How the current leakage protector works

A zero-sequence current transformer consisting of an iron core made of permalloy and a secondary coil wound around a toroidal core. The power phase and neutral wires pass through the circular holes to become the primary coil of the zero sequence transformer. The rear exit of the transformer is the protection range.

Under normal circumstances, the three-phase load current and the ground leakage current are basically balanced, and the phasor of the primary coil current flowing through the transformer is about zero, that is, the total magnetic flux generated by the iron core is zero, and the zero-sequence transformer is twice. The coil has no output. When an electric shock occurs, the electric shock current loops through the earth, that is, a zero-sequence current is generated. This current does not flow back through the primary coil of the transformer, which breaks the balance, so there is a zero-sequence flux in the core, so that the secondary coil outputs a signal. This signal is amplified and compared with the component. If the predetermined action value is reached, the execution signal is sent to the actuator to trip and the power is turned off.

It can be seen from the working principle that when the impedance difference between the three relative grounds is large, and the three relative ground leakage current phasors and the action value of the protector reach, the circuit breaker will be turned off or not powered. At the same time, the three-phase leakage current and the electric shock current phase are inconsistent or reversed, which will reduce the sensitivity of the protector. Current-type leakage protectors can be graded to achieve selective action.