Influence of Middle Gap Distance on Breakdown Characteristics of Triple Vacuum Gaps in Series

Abstract

The objective of this paper is to determine an influence of middle gap distance on the breakdown characteristics of triple vacuum gaps in series under the lightning impulse voltage. In the experiments, the triple vacuum gaps were built up by connecting three sphere-plane gaps in series. The diameters of the sphere electrode and the plane electrode were 18 and 50 mm, respectively. The middle gap distance d <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</inf> varied from 0.5 to 3.0 mm and the other two gap distance were fixed at 1.0 mm. The material of the electrodes was Cu. A negative standard lightning impulse voltage was applied with the up-down method. The results showed that, when d <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</inf> increased and the distances of the other two gaps were fixed, the voltage distribution across the triple vacuum gaps remained nearly unchanged. Only the maximum field strength of the middle gap decreased significantly. The 50% breakdown voltage U <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">50</inf> of the triple vacuum gaps increased from 76.06 to 139.8 kV as d <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</inf> increased from 0.5 to 3.0 mm. With the increase of d <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</inf> , the growth rate of U <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">50</inf> first increased, and then decreased after d <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</inf> reached 2.0 mm.