US730108A - Method of starting and regulating the speed of induction-motors. - Google Patents

Description

No. 730,108- PATENTED JUNE 2, 1903. P. J. M. GIRAULT. METHOD OF STARTING AND REGULATING THE SPEED OF INDUCTION MOTOR S.. APPLICATION FILED 0013.3, 1901.

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No. 730,108. PATEETED JUNE 2, 1903.

P. J. M. GIRAULT. I METHOD OF STARTING AND REGULATING THE SPEED OF INDUCTION MOTORS.

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METHOD OF STARTING AND REGULATING THE'SPEED or INDUCTION MOTORS.

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. UNITED STATES Patented June 2, 1903.

PATENT OFFICE.

METHOD-OF STARTING AND REGULATING THE SPEED OF INDUCTION-MOTORS.

SPECIFICATION forming part of Letters Patent No. 730,108, dated June 2, 1903.'

Application filed October 3, 1901. Serial No. 77,423. (No model.)

To all whom it may concern:

Be it known that I, PAUL JACQUES MA- THURIN GIRAULT, engineer, a citizen of the French Republic, residing at Paris, France, (post office address 71 Rue Damremont,

Paris, XVIIIZ) have invented certain new and and at the same time have the coils of theirinducing-fields closed on themselves and of resistance as small as may be desired. In the application of these arrangements the motor must consist, essentially, of two motors, (hereinafter called the component motors,) the corresponding polyphase induced-field windings ofwhich are connected in series,while the inducing-windings are so arranged as to exer-- cise on the common induced circuits a concordant action when the motor is working at its normal speed. The revolving parts or rotors of the component motors are connected mechanically, so as to insure the same slip relatively to the stationary parts or stators. When the motor is being started, only the circuits of the inducing-field of the first moto'r (hereinafter called principal motor) are fed directly,while the inducing-circuits of the other motor (hereinafter called the auxiliary component motor) are open. Under these circumstances very high electromot-ive forces are induced in the induced circuit of the principal motor. These clectromotive forces act on the induced circuits of the auxiliary motor, and said induced circuits act at this time as a strong self-induction coil, for the reason that the inducingcircuits of the auxiliary motor are open. The strength of the current corresponding. to the electrometive forces in the induced circuits of the principal motor is consequently weak. The conple of the whole apparatus is thereupon increased (or the angular velocity for a given resisting-couple is then increased gradually) by increasing little by'little the excitation of the inducing-fields of the auxiliary component motor until this said excitation reaches its normal value. I may obtain these results by the methods hereinafter described.

First. In each of the circuits of the inducing-field of the auxiliary motor I introduce a rheostat or a reactance-coil and the resistance or the inductance will be gradually decreased. To simplify matters, the rheostats or the coils of the various circuits may be combined. For instance, in the case of an N-phase motor it will/be possible if rheostats be used to group these rheostats in one single apparatus and operate simultaneously and in the same way each one of the N-phase circuits or operate alternately each one of them, so as to obtain a greater number of distinct positions for the same number of contacts of the rheostat. If rcactance-coils be used, (the case of an N-phase polyphase motor being still presumed,) it is possible to 0perate first the rheostats in the manner already explained and to replace in the well-known manner the N single-phase alternate-current ternating-current transformers by a single N-phase transformer. In this case care should be taken to switch in resistances or reactances, at least in the section or sections of the transformer or transformers which feed the inducing-fields under the smallest differences of potential; otherwise the risk would be run that the intensity absorbed by the principal motor would undergo too great a variation.

Third. Each of the inducing-circuits of the auxiliary motor may be connected in series with the corresponding inducing-circuit of the principal motor, and the number of coils of the auxiliary inducing-field may be caused to vary from zero at the time of starting to the maximum number; required when worle ing under normal conditions. In this case the value of the revolving flux of the inducing-field of the principal motor is not constant during the starting operations, as in the two previous cases. Forinstance, if the auxiliary motor is as regards construction identical with the principal motor the revolving flux of the principal motor will when the motor is started have a value which is practically double its normal value.

With regard to the three methods just described the following remark, which might have in some measure been anticipated from the foregoing, may he made. In the case of polyphase (N-phase) motors it is possible to effect simultaneously and in the same manner the operations already described on the N-phase inducing-circuits or, again, (in considering the whole of the said operations as effected by a series of successive jumps) operate during the interval of a jump alternately in each one of the inducing-circuits, so as to have a greater number of distinct positions for the same number ofcontacts. In the case of a single alternating-current motor it is likewise possible to effect the aforesaid operations simultaneously and in a like manner on the various inducing-circuits or alternately on each one of them in the interval of a jump.

In the description which follows and in which the accompanying drawings will be referred to various constructional forms of the motor will be given which are appropriate to the carrying out of the aforesaid three methods. The reasoning will apply in each case both to a single circuit of the inducingfields and to the corresponding circuit of the other inducing-field, and I will presume that analogous operations are effected simultaneously or alternately, as already stated, in the interval of a jump on all the other corresponding inducing-circuits of the two component motors. The examples given will therefore obviously apply to all the types of single or polyphase alternate-current induction-motors with revolving circular or elliptical inducing-field. I need not dwell on the simplifications which may be easily made in the case of polyphase currents. To simplify matters, I will presume that in the following examples the two component motors are of identical construction, and I will presume that the two induced fields consist of one single squirrel-cage, which will constitute for the induced fields a special case of two squirrel-cage windings connected in series.

Figure 1 shows two component motors A and A constructed in accordance with the foregoing description, A being, forinstance, the principal motor and A the auxiliary motor. In this figure the inducing-fields a, and (:1 are stationary-i. 6., they constitute the stators, while the induced fields Z), and b constitute the rotors. Let 0 be one of the inducing-circuits of the principal motor A and let 0 be the corresponding inducing-circuit of the auxiliary motor A The Various inducing-circuits of the two motors I shall call 0, 0' c and c 0'.) 6' &c., respectively.

In all the figures the arrows indicate the direction of the movements that have to be imparted to the corresponding handles in order to pass gradually from the switching-in circuit of the motor to the position corre-- gular velocity is caused to vary by a further movement of the handle f. Lastly the normal or maximum speed corresponding to a given torque is obtainedwhen the handle f is at the end of its stroke on the side corresponding to the zero value of the resistance 0.

Fig. 3 shows a diagram relating to my aforesaid second method. In this figure, c and 0 are the two corresponding inducing-circuits. 0 is fed directly, while 0 is fed by the transformer 6 under gradually-increasing differences of potential produced by operating the handle f. According to the arrangement shown in this figure the transformer is, more correctly speaking, an autotransformer, for it has only a single winding. Of course the handle has to be provided with a cutting-off device similar to that used in connection with accumulator cell-cutting-off switches. Moreover, care is taken to feed the circuit 0 through the transformer 02 only when the rheostat 71, whose resistance is variable, is switched in circuit with 0 If this rheostat were suppressed when the first sections of the transformer e are switched in circuit with 0 the electromotive force due to 0 could be left out of consideration relatively to that due to the mutual induction of 0 and of the inducingfield of the auxiliary motor A (for 0 being switched in the circuit acts on both inducing-fields and the inducing-field of A acts in its turn 011 0 As 0 would then be closed on a very small resistance, heavy currents could be generated in 0 and consequently also in the inducing-fields and in 0 which would be contrary to the purpose in view. Care is therefore taken to switch in the whole of resistance 7L before switching in, and in order to effect the starting of the motor the handle f is operated in such a manner that it does not connect any section or even only the first section of the transformere with 0 The switch 9 is then closed, and both the intensity of the current and the torque (or the speed for a given resisting couple) are gradually increased by increasing the number of active sections of the transformer 6 through the operation of the handle f and the simultaneous corresponding and gradual decrease of the resistance h, effected by moving the handle 2'. The normal or maximum speed which approximates synchronism is attained when both handles f and t' areat the end of their traverse, so that all the sections of c are active and the resistance of 72, is annulled. Of course the resistance It might be replaced by a variable reaction coil, the precautions mentioned in the foregoing being observed. Instead of operating simultaneously the handles f and i the handlef might be first operated alone and when it has reached the end of its traverse i might then be operated alone. It is also possible to act successively and at diiferent times onfand i, the whole of-these manipulations being carried out so as to obtain variations of the current and torque according to a predetermined law. Lastly it should be remarked that under certain circumstances the value of the resistance 7t might bevery small, even zero, as would be the case if the dimensions of the auxiliary motor were very small when compared with those of the principal motor.

Fig. 4 is a diagram relating to my aforesaid third method. In this figure the inducingcircuit 0 has 'a constant number of active coils, while the number of active coils of c is gradually varied by the movement of the handle from a zero value at the time of starting the motor to the normal value. In order to avoid too large a number of handles and fixed contacts in the case of multipolar motors,'each portion of the circuit 0., corresponding to the various poles is divided into a certain number of sections, which number would for each pole be equal to the number of variations to be effected. According to cases the similarly-situated sections are connected in series, Fig. 5, or in parallel. In Fig. 5 the case is presumed of one of the three inducing-windings of a three-phase motor. The free wire ends 00 y 7.6 at the top of the figure should be connected to the fixed contacts,over which the handle f of Fig. 4 is moved. The circular connections of Fig. 5 might be replaced by involute connections.

Each one of my three aforesaid methods might be carried into practice by means of suitably-arranged transformers for altering the voltage. With the reservations already made Figs. 6 to 9 show these modifications. Fig. 6 corresponds to Fig. 2, Figs. 7 and S to Fig. 3, and Fig. 9 to Fig. l. The winding 0 is fed through the medium of a transformer whose primary winding is designated by 19 and the secondary winding by 1,. The winding 0 is fed, respectively, in each case in accordance with my first and second methods, respectively, by means ofa transformer whose primary and secondary are designated,respectively, by and (1 In Fig. 7 the winding (1 correspon s to the winding 6 of Fig. 3. It will be noted that if in the arrangement shown in Fig. 7 the handle f is moved the number of inactive coils of the secondary winding increases as the handle f is moved farther away from the position which corresponds to normal working. The arrangement shown in Fig. 8 permits of. utilizing for the winding c, the inactive coils which are opposite the winding 0 The potential at which 0 is fed becomes thus higher as that of 0 becomes lower in the same manner as obtains in the case of my aforesaid third method, Fig. 4. In Fig. 9, which shows a modification of my third method, there are again two transformers the primary windings of which are 19, and 9 while the secondary windings q, and (1 are series connected. The characteristic feature of the four modifications shown in Figs. 6 to 9 is the use for each pair of corresponding inducing-windings of two transformers whose primaries are fed in parallel.

The modifications shown in Figs. 10 to 13 correspond, respectively, to those shown by Figs. 6 to 9-namely, that shown in Fig. 10 corresponds to Fig. 6, that shown in Fig. 11 to Fig. 7, that shown in Fig.12 to Fig.8, and that shown in Fig. 13 to Fig. 9. The common difference between these two kinds of modifications lies in the fact that in the modifications shown in Figs. 10 to 13 the primary windings p, and 13 are connected in series.

The modified forms shown in Figs. 14 to 17 correspond, respectively, to the former as follows: That shown in Fig. 14 corresponds to the arrangements shown in Figs.'G-and 10, that shown in Fig. 15 to those shown in Figs. '7 and 11, that shown in Fig. 16 corresponds to those of Figs. 8 and 12, and that shown in Fig. 17 corresponds to those shown in Figs. 9 and 13. The essential feature of the further modifications shown in Figs. 14 to 17 resides in the fact that the two transformers are reduced to a single one, the primaries p and 13 being combined into a single primary 1).

For the modification shown in Figs. 6 and 7, 10 and 11, 14 and 15 the secondary windings q, and g may be either independent, as shown in Figs. 6 and 7, or connected in series, as shown in Figs. 10 and 11, 14 and 15, and in this second case the corresponding windings c and 0 are also connected in series, and a conductor r s connects together the points 1" and s, which are respectively the points of connection of the windings q, and g and c,

and 0 All the modifications shown in Figs. 6 to 17 may be according to the case simplified by using single windings for the transformers in lieu of separate primary and secondary windings. Lastly only one of the windings 0 or 0 may be fed directly from the line, while the other is fed through the medium of a transformer.

The carrying into practice of my, first and second methods may be modified by connecting the windings c and 0 in series after the starting operations are completed. Thus Figs. 18 and 19 correspond to Fig. 2 (first method) and Fig. 20 to Fig. 3, (second method.) Feeding may be effected for the whole installation directly from the line or through the secondary of a transformer. In Figs. 18 and 19 the current'fiows directly into the winding 0 at the moment of starting, the winding 0 ICC being closed through a large resistance. As the starting operations are proceeded with the winding 0 is getting gradually switched in the circuit in series with 0 this being effected by means of two handles in the arrangement shown in Fig. 18 and by means of a single handle in that shown in Fig. 19. In the latter arrangement once the handle has been operated the switch tcan be opened. In other words, the resistance of the part of the circuit running from the handle fto the end 8 of the winding 0 is gradually increased and the resistance of the part of the circuit running from f through the resistance hand the handle 11 to the other end of the windmg 0 In Fig. 20 the difference of potential at the terminals of the system consisting of the winding and of the resistance h increased gradually, while at the same time the resistance h, switched in the circuit of this winding, is being decreased. It will be noted that in the case shown in this figure and in that shown in Figs. 10 and 11 the actions resulting from these manipulations are of a complex nature, owing to the fact that a gradually-decreasing self-induction is being introduced in circuit 0 All the cases I have considered necessitating the use of transformers these may of course undergo the simplifications that are in general use in polyphase-current practice such as, for instance, the substitution of an N-phase transformer for N single-phase transformers.

In all the cases that have been considered unequal component motors may be used. If the two component motors have a common shaft, they will necessarily have the same number of poles; but the diameters to which the stationary parts are bored may be different and the width of the core-iron sheets may also be different. The component motors may then have different numbers of poles; but it will then be necessary to connect them by mechanical means in such a manner that the ratio of their angular velocities be equal to the inverse ratio of the number of their poles. (This result may be obtained by means of wheel-gearing.) This condition is sufficient; but it will be besides advisable to give to the two component motors, at least in the neighborhood of synchronism, curves of variations of power proportional, or nearly proportional, to the slip, this being done for the purpose of insuring a better utilization of the materials. The rotor may in each of the component motors be either the inducingfield or the induced field. It is therefore. possible to realize all the combinations that are possible. The induced windings of the one or the other component motors may be of any kind allowing of the corresponding circuits of the induced field being connected in series. For instance, squirrel cage induced fields or rotors may be used, as shown 1n Fig. 1, or the coils may be closed on themselves and be of the ring-armature pattern, Fig. 21, or drum-windings may be used. Ring or drum polyphase windings or polyphase windings analogous to those of the armatures of direct-current dynamos may also be used.

To conclude the description of my invention I would remark that the same relates, essentially,to a motor (principal motor) whose induced circuits contain very high self-inductions, (constituted by the induced circuits of the auxiliary motor.)

To start this motor and increase the speed for a given torque, I decrease the influence of these self-inductions until it has entirely disappeared, this being obtained by gradually increasing the excitation of the auxiliary motor. By my process the parts which constitute and act as self-inductions when the motor is first started become, therefore, more and more active as the hcreinbefore-described operations are being carried out. Of course as in all the methods invoking self-inductions switched in the circuits of the induced field I may shunt the induced circuits of my principal motor and through this shunt also the self-inductions (induced circuitsof the auxiliary motor) by means of resistances of constant value and sufficiently large to produce an initial torque of sufficient magnitude to insure the starting of the motor. For example, when squirrel-cages are employed, as shown in Fig. 22 of the drawings, a ring d of sufficiently great resistance may be used, or when polyphase induced windings are employed the induced circuits d d d of the principal motor may be shunted by resistances d d d, as shown in Fig. 23. In Figs. 22 and 23 d d d indicate the induced windings of the auxiliary motor.

Having now particularly described and ascertained the nature of my said invention and in what manner the same is to be performed,

I declare that what I claim is The method of starting and regulating the speed of induction-motors made up of a plurality of component motors having polyphase induced-field windings connected in series, 1

which consists in supplying with current at the moment of starting, the inducing-field of only one of said component motors, the inducing-field of the other component motor being at such time in an open circuit, the inducing-fields being so arranged as to exercise on the common induced circuits a concordant action when the motor is working at its normal speed, and afterward, as the speed of the motor increases, increasing the excitation of the inducing-field of the second component motor from zero to its normal value.

In testimony whereof I have hereunto set my hand in presence of two subscribing witnesses.

PAUL JACQUES MATIIURIN GlRAULl.

Witnesses:

EDWARD P. MAOLEAN, EMILE KLOTZ.

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