Breakdown Characteristics of SF6/CF4 Mixtures in Test Chamber and 25.8kV GIS

SF 6 gas has excellent dielectric strength, but it causes global warming about 23900 times more than CO 2 gas which is the main cause of global warming. This shows necessity of the environment friendly dielectric gas which can replace SF 6 gas. We made the test chamber which simulated inner of the gas insulation switchgear (GIS) and 25.8kV GIS of 3 phase unity bundle operation tank type. The breakdown characteristics are carried out experiment with using impulse, the power frequency and partial discharge (PD) test. In this paper, shows breakdown characteristics of mixed rates and total pressure of SF 6 /CF 4 mixture under the ac voltage and standard lighting impulse voltage. In the result, it was observed that dielectric strength is increased by increasing content of SF 6 gas and increasing pressure of SF 6 /CF 4 mixtures. The PD inception voltages have hardly any effect on mixed rate of SF 6 gas in 25.8kV GIS. SF 6 gas possesses excellent dielectric properties and high degree of chemical stability. SF 6 gas has used the wide range of application in the field of high voltage insulation, such as gas-insulated switchgear and gas insulating transmission line[1]. According to Kyoto protocol (2005.2), despite its many important advantages, SF 6 gas made an issue of environmental influence. No single gas meets all the require property imposed by recent demands on power system, and this mixtures seems to be an appropriate alternative. Environmental point of view, intensive investigations have been focus on the breakdown characteristics of mixed gas which were made of SF 6 gas and buffer gas, such as N 2 gas or CO 2 gas[2][3]. PFCs (Perfluoro carbons) gases that are one of several substitute gas possess many advantages such as non-flammable, non-toxic and relative strong dielectric characteristics. There are CF 4 , C 2 F 6 , C 3 F 8, and C 3 F 6 among PFC gases. PFCs gases are apt to adsorb on the surface of electrode and insulator because activation energy is very high, and it is electronegative gas that number of electrons decreases with the time by inelastic collision. Because PFCs gases have high dielectric strength, PFCs are promised as substitute gas of electric power application. But it is difficult to carry out the experiment used SF 6 / PFCs mixtures because of various restriction and expense. Among PFCs, CF 4 have good electron …