May 27, 1924. 1 1,495,861
c. MACMILLAN INDUCTION MOTOR Filed Aug. 4, 1921 InVenfdrI Campbell 'Mcucmillom, by W 221 His mtorney 'Patented May 27, 1924.
UNITED STATES ATENT OFFICE.
CAMPBELL' MACMILLAN, F SCKENECTAJJY, NEW YORK, ASSIGNOR TO GENlZRAI-v ELECTRIC COMPANY, A CORPORATION OF NEW YORK.
Application filed August 4, 1921. Berta! No. 489,816.
To all whom it may concern:
, Be it known that I, Caarrnnu. MACMIL- LAN a citizen of the United'States, residing at che nectady, in the county of'Schenec- 6 tady, State of New York, have invented certain new and useful Improvements in Induction Motors, of which the following is a specification.
This invention relates to an induction |0 motor, and more particularly to an induction motor making use of a squirrel ,cage
\ In squirrel cage induction motorsof the ordinary form, ditliculty is usually expe- IJ rienced in that the starting current tends to be high and the starting torque rather low. To obviate these dijliculties. several arrangements have been suggested. For example, one arran ement Is that shown In the application of P ilip L. Alger Serial No.
.5 is made to have good starting and running characteristics by means of the proper choice of the. shape of the conductors making-up' "t-he squirrel cage. My invention constitutes an improvement on the device shown in the Alger application, so that standard material may be utilized. Furthermorc,.wit.h my
invention it is possible to use slightly shallower slots on the core of the secondary member. For the best results, the slots of the secondary core should be .nearly closed and narrow; It is difiicult to'punch a slot having a very thin opening. Thus another object of my invention is to facilitate the punching of these laminations for building teeth in the laminations making up the seconda core.
Re crrin now more in detailjco the drawings, in which like reference characters refer' to like partsthroughout, I indicate at 11 the stator member of the. induction motor. This stator member carries a ropriate windings12 located in slots 13. .i hc stator member may be wound in any well known appropriate mahner and the articular arrangement of the windings t ercon forms no part of my invention.' \Vithin the stator is located the core 14 for the secondary member of the induction motor, said core being mounted upon the shaft 15. The core -mcmber has a plurality of slots 16 which up the carry the conductor bars making town are squirrel cage. These slots as s nearly closed and have overhanging portions 17 and 18 which project from the inside surface of the slots at an oblique angle, as clearly shown in Fig. 4.
In order that the induction motor be operated with a low starting current and a high torque, it is necessary that the squirrel cage have a relatively high resistance during the starting period. For etiicient operation at full speed it is,-however. necessary that the resistance be considerably re iluced. This effect as pointed out in the Alger application referred to hereinbefore may be obtained by providing a com ound conductor in theslot, part of the con uctor being relatively narrow and deep so that its apparent resistance at the start may be increased due to eddy currents, while another portion is relatively wide. and shallow and so arranged that it has a high reactance during the starting period. In the 40 up a core having nearly closed slots. other objects and advantages of my invention will become apparent as the description proceeds.
For a better understanding of my invention, reference is to be had to the follow- 46 ing specification together with the. accompresent instance the. conductor which has a Y high equivalent resistance during the starting period comprises a U-shaped conductor 19 which lines the inside of each slot. At the upper end of the limbs the member 19 follows the contour of the nearly 'closed slot.
panying drawing, in which Fig. 1 is a diegrammatic view showing the arrangemeltt of the stator and the rotor members of my improved induction motor; Fig. 2 is an 60 enlarged cross section of one of the slots of the secondary member-sand its conductors; Fig. 3 is a fractional sectional view of the seconddry member showing how the end rings are fastened to the conductors;
6i and Fig. 4 is an enlarged view of one of the This U-shaped member has a relatively high resistance and is preferably made by splitting a thin copper tube and forming it into the proper shape before insu'ting it into the slot.
lhe conductor of relatively low resistance making up the second part of the compound conductor is represented by 20 and is enclosed between the limbs .of the U-shaped conductor 19. This member is caused to such as is-required in the resent instance .efi'ect is obtained. of the slots resultsrfrom the fact that the have a relatively high reactance during the n p subna nn1isl1- off'z'tlte' remainder-"lot the space. in- .t l
'slots. 'l'he arrangement is such that there is a .tight fit :alla'roun d the three niemh'r's 19,20 and 2l earried'in the slots so that-there is intimatemejchanicai contact of a considerable amount v hetween-f shown one of the -slots in a. lamination. In this case the center of the narrow slot'is slightly offset from the center of'the wide portion ofgthle slot, antl'themarrow portion Eli-is" made wider than that required; During-the assembly of the punehings, alternate layers are turned orersohthat the.lamina- --tiunso\,.erlap -to,-an extent sufficient to remines} the width of the slot to the desired the condnetnrs 20 and 19 as well as hetweeiFi'afiioiint. Thus in Fig. 2 I indicate by means the conductor) nndethegn'allsof the slot.
The arrangement furthermore-"mikes of ordinary. fstandard materiel.
During the starting eriod currents are produced into the contlnctor On account; f thelarge a: henyeen the condnrto'r 1 ltjand "the 20 it is necessarv to cnmn t't only oondurtor 20 to the end ring; 272 as -=lvy\vl |-in Fig. 2, The 0nd ring is shown its-Illa: ml onthejoulside of the Inn's so that the end ring re- 1 :n-tanre lnay he, reduced. Furthermore, the
dissiputiomof energy during the starting period ,oeeurso frmn tho-,mmhn-tur 19. and i1 is of p'rnnary importance thatntimate of fthe tlotted line 25 where the e e of the oil'setslofieoines' in the layer be ow that shown; f r l "While I hare'sllown in the accompanying Ldrinvinghutoneembodirhent of my inven- "t'oxi; '1 do not u'i'sh'to' be limited thereto but I in: to einbraee infthe 'a ended claimsall niodiiientiqns "falling atrl tvithin the .i-iitfiiiul seopeofjnjfi ins ehnom 1 j-hv Letters Patent of the Un1ted Stetes,-.is
11 eson nt)" press sem nn'eI mmdnctor 'hars 'oflon resistaneefjcari-red.hy snnl gore structure.AmljfOrming a squirrel Aft-age jofkfoml iaratiiwely high react-Z illltt' during thestarting period, andrelatl\il narrow conductors of comparatively l'iigh resistancebent so that eaeh encloses a "low resistance liar, and means for insuring that the. lniqh res|stance conductors' are n essed firm y age inst the lo\\ resistance contact between this eondncton vi'tli the hy good bltricalfiibntflct"between theeonadjoining material beonade so :is tn tlissi-.
pauthis energy. lly firmly ptwssipg, thevnnductoix lfi against the walls. (H the slot. in the manner heroinhefore-explained. this A saving in the dehth llt'llt-(H'l'l'. portions of the 'condllrtnr 1'9 occupy llss radial depth than" an equivalentdepth if they were parallel with the slot sides. 0-
It is ordinarilyobjectionable to construct dies that punch unusually narrow slots,
at 24 of Figs. 1 and '2. I in icate one means by -\\'lll(.l 1 It IS unnecessary to pnnch these extremely narrow slots. Thus n Fig! l is 1lnctors is obtained asfavell as intimate Inc-- rhamcal, contact between the high resistance conductor and (the core.
A" secondary ,n 1emlir 1:01 a dynamleleetric nnichine comprising a core strpcture haying, nearly closed slots, conductors of comparatively large resistance lining said slots for substantially' their. entire 'periphbury. a conductor hatin each slot forming a squirrel cage, and bars of magneticfmaterialsnb'stantially filling up the remainder ofthe-spaee in the slots. f e.
In witness whereof, I have hereunto set my hand this 2nd day of August,-1921.
airs and aga nst the chistructure. where