GB526750A - Improvements in and relating to the control of electric motors - Google Patents

Abstract

526,750. Reversing control of A.C. motors. BRITISH THOMSON - HOUSTON CO., Ltd. March 9, 1939, No. 7696. Convention date, March 9, 1938. [Class 38 (iii)] A split-phase motor, controlled by a reversing switch 19, has its starting connections changed by a speed-responsive switch 14, and a relay 22 is provided for the purpose of making reverse starting connections when the switch 19 is thrown, independently of movement of the switch 14 to its starting position, so that reverse torque is immediately exerted without waiting for the switch 14 to operate. With the switch 19 on contact 20 the primary windings 11, 12 are connected to the supply, a condenser 10 being in series with the winding 11. As the motor revs up to speed the centrifugal switch 14 moves -to contact 17 opening the circuit of the winding 11. The relay 22 is energized to open its contacts by connection across the condenser 10 when the switch 14 is in its starting position, and is maintained while the switch 14 is in its running position by connection in series with the winding 11. The motor is reversed by throwing the switch 19 to contact 21 the relay 22 dropping out so that the windings 11, 12 are connected to the supply directly in parallel. The motor is thus braked and when the switch 14 moves to contact 16, the condenser 10 is connected in circuit with the winding 12. The relay 22 is re-energized and the motor reverses, after it has come to rest. The switch 14 again moves to its contact 17 to cut out the winding 12. In a modification; Fig. 2, where the motor has a running winding 23 and a starting winding 24, reversal is effected by a switch 25 which reverses the winding 24 the relay 22 being de-energized as the switch 25 is thrown over and effecting connections for the winding 24 while the switch 14 is in its running position. The motor is subjected to a reverse torque while it decelerates to standstill, and the switch 14 controls the cutting out of the starting winding 24 as the motor accelerates in the reverse direction. In a further modification the motor has a condenser in that circuit of the starting winding 24 made by the switch 14 in its starting position. In other modifications, Figs. 4 and 5, not shown, the braking of the motor with a reverse torque is effected with a condenser or resistance additional to the starting condenser in circuit with one of the windings 11, 12.