Instantaneous bus-differential protection

CURRENT TRANSFORMER core saturation has contributed largely to the difficulty of obtaining satisfactory bus differential relaying in the past. The scheme here proposed uses differentially connected standard bushing current transformers, and is supported by test data permitting wide application. The relay used has high impedance in comparison to the resistance of the current transformer secondaries and this accounts for its successful operation in precluding false tripping on external faults even when one or more of the current transformers has become completely saturated.