USRE16121E - Alternating current dynamo-electric-machine winding - Google Patents

Description

5 2 9, 1 2 .w u J C. MACMILLAN ALTERNATI NG CURRENT DYNAMO HINE WINDING ELECTRIC MAC Original Filed Aug. 8, 1924 MacmiHam,

In ntor pb His Attofjey.

RM July 21,- 1925.

1 UNITED STATES- Re.'16,l2l PATENT oFFICE.

or SCHENECTADY, new yoamassmxon r enunnar. nnnc'rarc column, A conrona'rrou or NEW YORK.

* nrmuearmc CURRENT nrnmo-nnnc'rarc-macfimn wmnme.

Original Ho. 1,580,466,1dated Harsh 17, 1925, Serial No. 730,968, filed August 8, 1924. Application i Y v reissue filed Kay 22, 1925. Serial No. 82,205.

To all whom ithdflihoncehh Be it known that'g I, Cmranm. MAcMiL- LAN a citizen of the United- States, residing at ,chenectad in the county of Schenectady, State of ew;York, have invented certain new and useful Improvements in Alter- ,natin I Current Dynamo- Electric-Machine Win fication. I

My invention. relates to the windings of of which thefollowing is a speci- 'alternating current dynamo electric machines and its ob'ect. isto provide a simple and efiicientwin in arrangement which is om detrimental harmonies. Such a winding has a special value as'a winding for induction motors.

In selecting primary induction motor windings." for use in conjunction with squirrel cage secondaries, it is necessary to take certain precautions against the production of higher harmonics offlux. and current which might prove detrimental in operation. The objectional operatin features to lieguarded against 'arechie y: induction subsynchronou's and synchronous subsynchronous speeds commonly. called crawling s eds'and locking at' standstill. These decots are caused by higher harmonics of primarycurrent distribution, of permeance variations in the air gap, or by combinations of the two in certain relationships.

The harmonics of primary current distribution, or winding harmonics, may be care in the selection of approriate coi pitches in conjunction with the istribution constants whlch is determined by the number of phases and type of winding used. The permeance harmonics must be taken care of -by..a judicious selection of slot numbers, rimary and secondary. In the successful esign of an induction motor other factors mustvalsobe considered with the problem of eliminating harmful harmonies. Thus, it is desirable that the winding space he completely and efliciently utilized,and that the end connections be simple and not require an excessiveamount of 00p per. From a manufacturin stand int, it is desirable that thecoils similar and easily replaced..' The presentfinvention'relates to a double layer winding-in which the above-mentioned factors, going to make up a, successful design, are considered together for representation of how a. detrimental winding harmonic is reduced to a harmless value by such a winding arrangement.

Referring to Fig. 1, I have here represented a two layer primary stator winding for a two pole, three phasemotor having 36 slots with two coil sides per slot, one above the other. Thethree phases are represented by. distinguishing lines. Thus, phase A is represented by light full lines, phase B bvlheavy full lines and phase C by broken lines. It will be noticed that the coils are all similar and, hence, desirable from amanufacturing standpoint.

Hitherto it has been universally assumed that the best results from the point of View of current distribution for any specified 7 number of phases and slots per pole would always be obtained by-placilig all coils of one phase per poleiii'i'n adjacent slots. The truth of this assumption is evident when only the fundamental distribution of current is considered,="but when harmonics are taken into: consideration it may be more rofitable to make a slight sacrifice in the ighest value of fundamental distribution factor, in order to reduce the distributionfactors of harmonics, and I have discovered that such a result can be obtained in certain cases by interchanging the positions of marginal coils in adjacent phase belts without appreciably affecting the fundamental line connections to the phases, A, B, and C,

respectively. The connections between coils of a phase belt constitute the short connecductors in series.

' it will be seen that it has the followin AAAAAABBBBBBCCCCCC. The first- -mentioned arrangement having -marginal coils in adjacent phase belts interchanged is what I term an interspersed COll winding. By means of the usual vector polygon representation of distribution constants it can be shown that the particular interspersed coil arrangement shown is highly advantageous from. the point of view of suppressing the fifth harmonic without seriously affecting the fundamental distribution.

The vector polygon representation for this particular case is shown in Fig. 2 where it is compared to that obtained by the usual winding arrangement. In the present case, we have six slots per phase belt representing 60 electrical degrees so that the vector voltage per slot must be combined at angles. of 10 (electrical). The distribution factor for the usual winding would be represented by the length of the cord 20 21 in Fig. 2. By the term distribution factor I mean the ratio of the vector sum to the algebraic sum of the voltages contributed by adjacent c'on- Expressed algebraically, this is for the usual winding 2,

2 cos 5+2 cos 15 +2 cos 25 2 cos 5+2 cos 15+2 cos 35 6 which is only slightly less than that for the normal win ing.

Considering, now, "the fifth harmonic, the

slot intervals correspond to. 50 electrical degrees, that is to say, the voltage vectors for the fifth harmonic should be drawn, at

50 to each other so that the fifth harmonic distribution vector diagram per phase belt for the normal winding would be represented by the open polygon 26, 27, 28 in Fig.

2, and the distribution factor b the length of cord 2628. Expressed a gebraically,

this is: I

2 cos 25 +2 cos 75+2 cos 125 6 In most cases this fifth harmonic would be harmful and cause the mot-or tostick at a subsynchronous speed.

For the interspersed winding, the fifth harmonic voltage vector in the outside slots of the phase belt must be drawn at an angle of 100 instead of 50 to the next adjacent voltage vectors of the phase belt because of the intervening slot so that the vector diagram now becomes 29-31-273330 and the distribution factor equal to the len th of cord 2930. Expressed algebraica ly, this is 2 cos 252 cos 752 cos 175 6 Comparing these values, it is seen that the fundamental distribution factor has been reduced by 3% by interspersing the coils while the fifth harmonic has been reduced by 71%. The fifth harmonic is thus reduced to a value when it renders the crawling speed tendency negligible and harmless while the fundamental distribution is not appreciably decreased.

The same process of reasoning applies equally well to the other layer of the double layer winding shown in Fig. 1 and the superposition of the two layers detracts nothing from the relative immunity of each layer from harmonics. 7 Since a double layer winding is specified it is subject to changes in coil pitch without disturbing the interspersing in the separate layers. Thus, a coil pitch may be selected which renders the machine relatively immune from one detrimental harmonic, for example, the seventh harmonic in accordance with standard practics, and then the coils may be interspersed to render the winding relatively immune fromanother detrimental harmonic, for example, the fifth harmonic in accordance with the present invention.

In the most usual cases, the. number of slots may be such as to provide no opportunity for the complete elimination of one or two harmonics by reduced pitch and interspersing, but each method may secure a substantial compromise reduction in both harmonics, and the effect of both methods, used jointly, is to multiply together the reduction factors obtained by each method pitch value of the 5th harmonics to 95% and of the 7th harmonics to 27%. Interspersing, which in this case corresponds in -l25 separately. For example, in the case cited, a coil of 61% pitch only reduces the full.

cficct to a coil pitch reduction in each layer to 83%, reduces the full pitch values of the harmonics to and 19% respectively. The combined result is a reduction of the 5th harmonics to 95x15 1425, and, of the 7th to 27x/.19 0514 of full pitch values. This may be accomplished without appreciably lowering the efiiciency of the machine as regards normal operation. Thus, in Fig. 1, it is seen that the periphery of the-stator is completely utilized with no idle coils or slots, while similar form wound coils may be used without complicated or lengthy end connections.

harmful harmonic or not.

It is notalways easy to anticipate whether a particular machine will be subject to a The present invention afi'ords an easy way of changing connections after a machine has come to test and found to have a harmful harmonic so as to reduce such harmonic to a harmless value. Thus, suppose the machine having the same ole number, pitch, etc. as represented in ig. 1, but having the coils connected in the usual way without. interspersing, comes to test, and is found to have a harmful fifth harmonic.

It is only necessary to change the end connections of a few coils to render the machine immune to this harmful, harmonic. This is done by merely changing shorter end connections like 14 to the longer end connections like .15, so as to change the connection of the coils in adjacent slots in series at the extremities of each phase belt to the interspersed arrangement illustrated.

While I have hereinbefore especially mentionedalternating current motors, the invention is applicable to any alternating current dynamo electric machine having a distributed double layer winding where it is desired to eliminate or reduce detrimental harmonies for any reason. In accordance with-the provisions-of the patent statutes, I havedescribed the principle of'operation of my invention, together with the apparatus which I now consider to represent the best embodiment thereof; but

I desire to have it understood that the apparatus shown and described is only illustrai tive and that the invention rnay be carried outby other. arrangements. What I claim as newxandidesire to secure by Letters Patent of the United States is 1. A harmonic reducing winding arrangement for alternating current dynamo electric machines comprising a slotted magnetic member having a distributed double. layer alternating current winding therein, said winding being made up of similar coils with marginal coils in adjacent phase beltsinterchanged.

2. A harmonic reducing winding arrangement for alternating current dynamo electric machines comprising a slotted magnetic member having a distributed. double layer alternating current winding therein, said Winding having a coil pitch selected so as to make the winding substantially immunefrom a particular Winding harmonic and having marginal coils in adjacent phase belts interchanged to reduce the harmful effects of another winding harmonic.

3. A harmonic reducing winding arrangement for alternating current dynamo elec- .trical machines comprising a slotted magnetic member, a distributed double layer alternating current winding in said slots, said winding being made up of similar coils and having marginalcoils of the adjacent phase belts interchanged in both layers.

4. A primary member for induction motors comprising a slotted magnetic member having a distributed double layer alternating current winding therein, said winding being made up of similar coils with marginal coils in adjacent phase belts interchanged.

5. A primary member for induction motors comprising a slotted magnetic member having a distributed double layer alternat-- ing current winding therein, said winding having a coil pitch selected so as to makethe winding substantially immune from a particular winding harmonic and having mar ginal coils in adjacent phase belts interchanged to reduce the harmful effects of another winding harmonic.

6. A primary member for'induction motors comprising a slotted magnetic member,

a distributed doublelayer alternating cur- I rent winding in said slots, said winding bemg made up of similar coils and having marginal coils of adj acent phase belts interhaving a distributed double layer alternating current winding therein. said winding having a coil pitch selected to reduce harmful harmonics and having marginal coils in adj acent phase belts of both layers interchanged to obtain a still further reduction in such harmonics.

In witness whereof, havehereunto set my hand this 12th day of May 1925.

CAMPBELL MACMILLAN.

Images