A novel principle of directional relay for wind power integration based on model recognition in time-domain

The fault characteristics of wind power system which are reflected in the weak feed features, variation of system impedance, frequency deviation, and non-sinusoidal waveform, will cause the inadaptation of traditional directional relay to wind power integration system. To solve this problem, a new directional relay suitable for wind power system is proposed in this paper. The models of forward and backward fault in time domain on full fault component are firstly built. The fault current and voltage in the fault loop satisfy the positive R-L model when a forward fault occurs, while satisfy the negative R-L model when a backward fault occurs. Then waveform correlation in time domain is adopted to recognize the positive and negative R-L model. When the correlation coefficient is larger than 0, the fault is a forward fault, otherwise the fault is a backward fault. Thus the novel directional relay criterion is formed accordingly. To avoid voltage dead zone, the memory voltage waveform is utilized when the fault voltage is near 0 in the proposed scheme. Finally the proposed directional relay scheme is verified by the PSCAD based simulation results and field fault recording data of wind power integration system.