| 摘要 |
PURPOSE:To detect poor insulation even if two wires are poor insulation, by flowing an exciting current to a single-phase three-wire circuit by an inductance element and by measuring a leakage current before and after said operation. CONSTITUTION:Inductance element L and zero-phase rectifier ZCT are interposed in single-phase three-wire circuit 1 and switch S flowing an exciting current via resistance R0 is provided. As a result, even if two wires of circuit 1 becomes poor insulation having nearly equal resistance values Rg1 and Rg2 and that can not be detected by ZCT, Ig1' and Ig2' differ in value by inducing voltage (v) at respective phases R, S and T through turning on the switch S, so that ZCT can detect the defection. In this case, voltages V3 and V4 between respective lines are unchanged, so a load is not forced excessively and any special power supply for testing is not necessary. |
