Study of the decomposition of SF6 under dc negative polarity corona discharges (point-to-plane geometry): Influence of the metal constituting the plane electrode

Abstract

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.

Experimence Study of Trace Water and Oxygen Impact on SF6Decomposition Characteristics Under Partial Discharge

“…5 (a) that when the concentration of O 2 mixed in SF 6 is less than 460ppm, the formation of SO 2 F 2 decreases with the increase of O 2 . When the concentration of O 2 is higher than 460ppm, the concentration of SO 2 F 2 is positively correlated with the concentration of O 2 because an increase in the concentration of O 2 in SF 6 is equivalent to the dilution of SF 2 , SF 4 , SF 5 , and other low-sulfur and fluorine F. Thus, O 2 plays an inhibitory effect on the reaction:…”

“…Although the concentrations of SF 2 , SF 4 , SF 5 , and other low-sulfur components increase with the discharge, as the concentration of O 2 increases, the concentration of H 2 O released by the electrodes and the internal wall of the chamber is diluted at the same time. The rate of the reaction which plays a decisive role in the generation of SOF 2 is shown in the following reaction: Acquiring sufficient knowledge on the decomposition mechanism and the factors that affect variation in the reactions under PD will lay a solid foundation in using decomposed components of SF 6 to assess insulation status and will support related repair guidelines for gas insulated electrical equipment.…”

“…Although the concentrations of SF 2 , SF 4 , SF 5 , and other low-sulfur components increase with the discharge and promote the reaction in (18) ~ (19), with the increase in the concentration of O 2 , the concentration of H 2 O released by the electrodes and the internal wall of the decomposition equipment is diluted, making the rate of reactions in (8) to (11) and (15) decrease. Reaction (19) is at lower status when competing with reaction (14), (15) and (18), thus leading to the reduction in the amount of SO 2 F 2 generated within 10 hours.…”

“…Therefore, when traces of H 2 O exist, H 2 O has a capture function of F equivalent to the inhibition of the recovery reaction SF x + (6-x) F → SF 6 . H 2 O inhibits the low-fluoride sulfide SF x (x = 1, 2, 3, 4, 5) composite to SF 6 , so that the concentration of SF 4 , SF 5 , and other components are increased. Additionally, under PD, the trace amount of H 2 O has always been small compared with a variety of lowfluoride sulfide SF x .…”

“…High local electromagnetic energy caused by PD would cause SF 6 to decompose into several kinds of low-fluoride sulfide SF x [1][2][3][4]. If trace levels of H 2 O and O 2 exist in the equipment, the decomposed components would have further reactions with them and produce new characteristic components, such as SO 2 F 2 , SOF 2 , SO 2 , and so on [5][6][7][8][9][10][11]. The concentration and variation regularity of these characteristic components have close relationship with the patterns of insulation faults, as well as the trace levels of H 2 O and O 2 in gaseous SF 6 , making it more difficult to recognize the internal insulation deficiency when using them.…”