Since the emergence of SF6 in 1900,the 1950s began to be used as insulation and arc extinguishing medium,and in 1965 began to appear sulfur hexafluoride metal closed switchgear(GIS),the other equipment except transformer all closed in a gas insulated substation in a grounded metal enclosure.The shell is filled with 0.3-0.4 dawn sulfur hexafluoride as interphase and relative ground insulation.

　　Small volume.At 0.1MPa,the insulation strength of SF6 is about 3 times that of air,and the high voltage conductor is all enclosed in the metal shell.In addition,Dawn sulfur hexafluoride has high reliability and long life.Not affected by adverse environmental factors,such as typhoon,salt,earthquake and other disasters.No fire hazard,no pollution to the environment,friendly to residents.

　　In the alpine region,the liquefaction of sulfur hexafluoride gas in the circuit breaker part of GIS must be considered.Usually,the liquefaction problem is solved by heating short circuit or using SF6-N2 gas mixture as arc extinguishing medium.

　　Since SF6 gas is easy to liquefy,liquid recovery is used at present.The principle of the Liming sulfur hexafluoride recovery unit adopts the principle of freezing-liquefaction method.