Analysis of Fault Characteristics and Distance Protection Adaptability for VSC-HVDC-Connected Offshore Wind Farms

With the characteristics of low loss, low harmonic content and large transmission capacity, voltage source converter based high voltage direct current transmission (VSC-HVDC) has become the focus of the development for large-capacity and long-distance power transmission system connected with offshore wind farms. However, since the power supplies on both sides are controlled, the fault characteristics are changed, and the performance of the traditional distance protection is influenced. Based on the control strategy, the amplitude and phase angle of the equivalent positive and negative sequence impedances at the two sides of the transmission line are analyzed, and the current phasor expressions of the wind farm side and the VSC-HVDC side of the faulted line are derived. Then the adaptability of distance protection using power frequency component (DPPFC) of transmission line for VSC-HVDC-connected offshore wind farm is analyzed under different fault conditions. The results show that the amplitude and phase angle of the equivalent positive and negative sequence impedances of the wind farm and the VSC-HVDC system are affected by the control strategy of the converter and the fault conditions. The DPPFC is not suitable for VSC-HVDC-connected offshore wind farm system. The ability to avoid the effect of fault resistance of the DPPFC at the wind farm side gets worse. The simulation conducted by EMTP-RV verifies the effectiveness of the analysis.