Insulating Characteristics of Gas Mixtures with C3F8/C2F6 and N2/CO2

Summary

Since SF6 gas has excellent insulation characteristics and arc-extinguishing performance, it is used for the main equipment in power systems, such as gas-insulated switchgears, gas circuit breakers, and gas-insulated transmission lines. However, due to the problem of its significant global warming effect, SF6 gas was designated at the Third Conference of the Parties to the United Nations Framework Convention on Climate Change in Kyoto in 1997 as a greenhouse gas, emissions of which must be reduced. In the present study, alternative gases were selected from among mixtures excluding SF6 with the need to reduce GWP: Global Warming Potential in mind. Gas mixtures containing such substances and with a boiling point of -25?C or less, chemically stable, non-toxic, and not ozone-depleting were prioritized. Furthermore, the availability and environmental performance were taken into consideration when deciding on component gases. Consequently, to launch this series of studies, four types of gas mixtures were used combining a gas in Group A: C2F6, C3F8 – electronegative gases with relatively high dielectric strength – and a gas in Group B: N2, CO2 – gases existing in the natural world. The GWP of SF6 is 22,800 whereas that of C2F6 is 12,200 and that of C3F8 is 8,830, or several times smaller than that of SF6. In the present paper, insulation characteristics were experimentally obtained while varying the mixture ratio under a quasi-uniform electric field assuming GIS. Consequently, compared to the GWP of pure SF6, the GWP was about 12% to 38% for gas mixtures with C3F8 / N2 or C3F8 / CO2 and 18% to 70% for gas mixtures with C2F6 / N2 or C2F6 / CO2. Consequently, it emerged that, while assuming breakdown voltage proportional to gas pressure, the GWP was likely to be reduced by 30% to 90% while maintaining dielectric strength.

Additional informations

Authors

Petrovic, Yang Hao, Zhang Qiaogen