Improvements relating to control systems for electric induction motors

摘要

719,032. Control of A.C. motors; electromagnetic relays. HOOVER, Ltd. Jan. 22, 1953 [Jan. 26, 1952], No. 1920/53. Classes 38(3) and 38(5) A control system for a split phase electric induction motor having a pair of windings 3. 4 with angularly spaced axes has means-such as a manually operated switch 11- for connecting either winding at will across the A.C. supply 1, 2 whilst at the same time connecting the other winding, in series with a phase shifting impedance 30 and a plurality of contacts 17, 18; 171, 181 across the supply, and further means-such as electromagnetically operated relays 7, 8-energized by the current flowing in one of the windings for opening the contacts after a period of delay. The relays 7, 8 offer a time delay to the operation of contacts upon energization of the operating coils but upon de-energization of the coils the contacts operate instantaneously. Thus in placing the arm of the switch 11 to contact 9 for forward running the winding 3 is placed in series with the operating coil 28 of relay 7 across the supply 1, 2 thus energizing relay 7. At the same time winding 4 is placed in series with a condenser 30, contacts 171, 181; 17, 18 (the latter two not yet having been opened) and energizing coil 28 across the supply. The motor starts up with winding 3 on the running winding and winding 4 as the starting winding. Upon energization of coil 28 a core 27 will begin to rise against a spring 32 and the oil in a cylinder 26 until when it reaches the top thereof, an armature 23 will be attracted to the core thus opening the contacts 17, 18 to remove the starting winding 4 from circuit. To reverse the motor the switch 11 is moved to contact 10. The armature 23 immediately resumes its normal position since coil 28 becomes de-energized, windings 3 and 4 reverse their roles thus braking the motor to a stop and accelerating it in the reverse direction until when the core 271 reaches the limit of its travel, armature 231 is attracted, contacts 171, 181 open and winding 3 now the starting winding is removed from circuit. A copper member 29 forms a short circuited coil to prevent chatter of the relays.