Field Tests on a 345-Kv High-Capacity Oil Circuit Breaker at Philip Sporn Power Plant

1. A 345-kv OCB rated 25,000, was tested extensively at the Philip Sporn Station of the AEP system for performance on both line-dropping and fault-interruption duty. 2. The full-scale tests demonstrated the adequacy of the breaker over an extremely wide range of fault conditions and for line-charging current-switching duty up to and beyond the present maximum lineswitching requirements of the AEP system at 345 kv. 3. The line-dropping tests were free of the high transient overvoltages which accompany severe restrikes. In 57 3 phase tests at currents up to 226 amperes, there were three single restrikes with maximum transient voltages lower than those accompanying normal fault interruptions. 4. Fault duty tests included singlephase as well as both grounded and ungrounded 3-phase faults, high-speed reclosing, and a 4-operation AEP reclosing duty cycle at fault duties between 1,160 and 13,380 mva. The tests confirmed the usefulness of field tests and inspired confidence in the results of laboratory tests previously reported.2 5. The field tests also demonstrated the more severe duty imposed on a circuit breaker by 3-phase ungrounded faults. Arcing times for 3-phase ungrounded faults were found to be approximately one half-cycle longer than for grounded faults because of the higher power-frequency recovery voltage across the first pole to clear. Because of the rarity of 3-phase ungrounded faults in service, it is the opinion of the authors that industry standards should recognize a longer applicable rated interrupting time for this type of fault for breakers intended for application on effectively grounded systems.