Electricity Today T&D Magazine

Sulfur hexafluoride (SF₆) insulates medium- and high-voltage switchgears around the world. In its pure form, this non-toxic, inert gas helps the power transmission & distribution (T&D) industry operate more safely by extinguishing high-temperature arcs. With a much higher dielectric strength compared to other media, SF₆ also allows gas-insulated equipment (GIE) to be compact. The non-flammable gas is a potent arc quencher: In the high-heat environment of an electrical discharge, the six fluorine atoms split from the sulfur atom to capture an electron. After the discharge is quenched, the molecule quickly recombines.
As GIE ages, moisture enters the gas compartment to equalize with the dry SF₆ gas. However, humidity in the gas causes severe operational and safety issues. Water is an impurity that, by its very presence, lowers the overall system's dielectric strength. H₂O also prevents sulfur and fluoride from recombining fully. When SF₆ doesn't "self-heal" completely after each electrical arc,...