| 摘要 |
PURPOSE:To measure insulation resistance, by modulating a detecting low-frequency leakage current by prescribed carrier frequency in each branching circuit, injecting it between a branching circuit ground line and the ground, and separating a signal of each branching circuit by a filter at a measuring point of a transformer. CONSTITUTION:A ground line EL of a transformer T passes through a core of an oscillation transformer OT, and a measuring signal is injected. In a branching circuit connected through SW2, a branching leakage current is detected by a zero-phase current transformer ZCT1, is amplified by an amplifier AMP1, and after that, its noise component is eliminated by a filter LF1, and after that, is modulated by a frequency modulator MOD1 of carrier frequency F1, and is injected between a ground line of a branch line, abd the ground through the transformer T1. In the ground line EL of the transformer, a leakage current is detected by the zero-phase current transformer ZCT, is passed through a band pass filter BPF1 of the center frequency F1, and insulation resistance of the branching circuit can be measured in a hot-line state by taking the product of an output demodulated by a frequency discriminator DISC1 and an output of an oscillator OSC. |
