US2492395A

US2492395A - Electric motor controller

Info

Publication number: US2492395A
Application number: US637850A
Authority: US
Inventors: Frederick J Pavitt; Harold H Matthews
Original assignee: Individual
Current assignee: Individual
Priority date: 1944-12-04
Filing date: 1945-12-29
Publication date: 1949-12-27
Anticipated expiration: 1966-12-27

Description

Dec. 27, 1949 F. J. PAVITT ET AL ELECTRIC MOTOR CONTROLLER Filed Dec. 29, 1945 Inventors Fl Pal/iii and H. if Matt/raw y W a.

Afro ney Patented Dec. 27, 1949 UNITED ELECTRIC MOTOR CONTROLLER Frederick J. Pavitt and Harold H. Matthews, Brighton, England Application December 29, 1945, Serial No. 637,850 In ,Great Britain December 4, 1944 Section 1, Public Law 690, August 8, 1946 Patent expires December .4, 19.6.4

8 Claims.

This invention relates to electric motor controllers. The object of the invention is the provision of improvements in electric motor controllers, particularly in respect of the timing of the intervals between the cutting out of resistance sections when starting.

With the above object in View according to the main feature of the invention a starting resistance for the motor is adapted to be cut out in steps by a master controlling device operating in conjunction with a motor driven timing relay which controls the time interval between the cutting out of successive sections of the starting resistance.

The system may include a set of contactors for cutting out the several starter resistance sections whose circuits are made ready for completion by the timing relay, by the completion or the main motor circuits in the case of the first contactor, and by the previous contactor in the case of subsequent contactors. Preferably the last contactor when in inoperative condition makes the circuit of the timing relay motor ready for completion by operation of the master controlling device, so that operation of said device sets the timing relay into operation, and the cutting out of the final resistance section stops the timing relay.

The invention also comprises an improved construction of timing relay which comprises a plurality of sets of stationary contact members which are alernately bridged by one or more bridging contacts moved at a predetermined speed by the timing relay motor. For example, the relay may comprise an insulating disc rotatable through worm gearing by a driving motor, said disc having contact rollers projecting from its surface and adapted to bridge sets of fixed contact fingers. For control purposes the motor shaft may carry an eddy current disc running in the magnetic gaps of one or more electromagnets energised by control windings.

For adjustment purposes the speed of running of the timing relay motor is adapted to be adjusted by a variable resistance, whilst for control purposes the speed of running of the timing relay motor is adapted to be controlled automatically by an electric device, which is deenergised until the final contactor is operated but upon opening of a switch by said contactor becomes energised, so as to stop the timing relay motor immediately its energising circuit is broken. he r si n e ontactor .c i ci cui s ar c tr lled a tern t ly by successive sets f ti ing r l y a ts, wh st preierab y th r to of the timing relay carries a bridging contact for a pair of fixed contacts which replace the switch opened by the operation of the final resistance contactor and cause completion of the timing relay motor circuit through a braking coil. The timing relay may also have its speed controlled by an electrical braking device connected across the last re-. sistance section to be cut out, so as to decrease the speed of the timing relay with increase of motor load. Although the master controller may be of push button or other type, it may With advantage ,be of the drum type, in which case its connections are such that the resistance contactors can only operate in consequence of corresponding movement of the drum and thus only operate at time intervals determined by the timing relay.

In order that the invention may be more clearly understood and readily carried into practice, it is illustrated, by way of example only, by the accompanying drawings, in which:

Figure 1 is a circuit diagram of a D. C. motor control system according to the invention, and

Figure 2 is a perspective view of a construction of timing relay adapted for use in the control system of Figure 1.

The invention is illustrated as applied to a direct current motor starter in which a master controller Dc of the drum type is employed. We provide a timing relay Tr driven by means of a pilot motor Pm and adapted, so long as the pilot motor is running, alternately to bridge momentarily first one set of contacts 2, 4x, then another set of contacts I, 3.7: then the first set of contacts '2, 4:): again, then the second set of contacts again, 'i, 321:, and so on. Normally (that is before starting) the timing relay Tr is at rest With the first set .of contacts 2, 4x bridged. When the main switch C is closed and drum controller Dc is moved to the first forward notch, a circuit through the drum is established via strip 5, stud 6,, Wires 7, 8 and 9, relay contacts M and I l, which energises two contactors Cl, 02 in parallel. These accordi gly .close and thereby establish .a circuit at contacts l2 and i3 through the motor armature A and all sections or starting resistance SR for starting the motor in the forward direction.

Contactor CI upon closing closes auxiliary contacts l4 and through these auxiliary contacts and normally closed auxiliary contacts 1 5 on the .contactor GB for cutting out the last of the resistance sections, an .energisin circuit for the pilot motor is established through variable resistance V1- and Dc and the pilot motor Pm commences to drive the relay. Contactor C2, upon closing, also closes auxiliary contacts 29 but these at the moment effect nothing. But when, after a given time interval, the timing relay Tr reaches the position at which it bridges its second se't of contacts l, 338 a circuit is established energising the contactor C3 for cutting out the first of the resistance sections, said circuit extending from the positive main through the main switch C and drum contact 5, contact stud 6,

wires

1, 8, through the auxiliary contacts 25 of contactor C2, back through the drum again, via wires 2!, 22, contact stud 23, drum contacts 24, 25, wire 26, through the winding of contactor C3, wire 21, and across the contacts I and :c of the said second set of timing relay contacts, and wires l8, 59 to the negative main.

Contactor C3 accordingly closes switch 35, cutting out the first resistance section and speeding up the motor one step. Contactor C3 upon closing closes auxiliary contacts 28 which establish a maintaining circuit via wires 29, 30 direct from the winding of contactor C3 to the negative main.

The contactor C3 upon closing also closes second auxiliary contacts 3 I, but so long as the drum remains at the first notch I, nothing further happens. When the drum is moved to the second notch 2, nothing still happens until the next occasion upon which the timing relay Tr bridges its first set of contacts 2, 4m. When this takes place an energising circuit is established for the contactor C4 for cutting out the second of the resistance sections, said circuit extending from the positive main through the drum as before, through the auxiliary contacts 20 on contactor C2 as before, back to the drum as before, and,by fresh drum contacts 32, 33, closed whenthe second notch is reached, wire 34, through the energising winding of contactor C4, through the second auxiliary contacts 3| on contactor C3, and across the first and the last of the first set of timing relay contacts 2, w to the negative main.

Contactor C4 accordingly closes switch 36, cutting out the second resistance section and speeding up the motor another step. Contactor C4 upon closing closes auxiliary contacts 31 which establish a maintaining circuit direct from the winding of contactor C4 to the negative main via wires 29, 30.

The contactor C4 upon closing also closes second auxiliary contacts 38, but so long as the drum remains at the second notch 2, nothing further happens. When the drum is moved to the third notch 3, nothing still happens until the next occasion upon which the timing relay Tr bridges its second set of contacts 1, Ex. When this takes place an energising circuit is established for the contactor C5 for cutting out the third of the resistance sections, said circuit extending from the positive main through the drum as before, through the auxiliary contacts 20 on contactor C2 as before, back to the drum as before, and, by fresh drum contacts 39, 5, closed when the third notch is reached, wire 4! through the energising winding of contactor C5, through the second auxiliary contacts 33 on contactor C5, and across the second and the last of the second set of timing relay contacts 3, :r to the negative main.

Contactor C5 accordingly closes switch 42, cutting out the third resistance section and speeding up the motor another step. Contactor C5, upon closing closes auxiliary contacts 43 which establish a maintaining circuit direct from the winding of contactor C5 to the negative main.

Contactor C5, upon closing, also closes second auxiliary contacts 44, but so long as the drum remains at the third notch, nothing further happens. When the drum is moved to the fourth notch 4, nothing still happens until the next occasion upon which the timing relay Tr bridges its first set of contacts 2, 43:. When this takes place an energising circuit is established for the contactor C6 for cutting out the fou th of the resistance sections, said circuit extending from the positive main through the drum as before, through the auxiliary contacts 253 on contactor C2 as before, back to the drum as before, and, by fresh drum contacts 45, 46, closed when the fourth notch is reached, wire 42, through the energising winding of contactor C6, through the second auxiliary contacts 44 on contactor C5, and across the second and the last of the first set of timing relay contacts 4, .73 to the negative main.

Contactor C5 accordingly closes switch 48, cutting out the fourth resistance section. Contactor C6, upon closing, closes auxiliary contacts 49 which establish a maintaining circuit direct from the winding of contactor C6 to the negative main.

In the present description contactor is assumed to be the last of the resistance contactors, but it will be quite clear from the preceding description that the number of resistance contactors could be increased indefinitely by adding to the number of timing relay contacts in each of the aforesaid first and second sets 2, laand l, 39: respectively.

When the last contactor C6 closes, it opens the normally closed auxiliary contacts 55 hereinbefore referred to, and interrupts the aforeclescribed energising circuit for the pilot motor Pm of the timing relay Tr. There is, however, a

. second circuit for energising the said pilot motor. This second circuit is in parallel with the circuit passing in series through the auxiliary contact on the contactor C5 and the auxiliary contacts on the contactor Cl, and includes, in series, a cut-out switch 59 on the timing relay and the winding of a brake at which, when energised exercises a drag on the pilot motor. The cut-out switch 59 is normally closed and is only opened when the timing relay is the position for bridging its first set of contacts.

It will therefore be seen that normally, before starting, this second circuit is interrupted at the cut-out switch 50. After the pilot motor Pm has been energised through the auxiliary contacts l4, 15, on contactors Cl and C5, this second circuit will be closed except at those moments when the timing relay Tr is bridging its first set of contacts 2, 401? but it is, however, short circuited by the said auxiliar contacts 1 5, I5, so that the brake winding remains de-energised. When the auxiliary contact l5 on contactor C'S opens, the timing relay Tr will continue by momentum to move until the cut-out switch 5% closes and the pilot motor Pm will now be energised through its said second circuit which includes the Winding of brake 5|. The result of this is that the pilot motor Pm will run dead slow, due to the drag exercised by the brake 5!, and when the timing relay Tr again reaches the position at which the contacts of its first set 2, 511) are bridged, and at which the cut-out switch opens, said pilot motor Pm will instantly stop and the timing relay Tr will not over-run this position. Thus it is ensured that the timing relay Tr will always come to rest at the correct starting position.

It will be appreciated from the preceding description that. if the drumcontroller Do is moved straight from the off position to the lastnotch- 4, the contactors CI-CB will close in the same sequence, with an interval, before the cutting out of each resistance section, determined by the time taken for the timing relay Tr to move from one bridging position to the other. Thus the contactors Cl and C2 will instantly close; the contactor C3 will close when first the second set of timing relay contacts 3a: are bridged; the contactor C4 will close when next the first set of timing relay contacts 2, 4a: are bridged; the contactor C5 will close when next the second set of timing relay contacts I, 3a: are bridged, and the contactor C6 will close when next the first set of timing relay contacts 2, 4:: are bridged.

It will also be noted that when the drum controller Do is notched backwards, the contactors will drop outinstantaneously according to the drum positions without any delay occasioned by the timing relay Tr. It will be noted, however, that the timing relay Tr will be driven when the drum is notched back, until said drum reaches the off position, when the contactor Cl will drop out, opening its auxiliary contact l4 and. de-energising the first circuit of the pilot motor Pm, and the pilot motor will then be energised through its second circuit, at slow speed with the brake 5| on, until the timing relay Tr next reaches the starting position, when the cut-out switch 50 will open and the timing relay Tr will instantly stop at its starting position.

When the drum controller Dc is notched in the reverse direction the operation is extactl-y the same, except that instead of the contactors Cl and 02 closing, two other contactors Glu and 02a, will close, thereby establishing circuits for reverse running. Otherwise, these contactors Cl a and 02a function in the same way as the contactors Cl and C2, and the same contactors C3 to C6 operate for controlling the resistance sections. The pilot motor Pm of the timing relay Tr will of course always run in the same direction.

The main operating circuit of the motor is controlled by main switch C through the normally closed circuit breaker, CB which operates in thenormal manner in conjunction with the usual overload and no voltage releases.

The speed of the pilot motor Pm is adapted to be pre -set over a wide range by connecting one terminal thereof to one end of the resistance Vr and the other terminal to a variable tapping point of said resistance Vr.

The speed of said pilot motor Pm is also adapted to be automatically controlled by means of a control winding 19 which, according to its intensity of energisation, exercises a drag on said pilot motor. This control winding is connected by wires l9 and H across part of the series resistance SR of the main motor, viz across the last resistance section to be cut out, and thus, during the whole of the starting period up to the closureof the last resistance contactor C6, the energisation of said control winding will vary as the load,

of the main motor varies, so that the greater the load on the main motor, the slower the speed of the pilot motor Pm and timing relay Tr and the longer the minimum intervals between the cutting out of successive sections of resistance SR.

It will be readily appreciated that the direct current system above described can be readily re placed. by an alternating current system, the timing relay Tr functioning in exactly the sameway. No further description of this is deemed necessary. It will. also be appreciated that the drum controller DC could be dispensed with and the starter controlled by push button switches, the timing of the cutting out of the resistance sections then depending solely upon the timing relay Tr, much in the same way as if the drum con troller were" moved straight through to the last notch.

In the case of direct current systems only, analternative method of automatic control of the speed of the pilot motor Pm can be adopted. This consists in connecting the pilot motor across the armature A and part of the starting resistance SR of the main motor. The speed of the pilot motor Pm will be controlled by the baclc electromotive force of the armature A of the; main motor, and the speed of said pilot motor Pm" will vary inversely with the loading of the main motor. The resaso-n for using part of the starting resistance SR is to ensure that the pilot mo tor will runwhen the main motor is at a standstill. Resistance will thus be cut out if the main motor fails to start.

In the case of alternating current systems the aforedescribed control winding for the pilot mo tor can be connected, either direct or through a: current transformer in series with one of the starter feeders.

Itwill be seen that in this invention, except for the timing relay Tr, no special apparatus is used,

and the contactors are all standard con-tactorswith. nospecial attachments.

Also the timing relay is universal in its application, the same timing relay serving whether with alternating or direct current schemes or whether the system embodies a master controller or is push button operated. Again the timing re lay has no operating system but simply continues to bridge its two setsof contacts alternately.-

In a preferred construction illustrated by Figure 2, the timing relay Tr comprises a rotatable worm wheel 52, which may be made of synthetic resin, driven through the medium of a worm- 53 on the shaft 54' of the pilot motor. This worm wheel 52 has projecting at right angles from it, at a given distance from its centre, abridging contact in the form of an elongated roller 55 ro tatably mounted on a suitable fixed pin 56. Each set of timing relay contacts 2, 4x or I, 30: con sistsof a row of leaf-spring type contacts 51 parallel to each other and all at right angles to the bridging contact 55-, so" that it simultaneously engages all these when it reaches the appropriateposition. The tWo sets of timing relay contacts are of course diametrically opposite to each other,

sothat, assuming the pilot motor tobe running ata constant speed, the time intervals between the bridging of the tWosets are equal.

Instead of only one bridging contact 55, the: worm wheel may be provided with three located at one hundred and twenty degrees to each other, and two of these may be detachable so that the worm wheel 53 may have either one, two or three. Obviously, if there are three, it simply means that I the bridging of the two sets of timing relay contacts takes place at thrice the frequency, and this gives an additional control to the timing of the starter which, in conjunction with the pilot mo tor resistance Vr hereinto beforereferred to, affords a very wide range of p're-set timing control.

The cut-out as may consist simply of a leafspring contact 58 biased into engagement with a relatively stationary contact 59 and adapted to be engaged by a cam 60- on the worm wheel, and

lifted clear of said relatively stationary contact 59, when said worm wheel reaches the appropriate position. It will of course be appreciated that the opening of said cut-out switch 50 persists through several degrees of movement of the worm wheel 52, and the same applies to the bridging of the sets of timing relay contacts 2, 4a: and I, 3:13.

For applying the afore-described brake 5| to the pilot motor Pm an aluminum eddy current disc 6| is mounted on the motor shaft 54, and the brake winding 62 energises a magnet frame 63 having a gap in which the eddy current disc runs.

The afore-described control winding 10, if such is employed, may, as indicated by the chain dotted lines in Figure 2, energise a magnet frame similar to that energised by the brake winding 5| and having a gap in which the same eddy current disc 6| runs. In the case of a direct current system, this control winding is energised as previously described. In the case of an alternating current system, the control winding may be connected across part of the starting resistance or across two slip ring phases.

The pilot motor Pm is arranged to be considerably under-loaded, and is preferably a series commutator machine suitable for running on either alternating or direct current.

It will be appreciated that the timing relay Tr is essentially nothing but a change over switch with multiple contacts, and thus it may take forms other than the motor driven arrangement described. For example, it could take the form of an electro-magnet with time delay, each impulse of which operates a multiple change-over switch.

We claim:

1. In an electric motor control system, a main motor, resistance sections in circuit with said main motor, electromagnetic contactors having energising windings and adapted, upon energisation of said windings, to close and thereby respectively cut out said resistance sections, a pilot l a set of relay contacts close, which set includes r the contact corresponding to the contactor next due to close, the winding of said contactor is energised, means whereby, upon a contactor closing, its winding is maintained energised independently of its corresponding relay contact, and means whereby, upon closure of the contactor last due to close, said pilot motor is automatical- 1y brought to rest with said timing relay at a given starting position,

In an electric motor control system, a main motor, resistance sections in circuit with said main motor, electromagnetic contactors having energising windings and adapted, upon energisation of said windings, to close and thereby respectively cut out said resistance sections, a pilot motor, a timing relay driven by said pilot motor, said timing relay comprising a plurality of contacts which correspond respectively to said contactors, said relay contacts being divided into sets, which sets are adapted to close in cyclic order repeatedly as said timing relay is driven by said pilot motor, means for energising said pilot motor with the resistance sections all in circuit with the main motor, means whereby, each time a set of relay contacts close, which set includes the contact coresponding to the contactor next due to close, the winding of said contactor is energised, means whereby, upon a contactor closing, its winding is maintained energised independently of its corresponding relay contact, and means whereby, upon closure of the contactor last due to close, said pilot motor is automatically brought to rest with said timing relay at a given starting position, said last named means comprising two circuits through which said pilot motor is adapted to be energised, one of said circuits being interrupted upon closure of said contactor last due to close and the other being interrupted upon said timing relay reaching said starting position.

3. In an electric motor control system, a main motor, resistance sections in circuit with said main motor, electromagnetic contactors having energising windings and adapted, upon energisation of said windings, to close and thereby respectively cut out said resistance sections, a pilot motor, a timing relay driven by said pilot motor, said timing relay comprising a plurality of contacts which correspond respectively to said contactors, said relay contacts being divided into sets, which sets are adapted to close in cyclic order repeatedly as said timing relay is driven by said pilot motor, means whereby, each time a set of relay contacts close, which set includes the contact corresponding to the contactor next due to close, the winding of said contactor is energised, means whereby, upon a contactor closing, its winding is maintained energised independently of its corresponding relay contact, and means whereby the speed of said pilot motor is adapted to be increased and decreased, according as the armature current of the main motor decreases and increases.

4. In an electric motor control system, a main motor, resistance sections in circuit with said main motor, electromagnetic contactors having energising windings and adapted, upon energisation of said windings, to close and thereby respectively cut out said resistance sections, a pilot motor, a timing relay driven by said pilot motor, said timing relay comprising a pluralit of contacts which correspond respectively to said contactors, said relay contacts being divided into sets, which sets are adapted to close in cyclic order repeatedly as said timing relay is driven by said pilot motor, means whereby, each time a set of relay contacts close, which set includes the contact corresponding to the contactor next due to close, the winding of said contactor is energised, means whereby, upon a contactor closing, its winding is maintained energised independently of its corresponding relay contact, and a braking winding for said pilot motor, the energisation of which winding increases and decreases, according as the armature current of the main motor increases and decreases whereby the speed of said pilot motor is adapted to be increased and decreased, according as the armature'current of motor, resistance sections in circuit with said main motor, electromagnetic contactors having energising windings and adapted, upon energisation of said windings, to close and thereby respectively cut out said resistance sections, a pilot motor, a timing relay driven by said pilot motor, said timing relay comprising a plurality of sets of contacts, said plurality of sets together having a number of contacts corresponding in number to said contactors, and said plurality of sets being adapted to be closed in cyclic order repeatedly by rotation of said pilot motor, means whereby the winding of each of said contactors is energised in response jointly to the closure of the relay contact of corresponding number and the closure of the preceding contactor, and means whereby, upon a contactor closing, its winding is maintained energised independently of the relay contact of corresponding number.

6. In an electric motor control system, a main motor, resistance sections in circuit with said main motor, electromagnetic contactors having energising windings and adapted, upon energisation of said windings, to close and thereby respectively cut out said resistance sections, a pilot motor, a timing' relay driven by said pilot motor, said timing relay comprising a plurality of sets of contacts, said plua-rlity of sets together having a number of contacts corresponding in number to said contactors, and said pluralit of sets being adapted to be closed in cyclic order repeatedly by rotation of said pilot motor, means whereby the winding of the first contactor is energised in response to the closure of the first relay contact, means whereby the winding of each of the other contactors is energised in response jointly to the closure of the relay contact of corresponding number and the closure of the preceding contactor, and means whereby, upon a contactor closing, its winding is maintained energized independently of the relay contact of corresponding number.

'7. In an electric motor control system, a main motor, resistance sections in circuit with said main motor, electromagnetic contactors having energising windings and adapted, upon energisation of said windings, to close and thereby respectively cut out said resistance sections, a pilot motor, a timing relay driven by said pilot motor, said timing relay comprising two sets of contacts, the two sets together having a number of contacts corresponding in number to said contactors, and said two sets being adapted to be alternately opened and closed by rotation of said pilot motor, means whereb the winding of the first contactor is energised in response to the closure of the first relay contact, means whereby the winding of each of the other contactors is energised in response jointly to the closure of the relay contact of corresponding number and the closure of the preceding contactor, and means whereby, upon a contactor closing, its winding is maintained energised independently of the relay contact of corresponding number.

8. In an electric motor control system, a main motor, resistance sections in circuit with said main motor, electromagnetic contactors having energising windings and adapted, upon energisation of said windings, to close and thereby respectively cut out said resistance sections, a master controller of the drum type having an on notch and a number of running notches corresponding in number to said contactors, a pilot motor, a timing relay driven by said pilot motor, said timing relay comprising two sets of contacts, the two sets together having a number of contacts corresponding in number to said contactors, and said two sets being adapted to be alternately opened and closed by rotation of said pilot motor, means whereby the winding of the first contactor is energised in response jointly to the closure of the first relay contact and the positioning of said master controller at a running notch, means whereby the winding of each of the other contactors is energised in response jointly to the closure of the relay contact of corresponding number, the closure of the preceding contactor. and the positioning of the master controller be yond the notch of preceding number and means whereby, upon a contactor closing, its winding is energised independently of the relay contact 01 corresponding number.

FREDERICK J. PAVITT. HAROLD H. MATTHEWS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 769,406 Rennerfelt Sept. 6, 1904 945,093 Henderson Jan. 4, 1910 969,583 White Sept. 6, 1910 1,370,019 James Mar. 1, 1921 1,416,024 Hellmund May 15, 1922 1,457,920 Zweigbergk June 5, 1923