Patent GB-446888-A (GB)
Title: Improvements in or relating to electric motor control systems
IPC: H02P5/747
Filed: 1936-01-21
Abstract: 446,888. *Control of several A.C. motors. WESTINGHOUSE ELECTRIC & MANUFACTURING CO., East Pittsburg, U.S.A.-(Assignees of Bouton, E. M., and Williams, H. W.; 1500, North Branch Street, Chicago, U.S.A.) Jan. 21, 1936, No. 1871. Convention date, Feb. 28, 1935. [Class 38 (iii)] Regenerative and non-regenerative braking.- In a control system for a load, such as an elevator car 10, operable at different speeds, A.C. motors 16, 17 are individually disposed to drive the load at different speeds, and switching means are provided whereby one motor is connected to the A.C. source before the other motor is disconnected therefrom. The car 10 is supported by a cable 11 which passes over a sheave 12 and is attached to a counterweight 13. The sheave 12 is mounted on a shaft 14 which. is driven through reduction gear 15 by a shaft 18 carrying the rotors of the motors 16, 17. The low-speed motor 16 is provided with a large number of poles compared with those on the high-speed motor 17. When the motors are both deenergized, the car is stopped by a brake 19 provided with a shoe which engages a brake wheel 20 on the shaft 14, the brake being released when a winding 19w is energized. The stator windings of the motors are connected to the lines 23 ... 25 through a main switch 22, line contactor 26, up-and-down reversing switches 27, 28 and a transfer switch 29, which, in the de-energized position, connects to the low-speed motor 16. The bridging contacts 30 of the transfer switch are slidably arranged on the operating mechanism and biassed apart by springs 31, so that when the operating winding 29w is energized, the circuits for the high-speed motor 17 are completed before those for the low-speed motor 16 are interrupted. The elevator car 10 is provided with a control switch 54 for controlling the direction and speed of travel of the car. When the main switch 22 is closed, movement of the switch 54 to its first position in either direction energizes one of the up or down relays 57, 58 and a brake control relay 59. Closure of the contacts 57a or 58a of the relays 57 or 58 energizes the winding 27w or 28w controlling the up or down switch 27 or 28, and the winding 26w of the line contactor 26, and the motor 16 is connected to the line. The circuit of the winding 19w is now completed through contact 59a of relay 59 and contacts 26d of the line contactor 26, and the brake 19 is released. In order to operate the car at the high speed, the control switch 54 is moved to the second position, in. which the windings 29w and 41w of the transfer switch 29 and of an accelerating switch 41 are energized, whereby the motor 17 is connected to the line through a contactmaking wattmeter 45 and, after a time delay, resistances 40 in its stator circuit are cut out. The contact arm 48 of the wattmeter engages one of the contacts 49 ... 52 according to the load. The winding 62 of a brake discharge control relay is now energized through contacts 29e on the transfer switch 29 and 26e on the line switch 26. Operation of the relay 62 completes a holding circuit for the windings 26w, 27w, and at the same time opens contacts 62a controlling the amount of resistance in the discharge circuit of the winding 19w. If the control switch 54 is now restored to its first position, the motor 17 is de-energized and the motor 16 reconnected to the line to act as a brake. The stator winding of the motor 16 is provided with resistances 32 ... 35, the first three of which are braking resistances adapted to be short-circuited by relays 36 ... 38 having operating windings 36w ... 38w connected to the contacts 50 ... 52 of the wattmeter 45, in order that the braking effect may be adjusted to the load. The resistances 35 are used for inching and are controlled by a relay 39 having an operating winding 39w controlled by normally closed contacts 62c on the relay 62, and by contacts 27d, 28d on the up and down switches 27, 28. After a time interval, contacts 29e on the transfer switch 29 open to de-energize the relay 62. If it is now desired to stop the car, the control switch 54 is moved to the off position, when the motor 16 is de-energized and the brake 19 is applied. If it is desired to stop the car rapidly from the high-speed position, the control switch is at once moved to the off position. Owing to the time delay in the opening of the contacts 29e on the transfer switch 29, the relay 62 remains energized for a time, and its contacts 62a remain open, thereby allowing the releasing winding 19w of the brake 19 to discharge rapidly and set the brake at the maximum speed. In stopping the car from the low-speed position, the relay 62 is not energized, and the contacts 62a are closed, so that the winding 19w discharges more slowly and the brake is set at a slower speed.