This paper presents a method for fault location in transmission lines, which uses measurements from one substation during pre-fault and fault regimes to estimate unknown parameters of a wider power system model with an optimization algorithm. The optimization algorithm diminishes the difference between measurements and a power system numerical model output. This method incorporates random search within given limits of unknown parameters with a following search space reduction. An additional estimation of pre-fault regime model parameters reduces the number of free dimensions in the fault regime model thus increasing the feasibility of the fault parameter estimation. The utilization of a topological fault model with interconnected sequence networks allows accounting for fault resistance and presence of the zero sequence mutual coupling of parallel lines. Testing of the proposed method showed that it can provide results with a good tolerance despite using a system model with various simplifications.