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Publication numberUS2235075 A
Publication typeGrant
Publication dateMar 18, 1941
Filing dateApr 26, 1940
Priority dateApr 26, 1940
Publication numberUS 2235075 A, US 2235075A, US-A-2235075, US2235075 A, US2235075A
InventorsKimball Albert W
Original AssigneeWestinghouse Electric & Mfg Co
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Generator and power plant therefor
US 2235075 A
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Description  (OCR text may contain errors)

March 1941' A. w. KIMBALL GENERATOR AND POWER PLANT THEREFOR Filed April 26, 1940 u x 1\ \l 1 \1 //l w \\\w INVEN.TOR W X12254,

ATTORNEY m w /I\ WITN ESSES:

Patented Mar. 18, 1941 UNITED STATES PATENT oFFIcE Albert W. Kimball, Forest Hills, Pm, assignor to Westinghouse Electric 42 Manufacturing Company, East Pittsburgh, Pa'., a corporation of Pennsylvania Application April 26, 1940, Serial No. 331,745

6 Claims.

My present invention relates to a self-regulating direct-current commutator-type generator of a special type having a relatively flat volt-, age-characteristic from very low loads up to somewhere in the order of of the normal load which it may be called upon to carry, and a voltage-characteristic which is drooping with increased load-current thereafter, and my invention has more particular relation to a power plant including a prime mover, such as a gasoline engine, for driving such a generator. The particular application for which my invention was designed was for an anti-aircraft searchlight generator which is required to operate, most of the time, at a very lowload, such as 12amperes at 105 volts, called the listening load, during which time'the generator-output is utilized merely to energize certain apparatus associated with the searchlight. When the presence of aircraft is detected, however, a powerful searchlight is turned on, at which time the generator or power plant is called upon to deliver a short-time peak-load of approximately 325' amperes, which reduces as the arc is drawn, and stabilizes at approximately 162 amperes, at approximately volts. However, surges may occur which cause the current to vary within the range of 122 to 202 amperes. For stable operation of the Searchlight, it is necessary for the voltage to decrease approximately 1%, volts for each 10 amperes increase in load. Therefore the corresponding voltage-range must be approximately to 95 volts.

Heretofore, the equipment necessary to supply this service has included a special current-responsive solenoid, picking up at approximately 70 amperes and dropping out at approximately 35 amperes, for so changing the spring-tension on the engine-governor'as to increase the speed, from an idling speed of 900 R. P. M., during listening operations, to a full speed of 1200 R. P. M. when the searchlight is energized. At the same time, in these previous. installations, it was necessary to provide a voltage-regulator, or special voltage-control means in the generator, so that it would maintain acceptable voltage-conditions under the-various conditions of loading.

The principal object of my present invention is to dispense with all control-means or regulators, except the engine governor and the shunt field rheostat, when a single-speed power plant is used, that is, one which does not change the governor-setting when changing from low-load to high-load conditions. Such a power plant eliminates both the speed-changing solenoid for the engine and the voltage-regulator for the generator, a thing which was heretofore believed to be impractical while still obtaining the necessary operating-characteristics from the generator. I now utilize a prime mover having an approximately constant speed, with a speed-characteristic which droops, with load, by only the amount which is necessary for stable operation. Thus,

the listening-load speed can be approximately 1050 R. P. M., while the arc-load speed is approximately 1000 R. P, M. This materially simplifies the operation of the power plant, but it imposes a very special operating-condition on the generator, which has required special design, in order to cause the inherent voltage-regulation of the generator, without the assistance of any voltage-regulator, to give the required voltagecharacteristic. 1

The principal object of my present invention is to provide a self-regulating generator having certain special design-features, in combination, as will be subsequently described and claimed, whereby these special voltage-characteristics are obtained, and to provide a power plant including such a generator, the generator being provided with a cumulative series winding for compensating for the droop in the speed-characteristic of the prime mover and for compensat ing for the internal voltage-drop of the generator.

With the foregoing and other objects in view, my invention consists in the apparatus, combinations, circuits, systems and.methods hereinafter described and claimed, and illustrated in the accompanying drawing, wherein Figure 1 is a fragmentary transverse sectional view through a generator embodying my invention;

,Figs. 2, 3, 4 and 5 are explanatory'diagrams which will be referred to in the explanation of the special design-features relating to the main pole-pieces of the generator, and

Fig. 6 is a diagrammatic view of the power plant, and of the circuit-connections of the generator,

. As shown in Fig. 1, the illustrative form of embodiment of my generator comprises a statormember or field member, comprising an outer frame-ring or yoke-member I of magnetizable material such as a rolled slab of steel, four main pole-pieces 2 of magnetizable material, such as sheet-steel laminations which are held together by rivets 3, and tour interpole-pieces 4 which are also of magnetizable material which may be similar to the material 01' which the main pole pieces 2 are constructed. Each of the main pole-pieces 2 carries a self-excited shunt coil 5 and a cumulative series coil 6, while each of the interpolepieces carries a series-connected commutating or interpole-coil 1.

The generator is also provided with a commutator-type rotor-member comprising a slotted magnetizable armature-core B carrying armature-windings 9 and mounted upon a shaft Hi. In common with the other commutator-type direct-current generators, and as diagrammatically indicated in Fig. 6, the armature-windings 9 are connected to a commutator which is diagrammatically represented, in Fig. 6, as the surface of the armature 8, current being conducted to and from the commutator by means of brushes M.

In accordance with my invention, special design-features are embodied in both the main pole-pieces 2 and the commutating or interpolepieces 4. Each main pole-piece 2 is provided with a pole-face portion or surface l4 which is spaced, from the armature-core 8, by an air-gap which, in accordance with my present invention, is tapered, as indicated at [5. Each main polepiece 2 is also provided with a first pole-face tip IS in which the armature reaction produces a cumulative magnetomotive force, and a second pole-face tip H in which the armature reaction produces a differential magnetomotive force. This corresponds to a certain predetermined direction of rotation of the armature, as indicated by the arrow [8 in Fig. 1.

In accordance with my invention, the large end of the tapered air-gap I5, under each of the main pole-pieces 2, is under the first-mentioned, or cumulative-flux, pole-face 16. Also, in accordance with my invention, the first-mentioned or cumulative-flux tip I6 is of an unusually large sectional area, as compared to the more common generator-designs, so as to have sufiicient crosssection, in radial planes, to be substantially unsaturated for small load-currents; or for currents up to, say of the order of 60% of the normal load,

by which I mean a current-range of from say 40%, to say 80% o some loading-condition which I herein designate as the normal load, or even somewhat more or less than these limits. Also, in accordance with my present invention, the second-mentioned, or differential-flux, pole-tip I1 is specially designed so that it will be substantially saturated at no-load, and at small loadcurrents, and even up to rather substantial loadcurrents of approximately 60% load, where the demagnetizing armature reaction is very considerable, in this pole-tip H. In order to make the differential-flux pole-tip l1 saturate, its effective cross-sections must be reduced or restricted, by any suitable means, such as providing a hole l8 therein, as shown in Fig. 1, or by any equivalent means for reducing the effective cross-section of the magnetizable material which carries flux in a circumferential direction in said pole-tip II.

In accordance with my invention, the interpole-piece 4 is specially designed so that it will include therein a section of such reduced crosssection as to saturate at very small currents, such,-

for example, as 30 amperes, in the illustrative embodiment of my invention. This reduced-section region of each interpole-piece 4 may be provided in any convenient manner or means, the illustrated means consisting of a special mounting, at .the rear end of the interpole-piece 4, where it abuts against th frame-ring I of the generator. Thus, as shown in Fig. 1, the back end of the interpole-piece 4 is separated from the frame 1 by means of non-magnetic shims or spacers 20 providing, in effect, an air-gap between the interpole-piece 4 and the frame-yoke i.

In accordance with my invention, however, a magnetizable flux-carrying path of reduced section is provided, between each interpole-piece 4' and the frame I, by means of oversized attachingboltsj H which pass through the frame-yoke l and into the interpole-piece 4 for holding the interpole-piece in place. These holding-bolts 2|, of which there are preferably two for each interpole-piece, are made of steel or other magnetizable material, and provide a sufiicient cross-section to carry the interpole flux for small-current conditions, say, up to 30 amperes, after which the shanks of these bolts, where they pass through the non-magnetic spacer 20, become saturated, so as to begin to approach the same effect as an air-gap. To compensate for this saturation and the air gap at the back of the interpole, I provide an abnormally large number of turns on the interpole-windings 1, so as to overcompensate the machine until the bolts 2| become saturated, after which, with further increases in load, the overcompensation decreases until, at some point such as 162 amperes, the compensation is normal. The overcompensation at light loads produces a circulating current in the short-circuited armaturecoils 9 which are undergoing commutation, and this circulating current has a cumulative series effect in increasing the flux through the main pole-pieces 2 under these light-load conditions.

The efi'ect of my special design-features in connection with the main pole-piece 2 can be most readily understood by a study of the resulting field-forms. Thus, in Fig. 2, I have shown, in the solid-line curve 23, the no-load field-form of the flux under a main pole-piece of a machine having a uniform air-gap and normal pole-tips which are close to the saturation point when there is no armature reaction. When load comes on, I have assumed an armature-design and direction of rotation such as to have the armaturereaction produce a cumulative magnetomotive force on the right-hand side of the pole, and a differential magnetomotive force on the left-hand side of the pole, as indicated by the dotted-line curve indicated at 24 in Fig. 2. It will be noted that the right-hand tip saturates, so that there is very little increase in flux in it, whereas there is a considerable decrease in the magnitude of the flux carried by the left-hand pole tip, so that the over-all efi'ect is a reduction in the flux carried by the pole-piece under loadconditions.

Fig. 3 shows similar curves for a machine hav ing a tapered air-gap such as mine, but having normal pole-tips. Since the large air-gap under the right-hand tip reduces the flux-carried thereby, there is less saturation under no-load conditions. However, there is some saturation of the right-hand tip under load, with the result that the efiect of the armature reaction is to decrease the flux carried by the main pole-piece.

In Fig. 4, I show the efiect of .increasing the cross section of the right-hand pole-tip, while retaining the tapered air-gap and the normal design of the left-hand pole-tip. In this case, the result of the armature reaction is to produce little, if any, change-in the total flux carried by the main pole-piece, there being possibly a slight in,- crease in the flux under load conditions.

In Fig. 5, I show the efiect of reducing the section of the left-hand pole-tip so as to cause it to be saturated, even underload-conditions, whfle retaining the previously described unsaturated design of the right-hand pole-tip and the tapered air-gap. In this figure, it will be easy to see that the saturated condition of the left-hand pole-tip 6 prevents the armature reaction from reducing the flux as much as was previously the case, at the left-hand end ofthmpolepiece, while the unsaturated condition of the right-hand pole-tip permits a considerable increase in the flux passl ing through the right-hand half of the polepiece, with the result that there is a definite increase in the useful exciting-flux of the machine, as a result of armature-reaction, with increasing loads.

1 The effect of an overcompensated interpoledesign at light loads produces a cumulative compounding efiect, as previously described, as the result of the magnetizing armature-reaction of the circulating currents which flow in the short- 20 circuited coils during commutation. In this manner, I am enabled to secure an additional increase in the main-pole flux as the result of the armature-reaction, particularly at the light loads under the 30-ainpere value at which the inter- 25 pole-bolts 2| begin to saturate. In this manner,

I am enabled to better maintain the required generator-voltage during the listening load-conditions when the generator is delivering its lightest load, of the order of 12 amperes.

80 Fig. 6 shows .the general combinations and connections of a power-plant including a generator, as above described, and a. prime-mover 3!, which will preferably have an approximately fiat, or slightly drooping, speed-characteristic with increased loads. The positive and negative generator-temnnal-leads are indicated at and The main circuit may be traced from the negative lead through the series field-coil 6, the armature 8 and the commutating coil 1, to

o the positive lead The shunt coil 5 is illustrated as being shunted around the armature 8 and the commutating or interpole-coil 1, although other excitation-means are known for the shunt coil. The shunt-coil exciting-current is regulat- 45 able by means of a field-rheostat 32. The series exciting coil 6 is connected so as to produce cumulative compounding in an amount which is approximately correct to compensate for the IR. drop due to the resistance or the main circuit 50 of the generator, and also to compensate for the slight droop in the speed-characteristic of the prime mover ii. The compounding-efiect of the series winding 6 may be adjusted by means of an adjustable shunting-resistance 33 which is 55 connected therearound.

While I have illustrated my invention in a preferred form of embodiment, I wish it to be understood that various changes of omission, substitution or addition may be made by the skilled workers of the art without departing from some of the essential broader features of my invention. I desire, therefore, that .the appended claims shall be accorded the broadest construction consistent with their language and the prior art. 65 I claim as my invention:

- 1. A self-regulating direct-current commutater-type generator or a special typ having a relatively flat voltage-characteristic from very low loads up to somewhere in the order of 60% 70 of the normal load which it may be called upon to carry, and a voltage-characteristic which is drooping with increased load-current thereaiter, said generator comprising a field member comprising a yoke member, a plurality of main polepieces and a plurality of interpole-pieces, a rotor iace tip in which the armatur reaction produces 10 a differential magnetomotlve force, the large end of the tapered air-gap being at the first tip, the first tip being of sufiicient cross-section to be substantially unsaturated for small load-currents, and the second .tip being of such restricted crosssections as to be substantially saturated at noload and at small load-currents.

2. A self-regulating direct-current commutator-typegenerator of a special type having a relatively fiat voltage-characteristic from very low loads up to somewhere in the order of 60% of the normal load which it may be called upon to carry, and a voltage-characteristic which is drooping with increased load-current thereafter, said generator comprising a field member comprising a yoke member, a plurality of main polepieces and a plurality of lnterpole-pleces, a rotor member comprising an armature core separated from the main pole-pieces and interpole-pieces by air-gaps, a self-excited shunt coil on each main pole-piece, and a series-connected interpolecoil on each interpolepiece, each main pole-piece having a pole-face with a tapered air-gap, and each main pole-piece having a first pole-face tip in which the armature reaction produces a cumulative magnetomotive force and a second poleface tip in which the armature reaction produces a difierential magnetomotlve force, the large end of the tapered air-gap being at the first tip, the first tip being of suflicient cross-section to be substantially unsaturated for small loadcurrents, the second tip being of such restricted cross-sections as to be substantially saturated at no-load and at small load-currents, each interpole-piece including therein a section of such reduced cross-section as .to saturate at certain small currents, and the interpole-coils being of such number of turns as to produce overcompensation at all loads up to a certain predetermined large load-current. 5e

3. A self-regulating direct-current commutator-type generatorot a special type having a relatively flat voltage-characteristic from very low loads up to somewhere in-the'order of 60% or the normal load which it may be called upon to carry, and a voltage-characteristic which is drooping with increased load-current thereafter, said generator comprising a field member comprising a yoke member, a plurality of main polepieces and a plurality of interpole-pieces, a rotor member comprising an armature core separated from the main pole-pieces and interpole-pieces by air-gaps, a self-excited shunt coil and a cumulative series coil on each main pole-piece, and a series-connected interpole-coil on each interpolepiece, each main pole-piece having a pole-face with a tapered air-gap, and each main pole-piece having a first pole-face tip in which the armature reaction produces a cumulative magnetomotive force and a second pole-race tip in which the armature reaction produces a differential mags netomotive force, the large end of the tapered air-gap being at the first tip, the first tip being 0! sunicient cross-section to be substantially un; saturated for smallload-currents, and the second tip being of such restricted cross-sections as to be substantially saturated at no-load and at small load-currents.

4. A self-regulating direct-current commutator-type generator of a special type having a relatively fiat voltage-characteristic from very low loads up to samewhere in the order of of the normal load which it may be called upon to carry, and a voltage-characteristic which is drooping with increased load-current thereafter, said generator comprising a field member comprising a yoke member, a plurality of main polepieoes and a plurality of interpole-pieces, a rotor member comprising an armature core separated from the main pole-pieces and interpole-pieces by air-gaps, a self-excited shunt coil and a cumulative series coil on eachmain pole-piece, and a series-connected interpole-coil on each interpolepiece, each main pole-piece having a pole-face witha tapered air-gap, and each main pole-piece having a first pole-face tip in which the armature reaction produces a cumulative magnetomotive force and a second pole-face tipin which the armature reaction produces a differential magnetomotive force, the large end of the tapered air-gap being at the first tip, the first tip being of suificient cross-section to be substantially unsaturated for small load-currents, the second tip being of such restricted cross-sections as to be substantially saturated at no-load and at small load-currents, each interpole-piece including therein a section of such reduced cross-section as to saturate at certain very small currents, and the interpole-coils being of such number of turns as to produce overcompensation at all loads up to alargeload-current.

5. A power-planficomprising a prime-mover having a slightly drooping speed-characteristic with increasing loads, and a self-regulating direct-current commutator-type generator, saidgenerator comprising a field member comprising a yoke member, a plurality of main pole-pieces and a plurality of interpole-pieces, a rotor member comprising an armature core separated from the main pole-pieces and interpole-pieces by airgaps, a shunt coil and a cumulative series coil on each main pole-piece, and a series-connected interpole-coil on each interpole-piece, each main pole-piece having a pole-face with a tapered airgap, and each main pole-piece having a first poleface tip in which the armature reaction produces a cumulative magnetomotive force and a second pole-face tip in which the armature reaction produces a difierential magnetomotive force, the large end of the tapered air-gap being at the first tip, the first tip being of suflicient cross-section to be substantially unsaturated for small loadcurrents, the second tip being of such restricted cross-sections as to be substantially saturated'at no-load and at small load-currents, and the cumulative series coils having approximately the correct number of turns to compensate for the armature resistance drop and the droop in the speed-characteristics.

6. A power-plant comprising a prime-mover having a slightly drooping speed-characteristic with increasing loads, and a self-regulating direct-current commutator-type generator, said generator comprising a field member comprising a yoke member, a plurality of main pole-pieces and a plurality of interpole-pieces, a rotor member comprising an armature core separated from the main pole-pieces and interpole-pieces by airgaps, a self-excited shunt coil and a cumulative series coil on each main pole-piece, and a seriesconnected interpole-coil on each interpole-piece,

' each main pole-piece having a pole-face with a tapered air-gap, and each main pole-piece having a first pole-face tip in which the armature reaction produces a cumulative magnetomotive force and a second pole-face tip in which the armature reaction produces a difierential magnetomotive force, the large end of the tapered air-gap being at the first tip, the first tip being of sufficient cross-section to be substantially unsaturated for small load-currents, the second tip being of such restricted cross-sections as to be substantially saturated at no-load and at small load-currents, each interpole-piece including, therein a section of such reduced cross-section as to saturate at certain very small currents, the interpole-coils being of such number of turns as to produce overcompensation at all loads up to a large loadcurrent, and the cumulative series coils having approximately the correct number of turns to compensate for the armature-resistance drop and the droop in the speed-characteristic.

ALBERT W. KIMBALL.

Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US2433390 *Nov 16, 1944Dec 30, 1947Westinghouse Electric CorpMotor-generator
US2465186 *Nov 20, 1947Mar 22, 1949Westinghouse Electric CorpTapered-pole-face generator
US2475140 *Oct 30, 1944Jul 5, 1949Harnischfeger CorpRegulating generator
US2994796 *Jan 23, 1958Aug 1, 1961Curt Stoll K G Maschinen U AppSingle phase motor
US3201626 *Jan 29, 1962Aug 17, 1965Westinghouse Electric CorpDifferential bias auxiliary comutating field
US3493801 *Nov 21, 1967Feb 3, 1970Oerlikon MaschfD.c. electrical machine
US3497740 *Aug 17, 1967Feb 24, 1970Licentia GmbhElectrical rotating machine
US4041338 *Nov 20, 1975Aug 9, 1977General Motors CorporationDirect current dynamoelectric machine commutating pole assembly
US4573003 *Jul 9, 1985Feb 25, 1986Wisconsin Alumni Research FoundationAC Machine optimized for converter operation
US5015904 *Apr 27, 1990May 14, 1991Robert Bosch GmbhStator for an electrical machine
US5331245 *Jul 23, 1991Jul 19, 1994Papst Licensing GmbhPermanent magnet excited electric motor with improved torque ripple
US6879079 *Sep 20, 2001Apr 12, 2005Siemens AktiengesellschaftPermanent magnet rotor electrical synchronous machine with different alternatively arranged tooth pitch widths
Classifications
U.S. Classification310/186, 310/184, 290/1.00R, 310/226, 310/193, 310/216.77, 310/216.83
International ClassificationH02K23/40, H02K23/42
Cooperative ClassificationH02K23/42
European ClassificationH02K23/42