Type-testing of a new metal-enclosed 145 kV CO2/O2/C4-FN Circuit Breaker with a cross-platform Design

CO2 / O2 / C4-FN gas mixtures have successfully been used to replace SF6 in metal-enclosed circuit breakers designed for a wide range of voltage and short-circuit current ratings. The successful testing of two new circuit breakers, a 145 kV / 63 kA dead-tank circuit breaker and a 145 kV / 40 kA circuit breaker for gas-insulated switchgear applications, is summarized in this work. The two circuit breakers are both based on the same design philosophy, but each interrupter (one per phase) is housed in a separate enclosure in the case of the former, while all three interrupters are housed in the same enclosure in the case of the latter. Associated differences in testing strategies are highlighted. The robust, reliable performance of these circuit breakers enabled multiple test duties to be combined (by testing the harder of any differing requirements), wherever the applicable IEC and IEEE standards permitted this approach. The combination of test duties, for example to cover multiple test duties or to test according to two different standards, permitted more efficient, faster completion of the tests and reduced the costs of testing. The results of some key tests, including terminal fault tests, short-line fault tests, and shunt reactor switching and capacitive switching tests are presented.