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  Problemele energeticii regionale

E-Journal №3(38)2018



1 Analysis of the Content of Gases in Oil-Filled Equipment with Electrical Defects
Authors: Shutenko O.V.
  Abstract: Operational reliability assurance of oil-filled equipment is an urgent real-world problem which is especially essential for the facilities that have exceeded their lifetime. The objective of the research presented is improvement in the accuracy of oil-dissolved gas analysis data interpretation when distinguishing an oil-filled equipment fault. The desired result is achieved by means of both correction of criteria values used to identify the type of fault and increase in the number of faults recognized. The research technique chosen is analysis of dissolved gas percentage, their ratio values and graphic regions for facilities under various electric faults and comparison of the obtained data with the current standard requirements. Gas concentrations have been analyzed for 906 facilities with such faults as x-wax formation, partial discharge, spark discharge, creeping discharge, low- and high-energy discharge. It has been established that with the development of defects in oil-filled equipment, the content of gases for the same defect, can differ significantly. 40 types of electric fault differing in gas concentration levels, gas ratios and their graphs have been identified, which allows significantly increasing the number of distinguishable faults as compared with the current standards. Ranges of gas ratios and their percentage introduced in the paper as well as plotted graphic regions with fault type indication make it possible to reliably recognize the faults that are difficult to interpret with the current standard criteria. The presented results allow significantly increase the operational reliability of oil-filled equipment, and to reduce the costs of its maintenance and repair.
  Keywords: oil-filled equipment, dissolved gas analysis, faults diagnostics, defect type, gas ratios, percentage of gases, graphic areas.
2 Calculation and Investigation of Steady-State Asymmetric Modes of Three-Windings Three-Legs Power Transformer with Star/Star/Delta Windings Connection
Authors: Bosneaga V., Suslov V. Institute of Power Engineering Chisinau, Republic of Moldova
  Abstract: For the purpose of calculation and studying of steady-state asymmetrical modes of operation of three-windings, three-leg power transformer with an arbitrary winding connection scheme the mathematical model is proposed. This model makes it possible to take into account electromagnetic coupling between the windings, located on different legs. Windings connection scheme in developed model can be arbitrary, including some more complex schemes such as “double zigzag”, “polygon”, “triangle with extended sides”, etc. As the initial data for the model elaboration it is used usual datasheet for power transformers, including nominal values of power and voltages of the windings, short circuit voltages of the winding pairs, power losses in no-load and short circuit modes, no-load current, as well as additional similar data on transformer zero sequence parameters, provided additionally by manufacturer. Use of zero-sequence data allows reflecting one of the most important features of a three-leg transformer, in comparison with three-phase group of single-phase transformers due to electromagnetic coupling between windings, located on different legs. This leads to some peculiarities of its asymmetric modes. Calculations and analysis of the usual steady-state asymmetric modes, including short circuits and phase breaks were carried out on the base of power transformer with windings connection scheme Yn/yn/d-11. The conditions were found out when the magnetic flux tends to exit the magnetic circuit, which can lead to additional losses and local overheating. For considered modes, vector diagrams of currents and voltages of the windings, as well as relative values of magnetic fluxes in the legs are constructed.
  Keywords: transformer model, asymmetrical modes, three legs magnetic core, arbitrary winding connection circuits, unbalanced magnetic flux.
3 Numerical Method for Determining Potential Coefficients Matrix for Multiconductor Transmission Line
Authors: Patiuk V. Institute of Power Engineering Chisinau, Republic of Moldova
  Abstract: Consider the propagation of electromagnetic energy through multiconductor three-phase high-voltage transmission line with arbitrary number of conductors. The mathematical formulation of the problem represents the system of partial differential equations known as transmission line equations. When constructing the capacitance matrix of an electric line, it is necessary to solve the boundary problems for the Laplace equation with nonlocal boundary conditions. The aim of this research is to develop a new method for constructing a potential coefficients matrix, which allows us to express the voltage vector in the wires through the charge vector. The application of this method leads to the necessity of solving a boundary value problem for Laplace equations with nonlocal boundary conditions. A new type of non-local boundary conditions has been identified, which has not been previously investigated. The boundary conditions of this type are represented by the contour integral over the boundary of the region from an unknown potential. In the general case, the obtained problem does not have a unique solution. The theorem of existence and uniqueness of the solution for the boundary value problem for the Laplace equation with nonlocal boundary conditions is proved. However, the requirement that the potential on the wire surface is constant allows us to prove the existence and uniqueness of the solution for considered problem. In order to illustrate the application of the developed approach we have solved numerically the problem for the sector-shaped cable with three cores. The values of potential and capacitive coefficients obtained by calculation are given. The error of the values of the diagonal elements of the matrices of potential and capacitive coefficients is estimated as less than 0.1%.
  Keywords: telegraph equations, linear capacitance matrix, Laplace equation, nonlocal boundary conditions, electrical cable
5 Efficiency of Using Built-In Bundles of Cogeneration Steam Turbine Condensers for Make-up Water Heating
Authors: Shempelev A.G., Suvorov D.M., Iglin P.V. Vyatka State University Kirov, Russian Federation
  Abstract: The purpose of the study is to determine the conditions and efficiency of the use of built-in bundles of condensers of cogeneration steam turbines for make-up water heating during their work when the main bundles are disabled. The proposed method for estimating the heat flows entering the condenser when working with a closed sliding grid is used. The program of the thermal calculation program for steam turbine condensers and a computational mathematical model of a turbine plant type T-50-130 are applied. The heat fluxes entering the condenser were calculated in a wide range of influencing factors. An important result of the calculations is the identification of significant limitations of the applicability of this method of the make-up water heating according to the condition that the temperature of the make-up water at the exit from the built-in bundle is not exceeded. Calculation studies on the mathematical model of a condenser to determine the pressure in the condenser depending on the pressure in the lower heat extraction section with different levels of throughput of the closed sliding grid and different flow rates of the make-up water were carried out. Another result is a calculated estimate of the energy efficiency when using built-in bundles for heating the make-up water. It was found that heat saving in the considered modes always takes place, and when working on a heat mode, it is close to the heat load of the built-in bundles, and when working on an electric mode, it is several times lower.
  Keywords: cogeneration steam turbine, condenser, built-in bundle, make-up water heating, sliding grid, mathematical model, energy efficiency.
6 Heat Pump Utilizing Heat Exchangers with Variable Heat Transfer Surface
Authors: Sit M.L.1, Goncharov O.I.2, Juravliov A.A. 1, Burciu V.I. 1, Timchenko D.V.1 1Institute of Power Engineering, Chisinau, Republic of Moldova, 2Moscow State University, Moscow, Russian Federation
  Abstract: The paper deals with the heat pump designed mainly for heat supply systems using the qual-itative law of regulation of the heat supply mode (constant flow rate of the heat carrier). For this purpose, an air-to-water heat pump with carbon dioxide as a refrigerant and compressor driven be gas piston unit is used. The aim of the work is to develop a scheme in which the position of the operat-ing point of the heat pump compressor does not depend on fluctuations in the refrigerant flow rate, as well as using the heat produced by the gas engine - driven by the heat pump compressor. This goal achieves by elaboration of internal heat exchangers with an adjustable heat exchange surface area. The heat exchange surface area regulates by installing of an intermediate heat-conducting cy-lindrical element between the refrigerant and thermal agent circuits. The intermediate cylindrical element moved by using, for example, an electric stepper drive. The conditions, under which the sleeve can be considered as a thermally thin body. To increase the COP of the heat pump (HP), the additional heat exchanger, installed at the outlet of the ejector used in the pump has been used. It is. In the heat exchanger, the working fluid has been heated by using the waste heat of the gas piston unit (GPU. It had been shown that in the temperature control loop the PI controller may be used, and to compensate for the flow rate pulsations, it is necessary to use a combined control system.
  Keywords: : heat exchanger, variable heat transfer surface, control system, mathematic model, heat pump.
7 Hydrodynamic Features of Gas-Liquid Flow Movement in a Separation Device Plane Channel with an Oscillating Wall
Authors: Pavlenko I.V., Liaposhchenko O.O., Sklabinskyi V.I., Ivanov V.O., Gusak O.G. Sumy State University Sumy, Ukraine
  Abstract: In this paper, the movement of a gas-fluid flow in a plane channel with an oscillating wall was in-vestigated. The aim of the research is to increase the efficiency of separation equipment by imposing the vibration impact on a gas-liquid flow. This purpose was achieved by applying the phenomenon of selective coagulation of a dropping liquid. The novelty of the proposed approach concerns creating the mathematical model for determination of analytical dependences between the efficiency of the hydromechanical process and initial parameters of the separation device. As a result, quantitatively and qualitatively sufficient approximations for the scalar pressure and vector velocity fields were ob-tained with a permissible relative error in comparison with the results of numerical simulation. The presence of biharmonic fluctuation of particles was proved; besides, related dependencies for the cal-culation of vibration characteristics were obtained. Additionally, the paper presents the dependencies for identifying a range of thickness for a near-wall area. The system of dimensionless criteria was proposed for determining flow modes and relative trajectories of liquid droplets in a gas-fluid flow. The numerical simulation approach and related methodology of engineering calculations were pro-posed on the example of a plane channel of the separation device. Finally, the distance between ad-jacent zones of the pressure minimum was determined. As a result, it was found that this distance is equal to the wavelength of the vibrating impact to the flow that is an initial justification of further coagulation process of liquid droplets in a gas-liquid flow in a separation device.
  Keywords: vibration impact, local zone, pressure, dropping liquid, velocity field, trajectory of a particle.
8 Investigation of the Influence of Gas Pressure at the Inlet in Jet-Reactive Turbine on its Performance Indicators
Authors: Vanyeyev S.M., Meleychuk S.S., Baga V.N., Rodymchenko T.S. Sumy State University Sumy, Ukraine
  Abstract: The results of gas current calculations in a flow part in not reversive jet-reactive turbine at pressure upon an input to the turbine up to 10 МPа (earlier calculations were spent up to 0.9 МPа), executed in program complex FlowVision for the first time are presented in the article. The dependences of factors and parameters of efficiency of the jet-reactive turbine (JRT) from total pressure upon an input in the turbine are received. They are exposed in a graphic type. The primary goals of the research were: calculation of parameters of current of gas in a flow part of the jet-reactive turbine by means of program complex FlowVision at pressure upon an input of the JRT from 0.4 up to 10 МPа, the analysis of results of calculation, reception of dependences of different factors from total pressure upon an input in the turbine. The Influence of total pressure on an input in the JRT on various factors, such as: total pressure recovery factor, factor of hydraulic resistance and factor of outflow were investigated. It was discovered that total pressure recovery factor  increases for 27 % at an increase of pressure of an input of the jet-reactive turbine up to 4 МPа. It was determined that the hydraulic resistance factors related to the dynamic pressure at the inlet ξin and the turbine output ξout is reducing at 2.7 and 3.3 times, respectively, with an increase in pressure at the inlet of the jet- reactive turbine to 4 MPa.
  Keywords: jet-reactive turbine, flow part, total pressure, total pressure recovery factor, starting torque, specific starting torque.
9 Influence of Gas Physical Properties on Labyrinth Seals Throttling Characteristics
Authors: Bondarenko G.A., Vanyeyev S.M., Baga V.N., Bashlak I.A., Rodymchenko T.S. Sumy State University Sumy, Ukraine
  Abstract: The most important issue when designing the labyrinth sealing knots is the question of the correct-ness of the model tests results application. This task has not had a strong solution so far. For practi-cal calculations of labyrinth seals famous formulae for determining leakage through the hole are used. They are supplemented by coefficients obtained experimentally in conditions which practically had nothing to do with full scale ones: flat (non-circular) models are used, possible effect of the shaft rotation and the operating environment behavior are not taken into account. For the purpose of obtaining the answer to a question concerning the impact factor of gas physical properties on the flow characteristics of labyrinth seals a series of physical and numerical experiments on various gas-es were carried out. The studies were conducted under conditions maximum approximate to field ones. Pilot studies were conducted on a standard experimental bench to specify throttling character-istics of labyrinth seals. Numerical investigations were conducted using the СFD techniques on var-ious gases. Numerical study and experiment confirmed the influence of gas physical properties on throttling characteristics of labyrinth seals. The heavier the gas the more intensive symptoms are. Flow coefficient divergence of the seal run by air and vapor is about 30%. It has been proved and confirmed by experiments. Visualization of flow has been obtained. Studies have shown a signifi-cant impact of gas physical properties on leakage degree.
  Keywords: : labyrinth seal, prototype bench, physical properties, model tests, flow visualization.
10 Energy Efficiency Assessment of the Use of Expander-Generator Set in Cogeneration Systems
Authors: Gubarev V. Ia., Arzamastsev A. G., Sharapov A. I., Kartel A. Iu. Lipetsk State Technical University Lipetsk, Russian Federation
  Abstract: The purpose of the article is to assess energy efficiency of the expander generator application in cogeneration systems. It demonstrates that the research works devoted to this subject do not take into account the effect that gas parameters after the expander have on operating efficiency of the main power generating equipment that leads to a distortion of the assessment of expander energy efficiency. The energy efficiency is determined by specific fuel savings resulting from the use of a circuit with an expander compared to the option of gas throttling. It shows that spe-cific fuel saving is directly proportional to the increment value of the total specific useful work of the utility company when using expander generators. It was found that when using the ex-pander at the cogeneration plant the total specific useful work increment is less than the specific work of the expander generator. It is shown that the energy effect magnitude from the use of circuits with an expander at cogeneration boilers depends on the ambient air temperature. For an expander at cogeneration boiler houses with gas piston internal combustion engines at air tem-peratures below the optimum mixture temperature, the total increment of the specific work is equal to the specific work of the expander, at higher temperatures, the increment of the total specific work can be several times greater than the specific work of the expander. The prospects of preheating gas before the expander at the considered utility companies were analyzed.
  Keywords: expander-generator set, cogeneration boiler house, specific fuel economy.
11 Influence of Non - Condensable Gases on the Processes of Heat and Mass Transfer during Film Condensation of Steam in Heat Exchangers
Authors: Reshetnikov I.F., Shikhalev S.V., Tikhonov S.L. Ural State University of Economics Ekaterinburg, Russian Federation
  Abstract: The aim of the article is a quantitative assessment of the influence of non-condensable gases on the intensity of heat and mass transfer processes during film condensation of steam in the specific conditions for heat exchanger. The task is achieved by conducting experimental research of heat and mass transfer processes in film condensation of steam in the presence of non-condensable gases.The study was carried out by the method of stationary heat flow on an experimental kettle with a jacket (0,02 m3 capacity), industrial cooking boilers (0,04 m3 and 0,06 m3 capacity). Cylindrical kettles with a hemispherical and elliptical bottom were selected as the condensation surface. The results of the experiments are presented in the form of a criterion equation for determining the mass transfer coefficient for vapor concentration diffusion. When the concentration of a non-condensable gas reaches 40% an intensification of the resulting heat transfer coefficient from the vapor-gas mixture to the condensation surface is observed. The coefficient of heat transfer to the condensation surface depends on the concentration of non-condensable gases in the apparatus cavity. The results of the research indicate that it is possible to improve the heat exchangers with a jacket and allow an assessment of the heat input when removing the gas mixture from the jacket in the heating mode of the cookers at the design stage. Material research allows to develop automatiс systems and control parameters in the operation of apparatus with a jacket.
  Keywords: condensation, heat exchanger, heat transfer coefficient, mass transfer, steam – gas mixture, non – condensable gases.
13 Comparative Analysis of Energetic Performance of Various Photovoltaic Power Stations
Authors: Chalbash O., Berzan V., Postolati V. Institute of Power Engineering Chisinau, Republic of Moldova
  Abstract: Se analizează factorii de influență asupra producerii energiei electrice de către centralele fotovoltaice. Se constată, că micșorarea umbririi și orientarea după soare sunt soluții eficiente pentru sporirea producerii energiei electrice. Se prezintă o vedere generală privind particularitățile centralelor cu platforme staționare și platforme mobile cu orientare după soare. Scopul lucrări constă în argumentarea, elaborarea și descrierea abordării generalizate privind analiza funcționării și a modalităților de dirijare cu orientarea centralelor electrice PV după soare întru majorarea densității efective a energiei produse de diferite centralele fotovoltaice. S-a formulat conceptul și s-a elaborat modelul matematic generalizat pentru diferite centrale fotovoltaice cu platforme staționare și mobile, luând în considerare efectul de umbrire al modulelor fotovoltaice montate pe diferite platforme. S-a propus algoritmul de optimizare a orientării platformelor pentru fiecare interval de timp selectat. La bază a stat conceptul de descompunere a problemei optimizării după criteriul producerii valorii maxime a energiei electrice și ocupării celei mai mici suprafețe a terenului de amplasare a centralei. S-a elaborat softul de calcul a energiei electrice produse de către centralele fotovoltaice cu platforme staționare și mobile comandate în funcție de amplasarea lor în terenul destinat pentru această centrală. S-au determinat indicii specifici de producere a energiei electrice kWh/(m2*zi) pentru diferite centralele, ținând cont de factorul de umbrire. S-a constatat, că centralele dotate cu sisteme de orientare pe trei coordonate pot produce cel mai mare volum de energie, concomitent, asigurând indici de performanță energetică ridicați în comparare cu alte tipuri de centrale fotovoltaice.
  Keywords: photovoltaic plants, mathematical model, tracking the sun, shading factor, three-coordinate orientation system specific electricity production.
14 Optimizing the Ratio of Wind and Solar Power Stations
Authors: Kuznetsov N., Smertiuk V. Institute of Renewable Energy of the National Academy of Sciences of Ukraine Kyiv, Ukraine Lysenko O., Nesterchuk D., Adamova S. Tavria State Agrotechnological University Melitopol, Ukraine
  Abstract: The purpose of the research is to determine criteria and calculate optimal ratio of different renewable energy sources (RES) for hybrid systems, estimate the random component of power fluctuation and consider the opportunities for its minimization. As a subject of the study it is variable and poorly forecasted in a short-term prospect character of generated power can negatively affect modes of grid operation. This concerns stability of dynamic processes in the systems of power supply. To develop a mathematical model of these processes a number of factual data on the climatic parameters and energy consumption regimes during the joint operation of solar and wind stations was used. As an experimental study suggests, the initial data were collected and statistically processed. Based on the results, mathematical models were developed in the form of a composition of deterministic and stochastic components and theoretical studies on the search for optimal ratios of capacities of wind and solar power stations were carried out. The object of optimization in the work is the load variability. As a combined single criterion, it was proposed to use the coefficient of variation. The ratios of the wind and solar components of the power generation, considered in this study, has allowed us to determine variants with a minimal dispersion of RES generation or with a minimum ratio of dispersion to average generated power which depends on the average annual or seasonal weather conditions. As a rule, the share of wind power plants should be 10-40% of the total rated RES power, depending on the total share of RES.
  Keywords: renewable energy sources, solar power station, wind power station, optimization, and combined systems of power supply.
15 Low-Temperature Evaporative Air Coolers. Development and Analysis of Opportunities
Authors: Doroshenko A.V., Antonova A.R., Khalak V.F., Goncharenko A.S. Educational and Research Institute of Refrigeration, Сriotehnology and Eco-Energetics Odessa National Academy of Food Technologies, Ukraine
  Abstract: The purpose of the study is to develop and conduct a cycle of theoretical and experimental studies of low-temperature evaporative air coolers. The developed circuit solutions of the coolers ensure the reduction of the evaporative cooling limit from the temperature of the wet thermometer to the dew point temperature of the incoming air flow. The analysis of the fundamental capabilities of low-temperature air coolers are made taking into account modern solutions (patents) and publications in leading foreign scientific journals. The scientific novelty of the research consists in analyzing of the state of the air flow within the nozzle of the evaporative cooler. For the first time, the authors conducted studies taking into account the danger of “recondensation” of the processes of joint heat and mass transfer in an indirect type evaporative air cooler - a chiller, which provides an opportunity to analyze the state of the main and auxiliary air flows in the evaporative air cooler depending on the ratio of gas and liquid flows and initial parameters (temperature and moisture content) of the external air. A series of experimental studies of hydrodynamic processes and joint heat and mass transfer is developed, including the problem of stability and determination of the fluid “delay” in the packed layer, which allows determining the actual wetting of the packed surface, what is principally important when switching to multi-channel packing structures made of polymeric materials. On the basis of the obtained results, the analysis of the basic capabilities of low-temperature air coolers - chillers was carried out. The goal of reducing the limit of evaporative cooling is achieved by using new solutions, which allows to expand the area of practical use of evaporative cooling methods, for example, the use
  Keywords: low-temperature air coolers, heat and mass exchange equipment, evaporative cooling, cooling limits, process efficiency.
17 Steganoanalytical Method Based on the Analysis of Singular Values of Digital Image Matrix Blocks
Authors: Kobozeva A.A.1, Bobok I.I.1, Batiene L.Е.2 1, 2 Odessa National Polytechnic University 1 Odessa, Ukraine 2 Ouagadougou, Burkina Faso
  Abstract: The rapid development of digital steganography over the past decade involving numerous scien-tific publications in the open press, devoted to the new steganomethods and algorithms, have led to the possibility of wide use of the results obtained. At the same time, the organization of a ste-ganographic channel can lead to various kinds and degrees of negative consequences both for individuals and for society as a whole. Because of this, the need and relevance of providing ef-fective digital image steganalysis is currently increasing. One of the most widely used ste-ganographic methods today is the LSB-method. The specific area of its application is in the or-ganization of a hidden low bandwidth communication channel. Under these conditions, the ex-isting steganalitic methods turn out to be ineffective. The aim of this paper is to increase the ef-ficiency of image steganalysis in the conditions of low bandwidth of a covert channel organized by the LSB-method. Achieving this aim is carried out by developing a new method based on the analysis of the normalized separation of the maximum singular numbers of the image matrix blocks. The algorithmic implementation of the developed method is superior in efficiency when compared to the existing modern analogues, in terms of the covert channel for bandwidth values of less than 0.1 bpp. An important information component of the results of the proposed meth-od is its ability to determine the cover-image quality factor of the primary lossy compression.
  Keywords: steganalysis, digital image, least significant bit, low bandwidth, covert channel, cover, stego-message.
19 Tariff Policy in the Formation of the Price of Thermal Energy
Authors: Postolatiy V., Babich V. Institute of Power Engineering Chisinau, Republic of Moldova
  Abstract: Tariffs for energy and energy resources are the main factors determining the sustainable development of the economy. The aim of the paper is to determine and compare the dynamics evolution of the tariffs for thermal energy and the evolution of the gross domestic product (GDP).The data on the heat consumption and tariff change in the city of Chisinau were examined in monetary terms and in relative units compared to the base year 2009. The higher the tariffs, the more part of the GDP, characterized in the economy by the volume of "Output", is spent on "Intermediate consumption (PP)". The difference between "Output" and "Intermediate consumption" volumes is the "gross added value (VAB)", which is the main component of GDP. The analysis of the changes in the real GDP volume of the Republic of Moldova and the increase of the tariffs for the years 2009-2017 (taking into account the GDP forecast for 2018) show that the increase in the tariffs for thermal energy significantly exceeded the real GDP growth. Considering that the planned GDP growth is 4,7% and taking into account the change in the consumer price index (inflation rate), the calculated reduction of the thermal energy tariff in Chisinau is estimated at 28% compared to the existing value, so to 803 lei / Gcal compared to the currently regulated value of 1122 lei / Gcal. The conclusion was reached on the opportunity of applying the proposed methodology to justify current tariffs and in the near future not only extends to thermal energy tariffs, but also for other types of energy, material resources and services in the field of production and social sphere.
  Keywords: : heat power engineering, heat energy, centralized heat supply system, tariffs, statistical data and national accounts, Gross Domestic Product, macroeconomics.
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