Analysis of Zinc Oxide Grain Barrier under Slow-Front Overvoltages

The analysis presented in this work highlights the impact of slow-front overvoltages on the microstructure of zinc oxide (ZnO) varistors. Grain boundaries in ZnO varistors play a significant role in determining the overall electrical characteristics. The variation effects influence the varistor's electrical behavior, dielectric strength and nonlinear response of applied voltages. The impact of several surges applied on ZnO grain barrier height changes was deduced from the C-V characteristic curve measurements conducted before and after degradation. The Kruskal-Wallis Test is then applied to analyze the effect. ZnO varistor microstructure is studied using the SEM while the chemical composition is analyzed using EDS. Results indicate a significant decrease in grain barrier height with an increased number of surges applied, with the observed decreases in barrier height response ranging from 6.8% to 23.57% for manufacturer A and 16.75% to 40.32% for manufacturer B.