JPS54121175A - Leak detector - Google Patents

Abstract

PURPOSE: To enable leak detection to be performed even at the reverse connection of a power source and load and even at the missing phase and achieve the improvement of detection accuracy by forming the detector with a zero phase current transformer, rectifying smoothing circuit, voltage detecting circuit and switching circuit.

CONSTITUTION: When an unbalance current owing to leak occurs in an AC electric line, a zero phase current transformer ZCT outputs and the level voltage VCF of a rectifying smoothing circuit F' rises. The voltage V₁ across the load resistance R₁' of the FETF₁ of a voltage detecting circuit E' is the same voltage as VCF while VCF is low but when VCF continues to rise, V₁ is held at a constant voltage by constant current characteristics. In addition, the FETF₁ and F₂ are operated by exactly the same principle, but the voltage V₂ by the FETF₁ is applied to the gate and the output voltage V₂ becomes as illustrated. When the voltage VCF - V₃ of the gate and anode of the switching element SCR connected to the next stage becomes larger than the offset potential V₀', the switching element SCR goes ON to energize a trip coil TC, thus breaking the AC electric line through a circuit breaker.

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