Spark decomposition of SF6, SF6/N-2 (10 : 90 and 5 : 95) mixtures in the presence of solid additives (polyethylene, polypropylene or Teflon), gaseous additives (methane, ethylene, octofluoropropane, carbon monoxide or dioxide), water or oxygen

摘要

The present paper is a continuation of the investigations on the sparking-induced decomposition of SF6 and SF6/N-2 (10: 90) Mixtures which have already been carried out in our laboratory, both experimentally and numerically. It concerns the decomposition of SF6/N-2 mixtures (100 kPa) containing 100%, 10% or 5 % of SF6, under high-energy sparks (3.6 J spark(-1)) generated in a 340 cm(3) experimental cell between a stainless steel point and a stainless steel plane. Our attention was focused on the following main by-products: (SF4 + SOF4 (SOF4 + SO2F2), S2F10, CF4, CO and CO,? which were studied by varying the concentration of the impurities added H2O, O-2 (0-0.2%), in the presence of atoms such as H and C released from vaporized solid insulators (polyethylene [C2H4](n), polypropylene [C3H6](n), Teflon [CF2](n)) or from gaseous additives (methane CH4 (0-4%), ethylene C2H4 (0-2%), octofluoropropane C3F8 (0-5%)), with the aim of simulating the occurrence of sparking in electrical devices, especially along spacers. As SF6/CO2 and SF6/N-2/CO2 mixtures are reported to be able to constitute promising SF6 substitutes for industrial applications, we also studied the chemical stability of SF6 and SF6/N-2 (5: 95) mixtures in the presence of 0-20% CO2. The presence of additives CH4, C2H4, C3F8 or solid insulator (polyethylene, polypropylene, Teflon) leads to lower production of (SF4 + SOF2) and S2F10 in dilute SF6 than in pure SF6 when the percentages of additives or the amounts of solid insulator vaporized are high. Concerning the additive CO2, we observe an increased production of (SOF4 + SO2F2) and a formation of large quantities of CO, more pronounced in SF6/N-2 (5 : 95) mixtures than in pure SF6. In contrast, the presence of CO leads to a lesser degree of decomposition of diluted than undiluted SF6. [References: 28]