Residual voltage properties of ZnO varistors doped with Y2O3 for high voltage gradient

Rare-earth oxides can remarkably enhance the voltage gradient of ZnO varistors as growth inhibitor of ZnO grains. However, the effect of rare-earth oxides on the residual voltage properties of ZnO varistors has not been completely investigated. In this paper, ZnO varistor samples with various contents of Y₂O₃ dopant were prepared and tested under different currents of 8/20 mus impulse surge. When the doped Y₂O₃ content is no more than 0.75mol%, the residual voltage ratio of ZnO varistor sample decreases with the increment of Y₂O₃ content. When the doped Y₂O₃ content reaches 1 mol% or above, the residual voltage ratio of ZnO varistor sample increases remarkably. Such observed experimental results were explained based on the current localization phenomena inner ZnO varistor´s microstructure.