Study on the Unipolar Impulse Aging of ZnO Varistors and Their Condition Monitoring Methods Based on the Basic and Even-Order Harmonics of the Leakage Current Resistive Component
Jie Zhang, Yongxia Han, Licheng Li, Junwen Deng, Xin Luo, Yongchang Meng, Quan Sun
Abstract
The occurrence of frequent high impulse currents during the process of switching-on AC filter banks can accelerate the aging of arresters in ultrahigh-voltage direct-current (UHVDC) and HVDC transmission systems, threatening the safe operation of converter stations. Therefore, impulse aging tests with different current amplitudes were performed on zinc oxide (ZnO) varistors under a negative polarity 15/35 μs impulse current to provide a basis for the aging evaluation criteria of AC filter arresters in UHVDC and HVDC transmission systems. The ratios of even-order to basic resistive harmonic components linearly increase with the number of impulse groups and suddenly decrease after complete damage occurs. The variation trends of the ratios of even-order to basic resistive harmonic components were analyzed and discussed based on the current waveform and amplitude-frequency characteristics of the resistive component and the DC <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i> - <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</i> characteristics. Based on the results, a new criterion for the unipolar impulse aging of the ZnO varistor is proposed, i.e., the ratio of second to basic resistive harmonic components, and the application of ZnO varistor even-order harmonic characteristics in online monitoring is briefly discussed.