Abstract-Due to the rising role of overhead lines extra high voltage there is a need of application of modern electronic devices that allow controlling modes of bulk electricity system. Durable resonance overvoltage may cause damage of electrical power equipment. This kind of overvoltage is caused by properties of the network and can be eliminated by changing the ratio between the parameters of the network and its mode. Unlike switching overvoltage that exist centiseconds, resonance overvoltage not only occur unexpectedly, but they may go on for a long time until the automatic action or action of personnel will not change electrical schemes or operation modes. The resonance overvoltage are neglected when selecting insulation or parameters for high-voltage surge arrester as this protective measure is calculated to limit switching overvoltage, not to extinguish a long resonance process. Therefore, the probability and development of system accidents due to resonance overvoltage is significant. One of the main causes of equipment failure in the main electrical network is overvoltage.