Objective: the concept of the limit of power flow is widely used in general industrial power engineering to compare different ways of amplifying an electric network. In this paper, it is proposed to use it to evaluate the operation of traction networks of railways. Setting the traction power load is used in several simulation development of an express methodology for comparing various ways to enhance traction power supply is an urgent task. Methods: the paper uses mathematical modeling methods based on the theory of electrical circuits. The MATLAB software package was used as a modeling tool. Results: expressions are obtained for calculating the maximum transmitted power depending on the length of the substation zone. The dependence of the transmitted power on the minimum voltage on the current collector, the equivalent resistance of traction substations for DC sections, is analyzed. For alternating current sections, the dependence of the transmitted power on the power factor of the traction load is analyzed. The conclusion is made about the relevance of increasing the power factor of an alternating current electric rolling stock. Practical importance: the proposed technique will allow you to quickly assess the effect of using various methods of strengthening the traction power supply system.