INFLUENCE OF THE PLANE ELECTRODE (METAL T YPE AND CONDITIONING) ON THE SF6 DECOMPOSITION UNDER NEGATIVE CORONA DISCHARGES

The influence of plane electrode material (aluminium, copper, stainles s steel) on the decomposition of dry (no water added; similar or equal to 200 ppm(v) H2O) or damp (2000 ppm(v) H2O) SF6 (P-SF6 = 300 kPa) su bjected to point-to-plane negative corona discharges (($) over bar = 2 5 mu A.; 0 < Q less than or equal to 10 C) has been displayed by assay ing the quantities of the main gaseous by-products, SOF2, ''SOF4+ SO2F 2'', S2F(10) formed. This influence is all the more clear as the trans ported charge and the SF6 water content values are high. The use of an aluminium electrode is favourable to the ''SOF4 + SO2F2'' and S2F10 p roduction, while that of a stainless steel electrode favours the SOF2 production. The differences in the gas phase composition observed duri ng a test and according to the metal are almost totally due to the pas sivation of the plane electrode during the test. The use of ageing ele ctrodes leads to a decrease of the SOF2 formation and to an increase o f that of S2F10.