Influence of discharge production conditions, gas pressure, current intensity and voltage type, on SF6 dissociation under point–plane corona discharges

Abstract

The study of the formation of Sulfur Hexafluoride (SF6) dissociation products under point to plane corona discharges was carried out at PSF6=300 kPa using different discharges production conditions (50 Hz ac voltage, dc negative polarity voltage, mean discharge current intensity Ī varying between 2 and 45 μA for dc negative polarity voltage), for two plane electrode materials (aluminum and stainless steel), and moisture levels (200 and 2000 ppmv H2O). The stable gaseous by-products formed (SO2F2, SOF4, SOF2, and S2F10) were assayed by gas-phase chromatography. The results indicate an important effect of the metal constituting the plane electrode and of the moisture conditions whatever the SF6 pressure (100–300 kPa), discharges intensity (Ī) and voltage type studied. An effect of the increase of SF6 pressure up to 300 kPa was mainly observed for S2F10 and corresponds to a greater formation of this compound with PSF6. The influence of the mean discharge current intensity on SF6 by-product formation carried out for a transported charge of 1 C showed that for Ī≤10 μA, the effect varies according to the compound considered and depends on the water content of the SF6 and/or on the plane electrode material, whereas for Ī≳10 μA, the levels of the four compound studied hardly vary with the current. Comparison of results obtained under ac and dc voltage for a cumulated charge of between 0.5 and 11 C showed that (SO2F2+SOF4) and SOF2 were formed in larger quantities with ac than with dc, unlike S2F10 for which the opposite effect was observed.