The article discusses the methods of substitution of a compound motor load as a consumer of higher harmonics. Two substitution schemes were used. The calculation of the complex resistance against them was compared with the results of simulation modeling. The simulation was carried out in the MATLAB Simulink environment, with the use of the Specialized Power Systems library, in which a simulation model with motors and a source of harmonic distortion was developed. Five asynchronous motors with a squirrel-cage rotor of the AIR brand with powers varying from 0.75 to 5.50 kW were selected for the study. The simulation was carried out at different motor loads. The shaft torque varied with values of 50; 70; 90 and 100 % of the nominal values of each motor. A six-pulse diode rectifier was used as a source of harmonic currents in the network, generating harmonics with numbers 5, 7, ..., 25, corresponding to a pulse rate equal to six. Oscillograms of currents and voltages were recorded at the point of common connection of asynchronous motors and the rectifier, which were subsequently used to calculate the complex resistance. Based on the results of the work, amplitude-frequency and phase-frequency characteristics of the impedance of a composite motor load were obtained, the analysis of which revealed the incongruence of calculation methods with simulation modeling. Conclusions have been drawn on the need to continue research in this direction, since there are qualitative discrepancies in the functional dependence of the complex resistance on the harmonic number with the experimental data obtained for a single asynchronous motor. The results of the work can be used in calculating the voltage distortion factor and modeling modes associated with higher harmonics both at existing enterprises and during their design, which will increase the reliability and efficiency of electrical networks.

There is a large number of factors that affect the long-term permissible load currents of power cables, including environmental conditions, the method of laying, as well as the geometric, thermal and electrical characteristics of the cable structure. The catalogs of manufacturers of power cables with cross-linked polyethylene insulation do not specify the long-term permissible load currents, which would take into account the cross-sectional area of the screen, the presence of aluminum polymer tape and armor made of aluminum wires. These components can have a significant impact on the permissible load due to the currents induced in them during two-way grounding, which leads to additional heating of the cable. The purpose of this study is to analyze the influence of the above-mentioned factors on the long-term permissible load currents. The paper presents formulas for calculating the long-term permissible load current, which take into account the design features of the cables under consideration. The calculations have shown that the permissible load can decrease by 6 % with an increase in the cross-sectional area of the screen from the nominal row by one step. The introduction of an aluminum polymer tape into the cable structure changes the permissible load by no more than 2 %. The presence of armor can lead to a decrease in the permissible load by up to 18 % and its increase by up to 13 %, depending on the section of the core and screen, the method and conditions of laying. The calculation results obtained differ from the catalogdata by up to 25%. While the obtained errorsindicatetheneed to formcoefficientsfor a moreaccuratedetermination of the long-term permissible cable currents.

The modern development of power engineering is accompanied by a number of trends, among which one can note the decarbonization of energy production processes; an increase in the share of electricity in the balance of energy consumption due to the deep electrification of industry, transport and heat supply; decentralization of energy sources; an increase in the share of renewable energy sources, including the involvement in the turnover of secondary energy resources and energy from the disposal of organic waste; the development of practice active consumption and prosumerism. For the Republic of Belarus, in which forests are one of the main renewable natural resources and the most important national wealth that ensure the sustainable socio-economic development of the country, its economic, energy, environmental and food security, in the context of decarbonization of the power engineering sector, it is relevant to determine the importance and location of energy generating equipment using local fuels (LF), especially for heating capacities and polygeneration plants. The paper presents the results of a study conducted to evaluate the effectiveness of using mini-CHP plants on LF. The analysis of the archived data of the automated process control system of an operating mini-CHP with a heating ORC unit (Turboden 14 CHP) made it possible to evaluate its maneuverable characteristics with reference to the operating modes of the centralized heat supply system with a predominance of municipal and household heat load in it. It has been shown that the average rate of change in power is 1.5...3.0 % min; respectively, the time to reach rated power under normal conditions exceeds 40 minutes; the time to start the unit from a “cold state” varies from 20 minutes to 2 hours. Therefore the assumption has been confirmed that the studied ORC unit in particular and mini-CHP plants of a similar type as a whole cannot be considered and used as a maneuverable energy source without additional modernization. The conducted numerical study made it possible to show the opportunity of planning effective operating modes of a heating ORC unit in the configuration of the basic thermal circuit of a mini-CHP on LF with the integration of a hydrogen production module into it based on the forecast of the daily schedule of thermal energy consumption and taking into account the dynamics of changes in outdoor air temperature. Conceptual block diagrams of integrated polygeneration systems are also presented; they stand out for the use of hydrogen generation equipment from over-produced electricity during the operation of mini-CHP plants according to a thermal schedule and participation in the coverage of the electric load schedule of the Unified Energy System of Belarus. The use of thermal circuits with thermochemical hydrogen production technology and the operating mode of the ORC unit at rated power is shown to be promising for newly designed mini-CHPs on LF.

At present, an actual trend in the development of fuel and energy complexes in a number of countries is the diversification of generation via the involvement of local types of solid fuel. In this case, thermochemical processing of fuel is often carried out in a fluidized state. A significant proportion of dispersed fuels cannot be transferred to a state of stable fluidization. The solution in such cases is to create a fluidized bed of inert carrier, into which particles of the target fuel component are then introduced. In this work, a computational and experimental study of the fluidization of inert bulk material (haydite granules) was carried out. The key purpose of the work was to develop a mathematical model for the formation of a fluidized bed, which makes it possible to calculate the process based on its local characteristics, as well as to identify the model parameters and test it using experiment data. During the study the problems of developing a numerical method for calculating the distribution of velocities and concentrations along the height of the apparatus were solved, parametric identification of the proposed mathematical model was carried out, and empirical verification of the modeling results was carried out. The mathematical apparatus of the theory of Markov chains was used as the mathematical basis for constructing the model. The data from our own laboratory full-scale experiment were used to identify the parameters of the model and verify it. A comparison of calculated and experimental data showed the high predictive efficiency of the model for the given granulometric composition of the fluidizing product. The results of the laboratory full-scale experiments also showed a significant evolution of the granulometric composition of haydite granules during their long-term stay in a fluidized bed, which requires a separate study, as well as the introduction of appropriate amendments to the mathematical model for its further improvement.

The issues of the formation of inhomogeneities and cracks as well as the effects of their spontaneous healing are considered on the well-known principles and concepts of nonlinear dynamics and quantum technologies in order to fully describe the picture of possible processes of the genesis of heterogeneities and their self-organization. At the same time, the process of spontaneous overgrowth of micro-inhomogeneities in solid-state/metal products, such defects in which occur under different operating conditions, is discussed on the example of thermal power plants of various types with cyclic processes and vibrations. The mechanism of such healing is determined by dynamic processes of unsteady diffusion with certain temporal characteristics evaluated within the framework of the corresponding model concepts. A model of diffusion-limited aggregation of defects/particles implemented by the cellular automaton method from the Neumann neighborhood, a model of random and ballistic deposition, as well as a percolation approach are considered. The process of modification and development of a 3D fractured structure based on the Griffiths load theory for dislocations is described, taking into account the gradual sequential transition from a stable state to a growth stage. As a result of the action of such dynamic loads in a solidstate object, a rapid change in the parameters of microcracking is observed, which can be represented as local micro-explosions, viz. the growth and fusion of natural microcracks into larger ones; the emergence of new microcracks; the disclosure of large microcracks with the formation of defects of the next hierarchical level. In the overview aspect, the universal modes of operation of a nonlinear dynamic system, well-known in mathematics and physics and suitable for analyzing the stability and sustainability of thermal power plants, are considered. The ongoing processes are associated with different types and strategies for the development of heterogeneities, such as: collapse and stagnation; stable periodicity; parameters “at odds”; chaotic development within certain limits; disruption/sudden crisis; a sharp leap and a breakthrough in development. The proposed approaches can be useful in improving the real operational condition of chambers with working matter in power plants when they operate in various operating modes. 

The article is devoted to the processing of experimental data regarding the drying of thin wet materials. The calculated kinetic dependencies necessary to determine the drying duration can be obtained from solving differential mass transfer equations, but this task is analytically complex, since drying is a non-stationary process, and the transfer coefficients depend on the moisture content and temperature of the material in a very complex form. This necessitates experimental studies with the development of approximate simple empirical equations for determining the drying duration with a minimum number of constants determined from the experiment. When processing the experiment, the relative drying rate, generalized drying time, the ratio of drying time by periods and the ratio of the current moisture content to the critical one were accepted as stable complex generalized variables when processing the experiment. All variables are interrelated by the drying rate in the first period (the period of constant rate). As a result of processing experimental data on convective drying of ceramics, asbestos, felt, formulas were obtained that make it possible to determine its duration in the period of falling rate. The invariance caused by such experimental processing allows one to move from one variable to another, from one coordinate system to another, which significantly reduces the number of necessary experiments. Data processing and analysis of the resulting formulas shows that the drying curves are complex exponentials, and the main mediating variables are the relative drying rate and relative moisture content. Verification of the accuracy of experimental data processing and the reliability of the obtained empirical equations, which make it possible to calculate the drying duration for the specified materials, is presented. The spread of the calculated values compared to the experiment is about 10 %, which is within the accuracy of experimental data processing.