Influence of insulating gas on pressure rise in electrical installations due to internal arcs

Internal arcs cause a rapid increase in pressure in electrical installations. The type of insulation gas has influence on pressure rise. Typically SF6 is used in compact metal-clad switchgear. This gas has a high global warming potential. Because of this the replacement of SF6 by alternative gases such as CO2 is under discussion. The pressure developments in a closed vessel filled with CO2, SF6 and air are measured and compared. During internal arcing in gas-insulated switchgear the overpressure causes a rupture of a burst plate and heated gas escapes into the surrounding room mixing with air. The portions of electric energy causing overpressure are therefore determined depending on gas density. To perform pressure calculations, reliable gas data and arc voltages are necessary. The arc voltages in the test vessel have been measured. CO2/air gas data are provided in a wide range of pressure and temperature. The thermodynamic properties are directly calculated from the number densities and from the internal partition functions. The transport coefficients are deduced using the ChapmanEnskog method.