Influence of Non-uniform Distribution of Grains on Noise Absorption Characteristics of ZnO Varistors

摘要

Noise absorbing process of Zinc Oxide (ZnO) varistors was analyzed by using equivalent circuit of the sample varistors. Equivalent circuit for the ZnO varistor was proposed by considering the microstructure of a special type of varistor made for the experimental purpose. We considered every grain between the internal electrodes and made an equivalent circuit. The circuit's parameters were determined by PSpice circuit simulator. We regarded a portion of the internal electrode and made a uniform model with a non-uniform model. A dc motor was connected with these models in parallel to investigate the effects of the non-uniformity of the ZnO grains in noise absorbing characteristics of a varistor. Comparing to the uniform model, resonance occurred in the non-uniform model while absorbing noise, and thus the absorption of noise of the model was deteriorated. Transient current was calculated for each grains of these models to investigate the effect the deterioration of noise absorbing characteristics. Localized current was found in the non-uniform model when resonance occurred to absorb transient voltage from our calculations.