Effects of SiO2/Cr2O3 ratios on microstructures and electrical properties of high voltage gradient ZnO varistors

The effect of various proportions of SiO2 and Cr2O3 doping on the micro-characteristics and the electrical properties of the ZnO varistors were investigated. As the SiO2/Cr2O3 ratio increased, the voltage gradient increased and then decreased, the nonlinear coefficient alpha increased, while the leakage current showed the opposite trend, meanwhile the residual voltage ratio was almost stable. When the SiO2/Cr2O3 ratio was 1.7mol% vs. 0.6mol%, the ZnO varistors sintered at 1155 degrees C exhibited excellent comprehensive electrical properties with voltage gradient of 329.9V/mm, nonlinear coefficient of 65.1, leakage current of 0 mu A, residual voltage ratio of 1.663, and aging starting power of 0.72W. The varistors were in good condition after being struck 18 times of 250A square wave energy pulse impact, showing a great potential in the industrial application of power distribution systems.