A novel AC line distance protection scheme for AC/DC hybrid system based on fault likeness factor

Concerning the mal-operation of distance protection in AC/DC hybrid system due to commutation failure in DC system caused by AC-side fault, a novel AC line distance protection scheme based on fault likeness factor is proposed. First, by analysing the conducting state of converter in different time intervals, the expression of feed-in current from DC system to AC system is derived. On this basis, combining AC-side fault component network, the fault location equation considering the impact of feed-in current from DC system is established. Thus, by solving the equation consisting of information at multiple time sections, the fault location is calculated. And then, according to the consistency between the calculated fault location and actual fault location, the fault likeness factor is constructed to distinguish between in-zone and out-of-zone faults. Finally, simulation tests in RT-LAB verify that, the proposed scheme can identify in-zone and out-of-zone faults fast and accurately in the case of commutation failure caused by different types of fault, strongly immune to fault resistance.