A　simulation　system　for　power　grid　with　concentrated　large-scale　wind　farm　integration　is　established　based　on　the　electro-magnetic　transient　model　of　wind　turbine　equipped　with　doubly-fed　induction　generator　(DFIG),　which　is　built　by　real-time　digital　simulator　(RTDS).　Using　the　hardware　communication　interface　of　RTDS,　a　closed-loop　testing　experiment　is　accomplished　to　study　the　impacts　of　large-scale　wind　farms　on　the　existing　relay　protection　devices　for　wind　farm　outgoing　transmission　line.　This　paper　points　out　problems　existing　in　current　relay　protection　devices　as　follows:　fault　phase　selector　can　select　unwanted　phase　due　to　the　changes　of　fault　features　caused　by　special　network　connection　of　wind　farms;　blocking　condition　for　distance　protections　needs　to　bere-examined　due　to　the　weak　power-feed　characteristics　of　wind　farms;　and　power　frequency　parameter　based　relay　protection　devices　cannot　accurately　operate　due　to　the　special　transient　voltage　and　current　characteristics　of　wind　farms　during　fault　period.　Results　lay　the　foundation　for　improving　the　performances　of　the　existing　relayprotection　device　and　developing　new　principle　relay　protection.　©　2012　State　Grid　Electric　Power　Research　Institute　Press.