Investigation on Dispersion of Breakdown Voltage for Double Vacuum Gaps in Series Under Lightning Impulse Voltage

The objective of this article is to experimentally investigate the dispersion of breakdown (BD) voltage for double vacuum gaps (VGs) in series under a lightning impulse voltage. In the experiments, the double VGs were built up by vertically connecting two pairs of copper sphere-plane electrodes in series. The diameters of the sphere and plane electrode was 30 and 50 mm, respectively. The total gap distance <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$d$</tex><inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</inf> of two VGs was set as 4.0 and 5.0 mm. The experimental results express that, for both single VG and double VGs in series, with the increase of gap distance, not only the fluctuation range of BD voltage significantly increased, but also the dispersion of BD voltage became larger. By comparison, the 50% BD voltage of double VGs was higher than the single VG with the same <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$d$</tex><inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</inf>, which confirms the saturation effect of BD voltage for a long VG could be reduced by series-connecting multiple VGs. Moreover, under <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$d$</tex><inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</inf> of 4.0 and 5.0 mm, as single VG increased to double VGs, 100% BD voltage significantly increased by over 20 kV and 0% BD voltage slightly decreased by around 3 kV. Thus, the double VGs in series had a larger dispersion of BD voltage than the single VG.