Several large-scale wind turbine tripping accidents occurred in Jiuquan wind power base in2011. According to the on-site survey and analysis of these accidents related to relay protection，causes were found to bethe collection system defects and low correct operation rate of small current grounded line selectors of the unearthedneutral point collection system.By referring to both the characteristics of Jiuquan wind power base and arrangementof relay protection，the short-circuit features of wind power and its impacts on relay protection are analyzed.Thecollection system and the retrofit of the small current grounded line selector are improved by specificcountermeasures.Finally，further research subjects are put forward.