Surface flashover characteristics of epoxy insulator in C4F7N/CO2 mixtures in a uniform field under AC voltage

This paper reports on an investigation into the surface flashover of an insulator in a C₄F₇N/CO₂ mixture which is used as an alternative to SF₆. To date, no studies on this aspect have been reported in the literature. This study was done for a uniform field using a 220 kV AC experimental platform. The influence of molar fraction, gas pressure and creepage distance is reported and compared to that in SF₆. The results show that small quantities of C₄F₇N mixed in CO₂ can increase the surface flashover voltage but, as the fraction of C₄F₇N increases, saturation of the surface flashover occurs. The relative surface flashover voltage of 13.0% C₄F₇N/87.0% CO₂ is approximately 80% that of SF₆. The empirical formulae on the critical flashover electrical field has been obtained, which may be referenced in the design of environment friendly high voltage equipment.