Patent GB-766920-A (GB)
Title: A control system for self-excited traction motors
IPC: B60L7/04
Filed: 1954-09-03
Abstract: 766,920. Control of D.C. motors; controllers. LICENTIA PATENT-VERWALTUNGSGES. Sept. 3, 1954 [Sept. 11, 1953; Sept. 26, 1953], No. 25618/54. Class 38(3) Traction motors are adapted for seriesparallel regulation and are started and controlled by means of a cam controller clutched to a small pilot motor. -In order to provide rapid and smooth rheostatic braking operation, the controller may be initially driven at high speed until the resistance in the motor circuit reaches a value allowing the motor fields to be excited, whereupon the controller is halted for a period to allow the full excitation of the motors to be attained. The controller is then advanced in a step-by-step manner under the control of a relay responsive to the current in the motor circuit. To initiate the starting operation in the forward direction, drums 1a and 1b are positioned to energize coil V of reverser, 2 so that switche 5a closes contacts 511a, 513a, 514a, and power switch 3 closes contacts 304. A relay 19 is energized to complete the circuit of a pilot motor 23 and to energize a magnetic clutch for coupling the pilot motor to a main cam controller (not shown) for the switchgear in the traction motor circuit. When the cam controller reaches its first operative position, a drum 4 is driven to open contact 413 and uncouple the motor from the cam controller. To complete the series-connection of the traction motors, the drum 1b is moved to close contact 112b so that the pilot motor is re-coupled to the cam controller. When the current in the traction motor circuit reaches a predetermined value, a relay 16 closes contacts 161, 162, and a slow-acting relay 8 de-energizes relay 19, the clutch remaining energized, however, until the cam controller has completed its step whereupon a locking pawl falls into a recess and breaks the circuit of the clutch. This causes energization of a holding relay 17 which short-circuits a resistor 24 in the field circuit of the pilot motor and so reduces its speed. The holding relay also breaks the circuits of relays 16 and 8, and the latter, after a delay period, couples the pilot motor to the cam controller. A relay 14 responds when the current in the traction motor circuit reaches a high value whereby a slow-acting relay 15 is energized to operate relay 8 and interrupt further movement of the cam controller. As long as the high current condition in the traction motor circuit persists, the relays 14 and 15 operate intermittently to keep the relay 8 energized, further stepping of the cam controller being allowed when the traction motor current has fallen to a set value. This cycle is repeated when the motoring current again rises until the cam controller reaches the end position of the series-connection. To obtain the parallel motoring stage, the drum 1b is moved tc close contacts 113b, the cam controller being turned from the last series-position into the parallel positions. When a dead man's handle is released, or the. drum 1b is returned to the zero position, the power switch 3 is de-energized and the cam controller is returned to the " off position. To institute braking operation, the drum 1b is moved to close contact 114b, the power switch 3 being open and the changeover switch 5b being moved to close contacts 502b, 503b, 504b. The cam controller is turned from the zero position, whilst a relay 10 is de-energized to adjust to suitable values the calibrating resistors 11, 12, for the relays 14, 16. In braking from a high travelling speed, the traction motor fields are immediately excited, the relays 16 and 14 being immediately operative to regulate movement of the cam controller in a manner similar to that described. The pilot motor is connected to a lower supply voltage and runs with full excitation more slowly than during motoring. In braking from low travelling speeds, the braking current is not immediately built up and the cam controller runs at high speeds until a resistance stage is reached in which the relay 16 responds to halt the controller.