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E-Journal N4(48) 2020

"PROBLEMS of the REGIONAL ENERGETICS"

CONTENTS

0	Synchronous PWM Regulation of Inverters of Drive Installation with Two Stator Windings of Electrical Motor Authors: Oleschuk V. Institute of Power Engineering of Moldova Kishinau, Republic of Moldova
	Abstract: The aim of this work is to modernize schemes and algorithms of synchronous control and modulation for two-inverter based system for ac drive with dual stator windings of electric motor, in order to provide improved harmonic composition of its stator winding voltage. This goal is achieved by including in the control scheme of the system of functional dependencies linking voltage magnitude on stator windings of motor with the corresponding pole voltages of two inverters controlled by algorithms of synchronous multi-zone pulsewidth modulation (PWM), as well as by including in control scheme of current values of specialized phase shift between control signals of two inverters. It has been shown (and it is one of the basic contribution) that in two-inverter-based system with the developed control strategy voltage at stator windings of electric motor is characterized by a quarter-wave symmetry, and even-order harmonics, as well as subharmonics (of the fundamental frequency of system), are lacking in its spectra, including cases of control modes with fractional relationships between the switching frequency of converters and the output frequency of system. Results of determination of weighted total harmonic distortion factor of voltage waveforms show that at low and average values of modulation index of converters algorithms of continuous multi-zone modulation assure better integral spectral characteristics of voltage at stator windings of motor. In the case of increased values of modulation index of converters, improved spectral characteristics of voltage at stator windings of motor are achieved by the using of algorithms of discontinuous multi-zone modulation.
	Keywords: inverter, electric motor with two stator windings, PWM schemes and algorithms, voltage harmonic composition. DOI: https://doi.org/10.5281/zenodo.4316617
1	Investigation of Symmetrical Modes of Operation and Calculation of the Installed Capacity of Phase-Shifting Transformer, Based on Hexagon Connection Authors: Bosneaga V., Suslov V. Institute of Power Engineering Chisinau, Republic of Moldova
	Abstract: The scope of the work is to study the steady-state symmetrical load modes of operation of a new promising phase-regulating transformer circuit. This allows obtaining the value of the designed capacity of device. The device is based on a three-phase transformer windings connection into hexagon circuit, equipped with additional three phase regulating autotransformer, connected to hexagon circuit in a special manner. Besides, it should be equipped with semi-conductor switching keys, which give the possibility to control fast transition processes. The proposed circuit gives the possibility to round regulation of phase angle in the range of 0-360°, so the device could be used as frequency converter for flexible tie between energy systems with different frequencies and belongs to the group of FACTs controllers. The autotransformer provides the possibility of fine adjustment of the phase angle of the output three-phase voltage, so maintaining the flow of active power in the interconnection line. One of the most important features of such devices is the value of calculated designed capacity, which determines demand of the active materials for such devices. The scope of the work was achieved by conducted analytical study, based on electrical and transformer circuit’s theory. The currents in the windings of the device in symmetrical load modes were calculated for several variants of the phase-regulating unit circuit’s diagrams. On their basis, the maximum values of the devices currents and designed capacity for a number of the considered variants of circuits were determined, allowing a comparative analysis of different circuit modifications.
	Keywords: phase-shifting transformer, hexagon circuit, adjustable autotransformer, load modes, design power. DOI: https://doi.org/10.5281/zenodo.4316631
2	Selection of Frequency Estimation of 6-10 kV-Overhead Lines’ Technical Condition Based on Reliability Statistical Studies Authors: Basmanov V.G., Kholmanskikh V.M. Vyatka State University Kirov, Russian Federation
	Abstract: The aim of this work is to justify a criterion selection for the frequency estimation of the 6-10 kV-overhead lines’ technical condition (OL), using the reliability indicators of the overhead lines (failure intensity, mean time between failures, reconditioning intensity and recovery mean time). To achieve the goal a retrospective method was used for obtaining information on reliability and a statistical method for analyzing the reliability of the multiple-action products to justify the frequency criterion. Certain methods of mathematical statistics were applied to process the information obtained. In particular, the Kolmogorov criterion was used to support the hypothesis on the exponential law of distribution of the OL failures and the time of their recovery. Based on the analysis of the 6-year overhead line failures database, the exponential law hypothesis of distribution of the overhead line failures and the time of their recovery was accepted and confirmed. The most essential result is the experimental and theoretical confirmation that the complex indicator of reliability, i.e., the technical preparedness coefficient with account of self-eliminating failures, can be used as the frequency criterion for verification of the OL technical condition. High precision of the criterion has been proved even at a small number of failures. Significance of the results obtained consists in that, while controlling the dynamics of the coefficient and comparing it with the normative values with respect to the OL reliability category, it is possible in due time to fix a date for the OL technical condition checking.
	Keywords: overhead lines, technical availability factor, Kolmogorov criterion, criterion for the frequency of assessing overhead lines, mathematical model of reliability. DOI: https://doi.org/10.5281/zenodo.4316637
3	Method for Construction the Diagnostic Features Space of Switched Reluctance Motors Based on Integral Dynamic Models Authors: Fomin O. O., Ruban O. D., Rudkovskyi O. V. Odessa National Polytechnic University Odessa, Ukraine
	Abstract: The work is devoted to the problem of construction the diagnostic models for the nonlinear dy-namic objects. The aim of the work is to improve the reliability and fast operation in diagnosis of the states of electrical motors of under conditions of an a priori uncertainty. The a priori un-certainty results from an insufficient study of the processes, which occur in the objects of diag-nosis due to the operation in a wide range of external conditions and the presence of a great amount of disturbing effects along with environmental interferences. This aim is achieved by the development of the technical diagnosis method based on the information models of the nonline-ar dynamic objects of diagnosis, which are obtained using the nonparametric identification pro-cedure. As the information models of diagnostic objects, the integral nonparametric dynamic models based on multidimensional weight functions are considered. The most significant results consist in obtaining the method with a further development in construction of a space of diag-nostic features of the nonlinear dynamic objects based on the correlation analysis as a stage of the features’ filtration. The latter ensures the maximum diagnostic reliability. Significance of the obtained results: the application of the proposed method allows both high reliability of the object diagnosis under the priory uncertainty, and improvement of the diagnostic procedure fast opera-tion owing to the feature filtration. The proposed method was tested using the data of the diag-nosis of the switched reluctance motors.
	Keywords: nonlinear dynamic objects, diagnostic models, model reduction, feature selection, correlation analysis. DOI: https://doi.org/10.5281/zenodo.4316968
4	Effect of Vane Thermal Emission Cooling on the Efficiency of the Gas Turbine Power Plant Authors: Kolychev A.V. 1, Renev M. Е. 2, Savelov V. A. 1, Arkhipov P. A. 1 1 Baltic state technical University "VOENMEH", Saint Petersburg, Russian Federation, 2 - Saint Petersburg State University, Saint Petersburg, Russian Federation
	Abstract: The work is devoted to the problem of increasing efficiency of power gas turbine units (microturbines). One of ways to improve efficiency is to increase gas temperature in front of the turbine. Cooling of gas turbine elements is difficult. One of the solutions to the problem may be the method of thermal emission cooling. The purpose of this work is to estimate the potential effect of thermal emission cooling of turbine blades on efficiency. The mentioned aim is achieved by analyzing the main factors influencing the efficiency of the power gas turbine unit. Calculated estimations of thermal condition of turbine blades with thermo-emission cooling depending of electron work function and gas temperature in front of the turbine. The most significant results of the work are the obtaining of dependence of efficiency of power gas turbine unit on the value of electron work function (thermo emission cooling) and its surface temperature. Besides, as a result of numerical estimations it was established for the first time that the blade temperature of the turbine with thermal emission cooling can reach the value of about 1000 K at the electron work function 1 eV and at the gas temperature in front of the turbine 2700 K (by 7-8 % higher than modern power gas turbines). The obtained results can be applied in practice in terms of justification of thermal emission cooling application in gas turbines. The method of thermal emission cooling can be applied in micro turbines, large power turbines, aircraft engines.
	Keywords: thermal emission cooling, thermoelectronic emission, power gas turbine installations, efficiency. DOI: https://doi.org/10.5281/zenodo.4316996
5	Analysis of Efficiency of Rotary Piston Engines Use at Power Plants for Surplus Electrical Energy Accumulation Authors: Mytrofanov O., Proskurin A. Admiral Makarov National University of Shipbuilding Mykolaiv, Ukraine
	Abstract: This article is devoted to the methods for enhancing the power plants’ efficiency in accumula-tion of a surplus electrical energy obtained using the renewable energy sources. The study is aimed at analyzing the efficiency of perspective power plants for accumulation of the surplus electricity in the form of compressed air based on rotary piston engines. To achieve the goal a comparative analysis of efficiency of diabatiс and adiabatic schemes of the electric energy stor-age was performed. The analysis was found to reveal the major advantages and disadvantages, along with the design features of each type of schemes. The main ways to increase the efficien-cy of the compressed air storage units, using the rotary piston engines as the electrical energy generators, were established. The experimental operational characteristics of the rotary piston engines showed that they are relevant to the parameters of the power units of air accumulation. The most significant results reveal that the methods for the analysis and of generalization have been used to develop the principal schemes of diabatic and adiabatic power plants for the accu-mulation of the surplus electrical energy in the form of compressed air using rotary piston en-gines, which require no additional air heating prior to expansion. The significance of the results obtained is that the use of the rotary piston engines being a part of the diabatic accumulation unit, allowed a complete exclusion of CO2 emission into the atmosphere.
	Keywords: renewable energy sources, power plant, energy accumulator, rotary piston engine, compressed air, heating temperature. DOI: https://doi.org/10.5281/zenodo.4317046
6	Analysis of the Energy Efficiency of Different Methods of Adding Make-up Feed Water in the Steam Turbine Cycle CHPP Authors: Shempelev A.G. Vyatka State University, Kirov, Russian Federation
	Abstract: The article analyzes the energy efficiency of several methods of entering make-up feed water into the CHPP cycle. The purpose of the work is to assess the influence of the mass flow rates of the make-up feed water into the cycle of CHPP on its energy efficiency. This goal is achieved through the use of an adapted mathematical model of the turbine unit T-50-130, on which com-putational studies of variable operating modes were carried out and a comparative assessment of the energy efficiency of supplying make-up feed water to the condenser and the pipeline of main condensate. The value of the generated electric power and the specific heat consumption for electric power generation were taken as the main criteria determining the efficiency of the turbine unit. The most significant result of the research is the establishment of the fact that it is the condenser that is the best place to enter make-up feed water into the cycle of a cogeneration turbine according to the criterion of energy efficiency. The highest energy effect can be ob-tained by supplying make-up feed water to the condenser in the heating mode. The significance of the results obtained lies in the fact that their practical use will significantly increase the energy efficiency of steam turbine plants by supplying make-up feed water to their condensers. The results obtained differ from the known ones in that for the first time such studies were carried out on an extended mathematical model of a steam turbine unit.
	Keywords: cogeneration steam turbine, make-up feed water, regenerative heating system, mathematical model, energy efficiency. DOI: https://doi.org/10.5281/zenodo.4317048
7	Energy Efficiency of Heat Pumps Heating Systems at Subsoil Waters for South-East Regions of Europe Authors: Denysova A.E., Klymchuk O.A., Ivanova L.V., Zhaivoron O.S. Odessa National Polytechnic University Odessa, Ukraine
	Abstract: This article is devoted to the methods for increasing the operational efficiency of the single-stage and two-stage schemes of heat pump installations for heating systems, based on the energy saving principles. The major aim of the study is the analysis of methods for increasing the efficiency of alternative low-potential heat pump installations based on the subsoil waters, which correspond to the requirements of the energy saving technologies. To achieve the aim a comparative analysis of efficiency of different schemes of heat pump heating systems was performed for the consumers of the South-East of Europe. The rational schematic and constructive solutions and the system operational modes that ensure the increase in the efficiency of the alternative heating system for various climatic conditions were grounded. The main ways of increasing the efficiency of the low-potential heating systems using the heat pump units based on the subsoil waters were determined. Recommendations for the practical application of the alternative heating system solutions, depending on temperature of the outside air were developed. The significance of the obtained results consists in justification of conditions, which make it possible to use the single- and two-stage HPI schemes on the subsoil waters in the South-Eastern Europe. The most significant results are those recommending the increase in the operational efficiency of the heat pump systems on the subsoil waters for the heat supply for the consumers of the South-Eastern Europe. The analysis results can be used for designing the heating systems based on the heat pumps using the low-potential energy of the subsoil waters.
	Keywords: energy saving, efficiency, transformation coefficient, heat pump, subsoil waters, intermediate heat exchanger, subcooler, primary energy. DOI: https://doi.org/10.5281/zenodo.4317115
8	Thermal Four-Pole for Inclusion of Heat Pumps into the Heat Supply System with the CHP Authors: 1Sit M.L., 1Juravleov A.A., 2Patsiuk V.I., 1Timchenko D.V., 3Chernishov P.S., 4Lomovtsev P.B. 1Institute of Power Engineering of Moldova, Kishinau, Republic of Moldova 2Moldovan State University, Kishinau, Republic of Moldova 3Baltic State Technical University VOENMEH, Saint Petersburg, Russian Federation 4Odessa National Academy of Food Technologies, Odessa, Ukraine
	Abstract: The work deals with district heating systems based on cogeneration plants and the use of carbon dioxide heat pumps in them. Heat pumps are used in heating systems of buildings and use the heat of outdoor air as a source of low potential heat and, at the same time, the heat of return network water. The aim of the study is to develop the structure of a heat four-pole (HFP) for fitting of heat pumps with district heating system, determine the parameters of a heat exchanger with a variable surface area of the heat exchange installed in the return water line, and analyze one of the schemes of the HFP. The goal to be sought is achieved by solving the following tasks: development of requirements and justification of the HFP scheme, justification of it’s parameters. The most significant results are developed models of statics and dynamics of heat exchanger in HPF, means of the integration of carbon dioxide heat pumps into heat networks with high temperature schedules. The significance of the results obtained consists in deriving dependencies between the temperature schedule of heating system and HFP parameters, which can be used in the practice of designing a district heating systems with heat pumps. As a result of calculations, equations were obtained for the describing of the relationship between the area of the heat exchanger installed in the return water line, temperature drops at the ends of the heat exchanger, heat power of the heat exchanger.
	Keywords: heat exchanger, variable heat transfer surface, control system, mathematic model, heat pump. DOI: https://doi.org/10.5281/zenodo.4317194
9	Energy-Saving Seamless Insulation Systems for Frame Buildings Using Foamed Polyethylene Authors: 1Semenov V.S., 3Bessonov I.V., 2Ter-Zakaryan K.A., 1Zhukov A.D., 1Mednikova E.A. National Research Moscow State University of Civil Engineering; 2“TEPOFOL” Ltd.; 3Research Institute of Building Physics of Russian Academy of Architecture and Construction Sciences Moscow, Russian Federation
	Abstract: The purpose of the work was to substantiate the possibility of using rolled foamed polyethylene with a sheet thickness of 50 mm or more as thermal insulation for low-rise frame buildings. This goal was achieved by conducting experimental studies to determine the physical, mechanical and operational properties of foamed polyethylene, assessing the material's resistance to climatic influences and a full-scale assessment of the thermophysical characteristics of the material and the state of structures at the facility. The most significant results are: the results of determining the operating temperature range taking into account mechanical loading and tendency to creep; the results of assessing the effect of the reflective layer; the results of determining the tensile strength of the material on the surface and on the welded joint; field test results. It has been established that products based on foamed polyethylene are resistant to both climatic influences and mechanical loading, the material in the temperature range from minus 60 ° C to + 60 ° C has high operational resistance. The effect of the reflective layer applied to the foamed polyethylene on the mechanical characteristics of the material is insignificant, but it contributes to an increase in the thermal resistance of the insulating shell. Strength characteristics ensure the integrity of the seamless insulation envelope. The significance of the results obtained lies in the substantiation of the technical feasibility and economic feasibility of developing system solutions for the integrated insulation of frame buildings with rolled polyethylene foam.
	Keywords: energy saving, wooden frame, low-rise building, rolled foamed polyethylene, insulating shell, heat transfer resistance, thermal uniformity. DOI: https://doi.org/10.5281/zenodo.4018999
10	Jubilee Acad. Nicolae ANDRONATI at 85 years old