Study on Fault Current Suppression and Commutation Failure in Inverter Side of ±1100 kV DC System

In order to restrain commutation failure in HVDC transmission system, one of the traditional methods is reducing commutation reactance. But in order to ensure the fault current within the bearing limit of equipment, the commutation reactance usually cannot be much reduced. This paper proposes that reducing the short-circuit reactance of converter transformer from 24% to 8%. Considering the reduction of short-circuit reactance will cause the increase of short-circuit current, this paper put forward the method of installing fault current limiter in the net-side of converter transformer. In normal operation, the commutation failure can be restrained; When commutation failure occurs in some phase, the fault current limiter will be connected in the loop, which can not only limit short-circuit current flowing through the converter transformer, but also improve the continuous commutation failure. Simulation results show that this method is very effective in restraining commutation failure and suppressing fault current in HVDC transmission system.