Research On Fault Characteristics And Protection Scheme Of Wind Farm Transmission Line

With the rapid development of the global economy,energy shortage and environmental pollution are being increasingly serious.As a kind of renewable energy,wind energy is widely distributed,clean and abundant reserves.Doubly Fed Induction Generator(DFIG)is the most widely used wind turbine generator system,whose fault transient characteristics are quite different from the synchronous generator.The interconnection of wind farm is large scaled and centralized,the transmission lines of which are mostly above 110 kV in China,so it is necessary to study the influence of wind farm integration on relay protection in high voltage transmission line.The basic principle of DFIG variable speed constant frequency operation,equivalent circuit and power transmission relations are studied.Besides,the principle of coordinate transformation and mathematical model of DFIG under synchronous rotation coordinate are described.On this basis,the vector control strategy of rotor side and grid side converter is researched,which lays a theory foundation for the study on fault transient characteristics of wind farm.According to the vector form of DFIG mathematical model,the short-circuit current expression under symmetric and asymmetric fault is deduced,and the characteristics of steady short current are analyzed.A voltage source – impedance form of DFIG equivalent model is proposed for researching the performance of relay protection.Besides,the fault transient characteristics of large-scaled wind farm under the fault of transmission line are studied,which is verified by simulation model of DFIG based wind farm.On account of the variation of DFIG's internal potential,the performance of relay protection based on superposition principle,such as power frequency variation distance protection and sequence component direction element is researched.On this basis,an appropriate protection scheme applicable to wind farm transmission line is proposed.