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.
In this letter, the reactive power loss sensitivities as well as the active loss sensitivities are derived using the angle reference transposition. Four kinds of power loss sensitivities of all generators, including the slack bus, can be obtained by specifying the angle reference on a load bus that has no generation. As an example application, we show a formula with which these loss sensitivities can be used to derive the optimal P-Q allocation for minimizing the total system operating cost. A simulation is carried out on a sample system, and the results show that these loss sensitivities can also be used to obtain the optimal solutions in power system computations.
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