Abstract <p>Providing consumers with high quality electric power with minimum transmission loss is among the problems of electric power transmission through electrical grids. Increasing reactive power of electric consumers, estimated by the load power factor, results in an increase in electricity loss and quality deterioration. To evaluate the effect of the load power factor on the transmission of active load power and to determine the quality and energy efficiency of electricity transmission through power lines, the authors analyzed the change in the parameters of one phase of a three-phase network without compensation and with reactive power compensation. The problem is solved using methods for calculation of linear ac circuits with the given values of total or active load power, its resistance, and the resistance of power line wires. Then, the processes of power transmission in low-voltage ac networks are simulated using the Electronics Workbench software. The results show that the main changes in the parameters of the electric power system consisting of consumer loads receiving power supply through the power line connected to the low-voltage busbars of the power transformer occur when the system current determined by the load and transmission line resistances is changed. The quality of electric power transmission through the power line is determined by the system current and total load resistance, and the energy efficiency of electric power transmission through the power transmission line is determined by the squared system current and the ratio of the active resistances of the load and power line.</p>