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E-Journal N2(62)2024



1 Study of Special Unbalanced Load Modes of New Double-Autotransformer of the Flexible Alternating Current Link
Authors: Bosneaga V., Suslov V. Institute of Power Engineering of Technical University of Moldova Chisinau, Republic of Moldova
  Abstract: The purpose of the work is study of special asymmetric modes of new three-phase autotrans-former device for flexible connection of alternative current power systems. The universal model was developed for the device, containing two autotransformers - the main phase-shifting and the additional regulating autotransformer. The model allows studying both symmetric and almost any asymmetric modes of the considered circuit. It became possible to connect asymmetrically the loads in different phases of the regulating autotransformer, as well as arbitrary connect the regulating autotransformer itself to the hexagon taps. According to the calculated values of cur-rents, voltages and magnetic fluxes of the device the visual vectorial diagrams were constructed for the main and the regulating autotransformer, explaining specific of considered operating modes. It was shown that device’ currents in such modes contain symmetrical components of both zero and negative sequences. Also, at asymmetric connection of the regulating autotrans-former, the relative magnetic flux of the legs of the main and regulating autotransformers are asymmetrical, but in main autotransformer their sum is approximately equal to zero and magnet-ic flux practically does not escape into the surrounding space. Radically different situation is observed in the regulating autotransformer. The significant zero-sequence fluxes arise with the release of significant (about 50%) magnetic flux into the surrounding space. This requires spe-cial measures to be taken to limit its harmful effects on the operation of the autotransformer.
  Keywords: double-autotransformer device for flexible connection of AC power systems, unbalanced load, symmetrical components, distribution of relative magnetic fluxes.
2 Hybrid Active and Passive Cable Contour Shielding of Magnetic Fields of Double-Circuit Overhead Power Lines
Authors: Kuznetsov B.I.1, Kutsenko A.S.2, Nikitina T.B.3, Bovdui I.V.4, Chunikhin K.V.5, Voloshko O.V.6 1,4,5,6 Anatolii Pidhornyi Institute of Mechanical Engineering Problems of the National Academy of Sciences of Ukraine, Kharkiv, Ukraine 2 National Technical University "KhPI", Kharkiv, Ukraine 3 Educational scientific professional pedagogical Institute Ukrainian Engineering Pedagogical Academy, Kharkiv, Ukraine
  Abstract: The purpose of the work is to design a hybrid screen designed to reduce the level of the magnetic field generated by double-circuit overhead power lines, to increase the efficiency of shielding the original magnetic field in residential buildings, to the level of sanitary standards and to reduce the sensitivity of the system to changes in system parameters. To achieve this goal, the structure of a hybrid screen was determined, consisting of a double contour active and a cable contour passive part. The developed hybrid screen is characterized by increased efficiency in reducing the magnetic field of industrial frequency. Designing a hybrid screen comes down to solving a minimax vector optimization problem, in which the vector objective function is calculated based on solution to Maxwell's equations in a quasi-stationary approximation using the COMSOL Multiphysics software package. The solution to the minimax vector optimization problem is calculated based on multi-particle swarm optimization algorithms from Pareto-optimal solutions taking into account binary preference relations. During the design of the hybrid screen, the coordinates of the spatial location of the two compensation windings, as well as the magnitude of the currents and its phases in the windings of the active screen, were calculated. The important results are theoretical and experimental studies on the effectiveness of the designed hybrid magnetic field shield generated by double-circuit overhead power lines. The significance of the results obtained lies in the fact that practical recommendations are given for a reasonable choice of the spatial arrangement of two shielding windings of a robust system of hybrid shielding of the magnetic field generated by double-circuit overhead power lines.
  Keywords: two-circuit overhead power lines, magnetic field, hybrid shielding, theoretical and experimental studies.
3 Study of Start-up and Shutdown Modes of an Asynchronous Electric Drive for a Centrifugal Pump
Authors: Boiko A., Naidenko E., Besarab O., Maevskaya E. Odessa National Polytechnic University Odessa, Ukraine
  Abstract: The aim of this study is to investigate the commutation processes of an asynchronous short-circuited electric drive for a centrifugal pump. The set goal is achieved by solving two tasks: an-alyzing the dynamic modes of connection to and disconnection from the network of the asyn-chronous motor of the centrifugal pump for a given power supply scheme; assessing the qualita-tive and quantitative indicators of the transient processes of the electric drive. Among the most significant results of the study, it is possible to highlight the ability to form practical recommen-dations on the operation peculiarities of electric drives for a wide class of mechanisms. The conducted research allowed asserting that in an electrical system with capacitors directly con-nected to the stator winding and during both the connection and disconnection of the drive mo-tor of the centrifugal pump, voltages significantly exceeding the nominal ones may occur. It has been determined that considering the harsh operating conditions of pump units, such overvoltag-es represent a danger to the motor winding insulation. During the motor disconnection, signifi-cant overvoltages on the stator windings are possible if, for any reason, the capacitor's capaci-tance exceeds the calculated base value for the applied motor. The practical significance of the obtained results lies in the fact that the assumption of the motor transitioning to intensive braking mode and subsequent hydraulic shock upon disconnection from the network due to self-excitation did not prove to be true. The electric drive provides braking under the action of the load torque without mechanical overloads.
  Keywords: asynchronous motor, compensating capacitor, centrifugal pump, transient processes, motor start-up, motor disconnection.
4 Selection of Asynchronized Turbogenerators Parameters Taking into Account the Operating Mode
Authors: Shevchenko V.V., Duniev O.О., Pototskyi D.V. National Technical University "Kharkiv Polytechnic Institute" Kharkiv, Ukraine
  Abstract: The purpose of the work is to develop an algorithm for calculating currents in the asynchronized turbogenerator rotor windings when it operates at a power system with a variable load. Typically, synchronous turbogenerators of thermal power plants are used to maintain the balance of active and reactive power in the power system. But they cannot fully ensure the maintenance of bal-ance by switching to non-nominal modes: during periods of power consumption dips, reduce power to 50-70% and switch to under-excitation mode to compensate for reactive power. There-fore, it is promising to install asynchronized turbogenerators at power plants in parallel with syn-chronous turbogenerators, which remain stable over a wide range of changes in active and reac-tive power. The work analyzed data from the operation of asynchronous turbogenerators in dif-ferent countries. The subject of the study was an ASTG-200-2U3 asynchronized turbogenerator with two identical field windings. The goal of the work was achieved by calculating the field windings currents using the finite element method and modeling in the FEMM program when the load magnitude and nature changes. The most important results of the work are the proposed algorithm for calculating the asynchronized turbogenerators field currents depending on the load size and nature in order to maintain the frequency and voltage nominal values. The significance of the results obtained lies in the fact that practical recommendations have been obtained for choosing the asynchronized generator load angle depending on the load size and nature, includ-ing in the modes of consumption of reactive energy.
  Keywords: asynchronized turbogenerator, synchronous turbogenerator, the load nature, rotor winding, magnetic field modeling.
5 Modeling and Experimental Study of the Inrush Current of a High-Temperature Superconducting Transformer
Authors: Manusov V.Z.1, Ivanov D.M.1, Ivanova E.V.2 1Novosibirsk State Technical University, Novosibirsk, Russian Federation 2Siberian State University of Water Transport, Novosibirsk, Russian Federation
  Abstract: Inrush current in high-temperature superconducting (HTS) transformers is a little-studied phenomenon. After connecting to the power grid, a current flow through the windings which exceeding the critical current value of the superconducting tape. It may cause significant overheating and thermal damage of winding. The purpose of the study is to develop a mathematical model for calculating inrush current pulses in a HTS transformer and its verification by physical experiments. To achieve the goal of the study, a mathematical model has been developed that accurately represents the electromagnetic and thermal transient processes after HTS transformer is turned on at idling or under load. The model considers the critical parameters of the HTS tapes, the process of heating and cooling of the windings, quench characteristics, and the electrical and magnetic parameters of the transformer. Good compliance of the experimental results and mathematical modeling with a deviation of 1.99 % allowed us to verify the model. The most important result is the creation of a mathematical model of the HTS transformer at the moment of connecting to power grid. This model represents the temperature changing of the windings during the loss of superconductivity. The developed model can be used in the analysis and modeling of inrush current in designed and operating HTS transformers for any power. The obtained results are significant for determine the optimal starting characteristics, geometric and electrical parameters of HTS transformers. The proposed methods for reducing the inrush current ensure safe and reliable operation of the HTS transformer when switched on at idling or under load.
  Keywords: HTS transformer, inrush current, experimental research, Matlab/Simulink, energy efficiency, power transformer, liquid nitrogen, HTS tape.
6 Methods, Techniques, and Algorithms of Synchronous Multi-Zone Modulation of Signals of Voltage Source Inverters (literature review)
Authors: Oleschuk V., Tirsu M. Institute of Power Engineering of Technical University of Moldova Chisinau, Republic of Moldova
  Abstract: This publication provides a brief overview of the results of research work in the field of developing alternative methods, schemes, and algorithms of synchronous multi-zone modulation of signals of inverters of power con-version systems with reduced switching frequency of power switches. In particular, in the mentioned researches, the basic strategies, schemes, and algorithms of synchronous multi-zone modulation have been further devel-oped, modernized, modified, and disseminated in relation to new promising topologies of power conversion sys-tems, including: two-inverter-based electric drives with open windings of electrical motor; drive systems based on electric motor with two stator windings; dual three-phase electric drives of symmetrical and asymmetric type; five-phase power conversion systems, powerful six-phase systems based on four inverters, and two-inverter-based and three-inverter-based photovoltaic installations with multi-winding transformer. It is shown that the developed schemes and algorithms of synchronous space-vector modulation applied for control of inverter-based systems provide continuous synchronization and symmetry of the basic voltage waveforms of systems during the whole control range. It provides minimization of even harmonics and undesirable subharmonics (of the fundamental frequency) in spectra of the basic voltages of systems, leading to reducing of losses in systems and to increasing of its efficiency. Based on a comparative analysis of the integral spectral characteristics of the phase and line voltages of the systems, recommendations are formulated for the rational choice of schemes and algorithms of synchronous modulation for the relevant installations, depending on the modes of their operation.
  Keywords: voltage source inverter, pulsewidth modulation (PWM), adjustable speed ac drive, photovoltaic installation, five-phase and six-phase systems, phase and line-to-line voltages, spectra of voltage and current.
7 Small-Scale Power Plants Based on Organic Rankine cycle (ORC) using Low-Boiling Fluorocarbon Working Fluids when Operating at High Initial Cycle Conditions
Authors: Granchenko P.P., Sukhikh A.A., Kuznetsov K.I., Mereuca E.V. National Research University «Moscow Power Engineering Institute», Moscow, Russian Federation
  Abstract: The purpose of the work is to develop and analyze the operation of a thermal circuit based on the organic Rankine cycle (ORC) using low-boiling working substances of the fluorocarbon class when operating at high initial cycle parameters. This goal is achieved by energy analysis of single- and multi-stage thermal circuits of power plants with a turbine circuit operating on low-boiling fluorocarbon working substances, such as octafluoropropane C3F8 and decafluorobutane C4F10. It is proposed to integrate the ORC thermal circuit as an extension to a small-capacity gas turbine power plant (GTU), operating on synthesis gas after a biomass gasifier. The most im-portant results of the work are the possibility of implementing a cycle with a low condensation temperature of the medium, which allows, when using low-boiling working fluids, to significant-ly reduce the temperature of the heat removal process and, consequently, increase the efficiency of the cycle. The possibility of using the listed working substances in power plants with a turbine circuit, which until now have been used mainly as refrigerants for refrigeration and heat pump systems, has been shown. The significance of the results of the work lies in the fact that, based on the analysis of the energy complex, a circuit solution has been proposed and justified that can increase the energy efficiency of the power supply complex, increasing the volume of gen-erated electrical power and providing a number of technological and environmental advantages.
  Keywords: small-scale power plants, CCPP, gas turbine, fluorocarbon working substances, supercritical cycles, heat recovery, organic Rankine cycle (ORC), solid fuel gasification, synthesis gas, air-cooled condensers (ACC).
8 Thermal Analysis of Combustible Components of Municipal Solid Waste
Authors: Snezhkin Yu.F., Mykhailyk V.A., Korinchevska T.V. Institute of Engineering Thermophysics of the National Academy of Sciences of Ukraine Kyiv, Ukraine
  Abstract: . The use of municipal solid waste as a raw material for alternative fuel is a promising direction for waste recycling and substitution of solid fossil fuels. Therefore, selecting of fuel composition and studying of its properties is an urgent task. The aim of this work is thermal characteristics analysis of the combustible components of municipal solid waste, which are the most common in Ukraine, for further selection of a fuel composition that will satisfy the consumer's requirements. The goal is achieved by studying the thermal destruction of samples by thermogravimetry and differential thermal analysis when materials are heated to 1000 ºС in the presence of air oxygen. Paper, cardboard, plastic, biodegradable film, textiles, leather, wood were investigated in this work. The most important results are the received data on the characteristic temperatures of destruction stages, content of water, organic and mineral substances, ash, as well as the calculated values of rate and conditional thermal effect of decomposition of organic substances. Strong formation of gaseous substances was registered for samples of polyethylene and biodegradable film, polyethylene terephthalate and cotton fabric. These features should be considered in the technologies of production and combustion of fuel. The significance of the results also lies in the fact that it is recommended to use data on the thermal stability of materials in order to prevent their ignition during drying when developing fuel production technology. In addition, the calculated values of the conditional thermal effect made it possible to evaluate the thermal characteristics of the studied materials as components of solid alternative fuels.
  Keywords: thermogravimetry, differential thermal analysis, municipal solid waste, combustible components, decomposition kinetics, heat generation.
9 Control of Carbon Dioxide Bivalent Heat Pump on Heating of Buildings
Authors: 1Sit M.L., 1Juravleov A.A., 2Frid S.E., 1Timchenko D.V. 1Institute of Power Engineering of the Technical University of Moldova Chisinau, Republic of Moldova 2Joint Institute for High Temperatures of the Russian Academy of Sciences, Moscow, Russian Federation
  Abstract: The scheme of a bivalent heat pump (BHP) is considered, using both the heat of the water from the return network and the heat of the outside air as low-potential heat sources (LPH). The aim of the work is to create a BHP circuit that provides functioning at the variable heat load temperature. The goal was achieved by solving the following problems: analysis of methods of synthesis of BHP circuits, analysis of circuit operation under random disturbances and development of the automatic control systems for BHP. The most significant result of the work is: a heat pump circuit that can operate at variable pressures of the evaporator and the gas cooler. The next significant result is, for bivalent heat pumps intended for operation in heat supply systems with qualitative and qualitative-quantitative laws of thermal control, the introduction into the heat pump circuit of a heat exchanger installed in the return water circuit of the secondary building and cooled by outside air, as well as two control valves installed in series between the gas cooler and the evaporator, the first valve installed along the refrigerant flow being controlled by a signal based on the pressure difference between the outlet of the gas cooler and the separation vessel between the evaporator and the gas cooler, and the second by pressure in front of the evaporator. The significance of the obtained results lies in the increase of the COP of the heat pump, due to the increase of heat transfer in the gas cooler circuit. The HHP circuit differs from the known ones in that it uses two control valves and the heat exchanger for additional cooling of the return water of the BHP heated building.
  Keywords: bivalent heat pump scheme, automatic control, random disturbances, reliability, district heating, carbon dioxide.
10 Perfection of an Energy-Economic and Environmental Parameters of the Ground Source Heat Pump Systems with Preventing Freezing of the Soil around Ground Pipes
Authors: Denysova A.A., Ivanov P., Mazurenko A.S., Zhaivoron O.S. Odessa National Polytechnic University Odessa, Ukraine
  Abstract: This article is devoted to the methods for perfection of energy, economic factors, environmental factors and work modes of the ground source heat pump systems with the account of climate conditions. The purpose of the work is to predict and prevent freezing of the soil during long term of exploitation of the low-power and high-power ground source heat pump systems for jus-tifying rational conditions of implementation GSHP in Ukraine and South-East Regions of Eu-rope. This goal is achieved by solving the following problems: determining the energy-economic and environmental factors based on considering the work modes of the ground source heat pumps; evaluation of the operating efficiency of ground source heat pump systems based on minimizing fuel consumption and greenhouse gas emissions; perfection of solutions enable im-plementation of ground source heat pumps friendly to the environment and justifying rational conditions of implementation the ground source heat pumps for residential sector. The important results of the work are the obtained and analyzed data on the influence of energy and economic factors both environmental criteria on the work modes and scheme-constructive solutions of ground source heat pumps. Modeling of heat exchange processes in the soil around the soil tube shows that in order to avoid freezing of the soil, the minimum permissible specific number of vertical tubes should be at least 0.12–0.15 pieces/m2 of heated area. The significance of the re-sults consists in the possibility of using the results of numerical simulation for preventing freez-ing of the soil around ground pipes of the ground source heat pump systems.
  Keywords: efficiency; ground source heat pump; preventing freezing; ground pipes, temperature fluctua-tions.
11 Increasing the Efficiency of Blind Decoding of the Steganographic Method with Code Control of Additional Information Embedding
Authors: Sokolov A.V.1, Ihnatenko O.O.1, Balandina N.M.2 1Odesa Polytechnic National University, 2National University “Odesa Law Academy” Odesa, Ukraine
  Abstract: Modern energy systems are often used as a medium for information transmission, including confidential information, which makes relevant the task of ensuring its security, which today is solved using not only cryptographic but also steganographic means that ensure concealment of the very fact of confidential information transmission. The steganographic method with code control of the additional information embedding possesses practical important qualities, but in its original form requires the presence of a container for successful information extraction, which is not always desirable in practice, while the known modification of this steganographic method allows blind decoding is characterized by an insufficient level of resistance to attacks against the embedded message. The purpose of this paper is to improve the efficiency of the steganographic method with code control of the additional information embedding and blind decoding. This purpose was achieved by identifying two factors that determine the occurrence of errors during blind decoding of additional information in the steganographic method with code control: variation of sub-blocks, and errors caused by attacks against the embedded message. We pro-pose the theoretical and practical rationale for codewords that provide the best level of re-sistance to both factors. The most significant result of the paper is a reduction in the number of decoding errors of the steganographic method with code control of the additional information embedding and blind decoding by 12.01% compared to the result known in the literature through a reasonable choice of codewords used to embed the additional information.
  Keywords: steganography, code control, Walsh-Hadamard transform, compression attack, JPEG, robustness.
12 Energy-Efficient Dehydration Regimes for Agricultural Products with the Application of Suspension Heat Treatment
Authors: Popescu V.S., Tsislinscaia N.I., Melenchiuc M.G., Balan T.V., Vishanu I.V., Gydei I.P. Technical University of Moldova Kishinau, Republic of Moldova
  Abstract: The aim of this study is to determine the energy-efficient dehydration regimes for agricultural products based on suspension heat treatment method. In order to achieve this goal, an electrical plant was designed, developed, tested, optimized and implemented, on the basis of which the research was carried out, applying in the drying process, namely the process of technological processing in suspension with the contribution of convection. The research was focused on the example of drying different agricultural products; in particular, the following products were selected as the main object of the research: hawthorn, apple, quince, pear and grape seeds. These agricultural products were selected as at the moment they were not fully exploited. Because of their rich content of vegetable oils with specific properties, they are of great interest to the food industry, traditional medicine, cosmetology, pharmacology, etc., and their drying using conventional methods is difficult, particularly because of defects and adverse reactions, which frequently occur in the technological processing. The main results obtained using the designed installation, are: reduction of the electricity consumption and the processing time, increase in the productivity and quality of the final products. The significance of the results obtained in the research lies in solving a number of problems currently faced by the processors, in connection with the improvement of equipment and increasing the efficiency of the drying process, mainly by increasing the energy efficiency, processing speed, quality of products and profitability.
  Keywords: electrical installation, agricultural products, technological process, suspension heat treatment, dehydration.
13 Modeling of the Process of Functioning of the Digester of a Biogas Plant during Methane Fermentation of Сow Manure
Authors: Polishchuk V., Shvorov S., Titova L., Zubok T., Yevtushenko V., Dvornyk Ye., Valiev T. National University of Life and Environmental Sciences of Ukraine, Kyiv, Ukraine
  Abstract: Ensuring high and stable biogas output during digester operation is ensured by regulating and monitoring values of control parameters. The purpose of article is to develop model of process of functioning of digester during methane mono-fermentation of cow manure with establishment of values of control parameters. A solution to model was found to obtain dynamics of biogas yield, while experimental and simulated dynamics of biogas yield were as close as possible. The developed model is system of differential equations that describe changes in concentrations of substrate nutrients , methanogen biomass and dynamics of biogas output in digester . The system of differential equations was solved in Simulink package , obtaining dependencies and . The dependence was compared with results of studies conducted on laboratory biogas plant with digester with useful volume of 30 liters at temperature of 37°C with periodic substrate loading system. By selecting parameters of model, resulting function was compared with similar one obtained experimentally. It has been established that in model of digester functioning process during methane mono-fermentation of cow manure, following coefficients have following meaning: bacterial growth rate m3/(kg day); substrate assimilation ; bacterial growth rate m3/(kg day); rate of conversion of nutrients into biogas m6/kg. The obtained values of coefficients make it possible to carry out modeling of process of methane mono-digestion of cow manure and predict biogas yield at different initial values of concentration of methanogen biomass, concentration of substrate nutrients, digester volume, which is used in industrial biogas plants.
  Keywords: biogas, biogas plant, methane thank, mathematical model, modeling, substrate, nutrients, methanogens.
14 Automatic Re-tuning of Poor-Performing PI-based Control Systems
Authors: Stopakevych A. О.1, Stopakevych О. A.2, Tigarev A.M.1, Vorobiova О.M.1 1 State University of Intelligent Technologies and Telecommunications 2 National Odesa Polytechnic University Odesa, Ukraine
  Abstract: The goal of the work is to create a new method for automatic re-tuning of PI controllers. It is achieved by solving the following problems. The first problem is to develop a method to identify a FOPDT estimation model by analyzing the dynamics of a control loop with a PI controller. The second problem is to demonstrate that the use of the estimated model allows to obtain better processes in control systems with PI controllers by comparing the resulting FOPDT model with a number of reduced models. The third problem is to develop a five-stage algorithm for automatic re-tuning of PI controllers. The fourth problem is to verify the software implementation of the developed algorithm. The most significant result was that the basis for estimating the FOPDT model in a loop with a Ziegler-Nichols tuned PI controller was the estimation the ratio of the delay to the time constant of the FOPDT model based on an assessment of the process overshoot. When the real control plant dynamics did not match with the dynamics of the FOPDT model this way was found effective for finding the optimal tuning of the PI controller. The significance of the results obtained was a structural robustness in case of estimated FOPDT model usage. The effectiveness of the procedure has been demonstrated on both linear and nonlinear models. The developed procedure is proposed to be used to automate the procedure of re-tuning SISO control systems when the control loop performance degradation has been detected.
  Keywords: control system, automatic re-tuning of the PI controller, FOPDT evaluation model, delay, optimization, structural robustness, control performance, operation.
15 Application of Object Contrast for Forming Images Used in Technical Vision Systems for Navigation of Mobile Robots
Authors: Tymochko O.1, Boichenko О.1, Zakirov S.2, Holovniak D.3, Dmitriiev O.3, Padalka I.1 1Flying Academy of National Aviation University, Kropyvnytskyi, Ukraine 2Research Institute of Military Intelligence, Kyiv, Ukraine 3State Scientific Research Institute of Armament and Military Equipment Testing and Certification, Cherkasy, Ukraine
  Abstract: The purpose of the article is to substantiate the feasibility of using object contrast as an informative feature for the formation of images used in technical vision systems. This goal is achieved by studying the dependence of the contrast of objects in images on the viewing geometry and determining the conditions under which the greatest similarity of the compared images is ensured. The solution to the first problem is based on the presentation of reference information about sighted objects, taking into account the navigation parameters of mobile robots. By modeling in the MATLAB software environment for typical viewing conditions, selective images were obtained using randomly selected fragments from Google Earth Pro, the distribution of contrast values and the cross-correlation function of the original and selective images. The influence of viewing angles on the distribution of contrasts and the formation of the decisive function was determined. The studies were performed for viewing angles of -60˚, -80˚ and -90˚ for altitudes in the range from 500 to 600 meters. The most significant result is a model of a set of reference images, taking into account the influence of navigation parameters on the contrast of objects, as well as experimentally established dependences of the distribution of contrasts for typical viewing conditions. The novelty of the work lies in the fact that the procedure for generating images and the decision function using the contrast of objects has been further developed. This will significantly increase the efficiency of selection of objects with insignificant brightness characteristics.
  Keywords: mobile robot, object, contrast, navigation parameters, image quantization, decision function.
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