Lighting impulse withstand performance of CF3I-N2 gas mixture for 252 kV GIL insulation

Trifluoroiodomethane (CF3I) has been broadly proposed as one of the most potential replacements for SF6owing to its outstanding dielectric strength and eco-friendly property. In this study, the basic lighting impulse withstand performance of CF3I and nitrogen mixture with a volume ratio of 20/80 (CF3I-N2(20/80)) under several high gas pressures has been investigated. The withstand voltages (Uw) of two sphere-plate electrode systems were measured and the maximum withstand field strengths (Emax) were calculated to estimate its insulation ability for GIL product. At the same time, the properties of pure sulphur hexafluoride (SF6) and SF6-N2(20/80) gas mixture have been studied for comparison. As the main purpose of this study, a 252 kV gas insulated transmission line (GIL), original designed for pure SF6has been applied to verify the suitability of the CF3I-N2(20/80) mixture. With some design optimization, the CF3I-N2(20/80) gas mixture can supply sufficient withstand ability with enough safety margin for the GIL product.