GB721584A - Improvements in and relating to electric motor control systems - Google Patents

Abstract

721,584. Control of D.C. motors. BRITISH THOMSON-HOUSTON CO., Ltd., and CARTER, H. F. Aug. 27, 1951 [Sept. 13, 1950], No. 22528/50. Class 38 (3). A vehicle is driven by an electric motor M having a series field winding SF and a shunt field winding S, accelerating resistances R1, R2, R3, being connected in series with the armature of the motor. When a master controller is moved to its first position, contact P1 is closed to energize contactors 1A, 1, and to connect the motor to the line through contacts 1<SP>1</SP>, 1A<SP>1</SP>. Interlock 1A<SP>11</SP> closes to energize contactor 5, so closing contact 5<SP>1</SP> and energizing the shunt field winding to provide low-speed operation of the vehicle. Movement of the master controller to a second position closes a contact P2 to energize cyclically-operated relays T1, T2, T3, in turn. This sequential operation is due to the fact that energization of relay Tl opens contact T1<SP>1</SP> to remove a shortcircuit from the coil of relay T2, whilst energization of relay T2 opens contact T2' to remove a short-circuit from the coil of relay. T3. When contacts T2" close, contactor 2 is energized and contacts 2' remove resistor R1 from the motor circuit, whilst contacts 2<SP>111</SP> de-energize the contactor 1. Energization of relay T3 opens contact T3" to prevent further cyclic operation of the relays T1, T2, T3. However, when the master controller is moved to its final position, contacts P3 are closed to short-circuit the relay coil T1, and, after a period of delay, the relay Tl drops to recommence the cyclic operation of the relays. The de-energization of the relay Tl closes contacts T1<SP>11</SP>to energize contactor 3 and close contacts 3<SP>1</SP>, so short-circuiting resistors R1, R2. When the relay T2 drops after a further delay, the contactor 1 is re-energized. The contactor 4 is energized to remove a further portion of the armature resistance when the relay T3 drops. Relays Tl, T2, T3, are then successively energized, the contactors already closed being retained by interlocks. When the relay T1 drops at 'the start of another sequence, the contactor 2 is re-energized to connect the motor directly across the supply. The opening of relay T2 partially diverts the series field winding and opens the shunt field circuit. When the relay T3 opens, the series field winding is fully diverted. The control sequence may be halted by moving the master controller to its second position or by the intervention of a current-limit relay. After contacts P1, P2, P3, have been opened, braking is instituted by closing contacts Bl and B1', the shunt field winding being energized and a resistor connected across the armature of the motor and the series field winding.