Research On Single-phase Ground Protection Of Wind Farm Collector System

Wind power generation plays an important role in accelerating the green and low carbon transition of energy in the power industry.Due to the large scale of domestic wind farms and the farther distance from the load center,they are usually transmitted centrally over long distances through high-voltage transmission lines.Therefore,trip-off events of large scale wind turbines have a serious impact on the power system.At present,in the process of relay protection when single-phase ground fault occurs in the 35kV collector system,the weak feed of the wind farm is not considered,which has an adverse impact on the four characters of the relay protection:the zero-sequence current protection of the collector line does not meet the requirements of quickness,and the collector bus differential protection does not meet the requirements of selectivity.Therefore,it is of practical significance to propose an improved strategy for single-phase ground protection of collector lines and collector buses.According to the basic theory of direct-drive permanent magnet synchronous power generation system,the simulation models of the dynamic and mechanical system of wind turbine and of direct-drive permanent magnet synchronous generator are modeled in MATLAB/Simulink,and the operation characteristics of PMSG under different wind speeds are simulated,which verifies the correctness of the models and lays a foundation for the characteristic analysis of single-phase ground fault in wind farms.An actual wind farm system structure is designed,but the topology structure is not suitable for simulation calculation.An equivalent structure model based on complete polymerization method and grouping method is proposed,and the single-phase ground fault characteristics of wind farm are analyzed.It is concluded that the wind farm has weak feedback when the fault occurs,and the protection may not adapt to the problem.The configuration and setting of zero-sequence protection for existing collector lines are analyzed,and a conclusion is drawn that the existing protection cannot meet the requirements of quickness of protection.At the same time,a zero-sequence current protection based on zero-sequence current comparison is proposed.The improved zero-sequence current protection does not need to set delay,which solves the problem that the existing protection does not meet the requirements of quicknessThe configuration and setting of the collector bus differential protection for internal phase faults are analyzed,and it is concluded that the existing differential protection can only remove the internal phase short circuit fault,but cannot remove the single-phase ground fault,which does not meet the requirements of selectivity of protection.At the same time,a bus differential protection based on zero-sequence current comparison is proposed.The improved bus differential protection solves the problem that the existing protection does not meet the selectivity.