| 摘要 |
PURPOSE:To accurately detect leakage current, by applying a low frequency voltage signal to the grounding line of a grounded system. CONSTITUTION:The system provides a coupling transformer TR2 to which the grounded wire EL is passed through, zero phase current transformer ZCT, low frequency oscillating circut OSCC connected to TR2 with winding N1, PLL connected to TR2 with the winding N2, output amplifier of ZCT, clock oscillator CLOC consisting of counters, and BPF-2 in which the center frequency is controlled with the clock. The winding N2 outputs the voltage in phase with a low frequency voltage induced on the grounding line EL and it is fed to PLL. Further, the output of PLL is taken as nf1 to the frequency f1 of OSCC, the center frequency of F2 is determined in synchronizing with f1, only f1 component is detected with F2 from the leakage current flowing to ZCT, and the amplitude of the leakage current is accurately measured. |
