Sulfur Hexafluoride SF{sub}6

摘要

Sulfur hexafluoride (SF{sub}6) is a colorless, odorless, non-toxic and non flammable gas. With a gas density of 6.07 g/l (20°C,1 bar), SF{sub}6 is about 5 times heavier than air and one of the heaviest known gases. It is an extremely stable gas with high dielectric strength and excellent arc quenching properties making it an ideal for use in gas insulated substations (GIS) and related equipment in electrical transmission and distribution systems (Fig. 1, 2) Virtually all substations being built today use SF{sub}6 for circuit breakers and every GIS station relies on SF{sub}6 for insulation. In an ideal world, SF{sub}6 would be contained and remain within electrical enclosures, but in the real world such is not the case. SF{sub}6 is emitted in the atmosphere as equipment grows old, through valve fittings, flanges and porcelain bushings. SF{sub}6 can be released into the atmosphere during installation and equipment servicing. The EPA estimates that in 2000, 604 metric tons of SF{sub}6 was released from electrical power system or 14.4 million metric tons of carbon dioxide equivalent. At the same time, SF{sub}6 has been identified as a potent greenhouse gas, 22,500 times more effective at trapping infra-red radiation than an equivalent amount of CO{sub}2 with an atmospheric lifetime of 520 years.