Three-phase and zero-phase current sensors using Hall ICs

Three-phase current sensors are required in power-line distribution systems to monitor currents and protect systems from possible failures. Zero-phase current sensors also are required to detect leakage currents between power lines and the earth, thus preventing accidents such as a fire. This paper describes new three-phase and zero-phase current sensors which are based on a zero method. The sensors consist of Hall ICs, coils, and electronic circuits; no magnetic cores are used. The three-phase current sensor provides measurements of currents from 0.8 A to 720 A with excellent accuracy, while the zero-phase current sensor provides measurements from 90 mA to 20 A. The output signal levels are suitable for microprocessor-based metering and control systems. The sensors are relatively small and lightweight compared to a conventional current transformer (CT). Moreover, they withstand excess currents and do not yield burning or deterioration. They do not require expensive components so they have an advantage in cost compared to an optical-fiber current transformer.