GB464866A - Improvements in and relating to electric motor control systems - Google Patents

Abstract

464,866. Control of A.C. motors ; electricity supply. BRITISH THOMSONHOUSTON CO., Ltd. Sept. 25, 1935, No. 26559. Convention date, Sept. 27, 1934. [Class 38 (iii)] [Also in Group XXXV] A control relay 15 with voltage and current coils 17, 16, energized in accordance with the phase relation between the supply circuit voltage and the armature current of a synchronous motor 1, and also in accordance with the frequency of armature current pulsations when the motor is operating out of synchronism, effects the connection of the motor field 3 to an excitation source 10 when the motor speed increases above a predetermined value Upon operation of a switch 7, a self-maintaining contactor 5 closes to connect the motor armature 2 to the supply, the field 3 being connected across resistance 13 by the normally closed contacts of a field contactor 11. The current flowing to the motor is sufficiently large and lags the supply voltage sufficiently for the relay 15 to close its contacts 18. This effects energization of a relay 20 which closes its contacts after a time interval to maintain its own circuit, and prepare a circuit for the field contactor 11 which is completed when the relay 15 opens its contacts 18 and closes its contacts 19. This occurs when the motor current has a certain phase relation to the supply voltage, and the current pulsations in the armature circuit are at a frequency predetermined by a time device on the relay 15. The field contactor 11 then operates to effect direct-current excitation of the motor field. The contactor 11 also completes a short-circuit across the contacts 18 for a time interval, so that the operation is not affected by disturbances occurring as the motor pulls into synchronism. The contactor 11 also inserts reactance 22 in the circuit of the relay coil 17 and removes resistance 23 therefrom, so that the setting of the relay 15 is adjusted and the relay responds to disconnect the motor field at a different phase relation between the supply voltage and the armature current after the contactor 11 closes.