High-purity sulfur hexafluoride gas has excellent insulation and arc-extinguishing properties, which ensures the short-circuit breaking capacity and safety of the ring main unit. This requires manufacturers to completely evacuate the air from the gas chamber before filling it with sulfur hexafluoride, theoretically, the higher the vacuum degree, the better.

  Sulfur hexafluoride gas has a history of over a century. It is a synthetic inert gas created by two French chemists, Moissan and Lebeau, in 1900. Around 1940, the U.S. military used it in the Manhattan Project (nuclear military). It became commercially available in 1947. Currently, SF6 gas is primarily used in the power industry. SF6 gas is utilized in four types of electrical equipment for insulation and/or arc-extinguishing: SF6 circuit breakers and GIS (here referring to sulfur hexafluoride enclosed combined electrical apparatus, internationally known as "Gas Insulated Switchgear"), SF6 load switchgear, SF6 insulated transmission pipelines, SF6 transformers, and SF6 insulated substations. 80% of it is used in medium and high voltage power equipment.