PURPOSE: To prevent inconveniences due to common excitation or single automatic voltage regulation, by controlling the parallel operation through a single voltage selector and performing the automatic voltage regulation through voltahe selectors for the respective generators during the non-parallel operation.

CONSTITUTION: A common voltage detector VD is connected to a common bus. Relays RY1, RY2 are operated through auxiliary contacts K1, K2 interlocked with circuit breakers CB1, CB2 for the generators G1, G2 to shift the voltage detector VD through contacts C1, C2 of the relays. The voltage detector VD supplies a voltage detection signal to signal mixers M1, M2 contained in field controllers ES1, ES2 for the generators to apply inputs to power amplifiers FC1, FC2. Then, power is supplied to the field windings F1, F2 of the generators to perform the automatic voltage regulated operation of the generators. Voltage detectors ED1, ED2 for the automatic voltage regulation of the generators are selected to perform the non-parallel operation of the generators.