,transcriber's ,notes3 ,underscores before and after a word or phrase indicate italics in the original text4 ,equal signs before and after a word or phrase indicate bold in the original text4 ,small capitals have been converted to ,,solid capitals4 ,illustrations have been moved so they do not break up paragraphs4 ,misprints in the table ,,saving ,,due ,,to ,,heating ,,the ,,feed ,,water1 ,pg4 #aicf have been corrected1 they are3 ,init4 ,temp4 ,pressure ,old ,value ,new ,value #acj #dj 4#jied 4#jicd #bjj #dj 4#jijj 4#jiii #baj #dj 4#ajjj 4#ajaj #bcj #ajj 4#jaag 4#ajab ,in the original text1 there are two ,fig4 #bgfi's and two ,fig4 #bggj's4 ,the second of each has had an a suffix added1 i4e4 #bgfi;a and #bggj;a4 ,on line #gcig the word impedence was corrected to impedance4 ,superscripts are shown as d and subscripts are shown as d1 where d is an integer4 ,inconsistent spelling and hyphenation has been left as in the original4 ,,the ,,thought ,,is ,,in ,,the ,,question ,,the ,,information ,,is ,,in ,,the ,,answer ,,hawkins ,,electrical ,,guide ,,number ,,eight ,,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 ,,theo ,,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 #h ,,wave ,,form ,,measurement #a1hci to #a1hfh ,importance of wave form measurement--methods3 step by step2 constantly recording--classes of apparatus3 wave indication2 oscillographs--step by step methods--,joubert's2 four part commutator2 modified four part commutator2 ballistic galvanometer2 zero2 ,hospitalier ondograph--constantly recording methods3 cathode ray2 glow light2 moving iron2 moving coil2 hot wire--oscillographs--moving coil type2 construction and operation2 production of the time scale2 oscillograms--falling plate camera2 its use4 ,,switchboards #a1hfi to #a1hhd ,general principles3 diagram--small plant a4c4 switchboard--switchboard panels2 generator panel2 diagram of connections--simple method of determining bus bar capacity--feeder panel--diagrams of connection for two phase and three phase installations4 ,,alternating ,,current ,,wiring #a1hhe to #a1iad ,effects to be considered in making calculations--induction2 self- and mutual2 mutual induction1 how caused--transpositions--inductance per mile of three phase circuit1 table--capacity2 table--frequency--skin effect2 calculation2 table--corona effect2 its manifestation2 critical voltage2 spacing of wires--resistance of wires--impedance--power factor2 apparent current2 usual power factors encountered2 example--wire calculations--sizes of wire--table of the property of copper wire--drop2 example--current--example covering horse power1 watts1 apparent load1 current1 size of wire1 drop1 voltage at the alternator1 and electrical horse power4 ,,power ,,stations #a1iae to #a1ihh ,classification--central stations2 types3 a4c41 d4c41 and a4c4 and d4c42 reciprocating engine vs4 turbine--location of central stations2 price of land2 trouble after erection2 water supply2 service requiring direct current--size of plant2 nature of load2 peak load2 load factor2 machinery required2 example2 factors of evaporation2 grate surface per horse power--general arrangement of station2 belt drive with counter shaft2 desirable features of belt drive2 conditions1 suitable for counter shaft drive2 location of engine and boilers2 the steam pipe2 piping between engine and condenser2 number and type of engine2 superheated steam2 switchboard location2 individual belt drive2 direct drive--station construction--foundations--walls-- roofs--floors--chimneys2 cost of chimneys and mechanical draft2 high chimneys ill advised--steam turbine2 types3 impulse and reaction2 why high vacuum is necessary2 the working pressure--hydro-electric plants--water turbines2 types3 impulse1 reaction--isolated plants--sub-stations2 arrangement2 three phase installations2 reactance coils in sub-stations2 portable sub-stations4 ,,management #a1ihi to #b1aad ,the term management--selection2 general considerations--selection of generators2 efficiency of generators2 size and number2 regulation--installation2 precautions2 handling of armatures2 assembling a machine2 speed of generators2 calculation of pulley sizes2 gear wheels--belts2 various belt drives2 horse power transmitted by belts2 velocity of belt2 endless belts--switchboards2 essential points of difference between single phase and three phase switchboard wiring2 assembling a switchboard2 usual equipment4 ,operation of ,alternators--alternators in parallel2 synchronizing2 lamp methods2 action of amortisseur winding2 synchronizing three phase alternators2 disadvantage of lamp method--cutting out alternator2 precautions2 hunting--alternators in series4 ,transformers2 selection2 efficiency2 kind of oil used2 detection of moisture2 drying oil2 regulation2 transformers in parallel2 polarity test--motor generators2 various types and conditions requiring same--dynamotors2 precautions--rotary converters2 objections to single phase type2 operation when driven by direct current1 by alternating current2 most troublesome part2 efficiency2 overload2 starting2 starting current4 ,electrical measuring instruments2 location2 readings2 station voltmeters2 points relating to ammeters2 attention necessary2 usual remedies to correct voltmeter--how to test generators2 commercial efficiency2 various tests4 ,station ,testing3 resistance measurement by drop method--methods of connecting ammeter voltmeter and wattmeter for measurement of power--motor testing3 single phase motor--three phase motor1 voltmeter and ammeter method2 two wattmeter method2 polyphase wattmeter method2 one wattmeter method2 one wattmeter and ,y box method--three phase motor with neutral brought out2 single wattmeter method--temperature test1 three phase induction motor--three phase alternator testing3 excitation or magnetization curve test--synchronous impedance test--load test--three phase alternator or synchronous motor temperature test--direct current motor or generator testing3 magnetization curve--7shunt7 external characteristic--direct current motor testing2 load and speed tests--temperature test1 loading back method--compound dynamo testing3 external characteristic1 adjustable load--transformer testing3 external characteristic1 adjustable load--transformer testing3 core loss and leakage or exciting current test--copper loss--copper loss by wattmeter measurement and impedance--temperature--insulation--inte rnal insulation--insulation resistance--polarity--winding or ratio tests4 ,,chapter ,,lxiii ,,wave ,,form ,,measurement ,the great importance of the wave form in alternating current work is never denied1 though it has sometimes been overlooked4 ,the application of large gas engines to the driving of alternators operated in parallel requires an accurate knowledge of the wave form1 and a close conformation to a sine wave if parallel operation is to be satisfactory4 ,it is also important that the fluctuations in magnetism of the field poles should be known1 especially if solid steel pole faces be used4 ,if an alternator armature winding be connected in delta1 the presence of a third harmonic becomes objectionable1 as it gives rise to circulating currents in the winding itself1 which increase the heating and lowers the efficiency of the machine4 ,that the importance of having a good wave form is being realized1 is proved by the increasing prevalence in alternator specifications of a clause specifying the maximum divergence allowable from a true sine wave4 ,it is however perhaps not always realized that an alternator which gives a good pressure wave on no load may give a very bad one under certain loads1 and the ability of the machine to maintain a good wave form under severe conditions of load is a better criterion of its good design than is the shape of its wave at no load4 ,the question of wave form is of special interest to the power station engineer4 ,upon it depends the answer to the questions3 whether he may ground his neutral wires without getting large circulating currents2 whether he may safely run any combination of his alternators in parallel2 whether the constants of his distributing circuit are of an order liable to cause dangerous voltage surges due to resonance with the harmonics of his pressure wave2 what stresses he is getting in his insulation due to voltage surges when switching on or off1 etc4 ,it has been shown by ,rossler and ,welding that the luminous efficiency of the alternating current arc may be #dd per cent4 higher with a flat topped than with a peaked pressure wave1 while on the other hand it is well known that transformers are more efficient on a peaked wave4 ,also the accuracy of many alternating current instruments depends upon the wave shape4 ,in making insulation breakdown tests on cables1 insulators1 or machinery1 large errors may be introduced unless the wave form at the time of the test be known4 ,it is not sufficient even to know that the testing alternator gives a close approximation to a sine wave at no load2 since if the capacity current of the apparatus under test be moderately large compared with the full load current of the testing alternator1 the charging current taken may be sufficient to distort the wave form considerably1 thus giving wrong results to the disadvantage of either the manufacturer or purchaser4 ,illustration3 ,,fig4 #b1ehc4--;,general ,electric simultaneous record of three waves with common zero4 ,the desirability of a complete knowledge of the manner in which the pressure and current varies during the cycle1 has resulted in various methods and apparatus being devised for obtaining this knowledge4 ,the apparatus in use for such purpose may be divided into two general classes1 #a4 ,wave indicators2 #b4 ,oscillographs4 and the methods employed with these two species of apparatus may be described respectively as1 #a4 ,step by step2 #b4 ,constantly recording4 that is to say1 in the first instance1 a number of instantaneous values are obtained at various points of the cycle1 which are plotted and a curve traced through the several points thus obtained4 ,a constantly recording method is one in which an infinite number of values are determined and recorded by the machine1 thus giving a complete record of the cycle1 leaving no portion of the wave to be filled in4 ,illustration3 ,,fig4 #b1ehd4--;,general ,electric simultaneous record of three waves with separate zeros4 ,illustration3 ,figs4 #b1ehe and #b1ehf4--,oscillograms 7from paper by ,morris and ,catterson-,smith1 ,proc4 ,i4 ,e4 ,e41 ,vol4 ,,xxxiii1 page #a1jbc71 showing how the current varies in one of the armature coils of a direct current motor4 ,fig4 #b1ehe was obtained with the brushes in the neutral position1 and fig4 #b1ehf with the brushes shifted forward4 ,the various methods of determining the wave form may be further classified as3 ,joubert's method2 ,four part commutator method2 ,modified four part commutator method2 #a4 ,step by step ,ballistic galvanometer method2 ,zero method2 ,by ,hospitalier ondograph4 ,illustration3 ,,fig4 #b1ehg4--,oscillogram by ,bailey and ,cleghorne 7,proc4 ,i4,e4,e41 ,vol4 ,,xxxviii71 showing the sparking pressure or pressure between the brush and the commutator segment at the moment of separation4 ,the waves fall into groups of three owing to the fact that there were three armature coils in each slot4 cathode ray2 by use of various types glow light2 #b4 constantly recording of oscillograph1 moving iron2 such as moving coil2 hot wire4 ,illustration3 ,,fig4 #b1ehh4--,various wave forms4 ,the sine wave represents a current or pressure which varies according to the sine law4 ,a distorted wave is due to the properties of the circuit1 for instance1 the effect of hysteresis in an iron core introduced into a coil is to distort the current wave by adding harmonics so that the ascending and descending portions may not be symmetrical4 ,a peaked wave has a large maximum as compared with its virtual value4 ,a peaked wave is produced by a machine with concentrated winding4 ,joubert's ,method4--,the apparatus required for determining the wave form by this step by step method1 consists of a galvanometer1 condenser1 two1 two way switches1 resistance and adjustable contact maker1 as shown in fig4 #b1ehi4 ,the contact maker is attached to the alternator shaft so that it will rotate synchronously with the latter4 ,by means of the adjustable contact1 the instant of making that is1 of closing the testing circuit may be varied1 and the angular position of the armature1 at which the testing circuit is closed1 determined from the scale1 which is divided into degrees4 ,a resistance is placed in series with one of the alternator leads1 such that the drop across it1 gives sufficient pressure for testing4 ,ques4 ,describe the method of making the test4 ,illustration3 ,,fig4 #b1ehi4--;,diagram illustrating ,joubert's step by step method of wave form measurement4 ,ans4 ,for current wave measurement switch ,no4 #a is placed on contact ,f1 and for pressure wave measurement1 on contact ,g1 switch ,no4 #b is now turned to ,m and the drop across the resistance 7assuming switch ,no4 #a to be turned to contact ,f7 measured by charging the condenser1 and then discharging it through the galvanometer by turning the switch to ,s4 ,this is repeated for a number of positions of the contact maker1 noting each time the galvanometer reading and position of the contact maker4 ,by plotting the positions of contact maker as absciss1 and the galvanometer readings as ordinates1 the curve drawn through them will represent the wave form4 ,illustration3 ,,fig4 #b1eij4--;,four part commutator method of wave form measurement4 ,the contact device consists of two slip rings and a four part commutator4 ,one slip ring is connected to one terminal of the source1 the other to the voltmeter1 and the commutator to the condenser4 ,by adjusting ,r when a known direct current pressure is impressed across the terminals1 the voltmeter can be rendered direct reading4 ,illustration3 ,,fig4 #b1eia4--,modified four part commutator method of wave form measurement 7,duncan's modification74 ,by this method one contact maker can be used for any number of waves having the same frequency4 ,electro-dynamometers are used and the connections are made as here shown4 ,the moving coils are connected in series to the contact maker1 and the fixed coils are connected to the various sources to be investigated1 then the deflection will be steady and by calibration with direct current can be made to read directly in volts4 ,the apparatus is calibrated by passing a known constant current through the resistance4 ,illustration3 ,,fig4 #b1eib4--;,diagram illustrating the ballistic galvanometer method of wave form measurement4 ,the test may be made as described in the accompanying text1 or in case the contact breaker is belted instead of attached rigidly to the shaft1 it could be arranged to run slightly out of synchronism1 then by taking readings at regular intervals1 points will be obtained along the curve without moving the contact breaker4 ,if this method be used1 a non-adjustable contact breaker suffices4 ,in arranging the belt drive so as to run slightly out of synchronism1 if the pulleys be of the same size1 the desired result is obtained by pasting a thin strip of paper around the face of one of the pulleys thus altering the velocity ratio of the drive slightly from unity4 ,ballistic ,galvanometer ,method4--,this method1 which is due to ,kubber1 employs a contact breaker instead of a contact maker4 ,the distinction between these two devices should be noted3 ,a contact maker keeps the circuit closed during each revolution for a short interval only1 whereas1 a contact breaker keeps the circuit open for a short interval only4 ,fig4 #b1eib1 shows the necessary apparatus and connections for applying the ballistic galvanometer method4 ,the contact breaker consists of a commutator having an ebonite or insulating segment and two brushes4 ,in operation the contact breaker keeps the circuit closed during all of each revolution1 except the brief interval in which the brushes pass over the ebonite segment4 ,the contact breaker is adjustable and has a scale enabling its various positions of adjustment to be noted4 ,ques4 ,describe the test4 ,illustration3 ,,figs44 #b1eic and #b1eid4--,two curves representing pressure and current respectively of a rotary converter4 ,fig4 #b1eic1 pressure wave ,v1 fig4 #b1eid current wave ,c4 ,these waves were obtained from a converter which was being driven by an alternator by means of an independent motor4 ,the rotary converter was supplying idle current to some unloaded transformers and the ripples clearly visible in the pressure wave ,v1 correspond to the number of teeth in the armature of the rotary converter4 ,ans4 ,the contact breaker is placed in successive positions and galvanometer readings taken1 the switch being turned to ,f1 fig4 #b1eib1 in measuring the current wave1 and to ,g in measuring the pressure wave4 ,the results thus obtained are plotted giving respectively current and pressure waves4 ,ques4 ,how is the apparatus calibrated8 ,ans4 ,by sending a constant current of known value through the resistance ,r4 ,zero ,method4--,in electrical measurements1 a zero method is one in which the arrangement of the testing devices is such that the value of the quantity being measured is shown when the galvanometer needle points to zero4 ,in the zero method either a contact maker or contact breaker may be used in connection with a galvanometer and slide wire bridge1 as shown in figs4 #b1eie and #b1eif4 ,illustration3 ,,fig4 #b1eie4--;,diagram illustrating zero method of wave measurement with contact maker4 ,the voltage of the battery must be at least as great as the maximum pressure to be measured and must be kept constant4 ,ques4 ,what capacity of battery should be used8 ,ans4 ,its voltage should be as great as the maximum pressure to be measured4 ,ques4 ,what necessary condition must be maintained in the battery8 ,ans4 ,its pressure must be kept constant4 ,ques4 ,how are instantaneous values measured8 ,ans4 ,the bridge contact ,a is adjusted till the galvanometer shows no deflection1 then the length ,,as is a measure of the pressure4 ,the drop between these points can be directly measured with a voltmeter if desired4 ,ques4 ,how did ,mershon modify the test8 ,ans4 ,he used a telephone instead of the galvanometer to determine the correct placement of the bridge contact ,a4 ,illustration3 ,,fig4 #b1eif4--;,diagram illustrating zero method of wave measurement with contact breaker4 ,the voltage of the battery must be at least as great as the maximum pressure to be measured and must be kept constant4 ,ques4 ,how can the instantaneous values be recorded8 ,ans4 ,by attaching to the contact ,a1 a pencil controlled by an electro-magnet arranged to strike a revolving paper card at the instant of no deflection1 the paper being carried on a drum4 ,hospitalier ,ondograph4--,the device known by this name is a development of the ,joubert step by step method of wave form measurement1 that is to say1 the principle on which its action is based1 consists in automatically charging a condenser from each #ajjth wave1 and discharging it through a recording galvanometer1 each successive charge of the condenser being automatically taken from a point a little farther along the wave4 ,illustration3 ,,fig4 #b1eig4--;,diagram of ,hospitalier ondograph showing mechanism and connections4 ,it represents a development of ,joubert's step by step method of wave form measurement4 ,as shown in the diagram1 fig4 #b1eig1 the ondograph consists of a synchronous motor ,a1 operated from the source of the wave form to be measured1 connected by gears ,b to a commutator ,d1 in such a manner that while the motor makes a certain number of revolutions1 the commutator makes a like number diminished by unity2 that is to say1 if the speed of the motor be #ijj revolutions per minute1 the commutator will have a speed of #hii4 ,the commutator has three contacts1 arranged to automatically charge the condenser cc' from the line1 and discharge it through the galvanometer ,e1 the deflection of which will be proportional to the pressure at any particular instant when contact is made4 ,in fig4 #b1eig1 ,,gg' are the motor terminals1 ,,hh' are connected to the condenser cc' through a resistance 7to prevent sparking at the commutator7 and ,i1 ,i' are the connections to the service to be measured4 ,a permanent magnet type of recording galvanometer is employed4 ,its moving coil ,e receives the discharges of the condenser in rapid succession and turns slowly from one side to the other4 ,illustration3 ,,fig4 #b1eih4--,view of ,hospitalier ondograph4 ,in operation1 a long pivoted pointer carrying a pen and actuated by electro-magnets1 records on a revolving drum a wave form representing the alternating current1 pressure or current wave4 ,the movable part operates a long needle 7separately mounted7 carrying a pen ,f1 which traces the curve on the rotating cylinder ,c4 ,this cylinder is geared to the synchronous motor to run at such a speed as to register three complete waves upon its circumference4 ,by substituting an electromagnetic galvanometer for the permanent magnet galvanometer1 and by using the magnet coils as current coils and the moving coil as the volt coil1 the instrument can be made to draw watt curves4 ,fig4 #b1eih shows the general appearance of the ondograph4 ,cathode ,ray ,oscillograph4--,this type of apparatus for measuring wave form was devised by ,braun1 and consists of a cathode ray tube having a fluorescent screen at one end1 a small diaphragm with a hole in it at its middle1 and two coils of a few turns each1 placed outside it at right angles to one another4 ,these coils carry currents proportional to the pressure and current respectively of the circuit under observation4 ,illustration3 ,,fig4 #b1eii4--;,general ,electric moving coil oscillograph complete with tracing table4 ,the tracing table is employed for observing the waves1 and by using a piece of transparent paper1 the waves under observation appear as a continuous band of light which can be traced1 thus making a permanent record4 ,this is not1 however1 to be regarded as a recording attachment1 and can not be used where instantaneous phenomena are being investigated4 ,the synchronous motor for operating the synchronous mirror in connection with tracing and viewing attachment is wound for #ajj to #aae volts1 #be to #abe cycles1 and should1 of course1 be run from the same machine which furnishes power to the circuit under observation4 ,a rheostat for steadying and adjusting the current should be connected in series with the motor4 ,the beam from the vibrator mirrors striking this synchronous mirror moves back and forth over the curved glass1 and gives the length of the wave2 the movement of the vibrator mirror gives the amplitude1 and the combination gives the wave complete4 ,an arc lamp or projection lantern produces the image reflected by the mirrors upon the film1 tracing table or screen4 ,for the rotation of the photographic film1 a small direct current shunt wound motor is ordinarily used4 ,the ray then moves so as to produce an energy diagram on the fluorescent screen4 ,illustration3 ,,fig4 #b1fjj4--;,general ,electric moving coil oscillograph4 ,the moving elements consist of single loops of flat wire carrying a small mirror and held in tension by small spiral springs4 ,the current passing down one side and up the other1 forces one side forward and the other backward1 thus causing the mirror to vibrate on a vertical axis4 ,the vibrator elements fit into chambers between the poles of electro-magnets1 and are adjustable1 so as to move the beam from the mirror1 both vertically and horizontally4 ,a sensitized photographic film is wrapped around a drum and held by spring clamps4 ,the drum1 with film1 is placed in a case and a cap then placed over the end1 making the case light1 when the index is either up or down4 ,the loading is done in a dark room4 ,a driving dog is screwed into the drum shaft1 and which1 when the drum and case are in place1 revolves the film past a slot4 ,when an exposure is to be made1 the index is moved from the closed position1 thus opening the slot in the case and exposing the film to the beam of light from the vibrating mirrors when the electrically operated shutter is open4 ,the slot is then closed by moving the index to ,exposed4 ,a slide with ground glass can be inserted in place of the film case or roll holder to arrange the optical system when making adjustments4 ,the shutter operating mechanism is arranged so as to hold the shutter open during exactly one revolution of the film drum4 ,there are two devices connected to the shutter operating mechanism2 one opens the shutter at the instant the end of the film passes the slot2 the other opens immediately1 at any part of the film1 and both give exposure during one revolution4 ,the first is useful when making investigations in which the events are either recurring1 or their beginnings known or under control1 and the second when the time of the event is not under control1 such as the blowing of fuses or opening of circuit breakers4 ,the instrument is much used in wireless telegraphy1 as it is capable of showing the characteristics of currents of very high frequency4 ,illustration3 ,,fig4 #b1fja4--;,general ,electric moving coil oscillograph with case removed1 showing interior construction and arrangement of parts4 ,the oscillograph is furnished complete with a three element electro-magnet galvanometer1 optical system1 shutter and shutter operating mechanism1 film driving motor and cone pulleys1 photographic and tracing attachments1 #f film holders1 and the following repair parts1 for vibrators3 #f extra suspension strips2 #f vibrator mirrors2 #a box gold leaf fuses2 #a bottle mirror cement2 #a bottle damping liquid4 ,illustration3 ,,fig4 #b1fjb4--,oscillogram showing the direct current pressure of a #be cycle rotary converter 7below71 and 7above7 the pressure wave taken between one collector ring and one commutator brush4 ,the #ab ripples per cycles in the direct current voltage are due to a #acth harmonic in the alternating current supply4 ,glow ,light ,oscillograph4--,this device consists of two aluminum rods in a partially evacuated tube1 their ends being about two millimeters apart4 ,when an alternating current of any frequency passes between them a sheath of violet light forms on one of the electrodes1 passing over to the other when the current reverses during each cycle4 ,the phenomenon may be observed or photographed by means of a revolving mirror4 ,illustration3 ,,fig4 #b1fjc4--;,curves by ,morris1 illustrating the dangerous rush of current which may occur when switching on a transformer4 ,the circuit was broken at ,f and made again at ,g4 ,the current was so great as to carry the spot of light right off the photographic plate due to the fact that a residual field was left in the core after switching off1 and on closing the switch again the direction of the current was such as to tend to build up the full flux in the same direction as this residual flux4 ,the dotted lines have been drawn in to show how the actual waves were distorted from the normal4 ,moving ,iron ,oscillograph4--,this type is due to ,blondel1 to whom belongs the credit of working out and describing in considerable detail the principles underlying the construction of oscillographs4 ,the moving iron type of oscillograph consists of a very thin vane of iron suspended in a powerful magnetic field1 thus forming a polarized magnet4 ,near this strip are placed two small coils which carry the current whose wave form is to be measured4 ,the moving iron vane has a very short period of vibration and can therefore follow every variation in the current4 ,illustration3 ,,fig4 #b1fjd4--,siemens-,blondel moving coil type oscillograph4 ,the coil is in the shape of a loop of thin wire1 which is suspended in the field of an electro-magnet excited by continuous current4 ,the current to be investigated is sent through this loop1 which in consequence of the interaction of current and magnetic field1 begins to vibrate4 ,the oscillations are rendered visible by directing a beam of light from a continuous current arc lamp onto a small mirror fixed to the loop4 ,the light reflected by the mirror is in the form of a light strip1 but by suitable means this is drawn out in respect of time1 so that a curve truly representing the current is obtained4 ,the loop of fine wire is stretched between two supports and is kept in tension by a spring4 ,as the spring tension is considerable1 the directive force of the vibrating system is large1 and its natural periodicity very high4 ,the mirror is fixed in the center of the loop1 and has an area of #a square mm4 ,in order to protect the loops from mechanical injury they are built into special frames4 ,the mirrors are of various sizes1 the loop for demonstration purposes 7projection device7 being provided with the largest mirror and the most sensitive loop with a mirror of the smallest dimensions4 ,attached to the vane is a small mirror which reflects a beam of light upon some type of receiving device4 ,the ,siemens-,blondel oscillograph shown in fig4 #b1fjd1 is of the moving coil type1 being a development of the moving iron principle4 ,moving ,coil ,oscillograph4--,the operation of this form of oscillograph is based on the behaviour of a movable coil in a magnetic field4 ,illustration3 ,,figs4 #b1fje and #b1fjf4--,oscillograms reproduced from a paper by ,m4 ,b4 ,field on ,a ,study of the ,phenomena of ,resonance by the ,aid of ,oscillograms 7,journal of ,e4 ,e41 ,vol4 ,,xxxii74 ,the effect of resonance on the wave forms of alternators has been the subject of much investigation and discussion2 it is a matter of vital importance to the engineer in charge of a large alternating current power distribution system4 ,fig4 #b1fje shows the pressure curve of an alternator running on a length of unloaded cable1 the #aath harmonic being very prominent4 ,fig4 #b1fjf shows the striking alteration produced by reducing the length of cable in the circuit and thus causing resonance with the #acth harmonic4 ,it consists essentially of a modified moving coil galvanometer combined with a rotating or vibrating mirror1 a moving photographic film1 or a falling photographic plate4 ,the galvanometer portion of the outfit is usually referred to as the oscillograph as illustrated in figs4 #b1fjh to #b1fab1 representing diagrammatically the moving system4 ,in the narrow gap between the poles ,s1 ,s of a powerful magnet are stretched two parallel conductors formed by bending a thin strip of phosphor bronze back on itself over an ivory pulley ,p4 ,a spiral spring attached to this pulley serves to keep a uniform tension on the strips1 and a guide piece ,l limits the length of the vibrating portion to the part actually in the magnetic field4 ,a small mirror ,m bridges across the two strips as shown4 ,the effect of passing a current through such a vibrator is to cause one of the strips to advance while the other recedes1 and the mirror is thus turned about a vertical axis4 ,illustration3 ,,fig4 #b1fjg4--;,general view of electro-magnet form of ,duddell moving coil oscillograph1 showing oil bath and electro-magnet4 ,this instrument is specially designed to have a very high natural period of vibration 7about #a_/aj1jjj of a second7 so as to be suitable for accurate research work4 ,it is quite accurate for frequencies up to #cjj per second4 ,in the figure1 ,a is the brass oil bath in which two vibrators are fixed2 ,b1 core of electro-magnet which is excited by two coils1 one of which1 ,c1 is seen4 ,the ends of these two coils are brought out to four terminals at ,d1 so that the coils may be connected in series for #bjj volt1 or in parallel for #ajj volt circuits4 ,the bolts1 ,e1,e1 hold the oil bath in position between the poles of the magnet4 ,f1,f1,f 7one not seen71 are levelling screws2 ,g1,g1 terminals of one vibrator2 ,h1 fuse2 ,k1 thermometer with bulb in center of oil bath4 ,illustration3 ,,figs4 #b1fjh to #b1fab4--,vibrator of ,duddell moving coil oscillograph and section through oil bath of electro-magnet oscillograph4 ,the vibrator consists of a brass frame ,w1 which supports two soft iron pole pieces ,p1,p4 ,between these1 a long narrow groove is divided into two parts by a thin soft iron partition1 which runs up the center4 ,the current being led in by the brass wire ,u1 passes from an insulated brass plate to the strip1 which is led over an ivory guide block1 down one of the narrow grooves and over another guide block1 the loops round the ivory pulley ,o1 which puts tension on the strip by the spring ,n1 back to the guide block again1 up the other narrow groove1 and out by way of the insulated brass plate and lead ,u4 ,halfway up the grooves the center iron partition ,r is partially cut away to permit of a small mirror ,m1 bridging across from one strip to the other1 being stuck to the strips by a dot of shellac at each corner4 ,the figure illustrates one type of vibrator in which ,p is removable from ,w for ease in repairing4 ,in type #a1 these pole pieces ,p1,p are not removable4 ,the vibrators are placed side by side in the gap between the poles ,s1,s of the electro-magnet1 see fig4 #b1faj4 ,each vibrator is pivoted about vertical centers1 the bottom center fitting in the base of the oil bath1 and the one at the top being formed by a screw in the cock piece ,y4 ,it can thus be easily turned in azimuth1 its position being fixed by the adjusting screw ,l1 a spiral spring serving to keep the vibrator always in contact with this screw4 ,since each cock piece can be independently moved forward or backward1 each vibrator can be tipped slightly in either of these directions so that complete control over the mirrors is obtained and reflected spots of light may be made to coincide with that reflected from the fixed zero mirror1 which latter is fixed to a brass tongue in between the two vibrators4 ,a plano-convex lens of #ej cm4 focal length is fixed on the oil bath in front of the vibrator mirrors to converge the reflected beams of light4 ,it will be noticed that this lens is slightly inclined so that no trouble will be given by reflections from its own surface4 ,the normal distance from the vibrator mirrors to the scale of photographic plate is #ej cm41 and at this distance1 a convenient working deflection on each side of the zero line is #c to #d cm4 ,this is obtained with a ,r4,m4,s4 current through the strips of from 4#je to 4#a of an ampere according to wave form1 etc4 ,the maximum deflection on each side of the zero line should not exceed #e cm4 while the maximum ,r4,m4,s4 current through the strips should in no case exceed 4#a ampere4 ,each strip of the loop passes through a separate gap 7not shown in the figure74 ,the whole of the vibrator1 as this part of the instrument is called1 is immersed in an oil bath1 the object of the oil being to damp the movement of the strips1 and make the instrument dead beat4 ,it also has the additional advantage of increasing by refraction the movement of the spot of light reflected from the vibrating mirrors4 ,the beam of light reflected from the mirror ,m is received on a screen or photographic plate1 the instantaneous value of the current being proportional to the linear displacement of the spot of light so formed4 ,with alternating currents1 the spot of light oscillates to and fro as the current varies and would thus trace a straight line4 ,to obtain an image of the wave form1 it is necessary to traverse the photographic plate or film in a direction at right angles to the direction of the movement of the spot of light4 ,illustration3 ,,fig4 #b1fac4--;,duddell moving coil oscillograph with projection and tracing desk outfit4 ,the outfit is designed for teaching and lecture purposes4 ,in operation1 after the beam of light from the arc lamp has been reflected from the oscillograph mirrors1 it falls on a vibrating mirror which gives it a deflection proportional to time in a direction at right angles to the deflection it already has and which is proportional to the current passing through the oscillograph4 ,it is therefore only necessary to place a screen in the path of the reflected beam of light to obtain a trace of the wave form4 ,since the vibrating mirror is vibrated by means of a cam on the shaft of a synchronous motor1 which motor is driven from1 or synchronously with1 the source of supply whose wave form is being investigated1 the wave form is repeated time after time in the same place on the screen1 and owing to the persistence of vision1 the whole wave appears stationary on the screen4 ,the synchronous motor with its vibrating mirror1 mentioned above1 is located underneath the tracing desk4 ,when used in this position a wave a few centimeters in amplitude is seen through a sheet of tracing paper which is bent round a curved sheet of glass4 ,a permanent record of the wave form can thus easily be traced on the paper4 ,a dark box which is designed to hold a sheet of sensitized paper in place of the tracing paper1 can be fitted in place of the tracing desk4 ,thus an actual photographic record of the wave form is obtained4 ,if the synchronous motor be transferred from its position underneath the tracing desk to the space reserved for it close to the oscillograph1 the beam of light is then received on a large mirror which is placed at an angle of about #de degrees to the horizontal and so projects the wave form onto a large vertical screen which should be fixed about two and a half meters distant4 ,under these conditions a wave form of amplitude #ej cm4 each side the zero line may be obtained which is therefore visible to a large audience4 ,ques4 ,how are the oscillograms obtained in the ,duddell moving coil oscillograph8 ,ans4 ,in all cases the oscillograms are obtained by a spot of light tracing out the curve connecting current or voltage with time4 ,the source of light is an arc lamp1 the light from which passes first through a lens1 and then1 excepting when projecting on a screen1 through a rectangular slit about #aj mm4 long by #a mm4 wide4 ,the position of the lamp from the lens is adjusted till an image of the arc is obtained covering the three 7two moving1 one fixed7 small oscillograph mirrors4 ,the light is reflected back from these mirrors and1 being condensed by a lens which is immediately in front of them1 it converges till an image of the slit is formed on the surface where the record is desired4 ,all that is necessary now to obtain a bright spot of light instead of this line image is to introduce in the path of the beam of light a cylindrical lens of short focal length4 ,illustration3 ,,figs4 #b1fad and #b1fae4--,sectional view of permanent magnet form of ,duddell moving coil oscillograph4 ,this instrument has a lower natural period of vibration 7#a_/cjjj second7 than the type shown in fig4 #b1fab1 and therefore is not capable of accurately following wave forms of such high frequency1 but it is sufficiently quick acting to follow wave forms of all ordinary frequencies with perfect accuracy4 ,it is easier to repair1 and more portable owing to the fact that the magnetic field is produced by a permanent magnet instead of an electro-magnet4 ,this also renders the instrument suitable for use on high tension circuits without earth connection1 as1 owing to the fact that no direct current excitation is required1 the instrument is more easily insulated than other types4 ,ques4 ,what is the function of the mirrors on the vibrating vane8 ,illustration3 ,,fig4 #b1faf4--;,diagram of connections of ,duddell oscillograph to high pressure circuit4 ,the modification necessary for high pressure circuit only applies to the vibrator which gives the pressure wave and consists in adding two more resistances1 ,r#d and ,r#e4 ,referring to fig4 #b1fag1 it will be seen that in case fuse f#b blows1 or the vibrator be accidentally broken1 the full supply voltage is immediately thrown on the instrument itself4 ,this is not permissible in high voltage work and therefore the resistance ,r#e is introduced as a permanent shunt to the oscillograph vibrator4 ,the resistance ,r#d is an exact duplicate of ,r#b being a #ba ohm plug resistance box for adjusting the sensitivity of the vibrator to an even figure4 ,in practice ,r#e is usually a part of ,r#a1 and in most of the high voltage resistances1 two taps are brought out near one end to serve as ,r#e4 ,one of these taps is usually #ej ohms distant from the end terminal and the other only #e ohms from the end4 ,the use of these taps is as follows3 ,the large resistance consisting of ,r#a ,r#e is so chosen with respect to the voltage of the circuit under investigation that the current through ,r#a is about 4#a ampere4 ,it should never be more than this continuously4 ,then ,r#d is connected to the #ej ohm tap1 and since the resistance of the oscillograph vibrator circuit is variable from about #e to #bf ohms by means of ,r#d1 the current can be controlled through the oscillograph from about 4#jff to 4#jia of an ampere1 enabling an open wave form to a convenient scale to be obtained4 ,if it now be desired to record large rises of pressure1 such as may occur in cases of resonance1 the height of the wave must be reduced in order to keep these rises on the plate4 ,this is accomplished by disconnecting ,r#d from the #ej ohm tap and connecting it to the #e ohm tap1 when the current through the vibrator will be from 4#je to 4#jaf of an ampere according to whether the resistance ,r#d is in or out of circuit4 ,when1 instead of using the falling plate1 the cinematograph camera is being used1 it becomes necessary always to work on the #e ohm tap since the width of the film is much less than that of the plate1 and the current must therefore be less4 ,in experiments where sudden rises of voltage are expected it is often advisable to keep ,r#a as great as possible4 ,that end of the resistance ,r#a referred to as ,r#e in the diagram should be securely connected to the supply main and no switch or fuse used4 ,a switch may1 if desired1 be used in series with ,r#a1 provided it be inserted at the point where ,r#a joins the supply main remote from ,r#e4 ,it will be seen that fuses f#a and f#b are shown4 ,provided that the connections are always made in accordance with the diagram1 and the vibrators are always shunted by ,r#e or ,r#c respectively1 there is not much objection to the use of these fuses1 but on general principles it is wise to avoid fuses in high tension work and accordingly with each permanent magnet oscillograph1 dummy fuses are supplied1 which can be inserted in place of the ordinary fuses when desired4 ,the remark previously made about keeping both vibrators and the frame of the instrument at approximately the same pressure applies with additional emphasis in high pressure work4 ,ans4 ,they simply control the direction of a beam of light in a horizontal plane in such a manner that its deflection from a zero position depends on the current passing through the instrument1 and it is therefore evident that the oscillograph is not complete without means of producing a time scale4 ,illustration3 ,,fig4 #b1fag4--;,diagram of connections of ,duddell oscillograph to low pressure circuit1 ,r#a is a high non-inductive resistance connected across the mains in series with one of the vibrators4 ,s#b is a switch1 and f#b1 the fuse 7on the oscillograph in this circuit74 ,the resistance of ,r#a in ohms should be rather more than ten times the voltage of the circuit1 so that a current of a little less than 4#a of an ampere will pass through it4 ,the vibrator will then give the curve of the circuit on an open scale4 7,for the projection oscillograph1 the resistance ,r#a should be only twice the supply voltage1 since 4#e of an ampere is required to give full scale deflection on a large screen47 ,to obtain the current wave form1 the shunt ,r#c is connected in series with the circuit under investigation and the second vibrator is connected across this shunt4 ,here also f#a is a fuse1 ,s#a a switch1 and ,r#b an adjustable resistance box4 ,the switch ,s#a is however unnecessary if the plug resistance box supplied for ,r#b be used1 since an infinity plug is included in this box4 ,the shunt ,r#c should have a drop of about #a volt across it in order to give a suitable working current through the vibrator4 ,the resistance ,r#b is not absolutely essential1 but it is a great convenience in adjusting the current through the vibrator4 ,it is a plug resistance box1 the smallest coil being 4#jd of an ohm and the total #ba ohms4 ,being designed to carry 4#e ampere continuously it can be used with any other type of ,duddell oscillograph1 and by its use the sensitiveness of the vibrator can be adjusted so that a round number of amperes in the shunt gives #a mm4 deflection4 ,this adjustment is best made with direct current4 ,it should be noted in connecting the oscillograph in circuit1 that the two vibrators should be so connected to the circuit that it is impossible that a higher pressure difference than #ej volts should exist between one vibrator and the other1 or between either vibrator and the frame4 ,to ensure attention to this important point1 a brass strap is provided which connects the two vibrators together and to the frame of the instrument4 ,this does not mean that this point must necessarily be earthed since the frame of the instrument is insulated from the earth4 ,it is advisable1 however1 to earth it when possible4 ,illustration3 ,,figs4 #b1fah and #b1fai4--,two curves obtained with the falling plate camera and illustrating the discharge of a condenser through an inductive circuit4 ,when taking curve ,a the resistance in the circuit was very small compared to the inductance1 while before taking curve ,b an additional non-inductive resistance was inserted in the circuit so that the oscillations were damped out much more rapidly although the periodic time remained approximately constant4 ,ques4 ,how is the time scale produced8 ,ans4 ,either the surface on which the beam of light falls may be caused to move in a vertical plane with a certain velocity1 so that the intersection of the beam and the plane surface traces out a curve connecting current with time 7a curve which becomes a permanent record if a sensitized surface be used72 or1 the surface may remain stationary and in the path of the horizontally vibrating beam may be introduced a mirror which rotates or vibrates about a horizontal axis1 thus superposing a vertical motion proportional to time on the horizontal vibration which is proportional to current1 and causing the beam of light to trace out a curve connecting current and time on the stationary surface4 ,ques4 ,what kind of recording apparatus is used with the ,duddell oscillograph8 ,ans4 ,a falling plate camera1 or a cinematograph film camera4 ,illustration3 ,,fig4 #b1fbj4--,synchronous motor with vibrating mirror as used with ,duddell moving coil oscillograph4 ,since the motor must run synchronously with the wave form it is required to investigate1 it should be supplied with current from the same source4 ,the motor can be used over a wide range of frequencies 7from #bj to #abj74 ,when working at frequencies below #dj1 it is advisable to increase the moment of inertia of the armature1 and for this purpose a suitable brass disc is used4 ,the armature carries a sector1 which cuts off the light from the arc lamp during a fraction of each revolution1 and a cam which rocks the vibrating mirror4 ,it makes one revolution during two complete periods1 and the cam and sector are so arranged that during #a periods1 the mirror is turning with uniform angular velocity1 while during the remaining half period1 the mirror is brought back quickly to its angular position1 the light being cut off by the sector during this half period4 ,ques4 ,explain the operation of the falling plate camera4 ,ans4 ,in this arrangement a photographic plate is allowed to fall freely by the force of gravity down a dark slide4 ,at a certain point in its fall it passes a horizontal slit through which the beams of light from the oscillograph pass1 tracing out the curves on the plate as it falls4 ,illustration3 ,,figs4 #b1fba to #b1fbc4--;,interior of cinematograph camera as used on ,duddell moving coil oscillograph for obtaining long records4 ,the loose side of case is shown removed and one of the reels which carry the film lying in front4 ,the spool of film which is placed on the loose reel ,a1 passes over the guide pulley ,b1 then vertically downward between the brass gate ,d 7shown open in the figure71 and the brass plate ,c4 ,the exposure aperture is in the plate ,c and can be opened or closed by a shutter controlled by the lever ,m4 ,the groove in the plate ,c1 and the springs which press the gate ,d flat on the plate ,c1 prevent the film having any but a vertical motion as it passes the exposure slit4 ,e is the sprocket driving pulley which engages with the perforations on the film and unwinds it from the reel ,a to reel ,h4 ,outside the case on the far side of it is secured to the axle ,g a three speed cone pulley4 ,this is driven by a motor of about #a_/g horse power1 which also drives1 through the gears shown1 the sprocket pulley ,e4 ,close to the grooved cone pulley is a lever carrying a jockey pulley ,l1 and a brake1 which latter is normally held onto the cone pulley by a spring and so causes the loose belt to slip4 ,by pressing a lever which is attached to the falling plate camera case1 the brake can be suddenly released and at the same time the jockey pulley caused to tighten the belt onto the grooved cone pulley1 so that the starting and stopping of the film is controlled independently of the driving motor1 and being quickly accomplished avoids waste of film4 ,both reels are alike and each is made in two pieces4 ,the upper reel is loose on its axle and its motion is retarded slightly by a friction brake4 ,the lower reel is also loose on its axle1 but it is driven by means of a friction clutch1 the clutch always rotating faster than the reel so that the used film delivered by the sprocket pulley ,e is wound up as fast as delivered4 ,k is the front face of one reel1 the boss on it pushes into the tube on the other half ,h1 which serves not only to unite the two halves1 but also to secure the end of the film which is doubled through ,j4 ,the mean speed of the plate at the moment of exposure is about #ac feet per second4 ,this speed is very suitable for use with frequencies of from #dj to #fj periods per second4 ,a cloth bag is used to introduce the plate to the slide4 ,a catch holds the plate until it is desired to let it fall4 ,inside the case1 is a small motor1 #ajj or #bjj volts direct current1 driving four mirrors which are fixed about a common axis with their planes parallel to it4 ,illustration3 ,,fig4 #b1fbd4--,portion of oscillograph record taken with cinematograph film camera1 showing the rush of current and sudden rise of voltage at the moment of switching on a high pressure feeder4 ,by looking through a small slot in the end of the camera into these rotating mirrors1 the observer sees the wave form which the oscillograph is tracing out and is thus able to make sure that he is obtaining the particular wave form or other curve desired before exposing the plate4 ,illustration3 ,,fig4 #b1fbe4--,portion of oscillograph record taken with a cinematograph film camera showing the effect of switching off a high pressure feeder and illustrating the violent fluctuations produced by sparking at the switch contacts4 ,the plate falls into a second red cloth bag which is placed on the bottom of the slide4 ,the plates used are stereoscopic size1 #f #c 7#ag4a #h4c cm474 ,ques4 ,for what use is the cinematograph camera adapted8 ,ans4 ,for long records4 ,for instance1 in investigations1 such as observation on the paralleling of alternators1 the running up to speed of motors1 and the surges which may occur in switching on and off cable1 etc4 ,the cinematograph camera fits on to the falling plate case and by means of which a roll of cinematograph film can be driven at a uniform speed past the exposure aperture1 enabling records up to #ej metres in length to be obtained4 ,an interior view of the cinematograph camera is shown in fig4 #b1fba4 ,illustration3 ,,fig4 #b1fbf4--;,curves reproduced from an article by ,j4 ,t4 ,morris in the ,electrician4 ,on recording transitory phenomena by the oscillograph4 ,illustration3 ,,fig4 #b1fbg4--;,first rush of current from an alternator when short circuited1 showing unsymmetrical initial wave of current1 becoming symmetrical after a few cycles4 #be cycles4 ,illustration3 ,,fig4 #b1fbh4--,pressure wave obtained from narrow exploring coil on alternator armature1 indicating distribution of field flux4 ,the terminal voltage of the alternator is very nearly a sine wave1 #fj cycles2 about #ag volts4 ,,some ,,oscillograph ,,records ,illustration3 ,,fig4 #b1fbi4--,the waves of voltage and current of an alternating arc4 ,a1 voltage wave2 ,b1 current wave showing low power factor of the arc without apparent phase displacement4 #fj cycles4 ,illustration3 ,,fig4 #b1fcj4--,rupturing #fej volt circuit4 ,a1 current wave2 ,b1 #be cycle wave to mark time scale4 ,illustration3 ,,fig4 #b1fca4--;,first rush of current from alternator when short circuited1 showing unsymmetrical current wave1 also wave of field current caused by short circuit current in armature4 ,upper curve1 armature current2 lower curve1 field current4 ,illustration3 ,,fig4 #b1fcb4--,mazda 7tungsten7 lamp1 showing rapid decrease to normal current as filament heats up4 #be cycles4 ,illustration3 ,,fig4 #b1fcc4--;,current wave in telephone line corresponding to sustained vowel sound i1 as in machine2 voice pitched at ,a #aaj4 ,illustration3 ,,fig4 #b1fcd4--;,carbon lamp1 showing rapid increase to normal current as filament heats up4 #be cycles4 ,illustration3 ,,fig4 #b1fce4--,short circuit current on direct current end of rotary converter1 #ba1ejj amperes maximum4 ,upper curve1 direct current voltage2 lower curve1 direct current amperage4 ,duration of short circuit about 4#a second4 ,,chapter ,,lxiv ,,switchboards ,general ,principles of ,switchboard ,connections4--,the interconnection of generators1 transformers1 lines1 bus bars1 and switches with their relays1 in modern switchboard practice is shown by the diagrams1 figs4 #b1fcf to #b1fde4 ,the figures being lettered ,a to ,j for simplicity1 the generators are indicated by black discs1 and the switches by open circles1 while each heavy line represents a set of bus bars consisting of two or more bus bars according to the system of distribution4 ,it will be understood1 also1 in this connection1 that the number of pole of the switches and the type of switch will depend upon the particular system of distribution employed4 ,diagram ,a1 shows the simplest system1 or one in which a single generator feeds directly into the line4 ,there are no transformers or bus bars and only one switch is sufficient4 ,in ,b1 a single generator supplies two or more feeders through a single set of bus bars1 requiring a switch for each feeder1 and a single generator switch4 ,in ,c1 two generators are employed and required and the addition of a bus section switch4 ,d1 represents a number of generators supplying two independent circuits4 ,the additional set of bus bars employed for this purpose necessitates an additional bus section switch1 and also additional selector switches for both feeders and generators4 ,e1 shows a standard system of connection for a city street railway system having a large number of feeders4 ,illustration3 ,,figs4 #b1fde and #b1fdf4--;,diagrams illustrating general principles of switchboard connections4 ,this arrangement allows any group of feeders to be supplied from any group of generators4 ,illustration3 ,,fig4 #b1fdf4--;,fort ,wayne switchboard panel for one alternator and one transfer circuit4 ,diagram giving dimensions1 arrangement of instruments of board1 and method of wiring4 ,the different forms of standard alternating current switchboard panels for single phase circuits made by the ,fort ,wayne ,electric ,works are designed to fulfill all the usual requirements of switchboards for this class of work4 ,the line includes panels equipped for a single generator2 for one generator and two circuits2 one generator and one transfer circuit2 one generator1 an incandescent and an arc lighting circuit2 and also feeder panels of different kinds4 ,it also permits the addition of a generator switch for each generator4 ,f1 represents the simplest system with transformers4 ,it requires a single generator transformer bank1 switch and line4 ,the arrangement as show at ,f is used where a number of plants supply the same system4 ,g1 represents a system having more than one line4 ,in this case a bus bar and transformer switch is used on the high tension side4 ,h1 shows a number of generators connected to a set of low tension bus bars through generator switches1 and employing a low tension transformer switch4 ,i1 shows the connections of a system having a large number of feeders supplied by several small generators4 ,in this case1 the plant is divided into two parts1 each of which may be operated independently4 ,illustration3 ,,fig4 #b1fdg4--;,general ,electric small plant alternating current switchboard1 designed for use in small central stations and isolated plants4 ,they are for use with one set of bus bars1 to which all generators and feeders are connected by means of single throw lever switches or circuit breakers1 suitable provision being made for the parallel operation of the generators4 ,j1 represents the arrangement usually employed in modern plants where the generator capacity is large enough to permit of a generator transformer unit combination with two outgoing lines4 ,by operating in parallel on the high tension side only1 any generator can be run with any transformer4 ,the whole plant can be run in parallel1 or the two parts can be run separately4 ,illustration3 ,,fig4 #b1fdh4--;,crouse-,hinds voltmeter and ground detector radial switch1 arranged for mounting on the switchboard4 ,the switch proper is placed on the rear of the board with hand wheel1 dial1 and indicator only on the front side4 ,the current carrying parts are of hard brass1 with contact surfaces machined after assembling4 ,the contact parts are of the plunger spring type1 and the cross bar has fuse connections4 ,ground detector circuits are marked ,g and ,g- for two wire system1 and ,g1 ,g-1 ,,gn and ,,gn- for three wire system4 ,when the voltmeter switch is to be used as a ground detector1 two circuits are required for a two wire system1 and four circuits for a three wire system1 that is1 a six circuit voltmeter and ground detector switch for use on a two wire system has two circuits for ground detector and four circuits for voltmeter readings4 ,a six circuit voltmeter and ground detector switch1 for use on a three wire system1 has four circuits for ground detector and two circuits for voltmeter readings4 ,switchboard ,panels4--,the term panel means the slab of marble or slate upon which is mounted the switches1 and the indicating and controlling devices4 ,there are usually several panels comprising switchboards of moderate or large size1 these panels being classified according to the division of the system that they control1 as for instance3 #a4 ,generator panel2 #b4 ,feeder panel2 #c4 ,regulator panel1 etc4 ,in construction1 the marble or slate should be free from metallic veins1 and for pressures above1 say1 #fjj volts1 live connections1 terminals1 etc41 should preferably be insulated from the panels by ebonite1 mica1 or removed from them altogether1 as is generally the case with the alternating gear where the switches are of the oil type4 ,illustration3 ,,figs4 #b1fdi and #b1fej1--,wiring diagrams of ,crouse-,hinds voltmeter and ground detector switches4 ,fig4 #b1fdi voltmeter switch2 fig4 #b1fej voltmeter and ground detector switch4 ,a view of the switch is shown in fig4 #b1fdh2 it is designed for use on two or three wire systems up to #cjj volts4 ,the bus bars and connections should be supported by the framework at the back of the board1 or in separate cells1 and the instruments should be operated at low pressure through instrument transformers4 ,the panels are generally held in position by bolting them to an angle iron1 or a strip iron framework behind them4 ,generator ,panel4--,this section of a switchboard carries the instruments and apparatus for measuring and electrically controlling the generators4 ,on a well designed switchboard each generator has1 as a rule1 its own panel4 ,illustration3 ,,figs4 #b1fea to #b1fec4--;,diagrams of connections for generator panels4 ,key to symbols3 ,a1 ammeter2 ,a4,s41 ammeter switch2 ,c4,t41 current transformer2 ,f41 fuse2 ,f4,a41 direct current field ammeter2 ,f4,s41 field switch2 ,g4,c4,s41 governor control switch2 ,l4,s41 limit switch 7included with governor motor72 ,o4,s41 oil switch2 ,p4,i4,w41 polyphase indicating wattmeter2 ,p4,w4,m41 polyphase watthour meter2 ,p4,r41 pressure receptacle2 ,p4,p41 pressure plug2 ,rheo41 rheostat2 ,s41 shunt2 ,s4,r41 synchronizing receptacle2 ,s4,p41 synchronizing plugs2 ,t4,b41 terminal board for instrument leads2 ,v1 alternating current voltmeter4 ,illustration3 ,,figs4 #b1fed and #b1fee4--;,diagrams illustrating a simple method of determining bus capacity as suggested by the ,general ,electric ,co4 ,fig4 #b1fed relates to any panel2 the method is as follows3 #a4 ,make a rough plan of the entire board1 regardless of the number of panels to be ordered4 ,the order of panels shown is recommended1 it being most economical of copper and best adapted to future extensions4 #b4 ,to avoid confusion keep on one side of board everything pertaining to exciter buses1 and on other side everything pertaining to ,a4 ,c4 buses4 #c4 ,with single lines represent the exciter and ,a4 ,c4 buses across such panels as they actually extend and by means of arrows indicate that portion of each bus which is connected to feeders and that portion which is connected to generators4 ,remember that ,generator and ,feeder arrows must always point toward each other1 otherwise the rules given below do not hold4 ,note also that the field circuits of alternator panels are treated as ,d4 ,c4 feeders for the exciter bus4 #d4 ,on each panel mark its ampere rating1 that is1 the maximum current it supplies to or takes from the bus4 ,for ,a4 ,c4 alternator panels the ,d4 ,c4 rating is the excitation of the machines4 #e4 ,apply the following rules consecutively1 and note their application in fig4 #b1fed4 7,for the sake of clearness ampere ratings are shown in light face type and bus capacities in large type47 ,a4 ,always begin with the tail of the arrow and treat generator and feeder sections of the bus separately4 ,b4 ,bus capacity for first panel ampere rating of panel4 ,c4 ,bus capacity for each succeeding panel ampere rating of panel plus bus capacity for preceding panel4 7,see sums marked above the buses in fig4 #b1fed47 ,d4 ,for a panel not connected to a bus extending across it1 use the smaller value of the bus capacities already obtained for the two adjoining panels4 7,see exciter bus for panel ,c47 ,e4 ,the bus capacity for any feeder panel need not exceed the maximum for the generator panels 7see ,a4 ,c4 bus for panel ,g7 and vice versa 7see exciter bus for panel ,b74 ,hence the corrections made in values obtained by applying rules ,b and ,c4 ,the arrangement of panels shown in fig4 #b1fed is the one which is mostly used4 ,the above method may1 however1 be applied to other arrangements1 one of which is shown in fig4 #b1fee4 ,here the generators must feed both ways to the feeders at either end of the board so that in determining ,a4 ,c4 bus capacities it is necessary to first consider the generators with the feeders at one end1 and then with the feeders at the other end as shown by the dotted ,a4 ,c4 buses4 ,the required bus capacities are then obtained by taking the maximum values for the two cases4 ,illustration3 ,,fig4 #b1fef4--;,end view showing general arrangement of switchboards for #bdj1 #dhj1 and #fjj volt alternating current4 ,the cut shows a single throw oil switch mounted on the panel4 ,in the case of a dynamo1 a good representative panel would have mounted upon it a reverse current circuit breaker1 an ammeter1 a double pole main switch 7or perhaps a single pole switch1 since the circuit breaker could also be used as a switch7 a double pole socket into which a plug could be inserted to make connection with a voltmeter mounted on a swinging bracket at the end of the board2 a rheostat handle1 the spindle of which operates the shunt rheostat of the machine1 the rheostat being placed either directly behind the spindle1 if of small size1 or lower down with chain drive from the hand wheel spindle1 if of larger size1 a field discharge switch and resistance1 a lamp near the top of the panel for illuminating purposes1 a fuse for the voltmeter socket1 and1 if desired1 a watthour meter4 ,if the dynamo be compound wound1 the equalizing switch will generally be mounted on the frame of the machine1 and in some cases the field rheostat will be operated from a pillar mounted in front of the switchboard gallery4 ,if the generator be for traction purposes1 the circuit breaker is more often of the maximum current type1 and a lightning arrester is often added1 without a choke coil1 the latter as well as further lightning arresters being mounted on the feeder panels4 ,illustration3 ,,figs4 #b1feg and #b1feh4--,two views of a feeder panel1 showing general arrangement of the devices assembled thereon4 ,a1 circuit breaker2 ,b1 ammeter2 ,c1 voltmeter2 ,d1 switches4 ,in the case of a high pressure alternating current plant of considerable size1 the bus bars oil switches1 and the current and pressure transformers are generally mounted either in stoneware cells1 or built on a framework in a space guarded by expanded metal walls1 and no high pressure apparatus of any sort is brought on to the panels themselves4 ,illustration3 ,,figs4 #b1fei to #b1fff4--;,diagram of connections for three phase feeder panels4 ,key to symbols3 ,a1 ammeter2 ,a4,s41 three way ammeter switch2 ,b4,a4,s41 bell alarm switch2 ,c4,t41 current transformer2 ,f1 fuse2 ,o4,s41 oil switch2 ,p4,i4,w41 polyphase indicating wattmeter2 ,p4,w4,m41 polyphase watthour meter2 ,t4,b41 terminal board2 ,t4,c41 trip coils for oil switch4 ,feeder ,panel4--,the indicating and control apparatus for a feeder circuit is assembled on a panel called the feeder panel4 ,the most common equipment in the case of a direct current feeder panel comprises an ammeter1 a double pole switch1 and double pole fuses or instead of the fuses1 a circuit breaker on one or both poles2 in the case of a traction feeder a choke coil and a lightning arrester are often added4 ,illustration3 ,,figs4 #b1ffg and #b1ffh4--;,diagrams of connections for two phase and three phase installations3 ,a and ,a#a1 ammeter2 ,c4,c41 constant current transformer2 ,c4,t41 current transformer2 ,d4,r41 discharge resistance2 ,f1 fuse2 ,f4,s41 field switch2 ,l4,a41 lightning arrester2 ,o4,s41 oil switch2 ,p4,p41 pressure plug2 ,p4,r41 pressure receptacle2 ,p4,t41 pressure transformer2 ,s and ,s#a1 plug switches2 ,t4,c41 oil switch trip coil2 ,v1 voltmeter4 ,the equipment of a typical high pressure three phase feeder panel is an ammeter 7sometimes three ammeters1 one in each phase7 operated by a current transformer1 and oil break switch with two overload release coils1 or three if the neutral of the circuit be earthed1 the releases being operated by current transformers4 ,illustration3 ,,fig4 #b1ffi4--;,crouse-,hinds radial ammeter switch1 arranged for mounting directly on the switchboard4 ,it is designed for use with external shunt ammeters of any make or capacity1 and in connection with the required number of shunts1 makes possible the taking of current readings of a corresponding number of circuits by means of one ammeter4 ,the wiring diagram is shown in fig4 #b1fgj4 ,the switch when on a large system is often in a cell some distance behind the panel1 and is then controlled by a system of levers1 or by a small motor which is started and stopped by a throw over switch on the panel1 in which case there is generally a lamp or lamps on the panel to show whether the switch is open or closed4 ,air brake switches or links are placed between the bus bars and the oil switch to allow of the latter being isolated for inspection purposes1 and as a general rule no apparatus carrying high pressure current is allowed on the front of the panel4 ,with both direct and alternating current feeders1 a watthour meter is often added to show the total consumption of the circuit4 ,illustration3 ,,fig4 #b1fgj4--,wiring diagram for ,crouse-,hinds radial ammeter switch as illustrated in fig4 #b1ffi4 ,the switch proper is on the rear of the switchboard1 and the hand wheel dial and indicator on the front4 ,a typical three phase generator panel is provided with three ammeters1 one in each phase1 operated from three current transformers1 one to each ammeter1 a volt meter1 a power factor indicator1 and an indicating watthour meter1 all operated from one or more pressure transformers1 and the necessary current transformers1 the operating handle of the oil switch1 which is connected to the switch itself by means of rods1 two maximum releases operated by current transformers1 or a reverse relay for automatically tripping the switch1 lamps for indicating when the switch is tripped1 a socket for taking the plug which makes connection between the secondary of a pressure transformer and the synchronizer on the synchronizing panel1 and a lamp for illuminating purposes1 while on the base of the panel or on a pillar at the front of the gallery is mounted the gear for the field circuit4 ,this consists of a double pole field switch and a discharge resistance1 an ammeter1 a handle for the rheostat in the generator field1 and 7if each alternator have its own direct coupled exciter7 possibly also a small rheostat for the exciter field4 ,,note4--,in some cases where the capacity of the plant is not very great1 the oil switch is mounted on the back of the panel1 and the bus bars1 current transformers1 c41 on the framework1 also just at the back of the panel1 but under no circumstances1 in good modern practice1 is high pressure apparatus permitted on the front of the board4 ,where the capacity of the plant is very large1 the oil switches are operated electrically by means of small motors1 and in this case the small switch gear for starting and stopping this motor is mounted on the generator panel1 also the lamp or lamps to indicate when the switch is open1 and when closed4 ,,chapter ,,lxv ,,alternating ,,current ,,wiring ,in the case of alternating current1 because of its peculiar behaviour1 there are several effects which must be considered in making wiring calculations1 which do not enter into the problem with direct current4 ,accordingly1 in determining the size of wires1 allowance must be made for #a4 ,self-induction2 #b4 ,mutual-induction2 #c4 ,power factor2 #d4 ,skin effect2 #e4 ,corona effect2 #f4 ,frequency2 #g4 ,resistance4 ,most of these items have already been explained at such length1 that only a brief summary of facts need be added1 to point out their connection and importance with alternating current wiring4 ,induction4--,the effect of induction1 whether self-induction or mutual induction1 is to set up a back pressure of spurious resistance1 which must be considered1 as it sometimes materially affects the calculation of circuits even in interior wiring4 ,self-induction is the effect produced by the action of the electric current upon itself during variations in strength4 ,ques4 ,what conditions besides variations of current strength governs the amount of self-induction in a circuit8 ,ans4 ,the shape of the circuit1 and the character of the surrounding medium4 ,if the circuit be straight1 there will be little self-induction1 but if coiled1 the effect will become pronounced4 ,if the surrounding medium be air1 the self-induction is small1 but if it be iron1 the self-induction is considerable4 ,illustration3 ,,figs4 #b1fga to #b1fgf4--,the effect of self-induction4 ,in a non-inductive circuit1 as in fig4 #b1fgb1 the whole of the virtual pressure is available to cause current to flow through the lamp filament1 hence it will glow with maximum brilliancy4 ,if an inductive coil be inserted in the circuit as in fig4 #b1fgd1 the reverse pressure due to self-induction will oppose the virtual pressure1 hence the effective pressure 7which is the difference between the virtual and reverse pressures71 will be reduced and the current flow through the lamp diminished1 thus reducing the brilliancy of the illumination4 ,the effect may be intensified to such degree by interposing an iron core in the coil as in fig4 #b1fgf1 as to extinguish the lamp4 ,ques4 ,with respect to self-induction1 what method should be followed in wiring8 ,ans4 ,when iron conduits are used1 the wires of each circuit should not be installed in separate conduits1 because such arrangement will cause excessive self-induction4 ,the importance of this may be seen from the experience of one contractor1 who installed feeders and mains in separate iron pipes4 ,when the current was turned on1 it was found that the self-induction was so great as to reduce the pressure to such an extent that the lamps1 instead of giving full candle power1 were barely red4 ,this necessitated the removal of the feeders and main and re-installing them1 so that those of the same circuit were in the same pipe4 ,ques4 ,what is mutual induction8 ,ans4 ,mutual induction is the effect of one alternating current circuit upon another4 ,illustration3 ,,fig4 #b1fgg4--,measurement of self induction when the frequency is known4 ,the apparatus required consists of a high resistance or electrostatic a4c4 voltmeter1 d4c4 ammeter1 and a non-inductive resistance4 ,connect the inductive resistance to be measured as shown1 and close switch ,m1 short circuiting the ammeter4 ,connect alternator in circuit and measure drop across ,r and across ,xi4 ,disconnect alternator and connect battery in circuit1 then open switch ,m and vary the continuous current until the drop across ,r is the same as with the alternating current1 both measurements being made with the same voltmeter2 read ammeter1 and measure drop across ,xi4 ,call the drop across ,xi with alternating current ,e1 and with direct current ,ei1 and the reading of the ammeter ,j4 ,then ,l ,e#b ,ei#b #b f ,i4 ,if the resistance ,xi be known1 and the ammeter be suitable for use with alternating current1 the switch and ,r may be dispensed with4 ,then ,l ,e#b - ,xi#b ,ii#b #b f ,i1 where ,ii is the value of the alternating current4 ,the resistance of the voltmeter should be high enough to render its current negligible as compared with that through ,xi4 ,ques4 ,how is it caused8 ,ans4 ,it is due to the magnetic field surrounding a conductor cutting adjacent conductors and inducing back pressures therein4 ,this effect as a rule in ordinary installations is negligible4 ,transpositions4--,the effect of mutual induction between two circuits is proportional to the inter-linkage of the magnetic fluxes of the two lines4 ,this in turn depends upon the proximity of the lines and upon the general relative arrangement of the conductors4 ,illustration3 ,,fig4 #b1fgh4--,transposition diagram for two parallel lines consisting of two wires each4 ,illustration3 ,,fig4 #b1fgi4--,transposition diagram for three phase1 three wire line1 transposing at the vertices of an equilateral triangle4 ,the line is originally balanced and becomes unbalanced on transposing1 a procedure which should be resorted to only to prevent mutual induction4 ,illustration3 ,,fig4 #b1fhj4--,transposition diagram of three phase1 three wire line1 with center arranged in a straight line4 ,the inductive effect of one line upon another is equal to the algebraic sum of the fluxes due to the different conductors of the first line1 considered separately1 which link the secondary line4 ,the effect of mutual induction is to induce surges in the line where a difference of frequency exists between the two currents1 and to induce high electrostatic charges in lines carrying little or no current1 such as telephone lines4 ,,inductance ,,per ,,mile ,,of ,,three ,,phase ,,circuit -------------------------------------- ,diam4 ,distance ,self ,size in d in ,inductance ,b4 ,s4 inch4 inches4 ,l henrys4 -------------------------------------- #jjjj 4#df #ab 4#jjbcd #ah 4#jjbef #bd 4#jjbgj #dh 4#jjcab #jjj 4#da #ab 4#jjbda #ah 4#jjbfb #bd 4#jjbgg #dh 4#jjcah #jj 4#cfe #ab 4#jjbdh #ah 4#jjbfi #bd 4#jjbhe #dh 4#jjccj #j 4#cbe #ab 4#jjbed #ah 4#jjbgf #bd 4#jjbic #dh 4#jjcca #a 4#bhi #ab 4#jjbfj #ah 4#jjbha #bd 4#jjcjh #dh 4#jjcch #b 4#beh #ab 4#jjbfg #ah 4#jjbhh #bd 4#jjcjd #dh 4#jjcad #c 4#bbi #ab 4#jjbgd #ah 4#jjbid #bd 4#jjcaj #dh 4#jjcea #d 4#bjd #ab 4#jjbhj #ah 4#jjcjj #bd 4#jjcae #dh 4#jjceh #e 4#ahb #ab 4#jjbhf #ah 4#jjcjg #bd 4#jjcbc #dh 4#jjcef #f 4#afb #ab 4#jjbia #ah 4#jjcac #bd 4#jjcbi #dh 4#jjcfi #g 4#add #ab 4#jjbih #ah 4#jjcaj #bd 4#jjccf #dh 4#jjcgg #h 4#abh #ab 4#jjcjc #ah 4#jjcbe #bd 4#jjcda #dh 4#jjchd #i 4#aad #ab 4#jjcaj #ah 4#jjccb #bd 4#jjcdh #dh 4#jjchi #aj 4#ajb #ab 4#jjcah #ah 4#jjcdj #bd 4#jjcee #dh 4#jjcif -------------------------------------- ,this effect may be nullified by separating the lines and by transposing the wires of one of the lines so that the effect produced in one section is opposed by that in another4 ,of two parallel lines consisting of two wires each1 one may be transposed to neutralize the mutual inductance4 ,fig4 #b1fgh shows this method4 ,the length ,l' should be an even factor of ,l so that to every section of the line transposed there corresponds an opposing section4 ,illustration3 ,,fig4 #b1fha4--;,capacity effect in single phase transmission line4 ,the effect is the same as would be produced by shunting across the line at each point an infinitesimal condenser having a capacity equal to that of an infinitesimal length of circuit4 ,for the purpose of calculating the charging current1 a very simple and sufficiently accurate method is to determine the current taken by a condenser having a capacity equal to that of the entire line when charged to the pressure on the line at the generating end4 ,the effect of capacity of the line is to reduce the pressure drop1 that is1 improve the regulation1 and to decrease or increase the power loss depending on the load and power factor of the receiver4 ,illustration3 ,,fig4 #b1fhb4--;,capacity effect in a three phase transmission line4 ,it is the same as would be produced by shunting the line at each point by three infinitesimal condensers connected in star with the neutral point grounded1 the capacity of each condenser being twice that of a condenser of infinitesimal length formed by any two of the wires4 ,the effect of capacity on the regulation and efficiency of the line can be determined with sufficient accuracy in most cases by considering the line shunted at each end by three condensers connected in star1 the capacity of each condenser being equal to that formed by any two wires of the line4 ,an approximate value for the charging current per wire is the current required to charge a condenser1 equal in capacity to that of any two of the wires1 to the pressure at the generating end of the line between any one wire and the neutral point4 ,the self inductance of lines is readily calculated from the following formula3 ,l 4#jjjeeh #b4cjc log 7#b;,a d7 4#be per mile of circuit where ,l inductance of a loop of a three phase circuit in henrys4 ,note4--,the inductance of a complete single phase circuit ,l #b #c4 ,a distance between wires2 d diameter of wire4 ,,capacity ,,in ,,micro-,,farads ,,per ,,mile ,,of ,,circuit ,,for ,,three ,,phase ,,system ---------------------------------------- ,diam4 ,distance ,capacity ,size in ,a in ,c in ,b4 ,s4 inch4 inches4 micro-farads ---------------------------------------- #jjjj 4#df #ab 4#jbbf #ah 4#jbjd #bd 4#jaibb #dh 4#jadgd #jjj 4#da #ab 4#jbah #ah 4#jaiib #bd 4#jahgf #dh 4#jafch #jj 4#cfe #ab 4#jabd #ah 4#jaidf #bd 4#jahcb #dh 4#jafjd #j 4#cbe #ab 4#jbjgh #ah 4#jahih #bd 4#jafdb #dh 4#jaegj #a 4#bhi #ab 4#jbjbb #ah 4#jaieb #bd 4#jagdh #dh 4#jaed #b 4#beh #ab 4#jaigb #ah 4#jahah #bd 4#jagaj #dh 4#jaeaj #c 4#bbi #ab 4#jaich #ah 4#jagff #bd 4#jafgb #dh 4#jadhj #d 4#bjd #ab 4#jahgd #ah 4#jagbf #bd 4#jafcf #dh 4#jadeb #e 4#ahb #ab 4#jahcj #ah 4#jafij #bd 4#jafjb #dh 4#jadbf #f 4#afb #ab 4#jaghh #ah 4#jafed #bd 4#jaefj #dh 4#jadj #g 4#add #ab 4#jagdf #ah 4#jafah #bd 4#jaech #dh 4#jacgd #h 4#abh #ab 4#jagjh #ah 4#jaehf #bd 4#jaejh #dh 4#jacej #i 4#aad #ab 4#jaffj #ah 4#jaeeb #bd 4#jadgh #dh 4#jacbf #aj 4#ajb #ab 4#jafcf #ah 4#jaebb #bd 4#jadeb #dh 4#jacjd ---------------------------------------- ,capacity4--,in any given system of electrical conductors1 a pressure difference between two of them corresponds to the presence of a quantity of electricity on each4 ,with the same charges1 the difference of pressure may be varied by varying the geometrical arrangement and magnitudes and also by introducing various dielectrics4 ,the constant connecting the charge and the resulting pressure is called the capacity of the system4 ,all circuits have a certain capacity1 because each conductor acts like the plate of a condenser1 and the insulating medium1 acts as the dielectric4 ,the capacity depends upon the insulation4 ,for a given grade of insulation1 the capacity is proportional to the surface of the conductors1 and universally to the distance between them4 ,a three phase three wire transmission line spaced at the corners of an equilateral triangle as regards capacity acts precisely as though the neutral line were situated at the center of the triangle4 ,the capacity of circuits is readily calculated by applying the following formulae3 ,c #ch4hc sc #aj-c _/ log 7,d d7 per mile1 insulated cable with lead sheath2 ,c #ch4hc #aj-c _/ log 7#d;h d7 per mile1 single conductor with earth return2 ,c #ai4db #aj-c _/ log 7#b;,a d7 per mile of parallel conductors forming metallic circuit2 in which ,c ,capacity in micro-farads2 for a metallic circuit1 ,c capacity between wires2 sc ,specific inductive capacity of insulating material2 #a for air1 and #b4be to #c4g for rubber2 ,d ,inside diameter of lead sheath2 d ,diameter of conductor2 h ,distance of conductors above ground2 ,a ,distance between wires4 ,frequency4--,the number of cycles per second1 or the frequency1 has a direct effect upon the inductance reactance in an alternating current circuit1 as is plainly seen from the formula4 ,xi #b;f,l ,in the case of a transmission line alone2 the lower frequencies are the more desirable1 in that they tend to reduce the inductance drop and charging current4 ,the inductance drop is proportional to the frequency4 ,the natural period of a line1 with distributed inductance and capacity1 is approximately given by ,p #g1ijj _/ ,,lc where ,l is the total inductance in millihenrys1 and ,c1 the total capacity in micro-farads4 ,accordingly some lower odd harmonic of the impressed frequency may be present which corresponds with the natural period of the line4 ,when this obtains1 oscillations of dangerous magnitude may occur4 ,such coincidences are less likely with the lower harmonics than with the higher4 ,skin ,effect4--,the tendency of alternating current to confine itself to the outer portions of a conductor1 instead of passing uniformly through the cross section1 is called skin effect4 ,the effect is proportional to the size of the conductor and the frequency4 ,ques4 ,what effect has skin effect on the current8 ,ans4 ,it is equivalent to an increase of ohmic resistance and therefore opposes the current4 ,illustration3 ,,figs4 #b1fhc to #b1fhg4--,skin effect and shield effect4 ,fig4 #b1fhc1 section of conductor illustrating skin effect or tendency of the alternating current to distribute itself unequally through the cross section of a conductor as shown by the varied shading1 which represents the current flowing most strongly in the outer portions of the conductor4 ,for this reason it has been proposed to use hollow or flat instead of solid round conductors2 however1 with frequency not exceeding #ajj1 the skin effect is negligibly small in copper conductors of the sizes usually employed4 ,in figs4 #b1fhd and #b1fhe1 or #b1fhf and #b1fhg1 if two adjacent conductors be carrying current in the same direction1 concentration will occur on those parts of the two conductors remote from one another1 and the nearer parts will have less current1 that is to say1 they will be shielded4 ,in this case1 the induction due to one conductor will exert its opposing effect to the greatest extent on those parts of the other conductor nearest to it2 this effect decreasing the deeper the latter is penetrated4 ,after crossing the current axis1 the induction will still decrease in magnitude1 but will now aid the current in the conductor4 ,hence1 the effect of these two conductors on one another will make the current density more uniform than is the case where the two conductors adjacent to one another are carrying current in opposite directions1 as in figs4 #b1fhe and #b1fhf1 therefore1 the resistance and the heating for a given current will be smaller4 ,if the two return conductors be situated on the line passing through the center of the conductors just considered1 the effect will be to still further concentrate the current2 the distribution symmetry will be further disturbed1 and the resistance of the conductor system increased4 ,it is therefore difficult to say which of the two cases considered holds the advantage so far as increasing the resistance is concerned4 ,the case1 however1 in which the phases are mixed has much the smaller reactive drop4 ,if the conductor be large1 or the frequency high1 the central portion of the conductor carries little if any current1 hence the resistance is therefore greater for alternating current than for direct current4 ,ques4 ,for what condition may skin effect be neglected8 ,ans4 ,for frequencies of #fj or less1 with conductors having a diameter not greater than #jjjj ,b4 ,s4 gauge4 ,ques4 ,how is the skin effect calculated for a given wire8 ,ans4 ,its area in circular mils multiplied by the frequency1 gives the ratio of the wire's ohmic resistance to its combined resistance4 ,that is to say1 the factor thus obtained multiplied by the resistance of the wire to direct current will give its combined resistance or resistance to alternating current4 ,the following table gives these ratio factors for large conductors4 ,,ratio ,,factor ,,for ,,combined ,,resistance ---------------------------------------- -------- ,cir4 mils4 ,ratio ,cir4 mils4 ,ratio frequency factor frequency factor ---------------------------------------- -------- #aj1jjj1jjj #a4jj #gj1jjj1jjj #a4ac #bj1jjj1jjj #a4ja #hj1jjj1jjj #a4ag #cj1jjj1jjj #a4jc #ij1jjj1jjj #a4bj #dj1jjj1jjj #a4je #ajj1jjj1jjj #a4be #ej1jjj1jjj #a4jh #abe1jjj1jjj #a4cd #fj1jjj1jjj #a4aj #aej1jjj1jjj #a4dc ---------------------------------------- -------- ,corona ,effect4--,when two wires1 having a great difference of pressure are placed near each other1 a certain phenomenon occurs1 which is called corona effect4 ,when the spacing or distance between the wires is small and the difference of pressure in the wires very great1 a continuous passage of energy takes place through the dielectric or atmosphere1 the amount of this energy may be an appreciable percentage of the power transmitted4 ,therefore in laying out high pressure transmission lines1 this effect must be considered in the spacing of the wires4 ,ques4 ,how does the corona effect manifest itself8 ,ans4 ,it is visible at night as a bluish luminous envelope and audible as a hissing sound4 ,ques4 ,what is the critical voltage8 ,ans4 ,the voltage at which the corona effect loss takes place4 ,ques4 ,upon what does the critical voltage depend8 ,ans4 ,upon the radius of the wires1 the spacing1 and the atmospheric conditions4 ,illustration3 ,,fig4 #b1fhh4--;,electromagnetic and electrostatic fields surrounding the conductors of a transmission line4 ,the electromagnetic field is represented by lines of magnetic force that surround the conductors in circles1 7the solid lines71 and the electrostatic field by 7dotted7 circles passing from conductor to conductor across at right angles to the magnetic circles4 ,for any given size of wire and distance apart of wires there is a certain voltage at which the critical density or critical gradient is reached1 where the air breaks down and luminosity begins--the critical voltage where corona manifests itself4 ,at still higher voltages corona spreads to further distances from the conductor and a greater volume of air becomes luminous4 ,incidentally1 it produces noise4 ,now to produce light requires power and to produce noise requires power4 ,air is broken down and is heated in breaking down1 and to heat also requires power2 therefore1 as soon as corona forms1 power is consumed or dissipated in its formation4 ,when this phenomenon occurs on the conductors of an alternating current circuit a change takes place in relation to current and voltage4 ,on the wires of an alternating current transmission line1 at a voltage below that where corona forms--at a voltage where wires are not luminous--considerable current1 more or less depending on voltage and length of wire1 flows into the circuit as capacity current or charging current4 ,the critical voltage increases with both the diameter of the wires1 and the spacing4 ,the losses due to corona effect increase very rapidly with increasing pressure beyond the critical voltage4 ,the magnitude of the losses as well as the critical voltage is affected1 by atmospheric conditions1 hence they probably vary with the particular locality1 and the season of the year4 ,therefore1 for a given locality1 a voltage which is normally below the critical point1 may at times be above it1 depending upon changes in the weather4 ,such elements as smoke1 fog1 moisture1 or other particles 7dust1 snow1 etc47 floating in the air1 increase the losses2 rain1 however1 apparently has no appreciable effect upon the losses4 ,it follows then that in the design of a transmission line1 the atmospheric conditions of the particular locality through which the line passes should be considered4 ,ques4 ,how should live wires be spaced8 ,ans4 ,they should be so spaced as to lessen the tendency to leakage and to prevent the wires swinging together or against towers4 ,the spacing should be only sufficient for safety1 since increased spacing increases the self-induction of the line1 and while it lessens the capacity1 it does so only in a slight degree4 ,the following spacing is in accordance with average practice4 ,,spacing ,,for ,,various ,,voltages ------------------- ,volts ,spacing ------------------- #e1jjj #bh ins4 #ae1jjj #dj ins4 #cj1jjj #dh ins4 #de1jjj #fj ins4 #fj1jjj #fj ins4 #ge1jjj #hd ins4 #ij1jjj #if ins4 #aje1jjj #ajh ins4 #abj1jjj #abj ins4 ------------------- ,resistance of ,wires4--,for quick calculation the following method of obtaining the resistance 7approximately7 of wires will be found convenient3 #a1jjj feet ,no4 #aj ,b4 ,s4 wire1 which is about 4#a inch in diameter 74#ajai71 has a resistance of one ohm1 at a temperature of #fh ,f4 and weighs #ca4d pounds4 ,a wire three sizes larger1 that is ,no4 #g1 has twice the cross section and therefore one-half the resistance4 ,a wire three sizes smaller than ,no4 #aj1 that is ,no4 #ac1 has one-half the cross section and therefore twice the resistance4 ,thus1 starting with ,no4 #aj1 any number three sizes larger will double the cross sectional area and any wire three sizes smaller will halve the cross sectional area of the preceding wire4 ,this is true to the extreme limits of the table1 so that the area1 weight and resistance of any wire may be at once calculated to a close approximation from this rule1 intermediate sizes being obtained by interpolation4 ,for alternating current1 the combined resistance1 that is1 the total resistance1 including skin effect1 is obtained by multiplying the resistance1 as found above by the ratio factor 7see table page #a1hid74 ,illustration3 ,,figs4 #b1fhi to #b1fib4--,triangles for obtaining graphically1 impedance1 impressed pressure1 etc41 in alternating current circuits4 ,for a full explanation of this method the reader is referred to ,guide #e1 ,chapter ,,xlvii on ,alternating ,current ,diagrams4 ,a thorough study of this chapter is recommended4 ,impedance4--,the total opposition to the flow of electricity in an alternating current circuit1 or the impedance may be resolved into two components representing the ohmic resistance and the spurious resistance2 these components have a phase difference of #ij1 and they may be represented graphically by the two legs of a right angle triangle1 of which the hypothenuse represents the impedance4 ,similarly1 the volts lost or drop in an alternating circuit may be resolved into two components representing respectively #a4 ,the loss due to resistance4 #b4 ,the loss due to reactance4 ,these components have a phase difference of #ij and are represented graphically similar to the impedance components4 ,this has been explained at considerable length in ,chapter ,,xlvii 7,guide ,v74 ,illustration3 ,,fig4 #b1fic4--,mechanical analogy of power factor1 as exemplified by a locomotive poling a car off a siding4 ,the car and locomotive are shown moving in parallel directions1 and the pole ,,ab1 inclined at an angle 4 ,now1 if the length of ,,ab be taken to represent the pressure exerted on the pole by the locomotive1 then the imaginary lines ,,ac and ,,bc1 drawn respectively parallel and at right angles to the direction of motion will represent respectively the useful and no energy 7wattless7 components2 that is to say1 if the pressure ,,ab be applied to the car at an angle 1 only part of it1 ,,ac1 is useful in propelling the car1 the other component1 ,,bc1 being wasted in tending to push the car off the track at right angles to the rails1 being resisted by the flanges of the outer wheels4 ,power ,factor4--,when the current falls out of step with the pressure1 as on inductive loads1 the power factor becomes less than unity1 and the effect is to increase the current required for a given load4 ,accordingly1 this must be considered in calculating the size of the wires4 ,as has been explained1 the current flowing in an alternating current circuit1 as measured by an ammeter1 can be resolved into two components1 representing respectively the active component and the wattless component or idle current4 ,these are graphically represented by the two legs of a right triangle1 of which the hypothenuse represents the current measured by the ammeter4 ,this apparent current1 as is evident from the triangle1 exceeds the active current and lags behind the pressure by an amount represented by the angle between the hypothenuse and leg representing the energy current as shown in fig4 #b1fid4 ,illustration3 ,,fig4 #b1fid4--;,diagram showing that the apparent current is more than the active current1 the excess depending upon the angle of phase difference4 ,illustration3 ,,fig4 #b1fie4--;,diagram showing components of impedance volts4 ,compare this diagram with figs4 #b1fhi and #b1fga1 and note that the term reactance is the difference between the inductance drop and the capacity drop if the circuit contain capacity1 for instance1 if inductance drop be #aj volts and capacity drop be #g volts then reactance #aj-g #c volts4 ,ques4 ,what determines the heating of the wires on alternating current circuits with inductive loads8 ,ans4 ,the apparent current1 as represented by the hypothenuse of the triangle in fig4 #b1fid4 ,ques4 ,how is the apparent current obtained8 ,ans4 ,divide the true watts by the product of the power factor multiplied by the voltage4 ,example4--,a certain circuit supplies #bj kw4 to motors at #bbj volts and 4#h power factor4 ,what is the apparent current8 true watts #bj1jjj ,apparent ,current -------------------- -------- #aac4f amperes power factor volts 4#h #bbj ,ques4 ,what else1 besides power factor1 should be considered in making wire calculations for motor circuits8 ,ans4 ,the efficiency of the motor1 and the heavy starting current4 ,the product of the efficiency of the motor multiplied by the power factor gives the apparent efficiency1 which governs the size of the wires1 apparatus1 etc41 necessary to feed the motors4 ,allowance should be made for the heavy starting current required for some motors to avoid undue drop4 ,,table ,,of ,,approximate ,,amperes ,,per ,,terminal ,,for ,,induction ,,motors ,column headings3 ,a-#aaj volts ,b-#bbj volts ,c-#ddj volts ,d-#eej volts ---------------------------------------- ----------------------- ,two phase ,three phase ,horse ,single phase four wire three wire power----------------------------------- ---------------- ,a ,b ,c ,a ,b ,c ,a ,b ,c ,d ---------------------------------------- ---------------- 4#e #f4f #c4d #a4h #c4c #a4g 4#i #c4g #a4h #a #a #ad #g #c4e #f4d #c4b #a4f #g4d #c4g #a4i #b #bd #ab #f #aa #e4g #b4i #ac #f4f #c4c #b4e #c #cd #ag #h4e #af #h4a #d4a #ai #i4c #d4g #c4e #d #eb #bf #ac #bf #ac #f4e #cj #ae #g4e #f #e #gd #cg #ah4e #ch #ai #i4e #dd #bb #aa #i #aj #id #dg #bc4e #dd #bb #aa #ej #be #ab4e #aa #ae #ff #cc #af4e #gf #ch #ai #af #bj #hh #dd #bb #ajb #ea #be4e #bb #be #aaa #ee #bh #abi #fd #cb #be #cj #acd #fg #cc4e #aed #gg #ch4e #cb #dj #agh #hi #dd4e #bjd #ajg #ec4e #dd #ej #bjd #ajb #ea #bcf #aah #ei #eb #ge #cjh #aed #gg #cef #agh #hi #gg #ajj #djh #bjd #ajb #dgb #bcf #aah #ajj ---------------------------------------- ---------------- ,ques4 ,what are the usual power factors encountered on commercial circuits8 ,ans4 ,a mixed load of incandescent lamps and induction motors will have a power factor of from 4#h to 4#he2 induction motors above 4#h to 4#he2 incandescent and ,nernst lamps 4#ih2 arc lamps1 4#he4 ,wire ,calculations4--,in the calculation of alternating current circuits1 the two chief factors which make the computation different from that for direct current circuits1 is induction and power factor4 ,the first depends on the frequency1 and physical condition of the circuit1 and the second upon the character of the load4 ,ques4 ,under what conditions may inductance be neglected8 ,illustration3 ,,figs4 #b1fif to #b1fih4--;,example of wiring showing where inductance is negligible1 and where it must be considered in wire calculations4 ,ans4 ,in cases where the wires of a circuit are not spaced over an inch apart1 or in conduit work1 where both wires are in the same conduit4 ,under these conditions the calculation is the same as for direct current after making proper allowance for power factor4 ,ques4 ,under what conditions must induction be considered8 ,ans4 ,on exposed circuits with wires separated several inches1 particularly in the case of large wires4 ,sizes of ,wire4--,the size of wire for any alternating circuit may be determined by slightly modifying the formula used in direct current work1 and which1 as derived in ,guide ,no4 #d1 page #gdh1 is amperes feet #ba4f circular mils --------------------- 7#a7 drop ,the quantity #ba4f1 is twice the resistance 7#aj4h7 of a foot of copper wire one mil in diameter 7mil foot74 ,this resistance 7#aj4h7 is multiplied by #b1 giving the quantity #ba4f1 because the length of a circuit1 or feet in the formula1 is given as the run or distance one way1 that is1 one-half the total length of wire in the circuit1 must be multiplied by #b to get the total drop1 viz43 amperes feet #aj4h #b amperes feet #ba4f circular mils ------------------------- --------------------- drop drop ,it is sometimes however convenient to make the calculation in terms of watts4 ,formula 7#a7 may be modified for such calculation4 ,in modifying the formula1 the drop should be expressed in percentage instead of actual volts lost1 that is1 instead of the difference in pressure between the beginning and the end of the circuit4 ,in any circuit the loss in percentage1 or drop loss ------------------ #ajj impressed pressure from which loss impressed pressure drop --------------------------- 7#b7 #ajj ,substituting equation 7#b7 in equation 7#a7 amperes feet #ba4f circular mils ----------------------------- loss imp4 pressure ------------------------ #ajj amperes feet #b1afj -------------------------- 7#c7 loss imp4 pressure ,equation 7#c7 is modified for calculation in terms of watts as follows3 ,the power in watts is equal to the applied voltage multiplied by the current1 that is to say1 the power is equal to the volts at the consumer's end of the circuit multiplied by the current1 or simply watts volts amperes from which watts amperes ----- 7#d7 volts ,illustration3 ,,figs4 #b1fii to #b1gjc4--,stranded copper cables4 ,for conductors of large areas and in the smaller sizes where extra flexibility is required it becomes necessary to employ stranded cables made by grouping a number of wires together in either concentric or rope form4 ,the concentric cable as here illustrated is formed by grouping six wires around a central wire thereby forming a seven wire cable4 ,the next step is the application in a reverse direction of another layer of #ab wires and a nineteen wire cable is produced4 ,this is again increased by a third layer of eighteen wires for a #cg wire cable and a fourth layer of #bd wires for a #fa wire cable4 ,successive layers1 each containing #f more wires than that preceding1 may be applied until the desired capacity is obtained4 ,the cuts show sectional views of concentric cables each formed from ,no4 #aj ,b4 ,s4 gauge wires4 ,substituting this value for the current in equation 7#c7 and remembering that the pressure taken is the volts at the consumer's end of the line watts ----- feet #b1afj volts circular mils --------------------- loss volts watts feet #b1afj -------------------- 7#e7 loss volts#b ,this formula 7#e7 applies to a direct current two wire circuit1 and to adapt it to any alternating current circuit it is only necessary to use the letter ,m instead of the number #b1afj1 thus watts feet ,m circular mils ------------------ 7#f7 loss volts#b in which ,m is a coefficient which has various values according to the kind of circuit and value of the power factor4 ,these values are given in the following table3 ,,values ,,of ,m ---------------------------------------- --------------------------- ,,power ,,factor ,,system ---------------------------------------- ---------- #a4jj 4#ih 4#ie 4#ij 4#he 4#hj 4#ge 4#gj 4#fe 4#fj ---------------------------------------- ------------------ ,single #b1afjb1bdib1djjb1ffjc1jjjc1chjc1hdjd1dj je1aabf1jjj phase ---------------------------------------- ------------------ ,two #a1jhja1abea1bjja1ccja1ejja1fija1ibjb1bj jb1eefc1jjj phase 7#d wire7 ---------------------------------------- ------------------ ,three #a1jhja1abea1bjja1ccja1ejja1fija1ibjb1bj jb1eefc1jjj phase 7#c wire7 ---------------------------------------- ------------------ ,,note4--,the above table is calculated as follows3 ,for single phase ,m #b1afj power factor#b #ajj2 for two phase four wire1 or three phase three wire1 ,m 7#b1afj power factor#b7 #ajj4 ,thus the value of ,m for a single phase line with power factor 4#ie #b1afj 4#ieb #ajj #b1djj4 ,it must be evident that when #b1afj is taken as the value of ,m1 formula 7#f7 applies to a two wire direct current circuit and also to a single phase alternating current circuit when the power factor is unity4 ,in the table the value of ,m for any particular power factor is found by dividing #b1afj by the square of that power factor for single phase and twice the square of the power factor for two phase and three phase4 ,ques4 ,for a given load and voltage how do the wires of a single and two phase system compare in size and weight1 the power factor being the same in each case8 ,ans4 ,since the two phase system is virtually two single phase systems1 the four wires of the two phase systems are half the size of the two wires of the single phase system1 and accordingly1 the weight is the same for either system4 ,,values ,,of ,t ---------------------------------------- ----------------------- ,,power ,,factor ,,system ---------------------------------------- #a4jj 4#ih 4#ij 4#hj 4#gj ---------------------------------------- ------------------- ,single phase #a4jj 4#ih 4#ij 4#hj 4#gj ---------------------------------------- ------------------- ,two phase1 #d wire #b4jj #a4if #a4hj #a4fj #a4dj ---------------------------------------- ------------------- ,three phase1 #c wire #a4gc #a4gj #a4ee #a4ch #a4ba ---------------------------------------- ------------------- ,,note4--,this table is for finding the value of the current in line1 using the formula ,i ,w 7,e ,t71 in which ,i current in line2 ,e voltage between main conductors at receiving or consumers' end2 ,w watts4 ,for instance1 what is the current in a two phase line transmitting #a1jjj watts at #eej volts1 power factor 4#hj8 ,i #a1jjj 7#eej #a4fj7 #a4ac4 ,ques4 ,since there is no saving in copper in using two phases1 what advantage has the two phase system over the one phase system8 ,ans4 ,it is more desirable on power circuits1 because two phase motors are self-starting4 ,that is to say1 the rotating magnetic field that can be produced by a two phase current1 permits an induction motor to start without being equipped with any special phase splitting devices which are necessary on single phase motors1 because the oscillating field produced by a single phase current does not produce any torque on a squirrel cage armature at rest4 ,ques4 ,for equal working conditions1 what is the comparison between the single1 two and three phase system as to size and weight of wires8 ,ans4 ,each wire of the three phase system is half the size of one of the wires of the single phase system1 hence the weight of copper required for the three phase system is #ge of that required for the single phase system4 ,since in the two phase system half of the load is carried by each phase1 each wire of the three phase system is the same size as one of the wires of the two phase system1 hence1 the copper required by the three phase system is #ge of that required by the two phase system4 ,,miscellaneous ,,formul ,,for ,,copper ,,wires ,diameter squared circular mils ,circular mils 4#ghed square mils 4#jjjjjcjbg circular mils pounds per foot 4#jjcjbg circular mils pounds per #a1jjj feet 4#jaeihdg circular mils pounds per mile 4#jjchgi square mils pounds per #a1jjj feet 4#ccjcc circular mils feet per pound 4#jjjjjjbibd circular mils pounds per ohm 4#cdb circular mils ohms per pound 4#jifehe circular mils feet per ohm #aj4cecefh circular mils ohms per foot ,breaking weight of wire area breaking weight per square inch4 ,breaking weight per square inch area breaking weight of wire4 ,the weight of copper wire is #a-a_/g times the weight of iron wire of same diameter4 ,,example4--,what size wires must be used on a single phase circuit #b1jjj feet in length to supply #cj kw4 at #bbj volts with loss of #d1 the power factor being 4#i8 ,the formula for circular mils is watts feet ,m circular mils ------------------ 7#a7 loss volts#b ,substituting the given values and the proper value of ,m from the table1 in 7#a7 #cj1jjj #b1jjj #b1ffj circular mils ---------------------- #hb1dch #d #bbjb ,referring to the accompanying table of the properties of copper wire1 the nearest larger size wire is ,no4 #a ,b4 ,s4 gauge having an area of #hc1fij circular mils4 ,,table ,,of ,,the ,,properties ,,of ,,copper ,,wire ,giving weights1 length and resistances of wires of ,matthiessen's ,standard ,conductivity for both ,b4 ,s4 ,g4 7,brown ,sharpe ,gauge7 and ,b4 ,w4 ,g4 7,birmingham ,wire ,gauge7 from ,transactions ,october #aijc1 of the ,american ,institute of ,electrical ,engineers4 ,gauges4 ,to the nearest fourth ,length4,resistance4 significant digit4 ,weight4 ,diameter4 ,area4 ,lbs4 ,feet ,ohms per per per lb4#a1jjj ft4 #a1jjj feet4 ,circular ,b4 ,s4 ,b4,w4,g4 ,inches4 mils4 #fh ,f4 #jjjj #j4dfj #baa1fjj #fdj4e #a4efa 4#jdhic #jjjj #j4ded #bjf1ajj #fbc4i #a4fjc 4#jejbc #jjj #j4dbe #ahj1fjj #edf4h #a4hbi 4#jegcb #jjj #j4djif #afg1hjj #ejh4j #a4ifi 4#jfagj #jj #j4chj #add1djj #dcg4a #b4bhh 4#jgagj #jj #j4cfdh #acc1ajj #djb4h #b4dhb 4#jgghj #j #j4cdj #aae1fjj #cdi4i #b4heh 4#jhieg #j #j4cbdi #aje1ejj #cai4e #c4acj 4#jihaa #a #j4cjjj #ij1jjj #bgb4d #c4fga 4#aaej #a #j4bhic #hc1fij #bec4c #c4idg 4#abcg #b #j4bhdj #hj1ffj #bdd4a #d4jif 4#abhd #c #j4beij #fg1jhj #bjc4a #d4ibe 4#aedc #b #j4begf #ff1cgj #bjj4i #d4igg 4#aefj #d #j4bchj #ef1fdj #aga4e #e4hcb 4#ahbh #c #j4bbid #eb1fcj #aei4c #f4bgf 4#aifg #e #j4bbjj #dh1djj #adf4e #f4hbf 4#baci #d #j4bjdc #da1gdj #abf4d #g4iad 4#bdhj #f #j4bjcj #da1baj #abd4g #h4jag 4#beac #e #j4ahai #cc1ajj #ajj4b #i4ih 4#cabh #g #j4ahjj #cb1djj #ih4jh #aj4bj 4#caif #h #j4afej #bg1bcj #hb4da #ab4ac 4#chjc #f #j4afbj #bf1bej #gi4df #ab4eh 4#cidd #i #j4adhj #ba1ijj #ff4cj #ae4jh 4#dgbg #g #j4addc #bj1hbj #fc4jb #ae4hg 4#digc #aj #j4acdj #ag1ifj #ed4ce #ah4dj 4#egff #h #j4abhe #af1eaj #di4ih #bj4ja 4#fbga #aa #j4abjj #ad1djj #dc4ei #bb4id 4#gaij #i #j4aadd #ac1jij #ci4fc #be4bc 4#gijh #ab #j4ajij #aa1hhj #ce4if #bg4ha 4#hgae #aj #j4ajai #aj1chj #ca4dc #ca4hb 4#iigb #ac #j4jiej #i1jbe #bg4cb #cf4fj #a4adg #aa #j4jijgd #h1bcd #bd4ic #dj4ab #a4beg #ad #j4jhcjj #f1hhi #bj4he #dg4ie #a4ejc #ab #j4jhjha #f1ecj #ai4gg #ej4ei #a4ehf #ae #j4jgbjj #e1ahd #ae4fi #fc4gc #a4iig #ac #j4jgaif #e1agh #ae4fh #fc4gi #a4iii #af #j4jfejj #d1bbe #ab4gi #gh4ai #b4dea #ad #j4jfdjh #d1ajg #ab4dc #hj4dd #b4eba #ag #j4jehj #c1cfd #aj4ah #ih4bc #c4jgh #ae #j4jegjg #c1beg #i4heh #aja4d #c4agi #af #j4jejhb #b1ehc #g4hah #abg4i #d4jji #ah #j4jdijj #b1dja #g4bfh #acg4f #d4cab #ag #j4jdebfj #b1jdh #f4bjj #afa4c #e4jee #ai #j4jdbjjj #a1gfd #e4cdj #ahg4c #e4hgj #ah #j4jdjcjj #a1fbd #d4iag #bjc4d #f4cgd #ai #j4jcehij #a1bhh #c4hii #bef4e #h4jch #bj #j4jcejjj #a1bbe #c4gjh #bfi4g #h4deb #ba #j4jcbjjj #a1jbd #c4ajj #cbb4f #aj4aa #bj #j4jcaifj #a1jbb #c4jib #cbc4d #aj4ad #ba #j4jbhdfj #haj4a #b4deb #djg4h #ab4gh #bb #j4jbhjjj #ghd4j #b4cgc #dba4d #ac4ba #bb #j4jbecej #fdb4d #a4ide #ead4b #af4ab #bc #j4jbejjj #fbe4j #a4hib #ebh4f #af4eg #bc #j4jbbegj #eji4e #a4edb #fdh4d #bj4cb #bd #j4jbbjjj #dhd4j #a4dfe #fhb4f #ba4ci #bd #j4jbjajj #djd4j #a4bbc #hag4f #be4fc #be #j4jbjjjj #djj4j #a4baa #hbe4i #be4hh #bf #j4jahjjj #cbd4j 4#ihjh #a1jbj #ca4if #be #j4jagijj #cbj4d 4#ifii #a1jca #cb4ca #bg #j4jafjjj #bef4j 4#ggdi #a1bij #dj4de #bf #j4jaeidj #bed4a 4#gfib #a1cjj #dj4ge #bg #j4jadbjj #bja4e 4#fajj #a1fci #ea4ch #bh #j4jadjjj #aif4j 4#eicc #a1fhe #eb4hc #bi #j4jacjjj #afi4j 4#eaaf #a1iee #fa4bg #bh #j4jabfdj #aei4h 4#dhcg #b1jfg #fd4gi #cj #j4jabjjj #add4j 4#dcei #b1bid #ga4ij #bi #j4jaabfj #abf4g 4#chcf #b1fjg #ha4gj #cj #j4jajjcj #ajj4e 4#cjdb #c1bhg #ajc4j #ca #j4jajjjj #ajj4j 4#cjbg #c1cjd #ajc4e #cb #j4jjijjj #ha4j 4#bdeb #d1jgh #abg4h #ca #j4jjhibh #gi4gj 4#bdac #d1ade #abi4i #cc #j4jjhjjj #fd4j 4#aicg #e1afb #afa4h #cb #j4jjgiej #fc4ba 4#aiac #e1bbg #afc4h #cc #j4jjgjhj #ej4ac 4#aeag #f1eia #bjf4f #cd #j4jjgjjj #di4j 4#adhc #f1gdb #baa4c #cd #j4jjfcje #ci4ge 4#abjc #h1caa #bfj4e #ce #j4jjefae #ca4eb 4#jiedc #aj1dhj #cbh4d #cf #ce #j4jjejjj #be4j 4#jgefh #ac1baj #dad4b #cg #j4jjddec #ai4hc 4#jfjja #af1ffj #ebb4b #cf #j4jjdjjj #af4 4#jdhdc #bj1fej #fdg4a #ch #j4jjcife #ae4gb 4#jdgei #ba1jaj #feh4e #ci #j4jjceca #ab4dg 4#jcggd #bf1ejj #hcj4d #dj #j4jjcade #i4hhh 4#jbiic #cc1daj #ajdg4 ---------------------------------------- ---------------------------- ,drop4--,in order to determine the drop or volts lost in the line1 the following formula may be used drop 77 loss volts7 _/ #ajj7 ,s 7#a7 in which the loss is a percentage of the applied power1 that is1 the power delivered to the consumer and not a percentage of the power at the alternator4 ,volts is the pressure at the consumer's end of the circuit4 ,,value ,,of ,s ,,for #fj ,,cycles ---------------------------------------- ------------------------- 4#ih power factor 4#ij power factor ---------------------------------------- ------------------------ ,size of ,area ,spacing of ,spacing of wire in conductors conductors ,b4,s4 circular gauge mils4 ---------------------------------------- #a #c #f #ab #bd #a #c #f #ab #bd ---------------------------------------- ---------------- #ejj1jjj #ejj1jjj #a4baa4dea4faa4gga4iba4cba4hjb4aab4ddb4g e #cjj1jjj #cjj1jjj #a4aea4bia4cha4dha4ega4aia4dga4ffa4hdb4j b #j1jjj #baa1fjj #a4aba4bba4bha4cda4daa4aca4cca4dea4eha4f c #jjj #afg1hjj #a4jia4aha4bba4bha4bia4jha4bca4cca4dda4e c #jj #acc1ajj #a4jga4ada4aha4baa4bea4jca4afa4bda4cba4d j #j #aje1ejj #a4jea4aja4ada4aga4bja4jja4jia4afa4bba4b h #a #hc1fij #a4jda4jha4aja4aca4aea4jja4jea4jia4ada4a i #b #ff1cgj #a4jba4jea4jha4aja4aba4jja4jja4jda4jha4a b #c #eb1fcj #a4jba4jda4jfa4jga4jia4jja4jja4jja4jca4j f #d #da1gdja4jja4jba4jca4jda4jga4jja4jja4jja 4jja4jj #e #cc1ajj #f #bf1beja4jja4jja4jja4jja4jja4jja4jja4jja 4jja4jj #g #bj1hbj #h #af1eaj #i #ac1jija4jja4jja4jja4jja4jja4jja4jja4jja 4jja4jj #aj #aj1chj ---------------------------------------- ---------------- ---------------------------------------- ---------------- ,size 4#hj power factor 4#gj power factor of ,area ---------------------------------------- -------- wire in ,spacing of ,spacing of ,b4,s4 circular conductors conductors gauge mils4 ---------------------------------------- #a #c #f #ab #bd #a #c #f #ab #bd ---------------------------------------- ---------------- #ejj1jjj #ejj1jjja4bga4hib4beb4fdc4jca4ada4gbb4ab b4ecb4ib #cjj1jjj #cjj1jjja4aaa4dfa4fha4ijb4aba4jja4cca4ef a4ghb4ja #j1jjj #baa1fjja4jca4bga4dca4eha4gea4jja4ada4bi a4dea4fi #jjj #afg1hjja4jja4afa4bha4daa4eca4jja4jba4ae a4bha4ej #jj #acc1ajja4jja4jga4aea4bba4jja4jja4jja4jc a4aca4ba #j #aje1ejja4jja4jja4jga4aea4jja4jja4jja4jj a4jaa4ji #a #hc1fija4jja4jja4jja4jja4jja4jja4jja4jja 4jja4jj #b #ff1cgja4jja4jja4jja4jja4jja4jja4jja4jja 4jja4jj #c #eb1fcja4jja4jja4jja4jja4jja4jja4jja4jja 4jja4jj #d #da1gdj #e #cc1ajja4jja4jja4jja4jja4jja4jja4jja4jja 4jja4jj #f #bf1bej #g #bj1hbj #h #af1eaj #i #ac1jija4jja4jja4jja4jja4jja4jja4jja4jja 4jja4jj #aj #aj1chj ---------------------------------------- ---------------- ,the coefficient ,s has various values as given in the accompanying tables4 ,as will be seen from the table1 the value of ,s to be used depends upon the size of wire1 spacing1 power factor and frequency4 ,these values are accurate enough for all practical purposes1 and may be used for distances of #bj miles or less and for voltages up to #be1jjj4 ,the capacity effect on very long high voltage lines1 makes this method of determining the drop somewhat inaccurate beyond the limits above mentioned4 ,,value ,,of ,s ,,for #be ,,cycles ---------------------------------------- ------------------------- ,size 4#ih power factor 4#ij power factor of ,area ---------------------------------------- -------- wire in ,spacing of ,spacing of ,b4,s4 circular conductors conductors gauge mils4 ---------------------------------------- #a #b #f #ab #bd #a #c #f #ab #bd ---------------------------------------- ----------------- #ejj1jjj #ejj1jjj #a4jaa4aga4bca4bia4cfa4jba4bba4cea4dca4f a #cjj1jjj #cjj1jjj #a4jda4aja4aca4aha4baa4jja4jha4afa4bea4c a #j1jjj #baa1fjj #a4jca4jga4jia4aaa4ada4jja4jba4jga4aca4a e #jjj #afg1hjj #a4jja4jea4jfa4jia4aja4jja4jja4jba4jga4a a #jj #acc1ajj #a4jja4jca4jea4jfa4jha4jja4jja4jja4jba4j e #j #aje1ejj #a4jja4jaa4jba4jca4jda4jja4jja4jja4jja4j j #a #hc1fij #b #ff1cgja4jja4jja4jja4jja4jja4jja4jja4jja 4jja4jj #c #eb1fcj #d #da1gdj #e #cc1ajja4jja4jja4jja4jja4jja4jja4jja4jja 4jja4jj #f #bf1bej #g #bj1hbj #h #af1eaj #i #ac1jija4jja4jja4jja4jja4jja4jja4jja4jja 4jja4jj #aj #aj1chj ---------------------------------------- ----------------- ,size 4#hj power factor 4#gj power factor of ,area ---------------------------------------- -------- wire in ,spacing of ,spacing of ,b4,s4 circular conductors conductors gauge mils4 ---------------------------------------- #a #c #f #ab #bd #a #c #f #ab #bd ---------------------------------------- ----------------- #ejj1jjj #ejj1jjja4jja4aea4cja4dga4fba4jja4jja4af a4cca4di #cjj1jjj #cjj1jjja4jja4jja4jia4afa4bea4jja4jja4jj a4jba4ab #j1jjj #baa1fjja4jja4jja4jja4jca4aja4jja4jja4jj a4jja4jj #jjj #afg1hjja4jja4jja4jja4jja4jaa4jja4jja4jj a4jja4jj #jj #acc1ajja4jja4jja4jja4jja4jja4jja4jja4jj a4jja4jj #j #aje1ejja4jja4jja4jja4jja4jja4jja4jja4jj a4jja4jj #a #hc1fij #b #ff1cgja4jja4jja4jja4jja4jja4jja4jja4jja 4jja4jj #c #eb1fcj #d #da1gdj #e #cc1ajja4jja4jja4jja4jja4jja4jja4jja4jja 4jja4jj #f #bf1bej #g #bj1hbj #h #af1eaj #i #ac1jija4jja4jja4jja4jja4jja4jja4jja4jja 4jja4jj #aj #aj1chj ---------------------------------------- ----------------- ,,example4--,a circuit supplying current at #ddj volts1 #fj frequency1 with #e loss and 4#h power factor is composed of ,no4 #b ,b4 ,s4 gauge wires spaced one foot apart4 ,what is the drop in the line8 ,according to the formula loss volts drop -------------- ,s #ajj ,substituting the given values1 and value of ,s as obtained from the table for frequency #fj #e #ddj drop ------- #a #bb volts #ajj ,current4--,as has been stated1 the effect of power factor less than unity1 is to increase the current2 hence1 in inductive circuit calculations1 the first step is to determine the current flowing in a circuit4 ,this is done as follows3 apparent load current ------------- 7#a7 volts and watts apparent load ------------ 7#b7 power factor ,substituting 7#b7 in 7#a7 watts ------------ power factor watts current ------------ --------------------- 7#c7 volts power factor volts ,illustration3 ,,fig4 #b1gjd4--,rope type of stranded copper cable which is used when a high degree of flexibility is required4 ,the construction of this cable is the stranding together of seven groups1 each containing seven wires and producing a total of #di wires4 ,in cases when a greater carrying capacity is desired than can be obtained through the use of the #g #g or #di wire cable1 the number of groups is increased to nineteen thereby making a total of #acc wires 7#ai #g74 ,,example4--,a #ej horse power #ddj volt motor has a full load efficiency of 4#i and power factor of 4#h4 ,how much current is required8 ,since the brake horse power of the motor is given1 it is necessary to obtain the electrical horse power1 thus brake horse power #ej ,e4,h4,p4 ----------------- -- #ee4e efficiency 4#i which in watts is #ee4e #gdf #da1djc which is the actual load1 and from which actual load #da1djc apparent load ------------ ------ #ea1ged power factor 4#h ,the current therefore at #ddj volts is apparent load #ea1ged ------------- ------ #aag4f amperes volts #ddj ,,example4--,a #ej horse power single phase #ddj volt motor1 having a full load efficiency of 4#ib and power factor of 4#h1 is to be operated at a distance of #a1jjj feet from the alternator4 ,the wires are to be spaced #f inches apart and the frequency is #fj1 and loss #e4 ,determine3 ,a1 electrical horse power2 ,b1 watts2 ,c1 apparent load2 ,d1 current2 ,e1 size of wires2 ,f1 drop2 ,g1 voltage at the alternator4 ,a4 ,electrical horse power brake horse power #ej ,e4 ,h4 ,p4 ----------------- --- #ed4c efficiency 4#ib or1 #ed4c #gdf #dj1ejh watts ,,table ,,of ,,wire ,,equivalents 7,brown and ,sharpe gauge7 ---------------------------------------- ----------------- #jjjj #b #j #d #c #h #f #af #i #cb #ab #fd #ae #jjj #b #a #d #d #h #g #af #aj #cb #ac #fd #af #jj #b #b #d #e #h #h #af #aa #cb #ad #fd #ag #j #b #c #d #f #h #i #af #ab #cb #ae #fd #ah #a #b #d #d #g #h #aj #af #ac #cb #af #fd #ai #b #b #e #d #h #h #aa #af #ad #cb #ag #fd #bj #c #b #f #d #i #h #ab #af #ae #cb #ah #fd #ba #d #b #g #d #aj #h #ac #af #af #cb #ai #fd #bb #e #b #h #d #aa #h #ad #af #ag #cb #bj #fd #bc #f #b #i #d #ab #h #ae #af #ah #cb #ba #fd #bd #g #b #aj #d #ac #h #af #af #ai #cb #bb #fd #be #h #b #aa #d #ad #h #ag #af #bj #cb #bc #fd #bf #i #b #ab #d #ae #h #ah #af #ba #cb #bd #fd #bg #aj #b #ac #d #af #h #ai #af #bb #cb #be #fd #bh #aa #b #ad #d #ag #h #bj #af #bc #cb #bf #fd #bi #ab #b #ae #d #ah #h #ba #af #bd #cb #bg #fd #cj #ac #b #af #d #ai #h #bb #af #be #cb #bh #ad #b #ag #d #bj #h #bc #af #bf #cb #bi #ae #b #ah #d #ba #h #bd #af #bg #cb #cj #af #b #ai #d #bb #h #be #af #bh #ag #b #bj #d #bc #h #bf #af #bi #ah #b #ba #d #bd #h #bg #af #cj #ai #b #bb #d #be #h #bh #bj #b #bc #d #bf #h #bi #ba #b #bd #d #bg #h #cj ---------------------------------------- ----------------- ,b4 ,watts watts ,e4,h4,p4 #gdf #ed4c #gdf #dj1ejh ,c4 ,apparent load apparent load or kva 7actual load or watts power factor7 #dj1ejh 4#h #ej1fce ,d4 ,current current 7apparent load or kva volts7 #ej1fce #ddj #aae amperes ,e4 ,size of wires cir4 mils 7watts feet ,m7 7 loss volts#b7 7#dj1ejh #a1jjj #c1chj7 7#e #ddjb7 #ada1ddc ,from table page #a1ijg1 nearest size larger wire is ,no4 #jj ,b4,s4 gauge4 ,f4 ,drop drop 77 loss volts7 #ajj7 ,s 77#e #ddj7 #ajj7 #a4ag #be4gd volts ,,note4--,values of ,s are given on page #aiaj4 ,g4 ,voltage at alternator alternator pressure 7volts at motor drop7 #ddj #be4gd #dfe4g volts4 ,,chapter ,,lxvi ,,power ,,stations ,the term power station is usually applied to any building containing an installation of machinery for the conversion of energy from one form into another form4 ,there are three general classes of station3 #a4 ,central stations2 #b4 ,sub-stations2 #c4 ,isolated plants4 ,these may also be classified with respect to their function as #a4 ,generating stations2 #b4 ,distributing stations2 #c4 ,converting stations4 and with respect to the form of power used in generating the electric current1 generating stations may be classed as #a4 ,steam electric2 #b4 ,hydro-electric2 #c4 ,gas electric1 etc4 ,central ,stations4--,it must be evident that the general type of central station to be adapted to a given case1 that is to say1 the general character of the machinery to be installed depends upon the kind of natural energy available for conversion into electrical energy1 and the character of the electrical energy required by the consumers4 ,this gives rise to a further classification1 as #a4 ,alternating current stations2 #b4 ,direct current stations2 #c4 ,alternating and direct current stations4 ,the alternators or dynamos may be driven by steam or water turbines1 reciprocating engines1 or gas engines1 according to the character of the natural energy available4 ,illustration3 ,,fig4 #b1gje4--;,elevation of small station with direct drive1 showing arrangement of the boiler and engine1 piping1 etc4 ,ques4 ,why is the reciprocating engine being largely replaced by the steam turbine1 especially for large units8 ,ans4 ,because of its higher rotative speed1 and absence of a multiplicity of bearings which in the case of a high speed1 reciprocating engine must be maintained in close adjustment for the proper operation of the engine4 ,the higher speed of rotation results in a more compact unit1 desirable for driving high frequency alternators4 ,ques4 ,is the steam turbine more economical than a high duty reciprocating engine8 ,ans4 ,no4 ,location of ,central ,stations4--,as a rule1 central stations should be so located that the average loss of voltage in overcoming the resistance of the lines is a minimum1 and this point is located at the center of gravity of the system4 ,in fig4 #b1gjf is shown a graphical method of locating this important spot4 ,illustration3 ,fig4 #b1gjf4--;,diagram illustrating graphical method of determining the center of gravity of a system in locating the central station4 ,suppose a rough canvass of prospective consumers in a district to be supplied with electric light or power shows the principal loads to be located at ,a1 ,b1 ,c1 ,d1 ,e1 etc41 and for simplicity assume that these loads will be approximately equal1 so that each may be denoted by #a for example3 ,the relative locations of ,a1 ,b1 ,c1 ,d1 ,e1 etc41 should be drawn to scale 7say #a inch to the #a1jjj feet7 after which the problem resolves itself into finding the location of the station with respect to this scale4 ,illustration3 ,,fig4 #b1gjg4--;,exterior of central station at ,lewis1 ,ia42 example of very small station located in the principal business section of a town4 ,it also illustrates the use of a direct connected gasoline electric set4 ,the central station is located on ,main ,street1 which is the principal thoroughfare1 and is installed in a low one story building for which a mere nominal rental charge is paid1 the company having the option to buy the property later at the value of the land plus the cost of the improvements and simple interest on the same4 ,to the front of an old frame building about #af feet by #bh feet has been built a neat1 well lighted concrete block room1 about #af feet by #af feet1 carrying the building to the lot line and affording ample space for the generating set and switchboards1 and such desk room as is needed for the ordinary office business of the company4 ,in this room1 which is finished in natural pine with plastered walls1 has been installed a standard ,general ,electric #be kw4 gasoline electric generating set consisting of a four cylinder1 four cycle1 vertical water cooled1 #dc-ed ,h4,p4 gasoline engine1 direct connected to a three phase1 #b1cjj volt1 #fjj ,r4,p4,m4 alternator with a #abe volt exciter mounted on the same shaft and in the same frame4 ,with the generating set is a slate switchboard panel equipped with three ammeters1 one voltmeter1 an instrument plug switch for voltage indication1 one single pole carbon break switch1 one automatic oil circuit breaker line switch and rheostats4 ,instrument transformers are mounted above and back of the board4 ,for street lighting service a #d kw4 constant current transformer has been installed1 and with it a gray marble switchboard panel mounted on iron frames and carrying an ammeter and a four point plug switch4 ,on a board near the generator set are mounted in convenient reach suitable wrenches1 spanners1 and repair parts and tools4 ,to cool the engine cylinders five #f #h steel tanks have been installed in the old building1 a pump on engine giving forced circulation4 ,the solution consists in first finding the center of gravity of any two of the loads1 such as those at ,a and ,b4 ,since each of these is #a1 they will together have the same effect on the system as the resultant load of #a and #a1 or #b1 located at their center of gravity1 this point being so chosen that the product of the loads by their respective distances from this point will in both cases be equal4 ,the loads being equal in this case the distances must be equal in order that the products be the same1 so that the center of gravity of ,a ,b is at ,g1 which point is midway between ,a and ,b4 ,considering1 next1 the resultant load of #b at ,g and the load of #a at ,c1 the resultant load at the center or gravity of these will be #c1 and this must be situated at a distance of two units from ,c and one unit from ,g so that the distance #b times the load #a at ,c equals the distance #a times the load #b at ,g4 ,having thus located the load #c at ,h1 the same method is followed in finding the load #d at ,i4 ,then in like manner the resultant load #d and the load #a at ,e gives a load #e at ,s4 ,the point ,s being the last to be determined represents1 therefore1 the position of the center of gravity of the entire system1 and consequently the proper position of the plant in order to give the minimum loss of voltage on the lines4 ,ques4 ,is the center of gravity of the system1 as obtained in fig4 #b1gjf1 the proper location for the central station8 ,ans4 ,it is very rarely the best location4 ,ques4 ,why8 ,ans4 ,other conditions1 such as the price of land1 difficulty of obtaining water1 facilities for delivery of coal and removal of ashes1 etc41 may more than offset the minimum line losses and copper cost due to locating the station at the center of gravity of the system4 ,illustration3 ,,fig4 #b1gjh4--,map of ,cia ,docas de ,santos hydro-electric system2 an example of station location remote from the center of distribution4 ,in the figure ,a is the intake2 ,b1 flume2 ,c1 forebay2 ,d1 penstocks2 ,e1 power house2 ,f1 narrow gauge railway2 ,g1 general store2 ,h1 point of debarkation2 ,i1 transmission line2 ,j1 dead ends2 ,k1 sub-station4 ,santos1 in the republic of ,brazil1 is one of the great coffee shipping ports of the world1 and for the development of its water front has required an elaborate system of quays4 ,these have been developed by the ,santos ,dock ,company1 which holds a concession for the whole water front4 ,the company1 needing electric power for its own use1 has developed a system deriving its power from a point about thirty miles from the city1 where a small stream plunges down the sea coast from the mountain range that runs along it4 ,the engineers have estimated that #ajj1jjj horse power can be obtained from this source4 ,ques4 ,how then should the station be located8 ,ans4 ,the more practical experience the designer has had1 and the more common sense he possesses1 the better is he equipped to handle the problem1 as the solution is generally such that it cannot be worked out by any rule of thumb method4 ,illustration3 ,,fig4 #b1gji4--,station location4 ,the figure shows two distribution centers as a town ,a and suburb ,b supplied with electricity from one station4 ,for minimum cost of copper the location of the station would be at ,g1 the center of gravity4 ,however1 it is very rarely that this is the best location4 ,for instance at ,c1 land is cheaper than at ,g1 and there is room for future extension to the station1 as shown by the dotted lines1 whereas at ,g1 only enough land is available for present requirements4 ,moreover ,c is near the railroad where coal may be obtained without the expense of cartage1 and being located at the river1 the plant may be run condensing thus effecting considerable economy4 ,the conditions may sometimes be such that any one of the advantages to be secured by locating the station at ,c may more than offset the additional cost of copper4 ,ques4 ,what are the general considerations with respect to the price of land8 ,ans4 ,the cost for the station site may be so high as to necessitate building or renting room at a considerable distance from the district to be supplied4 ,if the price of land selected for the station be high1 the running expenses will be similarly affected1 inasmuch as more interest must then be paid on the capital invested4 ,the price or rent of real estate might also in certain instances alter the proposed interior arrangement of the station1 particularly so in the case of a company with small capital operating in a city where high prices prevail4 ,in general1 however1 it may be stated that whatever effect the price of real estate would have upon the arrangement1 operation and location of a central station it can quite readily and accurately be determined in advance4 ,ques4 ,with respect to the cost of the land what should be especially considered8 ,ans4 ,room for the future extension of the plant4 ,although such additional space need not be purchased at the time of the original installation it is well1 if possible1 to make provision whereby it can be obtained at a reasonable figure when desired4 ,the preliminary canvass of consumers will aid in deciding the amount of space advisable to allow for future extensions2 as a rule1 however1 it is wise to count on the plant enlarging to not less than twice its original size1 as often the dimensions have to be increased four and even six times those found sufficient at the beginning4 ,illustration3 ,,fig4 #b1gaj4--,section of the central station or electricity works at ,derby1 showing boiler and engine room and arrangement of bunkers1 conveyor1 ash pit1 grates1 boilers 7drum1 heating surface and superheater71 economizer1 flue1 turbines1 condenser pumps1 etc42 also location of switchboard gallery and system of piping4 ,ques4 ,what trouble is likely to be encountered with an illy located plant after it is in operation8 ,ans4 ,it may be considered a nuisance by those residing in the vicinity1 occasioning many complaints4 ,illustration3 ,,fig4 #b1gaa4--,view of old and new ,waterside stations4 ,the new station at the right has an all turbine equipment of ten units1 some ,curtis and some ,parsons machines1 two have a capacity of #ad1jjj kw41 and the remaining eight are of #ab1jjj kw4 each4 ,the old ,riverside station1 seen at the left is described on page #aidj4 ,thus1 if the plant be placed in a residential section of the community the smoke1 noise and vibration of the machines may become a nuisance to the surrounding inhabitants1 and eventually end in suits for damage against the company responsible for the same4 ,for these and the other reasons just given a company is sometimes forced to disregard entirely the location of a central station near the center of gravity of the system1 and build at a considerable distance2 such a proceeding would1 if the distance be great1 necessitate the installation of a high pressure system4 ,there might1 however1 be certain local laws in force restricting the use of high pressure currents on account of the danger resulting to life1 that would prevent this solution of the problem4 ,in such cases there could undoubtedly be found some site where the objections previously noted would be tolerated2 thus1 there would naturally be little objection to locating next to a stable1 a brewery1 or a factory of any description4 ,ques4 ,why is the matter of water supply important for a central station8 ,ans4 ,because1 in a steam driven plant1 water is used in the boilers for the production of steam by boiling1 and if the engines be of the condensing type it is also used in them for creating a vacuum into which the exhaust steam passes so as to increase the efficiency of the engine above what it would be if the exhaust steam were obliged to discharge into the comparatively high pressure of the atmosphere4 ,the force of this will be apparent by considering that the water consumption of the engine ordinarily is from #ae to #be lbs4 of feed water per horse power per hour1 and the amount of circulating water required to maintain the vacuum is about #be to #cj times the feed water1 and in the case of turbines with their #bh or #bi inch vacuum1 much more4 ,for instance1 a #a1jjj horse power plant running on #ae lbs4 of feed water and #cj to #a circulating water would require 7#a1jjj #ae7 7#cj #a7 #dfe1jjj lbs4 or #ee1hbb gals4 per hour at full capacity4 ,ques4 ,besides price what other considerations are important with respect to water8 ,ans4 ,its quality and the possibility of a scarcity of supply4 ,it is quite necessary that the water used in the boilers should be as free as possible from impurities1 so as to prevent the deposition within them of any scale or sediments4 ,the quality of the water used for condensing purposes1 however1 is not quite so important1 although the purer it is the better4 ,if the plant is to be located in a city1 the matter of water supply need not generally be considered1 because1 as a rule1 it can be obtained from the waterworks2 there will then1 of course1 be a water tax to consider and this1 if large1 may warrant an effort being made to obtain the water in some other way4 ,in any event1 however1 the possibility of a scarcity in the supply should be reduced to a minimum4 ,if the plant be located in the country1 some natural source of water would be utilized unless the place be supplied with waterworks1 which is not generally the case4 ,it is usual1 however1 to find a stream1 lake or pond in the vicinity1 but if none such be conveniently near1 an artesian or other form of well must be sunk4 ,if abundance of water exist in the vicinity of the proposed installation1 not only would the location of the plant be governed thereby1 but the kind of power to be used for its operation would depend thereon4 ,thus1 if the quantity of the water were sufficient throughout the entire year to supply the necessary power1 water wheels might be installed and used in place of boilers and steam engines for driving the generators4 ,the station would then1 of course1 be situated close to the waterfall1 regardless of the center of gravity of the system4 ,illustration3 ,,fig4 #b1gab4--,view illustrating the location of a station as governed by the presence of a water falls4 ,in such cases the natural water power may be at a considerable distance from the center of gravity of the distribution system because of the saving in generation4 ,in the case of long distance transmission very high pressure may be used and a transformer step down sub-station be located at or near the center of gravity of the system1 thus considerably reducing the cost of copper for the transmission line4 ,ques4 ,what should be noted with respect to the coal supply8 ,ans4 ,the facility for transporting the coal from the supply point to the boiler room4 ,in this connection1 an admirable location1 other conditions permitting1 is adjacent to a railway line or water front so that coal delivered by car or boat may be unloaded directly into the bins supplying the boilers4 ,if the coal be brought by train1 a side or branch track will usually be found convenient1 and this will usually render any carting of the fuel entirely unnecessary4 ,in whatever way the coal is to be supplied1 the liability of a shortage due to traffic or navigation being closed at any time of the year should be well looked into1 as should also the facility for the removal of ashes1 before deciding upon the final location for the plant4 ,illustration3 ,,fig4 #b1gac4--,view of a station admirably located with respect to transportation of the coal supply4 ,as shown1 the coal may be obtained either by boat or rail1 and with modern machinery for conveying the coal to the interior of the station1 the transportation cost is reduced to a minimum4 ,illustration3 ,,fig4 #b1gad4--;,floor plan of part of the turbine central station erected by the ,boston ,edison ,co41 showing two #e1jjj kw4 ,curtis steam turbines in place4 ,the complete installation contains twelve #e1jjj kw4 ,curtis steam turbines1 a sectional elevation being shown in fig4 #b1geh1 page #a1iga4 ,choice of ,system4--,the chief considerations in the design of a central station are economy and capacity4 ,when the current has to be transmitted long distances for either lighting or power purposes1 economy is attainable only by reducing the weight of the copper conductors4 ,this can be accomplished only by the use of the high voltage currents obtainable from alternators4 ,again1 where the consumers are located within a radius of two miles from the central station1 thereby requiring a transmission voltage of #eej volts or less1 dynamos may be employed with greater economy4 ,alternating current possesses serious disadvantages for certain important applications4 ,for instance1 in operating electric railways and for lighting it is often necessary to transmit direct current at #ejj volts a distance of five or ten miles4 ,in such cases1 the excessive drop cannot be economically reduced by increasing the sizes of the line wire1 while a sufficient increase of the voltage would cause serious variations under changes of load4 ,hence1 it is common practice to employ some form of auxiliary generator or booster1 which when connected in series with the feeder1 automatically maintains the required pressure in the most remote districts so long as the main generators continue to furnish the normal or working voltage4 ,the advantage of a direct current installation in such cases over a similar plant supplying alternating current line is the fact that a storage battery may be used in connection with the former for taking up the fluctuations of the current1 thereby permitting the dynamo to run with a less variable load1 and consequently at higher efficiency4 ,ques4 ,name some services requiring direct current4 ,ans4 ,direct current is required for certain kinds of electrolytic work1 such as electro-plating1 the electrical separation of metals1 etc41 also the charging of storage batteries for electric automobiles4 ,illustration3 ,,fig4 #b1gae4--;,example of central station located remote from the distributing center and furnishing alternating current at high pressure to a sub-station where the current is passed through step down transformers and supplied at moderate pressure to the distribution system4 ,in some cases the sub-station contains also converters supplying direct current for battery charging1 electro-plating1 etc4 ,ques4 ,how is direct current supplied8 ,ans4 ,sometimes the central station is equipped with suitable apparatus for supplying both direct and alternating current4 ,this may be accomplished in several different ways3 ,by installing both direct and alternating current generators in the central station2 by the use of double current generators or dynamotors1 from which direct current may be taken from one side and alternating current from the other side2 or by installing1 in the sub-station of an alternating current central station1 in addition to the transformers usually placed therein1 a rotary converter for changing or converting alternating current into direct current4 ,thus1 it is evident that the character of a central station will be governed to a great extent by the class of services to be supplied4 ,an exception to this is where the entire output has to be transmitted a long distance to the point of utilization4 ,in such cases a copper economy demands the use of high tension alternating current1 and its distribution to consumers may be made directly by means of step down transformers mounted near by or within the consumers' premises1 or it may be transformed into low voltage alternating current by a conveniently located sub-station4 ,where the current is to be used chiefly for lighting and there are only a few or no motors to be supplied1 the choice between direct current and alternating current will depend greatly upon the size of the installation1 direct current being preferable for small installations and alternating current for large installations4 ,if the current is to be used primarily for operating machinery1 such as elevators1 travelling cranes1 machine tools and other devices of a similar character1 which have to be operated intermittently and at varying speeds and loads1 direct current is the more suitable2 but if the motors performing such work can be operated continuously for many hours at a time under practically constant loads1 as1 for instance in the general work of a pumping station1 alternating current may be employed with advantage4 ,illustration3 ,,fig4 #b1gaf4--;,diagram illustrating diversity factor4 ,by definition diversity factor combined actual maximum demand of a group of customers divided by the sum of their individual maximum demands4 ,example1 a customer has fifty 7#ej7 watt lamps and1 of course1 the sum of the individual maximum demands of the lamps is #b4e kw4 watts 7connected load74 ,the customer's maximum demand1 however1 is #a4e kw4 ,hence1 the diversity factor,a of the customer's group of lamps is #a4e #b4e 4#f4 ,in the diagram the ordinates of the curves show the ratio maximum demand to connected load for various kinds of electric lighting service in ,chicago4 ,a ,,note4--,the diversity factor of a customer's group of lamps1 namely1 the ratio of maximum demand to connected load is usually called the demand factor of the customer4 ,size of ,plant4--,before any definite calculation can be made1 or plans drawn1 the engineer must determine the probable load4 ,this is usually ascertained in terms of the number and distances of lamps that will be required1 by making a thorough canvass of the city or town1 or that portion for which electrical energy is to be supplied4 ,the probable load that the station is to carry when it begins operation1 the nature of this load1 and the probable rate of increase are matters upon which the design and construction chiefly depend4 ,illustration3 ,,fig4 #b1gag4--,load curve for one day4 ,ques4 ,what is the nature of the load carried by a central station8 ,ans4 ,it fluctuates with the time of day and also with the time of year4 ,ques4 ,how is a fluctuating load best represented8 ,ans4 ,graphically1 that is to say by means of a curve plotted on coordinate paper of which ordinates represent load values and the corresponding absciss time values1 as in the accompanying curves4 ,what is the nature of a power load8 ,ans4 ,where electricity is supplied for power purposes to a number of factories1 the load is fairly steady1 dropping1 of course1 during meal hours4 ,in the case of traction1 the average value of the load is fairly steady but there are momentarily violent fluctuations due to starting cars or trains4 ,illustration3 ,,fig4 #b1gah4--,load curve for one year4 ,ques4 ,what is the peak load8 ,ans4 ,the maximum load which has to be carried by the station at any time of day or night as shown by the highest point of the load curve4 ,ques4 ,define the load factor4 ,ans4 ,the machinery of the station evidently must be large enough to carry the peak load1 and therefore considerably in excess of that required for the average demand4 ,the ratio of the average to the maximum load is called the load factor4 ,there are two kinds of load factor3 the annual1 and the daily4 ,the annual load factor is obtained as a percentage by multiplying the number of units sold 7per year7 by #ajj1 and dividing by the product of the maximum load and the number of hours in the year4 ,the daily load factor is obtained by taking the figures for #bd hours instead of a year4 ,illustration3 ,,fig4 #b1gai4--,load curve of plant supplying power for the operation of motors in a manufacturing district4 ,the horizontal dotted lines show suitable power ratings4 ,a properly designed steam plant has a large overload capacity1 a hydraulic plant has a small overload capacity1 and a gasoline engine plant has no overload capacity4 ,accordingly1 the peak of the load 7maximum load7 may be #be or #cj per cent4 in excess of the rated capacity of a steam plant1 not more than #e or #aj per cent4 in excess of the rated capacity of a hydraulic plant1 not at all in excess of the rated capacity of a gas engine plant4 ,ques4 ,what must be provided in addition to the machinery required to supply the peak load8 ,ans4 ,additional units must be installed for use in case of repairs or break down of some of the other units4 ,,example4--,what would be the boiler horse power required to generate #e1jjj kw4 under the following conditions3 ,efficiency of generators #he2 efficiency of engines #ij2 feed water of engines and auxiliaries #ae lbs4 per ,i4 ,h4 ,p42 boiler pressure #age lbs42 temperature of feed water #aej ,fahr8 ,with a rate of combustion of #ae lbs4 of coal per sq4 foot of grate per hour and an evaporation 7from and at #bab7 of #h lbs4 of water per lb4 of coal1 what area of grate would be required and how much heating surface8 #e1jjj kw4 #e1jjj 4#gdf #f1gjb electrical horse power ,to obtain this electrical horse power with alternators whose efficiency is #he requires #f1gjb 4#he #g1hhe brake horse power at the engine ,this1 with mechanical efficiency of #ij is equivalent to #g1hhe 4#i #h1gfa indicated horse power ,since #ae lbs4 of feed water are required for the engines and auxiliaries per indicated horse power per hour1 the total feed water or evaporation required to generate #e1jjj kw4 is #ae #h1gfa #aca1dae lbs4 per hour4 that is to say1 the boilers must be of sufficient capacity to generate #aca1dae lbs4 of steam per hour from water at a temperature of #aej ,fahr4 ,this must be multiplied by the factor of evaporation for steam at #age lbs4 pressure from feed water at a temperature of #aej1 in order to get the equivalent evaporation from and at #bab4 ,the formula for the factor of evaporation is ,h - h factor of evaporation ------- 7#a7 #ife4g in which ,h total heat of steam at the observed pressure2 h total heat of feed water of the observed temperature2 #ife4g latent heat1 of steam at atmospheric pressure4 ,substituting in 7#a7 values for the observed pressure and temperature as obtained from the steam table #a1aig - #aah factor of evaporation ------------ #a4aag #ife4g for which the equivalent evaporation from and at #bab is #aca1dae #a4aag #adf1gia lbs4 per hour ,,factors ,,of ,,evaporation ---------------------------------------- -------------------------- ,temp of ,,steam ,,pressure ,,by ,,gauge feed water4 ---------------------------------------- ----- ,deg4 ,fahr4 #ej #fj #gj #hj #ij #ajj #aaj #abj #acj ---------------------------------------- ------------------ #cb #a4bada4bafa4bbja4bbba4bbea4bbga4bbia4bc aa4bcb #dj #a4bjfa4bjia4baba4bada4bafa4baia4bbja4bb ba4bbd #ej #a4aiea4aiga4bjaa4bjda4bjfa4bjha4baja4ba ba4bad #fj #a4ahea4ahha4aiaa4aica4aifa4aiha4bjja4bj ba4bjc #gj #a4agea4agha4ahja4ahca4ahea4ahga4ahia4ai aa4aic #hj #a4afda4afga4agja4agca4agea4agga4agia4ah aa4ahc #ij #a4aeda4aega4afja4afba4afea4afga4afia4ag ja4agb #ajj #a4adda4adga4aeja4aeba4aeda4aefa4aeha4af ja4afb #aaj #a4acca4acfa4acia4adba4adda4adfa4adha4ae ja4aeb #abj #a4abca4abfa4abia4acaa4acca4acfa4acha4ad ja4ada #acj #a4aaca4aafa4aaha4abaa4abca4abea4abga4ab ia4acj #adj #a4ajba4ajea4ajha4aaja4aaca4aaea4aaga4aa ia4abj #aej #a4jiaa4jiea4jiha4ajja4ajba4ajda4ajfa4aj ha4aaj #afj #a4jhaa4jhda4jhga4jija4jiba4jida4jifa4ji ha4ajj #agj #a4jgja4jgda4jgga4jgia4jhaa4jhca4jhea4jh ga4jhi #ahj #a4jfja4jfca4jffa4jfia4jgaa4jgca4jgea4jg ga4jgi #aij #a4jeja4jeca4jefa4jeha4jfja4jfca4jfea4jf fa4jfh #bjj #a4jcia4jdca4jdea4jdha4jeja4jeba4jeda4je fa4jeh #baj #a4jbia4jcba4jcea4jcga4jdja4jdba4jdda4jd fa4jdg ---------------------------------------- ------------------ ,temp of ,,steam ,,pressure ,,by ,,gauge feed water4 ---------------------------------------- ----- ,deg4 ,fahr4 #adj #aej #afj #agj #ahj #aij #bjj #baj #bbj ---------------------------------------- ------------------ #cb #a4bcda4bcfa4bcga4bcia4bdja4bdaa4bdca4bd da4bde #dj #a4bbfa4bbga4bbia4bcja4bcba4bcca4bcda4bc fa4bcg #ej #a4baea4baga4baha4bbja4bbaa4bbca4bbda4bb ea4bbf #fj #a4bjea4bjga4bjha4baja4baaa4baba4bada4ba ea4baf #gj #a4aida4aifa4aiga4aiia4bjja4bjba4bjca4bj ea4bjf #hj #a4ahda4ahfa4ahga4ahia4aija4aiba4aica4ai da4aie #ij #a4agda4agfa4agga4agia4ahja4ahaa4ahca4ah da4ahe #ajj #a4afda4afea4afga4afha4agja4agaa4agba4ag da4age #aaj #a4aeca4aeea4aefa4aeha4aeia4afja4afba4af ca4afd #abj #a4adca4adea4adfa4adga4adia4aeja4aeaa4ae ca4aed #acj #a4acba4acda4acfa4acga4acha4adja4adaa4ad ba4add #adj #a4abba4abda4abea4abga4abha4abia4acaa4ac ba4acc #aej #a4aaaa4aaca4aaea4aafa4aaha4aaia4abja4ab aa4abc #afj #a4ajaa4ajca4ajda4ajfa4ajga4ajha4aaja4aa aa4aab #agj #a4jiaa4jiba4jida4jiea4jiga4jiha4jiia4aj aa4ajb #ahj #a4jhja4jhba4jhca4jhea4jhfa4jhha4jhia4ji ja4jia #aij #a4jgja4jgaa4jgca4jgda4jgfa4jgga4jgha4jh ja4jha #bjj #a4jeia4jfaa4jfca4jfda4jfea4jfga4jfha4jf ia4jga #baj #a4jdia4jeaa4jeba4jeca4jeea4jefa4jega4je ia4jfj ---------------------------------------- ------------------ ,temp4 of ,,steam ,,pressure ,,by ,,gauge feed water4 ---------------------------------------- ----- ,deg4 ,fahr4 #bcj #bdj #bej #bfj #bgj #bhj #bij #cjj ---------------------------------------- ------------------ #cb #a4bdfa4bdga4bdha4beja4beaa4beba4beca4be d #dj #a4bcha4bcia4bdja4bdaa4bdba4bdca4bdda4bd e #ej #a4bbha4bbia4bcja4bcaa4bcba4bcca4bcda4bc e #fj #a4baga4baha4baia4bbja4bbaa4bbba4bbca4bb d #gj #a4bjga4bjha4bjia4baja4baaa4baba4baca4ba d #hj #a4aifa4aiha4aiia4bjja4bjaa4bjba4bjca4bj d #ij #a4ahfa4ahga4ahha4ahia4aija4aiaa4aiba4ai c #ajj #a4agfa4agga4agha4agia4ahja4ahaa4ahba4ah c #aaj #a4affa4afga4afha4afia4agja4agaa4agba4ag c #abj #a4aeea4aefa4aega4aeha4aeia4afja4afaa4af b #acj #a4adea4adfa4adga4adha4adia4aeja4aeaa4ae b #adj #a4acda4acea4acfa4acga4acha4acia4adja4ad a #aej #a4abda4abea4abfa4abga4abha4abia4acja4ac a #afj #a4aaca4aaea4aafa4aaga4aaha4aaia4abja4ab a #agj #a4ajca4ajda4ajea4ajfa4ajga4ajha4ajia4aa j #ahj #a4jica4jida4jiea4jifa4jiga4jiha4jiia4aj j #aij #a4jhba4jhca4jhda4jhea4jhfa4jhga4jhha4jh i #bjj #a4jgba4jgca4jgda4jgea4jgfa4jgga4jgha4jg i #baj #a4jfaa4jfba4jfca4jfda4jfea4jffa4jfga4jf h ---------------------------------------- ------------- ,one boiler horse power being equal to an evaporation of #cd lbs4 of water from a feed water temperature of #bab ,fahr41 into steam at the same temperature1 the boiler capacity is accordingly #adh1aje #cd4e #d1bic boiler horse power4 ,the rate of evaporation is given at #h lbs4 of water 7from and at #bab ,fahr471 for which the fuel required is #adh1aje #h #ah1eac lbs4 of coal per hour4 ,for a rate of combustion of #ae lbs4 of coal per hour per square foot of grate1 grate area #ah1eac #ae #a1bcd sq4 ft4 ,for stationary boilers the usual ratio of heating surface to grate area is #ce3a1 accordingly the heating surface corresponding to this ratio is #a1bcd #ce #dc1aij sq4ft4 ,the above calculation is based on a rate of evaporation of #h lbs4 of water per lb4 of coal and a rate of combustion of #ae lbs4 of coal per sq4 ft4 of grate4 ,for other rates the required grate area may be obtained from the following table3 ---------------------------------------- ------------------------------ ,,grate ,,surface ,,per ,,horse ,,power 7,,kent7 ---------------------------------------- --------------------------- ,pounds of ,lbs4 ,pounds of coal burned per square foot of water of grate per hour from coal------------------------------------ and at per #bab h4p4 #h #aj #ab #ae #bj #be #cj #ce #dj per per pound hour------------------------------------ of ,square feet grate per horse power coal ---------------------------------------- ------------------- ,good coal #aj #c4de 4#dc4ce 4#bh 4#bc 4#ag 4#ad 4#aa 4#aj 4#ji and boiler #i #c4hc 4#dh 4#ch 4#cb 4#be 4#ai 4#ae 4#ac 4#aa 4#aj ,fair coal #h4fa #d4 4#ej 4#dj 4#cc 4#bf 4#bj 4#af 4#ac 4#ab 4#aj or boiler #h #d4ca 4#ed 4#dc 4#cf 4#bi 4#bb 4#ag 4#ad 4#ac 4#aa #g #d4ic 4#fb 4#di 4#da 4#cc 4#bd 4#bj 4#ag 4#ad 4#ab ,poor coal #f4i #e4 4#fc 4#ej 4#db 4#cd 4#be 4#bj 4#ag 4#ae 4#ac or boiler #f #e4ge 4#gb 4#eh 4#dh 4#ch 4#bi 4#bc 4#ai 4#ag 4#ad #e #f4i 4#hf 4#fi 4#eh 4#df 4#ce 4#bh 4#bc 4#bb 4#ag ,lignite and#c4de #aj4 #a4bea4jj 4#hc 4#fg 4#ej 4#dj 4#cc 4#bi 4#be poor boiler ---------------------------------------- ------------------- ,general ,arrangement of ,station4--,in designing an electrical station1 it is preferable that whatever rooms or divisions of the interior space are desired should determine the total outside dimensions of the plant in the original plans of the building than that these latter dimensions be fixed and the rooms1 etc41 be fitted in afterward4 ,,saving ,,due ,,to ,,heating ,,the ,,feed ,,water ,table showing the percentage of saving for each degree of increase in temperature of feed water heated by waste steam4 ---------------------------------------- ------------------------------ ,init ,pressure of steam in boiler1 lbs4 per sq4 inch above atmosphere temp------------------------------------ ----------------------------- of feed #j #bj #dj #fj #hj #ajj #abj #adj #afj #ahj #bjj ---------------------------------------- ------------------- #cb4jhgb4jhfa4jhee4jhea4jhdg4jhdd4jhda4j hci4jhcg4jhce4jhcc #dj 4#jhgh4jhfg4jhfa4jhef4jhec4jhej4jhdg4jhd e4jhdc4jhda4jhci #ej 4#jhhf4jhge4jhfh4jhfd4jhfj4jheg4jhed4jhe b4jhej4jhdh4jhdf #fj 4#jhid4jhhc4jhgf4jhgb4jhfg4jhfd4jhfb4jhe i4jhef4jhee4jhec #gj 4#jijb4jhij4jhhd4jhgi4jhge4jhgb4jhfi4jhf g4jhfd4jhfb4jhfj #hj 4#jiaj4jhih4jhia4jhhg4jhhc4jhgi4jhgg4jhg d4jhgb4jhgj4jhfh #ij 4#jiai4jijg4jijj4jhie4jhhh4jhhg4jhhd4jhh c4jhgi4jhgg4jhge #ajj 4#jibg4jiae4jijh4jijc4jhii4jhie4jhib4jhi j4jhhg4jhhe4jhhc #aaj 4#jicf4jibc4jiaf4jiaa4jijg4jijc4jijj4jhi h4jhie4jhic4jhia #abj 4#jide4jicb4jibe4jiai4jiae4jiaa4jijh4jij f4jijc4jija4jhii #acj 4#jied4jida4jicd4jibh4jibd4jibj4jiag4jia d4jiab4jiji4jijg #adj 4#jifc4jiej4jidc4jicg4jicb4jibi4jibe4jib c4jibj4jiah4jiaf #aej 4#jigc4jiei4jiea4jidf4jida4jicg4jicd4jic a4jibi4jibf4jibd #afj 4#jihb4jifh4jifa4jiee4jiej4jidf4jidc4jid j4jicg4jice4jicc #agj 4#jiib4jigh4jigj4jifd4jiei4jiee4jieb4jid i4jidf4jidd4jida #ahj 4#ajjb4jihh4jiha4jigc4jifi4jife4jifa4jie h4jiee4jiec4jiea #aij 4#ajab4jiih4jihi4jihc4jigh4jigd4jiga4jif h4jifd4jjfb4jifj #bjj 4#ajbb4ajjh4jiii4jiic4jihh4jihd4jihj4jig g4jigd4jigb4jifi #baj 4#ajcc4ajah4ajaj4ajjc4jiih4jiid4jiij4jih g4jihd4jiha4jigi #bbj -- 4#ajbi4ajai4ajac4ajjh4ajjd4ajjj4jiig4jii d4jiia4jihi #bcj -- 4#ajci4ajca4ajbd4ajah4ajab4ajaj4ajjg4ajj c4ajja4jiii #bdj -- 4#ajej4ajda4ajcd4ajbi4ajbd4ajbj4ajag4aja d4ajaa4ajji #bej -- 4#ajfb4ajeb4ajde4ajdj4ajce4ajca4ajbg4ajb e4ajbb4ajai ---------------------------------------- ------------------- ,,note4--,an approximate rule for the conditions of ordinary practice is a saving of #a per cent4 made by each increase of #aa in the temperature of the feed water4 ,this corresponds to 4#jiji per cent4 per degree4 ,the calculation of saving is made as follows3 ,boiler pressure1 #ajj lbs4 gauge2 total heat in steam above #cb #a1ahe ,b4,t4,u4 feed water1 original temperature #fj1 final temperature #bji;,f4 ,increase in heat units1 #aej4 ,heat units above #cb in feed water of original temperature #bh4 ,heat units in steam above that in cold feed water1 #a1ahe-bh #a1aeg4 ,saving by the feed water heater #aej #a1aeg #ab4if per cent4 ,the same result is obtained by the use of the table4 ,increase in temperature #aej tabular figure 4#jhfd #ab4if per cent4 ,let total heat of #a lb4 of steam at the boiler pressure ,h2 total heat of #a lb4 of feed water before entering the heater h'1 and after passing through the heater h''2 then the saving made by the heater is 7h''-h'7 7,h-h'74 ,under usual conditions the plans of an electrical station are readily drawn1 as they are generally of a simple nature4 ,the engines and generators will occupy the majority of the space1 and these are usually placed in one large room2 in some stations1 however1 they are located respectively in two adjacent rooms4 ,the boilers are generally located in a room apart from the engines and dynamos1 and in some cases a separate building is provided for them2 the pumps1 etc41 must be installed not far from the boilers1 and space must also be allowed near the boilers for coal and ashes4 ,illustration3 ,,fig4 #b1gbj4--;,floor plan of an electrical station having a belted drive with counter shaft4 ,fig4 #b1gbj shows the floor plan of an electrical station1 in which a countershaft and belted connections are used between the engines and generators4 ,referring first to the plan of the building itself1 ,a represents the engine and dynamo room1 ,b denotes the boiler room1 ,c the office1 ,d the store room1 and ,e the chimney connected with the boilers by means of the uptake w4 ,referring next to the apparatus installed1 ,s1 ,s1 ,s1 ,s represents a battery of four boilers2 these are connected by steam piping ,,vv to the two steam engines1 ,m and ,m1 which are belted to the countershaft ,o4 ,belted to the countershaft are the generators1 ,t1 ,t1 ,t1 ,t1 the circuits from which are controlled on the switchboard1 ,h4 ,ques4 ,what are the objections to the arrangement shown in fig4 #b1gbj48 ,ans4 ,the large space required by the belt drive especially in locations where land is expensive4 ,another objection is the frictional loss due to the belt drive with its countershaft1 etc4 ,illustration3 ,,fig4 #b1gba4--;,elevation of station having a belted drive with countershaft1 as shown in plan in fig4 #b1gbj4 ,ques4 ,what are the desirable features of the belt drive8 ,ans4 ,high speed generators may be used1 thus reducing the first cost1 and the multiplicity of speeds and flexibility of the system resulting from the use of a friction clutch4 ,thus in fig4 #b1gbj1 each pulley may be mounted on the counter shaft ,o with a friction clutch4 ,a jaw clutch may also be provided at ,z1 thus permitting the shaft ,o to be divided into two sections4 ,it is therefore possible by this arrangement to cause either of the engines to drive any one of the generators1 or all of them1 or both of the engines to drive all of the generators simultaneously4 ,ques4 ,under what condition is the counter shaft belt drive particularly valuable8 ,ans4 ,in case of a break down of any one of the engines or generators1 and also when it becomes necessary to clean them without interrupting the service4 ,illustration3 ,,fig4 #b1gbb4--,plan of station arranged for extension4 ,the space required for a central station depends upon the number and kind of lights to be supplied1 and upon the character and arrangement of the machinery4 ,in calculating the size of building required1 two things must be carefully considered3 first1 the building must be adapted to the plant to be installed in the beginning2 and second1 it must be arranged so that enlargement can be made without disarranging or interfering with the plant already in existence4 ,this is usually best secured by providing for expansion in one or two definite directions1 the building being made large enough to accommodate additional units that will be necessary at some future time because of the growth of the community and consequent increased demand for electric current4 ,ques4 ,how may the design in fig4 #b1gbj be modified for the installation of a storage battery8 ,ans4 ,if a storage battery be necessary1 a partition may be constructed across the room ,a1 as indicated by the dotted lines1 and the battery installed in the room thus formed4 ,illustration3 ,,fig4 #b1gbc4--;,interior of old ,riverside station showing at the right1 seven #f1jjj horse power alternators driven by reciprocating engines1 and at the left1 a number of turbine units aggregating #ij1jjj horse power4 ,ques4 ,mention a few details in the general arrangement of the building fig4 #b1gbj4 ,ans4 ,two doors to the room ,a may conveniently be provided at ,k and ,l1 the former connecting with the boiler room ,b1 and the latter serving as the main entrance to the station4 ,there is little that need be added to what has already been stated regarding the boiler room ,b4 ,the door at ,f provides for the entrance of coal and the removal of ashes1 while at ,p1 the pump and heaters may conveniently be located4 ,in the office ,c1 visitors may be received1 the station reports made out1 bulletins issued from time to time1 and whatever engineering problems arise may here be solved on paper by the engineer in charge of the plant4 ,the store room ,d will be found convenient for various supplies1 tools and appliances needed in the operation of the station4 ,these may here be kept under lock and key and the daily waste and loss resulting from carelessness avoided4 ,ques4 ,what important point should be noted in locating the engines and boilers8 ,ans4 ,they should be so placed that the piping between them will be as short and direct as possible4 ,ques4 ,why8 ,ans4 ,the steam pipe should be short to reduce the loss of heat between engine and boiler to a minimum1 and both short and direct to avoid undue friction and consequent drop in pressure of the steam in passing through the pipe to the engine4 ,entirely too little attention is given to this matter on the part of designers and it cannot be too strongly emphasized that1 for economy1 the steam pipe between an engine and boiler should be as short and direct as possible1 having regard of course1 for proper piping methods4 ,ques4 ,what should be provided for the steam pipe8 ,ans4 ,a heavy covering of approved material should be placed around the pipe to reduce the loss of heat by radiation4 ,for this purpose hair felt1 mineral wool and asbestos are used4 ,illustration3 ,,fig4 #b1gbd4--,view of engine and condenser1 showing how to arrange the piping to secure good vacuum4 ,locate the condenser as near the engine as possible2 use easy bends instead of elbows2 place the pump below bottom of condenser so the water will drain to pump4 ,at ,a is a relief valve1 for protection in case the condenser become flooded through failure of the pump1 and at ,b is a gate valve to shut off condenser in case atmospheric exhaust is desired to permit repairs to be made to condenser during operation4 ,a water seal should be maintained on the relief valve and special attention should be given to the stuffing box of the gate valve to prevent air leakage4 ,the discharge valve of the pump should be water sealed4 ,ques4 ,how should the piping be arranged between the engine and condenser1 and why8 ,ans4 ,it should be as short and direct as possible2 especially should elbows be avoided so that the back pressure on the engine piston will be reduced as near as can be to that of the condenser4 ,that is to say1 in order to get nearly the full effect of the vacuum in the condenser the frictional resistance of the piping should be reduced to a minimum4 ,where #ij turns are necessary1 easy bends should be used instead of sharp elbows4 ,the force of this argument must be apparent by noting the practice of steam turbine builders of placing the turbine right up against the condenser1 and remembering that a high vacuum is necessary to the economical working of a turbine4 ,see fig4 #a1dde1 page #a1ahb4 ,ques4 ,what are the considerations respecting the number and type of engine to be used8 ,ans4 ,in the illustration fig4 #b1gbj1 two engines ,m and ,m' are employed1 one belted to each end of the countershaft ,o4 ,these engines should be of similar or identical pattern2 for a small output they may be either simple or compound1 as the conditions of fuel expenditure may dictate1 but if the output be large1 triple expansion engines or turbines are advisable4 ,illustration3 ,,fig4 #b1gbe4--;,dry pipe for horizontal boiler3 it is connected to the main outlet and its upper surface is perforated with small holes1 the far end being closed4 ,with this arrangement steam is taken from the boiler over a large area1 so that it will contain very little moisture4 ,all horizontal boilers without a dome should be fitted with a dry pipe2 most engineers do not realize the importance of obtaining dry steam for engine operation4 ,corliss or similar slow speed engines may advantageously be used in either case4 ,in all cases the engine should be run condensing unless the cost for circulating water is prohibitive2 even in such cases cooling towers may be installed and effect a saving4 ,in operation1 during the greater part of the day1 one engine running two or perhaps three of the generators1 will carry the load1 but when the load is particularly heavy1 as in the morning and evening1 both engines and all the generators may be required to meet the demands4 ,illustration3 ,,fig4 #b1gbf4--,method of connecting a header to a battery of boilers4 ,where two or more boilers are connected to a single header1 the use of a reliable non-return boiler stop valve is necessary1 and in some countries their installation is compulsory4 ,a non-return boiler stop valve will instantly close should the pressure in the boiler to which it is attached suddenly decrease below that in the header1 and thereby prevent the entrance of steam from the other boilers of the battery4 ,this sudden decrease in pressure may be caused by a ruptured fitting or the blowing out of a tube1 in which event an ordinary stop valve taking the place of a non-return boiler stop valve would be inadequate1 as the loss of steam from the other boilers of the battery would be tremendous before an ordinary valve could be reached and closed1 assuming that it would be possible to do so1 which in the majority of cases it is not4 ,should it be desired to cut out a boiler for cleaning or repairs1 the non-return boiler stop valve will not permit steam to enter the boiler from the header1 even should the handwheel be operated for this purpose1 as it cannot be opened by hand1 but can1 however1 be closed4 ,a non-return boiler stop valve should be attached to each boiler and connected to an angle valve on the header4 ,a pipe bend should be used for connecting the valves1 as this will allow for expansion and contraction4 ,the pipe should slope a trifle downward toward the header and a suitable drain provided4 ,this drain should be opened and all water permitted to escape before the angle valve is opened1 thereby preventing any damage due to water hammer4 ,by exercising a little ingenuity in shifting the load on different machines at different times1 both engines and dynamos1 may readily be cleaned and repaired without interrupting the service4 ,ques4 ,for economy what kind of steam should be used8 ,ans4 ,super-heated steam4 ,the saving due to the use of superheated steam is about #a for every ten degrees ,fahr4 of super-heat4 ,it should be used in all cases4 ,ques4 ,how should the machines be located8 ,ans4 ,sufficient space should be allowed between them that cleaning and repairing may be done easily1 quickly and effectually4 ,illustration3 ,,figs4 #b1gbg and #b1gbh4--,method of preventing vibration and of supporting pipes4 ,the figures show top and side views of a main header carried in suitable frames fitted with adjustable roller4 ,while the pipe is illustrated as resting on the adjustable rollers1 nevertheless the rollers may also be placed at the sides or on top of the pipe to prevent vibration1 or in cases where the thrust from a horizontal or vertical branch has to be provided for4 ,this arrangement will take care of the vibration without in any way preventing the free expansion and contraction of the pipe4 ,ques4 ,how should the switchboard be located8 ,ans4 ,in fig4 #b1gbj1 the switchboard ,h is mounted against the wall dividing the room ,a from the room ,b1 and is in line with the machines4 ,the advantages arising from a switchboard thus installed are1 that the switchboard attendant working thereon can obtain at any time an unobstructed view of the performance of each individual machine1 and he has in consequence a much better control of them2 then1 too1 while he is engaged at the engines or generators he can also see the measuring instruments on the switchboard1 and ascertain approximately the readings upon them4 ,in cases of emergency it is sometimes necessary for the engineer in charge of a plant to be in several places at the same time in order to prevent an accident1 and that this seemingly impossibility may be approximated as nearly as possible1 it is essential that the controlling devices be located as closely together as is consistent1 and that no moving belt or pulley intervene between them4 ,these conditions are well satisfied in fig4 #b1gbj1 and owing to the short distances between the generators and the switchboard the drop of voltage in each of the conducting wires between them will be low4 ,this latter advantage is worthy of notice in a station generating large currents at a low pressure4 ,to offset the advantages just mentioned1 the location of the switchboard in line with the machines introduces an element of danger to the switchboard1 its apparatus1 and the attendant1 on account of the possible bursting of a flywheel or other parts of the machines from centrifugal force4 ,illustration3 ,,figs4 #b1gbi and #b1gcj4--,points on placing stop valves4 ,the first and most important feature is to ascertain whether the valve will act as a water trap for condensed steam4 ,fig4 #b1gbi illustrates a common error in the placing of valves1 as this arrangement permits of an accumulation of condensed steam above the valve when closed1 and should the engineer be careless and open the valve suddenly1 serious results might follow owing to water-hammer4 ,fig4 #b1gcj illustrates the correct method of placing the valve4 ,it sometimes occurs1 however1 that it is not convenient to place the valve as shown in fig4 #b1gcj and that fig4 #b1gbi is the only manner in which the valve can be placed4 ,in such cases1 the valve should have a drain1 and this drain should always be opened before the large valve is opened4 ,if the switchboard be placed in the dotted position at ,h'1 or1 in fact1 at the opposite end of the room ,a1 the damage to life and property that might result from the effects of centrifugal force would be eliminated1 but in place thereof would be the disadvantages of an obstructed view of the machines from the switchboard1 an obstructed view of the switchboard from the machines1 inaccessibility between these two1 and a greater drop of voltage in the majority of the conducting wires between the generators and the switchboard4 ,ques4 ,describe a second arrangement of station with belt drive and compare it with the design shown in fig4 #b1gbj4 ,illustration3 ,,fig4 #b1gca4--,plan of electrical station with belt drive without counter shaft4 ,the installation here represented consists of two boilers1 ,s1 etc41 and three sets of engines and generators1 ,t1 ,m1 etc4 ,sufficient allowance has been made in the plans1 however1 for future increase of business1 as additional space has been provided for an extra engine and generator set1 as indicated by the dotted lines4 ,ans4 ,a floor plan somewhat different from that presented in fig4 #b1gbj is shown in fig4 #b1gca4 ,here a belt drive is employed1 but no countershaft is used4 ,each generator1 therefore1 is dependent upon its respective engine1 and in consequence the flexibility obtained by the use of a countershaft is lost4 ,on the other hand1 there is less loss of mechanical power between the engines and generators in the driving of the latter1 and less floor space is necessary in the room ,a4 ,if1 however1 the floor area of this room be made the same as in the previous arrangement and the same number of machines are to be installed1 they may be spaced further apart1 affording in consequence considerably more room for cleaning and repairing them4 ,in operation1 the normal conditions should be such that any two of the engine and generator sets may readily carry the average load1 the third set to be used only as a reserve either to aid the other two when the load is unusually heavy or to replace one of the other sets when it becomes necessary to clean or repair the latter4 ,the switchboard may perhaps be best located at ,h1 as a similar position on the opposite side of the room ,a would bring it beneath one or more of the steam pipes and thus endanger it should a possible leakage occur from these pipes4 ,if located at ,h1 however1 it will be in line with the machines1 and therefore will be subject to the disadvantages previously mentioned for such cases2 consequently it might be as well to place it at the further end of the room1 either against the partition 7shown dotted7 of the storage battery room if this be built1 or else 7if no storage battery is to be installed71 against the end wall itself4 ,the nearer end of the room ,a would not be very desirable for the switchboard installation on account of being so far removed from the machines1 and therefore more or less inaccessible from them4 ,outside of what has now been mentioned1 the division of the floor plan and the arrangement therein is practically the same as in fig4 #b1gbj1 accordingly what has already been stated regarding the former installation applies1 therefore1 with equal force to the present installation4 ,ques4 ,describe a plant with direct drive4 ,ans4 ,this type of drive is shown in fig4 #b1gcb4 ,each engine is directly connected to a generator1 that is1 the main shafts of both are joined together in line so that the generator is driven without the aid of a belt4 ,ques4 ,what is the advantage of direct drive8 ,ans4 ,the great saving in floor space1 which is plainly shown in fig4 #b1gcb1 the portion ,a' representing the saving which results over the installations previously illustrated in figs4 #b1gbj and #b1gca4 ,ques4 ,how could the floor space be further reduced8 ,ans4 ,by employing vertical instead of horizontal engines4 ,ques4 ,what should be done before drawing the plans for the station8 ,ans4 ,the types of the various machines and apparatus to be installed should1 as nearly as possible1 be selected in advance so that their approximate dimensions may serve as a guide in drawing up the plans of the building4 ,illustration3 ,,fig4 #b1gcb4--,plan of electrical station containing direct connected units4 ,as shown1 space is provided for an extra boiler and engine and generator set1 as indicated by the dotted lines4 ,space also exists for a storage battery room if necessary1 and the partition dividing this room from the engine and dynamo room is shown by a dotted line as in previous cases4 ,owing to the great difference in these dimensions for the various types1 and in fact for the same types as manufactured by different concerns1 no definite rules regarding the necessary space required can here be given4 ,in a general way1 however1 the author has endeavoured to indicate by the drawings the relative amounts of space that ordinarily would be considered sufficient4 ,ques4 ,what is the disadvantage of direct drive8 ,ans4 ,a more expensive generator is required because it must run at the same speed as the engine1 which is relatively low as compared with that of a belted generator4 ,station ,construction4--,the construction or rearrangement of the building intended for the plant is a problem that under ordinary conditions would be solved by an architect1 or at least by an architect with the assistance of an electrical or mechanical engineer1 still there are many installations where the electrical engineer has been compelled to design the building4 ,in such instances he should be equipped with a general knowledge of the construction of buildings4 ,foundations4--,the foundation may be either natural or artificial2 that is1 it may be composed of rock or soil sufficiently solid to serve the purpose unaided1 or it may be such as to require strengthening by means of wood or iron beams1 etc4 ,in either case any tendency toward a considerable settling or shifting of the foundation due to the action of water1 frost1 etc41 after the station has been completed must be well guarded against4 ,to this end special attention should be given to the matter of drainage4 ,ques4 ,how should the foundation be constructed for the machines8 ,ans4 ,the foundations constructed for the machines should be entirely separate from that built for the walls of the building1 so that the vibrations of the former will not affect the latter4 ,if there be several engines and dynamos to be installed1 it is best to construct two foundations1 one for the engines and one for the dynamos4 ,if1 however1 there be considerable distance between the units1 it may be advisable to build a separate foundation for each engine and for each dynamo4 ,the material of which these foundations are composed should if the machines be of #bj horse power or over1 possess considerable strength and be impervious to moisture4 ,brick1 stone and concrete are desirable for the purpose1 and only the best quality of cement mortar should be employed4 ,care must be taken that lime mortar is not used in place of cement mortar1 as the former is not well adapted to withstand the vibrations of the machines without crumbling4 ,illustration3 ,,fig4 #b1gcc4--;,angle for foundation footing4 ,in ordinary practice the footing courses upon which the walls of the building proper rest1 consist of blocks or slabs of stone as large as are available and convenient to handle4 ,footings of brick or concrete are also used in very soft soils2 footings consisting of timber grillage are often employed4 ,a grillage of iron or steel beams has also been used successfully4 ,the inclination of the angle 1 of footing should be about as follows3 for metal footings #ge2 for stone1 #fj2 for concrete1 #de2 for brick1 #cj4 ,damp proof courses of slate1 or layer of asphalt are laid in or on the foundations or lower walls to prevent moisture arising or penetrating by capillary attraction4 ,ques4 ,describe a method of constructing foundations4 ,ans4 ,an excavation is made to the desired depth and a form inserted corresponding to the desired dimensions for the foundation4 ,a template is placed on top locating all the centers1 with iron pipes suspended from these centers1 two or three sizes larger than the anchor bolts4 ,at the lower end of the pipes are core boxes4 ,concrete is poured into the mould thus formed1 and when hard1 the forms are removed thus leaving the solid foundation4 ,the anchor bolts are inserted through the pipes and passed through iron plates at the lower end as shown in fig4 #b1gcd1 being secured by nuts4 ,by using pipe of two or three bolt diameters a margin is provided for adjustment so the bolts will pass through the holes in the frame of the machine thus allowing for any slight errors in laying out the centers on the template4 ,illustration3 ,,fig4 #b1gcd4--;,concrete foundation showing method of installing the anchor bolts4 ,ques4 ,what is the object of the openings in the bottom of the foundation8 ,ans4 ,in case of a defective bolt1 it may be replaced by a new one without injury to the foundation4 ,walls4--,regarding the material for the walls of the station iron1 stone1 brick and wood may be considered4 ,of these1 iron in the form of sheets or plates would be entirely fireproof1 but being itself a conductor would introduce difficulties in maintaining a high insulation resistance of the current carrying circuits2 it would also make the building difficult to heat in winter and to keep cool in summer4 ,stone in the form of limestone1 granite or sandstone1 as a building material is desirable for solidity and attractiveness2 it is also fireproof and an insulator1 but the high cost of such a structure for an electrical station usually prohibits its use except in private plants or in electrical stations located in large cities4 ,illustration3 ,,fig4 #b1gce4--,view showing part of template for locating anchor bolt centers1 pipes through which the bolts pass and bolt boxes at lower end of bolts4 ,the completed foundation is shown in fig4 #b1gcd1 with template removed4 ,the template is made of plain boards upon which the center lines are drawn1 and bolt center located4 ,holes are bored at the bolt centers to permit insertion of the pipes as shown4 ,brick is a good material and is readily obtained in nearly all parts of the country2 it is comparatively cheap1 and is also an insulating and fireproof material4 ,the bricks selected for this purpose should possess true sharp edges1 and be hard burned4 ,ques4 ,what are the features of wood8 ,ans4 ,wood forms the cheapest material that can be used for the walls of electrical stations1 and it usually affords satisfaction1 but has the disadvantage of high fire risk4 ,roofs4--,in fig4 #b1gcf is shown one form of construction for the roof of an electrical station4 ,the end view here presented shows the upper portion of the walls at ,b and ,d2 these support the iron trusses ,c1 and the roof proper ,,mn4 ,in many stations there is provided throughout the length of the building1 a monitor or raised structure on the peak of the roof for ventilation and light4 ,the end view of the monitor is shown at ,s in the figure2 its sides should be fitted with windows adjustable from the floor4 ,illustration3 ,,fig4 #b1gcf4--,one form of roof construction4 ,floors4--,the floor of the station should be so designed that it will be capable of supporting a reasonable weight1 but as the weights of the machines are borne entirely by their respective foundations the normal weight upon the floor will not be great2 for short periods1 however1 it may be called upon to support one or two machines while they are being placed in position or interchanged1 and due allowance must be made for such occurrences4 ,station floors for engine and dynamo rooms are1 as a rule1 constructed of wood4 ,where very high currents are generated1 however1 insulated floors of special construction mounted on glass are necessary as a protection from injurious shocks4 ,brick1 concrete1 cement1 and other substances of a similar nature are objectionable as a floor material for engine and dynamo rooms on account of the grit from them1 caused by constant wear1 being liable to get into the bearings of the machines4 ,where there are no moving parts1 however1 as in the boiler room1 the materials just mentioned possess no disadvantages and are preferable to wood on account of being fireproof4 ,,theoretical ,,draft ,,pressure ,,in ,,inches ,,of ,,water ,,in ,a ,,chimney #ajj ,,feet ,,high 7,for other heights the draft varies directly as the height7 ,temp4 in ,,temp4 ,,of ,,external ,,air4 7,,barometer #cj ,,inches7 ,chimney1 ,f4 #j #aj #bj #cj #dj #ej #fj #gj #hj #ij #ajj #bjj 4#dec 4#dai 4#chd 4#cec 4#cba 4#bib 4#bfc 4#bcd 4#bji 4#ahb 4#aeg #bbj 4#dhh 4#dec 4#dai 4#chh 4#cee 4#cbf 4#bih 4#bfi 4#bdd 4#bag 4#aib #bdj 4#ebj 4#dhh 4#dea 4#dba 4#chh 4#cei 4#ccj 4#cja 4#bgf 4#bej 4#bbe #bfj 4#eee 4#ebh 4#dhd 4#dec 4#dbj 4#cib 4#cfc 4#ccd 4#cji 4#bhb 4#beg #bhj 4#ehd 4#edi 4#eae 4#dhb 4#dea 4#dbb 4#cid 4#cfe 4#cdj 4#cac 4#bhh #cjj 4#faa 4#egf 4#eda 4#eaa 4#dgh 4#ddi 4#dbj 4#cib 4#cfg 4#cdj 4#cae #cbj 4#fcg 4#fjc 4#efh 4#ech 4#eje 4#dgf 4#ddg 4#dai 4#cid 4#cfg 4#cdb #cdj 4#ffb 4#fch 4#eic 4#efc 4#ecj 4#eja 4#dgb 4#ddc 4#dai 4#cib 4#cfg #cfj 4#fhg 4#fec 4#fah 4#ehh 4#eee 4#ebf 4#dig 4#dfh 4#ddd 4#dag 4#cib #chj 4#gaj 4#fgf 4#fda 4#faa 4#egh 4#edi 4#ebj 4#dib 4#dfg 4#ddj 4#dae #djj 4#gcb 4#fig 4#ffb 4#fcb 4#eih 4#egj 4#eda 4#eac 4#dhh 4#dfa 4#dcf #dbj 4#gec 4#gah 4#fhd 4#fec 4#fbj 4#eia 4#efc 4#ecd 4#eji 4#dhb 4#deg #ddj 4#ggd 4#gci 4#gje 4#fgd 4#fda 4#fab 4#ehd 4#eee 4#ecj 4#ejc 4#dgh #dfj 4#gic 4#geh 4#gbd 4#fid 4#ffj 4#fcb 4#fjc 4#egd 4#edi 4#ebb 4#dig #dhj 4#haj 4#ggf 4#gda 4#gaj 4#fgh 4#fdi 4#fbj 4#eia 4#eff 4#edj 4#eae #ejj 4#hbi 4#gia 4#gfj 4#gcj 4#fig 4#ffi 4#fci 4#faj 4#ehf 4#eei 4#ecd ,chimneys4--,these are generally constructed of brick and iron1 sometimes of concrete4 ,iron chimneys cost less than brick chimneys1 necessitate less substantial foundations1 and are free from the liability of cracking4 ,they must be painted to prevent corrosion1 are less substantial1 and lose considerably more heat by radiation than do brick chimneys4 ,illustration3 ,,fig4 #b1gcg4--;,an example of direct connected unit with gas engine power4 ,the view shows a ,westinghouse #bjj kva41 #d1jjj volt1 three phase1 #fj cycle alternator direct connected to a gas engine4 ,illustration3 ,,fig4 #b1gch4--;,curves showing comparative costs of chimney and mechanical draft4 ,in certain of these1 the cost of the existing chimney is known1 and that of the complete mechanical draft plant is estimated1 while in others1 the cost of mechanical draft installation is determined from the contract price1 and the expense of a chimney to produce equivalent results is calculated4 ,costs are shown for both single1 forced and induced engine driven fans and for duplex engine driven plants1 in which either fan may serve as a relay4 ,an apparatus of the latter type is the most expensive1 and finds its greatest use where economizers are employed4 ,both brick and iron chimneys1 require an inner wall or lining of brick1 which forms the flue proper1 and in order that this wall be not cracked by sudden cooling an air space is left between it and the outer wall4 ,in a brick chimney the inner wall need not extend much beyond half the height of the chimney1 but when iron is used it should reach to the top4 ,ques4 ,upon what does the force of natural draught in a chimney depend8 ,ans4 ,it depends upon the difference between the weight of the column of hot gases inside the chimney and the weight of a like column of the cold external air4 ,illustration3 ,,figs4 #b1gci and #b1gdj4--,substituting mechanical draught in place of chimney4 ,the relative proportions of a brick chimney1 and of the smoke pipe required when mechanical draft is introduced are forcibly shown in the illustrations1 which show the works of the ,b4,f4 ,sturtevant ,co41 at ,jamaica ,plain1 ,mass4 ,the removal of the boilers to a position too far distant from the existing chimney to permit of its longer fulfilling its office1 led to the substitution of an induced draft fan and the subsequent removal of the chimney4 ,the present stack or smoke pipe1 barely visible in fig4 #b1gdj1 extends only #ca feet above the ground1 and no trouble is experienced from smoke4 ,ques4 ,how is the intensity of the draught expressed8 ,ans4 ,in terms of the number of inches of a water column sustained by the pressure produced4 ,ques4 ,are high chimneys necessary8 ,ans4 ,no4 ,chimneys above #aej feet in height are very costly1 and their increased cost is not justified by increased efficiency4 ,illustrations3 ,,figs4 #b1gda to #b1gdd4--;,installation of forced draft system to old boiler plant4 ,the figures illustrate the simplest method4 ,the fan which is of steel plate with direct connected double cylinder engine1 is placed immediately over the end of a brick duct into which the air is discharged4 ,this duct is carried under ground across the front of the boilers1 to the ash pits of each of which connection is made through branch ducts4 ,each branch duct opening is provided with special ash pit damper1 operated by notched handle bar1 as illustrated in the detail4 ,this method of introduction serves to distribute the air within the ash pit1 and to secure even flow through the fuel upon the grate above4 ,of course1 the ash pit doors must remain closed in order to bring about this result4 ,a chimney of sufficient height to merely discharge the gases above objectionable level is all that is absolutely necessary with this arrangement4 ,although the introduction of a fan in an old plant is usually evidence of the insufficiency of the existing chimney to meet the requirements1 such a chimney1 will1 however1 usually serve as a discharge pipe for the gases when the fan is employed4 ,the fan thus becomes more than a mere auxiliary to the chimney2 it practically supplants it so far as the method of draught production is concerned4 ,the latest chimney practice is to build two or more small chimneys instead of one large one4 ,a notable example is the ,spreckels ,sugar ,refinery in ,philadelphia1 where three separate chimneys are used for one boiler plant of #g1ejj horse power4 ,the three chimneys are said to have cost several thousand dollars less than an equivalent single chimney4 ,very tall chimneys have been characterized by one writer as monuments to the folly of their builders4 ,illustration3 ,,figs4 #b1gde and #b1gdf4--;,comparison of chimney draft and mechanical draft4 ,the illustrations show a plant of #b1djj ,h4,p4 of modern water tube boilers1 #ab in number1 set in pairs and equipped with economizers4 ,fig4 #b1gde indicates the location of a chimney1 #i feet in internal diameter by #ahj feet high1 designed to furnish the necessary draft2 fig4 #b1gdf represents the same plant with a complete duplex induced draught apparatus substituted for the chimney1 and placed above the economizer connections4 ,each of the two fans is driven by a special engine1 direct connected to the fan shaft1 and each is capable of producing draft for the entire plant4 ,a short steel plate stack unites the two fan outlets and discharges the gases just above the boiler house roof4 ,all of the room necessary for the chimney is saved1 and no valuable space is required for the fans4 ,ques4 ,how is mechanical draft secured8 ,ans4 ,in two ways1 known respectively as induced draught and forced draught4 ,ques4 ,describe the method of induced draft4 ,ans4 ,a fan is located in the smoke flue1 and which in operation draws the gases through the furnace and discharges them into a short chimney4 ,ques4 ,describe the method of forced draft4 ,ans4 ,in this method1 air is forced into the furnace underneath the grate bars by means of a fan or a steam jet blower4 ,illustration3 ,,fig4 #b1gdg4--;,forced draft plant with hollow bridge wall at the ,crystal ,water ,co41 ,buffalo1 ,n4 ,y4 ,the air is delivered to the ash pit via the hollow bridge wall1 being supplied under pressure by the blower seen at the side of the boiler setting4 ,as shown1 the blower is operated by a small reciprocating engine2 however1 compact blowing units with steam turbine drive can be had and which are designed to be placed in the boiler setting4 ,ques4 ,what is the application of the two systems8 ,ans4 ,induced draft is installed mostly in new plants1 while forced draft is better adapted to old plants4 ,steam ,turbines4--,it is not the author's intention to discuss at length the steam end of the electric plant1 because too much space would be required1 and also because the subject belongs properly to the field of mechanical engineering rather than electrical engineering4 ,however1 because of the recent introduction of the steam turbine for the direct driving of large generators1 and the fact that it is now almost universally used in large central stations1 a detailed explanation of its principles and construction may not be out of place4 ,illustration3 ,,fig4 #b1gdh4--,longitudinal section of elementary ,parsons type steam turbine4 ,the turbine consists essentially of a fixed casing1 or cylinder1 and a revolving spindle or drum4 ,the ends of the spindle are extended in the form of a shaft1 carried in two bearings ,a and ,b1 and1 excepting the small parts of the governing mechanism and the oil pump1 these bearings are the only rubbing parts in the entire turbine4 ,steam enters from the steam pipe at ,c and passes through the main throttle or regulating valve ,d1 which1 as actually constructed1 is a balanced valve4 ,this valve is operated by the governor through suitable controlling mechanism4 ,the steam enters the cylinder through the passage ,e and1 turning to the left passes through alternate stationary and revolving rows of blades1 finally emerging from them at ,f and flowing through the connection ,g to the condenser or to the atmosphere1 depending upon whether the turbine is condensing or non-condensing4 ,each row of blades1 both stationary and revolving1 extends completely around the turbine and the steam flows through the full annulus between the spindle and the cylinder4 ,in an ideal turbine the lengths of the blades and the diameter of the spindle which carries them would continuously and gradually increase from the steam inlet to the exhaust4 ,practically1 however1 the desired effect is produced by making the spindle in steps1 there being generally three such steps or stages1 ,h1 ,j and ,k4 ,the blades in each step are arranged in groups of increasing length4 ,at the beginning of each of the larger steps1 the blades are usually shorter than at the end of the preceding smaller step1 the change being made in such a way that the correct relation of blade length to spindle diameter is secured4 ,the steam1 acting as previously described1 produces a thrust tending to force the spindle toward the left1 as seen in the cut4 ,this thrust1 however1 is counteracted by the balance pistons1 ,l1 ,m and ,n1 which are of the necessary diameter to neutralize the thrust on the spindle steps1 ,h1 ,j and ,k1 respectively4 ,these elements are called pistons for convenience1 although they do not come in contact with the cylinder1 but both the pistons and the cylinder are provided with alternate rings which form a labyrinth packing to retard the leakage of steam4 ,in order that each balance piston may have the proper pressure on both sides1 equalizing passages ,o1 ,p and ,q are provided connecting the balance pistons with the corresponding stages of the blading4 ,the end thrust being thus practically neutralized by means of the balance pistons1 the spindle floats so that it can be easily moved in one direction or the other4 ,in order to definitely fix the position of the spindle1 a small adjustable collar bearing is provided at ,r1 inside the housing of the main bearing ,b4 ,this collar bearing is adjustable so as to locate and hold the spindle in such position so that there will be such a clearance between the rings of the balance piston and those of the cylinder1 that the leakage of steam will be reduced to a minimum and1 at the same time1 prevent actual contact under varying conditions of temperature4 ,where the shaft passes out of the cylinder1 at ,s and ,t1 it is necessary to provide against in-leakage of air or out-leakage of steam by means of glands4 ,these glands are made tight by water packing without metallic contact4 ,the shaft of the turbine is extended at ,u and coupled to the shaft of the alternator by means of a flexible coupling4 ,the high pressure turbines are so proportioned that1 when using steam as previously described1 they have enough capacity to take care of the ordinary fluctuations of load when controlled by the governor through the valve ,d1 thus insuring maximum economy of steam consumption at approximately the rated load4 ,to provide for overloads1 the valve ,v is supplied to admit steam to an intermediate stage of the turbine4 ,this valve shown diagrammatically in the illustration1 is arranged to be operated by the governor and is1 according to circumstances1 located either as shown by the illustration1 or at another stage of the turbine4 ,illustration3 ,,fig4 #b1gdi4--;,arrangement of blading in ,parsons type turbine1 consisting of alternate moving and stationary blades4 ,the path taken by the steam is indicated by the arrows4 ,a turbine is a machine in which a rotary motion is obtained by transference of the momentum of a fluid or gas4 ,in general the fluid is guided by fixed blades1 attached to a casing1 and1 impinging on other blades mounted on a drum or shaft1 causing the latter to revolve4 ,turbines are classed in various ways as3 #a1 radial flow1 when the steam enters near the center and escapes toward the circumference2 and #b1 parallel flow1 when the steam travels axially or parallel to the length of the turning body4 ,turbines are commonly1 yet erroneously classed as3 #a4 ,impulse2 #b4 ,reaction4 ,ques4 ,what is the distinction between these two types8 ,ans4 ,in the so called impulse type1 steam enters and leaves the passages between the vanes at the same pressure4 ,in the so called reaction type1 the pressure is less on the exit side of the vanes than on the entrance side4 ,fig4 #b1gej is a sectional view of the ,parsons-,westinghouse parallel flow turbine4 ,steam from the boiler enters first a receiver in which are the governor controlled admission valves4 ,these valves are actuated by a centrifugal governor4 ,illustration3 ,,fig4 #b1gej4--,sectional view of ,parsons-,westinghouse turbine1 showing rotor and governor4 ,steam does not enter the turbine in a continuous blast1 but intermittently1 or in puffs4 ,the speed regulation is therefore accomplished by proportioning the duration of these puffs to the load of the engine1 this being effected by the governor1 fig4 #b1geb4 ,the governor of the turbine has only to move a small pilot valve1 or slide1 ,e1 which admits steam under the piston ,f1 and lifts the throttle valve proper off its seat4 ,as soon as the pilot valve closes1 the spring shifts the main throttle valve4 ,thus1 at light loads1 the main throttle or admission valve is continually opening and shutting at uniform intervals1 the length of time during which it remains open depending upon the load4 ,as the load increases1 the duration of the valve opening also increases1 until at full load the valve does not reach its seat at all and the steam flows steadily through the turbine4 ,the steam thus admitted flows into the annular passage ,a1 fig4 #b1gej1 by the opening ,s1 and then past the blades1 revolving the rotor4 ,when the load increases above the normal rated amount a secondary pilot valve is moved by the same means1 this in turn admitting steam to a piston1 similar to ,f1 which lifts another throttle valve4 ,this admits steam into the annular space ,i1 so that it acts upon the larger diameter of the drum or rotor1 giving largely increased power for the time being4 ,the levers or arms of the governor are mounted upon knife edges instead of pins1 making it extremely sensitive4 ,the tension spring may be adjusted by hand while the turbine is running4 ,illustration3 ,,fig4 #b1gea4--,sectional view of a combination impulse and reaction single flow turbine4 ,this is a modification of the single flow type1 in which the smallest barrel of reaction blading is replaced by an impulse wheel4 ,steam is admitted to the nozzle block ,a1 is expanded in the nozzles and discharged against a portion of the periphery of the impulse wheel4 ,the intermediate and low pressure stages are identical with the corresponding stages in the single flow type4 ,the substitution of the impulse element for the high pressure section of reaction blading has no influence one way or another on the efficiency4 ,that is to say the efficiency of an impulse wheel is about the same at the least efficient section of reaction blading4 ,this design is attractive1 however1 in that it shortens the machine materially1 and gives a stiffer design of rotor4 ,the entering steam is confined in the nozzle chamber until its pressure and temperature have been materially reduced by expanding through the nozzles4 ,as the nozzle chamber is cast separately from the main cylinder1 the temperature and pressure differences to which the cylinder is subjected are correspondingly lessened4 ,however1 probably on account of its small diameter at the high pressure section1 the straight ,parsons type has always shown itself to be adequate for all of the steam pressures and temperatures encountered in ordinary practice4 ,the governor does not actually move the pilot valve1 but shifts the point ,l in fig4 #b1geb4 ,a reciprocating motion is given to the rod ,i by a small eccentric on the governor shaft2 this is driven by worm gearing shown near ,o in fig4 #b1gej1 so that the eccentric makes one revolution to about eight of the turbine4 ,thus1 with a turbine running #a1bjj revolutions1 the rod ,i would be moved up and down #aej times per minute4 ,as the points ,a and ,h are fixed1 the motion is conveyed to the small pilot valve ,e1 thus giving #aej puffs a minute4 ,the governor in shifting the point ,l brings the edge of the pilot valve nearer the port and so cuts off the steam earlier4 ,the annular diameter or space between the rotor and the stator is gradually increased from inlet to exhaust1 the blades being made longer in each ring4 ,when the mechanical limit is reached1 the diameter of the rotor is increased as at ,i and ,d so as to keep the length of blade within bound4 ,balance pistons as at ,b1 ,c1 ,f are attached to the rotor1 their office being to oppose end thrust upon those blades in corresponding diameter of the rotor4 ,communication is established through the passage ,v and pipe ,m between the eduction pipe and the back of these pistons1 thus increasing the efficiency of their balancing and also taking care of any leakage past them4 ,a small thrust bearing ,t prevents end play of the rotor1 and is adjustable to maintain the proper clearance between the rings of blades2 this varies from inch at the admission to #a inch at the exhaust4 ,this bearing also takes up any extra unbalanced thrust4 ,a turbine should operate with a high vacuum1 because without this it does not compare favorably with an ordinary reciprocating engine from the point of economy4 ,illustration3 ,,fig4 #b1geb4--,sectional view of governor of the ,parsons-,westinghouse turbine4 ,separate air pumps are provided to create the vacuum4 ,where the ordinary type of vertical air pump is employed1 a booster or vacuum increaser is added1 as nothing below #bf inches is advisable1 #bh and #bi inches being always striven for4 ,it is also preferable to use a certain amount of super-heat with steam turbines4 ,to assist in producing the high vacuum1 exhaust passages are made large1 the eduction passage ,e in fig4 #b1gej being nearly twenty-three times the area of the steam pipe4 ,among other details1 a noteworthy feature is a small oil pump ,k1 which circulates oil through bearings of the machinery1 the oil being drawn from the tank under the governor shaft and gravitating there after use4 ,no pressure of oil is employed4 ,stuffing rings prevent leakage2 these consist of alternate grooves and collars in shaft and bearing1 like the grooves in an indicator piston4 ,ques4 ,why is a high vacuum desirable8 ,ans4 ,because the turbine is capable of expanding the steam to a very low terminal pressure1 and this is necessary for economy4 ,ques4 ,what may be said of the working pressures for turbines8 ,ans4 ,to meet the varied conditions of service1 turbines are designed to operate with3 #a1 high pressure1 #b1 low pressure1 or #c1 mixed pressure4 ,illustration3 ,,fig4 #b1gec4--,sectional view of a double flow turbine4 ,the maximum economical capacity of a single flow turbine is limited by the rotative speed4 ,the economical velocity at which the steam may pass through the blades of the turbine depends on the velocity of the moving blades4 ,the capacity of the turbine depends on the weight of the steam passed per unit of time1 which in turn depends on the mean velocity and the height of the blades4 ,for a given rotative speed1 the mean diameter of blade ring practicable is limited by the allowable stresses due to centrifugal force1 and there is a practical limit for the height of the blades4 ,now if the rotative speed be taken only half as great1 the maximum diameter of the rotor may be doubled and1 without increasing the height of the blades1 the capacity of the turbine will be doubled4 ,so with the single flow steam turbine as well as with the single crank reciprocating engine1 there is a practical limiting economical capacity for any given speed4 ,if this limit be reached with a single crank reciprocating engine1 a unit of double the power may be produced at the same speed by coupling two single crank engines to one shaft4 ,similar results are secured making a double flow turbine which is in effect1 as will be seen from the figure1 two single flow turbines made up in a single rotor in a single casing with a common inlet and two exhausts4 ,steam enters the nozzle block1 acts on the impulse element1 and then the current divides1 one-half of the steam going through the reaction blading at the left of the impulse wheel2 the remainder passes over the top of the impulse wheel and through the impulse blading at the right4 ,high pressure turbines operate at about the same initial pressure as triple expansion engines4 ,low pressure1 as here applied1 means the exhaust pressure of the reciprocating engine from which the exhaust steam passes through the turbine before entering the condenser4 ,mixed pressure implies that the exhaust steam is supplemented1 for heavy loads1 by the admission of live steam4 ,ques4 ,what determines the working pressure8 ,ans4 ,when all the power is furnished by the turbine1 it is designed for high pressure2 when operated in combination with a reciprocating engine1 low pressure is used for constant load1 and mixed pressure for variable load4 ,illustration3 ,,fig4 #b1ged4--,sectional view of a semi-double flow turbine4 ,this is a modification in which the intermediate section of reaction blading is single flow1 and the low pressure section only is double flow4 ,this would be analogous to a four cylinder triple expansion engine1 that is1 one with one high pressure1 one intermediate pressure and two low pressure cylinders--a design not at all uncommon in very large engines in which the required dimensions of a single low pressure cylinder would be prohibitive4 ,such turbines are useful for capacities greater than is desirable for a single flow turbine1 and which are still below the maximum possibilities of a double flow turbine of the same speed4 ,in such machines the best efficiency is secured by making the intermediate blading in a single section large enough to pass the entire quantity of steam4 ,a dummy similar to those used on the single flow ,parsons type1 shown at the right of the impulse wheel1 compels all of the steam to pass through the single intermediate section of the reaction blading1 and balances the end thrust due to this section4 ,when the steam issues from the intermediate section1 the current is divided1 one-half passing directly to the adjacent low pressure section1 while the other half passes through the holes shown in the periphery of the hollow rotor and through the rotor itself1 beyond the dummy ring1 into the other low pressure section at the left hand end of the turbine4 ,,note4--,there are logical engineering reasons for the existence of the several types of turbine1 viz41 single flow1 double flow1 and semi-double flow4 ,the double flow turbine is not inherently superior to the single flow design1 but is used under conditions for which the single flow machine is unsuitable4 ,similarly1 the semi-double flow is recommended only for conditions which it can meet more satisfactorily than either of the other types4 ,,note4--,low pressure turbines use exhaust steam from non-condensing engines and are valuable as an adjunct to existing plants for the purpose of increasing economy and capacity with a minimum outlay for new equipment4 ,,note4--,bleeder turbines are for use in plants which are required to furnish1 not only power1 but also considerable and varying quantities of low pressure steam for heating purposes4 ,in these turbines a part of the steam after it has done work in the high pressure stages may be diverted to the heating system1 and the remainder expanded through the low pressure blading and exhausted into the condenser4 ,in this way none of the energy of the heating steam1 due to the difference of pressure between the boiler and the heating system is wasted4 ,on the other hand if no steam is required for heating purposes1 the turbine operates just as efficiently as though the bleeder feature were absent4 ,illustration3 ,,fig4 #b1gee4--,westinghouse valve gear with steam relay4 ,in the smaller turbines1 the governor acts directly on the steam admission valves1 opening first the primary valve1 and then1 if necessary1 the secondary valve1 after the primary is fully open4 ,in turbines of the single flow ,parsons type1 the governor actuates two small valves controlling ports leading to steam relay cylinders which operate the admission valves4 ,the little valve controlling the relay cylinder for the secondary valve has more lap than the other and consequently does not come into action until the primary valve has attained its maximum effective opening4 ,the figure shows the general design of this type of valve gear4 ,the ,de ,laval steam turbine is termed by its builders a high speed rotary steam engine4 ,it has but a single wheel1 fitted with vanes or buckets of such curvature as has been found to be best adapted for receiving the impulse of the steam jet4 ,there are no stationary or guide blades1 the angular position of the nozzles giving direction to the jet4 ,the nozzles are placed at an angle of #bj degrees to the plane of motion of the buckets4 ,the best energy in the steam is practically devoted to the production of velocity in the expanding or divergent nozzle1 and the velocity thus attained by the issuing jet of steam is about #d1jjj feet per second4 ,to attain the maximum efficiency1 the buckets attached to the periphery of the wheel against which this jet impinges should have a speed of about #a1ijj feet per second1 but1 owing to the difficulty of producing a material for the wheel strong enough to withstand the strains induced by such a high speed1 it has been found necessary to limit the peripheral speed to #a1bjj or #a1cjj feet per second4 ,it is well known that in a correctly designed nozzle the adiabatic expansion of the steam from maximum to minimum pressure will convert the entire static energy of the steam into kinetic energy4 ,theoretically this is what occurs in the ,de ,laval nozzle4 ,the expanding steam acquires great velocity1 and the energy of the jet of steam issuing from the nozzle is equal to the amount of energy that would be developed if an equal volume of steam were allowed to adiabatically expand behind the piston of a reciprocating engine1 a condition1 however1 which for obvious reasons has never yet been attained in practice with the reciprocating engine4 ,but with the divergent nozzle the conditions are different4 ,the ,curtis turbine is built by the ,general ,electric ,company at their works in ,schenectady1 ,n4 ,y41 and ,lynn1 ,mass4 ,they are of the horizontal and vertical types4 ,in the vertical type the revolving parts are set upon a vertical shaft1 the diameter of the shaft corresponding to the size of the machine4 ,the shaft is supported by and runs upon a step bearing at the bottom4 ,this step bearing consists of two cylindrical cast iron plates bearing upon each other and having a central recess between them into which lubricating oil is forced under pressure by a steam or electrically driven pump1 the oil passing up from beneath4 ,illustration3 ,,figs4 #b1gef and #b1geg4--,westinghouse valve gear with oil relay4 ,governors for the larger turbines1 particularly those of the combination impulse and reaction double1 or single double flow type1 employ an oil relay mechanism1 as shown in the figure1 for operating the steam valves4 ,in these turbines the lubricating oil circulating pump1 maintains a higher pressure than is required for the lubricating system4 ,the governor controls a small relay valve ,a which admits pressure oil to1 or exhausts it from the operating cylinder4 ,when oil is admitted to the operating cylinder raising the piston1 the lever ,c lifts the primary valve ,e4 ,the lever ,d moves simultaneously with ,c1 but on account of the slotted connection with the stem of the secondary valve ,f1 the latter does not begin to lift until the primary valve is raised to the point at which its effective opening ceases to be increased by further upward travel4 ,in the ,westinghouse designs1 the operating valve1 ,a is connected not only to the governor1 but also to a vibrator1 which gives it a slight but continuous reciprocating motion1 while the governor controls its mean position4 ,the effect of this is manifested in a slight pulsation throughout the entire relay system1 which1 so to speak1 keeps it alive and ready to respond instantly1 to the smallest change in the position of the governor4 ,the oil relay can be made sufficiently powerful to operate valves of any size1 and it is also in effect a safety device in that any failure of the lubricating oil supply will automatically and immediately shut off the steam and stop the turbine4 ,a weighted accumulator is sometimes installed in connection with the oil pipe as a convenient device for governing the step bearing pumps1 and also as a safety device in case the pumps should fail1 but it is seldom required for the latter purpose1 as the step bearing pumps have proven after a long service in a number of cases1 to be reliable4 ,the vertical shaft is also held in place and kept steady by three sleeve bearings one just above the step1 one between the turbine and generator1 and the other near the top4 ,illustration3 ,,fig4 #b1geh4--;,elevation of new turbine central station erected by the ,boston ,edison ,co4 ,the turbine room is #fh feet1 #d inches wide and #fej feet long from outside to outside of the walls4 ,the boiler room is #adi feet1 #f inches by #fdj feet and equipped with twelve groups of boiler1 one group consisting of eight #eab ,h4,p4 boilers for each turbine4 ,the switching arrangements are located in a separate building as shown in the elevation4 ,the total floor space covered by boiler room1 turbine room and switchboard room is #b4fd square feet per kw4 ,the boilers are all on the ground floor4 ,see fig4 #b1gad for plan4 ,these guide bearings are lubricated by a standard gravity feed system4 ,it is apparent that the amount of friction in the machine is very small1 and as there is no end thrust caused by the action of the steam1 the relation between the revolving and stationary blades may be maintained accurately4 ,as a consequence1 therefore1 the clearances are reduced to the minimum4 ,the ,curtis turbine is divided into two or more stages1 and each stage has one1 two or more sets of revolving blades bolted upon the peripheries of wheels keyed to the shaft4 ,there are also the corresponding sets of stationary blades bolted to the inner walls of the cylinder or casing4 ,the governing of speed is accomplished in the first set of nozzles and the control of the admission valves here is effected by means of a centrifugal governor attached to the top end of the shaft4 ,this governor1 by a very slight movement1 imparts motion to levers1 which in turn work the valve mechanism4 ,the admission of steam to the nozzles is controlled by piston valves which are actuated by steam from small pilot valves which are in turn under the control of the governor4 ,illustration3 ,,fig4 #b1gei4--;,illustration of a weir4 ,to make a weir1 place a board across the stream at some point which will allow a pond to form above4 ,the board should have a notch cut in it with both side edges and the bottom sharply beveled toward the intake1 as shown in the above cut4 ,the bottom of the notch1 which is called the crest of the weir1 should be perfectly level and the sides vertical4 ,in the pond back of the weir1 at a distance not less than the length of the notch1 drive a stake near the bank1 with its top precisely level with the crest4 ,by means of a rule1 or a graduated stake as shown1 measure the depth of water over the top of stake1 making allowance for capillary attraction of the water against the sides of the weir4 ,for extreme accuracy this depth may be measured to thousandths of a foot by means of a hook gauge1 familiar to all engineers4 ,having ascertained the depth of water over the stake1 refer to the accompanying table1 from which may be calculated the amount of water flowing over the weir4 ,there are certain proportions which must be observed in the dimensions of this notch4 ,its length1 or width1 should be between four and eight times the depth of water flowing over the crest of the weir4 ,the pond back of the weir should be at least fifty per cent4 wider than the notch and of sufficient width and depth that the velocity of flow or approach be not over one foot per second4 ,in order to obtain these results it is advisable to experiment to some extent4 ,speed regulation is effected by varying the number of nozzles in flow1 that is1 for light loads fewer nozzles are open and a smaller volume of steam is admitted to the turbine wheel1 but the steam that is admitted impinges against the moving blades with the same velocity always1 no matter whether the volume be large or small4 ,with a full load and all the nozzle sections in flow1 the steam passes to the wheel in a broad belt and steady flow4 ,,weir ,,table giving cubic feet of water per minute that will flow over a weir one inch wide and from to #bj inches deep4 ---------------------------------------- ---------------- ,depth inches ---------------------------------------- ---------------- #j 4#jj 4#ja 4#je 4#ji 4#ad 4#ai 4#bf 4#cb #a 4#dj 4#dg 4#ee 4#fd 4#gc 4#hb 4#ib #a4jb #b #a4ac #a4bc #a4ce #a4cf #a4eh #a4gj #a4hb #a4ie #c #b4jg #b4ba #b4cd #b4dh #b4fa #b4gf #b4ij #c4je #d #c4bj #c4ce #c4ej #c4ff #c4ha #c4ig #d4ad #d4cj #e #d4dg #d4fd #d4ha #d4ih #e4ae #e4cc #e4ea #e4fi #f #e4hg #f4jf #f4be #f4dd #f4fb #f4hb #g4ja #g4ba #g #g4dj #g4fj #g4hj #h4ja #h4ba #h4db #h4fc #h4hc #h #i4je #i4bf #i4dg #i4fi #i4ia #aj4ac #aj4ce #aj4eg #i #aj4hj #aa4jb #aa4be #aa4dh #aa4ga #aa4id #ab4ag #ab4da #aj #ab4fd #ab4hh #ac4ab #ac4cf #ac4fj #ac4he #ad4ji #ad4cd #aa #ad4ei #ad4hd #ae4ji #ae4cd #ae4ei #ae4he #af4aa #af4cf #ab #af4fb #af4hh #ag4ae #ag4da #ag4fg #ag4id #ah4ba #ah4dg #ac #ah4gd #ai4ja #ai4bi #ai4ef #ai4hd #bj4aa #bj4ci #bj4fg #ad #bj4ie #ba4bc #ba4ea #ba4hj #bb4jh #bb4cg #bb4fe #bb4id #ae #bc4bc #bc4eb #bc4hb #bd4aa #bd4dj #bd4gj #be4jj #be4cj #af #be4fj #be4ij #bf4bj #bf4ej #bf4hj #bg4aa #bg4db #bg4gb #ag #bh4jc #bh4cd #bh4fe #bh4ig #bi4bh #bi4ei #bi4ia #cj4bb #ah #cj4ed #cj4hf #ca4ah #ca4ej #ca4hb #cb4ae #cb4dg #cb4hj #ai #cc4ab #cc4de #cc4gh #cd4aa #cd4dd #cd4gg #ce4aj #ce4dd #bj #ce4gg #cf4aa #cf4de #cf4gh #cg4ab #cg4df #cg4hj #ch4ae ---------------------------------------- ---------------- ,,note4--,the weir table on this page contains figures #a1 #b1 #c1 etc41 in the first vertical column which indicates the inches depth of water running over weir board notches4 ,frequently the depths measured represent also fractional inches1 between #a and #b1 #b and #c1 etc4 ,the horizontal line of fraction at the top represents these fractional parts1 and can be applied between any of the numbers of inches depth1 from #a to #be4 ,the body of the table shows the cubic feet1 and the fractional parts of a cubic foot1 which will pass each minute for each inch in depth1 and for each fractional part of an inch by eighths for all depths from #a to #be inches4 ,each of these results is for only one inch width of weir4 ,to estimate for any width of weir the result obtained for one inch width must be multiplied by the number of inches constituting the whole horizontal length of weir4 ,illustration3 ,,figs4 #b1gfj and #b1gfa4--,samson vertical runner and shaft1 and complete ,samson vertical turbine4 ,the runner is composed of two separate and distinct types of wheel1 having thereby also two diameters4 ,each wheel or set of buckets receives its separate quantity of water from one and the same set of guides1 but each set acts only once and singly upon the water used1 and the water does not act twice upon the combined wheel1 as some suppose4 ,in construction1 the lower or main set of buckets is made of flanged plate steel1 and cast solidly into a heavy ring surrounding the outer and lower edges1 and into a heavy diaphragm1 separating the two sets of buckets4 ,illustration3 ,,fig4 #b1gfb4--,water discharging from a needle nozzle due to a pressure of #afi lbs4 per sq4 in4 ,hydro-,electric ,plants4--,the economy with which electricity can be transmitted long distances by high tension alternating currents1 has led to the development of a large number of water powers in more or less remote regions4 ,illustration3 ,,fig4 #b1gfc4--,photograph of an operating tangential water wheel equipped with ,pelton buckets4 ,this economy is possible by the facility with which alternating current can be transformed up and down4 ,thus at the hydro-electro plant1 the current generated by the water wheel driven alternator is transformed to very high pressure and transmitted with economy a long distance to the distributing point where it is transformed down to the proper pressure for distribution4 ,a water wheel or turbine is a machine in which a rotary motion is obtained by transference of the momentum of water2 broadly speaking1 the fluid is guided by fixed blades1 attached with a casing1 and impinging on other blades mounted on a drum or shaft1 causing the latter to revolve4 ,there are two general classes of turbine3 #a4 ,impulse turbines2 #b4 ,reaction turbines4 ,illustration3 ,,fig4 #b1gfd4--,sectional elevation of one of the #e1jjj horse power vertical ,pelton-,francis turbines directly connected to generator1 as installed for the ,schenectady ,power ,co4 ,ques4 ,what is an impulse turbine8 ,ans4 ,one in which the fluid is directed by means of a series of nozzles against vanes which it drives4 ,ques4 ,what is a reaction turbine8 ,ans4 ,one in which the pressure or head of the water is employed rather than its velocity4 ,the current is deflected upon the wheel by the action of suitably disposed guide blades1 the passages being full of water4 ,rotary motion is obtained by the change in the direction and momentum of the fluid4 ,illustration3 ,figs4 #b1gfe to #b1gfh4--;,cross sections of ,lowel dam power house1 and wheel pits containing sixteen ,samson turbines3 ,the section ,c-,d gives an end view of the generator room showing the locations of the generators below the head level water4 ,they are secure against flood water1 or leakage1 by well constructed stuffing boxes in the iron bulkheads1 through which the turbine wheel shafts pass and connect to the generators4 ,section ,e-,f gives an end view of one of these wheel rooms or penstocks1 and shows the extension of the draft tube from wheel case into tail water4 ,the section ,a-,b shows the sub-structure of gravel and macadam under the controlling gates1 this forming also a portion or extension of the dam proper4 ,these gates turn on an axis made of two #ae inch ,i beams securely riveted together with plates and angle irons to which the wooden frame is attached4 ,the radius of the gates is #ad feet4 ,they are designed to allow the water to pass underneath the gate1 thus controlling any height of head water4 ,they are intended to take care of an excess of water at unusual stages of the river4 ,the whole affair has been well designed and executed4 ,this plant furnishes a good example of a secure1 and level foundation1 since the wheel houses and generator room are immediately on the rock4 ,it is necessary in all tandem plants to provide a very secure1 substantial super-structure so that the long line of turbines and shaft will always remain straight and in proper alignment with the generator and the turbine cases4 ,users cannot be reminded of this too often4 ,ques4 ,name three classes of reaction turbines4 ,ans4 ,parallel flow1 inward flow1 and outward flow4 ,parallel flow turbines have an efficiency of about #gj and are suited for low falls not over #cj feet4 ,inward and outward flow turbines have an efficiency of about #he4 ,impulse turbines are suitable for high heads4 ,illustration3 ,,figs4 #b1gfi and #b1ggj4--;,exterior and interior of hydro-electric plant at ,harrisburg1 ,va4 ,it is located on the south fork of the ,shenandoah ,river1 twelve and one-half miles distant4 ,a dam #gbj feet long and #ae feet high was built on a limestone ledge running across the river2 which with a fall of #e feet from the dam to the power house1 a quarter of a mile distant1 secured an effective head pressure of #bj feet4 ,the power house1 comprising the generator room and the wheel room1 also the machinery room1 are here shown4 ,the wheel room1 which is #bj #dj feet1 extends across the head race1 and rests upon solid concrete walls1 forming the sides and ends of the wheel pits4 ,the end wall is #f feet thick at the bottom1 and #d feet at the top4 ,it has three arched openings1 each #h feet wide and #i feet high1 through which the water escapes after leaving the turbines4 ,the intake is protected by a wrought iron rack #dj feet long4 ,the power is obtained by three #ej inch vertical shaft ,samson turbines1 with a #bj inch ,samson for an exciter4 ,the three large turbines have a rating of #a1cej horse power2 and are connected to the main horizontal line shaft by bevel mortise gears #g feet diameter and #ae inches face4 ,the couplings on the main shaft have #dh inch friction clutch hubs1 permitting either or each turbine being operated1 or shut down independently of the others4 ,the main shaft is #he feet long and #f inches diameter2 making #bhj revolutions4 ,this shaft carries two pulleys #gj inches diameter and #ch inches face for driving the generators4 ,the accompanying illustration shows the harness work1 gears1 pulleys1 etc41 furnished with the turbines4 ,the #bj inch horizontal shaft ,samson turbine of #gb horse power is direct connected to an exciter generator of #bj kw41 running #gjj rev4 per min4 ,the two large generators are driven #dej revolutions per minute by belts producing a three phase current of #fj cycles of #aa1ejj volts for the twelve and one-half miles transmission4 ,the line consists of three strands of ,no4 #d bare copper wire4 ,this current is used for lighting and power purposes1 and the plant is of the latest improved design and construction4 ,isolated ,plants4--,when electric power transmission from central stations first came into commercial use1 the distance from the station at which current could be obtained at a reasonable cost was exceedingly limited4 ,illustration3 ,,fig4 #b1gfi;a4--,triumph direct current generator set with upright slide valve engine4 ,illustration3 ,,fig4 #b1ggj;a4--,murray alternating current direct connected unit with high speed ,corliss engine and belt driven exciter1 #ej1 #ge and #ajj kva4 alternator and #aej ,r4,p4,m4 engine4 ,illustration3 ,,fig4 #b1gga4--;,direct connected direct current unit with ,ridgway high speed four valve engine4 ,illustration3 ,,fig4 #b1ggb4--;,buckeye mobile1 or self contained unit consisting of compound condensing engine1 boiler1 superheater1 reheater1 feed and air pumps2 it produces one horse power on #a lbs4 of coal1 built in sizes from #ge to #fjj horse power4 ,illustration3 ,,fig4 #b1ggc4--,westinghouse three cylinder gas engine1 direct connected to dynamo1 showing application of gas engine drive for small direct connected units4 ,consequently1 persons desiring electrical power were in the majority of cases forced to install their own apparatus for producing it1 this being the origin of isolated plants4 ,from the nature of the case it is evident that an isolated plant is as a rule smaller and more simple in construction than a central station1 and in consequence much more readily operated and managed4 ,it is generally owned by a private individual or a corporation and operated in conjunction with other affairs of a similar character4 ,a basement or other portion of a building is usually set aside in which the necessary apparatus is installed4 ,illustration3 ,,fig4 #b1ggd4--;,general ,electric #be kw41 gasoline electric generating set for lighting and power4 ,the engine has four cylinders #g #g1 and runs at a speed of #efj revolutions per minute4 ,the total candle power capacity in ,mazda lamps is #bj1jjj4 ,the ignition is by low tension magneto1 coil and battery4 ,carburetter is of the constant level type to which gasoline is delivered by a pump driven by the engine4 ,forced lubrication2 five crank shaft bearings babbitted2 valves in side2 overall dimensions #if #cd #fj high2 weight #e1jjj4 ,although electricity is now transmitted economically to great distances from central stations1 there is still a field for the isolated plant4 ,the average type of isolated plant has enlarged from a small dynamo driven by a little slide valve engine located in an out of the way corner to direct connected generators and engines of hundreds and even thousands of horse power assembled in a large room specially adapted to the purpose4 ,in the more modern of these1 the electrical outputs are each frequently equal to that of a town central station of respectable size1 and the auxiliary equipments are similar in every particular4 ,as a matter of fact1 in certain modern isolated plants the only feature that distinguishes them from central stations is that in the former case the owner of the plant represents the sole consumer and conducts other business in connection with it1 whereas in the latter case there are a large number of consumers uninterested financially in the enterprise1 which is itself generally owned and operated by a company conducting no other business4 ,illustration3 ,,fig4 #b1gge4--,plan of sub-station with air blast transformers and motor operated oil switches and underground #aa1jjj or #ac1bjj volt high tension lines4 ,sub-,stations4--,according to the usual meaning of the term1 a sub-station is a building provided with apparatus for changing high pressure alternating current received from the central station into direct current of the requisite pressure1 which in the case of railways is #eej to #fjj volts4 ,where traffic is heavy and the railway system of considerable distance1 sub-stations are provided at intervals along the line1 each receiving high pressure current from one large central station and converting it into moderate pressure direct current for their districts4 ,ques4 ,upon what does the arrangement of the sub-station depend8 ,ans4 ,upon the character of the work and the type of apparatus employed for converting the high pressure alternating current into direct current4 ,illustration3 ,,fig4 #b1ggf4--,plan of small sub-station with single phase oil insulated self-cooling transformers and hand operated oil switches #aa1jjj or #ac1bjj volts1 overhead high tension lines4 ,in general it should be substantial1 convenient to install or replace the heavy machines1 and the layout arranged so that the apparatus can be readily operated by those in attendance4 ,an overhead traveling crane is the most convenient method of handling the heavy machinery1 and is frequently used in large sub-stations4 ,fig4 #b1ggf shows a sectional view1 and fig4 #b1ggg1 a plan for a small sub-station containing two rotary converters and two banks of three single phase static transformers operating on a three phase system at #aa1jjj or #ac1bjj volts1 together with the auxiliary apparatus4 ,illustration3 ,,fig4 #b1ggg4--;,elevation of small sub-station1 as shown in plan in ,fig4 #b1ggf4 ,ques4 ,for three phase installations1 what are the merits of separate and combined transformers8 ,ans4 ,with separate transformer for each phase1 repairs are more readily made in case of accident or burnouts in the coils4 ,the three phase units have the advantage of low first cost4 ,sub-station transformers produce considerable heat1 due to the hysteresis and eddy currents1 and it is necessary to get rid of it4 ,small transformers radiate the heat from the shell and the medium sizes have corrugated shells which increase the surface and provide more rapid radiation4 ,large transformers are cooled by an air blast supplied by motor driven blowers or by water pumped through a coil of pipe which is immersed in the insulating oil of the transformer4 ,the large size oil insulated1 water cooled transformers are used on circuits of #cc1jjj volts or more4 ,in water turbine plants1 the water may be piped to the transformer under pressure and the pump omitted which cuts down the cost of operating4 ,air blast transformers usually have a damper or shutter for air control4 ,illustration3 ,,fig4 #b1ggh4--,marine portable transformer station on ,los ,angeles ,aqueduct4 ,the view shows three #bj kva4 ,westinghouse out door transformers installed on a float1 #cc1jjj volts high pressure2 #ddj volts low pressure2 #ej cycles4 ,ques4 ,explain the use of reactance coils in sub-stations4 ,ans4 ,in order that the direct current voltage of the ordinary rotary may be regulated by a field rheostat1 which calls for a corresponding change in the alternating current voltage1 a reactance coil is provided between the low tension winding and the converter4 ,without such a reactance the maintenance of the same voltage at full load as at no load involves excessive leading and lagging currents and consequently excessive heating in the armature inductors1 unless the resistance drop from the source of constant pressure is small1 or the natural reactance of the circuit high4 ,ques4 ,what is the effect of weakening the converter field8 ,ans4 ,a lagging current is set up which causes a drop in the reactance coil4 ,illustration3 ,,fig4 #b1ggi4--,sectional elevation of portable outdoor transformer type sub-station4 ,the high voltage switching and protective apparatus is mounted1 out of the way1 on the roof of the car1 but is operated from the switchboard with a standard remote control handle4 ,the transformer is carried directly over the truck at the uncovered end of the car and the low-tension leads from it run in conduit beneath the floor and up into the cab1 7which contains the converter and switchboard7 to the converter4 ,the positive lead runs through a conduit and ends in a terminal on the roof4 ,the energy thus makes a complete circuit of the car leaving at a point close to that at which it entered4 ,the low pressure alternating current as well as the direct current positive leads are carried below the car floor in iron conduit supported from the channel frame4 ,the field wires are carried through this conduit to the rheostat4 ,wiring for the lights is arranged to supply two1 #e light clusters4 ,one is fed with the #fjj volt direct current and the other with #dbj volt alternating current4 ,all lighting conductors are carried in metal moulding carried between the flanges of the channel iron ribs4 ,high wiring is carried entirely on the roof of the car where it is entirely out of the way and where the operator cannot come in contact with it4 ,the switchboard should be of the utmost simplicity4 ,usually the negative and equalizer switches1 and the field break-up switch are mounted on the frame of the converter4 ,the double throw switch for starting and running the converter can be mounted under the floor of the car and operated by handle at the switchboard4 ,the rheostat can be mounted back of the switchboard on brackets bolted to the car super-structure4 ,the switchboard need only carry the positive knife switch and circuit breaker1 and the alternating current ammeter1 voltmeter and power factor meter4 ,sometimes a watthour meter is added4 ,the positive lead is brought out through a conduit on the roof of the car and is arranged for bolting to the positive feeder4 ,the negative and equalizer terminals are located at the cab end of the car and are arranged so that connection can be easily made from them to the ground and1 if necessary1 to an equalizer circuit4 ,there is usually a sliding door at each end of the cab and two windows on each side4 ,above the doors1 transoms1 extending the width of the cab1 are arranged to drop so that a current of air will circulate through the cab under the roof1 carrying out the heated air4 ,there are also several ventilating holes beneath the converter in the floor of the car4 ,these provisions insure a constant circulation of air through the car which carries away all heated air4 ,ques4 ,state the effect of strengthening converter field4 ,ans4 ,a leading current is set up which gives a rise of voltage in the reactance coil4 ,hence when a heavy current passes through the series coil of a compound wound converter and tends to produce a leading current1 the reactance coil will balance it1 and improve the power factor of the whole line4 ,illustration3 ,,fig4 #b1ghj4--,westinghouse #cjj kw4 converter in portable sub-station4 ,portable ,sub-,stations4--,a portable sub-station constitutes a spare equipment for practically any number of permanent sub-stations and renders unnecessary the installation of spare equipment in each4 ,it can be used to increase the capacity of a permanent sub-station when the load is unusually heavy1 or to provide service while a permanent sub-station is being overhauled or rebuilt4 ,the transformer can be used for emergency lighting1 the primary being connected to a high pressure line and the secondary to the load1 if special provision be made at the time the transformer is built to adapt it for these applications4 ,illustration3 ,,fig4 #b1gha4--,switchboard end of ,westinghouse portable sub-station4 ,when an electric railway has a portable sub-station1 direct current can be provided at any point on the system where there is track at the high pressure line4 ,the direct current can be made available very quickly as its production involves only the transferring of the sub-station1 and its connection to the high pressure line4 ,portable sub-stations range in capacity from #bjj to #ejj kw41 and for all alternating current voltages up to #ff1jjj1 and frequencies of #be and #fj cycles4 ,although portable sub-stations usually must be of more or less special design to adapt them to the conditions under which they must operate1 there are certain general features that are common to all4 ,all members are readily accessible and there are no unnecessary parts4 ,the weight and dimensions are a minimum insuring ease of transportation4 ,live parts are so protected that the danger of accidental contact with them is minimized4 ,illustration3 ,,figs4 #b1ghb and #b1ghc4--,views of levelling device for ,westinghouse converter4 ,ques4 ,what are the advantages of using outdoor transformers on portable sub-stations8 ,ans4 ,all high pressure wiring is kept out of the car4 ,the transformer is more effectively cooled and the heat dissipated by the transformer does not warm the interior of the cab4 ,the transformer is much more accessible4 ,the car can be run under a crane and the transformer coils pulled out with a hoist4 ,taps for different high and low pressure voltages can be readily provided at the time the transformer is being built4 ,,chapter ,,lxvii ,,management ,the term management1 broadly speaking1 includes not only the actual skilled attention necessary for the proper operation of the machines1 after the plant is built1 but also other duties which must be performed from its inception to completion1 and which may be classified as #a4 ,selection2 #b4 ,location2 #c4 ,erection2 #d4 ,testing2 #e4 ,running2 #f4 ,care2 #g4 ,repair4 ,that is to say1 someone must select the machinery1 determine where each machine is to be located1 install them1 and then attend to the running of the machines and make any necessary repairs due to the ordinary mishaps likely to occur in operation4 ,these various duties are usually entrusted to more than one individual2 thus1 the selection and location of the machinery is done by the designer of the plant1 and requires for its proper execution the services of an electrical engineer1 or one possessing more than simply a practical knowledge of power plants4 ,the erection of the machines is best accomplished by those making a specialty of this line of work1 who by the nature of the undertaking acquire proficiency in methods of precision and an appreciation of the value of accuracy which is so essential in the work of aligning the machines1 and which if poorly done will prove a constant source of annoyance afterward4 ,the attention required for the operation of the machines1 embracing the running care and repair1 is left to the man in charge1 who in most cases of small and medium size plants is the chief steam engineer4 ,he must therefore1 not only understand the steam apparatus1 but possess sufficient knowledge of electrical machinery to operate and maintain it in proper working order4 ,the present chapter deals chiefly with alternating current machinery1 the management of direct current machines having been fully explained in ,guide ,no4 #c1 however1 some of the matter here presented is common to both classes of apparatus4 99 99 99 99 99 ,selection4--,in order to intelligently select a machine so that it will properly harmonize with the conditions under which it is to operate1 there are several things to be considered4 #a4 ,type2 #b4 ,capacity2 #c4 ,efficiency2 #d4 ,construction4 ,the general type of machine to be used is1 of course1 dependent on the system employed1 that is1 whether it be direct or alternating1 single or polyphase4 ,thus1 the voltage in most cases is fixed except on transformer systems where a choice of voltage may be had by selecting a transformer to suit4 ,in alternating current constant pressure transmission circuits1 an average voltage of #b1bjj volts with step down transformer ratios of #a_/aj and #a_/bj is in general use1 and is recommended4 ,for long distance1 the following average voltages are recommended #f1jjj2 #aa1jjj2 #bb1jjj2 #cc1jjj2 #dd1jjj2 #ff1jjj2 #hh1jjj2 and higher1 depending on the length of the line and degree of economy desired4 ,in alternating circuits the standard frequencies are #be1 and #fj cycles4 ,these frequencies are already in extensive use and it is recommended to adhere to them as closely as possible4 ,illustration3 ,,fig4 #b1ghd4--;,diagram of connections for testing to obtain the saturation curve of an alternator4 ,the saturation curve shows the relation between the volts generated in the armature and the amperes of field current 7or ampere turns of the field7 for a constant armature current4 ,the armature current may be zero1 in which case the curve is called no load saturation curve1 or sometimes the open circuit characteristic curve4 ,a saturation curve may be taken with full load current in the armature2 but this is rarely done1 except in alternators of comparatively small output4 ,if a full load saturation curve be desired1 it can be approximately calculated from the no load saturation curve4 ,the figure shows the connections4 ,if the voltage generated is greater than the capacity of the voltmeter1 a multiplying coil or a step down pressure transformer may be used1 as shown4 ,a series of observations of the voltage between the terminals of one of the phases1 is made for different values of the field current4 ,eight or nine points along the curve are usually sufficient1 the series extending from zero to about fifty per cent4 above normal rated voltage4 ,the points should be taken more closely together in the vicinity of normal voltage than at other portions of the curve4 ,care must be taken that the alternator is run at its rated speed1 and this speed must be kept constant4 ,deviations from constant speed may be most easily detected by the use of a tachometer4 ,if the machine be two phase or three phase1 the voltmeter may be connected to any one phase throughout a complete series of observations4 ,the voltage of all the phases should be observed for normal full load excitation by connecting the voltmeter to each phase successively1 keeping the field current constant at normal voltage4 ,this is done in order to see how closely the voltage of the different phases agree4 ,in fixing the capacity of a machine1 careful consideration should be given to the conditions of operation both present and future in order that the resultant efficiency may be maximum4 ,most machines show the best efficiency at or near full load4 ,if the load be always constant1 as for instance1 a pump forcing water to a given head1 it would be a simple matter to specify the proper size of machine1 but in nearly all cases1 and especially in electrical plants1 the load varies widely1 not only the daily and hourly fluctuations1 but the varying demands depending on the season of the year and growth of the plant's business4 ,all of these conditions tend to complicate the matter1 so that intelligent selection of capacity of a machine requires not only calculation but mature judgment1 which is only obtained by long experience4 ,illustration3 ,,fig4 #b1ghe4--,saturation curve taken from a #b1jjj kw41 three phase alternator of the revolving field type1 having #af poles1 and generating #b1jjj volts1 and #egf amperes per phase when run at #cjj ,r4,p4,m4 ,in selecting a machine1 or in fact any item connected with the plant its construction should be carefully considered4 ,standard construction should be insisted upon so that in the event of damage a new part can be obtained with the least possible delay4 ,the parts of most machines are interchangeable1 that is to say1 with the refined methods of machinery a duplicate part 7usually carried in stock7 may be obtained at once to replace a defective or broken part1 and made with such precision that little or no fitting will be required4 ,the importance of standard construction cannot be better illustrated than in the matter of steam piping1 that is1 the kind of fittings selected for a given installation4 ,with the exception of the exhaust line from engine to condenser1 where other than standard construction may sometimes be used to reduce the frictional resistance to the steam1 the author would adhere to standard construction except in very exceptional cases4 ,those who have had practical experience in pipe fitting will appreciate the wisdom of this4 ,for installations in places remote from large supply houses1 the more usual forms of standard fittings should be employed1 such as ordinary ,t's1 #de and #ij elbows1 etc4 ,in such locations1 where designers specify the less usual forms of standard fittings such as union fittings1 offset reducers1 etc41 or special fittings made to sketch1 it simply means1 in the first instance that they usually cannot be obtained of the local dealer1 making it necessary to order from some large supply house and resulting in vexatious delays4 ,as a rule1 those who specify special fittings have found that their making requires an unreasonable length of time1 and the cost to be several times that of the equivalent in standard fittings4 ,an examination of a few installations will usually show numerous special and odd shape fittings1 which are entirely unnecessary4 ,moreover1 a standard design1 in general1 is better than a special design1 because the former has been tried out1 and any imperfection or weakness remedied1 and where thousands of castings of a kind are turned out1 a better article is usually the result as compared with a special casting4 ,in the matter of construction1 in addition to the items just mentioned1 it should be considered with respect to #a4 ,quality2 #b4 ,range2 #c4 ,accessibility2 #d4 ,proportion2 #e4 ,lubrication2 #f4 ,adjustment4 ,it is poor policy1 excepting in very rare instances1 to buy a cheap article1 as1 especially in these days of commercial greed1 the best is none too good4 ,illustration3 ,,figs4 #b1ghf and #b1ghg4--,wheel and roller pipe cutters illustrating range4 ,the illustrations show the comparative movements necessary with the two types of cutter to perform their function4 ,the wheel cutter requiring only a small arc of movement will cut a pipe in an inaccessible place as shown1 which with a roller cutter would be impossible4 ,accordingly1 the wheel cutter is said to have a greater range than the roller cutter4 ,perhaps next in importance to quality1 at least in most cases1 is range4 ,this may be defined as scope of operation1 effectiveness1 or adaptability4 ,the importance of range is perhaps most pronounced in the selection of tools1 especially for plants remote from repair shops4 ,for instance1 in selecting a pipe cutter1 there are two general classes3 wheel cutters1 and roller cutters4 ,a wheel cutter has three wheels and a roller cutter one wheel and two rollers1 the object of the rollers being to keep the wheel perpendicular to the pipe in starting the cut and to reduce burning4 ,it must be evident that in operation1 a roller cutter requires sufficient room around the pipe to permit making a complete revolution of the cutter1 whereas1 with a wheel cutter1 the work may be done by moving the cutter back and forth through a small arc1 as illustrated in figs4 #b1ghf and #b1ghg4 ,thus a wheel cutter has a greater range than a roll cutter4 ,range relates not only to ability to operate in inaccessible places but to the various operations that may be performed by one tool4 ,,properties ,,of ,,standard ,,wrought ,,iron ,,pipe ---------------------------------------- --------- ,diameter ,thick- ,circumference4 ness4 ------------------------ ---------------- ,nominal ,actual ,actual ,external,internal internalexternalinternal ---------------------------------------- ------ ,inches ,inches ,inches ,inches ,inches ,inches ---------------------------------------- ------ 4#dje 4#bg 4#jfh #a4bgb 4#hdh 4#ed 4#cfd 4#jhh #a4fif #a4add 4#fge 4#did 4#ia #b4aba #a4eeb 4#hd 4#fbc 4#aji #b4fci #a4ieg #a4je 4#hbd 4#aac #c4bii #b4ehi #a #a4cae #a4jdh 4#acd #d4aca #c4bib #a #a4ff #a4ch 4#ad #e4bae #d4cce #a #a4i #a4faa 4#ade #e4ifi #e4jfa #b #b4cge #b4jfg 4#aed #g4dfa #f4did #b #b4hge #b4dfh 4#bjd #i4jcb #g4gec #c #c4e #c4jfg 4#bag #aj4iif #i4fcf #c #d4 #c4edh 4#bbf #ab4eff #aa4adf #d #d4e #d4jbf 4#bcg #ad4acg #ab4fdh #d #e4 #d4ejh 4#bdf #ae4gjh #ad4afb #e #e4efc #e4jde 4#bei #ag4dgg #ae4hdi #f #f4fbe #f4jfe 4#bh #bj4hac #ai4jed #g #g4fbe #g4jbc 4#cja #bc4iee #bb4jfc #h #h4fbe #g4ihb 4#cbb #bg4jif #be4jgf #i #i4fbe #h4icg 4#cdd #cj4bch #bh4jgf #aj #aj4ge #aj4jai 4#cff #cc4ggb #ca4dgg #aa #ab4 #aa4be 4#cge #cg4fii #ce4cdc #ab #ab4ge #ab4 4#cge #dj4jee #cg4g ---------------------------------------- ------ ---------------------------------------- --------------------------- ,length ,length of pipe of pipe ,nominal ,diam4 ,transverse areas4 per square contain-weight ,number foot of ing one per of ---------------------------------------- --- cubic foot4 thread ,nom4 ,external,internal ,metal ,ext'nal,int'nal foot4 per intern surfacesurface inch ---------------------------------------- ------------------ of ,inches,sq4 ins4,sq4 ins4,sq4ins4 ,feet ,feet ,feet ,pounds screw ---------------------------------------- ----------------------- 4#abi 4#jegc 4#jgag #i4dd #ad4ae #beac4 4#bda #bg 4#bbi 4#ajda 4#abdi #g4jge #aj4di #achc4c 4#db #ah 4#ceh 4#aiag 4#affc #e4feg #g4gc #gea4b 4#eei #ah 4#eed 4#cjdh 4#bdib #d4edg #f4ac #dgb4d 4#hcg #ad 4#hff 4#eccc 4#ccbg #c4fcg #d4fce #bgj4 #a4aae #ad #a #a4ceh 4#hfbf 4#died #b4ijd #c4fde #aff4i #a4ffh #aa #a #b4afd #a4dif 4#ffh #b4cja #b4gfh #if4be #b4bdd #aa #a #b4hce #b4jch 4#gig #b4ja #b4cga #gj4ff #b4fgh #aa #b #d4dc #c4cef #a4jgd #a4fjh #a4hdh #db4ia #c4fji #aa #b #f4dib #d4ghd #a4gjh #a4cbh #a4edg #cj4a #e4gci #h #c #i4fba #g4chh #b4bdc #a4jia #a4bde #ai4e #g4ecf #h #c #ab4eff #i4hhg #b4fgi 4#iee #a4jgg #ad4eg #i4jja #h #d #ae4ijd #ab4gc #c4agd 4#hdi 4#idi #aa4ca #aj4ffe #h #d #ai4fce #ae4ifa #c4fgd 4#gfd 4#hdh #i4jb #ab4cd #h #e #bd4cjf #ai4ii #d4caf 4#fhg 4#geg #g4b #ad4ejb #h #f #cd4dgb #bh4hhh #e4ehd 4#egg 4#fc #d4ih #ah4gfb #h #g #de4ffd #ch4gch #f4ibf 4#eja 4#edd #c4gb #bc4bga #h #h #eh4dbf #ej4jd #h4chf 4#ddc 4#dgh #b4hh #bh4agg #h #i #gb4gf #fb4gc #aj4jc 4#cig 4#dbg #b4bi #cc4gja #h #aj #ij4gfc #gh4hci #aa4ibd 4#cee 4#chb #a4hb #dj4jfe #h #aa #aac4jih #ii4djb #ac4fif 4#cah 4#cci #a4dejde4ie #h #ab #abg4fgg #aac4jih #ad4egi 4#bii 4#cai #a4bg #dh4ihe #h ---------------------------------------- ---------------------- ,open construction should be employed1 wherever possible1 so that all parts of a machine that require attention1 or that may become deranged in operation1 may be accessible for adjustment or repair4 ,the design should be such that there is ample strength1 and the bearings for moving parts should be of liberal proportions to avoid heating with minimum attention4 ,a comparison of the proportions used by different manufacturers for a machine of given size might profitably be made before a selection is made4 ,the matter of lubrication is important4 ,fast running machines1 such as generators and motors1 should be provided with ring oilers and oil reservoirs of ample capacity1 as shown in figs4 #b1ghh to #b1gid4 ,illustration3 ,,fig4 #b1ghh4--,sectional view showing a ring oiler or self oiling bearing4 ,as shown the pedestal or bearing standard is cored out to form a reservoir for the oil4 ,the rings are in rolling contact with the shaft1 and dip at their lower part into the oil4 ,in operation1 oil is brought up by the rings which revolve because of the frictional contacts with the shaft4 ,the oil is in this way brought up to the top of the bearing and distributed along the shaft gradually descending by gravity to the reservoir1 being thus used over and over4 ,a drain cock1 is provided in the base so that the oil may be periodically removed from the reservoir and strained to remove the accumulation of foreign matter4 ,this should be frequently done to minimize the wear of the bearing4 ,all bearings subject to appreciable wear should be made adjustable so that lost motion may be taken up from time to time and thus keep the vibration and noise of operation within proper limits4 ,selection of ,generators4--,this is governed by the class of work to be done and by certain local conditions which are liable to vary considerably for different stations4 ,these variable factors determine whether the generators must be of the direct or alternating current type1 whether they must be wound to develop a high or a low voltage1 and whether their outputs in amperes must be large or small4 ,sufficient information has already been given to cover these various cases2 there are1 however1 certain general rules that may advantageously be observed in the selection of generators designed to fill any of the aforementioned conditions1 and it is well to possess certain facts regarding their construction4 ,illustration3 ,,figs4 #b1ghi to #b1gid4--,self oiling self aligning bearing open4 ,views showing oil grooves1 rings1 bolts etc4 ,ques4 ,name an important point to be considered in selecting a generator4 ,ans4 ,its efficiency4 ,ques4 ,what are the important points with respect to efficiency8 ,ans4 ,a generator possessing a high efficiency at the average load is more desirable than a generator showing a high efficiency at full load4 ,ques4 ,why8 ,ans4 ,the reason is that in station practice the full load limit is seldom reached1 the usual load carried by a generator ordinarily lying between the one-half and three-quarter load points4 ,ques4 ,how do the efficiencies of large and small generators compare8 ,ans4 ,there is little difference4 ,illustration3 ,,fig4 #b1gie4--,rotor of ,westinghouse type ,t turbine dynamo set4 ,the dynamo is of the commutating pole type either shunt or compound wound4 ,the turbine is of the single wheel impulse type4 ,the wheel is mounted directly on the end of the shaft as shown4 ,steam is used two or more times on the wheel to secure efficiency4 ,a fly ball governor is provided with weights hung on hardened steel knife edges4 ,in case of over speeding1 an automatic safety stop throttle valve is tapped shutting off the steam supply4 ,this type of turbine dynamo set is especially applicable for exciter service in modern1 superheated steam generating stations where the steam pressure exceeds #abe pounds4 ,westinghouse ,type ,t turbines operate directly 7that is1 without a reducing valve7 on pressures up to #bjj pounds per square inch with steam superheated to #aej degrees ,fahrenheit4 ,ques4 ,how are the sizes and number of generator determined8 ,ans4 ,the sizes and number of generator to be installed should be such as to permit the engines operating them being worked at nearly full load1 because the efficiencies of the latter machines decrease rapidly when carrying less than this amount4 ,ques4 ,what is understood by regulation8 ,ans4 ,the accuracy and reliability with which the pressure or current developed in a machine may be controlled4 ,it is generally possible if purchasing of a reputable concern1 to obtain access to record sheets on which may be found results of tests conducted on the generator in question1 and as these are really the only means of ascertaining the values of efficiency and regulation1 the purchaser has a right to inspect them4 ,if1 for some reason or other1 he has not been afforded this privilege1 he should order the machine installed in the station on approval1 and test its efficiency and regulation before making the purchase4 ,illustration3 ,,fig4 #b1gif4--;,cross section of electrical station showing small traveling crane4 ,installation4--,the installation of machines and apparatus in an electrical station is a task which increases in difficulty with the size of the plant4 ,when the parts are small and comparatively light they may readily be placed in position1 either by hand1 by erecting temporary supports which may be moved from place to place as desired1 or by rolling the parts along on the floor upon pieces of iron pipe4 ,if1 however1 the parts be large and heavy1 a traveling crane such as shown in fig4 #b1gig1 becomes necessary4 ,ques4 ,what precaution should be taken in moving the parts of machines8 ,ans4 ,care should be taken not to injure the bearings and shafts1 the joints in magnetic circuits such as those between frame and pole pieces1 and the windings on the field and armature4 ,illustration3 ,,fig4 #b1gig4--;,cross section of electrical station showing a traveling crane for the installation or removal of large and heavy machine parts4 ,a traveling crane consists of an iron beam which1 being supplied with wheels at the ends1 can be made to move either mechanically or electrically upon a track running the entire length of the station4 ,this track is not supported by the walls of the building1 but rests upon beams specially provided for the purpose4 ,in addition to the horizontal motion thus obtained1 another horizontal motion at right angles to the former is afforded by means of the carriage which1 being also mounted on wheels1 runs upon a track on the top of the beam4 ,electrical power is generally used to move the carriage and also the revolving drums contained thereon1 the latter of which give a vertical motion to the main hoist or the auxiliary hoist1 these hoists being used respectively for raising or lowering heavy or light loads4 ,in the larger sizes of electric traveling crane1 a cage is attached to the beam for the operator1 who1 by means of three controllers mounted in the cage1 can move a load on either the main or auxiliary hoist in any direction4 ,the insulations of the windings are perhaps the most vital parts of a generator1 and the most readily injured4 ,the prick of a pin or tack1 a bruise1 or a bending of the wires by resting their weight upon them or by their coming in contact with some hard substance1 will often render a field coil or an armature useless4 ,owing to its costly construction1 it is advisable when transporting armatures by means of cranes to use a wooden spreader1 as shown in fig4 #b1gih to prevent the supporting rope bruising the winding4 ,illustration3 ,,fig4 #b1gih4--,view of armature in transit showing use of a wooden spreader as a protection4 ,if a chain be used in place of the rope1 a padding of cloth should be placed around the armature shaft and special care taken that the chain does not scratch the commutator4 ,ques4 ,if an armature cannot be placed at once in its final position what should be done8 ,ans4 ,it may be laid temporarily upon the floor1 if a sheet of cardboard or cloth be placed underneath the armature as a protection for the windings2 in case the armature is not to be used for some time1 it is better practice to place it in a horizontal position on two wooden supports near the shaft ends4 ,ques4 ,what kind of base should be used with a belt driven generator or motor8 ,ans4 ,the base should be provided with ,v ways and adjusting screws for moving the machine horizontally to take up slack in the belt1 as shown in fig4 #b1gii4 ,owing to the normal tension on the belt1 there is a moment exerted equal in amount to the distance from the center of gravity of the machine to the center of the belt1 multiplied by the effective pull on the belt4 ,this force tends to turn the machine about its center of gravity4 ,by placing the screws as shown1 any turning moment1 as just mentioned1 is prevented4 ,illustration3 ,,fig4 #b1gii4--,plan of belt drive machine showing ,v ways and adjusting screws for moving the machine forward from the engine or counter shaft to take up slack in the belt4 ,ques4 ,how should a machine be assembled8 ,ans4 ,the assembling should progress by the aid of a blue print1 or by the information obtained from a photograph of the complete machine as it appears when ready for service4 ,each part should be perfectly clean when placed in position1 especially those parts between which there is friction when the machine is in operation1 or across which pass lines of magnetic force2 in both cases the surfaces in contact must be true and slightly oiled before placing in position4 ,contact surfaces forming part of electrical circuits must also be clean and tightly screwed together4 ,an important point to bear in mind when assembling a machine is1 to so place the parts that it will not be necessary to remove any one of them in order to get some other part in its proper position4 ,by remembering this simple rule much time will be saved1 and in the majority of instances the parts will finally be better fitted together than if the task has to be repeated a number of times4 ,when there are two or more parts of the machine similarly shaped1 it is often difficult to properly locate them1 but in such cases notice should be taken of the factory marks usually stamped upon such pieces and their proper places determined from the instructions sent with the machine4 ,illustration3 ,,figs4 #b1hjj to #b1hjb4--,starrett's improved speed indicator4 ,in construction1 the working parts are enclosed like a watch4 ,the graduations show every revolution1 and with two rows of figures read both right and left as the shaft may run4 ,while looking at the watch1 each hundred revolutions may be counted by allowing the oval headed pin on the revolving disc to pass under the thumb as the instrument is pressed to its work4 ,a late improvement in this indicator consists in the rotating disc1 which1 being carried by friction may be moved to the starting point where the raised knobs coincide4 ,when the spindle is placed in connection with the revolving shaft1 pressing the raised knob with the thumb will prevent the disc rotating1 while the hand of the watch gets to the right position to take the time4 ,by releasing the pressure the disc is liberated for counting the revolutions of the shaft when every #ajj may be noted by feeling the knob pass under the thumb lightly pressed against it1 thus relieving the eye1 which has only to look on the watch to note the time4 ,ques4 ,what should be noted with respect to speed of generator8 ,ans4 ,each generator is designed to be run at a certain speed in order to develop the voltage at which the machine is rated4 ,the speed1 in revolutions per minute1 the pressure in volts1 and the capacity or output in watts 7volts amperes7 or in kilowatts 7thousands of watts7 are generally stamped on a nameplate screwed to the machine4 ,this requirement frequently requires calculations to be made by the erectors to determine the proper size pulleys to employ to obtain the desired speed4 ,illustration3 ,,fig4 #b1hjc4--;,home made belt clamp4 ,it is made with four pieces of oak of ample size to firmly grip the belt ends where the bolts are tightened4 ,the figure shows the clamp complete and in position on the belt and clearly illustrates the details of construction4 ,in making the long bolts the thread should be cut about three-quarter length of bolt and deep enough so that the nuts will easily screw on4 ,example4--,what diameter of engine pulley is required to run a dynamo at a speed of #a1dej revolutions per minute the dynamo pulley being #aj inches in diameter and the speed of engine1 #bge revolutions per minute8 ,the diameter of pulley required on engine is #aj 7#a1dej #bge7 #ec inches1 nearly4 ,rule4--,to find the diameter of the driving pulley1 multiply the speed of the driven pulley by its diameter1 divide the product by the speed of the driver and the answer will be the size of the driver required4 ,example4--,if the speed of an engine be #cbe revolutions per minute1 diameter of engine pulley #db inches1 and the speed of the dynamo #a1djj revolutions per minute1 how large a pulley is required on dynamo8 ,the size of the dynamo pulley is #db 7#cbe #a1djj7 #i inches4 ,rule4--,to find the size of dynamo pulley1 multiply the speed of engine by the diameter of engine wheel and divide the product by the speed of the dynamo4 ,illustration3 ,,figs4 #b1hjd and #b1hje4--;,a good method of lacing a belt4 ,the view at the left shows outer side of belt1 and at the right1 inner or pulley side4 ,example4--,if a steam engine1 running #cjj revolutions per minute1 have a belt wheel #dh inches in diameter1 and be belted to a dynamo having a pulley #ab inches in diameter1 how many revolutions per minute will the dynamo make8 ,the speed of dynamo will be #cjj 7#dh #ab7 #a1bjj rev4 per min4 ,rule4--,when the speed of the driving pulley and its diameter are known1 and the diameter of the driven pulley is known1 the speed of the driven pulley is found by multiplying the speed of the driver by its diameter in inches and dividing the product by the diameter of the driven pulley4 ,example4--,what will be the required speed of an engine having a belt wheel #df inches in diameter to run a dynamo #a1ejj revolutions per minute1 the dynamo pulley being #aa inches in diameter8 ,the speed of the engine is #a1ejj 7#aa #df7 #cei rev4 per min4 nearly4 ,illustration3 ,,fig4 #b1hjf4--,wiring diagram and directions for operating ,holzer-,cabot single phase self-starting motor4 ,location3 ,the motor should be placed in as clear and dry a location as possible1 away from acid or other fumes which would attack the metal parts or insulation1 and should be located where it is easily accessible for cleaning and oiling4 ,erection3 ,the motor should be set so that the shaft is level and parallel with the shaft it is to drive so that the belt will run in the middle of the pulleys4 ,do not use a belt which is too heavy or too tight for the work it has to do1 as it will materially reduce the output of the motor4 ,the belt should be from one-half to one inch narrower than the pulley4 ,rotation3 ,in order to reverse the direction of rotation1 interchange leads ,a and ,b4 ,suspended ,motors3 ,motors with ring oil bearings may be used on the wall or ceiling by taking off end caps and revolving #ij or #ahj degrees until the oil wells come directly below the bearings4 ,starting3 ,motors are provided with link across two terminals on the upper right hand bracket at the front of the motor and with this connection should start considerable overloads4 ,if the starting current be too great with this connection1 it may be reduced by removing the link4 ,temperatures3 ,at full load the motor will feel hot to the hand1 but this is far below the danger point4 ,if too hot for touch1 measure temperature with a thermometer by placing bulb against field winding for #aj minutes1 covering thermometer with cloth or waste4 ,the temperature should not exceed #ge degrees ,fahr4 above the surrounding air4 ,oiling3 ,fill the oil wells to the overflow before starting and keep them full4 ,see that the oil rings turn freely with shaft4 ,care3 ,the motor must be kept clean4 ,smooth collector rings with sandpaper and see that the brushes make good contact4 ,when brushes become worn they may be reversed4 ,when fitting new brushes or changing them always sandpaper them down until they make good contact with the collector rings1 by passing a strip of sandpaper beneath the brush4 ,rule4--,to find the speed of engine when diameter of both pulleys1 and speed of dynamo are given1 multiply the dynamo speed by the diameter of its pulley and divide by the diameter of engine pulley4 ,ques4 ,how are the diameters and speeds of gear wheels figured8 ,ans4 ,the same as belted wheels1 using either the pitch circle diameters or number of teeth in each gear wheel4 ,illustration3 ,,figs4 #b1hjg to #b1hji4--,wiring diagrams and directions for operating ,holzer-,cabot slow speed alternating current motors4 ,erecting3 ,in installing the motor1 be sure the transformer and wiring to the motor are large enough to permit the proper voltage at the terminals4 ,if too small1 the voltage will drop and reduce the capacity of the motor4 ,oiling3 ,maintain oil in wells to the overflow4 ,starting3 ,single phase motors are started by first throwing the starting switch down into the starting position1 and when the motor is up to speed1 throwing it up into the running position4 ,do not hold the switch in starting position over #aj seconds4 ,starter for single phase motors above ,h4,p4 are arranged with an adjusting link at the bottom of the panel4 ,the link is shown in the position of least starting torque and current4 ,connect from ,w to #b or ,w to #c for starting heavier loads4 ,two or three phase motors are started simply by closing the switch4 ,these motors start full load without starters4 ,the motor should start promptly on closing the switch4 ,it should be started the first time without being coupled to the line shaft4 ,if the motor start free1 but will not start loaded1 it shows either that the load upon the motor is too great1 the line voltage too low1 or the frequency too high4 ,the voltage and frequency with the motor running should be within #e of the name plate rating and the voltage with #aj to #ae while starting4 ,if the motor do not start free1 either it is getting no current or something is wrong with the motor4 ,in either case an electrician should be consulted4 ,solution3 ,to reverse the direction of rotation interchange the leads marked ,,xx in the diagrams4 ,temperature3 ,at full load the motor should not heat over #ge degrees ,fahr4 above the temperature of the surrounding air2 if run in a small enclosed space with no ventilation1 the temperature will be somewhat higher4 ,ques4 ,what should be noted with respect to generator pulleys8 ,ans4 ,a pulley of certain size is usually supplied with each generator by its manufacturer1 and it is not generally advisable to depart much from the dimensions of this pulley4 ,accordingly1 the solution of the pulley problem usually consists in finding the necessary diameter of the driving pulley relative to that of the pulley on the generator in order to furnish the required speed4 ,ques4 ,what is the chief objection to belt drive8 ,ans4 ,the large amount of floor space required4 ,illustration3 ,,fig4 #b1haj4--,tandem drive for economizing floor space with belt transmission4 ,belts of different lengths are used1 as shown1 each of which passes over the driving wheel d of the engine1 and then over the pulley wheel of one of the generators4 ,in such an arrangement the belts would be run lengthwise through the room in which the machines are placed1 and it is obvious that since the width of the room would be governed by the width of the machines thus installed1 this method is a very efficient one for accomplishing the end in view4 ,ques4 ,how may the amount of space that would ordinarily be required for belt drive1 be reduced8 ,ans4 ,by driving machines in tandem as in fig4 #b1haj1 or by the double pulley drive as in fig4 #b1haa4 ,ques4 ,what is the objection to the tandem method8 ,ans4 ,the most economical distance between centers cannot be employed for all machines4 ,ques4 ,what is the objectionable tendency in resorting to floor economy methods with belt transmission8 ,ans4 ,the tendency to place the machines too closely together4 ,this is poor economy as it makes the cleaning of the machines a difficult and dangerous task2 it is therefore advisable to allow sufficient room for this purpose regardless of the method of belting employed4 ,illustration3 ,,fig4 #b1haa4--;,double pulley drive for economizing floor space with belt transmission4 ,where a center crank engine is used both pulleys may be employed by belting a machine to each as shown4 ,although considerable floor space would be saved by the use of this scheme if the generators thus belted were placed at ,m and ,g yet still more floor space would be saved by having them occupy the positions indicated at ,m and ,s4 ,ques4 ,what is the approved location for an alternator exciter8 ,ans4 ,to economize floor space the exciter may be placed between the alternator and engine at ,s in fig4 #b1haa4 ,belts4--,in the selection of a belt1 the quality of the leather should be first under consideration4 ,the leather must be firm1 yet pliable1 free from wrinkles on the grain or hair side1 and of an even thickness throughout4 ,illustration3 ,,fig4 #b1hab4--,separately excited belt driven alternator showing approved location of exciter4 ,in an electrical station where alternating current is generated1 the alternators for producing the current generally require separate excitation for their field windings2 that is1 it is usually necessary to install in conjunction with an alternator a small dynamo for supplying current to the alternator field4 ,the exciter is a comparatively small machine2 in fact1 it requires only about #a per cent4 of the capacity of the alternator which it excites1 and so being small is often belted to an auxiliary pulley mounted on the alternator shaft4 ,considerable floor space would be occupied by an installation of this nature if the exciter be placed at ,m1 and belted to the alternator as indicated by the dotted lines4 ,by locating the exciter at ,s1 between the alternator and the engine1 much floor space will be saved and the general appearance of the installation improved4 ,if the belt be well selected and properly handled1 it should do service for twenty years1 and even then if the worn part be cut off1 the remaining portion may be remade and used again as a narrower and shorter belt4 ,besides leather belts1 there are those made of rubber which withstand moisture much better than leather belts1 and which also possess an excellent grip on the pulley2 they are1 however1 more costly and much less durable under normal conditions4 ,in addition to leather and rubber belts1 there are belts composed of cotton1 of a combination of cotton and leather1 and of rope4 ,the leather belt1 however1 is the standard and is to be recommended4 ,equally important with the quality of a belt is its size in order to transmit the necessary power4 ,the average strain under which leather will break has been found by many experiments to be #c1bjj pounds per square inch of cross section4 ,a good quality of leather will sustain a somewhat greater strain4 ,in use on the pulleys1 belts should not be subjected to a greater strain than one eleventh their tensile strength1 or about #bij pounds to the square inch or cross section4 ,this will be about #ee pounds average strain for every inch in width of single belt three-sixteenths inch thick4 ,the strain allowed for all widths of belting--single1 light double1 and heavy double--is in direct proportion to the thickness of the belt4 ,ques4 ,how much horse power will a belt transmit8 ,ans4 ,the capacity of a belt depends on1 its width1 speed1 and thickness4 ,a single belt one inch wide and travelling #a1jjj feet per minute will transmit one horse power2 a double belt under the same conditions1 will transmit two horse power4 ,illustration3 ,,fig4 #b1hac4--,one horse power transmitted by belt to illustrate the rule given above4 ,a pulley is driven by a belt by means of the friction between the surfaces in contact4 ,let ,t be the tension on the driving side of the belt1 and ,t'1 the tension on the loose side2 then the driving force ,t-,t'4 ,in the figure ,t is taken at #cd lbs4 and ,t' at #a lb42 hence driving force #cd-a #cc lbs4 ,since the belt is travelling at a velocity of #a1jjj feet per minute the power transmitted #cc lbs4 #a1jjj ft4 #cc1jjj ft4 lbs4 per minute #a horse power4 ,this corresponds to a working pull of #cc and #ff lbs4 per inch of width respectively4 ,example4--,what width double belt will be required to transmit #ej horse power travelling at a speed of #c1jjj feet per minute8 ,the horse power transmitted by each inch width of double belt travelling at the stated speed is #c1jjj #a ----- #b #f1 #a1jjj hence the width of belt required to transmit #ej horse power is #ej #f #h4cc1 say #h inches4 ,ques4 ,at what velocity should a belt be run8 ,ans4 ,at from #c1jjj to #e1jjj feet per minute4 ,ques4 ,how may the greatest amount of power transmitting capacity be obtained from belts8 ,ans4 ,by covering the pulleys with leather4 ,ques4 ,how should belts be run8 ,ans4 ,with the tight side underneath as in fig4 #b1had4 ,illustration3 ,,figs4 #b1had and #b1hae4--,right and wrong way to run a belt4 ,the tight side should be underneath so as to increase the arc of contact and consequently the adhesion1 that is to say1 a better grip1 is in this way obtained4 ,ques4 ,what is a good indication of the capacity of a belt in operation8 ,ans4 ,its appearance after a few days' run4 ,if the side of the belt coming in contact with the pulley assume a mottled appearance1 it is an indication that the capacity of the belt is considerably in excess of the power which it is transmitting1 inasmuch as the spotted portions of the belt do not touch the pulley2 and in consequence of this there is liable to be more or less slipping4 ,small quantities of a mixture of tallow and fish oil which have previously been melted together in the proportion of two of the former to one of the latter1 will1 if applied to the belt at frequent intervals1 do much toward softening it1 and thus by permitting its entire surface to come in contact with the pulley1 prevent any tendency toward slipping4 ,the best results are obtained when the smooth side of the belt is used next to the pulley1 since tests conducted in the past prove that more power is thus transmitted1 and that the belt lasts longer when used in this way4 ,illustration3 ,,fig4 #b1haf4--,the ,hill friction clutch pulley for power control4 ,the clutch mechanism will start a load equivalent to the double belt capacity of the pulley to which the clutch is attached4 ,ques4 ,what is the comparison between the so called endless belts and laced belts8 ,ans4 ,with an endless belt there is no uneven or noisy action as with laced belts1 when the laced joint passes over the pulleys1 and the former is free from the liability of breakage at the joint4 ,ques4 ,how should a belt be placed on the pulleys8 ,ans4 ,the belt should first be placed on the pulley at rest1 and then run on the other pulley while the latter is in motion4 ,the best results are obtained1 and the strain on the belt is less1 when the speed at which the moving pulley revolves is comparatively low4 ,with heavy belts1 particular care should be taken to prevent any portion of the clothing being caught either by the moving belt or pulleys1 as many serious accidents have resulted in the past from carelessness in regard to this important detail4 ,the person handling the belt should1 therefore1 be sure of a firm footing1 and when it is impossible to secure this1 it is advisable to stop the engine and fit the belt around the engine pulley as well as possible by the aid of a rope looped around the belt4 ,illustration3 ,,fig4 #b1hag--,sectional view of ,hill clutch mechanism4 ,in every case the mechanism hub ,a1 and in a clutch coupling the ring ,w1 is permanently and rigidly secured to the shaft and need not be disturbed when removing the wearing parts4 ,when erected1 the adjustment should be verified1 and always with the clutch and ring engaged and at rest4 ,if the jaws do not press equally on the ring1 or if the pressure required on the cone be abnormal1 loosen the upper adjusting nuts ,t on eye bolts and set up the lower adjusting nuts ,t until each set of jaws is under the same pressure4 ,should the clutch then slip when started it is evident that the jaw pressure is insufficient and a further adjustment will be necessary4 ,all clutches are equipped throughout with split lock washers4 ,vibration or shock will not loosen the nuts if properly set up4 ,the jaws can be removed parallel to the shaft as follows3 ,remove the gibs ,v1 and withdraw the jaw pins ,p1 then pull out the levers ,d4 ,do not disturb the eye bolt nuts ,t and ,t4 ,the outside jaws ,b can now be taken out4 ,remove the bolt nuts ,i allowing the fulcrum plates ,r to be taken off4 ,on the separable hub pattern the clamping bolts must be taken out before fulcrum plate is removed4 ,the inside jaws ,c may now be withdrawn4 ,always set the clutch operating lever in the position as shown in fig4 #b1haf to avoid interference with mechanism parts4 ,oil the moving parts of the clutch4 ,keep it clean4 ,examine at regular intervals4 ,ques4 ,under what conditions does a belt drive give the best results8 ,ans4 ,when the two pulleys are at the same level4 ,if the belt must occupy an inclined position it should not form a greater angle than #de degrees with the horizontal4 ,ques4 ,what is a characteristic feature in the operation of belts1 and why8 ,ans4 ,belts in motion will always run to the highest side of a pulley2 this is due partially to the greater speed in feet per minute developed at that point owing to the greater circumference of the pulley1 and also to the effects of centrifugal force4 ,if1 therefore1 the highest sides of both pulleys be in line with each other1 and the shafts of the respective pulleys be parallel to each other1 there will be no tendency for the belt to leave the pulleys when once in its proper position4 ,in order that these conditions be maintained1 the belt should be no more than tight enough to prevent slipping1 and the distance between the centers of the pulleys should be approximately #c4e times the diameter of the larger one4 ,illustration3 ,,fig4 #b1hah4--;,hill clutch mechanism ,smith type4 ,the friction surfaces are wood to iron1 the wood shoes being made from maple4 ,all parts of the toggle gear are of steel and forgings with the exception of the connection lever which is of cast iron4 ,ques4 ,what minor appurtenances should be provided in a station8 ,ans4 ,apparatus should be installed as a prevention against accidents1 such as fire1 and protection of attendants from danger4 ,in every electrical station there should be a pump1 pipes and hose2 the pump may be either directly connected to a small electric motor or belted to a countershaft1 while the pipes and hose should be so placed that no water can accidentally reach the generators and electrical circuits4 ,a number of fire bucket filled with water should be placed on brackets around the station1 and with these there should be an equal number of bucket containing dry sand1 the water being used for extinguishing fire occurring at a distance from the machines and conductors1 and the sand for extinguishing fire in current carrying circuits where water would cause more harm than benefit4 ,to prevent the sand being blown about the station1 each sand bucket1 when not in use1 should be provided with a cover4 ,neat cans and boxes should be mounted in convenient places for greasy rags1 waste1 nuts1 screws1 etc41 which are used continually and which therefore cannot be kept in the storeroom4 ,while it is important to guard against fire in the station1 it is equally necessary to provide for personal safety4 ,all passages and dark pits should therefore be thoroughly lighted both day and night1 and obstacles of any nature that are not absolutely necessary in the operation of the station1 should be removed4 ,moving belts1 and especially those passing through the floor1 should be enclosed in iron railings4 ,if high voltages be generated1 it is well to place a railing about the switchboard to prevent accidental contact with current carrying circuits1 and in such cases it is also advisable to construct an insulated platform on the floor in front of the switchboard4 ,illustration3 ,,fig4 #b1hai4--,method of joining adjacent switchboard panels4 ,switchboards4--,the plan of switchboard wiring for alternating current work depends upon the system in use and this latter may be either of the single phase1 two phase1 three phase1 or monocyclic types4 ,the general principles in all these cases1 however1 are practically identical4 ,fig4 #b1hbj shows the switchboard wiring for a single phase alternator4 ,as an aid in reading the diagram1 the conductors carrying alternating current are represented by solid lines1 and those carrying direct current1 by dotted lines4 ,illustration3 ,,fig4 #b1hbj4--,switchboard wiring for a single phase separately excited alternator4 ,the direct current circuits are represented by dotted lines1 and the alternating current circuit1 by solid lines4 ,the exciter shown at the right is a shunt wound machine4 ,by means of the exciter rheostat1 the voltage for exciting the field winding of the alternator is varied2 this1 in turn1 varies the voltage developed in the alternator since the main leads of the exciter are connected through a double pole switch ,g to the field winding of the alternator4 ,illustration3 ,,figs4 #b1hba to #b1hbe4--;,general ,electric diagrams of connections4 ,a1 ammeter2 ,c4,b1 circuit breaker2 ,c4,p1 candle power2 ,c4,t1 current transformer2 ,d4,r1 discharge resistance2 ,f1 fuse2 ,f4,s1 field switch2 ,l1 lamp2 ,o4,c1 overload coil2 ,p4,p1 pressure plug2 ,p4,r1 pressure receptacle2 ,r4,c1 reactance2 rheo1 rheostat2 ,r4,p1 synchronizing plug1 running2 ,r4,s1 resistance2 ,s1 switch2 ,s4,i1 synchronism indicator2 ,s4,p1 synchronizing plug1 starting2 ,s4,r1 synchronizing receptacle2 ,v1 voltmeter4 ,a rheostat is also introduced in the alternator field winding circuit to adjust the alternator pressure4 ,it may seem unnecessary to employ a rheostat in each of two separate field circuits to regulate the voltage of the alternator1 but these rheostats are not both used to produce the same result4 ,when a considerable variation of pressure is required1 the exciter rheostat is manipulated1 whereas for a fine adjustment of voltage the alternator rheostat is preferably employed4 ,sometimes a direct current ammeter is introduced in the alternator's field circuit to aid in the adjustment4 ,the main circuit of alternator after being protected on both sides by fuses1 runs to the double pole switch ,k4 ,these fuses serve as a protection to the alternator in case of a short circuit at the main switch4 ,it will be noticed the fuses are of the single pole type and are mounted a considerable distance apart2 this is to prevent any liability of a short circuit between them in case of action4 ,enclosed fuses are now used entirely for such work1 since in these there is no danger of heated metal being thrown about and causing damage when the fuse wire is melted4 ,enclosed fuses are also more readily and quickly replaced than open fuses1 the containing tube of each being easy to adjust in circuit1 and when the fuse wire within is once melted the tube is discarded for a new one4 ,the main circuit after passing through the main switch is further protected on both sides by circuit breakers4 ,leaving these protective devices1 the left hand side of the circuit includes the alternating current ammeter1 and then connects with one of the bus bars4 ,the right hand side of the circuit runs from the circuit breaker to the other bus bar4 ,as many feeder circuits may be connected to the bus bars and supplied with current by the alternator as the capacity of this machine will permit4 ,if1 however1 there be more than one feeder circuit1 each must be wired through a double pole switch4 ,in alternating current work the pressures dealt with are much greater than those in direct current installations1 so that proportionate care must be taken in the wiring to remove all possibility of grounds4 ,to locate such troubles1 however1 should they occur1 a ground detector is provided4 ,for this class of work the ground detector must be an instrument especially designed for high pressure circuits4 ,two of its terminals should be connected to the line wires and the third1 to ground2 in case of a leak on the line1 a current will then flow through the detector and by the position of the pointer the location and seriousness of the leak may be judged4 ,a step down transformer is also rendered necessary for the voltmeter and the pilot lamps1 owing to the high voltage in use4 ,the primary winding of the transformer is connected across the main circuit of the alternator4 ,this connection should never be made so that it will be cut out of circuit when the main switch is open1 for it is always advisable to consult the voltmeter before throwing on the load by closing this switch4 ,illustration3 ,,figs4 #b1hbf to #b1hbi4--;,general ,electric diagrams of connections4 ,a1 ammeter2 ,c4,b1 circuit breaker2 ,c4,p1 candle power2 ,c4,t1 current transformer2 ,d4,r1 discharge resistance2 ,f1 fuse2 ,f4,s1 field switch2 ,l1 lamp2 ,o4,c1 overload coil2 ,p4,p1 pressure plug2 ,p4,r1 pressure receptacle2 ,r4,c1 reactance2 rheo1 rheostat2 ,r4,p1 synchronizing plug1 running2 ,r4,s1 resistance2 ,s1 switch2 ,s4,i1 synchronous indicator3 ,s4,p1 synchronizing plug1 starting2 ,s4,r1 synchronizing receptacle3 ,v1 voltmeter4 ,ques4 ,how does the switchboard wiring for a two phase system differ from the single phase arrangement shown in fig4 #b1hbj8 ,ans4 ,it is practically the same1 except for the introduction of an extra ammeter and a compensator in each of the outside wires1 and in the use of a four pole switch in place of the two pole main switch4 ,the ammeters1 of course1 are for measuring the alternating currents in each of the two phases or legs of the system1 and the compensators are two transformers with their primary coils in series with the outside wires and their secondary coils in series with each other across the outside wires4 ,the transformers thus connected are known as compensators or pressure regulators1 and as such compensate for the drop in pressure on either side of the system4 ,ques4 ,how is the four pole main switch wired8 ,ans4 ,its two central terminals which connect directly with the line wires1 are joined together by a conductor1 and from this point one wire is led off4 ,this wire1 together with the two outside wires1 form the feeders of the system4 ,ques4 ,how many voltmeters are required for the two phase system8 ,ans4 ,one voltmeter is sufficient on the board if a proper switching device be employed to shift its connections across either of the two circuits2 otherwise1 two voltmeters will be necessary1 one bridged across each of these respective circuits4 ,the same reasoning holds true in regard to ground detectors1 so that one or two of these will be required1 depending upon the aforementioned conditions4 ,ques4 ,what are the essential points of difference between the single phase switchboard wiring as shown in fig4 #b1hbj1 and that required for a three wire three phase system8 ,ans4 ,the three phase system requires the use of a three pole switch in place of the two pole switch2 the insertion of an ammeter1 a circuit breaker1 and a compensator in each of the three wires of the system2 the presence of two ground detectors instead of one1 and the addition of a voltmeter switch if but one voltmeter be provided1 or else the installation of two voltmeters1 connected the one between the middle wire and outer right hand wire1 and the other between the middle wire and outer left hand wire4 ,illustration3 ,,fig4 #b1hcj4--;,diagram of switchboard connections for ,general ,electric automatic voltage regulator with two exciters and two alternators4 ,ques4 ,mention a few points relating to lightning arresters4 ,ans4 ,in most cases where direct current is used they are mounted on the walls of the station near the place at which the line wires enter4 ,if they be mounted outside the station at this point1 special precautions should be taken to keep them free from moisture by enclosing them in iron cases1 but no matter where they are located it is necessary that they be dry in order to work properly4 ,illustration3 ,,figs4 #b1hca and #b1hcb4--;,garton-,daniels alternating current lightning arrester2 diagram showing connections4 ,a lightning discharge takes the path indicated by the dotted line1 across the upper air gap ,a1 through resistance rod ,b1 ,c1 ,d1 across copper strip ,r on the base1 thence flowing to ground through the movable plunger ,m1 lower on gap ,n1 and ground binding post ,l4 ,the discharge path is practically straight1 contains an air gap1 distance of but #c_/cb inch1 a series resistance averaging but #bbe ohms4 ,the lightning discharge does not flow through the flexible lead connecting band ,d on the lower end of the resistance rod with the top of the movable plunger4 ,these two points are electrically connected by the heavy copper strip ,r1 and lightning discharges generally1 if not always1 take the path across this copper strip in preference to flowing through the inductance of the one turn of flexible cable4 ,when a discharge occurs from line to ground through any lightning arrester1 the air gaps arc over1 and so there is offered a path from line to ground for the line current4 ,this flow of line current following the lightning discharge to ground may vary anywhere from a small capacity current where the arrester is installed on an ungrounded circuit1 a moderately heavy flow on a partially grounded circuit1 to a very heavy flow on a grounded circuit--either a circuit operated as a dead grounded circuit1 or a circuit which has become accidentally grounded during a storm4 ,the path taken by this flow of line current from line to ground may be traced by following the path shown by the dashed line4 ,it1 as seen1 crosses upper air gap ,a1 flows through section ,b of the resistance rod to band ,c4 ,leaving band ,c it flows through the magnet winding ,h1 thence to band ,d on the resistance rod1 through flexible lead to upper end of movable plunger1 through movable plunger1 across lower air gap ,n1 to ground binding post ,l1 thence to ground4 ,the function of the short length of resistance rod ,,cd is as follows3 ,it has an ohmic resistance of about #cj ohms but is non-inductive4 ,magnet winding ,h1 connected to bands ,c and ,d on the ends of this short length of rod has an ohmic resistance of #c ohms1 but is highly inductive4 ,lightning discharges being of high frequency take the higher resistance but non-inductive path ,,cd in their passage from line to ground4 ,the flow of normal current from line to ground being of a very low frequency1 #be or #fj cycles in ordinary alternating current circuits1 zero in direct current circuits--takes the low resistance path through coil ,h in its path to ground4 ,section ,,cd of the rod is used therefore simply to shunt the inductance of winding ,h to high frequency lightning discharges1 leaving the lightning discharge path in the arrester a non-inductive highly efficient path4 ,in all ,garton-,daniels ,a4 ,c4 lightning arresters operating on non-grounded or partially grounded circuits1 the action of the air gaps and series resistance are together sufficient to extinguish the flow of normal current to ground at the zero point of the generator voltage wave4 ,if1 however1 as frequently happens1 the line grounds accidentally during a storm1 then the arrester does not have to depend for its proper operation on the arc extinguishing properties of the air gaps and resistance1 but the heavier flow of line current through the arrester energizes the movable plunger1 which raises upward in the coil1 opening the circuit between the discharge point ,m and the lower end of the plunger4 ,to limit the flow of line current to ground the resistance rod ,b is provided1 there being approximately #bbe ohms between the discharge point ,a and clamp ,c in the #b1ejj volt arrester4 ,this feature is particularly effective where the circuit is temporarily or accidentally grounded4 ,the series resistance prevents a heavy short circuit through the arrester and limits the current to a value that is readily broken by the cut out and is not enough to impede the passage of the discharge4 ,illustration3 ,,fig4 #b1hcc4--;,diagram of switchboard connections for ,general ,electric automatic voltage regulator with three exciters and three alternators4 ,if possible1 one place should be set aside for them and a marble or slate panel provided on which they may be mounted4 ,wooden supports are undesirable for lightning arresters on account of the fire risk incurred2 this1 however1 may be reduced to a minimum by employing skeleton boards and using sheets of asbestos between the arresters and the wood4 ,in parts of the country where lightning is of common occurrence and where overhead circuits are installed which carry high pressures1 heavy currents1 and extend over considerable territory1 it is advisable to have the station well equipped with lightning arresters of the most improved types4 ,in each side of the main circuit1 between the lightning arrester connections and the switchboard apparatus there should be connected a choke coil or else each of the main conductors at this point should be tightly coiled up part of its length to answer the same purpose4 ,a quick and effective way of coiling up a wire consists in wrapping around a cylindrical piece of iron or wood that part of the conductor in which it is desired to have the coils1 the desired number of times1 and then withdrawing the cylindrical piece4 ,the coils1 each of which may contain #ej or #bjj turns1 thus inserted in the main circuit introduce a high resistance or reluctance to a lightning current1 and thus prevent it passing to the generator2 there will1 however1 be an easy path to earth afforded it through the lightning arrester1 and so no damage will be done4 ,coils of the nature just mentioned may advantageously be introduced between the generator and switchboard to take up the reactive current developed upon the opening of the circuit1 and in the case of suspended conductors1 the coils may be used to take up the slack by the spring-like effect produced by them4 ,the safety of the operator should be especially considered in the design of high pressure alternating current switchboards4 ,such protection may be secured by screening all the exposed terminals1 or preferably by mounting all the switch mechanism on the back of the board with simply the switch handle projecting through to the front2 by pushing or pulling the switch handle1 the connections can thus be shifted either to one side of the system or to the other4 ,ques4 ,upon what does the work of assembling a switchboard depend8 ,ans4 ,it depends almost entirely upon the size of the plant1 varying from the simple task of mounting a single panel in the case of an isolated plant1 to the more difficult problem of supporting a large number of panels in a central station4 ,ques4 ,when the material chosen for a switchboard must be shipped a considerable distance1 what form of board should be used8 ,ans4 ,the board units or slabs should be of small dimensions1 to avoid the liability of breakage and expense of renewal when a unit becomes cracked or machine injured4 ,illustration3 ,,figs4 #b1hcd and #b1hce4--;,front and rear views showing ,general ,electric automatic voltage regulator mounted on switchboard panel4 ,ordinarily1 switchboards vary from five to eight feet in height and the widths of the panels vary from five to six feet4 ,in some boards the seams between the slabs run vertically1 and in others horizontally4 ,in order to render the assembling of the switchboard as simple as possible1 and its appearance when finished the most artistic1 these seams should run horizontally rather than vertically4 ,the edges of each of the slabs should also be chamfered so that there will be less danger of their breaking out when being mounted on the framework4 ,ques4 ,in assembling a switchboard1 how should the lower slabs be placed1 and why8 ,ans4 ,they should be suspended a little distance from the floor to prevent contact with any oil1 dirt1 water or rubbish that might be on the floor4 ,ques4 ,how are the slabs or panels supported8 ,ans4 ,they are carried on an iron or wooden framework with braces to give stability4 ,the braces should be securely fastened at one end to the wall of the station1 and at the other end to the framework of the board1 as shown in fig4 #b1hcf4 ,to fasten the switchboard end of the brace directly to the slate1 marble or other material composing the board is poor practice and should never be attempted4 ,if the station be constructed of iron1 these switchboard braces must be such that they will thoroughly insulate the board and its contents from the adjoining wall4 ,illustration3 ,,fig4 #b1hcf4--,method of supporting the framework of a switchboard4 ,ques4 ,what is the usual equipment of a switchboard8 ,ans4 ,it comprises switching devices1 current or pressure limiting devices1 indicating devices1 and fuses for protecting the apparatus and circuits4 ,illustration3 ,,fig4 #b1hcg4--;,diagram showing elementary connections of ,general ,electric automatic regulator for direct current4 ,it consists essentially of a main control magnet with two independent windings and a differentially wound relay magnet4 ,one winding1 known as the pressure winding1 of the main control magnet is connected across the dynamo terminals1 the other across a shunt in one of the load mains4 ,the latter is the compensating winding and it opposes the action of the pressure winding so that as the load increases1 a higher pressure at the dynamo is necessary to over compound for line drop4 ,in ordinary practice1 the voltage terminals are connected to the bus bars1 and the compensating shunt inserted in one of the principal feeders of the system4 ,in operation the shunt circuit across the dynamo field rheostat is first opened by means of a switch provided for that purpose on the base of the regulator and the rheostat turned to a point that will reduce the generator voltage #ce per cent below normal4 ,the main control magnet is at once weakened and allows the spring to pull out the movable core until the main contacts are closed4 ,this closes the second circuit of the differential relay1 thus neutralizing its windings4 ,the relay spring then lifts the armature and closes the relay contacts4 ,the switch in the shunt circuit across the dynamo field rheostat is now closed1 practically short circuiting the rheostat1 and the dynamo voltage at once rises4 ,as soon as it reaches the point for which the regulator has been adjusted1 the main control magnet is strengthened1 which causes the main contacts to open1 which in turn open the relay contacts across the rheostat4 ,the rheostat is now in the field circuit1 the voltage at once falls off1 the main contacts are closed1 and relay armature released1 and shunt circuit across the rheostat again completed4 ,the voltage then starts to rise and this cycle of operation is continued at a high rate of vibration1 maintaining not a constant but a steady voltage at the bus bars4 ,when neither the compensating winding nor pressure wires are used1 there will be no over compounding effect due to increase of load and a constant voltage will be maintained at the bus bars4 ,the compensating winding on the control magnet1 which opposes the pressure winding is connected across an adjustable shunt in the principal feeder circuit4 ,as the load increases the voltage drop across the shunt increases and the effect of the compensating winding becomes greater4 ,this will require a higher voltage on the pressure winding to open the main contacts and the regulator will therefore cause the dynamo to compensate for line drop1 maintaining at the bus bars a steady voltage without fluctuations1 which rises and falls with a load on the feeders1 giving a constant voltage at the lamps or center of distribution4 ,the compensating shunt may be adjusted so as to compensate for any desired line drop up to #ae per cent2 it is preferably placed in the principal lighting feeder1 but may be connected to the bus bars so that the total current will pass through it4 ,the latter method1 however1 is sometimes desirable1 as large fluctuating power loads on separate feeders might disturb the regulation of the lighting feeders4 ,adjustment is made by sliding the movable contact at the center of the shunt4 ,this contact may be clamped at any desired point and determines the pressure across the compensating winding of the regulator's main control magnet4 ,where pressure wires are run back to the central station from the center of distribution they may be connected directly to the pressure winding of the main control magnet1 and it is unnecessary to use the compensating shunt4 ,the pressure wires take the place of the leads from the control magnet to the bus bars and maintain a constant voltage at the center of distribution4 ,on some switchboards are also mounted small transformers for raising or lowering the voltages1 and lightning arresters as a protection from lightning4 ,in addition to the apparatus previously mentioned nearly all switchboards carry at or near their top two or more incandescent lamps provided with shades or reflectors1 for lighting the board4 ,ques4 ,what should be done before wiring a switchboard8 ,ans4 ,the electrical connections between the various apparatus mounted on the face or front of the board1 are made on the back of the board4 ,it is necessary that these connections be properly made else considerable electrical power will be wasted at this point4 ,the wiring on the back of the board should therefore be planned out on paper before commencing the work4 ,illustration3 ,,fig4 #b1hch4--;,diagram showing connections of ,general ,electric automatic voltage regulator for direct current as connected for maintaining balanced voltage on both sides of a three wire system using a balancer set4 ,in operation1 should the voltage on the upper bus bars become greater than that on the lower ones1 the middle and upper contacts on the regulator will close1 thus opening the relay contacts to the left and closing those to the right4 ,this inserts all the resistance in the field of balancer ,a1 and short circuits the resistance in the field of balancer ,b4 ,a will then be running as a motor1 and ,b as a dynamo1 thereby equalizing the two voltages until that on the lower bus bars becomes greater than that of the upper ones2 then the regulator contacts operate in the opposite direction and balancer ,a is run as a dynamo1 and balancer ,b as a motor4 ,this cycle of operation is repeated at the rate of from three to four hundred times per minute1 thus maintaining a balanced voltage on the system4 ,in laying out the plan of wiring care must be taken to allow sufficient contact surface at each connection2 there should be not less than one square inch of contact surface allowed for each #afj amperes of current transmitted4 ,illustration3 ,,fig4 #b1hci4--;,diagram of connections of ,general ,electric voltage regulators for one or more alternators using one exciter4 ,for the bus bars1 which1 by the way are always of copper1 one square inch per #a1jjj amperes is the usual allowance2 this is equal to #a1jjj circular mils of cross sectional area per ampere4 ,every effort should be made to give the bus bars the greatest amount of radiation consistent with other conditions1 in order that their resistances may not become excessive owing to the heat developed by the large currents they are forced to carry4 ,suppose1 for instance1 the number of amperes to be generated is such as to require bus bars having each a cross sectional area of one square inch4 ,if the end dimensions of these bars were each #a inch by #a inch1 there would be less radiating surface than if their dimensions were each #b inches by inch4 ,operation of ,alternators4--,the operation of an alternator when run singly differs but little from that for a dynamo4 ,as to the preliminaries1 the exciter must first be started4 ,this is done in the same way as for any shunt dynamo4 ,at first only a small current should be sent through the field winding of the alternator2 then1 if the exciter operates satisfactorily and the field magnetism of the operator show up well1 the load may gradually be thrown on until the normal current is carried1 the same method of procedure being followed as in the similar case of a dynamo4 ,illustration3 ,,figs4 #b1hdj and #b1hda4--;,general ,electric equalizer regulator designed to equalize the load on two machines1 and diagram of connections4 ,on loading an alternator1 a noticeable drop in voltage occurs across its terminals4 ,this drop in voltage is caused in part by the demagnetization of the field magnets due to the armature current1 and so depends in a measure upon the position and form of the pole pieces as well as upon those of the teeth in the armature core4 ,the resistance of the armature winding also causes a drop in voltage under an increase of load4 ,another cause which may be mentioned is the inductance of the armature winding1 which is in turn due to the positions of the armature coils with respect to each other and also with respect to the field magnets4 ,illustration3 ,,fig4 #b1hdb4--;,connection of ,general ,electric equalizing regulator for equalizing loads on an engine driven dynamo and rotary converter running in parallel4 ,should the load on the dynamo become greater than that on the rotary converter1 the middle and upper contacts on the regulator close1 and thus by means of the relay switch and control motor1 cause the feeder regulator to boost the voltage on the rotary until the loads again become equal4 ,should the load on the rotary converter become greater than that on the generator1 the regulator contacts operate in the reverse direction and the feeder regulator is caused to buck the rotary voltage4 ,alternators in ,parallel4--,when the load on a station increases beyond that which can conveniently be carried by one alternator1 it becomes necessary to connect other alternators in parallel with it4 ,to properly switch in a new machine in parallel with one already in operation and carrying load1 requires a complete knowledge of the situation on the part of the attendant1 and also some experience4 ,the connections for operating alternators in parallel are shown in fig4 #b1hdc4 ,in the illustration the alternator ,a is in operation and is supplying current to the bus bars4 ,the alternator ,b is at rest4 ,the main pole switch ,b' by means of which this machine can be connected into circuit is therefore open4 ,illustration3 ,,fig4 #b1hdc4--,method of synchronizing with one lamp2 dark lamp method4 ,assuming ,a to be in operation1 ,b1 may be brought up to approximately the proper speed1 and voltage4 ,then if ,b1 be run a little slower or faster than ,a1 the synchronizing lamp will glow for one moment and be dark the next4 ,at the instant when the pressures are equal and the machines in phase1 the lamp will become dark1 but when the phases are in quadrature1 the lamp will glow at its maximum brilliancy4 ,since the flickering of the lamp is dependent upon the difference in frequency1 the machines should not be thrown in parallel while this flickering exists4 ,the nearer alternator approaches synchronism1 in adjusting its speed1 the slower the flickering1 and when the flickering becomes very slow1 the incoming machine may be thrown in the moment the lamp is dark by closing the switch4 ,the machines are then in phase and tend to remain so1 since if one slow down1 the other will drive it as a motor4 ,now1 if the load increase to such extent as to require the service of the second alternator ,b1 it must be switched in parallel with ,a4 ,in order that both machines may operate properly in parallel1 three conditions must be satisfied before they are connected together1 or else the one alternator will be short circuited through the other1 and serious results will undoubtedly follow4 ,accordingly before closing main switch ,b1 it is necessary that #a4 ,the frequencies of both machines be the same2 #b4 ,the machines must be in synchronism2 #c4 ,the voltages must be the same4 ,ques4 ,how are the frequencies made the same8 ,ans4 ,by speeding up the alternator to be cut in1 or change the speed of both until frequency of both machines is the same4 ,illustration3 ,,fig4 #b1hdd4--;,diagram of connections of ,general ,electric automatic voltage regulator for several alternators running in parallel with exciters in parallel4 ,ques4 ,how are the alternators synchronized or brought in phase8 ,ans4 ,the synchronism of the alternators is determined by employing some form of synchronizer1 as by the single lamp method of fig4 #b1hdc1 or the two lamp method of fig4 #b1hde4 ,ques4 ,in synchronizing by the one lamp method1 when should the incoming machine be thrown in8 ,ans4 ,it is advisable to close the switch when the machines are approaching synchronism rather than when they are receding from it1 that is to say1 the instant the lamp becomes dark4 ,illustration3 ,,fig4 #b1hde4--,method of synchronizing with two lamps2 dark lamp method4 ,the two synchronizing lamps are connected as shown1 and each must be designed to supply its rated candle power at the normal voltage developed by the alternators4 ,now since the alternators are both running under normal field excitation the left hand terminals of each of them will alternately be positive and negative in polarity1 while the right hand terminals are respectively negative and positive in polarity4 ,if1 however1 the alternators be in phase with each other1 the left hand terminals of both of them will be positive while the right hand terminals are negative1 and when the left hand terminals of both machines are negative the right hand terminals will be positive4 ,hence1 when the machines are in phase there will be no difference of pressure between the left hand terminals or between the right hand terminals of the two machines4 ,hence1 if the synchronizing lamps be connected as shown1 both will be dark4 ,the instant there is a difference of phase1 both lamps will glow attaining full candle power when the difference of phase has reached a maximum4 ,as the alternators continue to come closer in step1 the red glow will gradually fade away until the lamps become dark4 ,then the switch may be closed1 thereby throwing the two machines in parallel4 ,if the intervals between the successive lighting up of the lamps are of short duration it is advisable to wait until these become longer even though the other conditions are satisfied1 because where the phases pass each other rapidly there is a greater possibility of not bringing them together at the proper instant4 ,an interval of not less than five seconds should therefore be allowed between the successive lighting up of the lamps1 before closing the switch4 ,illustration3 ,,fig4 #b1hdf4--;,inductor type synchroscope4 ,this type is especially applicable where pressure transformers are already installed for use with other meters4 ,as it requires only about ten apparent watts it may be used on the same transformers with other meters4 ,there are three stationary coils1 ,n1 ,m and ,c1 and a moving system1 comprising an iron armature1 ,a1 rigidly attached to a shaft suitably pivoted and mounted in bearings4 ,a pointer is also attached to the shaft4 ,the moving system is balanced and is not subjected to any restraining force1 such as a spring or gravity control4 ,the axes of the coils ,n and ,m are in the same vertical plane1 but #ij degrees apart1 while the axis of ,c is in a horizontal plane4 ,the coils ,n and ,m are connected in split phase relation through an inductive resistance ,p and non-inductive resistance ,q1 and these two circuits are parallel across the bus bar terminals #c and #d of the synchroscope4 ,coil ,c is connected through a non-inductive resistance across the upper machine terminals #a and #b of the synchroscope4 ,in operation1 current in the coil ,c magnetizes the iron core carried by the shaft and the two projections1 marked ,a and iron armature4 ,there is however1 no tendency to rotate the shaft4 ,if current be passed through one of the other coils1 say ,m1 a magnetic field will be produced parallel with its axis4 ,this will act on the projections of the iron armature1 causing it to turn so that the positive and negative projections assume their appropriate position in the field of the coil ,m4 ,a reversal of the direction in both coils will obviously not affect the position of the armature1 hence alternating current of the same frequency and phase in the coils ,c and ,m cause the same directional effect upon the armature as if direct current were passed through the coils4 ,if current lagging #ij degrees behind that in the coils ,m and ,c be passed through the coil ,n1 it will cause no rotative effect upon the armature1 because the maximum value of the field which it produces will occur at the instant when the pole strength of the armature is zero4 ,the two currents in the coils ,m and ,n produce a shifting magnetic field which rotates about the shaft as an axis4 ,as all currents are assumed to be of the same frequency1 the rate of rotation of this field is such that its direction corresponds with that of the armature projections at the instant when the poles induced in them by the current in the coil ,c are at maximum value1 and the field shifts through #ahj degrees in the same interval as is required for reversal of the poles4 ,this is the essential feature of the instrument1 namely1 that the armature projections take a position in the rotating magnetic field which corresponds to the direction of the field at the instant when the projections are magnetized to their maximum strength by their current in the coil ,c4 ,if the frequency of the currents in the coils which produce the shifting field be less than that in the coil which magnetized the armature1 then the armature must turn in order that it may be parallel with the field when its poles are at maximum strength4 ,ques4 ,what are the objections to the one lamp method8 ,ans4 ,the filament of the lamp may break1 and cause darkness1 or the lamp may be dark with considerable voltage as it takes over #bj volts to cause a #ajj volt lamp to glow4 ,ques4 ,what capacity of single lamp must be used8 ,ans4 ,it must be good for twice the voltage of either machine4 ,illustration3 ,,fig4 #b1hdg4--;,brilliant lamp method of synchronizing4 ,the synchronizing lamps are connected as shown1 and must be of the alternator voltage4 ,when the voltages are equal and the machines in phase1 the difference of pressure between a and a given point is the same as that between a' and the same point2 this obtains for b and b'4 ,accordingly1 a lamp connected across a b' will burn with the same brilliancy as across a' b2 the same holds for the other lamp4 ,when the voltages are the same and the phase difference is #ahj the lamps are dark1 and as the phase difference is decreased1 the lamps glow with increasing brightness until at synchronism they glow with maximum brilliancy4 ,hence the incoming alternator should be thrown in at the instant of maximum brilliancy4 ,ques4 ,what modification of the synchronizing methods shown in the accompanying illustrations is necessary when high pressure alternators are used8 ,ans4 ,step down transformers must be used between the alternators and the lamps to obtain the proper working voltages for the lamps4 ,illustration3 ,,fig4 #b1hdh4--,synchronizing with high pressure alternators2 dark and brilliant lamp methods4 ,in both methods the primaries of the transformers are connected in the same way across the terminals of the alternators as shown4 ,in the dark lamp method1 the connections between the secondary coils of the transformers must be made so that when each is subjected to the same conditions the action of the one coil opposes that of the other as in the dark lamp method2 then1 if the transformers be both of the same design1 there will be no voltage across the lamps when the alternators are in phase with each other4 ,if the ratio of each transformer is such as to give1 for example1 #ajj volts across its secondary terminals1 then the two incandescent lamps since they are joined together in series must each be designed for #ajj volts4 ,one #bjj volt lamp could be used in either method in place of the two #ajj volt lamps4 ,when1 therefore1 the alternators are directly opposite in phase to each other1 both the lamps will burn brightly2 as the alternators come together in phase the lamps will produce less and less light1 until when the machines are exactly in phase no light will be emitted at all1 at which instant the incoming alternator should be thrown in4 ,it must be evident1 if the transformer secondary connections are arranged as in the brilliant lamp method1 so that they do not oppose each other1 the lamps will be at maximum brilliancy when the alternators are in phase and dark when the phase difference is #ahj1 assuming of course equalized voltage4 ,ques4 ,how is the voltage of an incoming machine adjusted so that it will be the same as the one already in operation8 ,ans4 ,by varying the field excitation with a rheostat in the alternator field circuit4 ,ques4 ,how may two or more alternators be started simultaneously8 ,ans4 ,after bringing each of them up to its proper speed so as to obtain equal frequencies1 the main switches may be closed1 thereby joining their armature circuits in parallel4 ,as yet1 however1 their respective field windings have not been supplied with current1 so that no harm can result in doing this4 ,the exciters of these machines after being joined in parallel1 should then be made to send direct current simultaneously through the field windings of the alternators1 and from this stage on the directions previously given may be followed in detail4 ,ques4 ,what are the conditions when two or more alternators are directly connected together8 ,ans4 ,if rigidly connected together1 or directly connected to the same engine1 they must necessarily run in the same manner at all times4 ,when machines connected in this way are once properly adjusted so that they are in phase with each other1 their operation in parallel is even a simpler task than when they are all started together but are not directly connected4 ,ques4 ,when an alternator is driven by a gas engine1 what provision is sometimes made to insure successful operation in parallel8 ,ans4 ,an amortisseur winding is provided to counteract the tendency to hunting4 ,illustration3 ,,fig4 #b1hdi4--;,diagram of ,lincoln ,synchronizer4 ,in construction1 a stationary coil ,f1 has suspended within it a coil ,a1 free to move about an axis in the planes of both coils and including a diameter of each4 ,if an alternating current be passed through both coils1 ,a1 will take a position with its plane parallel to ,f4 ,if now the currents in ,a and ,f be reversed with respect to each other1 coil ,a will take up a position #ahj from its former position4 ,reversal of the relative directions of currents in ,a and ,f is equivalent to changing their phase relation by #ahj1 and therefore this change of #ahj in phase relation is followed by a corresponding change of #ahj in their mechanical relation4 ,suppose now1 instead of reversing the relative direction of currents in ,a and ,f1 the change in phase relation between them be made gradually and without disturbing the current strength in either coil4 ,it is evident that when the phase difference between ,a and ,f reaches #ij1 the force between ,a and ,f will become reduced to zero1 and a movable system1 of which ,a may be made a part1 is in condition to take up any position demanded by any other force4 ,let a second number of this movable system consist of coil ,b1 which may be fastened rigidly to coil ,a1 with its plane #ij from that of coil ,a1 and the axis of ,a passing through diameter of ,b4 ,further1 suppose a current to circulate through ,b1 whose difference in phase relation to that in ,a1 is always #ij4 ,it is evident under these conditions that when the difference in phase between ,a and ,f is #ij1 the movable system will take up a position1 such that ,b is parallel to ,f1 because the force between ,a and ,f is zero1 and the force between ,b and ,f is a maximum2 similarly when the difference in phase between ,b and ,f is #ij1 ,a will be parallel to ,f4 ,that is1 beginning with a phase difference between ,a and ,f of zero a phase change of #ij will be followed by a mechanical change on a movable system of #ij1 and each successive change of #ij in phase will be followed by a corresponding mechanical change of #ij4 ,for intermediate phase relation1 it can be proved that under certain conditions the position of equilibrium assumed by the movable element will exactly represent the phase relations4 ,that is1 with proper design1 the mechanical angle between the plane of ,f and that of ,a and also between the plane of ,f and that of ,b1 is always equal to the phase angle between the current flowing in ,f and those in ,a and ,b respectively4 ,as commercially constructed coil ,f consists of a small laminated iron field magnet with a winding whose terminals are connected with binding posts4 ,the coils ,a and ,b are windings practically #ij apart on a laminated iron armature pivoted between the poles of the magnet4 ,these two windings are joined1 and a tap from the junction is brought out through a slip ring to one of two other binding posts4 ,the two remaining ends are brought out through two more slip rings1 one of which is connected to the remaining binding post1 through a non-inductive resistance1 and the other to the same binding post through an inductive resistance4 ,a light aluminum hand attached to the armature shaft marks the position assumed by the armature4 ,ques4 ,what is the action of the amortisseur winding8 ,ans4 ,any sudden change in the speed of the field1 generates a current in the amortisseur winding which resists the change of velocity that caused the current4 ,the appearance of an amortisseur winding is shown in the cut below 7fig4 #b1hej7 illustrating the field of a synchronous condenser equipped with amortisseur winding4 ,illustration3 ,,fig4 #b1hej4--;,general ,electric field of synchronous condenser provided with amortisseur winding4 ,hunting is accompanied by a shifting of flux across the face of the pole pieces due to the variation in the effect of armature reaction on the main field flux as the current varies and the angular displacement between the field and armature poles is changed4 ,copper short circuited collars placed around the pole face have currents induced in them by this shifting flux1 which have such a direction as to exert a torque tending to oppose any change in the relative position of the field and armature4 ,this action is similar to that of the running torque of an induction motor and the damping device has been still further developed until in its best form it resembles the armature winding of a squirrel cage induction motor4 ,the pole pieces are in ducts1 and low resistance copper bars placed in them with their ends joined by means of a continuous short circuiting ring extending around the field4 ,such a device has proven very effective in damping out oscillations started from any cause1 the same winding doing duty as a damping device and to assist the starting characteristics4 ,ques4 ,how are three phase alternators synchronized8 ,ans4 ,in a manner similar to the single phase method4 ,thus the synchronizing lamps may be arranged as in fig4 #b1eha1 which is simply an extension of the single phase method4 ,ques4 ,are three lamps necessary8 ,ans4 ,only to insure that the connections are properly made1 after which one lamp is all that is required4 ,ques4 ,how is it known that the connections of fig4 #b1hea are correct8 ,ans4 ,if1 in operation1 the three lamps become bright or dark simultaneously1 the connections are correct2 if this action takes place successively1 the connections are wrong4 ,if wrong1 transpose the leads of one machine until simultaneous action of the lamps is secured4 ,illustration3 ,,fig4 #b1hea4--,method of synchronizing three phase alternators with1 three lamps1 being an extension of the single phase method4 ,ques4 ,what is the disadvantage of the lamp method of synchronizing8 ,ans4 ,lack of sensitiveness4 ,ques4 ,which is the accepted lamp method1 dark or brilliant8 ,ans4 ,in the ,united ,states it is usual to make the connections for a dark lamp at synchronism1 while in ,england the opposite practice obtains4 ,with the dark lamp method1 the breaking of a filament might cause the machines to be connected with a great phase difference1 whereas1 with the brilliant lamp it is difficult to determine the point of maximum brilliancy4 ,this latter method1 therefore may be called the safer4 ,ques4 ,what may be used in place of lamps for synchronizing8 ,ans4 ,some form of synchroscopes1 or synchronizers4 ,ques4 ,how does the ,lincoln synchronizer work8 ,ans4 ,the construction is such that a hand moves around a dial so that the angle between the hand and the vertical is always the phase angle between the two sources of electric pressure to which the synchronizer is connected4 ,if the incoming alternator be running too slow1 the hand deflects in one direction1 if too fast1 in the other direction4 ,when the hand shows no deflection1 that is1 when it stands vertical1 the machines are in phase4 ,a complete revolution of the hand indicates a gain or loss of one cycle in the frequency of the incoming machine1 as referred to the bus bars4 ,cutting ,out ,alternator4--,when it is desired to cut out of circuit an alternator running in parallel with others1 the method of procedure is as follows3 #a4 ,reduce driving power until the load has been transferred to the other alternators1 adjusting field rheostat to obtain minimum current2 #b4 ,open main switch2 #c4 ,open field switch4 ,ques4 ,what precaution should be taken8 ,ans4 ,never open field switch before main switch4 ,illustration3 ,,fig4 #b1heb4--;,general ,electric #ejj kw41 horizontal mixed pressure ,curtis turbine connected to a #ejj kw4 dynamo4 ,in a ,curtis turbine it is not necessary to use the whole periphery of the first stage for low pressure steam nozzles4 ,a section can be partitioned off and equipped with special expanding nozzles to receive steam at high pressure direct from the boilers4 ,such nozzles deliver their steam against the same wheel as do the low pressure nozzles1 but occupy only a small portion of its periphery4 ,the steam is expanded in these nozzles from high pressure all the way down to the normal pressure of the first stage1 and in such expansion acquires a high velocity and consequently contains a great deal of energy--much more than does an equal quantity of low pressure steam4 ,in consequence of this1 high pressure steam is used with a far lower water rate than is obtained with low pressure steam1 or with high pressure steam reduced to low pressure in a reducing valve4 ,this construction is called mixed pressure4 ,its function is the same as that of the reducing valve1 that is1 it makes up for a deficiency of low pressure steam by drawing direct on the boilers4 ,with this construction1 the full power of the turbine can be developed with3 ,all low-pressure steam1 all high pressure steam1 or1 any necessary proportion of steam of each pressure4 ,furthermore1 the transition from all low pressure to all high pressure1 through all the conditions intermediate between these extremes1 is provided for automatically by the turbine governor2 a deficiency of low pressure steam causes the high pressure nozzles to open automatically4 ,ques4 ,what is the ordinary method of cutting out an alternator8 ,ans4 ,the main switch is usually opened without any preliminaries4 ,ques4 ,what is the objection to this procedure8 ,ans4 ,it suddenly throws all the load on the other alternators1 and causes hunting4 ,ques4 ,what forms of drive are especially desirable for running alternators in parallel1 and why8 ,ans4 ,water turbine or steam turbine because of the uniform torque1 thus giving uniform motion of rotation4 ,with reciprocating engines1 the crank effect is very variable during the revolution1 resulting in pulsations driving the alternator too fast or too slow1 and causing cross current between the alternators4 ,ques4 ,is a sluggish1 or a too sensitive governor preferable on an engine driving alternators in parallel8 ,ans4 ,a sluggish governor4 ,alternators in ,series4--,alternators are seldom if ever connected in series1 for the reason that the synchronizing tendency peculiar to these machines causes them to oppose each other and fall out of phase when they are joined together in this way4 ,if1 however1 they be directly connected to each other1 or to an engine1 so that they necessarily keep in phase at all times1 and thus add their respective voltages instead of counteracting them1 series operation is possible4 ,,note4--,according to the practice of the ,general ,electric ,co41 #b degrees of phase difference from a mean is the limit allowable in ordinary cases4 ,it will1 in certain cases1 be possible to operate satisfactorily in parallel1 or to run synchronous apparatus from machines whose angular variation exceeds this amount1 and in other cases it will be easy and desirable to obtain a better speed control4 ,the #b degree limit is intended to imply that the maximum departure from the mean position during any revolution shall not exceed #b #cfj of an angle corresponding to two poles of a machine4 ,the angle of circumference which corresponds to the #b degree of phase variation can be ascertained by dividing #b by the number of pole2 thus1 in a #bj pole machine1 the allowable angular variation from the mean would be #b #aj of one degree4 ,illustration3 ,,fig4 #b1hec4--;,diagram of connections for synchronizing two compound wound three phase alternators4 ,a and ,a' are the armatures of the two machines1 the fields of which are partly separately excited1 the amount of excitation current being controlled by the series compounding rheostats ,b and ,b'1 which form a stationary shunt4 ,it is assumed that the alternator ,a is connected to the bus bars #a1 #b1 and #c1 by the switch #a,s4 ,if an increase make it necessary to introduce the alternator ,a'1 it is first run up to speed and excited to standard pressure by its exciter1 and then the double plug switch #c,s is closed1 connecting the primary of the station transformer ,t and ,t' with the bus bars through the secondary coil1 so that the synchronizing lamps light up when the secondary circuit is closed through the single pole switch #d,s4 ,the primary of the station transformer ,t is thus excited through the double pole switch #e,s1 connecting it with the outer terminals of the armature ,a'4 ,the two alternators will now work in opposition to each other upon the synchronizing lamps1 the transformer ,t being operated by the new alternator ,a' through the switch #b,s1 and the transformer ,t' being operated by the working alternator ,a1 from the bus bars4 ,if the new alternator be not in step with the working alternator1 the synchronizing lamps will glow1 growing brighter and dimmer alternately with greater or lesser rapidity4 ,in this case1 the armature speed of the new alternator must be controlled in such a manner that the brightening and dimming will occur more and more slowly1 until the lamps cease to glow or remain extinguished for a decided interval of time4 ,the extinction of the light is due to the disappearance of the secondary current1 and indicates that the alternators are in step4 ,the switch #b,s should now be thrown1 thus coupling the two machines electrically1 and both of them will continue to operate in step4 ,the double pole equalizer switch #f,s should now be closed1 connecting the two field windings in parallel and equalizing the compounding1 so that any variations of load will affect the two alternators equally4 ,after the alternators have been connected in parallel1 the switches #d,s and #e,s1 may be opened leaving the switch #c,s closed1 to operate the switchboard lamps ,k1 ,k1 as pilot lights from the bus bars4 ,transformers4--,these1 as a whole1 are simple in construction1 high in efficiency1 and comparatively inexpensive4 ,their principles of operation are also readily understood4 ,the efficiency of a transformer1 that is1 the ratio between full load primary and full load secondary is greatest when the load on it is such that the sum of the constant losses equals the sum of the variable losses4 ,in general1 transformers designed for high frequencies and large capacities are more efficient than those designed for low frequencies and small capacities4 ,as a whole1 however1 a transformer leaves but little to be desired as regards efficiency1 a modern #fj cycle transformer of #ej kilowatts capacity or more possesses an efficiency of approximately #ih per cent4 at full load and an efficiency of about #ig per cent4 at half load4 ,ques4 ,how should a transformer be selected1 with respect to efficiency8 ,ans4 ,one should be chosen1 whose parts are so proportioned that the point of maximum efficiency occurs at that load which the transformer usually carries in service4 ,in many alternating current installations1 comparatively light loads are carried the greater part of the time1 the rated full load or an overload being occurrences of short durations4 ,for such purposes special attention should be given to the designing or selecting of transformers having low core losses rather than low resistance losses1 because the latter are then of relatively small importance4 ,ques4 ,what kind of efficiency is the station manager interested in8 ,ans4 ,the all day efficiency4 ,this expression1 as commonly met with in practice1 denotes the percentage that the amount of energy actually used by the consumer is of the total energy supplied to his transformer during #bd hours4 ,the formula for calculating the all day efficiency of a transformer is based upon the supposition that the amount of energy used by the consumer during #bd hours is equivalent to full load on his transformer during five hours and is as follows3 #ew ,e ------------- #bd;c #er #ew where ,e the all day efficiency of the transformer1 w the full load in watts on the primary1 c the core loss in watts1 r the resistance loss in watts4 ,illustration3 ,,fig4 #b1hed4--,performance curves of ,westinghouse air blast #eej kw1 #aj1ejj volt transformer1 #c1jjj alternations4 ,ques4 ,what are the usual all day efficiencies8 ,ans4 ,the average is about #he per cent4 for those of #a kilowatt capacity1 #ib per cent4 for those of #e kilowatts capacity1 #id per cent4 for those of #aj kilowatts capacity1 and about #id4e per cent4 for those of #ae kilowatts capacity4 ,ques4 ,what becomes of the energy lost by a transformer8 ,ans4 ,it reappears as heat in the windings and core4 ,this heat not only increases the resistances of the windings and core1 producing thereby a further increase of their respective losses1 but in addition causes in time a peculiar effect on the iron core which is intensified by the reversals of magnetism constantly going on within it4 ,after about two years' service1 the iron apparently becomes fatigued or tired1 and this phenomenon is called aging of the iron4 ,since the life of the transformer depends to a great extent upon this factor1 the conditions responsible for its existence should as far as possible be removed4 ,means must therefore be provided in the construction to radiate the heat as quickly as it is generated4 ,ques4 ,what kind of oil is used in oil cooled transformers8 ,ans4 ,mineral oil4 ,illustration3 ,,fig4 #b1hee4--;,general arrangement of air blast transformers and blowers4 ,ques4 ,how is it obtained8 ,ans4 ,by fractional distillations of petroleum unmixed with any other substances and without subsequent chemical treatment4 ,ques4 ,what is the important requirement for transformer oil8 ,ans4 ,it should be free from moisture1 acid1 alkali or sulphur compounds4 ,ques4 ,how may the presence of moisture be determined8 ,ans4 ,by thrusting a red hot iron rod in the oil2 if it crackle1 moisture is present4 ,ques4 ,describe the ,westinghouse method of drying oil4 ,ans4 ,it is circulated through a tank containing lime1 and afterwards1 through a dry sand filter4 ,ques4 ,what is the objection to heating the oil 7raising its temperature slightly above boiling point of water7 to remove the moisture8 ,ans4 ,the time consumed 7several days7 is excessive4 ,illustration3 ,,fig4 #b1hef4--,small ,curtis turbine generator set as made by the ,general ,electric ,co41 in sizes from #e kw41 to #cjj kw4 ,it can be arranged to operate either condensing or non-condensing1 and at any steam pressure above #hj lbs4 for the smaller sizes and #ajj lbs4 for the larger4 ,there are only two main bearings4 ,a thrust bearing1 consisting of roller bearings and running between hardened steel face washers located at either end of the main bearings is provided solely for centering the rotor so as to equalize the clearance4 ,a centrifugal governor is provided 7in the smaller sizes7 completely housed1 and mounted directly on the main shaft end4 ,it controls a balanced poppet valve through a bell crank4 ,in the larger sizes 7#ge kw4 and above7 the governor is mounted on a vertical secondary shaft geared to the main shaft and controls a cam shaft which opens or closes a series of valves in rotation1 admitting the steam to different sections of the first stage nozzles4 ,in this way throttling of the steam is avoided4 ,there is also an emergency governor which closes the throttle valve in the event of the speed reaching a predetermined limit4 ,the speeds of operation range from #e1jjj ,r4,p4,m4 for the smallest size to #a1ejj ,r4,p4,m4 for the largest4 ,the lubrication system is enclosed and is automatic4 ,air leakage where the shaft passes through the wheel casing is prevented by steam seal4 ,ques4 ,what effect has moisture8 ,ans4 ,it reduces the insulation value of the oil4 4#jf per cent4 of moisture has been found to reduce the dielectric strength of oil about #ej per cent4 dry oil will withstand a pressure of #be1jjj volts between two #i inch knobs separated 4#ae inch4 ,ques4 ,what is understood by transformer regulation8 ,ans4 ,it is the difference between the secondary voltage at no load and at full load1 and is generally expressed as a percentage of the secondary voltage at no load4 ,ques4 ,what governs its value8 ,ans4 ,the resistance and reactance of the windings4 ,illustration3 ,,fig4 #b1heg4--;,cut off coupling for power transmission by line shafting4 ,it is used to cut off a driving shaft from a driven shaft4 ,its use obviates the use of a quill1 such as is shown in fig4 #b1heh4 ,ques4 ,how may the regulation be improved8 ,ans4 ,by decreasing the resistances of the windings by employing conductors of greater cross section1 or decreasing their reactance by dividing the coils into sections and closely interspersing those of the primary between those of the secondary4 ,,note4--,the term regulation as here used is synonymous with drop4 ,the voltage drop in a transformer denotes the drop of voltage occurring across the secondary terminals of a transformer with load4 ,this drop is due to two causes3 #a1 the resistance of the windings2 and #b1 the reactance or magnetic leakage of the windings4 ,on non-inductive load1 the reactive drop1 being in quadrature1 produces but a slight effect1 but on inductive loads it causes the voltage to drop1 and on leading current loads it causes the voltage to rise4 ,as the voltage drop of a good transformer is very small even on inductive load1 direct accurate measurement is difficult4 ,it is best to measure the copper loss with short circuited secondary by means of a wattmeter1 and at the same time the voltage required to drive full load current through4 ,from the watts1 the resistance drop can be found1 and from this and the impedance voltage1 the reactive drop may be calculated4 ,from these data a simple vector diagram will give1 near enough for all practical purposes1 the drop for any power factor1 or the following formula may be used which has been deduced from the vector diagram4 ,d 7,w ,x7#b 7,r ,p7#b - #ajj where ,r resistance drop2 ,x reactive drop2 ,p power factor of load2 ,w wattless factor of load 7#a - ,p#b72 ,d resultant secondary drop4 ,for non-inductive loads where ,p #ajj and ,w #j1 ,d ,x#b 7#ajj ,r7#b - #ajj4 ,in the case of leading currents it should be considered negative4 ,in transformers where there is a great difference in voltage between the primary and secondary windings1 however1 this remedy has its limitations on account of the great amount of insulation which must necessarily be used between the windings1 and which therefore causes the distances between them to become such as to cause considerable leakage of the lines of force4 ,ques4 ,how does the regulation vary for different transformers1 and what should be the limit8 ,ans4 ,those of large capacity usually have a better regulation than those of small capacity1 but in no case should its value exceed #b per cent4 ,illustration3 ,,fig4 #b1heh4--,quill drive4 ,this is the proper transmission arrangement substitute for heavy service1 requiring large pulleys1 sheaves1 gears1 rotors1 etc4 ,it is a hollow shaft supported by independent bearings4 ,the main driving shaft running through the quill is thus relieved of all transverse stresses4 ,the power is transmitted to the quill by means of a friction or jaw clutch4 ,when the clutch is thrown out the pulley or sheave stands idle and the driving shaft revolves freely within the quill4 ,as there is no contact between moving parts there is no wear4 ,jaw clutches should be used for drives demanding positive angular displacement4 ,they can only be thrown in and out of engagement when at rest4 ,all very large clutch pulleys1 sheaves1 or gears designed to run loose on the line shaft are preferably mounted on quills4 ,the letters ,a1 ,b1 ,c1 etc41 indicate the dimensions to be specified in ordering a quill4 ,ques4 ,what advantages have shell type transformers over those of the core type8 ,ans4 ,they have a larger proportion of core surface exposed for radiation of heat1 and a shorter magnetic circuit which reduces the tendency for a leakage of the lines of force into the air4 ,both types have advantages and disadvantages as compared with the other4 ,in the shell type1 there is less magnetic leakage1 but also less surface exposed for radiation1 and greater difficulty in providing efficient insulation between the two circuits2 in the core type there is more surface exposed for radiation and less difficulty in insulating the windings1 but there is also a great leakage of the lines of magnetic force into the outer air4 ,ques4 ,how are the windings usually arranged8 ,ans4 ,as a rule1 there is only one primary winding but the secondary winding is generally divided into two equal sections1 the four terminals of which are permanently wired to four connection blocks which may be connected so as to throw the secondary sections either in parallel or in series with each other at will4 ,ques4 ,what is necessary for satisfactory operation of transformers in parallel8 ,ans4 ,they must be designed for the same pressures and capacities1 their percentages of regulation should be the same and they must have the same polarity at a given instant4 ,one may satisfy himself as to the first of these conditions by examining the name plates fastened to the transformers1 whereon are stamped the values of the respective pressures and capacities of each4 ,although equal values of regulation is given as one of the conditions to be satisfied1 transformers may be operated in parallel when their percentages of regulation are not the same4 ,ideal operation1 however1 can be attained only under the former state of affairs4 ,suppose1 for instance1 a transformer having a regulation of two per cent4 be operated in parallel with another of similar size and design but having a regulation of one per cent4 ,the secondary pressures of these transformers at no load will of course be the same1 but at full load if the secondary pressure of the one be #ih volts1 that of the other will be #ii volts4 ,there will1 therefore1 be a difference of pressure of one volt between them which will tend to force a current backward through the secondary winding of the transformer delivering #ih volts4 ,this reversed current1 although comparatively small in value1 lowers the efficiency of the installation by causing a displacement of phase and a decrease in the combined power factor of the transformers4 ,ques4 ,describe the polarity test4 ,ans4 ,the test for polarity consists in joining together by means of a fuse wire1 a terminal of the secondary winding of each transformer1 and then with the primary windings supplied with normal voltage1 connecting temporarily the remaining terminals of the secondary windings4 ,the melting of the fuse wire thus connected indicates that the secondary terminals joined together are of opposite polarities1 and that the connections must therefore be reversed1 whereas if the fuse wire do not melt1 it shows that the proper terminals have been joined and that the connections may be made permanent4 ,illustration3 ,,fig4 #b1hei4--,single overhung tangential water wheel equipped with ,doble ellipsoidal buckets4 ,the central position of the front entering wedge or lip of the bucket is cut away in the form of a semi-circular notch1 which allows a solid circular water jet to discharge upon the central dividing wedge of the bucket without being split in a horizontal plane4 ,the object of this test is1 obviously1 not to determine the exact polarity of each secondary terminal1 but merely to indicate which of them are of the same polarity4 ,illustration3 ,,fig4 #b1hfj4--,motor generator exciter set driven by a ,pelton-,doble tangential water wheel4 ,the water wheel runner is mounted on the shaft overhung and the jet is regulated by either a hand actuated or governor controlled needle nozzle4 ,the speed of the water wheel is equivalent to the synchronous speed of the induction motor1 hence1 the latter floats on the line1 and under certain conditions may perform the functions of an alternator by feeding into the circuit1 should the water wheel tend to operate above synchronous speed4 ,should any interruption to the operation of the wheel occur1 causing a diminution of speed1 the induction motor would drop back to full load speed and take up the exciter load1 resulting in no appreciable drop of exciter voltage4 ,the only variation of speed possible is dependent upon the slip of the motor4 ,where two or more exciter sets are employed in the station1 an advantageous arrangement embraces the installation of a water wheel driven motor generator set and an exciter set1 consisting of merely the direct current generator and water wheel4 ,the induction motor being electrically tied into the circuit1 the possibility of a runaway of the water wheel is eliminated1 since its speed can only slightly exceed the synchronous speed of the system4 ,motor ,generators4--,in motor generator sets1 either the shunt or series wound type of motor may be employed at the power producing end of the set1 but the field of the generator is either shunt or compound wound1 depending upon whether or not it is desired to maintain or to raise the secondary voltage near full load4 ,in either case a rheostat introduced in the shunt field winding of the generator will be found very essential4 ,both generator and motor are so mounted on the base that their respective commutators are at the outer ends of the set4 ,by this means ample space surrounds all of the working parts1 and repairs can readily be made4 ,motor generators are frequently used as boosters to raise or boost the voltage near the extremities of long distance1 direct current transmission lines4 ,of these1 electric railway systems in which it is desired to extend certain of the longer lines1 form a typical example4 ,illustration3 ,,fig4 #b1hfa4--;,automatically governed ,pelton-,doble tangential water wheel driving exciter dynamo4 ,the water wheel is mounted on one end of the shaft1 while the opposite end is extended to carry a fly wheel of suitable design to compensate for the low fly wheel effect of the direct current armature4 ,two bearings support the shaft which carries the rotating elements of the unit4 ,a needle nozzle actuated by a direct motion ,pelton-,doble governor 7designed for operation by either oil or water pressure7 maintains constant speed4 ,owing to the great cost of changing such a system over to one employing alternating current1 or storage batteries1 or of constructing an additional power station1 these solutions of the problem are usually at variance with good judgment and the amount of money at hand4 ,the choice then remains between the purchase of additional wire for feeders1 the connection of a booster in the old feeders1 or the installation of both larger feeders and a booster4 ,of these1 it is generally found that either the second or the third mentioned alternative meets the conditions most satisfactorily4 ,a booster installed in a railway system for the purpose just mentioned1 would have a series wound motor1 and the conditions to which it must conform would be as follows3 ,the motor having a series winding must provide for the full feeder current passing through both armature and field windings4 ,owing to the varying loads on a railway system1 due to the frequent starting and stopping of cars1 the feeder current varies between zero and some such value as #aej amperes4 ,this fluctuation of current through the field winding will1 in ordinary cases1 vary the magnetization of the pole pieces from zero almost to the point of saturation2 that is1 the maximum feeder current will so nearly fill the magnet cores with lines of force that it would be quite difficult to cause more lines of magnetic force to pass through them4 ,so long as the point of saturation is not reached1 however1 the proportion of current to field strength remains constant1 and therefore the ratio of amperes to volts will not vary4 ,the severe fluctuations of the feeder current would1 if the motor were shunt or compound wound1 cause most serious sparking and various other troubles1 but in a series motor where the back ampere turns on the armature that react on the field vary in precisely the same proportion as the ampere turns in the field1 there exists at all times a tendency to balance the active forces and produce satisfactory operation4 ,if1 however1 the field magnet cores be very large1 they cannot so quickly respond1 magnetically1 to changes in the strength of the current1 and there is then greater liability of the armature reaction momentarily weakening the field and thereby producing temporary sparking4 ,ques4 ,are motor generators always composed of direct current sets8 ,ans4 ,no4 ,ques4 ,describe conditions requiring a different combination4 ,ans4 ,for purposes where for instance direct currents of widely different voltages are to be obtained from an alternating current circuit1 and it is desired to install but one set1 a motor generator consisting of an alternating current motor such as an induction motor1 and a dynamo must necessarily be employed4 ,in such sets1 it is common to find both motor and dynamo armatures mounted on a common shaft1 and the respective field frames resting on a single base1 although for connection on a very high pressure alternating current circuit1 separate armature shafts insulated from each other but directly connected together1 and separate bases resting on a single foundation1 are usually employed to afford the highest degree of insulation between the respective circuits of the two machines4 ,ques4 ,what is the objection to a set composed of alternating current motor and alternator8 ,ans4 ,the commercial field that would be naturally covered by such a set is better supplied by a transformer4 ,ques4 ,why8 ,ans4 ,because a transformer contains no moving parts1 and is therefore simpler in construction1 cheaper in price1 and less liable to get out of order4 ,dynamotors4--,a dynamotor differs from a motor generator in that the motor armature and the generator armature are combined into one1 thereby requiring but one field frame4 ,since the motor and generator armature windings are mounted on a single core1 the armature reaction due to the one winding is neutralized by the reaction caused by the other winding4 ,there is1 consequently1 little or no tendency for sparking to occur at the brushes1 and they therefore need not be shifted on this account for different loads4 ,ques4 ,how is a dynamotor usually constructed8 ,ans4 ,it is usually built with two pole pieces which are shunt wound4 ,ques4 ,why does the voltage developed fall off slightly under an increase of load8 ,ans4 ,because a compound winding cannot be provided4 ,illustration3 ,,figs4 #b1hfb and #b1hfc4--,method of putting on belts when the driver is in motion1 and device used4 ,the latter is called a belt slipper1 and consists1 as shown in fig4 #b1hfb1 of a cone and shield1 which revolve upon the stem1 ,b1 thus yielding easily to the pull of the belt4 ,a staff or handle ,c of any convenient length can be fastened to the socket4 ,the mode of operation is illustrated in fig4 #b1hfc1 which is self explanatory4 ,ques4 ,describe the armature construction and operation4 ,ans4 ,it consists of two separate windings2 one of which is joined to a commutator mounted on one side of the armature for motor purposes1 and the other to the commutator on the other side of the armature for generator purposes4 ,by means of two studs of brushes pressing on the motor commutator1 current from the service wires is fed into the winding connected to this commutator1 and since the shunt field winding is also excited by the current from the service wires1 there is developed in the generator winding on the rotating armature a direct voltage which is proportional to the speed of rotation of the armature in revolutions per second1 the number of conductors in series which constitute the generator winding1 and the total strength of the field in which the armature revolves4 ,this pressure causes current to pass through the generator winding and the distributing circuit when the distributing circuit to which this winding is connected by means of its respective commutator1 brushes1 etc41 is closed4 ,illustration3 ,,figs4 #b1hfd to #b1hff4--;,converter connections2 fig4 #b1hfd double delta connection2 fig4 #b1hfe diametrical connection2 fig4 #b1hff two circuit single phase connection4 ,for six phase synchronous converter1 two different arrangements of the connections are generally used4 ,one is called the double delta1 and the other the diametrical connection4 ,let the armature winding of the converter be represented by a circle as in figs4 #b1hfd and #b1hfe1 and let the six equidistant points on the circumference represent collector rings1 then the secondary of the supply transformers can be connected to the collector rings in a double delta as in fig4 #b1hfd1 or across diametrical pairs of pointer as in fig4 #b1hfe4 ,in the first instance1 the voltage ratio is the same as for the three phase synchronous converter and simply consists of two delta systems4 ,the transformers can also be connected in double star1 and in such a case the ratio between the three phase voltage between the terminals of each star1 and the direct voltage will be the same as for double delta1 while the voltage of each transformer coil1 or voltage to neutral1 is #a #c times as much4 ,with the diametrical connection1 the ratio is the same as for the two ring single phase converter1 it being analogous to three such systems4 ,hence six phase double delta ,e#a #c;,e #bb 4#fab;,e4 ,six phase diametrical1 ,e#a ,e #b 4#gjg;,e4 ,the ratio of the virtualvoltage ,e#j between any collector ring and the neutral point is always ,e#j 7,e #b7 #b 4#ced;,e4 ,for single phase synchronous converters1 consisting of a closed circuit armature winding tapped at two equidistant points to the two collector rings the virtual voltage is #a #b the direct current voltage4 ,while such an arrangement of the single phase converter is the simplest1 requiring only two collector rings1 it is undesirable1 especially for larger machines1 on account of excessive heating of the armature conductors4 ,in fig4 #b1hff1 which represents the armature winding of a single phase converter1 the supply circuits from two secondaries of the step down transformers are connected to four collector rings1 so that the two circuits are in phase with each other1 but each spreads over an arc of #abj electrical degrees instead of over #ahj degrees as in the single phase circuit converter4 ,to distinguish the two types1 it is generally called a two circuit single phase synchronous converter4 ,the virtual voltage ,e#b bears to the direct voltage the same relation as in the three phase converter1 that is single phase two circuit1 ,e#a #c #bb 4#fab;,e4 ,ques4 ,how is a dynamotor started8 ,ans4 ,it is connected at its motor end and started in the same manner as any shunt wound motor on a constant pressure circuit4 ,ques4 ,what precautions should be taken in starting a dynamotor8 ,ans4 ,the necessary precautions are1 to have the poles strongly magnetized before passing current through the motor winding on the armature2 to increase gradually the current through this winding1 and not to close the generating circuit until normal conditions regarding speed1 etc41 are established in the motor circuit4 ,ques4 ,how is the current developed in the machine regulated8 ,ans4 ,it can be regulated by the introduction of resistance in one or the other of the armature circuits1 or by a shifting of the brushes around the commutator4 ,ques4 ,are dynamotors less efficient than motor generators of a similar type8 ,ans4 ,no1 they are more efficient4 ,ques4 ,why8 ,ans4 ,because they have only one field circuit and at least one bearing less than a motor generator4 ,a motor generator has at least three bearings1 and occasionally1 four1 where the set consists of two independent machines directly connected together4 ,rotary ,converters4--,an important modification of the dynamotor is the rotary converter4 ,this machine forms1 as it were1 a link between alternating and direct current systems1 being in general a combination of an alternating current motor and a dynamo4 ,illustration3 ,,fig4 #b1hfg4--,skeleton diagram showing wiring of alternator1 exciter1 transformer and converter4 ,the cut also shows switchboard and connections4 ,it has practically become a fixture in all large electric railway systems and in other installations where heavy direct currents of constant pressure are required at a considerable distance from the generating plant4 ,in such cases a rotary converter is installed in the sub-station1 and being simpler in construction1 higher in efficiency1 more economical of floor space1 and lower in price than a motor generator set consisting of an alternating current motor and a dynamo which might be used in its place1 it has almost entirely superseded the latter machine for the class of work mentioned4 ,ques4 ,what is the objection to the single phase rotary converter8 ,ans4 ,it is not self-starting4 ,ques4 ,what feature of operation is inherent in a rotary converter8 ,ans4 ,a rotary converter is a reversible machine4 ,that is to say1 if it be supplied with direct current of the proper voltage at its commutator end1 it will run as a direct current motor and deliver alternating current to the collector rings4 ,while this feature is sometimes taken advantage of in starting the converter from rest1 the machine is not often used permanently in this way1 its commercial application being usually the conversion of alternating currents into direct currents4 ,ques4 ,how does a rotary converter operate when driven by direct current8 ,ans4 ,the same as a direct current motor1 its speed of rotation depending upon the relation existing between the strength of the field and the direct current voltage applied4 ,if the field be weak with respect to the armature magnetism resulting from the applied voltage1 the armature will rotate at a high speed1 increasing until the conductors on the armature cut the lines of force in the field so as to develop a voltage which will be equal to that applied4 ,again1 if the field be strong with respect to the armature magnetism1 resulting from the applied voltage1 the armature will rotate at a low speed4 ,if1 therefore1 it be desired to operate the converter in this manner and maintain an alternating current of constant frequency1 the speed of rotation must be kept constant by supplying a constant voltage not only to the brushes pressing on the commutator1 but also to the terminals of the field winding4 ,illustration3 ,,fig4 #b1hfh4--;,general ,electric synchronous converter with series booster4 ,this type of converter generally consists of an alternator with revolving field mounted on the same shaft as the converter armature4 ,the armature of the alternator1 or booster1 as it is usually called1 is stationary and connected electrically in series between the supply circuit and the collector rings of the synchronous converter4 ,the booster field has the same number of pole as the converter and is generally shunt wound4 ,a change in the booster voltage will correspondingly change the alternating voltage impressed on the converter and this regulation can1 of course1 be made so as to either increase or decrease the impressed voltage by means of strengthening or weakening the booster field4 ,the voltage variation can be made either non-automatic or automatic1 and in the latter case1 it becomes necessary to provide a motor operated rheostat controlled by suitable relays1 or the booster can be provided with a series field4 ,by means of a booster1 it is possible to vary the direct voltage of the converter with a constant alternating supply voltage1 and this voltage regulation is obtained without disturbance of the power factor or wave shape of the system4 ,synchronous converters are frequently installed in connection with ,edison systems1 where three wire direct current is required4 ,the three wire feature is obtained either by providing extra collector rings and compensator1 as with ordinary direct current generators1 or also by connecting the neutral wire directly to the neutral point of the secondary winding of step down transformers1 if such be furnished4 ,ques4 ,how does it operate with alternating current drive8 ,ans4 ,the same as a synchronous motor4 ,ques4 ,what is the most troublesome part and why8 ,ans4 ,the commutator1 because of the many pieces of which it is composed and the necessary lines along which it is constructed1 its peripheral speed must be kept within reasonable limits4 ,ques4 ,what should be the limit of the commutator speed8 ,ans4 ,the commutator speed1 or tangential speed at the brushes should not exceed #c1jjj feet per minute4 ,illustration3 ,,fig4 #b1hfi4--,wiring diagram for ,general ,electric synchronous converter with series booster as illustrated in fig4 #b1hfh4 ,ques4 ,name another limitation necessary for satisfactory operation4 ,ans4 ,the pressure between adjacent commutator bars should not exceed eight or ten volts4 ,if the commutator bars be made narrow in order to obtain the necessary number for the desired voltage with the minimum circumference and therefore low commutator speed1 the brushes employed to collect the current are liable to require excessive width in order to provide the proper cross section and yet not cover more than two bars at once4 ,ques4 ,how can the commutator speed be kept within reasonable limits1 other than by reducing the width of the commutator bars8 ,ans4 ,by using alternating current of comparatively low frequency4 ,for a rotary converter delivering #ejj volt direct current1 the proper frequency for the alternating current circuit has been found to be #be cycles per second4 ,ques4 ,when a rotary converter is operated in this usual manner on an alternating current circuit1 how can the direct current be varied8 ,ans4 ,it may be varied 7from zero to a maximum7 by changing the value of the alternating pressure supplied to the machine1 or it may be altered within a limited range by moving the brushes around the commutator1 or in a compound wound converter by changing the amount of compounding4 ,under ordinary conditions1 varying the voltage developed by changing the voltage at the motor end is not practical1 hence the voltage developed can be varied only over a limited range4 ,in addition to this1 the voltage developed at the direct current end bears always a certain constant proportion to the alternating current voltage applied at the motor end2 this is due to the same winding being used both for motor and generator purposes4 ,in all cases the proportion is such that the alternating current voltage is the lower1 being in the single phase and in the two phase converters about 4#gjg of the direct current voltage1 and in the three phase converter about 4#fab of the direct current voltage4 ,it is thus seen that whatever value of direct current voltage be desired1 the value of the applied alternating current voltage must be lower1 requiring in consequence the installation of step down transformers at the sub-station for reducing the line wire voltage to conform to the direct current pressure required4 ,ques4 ,what is the efficiency of a rotary converter8 ,ans4 ,it may be said to have approximately the same efficiency as that in the average of the same output1 although in reality the converter is a trifle more efficient on account of affording a somewhat shorter average path for the current in the armature1 reducing in consequence the resistance loss and the armature reaction4 ,ques4 ,may a converter be overloaded more than a dynamo of the same output1 and why8 ,ans4 ,yes1 because there is usually less resistance loss in the armature of the converter than in the armature of the dynamo4 ,illustration3 ,,fig4 #b1hgj4--,wiring diagram for three wire synchronous converter with delta-,y connected step down transformer with the neutral brought out4 ,it is evident that in this case each transformer secondary receives of the neutral current1 and if this current be not so small1 as compared with the exciting current of the transformer1 it will cause an increase in the magnetic density4 ,thus1 a two phase converter may be overloaded approximately #fj per cent41 and a three phase converter may be overloaded about #cj per cent4 above their respective outputs if operated as dynamos4 ,ques4 ,describe how a converter is started4 ,ans4 ,there are several methods any one of which may be employed1 the choice in any given case depending upon which of them may best be followed under the existing conditions4 ,if it be found advisable to start the converter with direct current1 the same connections would be made between the source of the direct current and the armature terminals on the commutator side of the converter as would be the case were a direct current shunt motor of considerable size to be started2 this naturally means that a starting rheostat and a circuit breaker will be introduced in the armature circuit4 ,the shunt field winding alone is used1 and this part of the wiring may be made permanent if1 as is usually the case1 the same source of direct current is used normally for separate field excitation4 ,illustration3 ,,fig4 #b1hga4--,wiring diagram of three wire synchronous converter with distributed ,y secondary4 ,this system eliminates the flux distortion due to the unbalanced direct current in the neutral4 ,two separate interconnected windings are used for each leg of the ,y4 ,the unbalanced neutral current flowing in this system may be compared in action to the effect of a magnetizing current in a transformer4 ,the effect of the main transformer currents in the primary and secondary is balanced with regard to the flux in the transformer core1 which depends upon the magnetic current4 ,when a direct current is passed through the transformer1 unless the fluxes produced by the same neutralize one another1 its effect on the transformer iron varies as the magnetizing current4 ,for example1 assume a transformer having a normal ampere capacity of #ajj and1 approximately1 #f amperes magnetizing current1 and assume that three such transformers are used with ,y connected secondaries for operating a synchronous converter connected to a three wire ,edison system4 ,allowing #be per cent4 unbalancing1 the current will divide equally among the three legs giving #h4cc amperes per leg1 which is more than the normal magnetizing current4 ,the loss due to this current is1 however1 inappreciable1 but the increased core losses may be considerable4 ,if a distributed winding be used1 the direct current flows in the opposite direction1 around the halves of each core thus entirely neutralizing the flux distortion4 ,whether the straight ,y connection is to be used is merely a question of balancing the increased core loss of the straight ,y connection against the increased copper loss and the greater cost of the interconnected ,y system4 ,the straight ,y connection is much simpler1 and it would be quite permissible to use it for transformers of small capacities where the direct current circulating in the neutral is less than #cj per cent4 of the rated transformer current4 ,the direct current may be derived from a storage battery1 from a separate converter1 or from a motor generator set installed in the sub-station for the purpose4 ,an adjustable rheostat will1 of course1 be connected in the field circuit for regulation4 ,before starting the converter1 however1 it is necessary to do certain wiring between the terminals on the collector side of the machine and the alternating current supply wires1 in order that the change over from direct current motive power to alternating current motive power may be made when the proper phase relations are established between the alternating current in the supply wires and the alternating current in the armature winding of the converter4 ,in order that proper phase relations exist1 the armature of the converter must rotate at such a speed that each coil thereon passes its proper reversal point at the same time as the alternating current reverses in the supply wires4 ,this speed may be calculated by doubling the frequency of the supply current and then dividing by the number of pole pieces on the converter1 but a far more accurate method of judging when the converter is in step or in synchronism with the supply current consists in employing incandescent lamps as shown in fig4 #b1hgb4 ,ques4 ,how is a polyphase converter started with alternating current8 ,ans4 ,this may be done by applying the alternating pressure directly to the collector rings while the armature is at rest4 ,there need be no field excitation2 in fact the field windings on the separate pole pieces should be disconnected from each other before the alternating voltage is applied to the armature1 else a high voltage will be induced in the field windings which may prove injurious to their insulation4 ,the passage of the alternating current through the armature winding produces a magnetic field that rotates about the armature core1 and induces in the pole pieces eddy currents1 which1 reacting on the armature1 exert a sufficient torque to start the converter from rest and cause it to speed up to synchronism4 ,ques4 ,how much alternating current is required to start a polyphase converter8 ,ans4 ,about #ajj per cent4 more than that required for full load4 ,ques4 ,how may this starting current be reduced8 ,ans4 ,transformers may be switched into circuit temporarily to reduce the line wire voltage until the speed become normal4 ,illustration3 ,,fig4 #b1hgb4--,wiring diagram showing arrangement of incandescent lamps for determining the proper phase relations in starting a rotary converter4 ,the alternating current side of a three phase converter is shown at ,c4 ,the three brushes1 ,d1 ,t and ,g pressing on its collector rings are joined in order to the three single pole switches ,h1 ,l and ,b which can be made to connect with the respective wires ,m1 ,r1 and ,v1 of the alternating current supply circuit4 ,across one of the outside switches1 ,h1 for example1 a number of incandescent lamps are joined in series as indicated at ,e1 while the three pole switch 7not shown7 in the main circuit1 between the alternator and the single pole switches is open4 ,if then the main switch just mentioned and the middle switch ,l be both closed1 and the armature of the alternator be brought up to normal speed by running it as a direct current motor1 the lamps at ,e will light up and darken in rapid succession2 the lighting and darkening of the lamps will continue until1 by a proper adjustment of the speed1 the correct phase relations be established between the alternating current in the supply circuit and the alternating current developed in the armature of the converter4 ,as this condition is approached1 the intervals between the successive lighting up and darkening of the lamps will increase until they remain perfectly dark4 ,there is then no difference of pressure between the supply circuit ,m ,r ,v and the rotary converter armature circuit1 so the source of the direct current may at that instant be disconnected from the machine1 and the switches ,h and ,b1 closed4 ,if the change over has been accomplished before the phase relations of the two circuits differed1 the converter will at once conform itself to the supply circuit and run thereon as a synchronous motor without further trouble4 ,the opening of the direct current circuit and the closing of the alternating current supply circuit may be done by hand1 but preferably by employing a device that will automatically trip the circuit breaker in the direct current circuit at the instant the switches in the alternating current circuit are closed4 ,in conjunction with this method1 the method of synchronizing shown in fig4 #b1hgb may be used1 thus1 in starting1 there is an alternating current between the brushes which pulsates very rapidly1 but when synchronism is approached1 the pulsations become less rapid until finally with the converter in step with the alternator the pulsations entirely disappear4 ,the light given by the lamps thus connected indicates accurately the condition of affairs at any one time1 varying from a rapidly fluctuating light at the beginning to one of constant brilliancy at synchronism4 ,illustration3 ,,fig4 #b1hgc4--;,diagram of motor converter4 ,this machine which is only to be used for converting from alternating to direct current1 consists of an ordinary induction motor with phase wound armature1 and a dynamo4 ,the revolving parts of both machines are mounted on the same shaft and from the figure it is seen that the armature of the motor and the armature of the dynamo are also electrically connected4 ,the motor converter is a synchronous machine1 but the dynamo receives the current from the armature of the motor at a frequency much reduced from that impressed upon the field winding of the motor4 ,assuming that the motor and the converter have the same number of pole1 the motor will rotate at a speed corresponding to one-half the frequency of the supply circuit4 ,the motor will operate half as a motor and half as a transformer1 and the converter1 half as a dynamo and half as a synchronous converter1 in that one-half of the electrical energy supplied to the motor will be converted into mechanical power for driving the converter1 while the other one-half is transferred to the secondary motor windings and thereby to the converter armature in the form of electrical power4 ,the capacity of the motor is theoretically only half what it would be if it were to convert the whole of the electrical energy into mechanical power because the rating depends upon the speed of the rotating field and not on that of the rotor4 ,if the two machines have a different number of pole1 or are connected to run at different speeds1 the division of power is at a different but constant ratio4 ,the machine starts up as an ordinary polyphase induction motor and the field of the converter is built up as though it were an ordinary dynamo4 ,motor converters are occasionally used on high frequency systems1 as their commutating component is of half frequency1 and thus permits better commutator design than a high frequency converter4 ,the advantage of this type of machine is that for phase control it requires no extra reactive coils1 the motor itself having sufficient reactance4 ,it is1 however1 larger than standard converters1 but smaller than motor generators1 as half the power is converted in each machine4 ,its efficiency is less than for synchronous converters1 and the danger of reaching double speed in case of a short circuit on the direct current side is very great4 ,it has been used abroad to some extent for #fj cycle work1 in preference to synchronous converters1 but with the present reliable design of #fj cycle converters1 and the general use of #be cycles1 where severe service conditions are met1 as in railroading1 motor converters should not be recommended4 ,ques4 ,if the armature of the starting motor have a starting resistance1 how must this be connected8 ,ans4 ,it should be connected in series with the armature inductors before the alternating voltage is applied4 ,as the motor increases in speed1 the starting resistance is gradually short circuited until it is entirely cut out of circuit4 ,illustration3 ,,fig4 #b1hgd4--,sectional view of ,general ,electric vertical synchronous converter4 ,in this construction1 the field frame carrying the poles is mounted on cast iron pedestals and is split vertically4 ,this allows the two halves of the frame to be separated for inspection or repairs of the armature4 ,the armature1 including commutator and collector rings1 is mounted on a vertical stationary shaft1 which is rigidly supported from the foundation4 ,the thrust of the armature is carried on a roller bearing attached to the top of the shaft and upper side of the armature spider4 ,the under side of the lower plate of the roller bearing is made spherical and fits into a corresponding spherical cup on the end of the shaft1 making the bearing self aligning4 ,the armature spider has a babbitted sleeve along the fit of the vertical shaft1 which acts as a guide bearing and has to take only the thrust due to the unbalancing effect of the rotating parts4 ,a circulating pump furnishes oil to the roller bearing1 the oil draining off through the guide bearing4 ,a marked advantage of this type of construction is the accessibility of the commutator for adjustment of the brushes1 etc41 as there is no pit or pedestal bearing to interfere4 ,,note4--,some converters are provided with a small induction motor for starting mounted on an iron bracket cast in the converter frame1 and whose shaft is keyed to that of the converter4 ,allowing for a certain amount of slip in the induction motor1 the field of this machine must possess a less number of magnet poles than the converter in order to enable the latter machine to be brought to full synchronism4 ,to start the induction motor1 it is simply necessary to apply to its field terminals the proper alternating voltage4 ,the bracket1 and therefore the motor1 is usually mounted outside the armature bearing on the collector side of the converter4 ,illustration3 ,,fig4 #b1hge4--,resistance measurement by drop method4 ,the circuit whose resistance is to be measured1 is connected in series with an ammeter and an adjustable resistance to vary the flow of current4 ,a voltmeter is connected directly across the terminals of the resistance to be measured1 as shown in the figure4 ,according to ,ohm's law ,i ,e ,r1 from which1 ,r ,e ,i4 ,if then the current flowing in the circuit through the unknown resistance be measured1 and also the drop or difference of pressure1 the resistance can be calculated by above formula4 ,in order to secure accurate determination of the resistance such value of current must be used as will give large deflections of the needle on the instruments employed4 ,a number of independent readings should be taken with some variation of the current and necessarily a corresponding variation in voltage4 ,the resistance should then be figured from each set of readings and the average of all readings taken for the correct resistance4 ,great care must be taken1 however1 in the readings1 and the instruments must be fairly accurate4 ,for example1 suppose that the combined instrument error and the error of the reading in the voltmeter should be #a per cent41 the reading being high1 while the corresponding error of the ammeter is #a per cent4 low4 ,this would cause an error of approximately #b per cent4 in the reading of the resistance4 ,in making careful measurements of the resistance1 it is also necessary to determine the temperature of the resistance being measured1 as the resistance of copper increases approximately 4#d of #a per cent4 for each degree rise in temperature4 ,use is made of this fact for determining the increase in temperature of a piece of apparatus when operating under load4 ,the resistance of the apparatus at some known temperature is measured1 this being called the cold resistance of the apparatus4 ,at the end of the temperature test the hot resistance is taken4 ,assume the resistance has increased by #ae per cent4 ,this would indicate a rise in temperature of #cg degrees above the original or cold temperature of the apparatus4 ,suppose then that in measuring the cold resistance1 results are obtained which are #b per cent4 low1 and that in measuring the hot resistance1 there be #b per cent4 error in the opposite direction4 ,this would mean that a total error of #d per cent4 had been made in the difference between the hot and cold resistances1 or an error of #aj degrees4 ,the correct rise in temperature is1 therefore1 about #bg instead of #cg degrees4 ,in other words1 an error of #b per cent4 in measuring each resistance has caused an error of approximately #cf per cent4 in the measurement of the rise in temperature4 ,the constant 4#d which has been used above is only approximate and should not be used for exact work4 ,for detail instructions of making calculations of resistance and temperature1 see ,standardization ,rules of the ,a4,i4,e4,e4 ,ques4 ,describe the usual wiring for the installation of a rotary converter in a sub-station4 ,ans4 ,commencing at the entrance of the high pressure cables1 first there is the wiring for the lightning arresters1 then for the connection in circuit of the high tension switching devices1 from which the conductors are led to bus bars1 and thence to the step down transformers4 ,illustration3 ,figs4 #b1hgf to #b1hgi4--;,how to connect instruments for power measurement4 ,there are several ways of connecting an ammeter1 voltmeter and wattmeter in the circuit for the measurement of power4 ,a few of the methods are discussed below4 ,with some of the connections it is necessary to correct the readings of the wattmeter for the losses in the coil1 or coils1 of the wattmeter1 or for losses in ammeter or voltmeter4 ,this is necessary since the instruments may be so connected that the wattmeter not only measures the load but includes in its indications some of the instrument losses4 ,if the load measured be small1 or considerable accuracy is required1 these instrument losses may be calculated as follows3 ,loss in pressure coils is ,e#b ,r1 in which ,e is the voltage at the terminals of the pressure coil and ,r is the resistance4 ,loss in current coil is ,i#b ,r in which ,i is the current flowing and ,r the resistance of the current coil4 ,in general let ,ev voltage across terminals of the voltmeter2 ,ew voltage across the terminals of the pressure coil of the wattmeter2 ,iw current through current coil of wattmeter2 ,ia current through current coil of ammeter2 ,rv resistance of pressure coil of voltmeter2 ,rw resistance of pressure coil of wattmeter2 ,r#aw resistance of current coil of wattmeter2 ,ra resistance of current coil of ammeter4 ,then the losses in the various coils will be as follows3 ,e#bv ,rv loss in pressure coil of voltmeter4 ,e#bw ,rw loss in pressure coil of wattmeter4 ,i#bw ,rv loss in current coil of wattmeter4 ,i#b;a,ra loss in current coil of ammeter4 ,if connection be made as in fig4 #b1hgf1 the correct power of the circuit will be the wattmeter reading ,w-7,e#bv ,rv ,e#bw ,rw7 in which ,ev ,ew4 ,in fig4 #b1hgg1 the power is ,w-,e#bw ,rw4 ,in fig4 #b1hgh1 the power is ,w-,i#bw,r#aw1 or the correct power is the wattmeter reading minus the loss in the current coil of the wattmeter4 ,in fig4 #b1hgi1 the power is ,w-7,e#bw ,rw ,i#b;a,ra7 ,the usual method of connection is either as in fig4 #b1hgf or fig4 #b1hgg4 ,in either case the current reading is that of the load plus the currents in the pressure coils of the voltmeter and wattmeter4 ,unless the current being measured1 however1 is very small1 or extreme accuracy is desired1 it is unnecessary to correct ammeter readings4 ,in fig4 #b1hgg a small error is introduced due to the fact that the actual voltage applied to the load is that given by the voltmeter minus the small drop in voltage through the current coil of the wattmeter4 ,if an accurate measure of the current in connection with the power consumed by the load be required1 the connections shown in fig4 #b1hgi are used1 and if extreme accuracy is required1 the wattmeter reading is reduced by the losses in the ammeter and in the pressure coil of the wattmeter4 ,the loss in the pressure coil of a wattmeter or voltmeter may be as high as #ab or #ae watts at #bbj volts4 ,the loss in the current coil of a wattmeter with #aj amperes flowing may be #f or #h watts4 ,it can be easily seen that if the core or copper losses of small transformers are being measured1 it is quite necessary to correct the wattmeter readings1 for the instrument losses4 ,in measuring the losses of a #be or #ej ,h4,p4 induction motor1 the instrument losses may be neglected4 ,a careful study of the above will show when it becomes necessary to correct for instrument losses and the method of making these corrections4 ,connections are seldom used which make it necessary to correct for the losses in the current coils of either ammeter or wattmeter1 as the losses vary with the change in the current4 ,on the other hand1 the voltages generally used are fairly constant at #aaj or #bbj1 and when the losses of the pressure coils at these voltages have once been calculated1 the necessary instrument correction can be readily made4 ,on a three phase system the transformers should be joined in delta connection1 as a considerable advantage is thereby gained over the star connection1 in that should one of the transformers become defective1 the remaining two will carry the load without change except more or less additional heating4 ,between the transformers and rotary converter the circuits should be as short and simple as possible1 switches1 fuses1 and other instruments being entirely excluded4 ,the direct current from the converter is led to the direct current switchboard1 and from there distributed to the feeder circuits4 ,,wattmeter ,,error ,,for ,a ,,load ,,of #a1jjj ,,volt-,,amperes 7,for a lag of #a degree in the pressure coil7 ---------------------------------------- -------- ,error of indication ,power factor,true watts ,error in per cent of true value ---------------------------------------- -------- #a4 #a1jjj 4#c #j4jc 4#i #ijj #g4f #j4he 4#h #hjj #aj4e #a4ca 4#g #gjj #ab4e #a4gh 4#f #fjj #ac4i #b4cb 4#e #ejj #ae4a #c4jb 4#d #djj #ae4i #c4ih 4#c #cjj #af4f #e4ed 4#b #bjj #ag4a #h4ee 4#a #ajj #ag4c #ag4cj ---------------------------------------- -------- ,,note4--,in the iron vane type instrument when used as a wattmeter1 the current of the series coil always remains in perfect phase with the current of the circuit1 provided series transformers are not introduced4 ,the error1 then1 is entirely due to the lag of the current in the pressure coil1 and this error in high power factor is exceedingly small1 increasing as the power factor decreases4 ,in the above table it should be noted that the value of the error as distinguished from the per cent4 of error1 instead of indefinitely increasing as the power factor diminishes1 rapidly attains a maximum value which is less than #b per cent4 of the power delivered under the same current and without inductance4 ,it should also be noted that the above tabulation is on the assumption of a lag of #a degree in the pressure coil4 ,the actual lag in ,wagner instruments for instance1 is approximately 4#jhe of a degree1 and the error due to the lag of the pressure coil in ,wagner instruments is1 therefore1 proportionally reduced from the figures shown in the above tabulation4 ,ques4 ,in large sub-stations containing several rotary converters how are they operated8 ,ans4 ,frequently they are installed to receive their respective currents from the same set of bus bars2 that is1 they may be operated as alternating current motors in parallel4 ,they are also frequently operated independently from single bus bars1 but very seldom in series with each other4 ,illustration3 ,,fig4 #b1hhj4--,single phase motor test4 ,in this method of measuring the input of a single phase motor of any type1 the ammeter1 voltmeter and wattmeter are connected as shown in the illustration4 ,the ammeter measures the current flowing through the motor1 the voltmeter1 the pressure across the terminals of the motor1 and the wattmeter the total power which flows through the motor circuit4 ,with the connections as shown1 the wattmeter would also measure the slight losses in the voltmeter and the pressure coil of the wattmeter1 but for motors of ,h4,p4 and larger1 this loss is so small that it may be neglected4 ,the power factor may be calculated by dividing the true watts as indicated by the wattmeter1 by the product of the volts and amperes4 ,ques4 ,how may the direct current circuit be connected8 ,ans4 ,in parallel4 ,,note4--,in motor testing1 by the methods illustrated in the accompanying cuts1 it is assumed that the motor is loaded in the ordinary way by belting or direct connecting the motor to some form of load1 and that the object is to determine whether the motor is over or under loaded1 and approximately what per cent4 of full load it is carrying4 ,all commercial motors have name plates1 giving the rating of the motor and the full load current in amperes4 ,hence the per cent4 of load carried can be determined approximately by measuring the current input and the voltage4 ,if an efficiency test of the apparatus be required1 it becomes necessary to use some form of absorption by dynamometer1 such as a ,prony or other form of brake4 ,the output of the motor can then be determined from the brake readings4 ,the scope of the present treatment is1 however1 too limited to go into the subject of different methods of measuring the output of the apparatus1 and is confined rather to methods of measuring current input1 voltage1 and watts4 ,the accuracy of all tests is obviously dependent upon the accuracy of the instruments employed4 ,before accepting the result obtained by any test1 especially under light or no load1 correction should be made for wattmeter error4 ,see table of wattmeter error on page #b1jge4 ,illustration3 ,,fig4 #b1hha4--,three phase motor test2 voltmeter and ammeter method4 ,if it be desired to determine the approximate load on a three phase motor1 this may be done by means of the connections as shown in the figure1 and the current through one of the three lines and the voltage across the phase measured4 ,if the voltage be approximately the rated voltage of the motor and the amperes the rated current of the motor 7as noted on the name plate7 it may be assumed that the motor is carrying approximately full load4 ,if1 on the other hand1 the amperes show much in excess of full load rating1 the motor is carrying an overload4 ,the heat generated in the copper varies as the square of the current4 ,that generated in the iron varies anywhere from the #a4f power1 to the square4 ,this method is very convenient if a wattmeter be not available1 although1 it is1 of course1 of no value for the determination of the efficiency or power factor of the apparatus4 ,this method gives fairly accurate results1 providing the load on the three phases of the motor be fairly well balanced4 ,if there be much difference1 however1 in the voltage of the three phases1 the ammeter should be switched from one circuit to another1 and the current measured in each phase4 ,if the motor be very lightly loaded and the voltage of the different phases vary by #b or #c per cent41 the current in the three legs of the circuit will vary #bj to #cj per cent4 ,ques4 ,what provision should be made against interruption of service in sub-stations8 ,ans4 ,there should be one reserve rotary converter to every three or four converters actually required4 ,ques4 ,why does a rotary converter operate with greater efficiency1 and require less attention than does a dynamo of the same output8 ,ans4 ,there is less friction1 and less armature resistance1 the latter because the alternating current at certain portions of each revolution passes directly to the commutator bars without traversing the entire armature winding as it does in a dynamo2 there is no distortion of the field and consequently no sparking1 or shifting of the brushes1 since the armature reaction resulting from the current fed into the machine and that due to the current generated in the armature completely neutralizes each other4 ,illustration3 ,,fig4 #b1hhb4--,three phase motor test by the two wattmeter method4 ,if an accurate test of a three phase motor be required1 it is necessary to use the method here indicated4 ,assume the motor to be loaded with a brake so that its output can be determined4 ,this method gives correct results even with considerable unbalancing in the voltages of the three phases4 ,with the connections as shown1 the sum of the two wattmeter readings gives the total power in the circuit4 ,neither meter by itself measures the power in any one of the three phases4 ,in fact1 with light load one of the meters will probably give a negative reading1 and it will then be necessary to either reverse its current or pressure leads in order that the deflection may be noted4 ,in such cases the algebraic sums of the two readings must be taken4 ,in1 other words1 if one read plus #ejj watts and the other1 minus #cjj watts1 the total power in the circuit will be #ejj minus #cjj1 or #bjj watts4 ,as the load comes on1 the readings of the instrument which gave the negative deflection will decrease until the reading drops to zero1 and it will then be necessary to again reverse the pressure leads on this wattmeter4 ,thereafter the readings of both instruments will be positive1 and the numerical sum of the two should be taken as the measurement of the load4 ,if one set of the instruments be removed from the circuit1 the reading of the remaining wattmeter will have no meaning4 ,as stated above1 it will not indicate the power under these conditions in any one phase of the circuit4 ,the power factor is obtained by dividing the actual watts input by the product of the average of the voltmeter readings the average of the ampere readings #a4gc4 ,what electrical difficulty is experienced with a rotary converter8 ,ans4 ,regulation of the direct current voltage4 ,ques4 ,how is this done8 ,ans4 ,it can be maintained constant only by preserving uniform conditions of inductance in the alternating current circuit1 and uniform conditions in the alternator4 ,while changes in either of these may be compensated to a certain extent by adjustment of the field strength of the converter1 they cannot be entirely neutralized in this manner2 it is therefore necessary that both the line circuit and the alternator be given attention if the best results are to be obtained from the converter4 ,ques4 ,what mechanical difficulty is experienced with rotary converters8 ,ans4 ,hunting4 ,ques4 ,what is the cause of this8 ,ans4 ,it is due to a variation in frequency4 ,the inertia of the converter armature tends to maintain a constant speed2 variations in the frequency of the supply circuit will cause a displacement of phase between the current in the armature and that in the line wires1 which displacement1 however1 the synchronizing current strives to decrease4 ,the synchronizing current1 although beneficial in remedying the trouble after it occurs1 exerts but little effort in preventing it1 and many attempts have been made to devise a plan to eliminate this trouble4 ,,note4--,three phase motor test2 polyphase wattmeter method4 ,this is identical with the test of fig4 #b1hhb1 except that the wattmeter itself combines the movement of the two wattmeters4 ,otherwise the method of making the measurements is identical4 ,if the power factor be known to be less than #ej per cent41 connect one movement so as to give a positive deflection2 then disconnect movement one and connect movement two so as to give a positive deflection4 ,then reverse either the pressure or current leads of the movement1 giving the smaller deflection1 leaving the remaining movement with the original connections4 ,the readings now obtained will be the correct total watts delivered to the motor4 ,if the power factor be known to be over #ej per cent41 the same methods should be employed1 except that both movements should be independently connected to give positive readings4 ,an unloaded induction motor has a power factor of less than #ej per cent41 and may1 therefore1 be used as above for determining the correct connections4 ,for a better understanding of the reasons for the above method of procedure1 the explanation of the two wattmeter method1 fig4 #b1hhb1 should be read4 ,the power factor may be calculated as explained under fig4 #b1hhb4 ,connect as shown in fig #b1hhb4 ,the following check on connection may be made4 ,let the polyphase induction motor run idle1 that is1 with no load4 ,the motor will then operate with a power factor less than #ej per cent4 ,the polyphase meter should give a positive indication1 but if each movement be tried separately one will be found to give a negative reading1 the other movement will give a positive reading4 ,this can be done by disconnecting one of the pressure leads from the binding post of one movement4 ,when the power factor is above #ej per cent4 then both movements will give positive deflection4 ,ques4 ,what are the methods employed to prevent hunting8 ,ans4 #a1 the employment of a strongly magnetized field relative to that developed by the armature2 #b1 a heavy flywheel effect in the converter2 #c1 the increasing of the inductance of the armature by sinking the windings thereon in deep slots in the core1 the slots being provided with extended heads2 and #d1 the employment of damping devices or amortisseur winding on the pole pieces of the converter4 ,illustration3 ,,fig4 #b1hhc4--,three phase motor test2 one wattmeter method4 ,this method is equivalent to the two wattmeter method with the following difference4 ,a single voltmeter 7as shown above7 with a switch1 ,a1 can be used to connect the voltmeter across either one of the two phases4 ,three switches1 ,b1 ,c and ,d1 are employed for changing the connection of the ammeter and wattmeter in either one of the two lines4 ,with the switches ,b and ,d in the position shown1 the ammeter and wattmeter series coils are connected in the left hand line4 ,the switch ,c must be closed under these conditions in order to have the middle line closed4 ,another reading should then be taken before any change of load has occurred1 with switch ,a thrown to the right1 switch ,b closed1 switch ,d thrown to the right and switch ,c opened4 ,the ammeter and the current coil of the wattmeter will then be connected to the middle line of the motor4 ,in order to prevent any interruption of the circuit1 the switches ,b1 ,d and ,c should be operated in the order given above4 ,with very light load on the motor the wattmeter will probably give a negative deflection in one phase or the other1 and it will be necessary to reverse its connections before taking the readings4 ,for this purpose a double pole1 double throw switch is sometimes inserted in the circuit of the pressure coil of the wattmeter so that the indications can be reversed without disturbing any of the connections4 ,it is suggested1 before undertaking this test1 that the instructions for test by the two wattmeter and by the polyphase wattmeter methods be read4 ,ques4 ,what method is the best8 ,ans4 ,the damping method4 ,the devices employed for the purpose are usually copper shields placed between or around the pole pieces1 although in some converters the copper is embedded in the poles1 and in others it is made simply to surround a portion of the pole tips4 ,in any case its action is as follows3 ,the armature rotating at a variable speed has a field developed therein which is assumed to be also rotating at a variable speed2 the magnetism of this rotary field induces currents in the copper which1 however1 react on the armature and oppose any tendency toward a further shifting of the magnetism in the armature and therefore prevent the development of additional currents in the copper4 ,since copper is of low resistance1 the induced currents are sufficient in strength to thus dampen any tendency toward phase displacement1 and so exert a steadying influence upon the installation as a whole4 ,illustration3 ,,fig4 #b1hhd4--,three phase motor1 one wattmeter and ,y box method4 ,this method is of service1 only1 provided the voltages of the three phases are the same4 ,a slight variation of the voltage of the different phases may cause a very large error in the readings of the wattmeter1 and inasmuch as the voltage of all commercial three phase circuits is more or less unbalanced1 this method is not to be recommended for motor testing4 ,with balanced voltage in all three phases1 the power is that indicated by the wattmeter1 multiplied by three4 ,power factor may be calculated as before4 ,electrical ,measuring ,instruments4--,in the manufacture of most measuring instruments1 the graduations of the scale are made at the factory1 by comparing the deflections of the pointer with voltages as measured on standard apparatus4 ,the voltmeters in most common use have capacities of #e1 #ae1 #ge1 #aej1 #cjj1 #ejj and #gej volts each1 although in the measurement of very low resistances such as those of armatures1 heavy cables1 or bus bars1 voltmeters having capacities as low as 4#jb volt are employed4 ,illustration3 ,,fig4 #b1hhe4--,test of three phase motor with neutral brought out2 single wattmeter method4 ,some star connected motors have the connection brought out from the neutral of the winding4 ,in this case the circuit may be connected1 as here shown4 ,the voltmeter now measures voltage between the neutral and one of the lines1 and the wattmeter the power in one of the three phases of the motor4 ,therefore1 the total power taken by the motor will be three times the wattmeter readings4 ,by this method1 just as accurate results can be obtained as with the two wattmeter method4 ,the power factor will be the indicated watts divided by the product of the indicated amperes and volts4 ,the difference between the design of direct current voltmeters of different capacities lies simply in the high resistance joined in series with the fine wire coil4 ,this resistance is usually about #ajj ohms per volt capacity of the meter1 and is composed of fine silk covered copper wire wound non-inductively on a wooden spool4 ,in the operation of an instrument1 if the pointer when deflected do not readily come to a position of rest owing to friction in the moving parts1 it may be aided in this respect by gently tapping the case of the instrument with the hand2 this will often enable the obstruction1 if not of a serious nature1 to be overcome and an accurate reading to be obtained4 ,illustration3 ,,fig4 #b1hhf4--,temperature test of a large three phase induction motor4 ,temperature tests are usually made on small induction motors by belting the motor to a generator and loading the generator with a lamp bank or resistance until the motor input is equal to the full load4 ,if1 however1 the motor be of considerable size1 such that the cost of power becomes a considerable item in the cost of testing1 the method here shown may be employed4 ,for this purpose1 however1 two motors1 preferably of the same size and type1 are required4 ,one is driven as a motor and runs slightly below synchronism1 due to its slip when operating with load4 ,this motor is belted to a second machine4 ,if the pulley of the second machine be smaller than the pulley of the first machine1 the second machine will then operate as an induction generator1 and will return to the line as much power as the first motor draws from the line1 less the losses of the second machine4 ,by properly selecting the ratio of pulleys1 the first machine can be caused to draw full load current and full load energy from the line4 ,in this way1 the total energy consumed is equivalent to the total of the losses of both machines1 which is approximately twice the losses of a single machine4 ,the figure shows the connection of the wattmeters1 without necessary switches1 for reading the total energy by two wattmeter method4 ,detailed connection of the wattmeter is shown in fig4 #b1hhc4 ,it is usual1 in making temperature tests1 to insert one or more thermometers in what is supposed to be the hottest part of the winding1 one on the surface of the laminae and one in the air duct between the iron laminae4 ,the test should be continued until the difference in temperature between any part of the motor and the air reaches a steady value4 ,the motor should then be stopped and the temperature of the armature also measured4 ,for the method of testing wound armature type induction motors of very large size1 see fig4 #b1hij4 ,for the approved way of taking temperature readings and interpreting results1 see the ,standardization ,rules of the ,a4,i4,e4,e4 ,ques4 ,describe a two scale voltmeter4 ,ans4 ,in this type of instrument1 one scale is for low voltage readings and the other for high voltage readings2 on these scales the values of the graduations for low voltages are usually marked with red figures1 while those for high voltages are marked with black figures4 ,a voltmeter carrying two scales must also contain two resistances in place of one2 a terminal from each of these coils must be connected with a separate binding post1 but the remaining terminal of each resistance is joined to a wire which connects through the fine wire coil with the third binding post of the meter4 ,the two first mentioned binding posts are usually mounted at the left hand side of the meter and the last mentioned binding post and key at the right hand side4 ,illustration3 ,,fig4 #b1hhg4--;,alternator excitation or magnetization curve test4 ,the object of this test is to determine the change of the armature voltage due to the variation of the field current when the external circuit is kept open4 ,as here shown1 the field circuit is connected with an ammeter and an adjustable resistance in series with a direct current source of supply4 ,the adjustable resistance is varied1 and readings of the voltmeter across the armature1 and of the ammeter1 are recorded4 ,the speed of the generator must be kept constant1 preferably at the speed which is given on the name plate4 ,the excitation or magnetization curve of the machine is obtained by plotting the current and the voltage4 ,the resistance corresponding to the high reading scale is composed of copper wire having the same diameter as that constituting the resistance for the low reading scale1 but as the capacity of the former scale is generally a whole number of times greater than that of the latter scale1 the resistances for the two must bear the same proportion4 ,illustration3 ,,fig4 #b1hhh4--,three phase alternator synchronous impedance test4 ,in determining the regulation of an alternator1 it is necessary to obtain what is called the synchronous impedance of the machine4 ,to obtain this1 the field is connected1 as shown above4 ,voltmeters are removed and the armature short circuited with the ammeters in circuit4 ,the field current is then varied1 the armature driven at synchronous speed1 and the armature current measured by the ammeters in circuit4 ,the relation between field and armature amperes are then plotted4 ,the combination of the results of this test1 with those obtained from the test shown in fig4 #b1hhg1 are used in the determination of the regulation of an alternator4 ,engineers differ widely in the application of the above to the determination of regulation1 and employ many empirical formulae and constants for different lines of design4 ,ques4 ,how is a two scale voltmeter connected8 ,ans4 ,in the connection of a two scale voltmeter in circuit1 the single binding post is always employed regardless of which scale is desired4 ,if1 then1 the voltage be such that it may be measured on the low reading scale1 the other binding post employed is that connected to the lower of the two resistances contained within2 if1 however1 the pressure be higher than those recorded on the low reading scale1 the binding post connected to the higher of the two resistances contained within is used4 ,,note4--,three phase alternator load test4 ,by means of the connection shown in fig4 #b1hhh1 readings of armature current and field amperes can be obtained with any desired load4 ,the field current can be varied also so as to maintain constant armature voltage irrespective of load2 or the field current may be kept constant and the armature voltage allowed to vary as the load increases4 ,the connections may also be used to make a temperature test on the alternator by loading it with an artificial load4 ,in some cases after the alternator is installed the connection may be used to make a temperature test1 using the actual commercial load the alternator is furnishing4 ,inasmuch as the capacities of the scales are usually marked on or near the corresponding binding posts1 there will generally be no difficulty in selecting the proper one of the two left hand binding posts4 ,illustration3 ,,fig4 #b1hhi4--,three phase alternator or synchronous motor temperature test4 ,in this test two alternators or synchronous motors of same size and type are used1 and are belted together1 one to be driven as a synchronous motor and the other as an alternator4 ,the method employed is to synchronize the synchronous motor with the alternator or alternators on the three phase circuit1 and then connect to the line by means of a three pole single throw switch4 ,the alternator is then similarly synchronized with the alternator of the three phase circuit and thrown onto the line4 ,by varying the field of the alternator it can be made to carry approximately full load1 and the motor will then be also approximately fully loaded4 ,the usual method is to have the motor carry slightly in excess of full load1 and the alternator slightly less than full load4 ,under these conditions the motor will run a little warmer than it should with normal load1 while the alternator will run slightly cooler4 ,temperature measurements are made in the same way as discussed under three phase motors4 ,the necessary ammeters1 voltmeters and wattmeters for adjusting the loads on the motors and generator are shown in above figure4 ,if pulleys be of sufficient size to transmit the full load1 with1 say one per cent4 slip1 the pulley on the motor should be one per cent4 larger in diameter than the pulley on the alternator1 so as to enable the alternator to remain in synchronism and at the same time deliver power to the circuit4 ,with very large machines under test1 it is inadvisable to use the above method as it is sometimes difficult to so adjust the pulleys and belt tension that the belt slip will be just right to make up for the difference in diameter of the pulleys1 and very violent flapping of the belt results4 ,to meet such cases1 various other methods have been devised4 ,one which gives consistent results is shown in fig4 #b1hij4 ,ques4 ,how is a two scale voltmeter connected when the binding posts are not marked8 ,ans4 ,if only an approximate idea is possessed of the voltage to be measured1 it is always advisable to connect to the binding post corresponding to the high reading scale of the meter in order to determine if the measurement may not be made safely and more accurately on the low reading scale4 ,in any case1 some knowledge must be had of the voltage at hand1 else the high reading portion of the instrument may be endangered4 ,illustration3 ,,fig4 #b1hij4--,three phase alternator or synchronous motor temperature test4 ,supply the field with normal field current4 ,the armature is connected in open delta as illustrated1 and full load current sent through it from an external source of direct current1 care being taken to ground one terminal of the dynamo so as to avoid danger of shock due to the voltage on the armature winding4 ,the field is then driven at synchronous speed4 ,if the armature be designed to be connected star for #b1cjj volts1 the voltage generated in each leg of the delta will be #a1ccj volts1 and unless one leg of the dynamo were grounded1 the tester might receive a severe shock by coming in contact with the direct current circuit4 ,the insulation of the dynamo would also be subjected to abnormal strain unless one terminal were grounded4 ,by the above method the field is subjected to its full copper loss and the armature to full copper loss and core loss4 ,temperature readings are taken as per standardization rules of the ,a4,i4,e4,e4 ,this method may also be used with satisfactory results on large three phase motors of the wound rotor type4 ,if the alternator pressure be above #fjj volts1 a pressure transformer should be used in connection with the voltmeter4 ,too much care cannot be taken to observe these precautions whenever the voltmeter is used1 for the burning out or charring of the insulation either in the fine wire coil or in the high resistance of the meter by an excessive current1 is one of the most serious accidents that can befall the instrument4 ,if a voltmeter has been subjected to a voltage higher than that for which it was designed1 yet not sufficiently high to injure the insulation1 but high enough to cause the pointer to pass rapidly over the entire scale1 damage has been done in another way4 ,the pointer being forced against the side of the case in this manner1 bends it more or less and so introduces an error in the readings that are afterward taken4 ,the same damage will be done if the meter be connected in circuit so the current does not pass through it in the proper direction1 although in this case the pointer is not liable to be bent so much as when it is forced to the opposite side of the meter by an abnormal current1 since then it has gained considerable momentum which causes a severer impact4 ,the extent of the damage may be ascertained by noting how far away from the zero mark the pointer lies when no current is passing through the instrument4 ,if this distance be more than two-tenths of a division1 the metal case enclosing the working part should be removed and the pointer straightened by the careful use of a pair of pinchers4 ,illustration3 ,,fig4 #b1hia4--;,direct motor or dynamo magnetization test4 ,the object of this test is to determine the variation of armature voltage without load1 with the current flowing through the field circuit4 ,the armature should be driven at normal speed4 ,the adjustment resistance in the field circuit is varied and the voltage across the armature measured4 ,the curve obtained by plotting these two figures is usually called magnetization curve of the dynamo4 ,it is usual to start with the higher resistance in the field circuit so that very small current flows1 gradually increasing this current by cutting out the field resistance4 ,when the highest no load voltage required is reached1 the field current is then diminished1 and what is called the descending 7as opposed to the ascending7 magnetization curves are obtained4 ,the difference in the two curves is due to the lag of the magnetization behind the magnetizing current1 and is caused by the hysteresis of the iron of the armature core4 ,ques4 ,what should be noted with respect to location of instruments8 ,ans4 ,if they be placed near conductors carrying large currents1 the magnetic field developed thereby will produce a change in the magnetism of the instruments and so introduce an error in the readings4 ,illustration3 ,,fig4 #b1hib4--,shunt dynamo external characteristic test4 ,the external characteristic of a shunt dynamo is a curve showing the relation between the current and voltage of the external circuit4 ,this is obtained by the connection as here shown4 ,the shunt field is so adjusted that the machine gives normal voltage when the external circuit is open4 ,the field current is then maintained constant and the external current varied by varying the resistance in the circuit4 ,by plotting voltage along the vertical1 against the corresponding amperes represented along the horizontal1 the external characteristic is obtained4 ,ques4 ,how should portable instruments be wired8 ,ans4 ,the wires must be firmly secured to the supports on which they rest1 so as to reduce the possibility of their being pulled by accident1 and so causing the instruments to fall4 ,a fall or a rough handling of the meter at once shows its effect on the readings1 for as much harm is done as would result from a similar treatment of a watch4 ,the hardened steel pivots used in all high grade voltmeters are ground and polished with extreme care so as to secure and maintain a high degree of sensitiveness4 ,the jewels on which the moving parts revolve are of sapphire1 and they too must necessarily be made with skill and carefulness2 if1 therefore1 the jewels become cracked and the pivots dulled by careless handling1 the meter at once becomes useless as a measuring instrument4 ,ques4 ,how should readings be taken8 ,ans4 ,the deflection of the pointer should be read to tenths of a division2 this can be done with considerable accuracy1 especially after a little practice4 ,illustration3 ,,fig4 #b1hic4--,load and speed test of direct current shunt motor4 ,the object of this test is to maintain the voltage applied to the motor constant1 and to vary the load by means of a brake and find the corresponding variation in speed of the machine and the current drawn from the circuit4 ,if the motor be a constant speed motor1 the field resistance is maintained constant4 ,the above indicates the method of connecting instruments for the test alone2 for starting the machine the ordinary starting box1 should1 of course1 be inserted4 ,for very accurate results1 a temperature correction should be applied to compensate the effect which the temperature of the atmosphere has upon the resistance of the meter when measurements are being taken4 ,in ordinary station practice the temperature correction is negligible1 being for resistance corresponding to the high scale in first class meters1 less than one-quarter of #a per cent4 for a range of #ce degrees above or #ce degrees below #gj degrees ,fahrenheit4 ,ques4 ,what attachment is sometimes provided on station voltmeters used for constant pressure service8 ,ans4 ,a normal index4 ,illustration3 ,,fig4 #b1hid4--,temperature test of direct current motor or dynamo2 loading back method4 ,in making temperature tests on a small dynamo it is usual to drive the dynamo with a motor and load the dynamo by means of a lamp bank or resistance1 the voltage across the dynamo being maintained constant1 and the current through the external circuit adjusted to full load value4 ,the temperatures are then recorded1 and when they reach a constant value above the temperature of the atmosphere1 the test is discontinued4 ,similarly1 in making a test on a small motor1 the motor is loaded with a dynamo and the load increased until the input current reaches the normal full load value of the motor1 the test being conducted as for a small dynamo4 ,when1 however1 the apparatus1 either motor or dynamo1 reaches a certain size1 it becomes necessary1 in order to economize energy1 to use what is called the loading back method1 as here illustrated4 ,the motor is started in the usual way1 with the dynamo belted to it1 the circuit of the dynamo being open4 ,the field of the dynamo is then adjusted so that the dynamo voltage is equal to that of the line4 ,the dynamo is then connected to the circuit and its field resistance varied until it carries normal full load current4 ,under these conditions1 if the motor and dynamo be of the same size and type1 the motor will carry slightly in excess of full load1 the difference being approximately twice the losses of the machines4 ,under these conditions the total power drawn from the line is equal to twice the loss of either machine4 ,temperature readings are taken as in other temperature tests4 ,ques4 ,what precaution must be taken in connecting station voltmeters8 ,ans4 ,care must be taken to guard against any short circuiting of the voltmeter1 which1 would mean a short circuiting of the generator1 and as a result the probable burning out of its armature4 ,the high resistance of the voltmeter prevents any such occurrence when it is connected in the proper way1 but should one side of the circuit be grounded to the metal case or frame of the meter1 a careless handling of the lead connected with the other side of the circuit would produce the result just mentioned4 ,illustration3 ,,fig4 #b1hie4--;,compound dynamo external characteristics test2 adjustable load4 ,the object of this test is to determine the relation between armature voltage and armature current4 ,shunt field is adjusted to give normal secondary voltage when the external circuit is open4 ,the load is then applied by means of an adjustable resistance or lamp bank1 and readings of external voltage and current recorded4 ,if the machine be normally compounded1 the external voltage will remain practically constant throughout the load range4 ,if the machine be under-compounded1 the external voltage will drop with load1 while if over-compounded1 there will be a rise in voltage with increase in load4 ,ques4 ,why do station voltmeters indicate a voltage slightly lower than actually exists across the leads8 ,ans4 ,since they are usually connected permanently in circuit2 a certain amount of heat is developed in the wiring of the instrument4 ,illustration3 ,,figs4 #b1hif and #b1hig4--,transformer core loss and leakage1 or exciting current test4 ,with the primary circuit open1 the ammeter indicates the exciting or no load current4 ,it should be noted that all instruments are inserted on the low voltage side1 for both safety of the operator and because the measurements are more accurate4 ,the no load primary current1 if the ratio of transformation be #aj3 #a1 will be one-tenth of the measured secondary current4 ,the wattmeter connected1 as shown1 measures the sum of the losses1 in the transformer1 in the pressure coil of the wattmeter1 and in the voltmeter4 ,on all standard makes of portable instruments1 the resistance of the wattmeter pressure coil and of the voltmeter is given1 and the loss in either instrument is the square of the voltage at its terminals1 divided by its resistance4 ,subtracting these losses from the total indicated upon the wattmeter1 gives the true core or iron loss4 ,it should be noted that in this diagram is shown an auxiliary transformer with a number of taps for obtaining the exact rated voltage of the transformer under test4 ,in fig4 #b1hig is shown1 in general1 the same connections as in fig4 #b1hif1 except that the auto-transformer has been replaced by a resistance4 ,if the line voltage available be not much in excess of the rated voltage of the transformer under test1 very little error is introduced by the use of the resistance method4 ,however1 if the difference be #aj per cent4 or more the auxiliary transformer shown in fig4 #b1hif should be used4 ,measurements made under the resistance method always give lower results than those obtained with the auxiliary transformer4 ,the effect of this heat increases the voltmeter resistance and consequently reduces the current below that which otherwise would pass through the meter2 since the deflections of the pointer are governed by the strength of the current1 station voltmeters invariably indicate a voltage slightly lower than that which actually exists across their leads4 ,illustration3 ,,fig4 #b1hih4--;,diagram of connections for calibrating a wattmeter4 ,the calibration of a portable wattmeter is accomplished with direct current of constant value which is passed through the series winding by connecting the source thereof with the current terminals4 ,a direct current voltage which may be varied throughout the range of the wattmeter is also applied to the instrument between the middle and right hand pressure terminals ,a and ,e the wiring in the meter between these terminals being such that its differential winding is then cut out of circuit4 ,the method of procedure consists in comparing the deflections on the wattmeter at five of six approximately equidistant points over its scale with the corresponding products of volts and amperes used to obtain them4 ,the changes in the wattmeter deflections are effected by merely varying the voltage1 the value of the current being maintained constant at a value which represents the full current capacity of the meter4 ,,note4--,checking up of a recording wattmeter4 ,this may conveniently be done by noting the deflections at short intervals on an ammeter connected in circuit1 and also the readings on the dial of the recording wattmeter during this period4 ,if this test be continued for an appreciable time1 the product of the pressure in volts1 the current in amperes1 and the time in hours1 should equal the number of watthours recorded on the counters of the dial4 ,,note4--,transformer testing4 ,in the early days of transformer building1 before the commercial wattmeter had been perfected1 leakage or exciting current was the criterion of good design4 ,after the introduction of the wattmeter1 core loss became the all important factor1 and for a long time the question of leakage current was lost sight of4 ,with the introduction of silicon steel1 leakage or exciting current again assumed prominence4 ,keeping in mind the fact that all characteristics of a transformer are of more or less importance1 it is essential that the user of such apparatus have at hand the necessary facilities for making tests of all such variable quantities4 ,the tests which all users of transformers should make1 are given in this chapter4 ,ques4 ,can direct current be measured by an alternating current voltmeter8 ,ans4 ,yes4 ,illustration3 ,,fig4 #b1hii4--,transformer copper loss by wattmeter measurement and impedance4 ,at first glance1 this method would seem better than the calculation of loss after measurement of the resistance4 ,however1 it should be noted that the wattmeter is1 in itself1 subject to considerable error under the low power factor that will exist in this test4 ,the secondary of the transformer is short circuited1 and a voltage applied to the primary which is just sufficient to cause full load primary current4 ,if full current pass through the primary of the transformer with the secondary short circuited1 the secondary will also carry full load current4 ,with connections as shown1 and with the full load current1 the voltmeter indicates the impedance volts of the transformer4 ,this divided by the rated voltage gives what is called the per cent4 impedance of the transformer4 ,in a commercial transformer of #e kw41 this should be approximately #c per cent4 ,the iron loss of the transformer under approximately #c per cent4 of the normal voltage will be negligible1 and the losses measured will be the sum of the primary and secondary copper losses4 ,as in the discussion of the core loss measurements1 the wattmeter readings must be corrected for the loss in its pressure coil1 the method of correction being the same as that discussed under the core loss measurement4 ,if the impedance volts1 as measured1 be divided by the primary current1 the impedance of the transformer is obtained4 ,the reciprocal of this quantity is known by the term admittance4 ,when two or more transformers are connected in parallel they divide the load in proportion to their admittance4 ,it is1 therefore1 important that the users of transformers know the impedance of the apparatus used1 in order to determine whether two or more transformers will operate satisfactorily in parallel4 ,for discussion of wattmeter error on low power factor1 see note on page #b1jge4 ,for accurate measurement of impedance1 the voltmeter should be connected directly across the terminals of the transformer rather than as shown in the diagram4 ,,note4--,transformer copper loss test4 ,the usual and best method of obtaining copper losses is to separately measure the primary and secondary resistance and calculate from these the primary and secondary copper losses4 ,for general diagram of connections and discussion of the drop method1 see fig4 #b1hge4 ,the current should be kept well within the load current of the transformer to avoid temperature rise during the test4 ,in other words1 the resistance of the coil is the voltage across its terminals divided by the current4 ,the resistance of the primary coil can be measured similarly4 ,the copper loss in watts in each coil will then be the product of the resistance and the square of the rated current for that coil4 ,the total copper loss will be the sum4 ,ques4 ,what would be the effect of placing a direct voltmeter across an alternating current circuit1 and why8 ,ans4 ,there would be no deflection of the pointer owing to the rapid reversals of the alternating current4 ,ques4 ,what are the usual capacities of alternating current voltmeters8 ,ans4 ,they are #c1 #g4e1 #aj1 #ab1 #ae1 #bj1 #fj1 #ge1 #abj1 #aej1 #cjj and #fjj volts1 but these capacities may each be increased by the use of a multiplier4 ,illustration3 ,,fig4 #b1ijj4--,temperature test of transformer with non-inductive load4 ,the figure shows the simplest way of making the test4 ,connect the primary of the transformer to the line as shown1 and carry normal secondary load by means of a bank of lamps or other suitable resistance1 until full load secondary current is shown by the ammeter in the secondary circuit4 ,the transformer should then be allowed to run at its rated load for the desired interval of time1 temperature readings being made of the oil in its hottest part1 and also of the surrounding air4 ,where temperatures of the coil rather than temperatures of the oil are desired1 it is necessary to use the resistance method4 ,this is obtained by first carefully measuring the resistance of both primary and secondary coils at the temperature of the room1 and then1 after the transformer has been under heat test for the desired time1 disconnect it from the circuit and again measure the resistance of primary and secondary4 ,for proper method of calculating the temperature rise from resistance measurements1 the reader is referred to the standardization rules of the ,a4,i4,e4,e4 ,in making resistance measurements of large transformers by the drop method care should be taken to allow both ammeter and voltmeter indications to settle down to steady values before readings are taken4 ,this may require several minutes4 ,each time the current is changed it is necessary in order to obtain check values on resistance measurements1 to wait until the current is again settled to its permanent value before taking readings4 ,all resistance measurements must be taken with great care1 as small errors in the measurement of the resistance may make very large errors in the determination of the temperature rise4 ,the method above described is satisfactory for small transformers4 ,where large units are to be tested1 the cost of current for testing becomes an important item4 ,the bucking test as in fig4 #b1ija1 is more economical4 ,ques4 ,how are station voltmeters usually attached to the switchboard8 ,ans4 ,they are usually bolted to the switchboard by means of four iron supports mounted on the back of the instrument2 two of these are fastened near each side of the case4 ,under certain conditions1 however1 as in paralleling of alternators1 it is convenient to have the alternating current voltmeter mounted on a swinging bracket at the side of the switchboard4 ,the voltmeter may then be swung around in any desired direction so as to enable the attendant to keep informed of the voltage while switching in each additional alternator4 ,illustration3 ,,fig4 #b1ija4--,transformer temperature bucking test4 ,for this purpose two transformers of the same size and ratio are required4 ,the connections are as shown4 ,full secondary voltage is applied1 and rheostats or auxiliary auto-transformers are inserted in the circuit to properly regulate the voltage4 ,the primaries are connected with one bucking the other1 and a voltage equal to twice the impedance voltage of either transformer inserted in the primary circuit4 ,it should be noted that when the secondaries are subjected to the full secondary voltage1 a full primary voltage exists across either primary1 but with the primaries connected so that the voltage of one is bucked against the voltage of the other1 the resultant voltage in the circuit will be zero4 ,by applying to the primary circuit twice the impedance voltage of either transformer1 full primary and secondary current will circulate through both transformers4 ,on the other hand1 by subjecting the secondaries to the full secondary voltage1 the iron of the transformer will be magnetized as under its regular operating conditions1 and the full iron loss of the transformer introduced4 ,this method permits the operation of two transformers under temperature test with their full losses1 without taking energy from the line equal to the rated capacity4 ,measurements of temperature are taken in exactly the same way as above4 ,this method is successfully employed for making temperature tests on transformers of all sizes4 ,ques4 ,how should an ammeter be operated to get accurate readings1 and why8 ,ans4 ,it should be cut out of circuit except while taking a reading1 because of the error introduced by the heating effect of the current4 ,illustration3 ,,fig4 #b1ijb4--,transformer insulation test4 ,in applying a #aj1jjj volt insulation test between the primary and secondary of a transformer1 the testing leads should be disconnected from the transformer under test1 and a spark gap introduced as shown1 with the test needle set at a proper sparking distance for #aj1jjj volts4 ,a high resistance should be connected in the secondary before closing its circuit1 and the voltage gradually increased by cutting out this secondary resistance until a spark jumps across the spark gap4 ,when the spark jumps across the spark gap1 the voltmeter reading should be recorded and the testing transformer disconnected4 ,the spark gap should then be increased about #aj per cent4 and the high tension leads connected to the transformer under test as indicated in the diagram4 ,in order to equalize the insulation strains1 all primary leads should be connected together1 all secondary leads not only connected together1 but to the core as well4 ,all resistance in the rheostat in the low tension circuit should then be inserted and the switch closed4 ,gradually cut out secondary resistance until the voltmeter shows the same voltage as was recorded previously when the spark jumped across the gap1 and apply this voltage to the transformer for one minute4 ,insulation tests for a period of over one minute are very unadvisable1 as transformers with excellent insulation may be seriously damaged by prolonged insulation tests4 ,the longer the strain to which any insulation is subjected1 the shorter the subsequent life of the insulation4 ,also the greater the applied voltage above the actual operating voltage of the apparatus1 the shorter the subsequent life of the insulation4 ,in testing small transformers1 the spark gap may be omitted and the voltage of the low pressure coil of the testing transformer measured4 ,this multiplied by the ratio of transformation gives the testing voltage4 ,in an ammeter having a capacity of #ej amperes1 the error thus introduced will be less than #a per cent4 if connected continuously in circuit with a current not exceeding three-quarters this capacity4 ,an ammeter of #ajj amperes capacity may be used indefinitely in circuit with less than #a per cent4 error up to one-half its capacity1 and for five minutes at three-quarters capacity without exceeding the #a per cent4 limit4 ,illustration3 ,,fig4 #b1ijc4--,transformer insulation test as made when a special high tension transformer be not available4 ,in this method a number of standard transformers1 connected as shown may be employed1 but great care should be taken to have such transformer cases thoroughly insulated from the ground and from one another1 in order to minimize the insulation strains in the testing transformers4 ,care should be taken to insert in the circuit of each testing transformer a fuse1 not in excess of the transformer capacity1 which will blow1 in case of a break down in the apparatus under test4 ,in testing insulation between secondary and core1 disconnect the primary entirely1 apply one terminal of the testing transformer to the secondary terminals of the transformer under test1 and the other terminal of the testing transformer to the core of the transformer under test4 ,this test should also not be in excess of one minute4 ,the #aej scale ammeter may be left in circuit for an indefinite length of time at one-third its full capacity1 and for three minutes at one-half its full capacity1 with a negligible error4 ,ammeters of #bjj and of #cjj ampere capacities must not continuously carry more than one-quarter of these loads respectively if the readings are to have an accuracy within #a per cent4 nor more than one-half these respective number of amperes for three minutes if the same degree of accuracy be desired4 ,in order to cut or shunt the ammeter out of circuit when not in use1 it is customary when wiring the instrument in place1 to introduce a switch as a shunt across it2 this switch is kept closed except when a measurement is being taken4 ,when currents larger than #cjj amperes have to be measured1 ammeter shunts are generally employed1 although ammeters up to #ejj amperes capacity are manufactured4 ,illustration3 ,,fig4 #b1ijd4--,transformer internal insulation test1 sometimes called double normal voltage test1 from the fact that most transformers are tested with double normal voltage across their terminals4 ,if either the primary or secondary of the transformer be connected to some source of current with voltage double that of the voltage of the transformer under test1 the insulation between adjacent turns1 and also the insulation between adjacent layers will be subjected to twice the normal operating voltage4 ,it is good practice to employ high frequency for this test in order to prevent an abnormal current from passing through the transformer4 ,sixty cycle transformers are usually tested on #acc cycles1 and #be cycle transformers on #fj cycle circuits for this double normal voltage test4 ,it is necessary to insert the resistance in the circuit of the transformer and bring the voltage up gradually1 the same as applying other high insulation tests in order to prevent abnormal rises in pressure at the instant of closing the circuit4 ,ques4 ,what is used in place of instrument shunts for high pressure alternating current measurements8 ,ans4 ,instrument transformers4 ,ques4 ,what important attention should be periodically given to measuring instruments8 ,ans4 ,they should be frequently tested by comparison with standards that are known to be correct4 ,electrical measuring instruments1 owing to the nature of their construction and the conditions under which they must necessarily be used1 are subject to variations in accuracy4 ,this feature is an annoying one on account of the difficulty of detecting it2 a meter may1 as far as appearances go1 be in excellent working order and yet give readings which are not to be relied upon4 ,ridiculous as it may appear1 the average station attendant may frequently be seen straining his eyes to read to tenths of a division on the scale of a meter which1 if subjected to test1 would show an inaccuracy of over #b per cent4 ,in testing a meter1 by comparing it with a standard1 in order to obtain the best results there should be one man at each meter so that simultaneous readings may be taken on both instruments1 and the man at the standard meter should maintain the voltage constant while a reading is being taken1 by means of a rheostat in the field circuit of the generator supplying the current4 ,illustration3 ,,fig4 #b1ije4--,transformer insulation resistance test4 ,the insulation1 besides being able to resist puncture1 due to increased voltage1 must also have sufficient resistance to prevent any appreciable amount of current flowing between primary and secondary coils4 ,it is1 therefore1 sometimes important that the insulation resistance between primary and secondary be measured4 ,this can be done1 as here shown4 ,great care should be taken to have all wires thoroughly insulated from the ground1 and to have an ammeter placed as near as possible to the terminals of the transformer under test1 in order that current leaking from one side of the line to the other1 external to the transformer1 may not be measured4 ,great care is required in making this measurement1 in order to obtain consistent results4 ,each meter should be checked or calibrated at five or six approximately equidistant points over its scale2 the adjustable resistance being varied each time to give a deflection on the standard meter of an even number of divisions and the deflection on the other meter recorded at whatever it may be4 ,having obtained the necessary readings1 the calculation of the constant or multiplying factor of the meter undergoing test is next in order4 ,this may best be shown by taking an actual case in which a #aej scale voltmeter is being tested to determine its accuracy4 ,the data and calculations are as follows3 ,readings on ,readings on ,constant standard meter meter tested #aej #adi4b #aej #adi4b #a4jje #abe #abe4j #abe #abe4j #a4jjj #ajj #ih4i #ajj #ih4i #a4jaa #ge #gc4f #ge #gc4f #a4jai #ej #ej4j #ej #ej4j #a4jjj #be #bd4h #be #bd4h #a4jjh ------ #f4jdc ,average constant for six readings1 #f4jdc #f #a4jjg4 ,illustration3 ,,fig4 #b1ijf4--,transformer winding or ratio test4 ,the object of this test is to check the ratio between the primary and the secondary windings4 ,for this purpose a transformer of known ratio is used as a standard4 ,connect the transformer under test with a standard transformer as shown4 ,leave switch ,s#b open4 ,with the single pole double throw switch in position ,s#a;,b1 the voltmeter is thrown across the terminals of the standard transformer4 ,with the switch in position ,s#a;,a1 the voltmeter is thrown across the terminals of the transformer under test4 ,the voltmeter should be read with the switch in each position4 ,if the winding ratio be the same as that of the standard transformer1 the two voltmeter readings will be identical4 ,it may be stated in general that before taking the readings for this test1 the zero position of the pointer on the meter tested should be noted1 and if it be more than two-tenths of a division off the zero mark1 the case of the meter should be removed and the pointer straightened4 ,furthermore1 it will be noticed from the readings here recorded that the test is started at the high reading end of the scale2 this is done in order that the pointer may gradually be brought up to this spot1 by slowly cutting out of circuit the adjustable resistance1 and thus show whether or not the pointer has a tendency to stick at any part of the scale4 ,if the meter seem to be defective in this respect1 it should be remedied either by bending the pointer or scale1 or by renewing one or both of the jewels1 before the comparison with the standard is commenced4 ,it is obvious from the readings recorded for the #aej scale voltmeter1 that as compared with the corresponding deflections of the standard1 the former are a trifle low4 ,in order to determine for each observation how much too low they are1 it is necessary to divide each reading on the standard by the corresponding reading on the meter tested4 ,the result is the amount by which a deflection of this size on the meter tested must be multiplied in order to obtain the exact reading4 ,this multiplier is called a constant1 and as shown1 a constant is determined for each of the six observations4 ,the average constant for the six readings is then found1 and this is taken as the constant for the meter as a whole2 that is1 whenever this #aej-scale voltmeter is used1 each reading taken thereon must be multiplied by #a4jjg in order to correct for its inaccuracy4 ,the most convenient and systematic way of registering the constant of a meter is to write it1 together with the number of the meter and the date of its calibration1 in ink on a cardboard tag and loop the same by means of a string to the handle or some other convenient part of the meter4 ,,note4--,transformer polarity test4 ,a test of importance in the manufacture of transformers1 and sometimes necessary for the user1 is the so called banking or polarity test4 ,the transformers from any particular manufacturer have the leads brought out in such a manner that a transformer of any size can be connected to primary and secondary lines in a given order without danger of blowing the fuses due to incorrect connections4 ,all manufacturers of transformers1 however1 do not bank transformers in the same way1 so that it is necessary in placing transformers of different makes to test for polarity4 ,this is done as shown in fig4 #b1ijf4 ,one transformer is selected as a standard and the leads of the second transformer connected as indicated in the diagram4 ,if the transformers be #a1ajj-b1bjj volts to #aaj-bbj1 two #aaj volt lamps are connected in the secondaries of the transformers as indicated1 while the primary of the transformer is connected across the line4 ,in transformers built for two primary and two secondary voltages1 it is necessary to test each primary and each secondary4 ,the diagram shows the method of connecting one #b1bjj volt coil and one #aaj volt coil to the transformer to be tested4 ,when the primary circuit of the transformer under test is closed1 and if the secondary leads of the #aaj volt coil under test be brought out of the case properly1 the two #aaj volt lamps should be brightly illuminated4 ,if1 on the other hand1 the two #aaj volt terminals have been reversed1 no current will flow through the lamps4 ,if these two terminals be found to be brought out correctly1 transfer the secondary leads of the transformer under test to the second #aaj volt coil4 ,upon closing the primary circuit1 the lamp should again be brightly illuminated4 ,repeat this process with each of the secondary coils and the other primary coil1 and if the lamps show up brightly in every case on closing the primary circuit1 all leads have been properly brought out4 ,if on any tests the lamps do not light up brightly1 the leads on the transformer must be so changed as to produce the proper banking4 ,ques4 ,what are the usual remedies applied to a voltmeter to correct a #c or #d per cent4 error8 ,ans4 ,they consist of straightening the pointer1 varying the tension of the spiral springs1 renewing the jewels in the bearings1 altering the value of the high resistance1 and1 in the case of a direct current instrument1 strengthening the permanent magnet4 ,ques4 ,how is the permanent magnet strengthened8 ,ans4 ,after detaching it from the instrument1 wrap around several turns of insulated wire1 and pass through this wire for a short time #c or #d amperes of direct current in such a direction as to reinforce the magnet magnetism4 ,ques4 ,how may the value of the high resistance of a voltmeter be altered8 ,ans4 ,determine the resistance of the voltmeter and add or subtract1 according as the reading is high or low1 a certain length of wire whose resistance is in per cent4 of the voltmeter resistance the same as the per cent4 of error4 ,,note4--,the complete calibration of a two scale voltmeter does not1 as might be supposed1 necessitate that the readings on both scales be checked with standards1 for since the resistance corresponding to the one scale is always some multiple of the resistance of the other1 the constants of the two scales are proportional4 ,for instance1 if ,s the reading at the end of the high scale of the voltmeter2 ,s#a the reading at the end of the low scale of the voltmeter2 ,r the resistance in the meter corresponding to the high scale2 ,r#a the resistance in the meter corresponding to the low scale2 ,k the constant for the high scale1 and ,k#a the constant for the low scale4 ,then ,,sk ,r ,s#a,k#a ,r#a from which ,k#a ,,skr ,s#a,r ,that is to say1 if the respective resistances corresponding to the two scales be known1 and the constant of the high scale be determined by comparison with a standard1 then by aid of these known values and the maximum readings on the two scales1 the constant of the low scale may be calculated4 ,it is also possible to calculate the constant of the high scale if the constant of the low scale be known1 together with the values of the resistances corresponding to the two scales2 for from the equation previously given4 ,k ,,rs#a,k#a ,r#a,s ,ques4 ,what is a frequent cause of error in an alternating current meter1 and why8 ,ans4 ,the deterioration of its insulation1 which permits the working parts of the instrument coming in contact with the surrounding metal case4 ,a convenient method of testing for deterioration of insulation is shown in fig4 #b1ije4 ,illustration3 ,,fig4 #b1ijg4--;,diagrams showing various synchronous converter transformer connections4 ,the diametrical connection is used most frequently as it requires only one secondary coil on each transformer1 this being connected to diametrically opposite points on the armature winding4 ,the middle points can be connected together and a neutral obtained the unbalanced three wire direct current having no distorting effect4 ,with diametrical secondaries1 the primaries should preferably be connected delta1 except with regulating pole converters where they must be connected ,y4 ,diametrical secondaries with delta primaries should not be used with regulating pole converters4 ,double star connection of secondaries may1 however1 be used with delta primaries1 and is free from the trouble of the triple harmonic of the transformer appearing in the primary4 ,in this case1 however1 the two secondary neutrals must not be connected with each other4 ,how to ,test ,generators4--,in the operation of electrical stations1 many problems dealing with the generators installed therein can be readily solved by the aid of characteristic curves1 which bear a relation to the generators similarly as do indicator diagrams to steam engines4 ,illustration3 ,,fig4 #b1ijh4--;,general form of characteristic curves for a series dynamo4 ,the general curve that may be expected is ,,oa4 ,it is obtained practically in the same manner as for the shunt characteristic curve1 except that no field rheostat is employed4 ,commencing with no load or amperes1 there will probably be a small deflection noticeable on the voltmeter1 due to the residual magnetism4 ,the other readings are taken with successive reductions of main current resistance4 ,the curve ,,oa thus obtained for a certain series generator is practically a straight line at the beginning1 representing thereby a proportional increase of voltage with increase of current1 but after a certain current is reached 7about #bj amperes in this case7 the curve flattens and takes a downward direction4 ,the turning point occurs in the characteristic curves of all series generators1 and it denotes the stage at which the iron magnet cores become so saturated with lines of magnetic force that they will not readily allow more to pass through them2 this turning point is technically known as the point of saturation1 and the current corresponding 7#bj amperes in this case7 is called the critical current of the dynamo4 ,the point of saturation in any given series machine is governed by the amount of iron in the magnetic circuit2 its position in the curve therefore varies according to the design of the generator as does also the critical current4 ,the value of the latter is important inasmuch as the valuable features of a series generator assert themselves only when the machine is supplying a greater number of amperes than that of the critical current1 for if the series generator be worked along that part ,m ,a of the curve to the right of the point of saturation it becomes nearly self-regulating as regards current1 because as the current increases the voltage drops4 ,in the diagram in addition to the characteristic curve ,o ,a1 which may more definitely be called an external characteristic curve on account of representing the conditions external to the generator1 there is shown a total characteristic curve1 ,o ,c ,b4 ,the latter curve represents the relation between the current and the total voltage developed in the armature1 and may be plotted from the external characteristic curve if the resistance of the armature between brushes and the resistance of the series field winding be known4 ,for example1 assume these combined resistances amount to 4#f ohm4 ,at #cj amperes there would be required #cj 4#f #ah volts to force this current through the armature and field windings4 ,at #cj amperes the external pressure is #fe volts1 as shown by the curve ,o ,a2 the total voltage developed for #cj amperes is1 therefore1 the external voltage plus the internal voltage or #fe #ah #hc volts4 ,plotting #hc volts for #cj amperes will give one point for the external characteristic curve of this machine1 and by determining in like manner the total voltages developed for six or eight different currents over the scale1 sufficient data will be at hand for plotting and drawing in the curve ,o ,c ,b4 ,in steam engineering1 a man who did not fully understand the method of taking an indicator diagram would be considered not in touch with his profession1 and in electrical engineering the same would be true of one ignorant of the method of obtaining characteristic curves4 ,the necessary arrangement or connection of the generator from which it is desired to obtain a characteristic curve1 consists in providing a constant motive power so that the machine may be run at a uniform speed1 and when the field magnets of the generator are separately excited the field current from the outside source must also be maintained constant1 preferably by a rheostat connected in the field of the auxiliary exciting machine4 ,it is also necessary in every case that means be provided for varying the main current of the generator step by step from zero to maximum4 ,this may best be done by employing a water rheostat1 as shown in fig4 #b1iji4 ,ques4 ,what instruments are needed in making a test of dynamo characteristics8 ,ans4 ,a voltmeter1 ammeter1 speed indicator1 the usual switches and rheostats4 ,ques4 ,how is the apparatus connected8 ,ans4 ,it is connected as shown in fig4 #b1iaj4 ,ques4 ,describe the test4 ,ans4 ,having completed the preliminaries as in fig4 #b1iaj1 the test should be started with the main circuit of the generator open4 ,then1 in the case of the shunt machine1 the speed should be made normal and the field rheostat adjusted until the voltmeter reading indicates the rated voltage of the machine at no load and readings taken4 ,the electrodes of the water rheostat should be adjusted for maximum resistance and main circuit closed1 and a second set of readings taken4 ,several sets of readings are taken1 with successive reductions of water rheostat resistance4 ,the results are then plotted on coordinate paper giving the characteristic curve shown in fig4 #b1ijh4 ,illustration3 ,,fig4 #b1iji4--,water rheostat4 ,it consists essentially of a tank of suitable size containing salt water into which are placed two electrodes having means of adjustment of the distance separating them4 ,the solution depends on the voltage4 ,pure water is seldom used for pressures under #a1jjj volts4 ,the size of the tank is determined by the size of the electrodes1 and roughly the size of the latter equal the number of amperes4 ,with a current density of one ampere per square inch1 a water solution gives a drop of #b1ejj to #c1jjj volts per inch distance between the plates4 ,where high voltage is used1 the water must be circulated through and from the tank by rubber hose allowing for #b1ejj volts1 a length of #ae to #bj feet of #a inch hose to prevent grounding4 ,in place of the arrangement shown above1 a barrel may be used for the tank1 and for the electrodes1 coils of galvanized iron wire4 ,this is the simplest form and is satisfactory4 ,ques4 ,what does the characteristic curve 7fig4 #b1iaa7 show8 ,ans4 ,an examination of the curve shows that the highest point of the curve occurs at no load or #j amperes2 that as the current is increased1 the voltage drops1 first slightly to the point ,b and then rapidly until the point ,e is reached1 when any further lowering of resistance in the main circuit to increase the current causes not only a rapid decline in the voltage but also of the current until both voltage and current become approximately zero4 ,illustration3 ,,fig4 #b1iaj4--;,connections for test of dynamo4 ,during the test1 one man should be assigned to the tachometer1 another man to the water rheostat1 and there should preferably be one man at each of the electrical measuring instruments4 ,in order to enable the man at the tachometer to keep the speed constant1 he should be in communication either directly or indirectly with the source of the driving power1 and the man at the water rheostat should be in plain view of the man reading the ammeter so that the latter party may signal him for the proper adjustment of the rheostat in order that the desired increase of current be obtained for each set of readings4 ,in some generators1 a very slight current results even when the terminals of the machine are actually short circuited2 that is1 due to residual magnetism in the pole pieces1 the lower portion of the curve often terminates1 not exactly at zero1 but at a point some distance along the current line4 ,the working portion of the curve is from ,a to ,c1 at which time the machine is supplying a fairly constant voltage4 ,from ,c to ,e shows a critical condition of affairs1 while the straight portion ,d ,o represents the unstable part of the curve caused by the field current being below its proper value4 ,the position of the point ,c determines the maximum power the machine is capable of developing1 being in this case 7#dg4e #be7 #gdf #a4ei horse power4 ,ques4 ,how may the commercial efficiency of a generator be determined8 ,ans4 ,to obtain the commercial efficiency1 the input and output must be found for different loads4 ,the input may be found by running the generator as a motor at its rated speed1 loading it by means of a ,prony brake4 ,the generator must be stripped of all belting or other mechanical connections1 supplied with its normal voltage and full load current1 and the pressure of the ,prony brake upon its armature shaft or pulley adjusted until the rated speed of the armature is obtained4 ,the data thus obtained is substituted in the formula4 #b ,l ,w ,r input in brake horse power ---------- 7#a7 #cc1jjj in which ,l length of ,prony brake lever2 ,w pounds pull at end of lever2 ,r revolutions per minute4 ,the output or electrical horse power for the same load is easily calculated from the formula amperes volts output in electrical horse power --------------- 7#b7 #gdf ,after obtaining value for 7#a7 and 7#b7 the commercial efficiency for the load taken is obtained from the formula output commercial efficiency ------ 7#c7 input ,having obtained the commercial efficiency1 the difference between the ideal #ajj per cent4 and the efficiency found will be due to certain losses in the generator4 ,these losses may be classified as #a4 ,mechanical4 #b4 ,electrical4 ,the mechanical losses are the friction of the bearings and brushes1 and air friction4 ,the electrical losses consist of the eddy current loss1 hysteresis loss1 armature resistance loss1 and field resistance loss4 ,in testing for these losses1 the generator to be tested should be belted to a calibrated motor which latter machine should preferably be of the constant pressure1 shunt wound type4 ,the friction of the bearings and belt of the generator are determined together by raising the brushes off its commutator and running it at the rated speed by means of the calibrated motor4 ,illustration3 ,,fig4 #b1iaa4--;,characteristic curve of shunt dynamo4 ,suppose in making the test1 the deflections on the meters for the first readings be #fc volts and #j amperes1 the plotting of these values will give the first point on the curve4 ,similarly1 the second readings with main circuit closed and maximum resistance in the water rheostat may be assumed to be #fb4e volts and #g4e amperes1 which plotted gives the second point ,b4 ,a still further lowering of the plate will permit a stronger current in the main circuit1 and the value of this together with its corresponding voltage will give a third point for the curve4 ,neither for this reading1 however1 nor for the following readings of the test should the field rheostat be altered4 ,when six or eight points ranging from zero to a maximum current have been obtained and plotted1 a curved line should be drawn through them such as shown through ,,abcdefg#j1 the characteristic curve of the dynamo4 ,while the curve may be sketched in free hand1 it should preferably be drawn by the aid of ,french curves4 ,in case the ,french curve cannot be exactly made to coincide with all the points as for instance ,c and ,d1 it should be run in between giving an average result1 and smoothing out irregularities1 or small errors due to the personal equation4 ,the meter of course must be correct or calibrated and the readings corrected by the calibration coefficient4 ,the amount of power as ascertained from the calibration curve of the motor for the voltage and current used therein when driving the generator as just explained1 is a measure of these two losses4 ,the power thus used is practically constant at all loads and is about #b per cent4 of that necessary to drive the generator at full load4 ,illustration3 ,,fig4 #b1iab4--;,characteristic curves for a compound dynamo4 ,if the machine be over compounded1 the characteristic curve has the form of the curve ,a ,b1 which curve was obtained from a machine over-compounded from #aah to #abc volts1 and designed to give #bjc amperes at full load4 ,the preliminary arrangements for testing a compound dynamo are similar to those for a shunt generator1 and if the shunt across the series field winding be already made up and in position1 the readings are taken precisely in the same manner4 ,it is generally considered sufficient if observations be recorded at zero1 1 1 and full load4 ,if it be desired to ascertain the effect which residual magnetism has upon the field magnets the current is decreased after the full load point is reached without opening the circuit1 and readings are taken in succession at 1 1 and zero load giving in this case the curve ,b ,c ,d ,e ,s4 ,it is thus seen that residual magnetism exerts no small effect upon the voltage obtained at the different loads1 for had there been no residual magnetism in the field magnets the curve ,b ,c ,d ,e ,s would have coincided with the curve ,a ,b4 ,the curve ,a ,b1 and the straight line ,a ,x drawn through the points ,a and ,b1 are almost identical1 and as ,a ,x represents the theoretical characteristic curve for the machine1 it is seen that compounding is practically perfect4 ,in order to insure such accurate results being obtained1 providing the machinery be correctly designed1 requires considerable care in taking the readings2 for example1 each step or load on the ascending curve should not be exceeded before the corresponding deflection is taken1 else the residual magnetism will cause the pressure reading to be higher than it actually should be1 and the following pressure readings will also be affected in the same manner4 ,in case the shunt to be employed across the series field has not been made up1 it is advisable to perform a trial test before taking the readings for the curve as previously described4 ,the trial test consists in taking two readings1--one at no load and the other at full load1 the shunt being so adjusted as to length and section that the desired amount of compounding will be obtained in the latter reading with normal voltage at no load4 ,if the first trial fail to produce the desired result by giving too low a voltage at full load1 the length of the shunt across the series field should be increased1 or its section should be reduced by employing a less number of strips in its makeup2 again1 if the voltage at full load be higher than that desired1 there must be made a decrease in length or an increase of section in the shunt employed4 ,the friction of the brushes can very conveniently be determined next by lowering them on the commutator and giving them the proper tension4 ,the increase in power resulting from the greater current that will now be taken by the motor to run the dynamo at its rated speed1 will be a measure of this loss4 ,in general1 its value will be about 4#e per cent4 of the total power required to drive the dynamo at full load1 and this also will remain constant at all loads4 ,the friction of the air upon the moving armature of the dynamo cannot be determined experimentally1 but theoretically this loss is small and may be estimated as 4#e per cent42 it is also constant at all loads4 ,the core loss may be determined experimentally by exciting the field magnets of the dynamo with the normal full load field current through the magnet coils1 and noting the increase of power required by the motor to maintain the rated speed of the dynamo thus excited under no load1 over that necessary under the same conditions with no field excitation4 ,this increase of power will be the value of the core loss4 ,the core loss is approximately #c per cent4 of the power required to operate the dynamo at full load1 and it is constant at varying loads4 ,if it be desired to divide the core loss into its component parts1 it is necessary also to run the dynamo under the same conditions as before with field excitation but at half its rated speed4 ,if1 then1 ,h the power lost in hysteresis at rated speed1 ,e the power lost in eddy currents at rated speed1 ,t the power lost in hysteresis and eddy currents at rated speed1 ,s the power lost in hysteresis and eddy currents at half speed4 there may be formed the two following equations3 ,h ,e ,t ,h ,e1 and ,s --- ---1 #b #b from which the elimination of ,h will give ,e #b,t - #d,s4 ,the value of the eddy current loss thus found will be about #a per cent41 and constant at all loads4 ,having previously ascertained the power lost in both eddy currents and hysteresis1 and knowing now the power lost in eddy currents alone1 it is easy to find that lost in hysteresis by simply subtracting the latter known value from the former4 ,the value of the hysteresis loss is therefore approximately #a per cent41 and it is constant at different loads4 ,there yet remains to be determined the armature resistance loss and the field resistance loss4 ,as for the calibrated motor1 this may be disconnected from the dynamo1 as it need not be used further in the test4 ,the armature resistance is the resistance of the armature winding of the dynamo1 between the commutator bars upon which press the positive and negative brushes4 ,assume that the value of the armature resistance be known1 call this value ,r ohms1 together with that of the full load armature current1 which is also known and which call ,i amperes1 this is sufficient data for calculating the armature resistance loss at full load4 ,it is evident that to force the full load current ,i through the armature resistance ,r will require a pressure of ,r volts1 and that the watts lost in doing so will be the voltage multiplied by the current4 ,the armature resistance is consequently ,,ir ,i ,i#b,r watts or1 expressed in horse power it is ,i#b,r #gdf ,at full load it is usually about #b per cent4 of the total power required to drive the generator fully loaded4 ,the armature resistance loss varies in proportion to the load1 in fact1 as the last expression shows1 it increases as the square of the armature current4 ,the field resistance loss is calculated in the same manner as just explained for the armature resistance loss1 it being equal in horse power to the square of the full load field current multiplied by the resistance of the field winding and divided by #gdf4 ,in a shunt dynamo it is practically constant at #b per cent4 of the total power at full load1 but in a series or in a compound generator it will vary in proportion to the load4 ,,hawkins ,,practical ,,library ,,of ,,electricity ,,in ,,handy ,,pocket ,,form ,,price #a ,,each ,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 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