Remote protection of three phase distribution transformers.

摘要

It is desirable to provide remote digital protection of distribution transformers. This specification discloses a protection system able to measure and compare increases in both negative and positive phase reference currents on a distribution cable feeding a transformer and to trigger a circuit breaker to isolate the cable only if the negative sequence current increase exceeds a predetermined proportion of any simultaneous positive sequence current increase. Consequently, energising with a 12.5% unbalance current has been found possible without false tripping.