US1256705A - Induction-motor. - Google Patents

Description

J. LEBOVICI.

INDUCTION MOTOR.

, APPLICATION FILED JUNE 2. P916. I 1,256,705. Patented Feb.19,1918

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vwemfoz J. LEBOVICI.

INDUCTION MOTOR.

APPLICATION FILED JUNE 2, ms.

1,256,705. Patented Feb. 19, 1918.

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Patented Feb. 19, 1918.

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I T IN tive operation.

UNITED STATES PATENT OFFICE.

JUSTIN LEIBOVICI, OF OAKLEY, OHIO, ASSIGNOR TO THE TRIUMI JI ELECTRIC COMPANY, A. CORPORATION OF OHIO.

INDUCTION-MOTOR.

To all whom it may concern:

Be it known that I, JUSTIN Lneovicr, a citizen of Roumania, residing at Oakley, in the county of Hamilton and State of Ohio, have invented certain new and useful/"Improvements in Induction-Motors, of which the following is a full, clear, and exact specification.

This invention relates to improvements in induction motors, particularly of the selfstarting type. By means of my invention the motor may be connected directly across the supply line. without excessive flow of starting current, and when full speed is approached or attained, the motor will automatically cause a change of connections of the motor windings" so as to operate with advantageous operating characteristics. My improved motor also operates with comparativelylow starting currentand high starting torque. 1

With my invention thestationary member may be of the usual form of construction, the same as used in the ordinary squirrel cage or slip ring induction motor. The rotor, however, is provided with a plurality of windings which are connected during starting to give high starting torque with comparatively low starting current and automatically re-connected upon approaching running conditions to give desirable operating characteristics. These windings are phase wound on the rotor, as distinguished from a squirrel cage winding. The invention may be applied to a motor adapted for operation on any number of phases. Primarily, my invention is based upon providing one set of phase windings widely different in resistance or reactance'per turn,

from that of another set of phase windings.

, In starting, these sets of phase windings are preferably in series with each other causing the current flowing, resulting from electromotive force generated in each set, to be met by a comparatively large total resistance of the windings due particularly-to the high resistance of certain of the windings which form a part of the total windings in'efiec- T his condition of course limits the starting current to a desirable amount and gives a starting torque .by reason of all of the-windings being efi'e'ctive in producing torque. With increasing speed, these sets of windings are automatically connected in diflerent relationship so that they Specification of Letters Patent. Patented Feb. 19, 1918.

Application filed June 2, 1916. Serial No. 101,211.

-all continue to remain active under running conditions but under conditions to present low resistance to the current in circuits forming closed local loops, or with the windings in parallel, or "otherwise, to greatly reduce the resistance compared with starting conditions. During runningconditions all of the windings etlectively cooperate to' produce torque, the relative amount being in proportion to the resistance per turn.

My invention will. be understood from the following description and accompanying drawings, in which Figure 1 is a diagram illustrating the rotor windings under starting conditions of one form of my invention; Fig. 2 is a similar diagram showing the connections under running conditions; Fig. 3

is a part sectional elevation of a motor embodying my invention. Fig. 4 is an end nation with a diagram of windings and circuits corresponding to Fig. 5. Fig. 7 is an elevation partly in section showing the centrifugal circuit changing device as viewed from the left of Fig. 6. V

The subject-matter disclosed in this specification is in some respects the same as disclosed in my prior application, Serial Number 80,170, filed February 24, 1916.

It will be understood that in all forms of my invention, the rotor windings are preferably distributed phase windings as distinguished from concentrated windings, the representations of windings'in the diagrams being as shown for convenience. By reason of this preferred distribution of all the windings, the heating during starting and running conditions is quite uniformly distributed over the rotor and so avoids excessive heating,

In Fig. 1, the rotor windings for a threeother. They are shown connected in star to a common point and the remainingterminals of these windings are connected to a circuit comprising connections 4 and switches 5, one of these switches being 10- cated in the connection 4 in the circuit extending between each of the windings as shown. These switches 5 are normally open "when the motor is at rest and also durin starting, but are centrifugal switches, whic are automatically actuated to close the circuit in which they are connected when the speed of the motor attains a predetermined value sufficient to permit the change to running conditions. Another set of windings 6, 7;, 8, are illustrated which are wound in 2,3. In some instances the windings 6, 7

tiveforces will be induced. in the two sets and 8 may have a different number of turns from the number of turns in windings 1,2,3.

. The windings 6, 7, 8, may be of different resistance material from that of the windings 1, 2, 3, in order to secure the desired wide difierence in resistance, but in some cases the two groups of windings may be of the'same resistance material and differ in size for securingthe wide difference in re- 'sistance per turn.

Whenstarting current is supplied to the stationary element of the motor; electromoof windings corresponding to their number of turns, and the direction of the induced electromotive force in windings 1 and 6 will be the same and will be additive, being in the same phase. Similarly, thedirection of electromotive force induced in windings 2 and 7 will be the same as in each other and additive. The same is true of the ,electromotive forces inducgd in windings 3 and8, as

indicated by the arrows in Fig. 1, assuming a certain instantaneous condition. During starting the centrifugalswitches 5 remain open. The direction of current in the windings willrtherefore be as indicated in Fig. 1, passing through the common connection 9 of windings 6, 7 and '3 and through the common connection 10 of windings 1, 2 and 3. It is apparent under these conditions that the passage as current through-the windings in series as explained, causes-all of the current flowing to be opposed bv'the high resistanee windings. resulting in a low starting current and high starting torque. Although in some cases, if desired, the resistopposition". passing through switches 5 will therefore be ance windings may be of such high amount as to result in such limitation of starting current as to secure only a normal starting. torque.

When the rotor reaches a predetermined speed which approaches normal running speed, the centrifugal switches 5 are automatically closed giving the running condition illustrated in Fig. 2. The direction of induced electromotive forcesthen remains the same as before, but by reason of the switches 5 being closed, the windings 1, 2 and 3 are locally connected giving a low resistance path for the current passing in these windings. These low resistance windings may therefore function with high efficiency during running. conditions in the usual manner. The high resistance windings 6, 7 and 8 are alsointerconnected locally so that the current resulting from the generation of electromotive force therein may freely pass in the local connections between these windings. These high resistance windings therefore also operate during running conditions ,to assist in the efiiciency and improve the operating characteristics of the motor during normal operation. Assuming the instantaneous condition the same aS that assumed in' Fig. 1, it will be seen from Fig. 2 that the current passing upwardly in winding 1 divides at the terminal of this winding, one portion passing to the left through a switch 5, and another portion passing to the right through a switch-5, and returning through windings 2 and 3. The path taken by the current pass ing upwardly through winding 6 will be partly to the left throughconnection 9 and winding 8 through a switch 5 and partly to the right through winding 7 and a switch 5, the direction of current being indicated by the arrows. Of course. the resultant current passing'through switches 5 will be the difference between the value of the current passingin windings 1, 2 and 3, and the value passing in windings 6, 7 and 8. because as shown by arrows in Fig. 2, the'direction pf these currents through switches 5 are in The actual value of current that tirough the low resistance windings less the amount ofcurrent passing through the high resistance windings.

It will be evident that although Figs. 1 and 2 are illustrated for three phase opera tion. the number and phase relation of thv windings may be' modified for any number of phases, as will be understood by those skilled in the' art.

Figs. 3 and 4 illustrate one form of cen-' trifugally acting switch controlling means for serving the function of the switches 5.

The stator of the motor is shown at 25 havlies the rotor core 13 which in turn carries spectively uponthree supporting arms 16,.

extending from a central supporting part 17 These contacts 15 are insulated from their supports and at their outer' ends each have a connection 18 extending to the rotor windings. Slidably mounted upon the rotor shaft is a movable switch element 19 in the form of a ring around the shaft and when moved outwardly will engage all three contacts 15 and make a common connection between them as is accomplished by the closure of the switches 5 above referred to. The engagement of the ring 19 with the contacts 15 thus serves to make a common connection between three differentpoints of the windings as is necessary in the forms of connections above described in connection. with Figs. 1 and 2 where three phase windings are utilized. It is obvious that for any other number of phases, or different requirement.

of switch connections, the construction of the switches may be correspondingly modified. In the construction here shown, three weights 20 are pivoted respectively on rods 21, which rods are carried by supports extending from the central support 17. A link connection 22 extends between each of these weights 20 and the short-circuiting ring 19. A spring 23 which encircles the shaft is inclosed within a sleeve 24 and seats between ring 19 and housing 14, tending to force the ring 19 out of contact with. switch. contacts 15.-

As the motor speed increases, the weights 20 gradually move outwardly by centrifugal force against theforceexerted by the spring 23 and when a predetermined speed is attained, the centrifugal force exerted is sufficient to bring the ring 19 in engagement with the contacts 15'and thus cause the rotor windings to be changed from connections for starting to the running connections {as already described.

Any suitable matically acting switches may be utilized with means for producing a definite closure and definite opening of the switches 5 at desired predetermined speeds. Also in some cases, instead of having the switches automatically actuated by centrifugal force, they may be operated by any means that will control them in accordance with some function of the speed. In some instances, instead of providing automatic switches for changing thecircuit connections of the rotor windings. the switches may be operated manually.

The diagram in Fig. 5 showsthe induction motor secondary windings 30, star connected.

These windings are phase windings and are of low resistance. Their extremities may be '46 is a pin 48,

form of centrifugal 'auto--.

connected together by the switches 31, but such connection will only be made in the normal full speed operating condition. The switches are open when the motor is at rest, and the comparatively high resistance windings 32 are connected in series with 30 respectively. The extremities of these Windings are adapted to be connected together by the switches In the same way, other coils such as 34, 35 and 36 with interposed switches 37 and 38 are arranged as shown clearly in Fig. 5. The extremities of the coils 36 are permanently connected by the conductor 39.

The coils 30 are of relatively low resistance compared to the remaining coils, but all of the windings are preferably distribuated and phase wound.

The rotor with these windings is carried by the shaft 40, which also carriesacentrifugal circuit changing mechanism shown in Figs. 6 and 7. 0n the shaft 40 is fixed. a housing 41 with an interior springseat 42 and a transverse wall carrying three radial rows of insulated contacts 43. v

The windings as heretofore described are indicated diagrammatically at the right of Fig. 6. From a point between two coils 30 and 32, a conductor 44 goes to an innermost contact 43 and similar connections are made by the other conductors 44, as clearly appears in Fig. 6. Each of the other radial rows of contacts. has its contacts 43 con-- nected by other conductors 44 aspartially indicated in the diagram at the right of Fig. 6.

burrounding the shaft 40 and acrossthe opening within the edge of the housing 41 is a disk 45 mounted on This disk hasthree rows of bosses with spring seats 46, and in each such spring seat a corresponding contact 43 .and held toward the same by a yielding spring 47 The innermost pins 48 of each radial row are connected to a single ring 49 and this r1ng'49 carries contact buttons 53 registering in position with the corresponding contacts such as 43. Other similar rings 50, 51 and 52,

successively larger, connect the remaining pins 48 in the same way.

The casing 30 has three pockets 54 which alternate in angular position with the rows the guide pins 46.

registering in position with of contacts 43.. In each pocket 54 is a centrifugal weight 55 pivoted on the transverse pin 56 and connected by a link 57 and corresponding stud 58- to the disk 45. Around the shaft 40 within the casing 41 are four helical springs 59, 60, 61 and 62, graded in size and smallest and weakest and 62 the largest and strongest. The successive springs are separated b loose rings 63. I The weakest spring 59 presses against the; innerface of the disk 45 and the strongest spring 62 presses strength, 59 being the against the bottom of the spring seat 42. It will be seen that these springs act in tandem tending to hold the disk 45 away from the contacts 43 and in opposition to the centrifugal force exerted by the weights 55.

When the motor is at rest, the contacts 43 will be disconnected so that the coils will all be star connected in three series, one such series being 30, 32, 34, 35, 36. The current being applied in the stator windings will produce a rotating field to which the rotor windings grill be subjected. On account of the greaf'slip in starting, very large electromotive forces will be impressed on the rotor windings, but since these are connected in series and all the coils except 30 are of relatively high resistance, the currents in the rotor windings will not be excessive. As the rotor accelerates under the influence of the rotating field, the centrifugal weights 55 shift the disk 45 to the right as viewed in Fig. 6, compressing the spring 59 to a considerable extent, but the other springs 60, 61 and 62 only slightly. Presently the ring 52 will be brought in electrical contact with the three outermost contact terminals 43, thus star connecting the three coils 36 between the conductor 39 and the ring 52, likewise star connecting the remaining coils in groups of four in each series between the center point and the ring 52. This reconnection of the coils 36 gives reduced resistance in the coil circuits and increased current therein so that the rotor goes on gaining in speed, and the centrifugal weights 55 continue to diverge from the shaft 40 and move thedisk 45 farther to the right. In this further movement of the disk 45 to the right, the spring 60 is compressed just as was the spring 59 in the first stage. The springs 47 associated with the outermostring 52 permit this further movement of the disk 45 and pres-r ently the ring '51 comes in electrical contact with the second circumferential row of terfl minals 43, and thus the coils 35 are star connected between the rings 51 and 52 and the number of coils remaining in each original series is reduced accordingly and the currents are increased on the same principle as already explained. It will not be necessary to carry the detailed description of the mode of operation farther. Eventually the speed will reach a point where the innermost ring 49 will be electrically connected to the innermost circumferential row of contacts 43 and the low resistance windings 30 of the rotor will be short circuited. Thereafter the currents will flow in the coils of each set such as 30, 32, 34, 35 and 36 in parallel and so far as the currents flow in the higher resistance coils 32, 34, 35 and 36, they will be in entire cordination with the currents in the low resistance coils 30.

In case of failure of voltage and of the motor coming to a stop, my invention serves to provide protection to the motor, because upon restablishment of the voltage supply, theautomatic switches would be open and the motor would start under normal starting conditions and automatically assume 5 member having a winding of low resistance per turn, and a winding of high resistance per turn in series in a closed circuit, and a normally open switch to be closed for higher motor speeds to connect together. points of such closed circuit between said windings, whereby the said windings will each be placed in an individual circuit through said switch and the current through the switch will be the differential current in the windings, said windings having additive effect during starting and running conditions and having similar characteristics as regards induction.

2. In an induction motor, 'asecondary member having a winding of low resistance per turn and a plurality of windings of high resistance per turn, all normally connected i in a closed circuit serially, and normally open switches to be closed successively. for higher motor speeds to connect said windings in individual closed circuits, said.

switches being adapted to be closed successively first to close the circuit for a high resistance winding, then for another high resistance winding, and finally for" said low 4 resistance winding, all the windings all the higher motor speeds to reconnect saidwind:

ings in individual closed circuits, all the windingson the secondary member being at all times in closed circuits and having additive effect during starting and running conditions, and having similar character-' istics as regards induction.

4. In an induction motor, a secondary mally open switchvautomatically closed for higher motor speeds to connect together prints of such closed circuit between said windings whereby the said windings will each be glaced in an individual closed circuit, sai windings having additive efiect during starting and running conditions and having similar characterlstics as regards 1nductlon.

In testimori whereof I afiix my signature,

two witnesses.

JUSTIN LEBOVICI. Witnesses LOWELL F. HOBART, J. M. SMITH.

in presence 0

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