HITACHI EARTH LEAKAGE RELAYS

Thai Version

This is a combination of a Fuse-Free Breaker and a leakage current detector for preventing fire or electric shock due to deterioration of electric insulation. It will provide perfect protection of a circuit against over-load, short-circuit, or earth leakage..

- Principle of operation
This device is composed of a zero current transformer for detecting leakage current, a control circuit, and a
Fuse-Free Breaker with a shunt trip. As shown if Fig.x magnetic fluxes cancel out each other, inducing no out-put voltage in the secondary coil while no leakage is present in load circuit.
i₁ + i₂ + i₃ = 0

If leakage current (lg) occurs in the load circuit, magnetic flux fg is included, producing a certain voltage across the
secondary coil.
i₁ + i₂ + i₃ = i_g

The induced voltage is supplied to the shunt trip coil of the Fuse-Free Breaker, through a control circuit composed of diodes and semiconductor control elements, to break the circuit.

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