GB1359130A - Automatic excitation control system for synchronous dynamo-electric machines - Google Patents

Abstract

1359130 Motor control system BRUSH ELECTRICAL ENG CO Ltd 30 March 1972 [31 Dec 1970] 61957/70 Heading H2J [Also in Division G3] An automatic excitation control for a synchronous dynamo-electric machine, i.e. motor or generator, includes means to boost the excitation for a period of less than one minute following a transient reduction in the line voltage to or from the machine. In an embodiment, and under steady state conditions, boost control circuit 11 is off, the excitation of synchronous motor 6 being controlled by power amplifier 5 by the difference between an actual supply signal B from detector 2 measuring, e.g., reactive power or current of three-phase supply 7, and a reference signal A from a Zener diode Zl fed from supply 7 via transformer T 1 and rectifier bridge D 8 -D 13 . A stabilizing signal D is obtained from rate circuit 15. Transient falls in the supply voltage are reflected through transformer T1, rectifier bridge D1-D6, smoothing circuit R1, R2, C1 and capacitor C2, to turn on transistors VT1, VT2, thus providing a boost signal C to amplifier 5, to increase the motor excitation and maintain synchronous operation. Diode D7 across the base of transistor VT1 ensures that transient rises in the supply do not cause a decrease in motor excitation. Resistors R1, R2 in the smoothing circuit set the sensitivity of boost control 11, whose supply, obtained from Zener diode Z2 in series with Zener Z1, sets the maximum for boost signal C, which is reduced to zero after a preset time as capacitor C2 discharges via resistor R3, or if the supply voltage increases rapidly.