| 摘要 |
PURPOSE:To enable to know an insulation resistance value relating to each branch circuit in the condition of a live wire, by injecting a signal for measurement through the earthing line of a transformer by producing a product of a leakage current and an earthing voltage at each branch circuit. CONSTITUTION:A signal for measurement is injected into an earthing line EL through the intermediary of an oscillation transformer OT. When the insulation resistance of a branch circuit connected to a switch SW2 is measured, a leakage current is detected by ZCT1 and a component of a commercial frequency is removed by a filter FIL1. Since the signal for measurement is impressed on an earthing circuit 2, it is detected between the earthing circuit 3 of the branch circuit and an earthing point E3. This signal is detected by a buffer amplifier AMP1, the component of the commercial frequency is removed by a low-pass filter LF1, a product of the output of FIL1 and the output of LF1 is produced by a multiplier MULT1 so as to obtain a voltage which accords in phase with the voltage component of the signal for measurement. By giving the output of the multiplier to a low-pass filter LPF1, the insulation resistance of the given branch circuit alone can be made known. |
