Effect of water vapor on the production of S{sub 2}F{sub 10} and S{sub 2}OF{sub 10} by spark discharges in SF{sub 6}

Because of its toxicity, S{sub 2}F{sub 10} is of concern to users of SF{sub 6}-filled electrical equipment. While no significantly high concentrations of S{sub 2}F{sub 10} has been found in high voltage power equipment, thus far, it is important to understand the mechanism of and the influence of SF{sub 6} impurities on the formation of S{sub 2}F{sub 10} in order to assess the potential buildup of this byproduct in high voltage equipment under a wide range of discharge conditions. Production rates of the compounds disulfur decafluoride (S{sub 2}F{sub 10}) and bis(pentafuorosulfur) oxide (S{sub 2}OF{sub 10}) have been measured following spark discharges in SF{sub 6} as a function of water content for water concentrations in the range 600--3,400 ppm (parts-per-million). Sparks were produced by capacitive discharge (80 J per spark) into SF{sub 6} at a pressure of 100 kPa. Absolute yields were determined from the spark energy from direct measurements of the voltage and current waveforms. In dry SF{sub 6} the spark yield of S{sub 2}F{sub 10} is 2.2 {times} 10{sup {minus}11} mol J{sup {minus}1}. Adding water to SF{sub 6} the spark yield of S{sub 2}F{sub 10} is 2.2 {times} 10{sup {minus}11} mol J{sup {minus}1}. Adding water to SF{sub 6} results in a decrease in the yield of S{sub 2}F{sub 10} and an increase in the S{sub 2}OF{sub 10} yields. Production of both S{sub 2}F{sub 10} and S{sub 2}OF{sub 10} are believed to be formed via the precursor SF{sub 5}. Mechanism for production of these two disulfur compounds will be discussed