Comanche peak switchyard event

This article discusses the electrical fault event that occurred on the 345 KV line between Comanche peak and Parker switching station. This event was caused by the failure of the primary and backup relay systems to operate on Breaker 8040 at Comanche Peak due to high contact resistance that had developed in the CHC fault detector relay in each relay system. Both relays have been replaced. Also, the protective relaying integrity of all lines out of Comanche Peak has since been validated. The ERCOT underfrequency load shedding relay scheme operated as designed to minimize the loss of load and generation. Also, the 138 kV source from Stephenville remained secure to Comanche Peak to maintain the nuclear safety systems. The immediate response to the event by all parties was good. Service was quickly and safely restored to the switchyard. The portion of the relay system that failed was identified, corrective action was taken, and the units were returned to service. Oncor has determined what happened, determined why the failure occurred, and developed a plan of action to prevent a reoccurrence.