Abstract
In this study, a downsized direct current (dc)-gas-insulated transmission line (GIL) model is applied to investigate the surface charging and discharging characteristics of the basin-type spacer in 0.1-MPa SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> and air. Under a low electric field, the surface charge accumulation is dominated by the bulk conduction of the spacer. As the charging voltage increases, gas ionization occurs in the localized strong electric field, taking over the dominant position. In 0.1-MPa SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> gas, flashovers typically develop along the convex surface of the spacer under both positive and negative voltages because the homo-charge accumulation induced by brush discharges on the concave surface aggravates the electric field distortion at the convex side. In air, the dc flashovers have the polarity effect. Under the negative voltage, the flashover development is similar to that in SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> gas. But for positive polarity, the space charge region of positive polarity intensifies the electric field ahead of the corona region, thus promoting the air-gap breakdown at the concave side of the spacer.
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