DC CURRENT DETECTOR AND DC EARTH FAULT CURRENT DETECTOR

摘要

PPROBLEM TO BE SOLVED: To provide a DC current detector which can detect accurately present DC current value without influence of hysteresis characteristics of a ZCT. PSOLUTION: The DC earth fault current detector 1A includes the ZCT 10 connected in series with a voltage dividing resistor 12 by inserting power source lines 110A, 110B and an electric wire 21 for offsetting, a comparison voltage value generator 13 which generates a comparison voltage value based on a voltage value voltage divided between the ZCT and the voltage dividing resistance in response to an impedance change of the ZCT, and a control circuit 14 for detecting the presence or absence of the generation of the DC earth fault current based on the comparison voltage value. The DC earth fault current detector 1A includes an offset current generator 22 for generating offset current to shift a minute current range to a current detectable range. The control circuit judges the generation of the DC earth fault current when the comparison voltage value is judged to be more than upper limit threshold value or more for earth fault judging, or judges the generation of the DC earth fault current when the comparison voltage value is judged to be less than lower limit threshold value or less for the earth fault judging. PCOPYRIGHT: (C)2005,JPO&NCIPI