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.