A. C. Voltage Ageing of Zinc - Oxide Ceramics

The study of a.c. voltage ageing, in various fluids (air, SF6, transformer oil), of zinc-oxide based ceramics for HV and EHV surge arresters enabled the following points to be elucidated: - two classes of blocks are identified: those, which exhibit a degradation in air and still a more significant degradation in SF6 or oil, and those which do not show any visible degradation phenomenon; - the degradation of blocks affects mainly their periphery. From these experimental results, it was possible to estimate the actual lifetime of a surge arrester, by taking into account the influence of the continuous operating voltage, overvoltages and thermal dissipation coefficient of the surge arrester. An accelerated ageing test applicable to ZnO based ceramics, that can be used in a.c. power system surge arresters, is proposed.