GB611509A - Improvements in or relating to electric motor control systems - Google Patents

Abstract

611,509. Control of D.C. motors. IGRANIC ELECTRIC CO., Ltd. May 15, 1945, No. 12166. Convention date, May 24, 1944. [Class 38 (iii)] Where a shunt motor A, which may be supplied through a rectifier 1 from A.C. mains, has a field rheostat providing for speed variation, sudden increase of excitation to reduce the speed of the motor causes a relay to respond to the p.d. across the field winding and thereby a resistance load R to be connected for a predetermined period to absorb regenerated energy and assist retardation of the motor. A relay 4, the actuating winding 4a of which is controlled by a relay 5, closes contacts 4b in response to the rise in potential across the field winding F which results from rapid reduction in the resistance of the field rheostat FR. The relay 5 is actuated momentarily by coils 5a, 5b jointly. The winding 5a is energized through a rectifier 7 by the charging current of a condenser 8 as the potential across field winding F rises, but the winding 5b and also winding 4a can be energized only if a relay 6, which responds to load current of the motor, has not lifted; the relay 5 is thus inoperative during acceleration of the motor. When the relay 5 operates it closes the energizing circuit for relay 4 and this energization is maintained whilst a charged condenser 10 is discharging through the relay coil 4a. Interlock contacts 4d, 4e prevent re-energization of relay 5 and allow condenser 8 to discharge through resistances and a rectifier 9. Acceleration of the motor with a low speed setting of the field rheostat is assisted by a relay 3a in the armature circuit which short circuits the rheostat.