PURPOSE: To provide an accident bus switching controller capable of preventing the spread of the influence of accident when switching buses during an accident in in-house power supply system by temporarily isolating a stationary variable voltage/variable frequency power supply unit thereby preventing a sudden decrease in residual voltage in an interrupted bus during bus switching without disturbing bus switching and the operation of various equipment after switching.

CONSTITUTION: An in-house normal service bus 6 with the power from a main generator 1 supplied through a power receiving circuit breaker 5 is connected to an in-house common bus 7 with the power supplied from the in-house normal service bus 6 and a separate system through a link breaker 11 and a stationary variable voltage/variable frequency power supply unit 13 is connected in a power source system, in which the state of bus switching performed during a failure of an upper-level power supply system of the in-house bus is detected from the opening/closing operation state of the power receiving circuit breaker 5 and link breaker 11 as well as the voltage condition of the in-house normal service bus 6. And the operation of the stationary variable voltage/variable frequency power supply unit 13 is temporarily stopped, and also a fault bus switching controller 20 is provided for re-operation upon completion of bus switching.