Research On The Protection And Reclosing Of High Voltage Transmission Line Integrated With Wind Farms

It is common understanding of all the nations in the world to develop new energy technologies to deal with the energy crisis and environmental crisis.Wind power generation is the most mature,the most large-scale developed and the most commercially promising in the new renewable energy generation technologies,which has been widely concerned by the world.With a rapid development,China's wind power industries are now facing a variety of problems.Lacking of research on the wind farms and their transmission line protection,the traditional protection is unable to adapt to the special nature of wind farms.It is difficult to remove the faults safely,reliably and quickly to ensure not only the safe and reliable operation of the wind farms but also the continuous and stable operation of transmission lines.At first,this paper analyzes the basic structures and principle of several common wind generators.On this basis,a detailed explanation of the doubly fed asynchronous generator(DFIG)to achieve the principle of wind power generation with variable speed and constant frequency is provided.Mathematical model of the doubly-fed wind turbine has been studied,obtained under mathematical equations synchronous rotating coordinate system.The working principle of back-to-back converter and the vector control method have also been introduced.The control strategy of the low voltage ride through the double fed induction generator is studied,based on which the transient characteristics of fault current in the wind farm is also provided.In the end,based on PSCAD/EMTDC,a wind farm model of Guizhou is built,and the fault transient characteristics of wind farms are simulated.The transmission line protection configuration access to wind farms of actual power grid is introduced.The action of current differential protection,distance protection and phase selection has been analyzed in different fault types,fault points and power output of wind farms,by which we got the conclusion that wind farms can affect the sensitivity of current differential protection,distance protection can be out of work in the three-phase short-circuit fault of transmission lines and that a wrong phase selection can be caused on the side of wind farm.These conclusions are verified by simulation.Finally,the wind farm reclosing configuration of actural power grid is introduced.Different reclosing mode,reclosing time and reclosing test mode has been analysed according to the fault characteristics of wind farm after the short circuit on transmission lines.The phenomenon that voltage rise may occur during single-phase reclosure time,which leads to large-scale wind farm separated from the power grid has been analysed,and arrives at the conclusion that reactive power is over compensation.According to the fault instance of the wind farm of GuiZhou,advantages and disadvantages of different reclosing mode has been compared.Reasonable reclosing configuration of the wind power transmission line is put forward in the end.