A pilot protection method for the wind farm transmission line based on interaction power difference

Traditional protection methods for the wind farm transmission lines do not consider the difference between Doubly-fed Induction Generators(DFIG), and they may easily mal-operate or fail to operate. To solve this problem, a new pilot protection method for the wind farm transmission line based on the interaction power difference is proposed. First, the expression of the interaction power in the wind farm is derived according to the terminal voltages of different DFIGs. And then, the interaction power is decomposed into the inter-generator interaction power and the generator-grid interaction power, which reflect the power interaction between different DFIGs in the wind farm and the power interaction between DFIG and the external system. When an internal fault occurs on the transmission line, the interaction power between different DFIGs in the wind farm can offset one another and only the generator-grid interaction power is output to the transmission line. When an external fault occurs, the interaction power between different DFIGs in the wind farm cannot offset one another, and part of the inter-generator interaction power is output to the transmission line together with the generatorgrid interaction power. Based on different characteristics of the interaction power under internal and external faults, a protection criterion is constructed to distinguish different fault cases. Finally, simulation results of RT_LAB (Real Time Lab) experimental tests verify that, the proposed method can correctly distinguish different types of internal and external faults, unaffected by the fault location and fault resistance.