ABSTANDSSCHUTZ VON DREIPHASEN-VERTEILTRANSFORMATOREN

It is desirable to provide remote digital protection of distribution transformers. A protection system is disclosed which is able to detect increases in transient D.C. current flowing in the respective phases of a distribution cable (10) feeding a transformer and also to detect increases in other selected functions of supply parameters for identifying and quantifying a fault current flowing in the distribution cable (10). Increases in these other functions are analysed to identify whether the increases indicate a fault current. Any such fault current can then be quantified and the triggering of a circuit breaker (19) initiated to isolate the supply cable on identifying a fault current. The circuit breaker (19) is not triggered for any increases in the other functions for as long as there is a detected increase in D.C. current in any phase.