Potential of CF3I gas mixture as an insulation medium in gas-insulated equipment

SF6 is a widely used gas medium in gas-insulated equipment. Due to the high global warming potential and long atmospheric lifetime of SF6, there has been research into a new environmentally friendly replacement gas. This paper describes the research carried out at Cardiff University on CF3I gas and its mixture as a substitute insulation medium for SF6 in gas-insulated lines (GIL). A reduced-scale coaxial test system having the electric field properties of a full-scale 400 kV GIL system was fabricated. The design of the reduced-scale coaxial test system was simulated to ensure that the highest electric field would be along the center of the conductor. The coaxial prototype was then tested under a standard lightning impulse (1.2/50) in order to determine the 50% breakdown voltage for such a system when insulated with CF3I gas mixture. It was found that CF3I has the potential to replace SF6 as an insulation medium in GIL. A full-scale short length GIL demonstrator is being assembled in the laboratory to evaluate further the feasibility of using a CF3I gas mixture as an insulation medium.