Decomposition products from negative and 50 Hz ac corona discharges in compressed SF6 and SF6/N2 (10:90) mixtures.: Effect of water vapour added to the gas

layer of aluminium (gap space 2.3 mm for pure SF6 and 3.4 mm for SF6/N-2) The gaseous decomposition products SOF4, SO2F2, SF4 + SOS, SO2, S2OF10, S2F10, S2O2F10, S2O3F6, SF5NF2, NF3 and (SF5)(2)NF were assayed by gas chromatography at the end of each run. The comparison of the formation rates of the byproducts detected in SF6 and SF6/N-2 mixtures led to the following conclusions. The use of wet SF6/N-2 presents an additional advantage with respect to pure wet SF6 besides those mentioned above; the production rates of all the usual SF6 decomposition products are much lower with the wet SF6/N-2 (10:90) mixture than with wet SF6. More exactly the addition of 0.3% H2O to SF6/N-2 greatly affects the production rates of all the compounds whose formation needs SF5 radicals as SOF4; so the lower quantity of products formed in SF6/N-2 is in fact more due to the particularly inhibiting effect of water than to the low percentage of SF6 in the mixture. The production of NF3, SF5NF2 and (SF5)(2)NF remains very low compared to the other gaseous byproducts.