During the design of extra-high-voltage transmission lines, studies of the influence of asymmetry due to the phase difference of the parameters on its processes and the electrical network were performed. To compensate for this source of asymmetry for transmission lines longer than 100 km, a relatively simple technical means was proposed and implemented—phase transposition (change of the mutual location of phase wires in space). However, at the same time transposition causes additional capital costs in construction and reduces reliability during operation, so when designing a specific transmission line, extra-high-voltage is desirable to evaluate the effectiveness of the use of this measure in the real electricity network. Thus, under certain conditions, even for a transmission line 600 km in length, it was possible to perform either an incomplete transposition cycle, or abandon this measure altogether.

Abnormal resonant overvoltages in asymmetrical modes of bulk electrical power networks arise unexpectedly and can reach dangerous values. At the same time, there are no special devices in the networks to protect the equipment from this durable kind of overvoltages. The aim of the work is analyze the use of controlled shunt reactors to suppress the causes of abnormal resonance overvoltages in open-phase asymmetrical modes. The investigations were carried by analytical expression of resonant length and compensation degree of the line. As an example of an asymmetric mode, of the line is considered single phase auto reclose. The task is different from the traditional design, in which the technical and economic indicators of the normal regime serve as the criterion for choosing the parameters of the controlled shunt reactors. It was concluded that it is expedient to take into account the probability of occurrence of abnormal resonant overvoltages in solving design and operational problems of optimization of flow distribution of reactive capacities in bulk power electrical networks with the help of controlled shunt reactors.

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. The switching control unit Switchsync F236 is one of such devices which enables to connect and disconnect contacts of poles circuit breakers at required time. This function of Switchsync F236 can be used not only for interruption of short circuit. One of the objectives of application Switchsync F236 is prevention of resonance overvoltage occurrence at closing extra high voltage line on no-load autotransformer. Durable resonance overvoltages may cause damage of electrical power equipment. This kind of overvoltages is caused by properties of the network and can be eliminated by changing the values of network parameters. Unlike switching overvoltages that exist centiseconds, resonance overvoltages 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 mode. The resonant overvoltages are neglected when selecting insulation or parameters for high-voltage surge arrester as this protective measure is calculated to limit switching overvoltages, not to extinguish a long resonance process. Therefore, the probability and development of system accidents due to resonance overvoltages is significant. The importance of application and prevention of resonance ovevoltages caused research area which is presented in article.

This study aimed to develop a cost-effective, environmentally sustainable, and technologically advanced dielectric fluid by utilizing the beneficial properties of natural ester-based vegetable oils, offering a promising alternative for transformer insulation and cooling applications. The novelty of this research lies in the formulation of a nanofluid that combines three distinct vegetable oils—castor, flaxseed, and blackseed—creating a unique base fluid. SiO₂ nanoparticles were incorporated into the fluid to leverage their multiple advantageous characteristics. Extensive experiments were conducted to evaluate the superior properties of the proposed nanofluid, focusing on key dielectric properties, such as relative permittivity (ε_r) and the dielectric dissipation factor (tan δ). Comparative analyses with conventional mineral oil, which was used as a benchmark, demonstrated the significant advantages of the vegetable oil-based nanofluid. The novel formulation outperformed all other tested samples, highlighting its exceptional performance. Additionally, three preparation methods were examined, with the green synthesis technique producing the nanofluid with better dielectric properties. Through a detailed presentation of empirical data and compelling arguments, this study confirms the potential of natural ester-based vegetable oil nanofluids as a highly promising alternative, driven by their intrinsic properties and the environmentally friendly synthesis method employed.