Basic Impulse Performance of High-pressure CF3I-N2 Gas Mixture and Its Application for 126 kV GIL

In this paper, the basic lighting impulse breakdown performance of trifluoroiodomethane and nitrogen mixture with a volume ratio of 20% CF3I - 80% N2under 7 bar absolute gas pressure has been investigated. The 50% lighting impulse breakdown voltages (U50) of three types of electrode gap were measured to investigate the dielectric behavior of the gas mixture. The maximum breakdown field strengths (Emax) have been calculated to evaluate the influence of the electrode gap, which can be used to estimate whether breakdown occurs. At the same time, the characteristics of pure sulphur hexafluoride (SF6) and 20 % SF6– 80% N2gas mixture have been studied for a comparison. In order to evaluate the potential of CF3I-N2 mixture to replace SF6in high voltage equipment, a metal enclosed gas insulated transmission line (GIL) was applied, which was initially designed to be insulated with pure SF6. Also to ensure sufficient safety margin for GIL product, the grounded shield ring embedded in the epoxy disc-insulator was used to reduce the electrical field strength in the gas.