Experimental Investigation on Impulse Breakdown Characteristics of Multiple Sphere-Plane Electrode Vacuum Gaps in Parallel

The objective of this paper is to experimentally investigate the breakdown characteristics of multiple sphere-plane electrode vacuum gaps in parallel under a lightning impulse voltage. In the experiments, the multiple vacuum gaps were realized by parallel-connecting several identical vacuum interrupters (VIs) in a horizontal arrangement. The number of parallel VIs was 2 and 3. A pair of sphere-plane electrodes was arranged in the VI. The diameters of the sphere and the plane electrode was 14 and 50 mm, respectively. The material of the electrodes was Cu. The gap distances of all VIs were fixed at 1.0 mm. A negative standard lightning impulse voltage was applied by an up and down method. The experimental results express that, for the double and triple sphere-plane electrode vacuum gaps in parallel, when all gap distances were fixed at 1.0 mm, most of breakdowns occurred in the VI2, which had the lowest dielectric strength. Moreover, when the dielectric strength of one gap was about 9% higher than the gap with the lowest dielectric strength, the breakdown would not occur in this gap. The dielectric strength of multiple vacuum gaps in parallel should be determined by that of the gap with the lowest dielectric strength.