ABSTRACT
Overcurrent protection with fuses or relays provided the –rst type of transformer fault protection [4], and it continues to be applied in small-capacity transformers. e di›erential principle for transformer protection was introduced by connecting an inverse-time overcurrent relay in the paralleled secondaries of the current transformers (CT) [4]. e percentage-di›erential principle [5], which was immediately applied to transformer protection [4,6,7], provided excellent results in improving the security of di›erential protection for external faults with CT saturation.
