Diagnosis of ZnO Surge Arrester Using Resistive Leakage Current Extraction

Surge arresters play a critical role in protecting transmission lines and power generation equipment by discharging temporary overvoltages to the ground. Since the mid-1980s, Zinc Oxide (ZnO) arresters have been widely utilized in power plants, substations, and transmission lines. The operating voltage is applied directly to the ZnO blocks, resulting in a continuous flow of a minute leakage current. This steady-state leakage current is a composite of capacitive and resistive components. While an increase in the resistive leakage current indicates arrester degradation, accurately measuring this component in the field remains a significant challenge. Since 2000, various techniques have been reported to estimate resistive current, such as analyzing third-harmonic components or extracting the resistive portion from the total leakage current by applying an external voltage. In this study, a resistive leakage current detection algorithm based on phase analysis was implemented to measure total leakage current without voltage application, utilizing A/D conversion and microprocessors. A specialized measurement device was designed and fabricated, and its performance was validated through comparative tests with voltage-injection type equipment in a laboratory setting. Furthermore, field measurements were conducted overseas, confirming the thermal degradation of arresters where leakage current levels exceeded standard thresholds.