The technique of selecting surge suppressors (SPDs) taking into account the peculiarities of power transmission lines is presented. This technique makes it possible to achieve the required level of electromagnetic compatibility of elements of equipment of overhead lines with insulated wires. Selection of arresters is made according to several parameters, including coordination of lightning and switching overvoltages. In three-phase networks, special attention must be paid to short-term overvoltages. The correct selection of arrester according to this criterion is conditioned by the reliability of resonant overvoltages estimation or the probability of occurrence of arc overvoltages. This methodology makes it possible to achieve the required level of electromagnetic compatibility of elements of power line equipment.
Analysis of scientific and technical achievements in the field of transmission and distribution of medium voltage electricity showed that one of the main ways to improve the reliability and efficiency of 6(10) kV overhead lines is the replacement of bare wires with protected wires and installation of appropriate overvoltage and overcurrent protection devices. In this case, the probability of occurrence of multiphase short circuits and single-phase earth faults is reduced. However, thermal and lightning effects can damage the insulation and melt the wires, which will require significant costs to restore power. Therefore, when using protected wires, it is necessary to increase the sensitivity, speed and reliability of relay protection and network automatics of distribution networks, which is achieved by using digital relays. The current cutoff based on electromechanical relays can be used under certain conditions as an additional protection together with overcurrent protection (overcurrent protection). The trip relay operates without time delay (f P . 3 = 0) and protects only part of the area protected by overcurrent protection, but it quickly disconnects the largest and most dangerous fault currents for isolated conductors (near the supplying power substation). The most promising in terms of protection of overhead lines with protected wires from two- and three-phase short circuits are digital (microprocessor) relays of protection of electrical installations. Digital relays have wide functionality with low weight and dimensions, have high accuracy and perform continuous diagnostics and self-diagnostics.
