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

Sulphur hexafluoride is synthesised as a persistent and non-toxic gas with an exceptional dielectric strength. In contemporary medium-voltage switchgear within power distribution systems, SF6 gas is used for the insulation and the extinction of electric arc. The application of SF6 has advantages in terms of gas physicochemical characteristics and performance; the dimensions, the cost-effectiveness, the reliability of the switchgear equipment and the duration, as well as the cost of maintenance were significantly reduced. SF6 is a known greenhouse gas, which 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 (R) 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 cause a serious health hazard in the case of leakage in urban areas, rendering red threat zones from 10 to 60 m in radius.