GB429194A - Improvements relating to the control of electric motors in traction systems - Google Patents

Abstract

429,194. Master control of D.C. motors. RAMSDEN, H. K., 26, Ashlands, Ashton-on- Mersey, and ASSOCIATED ELECTRICAL INDUSTRIES, Ltd., Crown House, Aldwych, London. Nov. 28, 1933, Nos. 33349 and 36142. [Class 38 (iii)] Regenerative and non-regenerative braking.-In a traction system in which a motor is accelerated by advancing a master controller from an "off" position, and decelerated by retracting the controller, the initial return movement renders switching means effective to give regenerative braking, while upon further return movement the switching means are effective not only to subject the motor to regenerative braking, but also, in response to the slowing of the motor to a given speed, automatically to subject the motor to rheostatic braking. Movement of the master controller C through its first five positions effects the connection of the driving motor A to the supply, and its gradual acceleration by removal of armature resistance r in steps. Further movement of the controller reduces the shunt field excitation in steps. Upon the return of the controller the motor is regeneratively braked until the third position is reached, whereupon the resistance contactor R3 is opened and opens its auxiliary contacts R3-in so that, when the motor slows to a given speed, and a relay RR responsive to the regenerated current opens it contacts, the line switch LS1 is de-energized and completes at its auxiliary contact LS1 out the circuit for a rheostatic braking contactor B which connects a braking resistance r, b, across the motor. The armature resistance contactor R4 when closed at the fourth position of the controller during acceleration maintains itself over R4 in until the " off " position of the controller is reached during braking. The rheostatic braking contactor B is rendered ineffective during forward accelerating movement of the controller through positions 1-4 by interlock contacts R4-in on the contactor R4. A relay OR responds under over-voltage conditions to energize the contactor B to establish the rheostatic braking circuit independently of the controller. In a modification, the rheostatic braking circuit is connected between the armature resistance contactors R1, R2, so that the armature resistance forms at least part of the braking circuit. In this arrangement the opening of the line contactors deenergizes the contactors R1-R4. In a further modification the interlock contact LS1-out in the circuit of the coil of the contactor B is replaced by an interlock on the resistance contactor R3, and the rheostatic braking circuit is completed with the line contactors closed, the latter being opened upon operation of the contactor B. In still further modifications an interlock between the circuit of the coil B and the line contactor LS1 or the resistance contactor R3 is omitted, and the circuit for the coil of the contactor B is closed at the controller only for the first three positions. The contactor B is prevented from operating during accelerating movement of the controller through the first three positions by the interlock R4-in. The contactor series may have sequence interlocks. The line contactors may be energized over the same circuit when running as for starting, or one of them as shown may maintain itself after being energized in the first position of the controller over contacts as. An additional rheostatic brake or a mechanical power brake may also be provided.