Insulation Performance of Environmentally Friendly, Fluoroketone Based Insulation Gas Mixtures

In recent years, various gas mixtures have been proposed as alternative for SF6 as insulation gas in medium- and high voltage (MV, HV) switchgears, which exhibit a very low Global Warming Potential (GWP), but have lower specific insulation performance than SF6, which must be compensated for example by higher filling pressure. For a proper dimensioning of such an insulation system, a large statistic on breakdown characteristics is needed. In this report, the influence of different filling pressures and of the concentration of the dielectric dominant additive (namely Fluoroketones) on the dielectric breakdown behavior is presented. Therefore, numerous breakdown tests with AC (50 Hz) and lightning impulse voltage (1.2 µs/50 µs) have been performed on stainless steel electrodes (sphere-sphere) to establish reliable limit values of the inner dielectric strength of those gas mixtures. The non-condensing background gas was chosen to be dry synthetic air (80% N2, 20% O2). Simple approximation formulas are derived to accomplish a fast estimation of the dielectric strength of those gas mixtures.