GB493354A - Improvements in and relating to the control of alternating current motors - Google Patents

Abstract

493,354. Control of A.C., motors; controllers. BRITISH THOMSON-HOUSTON CO., Ltd., PETCH, JUN., T. H., and LIDDIARD, H. W. C. April 2, 1937, No. 9434. [Class 38 (iii)] Dynamo-electric braking.- Upon return of an induction motor controller towards its off position contacts are opened, and, if no deceleration is produced the opening of these contacts is effective to reverse the connections of the motor to the supply. A control lever 11, Fig. la, coupled to a master controller 204, Fig. 2, is pivoted on an axis 12, on which is mounted a segment 13 carrying contacts A, B, C, D, the segment 13 being coupled to a drum 14 engaged by brake shoes 15 biassed by a spring 18. The control lever 11 carries bridging contacts co-operating with the contacts A, B, C, D. With the controller 204 in its off position the coil 28a of a contactor is energized to close contacts 28b, 28c, 28e, 28g and 28,j, and open contacts 28d, 28f, 28h. When the controller is moved in the forward direction the switches A, B, are closed or remain closed so that the coil 28a is maintained energized through a segment 205. A coil 21a is energized over interlock contacts 22c, 23c, of contactors 22b and 23b, and the forward contactor 21b closes to start the motor 201 in the forward direction. Further movement of the controller energizes in sequence coils 23a, 24a, 25a, 26a, 27a, whereby accelerating contactors close to cut out steps of resistance 203. When deceleration is required the lever 11 is moved towards the off position first opening switches A and B. The coil 28a is maintained energized over contacts 217 of a reverse power relay, contacts 216 of an over-speed device and contacts 215 of a device which operates to open these contacts when the speed of the motor does not correspond with the position of the control lever. Thus with positive loading of the motor, the motor remains connected to the supply, and is decelerated by the insertion of steps of starting resistance 203 but if the loading is negative, the contacts 215, 216, 217 effect de-energization of the coil 28a. Thus the contactor 21b is opened and the reverse contactor 22b closed, the contactors controlling the resistance 203 also opening. The motor is thus connected reversely to the supply. When the switches C and D close the coil 23b is energized to give a second braking control step. Further movement of the controller towards the off position gives braking control until the off position is reached, and the control circuits restored to their original condition in readiness for the next operation. If, after opening of the switches A and B by movement of the controller toward its off position, the controller is then moved away from the off position with positive loading acceleration takes place by removal of starting resistance, while with negative loading acceleration commences when the switch A recloses. The device 215 may take the form of a governor co-operating with a cam operated by the lever 11.