A 500-kV Circuit Breaker Using SF6 Gas

The first 500-kV 35 000-MVA breakers to go in service in the United States have been developed and subjected to extensive testing. They are built of modules which can be combined for voltages of 345 kV, 500 kV, and 700 kV. The interrupting medium is SF6 gas in a completely sealed 2-pressure system, operating at constant densities. At 75°F, the higher pressure is about 240 psi; the lower is 45 psi. Contacts and blast valves of each pole unit are connected by a mechanical linkage operated by a pneumatic mechanism. The first breakers, using a mechanism designed for other breakers, have an interrupting time of 3 cycles. A special mechanism, designied for the new SF6 breakers, gives them an interrupting time of 2 cycles.