Recent Trends in Development of High Voltage Circuit Breakers with SF6 Alternative Gases

Abstract

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.

Axial Blast Type Discharge Chamber with Moving Electrode

“…Gas leaves from the discharge chamber into receiver volume after break of a diaphragm (8). The cavity behind the piston plays a role of the shock-absorber since gas is squeezed out from it through a narrow slit between a tube (5) and the fluoroplastic cartridge (9). Windows (10) are purposed for optical diagnostics.…”

“…But SF 6 is a potent greenhouse gas [4]. And general world position on the reduction of SF 6 gas usage [4][5][6] demands development of new approaches in electric-power industry, namely, a wide search of new arc-interruption environments, and also new insulation and electrode materials suitable to work in these environments at high current amplitudes.…”

Ablation-Dominated Arcs in CO2 Atmosphere - Part I: Temperature Determination near Current Zero

“…Gas mixtures containing fluoro-nitriles (C 4 F 7 N) or fluoro-ketones (C 5 F 10 O) as minority components (<20 %) have been identified as most promising alternatives to SF in high-voltage gas-insulated switchgear applications, because of their low global warming potential together with their dielectric strength values being comparable to SF 6 [5][6][7]. Due to high boiling points (at 1 bar) of the fluoro-ketones (27 • C) and fluoro-nitriles (-4.7 • C), gas mixtures with carbon dioxide CO 2 as buffer gas prevent liquefaction at temperatures below -30 • C. One of the most promising alternatives that has less limitations concerning temperature range and greenhouse effect but reasonable electrical insulation is CO 2 [8][9][10]. Moreover, some of the experimental techniques and results obtained for CO 2 will be relevant for other alternative gases that are usually applied with CO 2 as buffer gas.…”

Comparison of gases for electrical insulation: Fundamental concepts

“…The most popular alternatives are the atmospheric gases CO2, N2 and O2 [5], [15] and mixtures of these gases with synthetic compounds such as the fluorinated nitrile C4F7N [8], [16], [17], the fluorinated ketone C5F10O [6], [7], trifluoroiodomethane CF3I [20]- [23] or the hydrofluoroolefin HFO-1234ze(E) [25]- [27]. These synthetic compounds have significantly reduced atmospheric lifetimes compared to SF6 [28]- [33] and are typically added in relatively small concentrations to atmospheric gases, achieving an electric strength close to that of SF6 [34]. Insulation gases affect two relevant technical parameters of electrical equipment, which are the maximum operating voltage, limited by the partial discharge inception or the breakdown voltage, and the minimum operating temperature, limited by the dew point of the gas mixture.…”

“…The comparison is more challenging for mixtures due to the additionally degree of freedom of mixing two or more compounds in arbitrary mole fractions. Several previous studies solely compare properties of the pure compounds [9], [11], [35] or tabulate properties of gas mixtures at specific concentrations and pressures [10], [34], [36]. However, comparing the performance of different mixtures and choosing the optimum gas composition and pressure remains a major challenge.…”