Degradation due to energy pulse in high-energy ZnO varistors

Abstract

The degradation phenomena due to the energy pulse in the high-energy ZnO varistors used for de-exitation and overvoltage protection of hydroelectric generator are investigated. The energy pulse, obtained by releasing the energy stored in an inductor, can be equivalent to the combination of the DC field components and the energy component. The variations of the characterized voltages, nonlinear coefficients and pre-breakdown V-A characteristics, increase with the number of the applied energy pulse. The asymmetrical variations of the electric properties of the high-energy ZnO varistors after the energy pulse arise from the deformation of the double Schottky barriers due to the ion migration occuring in the depletion layer and in the grain boundary.

Keywords

high-energy ZnO varistors / energy pulse / degradation / V-A characteristics / grain boundary barrier / ion migration

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