Abstract: An active filter device simple in construction and low in price in which higher harmonic components can be stably suppressed without requiring a passive filter even when a load to be compensated includes a capacitative load.

Abstract: A static var generator using self-commutated inverter being able to resume its operation securely and smoothly immediately after a system grounding accident disappears and whose system can be stabilized securely after the accident is provided. The static var generator using self-commutated inverter of the present invention is provided with an accident-detecting circuit 21 comprising band pass filters 22a and 22b extracting the second harmonic components contained in active voltage feedback signals Vp- and reactive voltage feedback signals V.sub.Q -, comparators 23a and 23b comparing these output signals and a prescribed set value and judging of the occurrence of an accident, and an OR circuit 24 operating logical sums of these both output signals. Further, the static type power generator of the present invention comprises a reactive current reference zero controlling circuit 20 controlling a reactive current reference signal I.sub.

Abstract: A fault-determining apparatus includes parity error checking for data transferred from a main storage and an input/output unit to a CPU which has an interrupt procedure called by the detection of a parity error for recording a parity error signal in a trace recording memory along with a fault-detection signal and data transferred to a data bus from predetermined addresses of interest in the main storage and the input/output unit.