Distance protection for transmission lines of DFIG-based wind power integration system

This paper proposes a distance relay in time domain based on the R-L differential-equation algorithm which is suitable for wind power integration system. However, the conventional R-L differential-equation algorithm cannot detect the correct fault direction if the fault point is very close to the relay location. Therefore, this paper mainly focuses on this problematic conditions and proposes a solution. The instantaneous value equivalent model of DFIG is established and characteristics of the transient electromotive force (EMF) of DFIG after the faults are also analyzed, which shows that the EMF of DFIG has the inertia within a short time after the faults. The memory voltage drop and actual voltage drop on equivalent impedance from relay location to back-side and opposite-side equivalent power sources are introduced in this paper to detect the fault direction. Meanwhile, the characteristics of the memory voltage drop and actual voltage drop under forward and reverse fault conditions are deduced, respectively. With the differentiated correlation coefficient between the memory voltage drop and actual voltage drop under different fault conditions (forward and reverse fault), the fault direction identification criterion is formed accordingly. Finally, an extensive performance evaluation using PSCAD/EMTDC simulation corroborates the effectiveness of the proposed method. Results show that the proposed method can detect the fault direction quickly with high sensitivity during zero-voltage fault conditions.