Decomposition characteristics of SF<inf>6</inf> under overheating conditions

Overheating is one of the severe defects in gas-insulated switchgear (GIS). However, researches on decomposition characteristics of SF ₆ under overheating conditions are relatively limited. In this paper, SF ₆ decomposition products are studied under three overheating conditions which are overheating of solid insulation, overheating of metal, and overheating of metal adjacent to insulating material. Influence of overheating temperature, gas pressure, initial moisture content and adsorbent on the decomposition characteristics of SF ₆ is discussed. The results show that typical decomposition products of SF ₆ under overheating of solid insulation are H ₂ , CO, CO ₂ , CH ₄ , SOF ₂ , SO ₂ , H ₂ S, COS and CF4, and typical decomposition products of SF ₆ under overheating of metal are SOF ₂ , SO ₂ , CO and CO ₂ . Besides, typical decomposition products of SF ₆ under overheating of metal adjacent to insulating material are CO, CO ₂ , SOF ₂ , SO ₂ , CF ₄ , CS ₂ and COS. Types of overheating can be recognized by characteristic ratio of (SOF ₂ +SO ₂ )/(CO+CO ₂ ): for overheating of solid insulation, the ratio is 0 to 0.25, and for overheating involving metal, it is greater than 1. Two types of overheating involving metal can be distinguished by their characteristic products such as CS ₂ , COS and CF ₄ .