Reduction of trip operating time of electronic type ELCB to 9 mili-seconds for safety improvement of electrical facility

Abstract

ELCB (Earth leakage circuit-breaker) is a circuit breaker used in a low-voltage AC (Alternating Current) electrical circuit to provide electric shock protection and to prevent fires from current leakages. Trip operating time of ELCB depends on the magnitude of leakage current and the duration time of leakage accident. In this paper, the circuit and electrical signal after ZCT (Zero-sequence Current Transformer) output terminal of existing ELCBs are analyzed. As a result of measurement, electronic trip type ELCBs in present market have shown up to 27 ms of self-trip operating time under 30 mA of leakage current. This 27 ms of time delay is due to the problem that the IC in electronic circuit detects only the reverse-half cycle of sinusoidal leakage current. In this paper, the authors design a new electronic circuit that minimizes the delay factors of existing circuits. And as a result of an experiment, the trip operating time could be shortened within 9 ms. Shortened trip operating time implies reduction of shock duration of leakage current. Since the electric shock to human body and the outbreak possibility of fire are inversely proportional to square root of shock duration, faster trip operation of ELCB proposed in this paper will contribute to providing shock protection to human body and preventing fires from current leakages.