The influence of electrical partial discharges on the performance of zinc oxide surge arrester ceramics

In recent years there has been growing awareness that these gapless arresters have failed in service after a comparatively short time. Some failures in multiunit constructions may be attributed to overheating of the metal oxide elements due to the transfer of external leakage currents due to pollution into the metal oxide elements at the intermediate flange position. A further mechanism of failure has been identified caused by high electrical stress concentrations promoted by dry bands resulting in partial discharge activity. The general trend for failure is a gradual erosion of the outer coating of the zinc oxide element. The authors give an introduction into the preliminary investigation which is being undertaken at Brighton Polytechnic to identify these failures and to indicate the direction in which the research work should be focused for the future. The paper discusses the measuring system developed, and demonstrates some effects of electrical partial discharges on the outer surface using Scanning Electron Microscope/Energy Dispersion X-Ray Analysis (SEM/EDAX) techniques. This has been performed on both new and failed ZnO discs