Study on widespread ageing and improvement measures of ACF arresters in a?500kV converter station

Widespread aging phenomenon of AC filter (ACF) arresters have occurred in a +/- 500 kV converter stations in China, threatening the safe operation of the HVDC transmission project. Therefore, the disassembly experiments of the ACF arresters that was out of operation were carried out, it is found that there exists obvious polarity effect in the DC reference voltage U1mA, which can be attributed to the unipolar impulse current which the arrester is frequently subjected to. The widespread aging phenomenon of the ACF arresters was caused by the frequent unipolar impulse current has been further confirmed through the electromagnetic transient simulation. Furthermore, based on the monitored waveform data, it is speculated that pre-breakdown may occur during the process of switching-on the ACF circuit breakers, resulting in the arrester being frequently subjected to unipolar impulse current. Hence, a three-dimensional finite element electrostatic field model of SF6 circuit breaker is established to simulate the relationship between the breakdown voltage and the applied voltage, and further to verify the pre-breakdown is the root cause of the frequent action of ACF arresters. Finally, the improvement methods and measures for reducing the action frequency of impulse current acting on the arrester are put forward.