No 1 (2024)

The article deals with the issue of clustering electric power systems (EPS) into reliability zones for the formation of energy calculation models (ECM) of EPS, designed to perform calculations of adequacy indicators. The substantiation of the ECM detailing depth is based on taking into account two EPS properties: reliability, namely, on the basis of calculated estimates of the limits of applicability of deterministic and probabilistic reliability criteria, and economy, namely, on the basis of a comparison of cost estimates of measures to ensure reliability. In the first part of the article, to solve the problem, it is proposed to use a number of engineering approaches that take into account the reliability and efficiency of the EPS. The experimental studies section presents the results of applying the proposed algorithms for the formation of the ECM of the unified energy system of Siberia.

Numerical simulation of water spray evaporation in hot flue gas flow provided a dataset that was used to find correlation between evaporation efficiency and nozzle design parameters: mean droplet diameter, spray cone angle and hollowness. Fitted with linear model simulation data were extrapolated outside their original ranges to find the maximum, and corresponding efficiency vector. This vector was interpreted as a preferred direction of nozzle design optimization: provide wide hollow cones. Moreover, it was shown that positive correlation between evaporation efficiency and spray cone outer angle becomes stronger as its hollowness increases. However, it was pointed out that evaporation efficiency of narrow hollow sprays can be less than of full cone sprays in certain conditions. It was also found that droplet size when below 1 mm is almost irrelevant to spray evaporation efficiency.

The presented article is devoted to the study of the temperature field in a laminar fluid flow moving in a round pipe. In this case, it is assumed that the flow of the medium is stationary with a parabolic velocity profile and its thermal properties are constant. The paper studies an approximate analytical method for calculating the temperature distribution in a fluid flow. Relatively simple mathematical dependences are obtained for determining the first eigenfunction and the first characteristic root of the problem under consideration. The recommended expressions are highly accurate and make it possible to quickly investigate the heat transfer process in the area of the ordered regime of fluid flow in the channel, which, as a rule, is the main one.

We stated the problem of determining the temperature field of an isotropic half-space with a film-coated surface while undergoing heat exchange with the environment. A non-steady-state heat exchange mode with time-varying heat transfer coefficient and ambient temperature is researched. We identified sufficient conditions, the fulfilment of which makes it possible to implement a self-similar heat exchange process in the analyzed system. The physical properties of the studied self-similar process are qualitatively investigated and we established its specific features. The possibility of realizing the mode of temperature control of the boundary of an isotropic half-space with a film coating is theoretically substantiated in case of non-steady-state heat exchange with the environment.

In modern hybrid power systems, the total system inertia is not a constant value and at any given time depends on the share of renewable energy sources (RES) generation that are connected to the network via power converters. Because of this, the restrictions required in the power systems on the rate of change of frequency and the magnitude of its deviation during disturbances become difficult to achieve with conventional approaches and measures. Therefore, the transition to a new strategy of RES control, in which the power converter becomes the grid-forming, allowing the latter to perform a number of necessary system services, is relevant. To this end, a control algorithm based on the virtual synchronous generator (VSG), which imitates the properties and capabilities of conventional synchronous generation for RES units, can be used. However, due to constantly changing operating conditions in hybrid power systems, the virtual inertia formed by VSG must be adaptive. At the same time, the efficiency of adaptive algorithms largely depends on the VSG structure used. In this connection, the paper proposes a modified VSG structure for which the transfer function of the active power control loop is formed. It was used to perform a comparative analysis of traditional and modified VSG structures. The analysis results are proved that the developed structure does not have three principal contradictions. It is possible to flexibly control the modified VSG parameters to achieve the desired quality of the dynamic response at any stage of the transient process due to these special properties. The influence of tuning parameters on the inertial and damping properties of VSG is analyzed in the second part of the paper. The adaptive algorithms of the parameters changed depending on the emerging grid conditions have been developed on the basis of the obtained results. The obtained analytical results are confirmed by nonlinear dynamic simulation.