SF6 samples (PSF6=100 or 200 kPa) were submitted to point-to-plane dc negative polarity corona discharges in the presence of water [concentration=2000 ppmv (parts per million by volume)] or without the addition of water. The stable gaseous byproducts formed, (SO2F2, SOF2, and S2F10) were assayed by gas-phase chromatography. The variation of their yields against the charge transported (up to 10 C) was studied for two metals (aluminum and stainless steel) constituting the plane electrode, at various values of the SF6 pressure, the water content, the gap spacing (2.5 and 8 mm), and the discharge current [12≤Ī (μA)≤25]. The results indicate an important effect of the metal constituting the plane electrode and of the moisture conditions, particularly on the production of SOF2 and S2F10.
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.
L'influence du type du métal constituant l'électrode plane (aluminium, cuivre, acier inoxydable) sur la décomposition de SF6 (PSF6=300 kPa) sec (pas d'eau ajoutée ; ≃ 200 ppmv H2O) ou humide (2000 ppmv H2O) soumis à des décharges couronne (géométrie pointe-plan; tension continue de polarité négative ; $\bar{I}=25~\mu$A ; 0 < Q ≤10 C) a été mise en évidence en dosant les quantités des principaux sous-produits gazeux, SOF2, “SOF4+SO2F2”, S2F10, formés. Cette influence est d'autant plus nette que la valeur de la charge transportée et que le taux d'humidité du SF6 sont élevés. L'utilisation d'une électrode en aluminium favorise la formation du “SOF4 + SO2F2” et du S2F10, celle d'une électrode en acier inoxydable favorise par contre celle du SOF2. Les différences de composition de la phase gazeuse observées au cours d'un essai et selon le métal sont quasi totalement dues à la passivation de l'électrode plane en cours d'essai. L'utilisation d'électrodes vieillies entraîne une diminution de la formation de SOF2 mais augmente par contre celle du S2F10
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