UC-NRLF 
 
 ^B 273 bT4 
 
 ELEMENTS 
 
 OF 
 
 
 APPLIED ELECTRICITY 
 
 BY 
 
 H. H. BLISS 
 
 State Supervisor of Trade and Industrial Education for Nevada, 
 
 Formerly in charge of Extension Engineering Courses 
 
 for the University of California 
 
 ii 
 
 •i \-:A 
 
 PUBLISHED BY 
 
 JOURNAL OF ELECTRICITY 
 
 SAN FRANCISCO. CALIFORNIA 
 
 1920 
 
Digitized by the Internet Archive 
 
 in 2007 with funding from 
 
 IVIicrosoft Corporation 
 
 http://www.archive.org/details/elementsofapplieOOblisrich 
 
ELEMENTS 
 
 OF 
 
 APPLIED ELECTRICITY 
 
 H. H. BLISS 
 
 State Supervisor of Trade and ntdrCStrml Education for Nevada . 
 
 Formerly in charge of Extension Engineering Courses 
 
 for the University of California 
 
 FIRST EDITION 
 
 Copyright. 1920. by Journal of Electricity 
 
 PUBLISHED BY 
 
 JOURNAL OF ELECTRICITY 
 SAN FRANCISCO. CALIFORNIA 
 
 1920 
 
PREFACE 
 
 What do you know about electricity? Can you explain 
 simple circuits, losses, power and efficiency, wiring calcula- 
 tions, how generators and motors are installed, how they 
 work, what efficiency means and how to calculate it, and how 
 current for electric lighting and heating is estimated? 
 
 "Know the fundamentals" is the cry of the hour. Here 
 is a series of discussion which has appeared in the columms 
 of the Journal of Electricity in cooperation with the Extension 
 Division of the University of California on the all-important 
 subject of elementary laws of electricity. The forwarding 
 of this movement is a matter that strongly appeals to every 
 member of the electrical industry — manufacturers, jobbers, 
 central station men, electrical contractors and dealers — and 
 has received the heartiest endorsement of the electrical indus- 
 try from all quarters. These discussions which appeared in 
 the columns of the Journal of Electricity during the year of 
 1919-1920 under the endorsement of the California Electrical 
 Cooperative Campaign, an organization composed of all mem- 
 bers of the electrical industry, have received wide and em- 
 phatic endorsement. 
 
 The author, Mr. H. H. Bliss, for a number of years 
 was head of the technical instruction of the Extension Divis- 
 ion of the University of California, and while occupying that 
 position gave this course through the University Extension in 
 cooperation with the Journal of Electricity. The course 
 proved unusually successful, and aroused interest throughout 
 the West in the study of fundamentals. It is with this same 
 hope that this group of papers may prove of increasing help- 
 fulness that the Journal of Electricity has compiled these 
 pages into book form in order that a permanent record may 
 be had with these papers in one volume so that the biggest 
 and most intensified use of this valuable collection may be 
 offered to that ever growing group of young and enthusiastic 
 as well as ambitious men in our industry who wish to forward 
 themselves to greater remuneration from their employers and 
 to greater usefulness in their chosen profession. 
 
 ROBERT SIBLEY, Editor, 
 
 Journal of Electricity. 
 
 ■;1 -' .^oiri 
 
 ^>TT 
 
 
TABLE OF CONTENTS 
 
 Chapter Page 
 
 IV Ohm's Law and the Electric Circuit 1 
 
 IL Series and Multiple Circuits 8 
 
 III. Power — Losses — Efficiency 15 
 
 IV. Electromagnets — Transformation of Energy 21 
 
 V. Wire Calculations 28 
 
 VL The Generator 35 
 
 VII. Armature and Field Windings 42 
 
 VIII. Losses and Reactions in D.C. Generators 49 
 
 IX. Electrolysis '..... 55 
 
 X. Electric Motors 63 
 
 XL Motor Characteristics 71 
 
 XIL Electric Meters 78 
 
 XIII. Lamps and Illuminations 86 
 
 XIV. Induction — Transformers — Interpoles 94 
 
 438289 
 
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ELEMENTS 
 
 OF 
 
 APPLIED ELECTRICITY 
 
 I 
 
 OHM'S LAW AND THE ELECTRIC CIRCUIT 
 
 Our discussion of electrical principles and prac- 
 tice begins with the consideration of Ohm's Law, 
 which is the basis of all quantita- 
 tive knowledge of circuits and ma- 
 chines. Its fundamental character 
 is recognized in the industry, and 
 the National Electric Light Associ- 
 ation has adopted * for its official 
 emblem the Ohm's Law formula 
 "C = E/R," which appears upon all the stationery 
 and official documents of this nation-wide organi- 
 zation. 
 
 Electric Currents. — In order to utilize electric 
 energy it is necessary to connect the source of the 
 current, such as a battery or generator, to other 
 apparatus, such as motors, heaters, or lamps. There 
 must be a continuous path for the current from the 
 source to the point of use and back again to the 
 source. As soon as this circuit is broken at any 
 point the current stops. 
 
 The materials which can carry electricity are 
 called "conductors." They include all metals, both 
 when solid and liquified (as mercury or melted iron) ; 
 carbon; impure water; earth; moist woods, etc. 
 Materials which stop the flow of electricity more or 
 less completely are termed "insulators.'' These in- 
 
2 ': V^ / '. APFIilED ELECTRICITY 
 
 ^dIi^;lrteL^^s^•|)of•cela^^^ marble, slate, rubber, paper, 
 cloth* wax, ary\^6od','etc. The fact that any water, 
 except chemically pure distilled water, can carry 
 electricity causes such materials as wood, cloth, 
 paper, dirt, etc., to fall into one class or the other 
 according to whether they are dry or wet. And 
 
 A current of gas may 
 be measured in cubic 
 feet per minute, by 
 means of this meter 
 and a watch; an elec- 
 tric current is more 
 easily measured, in 
 "coulombs per second" 
 or "amperes," by means 
 of a single instrument, 
 the ammeter. The^cur- 
 rent in either case must 
 go through the meter. 
 (See Fig. 1., 
 
 small particles or veins of metal in insulating ma- 
 terials sometimes lead the current to places where 
 it is a source of annoyance or danger. Air is gen- 
 erally an insulator, but under certain circumstances 
 it becomes a conductor, as, for example, in the elec- 
 tric arc where large currents flow for a short dis- 
 tance through air. 
 
 Measuring Electric Current. — A current of 
 water in a pipe or a river can be metered in various 
 ways, and the rate of flow can be stated in terms of 
 gallons per second. In a similar way the rate of 
 flow of an electric current can be stated as so many 
 "coulombs per second," but it is more customary to 
 substitute for this phrase the single word "amperes." 
 A statement that "the current is 16 amperes" means 
 that 16 coulombs pass a given point in the wire 
 every second. 
 
OHM'S LAW AND THE ELECTRIC CIRCUIT 3 
 
 Tungsten lamps take currents ranging from .23 
 to .91 amperes in the sizes commonly used (25 to 
 100 watts) ; arc lamps take from 3 to 20 amperes ; 
 a 10 horsepower motor on a 250 volt circuit will take 
 about 40 amperes. 
 
 To measure the rate of flow in an electric cir- 
 cuit we use an instrument called an ''ampere meter" 
 or "ammeter.'' It is inserted into the circuit, as 
 shown in Fig. 1, so that the current must go through 
 the instrument between the source and the load. 
 A needle shaped pointer moving over a scale gives 
 a reading of the current in amperes. 
 
 Fig. 1- — The current goes through the ammeter between the battery and 
 the lamp. When the switch (S) is opened the battery (B) can no longer 
 send current to the lamp and the ammeter needle points to the zero mark. 
 
 Resistance. — ^If in the circuit of Fig. 1 we re- 
 place the lamp by one of different candle power or by 
 a piece of fine iron wire or by an electric bell, we 
 shall find the ammeter giving an entirely different 
 reading. The battery tries equally hard to force 
 electricity through the circuit, but the amount it 
 can send depends upon the apparatus through which 
 the current must flow. We may say that the lamps 
 differ in the amount of "resistance" they offer to the 
 passage of electricity. If one takes three times as 
 many amperes as a second, we may say that it has 
 one-third the resistance of the second. 
 
 Electrical resistance is measured in "ohms." 
 It is thought of as a sort of "electrical friction," 
 like the opposition a rough pipe offers to the flow of 
 water through it. The resistance of a 25 watt Tung- 
 sten lamp is about 485 ohms; that of an electric 
 
4 APPLIE^D ELECTRICITY 
 
 iron, about 25 ohms; the resistance of a piece of 
 copper wire 1/10 inch in diameter and 1000 feet 
 long is one ohm. 
 
 When this switch is 
 opened it stops the cur- 
 rent in a high tension 
 power line by interpos- 
 ing an air resistance of 
 millions of ofhms. When 
 closed, the resistance 
 of the switch is practic- 
 ally zero. The current 
 carried may amount 
 to 300 amperes. To pre- 
 vent the escape of cur- 
 rent, under the enor- 
 mous pressure of 110,- 
 000 volts, the switch 
 has to be supported 
 upon these huge insu- 
 lators. Switches of this 
 type are to be used in 
 connection with the 
 Chicago, Milwaukee & 
 Pu get Sound — the first 
 electric transconti- 
 nental railway. 
 
 Pressure. — We come now to the consideration 
 of a third factor in electric circuits, namely, the 
 "pressure" which forces the current through the 
 wires. There is evidently something in a battery 
 or an electric generator which forces electricity to 
 go out at one terminal and to come back at the 
 other, just as a pump sends water out at one place 
 and draws it in at another. Of course, an open 
 switch or a closed valve may block the flow, but the 
 electric pressure or water pressure is still ready to 
 start the current when opportunity is offered. 
 
 Water pressure is measured in pounds per 
 square inch, by means of a pressure gage. The unit 
 of electrical pressure is the "volt." The pressure 
 or "voltage" in ordinary house circuits is about 110 
 volts; a dry battery has a pressure of about 1.5 
 volts; the voltage applied to street car motors is 
 usually about 550. 
 
OHM'S LAW AND THE ELECTRIC CIRCUIT 5 
 
 There should be no confusion about the words 
 ampere and volt. The number of amperes indicates 
 the rate of flow, without reference to the pressure 
 driving the current. Then "110 volts'' indicates only 
 a tendency to send current with no reference to how 
 much, if any, actually flows. We may have 110 volts 
 and 1, 5, or 500 amperes, or no flow at all, depending 
 upon the resistance in the circuit. 
 
 V 
 
 1 
 
 
 M 
 
 1 
 
 Fig. 2. — Voltmeter Vi measures the electromotive force of the generator ; 
 V2 measures the pressure applied to the motor. 
 
 To measure pressure we use a "voltmeter," an 
 instrument which somewhat resembles an ammeter. 
 To find what voltage is sending (or available to 
 send) current through a circuit or piece of appara- 
 tus, we connect one terminal of the voltmeter to each 
 end of the circuit or to each terminal of the appa- 
 
 Here is an electric warming pad — quite a companion on cold nights. 
 Attached to a 110 volt circuit it takes a current of one-half an ampere. 
 What is its resistance? 
 
 ratus. In Fig. 2 the voltmeter marked ''Y^' meas- 
 ures the ^'voltage across the motor" (the pressure 
 tending to send current through the motor), while 
 the other voltmeter measures the pressure the gen- 
 
APPLIED ELECTRICITY 
 
 erator exerts to send current through the whole cir- 
 cuit. The two instruments need not give equal 
 readings. 
 
 Ohm's Law. — One volt is the pressure needed to 
 
 send one ampere through one ohm resistance. From 
 
 this it follows that the number of volts required to 
 
 send a current through any resistance is equal. to 
 
 the product of the numbers of amperes and ohms. 
 
 This statement, which is known as Ohm's Law, may 
 
 Here is a typical exam- 
 ple of the use of insu- 
 lators and conductors in 
 long distance transmis- 
 sion of electric power. 
 The famous crossing of 
 the lines of the Pacific 
 Gas & . Electric Com- 
 p a n y, at Carquinez 
 Straits in California 
 was for years the most 
 daring enterprise of its 
 kind and today it ranks 
 as the second longest 
 span in the world. Each 
 of the six cables con- 
 sists of 19 strands of 
 steel wire, making a 
 composite size for each 
 cable of %-inch diam- 
 eter, with the remark- 
 able length of 6200 ft. 
 Assuming that a cable 
 6200 ft. long, equiva- 
 lent to No. 1 copper 
 wire, has a resistance 
 of 0.77 ohms and a 
 carrying capacity of 
 150 amperes, what is 
 
 the voltage required to force the current through this 
 resistance, according to Ohm's Law? 
 
 be indicated by a brief formula : "Volts = amperes 
 X ohms.'' Other ways of writing it are: "Am- 
 peres = volts -f- ohms" and "Ohms = volts -^ am- 
 peres.'' All three formulas should be memorized. 
 
 The second of the three formulas may be writ- 
 ten : "Current = electromotive force -^ resistance." 
 Using initials instead of words, C = E -^ R. This is 
 
OHM'S LAW AND THE ELECTRIC CIRCUIT 7 
 
 the symbolic representation of the law as used in 
 the emblem of the N. E. L. A. shown at the head of 
 the chapter. 
 
II 
 
 SERIES AND MULTIPLE CIRCUITS 
 
 Series Circuits. — Many electric circuits consist 
 of several different parts through which the current 
 passes in "series." This means that the electricity- 
 must go through one part after another. Make a 
 clear distinction between this arrangement and the 
 "multiple" circuit in which the current divides and 
 flows through several branches. Fig. 3 illustrates 
 the first and Fig. 4 the second type. 
 
 What is said about these applies to direct cur- 
 rent circuits and also to those alternating current 
 
 aohms 
 
 120 V. 
 
 SLohma 
 
 Fig. 3. — Resistances in Series. In spite of the varying resistance of the 
 various elements of the circuit, the current passing through each is the 
 same — 3 ajmperes. 
 
 circuits which contain only simple resistance and no 
 electromagnetic apparatus or condensers. 
 
 The current leaving the generator in Fig. 3 goes 
 first through an ammeter, then through the upper 
 wire, then through a lamp, then through a resistance 
 coil, and finally back to the generator through the 
 lower wire. It is obvious that if 3 coulombs per 
 second (3 amperes) pass through the generator to 
 the ammeter, the same number must travel along 
 the upper wire through the lamp and the coil and 
 
 8 
 
SERIES AND MULTIPLE CIRCUITS 9 
 
 back to the generator through the lower wire. If 
 any more coulombs passed out through the ammeter 
 than came back through the lower wire there would 
 be an accumulation of electricity somewhere in the 
 right hand part of the circuit ; if any more returned 
 to the generator than left it there would be a pro- 
 duction of coulombs somewhere in the right hand 
 part of the circuit. Both of these alternatives are 
 impossible with this apparatus and hence we con- 
 clude that: 
 
 In a series circuit the current is the same 
 everywhere. 
 
 If a resistance of 2 ohms is in a series of another 
 of 3 ohms, the electromotive force must overcome 
 5 ohms in sending current around the circuit. If we 
 apply 20 volts the amperes will amount to 20-^-5 
 or 4. 
 
 In a series circuit the total ohms = the sum of 
 separate resistances. 
 
 To find the voltage across each one of the re- 
 sistances in the previous example we apply Ohm's 
 Law as usual : 4X2 = 8 volts across one, and 
 4 X 3 = 12 volts across the other. Across the whole 
 combination the pressure =: 4 amps. X 5 ohms = 20. 
 This result is also found by adding the two voltages 
 8 and 12. 
 
 Pressure across a series of resistances equals 
 sum of the voltages across the separate resistances. 
 
 In Fig. 3 a lamp of 31 ohms resistance is in 
 series with a coil having 5 ohms. Current is supplied 
 from a 120 volt generator through two line wires of 
 2 ohms each. What current flows and what pressure 
 is used to force this current through the lamp ? The 
 total resistance is 40 ohms. Hence the current ^=3 
 amperes. To drive 3 amperes through 31 ohms re- 
 quires 3 X 31 or 93 volts, which is the pressure 
 across the lamp. 
 
 Voltage Drop. — In this example we find the 
 pressure across the lamp considerably lower than 
 that supplied by the generator. There has been a 
 
SERIES AND MULTIPLE CIRCUITS 
 
 11 
 
 drop in the voltage from 120 to 93, or 27 volts. This 
 may also be calculated by Ohm's Law. The resist- 
 ance of the circuit between the generator and the 
 
 .Oohrm 
 
 Fig. 4. — Resistances in Multiple. The current divides between the lamp 
 and the resistance coil, 3 amperes being carried by the one, 5 by the other. 
 
 lamp totals 9 ohms. The pressure necessary to 
 force the 3 amperes through this is, of course, 3X9 
 or 27 volts. 
 
 This municipal Christmas tree in a California city was lighted by 70 
 lamps in parallel. Each lamp took .23 ampere and the circuit voltage 
 was 110 at the tree. The current was brought from a transformer on 
 two wires of .12 ohm each. Can you calculate the resistance of each 
 lamp, the combined resistance of all of them, the voltage drop in the 
 wires and the voltage at the transformer? 
 
 The voltage drop in any conductor equals the 
 pressure required to force the current through its 
 resistance. 
 
12 
 
 APPLIED ELECTRICITY 
 
 The drop between a generator and its load de- 
 pends, then, upon both the Hiie resistance and the 
 number of amperes. 
 
 Resistances in Multiple. — When several lamps 
 are located in one lighting fixture they are generally 
 not connected in series with each other. Though 
 
 Two 400-horsepower motors are connected in multiple on the same power 
 circuit. They are furthermore "direct connected" to the same shaft, so 
 that the load is divided equally between them and the motors take equal 
 currents. They lift the mine hoist at the South Eureka gold mine on the 
 Mother Lode in California. 
 
 they are all governed by one wall switch, any lamp 
 can be burned out or unscrewed without affecting 
 the others. In a series circuit this could not be 
 done. 
 
 In Fig. 4 we have a simple example of two re- 
 sistances, a lamp and a coil, connected in "multiple" 
 with each other; that is, connected so that the cur- 
 rent flowing through the ammeter divides and part 
 goes through the lamp and part through the coil. 
 
SERIES AND MULTIPLE CIRCUITS 
 
 13 
 
 Either can be disconnected without stopping the 
 current in the other. This arrangement is some- 
 times spoken of as a "shunt" connection or a "paral- 
 lel" connection. 
 
 Suppose that there is a pressure of 30 volts 
 between the line wires at' point E, close to the load. 
 This is a measure of the effort to send current 
 
 These two fans operate in multiple on the same circuit. Hence either can 
 be turned off without stopping the other. If the line current is 5 amperes 
 at 110 volts when both are operating, what is the voltage and amperage 
 for each motor? What is the resistance of a heater which takes as much 
 current as three fan motors ? 
 
 through the lamp and, if the lamp has 10 ohms re- 
 sistance, it will carry a current of 3 amperes. The 
 same pressure tends to send current through the 
 coil, and, if that has 6 ohms, it will carry 5 amperes. 
 The ammeter will read the sum of these two cur- 
 rents, 8 amperes. 
 
14 APPLIED ELECTRICITY 
 
 In a multiple circuit the voltage is the same 
 across every branch; total current equals the sum 
 of the branch currents. 
 
 Combined Resistance. — As the combination of 
 resistances shown in Fig. 4 takes more current than 
 either one alone, we realize that the combination 
 offers less resistance to current flow than either of 
 its parts. Considering the lamp and coil as united 
 into a piece of apparatus with terminals at B andC, 
 we may compute its resistance from Ohm's Law as 
 volts -^- amperes : 30 -^- 8 = 3.75 ohms. 
 
 A standard way to calculate is to assume one 
 volt applied to the circuit, add the currents which 
 would flow, and divide their sum into the one volt. 
 Trying this on Fig. 4 we have 1/10 + 1/6 = 16/60, 
 the combined current. The resistance = 1-=- 16/60 
 = 60/16 = 3.75 ohms. 
 
 In a multiple circuit combined resistance is less 
 than ohms in any one branch; combined resist- 
 ance =^1-^ sum of reciprocals of branch resistances. 
 
Ill 
 
 POWER— LOSSES— EFFICIENCY 
 
 In stating the "power" of a motor we tell not 
 only how much the machine can do but also how 
 quickly it can do it. A single horse is able to haul 
 an automobile to the top of a certain long hill, but 
 it takes a 40 horsepower engine to perform the work 
 in five minutes. We have, then, two factors which 
 determine the amount of power, the force required 
 and the rate at which it drives the load. 
 
 Fig. 5 — Metering electric power with a watt meter. The reading depends 
 both upon the volts (see connection to the pressure coil, P) and upon 
 the amperes (see connection to the current coil, C). 
 
 In an electric circuit we have what corresponds 
 to a force (the "voltage'' or "pressure") and a quan- 
 tity of electricity which is driven through the wires 
 by this electromotive force. The rate at which the 
 electricity is carried is indicated by the number of 
 amperes of current, or "coulombs per second." Both 
 
 15 
 
16 APPLIED ELECTRICITY 
 
 the voltage and the current, then, are factors in the 
 power necessary to force electricity around a circuit. 
 
 It has been agreed that the simplest practical 
 unit of power would be that required to drive one 
 ampere by a pressure of one volt. This unit is 
 called the "watt" in honor of the man who gave the 
 world its first notions of power. Then if one volt 
 drives current at the rate of 3 amperes, the power is 
 3 watts. If it takes 2 volts to drive 3 amperes, the 
 power is twice as much, or 6 watts. In general, the 
 number of watts equals the product of the number 
 of volts times the number of amperes. 
 
 This statement holds good in direct current cir- 
 cuits and in those alternating current circuits which 
 include no coils, condensers or long parallel lines. 
 With one or more of these, there are reactions which 
 reduce the power requirement below the number of 
 "volt-amperes." The following expression is correct 
 in all cases: 
 
 Watts --= volts X amperes X power factor, 
 where the "power factor" is equal to one or less, 
 generally expressed as a percentage. It varies from 
 60% to 90% in most cases of alternating current 
 motors and transformers, and is 100% for heaters, 
 resistance boxes, incandescent lamps, etc., and for 
 all direct current circuits. 
 
 Watts, Kilowatts and Horse Power. — ^The direct 
 current load carried by an average power house may 
 be 2000 amperes at 550 volts. The output of the ma- 
 chines, then, equals 550X2000 = 1,100,000 watts. 
 This is too large a number to be handled conven- 
 iently, and it is customary in all such cases to use 
 a larger unit, namely, the "kilowatt," which equals 
 1000 watts. Then the load above is expressed as 
 1100 kw. (kilowatts). The general formula is: 
 
 Kilowatts = volts X amperes X power 
 factor -^ 1000. 
 
 It is perfectly feasible to measure the power in 
 electric circuits in terms of the "horse power," 
 which was invented primarily for such machines as 
 
POWER— LOSSES— EFFICIENCY 17 
 
 the steam engine. It has been established by calcu- 
 lation and measurement that one horsepower equals 
 746 watts, or approximately % kw. Thus it is pos- 
 sible to transfer quantities from one system to the 
 other with little difficulty: 
 
 20 hp. (horsepower) = % of 20, or 15 kw., and 
 
 50 kw. = 4/3 of 50, or 66.7 hp. (approximately) . 
 
 Among the many household uses for electric energy, one of the most 
 convenient is illustrated here. With a certain piece of sewing in the 
 machine the motor was found to take a current of 4 amperes, while a 
 watt meter (connected as in Fig. 5) read .12 kw. What was the voltage 
 of the d.c. circuit which supplied the current? 
 
 Power Measurement. — The horsepower output 
 of a gas engine is conveniently measured mechan- 
 ically by making it move a load. One horsepower is 
 required to lift one pound at the rate of 550 feet per 
 second, or to lift 550 lbs. one foot per second. For 
 calculation, 
 
 Hp. = pounds pull X f^^t per second -f- 550. 
 
 Electric power may be measured either by 
 means of a wattmeter, connected as shown in Fig. 5, 
 or by a combination of ammeter, voltmeter and 
 power factor meter. The power factor meter is, of 
 course, not used with circuits which are known to 
 have 100% power factor. The wattmeter has both 
 a "pressure coil" (terminals at P in Fig. 5) and a 
 "current coil" (terminals at C), and their reaction 
 upon each other determines the reading, which is 
 thus proportional to both volts and amperes. On 
 
i5i_2 
 
POWER— LOSSES— EFFICIENCY 19 
 
 a.c. (alternating current) circuits the wattmeter is 
 able to take account of power factor also. 
 
 Losses and Efficiency.— The voltage at the gen- 
 erator end of a short d.c. (direct current) trans- 
 mission line is 250 volts. At the receiving end a 
 voltmeter reads 230 and an ammeter reads 50. The 
 
 This heater has a resistance of 27.5 ohms. What current does it take on 
 a 110 volt circuit? How many watts of power? How many kw. ? How 
 many electrical horse power? 
 
 voltage drop is then 20 volts. The power given the 
 line by the generator = 250 X 50 = 12500 watts or 
 12.5 kw. That delivered by the line = 230 X 50 = 
 11500 watts or 11.5 kw. There is a loss of power 
 of one kw. which is used up in forcing the current 
 through the wires. 
 
 Such a loss always occurs, and it results in heat- 
 ing the wires, just as the energy expended in mov- 
 ing a train changes to heat in the parts where there 
 is friction. 
 
 It is possible to calculate the watt loss in a d.c. 
 circuit by multiplying the voltage drop in the line 
 by the current, as the watts in any part equal volts 
 across that part times amperes. Thus in the exam- 
 ple above we find 20 X 50 = 1000 watts. Further- 
 
20 APPLIED ELECTRICITY 
 
 more, since the volt drop equals ohms X amperes, 
 the watt loss = ohms X amperes X amperes, or the 
 product of resistance times the square of the cur- 
 rent. This last is a most important relation, and it 
 applies to all circuits, both d.c. and a.c. 
 
 When we speak of the "efficiency" of a trans- 
 mission system we have in mind a comparison of the 
 power delivered with power put into the line at the 
 generating end. Strictly, the efficiency is the num- 
 ber found by dividing the "output'' of the line by the 
 "input." As an example, consider a system which 
 delivers 9,000 kw., the current" being 800 amperes 
 and the total line resistance 3 ohms. The loss = 
 3 X 800 X 800 = 1,920,000 watts, or 1,920 kw. The 
 input to the line = 9,000 + 1,920 = 10,920 kw. Then 
 the efficiency of transmission = 9,000 -f- 10,920 = 
 .824, which is 82.4%. 
 
 A mechanical machine, such as a waterwheel, 
 may give out 40 h.p. while receiving 50 h.p. from 
 the water. Its efficiency = 40 -f- 50 == 80 % . No 
 machine has ever been made with efficiency as great 
 as 100%, for some of the energy put in is always 
 lost by friction. No transmission of electricity is 
 100% efficient, for energy is always converted into 
 heat in overcoming resistance. 
 
ELECTROMAGNETS— TRANSFORMATION 
 OF ENERGY 
 
 A soft iron bar with a coil of wire around it 
 becomes a magnet when current flows through the 
 wire. The magnetism disappears when the current 
 stops, so that whatever had been picked up now 
 falls away. A similar "electromagnet" may be made 
 without any iron, but the pull it exerts is far less. 
 
 Magnetic effects are explained on the theory 
 that an electromagnet or a permanent steel magnet 
 produces "lines of force'' which issue from one end 
 or "pole" and return to the other end, and then 
 pass through the instrument itself. Thus eacK line 
 of force is a complete, closed curve. 
 
 The end of the magnet out of which the lines 
 come is called the "north pole" for it is found that, 
 whenever it is so supported as to be free to turn 
 (as by floating it upon a cork or balancing it upon 
 a pivot), this end turns toward the north. The 
 force lines (often called "magnetic flux") enter the 
 magnet at the "south pole," after passing through 
 the air or any iron or steel objects in the neigh- 
 borhood. 
 
 Magnetic flux runs through all substances, but 
 far more easily through iron and steel than any 
 other material. Thus a current flowing in a simple 
 coil produces lines of force, but with an iron core in 
 the coil many more lines are found. And if an iron 
 path is provided for the lines outside the magnet, so 
 they do not have to go through any other material, 
 a large flux can be produced with a small current. 
 
 21 
 
22 APPLIED ELECTRICITY 
 
 Hence, electromagnets are often made in the shape 
 of a horseshoe, and iron paths are provided for the 
 external flux in such electromagnetic machines as 
 generators and motors. 
 
 The amount of flux produced by a magnet de- 
 pends upon the number of turns in the coil and upon 
 the current, as well as upon the material the lines 
 traverse. It is found that 8 amperes through 20 
 turns give exactly the same flux as 40 amperes 
 
 This is a hand magnet 
 used in various ways 
 such as the handling of 
 hot castings, removing 
 iron and steel from 
 materials for making 
 solder and recovering 
 nails from sweepings. 
 
 through 4 turns. In other words, the product of 
 amperes X turns (which is called the "ampere- 
 turns'") determines the tendency to produce flux, 
 while the number of lines actually set up depends 
 also upon the nature of the magnetic path. 
 
 Ammeters. — Applications of electromagnetism 
 are found in the ammeters used for measuring cur- 
 rents on switchboards and elsewhere. One type is 
 illustrated in Fig. 6, which shows the d'Arsonval 
 movement found in one type of ammeter. When the 
 current to be measured flows around the coil at- 
 tached to the pointer, the coil becomes a magnet 
 with each face one pole. These are attracted to the 
 opposite sides of the permanent steel magnet con- 
 stituting the frame, which causes the coil to turn 
 against the restraint of springs. If the current in- 
 creases, the turning effort becomes stronger, so that 
 the pointer is carried farther along the scale. 
 
ELECTROMAGNETS 
 
 23 
 
 The KOowatt Hour. — If a man uses 3 kw. for 
 four hours he makes only half as much demand on 
 the power company as if he used 3 kw. for eight 
 hours, and he gets only half as much work done by 
 his motor. In one case he uses 4 X 3 or 12 "kilowatt- 
 
 Fig. 6. — Current entering the ammeter through the spiral spring makes 
 the coil and its iron core an electromagnet 
 
 hours" of electrical energy, and in the other case 
 8X3 or 24 kw-hr. The cost of electric service 
 depends on both the power and the time; the usual 
 custom is to base the charge on the "kilowatt-hour," 
 which is the energy supplied in one hour by one kw. 
 The retail price of one kw-hr. varies from one to 5 
 cents for heating, cooking and motors, and from 6 to 
 15 cents for lighting. Energy is sometimes sold by 
 the horsepower-hour (% of a kw-hr.), and some- 
 times by the horsepower-year (especially for pump- 
 ing irrigation water). 
 
24 APPLIED ELECTRICITY 
 
 At 6 cents per kw-hr. $1.80 will buy 30 kw-hr. 
 The power may be 30 kw. for 1 hour; or 10 kw. for 
 3 hours; or 6 kw. for 5 hours; or l/^ kw. for 60 
 hours; or 4 kw. for 3 hours and 9 kw. for 2 hours. 
 Evidently a statement of a number of kw-hr. does 
 not tell anything at all about the number of kw. (or 
 power). Instruments that measure kw-hr. are not 
 "watt-meters" but "watt-hour meters." 
 
 WESTERN ELECTRIC HOT PLATE AND KLAXON HORN 
 
 Here are two devices for transforming electric energy into other forms — 
 sound in the Klaxon horn and heat in the hot plate. The latter takes 
 4 amperes on a 220 volt circuit — how many British thermal units will it 
 give out in an hour? If one-half of the heat escapes to the air, how hot 
 will a gallon of water (8 lbs.) get in half an hour if its temperature is 
 60° when it is set upon the hot plate? 
 
 If you know the kw-hr. and the number of 
 hours, you can find the average kw. In the example 
 above, if it is given that the 30 kw-hr. are used in 
 5 hours we can say that the average power is 6 kw. 
 — but it may be 4 kw. for 3 hours and 9 for 2 hours. 
 Note the particular meaning of the word "average** 
 here; average kw. = number of kw-hr. divided by 
 the number of hours. 
 
 Heat Energy. — It has been found by numerous 
 careful experiments that when one kw-hr. of elec- 
 trical energy is used up in overcoming "electrical 
 friction** or resistance, a certain definite amount of 
 heat is developed, namely, enough to heat 3,412 
 pounds of water one degree hotter (by Fahrenheit 
 thermometer). This is generally expressed by say- 
 ing that 1 kw-hr. = 3,412 "British Thermal Units** 
 or 3,412 B.t.u. Also when one kw-hr. of mechanical 
 energy (1 1/3 h.p. hours) is used up in overcoming 
 
g S -5 ft S ^ ®. . 2> S XJ 4> oj c ^ 
 
 ■Ml~ § *"-"3 » « 5-£ £ -^ «.£ 0,=^ St! 
 
26 
 
 APPLIED ELECTRICITY 
 
 friction 3,412 B.t.u. of heat is developed. One horse- 
 power-hour similarly gives 2,545 B.t.u. 
 
 In a steam or gas engine it is possible to meas- 
 ure the heat developed by the fuel and the heat 
 wasted in the exhaust, radiation, etc. The loss of 
 heat is always less than the heat developed, the dif- 
 ference being a certain definite number of B.t.u. in 
 each case. It is found that this difference, divided 
 
 INSIDE THE FARM HOUSE 
 
 This installation of an electric range and an electric water heater in a 
 ranch home in California uses $6.00 worth of electric energy per month 
 at a rate of 3 cents per kw-hr. What was the average current taken, if 
 the apparatus was used on a 110 volt circuit 5 hours a day for 30 days? 
 
 by 2,545, gives the number of h.p. hours of mechan- 
 ical energy developed. Or, the ''useful" B.t.u. divided 
 by 3,412 = the number of mechanical kw-hr. Thus 
 it is proved that 3,412 B.t.u. can be changed to 
 1 kw-hr., or 1 kw-hr. can be changed to 3,412 B.t.u. 
 Mechanical energy, electrical energy, and heat are 
 simply three forms of the same thing; by various 
 devices we can make energy take any form desired. 
 
 Efficiency of Transformation. — In many trans- 
 formations of energy, there is a "loss" of some of 
 
ELECTROMAGNETS 27 
 
 the energy — loss in the sense that the energy- 
 changes into some form that is not desired, or goes 
 to some place where it is not wanted. For example, 
 in a motor we wish electrical energy to be converted 
 to mechanical, but inevitably some energy goes into 
 heat through friction, resistance in the wires, etc. 
 If the motor has an efficiency of 80%, 20% of the 
 electrical input is expended in undesired ways. Sim- 
 ilarly, in an electric water heater we desire the con- 
 version of the electrical energy into heat in the 
 water, but some heat is sure to escape to the sur- 
 rounding air, material of the container, etc. The 
 efficiency of such a device = useful B.t.u. -^ total 
 B.t.u. produced from the electrical energy ; or eff . = 
 useful B.t.u. -^ 3,412 X kw-hr. expended. On the 
 other hand, an electric air heater in a room has per- 
 fect or 100% efficiency, for all the heat must get into 
 the air and objects where it is wanted. 
 
 Engines which are used for the purpose of con- 
 verting heat into mechanical energy are compara- 
 tively inefficient. A large part of the heat given to 
 them is sent out again as heat and not as work. 
 Most of it goes out through the exhaust, but in 
 many cases (as in gas engines) a large part of the 
 heat is passed out through the cylinder walls to the 
 cooling water. The efficiency of steam and gas en- 
 gines in practice varies from 10% to 30%. 
 
WIRE CALCULATIONS 
 
 Wires used to carry electricity are usually of 
 copper, aluminum or iron. In the United States 
 copper and aluminum wires are made in various sizes 
 according to an arbitrary set of dimensions known as 
 the "Brown & Sharpe (or American Standard) Wire 
 
 
 11 
 
 
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 Fig. 7. — Connecting 
 block for an interior 
 telephone system. If 
 each wire is No. 18, 
 what is the resistance 
 of 200 feet of the cable 
 if all the wires are con- 
 nected together at each 
 end? 
 
 Gage." A wire known as No. 5, for example, has a 
 diameter of .1819 inch, and No. 10 has a diameter 
 of .1019 inch. The largest size in this gage is 
 No. 0000, the next is No. 000, then 00, then 0, then 
 Numbers 1 to 40, of which the last is the smallest 
 wire (.00315 inch diameter). 
 
 28 
 
WIRE CALCULATIONS 29 
 
 It is customary to express the diameter in 
 "mils" (one mil = .001 inch) rather than in inches. 
 Then No. 5 wire is 181.9 mils thick, and No. 10 is 
 101.9 mils thick. The cross section area of a wire 
 can not be expressed conveniently in square inches; 
 it is found preferable to use, instead, the "circular 
 mil" (cm.) as a unit. For wires and cables larger 
 than No. 0000 the size is designated by their circular 
 mil area. The diameter of a solid wire is found by 
 taking the square root of its cm. area. When the 
 diameter is known, the cm. area is found by squar- 
 ing the number of mils in the diameter. 
 
 Wire tables are found in all electricians' text 
 books and hand books. From these one can quickly 
 determine the characteristics of copper wire of any 
 size. The tables differ somewhat in arrangement, 
 but practically all of them give the diameter and the 
 section area for each numbered size, together with 
 the resistance and the weight of 1000 feet of wire. 
 The partial table on p. 32 gives figures for a number 
 of sizes of copper and aluminum wire. 
 
 If one knows that the resistance of one foot of 
 36 wire is .414 ohm, it is easy to compute the resist- 
 ance of any length. Six feet, for instance, will have 
 6 X .414 or 2.484 ohms, for we have six resistances 
 of .414 ohm each connected in series. Then the 
 resistance of 220 feet of No. 18 copper wire is 220 
 times 1/1000 of 6.374 (see table), for 6.374 ohms is 
 the resistance of 1000 feet. 
 
 The weight of any length of bare wire is figured 
 in exactly the same way from the tabulated figures 
 of the lbs. per thousand feet. Manufacturers and 
 dealers supply with price lists tables of the weights 
 of wires insulated in various ways. 
 
 In the table below the resistances are given for a 
 temperature of 68° Fahrenheit. For any other tem- 
 perature the figures are incorrect, since the resist- 
 ance of metals increases with rising temperature. 
 For copper and aluminum the ohms increase about 
 0.2% for each degree, so that at 88° the resistance 
 is 4% greater than indicated by the table. 
 
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WIRE CALCULATIONS 
 
 31 
 
 Allowable Current. — Wires carrying current 
 become heated, and the temperature rises until the 
 loss of heat to the surroundings equals the heat 
 developed. Then the temperature remains station- 
 ary. The hotter the wire becomes, the more heat it 
 
 For replacing carbon lamps in "lamp banks" used as rheostats, these 
 
 resistor units are being used. This particular one absorbs 60 watts at 
 
 120 volts. What length of No. 36 copper wire has an equal resistance? 
 What length of No. 36 nichrome? 
 
 can give off per second, so that (unless it is sur- 
 rounded by a non-conductor of heat like asbestos) 
 the temperature of a wire depends upon the watt 
 loss in it, which in turn depends upon the current. 
 
 The insulation upon conductors used in inside 
 wiring will deteriorate if exposed to heat, and hence 
 the temperature rise of the wires must be strictly 
 limited. The National Board of Fire Underwriters 
 issue in the '^National Electric Code*' a table of the 
 current to be allowed in copper wires used for 
 
 This vacuum cleaner 
 hose must carry a large 
 current of air with lit- 
 tle resistance. Hence it 
 is made as large as 
 practicable. What would 
 be the loss of pressure 
 in a similar tube twice 
 as long? 
 
 interior wiring. This is given in the wire table 
 accompanying this lesson. Note that the current 
 in rubber insulated wire must be kept smaller than in 
 wires with other insulations, on account of the fact 
 that rubber deteriorates at lower temperature than 
 other insulations. 
 
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 *2g 
 
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WIRE CALCULATIONS 33 
 
 Aluminum, Iron, and Other Wires. — Since alum- 
 inum has a lower conductivity than copper, wires 
 of aluminum must be larger than copper wires for 
 the same current. But its density is so much lower 
 than that of copper that the larger aluminum wire 
 weighs much less than the copper it replaces. 
 Knowing the size of copper needed for a certain 
 load, one can select an aluminum wire two sizes 
 larger (in the B. & S. gage) and figure the weight as 
 1/^ that of the copper. 
 
 Iron wire, used to some extent for telephone 
 lines, has much higher resistance than copper or 
 aluminum. It is manufactured in sizes different 
 from those in the B. & S. gage, the system followed 
 being called the "Birmingham wire gage." The grade 
 known as "Best Best" (B.B.) has the following 
 characteristics in two sizes much used : 
 
 No. (B.W.G.) CM. Lbs. per mile Ohms per mile 
 
 9 21904 314 17.84 
 
 14 6889 99 56,56 
 
 Suppose that No. 14 B.B. wire is to be used to 
 make a resistance for an arc lantern. If the line 
 voltage is 110, the pressure across the arc 70 volts, 
 and the current to be used is 18 amperes, how many 
 pounds of wire should be bought? The drop in the 
 wire = 110 — 70 --40 volts; the resistance = volts/ 
 amperes = 40/18 = 2.22 ohms. The table gives the 
 ohms per mile for No. 14 as 56.56, hence the ohms 
 per foot = 56.56/5280 = .0107 ; 2.22/.0107 =207, the 
 number of feet of wire. The lbs. per mile is given as 
 99; 99/5280 = .0187 lbs. per foot; hence our wire 
 weighs 207 X .0187 lbs. or 3.88 pounds. 
 
 When resistance is desired, it is usual to take 
 instead of iron a wire of some composition, such as 
 "German Silver,^' "Climax," or "Nichrome.*' The 
 German silver is an alloy of copper, zinc and nickel ; 
 most other special resistance materials are alloys of 
 steel with nickel, etc. 
 
 These materials are made into flat and square 
 conductors and round wires, the B. & S. gage being 
 
34 APPLIED ELECTRICITY 
 
 genierally adopted for the round wires. To calculate 
 the resistance of any wire, find the ohms of a piece 
 of copper wire of the same size and length, and mul- 
 tiply by the proper multiplier : for Nichrome multi- 
 ply by 60; for Climax multiply by 50; for German 
 Silver (ordinary, with 18% nickel) multiply by 20; 
 for Brass multiply by 4.4; for Aluminum Bronze 
 multiply by 7.5; for Steel multiply by 8.3. To find 
 the weight of Nichrome wire multiply the weight 
 of a similar copper wire by .92 ; for Climax multiply 
 .by .92; for 18% German Silver multiply by .95; for 
 Steel multiply by .88. 
 
VI 
 
 THE GENERATOR 
 
 Faraday's Discovery. — As shown by the electro- 
 magnet, an electric current can produce magnetism ; 
 it was to be expected that electric current could be 
 produced from a magnet. After many fruitless 
 efforts Faraday in 1831 discovered how to do it ; with 
 the arrangement shown in Fig. 8 he succeeded in 
 causing a flow of current through the sensitive am- 
 meter whenever he moved the magnet into or out 
 of the coil. The current stopped as soon as the 
 movement stopped; leaving the magnet in the coil 
 produced no current. But moving the coil off the 
 magnet while the latter was held still caused the 
 current to flow just as if the magnet itself had 
 moved. 
 
 The effects produced by moving the magnet or 
 the coil may be said to be caused by the cutting of 
 the wires by lines of force. As soon as the cutting 
 stops, the circuit is dead. The current through the 
 ammeter depends upon the resistance of the connect- 
 ing wires as well as upon the motion of the magnet ; 
 so it is better to replace the ammeter by a voltmeter 
 and make further investigations of the phenomenon 
 on the basis of electromotive force. 
 
 This e.m.f. is said to be "induced'' by the mag- 
 netic lines, just as pieces of iron acquire ''induced 
 magnetism'' in the neighborhood of a magnet. 
 
 35 
 
36 
 
 APPLIED ELECTRICITY 
 
 Experiments with coils of various numbers of 
 turns, with magnets moving slowly and rapidly, and 
 with magnets of different strengths, lead to this 
 conclusion: The induced e.m.f. depends upon the 
 number of lines of force, the speed with which they 
 cut the wire, and the number of turns of wire in 
 series . (A strong magnet has, of course, more lines 
 of force than a weak one.) It was found possible to 
 
 ' ' / 
 
 s' 
 
 \ \ \ 
 
 V'>. 
 
 N 
 
 1 1 >' 
 
 Fig. 8. — ^The details of Faraday's arrangement for causing a flow of cur- 
 rent through an ammeter by moving the magnet into and out of the coil. 
 
 get a definite numerical statement, as will be ex- 
 plained later in connection with the voltage of 
 generators. 
 
 Faraday's apparatus always produced an alter- 
 nating voltage; pulling out the magnet induced an 
 e.m.f. opposite to that caused by putting it in. 
 Inserting the S pole induced a voltage opposite to 
 that caused by inserting the N pole. The only way 
 to get a current through the ammeter of Fig. 8 
 continuously in the same direction is to reverse the 
 connections with every movement of the magnet. 
 
 The A.C. Generator. — On account of the mechan- 
 ical advantages of rotary over reciprocating motion, 
 generators are built commercially with either the 
 magnets or the coils revolving. Fig. 9 gives a gen- 
 eral idea of the arrangement of a "revolving field'' 
 alternator. We have here a magnet turning on a 
 shaft so that the lines of force close to its poles cut 
 across the stationary wires A and B. The N pole 
 induces in wire A a voltage directed toward the back 
 
THE GENERATOR 
 
 37 
 
 of the machine, while in B the S pole sets up an 
 e.m.f. in the forward direction. The wires are 
 joined at the rear and connected to a lamp in front, 
 which at the instant shown has current flowing in 
 it from right to left. When the poles are turned far 
 enough to exchange places, the electromotive force 
 is again induced but in the opposite direction, so 
 
 Fig. 9.- 
 
 -The plan of the "revolving field" alternator. At the instant shown 
 the lamp has current in it from right to left 
 
 that the current flows from left to right in the lamp, 
 having stopped when the magnet was halfway be- 
 tween the two positions. Thus is produced an alter- 
 nating current, which might be "rectified" so as to 
 flow always in the same direction through the lamp 
 by reversing the lamp connections twice in each rev- 
 olution of the magnet. 
 
 The **revolving field'' usually contains, instead 
 of a single permanent magnet, a number of strong 
 electromagnets. An iron ring is placed around the 
 outside of the "inductors" (wires cut by the lines 
 of force) so that the flux may get from pole to pole 
 with as little difficulty as possible. Thus there is 
 provided a large number of lines of force, and by 
 turning the shaft rapidly it is possible to induce sev- 
 eral volts in one inductor. Finally, a number of 
 wires are connected in series, so that the generator 
 produces any voltage desired. 
 
38 
 
 APPLIED ELECTRICITY 
 
 The D.C. Generator. — A revolving field machine 
 is not v^ell adapted for producing direct currents. 
 The d.c. generator in Fig. 10 has therefore a station- 
 ary field and revolving "armature." (The armature 
 is the structure which includes the inductors and 
 the iron core to which they are attached ; the core is 
 omitted from Fig. 10 for the sake of clearness.) 
 
 Fig. 10. — A d.c. generator with a stationary field and revolving armature 
 for producing a direct current. In the position shown the wire A has induced 
 in it a voltage directed forward, which drives current out of the armature 
 through the sliding contact between a "segment" (B) and a brush (C). 
 The segment B is attached to the armature and revolves with it, so that 
 when A reaches a position close to the N pole it is in contact with the 
 other brush, and segment E has come around to brush C. Thus the wire 
 passing the S pole always sends current out to brush C, and so downward 
 through the lamp, L. 
 
 With this simple arrangement the voltage drops 
 to zero twice in every revolution. If a second coil 
 were put on the armature at right angles to the first 
 coil, it would have a strong e.m.f. when the first 
 e.m.f. is zero. With the ring split into four parts 
 instead of two, and the new coil connected to two of 
 the segments, a fairly uniform pressure could be 
 produced. In practice many coils are used on the 
 armature and correspondingly many segments are 
 built into the ''commutator" as the split-ring device 
 is called. 
 
THE GENERATOR 39 
 
 It should be clear that a d.c. generator pro- 
 duces an alternating current which is "rectified'' or 
 made into direct current by means of the commu- 
 tator. Many d.c. machines are made with more 
 than two poles; in these there are usually as many 
 brushes as poles. Carbon is the material used in 
 the brushes, chiefly because of its resistance which 
 is useful in limiting the short circuit currents which 
 
 In a Columbia River salmon cannery this 6 kw., 120 volt d. c. generator 
 produces all the current necessary to operate the lights and motors. It is 
 driven by a 10 h. p. semi-Diesel oil engine. What is the efficiency of the 
 generator and what current does it supply when fully loaded? How many 
 pounds of oil are used in 8 hours if the average load is 40 amperes, the 
 engine efficiency is 30% and the fuel gives 19000 B. T. U. per lb.? 
 
 tend to flow from one *'bar" (segment) of the com- 
 mutator to the next while the brush is touching 
 both. 
 
 Generator Voltage. — It is customary to specify 
 the strength of the magnets used in generators by 
 the number of lines of force they produce. This 
 system is, of course, based on an arbitrary standard, 
 for a line of force is merely a convenient term to 
 use in connection with magnets and it has no tangi- 
 
THE GENERATOR 41 
 
 ble existence. In practice the electromagnets most 
 used have from 100,000 to several million lines 
 issuing" from their N poles. It is to be noted that 
 one inductor cuts across all these lines once when 
 passing the N pole of a magnet and again when 
 passing the S pole, so that the total number of cut- 
 tings during one revolution equals the product of the 
 number of poles times the lines per pole. 
 
 The standards of pole strength and electro- 
 motive force have been so selected that one volt is 
 the e.m.f. induced by cutting one wire in one second 
 by 100,000,000 lines of force. Putting inductors in 
 series adds their voltages, so that 
 
 Generator Voltage = No. Poles Passed per 
 Second X Flux per Pole X No. Wires in 
 Series -f- 100,009,000. 
 
 This formula gives the average voltage for an 
 alternating or fluctuating current, or the steady 
 voltage in a d.c. machine. The number of wires in 
 series may be the total number of inductors on the 
 armature, or one-half that number, or one-fourth 
 or one-sixth, or less. Direct current generators 
 usually have enough coils and commutator segments 
 to make the voltage practically constant at the value 
 given by the formula. 
 
VII 
 
 ARMATURE AND FIELD WINDINGS 
 
 Of all the types of generators, the simplest is 
 the alternating current magneto, which is used for 
 ringing telephone bells and for ignition in gas 
 engines. The magnetic flux is supplied by one or 
 more stationary permanent magnets of horseshoe 
 shape. The armature generally consists of a single 
 coil wound upon an iron core, which revolves between 
 the magnet poles. One end of the winding may be 
 
 Fig. 11. — Shunt generator. Coils of small wire on the magnet poles are 
 connected in multiple or shunt with the load. 
 
 "grounded" (connected to the metal of the arma- 
 ture) while the other is connected to the external 
 circuit through a sliding contact. 
 
 All other generators have electro-magnets for 
 producing the "magnetic field" or flux. The wires 
 which carry the current around these magnets con- 
 stitute the "field winding." 
 
 42 
 
ARMATURE AND FIELD WINDINGS 43 
 
 The magnets are ^'excited'' by sending direct 
 current through these windings, the current being 
 produced either by the generator itself or by some 
 external source. Direct current generators are almost 
 always ''self excited/' while a.c. machines are "sepa- 
 rately excited" by the use of small d.c. generators 
 called "exciters." A few alternators have special 
 arrangements for producing small amounts of 
 direct current, thus saving the expense of an extra 
 machine. 
 
 In Fig. 11 is shown the simplest arrangement for 
 self excitation, a direct current machine with the 
 field winding connected in piultiple or "shunt" with 
 the load. The diagram on the right is a preferable 
 way to represent the same arrangement. Many 
 turns of fine wire are used, which offer enough re- 
 sistance to limit the field current to a small value, 
 and yet give sufficient "ampere-turns" almost to 
 saturate the iron with magnetism. 
 
 When the machine is stopped the current dies 
 out of the shunt field and the magnetism disappears, 
 with the exception of a small amount which is known 
 as "residual magnetism"; that is, the iron has to a 
 slight extent the characteristics of a permanent 
 magnet. When the generator is again brought up 
 to its running speed, it is found that a low voltage 
 is produced, and if the shunt field switch is then 
 closed, a small current is sent through the coils. 
 This increases the magnetism and raises the voltage, 
 which comes up, little by little, to the pressure for 
 which the machine is designed. 
 
 To control the electromotive force of a genera- 
 tor, it is customary to insert a variable resistance 
 or "rheostat" in series with the field winding. Thus 
 the current and flux can be altered at will, and hence 
 the voltage, which depends on the strength of the 
 magnets, can be raised or lowered within wide limits. 
 (See the rheostat, R, in Fig. 12.) 
 
 An additional feature of the field winding of 
 most d.c. generators is shown in the "series winding" 
 in Fig. 12. A few more turns of wire are put around 
 
r. c 
 
 35 
 
 o <u 
 
 00 S 
 
 II 
 
 t3 4) 
 
 P5 ^ 
 
 ^ o 
 
 O ft 
 
 1 
 
 < bo 
 
ARMATURE AND FIELD WINDINGS 
 
 45 
 
 the magnet poles and this wire (which is made of 
 large size) is connected in series with the load. The 
 additional magnetism thus produced raises the gen- 
 erated voltage as the current increases, and thus 
 
 \QQStSir- 
 
 Fig. 12. — Compound wound generator. The load current passing through 
 the series coils tends to raise the generated voltage as the load increases. 
 The rheostat in the shunt circuit enables the operator to change the 
 voltage at will. 
 
 compensates for the increased *'line di^op'* at heavy 
 loads. A generator thus equipped is said to be "com- 
 pound wound.'' 
 
 The field coils of an alternating generator are 
 connected to the exciter through a rheostat. If the 
 alternator field revolves, it is necessary to get the 
 
 Voltage regulation by the 
 shunt field rheostat is 
 sometimes not sufficiently 
 accurate. This series 
 rheostat and ammeter are 
 used to keep the current 
 constantly equal to 20 
 amperes in the 600 watt 
 gas filled lamp used in 
 many moving picture 
 projectors. What is the 
 lowest possible generator 
 voltage for this service? 
 
 current to and from the windings through sliding 
 contacts on "slip rings." This is preferable to using 
 sliding contacts for the generator current, which is 
 usually at high voltage and of much greater volume 
 than the exciting current. 
 
 Armature Winding. — Direct current generators 
 usually have drum shaped armatures, built of many 
 thin circular leaves or "laminations" of iron or steel. 
 The wire is placed in slots cut lengthwise along the 
 
46 
 
 APPLIED ELECTRICITY 
 
 cylindrical surface and connected at numerous points 
 to the copper commutator bars. 
 
 In Fig. 13 is shown a very simple winding for a 
 '^bipolar" (2 pole) machine having 6 slots in the 
 armature, 12 inductors and 6 commutator bars. The 
 letter B indicates the bar in contact with one of the 
 brushes — let us say the "positive'' brush, or the one 
 at which the current leaves the armature. Then the 
 current enters the winding at A, and flows along the 
 wires to inductors numbered 1 and 7, both of which 
 
 N 
 
 Fig. 13. — Armature of bipolar d.c. generator seen from end of shaft. Note 
 connections of inductors (in the slots) to each other and to the commutator 
 bars. Other interconnections at the other end of the armature are invis- 
 ible in this view. 
 
 are under the influence of the N pole. Obviously, the 
 machine must be turning in such a direction that 
 voltage in wires under the N pole is directed into the 
 paper, or away from the observer. Similarly, the 
 inductors under the S pole must urge the current 
 "out" or toward the observer. 
 
 Now we must imagine a wire across the back of 
 the armature which carries the current from the far 
 
ARMATURE AND FIELD WINDINGS 
 
 47 
 
 end of inductor No. 1 to the far end of No. 2. The 
 pressure generated in No. 2 then assists that of No 1, 
 and the current is forced along the wire shown, 
 across the front end of the armature, to inductor 
 No. 3, passing a commutator bar which is inactive 
 because out of contact with either brush. The cur- 
 rent flows ''in'' along No. 3, across the back of the 
 armature to No. 4, across the front to No. 5, then 
 across the back to No. 6, finally reaching bar B and 
 leaving the armature. Six inductors in series have 
 
 r 
 
 1 
 
 /. 
 
 
 
 I m 
 
 ^^^^^^^^Ko^^^^^^^^ 
 
 ....... -.. 
 
 This shows how the 
 formed coils are placed 
 on the armature and the 
 terminals connected to 
 the risers from the com- 
 mutator bars. 
 
 added their voltages, so that if the average pressure 
 induced in each is .9 v., the machine generates 5.4 v. 
 The other inductors, commencing with No. 7, 
 and working through Nos. 8, 9, 10, 11 and 12, per- 
 form a service exactly similar to that of the first 
 set, producing a voltage of 5.4 in parallel or multiple 
 with the first voltage considered. If the current is 
 5 amperes in each wire, the total current sent out 
 of Bar B is 10 amperes. Thus we have the armature 
 current twice that in one inductor, and armature 
 voltage equal to the product of half the inductors 
 times the average e.m.f . in one. 
 
48 APPLIED ELECTRICITY 
 
 Generators with 4, 6 or more poles are not un- 
 common. The armatures may be so wound that 
 there are only 2 parallel paths for the current or 
 so that there are as many paths as poles, or with 
 other numbers dependent upon variations in the 
 methods of connection. With the ''lap" or "multi- 
 ple" winding there are at least as many paths as 
 poles, and there must be as many brushes as poles. 
 With "series" or "wave" winding there are, in gen- 
 eral, only two parallel paths, and there may be either 
 2 brushes or as many brushes as poles. 
 
 There are often more than 2 inductors in one 
 slot, especially in small machines. This necessitates 
 cross connections on the front end of the armature 
 in addition to those running to the commutator 
 bars. Referring to Fig. 13, the wire might run "in" 
 along the top of slot c, then across the back and 
 "out" along the bottom of d, then across to slot c 
 again (avoiding the commutator) and thus through 
 c and d several times. The coil may be wound on a 
 "form" and taped and varnished before being put 
 upon the armature, and this is the usual practice for 
 "multipolar" machines (having 4 or more poles). 
 
 The armature of Fig. 13 could be made to pro- 
 duce alternating current by taking away all the com- 
 mutator bars except A and B and changing each of 
 these to a "slip ring," so that each would be continu- 
 ously in contact with the same brush. 
 
VIII 
 LOSSES AND REACTIONS IN D.C. GENERATORS 
 
 Copper Losses. — When a d.c. generator is send- 
 ing current through a line and a load, as in Fig. 14, 
 the number of amperes is found by dividing the gen- 
 erated voltage by the total ohms of the circuit, which 
 means the sum of the resistances of the load and 
 the line plus the resistance in the armature, commu- 
 tator and brushes. It is to be emphasized that the 
 
 Fig. 14. — Separately excited d.c. generator. 
 
 electromotive force has to overcome resistance in the 
 generator as well as in the external circuit. Thus 
 there is a conversion of electric energy into heat 
 energy in the inductors, the watts wasted here being 
 termed the "armature copper loss." It is calculated 
 by multiplying the armature resistance by the square 
 of the number of amperes flowing through it ; in Fig. 
 14, this is the same as the line current, but in Fig. 
 16 it is greater by the amount of current used in the 
 shunt field. 
 
 One can measure the resistance of an armature 
 by sending a small current through it, measuring 
 the voltage drop, and calculating by Ohm's law. 
 
 49 
 
50 
 
 APPLIED ELECTRICITY 
 
 The resistance of an armature may also be de- 
 termined from the size and length of the wire used 
 in winding. 
 
 As shown in Fig. 15, an armature coil may con- 
 sist of a single turn of wire, running from one com- 
 mutator bar to and through the top of one slot, then 
 across the back of the armature and forward through 
 the bottom of another slot to the bar adjacent to 
 
 Fig. 15. — "Multiple Winding" for a 6 pole d.c. armature. The heavy 
 radial lines with arrow heads represent the inductors. The dotted induc- 
 tors are in reality placed beneath the solid ones shown beside them. The 
 brushes are drawn inside the commutator to simplify the sketch. 
 
 the first one. The radial part of the line represents 
 the inductor, which is shown dotted when at the bot- 
 tom of a slot. 
 
 In small machines there are usually several 
 turns per coil, the wire running around several times 
 through the same two slots, with the ends connected 
 to adjacent bars. If each coil in Fig. 15 contained 30 
 turns of No. 10 wire, of a total length of 80 ft., its 
 resistance would be 80 X .000997 = .08 ohm. As 
 there are 24 coils and 6 brushes, there are four coils 
 
LOSSES AND REACTIONS 51 
 
 in series, with a resistance of 4 X -08 or .32 ohm. 
 Current flows through the armature in 6 parallel 
 paths, and hence the combined resistance = .32 -^ 6 
 = .053 ohm. 
 
 The "current rating'' of an armature is the num- 
 ber of amperes it can safely carry. It is evidently 
 equal to the current which one wire can carry multi- 
 plied by the number of parallel branches in the 
 armature. 
 
 If the safe current in each inductor of the arma- 
 ture of Fig. 15 is 15 amperes, the current rating is 
 6 X 15, or 90 amperes. There being 120 inductors 
 in series, the generated voltage = 120 X -7 if condi- 
 tions of flux and speed are so arranged as to give .7 
 volt per inductor. The power generated t=: 84 X 9^ 
 = 7560 watts. The armature copper loss = 90 X 90 
 X .053 = 430 watts, so that the output of the arma- 
 ture is 7130 watts. 
 
 The same armature might have a "series" or 
 "wave" winding, which has only two parallel paths. 
 With the same total number of inductors there would 
 be 360 in series and a voltage three times as high 
 as with the multiple winding. The current could, 
 however, be only 30 amperes, and the power would 
 be the same as before. The armature copper loss 
 may be shown to be the same with both methods of 
 winding. 
 
 There is resistance at the contact of the brushes 
 and the commutator and in the material of the 
 brushes. This causes an electrical loss which varies 
 with the load carried. 
 
 Another important loss of power occurs in the 
 field windings. In Fig. 14 suppose the field resistance 
 to be 17 ohms and the current supplied to be 3 am- 
 peres. The power loss = 3 X 3 X 17 = 153 watts. 
 If the rheostat is set at 4 ohms, there is a further 
 loss there of 36 watts. Compound generators have 
 copper losses in both shunt and series fields. Thus, 
 if the "brush voltage" is 120 in Fig. 16, the shunt 
 current 8 amperes, the load current 200 amperes and 
 the series field resistance .01 ohms, the shunt loss = 
 
I • a2 c 
 
 '-^ e- 5 ^ 
 "^ « j2 ft 
 
 'lis 
 
 2 fe »^ 
 
 h a> g q; 
 
 
 iJ ft 
 
 0^ 
 
 ^ a> ft 
 
LOSSES AND REACTIONS ^3 
 
 120 X 8 = 960 watts and the series field loss = 
 200 X 200 X -01 = 400 watts. 
 
 Mechanical and Iron Losses. — In a d.c. generator 
 there are three kinds of mechanical power losses and 
 two different iron losses. The former include bear- 
 ing friction, "windage'' or air friction, and friction 
 
 Fig. 16. — This compound wound generator has a loss of 960 watts in the 
 shunt winding and 400 watts in the series coils. 
 
 between the stationary brushes and the moving com- 
 mutator. The iron losses include those due to "hys- 
 teresis" and "eddy currents.'' 
 
 Armatures are influenced by the poles which 
 surround them and become magnets themselves. As 
 they rotate their magnetic condition must be contin- 
 ually changing, for each particle of iron is magnet- 
 ized as it passes one pole and remagnetized in the 
 opposite sense when it reaches the next. The par- 
 ticles oppose this change by what seems like internal 
 friction, and the energy thus wasted (changed into 
 heat) is the "hysteresis loss." 
 
 As the lines of force cut through the armature 
 iron, currents of electricity are induced in it by 
 exactly the same process as the currents in the 
 armature wires. These "eddy currents" require the 
 expenditure of energy and produce heat. To minim- 
 ize the currents, which tend to flow parallel to the 
 inductors, the armature is built of thin circular 
 sheets, or "laminations" of iron. The oxide on the 
 faces of the sheets forms an insulator which pre- 
 
54 APPLIED ELECTRICITY 
 
 vents passage of the currents and thus reduces the 
 eddy loss to a relatively small amount. 
 
 Armature Drop and Reaction. — In a separately 
 excited machine (Fig. 14) or a shunt generator the 
 brush voltage is lower when a load is carried than 
 when the external circuit is open. One cause is the 
 "armature drop/' another is the *'brush contact 
 drop" and a third is the "armature reaction.'' It is 
 to overcome these as well as "line drop" that the 
 compound winding shown in Fig. 16 is used. 
 
 There is always a voltage drop in a conductor 
 which carries current, and this is true even in an 
 armature where voltage is being generated. Then 
 in the armature of Fig. 15 with a resistance of .053 
 ohm, the drop is 90 X -053 = 4.77 volts when the 
 machine produces 90 amperes. This would reduce 
 the voltage from the generated pressure of 84 to 
 79.23 volts. 
 
 Due to the contact resistance between the com- 
 mutator and brushes there will be a further drop 
 of about one volt. 
 
 The armature inductors carrying current tend 
 to make the armature a magnet with poles between 
 the pole pieces of the generator. This results in 
 lessening the total flux through the armature and 
 makes other disturbances which lower the efficiency 
 of the machine. The whole effect, known as "arma- 
 ture reaction," varies with the amount of current 
 being drawn by the external circuit. Armature 
 reaction is counteracted in various ways, such as 
 shifting the brushes, building the generator with 
 "interpoles," and putting "compensating windings" 
 upon the pole faces. 
 
IX 
 ELECTROLYSIS 
 
 The word "Electrolysis" is used to indicate the 
 carrying of an electric current through a solution. 
 It is found that absolutely pure water is an almost 
 perfect insulator, but that the presence of an appre- 
 ciable amount of any one of a number of substances 
 makes the liquid a fairly good conductor. These 
 soluble substances are called "electrolytes/' and they 
 
 Fig. 17. — The d.c. generator sends current through the liquid from the 
 "anode" (marked "+"), to the "cathode" (" — ") when the switch is 
 down. If the plates are lead and the electrolyte sulphuric acid, a battery 
 is thus produced, capable of ringing the bell when the switch is up. 
 
 include acids, salts, and "bases" (or alkalis). Sugar 
 is not an electrolyte. 
 
 The current is carried into and out of the solu- 
 tions generally by metal "electrodes," the one where 
 the current enters the liquid being called the positive 
 or "anode," and the other the negative or "cathode." 
 When the electrodes are far apart the current must 
 pass through a long body of liquid, hence meeting 
 
 55 
 
56 APPLIED ELECTRICITY 
 
 high resistance; when the electrodes are large the 
 conducting body of liquid has a cross section, which 
 lowers the resistance. Hence in all kinds of bat- 
 teries, including stoVage cells (* 'accumulators"), the 
 effort is made to have the electrodes as large and as 
 near together as possible, for the current must flow 
 between them and resistance causes loss of energy. 
 
 Chemical Effects. — When current flows through 
 a solution, as in Fig. 17 when the switch is closed, it 
 tends to separate and release at the electrodes the 
 components of the electrolyte. For example, sulphu- 
 ric acid is a union of hydrogen with the ^'sulphate 
 
 DDOH 
 
 Z^Ql 
 
 
 — ■ — — — /»•</ C9<t*r0^ cab/*.. 
 
 Fig. 18. — Current returns to the generator by the rails and through the 
 earth. Part of the earth current is diverted to the lead covered cable 
 and electrolysis destroys the sheath. 
 
 ion'' ; when current passes through dilute sulphuric 
 acid the hydrogen is found to collect at the negative 
 electrode and the sulphate is set free at the anode; 
 being chemically active it immediately combines 
 with water there, and liberates some oxygen. This 
 gas may appear as bubbles upon the anode or it may 
 unite chemically with the material of the anode ; the 
 hydrogen at the cathode may appear as bubbles or 
 combine chemically with the material of that elec- 
 trode. 
 
 In weak solutions the resistance is practically 
 proportional to the amount of electrolyte present. 
 This fact is utilized ingeniously by certain California 
 engineers who determine by a single test the salinity 
 of water in their steam boilers. A pair of electrodes 
 fixed at a certain distance apart are immersed in a 
 sample of the water and connected to a known volt- 
 age through a mil-ammeter. A single reading thus 
 determines the resistance, from which is known the 
 number of grains of salt in a gallon of water. Then 
 
ELECTROLYSIS 
 
 57 
 
 water which is too impure is blown out and fresh 
 water substituted. 
 
 Moist earth carries current readily and makes 
 trouble between electric railway companies and the 
 people who own subterranean piping or metal cov- 
 
 Salinity tester used by the Pacific Gas & Electric Company. A bottle of 
 boiler water is brought up around either pair of electrodes and the mil- 
 ammeter reads the current. The instrument is also calibrated to give a 
 direct reading of the amount of salt present. 
 
 ered cables. Where a current leaves a metallic con- 
 ductor (which is, then, the anode) the metal is dis- 
 solved and removed. 
 
 Storage Batteries. — If two lead plates are used 
 as electrodes in dilute sulphuric acid and a direct 
 current sent through the solution, as in Fig. 17, it is 
 noticed that the arrangement soon becomes a bat- 
 tery, capable of sending electricity through a wire, 
 though it was not a battery before the "charging 
 
58 APPLIED- ELECTRICITY 
 
 current" passed. This current changes the positive 
 electrode to "lead peroxide" by giving oxygen to it, 
 while the cathode remains lead. The chemical action 
 of the acid upon the lead peroxide and the lead then 
 causes an e.m.f . to be set up tending to send current 
 out from the peroxide to the lead plate; the electrode 
 by which the charging current entered the cell is the 
 
 
 ■wJnlP^^^^IHHIlii 
 
 1 
 
 ^n 
 
 
 ■ 
 
 ■ m- 
 
 
 ^ 
 
 
 ■i. l^^^a^^iiliUliii ill iiii 
 
 M^ 
 
 
 m. ^■■■■■i 
 
 HB 
 
 "Do It Electrically" is the motto aboard this submarine. Large storage 
 batteries are charged by gas engines when the boat is on the surface 
 and they supply power for propulsion, lights, cooking, and many other 
 purposes when the boat is submerged. 
 
 one by which current tends to go out when the cell 
 is discharged by throwing the switch upward. 
 
 The chemical action during discharge is as fol- 
 lows : The hydrogen of the acid goes to the peroxide 
 plate and takes off some of the oxygen, forming 
 water, which dilutes the acid. The remaining oxy- 
 gen of the peroxide plate is exchanged for sulphate 
 ions, so that the plate becomes lead sulphate. Other 
 sulphate ions go to the lead plate and combine with 
 it, forming lead sulphate. So the sulphuric acid be- 
 comes weaker, losing hydrogen and sulphate ions; 
 both plates become coated with lead sulphate. 
 
 Sending a charging current through again ex- 
 actly reverses this action, taking sulphate ions off 
 both plates and taking oxygen from the water to 
 
ELECTROLYSIS 
 
 59 
 
 make the positive plate into lead peroxide. The sul- 
 phuric acid is increased in strength. 
 
 These lead storage cells are very widely used. 
 They are built commercially with the active materi- 
 als (spongy lead and lead peroxide) in grooves or 
 holes upon a lead backing. One cell generally con- 
 tains several positive plates and several negative 
 plates similarly interconnected, the two kinds being 
 
 This small storage battery does the work of two shelf-fuls of dry cells. 
 It is charged for a few minutes each hour by means of a clock operated 
 connection to a d.c. circuit. 
 
 interspaced and prevented from short-circuiting by 
 wood and rubber separators. A number of these 
 cells connected together form a "battery.'' 
 
 All cells of the same kind have equal voltage, 
 the size and number of plates affecting only the re- 
 sistance and the ^'capacity" of the cell — of course in 
 a large cell there is more active material than in a 
 small one, and it can give more ampere-hours before 
 it is discharged. 
 
 The voltage of a battery equals the sum of the 
 voltages of all the cells connected in series; if sev- 
 eral cells are connected in parallel the pressure is no 
 higher than that of one of them. The terminal volt- 
 age of a discharging battery is less than the gen- 
 erated voltage when current is flowing, just as in a 
 generator. The current must pass through resist- 
 
ELECTROLYSIS 61 
 
 ance in the cells themselves, and hence there is a 
 voltage drop, depending on the current and the re- 
 sistance. Toward the end of the discharge the 
 resistance increases, causing the terminal voltage to 
 diminish rapidly. The volts per cell, when discharg- 
 ing, drop from about 2.1 to 1.8. 
 
 The Edison Storage Cell. — In order to overcome 
 some of the undesirable features of the lead battery, 
 such as weight, acid fumes, and the necessity for 
 constant and skilled supervision, Edison invented the 
 nickel-iron storage cell which has become popular 
 for electric automobiles and many other uses. The 
 positive plate contains perforated tubes of nickel hy- 
 drate while the negative plate contains pockets of 
 iron oxide. The electrolyte is a solution of caustic 
 potash (chemically pure lye) , which does not give off 
 fumes. It is not changed in the processes of charg- 
 ing and discharging, which are chemically equivalent 
 to transferring oxygen from one plate to the other. 
 
 The voltage of a single Edison cell is about 1.3, 
 while the lead cell has about 2 volts. The pressure 
 needed to charge an Edison cell is about 1.7 volts; 
 to charge a lead cell, 2.3 volts. These figures are, of 
 course, higher than the counter pressure generated 
 in the cells, because the charging voltage has to over- 
 come the voltage drop due to cell resistance as well 
 as the voltage of the cell itself. 
 
 Primary Batteries. — Many batteries are in use 
 in which the material of one plate is so changed and 
 removed by the chemical reactions which cause cur- 
 rent to flow that it cannot be restored by forcing 
 current through the cell in the reverse direction. 
 These are called "primary batteries" in distinction 
 from accumulators which are sometimes called **sec- 
 ondary batteries." On account of its convenience 
 and low resistance the "dry cell" is one type of pri- 
 mary battery very much used, and there are a num- 
 ber of different kinds of wet cell in use. To make 
 a battery for experimental purposes one has only 
 to put two pieces of metal of different kinds (or a 
 piece of carbon and metal) into a solution of salt, an 
 
62 APPLIED ELECTRICITY 
 
 acid or an alkali. A dime and a copper cent separated 
 by a piece of moist blotter will produce enough cur- 
 rent to make a click in a telephone receiver. The 
 action of such a battery depends upon the difference 
 in the chemical action upon the two electrodes. 
 Since any electrolyte acts differently upon every kind 
 of solid conductor, any two metals (or carbon and 
 one metal) will serve for a battery with any electro- 
 lyte. The voltage is different for every combination, 
 varying from a very small value up to about 2 volts. 
 The "dry cell" which has sal ammoniac for its elec- 
 trolyte (mixed with some filler to a sort of paste and 
 sealed into the cell with wax) generates a pressure 
 of 1.5 volts. 
 
ELECTRIC MOTORS 
 
 Theory of Motor Action. — Oersted in 1819, laid 
 the foundation of the modem electric motor when 
 he discovered that current in a wire affected a nearby 
 compass needle. He showed that the electricity 
 tends to cause the movement of a magnet pole in a 
 circle around the conductor. In Fig. 19, for instance, 
 the current in wire A exerts a force upon the nearby 
 north pole, trying to make it move upward, then to 
 the right, then downward. A south pole wo|ild tend 
 to circle the wire in the opposite direction. 
 
 Fig. 19.- 
 
 -Current in Wire A tends to force the north pole upward, 
 reaction drives the wire itself downward. 
 
 The 
 
 Direct current motors are built with stationary 
 poles, so that the wires themselves are made to 
 move, just as a man trying to push a piano across a 
 room may drive himself backward. Then in Fig. 19, 
 wire A moves downward and the wire adjacent to a 
 
 63 
 
64 
 
 APPLIED ELECTRICITY 
 
 south pole moves upward. One can always determine 
 the direction by remembering the old Right Hand 
 Rule: Grasp the wire with the thumb pointing 
 along it in the direction of current flow ; then a north 
 pole will follow the fingers around the wire. 
 
 The armature of a motor is built of laminated 
 iron with slots for the conductors. (See Fig. 20.) The 
 
 Fig. 20.— A motor armature. The currents in the wires may be thought of 
 as producing poles in the armature iron which are attracted and repelled 
 by the field poles. 
 
 commutator of a d.c. machine acts to keep the cur- 
 rent always flowing in the same direction in the 
 vicinity of any pole. In Fig. 20 it flows "out" (toward 
 the observer) beside the north pole as indicated by 
 the dots (arrow points) ; it flows "in" (into the 
 paper) beside the south pole as shown by the (+) 
 marks (arrow feathers). 
 
 If an armature such as that in Fig. 19 is supplied 
 with an alternating current which reverses exactly 
 **in step'' with the rotation, so that current flows 
 "in" along the other wire when that is beside the 
 north pole, the machine will run and carry a load. 
 This is the principle of the ^'synchronous motor." 
 It follows that any electric generator will operate 
 as a motor if supplied with current under proper 
 conditions. 
 
ELECTRIC MOTORS 
 
 65 
 
 Another way to study the action of a motor is 
 to think of the armature as an electromagnet. The 
 coils in Fig. 20 tend to produce a north pole at the 
 top of the armature and a south pole below. These 
 are pulled and pushed by the field magnets according 
 to the rule : Unlike poles attract and like poles repel 
 each other. -As the armature rotates, its poles con- 
 tinually shift through the metal and keep in their 
 
 ! 
 
 
 
 IK 
 
 \^ m 
 
 w ■ 
 
 ; '/ 
 
 
 li ^ 
 
 »■ 
 
 
 
 IM 
 
 Ui 
 
 ^ ^ \ 
 
 ^ i 
 
 jgm 
 
 gii»fa--.-.dl 
 
 
 S-r^ 
 
 1 
 
 
 L^^ 
 
 
 ^H^ ^p. 2 
 
 
 p^H 
 
 1 
 
 I 
 
 k 
 
 
 ^m * *^^H^^^^B 
 
 
 s 
 
 1 
 
 Direct current motors of 15 hp. each drive these deck winches. What is 
 the current input to one of the 116-volt motors when a load of 25000 lbs. 
 is being hoisted 3 ft. per sec. if the overall efficiency of the machinery is 
 55%? 
 
 positions at the top and bottom, because the wires 
 at the right are always carrying current in while 
 those at the left carry it out. 
 
 Counter Electromotive Force. — In a rotating 
 motor armature the wires are passing at high speed 
 through lines of force. This must set up a voltage in 
 these wires, whether they carry current or not, for 
 an e.m.f. is always induced in a conductor being cut 
 by lines of force. This voltage may either help or 
 hinder the current flow; if it helps, there will be 
 
66 APPLIED ELECTRICITY 
 
 more current and more magnetic force the faster the 
 armature goes, which is contrary to reason and ex- 
 perience. We conclude that the induced e.m.f. op- 
 poses the current and the voltage driving it, and 
 name it "counter e.m.f/' or "back e.m.f." 
 
 The number of amperes through the armature 
 depends, then, upon three things: the armature re- 
 sistance, the applied voltage, and the back e.m.f. 
 If we had a battery circuit of 2 ohms total resistance 
 with 6 dry cells in series, the voltage would be 
 6 X 1.5 =^ 9 volts, and the current 4.5 amperes. If 
 one of the cells were connected backward, however, 
 the effective voltage would be 7.5 — 1.5 or 6 volts, 
 and the current 3 amperes. With two cells connected 
 backward we should obtain 1.5 amperes. If three 
 cells were opposing the rest there would be no cur- 
 rent, for the net voltage would be zero. 
 
 If the counter voltage of a motor equaled the 
 applied pressure, no current could flow, and no power 
 would be drawn from the line. Hence the back e.m.f. 
 is always less than the applied voltage, for it takes 
 power to run a motor, even when unloaded. The 
 armature current = (applied volts — back e.m.f.) h- 
 armature ohms. 
 
 Motor Starting. — When an armature is sta- 
 tionary it cannot produce any counter e.m.f. If the 
 full voltage were applied a very heavy current would 
 flow, and for the protection of the windings it is 
 customary to provide some sort of starting appa- 
 ratus which limits the current to a safe value. Direct 
 current shunt motors (which are wound the same as 
 shunt generators) are started with a variable re- 
 sistance in series with the armature, as shown in 
 Fig. 21. By means of a sliding contact the resistance 
 is lowered step by step as the motor gains speed, and 
 it is all out when full speed is nearly reached. 
 
 Alternating current motors are often started by 
 applying pressure less than the normal line voltage. 
 "Compensators'' which are "step down transform- 
 ers'' are connected to the line and supply current at 
 
ELECTRIC MOTORS 
 
 67 
 
 low voltage during the starting period. In other 
 cases resistance is introduced into some of the motor 
 circuits, while sometimes the connections of the coils 
 are changed temporarily to produce effects equivalent 
 to changing from parallel to series circuits. 
 
 Fig. 21. — starting box for d.c. shunt motor. To protect the armature 
 winding, when it is producing little or no back electromotive force, the 
 line current is sent through a series resistance which is decreased as the 
 motor speeds up. 
 
 Alternating Current Motors. — Synchronous mo- 
 tors are used when it is desired to operate machinery 
 at a speed exactly proportional to that of the gen- 
 erators supplying the current. 
 
 For driving the d.c. generators for electric rail- 
 ways and in other applications requiring large 
 amounts of power it is usual to install synchronous 
 motors in preference to other tjrpes, largely on ac- 
 count of their beneficial effect on the power factor 
 of the transmission line. 
 
 Since they can not carry a load except when 
 exactly in step with the alternations of the current 
 supply, it is necessary to bring them up to speed by 
 some special device. Sometimes the d.c. generator 
 is connected to the direct current line and run as a 
 motor during the starting period; in other installa- 
 
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ELECTRIC MOTORS 69 
 
 tions the synchronous motor is started without load 
 by means of a small a.c. motor of another kind. 
 
 For all ordinary applications, the * 'induction 
 motor'' is most widely used. The construction is 
 simple, cheap and rugged, and operation and mainte- 
 nance are easy and inexpensive. The tj^ical motor 
 
 There are far less "kicks" in the mines since the electric motor displaced 
 the time-honored mule locomotive. In some mines trolley lines are used ; 
 in others the motors are driven by storage batteries carried by the locomo- 
 tives themselves (as in this illustration). 
 
 of this type has no sliding contacts and only the 
 simplest elements of a winding upon the revolving 
 part or *'rotor." 
 
 Alternating currents in coils wound about por- 
 tions of the iron "stator'' (stationary part) of an 
 induction motor produce magnetic poles which are 
 north when the current flows one way and south 
 when it reverses. Other poles of opposite polarity 
 are produced between these by coils wound in the 
 opposite direction. The result is that north poles ap- 
 pear at several points around the stator and shortly 
 after (when the current has reversed) they appear 
 in different places. By the use of two or more alter- 
 nating currents which reverse at different times 
 there is produced a smooth progression of the poles 
 
70 APPLIED ELECTRICITY 
 
 around the inside of the stator, and this is known as 
 the "revolving field." 
 
 Just as in the alternating generator, the wires 
 near the poles of a revolving field are cut by the 
 moving lines of force and have e.m.f. induced in 
 them. Thus the conductors of the rotor, which are 
 short circuited upon each other, carry heavy induced 
 currents, but no electrical contact with the supply 
 circuit is needed. The reaction between these in- 
 duced currents and the magnet poles of the stator 
 causes the rotor to turn. As it gains speed it almost 
 catches up with the revolving field but it never runs 
 quite as fast. If it did, there would be no more 
 induction of e.m.f. on the rotor, for each wire would 
 keep beside some pole and there could be no cutting 
 of the inductors by lines of force. The difference 
 between the speeds of the rotor and the revolving 
 field is known as the '*slip," and this varies whenever 
 the load is changed. 
 
XI 
 
 MOTOR CHARACTERISTICS 
 
 Direct Current Motors. — For operation upon d.c. 
 circuits motors are built of three different types. 
 They are known as series, shunt and compound 
 motors, the names referring to t>.e connection be- 
 tween the armature and the field winding, as in the 
 
 A Westinghouse motor-generator set run by direct current and producing 
 alternating current. This last is raised to high voltage by means of 
 transformers and then "rectified" for use in precipitating dust in flue gases. 
 
 case of d.c. generators. The magnet coils in a series 
 motor consist of a few turns of large wire carrying 
 the whole current of the machine. A shunt motor 
 has field windings of small wire and many turns, 
 connected in multiple or shunt with the armature. 
 Both series and shunt coils are put upon the field of 
 a compound motor. 
 
 71 
 
72 APPLIED ELECTRICITY 
 
 The "torque" or turning effort of a motor de- 
 pends upon the strength of the magnetic field and 
 hence is proportional to the field current except for 
 the disturbing effects of saturation and armature 
 reaction. Therefore, decreasing the field Current to 
 half value cuts the torque approximately in two. 
 
 This direct current G-E fan runs at 1500 r.p.m. When the fan blades 
 are removed, the motor runs at about 3500 r.p.m. Is the field shunt. sfs-ifsL 
 or compound wound? 
 
 This is on the assumption that the current in the 
 armature remains constant, for the torque is directly 
 proportional also to armature amperes. Then in a 
 series motor, where the same current flows through 
 armature and field, triple current would give nine 
 times the torque were it not for the disturbing fac- 
 tors mentioned above. (On test a certain 500-volt 
 machine was found to give with 60 amperes five 
 times as great a torque as with 20.) 
 
 Series motors are used for electric railways, 
 hoists, cranes, etc. When a street car starts up-hill 
 from the level the motors at once lose speed and the 
 counter e.m.f. decreases. More current is thus per- 
 mitted to flow and this raises the torque of the 
 motors sufficiently to carry the increased load. This 
 flexibility in regard to torque and speed is what 
 makes the series d.c. motor the most convenient for 
 all such applications as hoisting and traction where 
 heavy and variable loads must be frequently started 
 and stopped. It is necessary to keep a series motor 
 coupled to its load, however, and to control it care- 
 
MOTOR CHARACTERISTICS 73 
 
 fully, for if the load is removed the speed will run 
 very high, possibly ruining the armature by cen- 
 trifugal action. 
 
 Shunt Motors. — When a shunt motor is operated 
 without a load it does not run faster than a certain 
 speed, behaving like a steam engine with a governor, 
 in contrast to the series motor which acts like an un- 
 governed automobile engine. At the "no load speed" 
 of a shunt motor it develops a back e.m.f. almost 
 equal to the applied voltage, so that only a small 
 current can flow. A slight increase in the speed would 
 raise the back e.m.f. so high that no current could 
 enter the armature and the machine could take no 
 power from the line. 
 
 When a shunt motor is required to drive a load 
 it must absorb more watts than when running idle. 
 Suppose 100 volts applied to the armature and the 
 back e.m.f. at no load equals 99. The net voltage 
 driving current through the armature is, then, 1 volt, 
 and the current will be 10 amperes if the resistance 
 is 0.1 ohm. If a load is then applied which requires 
 an input of 4 kw., the current must rise to 4000 -f- 
 100, or 40 amperes, which means that the net voltage 
 must be 40 X 0.1 = 4. The back e.m.f. must drop to 
 96 volts, which means that the speed must drop to 
 96/99 of the no load speed. At full load a shunt 
 motor runs about 5% slower than at no load. 
 
 It is often desirable to run a shunt motor at 
 other than normal speed. In a machine shop, for 
 instance, a motor driven lathe should have several 
 available speeds suitable for different jobs. There 
 are four ways of accomplishing this: (1) By install- 
 ing a multivoltage system; (2) by rheostat control 
 of armature current; (3) by changing the field flux 
 mechanically; (4) by rheostat control of the field 
 current. 
 
 With two or more generators one can apply to 
 the motor armature different voltages and obtain 
 speeds in proportion. The field strength may be kept 
 constant by using always the same voltage for ex- 
 
74 
 
 APPLIED ELECTRICITY 
 
 citation. A similar effect may be obtained by put- 
 ting a rheostat in series with the armature and thus 
 lowering the applied e.m.f . by means of the voltage 
 drop. This method is wasteful of power, while the 
 first is expensive and complicated. 
 
 Weakening the field of a shunt motor by moving 
 the poles and armature farther apart or by putting 
 
 Fig. 22. — Cutting down the field current in this shunt motor by means of 
 the rheostat causes the armature to run faster. It must do this to keep 
 the counter electromotive force nearly equal to the voltage of the line. 
 
 resistance into the exciting circuit changes the speed 
 (see Fig. 22). Suppose the unloaded 100-volt motor 
 considered above had its field weakened 7% — what 
 alteration in speed would occur? The back e.m.f. 
 would instantly fall to about 92 volts and a large 
 current would flow (8 -^ 0.1 = 80 amperes) . This 
 would produce a strong torque and speed up the 
 armature until the back e.m.f. reached approxi- 
 mately^ its former value. Weakening the field 
 increases the speed. 
 
 Compound Wound Motors. — Some motors have 
 a series winding in addition to the shunt coils on the 
 field poles. Imagine current supplied to a compound 
 generator, entering at the positive (+) terminal 
 (from which the current was sent out when the 
 machine was generating) . Would the series field help 
 or oppose the shunt field, and which way would the 
 armature rotate ? The current would flow in the old 
 direction through the shunt coil (from the + to 
 the — brush), but in the reverse direction through 
 the series coil. Hence the field will be weakened by 
 the series coil. The armature will rotate in the old 
 
MOTOR CHARACTERISTICS 75 
 
 direction, for it must produce an induced e.m.f. 
 opposing current, and hence directed out at the + 
 brush. When a load is put upon this motor the in- 
 creased current in the series coil tends to weaken 
 the field and hence to increase the speed. Thus a 
 compound motor can be arranged to have a constant 
 speed with varying load. 
 
 A "cumulative compound winding" is produced 
 when the series coil is connected the opposite way, 
 so as to assist the shunt coil. Such a winding gives 
 a strong torque at starting, due to the heavy series 
 current and the strong field it produces. An increase 
 of load in such a machine causes the speed to drop 
 more than with a simple shunt winding, as the in- 
 crease of current strengthens the field. Such a char- 
 acteristic is desired for such machines as punch 
 presses, shears, etc. These motors with various de- 
 grees of compounding are used also for elevators, 
 rolling mill machinery, etc. 
 
 Alternating Current Motors. — A synchronous 
 motor runs at a constant speed which is determined 
 by the number of poles and the frequency with which 
 the supply current reverses its direction. Adding or 
 taking off the load changes the number of amperes, 
 and varying the field strength changes the "phase 
 relation" of the supply current, but the motor runs 
 at constant speed unless the load is heavy enough to 
 make it "fall out of step" and come to a standstill. 
 
 Induction motors without load run at nearly 
 synchronous speed. This can be calculated from the 
 number of poles and the frequency of the supply cir- 
 cuit. For "60 cycle current" the revolutions per 
 second = 60 -^ no. of pairs of poles. Thus a 6 pole 
 motor makes 20 revolutions per second or 1200 r.p.m. 
 unloaded. The 50 cj^cle current used in Southern 
 California drives a 4 pole synchronous motor at 1500 
 r.p.m. 
 
 As the load on an induction motor is increased 
 its speed decreases, the "slip" varying from prac- 
 tically zero to 5% or more. Some motors, specially 
 
MOTOR CHARACTERISTICS 
 
 77 
 
 built with high resistance rotors, have a slip of 10 or 
 15%. Such machines are used for driving the rolls 
 in steel mills and similar work where the load is 
 heavy and intermittent. With a punch press, for 
 instance, such a motor can speed up and deliver 
 energy to a heavy flywheel during the interval be- 
 tween operations, and then slow down to give the 
 
 An induction motor driving a wood saw. This small machine runs at 
 1200 r.p.m. when unloaded, and is rated at 5 hp. Calculate the number of 
 poles and the frequency of the alternating current supply. 
 
 flywheel a chance to do much of the work of driving 
 the punch. A constant speed motor would be of very 
 little value for such applications for it would be very 
 heavily overloaded part of the time and idle for the 
 remainder. The cumulative compound d.c. motor and 
 the induction motor with large slip are much used 
 with flywheels for this class of work. 
 
XII 
 
 ELECTRIC METERS 
 
 Direct Current Instruments. — Practically all 
 electrical meters operate by reason of the production 
 of magnetic fields by electric currents. The earliest 
 indicating instrument was merely a single wire held 
 above a compass needle. A flow of electricity in the 
 wire caused the needle to turn through an angle de- 
 pendent upon the strength of the current. Running 
 the wire below the needle doubled the turning 
 moment and it was a short step to the simple gal- 
 vanometer which consisted of a compass mounted in 
 a coil of wire with the needle perpendicular to the 
 axis of the coil. 
 
 There are serious disadvantages connected with 
 the use of the "moving needle" type of instrument, 
 and these are eliminated in the "moving coil" and 
 "magnetic vane" meters now commonly used. The 
 moving coil meter of the D'Arsonval type has a coil 
 like the armature winding of a motor, and this is 
 placed in a magnetic field. When current (which is 
 led into and out of the coil through spiral springs 
 around the shaft) flows through the winding, the 
 armature turns for the same reason that a motor 
 revolves, but the springs restrain the motion so that 
 the attached pointer moves only a limited distance. 
 The torque depends upon the armature current, and 
 hence the pointer indicates upon its scale a reading 
 proportional to the current. (See Fig. 6, p. 23.) 
 
 In instruments of this type every motion of the 
 coil causes the metal bobbin upon which it is wound 
 to move through a strong magnetic field. This in- 
 
 78 
 
ELECTRIC METERS 79 
 
 duces eddy currents in the metal, the effect of which 
 is to slow the motion and prevent vibration of the 
 coil after the needle reaches the point where the 
 reading should be made. Such instruments are called 
 "dead beat/' Other meters do not depend upon eddy- 
 current "damping" but contain air chambers in which 
 move vanes which stop vibration by air friction. 
 
 ZenoAdjuster 
 
 Edgewise Ammeter. This instrument is used on station switchboards for 
 metering direct current. 
 
 Light moving coils with delicate springs can not 
 carry heavy currents, and ammeters of this type 
 usually contain "shunts'* which carry a definite frac- 
 tion of the total amperes in multiple with the coil. 
 The scale of the instrument is marked or "cali- 
 brated" to indicate the total current flowing in the 
 coil and shunt. 
 
 A "milliammeter" or "mil-ammeter" is adapted 
 to measure small currents and marked in thou- 
 sandths of an ampere. Suppose the coil of such an 
 instrument to have a resistance of 9 ohms and imag- 
 ine a coil of 991 ohms connected in series with it 
 inside the case. There would be a total of 1000 ohms 
 between terminals, and if a pressure of 30 volts were 
 applied, the current flow would be only 0.030 am- 
 peres or 30 mil-amperes. The scale reading would 
 be 30, exactly equal to the voltage. A voltmeter, 
 then, is simply a very sensitive galvanometer or am- 
 meter with large resistance. Such an instrument is 
 calibrated by connecting it in multiple with a stand- 
 
80 APPLIED ELECTRICITY 
 
 ard voltmeter and altering the voltage by suitable 
 steps. 
 
 If it is desired to use a 150-volt voltmeter on a 
 1200-volt circuit it is necessary to put more resist- 
 ance in series with it. Manufacturers supply "multi- 
 pliers" which are simply resistance coils to be used 
 in this way. The meter reading must be multiplied 
 by the appropriate factor to get the pressure. 
 
 Multiplier to use in connection with a voltmeter or wattmeter. What 
 resistance should it have to make a 9000-ohm voltmeter read 140 on a 560- 
 volt circuit? What would the multiplier be called? 
 
 Electrodynamometer Instruments. — ^Many mov- 
 ing coil ammeters and voltmeters have magnetic 
 fields produced either by permanent magnets or by 
 electro-magnets excited by a steady current. The 
 "electro-dynamometer'' ammeter or voltmeter, how- 
 ever, has a field coil connected in series with the 
 moving coil, so that the torque depends upon the 
 square of the current. The instruments contain no 
 iron, and the reaction between the coils is spoken of 
 as electro-dynamic, rather than electro-magnetic. 
 The reading scale of such an instrument is not regu- 
 lar or uniform but the marks are much wider apart 
 at some places than others. 
 
 The power in a d.c. circuit equals the product 
 of volts times amperes, and it can be conveniently 
 metered by an electro-dynamometer instrument. The 
 moving coil (with high resistance) is connected 
 across the line and takes a current proportional to the 
 voltage. The stationary coil is put in series with 
 the load and so carries the load current. The torque 
 
ELECTRIC METERS 81 
 
 developed is proportional to the product of pressure 
 and current and hence the scale may be calibrated in 
 watts or kilowatts. The divisions may be very 
 nearly uniform. Such a wattmeter may be used for 
 high voltages by connecting a multiplier in series 
 with the voltage coil, and for large currents with the 
 help of shunts like ammeter shunts. 
 
 General Electric Wattmeter. Why are there more terminals than on a 
 voltmeter ? Is this instrument built for a switchboard or for occasional use ? 
 For connections, see Fig. 5— ^page 15. 
 
 Metering Alternating Currents. — If the current 
 is reversed in a moving needle instrument or in one 
 having a moving coil and a permanent magnet, the 
 pointer will be seen to deflect in the opposite direc- 
 tion. Such meters can not, then, be used on alternat- 
 ing current circuits. Electro-dynamometer instru- 
 ments, however, operate perfectly with alternating 
 current, for the field of the stationary coil reverses 
 as often as the current in the moving coil, thus pro- 
 ducing torque always in the same direction. Hence 
 electrodynamometers are often used for a.c. circuits, 
 as ammeters, voltmeters and wattmeters. They may 
 be calibrated with direct current and used on either 
 kind of circuit. 
 
 Various other meters have been developed for 
 use with both direct and alternating current. The 
 "electrostatic voltmeter" consists of moving and 
 stationary vanes which are charged with static elec- 
 tricity by connecting to the opposite sides of a high 
 
82 APPLIED ELECTRICITY 
 
 potential circuit. The vanes are drawn toward each 
 other, moving a pointer against the restraint of a 
 spring. A fountain pen rubbed upon a coat sleeve 
 will attract bits of paper by a similar electrostatic 
 action. 
 
 A device used for both ammeters and voltmeters 
 is the "hot wire." Current through a piece of re- 
 sistance wire heats it, causing expansion which per- 
 mits a spring to pull a pointer across a scale. Another 
 scheme is to use for a voltmeter or ammeter a sta- 
 tionary coil surrounding two light parallel iron rods, 
 one of which is fixed in position. The other is 
 attached to the pointer and can move around the 
 inside of the coil, always keeping parallel to the fixed 
 rod. Both rods are magnetized when current flows, 
 and the repulsion of like poles causes one to move 
 away from the other. Still another device consists 
 of a soft iron plunger which is sucked into a coil 
 when current flows around it, the plunger being sup- 
 ported by the spindle which carries the pointer. 
 Pocket instruments for testing dry cells are of this 
 type. All these meters will work with more or less 
 accuracy upon alternating as well as direct current 
 circuits, for, obviously, reversing the current does 
 not reverse the effect upon the pointer. 
 
 Many alternating current voltmeters, ammeters 
 and wattmeters are of the "induction type." In 
 these a rotating field is produced, as in the induction 
 motor, and this induces in the rotor short circuit 
 currents which tend to turn it on its axis. A re- 
 straining spring and a pointer complete the moving 
 element. Such instruments can, of course, only be 
 used on a.c. circuits. An induction wattmeter has 
 certain coils connected across the line and others in 
 series with the load; ammeters and voltmeters have 
 all their coils in series. 
 
 Watthour Meters. — Instruments for measuring 
 energy consumption are often mistakenly called 
 "wattmeters." A watthour meter is a small electric 
 motor so constructed as to use up very little en- 
 ergy and yet to run at a speed proportional at all 
 
ELECTRIC METERS 
 
 83 
 
 times to the power taken by the electrical load on 
 the line. By means of a revolution counter a record 
 is made on the dial of the number of revolutions 
 of the armature, thus accounting for the kw-hr. 
 
 Interior of a direct current watthour meter. Note the four permanent 
 horseshoe magnets and the retarding disc between their poles. 
 
 that have passed the meter. Many d.c. watt- 
 hour meters have commutators and brushes, the 
 armatures being of high resistance and connected 
 across the line so as to carry current proportional 
 to line voltage. The field is then connected in series 
 with the load. Such meters have no iron at all in 
 the magnetic circuit, which means that the flux and 
 torque are proportional to the voltage and current 
 and no complications are caused by variations in 
 permeability, etc. 
 
 Reversing the current in both the armature and 
 series coils of such a meter gives torque in the pre- 
 vious direction, and hence it may be used on a.c. 
 circuits. For several reasons, however, watthour 
 
84 
 
 APPLIED ELECTRICITY 
 
 meters of the induction type are generally preferred 
 for such service. These are simply induction motors, 
 lacking commutator and brushes, and thus having no 
 moving contacts. 
 
 It is necessary in all watthour meters to restrain 
 the motion of the armature or else even a light load 
 would cause rapid rotation and high readings on the 
 
 Testing meters taken from 
 residences in Fresno, Cal- 
 ifornia. Are these watt- 
 meters or energy meters? 
 
 dials. Usually a disc of aluminum is attached to the 
 armature shaft and arranged to rotate close to the 
 poles of strong permanent magnets. Eddy currents 
 are set up which hold back the disc with a force pro- 
 portional to the speed, and the result is that the 
 speed is made proportional to the driving torque of 
 the armature. In induction watthour meters the 
 retarding disc serves also as armature, the revolving 
 field setting up in one part of it eddy currents which 
 cause it to move, and the stationary magnets setting 
 up in another place currents which retard it. 
 
 Curve Tracing Meters. — ^Many meters are in 
 service which make graphical records, or charts. 
 The curve drawn by a recording voltmeter, for in- 
 stance, tells the voltage at every instant during a 
 
ELECTRIC METERS 85 
 
 period of twenty-four hours. New sheets are in- 
 serted daily and thus continuous record is kept, 
 which at any future time may be called upon for 
 information regarding pressure fluctuations, short 
 circuits, etc. Station operators who fall asleep on 
 the ^'graveyard watch'' sometimes are thus betrayed 
 by a record of voltage too high or too low during half 
 an hour. 
 
 Such an instrument includes a meter with a pen 
 mounted on its pointer, and a clock for moving a 
 piece of paper uniformly past the point of the pen. 
 The mechanism of the meter may be similar to that 
 of an ordinary electrodynamic voltmeter or watt- 
 meter, but with sufficient turns of wire to give strong 
 forces to overcome pen friction, etc. Other record- 
 ing instruments make use of relays so that the pen 
 is moved by electromagnets operating when the 
 metering mechanism closes certain contacts. 
 
XIII 
 LAMPS AND ILLUMINATION 
 
 Commercial and home portrait pho- 
 tographers use gas filled Mazdas in 
 deep reflectors to illuminate their 
 subjects. 
 
 LL sorts of lamps are 
 used for producing ar- 
 tificial light, but in this 
 country the incandes- 
 cent lamp is used to a 
 greater extent than all 
 others combined. Until 
 recent years the car- 
 bon filament lamp of 
 this type was the 
 standard, but the su- 
 perior economy of 
 metallic filaments has 
 caused the carbon lamp 
 to be practically displaced by the tungsten lamp. 
 The latter gives approximately three times as much 
 light as the former for the same power consumption. 
 In lamps of medium and large size it is found 
 that the efficiency is increased by filling the bulb 
 with an inert gas, such as nitrogen. The ordinary 
 tungsten lamp has the air removed, the filament 
 being allowed to glow in an almost perfect vacuum. 
 The gas permits the filament to be heated to a higher 
 temperature. This means that a larger proportion of 
 the energy expended in heating the wire is radiated 
 off in light waves. For instance, the vacuum lamp 
 in the 100-watt size gives only 80% as much light 
 as the gas filled 100-watt lamp. 
 
 86 
 
LAMPS AND ILLUMINATION 
 
 87 
 
 Lamps carrying large currents have better effi- 
 ciencies than those of smaller amperage. The 200- 
 watt 220-volt Mazda has the same efficiency as the 
 100- watt 110-volt lamp, and only 86% as high effi- 
 ciency as the 200-watt 110-volt lamp. 
 
 Local lighting gives the largest proportion of the total light of the lamps 
 at the point of use 
 
 Candle Power and Foot Candle. — If an incandes- 
 cent lamp, hung in the usual position with base up- 
 ward, gives off in a horizontal direction as much 
 light as a standard candle, it may be called a "one 
 
3 O 
 
 si 
 
 ot'T 
 
 Ho; 
 
LAMPS AND ILLUMINATION 89 
 
 candle power" (one c.p.) lamp. More accurately we 
 say that its "horizontal candle power" is one. This 
 point must be emphasized, for the amount of light 
 sent in other directions is not the same. 
 
 If a lamp is located at the center of a globe or 
 sphere, it sends light to nearly every point on the 
 inner surface; but different amounts to different 
 places. The average candle power in all directions is 
 called the ''mean spherical candle power," and it is 
 usually considerably less than the ''horizontal candle 
 power." Ordinary lamps have a mean spherical c.p. 
 equal to about .8 of the horizontal c.p. 
 
 If a very concentrated one c.p. light is one foot 
 from a wall, the illumination at the point on the wall 
 nearest is one "foot candle." Every other part of 
 the surface is less brightly lighted, since it is more 
 than a foot away. However, if the wall were warped 
 so that a considerable part of it was exactly one 
 foot from the light, the illumination would be one 
 foot candle all over that part. A spot on a wall one 
 foot from a lamp of 20 horizontal c.p. would be illum- 
 inated with an intensity of 20 foot candles. 
 
 For various purposes different intensities of 
 illumination are required. In the operating room of 
 a hospital the illumination on the "working plane" 
 (the plane level with the table top) should be 12 or 
 more foot candles; in a dining room 2 foot candles 
 would be satisfactory. Following are the suggestions 
 of various illuminating engineers for a few cases : 
 
 Auditorium 
 
 1 to 
 
 3 
 
 Lavatory 
 
 2 to 6 
 
 Cigar Store 
 
 4 to 
 
 6 
 
 Library (tables) 
 
 3 to 4 
 
 Coil Winding 
 
 4 to 
 
 12 
 
 Office 
 
 4 to 10 
 
 Department Store 
 
 4 to 
 
 10 
 
 Outdoor Construction .5 to 2 
 
 Drafting Room 
 
 7 to 
 
 12 
 
 Proof Reading 
 
 4 to 12 
 
 Drug Store 
 
 3 to 
 
 8 
 
 Residence-Cellar 
 
 0.6 
 
 Elevator 
 
 1 to 
 
 3 
 
 Residence-Kitchen 
 
 2.0 
 
 Engine Room 
 
 3 to 
 
 9 
 
 Residence-Parlor 
 
 1.5 
 
 Garage 
 
 3 to 
 
 9 
 
 Shoe Store 
 
 3 to 5 
 
 Grocery 
 
 3 to 
 
 6 
 
 Stairs and Halls 
 
 .5 to 2 
 
 Laundry 
 
 3 to 
 
 9 
 
 Telephone Exchange 
 
 3 to 9 
 
 Reflectors. — Reflectors or shades are used with 
 nearly all incandescent lamps, though they absorb 
 much of the light and therefore are far less than 
 
90 
 
 APPLIED ELECTRICITY 
 
 100% efficient. A surface of porcelain over steel, 
 which is much used in shop and factory reflectors, 
 absorbs about 35% of the light that falls upon it. 
 
 There are two good reasons for the use of bell- 
 shaped reflectors for interior lighting: (1) they put 
 
 Indirect lighting in the new and beautiful California Theater, San Fran- 
 cisco. Note the individual reflector for each lamp. 
 
 the greater part of the light where it is wanted and 
 (2) they protect the eyes by making it impossible 
 to see the glaring filament unless one looks in an 
 unusual direction. An ordinary bare lamp throws 
 
LAMPS AND ILLUMINATION 91 
 
 very little light downward (past the tip), and so is 
 very inefficient if hung vertically over the work to be 
 lighted. Furthermore the intense light which enters 
 the eye of a person who has a bare lamp within his 
 angle of vision is not only annoying but also painful 
 and injurious. 
 
 Indirect Lighting. — In some cases the reflectors 
 are turned upside down and arranged to throw all 
 the light toward the ceiling. Then the useful light 
 in the room is only that which is reflected downward 
 from the ceiling or from special white surfaces placed 
 above the lamps. This is known as "indirect" or 
 "totally indirect" lighting. Note that the reflectors 
 are completely opaque. 
 
 The method is very considerably adopted be- 
 cause it gives freedom from eye strain. It requires 
 more wattage than any other system, and tends to 
 decrease rapidly in efficiency on account of the col- 
 lection of dust. Some objection is made to indirect 
 lighting on the ground that shadows are largely elim- 
 inated, which makes it difficult to see the details 
 clearly. It has been claimed, however, that with the 
 same eye fatigue from two to five times as much 
 drafting and similar work can be done under indirect 
 lighting as with any other artificial light. 
 
 A modified method, known as "semi-indirect" 
 lighting, is widely used. A translucent reflector is 
 put under the lamp, permitting a portion of the light 
 to come through as well as reflecting much .light to 
 the ceiling. This is fairly efficient and has many 
 advantages, but is open to some of the objections 
 to both the ordinary and the indirect systems. 
 
 If reflectors were perfectly efficient and walls 
 and ceilings reflected all the light that reached them, 
 absorbing none, the total light flux from the lamps 
 would reach the working plane. In most installations 
 it receives only from 20 to 60% of the light emitted 
 by the lamps. 
 
 By multiplying the required foot candle inten- 
 sity in any room by the area of the working plane 
 
92 
 
 APPLIED ELECTRICITY 
 
 (which equals the floor area) we obtain a measure 
 of the useful light necessary. This figure has to be 
 multiplied by a factor of from 1.7 to 5 or more to 
 find the total light the lamps must give. Below are 
 
 
 Warehouse lighted by large lamps (300-watt gas filled) at a total expendi- 
 ture of .15 watt per sq. ft. What is the size of the squares into which 
 the ceiling is divided by the lighting fixtures? What part of the light is 
 wasted if the illumination averages one foot candle at the working plane 
 
 listed some approximate factors for small rooms with 
 light ceilings: 
 
 Reflector IJght Dark 
 
 Walls Walls 
 
 Prismatic glass bowl 2.7 3.0 
 
 steel bowl (deep) 2.6 3.0 
 
 Light opal glass 3.4 3.7 
 
 Totally indirect 5.0 6.2 
 
 Semi-indirect 4.3 5.3 
 
 A 25-watt Mazda lamp has a mean spherical 
 candle power of 17.7. If it were surrounded by a 
 spherical shell one foot in radius, the inner surface 
 of the shell, being one foot from the lamp, would 
 receive an average illumination of 17.7 foot candles. 
 As there are 12.57 sq. ft. of surface, the total light 
 

 Ordinary Tungsten 
 
 Watts 
 
 Spherical c.p. 
 
 Total light 
 
 15 
 
 10.0 
 
 125 
 
 25 
 
 17.7 
 
 223 
 
 40 
 
 29.4 
 
 369 
 
 60 
 
 45.8 
 
 575 
 
 100 
 
 79.5 
 
 997 
 
 LAMPS AND ILLUMINATION 93 
 
 emitted by the lamp may be figured as 17.7 X 12.57 
 = 223 units. Similarly a 500-watt gas filled lamp 
 (mean spherical c.p. = 694) produces a flux of 
 694 X 12.57 = 8720. 
 
 Such numbers are found in the following table 
 for the most common lamps: 
 
 Gas Filled (Mazda C) 
 
 Watts Spherical c.p. Total ligrht 
 
 75 69 865 
 
 100 100 1257 
 
 150 163 2050 
 
 200 232 2920 
 
 300 385 4830 
 
 What size lamp should be used in the six indirect 
 lighting fixtures in a reading room 23 x 30 ft. with 
 light ceiling and dark walls? Take foot candles =3.5 
 by the first list ; the area =: 690 sq. ft., hence the 
 useful light = 3.5 X 690 = 2415 units. The total 
 light =: 6.2 times this, or 15,000 units, which re- 
 quires 2500 units of light from each of the six fix- 
 tures. Hence, select 200-watt gas filled lamps. 
 
 Similar calculations are made for many effective 
 lighting installations, but the design is not generally 
 as simple as this example might suggest. Consid- 
 erations of art, utility, and the plans of the owners 
 and architect complicate the situation, so that much 
 study and experience are required to develop power 
 to plan satisfactory lighting systems. 
 
XIV 
 INDUCTION— TRANSFORMERS— INTERPOLES 
 
 Induction Coils. — If a coil carrying current is 
 thrust into another coil, an electromotive force will 
 be induced in the latter, due to the cutting of the 
 
 b 
 
 
 
 
 1 
 
 
 ) 
 
 
 
 ■ 
 
 
 
 V 
 
 
 
 
 
 
 
 
 
 """* 
 
 
 Fig. 23. — The Induction Coil consists of two independent coils with the same 
 core. Varying current in the Primary (P) induces e.m.f. in the sec- 
 ondary (S). 
 
 wires of the second by the lines of force. If the 
 "primary coir' (P, Fig. 23) has an iron core, it will, 
 of course, have a greater flux than otherwise, and 
 so produce more **interlinkages" of lines of force 
 with the turns of wire of the secondary, S. The 
 voltage set up is proportional to the number of inter- 
 
 94 
 
INDUCTION— TRANSFORMERS— INTERPOLES 95 
 
 linkages (number of lines X number of secondary 
 turns) and the quickness with which they are pro- 
 duced — one volt if the rate is 100,000,000 per 
 second. Leaving the primary standing within the 
 secondary induces no voltage, and the needle of the 
 voltmeter stays at zero. But breaking the primary 
 circuit at K produces the same effect as withdrawing 
 coil P, destroying the interlinkages and moving the 
 voltmeter pointer in the negative direction. Closing 
 K sets up the linkages and gives a positive indication 
 on V. Thus we obtain an alternating current in S 
 by starting and stopping the primary direct current, 
 but we get no effect with a steady primary current 
 when the coils are stationary. 
 
 If we replace K by a telephone transmitter, any 
 sound near it will cause motion of the diaphragm, 
 with consequent variation in the resistance of the in- 
 strument. When the primary current rises, it in- 
 creases the flux and sends current in one direction 
 through the secondary circuit; when it decreases it 
 produces secondary current in the opposite direction. 
 The apparatus (P and S) thus used constitutes the 
 "induction coir' found in every telephone circuit. 
 The ordinary induction coil, used to shock people for 
 the betterment of their health or to produce sparks 
 for ignition and wireless telegraphy, consists of the 
 primary and secondary coils and some apparatus for 
 suddenly opening and closing the circuit at K. 
 
 Transformers. — When alternating current is 
 supplied to the primary coil, the apparatus becomes 
 a "transformer." The flux produced by the primary 
 and linking with the secondary is directed first one 
 way and then the other as the supply current flows 
 forward and backward. Every time the flux comes 
 to a maximum and commences to decrease, the sec- 
 ondary voltage stops and reverses. Thus is obtained 
 an alternating e.m.f . of the same "frequency" (num- 
 ber of cycles per second) as the primary current. 
 
 The ratio of the induced voltage to the pressure 
 applied to the transformer is almost exactly the same 
 as the ratio of secondary to primary turns. Under 
 
96 
 
 APPLIED ELECTRICITY 
 
 operating conditions the secondary voltage is a little 
 lower than is indicated by this relation, on account of 
 drop due to resistance and the "leakage" of part of 
 the flux (some lines are produced by one coil and fail 
 to link with the other). 
 
 Iron cores are used in induction coils and trans- 
 formers, the latter usually having a complete iron 
 path for the flux, while the former have **open cores" 
 which are merely straight bars of iron. Of course 
 the laminated construction must be used for all cores 
 
 Fig. 24. — At one instant the current and magnetic lines of the power 
 circuit are as indicated. When they reverse, the lines which reach the 
 telephone wires induce a voltage there. 
 
 carrying an alternating flux, to prevent undue losses 
 by eddy currents. (See illustration of transformer 
 construction, p. 52.) 
 
 Whether or not iron cores are used, the chang- 
 ing flux due to varying current in one circuit will set 
 up an alternating e.m.f. in any other circuit with 
 which the lines become linked. Thus the apparatus 
 of Fig. 23 will give evidence of a small effect on V, 
 even if the coils are separated as shown and contain 
 only an air core. 
 
 This "mutual induction" is often troublesome. 
 Coils near together on a telephone switchboard used 
 to affect one another and produce "cross talk" until 
 each coil was surrounded by an iron case which kept 
 the flux from straying. In a telephone line near an 
 
INDUCTION— TRANSFORMERS— INTERPOLES 97 
 
 a.c. power circuit (Fig. 24) alternating currents are 
 induced by the lines of force which link with the tele- 
 phone wires. It is to overcome mutual induction that 
 the conductors of power lines and telephone systems 
 are crossed over each other or "transposed" at inter- 
 vals. 
 
 Self Induction. — Flux set up by a coil links first 
 of all with the wires of that coil, and this interlink- 
 ing produces inductive effects similar in principle to 
 
 In this induction motor the alternating current in the primary winding 
 is choked down to a safe value by self-inductance. Short circuited currents 
 are induced in the rotor by what resembles transformer action. 
 
 those of mutual induction. When K is opened (Fig. 
 23) a spark appears there, more evident if there 
 is an iron core in the coil. A voltage is induced by 
 the change of linkages, and this may be far higher 
 than the battery voltage. Indeed, one may obtain 
 a very perceptible shock with a small electromagnet 
 (such as that in an electric door bell) and a single 
 dry cell. 
 
 The voltage induced by the cutting down of bat- 
 tery current and consequent reduction of linkages 
 is, naturally, so directed as to oppose this diminution 
 of current. Thus the current is kept flowing through 
 the increasing resistance of the opening key, crossing 
 the air gap in a spark or arc. The faster the gap is 
 opened the greater the voltage induced. 
 
 Low speed gas engines sometimes have the 
 ''make and break" spark for ignition. A pair of con- 
 tacts inside the cylinder are caused to touch, and 
 
INDUCTION— TRANSFORMERS— INTERPOLES 99 
 
 current flows from a battery through a coil of high 
 "self inductance" (having an iron core and many 
 turns of wire) . When the circuit is suddenly broken, 
 a spark jumps across the break and ignites the ex- 
 plosive charge. A similar device is used for lighting 
 gas lamps and stoves. 
 
 When an electromotive force is applied to a cir- 
 cuit containing self induction, the current grows but 
 slowly, for the increasing interlinkages induce a 
 counter voltage. An alternating e.m.f . sends through 
 an inductive coil a current which is small compared 
 with what it could send through an equal non-induc- 
 tive resistance, because the voltage begins to de- 
 crease before the current has time to rise much. 
 Furthermore, the voltage falls to zero and reverses 
 some time before the current does. Such a current 
 is said to be "lagging,'' and in these cases the power 
 factor is less than 100%. Small induction motors 
 often take current lagging so much that the power 
 factor is 80% or less. 
 
 Commutation. — Fig. 25 represents a four pole 
 d.c. generator at the instant when each of the brushes 
 touches two commutator bars. The coil including 
 inductors numbered 1 and 6 is short circuited by 
 brush A at this time. Just before the brush touched 
 the left hand bar, current was flowing in inductor 
 No. 1 the same way as in Nos. 2 and 3; an instant 
 later, when brush A no longer touches the right 
 hand bar, current must flow the opposite way in 
 No. 1, for it will then be under the south pole. The 
 current in the coil must stop and reverse in the time 
 it takes a commutator segment to pass across the 
 face of one brush — possibly 1/500 sec. in an ordinary 
 machine. 
 
 Self induction keeps the current flowing in the 
 coil after it is short circuited, thus producing heat 
 and making trouble at the face of the brush. To 
 remedy this an "interpole'' (IP, Fig. 25) may be 
 placed between the main poles. The flux it produces 
 must be enough to overcome the m^gjietizing effect 
 of armature reaction and in additiaij induce* iii^ the 
 
100 
 
 APPLIED ELECTRICITY 
 
 short circuited coil a voltage opposing the e.m.f. of 
 self induction and assisting the starting of current 
 in the new direction. The interpole winding is con- 
 nected in series with the armature and hence its 
 strength is proportional to the armature current. 
 
 Fig. 25. — Four pole d.c. generator armature. The heavy radial lines num- 
 bered 1, 2, 3, etc., represent the inductors. To avoid confusion the brushes 
 are drawn inside the commutator. 
 
 The interpole shown should have south polarity, 
 to prepare the inductors for the south pole they are 
 about to reach. Three more interpoles would be 
 used, one in each gap between main poles, and each 
 of the same polarity as the main pole which fol- 
 lows it. 
 
 On motors interpoles are much used also. Here 
 each one has the same polarity as the main pole 
 which an inductor passes before it reaches the inter- 
 pole. 
 
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