Surface Flashover Characteristics of the 252-kV Conical Insulator in C4F7N/CO2 Gas Mixture

This article reports on an investigation into the surface flashover characteristics of the 252-kV conical insulator in a C4F7N/CO2 mixture, which is used as an alternative to sulphur hexafluoride (SF6). This study was done for a quasi-uniform field using a 252-kV experimental platform. The influence of molar fraction and gas pressure is reported and compared to that in SF6. Results show that small quantities of C4F7N mixed in CO2 can increase the surface flashover voltage. Four types of discharge traces are observed in the experiment, and most traces are on the concave side under both ac and lightning impulse (LI) voltage. The polarity effect is observed in C4F7N/CO2 gas mixtures. An empirical formula is fitted for C4F7N/CO2 mixtures by experimental data under LI(–), and 0.7-MPa 9%C4F7N/91%CO2 mixture has great potential to replace 0.5-MPa SF6.