Characteristics of sequence impedances of DFIG wind farm and the impacts on the phase selection elements

Considering characteristics of sequence impedances of DFIG wind farms, an analytical method is used to identify factors affecting phase selectors in wind farm protections. The expressions of sequence impedances after crowbar being applied show that the positive and negative sequence impedances of DFIG are functions of rotor speed and crowbar resistance. Additionally, the hypothesis that the positive and negative sequence impedances of the system are approximately equal does not hold for DFIG wind farms. Furthermore, the reason why phase selection elements based on variation components and sequence components can´t apply to DFIG wind farms is given based on above conclusions. Finally, the results of RTDS simulation demonstrate the validity of these theoretical analyses.