A afier fresented at the Twelfth Genera Mee ineof the Anerican Institute of Electrical En-neers, Niagara Falls, N. J.June 26/hA 189SPresident Duncan in the Chair.

SOME FEATURES OF ALTERNATING CURRENTSYSTEMS.

BY CRAS. PROTEUS STEINMETZ.

In the followinlg I intend to review some of the work done inthe last few years in exploring the actions and reactions of alter-nating currents. I shall endeavor to avoid as far as possible theuse of mathematics, but I must beg you to believe that all thestatements made are paralleled by exact mathematical calculationswhich have been partly published already, or which will be pub-lished in due time, but which if introduced in the present paper,would extend beyond the scope intended.The practical applications of the modern alternating current

system date from the introdLction of the alternating currenttransformer. The possibility of transforming the voltage, andthus to use high voltage in the line and low voltage in the con-stumer circuit, gave the alternating current system a superioritynot shared by the continuous current system, and thereby putthe latter out of competition wherever great distance had to betraversed. A further advantage has been added in the last fewyears only, by the superiority of the alternating current motorover the continuous current motor, due to its greater reliability,better speed regulation and ability to stanid overloads whichmade it preferable at least for higlh grade work.

It was not so in the beginning of the period of alternating cur-rent distribution. lF'or a long time the system labored under thedisadvantage of not being able to snLpply motive power, beingavailable for lighting only. The inability to operate motors wasthe miiore serious as the alternating current systein by its verynature is specially suited for long-clistance transmission. In long-

326

STI'NMET7ONALTVRNATINGCURRBNTSYSTEMS. 327

distance transmission, however, the object aimed at is in general,at least partly, mechanical power. Thus the alternating cinrrentmnotor became the problem of those times. The alternating currentgenerator, when running at synchronism iD parallel with othergenerators, will keep on revolving even if the driving power isremoved, and will operate as a " synehronous motor" keepingabsoluitely in step with the generator. Such synchronous motorsare quite extensively used now, especially for large units. Theyhave, however, the disadvantage that they are not self-starting, butmust be brought up to synchronism before operating as reversedgenerators. Thlus, either external starting devices had to be usedor the synchronous motor made what is called " self-starting;"that is built so as to operate in starting and ruinning below syn-chronism as a synchronous, or induction motor, or that varietyof the latter which is called the "reaction motor." Thus, the

A B

Fia. 1.

reversibility of the alternating current generator did not bringa complete the solution of the motor problem.The solution of the alternating current motor problem had

to be expected, either by the adaption of tlle continuouscurrent motor to alternating currenat circuits, or by the discoveryof an entirely new principle. The introduction of polyphasesystems appeared to give the solution in the polyphase inductionmotor.

If by a system of E. M. F.'s displaced in phase from eaelh other,currents displaced in phase are sent through the field circuits of amotor with short-circuited armature, rotation of the latter isproduced.

This motor necessitates the use of polyphase systemls, that is,systems comprising several circuits differing from each other inphase of their E. M. F.'s and currents. Sunh polyphase systemns

328 STEINMT7TZONALIERNATINGCURRJENTSYS-TES. [June26,

require the subdivision of the single phase load, as lights, into andbetween several circuits, and require an approximately equal di-vision to avoid on the one hand overloading of an individual cir-cuit of a generator, while the generator as a whole is not yet fullyloaded, and on the other hand to avoid the feature of "1 unbalanc-ing " noticed in such systems. Since the different circuits ofthe polyphase system originate in the same generator, and thefield excitation of an alternator has to be varied with the load, itis obvious that two circuits isstuing from the same generator whenloaded differently, will require different field excitations and thusat the same field excitations will show different voltages, the lesserloaded circuit, a higher voltage. The drop of voltage in thetransmission and distributtion lines being larger in the higher

FiG. 2.

loaded circuit, will decrease the voltage of this circuit still more,and thus increase the unbalaniciug efect. IH ence, even if thevariation or potential at the generator terminals due to differeniceof load of the different phases should be small, it will be inereasedby the lines.

However, aside fronm this difficulty, the experience of the lastfew years seeims to show that the complication of subdividing thecircuits in the polyphase system is sufficient in most cases to ex-clude its use, and thus, comnparatively little use has been made ofthe polyphase systems for light and power distribution. It hasbeen different with long-distance transmission of large units, andpower distribution, where polyphase systems have establishedthemselves quite externsively.

Hence, the polyphase system did not completely solve theproblem of alternating currect light and power distribution,

1895.] STINMETZO0 ALTERNATINGCURVENTSYSTEMS. 329

and in returning to the single phase system, attempts weremade to derive from the single phase system by "splitting ofphase," a polyphase system for the operation of mnotors.The futility of all attempts to derive a polyphase system from

a single phase system, I have previouslv shown'.It is possible in a single phase systemn to resolve the E. M. F. S

into components in quadrature with each other or in any otherphase relation. The insertion of a reactive coil into a lainp eir-cuit produces two E. M. F.'s approximately in quadrature witlheach other and differing in phase with the main E. M. F., and bytheir combination any other phase di$erences can easily be pro-duced. A condenser in series in the circuit, or an electrolyticcell will give plhase displacement of E. M. F. also. But wheneverE. M, F.'s displaced in phase are produced in this way, the cur-

FIG. 3.

rents are in phase with each other or are insignificant.Inversely, differences of phase of current can be prod-uced inl

the single phase circuit. The current is an open magnetic cir-cuit transformer at open secondary circuit, and the current in atransformer under full load, are practically in quadrature. Orstill inore, if on the same iron core two coils are wound and con-nected in parallel as shown in Fig. 1, the two currents in thesecoils can by changing the relative number of turns be mnadeto have any phase difference from zero to 1800, but the E. M. F. Sare in phase. All attempts to use such phase differenees producedin the single phase circuit for the operation of polyphasemotors signally failed. While it is possible to operate motors in

1. TRANSACTIONS, 1892, Vol. ix, p. 91.

330 STEINM TZ OALTT2RNA INGCURRENTSYSTEI S. [J'une 6

this way, and this is being done to a certain extent, the currentrequired is far in excess of the torque produced thereby. Suchcircuits of displaced phase lose their phase displacemtient as soonas work is required from them. The cauise is that phase displace-mnent of current, and phase displacement of E. M. F. cannot beproduced simultaneously in a single phase circuit. This is a con-sequence of the law of conservationi of energy.

In a contiinuous current circuit, current, E. XT. F., and tlhus thepower as their product are constant.

In a single phase alternating current circuit, the E. M. F. alter-nates, passing through zero twice per period. The current producedthereby alternates also, passing tl-hrough zero either at the samemoment with the E. M. F., in a non-inductive circuit, or at a dif-ferenit monent.

FIG. 4.

Thus the power of the alternating circuit is fluctuating andvaries twice per period, that is with the double freqi eney of theE. M. F. or the current between a maximum valie and zero in thenon-inductive circuit, between a maximum value and a negativemaximumn value in a circuit with phase displacement -between clur-rent and E. M.. x, in the latter case, passing twice through zero perhalf wave, as shown in the diagram Figs. 2 and 3, where the E.I. F. is represented by the drawu line e, the current by the drawnline o, and the power by the dotted line w.

In the polyphase system, as a quarter phase with two E. M. F.'sin quadrature producing two currents in quadrature, as in Figs.4 and 5, or in a three phase systemn with thiree E. xM. .'s produc-ing three cLrrents, as in Figs. 6 and 7, the energy wave of eachphase is fluctuating as in the single phase systemn. The surm of

1895.] ST INMEIZ ONALTERB ATtNG CURRENTSYSTEMS. 331

all the energy waves, however, or the total flow of eniergy is con-stant.From the law of conservation of energy, it follows thus, that

a change from a single phase to a polyphase circuit or in-versely, is possible only by means of apparatus able to store en-ergy, and that the total amoulnt of energy between the mean andmaximum valuie in the single phase circuit must be stored and re-turned during the time the single phase wave is below the meani.Means to store the energy are, electro-magnetism, electro-

static charge, electro-chemnical force and mechanical motion.Electro-inagnetic and electro-static storage are 'in most cases ex-eluded by low ellergy efficiency and especially low weight effi-ciency and ineonvenience. Electro-chemical storage shows a verylow efficiency, and the only efficient way of storing energy ap-

FIG. 5,

pears to be mechanical momentum. This offers a high weightefficiency also, but is for most cases excluded by the complicationdue to revolving miachinery.

Excluding storage of energy, we see that the nature of the flowof energy constitutes an es8sentat feature of an alternating cur,-rent sy8tem.The phase relation does not represent an essential feature,

since, as seen, starting from a single phase generator we canget currents of different phase relation and E. M. F.'S of dif-ferent phases, but if the currents are displaced in phase, theE. M. F.' s are in phase and iilversely, so as to preserve thenature of the energy flow. Again, starting with a quarterphase generator we can transform by stationary transform-ers without storage of energy, that is at full efficiency, to

332 STEINME ZONALTERNA TING CURRANT SYSTEMS, [June 26,

three phase and back again to quarter phase or five phase or anyother symmetrical or unsymmetrical plhase relation. In all thesetransformrlations, however, the nature of the energy flow remainsconstant. Hence the best classification of the alternating currentsystem is by this feature, the classificationl by the number ofphases having become meaningless with the possibility of trans-formation from one polyphase system to any other. Thlus we shallcall an alternating current system of constant flow of energy, abalanced system; an alternating current system in which theflow of energy pulsates between a maximum anid a miinimum, asystem of balance factor x, where x is the ratio of the minimumvalue to the nean value or energy flow. Hence the balanced

FIG. 6.

polyphase system has the balance factor, one; the single phasesystenm the balance factor, zero.

I may add here that the names "' polyphase " and " single phase"are really wrong, and the latter name meaningless, since "phasebecomes a meaninng only as "difference of phase."The systems are characterized correctly, not by the existence of

one or several phases, but by the existence of one or severalwaves of energy, or cycles, and for this reason I rather prefer thedenotation " polycyclic " for a system of many waves of energy,"nonocyclic" for a system with one wave of energy. Hence:The monocyclie sy8tem is an alternating current system of bal-

ancefactor zero.The balanced polycyc c 8ystem has the balancefactor one

1895.] S XEINJIETZ ONALTURNAT IN CURRENTSYSTElS. 333

The three phase or quarter phase system witlh equal load on allbranches hias the balance factor one.A three phase system with two branches loaded and one un-

loaded has the balance factor .5.A three phase system with one branch loaded and two unloaded

has the balance factor zero.A quarter phase systemn with one branch loaded and the otlher

unloaded has the balance factor zero.Still from another point of view, we are driven to recognize

the inmportance of the flow of energy as characteristic in alter-niating current circuits.

In a continuous current circuit, the direction of transmtlissioin,or direction from the generator to the consumner circuit, is in thedirection of decreasing voltage.

FiG. 7,

In ani alternating currenit ci'rcuit, the voltage at the co-nsumerterminals of the line may be higher than at the ffenerator termil-nals of the l'ine, anld the power be transmitted froin lower tohligher voltage. This is the case in a line of nioticeable induct--

anefeeding into a circuit with leadi-ng current. Inversely thecurrent received -from- the line at the consumer termi-nals may belarger tha-n the current issuinig from the generator into the line.This is th-e case with a line of noticeable capacity feeding into acircuit with laggiDg current. Th-ese features are made use of nowin long-d'istance tr-an'smis'sionls for controlling the potenutialanid the current flow in line and receiver circuiit.

Hence, the direction of transmission in an alternating currentcircuiit is not necessarily the direction of decreasing voltage or de-

334 STEINMETZ ONALTERNAT'ENG CURRENTSYSIE S. [June26,

creasing current, but it is the direction of decreasing energy flow.That is, attaehing a wattmeter to two points of the line, thewattmeter nearer the genierator will always give a higher readingthan that farther away from the generator.

Anl apparent disadvantage of this definition by the natuire ofthe energy flow, is that with a change of the distribution of load,the niature of the system, or at least its balance factor varies. Butin this case the chlaracteristic feature of the system in realityclhanges. It is obvious, for instarnce that if one branch of a threephase generator only is loaded, the eircuit, as well as the gener-

FIG. 8.

FIG. 9.

ator acts in every way as single phiase and is i-ndeed single phase,and the remaining generator circuLit merely dead wire.The total flow of power in an alterniating cuirrenit system can

be represented also by a polar diagram, with the instantanleousvalues of power as radii vectors, and the angle corresponding totime as amplitude, one complete period being represented- by acomplete revolution or 360'. This gives a powAer diagrami of thealternating. current systein corresponding to th-e comnpound i-ndi-cator diagrami- of the steam engine.

In a single Phase system Of E. M. F.,e,_ E=sin

antdcurrent:

1895(1 STEINMETZ ON ALTERNATING CURREINTSYTEMS. 335

o= C sin (D-Co);the power is:

w = e z E C sin s sin (co)- '/2EC osCo -cos (2 9-Co,

and the average power:v = 1/2 E C cos (0.

In polar coordinates, the power diagram of the two circuitsshown in Figs. 2 and 3 is represented by Figs. 8 and 9; Fig. 8representing a non-inductive circuit, Fig. (9 a circuit with 6O lag.

In a system comprising seveial E. M. 'S and currents, in every

,\ W

1 ,~~~0 7w

PIe, 10.

part of the circuit the power can be represented in the form:Zi = 1/ EL C'1 cos (L, - cos (2 9c - i) 1,

and, adding the power values of all the circuits, we get for thetotal power of the systenii an expression of the form:

w = wi =A + Bcos (2 5 )w,ith the average value of power:

TF= A,the maximum value of power:

XTV,=A + BSthe minimum value of power:

Y2= A B.

336 STEINMETZ ONAL TERNATINGCUR EN7TSY 5YEM. [June 26,

The max'imunm and the miniiminum values of power take placeat right angles with each other, or in quadrature, and we canthus speak of the two axes of the power diagram,the large axisWI, and the small axis W2.The balance factor is:

- A-A

The balanced polycyclic systemn gives:B =O,

o01 a coinstant flow of power, wlhich would b)e represenlted by acircle. Thle nature of the curves representing the power charac-teristic is founrd by reduction to rectangular coordinates.

In the eqtuatiorn:W A + B cos (2 -

substitute:w= S+2

tan ( - _ _2 x

it is:

t/ xl +y - A + 2 BY

Vx2+y2~~A+2Bx2+ y,or:

(X2+ y2)3 x2(A + 2 B) + y2 (A- 2 B)(2,a sextic equation, with the center as quadruple poiiit.

Substituting:A WW average power,

A - B= x = balance factor,A

gives(,2 _Y2)3W2 Id2 (3 2 x) + y2 (2 x 112,

In a single-phase circuit, it is:x - 0,

(X2 = y2)3 =W 2(3 X _2)2In a balanced polycyclic circuit:

ay2 + y2 _=In a polycyclic sy4tem of balance factor:

x =.-)(d2 + Xy2)3 44 X1TV2e

1895.] STEINMZET 0 ALlTEI7Ns4lNG CURRENTSYSTKVS. 337

As an instance of a polycylic system of a balance factor lessthan uinity, the "Inverted TIhiree-phase System" ("polyphasenonocyclic ") may be discussed.If in a three-phase system, two transformers are connected with

their primaries into two branehes of the system, and one of thesecondaries is reversed with regard to the other, the two secondaryE. M:. is a- e1 and eb = e2 difer in phase by 60, while thecorresponding primilary E. M. F.'s AC and CB difFer by 120.The secondary system produieed hereby has features in conimon

with the three-phase as well as with the Edison three-wire systenm,and forms a connecting lilnk between both systems. It has thebalance factor: z = .5. The E. M. F. between the outside wiresa b is 4/V3 times the E. M. F. per eircuiit, ac and eb. W ith bothbranches ac and c equally loaded, the currenits in all three linesa, b, c are equal, and their sum is zero, exactly as in a three-phasesystem.

If the load of one bran-ch, say eb, is reduced from equality withthe load on (to, down to zero, the current in b decreases constantly,while the current in the common line c first decreases, reaches amninimum, and theni increases again, reaching at no-load on eb thesame value as at fuill load on eb. That is, if the load on onebranch is thrown off, the current in the common wire remainsthe sane in intensity, but shifts in phase by 600,

In Fig. 10, the three E. M. F.'s ac, eb and ab are shown asel. el, e, the three currents in a, b, c as e1, C2, C, in drawn lines,while the watt-curves of the two branehes ct and eb are shown asqwl and w2, and the total watts of the system as w, in dotted lin-esfor a inon-inductive eirecuit.

Fig. 12 gives the power diagram of the system iTn polar co-ordinates.With an inductive circuit of an angle of lag of 60, the balance

factor of the system becomnes X = 0, and the low of powersingle-phase, as shown in Fig. 11 and 13.

In an alternating cuLrrent system there is a certain tendency tonaintain its balance factor.Let us consider the field characteristic of an alternating cur-

rent generator, that is, the initercdependence of volts at the arma-ture terminals and arnperes at constant field excitation. Suieh acLLrve, th-e field characteristies of a 300 K. w. threephaser used forlonlgdistance transmission by step-up and stepdown transformers,

338 S' INMN E7,ON'ALTERNATIN GCURREN 'SYSTEK Ll[June 26,

is shown in Fig. 14 with the ampere output as abscissTe, andvolts at armature termninals as ordinates, and the iW-. w. outputas ordinates. The ampere-volt curve is similar to a quadrantof an ellipse, that is at and near open circuit, the voltageis approximately constant for variation of current, and themachine regulates for constanit potential. At and near short-eir-cuit the current is approxihiiately constant for varying voltage, anldthe machine regulates for constanit current. The output of themachine, as shown in dotted line in Fig. 14. increases frotm zeroat open circuit, reaclhes a maximuni of 345 1xW at 575 volts

e

FIG. 11,

and 345 amperes, anld decreases again to zero at short-circuit.Near the maximum output there is a wide ranige, w\shere the i'a-chinie regulates approxirmlately for constant power. That is, anlincrease of currenit reduces the voltagbe, anid a decrease of eurrentiniereases the voltage, so as to maintain approximlately constantpower.The proper working point of an alternator lies somewhat be-

low, but quite near the, maxinmum outpuLt point. Operating inthis range near the maximum output point, buLt still far enouglhbelow to ensure sufficient synehronizing powrer for parallel run-nino, the generator gives the best weight efficiency and energy

1895.] STME MElZ ONALTERNAlNG CURRENTSYSTEMS. 3'9

efficiency, and is most reliable in its operation in-so-far as it isvery easy to synchronize without too careful and delicate adjust-ment, the cross-currenits in parallel operation are insignificant andthe machine will keep in step, even under very exacting conidi-tions, as for instance, if the field circuit of one is broken, and willnot be damaged or damage the prime mover by an accidenltalshort-circuit of the systein, or a falling out of step or ary othersuch accident.In a polycyclic maclhine in this range near the maximumi out-

put point, self-regulation for constant power takes place, not onlyfor variation of the total load, but also for variations of the loadbetween the different circuits. Thus, in a three phaser like thepresent one in Fig. 14, if the load of onie circuit is decreased, thevoltage in this cirecnit will iure'ase, and the voltage in the twoother circuits change so in size and phase as to restore the system-l,to a certain extent, to constancy of flow of energy, or in otherwords:

The mult lpe-eruiit yenerator regulates, or tends to regulate,near te ma ximum output .po,t for constancy of the balancefactor. Thus, the polycyclic nac hine with balanced circuitregulates for constancy of the flow of energy; the monocyclicmachine regulates for a balance factor zero.

This self-regulation takes place by a change of voltage and ashiftinig of phase of the different generator circuits. It is thiere-fore in gerneral objectionable.A sirniiar action takes place in mnultiple circuit motors, induction

-motors as well as synchronous motors, etc.In the Multiple circuit alternating current motor, as for

inistance, a three-phase iniduction motor, the couLnter E. M. F.'Sin the different eircuits are equal (or rather proportional to therespective 1num-lber of turns of the different circuits).

If the impressed E. M. F's are equal, the currents flowing in-to the motor' circuits are equal also, since they are produced bythe differeniees between i i pressed and counter E. M F.'S. If,however, the impressed E. M. F.'s become unequal, even to a sm-lallextent only, the differeniees between the impressed and counterE. M. F.is become rapidly very different, and the currents thuisunequal. For instaniee, if in the three-phase indtuction motor oneof the E. M. F.'S falls by 10 per cenlt. below the, other two, it willhe equ.al with, or even less thati the counter E M. F., and thecircuit of this E. M. F. will take no cuirrent, or will even return

340 STEINXEY VONALTERNA.TINGCURBENSYS'JT, S. [June26,

current into the system, and the currents of the two otlherbranches will increase correspondingly.

In this regard the m-ultiple circutit motors are very sensitive,and a small variation in the size or the phase of the imipressedE. MI. F. causes a large variation in the currents, shifting the cur-rent from the branch of the low impressed E. M. F. to that of high

FIG. 12.

FIG 13.

E. M. F. It is thus obvious that, withi a considerable nuLmber ofmultiple cilrcuit motors in the polycycli'c system, even a largeinequality in tlhe distribution of the single phase consumirer cir-cuits, as lights, between the ge-nerator branches, will not unbalanceethe system. The generator will regulate for constant flow of

1805,] ST'1NJETZ ONALTERNAZTING CURRENTSTSTJ S. 341

energy and tend to raise the voltage on the lesser loaded, to lowerit on the more loaded branclh. The motors, however, in this casetake more current from the branch of higher voltage, the lesserloaded branchl, and less currenit from the higher loaded branch,or even return currents therein and so restore the balance ofthe system with regard to constancy of flow of energy and con-stancy of voltage and of phase relation. This feature of automaticself-regulation for constancy of flow of energy by the generator,and constancey of voltage and phase relation by the motors, iswith proper design of the system very mnarked, and holds thesystemn balanced very closely, even witlhin wide ranges of load.As before stated, this self-regulation in reality tends towards

constancy of the balance factor of the system. Thus in a mono-cyelic system, or a system with balance factor zero, as giveni by astandard monocyclic machine with mnain or energy coil, andteaser or supplementary coil, as soon as current is taken off fromithe teaser circuit the voltage therein drops, and thus reduces thecurrent, and at the same time displaces it in phase so as to main-tain the flow of energy pulsating, or with balance factor approxi-inately zero.

It will be seen that all these featnLres are internal reactions ofthe alternators and multiple circuit motors and the system ingeneral, which, while probably noticed before, have not beenunderstood and therefore considered as objectionable features,as for instance the " unbalancing " of the generator or the" unequal distribution of current ? in irnduction motors. Reeog-nized in their significance, these phenomena allow a veryeffective and perfect control of the alternating current system.

After this diversion we may return to the mnotor problem. Asseen, the polyphase system, characterized by a constant flow ofenergy, promised a solution of the motor problem for polyphasecircuits. But it was not possible to produce polyphase circuitsfrom sinlgle plhase alternators without storage of energy.'Thus it remains to be seen whether those features which made

the induLction motlor work on polyphase circuits are essentialfeatures of the polyphase systermi or not.The problem of the alternating current motor may be ap-

proached from still another side, from the viewpoint ofadapting the continuous current motor to alternating current circuits. In similar lines to this, w-ork has been done by Vandepoele, Eickemeyer, Stanley, myself, and others in this country,'by Kennedy and others abroad.

342 STETNMET7 ONALTERNATING CU REXNTSYSTEMS. [June 26

The continuous current miotor, as shown diagrammnatically inFig. 15, consists of two different elements movable with regard toeach other, tbe field and armature. Potation of the motor isdue to the action of the magnetic field upon the currents flow-ing in the armature. Thus, the electric circuit of a conitinuouscurrent motor consists of the field exciting circuit producing themagnetic flux which passes through and acts uipon the armature,anid the armature or power circuit whose current is sent throughthe armature by the brushes in such direction as to produce acurreit polarization at right angles (in a bipolar motor) to themagnetic field flux. The possibilitv of operating such a motor

00 . ___

1). _ _ _ _ _ _i

1895.] STEIN ETZ O ALTERNANTNG CURRENT SYSTEMS. 348

nating current series mnotors with lamrinated field, have been triedbut have been a complete failure in all but the sntiallest sizes, asfan motors, due to their excessive and incurable sparking. Asseen in Fig. 15, in the moment of commutation, the armature coilencloses the whole field flux, and thus in this moment does notCllt lines of magnetic force by its rotation, that is, no E. M. F. isinduced therein and commutation possible'. If, however, the mag-netic flux is alternating, the armature coil Under the brush whichencloses the total alternating flux, is a short-circuited secondaryto the field coil as primary, and thus, independent of its rotationby transformer actioni, an E. M. F. will be induced therein whichtends to produce a current of the saine m. M. F. as the field excit-ing coil. A numerical instance will show how excessive this cur-rent is. Assumnitng the total field exciting ampere-turns only aslarge as the armature ampere-turns, and only 10 commutator seg-ments between brushes, then in the short-circuited coil, we willget nearly ten times as large a current as the Inain current, andthus in this one coil ten times the current-heating as in the wholeother part of the armnature. If the armature does not start in-stantly, this current will burn out the coil, but even if the arma-ture starts, vicious and destruictive sparkinig forbids the use ofsuch a motor.

In the, continuous current motor the use of brushes and thus ofa con:i- utator, constituites the only way to produce the current inthe armature. In the alternating current inotor the requ;ired cur-rent in the armiature can be produced by induction, by acting uponthe armiature as secondary in the proper direction by a primarycoil, which may either directly surround the armnature, as shown inFig. 16, or surround additional pole-pieces as shown in Fig. 17.The apparatus in this case combines the features of the alternat-ing current transformer with th-ose of the direct current motor.It consists of an exciting circuit, producing the magnetic flux,and an energy circuit, stationary with regard to the exciting cir-cuit. The energy eirc-uit induces as primary in the armnatuire assecondary, the current acted upon by the field magnetism. Thearmature current is in phase with, lbut in opposition to the prim-ary current. The primary current will supply the power of themotor and is thus practically in phase with the primar-y inain .M. F. The field magnetism will be in phase with the armaturecurrenit, that is in phase with the primary current.

1. In reality the brush position is shifted intentionallv so as get soniie nE. . r.in the armature coil, which it required for forced commutation,

344 STEISETZ O ALTERNAfIIN CUREANT SYSI'E S. EJune 26,

To get the field excitation in phase with the inaiin current, theexciting current must be in phase with the main E. M. F. Since,however, in an alternatinig magnetic cireuit, the magnetizing cur-rent lags approximately 900 behinid the impressed . M. F., it fol-lows that the E. M. F. impressed upon the field circuit must be 9(0ahead of the Main E. M. F. Or in other words to prodtuce in sucha transformer motor a magnetic field in phase with the inducedarmature curreit, but displaced at right angles in space, a sup-plementary E. M. F. is required, approxinately 900 displaced fromthe nmain or power E. M. F. Being in quadrature with its current,this E. M. F. represents no power, and thus need inot be suppliedby the generator. but mriay originate from a nmotor or other multi-ple circuit apparatus.We see thus that the alterniating current milotor requires a sup-

CD~~~~~~~~~~~~~~~~~~~~~~~~~~~C

FIG. 15. FIG. 16.

plementary circuit forits operation, the so-called "teaser circuit"of the monoocyclic systeim. One difficulty, however, is met here.Since the movable armature acts as secondary to the stationaryprim-ary main cireuit, the armature miiust contain a number ofcircuits closed upon themselves, but displaced in position fromeach other, so as to form in any position a secondary circuit to theprimary.

In this case the armature circuit will form closed'secondary cir-cuits also to the field exciting circuits, and energy be supplied by thesupplementary circuit, mnaking this a power circuit. This would re-quire the teaser circuit to have capacity enough to supply energy,and in short make a polyphase system. Thus, means have to be pro-vided to avoid this feature. Since all the armature cireuits passthrough the same magnetic field, the E. M. F. induced therein perturn will be the sa ne, and equal to that in the power eirouit, less

t895j STYL-ETR ON ALTERNATING CURRENT SYSTEMi. 345

the drop of voltage by resistanice and reactailre. If now the volt-age of the exciting circuit per turn, is greater than that of thearmatuire, transfer of energy will take place from the excitingcircuit to the armature. If the . M. F. iS the same, no transferwill take place, and the exciting current will fulfil its purpose ofmere magnetization. If the E. M. F. iS less, energy will be trans-ferred backward fromn the armature to the exciting circuit. Thuswe see that to avoid energy transfer between armature and ex-citing circuit, the E. M. F. of the latter per turn, must be equal tothat induced in the arrnatuure. At constant impressed . M. F. OInthe primnarqy power circuit, the E. 1. F. induced in the armaturedecreases with increasing load; that is, increasing current. Thlusat constant F. M. F. impressed upon the exciting eire it, at lightload, the armature E. M. F. will be higher than the exciting E. M.F. and enrergy be tranisferred backward fromn armatuLre to excitingcircuit. At some intermediate load, armature and exciting cir-cuit will be equal, and at higher load the armnature E. M. F. willbe lower than that of the excitinig circuit, and energy be trans-ferred froni the exciting circuit to the armature. In this case, allexeiting circuits being connected together, this supplementarycircuit acts as an equalizing circuit in transferring energy frommotors operatintg under light load, to motors operating under over-load. While this action may be advantageous to a certain extent,it is obvious that the current flowing over the equalizing circuitshould be as small as possible, because if a large energy currenit isallowed to pass over the teaser circuit, this circuit beconres an en-ergy circuit also, and must tlhus have sufficienit current capacityto carry the power. That means the generator becomes more orless a polyphase gene:rator, and a distributioni of circuits between thephases becomues necessary, the very feature it is intended to avoid.For this purpose the E. MI. F. at the exciting eircuit is not keptconistanit but reduced at inereasinig, increased at decreasing loadso as to be always very nearly equal to the armature E. MI. F., andthis is done by giving the teaser or supplemnentary circuit a suffi-cently large resistance and reactance, so that an increase of cur-remit drops, and decrease raises the E. M. F.We have niow arrived at the modification assumed by the con-

tinuons current motor in its adaption to alterniating currenteireiits

1st.-The armature cuirrent is induced by a primary energy cir-cuit, instead of being led in by brushes.

346 S INt IZ ONALT 'RNA 7'ING CU NRRNY SYS 1'EY. [June ''6,

2nd.-To keep the field excitation in plhase with the armaturecurrent, it is derived from an auxiliary circuit of displacedE. M. F.

3rd.-To avoid energy transfer between field exciting circuitand a-rmature, the E. M. F. at the terminals of the field excitingcoil is kept approximately equal to the E. M F. induced in tlhearmature, by the internal reactions of the system.

This is the monocyclic mnotor.The calculation of such a motor is now siinple, and done on

the hand of the previous explanation of its action. The torque,anid thus the output of the motor, are determined by the fieldmagnetization, the armature current, a-nd the angular space dis-placeme'nt between thern. The field magnetization is determinedby the imipressed E. M. F. of the exciting circuit, and the arma-

=7- ~-B =

FiG. 17. 'FiG 18.

ture cur-renit is determined by the equations of the alterniati'ngcurrent transformer, as secondary c rents induced by the primaryenergyv cu-rrent. Sinee nio energy trantsfer should take placebetween th-e exciting circuit and the armature, it follows that thecounter E. M. F. at the exciting eircuit, is equal to the E. M. F.induced in the armatLure, and thuLs the magiletic flux can'becalculated from the latter.

This leads us to the theory of the inductionimotor as outlinedby me in the TrZANSACTIONS Of 1894 p. 669, equatilons as seeiistrictly analogous to those of the alterniatiing current transforimer.

Since the E. M. F. required at the terainals of the excitin gcr-cuit, in such a motor, is in quadrature with the main E. M. F.eobviouslysach a motor coudldbe operated from a quarter-phase

1895.] STEINMETZ O ALTERNATING CURRENT SYSTESW 347

circuit also. It wouild in this case, hlowever, qffer the disadva'n-tage of loading the two circuits unevenly, the one circuit with alarge energy current in phase with the E. M. F., the other circuitwith a smnall and lagging exciting eurrent.An equal load on both branclhes of the system can be secured

by using a double motor. In this case the first phase is used tofeed the energy cireLit of the one, and the exciting eirenit ofthe other motor, the second phase for feedilng the exciting circuitof the first, and the energy circuit of the second motor. Goingstill a step further, one and the same field pole can. be used forexciting the field of the one, and inducing the armature currentsof the other motor, by cross-connecting the armature, or usingone armature within two fields placed side by side of each other,as outlined diagrammatically in Fig. 18. As you see, we get hereour well-known friend the Stauley mnotor, consisting of twoarmatures with common winding acted upon by two fields, insuch a way that each field sends the magnetic flux through thearmature, and at the same time induces currents in the armaturewinding which are acted upoll by the magnetic flux produced bythe other field.Going still a step farther in this direction, one armature only

may be used in one double field, bv bringing both sets of fieldpoles into the same plane as shown diagrammatically in Fig. 19.Here we have two magnetic field fluxes in quadrature with eachother, each acting upon the cuirrents induced in the armature bythe other flux. Obviously it is unessential theoretically whetherwe have a double motor witlh two fluxes in quadrature, or a triplemotor with three flu;xes under equal angles. The equations ofthe motor and its calculation remain the same as mnentionedabove.As seen, starting from the continuous current motor, by Sule-

cessive steps we arrived at the so-called " rotary field mnotor"withouLt rnakirng use of the hypothesis of the revol ing field. Inthe last type of motor and to a lesser extent in the precedingtypes, the actioni of thbe motor can also be explained thus:

Th-e E. M. F.'s of displaced phase imnpressed upon the motor cir-cuits, produce currents in these circuits which combine in theirmagnetizing action to a resultant m. M. F. This resultant Ni. x.F. rotates at constant, or approximately constant, intensity, anidat a uniiform velocity, the velocity of synchronism, through themotor field, and produiees thereby a system of rotating magnet

348 STIINMET 0ZN AIThERNA TING CURREN SYjS.TEMS. [June 26,

poles, which by their drag upon the currents induced by themin the armature, cause the armature to revolve. This theoryis very beauLtiful by its simplicity. It has, however, the disad-vantage of not giving due prominence to the transformner featureofthe motor and to the muLiltiple circuit feature. Therefore, it hasnot proved suitable as far as I know for the caleculation of suelhmotors, and has in this regard rather retarded the progress of in-ductioni motor design, by deflecting the attention from the mul-tiple circuit transformer feature of the motor. If, for instantce,in the motor in Fig. 19, one of the cireuits was opened, the fieldsliould be expected to cha-nge from rotating to puilsating, tllat isvarying between maximum and zero. It does not change, how-ever, but remnains the same. But under certain circumstances,the rotation of currents may even be in opposition to the rota-

FIG. 19, FG. 20.

tion of the motor amatLire. Inserting in the two circuits of themotor in Fig. 19 a field explorinig device consisting of two smriallcoils A and B, Fig. 20, in quadrature with each other, and with alight movable iron disk c in their commnron center, we can by therotation of this iron disk find the so-called rotation of the cur-rents in the two circuits, and its direction. If equal E. M. F.'s areimnpressed upon the two eircuits of the motor, the iron disk c willrotate rapidly in the same direction as the inotor armature. Reduc-ing onie of the two E. M. F.'s gradually, we sho' ld expeet to see therotatilg field change from uniform rotation to elliptical rotation,so that, for instance, if B iS 10 per cent. lower than A, the " rota-ting field" should pulsate by 10 per cent. In reality the action ofthe motor is such as would require a constant and uniiformly rota-tinig field for its explanation.

1895. STEINMETZ ONALT]RNATING CURREIVT SYSTEMS. 349

The strangest feature, however, is the behiavior of the iron diskc. With increasing difference between the E. M. F.'S, A and B,the disk slows down, comes to rest, and then begins to revolve inthe opposite direction, showing that one of the currents has re-versed, and the direction of rotation of the primary currents intile motor and thus theit m. M. F'S. is reversed. The motor, how-ever, keeps on revolving in thie saine direction as before, that isin opposite direction to the primary currents. The explanation ofthis phenomenonl follows from the preceding discussion of tlhemultiple circuit transformer feature of the motor. With the de-crease of the E. M. F., B, the transformer actioni between armatureand circuit B reverses its sign, and currenit returnis flroM B. Thnis,with increasing difference between A and B, the current A COnI-stantly increases while B decreases, reaches a miiinimum whenthe exploring disk c stops, and then increases again. This experi-mnent is very instructive in showing the internal reactions of theinductilon motor.