Voltage frequency-based adaptive reclosing strategy for flexible DC power grids

Overhead lines (OHLs) in High Voltage Direct Current (HVDC) systems are vulnerable to temporary faults. Recovering power transmission by reclosing is of considerable significance to the grid reliability. However, the traditional auto-reclosing strategy will result in a secondary shock to the direct current (DC) system if the fault is permanent. Besides, a long delay is required to ensure that all types of temporary faults are cleared. To address these two challenges, this paper proposes an adaptive reclosing algorithm which can actively identify the fault property and fault disappearance time. Firstly, the discharging process of the fault point is analyzed, and the dominant frequency characteristics of the fault voltage under different fault properties are revealed. Then, the fault property and the fault disappearance time are identified based on the change time of the dominant frequency. Moreover, the influencing factors, including the fault resistance and the dead zone, are also analyzed. Finally, the algorithm is verified under different fault locations, fault resistances, arc lengths, noises, sampling frequencies and dead zone in PSCAD/EMTDC. The results show that the algorithm is effective, and its dead zone is less than 8% of the line.