Self-calibration method for coreless Hall effect current transformer

Current transformers (CTs) are an indispensable equipment for power system current measurement. If a fault occurs in a power system, iron cores of CTs may face saturation problem and cause current measurement errors, resulting in false responses in protection relays. This research proposed a new current measurement technology using Hall integrated circuits (Hall ICs) symmetrically surrounding a power cable to measure the current flowing in it. This new electronic current transformer is called coreless Hall-effect current transformer (HCT). However, there is a dc offset voltage of about 2.5V existing in Hall ICs and thermal drift phenomenon of this dc offset may arise due to ambient temperature. Both are factors affecting accuracy of the HCT. This paper proposes an automatic dc offset calibration method to eliminate the dc offset voltages of Hall ICs and also uses digital filters to filter out noises to get better accuracy. This research also follows IEC 60044-8 electronic current transformer standard to perform the current accuracy test. Results show that accuracy can achieve class 0.5 for measuring CTs.