Alternating Current Motors

Friday, March 6, 1891
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.1 ELECTRIC POWER. |;\/ol.. ll., No. 13. ALTERNATING CURRENT MOTORS. BY \\', Xl. I".\IRI"AX. In English patent 4,120 of 1881, to l)eprez and Carpen- tier for " Distributing Electric Currents and Tansuutting Power hy Electricity " on page 4, lines 20 e/seq. is described a11 urrangelnciit of apparatus in which an altcrnatc current generator (presumably a magneto electric machine) supplies current to a circuit. Connected with the leads of said circuit, either in series or multiple arc, are magncto electric machines, whose arm itures have no conunutators but simply collector rings, and to these rings are supplied the alternate cu1'rents from the source. lt is stated that these motors would run at precisely the same speed as the generator. It is evident that these motors would have to be started in order to get them up to " synchronism " before they would run at all. This is the earliest mention, as lar as is known to the writer, of running alternate current generators as motors hy alternating currents. Nothing seems to have been done in this line until sometime before 1883, when Dr. I-Ioplcinson made an elaborate series of experiments on the action of alternate current generators coupled in various ways. In the course of experiments he verified the statement made in the English patent No. 4,120 of IS8I, bcuire referred to. Ile found that if an alternate current generator was connected to the circuit of another similar generator supplying alternate currents, the first generator would run as a motor and at precisely the same rate as the armature of the second generator. But the great difficulty was that the motor had to be started by some outside means, and that it would readily get out of synchronism when overloaded. Dr. Hopkinson's experiments are described in a lecture on electric lighting delivered by him before the British Institution of Civil Engineers in 1883. ln the /om'/za/q’/he Sorilvj' qf 72'/tgra/>hir Erlgiaznmr and li/rr/112121/1.r for 1884, Vol. 13, pages 524. cl rrq. is a repo1't of a lecture by Dr. Siemens in which he stated that by constructing the cores of the armature and field magnet of a direct current dynamo of his own type in the way that Prof Hughes had suggested in a lecture a year or so before, i. c., by making them of very thin sheets or laminae so that they could be very rapidly magnetized and demagnetized, he could supply such a machine with an alternating_ current and it would start from rest, and run as a motor \vould run supplied by a continuous current. He tried connecting the armature and field magnet coils ofthe machine both in series and shunt, and found that the motor would run in either case. Of course the reason of this \vas that the current changing in armature and field magnet coils at the same time the cores of both were de- energized and magnetized in the opposite sense at approx- imately the same time, and hence the poles ofboth elements always presented the same relative polarity. But there are two difiiculties presented in this type of motor. These are: First z That the cores do not change their polarities at precisely the same time; and . Second : That even though laminated the rapid alterna- tions cause a heating of the cores by waste currents and hence loss of energy. Next come the noted experiments of Prof Elihu Thom- son described in a paper before the American Institute of Electrical Engineers ’ on “ Novel Phenomena of Alternat- ing Currents.” Prof. Thomson found that when a core energized by an alternating current flowing in a coil around it had a closed conductor brought near it the first coil tended to repel the second conductor away from it. The reason given by Prof Thomson was that the secondary currents induced in the closed conductor were so far retarded by selfinduction that 1 vm. 1\'sf1'mnsa¢\im\§., iss7,p. iso. the currents in alternating coil and thc closed conductor during the greater part of each “ wave " were in opposite directions and hence repulsion between the respective coils ensued. To utilize this principle Prof Thomson constructed a motor as follows : A coil with or without a core is mounted upon a shaft, the ends of the coil are connected to two seg- ments of a 4-segment commutator; upon the commutator rest two brushes which are connected to each other by a closed circuit, over this moving coil is mounted a fixed coil with its magnetic axis in the same direction as the first coil. This second coil may or may not have a core. The hxed coil is connected to a source of alternating current. The brushes are so arranged that they rest upon the two seg- ments connected to the ends of the moving coil when said coil is in a position to have the repulsive effect of the other coil come intoplay, i. r., when thcmoving coil is at anangle to the plane ofthe fixed coil. When the removing coil is in other positions, its ends being connected to segments on which the brushes are not resting, it is open and of course no current is then flowing in it. lly increasing the segments in the proper proportion any number ofcoils may bc placed upon the same shaft; the brushes in this case also only closing the circuit of that coil which is in proper position to be acted on. The efficiency of this motor has not been (lClt‘l'll\llltJ(l_ l)r. llnncan ofthe johns Ilopkins University in a lecture lit-lore the American Institute of Electrical Engineers, February 14th, 1888, describes several types of alternating current motors! Among the various types he mentions, is an alternate generator used as a motor, thc armature being supplied with alternating currents uncommutatcd and its field magnet with the same current rectified by a coinmutator on the shaft. In this case the motor should have highly laminated field magnet cores, but it will start as Dr. Duncan says, from rest and increase in speed until it reaches synchronism with the generator. For, as long as it is not in synchronism \vith the generator, the polarity of thc field magnet cores will be reversed as often as that ofthe armature is reversed until the armature poles get opposite the field magnet poles \VllCIl the brushes pass from one set of segments to the other and the relation ofpolarities of the arinature and held mag- net changes. When the armature gets into synchronism, the field magnet receives practically a continuous cur- rent. I)r. Duncan also suggests that, with a synchronizing motor, may be combined several types of the self-starting motors for the purpose of bringing the main motor to speed. Either the alternate current motor with the rectified field magnet current or the Thomson type of motor above de- scribed may be used for this purpose. Dr. Duncan thinks a very efficient motor \vould be the following: construct a motor with both commutator and collector rings, each hav- ing its respective set of brushes. Start the motor with a continuous current supplied to the brushes on tl\e commu- tator, and \vl1entl1e motor has reached a proper speed by changing a switch, break the first circuit, and complete the circuit of the second set of brushes by connecting them to an alternating current source. Thus the motor starts as a direct current motor and then afterwatrds it becomes an alternating current motor. The objection to this type is that two circuits are necessa1'y, one connected to a continu- ous current source, and the other to an alternate current source. Lieut. F. _larvis Patten, at the same meeting at which Dr. Duncan delivered his lecture, described a motor constructed as follows ; two series of copper discs are arranged around tl1e inner side of a frame, the cross section of which is a polygon. These discs form closed circuits of great self in- duction and fbrm what is called the armature of the machine. ¢_ ‘- ‘|‘m.\-saints of ,\meram\ institute of 1;is\~u;t»ai Engineers 'i for April, ixss, vnu. 5, page 219, ff W.

,l1\Nll-\lW, I8<)0.] IEl.l'§C'l`RIC POWER. 5 Extending lengthwise within this frame through its center is a shalt upon which are arranged, under the discs, two series of poles, wound with coils, the poles of one set occupy cir- cuunterentially a position 45° removed from the poles of the other set, so that when one set of poles is directly beneath the discs around said set, the poles of the other set are half way between the discs of the other set. On the shalt is a “sun-flower" commutator upon which rests a brush con- nected to one ofthe leads of an alternating current genera- tor. Une series of alternate segments of the commutator is connected in one set and the other series of segments in another set by connecting wires. Each series is connected to an independent circuit which includes the coils ofoaie set of poles, the other ends of said circuits being connected to a ring upon which rests a brush connected to the other lead of the generator, ily this means, as the commutator rotates, the alternate current will he set, first through one set of polar windings and then through the other. "W" ' .4 ‘¥.:»» ¢ fé 3 . ,. , _]» ‘ = I in ls, rp , .t._=_.,==;====;=a:=== » “"i5-' “ ..i!;?/ 5 _ju .| NX ||u: a W. 1-' l» fi ,. »' -1 ,, 0 Flo. i. is is a §\=ui..»m\,~ Cust etlugwfiui ui an aitemaitug current source; c, cr, cr, are wus, the turtriinals of your-it are emuiertutt to segment, .,l; 2,1;5,_t; respectively lu a toiunuuatur; upon this couuuutatur rest the brushes, It, Ili, which are rou- uwtai il. utah slim- ii, a t-tmltttrior. _ts each -.r mg coils, ly ci, cs, get into ure ,.\-..,.er|.t,.al|..u, titer..-"sites ix, nt, elosctlu: coil upl.u_at§¢_ir,ru.l| theutltercllows uit-.cut ru. aim.-t.=.\n.,4 Cm-mit uuiliaat rl-nm warrant- amlli. By proper arrangement, each set of poles will be ener- gized at the time the armature closed circuits would have their greatest action or “ pull." This motor is obviously a modification ofthe Thomson repulsion motor. ()n the 22I\(l of /\pril, 1888, in an Italian paper (/,’]?/z'/- /riri/iz) devoted to electrical science and its applications, appeared an account of a very remarkable invention by Prof Iferraris of Turin. The article is called “Electro Dynamic Rotation.” In a course of experiments on the action and properties of alternating currents, the professor was led to consider the relationship of currents of different phases to each othci', i. e., currents whose periods of maxi- mum strength and electro-motive force do IIOI coincide. In the beginning ofthe article, the professor proposes to sup- erpose the fields due to t\vo alternating currents of differing phase. He assumes that the direction of said fields is ap- proximately at right angles. He then shows by a short mathematical demonstration that the resultant field would rotate about a center, O, with uniform velocity, and that said field would be of constant intensity. He then goes on to show how the described effect can be produced. It may be accomplished in several ways; one mode is to pass an alternating current through the primary coil of a transformer anti to utilize the said primary current and also the second- ary current of said transformer as follows 1 Place two coils with their axes at right angles and send the primary current through one ofthe coils and the secondary current through the other of the coils. The secondary current from the transformer must of necessity differ in phase from the prim- ary current, for it takes an appreciable time to magnetize the core by the primary current and then for the core to in- duce a current in the secondary winding. This retardation in most transformers causes the secondary to “ lag" behind the primary almost halfa phase. To get proper results the currents must differ approximately one-fourth or three- fourths ofa phase, i. e., the maximum period of one current must nearly coincide with the minimum period ofthe other. In order to get the necessary difference of phase a suita- ble resistance may he inserted in the secondary circuit. The resultant field due to currents Howing in these two coils will approximate to the theoretical rotary field. Another way to get the two oscillatory component fields is to use the secondary currents produced by two transformers or two portions of one transformer. Of course the secondary windings or the cores of the t\vo transformers, or the two parts of one transformer, must differ enough to cause the re- quired difference of phase, i. e., the secondary windings must differ in the number of convolutions or in cross-section of the \vire, or the cores must be of different masses or mag- netic susceptibility. A third way, the professor states, is to use currents in t\vo derived circuits of an alternating current circuit. In one of the circuits is introduced a coil of small resistance and high self-induction and in the other a resist- ance of no selllinduction. In the circuit in which the high selfinduction coil is placed, the current will lag behind the current in the other circuit. If in any of the resultant fields a closed conductor is placed, currents will be induced therein which will tend to form poles, which poles \vill be dragged along bythe rotary field, and if the conductor be properly mounted upon a spindle it will rotate with the field. D+ Tlmllli s' st 5° s= 5' s* s‘ st ,séss l-és; 1-éééé vééés séééw ééé-» ~ééé»is;ééil /li /lf rr/ Vi/ ittiiit \\\ \t\ ,,_ _/ E :gk im' °‘ ¢= l7l(Y 2. 'rite alternating current utters at mtg h, uw" alternately nous titmugti si, sg, s5_ s _ami sz, ss, se, ss, it, the respective sus of ctmuimimar segments, ci, cs, e5, d7, mul cz, e4, cs, cs, 'rite coils, s, etc., and emumutataf are mounted mt the smite shaft, 3 second timsh if resting mt the wlunmiaiur takes our itiqaiigrilat- ing current; amuiui tum revolving wits are the staii.»im,» assert eueum on the mnulr rmiue concentric around me smut. About a month after Professor Ferraris’s discovery was announced in L’ Elellrzkila, there were issued to Mr. Nikola Tesla, of New York City, several patents which set forth a method of producing rotary motion by alternating currents. The general idea ofa rotary resultant field is the underlying principle of these patents, as it'is the principle of Ferrariss motive device. As Mr. Tesla well says, in all continuous current motors, there is a progressive shifting of the poles of one element while the poles of the other element are fixed. This will be plain on carefully regarding the action of the current in the armature of a Gramme motor for example. Rotation in such a motor is, of course, produced by the at- traction and repulsion of the armature poles by those ofthe field magnet. The position of the brushes upon the com- niutator determines the poles of the armature, 11 fn, the places where the current flows into and out of the armature coils; now, as the armature advances in its rotation the

6 ELECTRIC qrushes are being continually moved back as regards any fixed point in the armature core, and hence the polar points in the same core are being shitled continuously back as re- A A 1 - ::::::::: ,/ 5 » \ "';:::: Mil!!! / O \ nuiiii r ; `. eessanas. ` I { f' aasas sa a l;EEEiE5"' 1 ; EEEEEEE, .am r : l .t A' Fly. 3 /t. .\' me one set nrwits smmcctcrl to comluctors supplying site-nmnng eur- mit. n, n' nrt- mmiiier set arming eanneeiett tr, ure other m»u|\»t~t<»\-s sn,»|»|y§n,¢ a|r=nmt.- currents “ruse phases me displaced from time ofthe nm sonrre. t* is me .~...,iy .ir eu,-per) muunterl to rotate through nie imitmtee urine rutars' liutrl uftorce. gards any point in the core though they are fixed as regards space, Now Nr. 'I`esla thought that ifby means ofalternat- POWER. [Vo1.. II., No. 13. nected to the leads of an independent circuit. As each set of coils occupies a different circumferential position it is evi- dent that each set cuts the maximum number of lines of force at a different time from the other. Hence the currents in the various sets of coils will diH"er or be displaced in phase. One ofthe motor elements is pro- vided with magnetizing coils connected in diametrically op- posite pairs or groups to independent terminals. To these independent terminals are connected 'respectively the inde- pendent circuits ofthe generator. This element of the motor is usually stationary, but if rotary, then the connection must be made through rings, upon which rest brushes connected to the generator cir- cults. » As the currents rise and fall in the generator circuits, the motor energizing circuits are energized in succession and the polar points are progressively shined continuously forward and thus a rotary Held is obtained. The other element of the motor may be a single magnetic body having no coils, a coil wound with closed coils or it may be similar to the hrs( element of thc motor. In this case the t\vo poles of the two elements are shifted in opposite directions. Tesla has, in a number of subordinate patents, made many specitic improvements. Other inventors have also made advances in this same line. L T g G 1, V , ,, Q; , _ _ i a it .,,§,' §¢"i‘. p5iEi=l _A 2 5!!|'|'|'=el gg.. M ‘ If , 0 rm. 4. G is an aitemttting Current genmtur having nie new magnet with paras, N. s. l`|\on nie at-mature we is watititi the two mais it, ng at mint angles to meh outer. 'rue ends ot um mn. n_ are eamiceteti mfangs. n, h. The entisnr can nfmemnrmet twang; w,w. upon \>, r., mst in-‘hires ftuiiia-tai in t~n-aut, i., i.. Wm. h’, h', brushes wllich are connected to circuit. lf, I/_ i., 1. is mn-.t~<-tett ia inns r, c, on me element urine mutt. ami ix |.' to wus c' t". on thu was nun "agua, nut fn right argues it. C. <1 n is tiwititefexctnait or the tn.-tar. As the garter-att»r rotates sitefnme cutrenls are inunfai in it anti ir. Inn it-iw.. the entreat in B' is at A nmxannnii, umm in is -5 at a .na-iitnttm. time the ent-"its I.. Lf mi ix ix receive in succession currents, which lIo\\'in f to coils C and C’ in turn cause said coils to ti»rn\ poles in the eienwnt R, as ine fans me at right aligns, snail pines wan iw at nent angles, are so ar poles fi-ang tt-nn” ure other- get is nnnng and ui-ence, as nie currents are =\\tenm\m,<, matinee n t-.»n=\\n.N ofthe ,iam ,wits in t-...¢, it. ing currents he could produce a continuous shifting of the polnrities in one element ofa motor he could obtain rotation. This was the problem. No\v, he found that if he should at any one instant magnetize two opposite points of a station- ary core and then magnetize two opposite points 90° from there, the magnetization of the first points having ceased, then he should again magnetize the tirst points, but with op- posite polarity to that which they before had ; and then in time magnetize the second set, but with opposite polarity, he would have the desired rotary field. This he found he could accomplish by two sets of alternat- ing currents, whose phase differed by about 9o°, i. e., the maximum periods of one set coinciding with the minimum periods of the other. To produce said currents he wound the core of a drum armature with sets of coils placed at angles to each other and connected the ends of each set with independent rings. The rings of each set were con- DIRECT FROM ALTERNATING CURRENTS~ IIY HAROLD IIINNEY. The interest aroused bythe article on the “ Tesla System of Obtaining Direct from Alternating Currents without the Use ofa Coxninntator," which appeared in the E/ec/rzkal Il/az'/fi of November 2, 1889, p. 290, has lcd to a reply in the London /I/crfriral E7lgi7l£Cl' for November 15, p. 386. The English article denies the operativeness of all forms of the device in the following terms: “The great reputa- tion of Mr. Tesla as an ingenious inventor, combined with the excellent character of the journal, which, in all seriousness, puts forward his latest invention, might hon'- ever lead men to think that, notwithstanding its startling character, this invention is really good, and will work. If so, they will waste much time over a hopeless problem, and it is principally to prevent this that we propose to briefly point out in what the fallacy lies."