GB603515A - Improvements in and relating to electro-magnetic control gear for dynamo-electric machines - Google Patents

Abstract

603,515. Control of A.C. motors ; electromagnetic switches. ENGLISH ELECTRIC CO., Ltd., and PEARSON, E. Oct. 22, 1945, No. 27818. [Classes 38 (iii) and 38 (v)] A starting device for an alternating-current motor having a starting and a running winding comprises an operating coil 1 which is connected in series with the running winding, two ferro-magnetic members 2 and 4 which are relatively movable and are arranged to separate when the coil 1 is energized, and switch contacts 5 and 9 which are operated by such movement to maintain the starting winding in circuit when the motor-current is above a predetermined value and to disconnect the starting winding when the motor current falls below that value. The ferro-magnetic member 2 carries a terminal block 3. The member 4 is mounted on a spring strip 6 which is provided with a copper disc 7 for eddy-current damping. A spring strip 8 carries the contact 9 which is adjustable relatively to the contact 5 by means of a cam 10. A bimetallic strip, 11, which is connected in series with the motor-running winding, mounts a contact 12 co-operating with a contact 13 on the strip 8 to afford an overload release. An auxiliary heater with or without a reflector may be placed near the strip 11 which may be so located as to be influenced by the temperature of the motor windings. The strip 6 can be bimetallic to increase the contactpressure between the members 5 and 9 when the strip carries current. The member 2 may be spring-mounted. The strip 11 may carry additional contacts to provide warning on overload. Preferably the coil 1 is provided with a casing of magnetic material which is dust-proof or allows for evacuation of air from the switch-working space or oil immersion of the working parts. The whole assembly may be built into or on to a suitable part of the motor, may form the motor terminal box, or may be disposed remotely from the motor.