Optical Sensing of SF6 Dissociation Levels in Electrical Discharges

Abstract

Sulphur hexafluoride (SF6) is widely used as an insulating medium in high voltage systems including switchgear, transformers and transmission lines. If electrical breakdown occurs in SF6, a corona, glow or arc discharge forms, and this results in dissociation of SF6 molecules. However, if the SF6 gas is pure and the walls of the containing vessel are chemically inert, the products of dissociation tend preferentially to recombine at a rapid rate to reform SF6. If any chemical reaction with gas impurity or wall material occurs during or immediately following a discharge, recombination may be substantially reduced and the insulating efficiency of the high voltage system is degraded as a consequence of the loss of SF6. Invariably, it is the latter process that takes place, because of the presence of contaminants such as oxygen and water vapour.