New SF6 EHV Circuit Breakers for 550 KV and 765 KV

An SF6 power circuit breaker for EHV service at 550 kV and 765 kV is described. Redesign and modification of the existing structure has reduced the number of modules required at 550 kV and has uprated the three module design for 765 kV application. The dielectric strength has been increased by increasing the minimum operating gas pressure from 30 psig to 45 psig. Control of moisture is insured by the addition of large driers in the gas circulating system and careful attention to installation and servicing procedures. Switching surge control is provided by resistor insertion on closing, with additional control available in the form of two-step resistor closing. Modular construction permits verification of the breaker ratings by testing a single module or a single break. Preliminary development tests on a single break and a single column have verified the adequacy of the design for 550 kV and 765 kV circuit breaker applications.