Protection system using differential transformer - operates circuit breaker when leakage current occurs in LV supply network

摘要

The leakage current protection system, for low voltage supply networks, responds to leakage currents of 5 mA and less using a differential transformer. The network phase lines form the primaries of the transformer. The transformer has an iron core (5) which is premagnetised with an AC current (1) derived from the network. This AC current is passed both to the secondary for premagnetisation and to a storage capacitor (12) whose stored energy operates the circuit breaker (14) when a current leak occurs.