GB659945A - Improvements in or relating to electric motor control systems - Google Patents

Abstract

659,945. Control of D.C. motors. WESTINGHOUSE ELECTRIC INTERNATIONAL CO. May 9, 1949, No. 12325. Convention date, May 21, 1948. [Class 38(iii)] A control system for a plurality of electric motors having series field windings comprises a plurality of acceleration controllers for controlling the motor current, a reversible pilot motor for driving said acceleration controllers in unison, switches co-operating with said acceleration controllers to connect the motors first in series-circuit relation and then in parallelcircuit relation, and additional switches co-operating with said acceleration controllers to establish dynamic braking connections for the motors, said acceleration controllers during both series-circuit and parallel-circuit operation being operated by the pilot motor in one direction during acceleration and in the opposite direction during dynamic braking. Traction motors TM1. TM2, are connected in series when switches LS1, G, S1-S4 are closed, the motors being accelerated when a reversible pilot motor PM drives rollers 31, 32 and 41, 42 towards the left from the position shown, so removing portions of sectionalised resistors 33, 34 and 43, 44. The resistor-sections are connected to contact-fingers which are forced against bus-bars when engaged by the rollers. When the rollers reach the sixth positions (shown dotted), switches LS2 and J are closed to establish a transition bridge circuit for the motors; switches S1-S4 are then opened and switches P1-P4 closed, the transition from series to parallel connection of the motors being completed when switch J is opened. During parallel operation the rollers are moved leftwards from the seventh to the tenth, end, positions, controllers F1, F2 then being actuated to shunt the series field windings of the motor step-by-step until maximum speed is reached. Coasting is provided by opening switches LS1, G, LS2, P1-P4, the controllers F1, F2 remaining in the position providing minimum field excitation. Switches B, B1-B4 are closed to establish dynamic braking connections, but since the motors have minimum field excitation and the total armature resistance is included, only a small braking-current is developed during coasting. The braking connections are such that field windings 14, 13 are respectively placed across armatures 11, 12, thereby reversing the armature currents and causing the motors to act as generators. The braking-effort is increased by increasing the field excitation and then moving the rollers from the tenth to the first positions, thereby removing resistors 33, 34, 43, 44. The operation of the rollers may be automaticaJly controlled by current-responsive relays. The controllers F1, F2 may be operated by an air engine.