Patent GB-695530-A (GB)
Title: Improvements in and relating to electric motor control systems
IPC: B60L15/04
Filed: 1951-10-22
Abstract: 695,530. Control of several D.C. motors. BRITISH THOMSON-HOUSTON CO., Ltd. Oct. 22, 1951 [Oct. 26, 1950], No. 24586/51. Class 38 (iii) A control system for a plurality of series traction motors 1-4 comprises a pilot motor 5 adapted to drive a controller MCC having cam-operated contacts (including reversing and field-shunting contacts) which control the traction motor power circuits, and another pilot motor 8 driving a controller RCC having main fingers operating both in motoring and braking to provide a plurality of resistance-steps. The pairs of motors, 1, 2, and 3, 4, are permanently in series and the series-pairs are connected in parallel for motoring operation. During braking, an appropriate portion of the resistance 7 is included in circuit, the armatures of the traction motors being crossconnected with the field windings of the other pair. The movement of both the controllers MCC and RCC is regulated by a current-limit relay CL having a coil 6 responsive to the main motor current, a lift coil 37 connected across the armature of each pilot motor so that the relay will operate only when one or both of the pilot motors are energized, and a brake coil 38 arranged across a portion of the main motor braking circuit. Each of the controllers is provided with a notching arrangement, the armatures of the pilot motors being short-circuited for stopping in the correct positions. A battery 9 connected to train wires 101-105 supplies the control circuit, and a battery 21 supplies the pilot motors which have reversing field windings. Assuming that the vehicle has stopped after operation in reverse and it is desired to go forward, reversing switch 16 is moved to close contact F and switch 15 is closed to energise coil DRF so allowing relay DR to drop, the relay COR being energised in addition. The pilot motor 5 is then energized through its field winding CCW and the controller MCC is driven from its reverse to its forward section. The forward controller contacts 1f-4f are closed, and afterwards the relay LB and, contacts M1, M2, are actuated to apply power to the traction motors through resistance 7, contact M3 providing a cushioning effect. The controller RCC is first returned to the zero position and, when relay LB is energized, it progresses to remove accelerating resistance under the control of the relay CL. Interlocking between the controllers MCC and RCC ensures that field shunting does not take place until the whole of the resistance 7 has been removed. For coasting operation, switch 15 is released to deenergize relays LB and COR and the controller MCC is returned towards the "off" position until braking contacts B1, B2, are closed. If the vehicle is operating at maximum speed the traction motor field windings are shunted, and sufficient current is allowed through coil 38 to cause the controller MCC to notch slowly under the control of the relay CL. Subsequently full field excitation of the traction motors is restored and the braking resistance is gradually cut out. If the vehicle is coasting and braking operation is desired, switch 14 is opened, the relay BR drops, and the relay CL is re-calibrated to regulate for smaller motor current. In going from coasting to braking operation, switch 14 is closed so energizing relays BR and COR. The controller MCC is returned towards its power position until, at a certain point, the relay COR drops and the controller is reversed. This movement of the controller provides shunting of the traction motor fields to remove braking-effort The contact 14 may be interlocked with the air braking system to cause additional dynamic braking when mechanical braking is applied. The controller MCC may be automatically returned to its "off" position in response to a failure of the battery charging equipment. A master station may be provided to control the traction motors of a number of vehicles forming a train, each vehicle having a separate control circuit supply source with means whereby the control circuit of any vehicle can be energized from that of another vehicle of the train.