RCBO's principle of leakage action

Update date:2018-06-08 Source:MAXGE

RCBO's principle of leakage action

The zero-sequence current transformer of an earth-leakage circuit breaker is composed of a core made of permalloy, and a secondary coil wound on a toroidal core to form a detection element. The power line and the neutral line pass through the round hole to become the primary coil of the zero-sequence transformer. The rear outlet of the transformer is the protection scope.


Under normal circumstances, the three-phase load current and ground leakage current are basically balanced. The phasor of the primary coil current flowing through the transformer is approximately zero, that is, the total magnetic flux generated by it in the core is zero, and the zero sequence transformer is secondary. No output coil. When an electric shock occurs, the electric current is looped through the earth, and a zero-sequence current is generated. This current does not flow back through the primary coil of the transformer, breaking the balance, so there is a zero-sequence flux in the core, which causes the secondary coil to output the signal. 

Leakage circuit breakers

This signal is amplified and compared by the comparator. If it reaches the predetermined operating value, it sends an execution signal to the actuator to trip and the leakage circuit breaker(RCBO) cuts off the power.


It can be seen from the working principle that when the three relatively large impedance differences, three relative leakage current phasor and reach the protector action value, will make the circuit breaker trip or send power. At the same time, the three-phase leakage current and the phase of the electric shock current are inconsistent or in anti-phase, which will reduce the sensitivity of the protector. The current leakage protector can implement graded protection to achieve selective action.

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