Patent GB-510561-A (GB)
Title: Improvements in or relating to electric motor control systems
IPC: H02P3/12
Filed: 1938-03-09
Abstract: 510,561. Master control of D.C. motors. GENERAL ELECTRIC CO., Ltd., and CROFT, E. H. March 9, 1938, No. 7389. [Class 38 (iii)] Regenerative and non-regenerative braking. In an electric motor control system of the kind in which a motor is adapted to operate regeneratively and in which over-voltage protective means, upon operation, effect braking other than the regenerative braking of the motor the protective means comprises a braking control means normally held latched against a bias in an inoperative position and arranged to be tripped free upon the occurrence of overvoltage to effect braking. Power is supplied from positive and negative trolleys 1, 2 to a compound motor having an armature 5, series field winding 4, starting and braking resistance 3, shunt field winding 12 and shunt field resistance 14. The starting resistance 3 can be cut out in sections by electromagnetically operated contactors 8, 9, 10, 11 and the shunt field current can be controlled by similar contactors 16, 17 across the series resistance 14 or interrupted by a further contactor 15. A positive line switch LP is in series with the resistance 3 and the protective device 6 takes the place of a negative line switch. A switch 21 has a movable contact 22 connected to a reverser 7, an upper fixed contact 23 connected to the negative trolley 2 through a contact breaker CB2 and a lower fixed contact 24 connected to a tapping on the resistance 3. In its upper position the contact 22 provides for normal running or regenerative braking while in its lower position it disconnects the armature 5 from the supply and provides a rheostatic braking circuit through the resistance 3. The protective device consists of a pivoted arm 31 attached to the movable contact 22 and biassed in a clockwise direction by a spring 25. It may be latched in its upper position by engagement with a pivoted latch 26, this latch being retractable by an over-voltage winding 27 so that the arm 31 may move to its lower position and complete the braking circuit. The arm 31 is reset by energisation of a winding 29 which brings an arm 28 into engagement with a projection 30 on the arm 31. If the winding 29 becomes de-energised, as by moving the speed controller to " off," the retraction of the arm 28 by a spring 32 causes the arm 28 to trip the latch 26 by striking a projection 33. The motor is controlled by a speed controller SC and a brake controller BC both shown in their " off " positions. In this position fingers 60, 61 and 62, 63 of the brake controller are respectively bridged by segments 66, 67 and fingers 46 and 52 of the controller SC are rendered alike. As the controller SC is moved towards position I an advance step 69 on the segment 34 allows energisation of the winding 29 to set the switch 21 in its upper running position with consequent closing of auxiliary contacts 21NO1 and 21NO2 the first of which retains the winding 29 energised after the step 69 is passed. When the controller reaches pcsition I a circuit is completed through normally closed contact 11NC2 and positive line switch winding LPW to start the motor with full series resistance 3 and also with windings 15W, 16W, 17W energised to provide full shunt field. In positions II, III, IV, V the windings 8W, 9W, 10W are selectively energised to reduce the starting resistance, while in position VI the winding 11W is energised alone to short circuit the resistance 3, close normally open auxiliary contacts 11NO and open contacts 11NC2. In positions VII, VIII, IX the shunt field is weakened in steps, being completely cut out in the last position. If the controller SC is moved back while the motor is running regenerative braking may occur and if over-voltage results the winding 27 becomes energised sufficiently to withdraw the latch 26, allow the contact 22 to move to its lower position and cause rheostatic braking. Thereafter motoring can only take place if the controller SC is first moved back to its "off" position to re-energise the winding 29. If the brake controller BC is moved from "off" while the controller SC is in an " on " position the flanges 60-63 part from the segments 66, 67 so that the controller SC is rendered inoperative and the de-energisation of the coil 29 causes the switch 21 to be positioned for rheostatic braking. The three positions of the controller BC provide for excitation of the shunt field in series with its resistance 14 and with this resistance cut out in two steps.