Textbook for universities. Parameters, technological processes and load schedules of both individual electric receivers and electric consumers are described. The concept of the term "design load" is given and the main methods for determining design loads at various hierarchical levels of power supply systems are described. Information is given on the design of power lines, step-down substations and the main electrical equipment of electrical networks. Circuit solutions of power supply systems are described. Bases of calculation of steady modes of electric networks are given; issues of calculation of power losses and reactive power compensation are covered. Approaches to calculations of short-circuit currents and design of power supply systems of facilities for voltage of 6 - 100.4 kV are described. The issues of improving the efficiency of power supply systems were considered.