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603,387. Control of D.C. motors. GENERAL ELECTRIC CO., Ltd., and TURRALL, J. C. Oct. 19, 1945, No. 27522. [Class 38 (iii)] Varying field.-When the speed of a motor reaches or exceeds a given value, switching means operate automatically to increase the field excitation to prevent further speed increase or to reduce it to the given value. A series field diverter may be controlled by a relay which is lifted through operation of the controller when accelerating and is retained by armature current so as to release under excess speed conditions. In the Figure, a trolleybus motor armature 4 and series field winding 5 can be connected to trolleys 1 and 2, through starting resistance 7 and reverser 16, by the line switches 12 and 14 ; the shunt field winding 6 can be connected to the trolleys through resistance 10 by contactor 26. The speedresponsive relay has a divided winding 13 in series with the motor, a lifting winding 34, and contacts 35. The master controller 31 on its first step energizes the line switches 12 and 14, and the under-voltage relay 33. On its second step-if relay 33 closesthe controller energizes the shunt field contactor 26 and the winding 34 which lifts the speed-responsive relay and closes contacts 35. On subsequent steps the controller energizes the starting resistance contactors 18-21. On the eighth step the controller de-energizes the field contactor 26 and winding 34, and if the armature current be sufficient for winding 13 to hold 35 closed, the contactors 22 and 23 can be closed on the next steps, to connect diverter resistances 8 and 9 in parallel with a part of the series field winding and the part 13A of the relay winding; the ampere-turn ratio of the two parts 13A and 13B is the same as that of the two parts of the series field winding. Should the vehicle speed exceed say 30 m.p.h. the reduced armature current will drop the relay 13 and open contacts 35, which can be re-closed only by moving the controller back to re-energize winding 34 ; the diverter contactors 22 and 23 will re-open unless the vehicle be running down hill. To compensate for varying line voltages, the relay may have a winding responsive to line voltage and opposing winding 13. The brake controller 32, electrically interlocked with controller 31, energizes a dynamic braking contactor 39 which deenergizes line switches 12 and 14; the brake controller can also apply air brakes. The reverser 16 can disconnect the armature and series field from the trolleys and connect them to a battery 3 through the battery switch 17.
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