Deterioration of metal oxide surge arrester element caused by internal partial discharges under polluted conditions

In order to clarify the influence of internal partial discharges on metal oxide surge arrester elements (ZnO varistors) caused under polluted conditions, tests simulating internal partial discharges were made. In the simulation tests, internal partial discharges occurred between the ZnO varistor side surface and the needle in both air and nitrogen atmospheres. It was found that the deterioration of the ZnO varistor occurs in an air atmosphere. Some aspects in the deterioration of ZnO varistors were elucidated from measurements of the V-I characteristics, analysis of the gas generated, observations by scanning electron microscope, and thermally stimulated current spectra. It is shown that the deterioration of a ZnO varistor under partial discharge conditions in air may be caused by both the erosion of the side surface of the ZnO varistor and the action of some generated gases. This deterioration may be accelerated under service conditions.<>