Investigation of dielectric breakdown probability distribution for vacuum disconnecting switch

A vacuum insulation system has little effect on environments. Therefore, the vacuum insulation system is expected to find wider application, such as disconnecting switch and earthing switch. To investigate the reliability of equipment of vacuum insulation, a study was carried out to clarify breakdown probability distributions in vacuum gap. Experiments were carried out to compare a uniform field gap and nonuniform field gap on the breakdown probability distributions. Further, experiments were carried out to investigate effects of no-load switching on the breakdown probability distributions for vacuum disconnecting switch. The electrode materials were oxygen-free copper and copper-chromium alloy. The test results show that the breakdown probability distribution of the vacuum gap can be represented by a Weibull distribution using a location parameter, which show the voltage that permits a zero breakdown probability. When aiming for highly reliable vacuum disconnecting switch, an important factor is insulation design with the location parameter just mentioned take into account. The location parameter obtained Weibull plot depends on electrode area. This is probably because the existence probability of factors as weak-points for breakdowns such as micro-protrusions and microparticles depends on the electrode area. The shape parameter obtained Weibull plot of vacuum gap was 10∼13, and is constant irrespective non-uniform field factor. The breakdown probability distribution after no-load switching can be represented by Weibull distribution using a location parameter. The shape parameter after no-load switching was 6∼8.5, and is constant, irrespective of gap length. This indicates that the scatter of breakdown voltage was increased by no-load switching. It is supposed that the cause of this phenomena is generation of microparticles and field emission site on the surface of copper-chromium contacts.