The invention pertains to the field of electric power engineering and can be used for creating new fault location devices taking into account that usage of known fault location methods for short-circuit distance determination causes errors in case of large line power flows in pre-fault regime. The proposed method determines unknown parameters both for the pre-fault and fault regimes. Measurements of the instantaneous current and voltage signals for the monitored line and another line from the same substation are made, converted analogue-to-digital form and processed with random noise filters using orthogonal and symmetrical component filters. Measurements are performed and processed separately for the pre-faut and short-circuit regimes. Determination of the unknown parameters for both regimes is done by optimization of objective function, i.e., by minimization of the difference between the measurement and model output currents and voltages. The identified parameters of the load regime are fed into the short-circuit regime model, facilitating the identification of the short-circuit regime parameters. Upon the identification of the unknown short-circuit regime parameters, the short-circuit distance and the fault resistance are output to the interface.