The tower structure and geometrical arrangement of transmission line conductors in the power system depend on various technical, economic, and geographical factors and the age of construction of the lines. Thus, the arrangement of lines may not be transposed or follow the standards of the electricity industry. The untransposed conductors cause asymmetric couplings in the transmission lines, directly leading to destructive effect on the function of distance protection and accurate determination of the fault location. Fault location in untransposed transmission lines is presented as a novel research piece by investigating the circuit equations of positive-negative-zero sequences and using synchronous voltage measurements taken from the near and far terminals of the transmission line together with measuring the current of one terminal. In this algorithm, the effect of mutual interphase impedance and admittance due to the untransposed structure of the line is fully taken into account. Fault location equations are designed based on the complete equivalent circuit of the untransposed transmission line using the modeling of all effective parameters. As the presented design adopts the current measurements of one terminal, the destructive effect of the current measurement systems is dropped. The Simulink model of the suggested design has been implemented in Digsilent Power Factory software and the algorithm has been programmed in MATLAB software. The performance of the proposed algorithm has been tested and evaluated for a two-terminal network in normal and critical fault conditions, as well as for a 39-bus untransposed New England network. According to the obtained results, the average estimation error of all scenarios is approximately equal to 0.07%. The results presented in the simulation and sensitivity analysis section confirm the accurate and correct performance of the algorithm.
