Impulse Withstand Voltage Characteristics Of High Voltage Insulation Structure In Vacuum

The surface flashover performance of insulators is the critical factor strongly influencing the voltage hold-off capability of high voltage vacuum devices.Studies on the pulsed voltage hold-off property of the insulating geometry in vacuum could be quite helpful in designing of the insulating geometry for special electronic vacuum devices.In this thesis,the theory-mechanisms of the surface flashover characteristic on solid dielectric material in vacuum and the major factors influencing the voltage hold-off capability of the solid dielectric material in vacuum are reviewed.The experimental system for the single microsecond pulse voltage hold-off test of alumina ceramics in vacuum is setup.The characteristic method of the voltage hold-off property for the alumina ceramic in vacuum is investigated.Based upon the results of simulation for the insulator shape and the attached metal electrode geometry on the electric field at the cathode triple junction(i.e.the interface where the insulator,cathode and vacuum are in close proximity),the different shapes of the cylindrical alumina ceramic insulators and various geometries of electrodes are designed and manufactured.Under the condition of the single pulsed high voltage,the influences of shapes and materials of alumina ceramic insulators(95 alumina ceramic and BK94 ceramic),the geometries of attached electrodes,as well as the degree of vacuum on the voltage hold-off performances on the cylindrical alumina ceramic insulators are experimentally studied.The primary initiating mechanism of the surface flashover of the ceramic insulator in vacuum under the condition of the single microsecond pulse high voltage are explored and discussed in brief.The results indicate that the reasonable metal electrode geometry and insulator shape can weaken the macroscopic filed at the triple junction of the ceramics insulators so that the breakdown voltage of ceramics insulators can be raised significantly.The reliable voltage hold-off of the recess electrode is up to 150 kV and nearly 50%higher than that of the plate electrode.The voltage hold-off of the BK94 alumina ceramic is almost 20%higher than that of 95 alumina ceramic.In the dynamic vacuum system and the sealed vacuum device,the voltage hold-off performance of the alumina ceramic insulators is not dependent on the degree of vacuum above 10^-1Pa.