Decomposition of SF6 and Production of S2F10 in Power Arcs

Abstract

Decomposition of SF6 in electrical discharges produces many toxic solids and gases. S2F10 is the most toxic of the gaseous byproducts and has been found in arcs, sparks and corona [1]. Of these, S2F10 production in arcs is the least understood, in part because S2F10 is known to decay rapidly at temperatures above 250°C [1]. As temperatures in an arc are considerably higher, it is believed that S2F10 cannot be formed directly by an arc. The first experiments where S2F10 was detected in SF6 decomposed by a power arc employed a burn-through configuration into another chamber containing SF6 at a lower pressure [2,3]. In those experiments the S2F10 may have been formed during the volume expansion and cooling of the SF6 decomposition products into the second chamber. We have conducted a series of tests of a power arc discharge contained completely within a bus duct configuration. Among the many other gaseous byproducts, we have detected S2F10 at or below the part per million (ppm) by volume level, proving that S2F10 can be formed directly by a power arc within SF6-insulated equipment. The relative production rate of S2F10 with respect to that of SOF2 and SF4, however, implies that S2F10 is not a significant contributor to the hazard of exposure to decomposed SF6.