Impact of UPFC on distance protection in AC transmission system

In this paper, analytical and simulation results are carried out about the application of distance protection with the presence of the unified power flow controller (UPFC) in the AC system. Combined with the UPFC protection, the impact of UPFC on distance protection is analyzed under different operation conditions. The influence to the distance protection is bigger when the series unit remains in the system after fault occurs. The simulation results show the impact of UPFC on protection for different operation conditions and different fault locations.