INSULATION RESISTANCE DETERMINING SYSTEM, INSULATION RESISTANCE DETERMINING APPARATUS AND INSULATION RESISTANCE DETERMINING METHOD

摘要

An insulation resistance determining system (50) comprises an insulation resistance determining part configured by connecting a coupling capacitor (52), a detection resistor (54) and a pulse oscillating circuit (56) in series with a common mode potential measuring point (30); and an insulation resistance judging part having a filter (58), which processes an AC signal (v<SUB>x</SUB>) at a junction between the coupling capacitor (52) and the detection resistor (54), an amplifier (60), a wave-height value determining circuit (62) and a control part (70). The control part (70) has functions to detect an insulation resistance reduction in response to an output of the wave-height value determining circuit (62); to request an HVCPU (40) to vary the common mode potential so as to determine a failure of the insulation resistance determining part; and to determine a failure of the insulation resistance judging part from an output change of the wave-height value determining circuit (62) between before and after the common mode potential variation.