ABSTRACT
A three-phase transformer, either step-up or step-down, is an integral part of any power system. Small distribution transformers are protected by dropout fuses, whereas high-capacity transformers require more sophisticated relaying. Such transformers are subjected to three-phase, L-L-G, L-L, L-G and interturn faults, and, the resulting short-circuit current being abnormal, the transformer needs to be disconnected from the remaining healthy system, with the help of reliable relaying, to avoid damage.
