Influence of glow discharge pre-treatment on dielectric parameters in vacuum gaps

The dielectric properties of vacuum circuit breakers gain in importance, because the dielectric "management" in vacuum circuit breakers influences more and more design, development, production strategies and costs. Especially the economics of such solutions decide the application of vacuum circuit breaker technology in the high-voltage field. Against this background special attention is also paid to the conditioning process to finish the surface of the contacts and shields. After this, the final dielectric strength performance of vacuum interrupters can be evaluated using withstand voltage and additional micro discharge current measurements. The investigations of model assemblies require a special pre-treatment to achieve comparable results. The most important point here is a conditioning routine with glow discharges in the vacuum test vessel to eliminate adsorbed gas layers. Its influence on withstand voltage and further conditioning behaviour of the test assemblies is shown. The data, however, depend on many factors, such as material composition, surface structure, cleaning procedures, adsorbed gas layers or particles on the upper surface. The dependence of the roughness of the surface is much more pronounced than that of the size of the surface area. The technically interesting area is changing the reduction factor only slightly. However, the reduction factor for the surface roughness is the crucial parameter.