Influence of compaction manufacturing process on the physical and electrical characteristics of high-voltage varistor

The zinc oxide varistor was originally used as surge protection in electronic circuits. Its energy handling capability was extensively developed by many companies for use in high-voltage surge arresters. Although varistor technology is well known, there is a need for continuous improvement in the varistor manufacturing process in order to achieve a reliable product that meets the requirements of the various international standards. This project focuses directly on the optimization of dry pressing techniques in the manufacturing process of high-voltage varistors in order to attain uniform density, low porosity and uniform distribution of secondary intergranular phase within the grains. The microstructural characteristics of varistor discs pressed in a double-action press machine (70 MPa) before (green) and after sintering are similar to those pressed under isostatic pressure, indicating the efficiency of double-action pressing. The breakdown electric field at 10 mA and nonlinearity coefficient (alpha) remain practically constant with increasing compaction pressure, increasing only in samples pressed above 70 MPa.