GB882625A - Improvements in or relating to electric motor control systems - Google Patents

Abstract

882,625. Control of several D.C. motors. BROOKHIRST IGRANIC Ltd. Nov. 3, 1959 [Nov. 3, 1958], No. 37249/59. Class 38 (3). A control system for a drive having at least three series-wound reversible motors includes dynamic braking means rendered effective when the motors are disconnected from the power supply, the braking means comprising means for energizing the series field winding of each motor by the current generated by one of the other motors in the same direction as the immediately preceding power energization of each such field winding regardless of whether the motors were operated in the forward or reverse direction. As shown, motors 1, 2 and 3 are connected in parallel across positive and negative supply lines L1, L2, the field F1 of motor 1 and the armatures A2, A3 of motors 2 and 3 each being connected in reversing bridge networks, the arrangement being such that with the motors disconnected from the supply armature A2 is in series with dynamic braking resistors DBR1, DBR2 and field F1, armature A1 is in series with resistors DBR3, DBR4, DBR5 and fields F2, F3, and armature A3 is in series with resistor DBR6. In operation, with the operating coil of a relay UV energized, contacts UV1 close to energize a relay DB and contacts UV2 close a point in the energizing circuit of contactors M, F and R. Relay DB opens contacts DB1 to DB6 to interrupt the dynamic braking loop circuits, closes contacts DB7 to energize contactor M and closes contacts DB8 to close a point in the energizing circuit of contactors F and R. Contactor M closes contacts M1, M2 and M3 in the power circuits of motors 1, 2 and 3. Closure of switch SW energizes either contactor F or contactor R which close contacts 1F1 to 3F2 or 1R1 to 3R2 in the reversing bridge networks so that the motors run in the forward or reverse directions as required. If voltage failure occurs, relay UV responds and contacts UV1 and UV2 open to de-energize contactors M, F and DB, thereby opening the reversing bridge contacts and the contacts M1, M2, M3 to disconnect power from the motors, and closing contacts DB1 to DB6 to establish the three dynamic braking loop circuits, the braking effect of one of the motors being reflected in the field excitations of the other motors to maintain braking on all three motors. In a modification (Fig. 2, not shown), armature A1 is connected in series with field F3 and resistors DBR3 and DBR4, and armature A3 is in series with resistor DBR5 and field F2, a rectifier bridge being employed to maintain unidirectional excitation of field F2 with reversal of counter EMF of motor 3. Spring- closed contacts may replace the rectifier bridge (Fig. 3, not shown), or the reversing contacts of motor 3 may be used for connecting armature A3 to field F2 for dynamic braking (Fig. 4, not shown).