Impact of AC-DC Compound Power System on Distance Protection Transient Overreach and Resolving Measures

The traditional distance protections applied to the AC-DC power system usually induce transient overreach,especially for the Inverter commutation failure in DC system. It is found that the transient overreach in AC-DC power system is due to fault transient signals containing a large number of low-frequency components of the slow decay and non-periodic components and high frequency components. The voltage and current of tuning point based on distributed-parameter model are calculated,and the equations for identifying the distance between tuning point and the point of failure by R-L model are established to put forward a protection scheme. The simulations show the ability for distinguish internal fault from external fault and preventing transient overreach.