US2666882A - Auxiliary commutating field - Google Patents

Description

Jan. 1954 M. J. PASCULLE AUXILIARY 'COMMUTATING-FIELD Filed June 14. 1952 ATTORN EY Patented Jan. 19, 1954 UNFIZFELD STATES PATENT OFFICE AUXILIARY COMMUTATING FIELD Maurice J; Pasculle, Pittsburgh, Pa., assignor to -Westingho'use Electric Corporation, East Pittsburgh,-Pa.-,,, a corporation of Pennsylvania 1 Application June 14, 1952, Serial No. 293,637

21 Claims. (01. 318-350) 1 My invention 'relates" to mean'sfor improving the commutation'of' direct currentdynamoelectric machines; and'itisparticularly'applicable to variable-speedshunt type motors; which are of such a size as to requirevariation of the com-i mutating-pole excitation under different shuntfield excitationsiin" order to obtaingood commutation.

In large variable-speed direct-current motors, in which a considerable speed variation is ob- 'tained by adjustment" of the shunt-field excitation, it has been knowmiorsome time, that when the shunt-field excitation is increased; at some predetermined load such as full-load; certain increases mustbemad'e'in the interpole-flux which 'is produced by the seriescommutating-pole winding. Otherwise:pocrcommutation results. The reason for this phenomenon is notaltogether clear. It is supposed, in" some 'vague way, that saturation mustb'eat the bottom ofthedifiiculty, and massive field=frames are usually provided in used, becausethe' currents which are involved are large, commutation difilcult'to-achieve, and

the conditionsof" individual motors are sufficiently different to? require individual; factory-adjustmentsone'ach motor:

An' important' obj ect' of {my invention is to improve the eommutation' of' an adjustable-field variable-speed direct current'motor, byusing the shunt-field current or" voltage to excite an auxiliary commutat-ing-fi'eld winding.

Heretofore; thenecessaryindividu'al adjustment "has been commonlyaccomplished 'by meansof a shunt, havingthe-necessary variable resistance, connected acrossthe-terminalsof the series commutating winding and mechanically connected to the shunt-field rheostat.- Sometimes as much as 100 amperes ormorehave ha'd 'to' becarried by these shunts, and 'the valueof the shunt-resistance has been-subject to considerable variation.

I Eachmotor-has-had"to'be shop-tested at some predetermined load; such as full-load; atseveral different values of the s'hunt field excitation, in

order todetermine theproper-value of the shuntresistance aty each 'o'r these excitations, Then a suitable' shunt varying"rheostat hadto' be made up, mechanically coupled to the shunt-field rheostat, so as to have the proper valuesat the various tested points. Hence, it has been difficult to stock a sufficient variety of shunts to serve the requirements of all motors which are being made at a particular factory. This has resulted in delays in the shipments of the motor, which have had to be tested after the motors were otherwise finished and ready for shipment, and then a wait has'been involved, in all too many instances, while the-factory had to send away for a special high-current shunt having particular exact values of resistance at'the various points.

Furthermore, no-load sparking hasbeen a problem on someof these motors-and generators, generally as a result of spray-flux iromthemain pole-tip into the commutating zone, due to unexplainable variations in individual motors as they come through the factory. When this noload sparking has occurred, considerable time and money have been spent on the test-floor, by minutely adjusting-the brushes to their positions of best commutation, sometimes machining off the edges of the main'pole-tips, and sometimes resorting to other expedients.

While the ideal interpole-flux at no load'assumes that there will be no flux-fringing or spraying, and hence assumes a zero commutating flux under said no-load conditions, there is always a certain amount of flux-fringing, even though such flux-fringing only occasionally reaches such magnitudes as tocausecommutator-sparking at no load. My invention provides a cumulatively acting auxiliary commutating winding, which is adjustably excited from the same current or' voltage which is'applied to the shunt-field winding. Since the shunt-field excitation is never zero, the excitation of 'my'auxiliary commutating winding is never zero, thus producing an interpole-excitation in the direction which is necessary to reduce or prevent no-load sparking, While at the'same time eiiecting the necessary adjustment of the interpole-fiux under different shunt-field excitation-conditions.

An important object of my invention istherefore to provide an auxiliary commutating windin g, drawing a current which is: considerably smaller than that which flows through the main or series commutating winding, so that it is relatively easy' and inexpensive to adjust "the excitation of the auxiliary commutation winding, and so that other advantages may-beobtained, as will be pointed out hereinafter. Auxiliary commutating windings have been known before, in

other types of machines, and'ior other purposes,

3 and with other connections and adjustments, as shown for example in a Miner Patent 2,530,9 granted November 21, 1950, but my invention differs therefrom in the details of their use and application, as well as in the results which are accomplished.

In the case of variable-speed direct-current motors, the objects and accomplishments of my invention include also the achievement of a fiatter speed-characteristic on overloads.

With the foregoing and other objects in view, my invention consists in the machines, combinations, systems, connections, parts, and methods of design and operation, as hereinafter described, and illustrated in the accompanying drawing, wherein:

Figure 1 is a diagrammatic view of circuits and apparatus, illustrating my invention in a preferred form of embodiment,

Figs. 2, 3 and 4 are similar views illustrating modified connections and applications of my invention, and

Fig. 5 is a fragmentary view illustrating the positioning of the windings on the field-frame of an illustrative motor or generator embodying my invention.

My invention, while possibly not altogether limited thereto, is particularly applicable to, or needed in, direct-current shunt-excited dynamoelectric machines, particularly motors, in sizes above a 28-inch armature-diameter, with polenumbers ranging from 6 poles, with a 32-inch armature-diameter, up to 24 poles, with a 144- inch armature-diameter, or even larger machines, if they are built. My invention is particularly applicable to variable-speed motors, which require shunt-field excitations which are varied over a rather considerable range, for considerable speed-variation or control. At present, the largest commercial use of my invention is in the field of variable-speed motors, such as are used in steel-mills, and in many other industrial uses.

In Fig. 1, I have diagrammatically indicated my invention as applied to a motor which includes an armature M, a shunt-type field-winding II] which may be either separately or selfexcited, a series compensating winding It, a series commutating winding l2, and an auxiliary commutating winding l3. The motor is essentially a shunt-motor, which either has no series field winding (as shown), or if a series field winding is used at all it will have only a small compounding-effect.

As shown in Fig. 5, the field-frame of the motor comprises a cylindrical yoke [4, having main poles l5 and commutating poles or interpoles l6 bolted thereto. In accordance with a known practice, the main poles have a pole-shank portion 20, which carries the shunt-field winding which is diagrammatically indicated at ID in Fig. 5, and a pole-tip portion 2| having slots 22 for receiving the compensating winding H. The interpole I6 carries both the main or series commutating winding I2 and the auxiliary commutating winding l3, both of which are diagrammatically indicated in Fig. 5. In accordance with a known practice, the rear end 26 of the interpole I5 is spaced from the yoke or frame-member II by means of a plurality of magnetizable shims 21, the number of which can be varied, for the purpose of adjusting the efiective interpolar airgap 28 between the face 29 of the interpole and the periphery of the armature or rotormember M. It will be understood that the numberofthe rear-end shims 2'! can be adjusted 4 by removing the bolts 30, and then reassembling the interpoles IS, with the desired number of shims back of them.

Referring again to Fig. 1, it will be seen that my shunt-field winding [0 is provided with fieldwinding terminals which are marked E-- and E+. In most commercial applications of my invention, the shunt-field winding ID will be separately excited, so that the field-winding terminals E and E-lwill be connected to a separate source of excitation, other than the voltage which appears across the terminals of the armature M, although my invention is also applicable to a self-excited machine, in which the field-winding terminals E- and E+ are connected across the supply-line and or across the terminals of the armature M, as indicated in Figs. 3 and 4. In either event, Whether separately excited or self-excited, my shunt-field winding ID is necessarily provided with a shunt-field excitation-circuit 3| which includes a shunt-field regulating-means 32, either manual or automatic, for varying the excitation of the shunt-field winding over a considerable range, this regulatingmeans being indicated in the form of a fieldrheostat 32, which is intended to be representative of any field-varying means.

The main armature-circuit of the motor, as shown in Fig. 1, is connected across a suitable constant-voltage direct-current supply-line, represented by the terminals and such as a GOO-volt direct-current line, for example. The series compensating winding II and the series commutating winding l2 are connected as a series-winding circuit-portion l l-l2, which is in turn connected in series with the armature M, and all three serially connected parts are connected across the supply-line represented by the terminals and When the shunt-field winding I0 is separately excited, its excitation-terminals E+ and E- are commonly connected to a constant-voltage supply-line having a smaller voltage, for example 200 volts, although of course I am not limited to these details, in the application of my invention.

In accordance with my present invention, I provide a commutation-controlling means, for variably exciting the auxiliary commutating winding l3. The auxiliary commutating winding 13 is made of much smaller wires or conductors, than the series commutating winding l2, and the auxiliary commutating winding I3 is adapted to carry much smaller currents than the series commutating winding l2. Also, in accordance with my invention, the auxiliary commutating winding I3 is cumulative with respect to the main or series commutating winding l2.

It is an important feature of one aspect of my invention, that some means must be provided for varying or controlling or regulating or adjusting the exciting-current in the auxiliary commutating winding l3, either for making a preliminary general adjustment, suited to the idiosyncrasies or individual requirements of an individual machine, or for adjusting the excitation automatically in response to. the magnitude of the shunt-field adjustments of the machine.

Thus, in Figs. 1, 2, 3, and 4, I have shown excitationmeans or connections, for causing the excitation of the auxiliary oommutatingwinding I 3 to vary in response to variations in the excitation of the shunt-field winding I0. In many instances, the excitation of the shunt-field winding I0 is varied, by manual adjustmentsof the field-rheostat 32, so; as to vary the speed of the '--m'otor. In 'Figs.'"1"and{3 I mgwin'dmg l3 is fconnected 'irfseries' with the sliunt-field winding 3 l0, "and' said auxiliary commutating winding l'3'is shunted by a variable- 'resistanoe shunt33', whichservesas'an adjust- "ment-means; whereby to adjust the ratio of responsivenessof the "excitation of the auxiliary the fishery-cameramcommutating winding IS in dependence upon the excitation of the shunt-field windinglfl.

" While the essential connections and physical structures have thus far been described, it is important to note the relative degrees or magnitudes of the total effective interpolar excitation which is provided by'the combinedoperation of both of the commutating windings l2 and I3. It

tions. r The adjustment of 'theinterpolarfiux ismade initially, once and for all, tersre'tne. motor is shipped, by'means'of factory-West's atf'the previously mentioned load condition which is atleast as large as full load." While this lead is being "maintained, the shunt fieldrheostat' 32 is" varied from its maximum toits"minimum position, and the optimum interp'ole-"flux is determined at both maximum andmini'mum' shunt field' rheostatsettings. This gives the number 'ofamp'ere-turns difierence, between the excitation of the auxiliary is necessary, also, to bear in mind the essential object of my invention, which is to provide the interpolar excitation-control or adjustment which is necessary to give each individual machine satisfactorycommutation, and to do this without requiring the heavy-current shuntingresistors which have been previously used, in this '1 type of machine, for adjus'ting the excitation of the main series commutating winding I2.

The ideal interpolar or eommutating excita- "tion-curve for a 'directcurrent machine, plotting 'the total effective ampere-turns on the interpole [6 (in excess of the excitation necessary for compensation) against the load or armature-current, is a straight line, starting at zero ampere-turns at -no-load, and running-up to a certain definite magnitude, or-narrow-range of magnitudes, at a predetermined load which is at least as large as full load, and sometimes somewhat higher than full load. In other words, the commutating conditions must be right, not only at no load, but also at this predetermined load-value which is full-load or higher than full-load. At extreme overloads, such as double full load, or two and three-quarters times full load, interpole-saturation definitely comes into the picture, and the interpolar excitation need not always be ideal for such conditions.

The motors to which my invention is applied are big machines, which are individually handadjusted, on the test-floor, to have the proper operating-characteristics, before said machines are sold or put into use. The main or series commutating winding I2 is made of heavy strap-conductors, frequently having only one turn for each interpole, and the number of turns (and hence the ampere-turns), of this main series commutating winding l2, cannot readily be adjusted, except by means of the previously used commutating-winding shunt, or a cumulative auxiliary commutating winding l3, as in my present invention. It is essential that the total interpolar flux shall approximate an ideal value at the previously mentioned predetermined load-condition which is at least as large as full load, and if the machine is an adjustable-field variable-speed motor, involving the adjustment of the shunt-field current over a considerable range, say from full-field to a value which is from 15 to 25% of the full-field current, the ideal value of said total interpolar commutating winding {3 at'full field and at short field of the motor; 'At the same time, the optimum value of the interpolar-airgap 28'is determined. V

A check is also made at no load," leaving the shunt-field rheostat 32 in its maximum-field position, to see whether the'excitation of the auxiliary cumulative interpole-winding I3 is too great to bewithin the tolerable interpole-excitation range at which sparkless commutation is obtained at no load. Since there is always some fringing of the flux from the inain-poletips'Zl to the commutating zone; the cumulative'interpolar flux of the auxiliary winding- I3 is in the proper direction for overcomin'g'the-efiects of this flux fringing. Usually the optimum amount of auxiliary-winding interpolar-excitation which is determined on full-load tests is quite acceptable at no load. In some rare instances, this interpolar-excitation maybe too'much-at' no'load, in which case it may benecess'ary to reduce the auxiliary-winding excitation somewhat, so as to obtain not quite the'best" commutation atfull load, but still giving preference to the commutation-conditions at full load, as distinguished from the commutation-conditions at no load.

It will be understood of course, that once the excitation of my auxiliary commutatingwinding l3 has been adjusted on' the 'test-fioor'gby the proper adjustment or choice of the value of the resistance 33 or 34, as the case may be, then that resistance-value will thereafter remain unchanged, throughout the subsequent use of the motor.

The motor is then taken off of test, and the interpolar retaining-bolts 30 are removed, so that the number of shims 21 can be varied initially, once and for all, before the motor is shipped, as may be needed, to make the interpolar airgap 28 have the optimum value which was determined on test.

The interpolar airgap 28 may be adjusted, for example, at the base (or lowest) speed, or fullfield excitation, so as to require a total interpolar excitation of 2200 ampere-turns at full load, which may be made up by 2000 ampereturns supplied by the series commutating winding [2, and 200 cumulative ampere-turns supplied by the auxiliary commutating winding l3 of Fig. 1. Then at two times full load, still at base speed, the total interpolar excitation will be 2X2000+200=4200 ampere-turns, which is 200 ampere-turns short of the ideal double-load interpolar excitation which would be 2 2200=4400 ampere-turns. This has the effect of shuntin out 200 ampere-turns from the commutating pole at double load, and in the case of a motor, this effect is very beneficial in producing under-compensation at overloads, thus dropping the speedcharacteristic at overloads, and overcoming the tendency for the speed to rise when the motor is overloaded. This is quite a desirable characteristic.

It is important to observe that the amount of auxiliary-winding commutating-excitation shall be within the tolerable range during which commutation shall be satisfactory, both at no load and at full load. In fact, my whole invention is possible because of the fact that these motors do not, in general, have just one exact value of interpolar excitation which is necessary to produce satisfactory commutation at any given load, but there is a certain small range of commutating values which are quite acceptable, thus enabling me to produce the effect of the old loadresponsivecommutating-winding shunts, by using an auxiliary commutating winding I3 having an excitation which is largely independent of the load.

It will be apparent, from the foregoing, that I have overcome the disadvantages of the previously needed heavy-current commutatingwinding shunts, by the use of auxiliary multiturn commutating-windings which carry much smaller currents, and which interpose no problem insecuring the necessary adjustments. I wish it to be understood that my invention is not limited to the precise illustrations given.

I claim as my invention:

1, A variable-speed direct-current motor including an armature, a shunt-type field-winding, a shunt-field excitation-circuit including means for varying the excitation of said shunt-type field-winding over a considerable range, a series compensating winding, a series commutating winding, an auxiliary ccmmutating winding, means for energizing the auxiliary commutating winding from the excitation-circuit of the shunt-type field-winding, the excitation of the auxiliary commutating winding being cumulative with respect to the excitation of the series commutating winding, and a ratio-adjustment means whereby to initially adjust the ratio of responsiveness of the excitation of the auxiliary commutating winding in dependence upon the excitation of the shunt-type field-winding, said motor having adjustable-gap interpoles which carry the two commutating windings, said adjustable-gap interpoles having a gap-adjustment means whereby to initially adjust the effective interpolar airgap.

2. The invention as defined in claim 1, characterized by said ratio-adjustment means having such an adjustment that the degree of variation in the interpolar excitation under difierent excitations of the shunt-type field-winding is substantially as required for good commutation at a predetermined load-condition approximating a load at least as large as full load, while the excitation of the auxiliary commutating winding is within sparking-tolerable limits at no load, and further characterized by said gap-adjustment means having such an adjustment that the eifective interpolar airgap makes the interpolar flux approximate an ideal good-commutation value at said predetermined load-condition at a maximum excitation of said shunttype field-winding.

MAURICE J. PASCULLE.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,188,396 Binder June 27, 1916 1,215,786 Fahrmbacher Feb. 13, 1917 1,910,473 McNeil May 23, 1933 2,508,151 Fisher May 16, 1950 2,519,272 Miner, Jr. Aug. 15, 1950 2,530,982 Miner, Jr. Nov. 21, 1950 FOREIGN PATENTS Number Country Date 98,099 Austria Oct. 10, 1924

Images