US1070648A - Control system for induction-motors. - Google Patents

Description

G. H. WHITTINGHAM. CONTROL SYSTEM FOR INDUCTION MOTORS,

APPLICATION FILED 111 10.12, 19-12.

1,070,648: Pat nted Aug. 19, 1 9L113 s SHEETS-$113313? W17 L VESSES G. H. WHITTINGHAM.

CONTROL SYSTEM FOR INDUCTION MOTORS.-

APPLIOATION FILED DEC. 12, 1912.

I 1 70,648 Patented Aug: 19,- 1913;

3 SHEETS-SHEET 2.

G. H. WHILTTINGHAM.

CONTROL SYSTEM FOR INDUCTION MOTORS.

APPLICATION FILED DEO.12, 1912.

Patented Aug. 19, 1913.

3 SHEETS-SHEET 3.

INVENTOR r a I ,Attorneys,

UNITED STATES PATEnT-oFFIcE.

GEORGE H. WHITTINGHAM; OF BALTIMOREL- MARYLAND, ASSIGNOR TO MONITOR MANUFACTURING COMPANY OF BALTIMORE CITY, OF BALTIMORE, MARYLAND, A

CORPORATION OF MARYLAND.

CON TROL-SYSIEM FOR INDUCTION-MOTORS.

Specification ot'Letters Patent.

Patented Aug. 19,1913.

Application filed December 12, 1912. SeriaVNo. 736,390.

To all whom it mag concern:

Be it known that I, GEORGE H. VVHI'rrr c- HAM, a citizen of the United States, resid ing at Baltimore, Maryland, have invented certain new and useful Improvements in Control Systems for Imluction-Motors, of which the following is a specification.

This invention relates to controlling means for electric motors, and more particularly to means for starting and varying the speed of alternating current motors of the induction type. In this class of apparatus it is the usual raetice to provide a resistance adapted to )8 connected with the rotor windings at starting, for the purpose of limiting the current induced therein, while the motor is being accelerated. \Vhen normal speed is reached, such resistance is cut out, either manually or by some automatic device, and the rotor windings shortcircuited on themselves, so that the motor continues to run at constant speed. In many classes of service, however, it is necessary, or desirable, that means be provided for causing such an induction motor to operate at any one of a number of different speeds. Such variations of speed can be conveniently obtained by inserting more or less resistance in the secondary or rotor circuit, as by means of some form of adjustable rheostat. But if too much resistance be inserted, the motor will not beable to start under load, and it is necessary to move the rheostat arm back and 'forth, with all attendant difliculties as to arcing and uncertainty of results.

The object of the present invention is to provide simple and efficient means for always inserting a proper definite amount of resistance at starting, and for inserting any desired amount for running, whereby any predetermined speed may be obtained. In other ,words, I provide means for varying from zero to maximum, the value of the running resistance, while preserving the value ofthe starting resistance constant, so that the former may be made either greater or less than the latter. Once a motor has started, it will operate, at low speed, with a greater resistance in the rotor circuit than would be possible starting under load. Hence I propose to insert, at starting, a certain resistance best suited to produce the proper torque and acceleration,-and' sistance selected with a new to obtaining.

the exact speed desired. To this end I provide a single rheosta serving to constitute both the starting and. running resistances, the former being lixed, the latter variable, and a double-throw switch, by means of which either resistance may be operatively inserted in the rotor circuit, \Vith this arrangement, it will be seen, having once determined the running speed desired, and having selectively adjusted the running resistance to the corresponding value, the starting and stopping of the motor can be controlled entirely by the double-throw switch, Without disturbing the adjustment of the resistances, and the motor will always run at the same predetermined speed. i

In order that the invention may be clearly understood, reference is had to the accompanying drawings, forming part of this specification, and in which Figure 1 is a diagram illustrating the essential features of my improved control system, and showing a manually operated switch; Fig. 2 is a similar view showing an automatic, electro-magnetic switch for er-,

forming the same functions, and provided with a time controlled retarding means; Fig. 3 is a similar view, illustrating such switch as provided with a current controlled retarding means.

Referring to the drawings in detail. and particularly to Fig. 1 thereof, M designates an alternating current motor of the induction type, shown as a three-phase motor, the rotor of which is provided with the usual three slip rings R. t

S designates the main line switch, which is connected with the primary or stator windings of the motor, by means of the three conductors 1, 2, 3, in two of which may be connected a reversing switch S, if desired.

Froinsuitable brushes bearing upon theslip rings R, extend wires-11, 12 and 13, to three banks of resistances From fixed points in these resistances extend conductors 17, 18 and 19, respectively, to a series of fixed contacts 20, 21 and 22.

A swinging arm 23, pivoted at 23, carries three insulated contacts 24, 25, 26 adapted to engage respectively, with the resistances 14, 15 and 16, and to be adjustably post- 14, 15 and 16.

iii

tioned at any point intermediate the ends ot' such resistances by moving the lever manually upon its pivot. From the contacts as, and 26, extend wires 27, 28 and 29, respectively, to fixed contacts 30, 31 and 32, arranged opposite to and corresponding with the contacts 20, 21 and 22.

Pivoted between the two sets offined con tacts above mentioned,- is a three-pole, doublet-brow, short-circuiting switch, comprising a cross-bar 36 of conducting material, and arms 3'? pivoted at 38. An open ating handle 39 of insulating material is attached to the bar 36. ries a series of contact blades 83, 3d and 35,

such blades being preferably arc-shaped,

and projecting on both sides of the'bar 36. lhese blades are adapted to" engage with either set of fined contacts 20, 21, 22, or 30, 31, 32, according to the position of the switch,

and when so engaged it will be seen that such contacts are short-circuited by means or the bar 36. The contacts and blades are preferably so designed that -the blades will engage with one set of contacts before breaking, connection with the other set, whereby sparking is prevented.

That portion of the resistances 141, 15

' and 16, included between the wires 11, 12,

13, and 17, 18, 19, is designated by the refer ence characters 14's, 15 16, and constitutes the starting resistance. That portion of the resistances included between the. wires .11, 12, 13, and the adjustable contacts 24,

25 and 26, constitutes the running resistance.

The apparatus is shown in Fig. 1 as in running position. The arm 23 has been set at such a point as to include a running resistance adapted to give the running speed desired. The primary switch S being closed,

land the double-throw switch being thrown into'engagement with the contacts 20, 21. and 29., the motor will start under load with only the starting resistances 14:, 15 16*, in the motor circuit, the remainder of the banks of resistances being short-circuited. This starting resistance is so proportioned as to give the necessary torque. After the 1 motor has speeded up, the double-throw switch may then be thrown into the position shown inFig. 1, in which position all of the resistances to the left of the arm 23 will be included in the rotor circuit. In the example shown, "this running resistance is greater than the starting reslstance, and the motor will, therefore, settle down to a running speed which is comparatively low.

'lf, however, a higher running speed had been desired, the arm 23 would have been shifted farther toward the left, and in its extreme position, in which all of the resistances would be short-circuited when the double-throw switch is thrown to running position, the full maximum speed of themotor would be obtained, It will thus be This bar also car inmate seen, that by adjusting the arm 23 and the contacts carried thereby, to any desired position, any predetermined amount of resistance can be retained in the rotor circuit, under. running conditions, and thus any desired and definite speed can be produced. It will be also particularly notedythat such adjustment of the running resistance can I be made without many way disturbing the starting resistance, which latter is always represented by the fixed values 14*, 15*, 16, regardless of the position of the arm 23. The motor can be stopped by opening the main switch S, and upon start-mg again, the double-throw switch would be moved over into starting position for a short time, and then thrown back into running position, thus always startin with the same torque andrunning with t e same speed.

The operation of moving the doublesition, and back again to starting position, whenever the motor is stopped, can be carried out automatically by the arrangement shown in Fig. 2. In this figure, reference numerals, corresponding to those of Fig. 1,

The main switch S connects with leads 1, '2 and 3, as above, the lead3 extending directly to the primary winding of the motor. The leads 1 and 2, however, in this case,

which are mounted movable plunger contacts 6 and 1', respectively. These contacts are slidably supported by these brackets in a vertical position, and are held in the position shown by springs G and 7, operating in conjunction with gravity, their downward movement being limited as by means of stop-pins 6" andY. Adapted to ing the other member of the primary switch, are a pair of movable contacts 8 and 9, carried by but insulated from a cross bar 10. The contact 8 is connected by means of a flexible lead 8 with a binding post 52, and the contact 9 is connected by means-of a flexible lead 9, with a similar binding post. From these two binding posts extend conduct rs 1 and 2 to the bar 10 is carried by the upper end of a vertical-ly extending'plunger 10', which forms the'core of a. solenoid 60, hereinafter re ferred to.

In the apparatus shown in Fig. 2, the contacts 20, 21 and 22, 80, 31 and 32, are shown as in the form of buttons or blocks and are adapted to be engaged by similar sets of contacts carried by the two shortequivalent' of the double-throw switch of Fig. 1. The bars 40 and 41 are preferably insulated from each other, but are rigidly connected by means of a plunger 42, which throw switch from starting to running p0 have been employed, as far as they go.

are connected with brackets 4 and 5, in

primary winding of hemotoia' The cross engage the contacts 6 and 7, and constitutv circuiting bars 40 and 4.1, constituting the,

constitutes the. ooreof a solenoid 43. One end of this solenoid is connected by means of a wire 44 with the pivot point 45 of a switch arm 46, whichis adapted to engage an adjustable contact pin 47, connected by means of a wire 48, with one of the main leads, such as 2- The-switch arm 46 is so located that the plunger 10 rests directly upon it, but is not connected thereto. Normally the weight of the plunger is sufficient to hold the switch arm in the position shown in the drawings, against the tension of a spring 49 which surrounds a piston rod 49 pivoted to the switch arm 46. The lower end of this piston rod 49 carries a piston which works in a suitable dash-pot 50, the operation being that when relieved of theweight of the plunger 10, the spring 49 will slowly raise the switch arm 46 into engagement with the contact 47, the dash pot serving to retard such movement. The other end of the solenoid 43 is connected by means of a wire 51 with the binding post 52. One end of the solenoid 60 is connected by means of a wire 61 with one of the main leads such as 2, outside of the primary switch, while the other end of the solenoid is connected by means of a wire ('52, with a pilot switch 63, the other side of which is connected by a wire 64- with another of the main leads such as 3.

The apparatus above described will be readily understood from a description of its operation. The switch S being closed, and it being desired to start the motor, the operator closes the pilot switch 63. This completes a circuit between the two leads 2 and- 3, including the solenoid 60, and such solenoid is, therefore, energized. The plunger 10 is instantly lifted and the contacts? and 9 brought into engagement with the correspending contacts 6 and 7, thus closing the main primary circuit of-the nrotoix- It will be noted that the plunger 42 is ddwn in the position shown, and that in such position, all of the resistance except the sections 14", 15, 1G, is short-circuited by the bar 40. The sections mentioned are, therefore, normally in circuit, and when the contacts 6, 7,

8 and 9 are brought into engagement as before described, these sections of resistance act as a starting resistance for the motor in the same manner as described in connection with Fig. 1. After the plunger 10' has been lifted the arm 46 be ins to move.

upward, urged by the spring 49, and after a predetermined time interval, controlled by the dash pot, will engage the Contact 47.

when this occurs, the circuit of. solencid.43

is crzmpleted, between main leads 1 and 2',

and the solenoid thus energized. The plunger 42 is then immediately lifted, removing the short-c1rcuit1ng bar 40 from the contacts 20, 21 and, 22, and bringing the short clrcuiting bar 41- into engagement with the contacts 30, 31 andfJQ. This has the efi'ect of' removing the starting resistance from the rotor circuit and inserting the running resistance therein, in the same manner as described in connection with the movement of the double-throw switch of Fig. l. The motor will then continue running at llupredetermined speed desired. until the switch 63.is.. opcned. When this occurs the plunger 10' will immediately drop down, thus opening the primary circuit at con tacts (i and 7, and at the same time forcing the arm 46 away from contact 47, thus opening the circuit of solenoid -l l, and restoring the parts to the position shown in Fig. 2. In this position it will be noted that the starting resistance is again operalively connected in the motor circuit, ready for the next starting operation.

In Fig. 3 I have shown a method in which the retarding action can be produced by current controlled means instead of by the dash pot. In this arrangement, one of the leads connected with the starting resistance, such for instance, as the lead 19, is extended so as to include a coil 53 constitutingui solenoid. It is obvious also that the termimils of solenoid 53, instead of being directly connected with the lead as shown, could be connected with a current transformer, associated with such lead. The core 54 of the solenoid 53 is pirotally connected to one end-55 of a rocker, such rocker having a switch arm -16 correspomling with the switch arm 46 of Fig. 2. The other end 56 of the rocker is adapted to engage under a washer or lug 57 carried by the extended end 58 of one of the plunger contacts such (3. The spring (3 and weight of such plunger contact is sulficientto normally hold the switch 46 in open position, as shown'in the drawings, counterbalancing the weight of solenoid core 54. One side of the solenoid 43 is, as above, con nected by means of a wire 44 with the pivot point 45 of the switch arm 46, while a. wire 48 connects the contact 47 with the line 2'. The other side of the solenoid 43 is connected by means of a wire 51 to the binding post 52 as in Fig. 2.

I The operation will be apparent. Upon closure of the pilot 63,- the core of solenoid 60 is hiovedsharply upward, forcing its contacts into engagement with the lungers 6 and 7, closing the primary circuit and lifting said plunge'rs. The rocker carrying switch arm 46 is thereby freed from the influence of the plunger 6, and is permitted to move under the control of solenoid However, so long as the starting current in the rotor circuit remains above a predetermined value, the solenoid 53 will be so strongly energized as to hold its core 54- up and maintain the switch-arm 46 out of 'en-.

gagement with contact 47. Then, however,'the starting current has fallen to a safe value, the solenoid 53 Will release its core and permit it to fall, thus moving the switch arm 46 into engagement with the contact. t? and closmg the circuit of solenoid 43. This solenoid being energized, substitutes the running resistance for the starting resistance in the manner described in connection with Fig. 2. Nhen the switch 63 is opened, the plungers (i and 7 drop down again, and in so doing, the projection 57 on plunger 6 engages the rocker arm 56 and opens the switch 46.

Although, in Fig. 2, I show time-controlled means for delaying the action of the double-throw switch, and in Fig. 3, currentcontrolled means, for producing such an eifect, it will he noted that in both figures, I

have shown apparatus which serves to interpose a time interval between the closing of the primary switch and the movement of the secondary or douhlethrow switch, and this time interval islneccssary in order that the motor may be allowed to attain the pro er speed before the running resistance is t irown in.

lVhat I claim is:

1. Controlling means for induction motors comprising a bank of resistance adapted to be connected with each slip ring thereof,

a switch for utilizing a portion of such resistance for starting, and for utilizing another portion for running, and means independent of such switch for varying the value of said last mentioned portion.

2. Controlling means for induction motors comprising a bank of resistance adapt ed to be connected with each slip ring thereof, and switching means for utilizing a fixed portion of such resistance for starting, and any desired portion of said resistance t'r'r running.

3. The combination with an induction motor having slip rings, of banks of resistance connected with said rings, means for utilizing a fixed portion of said resistance for starting purposesfand means for utilizing a 'certain predetermined portion for running,

whereby definite variations in speed may he produced.

4. The combination with an induction motor, of sets of resistances connected with the rotor winding, means for slmrt-circuiting a fixed portion of said resistances for starting, and means for short-circuiting a variable portion for runnin 5. The combination with an induction motor, of sets of resistances therefor, a doubleings for running, and means for varying the running resistance as desired.

6. The combination wlth an lnductlon mo- B ES'T AVAILABLE CG tor, of starting and running resistances therefor, and means for varying the rum ning resistance, while always maintainingthe starting resistance constant.

7. Controlling means for induction motors comprising banks of resistances, a set of fixed contacts connected with a definite point intermediatc the ends of said banks, a set of, adjustably mounted contacts adapted to cone nectwith any desired point of said bankaa, second set of fixed contacts connected with said adjustably mounteit'l contacts, and a; double throw switch adapted to engage either set of fixed contacts.

8.'Controll'ing means for induction motors comprising a main primary switch, a. double throw secoqdary switch, means for closing the primary switch, means controlled hy such primary switch for automatically moving said dci ble-throw switch, and means for delaying siich movement.

9. Controlling means for induction motors comprising a mainprimary switch, a double throw secondary switch, means for closing said primary switch, and means for automatically moving said double throw switch after said primary switch has been closed.

10. Controlling means for induction mo tors comprising a main primary switch, a double throw secondary switch having starting and running positions, and having a normal bias to f starting position, means for closing said primary switch, and means for automatically moving said double throw switch to running position after said primary switch hasheen closed.

11. Controlling'means for induction -m0 tors comprising a main primary switch, a double throw secondary switch having starting and running positions, and having a normal bias to starting position, means for closing said primary switch, and means controlled by such switch for automatically moving said douhle throw switch to running position, and for maintaining it in such position so long as said primary switch remains closed.

12. Controlling means for induction motors comprising a main primary switch, and a double throw secondary switch, means for closing said primary switch, means con trolled by such switch for automatically moving said double throw switch, and means for interposing a time interval between the closing of the primary switch, and the'movement of said double throw switch.

13. Controlling means for induction m0- tors, comprising a main primary switch,--a double throw secondary switch, means for closing said primary switch, nieans controlled by such switch for automatically moving said double throw switch from one position to the other, and current-controlledt means for delaying themovemenflof said" (10111110 throw switvh after the primary swil ih 1151s rinsed.

14TH- rmnhinutinn with an imhu'iinn motor. (If "starting and rlnming" rcsifiuwus tlwrvlur, :1 double (brow mvitvh serving: wlrr-n in one. positron, tn Jllllflt the stzu'iing lwislzuu-c with the rotor wind lugs, and when in another POSIUUII to c011- nect the running l'QSihtiUll'U with th rotm- \Yitnosxrs:

F111 Ix 1K. SULLIVAN, A. V. JAVINR

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