The purity of SF6 gas is extremely important for the safe and reliable operation of gas-insulated equipment. The impurities in SF6 gas mainly include air, CF4, moisture, nitrogen compounds, mineral oil, fluorides, etc. These impurities may come from the following four aspects: ① Decomposition products generated by SF6 gas under the action of arc, spark discharge, or corona discharge, mainly low fluorides; ② When gas-insulated equipment undergoes major maintenance, gas recovery devices are usually used to recover SF6 gas from the equipment, during which moisture and mechanical oil may be mixed in; ③ Certain impurities, mainly air, may also be introduced when filling gas-insulated equipment with gas; ④ Trace impurities may remain from the manufacturing process. To limit the content of impurities in SF6 gas, China stipulates that the purity of new SF6 gas shall not be less than 99.8%, the purity of SF6 gas after being filled into equipment shall not be less than 97%, and the purity of SF6 gas during operation shall not be less than 95%.
