The textbook contains a description of mathematical models of elements of electrical systems and networks, which are used in calculations of steady modes for specialized software and computer systems. Issues of data preparation and analysis of steady-state modes calculation results are considered. Theoretical materials and tasks are presented for practical calculations in the tasks of determining the area of ​ ​ permissible modes and regulating the voltage of electrical networks, increasing the transmission capacity, improving the quality of electrical energy and reducing power losses.