The effect of aluminium additive on the electrical properties of ZnO varistors

Reliable and undisturbed operation of electric and electronic circuits is mainly achieved through the use of appropriate overload protection elements such as overvoltage surge arrestors. The stability of metal oxide varistors which are used insures that the circuits are adequately protected. The point of adding the varistor material with aluminium is the extension of the nonlinearity of I-V characteristic in high current region. In this work, both the aluminium doping for ZnO varistors, and the effect of this doping on the ageing processes in varistors were investigated. The current trend towards the production of better and more robust surge arrestors which utilize mainly ZnO varistors motivated these studies. The fundamental technological impediments include the repeatability of manufactured varistors and their susceptibility to ageing factors such as current shocks, elevated operation temperature and the extended effect of the operation potential. Improving the varistor imperviousness to ageing continues to be an imperative but, as yet, unsolved problem.