GB635332A - Improvements relating to control systems for electrically-operated winding gear and the like - Google Patents

Abstract

635,332. Control of A.C. motors. BRITISH THOMSON-HOUSTON CO., Ltd., PETCH T. H., and LIDDIARD, H. W. C. May 1, 1944, No. 8172. [Class 38 (iii)] In an emergency, dynamo-electric braking is automatically applied to an induction motor, operating winding equipment or the like, and a predetermined rotor resistance is inserted, mechanical braking being suspended until the motor speed falls below a certain value. Whilst winding with dynamo-electric braking applied to the motor, a predetermined rotor resistance is inserted and mechanical braking is held off until a low speed is reached. An induction motor 1M is braked by disconnecting it from the three-phase alternating current source and applying direct current excitation to the stator by means of exciters El and E2. E2 operates at substantially constant speed and field strength, whilst El is coupled to the motor 1M and has fixed excitation, a reversing switch RS, driven by the induction motor, being used to energize the appropriate coil, RD or FD, so that closing of switches FD1 or RD1 affords a reversal of the field of the exciter El, when the induction motor reverses, to maintain a fixed polarity. The exciter E2 is driven by an induction motor IM1 and has an exciter E3 and a fly-wheel FW coupled to it. Across the armature of the exciter El is connected a direct current motor FM driving a fly-wheel FW1. In series with the armature is a relay coil RR with contacts RR1. If the rate of decrease of the voltage generated by the exciter E 1 becomes excessive, the coil RR will be energized to open the contacts RR1 and insert a resistance FR3 in series with the-fields EF1 and EF2, thereby reducing the braking-torque. When the rate of fall of speed ceases to be excessive, the dynamo-electric braking effort is restored. A graded protective arrangement may be provided, comprising additional relays and resistance-sections. A transformer with a primary winding across the armature of the exciter, and a secondary connected to the relaycoil may provide alternative protective means. Normal operation is effected by a controller C, and operation withdynamo-electric braking, for example when lowering heavy loads, by a controller B. When operating with alternating current power, initiation of emergency conditions will cause the de-energization of relaycoils LVR and ACF. Contacts ACF4 will open and cause either of contacts F1 or R1 to open. The main switch OCB has already opened. A coil EDB is de-energized and a relay-coil PD is energized to energize a coil D and close the contacts D1. Contacts EDB3 close the circuit to the fields EF1 and EF2, and contacts EDB2 energize one of the rotor contactor coils 5, the rotor contactors having previously been opened due to contacts F2 and R2 opening to open contacts PA2. In this case, the contactor coil 5 is energized, but other contactor coils may be closed in timed sequence, at a rate depending on the speed of the motor IM, or at a rate dependent on the current in the resistances MR. A brake coil BSC, which controls a brake solenoid BS, is now dependent upon limit switches FBLS1 and FBLS2, and a contact SR1 pertaining to a relay coil SR, the voltage supplied to which is substantially proportional to the speed of the motor IM. If the alternating current supply fails under the above conditions, the motor IM1 will not continue to drive the exciters E2 and E3 and a rectifier RE will cease to deliver power to bus-bars Y and Z, sufficient power is obtained from the fly-wheel FW, with the exciter E3, however, to supply the bus-bars Y and Z and excitation for El and E2. When operating with dynamo-electric braking applied to the induction motor, the coil AFC is again de-energized under emergency conditions to de-energize the coil EDB and open rotor contactors which may be closed. Coil PD is maintained energized and coil D energized to close contacts D1. The excitation of fields EF1 and EF2 is maintained and the opening of contactors replaced by the closing of contactor coil 5. Further operation is similar to that obtaining with alternating current driving. Specification 535,732 is referred to.