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A new fault location algorithm for double-circuit transmission lines with availability of complete measurements from two anti-parallel end of the line is presented. Sequence voltage and current phasors from these ends are taken as inputs and no synchronisation between them is needed. Using the pre-fault data, the synchronisation angles between measurements at the reference and the anti-parallel ends are obtained. Using the fault data, the faulted circuit is determined and the sequence voltages and currents at the fault point are calculated as a function of the fault distance. Finally, using the fault boundary conditions that exist for a given fault type, the fault location is derived and solved by an iterative method. Owing to zero-sequence mutual coupling, it is not straightforward to express the zero-sequence voltage and current at the fault point as a function of the zero-sequence voltages and currents at the two measuring ends and the distance to fault. To overcome this problem, a modal transformation matrix is introduced to obtain the modal networks, which are decoupled and can be analysed independently. Based on distributed parameter line model, the proposed algorithm fully considers the effects of shunt capacitances and thus achieves superior locating accuracy, especially for long lines. Mutual coupling between circuits, source impedances and fault resistance do not influence the locating accuracy of the algorithm. The simulation results using ATP-EMTP and MATLAB demonstrate the effectiveness and accuracy of the proposed algorithm.