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E-Journal №1-3(42)2019

"PROBLEMS of the REGIONAL ENERGETICS (special issue)"


1 The Method of Determining the Turbogenerator Characteristics Using Automated Numerical Calculations of Magnetic Fields
Authors: Milykh V. I., Revuzhenko S. A. National Technical University «Kharkiv Polytechnic Institute» Kharkiv, Ukraine
  Abstract: A typical way for obtaining the characteristics of the electric machines are the methods based on the theory of the magnetic circuits. These methods contain assumptions that lead to significant errors in the calculation results. Modern software allows to perform calculations of the magnetic fields using the numerical methods, and, it is thus possible to obtain more adequate characteristics of the electric machines, which are indicative of their working properties in operation. Hence, the aim of this study is to describe the method of obtaining the characteristics of a high power turbogenerator by the calculation of its magnetic fields. The proposed methods for determining the characteristics of the electric machine under study are based on the iterative methods using the automated numerical calculations of the magnetic fields. The calculations were carried out using the FEMM software finite element method and the Lua script. The paper presents characteristics of turbogenerator such as the idle speed and short circuit, angular, stator winding excitation, adjusting and U-shaped. The adequacy of the calculations was checked by comparing the obtained characteristics with those calculated by classical methods. The most important results of the work are the obtained differences in determining the characteristics by numerical calculation and calculations using the theory of magnetic circuits. Their significance lies in the fact that the modernization of turbogenerators often takes an increase in their power by an amount commensurate with the error by using the classical method of obtaining characteristics based on the theory of magnetic circuits.
  Keywords: turbogenerator characteristics, electromagnetic values, magnetic field, iterative numerical calculations.
2 Control of an Electrical Vector Drive of a Mechanical Variable Masses’ System
Authors: Kvashnin V. V., Babash A. V., Kosenko V. A., Kvashnin V. O., Klimenko G. P. Donbass State Engineering Academy Kramatorsk, Ukraine
  Abstract: The aim of this paper was the development of a positional system model for a vector control of a static loads’ stand using the electrical drive and the study of the effect of various types of speed controllers and their settings on the dynamics of the transient processes during the simulation of the regulation and disturbance actions. This goal was achieved by the development of a vector control system model using the stand electric drive with the PID-speed controller setting, which ensured minimal speed errors and restrictions in the dynamic loads during the regulating and disturbing action. The synthesis of the current control circuits of the stator and speed in the torque control channel was performed. It was shown that using the existing PI-regulators of speed and current and their settings, the speed dynamic error was found to be as high as 21% at a regulating action, whereas during the disturbing action it was 8%. The achievement of the above indicators of the regulation quality was possible in the presence of the intensity setter at the speed regulator input. In this case the dynamic speed error while operating under control increased substantially. The introduction of the speed PID controller made it possible to reduce dynamic errors, however, it gave no desired results with the standard configuration. Changing the controller’s proportional part parameters allowed us to minimize the dynamic speed error while operation, both under regulating or disturbing influences.
  Keywords: vector control, PI controller, PID controller, correction, quality indicators, mathematical model, functional scheme.
3 Eco-design of Electric Equipment
Authors: Tsutsuianu O. Romanian National Committee of the World Energy Council Bucharest, Romania
  Abstract: In the last time, some factors and especially the environmental protection requirements have forced to add the ecological criterion for design of electric equipment, within a new Eco-design concept. The essence of this concept consists in the integration of environmental aspects at project phase, taking into account full life cycle of product. The work presents some theoretical and practical aspects of eco-design for electric equipment. The actual eco-design conception com-bines Qualitative Assessment of Life Cycle Criteria with a quantitative method based on the Product Carbon Footprint. The calculation of the last indicator means the quantification of the greenhouse gases emissions (kgCO2 equivalent) during the life cycle of products and services. From the study of the technical literature and its own practical work, the author has found that "maintenance", one of the phases of the life cycle of electric equipment, is not sufficiently analyzed and quantified in terms of negative impacts on the environment, including CO2 emissions involved in the service performed. As a result, it has achieved himself and in collaboration with other specialists studies and research, with the ultimate objective of establishing environmental performance indicators in this field. Thus, the main objective of this paper refers to the original contribution of the author who has established two such indicators, namely: 1. Absolute indicator "CO2 emissions involved in service (Es) [kg CO2]" and 2. Relative indicator "Specific CO2 emissions involved in service (es) (kg CO2 / euro)".
  Keywords: environmental legislation, eco-design, life cycle of product/service, product carbon footprint, environmental performance indicator, CO2 emissions.
4 Power Balanced Adjustment of Quad-Inverter Installation with Modified Discontinuous PWM
Authors: Oleschuk V., Ermuratskii V. Institute of Power Engineering of Moldova Kishinau, Republic of Moldova
  Abstract: Abstract. Purpose of this work is in the development and modification of control scheme and of basic algorithms of discontinuous space-vector modulation for synchronous and balanced regu-lation of multi-inverter topology of six-phase open-end winding installation with four insulated dc sources. This purpose has been achieved due to including in the control and modulation scheme of specialized control correlations connecting coefficients of modulation of inverters, required power ratio between dc-links, and voltages of the corresponding dc sources. So, basic novelty of this research is in the fact, that the elaborated and investigated control and modula-tion algorithms for installation on the base of inverters with discontinuous space-vector modula-tion (with both 300-non-switching intervals and 600-non-switching intervals) insure both required power sharing capability between dc links and advanced harmonic composition (without even harmonics and subharmonics) of spectra of the phase and line voltages of six-phase installation. Mutual comparison of behavior of system with two basic schemes of modified discontinuous pulsewidth modulation (PWM) has been executed. Investigation of harmonic composition of the phase voltage of multi-inverter system illustrates an important fact, that for the all analyzed con-trol modes, connected with balanced adjustment of drive under different conditions, phase volt-age of installation has symmetry for any control regimes, including control modes with fraction-al frequency ratios between switching frequency of converters and fundamental frequency of installation, with absence in its spectra of undesirable subharmonics. Factor of minimization of subharmonics in spectra of voltage and current of ac drives of different topologies is especially important for the medium-voltage medium-power installations on the basis of PWM converters.
  Keywords: voltage source inverter, induction motor, modulation strategy, voltage spectra, integral harmonic composition.
5 District Heating Systems in Republic of Moldova: Reality and Perspectives
Authors: Leu Vasile1, Cernei Mihail2 1Technical University of Moldova, Faculty of Energetics and Electrical Engineering 2State Agrarian University of Moldova, Faculty of Agricultural Engineering and Auto Transportation, Republic of Moldova
  Abstract: The article presents the history of centralised distric0.t heating systems in Republic of Moldova, evolution, current state and prospects for short-term investments financed by raising funds from external creditors. Centralized heating in the Republic of Moldova is analyzed in the light of the activities of the license holders, regulated by the National Energy Regulatory Agency, particularly of those from mun. Chisinau and mun. Balti. In most cases, this centralized heating supply systems are in operation over 50 years already, so their rehabilitation is very appropriate considering their over dated lifetime period, and the moral and physical wear. At the level of heat sources, the physical wear of the fixed assets is about 70%. The heat transportation and distribution networks are being now renovated, using pre-insulated pipes from expanded polyurethane, at the level of 10%, and the growth of the renovated pipes share will lead to the lowering of the energy losses in this systems. The scope of the paper is the analysis of the key technical indicators and the description of the experience regarding the projects related to the enhancement of energy efficiency of centralized heating systems in mun. Chișinau and mun. Bălți, projects that are carried out in the last years, and implemented with the financial support of the foreign partners. Are analyzed main functioning indicators of the centralized heating systems for the period 2015-2018 years, inclusive production volumes, supply, and level of heat losses. A short analysis regarding centralized heating in some European Union countries, has been presented, as well.
  Keywords: : centralised district heating system, heating networks, heat energy, central district heating plant, individual heating plant.
6 Mathematical Model of a Three-Phase Electric Line with Split Phases
Authors: Patsyuk V. I., Berzan V. P., Ribacova G. A. Institute of Power Engineering Chisinau, Republic of Moldova
  Abstract: An increase in the voltage of electric lines leads not only to an increase in their natural power, but also to the problem of increasing the power losses due to the corona discharge. The use of phases with split wires is used as a technical solution to reduce such losses. The splitting of wires affects the parameters of the line that leads to a change in natural and transmitted power. Therefore, improving the accuracy of calculating the parameters of lines with split phases is an actual problem. The purpose of this work was to develop a mathematical model of a three-phase line with split phases and to evaluate the accuracy of determining its capacitive parameters using the equivalent diameter of the split phase and the finite volume method for calculating the distribution of the electric field parameters based on Maxwell's equations. Using the finite volume method, the values of potential and capacitance coefficients were determined for each of the 15 wires of the 750 kV transmission line. These values were calculated by the mirror image method as well. These calculations for various configurations of the wires arrangement in the split phase gave very close results. It was substantiated the possibility of applying the finite volume method to calculate the parameters of circuits with complex geometry by the criterion of limiting
  Keywords: Maxwell's equations, numerical method, electric field distribution, equivalent radius, capacitive coefficients, long line parameters.
7 Compact Controllable Overhead Transmission Lines
Authors: Postolaty V. M. Institute of Power Engineering Chisinau, Republic of Moldova
  Abstract: Compact controllable high-voltage power lines (HVPLs) are a new generation of alternating current power transmission lines, representing the newest achievements in the field of power transmission and control means, new technical solutions for the design, insulation, connection layouts and control systems. The main distinctive features of the compact controllable HVPLs are: extremely reduced phase-to-phase distances adopted relative to the minimal required insulation distances (dielectric strength of the phase-to-phase gaps) at a maximum operating voltage and also under lightning and commutation overvoltage; new phase configurations, where tower’s grounded parts (poles, cross-arms, suspension hubs) placed outside of the interphase space; insulating elements (insulating spacers or screeds) between closely adjacent HVPL phases installation if required, fixing the selected distance between phases and dampening conductor’s vibration or galloping under severe weather conditions, which ensures high mechanical stability and reliability of the adjacent phases in spans; angular phase shifts establishment between the voltage vectors applied to the compact controllable HVPL adjacent phases; implementation of high-speed phase control devices and adjustable compensation devices (FACTS type). Compared to the conventional high-voltage power lines, compact controllable ones with FACTS devices ensure the following: 1.2-1.6 times increase in throughput; reduction of total costs per transmission capacity unit by 20 – 30%; 1.5-2 times alienated land reduction in case of equal power transmission; reduction of electric field intensity in the HVPL external space, and, hence, mitigation in the environmental effect; ability to control power flows and their directions; and total energy losses reduction in the power system.
  Keywords: transmission lines, high voltage, compact, controllable, self-compensating, equivalent parameters.
8 Power Converter with High Value of Power Factor
Authors: Ermurachi Iu., Berzan V. Institute of Power Engineering Chisinau, Republic of Moldova
  Abstract: Increasing the energy efficiency of using electricity is a current problem. As a modern solution, the development of power equipment based on power electronics was presented. These devices, which absorb relatively large powers from the low-voltage grid, lead to the distortion of currents in the power supply network and to the reduction of the power factor, leading to increased loss-es in supply networks. The aim of the paper is to develop an innovative solution to increase the power performance of power electronics devices as a result of improving their power factor. The scientific innovation consists in the realization of the technical solution for the fusion of the power factor correction and power conversion improvement in the unique functional block, which has an AC / DC power converter. A simulation model of the AC /DC converter mode has been developed. The efficiency of power factor improvement of the AC / DC converter and op-eration in switching mode at the zero voltage of the transistor in the primary circuit of the trans-former has been demonstrated. It has been experimentally demonstrated the possibility of manu-facturing AC / DC converters with cumulative power factor correction functions and output voltage stabilization. The magnitude of the voltage pulses (alternate component) on the rectifier's filter capacitors does not exceed the maximum allowable operating value of the capacitor. This ensures increased efficiency of the converter. The AC / DC converter has an efficiency of 98% and power factor equal for the 1500 W power supply and the 220/12V.
  Keywords: converter, zero-voltage-switch, fly-back, forward, mathematical simulations, energy efficiency.
9 Trends and Risks in the Natural Gas Supply of the Republic of Moldova
Authors: 1Berzan V., 1Postolati V., 1Bykova E., 2Cernei M., 2Volconovich L. 1Power Engineering Institute 2State Agrarian University of Moldova Chişinau, Republic of Moldova
  Abstract: Sustainable economic development is also determined by the availability of primary energy supply. Geographical incoherence of energy production and consumption areas leads to new challenges in providing consumers with energy. The purpose of this work is to analyze and assess trends and problems related to the provision of energy resources, mainly of the natural gas for Republic of Moldova in the context of new challenges in the natural gas market and rhe changes in their transport infrastructure. The investigative methodology is based on the analysis of time series of production, consumption and import of energy resources at global and regional level in 1990-2017. It is proposed to using the linear approximation functions. The coefficients and the its signs of these functions ("plus" or "minus") and the value of and the determination coefficient are used for the quantitative analysis of the production, consumption and import trends of primary energy and natural gas. Europe and Asia ensure their energy balance by massive energy imports. The Southeast European region, including the Republic of Moldova, imports large sums of primary energy resources. The need to import natural gas in the Romania-Moldova-Ukraine sub-zone is currently estimated at about 12 million tons of oil equivalent. The new energy corridors for the transportation of natural gas will lead to new challenges regarding the natural gas supply of the Republic of Moldova. Information on possible scenarios of natural gas supply to the Republic of Molodova is presented and the estimated costs for natural gas transport for these scenarios are presented.
  Keywords: production and consumption, numerical series, approximation functions, energy corridors, necessary import, cost of natural gas transportation.
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