Characteristics of commutation failure based on fault recording

Commutation failure of the high-voltage direct current (HVDC) transmission system is common fault in a converter station. The fault recording in one converter station when commutation failure caused by the disturbance of the AC system was collected, and the turn-off angle of valves, zero-crossing offset, and landing amplitude of bus voltage were calculated and statistically analysed. The results suggested that, in the case of commutation failure, the turn-off angle of the 82% of cases was <8 degrees, and there were a few cases whose turn-off angle was very nearly the same as that in normal operation. The number of cases whose zero-crossing offset was <10 degrees accounted for 95% of the total, and the zero-crossing offset of the AC bus line voltage generally presented a positive correlation with the reverse cut-off time of the valves. The landing amplitude of the AC bus voltage before the time point for commutation failure analysis fall within 10% for >90% cases, and the average was approximate to 4.6%. The number of cases, whose zero sequence voltage peaks was <50kV, accounted for 97% of the total. The results will provide basic data for analysing the main influencing factors of commutation failure and setting up countermeasures for the HVDC system.