| 摘要 |
PURPOSE:To compensate the influence of a fluctuation of a phase characteristic in an insulation resistance measuring circuit by a simple circuit constitution, so that an acculate insulation resistance can be measured, by always correcting a phase shift of a measuring signal. CONSTITUTION:A grounding conductor LE of a power receiving transformer T having a load Z is allowed to pass through a transformer OT connected to a low frequency signal oscillator OSC of a frequency f1, and a low frequency voltage is applied to cable ways 1, 2. Subsequently, a leakage current which is fed back to the grounding conductor through an insulation resistance R0 existing between the cable way and a ground, and a ground floating capacity C0 is detected by a zero-phase current transformer ZCT. It is inputted to synchronous detectors MULT1, MULT2 through an amplifier AMP, and a filter FIL for selecting only a component of the frequency f1. On the other hand, an output of the oscillator OSC is inputted to the synchronous detector through a phase shifts PS, a 90 deg. phase shifter PSS, and a phase shifter PASS, and from a subtracting circuit SUB, a voltage being inversely proportional to the insulation resistance R0 is outputted.
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