DIFFERENTIAL PROTECTIVE RELAY FOR ELECTRICAL BUSES WITH IMPROVED IMMUNITY TO SATURATION OF CURRENT TRANSFORMERS

摘要

A differential protective relay and method for a microprocessor-based bus differential protective relay that ensures fast and sensitive operation under internal fault conditions and offers improved stability during external fault and other non-internal fault conditions. The method uses a two-slope differential characteristic to cope with small CT transformation errors without reducing relay sensitivity. The method can also use a saturation detector to switch dynamically between the 1-out-of-2 and 2-out-of-2 operating mode depending whether or not the CTs saturate. In a 2-out-of-2 operating mode, both the differential and directional elements must confirm a fault for the relay to trip. In a 1-out-of-2 mode, if saturation is not detected, the relay can trip without checking the fault direction.