Failure analysis of ZnO arresters in the 500kV AC filter of the HVDC/UHVDC power transmission system

The ZnO arresters in 500kV AC filters in many converter stations have abnormal discharge during operation, which accelerated the aging of arresters and even caused arresters out of work. In this paper, through the disassembly experiment of the whole arresters and the test of the electrical characteristic parameters of the varistors, the failure reason and aging characteristics are preliminarily analyzed. Firstly, it is found that there are obvious cracks and surface discharge traces on one individual varistor of the F1 arrester for AC filter; while disassembling the F2 arrester for AC filter, it is found that the appearance of the porcelain sleeve and the internal va ristors of the arrester are intact. Secondly, The electrical characteristic parameters measurement results show that the electrical characteristic parameters of each varistor of F1 arrester for AC filt er are dispersed, as high as 8%; the DC reference volta ge U1mA and leakage current IL at 0.75 times U1mA of each varistor of F2 arrester for AC filter have obvious polarity effect. Therefore, it is preliminarily inferred that the frequent large impulse current is the main reason of the arresters failure, and p arameters dispersion and polarity effect of the varistors in one arrester are critical influencing factors.