GB239650A - Improvements in and relating to the automatic control of electric motor converters - Google Patents

Abstract

239,650. British Thomson-Houston Co., Ltd., Whitaker, F. P., and Sarjeant, C. J. July 11, 1924. Synchronizing dynamo-electric machines.-In an automatic control system for a motor converter, a generator 8 driven by the converter is connected to am auxiliary field winding 7 of the converter on starting in order to fix the polarity. On closing a control switch 1, the coils 2, 3 of the main switch 4 and the auxiliary field contactor 5 are connected to the control bus-bars. The switch 4 connects the stator windings 6 of the converter to the alternating-current mains, and the machine starts to rotate, the rotor windings being conneced through the slip rings in series with non-inductive resistances A1 - - A3 and choking coils B1 - - B3 permanently connected in parallel. At the instant of closing the main switch 4, maximum voltage is obtained across the starting resistances, and a relay 9 connected across one of these lifts its plunger and completes the circuit of the coil 11 of an auxiliary contactor 12. The latter completes a maintaining circuit for the coil 11, and prepares the circuit of the coil 19 of the resistance shortcircuiting contactor 20. The latter circuit is completed through a contactor 33 when the plunger of the relay 9 returns to its normal position, which takes place when the machine is running in synchronism and the voltage drop across the starting resistances is a minimum. The closing of the contactor 20 short-circuits the slip rings of the converter and completes, through a limit switch 45, 46, the circuit of a motor 47 which operates a short-circuiting device 55. Auxiliary field contactors 22, 25 short-circuit portions of a resistance 28 in series with the main field winding 29 at the proper times in order to give the correct field strengths for synchronizing and normal running of the converter. An interlock switch 36, 37 on the contactor 20 disconnects the auxiliary field winding 7 from the generator when synchronism is reached. Specification 171,796, [Class 38 (ii), Electric currents, Converting &c.], is referred to.