Integration of a Three-Phase and Zero-Phase Current Sensor Using a Coaxial Bar Structure

Abstract

This paper describes the integration of a three-phase current sensor and a zero-phase current sensor via a coaxial bar structure. A coaxial bar structure was therefore used, as it improves the accuracy due to the exclusive use of the zero current transformer (ZCT) and the current sensor. The ZCT’s high-sensitivity magnetic sensor is an MI element, while the current sensor employs a Hall-effect IC. As a result, a sensitivity ratio (the ratio of leakage to residual output) of over 8:1 is obtained for the ZCT, demonstrating the structure’s ability to isolate leakage current. Meanwhile, the linearity error of the three-phase current remains at ±7.9%, well under the ±10% specification. Thus it can be seen that this structure was many advantages, while its sole disadvantage with respect to the conventional ZCT is increased manufacturing cost.