Patent GB-432754-A (GB)
Title: Improvements in electric motor control systems
IPC: H02P3/08
Filed: 1934-05-08
Abstract: 432,754. Control of D.C. motors. GENERAL ELECTRIC CO., Ltd., Magnet House, Kingsway, London, and CROFT, E. H., c/o General Electric Co., Witton, Birming- ham. May 8, 1934, No. 13895. [Class 38 (iii)] Varying E.M.F.; regenerative braking.- Motors 10, 14 are controlled both for power and regenerative operation by means of a booster 2, and during regenerative braking the motor fields 17, 18 are supplied from a source 33 connected in series with a stabilizing resistance 29 which carries regenerated current, and in which the voltage drop opposes the voltage of the source 33. In order to start a vehicle driven by the motors 10, 14, contactors B1, B2 are closed to start a motor 1 driving the booster 2, series resistance 3 being then cut out in steps to accelerate it to full speed. A line contactor LS1 is then closed together with a contactor 19 to connect the motors 10, 14 across the supply in series with the booster 2. At this stage contactors 21, 22, and 24-28, are closed so that the booster field 20 is at full strength and the booster voltage in a direction determined by the closure of field reversing contactors 21, 22, and which is such that the booster opposes the line voltage. The line voltage slightly exceeds the maximum booster voltage and the motors 10, 14 run at minimum speed. The contactors 24-28 are then opened in sequence to insert resistance 23 in the booster field 20 and gradually reduce the booster voltage thereby accelerating the motors 10, 14. The circuit of the field 20 is then opened and closed in the reverse direction with all resistance 23 inserted. The booster voltage now aids the supply and the motors 10, 14 are further accelerated by increasing the field 20 by cutting out the resistance 23 in steps. Upon backward movement of the controller the line switch LS1, and contactor 19 are opened, and regenerative contactors 31, 34 are closed, and when the field 20 of the booster 2 has been so adjusted that the combined voltage of the motors and booster has attained a suitable value, the line switch LS1 is closed under the control of a voltage balance relay. The field windings 17, 18 of the motors under these conditions are supplied from an exciter 33, through the resistance 29 which carries the regenerated current and gives a voltage drop in opposition to the voltage of the exciter 33. The exciter 33 which is driven by the motor 1 has a field winding 36 supplied from the line in series with a field winding 7 of the booster motor 1, and also a field winding 35 in series with the armature of the motor 1. Regeneration is maintained as the motor speed falls by further backward movement of the controller which actuates the contactors regulating the booster field 20 in the reverse order of that on forward movement. When the first position is reached the stabilizing resistance 29 is reduced by closure of a contactor 30. In addition to the field winding 20, the booster has a shunt winding 15 and a series winding 11 which prevents regenerative surges. The stabilizing resistance 29 also prevents undesirably great changes of current in the motor circuit. When the motors are being regeneratively braked with the booster opposing the motors, the booster tends to drive its motor 1, and the greater the power regenerated the lesser is the current in the armature circuit of the motor 1, and since this circuit includes a field winding 35 of the exciter 33, the lesser is the excitation of the motor fields 17, 18, so that the regenerated power is kept within safe limits. Additional control may be obtained by supplying the field winding 36 of the exciter 33 from the line independently of the field winding 7 of the booster motor 1, and regulating it by a series resistance. The arrangement may also be modified by connecting the field 35 of the exciter 33 across the booster armature instead of in series with the armature of the booster motor.