Criterion of single-phase fault nature of AC line considering the influence of commutation failure

The amplitude of AC line current at the inverter side is affected by DC commutation failure and fluctuates for a short time after single-phase trip.The fluctuation range increases with the increase of the number of DC commutation failures,resulting in the misjudgment of the traditional single-phase fault nature criterion based on the amplitude of the recovery voltage. To solve this problem,a transmission line fault equivalence model is built firstly to evaluate the impact of DC commutation failure on the sound phase voltage. Then the time domain expressions are derived for the disconnected phase voltage during the recovery voltage stage for different fault nature. After that,a single-phase fault nature identification criterion based on time domain voltage integration is proposed,and its effectiveness is verified by PSCAD/EMTDC simulation. The results show that the proposed method has good resistance to transition resistance and DC interference,and the fault nature identification criterion is suitable for DC commutation failure.