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Study on short circuit characteristics of DFIG and its impact on current protection of collector lines in wind farms

The scale of doubly-fed induction generator (DFIG) connecting to the power system is expanding continuously and DFIGs own low voltage ride through (LVRT) capability during the fault, so current protection of collector lines ignoring feeding current of winding generators simply would cause the performance of protection degrading. In this paper, for the purpose of meeting the requirement that wind farm providing reactive power to the system under the condition of a short circuit fault occurring on collector lines, a short current circuit calculation model and formula of the DFIG with a LVRT strategy with continuous excitation is established and proposed. Based on Matlab/Simulink, the model of wind farm connecting to the power system is established, by which the proposed short-circuit calculation model is verified correctly. Based on the short-circuit calculation model, the contribution of adjacent wind generators' feeding currents is studied by setting the system capacity, scale of wind farm and fault location as independent variables. From the results of simulation and calculation, with the enlarging scale of wind farms, it is essential for the current protection to take short circuit current through non-fault lines into consideration, moreover, the setting value of current protection is required to consider the actual conditions of the DFIGs in operation and adaptive protection scheme could be considered.