Abstract
We have studied charging and flashover characteristics of a glass insulator with 0.3 - 50 mm long under DC voltage excitation in vacuum. We conducted flashover tests, charge measurements and calculation of surface charge distribution. The insulator was borosilicate, and was in the shape of a right cylinder. The side surface of the specimen was polished to have an average roughness of sub microns or roughened up to several microns. The charging characteristics of insulators were investigated by using an electrostatic probe, which was embedded in the plane cathode and allowed a time resolved measurement of the charging process. As a result, we have confirmed that roughening the surface mitigates the surface charging and thus improves the insulation strength for a specimen up to 50 mm in length. These results are useful not only for high voltage VCB's but also for other equipment that uses high voltage in vacuum such as particle accelerators.
