Patent GB-480453-A (GB)
Title: Improvements in or relating to electric motor control systems
IPC: B60L15/36
Filed: 1936-09-04
Abstract: 480,453. Control of D.C. motors. GENERAL ELECTRIC CO., Ltd., CROFT, E. H., and TURRALL, J. C. Sept. 4, 1936, No. 24235. [Class 38 (iii)] In a traction system wherein the motors of a plurality of vehicles, are supplied in parallel and in which backward movement of the motor controller, on a vehicle, towards the off position effects regenerative operation of the motor, automatic over-voltage protective means for braking the vehicle is effective only during regenerative conditions, being rendered inoperative by current flow in the motoring direction. Each vehicle motor, Fig. 1, comprises a reversing switch 2 for the armature 1, series field 3 and shunt field 4, and is fed from trolleys 7, 8 through manually operated circuit breakers CB1, CB2, and a controller which in known manner first closes line switches LN, LP to start the motor as a series motor, then closes contactors S1, S2, S3, for maximum shunt field and then cuts out the series resistance 5 step-by-step by contactors R1 ... R4, Further movement of the controller by opening S2, S3 weakens the shunt excitation and by opening S1 converts the motor into a series motor, regeneration being obtained when the controller is moved backwards to increase the shunt excitation. The over-voltage protective relay S, Fig. 2, comprises a magnetic circuit 10, and series and voltage coils SC, VC, Figs. 1, 2. The series coil SC is carried on a rotary armature 11 biassed in the clockwise direction by a spring. During regeneration the series coil SC assists the spring to bridge contacts 13 by member 12, and when the motor terminal voltage exceeds a predetermined value the armature 15 of the voltage coil VC bridges contacts 14 to energize the coil 9C of contactor 9 whereby a loading resistance LR is connected across the motor armature. During motoring however, over-voltage conditions produced for example by another trolley bus, do not operate the contactor 9 as the contacts 13 are not bridged since the biassing spring is opposed by the coil SC. Modifications. The over-voltage relay may have series and voltage windings which oppose each other during motoring but assist each other during regeneration to close contactor 9 to insert the loading resistance LR. The relay may however be dispensed with, the contactor being provided with the shunt and series coils. In another arrangement, a polarized relay is adapted to render the over-voltage relay, connected across the motor terminals, inoperative during motoring. The polarized relay is energized by the motor current or a proportion thereof and closes its contacts only during regeneration, these contacts being in series with the contactor coil 9C and the normally open contacts of the over-voltage relay. Alternatively the contacts of the polarized relay are connected in series with the coil of the over-voltage relay and the contacts of the latter in series with the contactor coil 9C. The over-voltage relay may be dispensed with, however, the contactor itself being adapted to close at the predetermined over-voltage, in which case the contactor coil is in series with the contacts of the polarized relay. The vehicle may be provided in addition with a pedal for giving regenerative braking and, if desired, rheostatic or, and, mechanical braking.