In order to avoid grid cascading trip caused by power flow transfer, a search method for key lines based on power flow transfer when single line disconnection is proposed. Searching for several shortest paths between the end points of the removed line base on reactance weighting matrix and branches of all paths form the initial branch set. Then define the power flow stability index to filter the initial branch set to determine the key lines with overload risk. The simulation example shows that the proposed method can quickly and accurately find the dangerous line when power flow transfer, and overcome the shortcomings of the formula complexity of the previous method and the large amount of calculation, which saves time for the subsequent power flow control of circuit network. The proposed method was verified in the IEEE30 node system.

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