Study on the Frequency and Temperature Dependence of Electrical Conductivity of Zinc Oxide Valve Plate

Under the action of overvoltage and harmonic voltage, the onboard zinc oxide arrester of electric motor units (EMUs) will affect its action characteristics due to heating. In this article, the nonlinear current–volt characteristics of the arrester valve plate are measured experimentally to study the dependence of the electrical conductivity of the zinc oxide valve piece on temperature and frequency under ac voltage. The current–volt characteristic curve of the arrester valve piece shifts to the right in turn as the temperature rises. The corresponding resistive leakage current of 3500-V valve plate increases by 250% as the temperature increases from 20 °C to 120 °C. The voltage value of the corresponding valve piece at the resistance current of 1 mA gradually decreases with the increase of temperature, and the maximum drop of the voltage of a single valve piece is close to 25%. The high-frequency conductivity of the valve plate is increased by 31% compared with that under power frequency. The dependence characteristics are divided into three parts: linear region, transition region, and nonlinear region. The conductivity dependence characteristics of zinc oxide valve sheet on frequency and temperature are studied by bivariate fitting. The fitting model is established based on the Arrhenius formula, Schottky barrier model, and Richardson equation. The correlation coefficient of fitting results is above 0.99.