Research On The Large Current Capacity Of Zinc Oxide Varistors

Zinc Oxide varistors which are charactered by a high nonlinear voltage-current speciality, excellent surge withstanding capability and wide range working stability have been found great applications in the fields of electrical and electronics to protect electrical circuits.And the research into manufacture ZnO varistors with high peak current and performance has attracted lots of attentions both at home and abroad, and has prominent meaning in the future too. In order to improve the electrical performance of ZnO varistors further, the Sol-Gel process was adopted to improve the homogeneous distribution of additives and decrease the pores in ZnO varistors. In this dissertation, the Sol-Gel method and mechanism were investigated deeply for preparation of multiplex composite nanometer additives, then the conduction, degradation and failure mechanisms and the influencing factors of excellent surge withstanding capability of ZnO varistors were discussed and summarized in details.The powders of ZnO varistors fabricated by blending and grinding of ZnO, SiO2 and multiplex composite nanometer additives prepared by the Sol-Gel method were used to manufacture varistors with the size of 8.5mm in diameter and 1mm in thickness under proper technique. The performances of ZnO varistors made from the Sol-Gel method were tested and analysed. The results show that the Sol-Gel powders are homogeneous in distribution of dopants and the grains are small in size and regular in microstructure. Compared to the conventional and the chemical coprecipitation techniques, the varistors made from the Sol-Gel method show great improvement in the electrical properties: The 8/20μs surge absorption capability of ZnO varistors attains to 2100A and the withstanding rectangular current pulse(2ms) capability of ZnO varistors preponderates over 38J. The leakage current IL is approximately 1.1μA ,the varistor voltage U1mA is 287V and the nonlinearity is 49.In order to have an intuitionistic comparison to the performances of ZnO varistors, which were manufactured by the conventional, the chemical coprecipitation methods and the Sol-Gel method, their electrical performances were analysed and compared. The results show that the varistor voltage of the varistors manufactured by both the chemical coprecipitation method and the Sol-Gel method are more than that of the conventional method, the leakage current and the nonlinearity have little difference, and their rectangular current pulse(2ms) capability are improved significantly, twice as many as...