Study on the Influence of Impulse Current Waveform on Impulse Aging Characteristics of ZnO Varistors of AC Filter Arrester

The AC filter arresters in several converter stations of ultrahigh-voltage (UHV) and high-voltage direct-current (HVDC) transmission system have accelerated aging, and the measured impulse current waveform is different from the standard lightning impulse current waveform, which pulse width is longer. Therefore, in this paper, impulse aging tests with current amplitude of 27 kA were performed on zinc oxide (ZnO) varistors under negative polarity 15/35μs and 8/20μs impulse currents to explore the influence of different impulse current waveforms on the impulse aging characteristics of ZnO varistors of AC filter arrester. Firstly, according to the test to verify the repetitive charge transfer rating in IEC60099-4, two groups of new ZnO varistor samples were subjected to 10 groups of accelerated aging tests with two consecutive impulses with current amplitude of 27 kA. Secondly, the forward and reverse DC reference voltage (U0.1mA and U1mA), AC reference voltage (U*0.1mA and U*1mA) and residual voltage (U10kA) of the samples during impulse aging were measured. And then, we calculate the nonlinear coefficient and residual voltage ratio. Finally, the change trend and average change rate of electrical characteristic parameters of the two groups of samples during impulse aging were compared and analyzed. The results show that under the same amplitude of impulse current, the longer the pulse width, the greater the energy absorbed by the sample, the stronger the thermal aging effect, and the aging rate of the sample is relatively accelerated, but there is no direct relationship with the impulse current pulse width.