Andrii Hadai’s research while affiliated with Lutsk National Technical University and other places

The relevance of the study, in particular, in the Volyn region, is due to the need to ensure the reliability and efficiency of the energy infrastructure in the face of growing challenges associated with the war between Russia and Ukraine, technological development and ensuring the country’s energy security. The purpose of the study is to develop a model of the optimal switching scheme for the Volyn region’s power grids during blackout to minimize the negative consequences and ensure priority power supply to critical facilities. The methods used include mathematical modelling, simulation, optimization, sensitivity analysis, and others. The study optimized the power grid switching scheme under the risk of war and other crisis situations, including a thorough analysis of various options in the event of a blackout. Taking into account additional aspects of grid safety and reliability, the optimal routes for power transmission, placement of backup power sources were identified and effective algorithms for grid management were developed. By optimizing the grid switching scheme, the damage caused by blackouts can be minimized, and power supply can be restored quickly. The results confirmed that an optimal switching scheme can significantly reduce blackout time and its impact on the economy and the lives of the population. The development of optimal switching schemes for power grids is an important step towards increasing the resilience of Ukraine’s electricity system to crisis situations. The study has highlighted the importance of developing such models to ensure energy security and resilience of the power grid under the threat of blackouts, which affects the practical aspects of power supply management and economic development. The practical significance of the study is to improve strategies for managing the power grid in blackout conditions, contributing to the resilience of energy systems and economic development

The analysis of existing principles of selectivity indicates the complexity and incompleteness of ensuring the coordination of the operation of protection devices in distribution networks of 0.4 kV consumers. Current selectivity is ensured only in the area of action of short-circuit currents. To ensure it, electromagnetic or electronic decouplers with a constant deceleration setting are required. This type of disconnectors is used to perform time selectivity and limit the thermal impact of short-circuit currents on the electrical installation and device. The use of devices with "pseudo-time" selectivity ensures the selectivity of the operation of automatic switches in the area of short-circuit currents. Selectivity "SELLIM" is provided with a speed of 0.01 s, but it is possible only in automatic circuit breakers "Schneider Electric". Logical selectivity requires a communication channel between switching devices and the presence of circuit breakers with appropriate communication ports. It is easiest to ensure selectivity by using switches from the same manufacturer using selectivity tables. But such a solution is not always found in practice. The method of energy selectivity allows, taking into account the ratio between ratings, to implement either partial selectivity or full selectivity up to the limit of the breaking capacity of automatic switches. To ensure energy selectivity between two or more current-limiting devices, it must be taken into account that depending on the location of the short circuit, a different number of circuit breakers will be involved in limiting the emergency current, and therefore, the value of the limited current will also be different. By using circuit breakers with a high level of current limitation and a tripping speed that is inversely related to the short-circuit current, full selectivity can be provided at several levels of the network. This makes it possible to simplify the analysis of selectivity, minimize electrodynamic and thermal effects and reduce the level of voltage drop due to the action of a short circuit. Improvement of electrical installation protection systems makes it possible to design power supply systems without excessive reserves of electrical equipment overload, which reduces their cost, dimensions and weight. On the other hand, in the event of malfunctions in the operation of electrical equipment, this limits emergency currents and prevents failure of the undamaged part of the electrical installation, which significantly reduces downtime. Key words: selectivity, relay protection devices, circuit breakers, electrical devices, 0.4 kV network.

The relevance of the problem under study is determined by the need to create a sustainable, efficient and environmentally safe energy complex. The growth of the world population, industrial development, and overall energy demand endanger the provision of society’s energy needs, making the need for research urgent at the present time. The purpose of the study is to examine optimal energy optimisation strategies, including alternative energy, compensation of reactive power, and energy efficiency management, to ensure the stable and efficient functioning of the energy complex. Among the methods used, analytical, classification, functional, statistical, and synthesis methods were applied. In investigating the optimisation of energy solutions, a thorough analysis of various aspects of alternative energy, reactive power compensation, and energy efficiency management was conducted. This analysis encompassed various aspects and parameters related to these areas, including technical, economic, and environmental indicators. As a result of the study, it was established that alternative energy has significant potential for ensuring sustainable development of the energy system. It can serve as a reliable source of energy that does not harm the environment and is not dependent on limited resources. In addition, reactive power compensation was recognised as an effective way to avoid energy losses in the system. This strategy helps to ensure more efficient energy use and reduce losses during transmission and distribution. Energy efficiency management also proved to be a key aspect in achieving energy supply sustainability. This allows optimising resource utilisation, reducing energy costs, and mitigating the negative impact on the environment. The practical value of the study lies in the development of innovative recommendations and strategies for energy optimisation, which will contribute to the creation of a stable, efficient, and environmentally safe energy complex and enhance its compliance with current and future challenges, making a considerable contribution to the development of science and the energy sector