Evaluation method of operating state of 1000 kV AC arrester based on digital phase-locking algorithm

The 1000 kV AC metal oxide arrester (MOA) is a critical protection device in ultra-high voltage (UHV) substations, making the accurate evaluation of its operational status paramount. While the harmonic analysis method has proven effective for assessing the leakage current of low-voltage MOAs, its application to 1000 kV AC MOAs faces challenges. Due to the complex structure and the large number of resistor columns in UHV MOAs, the bottom leakage current often shows insignificant changes even when internal defects exist, making timely fault detection difficult using conventional methods. To address this, this paper establishes a simulation model of a UHV arrester using ANSYS software. It analyzes the factors affecting the change rate of characteristic currents and the measurement accuracy for condition assessment. Experimental studies reveal the variation patterns of the MOA’s bottom leakage current under different operating conditions. Subsequently, an accurate measurement method for the full current, resistive current, and harmonics of UHV MOA is proposed, based on a digital lock-in amplification (DLIA) algorithm, to facilitate precise condition evaluation. This method effectively extracts characteristic current signals under varying signal-to-noise ratios. Key findings include the determination of an optimal signal sampling frequency and quantified harmonic measurement results following MOA aging. The proposed DLIA-based measurement demonstrates high accuracy, with the resistive current measurement error reduced to less than 1.0% and harmonic distortion analysis significantly enhanced, thereby fully meeting the precise requirements for the operational status evaluation of 1000 kV AC MOAs.