The insulation resistance measurement method null of compensating the influence of grounding resistance

摘要

PURPOSE:To compensate for effect of an earth resistance by providing a core of a transformer with a low frequency voltage applied thereto and a current transformer for detecting a leakage current with a connection wire piercing in the opposite phase to an electric circuit to terminate it with a first variable capacitor. CONSTITUTION:A first variable capacitor Cv is so adjusted to minimize a low frequency leakage current component contained in an output of a current transformer ZCT and an earth electrostatic capacitance Co is detected to determine the size I1 of a low frequency component obtained after the adjustment. Then, a specified value C of capacitor is forcibly inserted between an electric circuit and the ground and the first variable capacitor Cv is so adjusted to minimize a low frequency leakage current component then contained in the current transformer ZCT and then, the size I2 of the low frequency component obtained is determined. Then, these two components I1 and I2 are used to compute (I1-K2I2)/(1-K2) [wherein K=Co/(Co+C)], thereby measuring an insulation resistance of the electric circuit.