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  Problemele energeticii regionale

E-Journal N1(39)2019



1 Calculation of the Exchange Fund of Electrical Equipment of Industrial Enterprises
Authors: Basmanov V.G., Kholmanskikh V.M., Cherepanov V.V., Ozhegov A.N., Zakalata A.A. Vyatka State University Kirov, Russian Federation
  Abstract: The purpose of this work is the theoretical substantiation and development of a practical method for calculating the exchange fund of electrical equipment of an industrial enterprise. The purpose is achieved through the use of separate methods of queuing theory if the flow of applications for repairs and restoration are the simplest. It is confirmed by the results of statistical studies. Therefore, for the mathematical description of the repair problem the authors use the scheme , which corresponds to the process of death and reproduction. As a criterion for optimizing the exchange fund of electrical equipment it is proposed to use the zero probability waiting for the replacement of a faulty electrical component with a working from the exchange fund. For the case of the simplest flow of applications for service, the authors suggest to use the Peck and Hazelwood tables, which significantly simplify the calculation of the exchange fund for known failure rates and electrical equipment recoveries. For practical use of the proposed method, the authors have developed convenient forms for presenting initial data for calculating the exchange fund, and it is proposed to present the results of calculations in the form of several options for the optimal number of electrical equipment in the exchange fund depending on the accepted level of zero expectation probability, the number of elements from the exchange fund and their recovery time. The proposed method will optimize the exchange fund of electrical equipment and reduce the cost of its formation.
  Keywords: exchange fund, probability of zero expectation, recovery rate, optimality criterion, system reliability, queueing systems.
DOI: 10.5281/zenodo.2650407
2 Hysteresis and Eddy Currents Effects Simulation in Idling Mode of the Transformer
Authors: Yarymbash D.S., Kotsur M.I., Yarymbash S.T., Divchuk T.Ye. Zaporizhzhia National Technical University Zaporizhzhia, Ukraine
  Abstract: The design parameters errors of the power transformer in idle mode can reach 15-20%. or more, because engineering techniques disregard the all factors. To reduce the error of engineering techniques modifying the circuit-analytical model. However, their field of application is limited. Therefore, the aim of the work is to develop interconnected circuit and field models that ensure high accuracy of idling parameters by allow for the parameters of the external network, transformer design features and nonlinear magnetic properties of electrical steel, asymmetry and non-sinusoidal idling currents. To achieve this aim, an improved approach is proposed. The scientific novelty of this approach provides conjugation of the external network objects, represented by the elements of the circuit model, with the testing transformer. For idle mode, it is represented as a spatial magnetic field model. The reduction of the computational time was performed by doubling cancellation of the volume of 3D three-phase transformer domain and the conformal transition to the 2D geometric domain. Determination of the effective magnetic characteristics of electrical steel according to single-phase idling experiment data, allows taking into account the combined effect of hysteresis and eddy currents, design and technological factors on the specific losses and magnetization power. This ensures high accuracy of the description of the interrelation between magnetic flux density and magnetic field strength, reducing of current error and relative errors in the calculation of idling losses up to 1.41% and 1.2% for the 3D model and up to 5.18% and 3.2% for the 2D model.
  Keywords: circuit field model, three phase transformer, idling mode, magnetic field, finite element method, harmonic analysis, non-sinusoidal and asymmetrical currents.
DOI: 10.5281/zenodo.2650413
3 Definition of Optimal Structure of Power Network
Authors: Kimstach O.Yu. Admiral Makarov National University of Shipbuilding Nikolayev, Ukraine
  Abstract: The purpose of the paper is to form a method for finding the optimal structure of the power network. For the basic criteria of the required method the maximum simplicity, versatility and objectivity are assumed. The properties of existing power grids of various countries and the methods of their analysis and design were analyzed. The research is based on the method of rel-ative comparative assessments. In the paper a set of particular optimization criteria was substan-tiated, which objectively characterize the power network. These criteria include a complex as-sessment of the length, an energy assessment, a wires mass assessment and a reliability assess-ment. A complex length assessment consists of total length assessment of power lines and as-sessment of total lengths ratio of power lines to conventionally low and high voltages. The over-all reliability coefficient of the power supply was proposed to use as a reliability criterion. This factor conventionally represents the level of duplication of power supply in terms of free power and transmission capacity of the power lines. The algorithm for determining the values of partial criteria was considered. The partial optimization criteria were combined using the complex addi-tive criterion. The example of finding the optimal structure of a local distribution power network was given. As variants for the structures of the power network, the schemes of a looped, a trunk passage, a trunk-radial and a trunk with branch were used. In accordance with the method of relative comparative assessments, it was found, that the looped type is optimal.
  Keywords: power grid, power network, structure, method of relative comparative assessments, criterion, optimization.
DOI: 10.5281/zenodo.2650415
4 The Use of Chokes to Improve the Quality of the Static Frequency Converter
Authors: Kalinin L.P., Zaitsev D.A., Golub I.V., Tirshu M.C. Institute of Power Engineering Kishinau, Republic of Moldova
  Abstract: The aim of the work is to develop technical measures to improve the quality of the power transmission process through electrical link, which contains a frequency converter based on a PST (phase-shifting transformer) with circular rotation of the output voltage phase in relation to the input, made according to the triangle scheme and controlled by means of power electronics. To achieve this goal, the use of longitudinal inductive elements (chokes) has been proposed as one of the measures that significantly improves the controlled mode parameters in the process of frequency conversion. The problem has been solved by performing computational experiments on simulation models of electrical links, combining two power systems with a frequency of 60 and 50 Hz, respectively. The structure of electrical links at various stages of the study has included several circuit variants of a frequency converter (single-channel circuit, dual-channel with reversing control winding sections, dual-channel circuit without reversing control winding sections) and has developed by authors earlier. In the process of research, the value of inductance of chokes has been changed, as well as their place of connection. The controlled transmission's characteristics have been analyzed as well. The novelty of the work lies in the use of longitudinally included inductive elements as a possible solution to the problem of improving the quality of power transmission when combining power systems with different operating frequencies using static frequency converters. The optimal values of the parameters of inductive elements, comprised between 0.03-0.035Hn for all circuit versions of the converter, have been identified.
  Keywords: interconnection, FACTS – controller, static frequency converter, phase-shifting transformer, choke, active power deviation, total harmonic distortion.
DOI: 10.5281/zenodo.2650950
5 New Approach for Voltage Drop Estimation in the Busbars of Work-shop Networks at Higher Current Harmonics Influence
Authors: Kotsur M.I., Yarymbash D.S., Bezverkhnya Yu.S., Kotsur I.M. Electrical Engineering Faculty, Zaporizhzhia National Technical University Zaporizhzhia, Ukraine
  Abstract: The presence of higher current harmonics has a negative impact on the efficiency and reliability of the elements of network. Higher current harmonics can lead to significant increases of resistance, voltage drop and active losses in busbar, also to decreasing network power factor. Existing engineering techniques can’t provide a reliable calculation of the parameters of busbars at higher current harmonics influences. Therefore, the aim of the work is to develop a new approach of parameters determination and the voltage drop estimation in busbar at higher current harmonics influence. Mathematical model of electromagnetic processes in busbar, which takes into account their design features, non-linearity of magnetic and electrophysical properties, proximity effects, surface and external surface effects, was developed and proposed. This model will allow to determinate the components of active and reactive resistances of busbar, voltage drops for each eigenvalue of the amplitude and frequency of current harmonics. Based on field simulation results was obtained the functional dependence in bicubic polynomial form. For effective spectra and amplitudes of higher harmonics, at selecting the corresponding polynomial coefficients, it will allow to determinate the components and the resulting values of voltage drops for an individual busbar’s design without spending time on field simulation. Based on the proposed approach, a method will be developed for the busbar's parameters identification and voltage drop estimation. This will allow effectively define the network configuration, installed capacity of compensating devices, which will provide the reliability of electrical collectors with the declared technical data and etc.
  Keywords: busbar, electromagnetic field, model; interpolation, current harmonics, short-circuit ratio.
DOI: 10.5281/zenodo.2650419
6 Reduction of Active Power Loss at 110/220 kV Node Substations Using Fuzzy Controller
Authors: Krysanov V.N., Burkovsky V.L., Danilov A.D. Voronezh State Technical University Voronezh, Russian Federation
  Abstract: One of the most important informational components of control systems is the data of the static load characteristics of each transformer of the substation. Currently, the evaluation of real static characteristics of the load is determined generally by the following methods: computation-al, analytical, passive and active experiments. These methods exhibit significant disadvantages regarding accuracy and cost rating and encounter plenty of parameters that are difficult to for-malize (including climatic factors). The purpose of this work is to reduce electric power losses at 110/220 kV substations by implementation of a new control system for power transformers. This goal has been achieved by using a fuzzy controller in the structure of the control system for power transformers of 110/220 kV tie substations. The presented solution is multi-functional and can be extended to a wide class of power facilities. The results of the simulation of the transformer voltage regulation process, performed in the MatLAB application environment, showed that the implementation of a new fuzzy controller structure had improved the efficiency of the substation power control system in forecasting and management (compared to classical solutions based on regression and probabilistic models). Herewith, the most accurate accounting of consumer load, the maximum use of equipment at the substation for voltage regulation at the points of release and a significant reduction of active power losses at the tie substations 110/220 kV (up to 12,12%) compared to already known solutions were observed.
  Keywords: electrical substations 110/220 kV, loss of electrical power, voltage control, control system, static load characteristics, mathematical modeling, neuro-fuzzy networks.
DOI: 10.5281/zenodo.2650421
7 Research of the Electric Power Conversion in Wind Turbines with the Aerodynamic Multiplication
Authors: Alekseevskiy D.G.1, Andrienko P.D.2, Nemykina O.V.2 1Zaporizhzhya National University, 2Zaporizhzhya National Technical University, Zaporizhzhya, Ukraine
  Abstract: The paper deals with the research of busbar power losses depending on electrical equipment installation and the dynamic change of the generated power of a wind turbine with the aerodynamic multiplication. The analysis of the electricity conversion electromechanical system is carried out on the example of the first Ukrainian pilot wind turbine with the aerodynamic multiplication of the TG-1000 type. The aim of the article is analytic method creation of analysis of power relative losses in busbars of electrical equipment depend on its arrangement, as well as the research of electromagnetic processes in the electromechanical system depend on the wind flow speed at the height axis of the turbogenerators setted on the blades of the wind wheel (WW) turbine by computer modelling method. This aim achieves by the rectifiers series connection and their location changing (generator clips), which allows the DC energy transfer inside the wind turbine. The research results have showed that power losses reduce in busbars and lead to increase wind turbine efficiency and decrease cable consumption. Electromagnet processes modelling of visual block model have evidenced the adequacy of the assumptions in the determination of the power losses. It has been obtained that the wind flow speed irregularity at the height axis of the turbogenerator and steering angle between turbogenerator axis and wind wheel rotation plane provokes the power generation variances, which pulse according to wind wheel rotation speed. In addition, balanced current of the circuit has provided the symmetrizing amplitudes of the power generator.
  Keywords: electromechanical system, wind turbine, aerodynamic multiplication, frequency converter, autonomous inverter, energy conversion, efficiency.
DOI: 10.5281/zenodo.2650423
9 Improving Heat Exchange Systems of Turbogenerators for Increase of their Efficiency
Authors: Minko A.N.1, Shevchenko V.V.2 1PRD company «Ankor-Teploenergo», 2National Technical University «Kharkov Polytechnical Institute» Kharkov, Ukraine
  Abstract: The goal of this work is to define parameters that characterize turbogenerator heat exchanger ef-ficiency and to develop recommendations for its increase by improving the heat exchanger de-sign in different modes and ranges of electromagnetic loads for different cooling medium types (air, hydrogen, water). The paper uses the results of studies of the thermal state of turbogenera-tors of foreign and domestic authors, where it is noted that the global economic crisis has com-plicated the possibility of timely replacement of turbine generators that have expired, therefore partial replacement and/or modernization is most often used. At the same time, in all the electri-cal engineering plants of the world, the task of increasing the power of turbogenerators is solved without changing their dimensions, which is possible only with the improvement of cooling sys-tems. Therefore, the outer dimensions of the heat exchanger and its connection node to the tur-bogenerator were preserved in our studies. Gas coolers with different sections and moves num-ber of cooling medium and heat-removing elements arrangement were reviewed. Data of TGV-200-550, TA-35-120 turbogenerators were used in calculations. The regime coefficients, that al-low to consider the type of cooling medium, thermophysical parameters, temperature changes, coolant rate, inlet cooler pressure, number of gas strokes inside the heat exchanger, cooler tubes’ heat exchange surface area and finning type were introduced. The heat exchanger thermal stresses were determined depending on the cooler tubes’ geometry and heat exchange surface area in the working temperature range.
  Keywords: turbogenerator, cooling system, heat exchanger efficiency, mode parameter, electromagnetic loads, optimal layout.
DOI: 10.5281/zenodo.2650425
10 Control of Heat Exchanger with Variable Heat Transfer Surface Area
Authors: Sit M.L., Patsiuk V.I., Juravliov A.A., Burciu V.I., Timchenko D.V. Institute of Power Engineering, Chisinau, Republic of Moldova
  Abstract: The work deals with the development of a control system for heat exchangers with variable surface area of heat transfer, used, in particular, for heat pumps intended primarily for heat supply systems using the high-quality law of regulation of the heat supply mode (with a con-stant flow rate of the heat carrier). The aim of the work is to develop a scheme for the control of a heat exchanger with a variable surface area of heat exchange in which main disturbances will be compensated: i.e. the temperature of the heat carrier, heat carrier’s flowrates, and changes in the thermophysical parameters of the heat carriers. This goal has been achieved us-ing a custom PID controller in the contour of control of the drive of the moving heat-insulating insert. To solve this problem, we obtained the equations of the statics of the heat exchanger with regard to the adjustable insert, the dynamic model of the heat exchanger tak-ing into account this insert. The novelty of the work is control laws of an adjustable heat-conducting insert between the primary and secondary coolants of the heat exchanger, which allow compensating the main disturbances, which influence the heat exchanger. A method has been developed for solving differential-integral equations of heat exchanger statics with an insert (HEI), which allowed analytically expressing the ratio of average integral heat carrier temperatures in a heat exchanger depending on the heat exchanger length, which allows build-ing a control system for a heat exchanger with a variable heat exchange surface area.
  Keywords: heat exchanger, variable heat transfer surface, control system, mathematic model, heat pump.
DOI: 10.5281/zenodo.2650427
11 Efficiency Analysis of Methanol Usage for Marine Turbine Power Plant Operation Based on Waste Heat Chemical Regeneration
Authors: Cherednichenko O.C. Admiral Makarov National University of Shipbuilding Mykolaiv, Ukraine
  Abstract: The issues of improving the efficiency of methanol usage as a promising marine power plant fuel with low carbon content are discussed. The main aim of the research is an analysis of characteristics of advanced marine gas turbine power plants with the combined thermodynamic and thermochemical regeneration of waste heat. The possible methanol conversion at the expense thermochemical heat regeneration of marine engines recoverable resources has been revealed. The analysis of parameters influences of the waste heat recoverable resources, as well as restrictions related to the engine system of gas fuel injection, on the efficiency of methanol conversion has been carried out. It was demonstrated that the simulation of methanol steam conversion processes results in the pressure increase in the reactor, which, in its turn, causes a shift of conversion efficiency process towards higher temperature area. The calculation scheme of steam injection gas turbine plant with the joint thermodynamic and thermochemical regeneration of waste heat is demonstrated. The results of mathematical simulation of the processes in regeneration plant under the 3.4 MW constant capacity and heat exchanger thermal ratio of 0.85 were obtained. The cycle optimization has been based on the efficiency of plant under the conditions of variation of water/methanol ratio and gas temperatures in thermochemical regenerator. The efficiency increase constituted 4% relative to characteristics of the base engine operating on methanol. The estimation of carbon content in produced syngas has shown that thermochemical regeneration of methanol conversion by using the waste heat can reduce the energy efficiency by 1.5 times.
  Keywords: ship power plant, methanol reforming, thermochemical regeneration, gas turbine engine, waste heat.
DOI: 10.5281/zenodo.2650429
12 Bibliometric Assessment of Research on Energy in the World, in the Eastern Europe and in the Republic of Moldova
Authors: Turcan Nelly1,2, Cujba Rodica1,3 1Information Society Development Institute 2Moldova State University 3Technical University of Moldova Chisinau, Republic of Moldova
  Abstract: Society is becoming increasingly dependent on energy. It is a stimulating factor for economic growth and technological change, but also the most significant limiting factor. The analysis of research trends on energy is of great importance because it provides a picture of the development directions of the future. The goal of the paper is to evaluate the performance and tendencies of researches on energy in the World, Eastern Europe region and in the Republic of Moldova. This goal is achieved by using bibliometric methods. Bibliometrics has become standard method for measuring the impact of research, which is accepted as a valid way of ranking scientific performance and tendencies. The novelty of the work consists in the wider geographical and chronological coverage of the study in comparison with similar studies, as well as that the analysis was carried out based on data extracted from two international and one national databases: Scopus Elsevier, Web of Science Core Collection and National Bibliometric Instrument. It was revealed that on global, regional and national levels the number of papers on energy increases quicker than the total number of publications. There is also a growth of the share of publications on energy from total number of documents on global, regional and national levels. The contribution of the Eastern Europe in the global information flow on energy increases slowly but stable. Lower speed of increase of the contribution of the Republic of Moldova in the regional (EE) information flow on energy is detected.
  Keywords: research on energy, energetical sector, energy research trends, energy research productivity, bibliometric assessment, information flow on energy.
DOI: 10.5281/zenodo.2650736
14 New Approaches to Macroeconomic Stability
Authors: Postolaty V.M. Institute of Power Engineering Kishinau, Republic of Moldova
  Abstract: The structure of the economy of the Republic of Moldova was reviewed and the analysis of the main macroeconomic indicators, including the energy sector, was conducted. For a long period, data on the state of Moldova’s energy, technical and economic indicators and development trends have been analyzed. Particular attention is paid to the definition of changes in the value of the real gross domestic product (GDP), taking into account the coefficient of deflation. The quantitative dependence of GDP on the volumes of "Output" and "Intermediate Consumption" is shown. It is revealed that the more “Intermediate Consumption”, the lower the GDP, ceteris pa-ribus. The major share of the cost of the industry sector is covered by “Intermediate Consump-tion”, which in turn is higher, the higher the tariffs for energy, materials and other services pro-vided by the industries to each other. It was concluded that tariff growth should not overtake real GDP growth over the past few years. The results of the calculations and their analysis show that, in reality, the growth of tariffs is far ahead of the growth of real GDP, which does not con-tribute to the stable development of the country's economy. It was proposed to revise tariffs, in particular for energy resources, and to bring the rates of their change in line with the growth rates of real GDP. An approach has been formulated for determining the marginal levels of tariffs, based on the condition that their growth rates do not exceed the growth rates of real GDP.
  Keywords: gross domestic product, Intermediate consumption, tariffs, energy resources, macroeconomic stability.
DOI: 10.5281/zenodo.2650960
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