| 摘要 |
PROBLEM TO BE SOLVED: To detect a ground fault accurately by a relay without being affected by conditions such as temperature characteristics of a current transformer. SOLUTION: When a ground fault occurs on a line An branched from a main circuit, a current transformer CTn detects an earth current caused by the ground fault, and a relay RYn detects and annunciates the occurrence of the ground fault based on the detection signal. The current transformer CTn is equipped with a feedback circuit 13 continuing to deliver a counter correction current IFB equal to the detected earth current until the sum of the correction current IFB and the earth current becomes zero and enabling the relay RYn to detect the occurrence of the ground fault based on the correction current IFB, and an amplification-degree adjusting circuit 20 for automatically varying, based on the output of a peak-value detecting circuit 10, the amplification degree of an amplifying circuit 9 provided in the preceding stage of the peak-value detecting circuit 10 for amplifying the waveform of a signal in order to keep constant the output voltage of the peak-value detecting circuit 10 detecting a peak value of the waveform of the detected signal.
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