Influence Of Different Additives On The AC Degradation Characteristics Of ZnO Varistor

As the development of high voltage transmission and UHV transmission, ZnO arrester is wildly used in power system to protect equipments against essential over-voltage, lighting over-voltage and other over-voltage. The stable and safe operation of power system is directly affected by the performance of ZnO arresters, which decided by the electrical characteristics of ZnO Varistors. Usually, ZnO arresters are used without series gap, which means the long-term operating voltage will give rise to degeneration. The study of AC degeneration mechanism of ZnO varistors by carrying out research on the influence of different additives on electrical characteristics of ZnO varistors is of great significance on the improvement of ZnO varistors.In this paper, three kinds of additives and different AC ageing time were considered, the voltage-current (V-I) characteristics tests, scanning electron microscope (SEM) tests, Thermally stimulated current (TSC) tests and capacitance-voltage [C-V) characteristics tests were carried out on ZnO varistors before and after AC ageing test. A conclusion can be drawn, by comparing the varistors voltage, grain size, TSC trap level and barrier parameters, that the additives will change ZnO grain size and the defect concentration, which leads to the change of varistor voltage. The TSC trap level and trapped charge increase a lot, the barrier height decreases a lot compared to that of the ZnO varistors before AC ageing test. When the doping ratio of the additives exceed a certain amount, the variation of the concentration of znic interstitial and the compactness of ZnO grain will lead to the deterioration of ZnO varistors, which is account for the aggravation of AC degeneration. Based on the researches, a conclusion can be drawn that the electrical properties of ZnO varistors can be greatly improved by doping0.6mol%Y2O3,0.7mol%Bi2O3and1.0mol%Co2O3.