Mechanism and Effect of DC Charge Accumulation on SF6 Gas Insulated Spacers

Surface fluorinated epoxy resin for high voltage DC application

“…A large amount of space charge started to accumulate along the surface of cast epoxy spacers with prolonged DC stress, which may distort the local electric field. A study done by Fujinami et al listed three possible factors for this phenomenon [7]; (i) micro discharge or field emission from surface projections, (ii) motion of dust particles, and (iii) natural ionisation of SF₆ gas in a prolonged time range. To overcome the charging problem, they proposed the design of anti-charging spacer profile which has no normal field component on the surface.…”

“…This improvement should lead to an increase in the surface flashover strength as the accumulation of surface charge is one of the critical parameters that influence the surface flashover performance [7]. In general, the surface flashover strength is defined as the limiting voltage stress beyond which the insulation surface can no longer maintain its integrity.…”

Micro discharges in HVDC gas insulated systems

“…In a healthy insulation system with no protrusions at the electrode, this effect should play a minor role as field strengths in the range of 100 kV/mm are required for substantial currents to be emitted [8,13].…”

“…There are in principle three different charge sources in the gas: Natural ionization due to cosmic background radiation and radioactive elements in the ground [6], micro discharges from microscopic protrusions (roughness) on the electrodes [6][7][8][9], and field emission at highly stressed cathodes or macroscopic protrusions [6][7][8][9]. 7,8,9 In the literature [10][11][12][13] it was shown that in arrangements where partial discharge cannot be detected by classical measurement methods, additional charges due to micro discharge can nevertheless be present. The aim of this contribution is to analyze these micro discharges and quantify the resulting discharge currents and their impact on the charging of HVDC insulator surfaces.…”

Approche physique du développement de streamers positifs sur une surface de glace =

“…Le premier suggère que les charges produites autour d'une électrode diffusent dans le gaz de remplissage à travers les lignes de champ pour s'accumuler vers le centre de la surface diélectrique [103,104,113]. Le second préconise la circulation de charges sur la surface par l'effet du courant de faite [102,114,115], tandis que le dernier propose la migration vers l'extérieur de la surface, de charges produites à l'intérieur du diélectrique [73,100].…”