Influence of electric field distribution on charging mechanism on alumina dielectrics by triple junction in vacuum

Surface flashover characteristics in vacuum is very important for HV insulation design of vacuum interrupter. It should be paid attention to the fact that the insulation characteristics on the dielectric surface are strongly influenced by field emission of electron at a triple junction and the accumulated charges on the dielectric surface. In order to clarify charging mechanism, the authors measured the charging characteristics for various types of triple junction configuration. In particular, they focused on the influence of electric field distribution along solid dielectrics and near the cathode triple junction (CTJ) on the charging characteristics. Through the discussion on experimental results, they confirmed that electric field distribution strongly affected 2-dimensional (2D) distribution of surface charge on dielectric sample. Consequently, it is found that positive charging is generated on Al₂O₃, when incident angle of electric line of force on the Al₂O₃ surface becomes larger than 60 degree