US1732712A - Variable-voltage-control system - Google Patents

Description

Uct. 22, 1929.

E. M. BOUTON Er AL 1,732,712

VARIABLE VOLTAGE CONTROL SYSTEM Filed Feb. 6, 1922 i 21 I Q E /sr: 5 fZaZ /W\? D Ed INVENTORS d fla ATTORNEY tion.

Patented 0a. 22, 1929 UNITED STATES PATENT OFFICE EDGAR E. BOUTON; OF EAST PITTSBURGH, PENNSYLVANIA, AND CRANFOBD P. WALKER, Q1? LOS ANGELES, CALIFORNIA, ASSIGNORS '10 WESTINGHOUSE ELECTRIC MANUFACTURING COMPANY, A COBIPOBATIQA' 0E PENM$YLVANIA VABUaELE VQLTAGE-CQN 551E033 SYSTEM.

implication. .Ee'hruary 8, 1.9522. Serial .Tfo. 534,434.

@ur invention relates to motor-control systerns and ithas particular relation to such systems of control as are employed In con: nection with elevators, hoists and similar machines.

One object of our invention is to provide means for controlling the eflect of the field excitation of a generator that is employed for supplying energy to a hoist motor.

Another object of our invention is to provide a system of elevator control that is automatic in its operation, within certain limits, for effecting accurate stops of the elevator car independently of the skill of the car operator.

We propose to employ a system embodying what is known as the Ward Leonard connec- For controlling the stopping or retardation of the hoist motor, we employ a 'relay having its operating coil connected in series relation with the separately excited field-magnet winding of the generator. A suitable circuit is established by the relay contact members when the field winding is f-normally energized. Switches are provided for reversing the generator field winding and have back-contact members for completmg a discharge path in shunt relation to the generator field-magnet winding.

When the reversing switches are opened to deenergize the field-magnet winding, a discharge circuit is maintained through the operating coil of the above-mentioned relay, until the field current has reached a predetermined low value, whereupon the relay in terrupts the field discharge circuit. A. circuit .is then established through back-contact members of the relay,whereby the separately excited field-magnet winding of the generator is connected across the generator-armature terminals in such relation as to de-energize the generatorfield-winding. The foregoing method of controlling the generator-field magnetization prevents too rapid deceleration of the hoist motor.

The elevator car is normally controlled by addition, a rheostat is provided in the car for controlling the field excitation of the generator. For insuring accurate. stopping of a diagrammatic representation of circuits and apparatus embodying our invention.

Fig. 2 is a simplified diagrammatic view of the main circuits illustrated in Fig. 1.

Referring particularly to Fig. 1, a hoist motor having an armature 1 is connected in a loop circuit that receives energy from a enerator having an armature 2 and a series aid-magnet winding 3. Any suitable means may be provided for driving the generator armature. The separately excited fieldmagnet windings 4: and 5 of the motor and generator, respectivel are supplied with energy from any suitable source, represented as a battery 6. Mechanically interlocked reversing switches 7 and 8 control the connec= tions of the generator separately excited fieldmagnet winding.

A relay 9 is provided with an operating coil 10 for connection in circuit with the separately excited field-magnet winding 5 of the generator. During normal operation of the generator, the relay coil 10 is energized to interrupt a circuit through a back-contact member 11 of the relay 9. Therefore, upon opening the circuit of the separately excited field-magnet winding 5 by means of reversin switch 7 or reversing switch 8, a local circuit is established, comprising the fielddnagnet winding 5, relay coil 10 and an adjustable resistor 12 of low ohmic value.

At a predetermined value of the generator field current, relay 9 opens the circuit through resistor 12 and closes a circuit through the contact members 7 and 8 of reversing switches 7 and 8 to connect the field-magnet winding 5 in shunt relation to the generator armature 2. In this manner, the generator field current is first controlled in accordance with the value of resistor 12 and then is en- In tirely; dissipated by connecting the field-mag net winding in proper relation to the generator armature, which is then supplying a voltage opposed to that of the fi -magnet winding 5. The efiect of this connection of the separately excited field winding of the generator is to completely demagnetize the generator field, overcoming the normal residual' magnetism of-the field iron and the magnetizing effect of the series field winding. The volta e of the generator is thus reduced to zero and t e motor is stopped. Obviously, the inherent characteristics of such connection are such as to effect a dynamic-braking action the force of which is proportional to the current in the motor armature circuit and, hence, proportional to the load on the motor. Deceleration' of the armature 1 is smoothly effected and any tendency towards creepage of the elevator is eliminated upon complete demagnetization of the generator field windmg by a relay 14, in a well-known manner, for assisting in stopping the armature 1 and for maintainingit in its inoperative position. An elevator car 15, whichis adapted to be driven by the armature 1, is controlled by a car switch 16 and a generator-field-rheostat 17; the lattermay be independently operated or may be operativel connected to the car switch. In the (fi position of the car switch 16, a slow operating speed of the hoist motor may be obtained by means of an auxiliary switchin .mechanism having up and down reversing switches 18 and 19, respectively. v

A cam 21 is located adjacent to the path of the car at each floor and cooperates with contact members 18 and 19. Various safety devices which are not essential to the operation of our system have been omitted from the drawing. We have,- however, provided overtravel limit switches 22 and 23 and an overspeed governor switch 24 that is con.- trolled in accordance with the speed of the motor armature 1.

Referring particularly to Fig. 1 of the drawing, we may assume the elevator car 15 to be at the second floor, the control switches in their inoperative, or illustrated, positions, and the armature 2 of the generator operating at normal'speed with no field excitation.

To operate the car to the third floor, the car switch 16 is actuated to the right from its illustrated osition, thereby establishing a circuit for t e operating coils of the reversing switch 7 and of the brakerelay 14 extending from the positive terminal of battery 6, through overspeed governorswitch 24, limit switches 22 and 23, operating coil of relay 14, operating coil of reversing switch 7, and car switch contact members 25 and 26, to the negative terminal of the battery 6.

' Reversing switch 7 and relay 14 thereupon close to complete circuits for the generator shunt field-magnet winding 5 and the operating coil of electromagnetic brake 13, respectively, the latter having its operating coil A n electromagnetic brake 13 is controlledi am directly connected, through the relay 14, to the battery 6. A circuit for the field-magnet windin 5 extends from the positive terminal of the attery 6, through conductor 27, contact member 7 of reversing switch 7 fieldmagnet winding 5, relay coil 10, contact member 7 of reversing switch 7 and rheostat 17, to the negative terminal of the battery 6.

The consequent release of electromagnetic brake 13 permits the hoisting motor to operate at a slow speed, which is determined by the field excitation of the generator. field rheostat 17 is next operated to reduce the amount of resistance in the generator fieldwinding circuit and to effect a corresponding increase in the voltage generated and delivered by the generator armature to the armature 1 of the hoisting motor.

The energization of the field-magnet winding 5 cfi'ects the closure of relay 9 by means of operating coil 10, the energizing circuit for which has already been traced. The function of relay 9 is to control circuits that are established during slow-down of the hoisting motor, as will be described later.

It will be noted that the series field. winding 3 for the generator 2 will be excited in proportion to the load upon the elevator motor 1 and will efiect an increase or decrease in the total field strength of the generator 2 to correspond to the variations in load upon the elevator car 15. That is, with a heavy lifting load, the field strength of the generator 2 will be built up correspondingly, and, with a descending overhauling load, the field strength will be weakened correspondingly, thereby producing a regulating effect upon the motor 1 to maintain the speed of the motor' substantially uniform under various' loading conditions.

As the elevator car 15 approaches the third floor, the car switch 16 is returned to its inoperative or Oil position to eflect a landing. In case the car 15 tends to stop before attaining the level ofthe third floor, switch member 18 is actuated by the cam 21 to maintain a slow operating speed of the hoisting motor by establishing contact between the stationary contact member 28 and the movable switch member 18, which are electrically connected to contact members 26 and 25, respectively. The operating circuit previously traced is, therefore, maintained until the car attains the desired level.

It is assumed that, prior to the release of car switch 16 by the operator, the desired slow operating speed is eflected by manipulation of the rheostat 17 so that there is suflicient energy supplied from the generator to the motor armature 1 to insure response to the actuation of the leveling-switch member 18. When the car 15 is substantially level with the third floor, switch members 18 and 19 assume positions corresponding to that illustrated, with respect to the cam 21, and

The

the circuit for reversing switch 7 and brake relay 14 is interrupted by the separation of switch member 18 from stationary contact member 28.

Upon opening, reversing switch 7 establishes a circuit, through its back contact member 7, that provides a discharge path for the 9 to the other terminal of field-magnet winch ing 5.

When the current in the generator separately excited field Winding has fallen to a suitable value, relay 9 opens and establishes a circuit through its back-contact member 11 to connect the field-magnet Winding 5 across the terminals of the generator armature 2.

. The connections are predetermined in such manner as to insure complete de-energization of the field-magnet winding 5, as previously explained.

It may be assumed that current originally traversed the armature 2 in the direction indicated by the corresponding arrow, prior to stopping the car at the third floor. It may also be assumed that the current traversing field-magnet winding 5 flowed in the direction indicated by the corresponding arrow.

It will be noted that the current in the winding 5 flows in the opposite direction to the current traversing the armature 2, when the armature and field-magnet windings are connected through the back-contact member 11 of relay 9.

The circuit through field-magnet winding 5 at this time extends,-through the relay coil 10, back-contact member 7, relay contactmember 11, armature 2, and back-contact member 8 to field-magnet winding 5.

If, however, the flow of field current is in the opposite direction to that first assumed, the main current through generator armature 2 also flows in the opposite direction, and, since the relative directions of'currents are, in this case, the same, the resultant effect is unchanged, whereby complete discharge of the generator field-magnet winding 5 is insured, irrespective of the direction of the operating current traversing the armatures 1 and 2. The direction of this operating current, of course, is normally determined by the direction of the current through the generator field-magnet winding 5 and is controlled by reversing switches 7 and 8 and in a wellknown manner. v a

The value of the current supplied to the separately excited field winding 5 of the gen.- erator 2 under these conditions will obviously armature 2, before slowin armature 1 is control ed thereby. Under cer' tain load conditions of the elevator, a slight field excitation is sufiicient to cause the armature 1 to rotate at a very slow or creeping speed in spite of the setting of the brake 13. This actien is detrimental to the control of the elevates", since is desirahie to eiiect accurate stoppin ndependentiy oi the load in the eleva e v. r

use he understand that, in pass-sli ger are new: service particularly, it is net desiraine, stopping, to immediately connect the shunt field-magnet winding 5 in the previousiy described reversed relation to the down the elevator, because reduction in the speed of armature 1 is thereby efi'ected too abruptiy. We have, therefore, provided a relay 9 which is controlled by the excitation of the field-magnet winding ii in such manner as to insure a predetermined degree of slow down of the hoisting motor prior to establishing these re versed field-winding connections.

In case the elevator operator failed to release the car switch 16 soon enough,-the car 15 would travel beyond the level of the third floor. switch member 19 to engage stationary contact member 28, thereby completing a circuit for the reverse direction of operation of the armature 1 by effecting the closure of reversing switch 8 and brake relay 14 and the consequent release of the electromagnetic brake 13. The circuit for the operating coils of relay 14 and switch 8 extends from one terminal of battery 6, as previously traced, through governor switch 24, limit switches 22 and 23, the o erating coils of relay 14 and switch 8, an contact members 19 and 28, to the other terminal of battery 6. The control system for eiiecting movement of the car downward, within the leveling zone, which movement is controlled by the cam 21, is similar to that described for the upward motion.

Operation of the elevator downward, b the movement of the master switch to the le t of its illustrated position, is effected in a manner similar to the u ward movement and is so well understood by those "familiar with elevator operation that it is-considered unnecessary to further explain the details of operation.

In practice it will be found advantageous to control the rheostat 17 in accordance with the movement of the car switch 16, so that minimum field excitationis provided prior to returning the car switchto its inoperative position.

Our system ofcontrol is simple and eflec- In such case, cam 21 would actuate tive and the automatic control of the field excitation, durin deceleration of the elevator, has been foun to be of great value in connection with a Ward Leonard system. Other means for controlling the relay 9 are at once apparent, as for example, to connect the operating coil 10 acrossthe terminals of the armature, or to otherwise control it in accordance with the speed of the hoistin motor. If desired, the relay 9 may be contro led by a time-limiting device of any well known character, such as a dash pot.

Modifications of our system will be apparent to those familiar with the art and may be made without departing from the spirit of our invention. Therefore, we do not wish to be limited to the exact methods that we have found preferable.

We claim as our invention:

1. The combination with a generator and a motor electrically connected thereto, of means for controlling the degree of excitation of a field-magnet winding of said generatonand a switch controlled in accordance with the value of the field current for further controlling the excitation of said winding.

2. The combination with a motor and a gen- I erator for supplying energy to the motor, of

a source of energy for a field-magnet winding of said generator, a discharge circuit, efi'ective u on failure of said energy, for controlling the rate of change in the field current, and a relay controlled in accordance with the value of said field current for controlling said discharge circuit.

3. The combination with a motor and a generator for supplying energy to the motor, of electro-responsive means for connecting a field-magnet winding of said generator in a closed circuit of low resistance and for thereafter automatically connecting the armature and the field-magnet winding in a closed circuit, to effect a gradual reduction in speed of said motor.

4. The combination with a generator havnet winding thereon and means, comprising reversing switches and a relay controlled in accordance with the value of the current traversing said winding, for connecting said winding 1n shunt relation to the generator armature to effect, de-energization of said field magnet.

6. The combination with an elevator car and a hoisting motor therefor, of a generator for controlling the motor, a reversing switch for controlling the effect of a field-magnet windin of said generator, a switch controlled y the movement of the car for controlling the reversing switch, and a relay controlled in accordance with the value of the generator field-current for further controlling the generator.

7. The combination with an elevator car and a hoisting motor therefor, of a generator for controlling the motor, means controlled in accordance with the movement of the car for controlling the field excitation of the generator, and means controlled in accordance with the value of the generator field-current for further controlling said generator.

8. The combination with an elevator'car and a hoisting motor therefor, of a generator for controlling the motor, a switch controlled in accordance with the movement of the car for controlling the efl'ect of a field-magnet winding of said generator, and a switch controlled in accordance with the value of the current traversing said winding for further controlling the generator.

9. The combination with an elevator car and a hoisting motor therefor, of a generator having a shunt type field-magnet winding for controlling the motor, reversing switches for the field-magnet winding controlled in accordance with movements'of the car, and a relay Y co-operating with the reversing switches and controlled in accordance with the value of the current traversing said fieldmagnet winding, for controlling said generator.

10. The combination with an elevator car and a hoisting motor therefor, of a generator having a shunt type field-magnet windin for controlling the motor, reversing switches for the fieldmagnet winding'controlled in accordance with movements of the car and a relay, co-operating with the reversing switches and controlled in accordance with the value of the current traversing said field-magnet winding, for controlling the effect of said field-magnet winding.

11. The combination with an elevator car and a motor therefor, of a generator having a shunt type field-magnet winding and electrically connected to the motor, reversing switchesfor controlling the shunt-fieldmagnet winding, a switch controlled by movements of the car for controlling the reversing switches, and a relay co-operating with said reversing switches and controlled in accordance with the value of the current traversing said field-magnet winding for modifying the efiect of said reversing switches.

12. The method of decelerating a motor connected in circuit with a generator which consists in interrupting the generator field- Winding circuit, establishing a discharge circuit for the field-magnet winding to control the rate of decay of the field magnetization and. finally interrupting the discharge circuit at a predetermined value of field cur- Ifent and connecting the field-magnet winding in circuit with the generate! armature to entirely dissipate the energy of said generator field.

In testimony whereof, we have hereunte subscribed our names this 10th day of January, 1922, and this 19th day of January, 1922, respectively' EDGAR M, BOUTON, GRANFORD P

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