Effect of duct configuration on DC currents at oil/pressboard interfaces

Regarding the role played by liquid/solid interfaces on the breakdown strength of a stressed gap, previous workers have suggested that liquid motion in an oil gap is altered by the presence of a spacer. It has been hypothesized that this change reduces the voltage level at which flashover takes place. The reasoning is in part based on current measurements made using segmented electrodes situated in the vicinity of stressed interfaces. Work involving such electrodes and two pressboard spacers placed asymmetrically in a normally uniform field oil gap is reported. The arrangement is such that the exposed spacer surfaces are adjacent to different volumes of stressed oil. It was intended to verify whether or not the length of duct so formed affects the current distribution. It was shown that the design of the segmented electrode is crucial. The main conclusion is that the influence of the spacers on liquid motion is not as large as previously reported