Directional Relay of Wind Farm Transmission Line Based on Traveling Wave Polarity Comparison

The amplitude and phase of the equivalent positive sequence impedance of the wind farm considerably fluctuate during a fault, and the extraction of the sequence fault component is affected by the frequency deviation. As a result, the operating performance of traditional directional relay is affected. This paper proposes a directional relay based on the polarity comparison of traveling waves. First, the polarities of the voltage and current traveling waves are analyzed under the forward and reverse faults. Second, an improved wavelet transform algorithm based on the complementary detail coefficients of adjacent windows is proposed to detect the fault traveling wave. This algorithm eliminates the signal loss problem of wavelet transform. Finally, the Pearson correlation coefficient is introduced to measure the correlation between voltage and current traveling waves, and the action criterion of the directional relay is constructed to realize fault direction discrimination. PSCAD/ETMDC simulation results show that the proposed directional relay can identify the fault direction correctly.