induction motor1 developing the motive torque for the meter4 ,ques4 ,how is this torque counter balanced8 ,ans4 ,by the retarding element so that the speed is proportional to the torque4 ,ques4 ,how should the disc be made and why8 ,ans4 ,as light as possible to reduce wear on the bearings to a minimum4 ,illustration3 ,,fig4 #b1edh4--;,bearing system of ,sangamo single phase induction watthour meter4 ,the upper pivot1 or bearing is made of tempered steel wire and of sufficiently small diameter to be quite flexible in the length between the top of the brass shaft and the guide ring in which it rotates4 ,the guide ring1 made of phosphor bronze1 has the heavy hole lined and burnished4 ,the upper bearing screw1 in which the bronze bushing is carried1 is so constructed that a long brass sleeve closely surrounds the upper pivot of the spindle4 ,any blow against the moving system1 caused by accident or short circuit1 will slightly deflect the shaft until the steel pivot touches against the side of the shell1 thus preventing danger of breaking off or bending the upper pivot4 ,at the same time a cushioning or flexible action between the shaft and the bearing shell is secured1 thus eliminating the effect of vibration in the moving system1 which would tend to produce rattling4 ,the lower bearing consists of a cup sapphire jewel1 supported in a threaded pillar1 the upper end of which is provided with a sleeve so located that it prevents the moving element dropping out during shipment4 ,this protecting sleeve is held friction tight on the shaft and can be removed if it be desired to inspect the jewel4 #c4 ,the ,retarding ,element4--,this part acts as a load on the induction motor and enables the adjustment of its speed to normal limits4 ,in order that the speed shall be proportional to the driving torque1 which varies with the watts in the circuit1 it is necessary that the torque of the retarding device be proportional to the speed4 ,for this reason a short circuited constant field generator1 consisting of a metal disc rotating between permanent magnet poles1 has been generally adopted4 ,ques4 ,how is the retarding torque produced8 ,ans4 ,eddy currents are induced in the disc in rotating through the magnetic field which1 according to ,lenz's law1 oppose the force that produces them1 thus developing a retarding torque4 ,ques4 ,how is the constant field for the retarding disc produced8 ,ans4 ,by permanent magnets4 ,the retarding disc may be the same disc used for the moving element1 in which case the meter field acts on one edge while the permanent magnet field acts on the edge diametrically opposite4 ,this arrangement simplifies the number of parts and saves space and weight of moving element4 ,ques4 ,what error is likely to be introduced by the retarding element8 ,ans4 ,if the strength of the permanent magnets change from any cause1 the retarding torque will be changed and the calibration of the meter rendered inaccurate4 ,ques4 ,how may the strength of the permanent magnets be changed8 ,ans4 ,they may become weak with age1 or affected by the proximity of other magnetic fields4 ,the series coil of the meter may1 under short circuit so affect the strength of the permanent magnets as to render the meter inaccurate4 ,ques4 ,what precautions are taken to keep the strength of the permanent magnets constant8 ,ans4 ,weakening with age is prevented by the process of ,aging4 ,the effect of neighboring fields is overcome by iron shields2 this prevents the electromagnets affecting1 through overloads1 the strength of the permanent magnets4 #d4 ,the ,registering ,element4--,this mechanism comprises the dials1 pointers1 and gear train necessary to secure the required reduction in speed4 ,this gear train is driven directly by the rotor and therefore its friction should be low and constant4 ,the dials should be easily read and should register directly in kilowatt hours4 ,if a constant be used to reduce the reading to kilowatt hours1 it should be some multiple of #aj1 to avoid errors in multiplication4 ,by means of suitable gears in the meters this is easily accomplished4 ,illustration3 ,,fig4 #b1edi4--,register dial of ,sangamo single phase induction watt hour meter 7full size74 ,the dial circles read #aj1 #ajj1 #a1jjj1 and #aj1jjj kilowatt hours from right to left4 #e4 ,the ,mounting ,frame and ,bearings4--,these parts have an important influence on the accuracy of the meter1 as it is in the bearings that most of the friction in the meter occurs4 ,the frame should be rigid and free from vibration1 so that the bearings will be at all times in perfect alignment4 ,initial friction is unavoidable in any meter construction and can be easily compensated for4 ,a change in the initial friction1 however1 due to wear of bearings1 makes readjustment necessary4 ,in selecting a meter the special attention should therefore be given1 to the construction of the bearings1 particularly the lower1 or step bearing which supports the weight of the moving element4 ,illustration3 ,,fig4 #b1eej4--;,canadian dial of ,sangamo single phase induction watt hour meter4 ,it has a small test circle indicating one kilowatt hour per revolution in all sizes where the first regular circle indicates #aj4 ,this is provided to conform with the requirements of the ,canadian government and it is intended that the hand on the test circle shall make not less than revolution in one hour with full load on a meter4 ,in the case of a #aj ampere meter1 it will make one complete revolution in one hour and for a #bj ampere1 two revolutions1 and so on4 ,the train or indicating mechanism is carried on a rigidly formed and swaged brass bracket accurately located by two dowel pins set in the top face of the main grid1 and is held to the grid with two screws easily accessible when it is desired to remove the train for any purpose4 ,all indicating trains used on type ,h meters are marked with symbols on the back of the train and on the compound attachment to indicate the gear ratio of each combination2 this ratio being different for meters of different capacities in order to obtain a direct reading in kilowatt hours on the dial4 ,ques4 ,describe a good construction for the step bearing4 ,ans4 ,a desirable construction would consist of a very highly polished and hardened ball with jewel seats4 #f4 ,the ,friction ,compensator4--,the object of this device is to overcome the initial friction of the moving parts4 ,it is evident that if this initial friction were not compensated some of the driving torque of the meter would be used in overcoming it1 and the meter would therefore not rotate at very light load1 and not fast enough at other loads1 thus rendering the registration inaccurate1 especially at light loads4 ,illustration3 ,,fig4 #b1eea4--;,base and shunt coil of ,sangamo single phase induction watt hour meter4 ,since the shunt or pressure coil sometimes breaks down or burns out1 due to abnormal line conditions or accident1 provision is made for easy replacement4 ,the shunt magnet with its coil is held to the base by two dowel pins and four screws1 enabling it to be removed as a unit as shown4 ,a new core and coil may then be substituted without the necessity of removing and replacing laminations4 ,the shunt coil in #be cycle meters is wider and contains more steel than the #fj and #acc cycle coils1 the winding also being correspondingly increased4 ,the return plate and series coil laminations are also changed in proportion to correspond to the increased width of the shunt magnet4 ,the laminations forming the core are laced into the shunt coil1 and subjected to enormous hydraulic pressure1 the rivets being set at the same time1 to form a compact unit and eliminate humming4 ,the laminated core of the shunt element has but a single air gap in which these discs rotate4 ,since meters are usually run at light loads it is important that an efficient light load adjustment or friction compensator should be provided4 ,ques4 ,what important point should be considered in the design of the friction compensator8 ,ans4 ,the compensating torque must not cause the moving element to rotate or creep without current in the series coil4 ,the rotation of a meter is caused by two distinct torques1 the varying meter torque1 dependent on the power in the circuit1 and the constant torque adjusted to compensate the initial friction4 ,the friction at all speeds is not exactly the same as the initial friction1 and therefore the friction compensating torque may be in error a few per cent4 at high speeds4 ,illustration3 ,,figs4 #b1eeb ,,and #b1eec4--;,arrangement of magnetic circuit of ,sangamo single phase induction meter4 ,fig4 #b1eeb1 front view2 fig4 #b1eec1 rear and side view4 ,as shown1 the gap of the shunt held in which the disc rotates1 projects in between the poles of the series magnet1 the return plate bending around so as to clear the upper leg of the shunt magnet4 ,this gives the desired proximity of shunt and series fields with a maximum radius of action for both sets of field4 ,in all capacities up to and including #fj amperes1 #b wire and #c wire1 round wire and taped series coils are used1 and in capacities of #hj and #ajj amperes1 strap windings4 ,meters exceeding #ajj ampere capacity have five ampere coils and are operated from external current transformers having #e ampere secondaries4 ,the series windings or coils are mounted on a laminated iron ,u shaped magnet having a laminated return path above the disc of the meter1 thus forming air gaps in which the disc rotates4 ,the series coils in all capacities not having strap windings are held firmly in position on the yoke so that they cannot slip up from the lowest position4 ,this is accomplished by means of a pair of spring brass clips slipped through the coils on the rear face of the yoke1 the clips being held by the two screws which fasten the series magnet to the main grid4 ,as an additional precaution1 spring steel lock washers are put beneath the heads of the holding screws1 thus eliminating any chance of the series magnet loosening and changing position4 ,if the compensating torque be small compared with the driving torque1 this small error percentage is negligible in its effect on accuracy4 ,the smaller it is1 the greater will be the accuracy at all loads1 and therefore1 as the compensating torque is adjusted to balance the initial friction1 the initial friction should be small compared with the driving torque4 ,a high driving torque and low initial friction are therefore desirable1 but any increase in the driving torque which necessitates an increase in friction1 is obviously useless4 ,the desirable feature of a meter is high ratio of torque to friction4 ,as the friction is practically proportional1 to the weight of the moving element1 in meters having the same form of bearing1 the ratio of torque to weight of rotor gives an approximation to the ratio of torque to friction1 but the design of bearing should not be overlooked4 ,a meter having a high torque obtained by using a thick and consequently heavy disc1 often has a lower ratio of torque to weight than another with lower torque1 and is consequently likely to be less accurate over a given range4 ,furthermore1 the heavy disc is a distinct disadvantage because it produces more wear on the bearings and thus reduces the life4 ,illustration3 ,,figs4 #b1eed ,,and #b1eee4 ,connections of ,sangamo single phase induction meter4 ,fig4 #b1eed1 #b wire meter1 #e-ajj ampere capacity2 fig4 #b1eee1 #c wire meter1 #e-ajj ampere capacity4 #g4 ,the ,power ,factor ,adjustment4 ,this adjustment is necessary to make the phase angle between the shunt and series field components #ij with unity power factor in the metered circuit4 ,owing to the resistance and iron loss in the shunt field circuit1 that field is not shifted quite #ij with respect to the voltage4 ,yet exact quadrature is necessary to make the strength of the resultant field1 and consequently the rotor speed1 proportional to the power factor1 as explained in the discussion of the field producing element4 ,ques4 ,what is the usual construction of the power factor adjustment8 ,ans4 ,it usually consists of a short circuited loop enclosing part or all of the shunt field flux4 ,ques4 ,how does this loop act8 ,ans4 ,it acts like the secondary of a transformer4 ,the flux induces a current in it which1 acting with the current in the shunt coil1 produces a slightly lagging field4 ,by shifting the position of the resistance of the short circuited loop1 the lag may be so adjusted that the shunt field flux is in exact quadrature with the voltage4 ,it should be noted1 however1 that this adjustment makes the meter correct at or near one frequency only4 ,this feature is not objectionable if reasonable accuracy be maintained within the limits of normal variation of frequency4 ,illustration3 ,,figs4 #b1eef ,,and #b1eeg4 ,connections of ,sangamo single phase induction meter4 ,fig4 #b1eef1 #b wire meter exceeding #ajj amperes2 fig4 #b1eeg1 #c wire meter exceeding #ajj amperes4 #h4 ,frequency ,adjustment4--,this is often desirable1 particularly for systems operating at #acc cycles4 ,most makes of meter are provided with means for changing the adjustment from #acc to #fj cycles in case of change in the system4 #i4 ,the ,case and ,cover4--,these parts should be dust and bug proof1 to avoid damage to the bearings1 insulation and moving parts1 and should of course be provided with means for sealing4 ,terminal chambers so arranged that the cover of the meter element need not be removed in connecting up1 are an important feature1 particularly in meters that require no adjustment at installation1 as they prevent entrance of dust into the main meter chamber4 ,a window through which the rotation of the disc can be observed in checking1 should be provided for the same reason4 ,illustration3 ,,fig4 #b1eeh4--;,faraday disc1 or mercury motor ampere hour meter2 view showing electric and magnetic circuits4 ,the ,faraday ,disc1 or ,mercury ,motor ,ampere ,hour ,meter4--,on this type of meter the mercury motor consists essentially of a copper disc floated in mercury between the poles of a magnet and provided with leads to and from the mercury at diametrically opposite points4 ,the theoretical relations of the various parts are shown in fig4 #b1eeh4 ,illustration3 ,,fig4 #b1eei4--;,diagram showing relative direction of current1 magnetic flux1 and motion of disc in ,faraday disc1 or mercury motor ampere hour meter4 ,ques4 ,explain its operation4 ,ans4 ,the electric current1 as shown in fig4 #b1eeh1 enters the contact ,c1 passes through the comparatively high resistance mercury ,h to the edge of the low resistance copper disc ,d across the disc to the mercury ,h and out of contact ,c'4 ,the magnetic flux cuts across the disc on each side from ,n to ,s1 making a complete circuit through ,m and ,m'4 ,the relative directions of the magnetic flux and the current of electricity as well as the resulting motion are shown in fig4 #b1eei4 ,according to the laws of electromagnetic induction1 if a current carrying conductor cut a magnetic field of flux at right angles1 a force is exerted upon the conductor1 tending to push it at right angles to both the current and the flux4 ,when connected to an eddy current damper or generator which requires a driving force directly proportional to the speed of rotation1 the mercury motor generator becomes a meter4 ,the speed of such a meter is a measure of the current or rate of flow of the electricity through the motor element1 and each revolution of the motor corresponds to a given quantity of electricity4 ,then1 by connecting a revolution counter to this motor generator1 a means is provided for indicating the total quantity of electricity in ampere hours that is passed through the meter4 ,illustration3 ,,fig4 #b1efj4--,sectional view of ,faraday disc or mercury motor ampere hour meter as made by ,sangamo ,electric ,co4 ,the illustration does not show the magnets and indicating mechanism4 ,ques4 ,how is the flux produced in the alternating current form of ,faraday disc meter8 ,ans4 ,by the secondary current of a series transformer4 ,frequency ,indicators4--,a frequency indicator or meter is an instrument used for determining the frequency1 or number of cycles per second of an alternating current4 ,there are several forms of frequency indicator1 whose principle of operation differs1 and according to which1 they may be classed as #a4 ,synchronous motor type2 #b4 ,resonance type2 #c4 ,induction type4 ,illustration3 ,,fig4 #b1efa4--;,circuit diagram of simple shunt ,sangamo ampere hour meter4 ,it is rated at #aj amperes1 larger currents being measured by using shunts4 ,in operation1 the main or line current to be measured passes through the shunt1 while a part proportional to the drop across the shunt1 is shunted through the meter and measured4 ,the only effect of reversing the current will be to reverse the direction of rotation of the meter4 ,in battery installations it is never possible to take the same number of ampere hours from a battery as are put into it1 hence1 if the simple shunt ampere hour meter be used for repeated and successive charges and discharges1 it will be necessary to reset the pointer to zero each time the battery is fully charged4 ,when the shunt meter is equipped with a charge stopping device1 the pointer is reset while charging1 to allow for a predetermined overcharge4 ,illustration3 ,,fig4 #b1efb4--;,circuit diagram of ,sangamo differential shunt type ampere hour meter for use in battery charging4 ,since a battery absorbs more energy on charge than it will give out on discharge1 at its working voltage1 it is usually given a certain amount of overcharge4 ,this makes desirable a meter that automatically allows for the proper amount of overcharge4 ,such a meter indicates at all times the amount of electricity available for useful work without resetting the pointer every time the battery is charged4 ,in other words1 the battery and the meter would keep in step for considerable periods of time without readjustment4 ,the ,sangamo differential shunt meter is designed to meet these requirements1 and it consists essentially of a ,sangamo meter with two shunts connected as shown4 ,the relative value of shunt resistance is adjustable by means of slider ,g1 so that the meter can be made to run slow on charge or fast on discharge1 whichever may be desired4 ,the usual method is to allow the meter to register less than the true amount on charge and the exact amount on discharge1 the difference representing the loss in the battery1 or the overcharge4 ,if the meter be provided with a charge stopping device1 the battery can be given an amount of overcharge predetermined by the setting of the slider ,g4 ,therefore the amount of overcharge can be fixed in advance by a skilled man and the actual charging done by any unskilled person1 since all there is to do is to make the connection4 ,ques4 ,how is a synchronous motor employed as a frequency indicator8 ,ans4 ,a small synchronous motor is connected in the circuit of the current whose frequency is to be measured4 ,after determining the revolutions per minute by using a revolution counter1 the frequency is easily calculated as follows3 frequency 7revolutions per second number of poles7 #b4 ,illustration3 ,,figs4 #b1efc and #b1efd4--;,frahm resonance type frequency meter4 ,fig1 #b1efc1 portable meter2 fig4 #b1efd1 switchboard meter4 ,the readings are correct in either the vertical or horizontal position4 ,the energy consumption at #ajj volts is about #a to #b volt amperes1 and is approximately proportional for other pressures4 ,the regular portable meters are arranged for pressures of from #ej to #cjj volts1 and for this purpose they are fitted with terminals for #fe1 #ajj1 #acj1 #ahj1 and #bej volts4 ,in order to obtain full amplitude at intermediate pressures1 a milled headed screw is provided for adjusting the base piece mechanically1 and thereby permitting of regulating the pressure range within #bj per cent2 this insures indications of maximum clearness4 ,should it be desired to extend the standard pressure range of #ej to #cjj volts1 up to #fjj volts1 two further terminals for #cej and #ejj volts are necessary1 so that these instruments are provided with eight fixed terminals in addition to the mechanical regulating device4 ,instruments which are intended for connecting to one specific supply or to the secondary of a pressure transformer1 require only a single pressure range1 say #ajj volts1 with the aforementioned regulating device4 ,the frequency range is from #g4e to #fjj cycles per second4 ,in order to obtain easily readable indications1 one reed is provided for every quarter period for frequencies below #cj1 for every half period for frequencies between #cj and #hj1 and for every whole period for frequencies between #hj and #adj4 ,the use of a smaller number of reed1 that is to say1 of larger intervals between the periods of vibration of adjoining reeds1 is only recommended for circuits having very variable frequencies1 as otherwise no reed might respond to the vibrations caused by intermediate frequencies4 ,the arrangement of the separate reeds on a common base piece1 permits supplying any combination of interval that may be required4 ,it is often desirable to secure two ranges with one set of reed4 ,to do this a second electromagnet is supplied4 ,it is polarized1 and operates on the same base plate4 ,in the case of alternating current when the unpolarized magnet is used the reeds receive two impulses during each cycle1 while with the polarized magnet they receive but one impulse per cycle4 ,a commutator is provided to easily make the change from one range to the other4 ,if there be two sets of reed1 the one commutator may be connected to change both4 ,this device is only applicable when alternating current is measured4 ,instruments with unpolarized magnets are made with frequencies of #ae to #cjj cycles per second4 ,ques4 ,describe the resonance method of obtaining the frequency4 ,ans4 ,in construction1 the apparatus consists of a pendulum1 or reed1 of given length1 which responds to periodic forces having the same natural period as itself4 ,the instrument comprises a number of reeds of different lengths1 mounted in a row1 and all simultaneously subjected to the oscillatory attraction of an electromagnet excited by the supply current that is being measured4 ,the reed1 which has the same natural time period as the current will vibrate1 while the others will remain practically at rest4 ,illustration3 ,,figs4 #b1efe and #b1eff4--,side and end views of ,frahm resonance type frequency meter reeds4 ,owing to the principle employed in the meter it is evident that the indications are independent of the voltage1 change of wave form1 and external magnetic fields4 ,the construction and operation of the instrument may be better understood from figs4 #b1efe and #b1eff1 which illustrates the indicating part of the ,frahm meter4 ,this consists of one or more rows of tuned reeds rigidly mounted side by side on a common and slightly flexible base4 ,the reeds are made of spring steel1 #c or #g mm4 wide1 with a small portion of their free ends bent over at right angles as shown in fig4 #b1eff and enameled white so that when viewed end on they will be easily visible4 ,the reeds are of adjustable length1 and are weighted at the end4 ,a piece of soft iron1 rigidly fastened on the base plate which supports the reeds1 forms the armature of a magnet4 ,when the magnet is excited by alternating current1 or interrupted direct current1 the armature is set in vibration1 and that gives a slight movement to the base plate at right angles to its axis1 thereby affecting all the reeds1 especially those which are almost in tune with its vibrations4 ,the reed which is in tune will vibrate through an arc of considerable amplitude1 and so indicate the frequency of the exciting current4 ,ques4 ,for what use is the resonance type of frequency meter most desirable8 ,ans4 ,for laboratory use4 ,illustration3 ,,fig4 #b1efg4--,westinghouse induction type frequency meter4 ,the normal frequency is usually at the top of the scale to facilitate reading4 ,the damping disc moves in a magnetic field1 thus damping by the method of eddy currents4 ,the standard meters are designed for circuits of #ajj volts nominal and can be used for voltages up to #abe volts4 ,for higher voltages1 transformers with nominal #ajj volt secondary should be used4 ,ques4 ,describe the induction type of frequency meter4 ,ans4 ,it consists of two voltmeter electromagnets acting in opposition on a disc attached to the pointer shaft4 ,one of the magnets is in series with an inductance1 and the other with a resistance1 so that any change in the frequency will unbalance the forces acting on the shaft and cause the pointer to assume a new position1 when the forces are again balanced4 ,the aluminum disc is so arranged that when the shaft turns in one direction the torque of the magnet tending to rotate it decreases1 while the torque of the other magnet increases4 ,the pointer therefore comes to rest where the torques of the two magnets are equal1 the pointer indicating the frequency on the scale4 ,illustration3 ,,fig4 #b1efh4--,langsdorf and ,begole frequency meter4 ,the operation of this meter is based on the fact that if an alternating pressure of ,e ,volts be impressed on a condenser of capacity ,c1 in farads1 the current in amperes will be equal to #b ,,ec1 provided the pressure be constant4 ,in construction1 the scale is mounted on the same axis as the pressure coil1 across the mains so as to render the instrument independent of variation of voltage4 ,for a discussion of this meter1 see ,electrical ,review1 vol4 ,,lviii1 page #aad4 ,illustration3 ,,fig4 #b1efi4--;,general ,electric horizontal edgewise1 induction type frequency indicator4 ,it is provided with an external inductance and resistance placed in a ventilated cage for mounting on the back of the switchboard4 ,means are provided for adjusting the instrument for the characteristics of the circuit on which it is installed4 ,standard instruments are wound for #ajj to #abe volt circuits only1 but can be wound for circuits up to and including #fej volts4 ,instruments for use on circuits in excess of #fej volts are always provided with pressure transformers4 ,the normal operating point is marked at approximately the center of the scale1 thus giving the advantage of very open divisions4 ,the standard frequencies are #be1 #dj1 #fj1abe and #acc4 ,ques4 ,what is the object of the aluminum disc8 ,ans4 ,its function is to damp the oscillations of the pointer4 ,illustration3 ,,fig4 #b1egj4--,westinghouse rotary type of synchroscope or synchronism indicator4 ,the indication is by means of a pointer which assumes at every instant a position corresponding to the phase angle between the pressures of the busbars and the incoming machine1 and therefore rotates when the incoming machine is not in synchronism4 ,the direction of rotation indicates whether the machine be fast or slow1 and the speed of rotation depends on the difference in frequency4 ,the pointer is continuously visible1 during both the dark and light periods of the synchronizing lamps4 ,synchronism ,indicators4--,these devices1 sometimes called synchroscopes1 or synchronizers indicate the exact difference in phase angle at every instant1 and the difference in frequency1 between an incoming machine and the system to which it is to be connected1 so that the coupling switch can be closed at the proper instant4 ,there are several types of synchronizer1 such as #a4 ,lamp or voltmeter2 #b4 ,resonance or vibrating reed2 #c4 ,rotating field4 ,the simplest arrangement consists of a lamp or preferably a voltmeter connected across one pole of a two pole switch connecting the incoming machine to the busbars1 the other pole of the switch being already closed4 ,if the machines be out of step1 the lamps will fluctuate in brightness1 or the voltmeter pointer will oscillate1 the pulsation becoming less and less as the incoming machine approaches synchronous speed4 ,synchronism is shown by the lamp remaining out1 or the voltmeter at zero4 ,illustration3 ,,fig4 #b1ega4--;,general ,electric synchronism indicator4 ,the synchronism indicator is a motor whose field is supplied with single phase current from one of the machines to be synchronized1 and its armature from the other4 ,the armature carries two inductance coils placed at a large angle1 one supplied through a resistance1 the other through an inductance4 ,this arrangement generates a rotating field in the armature1 while the stationary field is alternating4 ,the armature tends to assume a position where the two fields coincide when the alternating field passes through its maximum2 hence1 the armature and pointer move forward or backward at a rate corresponding to the difference of frequency1 and the position when stationary depends on the phase relation4 ,when the machines are running at the same frequency and in phase the pointer is stationary at the marked point4 ,in construction1 it is like a small1 two phase1 bipolar synchronous motor1 the field being supplied with alternating instead of direct current4 ,the armature is mounted in ball bearings in order to make it sufficiently sensitive and smooth in operating4 ,the armature coils are not exactly #ij degrees apart1 since it is not possible to get the current in the two coils exactly in quadrature without introducing condensers on other complicated construction4 ,standard ratings are for #aaj and #bbj volt circuits4 ,synchronism indicators should be ordered for the frequency of the circuit on which they are to be operated1 although the instruments may be used on circuits varying #aj per cent to #ae per cent from the normal4 ,the words ,fast and ,slow on the dial indicate that the frequency on binding posts ,e and ,f is respectively higher or lower than that on ,a and ,b2 or1 in other words1 clockwise rotation of the pointer means that the incoming machine is running at too high speed1 counter clockwise rotation indicating too low speed4 ,ques4 ,how does the resonance type of synchronism indicator operate8 ,ans4 ,on the same principle as the resonance type of frequency indicator1 already described4 ,ques4 ,what is the principle of the rotating field type of synchronism indicator8 ,ans4 ,its operation depends on the production of a rotating field by the currents of the metered circuits in angularly placed coils1 one for each phase in the case of a polyphase indicator4 ,in this field is provided a movable iron vane or armature1 magnetized by a stationary coil whose current is in phase with the voltage of one phase of the circuit4 ,as the iron vane is attracted or repelled by the rotating field1 it takes up a position where the zero of the rotating field occurs at the same instant as the zero of its own field4 ,in the single phase meter the positions of voltage and current coils are interchanged and the rotating field is produced by means of a split phase winding connected to the voltage circuit4 ,illustration3 ,,fig4 #b1egb4--;,general ,electric external resistance and inductance for #aaj volt synchronism indicator4 ,both the resistance and inductance are intended to be placed behind the switchboard4 ,illustration3 ,,figs4 #b1egc to #b1egf4--;,connections of ,general ,electric synchronism indicator4 ,fig4 #b1egc1 connections with grounded secondaries on pressure transformers2 fig4 #b1egd1 connections with ungrounded secondaries on pressure transformers2 fig4 #b1ege1 connections for #bjj to #bdj volt circuits1 with six point receptacles2 fig4 #b1egf1 connections for checking location of needle4 ,the various letters referred to in the diagrams will be found marked on the ends of the instrument studs and back of reactance coil box4 ,it is important that the instrument be connected in circuit in the proper manner so that the needle will come to the mark on the upper part of the scale when synchronism is obtained4 ,in case the pointer become moved or a change in its position be necessary1 it is advisable to make a check on the indication before relocating the needle4 ,this test can be made as follows3 ,connect together 7fig4 #b1egc7 studs marked ,b and ,e and connect stud ,a to terminal ,f on the external reactance box4 ,when these connections are made1 the instrument can be connected to a single phase circuit of normal voltage and if the instrument be correct1 the pointer will stand vertically at the point of synchronism4 ,if it do not1 the needle can be moved and should be fastened in the correct position4 ,the synchronizing lamps when connected as illustrated in the diagrams1 show dark when synchronism is reached4 ,this is the only connection possible when grounded secondaries are used1 as in fig4 #b1egc1 and for the high voltage indicators when used as in fig4 #b1ege1 but with ungrounded secondaries 7fig4 #b1egd7 the lamps may be connected as indicated1 when they will show bright at the moment of synchronism4 ,the connections to the synchronism indicator remain the same as before4 ,power ,factor ,indicators4--,meters of this class indicate the phase relationship between pressure and current1 and are therefore sometimes called phase indicators4 ,there are two types3 #a4 ,wattmeter type2 #b4 ,disc1 or rotating field type4 ,illustration3 ,,fig4 #begg4--;,general ,electric synchronizing receptacle and plug for use with synchronism indicator4 ,illustration3 ,,fig4 #b1egh4--,westinghouse rotating field type power factor meter4 ,the rotating field is produced by the currents of the metered circuits in angularly placed coils1 one for each phase of the system1 in the case of polyphase meters4 ,in the three phase meter the rotating field is produced by three coils spaced #fj apart2 in the two phase meter by two coils spaced #ij2 in the single phase meter the positions of voltage and current coils are interchanged and the rotating field is produced by means of a split phase winding1 connected to the voltage circuit4 ,there are no movable coils or flexible connections4 ,single phase meters indicate the power factor of a single phase circuit1 or of one branch of any polyphase circuit4 ,special calibration is necessary in order to use a single phase instrument on a three phase circuit unless the voltage coil be connected from one line to the neutral4 ,polyphase meters indicate the average angle between the currents and voltages and are superior for polyphase service to meters having only one current coil4 ,in the wattmeter type1 the phase relation between the pressure and the current fluxes is such that on a non-inductive load the torque is zero4 ,for instance1 in a dynamometer wattmeter1 the pressure circuit is made highly inductive and the instrument then indicates volts amperes sin instead of volts amperes cos 1 that is to say1 it will indicate the wattless component of the power4 ,a dynamometer of this type is sometimes called an idle current wattmeter4 ,illustration3 ,,fig4 #b1egi4--,single phase power factor meter of the rotating field or disc type4 ,ques4 ,describe a single phase power factor meter of the disc or rotating field type4 ,ans4 ,it consists of two pressure coils1 as shown in fig4 #b1egi1 placed at right angles to each other1 one being connected through a resistance1 and the other through an inductance so as to split the phase and get the equivalent of a rotating magnetic field4 ,the coils are placed about a common axis1 along which is pivoted an iron disc or vane4 ,the magnetizing coils ,,fg are in series with the load4 ,if the load be very inductive1 the coil ,m experiences very little torque and the system will set itself as shown in the figure4 ,as the load becomes less inductive1 the torque on ,s decreases and on ,m increases so that the system takes up a particular position for every angle of lag or lead4 ,ground ,detectors4--,instruments of this name are used for detecting 7and sometimes measuring7 the leakage to earth or the insulation of a line or network and are sometimes called ground or earth indicators1 or leakage detectors4 ,for systems not permanently earthed anywhere1 these instruments are nearly all based on a measurement of the pressure difference between each pole and earth1 two measurements being required for two wire systems1 and three for three wire1 whether direct current single phase1 or polyphase alternating current4 ,in the case of direct current systems1 the insulation1 both of the network and of the individual lines1 can be calculated from the readings1 but with alternating current1 the disturbance due to capacity effects is usually too great4 ,in any case1 however1 the main showing the smallest pressure difference to earth must be taken as being the worst insulated4 ,for low tension systems moving coil 7for alternating current7 or moving iron instruments 7for direct current7 are the most used1 while for high tension systems electrostatic voltmeters are to be preferred4 ,on systems having some point permanently earthed at the station1 as for instance the neutral wire of direct current system1 or the neutral point of a three phase system1 an ammeter connected in the earth wire will serve as a rough guide4 ,it should indicate no current so long as the insulation is in a satisfactory state1 but on the occurrence of an earth it will at once show a deflection4 ,the indications are1 however1 often misleading1 and serve more as a warning than anything else4 ,illustration3 ,,fig4 #b1ehj4--,westinghouse single phase electrostatic ground detector4 ,illustration3 ,,fig4 #b1eha4--,westinghouse three phase electrostatic ground detector4 ,illustration3 ,,fig4 #b1ehb4--,wallis-,jones automatic earth leakage cut out4 ,it is an instrument which so protects a direct current circuit that the circuit is broken whenever a leak occurs from either main to earth1 and so that the circuit cannot be permanently re-established until the leak has been removed4 ,the instrument and its connections may be explained by the aid of the accompanying diagram1 in which ,t and ,t represent the points of connection from the mains1 and ,t and ,t1 the points of connection to the circuit to be protected4 ,so ,s1 and ,s will preferably be ordinary tumbler switches1 but they are diagrammatically represented as plain bar switches1 their fixed contacts being diagrammatically represented by dotted circles4 ,when the three switches ,s1 ,s1 and ,s are closed1 the current passes from ,t to ,t through the small resistance ,r1 through circuit ,l to ,t1 and back through the resistance ,r to ,t4 ,in shunt with ,r and ,r1 are the two moving coils ,c and ,c1 working in the magnetic field of the magnets ,,ns1 ,,ns1 and rigidly fixed on one spindle1 which is broken electrically by an ebonite block ,e4 ,the points of connection to the shunts are adjusted so that when the same current passes out through one and back through the other1 the effect on the two coils is equal and opposite1 and there is thus no movement4 ,should1 however1 any minute portion of the current through ,r leak to earth instead of returning via ,r1 the balance is disturbed1 ,c becomes stronger than ,c1 the system is deflected1 and a contact is made by the arm ,a at ,b1 no matter in which direction the coils deflect4 ,the system is similarly deflected for a leak on the other lead4 ,in the diagram these contacts are shown at right angles to their normal plane4 ,as soon as the contact is made1 the electromagnet ,m is energized1 the arm of ,s is released and the spring at once pulls it off its contact1 at the same time breaking ,s4 ,the positions of the blades when the switches are open are shown dotted4 ,the only means the user has of closing the circuit is by putting on ,s by the handle ,h1 which is outside the locked box4 ,the first effect of putting on ,s is to break its circuit2 it then by means of the slotted bar ,p begins to pull on ,s and ,s1 which can thus be closed again1 and held closed by the trigger as before4 ,the circuit1 is1 however1 still broken till ,s is pushed back4 ,then if the leak be still on1 the slot in ,p allows ,s and ,s to open at once as before4 ,it is therefore impossible to keep the circuit closed while the leak exists4 ,the working condition of the instrument can be tested at any time by switching a lamp on in the circuit and depressing one of the keys ,k1 ,k4 ,this short circuits ,r or ,r1 throws the coils out of balance1 and the switch opens4 ,the contact arm is closed in an inner dust tight case1 and it will be noted that it makes contact only2 the break occurs at the switches1 thus avoiding any sparking4 ,since the two coils work in the two gaps of one and the same field1 changes in the strength of the magnets have no effect1 the apparatus is enclosed in a locked metallic box1 and the only part to which the user has access is the handle ,h1 and1 if desired1 the testing keys ,k ,k4 ,,hawkins ,,practical ,,library ,,of ,,electricity ,,in ,,handy ,,pocket ,,form ,,price #a ,,each 99 99 99 99 99 ,they are not only the best1 but the cheapest work published on ,electricity4 ,each number being complete in itself4 ,separate numbers sent postpaid to any address on receipt of price4 ,they are guaranteed in every way or your money will be returned4 ,complete catalog of series will be mailed free on request4 ,,electrical ,,guide1 ,,no4 #a ,containing the principles of ,elementary ,electricity1 ,magnetism1 ,induction1 ,experiments1 ,dynamos1 ,electric ,machinery4 ,,electrical ,,guide1 ,,no4 #b ,the construction of ,dynamos1 ,motors1 ,armatures1 ,armature ,windings1 ,installing of ,dynamos4 ,,electrical ,,guide1 ,,no4 #c ,electrical ,instruments1 ,testing1 ,practical ,management of ,dynamos and ,motors4 ,,electrical ,,guide1 ,,no4 #d ,distribution ,systems1 ,wiring1 ,wiring ,diagrams1 ,sign ,flashers1 ,storage ,batteries4 ,,electrical ,,guide1 ,,no4 #e ,principles of ,alternating ,currents and ,alternators4 ,,electrical ,,guide1 ,,no4 #f ,alternating ,current ,motors1 ,transformers1 ,converters1 ,rectifiers4 ,,electrical ,,guide1 ,,no4 #g ,alternating ,current ,systems1 ,circuit ,breakers1 ,measuring ,instruments4 ,,electrical ,,guide1 ,,no4 #h ,alternating ,current ,switch ,boards1 ,wiring1 ,power ,stations1 ,installation and ,operation4 ,,electrical ,,guide1 ,,no4 #i ,telephone1 ,telegraph1 ,wireless1 ,bells1 ,lighting1 ,railways4 ,,electrical ,,guide1 ,,no4 #aj ,modern ,practical ,applications of ,electricity and ,ready ,reference ,index of the #aj ,numbers4 ,theo4 ,audel ,co41 ,publishers4 #gb ,,fifth ,,avenue1 ,,new ,,york ,,transcriber',s ,,notes ,silently corrected simple spelling1 grammar1 and typographical errors4 ,retained anachronistic and non-standard spellings as printed4 ,enclosed italics markup in underscores4 ,enclosed bold markup in tildes4