Study On Single-Line-to-Ground Fault Location Method For Transmission Line And Collecting Power Line Of DFIG-Based Wind Farm

With the proposal of carbon peaking and carbon neutrality goals,the construction of the new generation power system with renewable energy as the main component has become an important goal of energy supply side reform.Among all kinds of renewable energy,wind power has the characteristics of mature technology development and wide distribution of resources.With its great expansion in power system,the requirements for its reliability from the system are increasing.If fault occurs on transmission line or collecting power line cannot be located and repaired in time,a large number of wind generators will trip off for a long time,which threaten the utilization of renewable energy and the stability of the system.Therefore,wind farms should be equipped with fast,accurate,low-cost and automatic fault location functions to ensure the normal production,collection and transmission of wind power.In this thesis,the common single-line-to-ground fault is taken as the research object,the electrical characteristics of DFIG-based wind farms during faults are analyzed,and the corresponding fault location methods are proposed according to the characteristics of transmission line and collecting power line respectively.For the fault location of transmission lines,the characteristics of the stator current from DFIG during the fault on transmission lines are analyzed.It is pointed out that the Fourier algorithm cannot filter the speed frequency component in the stator current generated in the process of low voltage ride through,so the accuracy of the traditional fault location method is insufficient.On this basis,a zero-sequence phase correction method based on VMD is proposed,and the speed frequency component is filtered by using the function of VMD to distinguish similar frequency components,so as to eliminate its influence on fault location calculation.Simulation results on PSCAD/EMTDC platform show that the proposed method can effectively improve the single-line-to-ground fault location accuracy on transmission lines.For the fault location of collecting power lines,single-ended impedance method based on zero-sequence current is taken as the foundation.It is pointed out that on multi-branch radial lines,which is common in wind farms,single-ended measuring devices may obtain the same data in different fault case,thus single-end impedance methods can only obtain multiple suspected fault points,while multi-end methods need to add a large number of measuring devices,which is expensive and difficult to be applied in engineering.The principle of adding minimum number of measuring devices for locating single-line-to-ground fault of multi-branch line is given in this thesis,and the method of fault branch discrimination and fault location based on multi-terminal information is proposed.Simulation results on PSCAD/EMTDC platform show that the proposed method can correctly identify the fault branch and locate the actual fault point on collecting power lines with various topologies,and the number of measuring devices used is less than that of the existing methods.The method proposed in this thesis can realize the accurate location of single-line-to-ground fault on transmission lines and collecting power lines,reduce the time spent on locating and repairing faults,which means an excellent engineering application prospect.