GB356398A - Improvements in or relating to electric motor control systems - Google Patents

Abstract

356,398. Master control of several motors ; controllers. GENERAL ELECTRIC CO., Ltd., SAUNDERS, C. W., Magnet House, Kingsway, London, WILSON, H. W., and EMMS, S. A. G., of General Electric Co., Witton, Birmingham. July 23, 1930, No. 22226. [Class 38 (iii).] Checked by motor current.-Several motors can be connected to a common starting means and thereafter connected directly to a supply circuit, means being provided to limit the total load connected to the starting means at any.one time. To start any one motor 2, the corresponding button 5 is closed causing closure of starting contactor 7 provided field rheostat 4 is in the strong field position, coil 40 of the contactor 7 being supplied through coil 39 of protective relay 36 and this coil 40 having in parallel therewith a resistance 45 of such a value that the current through the coil 39 is proportional to the power of the motor 2. Closure of contactor 7 causes maintenance of its coil 40 through a coil 38 of the relay 36, closure of negative line contactor 9 provided lock-out relay 11 is closed, connection of the motor 2 through starting resistance 12, 19 to the positive supply, and closure of contactor 35 to start pilot motor 32 to drive the starting means to cut out the resistance 12, 19. The motor 32 has an additive field 34 energized proportionally to the armature current of the motor 2, so that the rate of cutting-out the resistance is restricted. When the last section 19 of resistance is excluded, a segment 31 completes a circuit to cause closure of running contactor 8, the closure of which opens the maintaining circuit of starting contactor 7. If several buttons 5 are closed substantially simultaneously the corresponding motors are connected in parallel to the starting means provided that the total current through coil 39, which current is proportional to the total power of the motors, is not sufficient to open the relay 36. If after one or more buttons 5 have been closed and the corresponding contactors 7 and 9 have closed, other buttons 5 are closed then the contactors 7 corresponding to these other buttons will close provided that the combined effects of coils 38, 39 do not open the relay 36. Should the pilot motor 32 have only just commenced to operate, then the contactor 9 corresponding to these other buttons will also close, and the associated motors will all be started in parallel. However if the motor 32 has driven the segment 30 into engagement with its fixed contact, then the lock-out relays 11 will have opened and so prevent the closure of these contactors 9 associated with these other buttons, until such time as the pilot motor 32 has completed the starting cycle, whereupon these contactors 9 close and the pilot motor 32 performs another starting cycle. A modified arrangement is disclosed in which during one starting operation, contactors 7 of other motors may be closed in readiness for the next starting operation, the total power of such further motors being limited only by the full rating of the starting means and not being limited, as in the system described above, by the difference between the full rating and the actual rating of those motors being started. The resistance starter may be a contactor starter, or be replaced by a negative booster, or by a stardelta or auto-transformer starter.