Experimental studies of the air gap breakdown triggered by a free conducting particle in DC uniform field

To address the problem of metal-particle pollution in DC gas insulation, an experimental platform is built for observing the particle's motion and discharge. And the breakdown process is observed using a high-speed camera. Based on the platform, the mechanical analysis of the air-gap breakdown with free spherical metal particles is conducted in a DC uniform field. In addition, different states of particle lifting, direct breakdown, or moving breakdown are also considered. It is observed that there are three kinds of breakdown models under the DC uniform field that consider the effects of the metal particles, including still-direct breakdown, micro-discharge breakdown, and lifting-voltage breakdown, among which the lifting-voltage breakdown occurs only when the particle is close to the upper electrode for the first time. The breakdown voltage decreases with the radius, and for the moving particles, the bigger the radius, the larger the breakdown gap. The proposed research provides fundamental basis in evaluating the dangerous level of free conducting particles within DC GIL as to improve the insulation design.