Abstract: To address the fault location problem of active distribution networks with unmeasurable branches, this paper proposes a novel fault location method utilizing synchronized power-frequency electrical quantities at both terminals of the line. Based on the characteristic differences between T-connected distributed generation (DG) and T-connected loads, fault models are established respectively. For T-connected DG branches, control constraints are applied to compensate for unknown information on T-connections, and a rotation factor is introduced to correct synchronization errors. For T-connected load branches, the composite sequence network decomposition method is utilized to solve the underdetermined equations resulting from incomplete branch information, which can effectively realize fault location for asymmetric phase-to-phase faults. Simulation tests based on PSCAD demonstrate that, under the most complex operating conditions, the relative fault location errors of the two proposed methods are less than 5%, validating the effectiveness of the proposed methods and providing a new solution for fault location in complex distribution networks.