A Review of Electrical Breakdown in Mixtures of SF6 and Other Gases

The outstanding electrical and arc-quenching characteristics of sulphur-hexafluoride (SF6) have already set new trends and standards for the construction of high voltage equipment. Intensive research is being carried out on the electrical properties of SF6, other electronegative gases and their mixtures with more common gases. The aims are to obtain an economical insulation with optimal electrical properties and to acquire a better understanding of their prebreakdown and breakdown behavior. Recently [1] we reviewed the breakdwon mechanisms operating in compressed gases and discussed the theoretical results in the light of experimental measurement in SF6. This paper deals with the breakdown and prebreakdown behavior of SF6 mixtures with other electron attaching and non-attaching gases. Uniform and non-uniform field breakdown under the applications of direct, alternating and impulse voltages is discussed. Improvement in properties such as higher breakdown voltages in non-uniform field gaps, less sensitivity to the electrode surface roughness and to the presence of contaminants and improved arc interruption characteristics of SF6-gas mixtures are discussed.