Dielectric withstand and breaking capacity of SF6 circuit breakers at low temperatures

The influence of low temperatures on the dielectric withstand and the breaking capacity of a puffer-type SF₆ circuit breaker was studied. Results of a dielectric and breaking tests are analyzed for temperatures ranging from -50°C to 20°C. The tests suggest that the decrease in performance at lower temperatures is related not only to the gas density but also, and principally, to the real pressure of the gas in the interruption chamber, which would take account of both the gas temperature and its density. The test results also indicate that drops of liquid on the breaker contacts or adjacent parts do not seem to jeopardize the dielectric withstand of the intercontact gap