Sulphur hexafluoride in modern medium-voltage switchgear: advantages, hazards, and environmental impact

Abstract

Sulphur hexafluoride (SF₆) is synthesised as a persistent and non-toxic gas with exceptional dielectric strength. In contemporary medium-voltage switchgear within power distribution systems, SF₆ gas is utilised for insulation and the extinction of electric arc. The application of SF₆ has advantages in terms of gas physicochemical characteristics and performance; the dimensions, cost-effectiveness, and reliability of the switchgear equipment, and duration and cost of maintenance were significantly reduced. SF₆ is a known greenhouse gas, that tends to accumulate in the lungs, inducing oxygen depletion and respiratory complications. The by-products of SF₆ formed during the electric arc can be harmful and toxic. The equipment containing SF₆ is being replaced in the EU and worldwide. Using ALOHA^® software the scenarios of leakage for SF₆ and by-products were modelled in urban areas, where the switchgear is frequently placed. In areas where the circulation of wind is lower (urban areas), in hazardous situations, it is not possible to depend on high dispersion levels or minimisation of concentration and threat. The models have shown that SF₆ poses an environmental problem and its by-products a serious health hazard in the case of leakage in urban areas, rendering red threat zones from 10 to 60 m in radius.