System for maintaining excitation of an alternator during excessive

Abstract

A system for supplying power to a field winding to maintain excitation of an alternating current generator during excessive output current conditions, the generator having a plurality of output lines for supplying power to a load and the field winding being supplied during normal operating conditions by a shunt type voltage regulator responsive to the output voltage of the generator. The system includes a current transformer having a primary winding in series with an output line of the generator, a secondary winding, and a tertiary winding shunted by a capacitance. A rectifier circuit rectifies the voltage supplied by the secondary winding, the output terminals of the rectifier circuit being connected in series with the regulator output terminals to supply power to the field winding. A control circuit, connected to the output of the generator and responsive to output current conditions enables the rectifier circuit output during excessive output conditions. Power from the rectifier circuit is supplied to the field winding only when an excessive output current condition exists. Additional circuitry prevents the enabling of the rectifier output if a decrease in generator voltage is accompanied by a decrease in generator frequency which substantially corresponds to a desired response of the voltage regulator. Another circuit disables the voltage regulator when the currents in the output lines of a multi-phase generator are not substantially equal during excessive output current conditions.