AC ageing performance of Ag<SUP align="right">+</SUP> doped high voltage gradient ZnO varistors

Zinc oxide (ZnO) varistor exhibiting excellent nonlinear volt-ampere characteristics, has now been widely applied to overvoltage protection in electrical equipment. However, the greater severity of AC ageing is a realistic issue facing the high-voltage gradient varistors used in ultra-high-voltage surge arresters. To some degree, silver (Ag) doping is effective in improving the performance of varistors. In spite of this, it remains necessary to explore its influence on the ageing process of varistors. In this study, an investigation is conducted into the microstructure, macroscopic electrical properties, and barrier potential of varistors with different Ag doping concentrations, so as to determine the optimal level of doping concentration required for improving the long-term stability of varistors. Furthermore, the mechanism of Ag+ improving ageing resistance is accounted for in theory. The research results indicate the best anti-ageing performance is achieved at the doping concentration of 50 ppm.