Review
We discovered the differential relay was programmed as a generator-only, whereas the correct program should have been a generator-transformer differential relay, due to the zone of protection coverage determined by the position of the CT’s installed either side of the HV/LV transformer.
Primary injection testing revealed that the orientation of the generator LV CT’s were in reverse polarity, resulting in the differential scheme identifying an in-zone fault for ‘through-load’ generator operations.
