INFLUENCE OF COOLING RATE ON ELECTRICAL-PROPERTIES OF ZINC OXIDE-BASED VARISTORS

The influence of the cooling rate on the microstructure, the nonlinear parameter a, the breakdown voltage V1mA/cm2, the dielectric properties and the leakage current of the ZnO varistors was investigated. The morphology of the microstructure has different appearances under the effect of the varying cooling rates. The nonlinear parameter and the breakdown voltage reached a maximum as the cooling rate was adequately chosen. In the frequency range of 600 approximately 1 MHz, the dielectric properties of the samples dealt with at different cooling rates showed a similar tendency. However, the leakage currents of the samples showed different behavior under a constant voltage stress. As a result, the physical and electrical properties of the ZnO varistors can be said to be affected by the cooling rate.