Abstract: The collector line short-circuit fault is one of the most common faults for the grid-connected doublyfed wind farms. Because the introduction of the crowbar discharge resistor，after the unsymmetrical faults of the collector line，the positive and negative sequence impedances of DFIG will produce the different characteristics according to the different slip rate. Then the selectivity of the traditional adaptive instantaneous overcurret protection is affected and a good deal of DFIGs may be cutted off incorrectly，the internal reliability and grid-connection stability of the doubly-fed wind farm are reduced. In view of the above situation，an improved adaptive instantaneous overcurret protection（IAIOP）based on the impedance characteristics of the crowbar circuit was proposed for the 35 kV collector line to improve the protection performance of the doubly-fed wind farm. Meanwhile，the setting calculation of the proposed IAIOP was also analyzed in detail. The correctness and effectiveness of the proposed protection method and setting calculation were validated by the simulation model in the PSCAD.

      Key words: short-circuit fault of the collector line； doubly-fed wind farm； instantaneous overcurret

protection；setting calculation；impedance characteristics