Cooperation of relay protection for grid-connected wind power with low-voltage ride-through capability

The wind turbine with low-voltage ride-through capability is required not to disconnect from grid under certain fault conditions,for which the relevant relay protections should cooperate with it.The cooperation between the relay protection of transmission system beyond the wind farm outgoing line and the relay protection of wind farm is analyzed for different faults of transmission system components,wind farm outgoing line,wind farm internal grid and wind turbine.The current configuration of relay protection for the wind farm centrally connected to power grid is analyzed and it is pointed out that,the selectivity of wind turbine protection and converter protection is not enough,which leads to the disconnection of wind farm from grid before the fault is removed by wind farm internal relay protection or system relay protection,and the current configuration regards the wind power as a distribution network with single source,which neglects the contribution of wind turbine to short-circuit fault.Improvements are proposed for the relay protections of wind turbine,main transformer and outgoing line to ensure the successful low-voltage ride-through,and their problems are pointed out.