Appointed to analyse a protection issue at a Data Centre in Paris. The standby generators were tripping on differential protection.
The Issue – Appointed to analyse a protection issue at a Data Centre in Paris. The standby generators were tripping on differential protection.
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.
We proposed alternative settings and logic for the generator differential relays (8x in total) to account for the HV/LV transformer being within the differential zone.
The client accepted our proposal in which we fully implemented into the relays and commissioned; generator LV CT polarity reversed by our Commissioning Team.
Generator load checks performed with differential schemes ‘stable’ after all changes made.