Openable-core AC and DC leakage-current detector

Abstract

This paper deals with the characteristics of a detector developed to measure small alternating current (AC) or direct current (DC) currents by means of two identical split ferrite cores. To measure the DC current, the asymmetry in the magnetization current caused by an alternating reference voltage in a magnetic modulator is used. The modulation frequency of such a magnetic modulator is generally less than 1 kHz. For high-frequency current measurements, a magnetic modulator cannot be used because of the modulation frequency limit. The error increases and linearity of the detector decreases when high-frequency currents are measured. We have improved the error and linearity of the detector by using a different technique for AC/DC measurements. To measure AC currents, instead of using a modulator such as a zero-flux current transformer, we used a two-stage current transformer with switches and an electronic circuit to improve the linearity and reduce the errors of the transformer. We produced a hand-held AC/DC leakage-current detector using openable cores and a miniaturized electronic circuit. The error of the current ratio is less than 0.3% over a current range 200:1 and the phase angle is less than 10 mrad. Current measurement ranges are from 10 mA to 2 A for frequencies ranging from DC to 10 kHz.