Improvement of Dielectric Strength of Vacuum Interrupter by Installing Barrier on Insulator Surface

Surface discharge phenomenon along insulator surface in vacuum is a problem to be solved for expanding application field of vacuum circuit breakers (VCBs). The originality of present research is that the attempt to suppress the vacuum surface flashover by installing a physical barrier on insulator surface, and to achieve an improvement of its withstand voltage. Furthermore, the effect of an installed barrier can be explained by the vacuum surface flashover mechanism. In the experiment, voltage and current waveforms of vacuum surface discharge were measured under a negative standard lightning impulse voltage applied to a cylindrical specimen consisting of metal electrodes and an insulator. The flashover voltage and anode current waveform, which would represent the electron current flowing into the anode due to part of secondary electron emission avalanche (SEEA), were measured and compared in cases with and without a barrier installed on the insulator surface. The result shows the flashover voltage was improved to 40% by installing the barrier. The barrier on inner wall of cylindrical insulator would have two effects on vacuum surface discharge. One is the suppression of development of SEEA, the other is the extinction of conductive channel before complete flashover. The latter is a unique phenomenon to be clarified in the present article.