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The available knowledge of state-of-the-art of SF6 alternative gases in switching applications was collected and evaluated in an initiative of the Current Zero Club together with CIGRE. The present contribution summarizes the main results of this activity and will also include the latest trends. The main properties and switching performance of new gases are compared to SF6. The most promising new gases are at the moment perfluoroketones and perfluoronitriles. Due to the high boiling point of these gases, in HV applications mixtures with CO2 are used. For MV insulation perfluoroketones are mixed with air, but also other combinations might be possible. The dielectric and switching performance of the mixtures, with mixing ratios that allow sufficiently low operating temperatures, is reported to be only slightly below SF6. Minor design changes or de-rating of switchgear are therefore necessary. Differences between the gas mixtures are mainly in the boiling point and the GWP.

Gases and gas mixtures with lower environmental impact are being investigated as possible alternatives to SF6 as the switching medium in high voltage circuit breakers. One of the most important aspects of the investigation is the thermal interruption characteristic which depends on flow acceleration, and efficient cooling of the arc around current zero. In the present work, the influence of the gas properties on the thermal interruption capability is investigated using Computational Fluid Dynamics (CFD). A gas mixture of fluroketones with CO2 as background gas is considered. The underlying thermal interruptions behavior of this gas mixture is compared with that of SF6• The individual influence of the axial flow parameters namely pressure, velocity, Mach number and density on thermal interruption is studied. A thermal interruption proxy parameter is derived by combining the axial flow variables, which can better characterize the thermal interruption. The differences between the different gases using this proxy are presented. The design parameters influencing the pressure build-up and thermal interruption behavior are investigated and discussed.

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