Breakdown Characteristics of Double Vacuum Gaps in Series Under Lightning Impulse Voltage: Optimal Gap Distance Distribution

An optimal distribution of gap distance for the double vacuum gaps (VGs) in series can improve its dielectric strength. The objective of this article is to quantitatively determine the optimal distribution of gap distance for the double VGs in series. The double VGs were built up by vertically connecting two pairs of copper sphere-plane electrodes in series.
${d}_{u{\%{}}}$
was the percentage of the upper VG distance in the total gap distance
${d}_{T}$
of 5 mm. A negative standard lightning impulse voltage (LIV) was applied in the dielectric test. The experimental results reveal that, under
${d}_{u{\%{}}}$
of 70%, the breakdown (BD) voltage of double VGs reached the maximum 192.7 kV, which was 13.2% higher than that of a single VG with the same
${d}_{T}$
. Therefore, the optimal gap distance distribution of double VGs was determined to be 70%/30% in this experiment. Moreover, when
${d}_{u{\%{}}}$
was less than 40% or greater than 90%, the dielectric strength of double VGs was mainly determined by the VG with a longer distance. When
${d}_{u{\%{}}}$
was in the range of 40%–90%, the dielectric strength of double VGs can be supported by both VGs and significantly improved. The dielectric strength should reach the maximum on the condition that the maximum electric field strengths at the cathode of two VGs were balanced.