This article describes calculation of operation modes of railway traction power-supply systems, dc power-supply systems in particular. The procedures recommended for the calculations have been obtained under certain assumptions, which simplify the calculations, however, are the reasons of errors. In order to minimize discrepancies between calculations and experimental data, it is required to develop improved simulation models and software complexes on their basis. Brief analysis of potential applications of improved simulation models is given, one of such applications is the determination of parameters and properties of energy-storage systems. An approach is described to development of simulation model on the basis of substitution layout of a network segment, traction specifications of electric rolling stock and other elements. The studies have been performed on the basis of simulation model, which demonstrate that the use of electric energy-storage system is capable to solve certain problems, in particular, to increase carrying capacity and traffic intensity, to increase energy efficiency of electric power traction system. Qualitative estimations of these specifications are given.