Improvement of energy-handling capability of the ZnO varistors prepared by fractional precipitation on the seed materials

The improvement of the voltage gradient and energy-handling capability of the ZnO varistors is necessary for reliability and protection level in conjunction with the reduced mass of the surge arresters. The varistor processing variables were investigated and then energy-handling capabilities were evaluated. To reduce influence on the chemical co-precipitation process the method of fractional precipitation on seeds was used. In this study the influence of precipitant, dispersant, pH value, and temperature on the uniformity of the sediments and calcined additive powders was evaluated. It was observed that when the sediments were dried by the half-dry method via calcination in the range 600-650 °C, the calcined powders of the additives obtained had either no agglomeration or little agglomeration of the particles. The influence of the additive powders on spray dried granules and their forming were also studied. Eventually ZnO varistor blocks possessing varistor voltage gradient in the range 210-260 V/mm and the energy handling capability of about 270 J/cm ³ have been achieved.