Effects of SiO 2 /Cr 2 O 3 ratios on microstructures and electrical properties of high voltage gradient ZnO varistors

The effect of various proportions of SiO 2 and Cr 2 O 3 doping on the micro-characteristics and the electrical properties of the ZnO varistors were investigated. As the SiO 2 /Cr 2 O 3 ratio increased, the voltage gradient increased and then decreased, the nonlinear coefficient α increased, while the leakage current showed the opposite trend, meanwhile the residual voltage ratio was almost stable. When the SiO 2 /Cr 2 O 3 ratio was 1.7 mol% vs. 0.6 mol%, the ZnO varistors sintered at 1155 °C exhibited excellent comprehensive electrical properties with voltage gradient of 329.9 V/mm, nonlinear coefficient of 65.1, leakage current of 0 µA, residual voltage ratio of 1.663, and aging starting power of 0.72 W. The varistors were in good condition after being struck 18 times of 250 A square wave energy pulse impact, showing a great potential in the industrial application of power distribution systems.