US1207744A - Asynchronous motor. - Google Patents

Description

R. GOLDSCHMIDT.

ASYNCHRONOUS MOTOR.

APPLICATION men MAY 21. m2.

1,207,744. 'Paten'ted Dec. 12, 1916.

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ASYNCHRONOUS MOTOR.

APPLlCATlON FILED MAYN. 1912.

1,207,744. Patented Dec. 12,1916.

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RUDOLF GOLDSCI-IMID'I, OF DABMSTADT, GERMANY.

ASYNCHRONOUS MOTOR.

Specification of Letters Patent.

. Patented Dec. 12, 1916.

Application filed May 21, 1912. Serial No. 698,821.

To all whom it may concern Be it known that I, Rnnonr GoLDsoHMID'r, a citizen of Germany residing at Darmstadt Germany, have invented a new and Improved Asynchronous Motor, of which the following is a specification.

This invention relates to an asynchronous three phase or induction motor or machine of novel construction and more particularly to one having an armature which is provided with a single-phase winding.

One of the chief advantages of my device lies in the fact that its operation corre sponds in all respects to that of an induc tion motor provided with a slip-ring arm-ature of known construction.

In the accompanying drawing: Figure 1 is a diagram of an asynchronous threephase motor embodying my invention; Fi 2 a similar diagram of a double motor provided with an interpolated inductance and resistance; Fig. 3 a diagram of a similar double motor showing one of the phases of each single motor directly connected with each other and with an inductance and starting resistance; Fig. 4: a diagram similar to Fig. 3 showing three phases in lieu of one phase; Fig. 5 a diagram similar to Fig. 2 showing the stator windings displaced 90 in lieu of displaced rotor windings; Fig. 6 a diagram of a double motor showing but a single stator winding for the primary current and separate stator windings for the secondary currents; Fig. 7 a diagram similar to Fig. 6, showing three phases; Fig. 8 a diagram of a double motor showing the windings for the secondary currents combined and separate stator Windings for the primary currents; Fig. 8 a diagram similar to Fig. 2 showing the starting resistances connected to secondary inductance windings; Fig. 9 a diagram of subdivided and interconnected stator windings of a double motor; Fig. 9 a diagram of a complete motor constructed according to Fig. 9; Fig. 10 a diagram of a motor provided with a founpole rotor one phase only being illustrated; Fig. 1.1 a diagram of a bipolar single-phase-single-axial motor showing the position of maximal induction between stator and rotor; Fig. 11 a similar diagram. showing the position of minimal induction; Fig. 12 a diagram of a motor similar to Fig. 11, showing the rotor provided with seven windings; Fig. 13 a diagram of a motor provided with a four-pole stator and a fiVe-aXial-single-phase rotor; Fig. Li a diagrammatic perspective view of a poly-aXial-single-phase rotor; and Fig. 15 a diagram of a three-phase rotor having siX windings, and Fig. 16 a similar diagram showing three windings eliminated.

In Fig. 1, the letter M indicates an asynchronous three-phase motor comprising a stator S and a rotor R, while G represents a three-phase generator. The rotor R is provided with a single phase or single axial winding. which may be formed by lifting one brush off a rotor provided with a threephase winding and with slip-rings. If preferred, the rotor may also be provided with a short-circuited winding without sliprings. It is well known that a motor of the construction described runs light at half the sychronous speed and is able to furnish power at a number of revolutions which I corresponds to wherein f is the speed or frequency of the rotating field; while 1 is the lowering of the speed below halt. synchronous speed in percentage of f which lowering will hereina'ter be called the slip. Supposing now that the single phase alternating field which is produced by the rotor current in known manner be replaced by two rotating fields that move in opposite directions relatively to the rotor with a frequency there arise in the winding of stator S two voltages owing to the reaction of the two rotating field components upon said windin One of these voltages of the frequency B (rotor speed) +f (rotor field-speed) =f is the counterelectromotive force corresponding to the power which must be spent by generator G. The other component produces currents of the frequency 2f... The

generation of these currents of the double slip-frequency constitute the base of the present invention. The currents of the frequency 27 must normally be equalized,

through the windings of generator G. According to my present invention provision is made that the currents of this double slii frequency generated in the stator winding are not equalized through the generator windings, but are separately conducted through a starting resistance, so that the starting of my motor will he analogous to that of a motor prov' led with a slip-ring armature.

Difliculties would not be encountered in diverting the slip currents by means of condensers, but it is obvious that with the relatively low frequencies employed in strong current engineering, the condensers would constitute an expensive and unwelcome adjunct, even if used only for starting pa"- poses. So also the employment of choking coils would involve disadvantages owing to the increase of self-induction, although with the low slip-frequency the inductive loss of voltage would be comparatively small. By the transformation of the slip frequency occurring in the motor, even this small wattless component however would unfavorably affect the power factor and the overload capacity. But nevertheless it might be pos sible to make use of the above described methods irrespective of their expensiveness and the presence of the above mentioned disadvantages.

A separation of the currents of the primary frequency from those of the secondary or slip frequency may also be effected by coupling two motor in such a way, that the aXes of the single phase rotors are relatively displaced for 90 electric degrees, 2'. e. for one half of the pole-pitch. Such a device is illustrated in F 2, in which S, and are the respective stator windings of motors M, and M Between the three phases of the windings S, and S is interpolated a three-shank inductance T. The ends a, b,- c, (Z; and e, 7' of the shank "indings are respectively conn cted to the starting resistances r, while the motor current is supplied to the middle of the inductance winc ings as at g, h and 7c. The current supplied by generator G or by some other source of energy passes the inductance windings in such a manner, that the magnetization induced by said generator current in both halves of each inductance winding is neutralized. In this way the current encounters a small inductive resistance and branches uniformly over both windings S, and 8,, so that the rotating fields of motors M and M are of equal phase. As however the axes of rotors R, and R, are displaced 90 corresponding to a pole-pitch of 180, the currents of the double slip-frequency produced in the windings S and S have a phase-displacement of 180. If inductance T were absent and if both motors were directly connected in parallel, the currents of the double slip-frequency would be compensated between the stator windings, and neither the network nor the generator would be influenced by these currents. Or, in other words, both motors without inductance T would constitute an equivalent of one motor having a shortcircuit rotor. By interpolating inductance T, the compensation of the currents of the double slip frequency over said inductance is impeded owing to its seliiinducthm, so that these currents will pass the starting resistances 7. Only after the latter have been short circuited, a short circuit is provided for said secondary currents. By the construction described, the network has been depleted of currents of low frequency, and the motor may be started in a most eflicient manner without the use of slip-rings. The combination of motors M, and M into one machine, the accommodation of windings S and S in one housing and the mounting of rotors R, and R on one shaft, does not induce practical dilliculties, although said combination is not imperative. In lieu of interpolating the inductance T between the windings S and 5,, the latter may also be directly connected in series, while the inductance is connected in parallel to said stator windings. Such an arrangement is illustrated in Figs. 3 and i, which show the construction respectively for one phase, and for three phases. In lieu of displacing the rotor windings, the stator windings may be displaced 90, as illustrated in Fig. 5.

Although the inductance T of Fig. 2 is only required for starting or for regulating the number of revolutions, so as to be out out or short-circuited during the normal operation, it may be entirely omitted, so that the connections illustrated in Fig. 2 are simplified by removing said inductance. In this case there are provided on the stators two windings S and S, for the compensation of the currents of the double slip-freouency (Fig. 6). It is then also possible to unite the stator windings of both motors which are passed by the primary currents, condition being however, that both stators are contained in a common housing. Such a construction for a single phase is illus trated in Fig. 6, in which S indicates a common phase winding for both stators. S, is a winding for the currents of double slipfreouency generated in the stator pertaining to rotor R while S, is a winding for the corresponding currents generated in the stator pertaining to rotor R The tensions induced in the common winding S by the currents of the double frequency become neutralized, while they will. generate currents in the windings S and S, as they sum up in these windings, said generated currents being regulated by resistance 1" during starting. By tripling the stator windings,

the arrangement described may be applied to threephase current, as illustrated in Fig. 7. It is further possible to combine the windings for the currents of double slip frequency, if the windings for the primary currents are split up and joined in dilferential connection, i. e. in such a manner that the electromotive forces in the different sections of the windingsare opposed to each other, whereby only the current can pass able dimensions, it is nevertheless objectionable. It may be entirely dispensed with by subdividing the stator windings and connecting them in the form of a Wheatstone bridge. Each phase of the two combined motors is separated into the sections m, n and m a respectively, said sections being indicated in the diagrammatic Fig. 9 by straight lines, the full lines pertaining to one motor, while the dotted lines pertain to the other motor. Fig. 9 'illust'rates in full lines the complete connections for two combined three-phase motors. The four winding halves m, 11, m n pertaining to each phase are bridgewise connected in such a manner that each two adjoining bridge sections pertain to different motors, while opposed bridge sections pertain to the same motors, the points of connection being marked 1, 2, 3, 4. The points 2 of the three phases are united to the neutral point, while the current is supplied to the points 1. The supplied current has the same potential between the points 3 and 4, so that resistances may be interpolated between these points without affecting the network circuit in any manner. But as the currents of double slip frequency generated by the counter-electromotive forces of the rotor in bridge branches 1-3 are displaced for 180 against those produced in branches 14 (which remark also applies to branches 2-3 and 2-4) the slip-currents will be regulated for starting purposes by the resistances interpolated be tween the points 3 and 4. Or in other words, it is possible to gradually start the motor and to regulate the speed by cutting in the starting and regulating resistances between points 3 and 4.

The above described combination of two motors will be particularly advantageous wherever two motors are to be maintained at a uniform speed, as is for instance the case with traveling cranes.

The electromotors hereinabove described work in the same manner as a motor with a slip-ring rotor, although they are provided with a short-circuited rotor winding, while at the same time the power of a given type is increased. In some cases the combii'iation of two motors may prove a disadvantage more especially on account of the higher cost of two motors which almost negatives the advantage gained by the increased power.

Fig. 10 illustrates a motor with a fourpole stator winding of which only two are shown. The rotor windings displaced for 90 electric degrees are not carried by two separate rotors, but by one rotor, on which they are locally spaced from each other, one of the three stator phases only being shown for the sake of greater clearness. The rotor may be considered as made up of four quadrantal pole-sections, two adjoining sections being arovided with a common windin while each of the other two sections is provided with a winding The axes of the windings W and are mutually displaced 90 electric degrees, so that the currents generated therein by the stator windings are also displaced 90 electric degrees. Their reaction on the stator windings causes th erefore, as above explained, a displacement of 2 90z180 electric degrees.

The electromotive forces of the rotorreaction generated in the stator windings since both halves of W are displaced 90 electrical degrees against 'VV and together counteract or neutralize the total reaction of W The two halves of W are mutually displaced 180 electrical degrees, so that the currents produced by their reaction in the stator windings will be of the same phase. The speed will depend entirely on the amount of resistance (7) included in the circuit. In this way means are provided for separating the rotor-reaction currents from the stator currents, and for starting and regulating the motor provided with a short-circuited rotor winding, analogous to a motor having a slip-ring rotor.

Fig. 10 illustrates for one stator phase the above described method of employing an inductance T, to which is connected in parallel the starting resistance 1". Although this figure shows but one phase of the stator, the connections for more phases may be provided in an analogous manner. If the sub division of the stator phases and their bridging is to be applied to the construction shown in Fig. 10, each of the windings S and S should be divided into two sec tions and connected as disclosed in Fig. 9, so as to permit the elimination of inductance T.

The above described constructions relate only to the so called single-axial type of single-phase rotors, while a further development of my invention comprises a form of rotor, which may be termed single-phasemulti-axial, which provides a separate path for the reactionary currents of double slipfrequency, thereby procuring certain advantages over the single-phase and singe-axial rotors, the operation of which is based upon the principle that the mutual induction between the stator windings and rotor windings are periodically changed during rotation.

In Figs 11 and 11, a single-phase-singleaxial motor isillustrated, of which Fig. 11 shows the position of maximal mutual induction between rotor and stator, while Fig. 11 shows the position of minimal induction. If 7) designates the pole number, f the periodiciay per second and a the number of revolutions when running under no load Considering that the operation of a motor provided with a single-phase-single-axial rotor is based upon the principle of mutual induction between the stator windings and rotor windings, it may be said that the number of revolutions per second is directly proportional to the frequency, and inversely proportional to the number of changes of induction per revolution. Thus there is shown in Fig. 12 a motor, in which the number of rotor windings has been raised to 7, so that the number of revolutions will be reduced at the ratio 1:7.

Fig. 13 illustrates a motor with a fourpole stator and a. five-axial-singlephase short-circuited rotor. At a periodicity of 50. the number of revolutions per minute of this motor when running under no load equals 600.

In order to obtain the above described advantage of readily separating the reaction currents, the number of rotor-axes should be so selected that some of the stator windings are located at the point of maximal mutual induction with the rotor windings, while other stator windings are not at all interlinked with the rotor windings. Such a relation of the windings is embodied in Fig. 13 where the mutual induction with the rotor is a maximum at the stator winding 8,, while said induction is minimum at stator winding 8,. The dotted lines of force emanating from winding S show cleary that no rotor windings are encompassed thereby.

After the rotor has been turned through an angle of 36, the conditions are exactly reversed. In manner analogous to that hereinabove described with respect to the windings of the double motor, the reaction currents may be conducted through resistances and regulators, Fig. 13 showing however the use of a choking coil. It is obvious that the above described method of starting the motor through a transformer, or through bridge-connections may also be applied to the motor illustrated in this figure.

The simplest form of a polyaxial-singlephase rotor is illustrated in Fig. 14, which may be obtained by removing several groups of bars from a conventional short-circuit squirrel-cage rotor, whereby the number of groups should correspond to the number of axes. In the construction shown in Fig. 13, there has been adopted this form for the bars a, which are the farthest separated. For the remaining windings n it is of advantage to use single short-circuited windings, as otherwise compensating currents are liable to arise between adjoining bars. If with a common four-pole three-phase motor having a three-phase rotor, 2'. e. a rotor provided with six windings (Fig. 15), the second winding of each phase is cut out, three windings only will remain active, and the rotor will thus act as a single-phase-threeaxial rotor (Fig. 16). The cutting out of the second windings may be effected by lifting oif the corresponding brushes or by using cut-out means (not shown). In this way, the usual motors may be adapted to two synchronous numbers of revolutions. On the other hand, it is possible to adapt a single-phasepoly-axial rotor which may for instance be provided with short-circuit windings, for two numbers of revolutions by adding to said windings another winding leading to slip-rings or to a short-circuiting device, and by thus converting the previously single-phase rotor winding into a polyphase winding. 7

It is obvious that the induction machines described hereinabove as asynchronous motors, may also be employed with a higher number of rotations as induction generators, and that they may also be used as frequencytransformers.

I claim:

1. An asynchronous motor comprising a current-supplied stator winding and a single phase rotor which is adapted to induce in the stator winding secondary currents, and a separate circuit for said secondary currents, said circuit including a starting resistance.

2. An asynchronous motor comprising a current-supplied stator winding and a single phase rotor which is adapted to induce in the stator winding secondary currents, and a separate circuit for said secondary ourrents, said circuit including a starting resistance and an inductance.

3. An asynchronous motor composed of two stators having current-supplied Windings and supplementary windings and of two rotors having single-phase windings, the two component parts of one of said motorcomprising elements being mutually displaced for one half of the pole pitch, Whereby the rotors are adapted to induce in the 10 supplementary stator windings secondary currents of the double slip frequency, and a starter in circuit with said supplementary windings. I

' RUDOLF GOLDSCHMIDT. Witnesses:

ARTHUR E. ZUMPE,

KATHERYNE KooH.

Copies of this patent may be obtained for five cents each, by addressing the Commissioner of Patents, Washington, D. G.

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