Sparking-induced decomposition of 10% SF6-90% N2 mixtures:: effect of a solid organic insulator, oxygen and water

The chemical stability of 10% SF6-90% N-2 mixtures (100 kPa pressure) has been studied under sparking in the presence or absence of an organic insulator (teflon, kel'F, polyethylene, polypropylene. nylon. megelit), and/or added impurities (0.2%; O-2 or H2O). The study was carried out experimentally and numerically. The production rates of the main decomposition products of SF6: (SF4 + SOF2), S2F10, etc, and of products containing nitrogen, NF3, N2O, were evaluated. The results from the model led to trends similar to those observed experimentally concerning the effects on gas phase composition, of the presence of atoms such as O, H, C, etc, from the vaporized Insulator and/or the added impurities. A comparison of the chemical stability of the SF6-N-2 mixture with that of pure SF6 has also been made. The results can be summarized as follows: in all cases, the major byproducts formed were (SF4 + SOF2) and S2F10; the use of the SF6-N-2 mixture instead of SF6 led to the decreased formation of degradation products: vaporization of an organic insulator caused an increase in the production of degradation products which was less intense for the mixture than for pure SF6; the study carried our with nitrogen-diluted SF, showed the importance of foreign atoms (C. H. O. etc) on the proportion of SF6 that is not regenerated. Owing to their tendency to trap fluorine atoms. the impurity atoms prevent SF6 from recombining and can thus lead to the deterioration of the dielectric qualities of the gas mixture.