With the increase of wind farms integrated into the power system, the fault characteristics affected by the wind turbines bring challenges to traditional power frequency based protection for wind farm outgoing lines. Considering the fault transient components contain lots of fault information, a novel transient differential current waveform characteristics based protection is proposed. The protection uses the transient full-time differential current within 5ms after fault, which can reduce the influence of different wind turbine controls and improve the operation speed of protection. In the proposed protection, the least square curve fitting method is used to extract the main frequency of the transient current waveform of each phase. Then, the fault phase and non-fault phase are distinguished according to the protection criterion. The transient simulation results show that under different fault locations and types, the protection scheme can identify the fault phase of internal faults sensitively and reliably. With low requirement for sampling frequency, the protection performance is robust to high fault resistances and noise disturbance.

differential current,transient protection,transmission line,wind farm,waveform fitting