Dead Tank Ready for cooldown3AP1 DT up to 170 kV with mixed gases for lowest temperature applications 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 tetrafluormeth-ane (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. Additionally, the rated filling pressure is increased by 1.5 bar to 7.5 bar. Consequently, the new low-temperature circuit-breaker with mixed gases offers mainly the same technical key ratings as the standard circuit-breaker that is used for low temperature conditions down to -30 °C. The normal rated current, in particular, was certified for the same values as the standard breaker with pure SF6 filling. For a 60 Hz application, the short-circuit current needs an insignificant line-to-ground of 3 nF (not required for 50 Hz). Usually, this capacitance value is available in power grid configurations with capacitive voltage dividers. Obviously, a circuit-breaker installation that provides this value within the grid configuration doesn't need the external capacitors.This gives the customer the possibility to use standard equipment without any major modifications. The new mixed gas solution is an alternative option to the proven devices with tank heaters for operation in harsh weather conditions with temperatures down to -60°C.

3AP1 DT 145 kV* design 1995 with tank heaters 3AP1 DT 145 kV* enhanced design 2015 with mixed gas solution 400.000 _ CO2 footprint In terms of overall global warming potential (GWP), the mixed gas solution also offers advantages for a 100-year time horizon, because the GWP of CF4 (7,400) is three times lower than that of SF6 (22,800). Additionally, the new dead tank offers a leakage rate of less than 0.1 percent per annum of gas losses for the complete circuit-breaker. In comparison to other low-temperature applications with tank heaters, the mixed gas solution shows a markedly reduced CO2 footprint....