Breakdown characteristics of triple vacuum gaps in series under lightning impulse voltage: Effect of floating potential gap

Abstract

Inside a high-voltage vacuum interrupter, multiple floating shields form the multiple vacuum gaps (VGs) in series. When the number of series VGs exceeds three, there will exist floating potential VGs in which both electrodes have floating potentials. The floating potential VG is important for the dielectric strength of multiple VGs in series. The objective of this paper is to quantitatively determine the effect of the floating potential VG distance on the breakdown (BD) characteristics of triple VGs in series. In the experiments, triple VGs were built up by series-connecting three pairs of sphere-plane electrodes vertically. A negative standard lightning impulse voltage (1.2/50 μs) was applied. The experimental results revealed that a critical gap distance of the floating potential VG was required to support the dielectric strength of triple VGs in series. The distance was approximately 0.7 mm in this experiment. The critical distance of the floating potential VG can be determined by an intersection of the maximum electric field strength at cathode and the 100% BD electric field strength of the floating potential VG. This method can be used to estimate the critical distance of the floating potential VG in a high-voltage vacuum interrupter.