Insulation Coordination Qualities of 500-kV SF6 Circuit Breakers

High-voltage laboratory tests on a 500-kV SF6 circuit breaker are discussed and analyzed in terms of insuring effective insulation coordination on a live-tank breaker for either 1550-kV or 1800-kV BIL service. Sixty-cycle, impulse, switching surge, and corona level tests were made at minimum operating (alarm) pressure. Additional tests at 0 psig revealed a 60-cycle withstand in excess of twice line-to-neutral voltage. A uniquely designed horizontal, live-tank, circuit-breaker bushing is presented and shown to have excellent contamination resistance, even when wet. The need for parallel protective gaps is stressed to relieve the current transformer from acting as the coordinating element.