Dead-tank circuit breaker 3AP1 DT

SF6 gas-insulatedshort-circuithigh-voltage

Secured power supply in rough environmental conditions To secure global power supply over the long term, reliable equipment is essential. This naturally also applies to applications in rough environmental conditions. In particular, low temperatures affect the performance of high-voltage circuit breakers. The most common medium used for arc-extinguishing and high-voltage insulation is sulphur hexafluoride (SF6). One major technical limitation of SF6, however, is the condensation temperature, especially when this gas is used with significant overpressure. At rated lockout pressure and temperatures lower than approx. –30 °C liquefaction occurs and the remaining SF6 gas densitiy would not be sufficient to ensure the full switching performance of the circuit breaker. An appropriate solution is the use of a mixture of SF6 and tetrafluormethane (CF4). The mixture of these two gases represents an optimum solution for covering the low-temperature applications without affecting switching performance. The mixture ensures a liquefaction-free insulation and arc-extinguishing medium as the SF6 partial pressure is sufficiently reduced. Based on the existing circuit breaker design, the pure SF6 filling will be replaced by a composition of • 43 percent SF6 and 57 percent CF4 for applications down to −50 °C, and • 25 percent SF6 and 75 percent CF4 for conditions down to −60 °C.