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Mechanism of polarity effect on lightning impulse breakdown characteristics for series-connected vacuum gaps
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DOI：10.1016/j.vacuum.2026.115575.png)
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Abstract
En 中文
With the increase of voltage level, the polarity effect of breakdown (BD) in series-connected gaps has a significant impact on the insulation performance of vacuum circuit breakers. The objective of this article is to quantitatively investigate the polarity effect on lightning impulse BD characteristics of double vacuum gaps (VGs) in series and clarify its underlying mechanism. In the experiments, double VGs were formed by vertically connecting sphere-plane electrode pairs. The vacuum level was 10−5 Pa. Positive and negative lightning impulse voltages (LIVs) were separately applied to test the BD voltage. The results reveal that, the BD voltages of double VGs under positive LIV were higher than those under negative LIV. Their difference gradually increased with the total gap distance, reflecting a more pronounced polarity effect. Moreover, the BD voltage exhibited a nearly identical negative-exponential dependence on the maximum electric field strength at cathode for both LIV polarities. Owing to the asymmetric field distribution, the difference in cathode field strength could be considered the primary cause of polarity effect for series-connected VGs. On these bases, a prediction method was proposed for both positive and negative BD voltages using the maximum field strength at cathode, with an error of less than 5%.
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