Transfer-Trip Implementation Considerations in Protecting Generating Facilities
Transfer-trip is a widely used and growing method of protecting equipment. With reliable, redundant communications paths, it is highly effective at quickly removing equipment from service during system transients. Special considerations must be made when implementing transfer-trip at generating facilities. Particularly, the generating unit (or units) must be removed from service as quickly as possible during system transients while maintaining the ability to stay online during normal operations. This is especially challenging at sites with legacy equipment that may not be entirely in control of the generation owner. This paper will examine transfer-trip from the perspective of protecting generating equipment and the challenges TVA encountered at a non-TVA owned customer site where this protection was implemented. This protection features logic implemented in the line current differential relays that protect the feeder to the generating unit. It will examine the unique protection challenges encountered and how TVA addressed each one as they occurred. It will also demonstrate how the final protection scheme improves trip time over traditional generator backup protection.