Breakdown of CF3I gas and its mixtures under lightning impulse in coaxial-gil geometry

SF₆ is widely used in modern transmission and distribution networks because of its outstanding dual qualities: arc quenching and dielectric insulation. As a gas medium, SF₆ is chemically inert, non-toxic, and non-flammable, which makes possible the construction of compact SF₆ switchgear. One major known disadvantage of the gas is that it has a global warming potential which is 23,900 times higher than CO₂. This has led to research into alternative gases with a much lower environmental impact, and one of the emerging candidates is CF₃I. The high boiling temperature of CF₃I means that it has to be used as part of a mixture inside gas-insulated equipment. To carry out the investigation on CF₃I, a scaled-down coaxial system that replicates the maximum electric field of a 400 kV GIL system was designed and fabricated. The insulation performances of CF₃I/CO2 and CF₃I/N2 gas mixtures were then examined by measuring the 50% breakdown voltage, U50, using a standard lightning impulse waveform (1.2/50) under absolute pressures of 1 to 4 bar. The experimental results show that CF₃I gas mixtures have promising potential as an insulation medium for application in gasinsulated lines.