Analysis of directional pilot protection on transmission line with wind farm integration

Increased integration of wind power makes higher demands on the stability and protection of Power System. Wind farms are connected to power grid through transmission line. When single-phase fault occurs on the line, positive and negative sequence currents are not equal and are much smaller than zero sequence current. Phase selector based on the theory of current- difference sudden-change may mistake single-phase fault for phase-to-phase fault because positive and negative branch coefficients are not equal. Considering a case of mal-operation of directional pilot protection, the paper studies the impedance characteristics of asynchronous wind generator, analyzes the causes of weak feed and different branch coefficients, and explains their contribution to fault phase selector´s mal-operation. The results are validated by simulation and an improvement for fault phase selection with wind farm integration is proposed.