Abstract: The present invention is composed of: positive and negative control power sources P and N, first and second semiconductor device groups A and B in which a plurality of semiconductor devices 12 and 13 and also 15 and 16 are series-connected to these positive and negative control power sources P and N, switching signal source 17 that supplies ON/OFF control signals to semiconductor devices 12 and 13 and also 15 and 16 of these first and second semiconductor device groups A and B, and delay circuits 18 and 19 that delay for a specified time the ON/OFF control signals supplied to any one of semiconductor devices 12 and 13 and also 15 and 16 of first or second semiconductor device groups A and B from this switching signal source 17.

Abstract: A fault detector apparatus for a power converter in which a plurality of GTOs, functioning at a predetermined potential, are used. The apparatus includes a first fault-detecting circuit, coupled to the gate-cathode path of one of the GTOs, for generating a first fault signal when this GTO malfunctions, a second fault-detecting circuit, coupled to the gate-cathode path of another one of the GTOs, for generating a second fault signal when this GTO malfunctions, a photocoupler for transmitting a DC-isolated optical signal corresponding to the first fault signal, and one optical fiber system for transmitting a DC-isolated output signal, corresponding to the logical sum of the optical signal transmitted by the photocoupler and the second fault signal, to external circuits set at a potential different from the potential at which the GTOs are arranged. The fault-detecting circuits are provided in the same number as the GTOs. The fault-detecting circuits are coupled by the optical signals.

Abstract: A turbine helper drive apparatus has an induction motor coupled to a turbine, and a power converter for power-controlling the motor. Part of the load of the turbine is shared by the motor in accordance with preset power for power control, so that auxiliary drive to compensate for the insufficient capacity of the turbine is performed and cheaper, late-night electric power is effectively utilized.