Traditional off-line line parameters measuring is complicated in operation and has poor applicability. And the symmetry of line parameters influences the choice of on-line measurement methods. Generally, it's is asymmetric. Therefore, the paper proposes an on-line measuring method of power frequency impedance parameters for asymmetric transmission lines. First, three-phase unbalanced transmission line model are built and power frequency impedance parameters calculation equations are obtained.

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... e equations are underdetermined and have no specific solutions. By changing the line topology, multiple measurement are preformed and plenty sets of data are obtained. Then after adopting the least squares method in complex domain, the exact solutions are finally derived. The simulation results show that the errors of zero sequence impedance mode and impedance angle reach-0.2501% and 0.1533% respectively, the errors of positive sequence impedance mode and impedance angle reach -0.1974% and 0.1011% respectively, far less than the error requirement of practical engineering. The method in this paper is of high accuracy, which can provide a theoretical basis for three-phase unbalanced transmission line parameters on-line measurements.