The paper describes the issue of protecting high-voltage transmission lines using distance protection. An analysis of the calculation of the measured impedance of distance protection is presented for different types of short circuits, as well as its visualization and interaction with the MHO and polygonal type operating characteristics. The influence of the transition resistance at the fault location on the measured impedance of distance protection is also analyzed. Finally, on the example of a specific section of the 110 kV transmission network, a method of calculating the settings of the distance protection parameters of a single transmission line is presented, using numerical relay devices type 7SA6x from Siemens.