Influence of eccentrically mounted vapor shields on the dielectric strength of vacuum interrupters

The breakdown mechanism in vacuum is primarily a process that is related to the electrode surfaces. The theoretical critical field value for a vacuum breakdown is much higher than the practically determined values. Reason is that the critical field strength consists of the geometric and the microscopic field. This fact is represented by a field enhancement factor. Its value is often discussed, but there are no usable values for real applications. The question is how small deviations of the field strength, caused by ir-regularities of the geometry, affect the dielectric behaviour of the interrupter. Are these deviations the cause of the dielectric interrupter performance worse than expected, or is the breakdown caused by the surface treatment/surface condition? In this contribution the…