Breakdown Characteristics of CF3I/CO2 Gas Mixtures under Fast Impulse in Rod-plane and GIS Geometries

SF6 is widely used in modern electricity transmission and distribution networks due to 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. However, the global warming potential over 100-yr for SF6 gas is 23,900 times higher than CO2. This has led to research into alternative gases with much lower environmental impact, and one of the emerging candidates is CF3I gas and its mixtures. This paper describes collaborative work investigating the breakdown of a CF3I/CO2 gas mixture with a rod-plane configuration. The breakdown characteristics of 30/70% CF3I/CO2 gas mixture was experimentally determined using (i) a lightning impulse generator (1.2/50) and (ii) a steep-front impulse voltage generator (rise time of 16 ns). The test results show the breakdown voltage of the CF3I/CO2 gas mixture for different gap distances and gas pressures, and the V-t characteristics are presented in the range 20 ns to 20 µs. Furthermore, V-t characteristics are presented for a medium-voltage GIS unit, designed for SF6 gas but tested with a 30/70% CF3I/CO2 gas mixture.