Internal and external leakage current decomposition of surge arresters using discrete fourier transform

Surge arresters are over voltage protection devices that provide protection to power transmission and distribution systems from over voltages caused by lightning surges, switching operations in power systems and temporary over voltages caused by faults. However, they are subjected to aging due to environmental conditions and overheating. Therefore to avoid catastrophic failures of surge arresters, it is necessary to evaluate their performance either by online monitoring or offline testing of the resistive leakage current which is considered as one of most techniques for assessing the degradation level of surge arresters. This paper presents an efficient technique for decomposition of leakage currents of surge arresters using discrete Fourier transform. The paper aims to decompose the leakage current, either internal or external, into its resistive and capacitive components. After, separating the two current components, the third harmonic resistive current, which is considered an important indicator of SA degradation, is extracted from the resistive current component. In this paper, diagnosis of three different 33 kV, 10 kA distribution-class surge arresters, namely Zinc Oxide Polymeric-, Zinc Oxide Silicon Rubber-and Silicon Carbide Porcelain-housed surge arresters is presented. Both the internal and the external currents were measured for each arrester up to its maximum continuous operating voltage.