Fault Characteristic Study Of Large Scale Wind Farm

As the most promising new industry, wind power technology is the best choice to solve the energy crisis, environmental problems, and to maintain sustainable development in China. With the development of large scale grid-connected wind farm, the requirement of grid-connected wind turbine is gradually improved. In actual operation, unreasonable protection configuration of collector line expands the fault range easily, resulting in the large scale cascading trip-off of wind turbines. The safe and stable operation of power system is seriously threatened. Therefore, the study of the protection principle of wind farm, especially the protection and configuration principle of collector line, is of great significance in the development of China wind power technology.According to the parameters and the actual operation of wind farms, wind farms model was built on the PSCAD/EMTDC platform. The output characteristic of wind turbine was simulated in the case of wind speed fluctuations or various types of external faults. Besides, short circuit current of wind turbine was quantitatively analyzed further. On the basis of the protection configuration of wind farm, the setting value of collector line protection was calculated, and the risk and problems was pointed out. Combined with the low voltage ride through capability of wind turbine, setting principle of instantaneous overcurrent protection was redefined. The short-circuit current should be higher than the minimum one which occurred when all the wind turbines of the collector line were just off the grid. On the other hand, directional element was equipped to prevent misoperation in the non-fault conditions. It was suggested that the power supply characteristics of wind turbines should be considered for wind farm protection in the future. The collector line realized full line high speed operation through optical fiber current differential protection. Comparing overcurrent protection, improved overcurrent protection and optical fiber current differential protection by simulation, we verified that the improved scheme and current differential scheme can effectively improve the rapidity and selectivity and reduce the possibility of large scale cascading trip-off of wind turbines.