JPS6488166A - Detecting method for poor electric insulation part - Google Patents

Abstract

PURPOSE:To measure insulation resistance and to detect a poor insulation part by applying an AC voltage of low frequency between a cable run and the ground, coupling current transformers with the cable run at two optional points on the cable run, and detecting the difference between the outputs of the current transformers. CONSTITUTION:An oscillator OSC is coupled with the low-voltage ground line, etc., of a power receiving transformer and the low-frequency voltage of frequency different from the commercial frequency is applied. Then when the ring-shaped core current transformers ZCT1 and ZCT2 are positioned at points A and B, the outputs of the ZCT1 and ZCT2 are inputted to a subtracter SUB through amplifiers AMP1 and AMP2 adjusted to the same characteristics by a variable gain device VR and a phase adjusting device PH. The output of the SUB is passed through a filter F1 and rectified by a rectifying circuit DET to detect the difference between leak currents. The insulation resistance in a specified section is therefore measured without being affected by front and rear sections and the poor insulation position is detected including abnormality of load facilities.