Transient Current Similarity-Based Protection for Interconnecting Transformers in Wind Farms

Large-scale wind farms are usually integrated into transmission systems through interconnecting transformers. Applying traditional, steady-state, fundamental frequency-based differential protection (DP) strategies in these interconnecting transformers creates challenges. First, the fault current of wind farms might be dominated by non-fundamental frequency components caused by the activation of their own protection systems during low-voltage ride-through (LVRT). Second, the fault current contains low-order components that may affect the second-harmonic restraint algorithm of the transformer DP, thereby blocking the differential relay for a long time. Therefore, a novel transient current similarity-based protection scheme is proposed to deal with these issues. The current protection scheme uses the fundamental frequency and non-fundamental frequency characteristics and can, therefore, reduce the influence of LVRT to a minimum. The proposed method uses transient current (within 15 ms after fault inception) and ignores the features of steady-state fault current. In the proposed method, an improved Hausdorff distance algorithm is used to calculate the similarity of transient current signals at both ends of the interconnecting transformer. The simulation results demonstrate that using a common sampling frequency, the proposed protection scheme reveals current information, correctly identifies magnetizing currents and internal transformer faults in a short period, and achieves superior performance in cases of abnormal data, missing data and noise.