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  Problemele energeticii regionale

E-Journal №1(33)2017



1 Analysis of the Processes of Short-Currents Limiting by Transformer with High-Temperature Superconducting Windings
Authors: Manusov V.Z., Pavlyuchenko D.A., Ahyoev J.S. Novosibirsk State Technical University Novosibirsk, Russian Federation
  Abstract: An important advantage of transformers with high-temperature superconducting winding is their ability to limit the short-circuit currents. The article discusses a physico-mathematical model that analyses transient processes at short-circuit currents in electrical networks containing transformers with a high-temperature superconducting winding. One of the main ideas and objectives of this work is to investigate the process of short-circuit currents limiting by means of a transformer with a high-temperature superconductor winding, which makes it possible to combine two series-connected elements in one device: transformer and a reactor. The effectiveness of this method is due to the fact that when the short-circuit currents exceed the critical value of the temperature of the superconductor winding, it goes to the normal state with high winding resistance for short-circuit currents. It is important to know when a superconductor should go over to a normal state with the loss of superconductivity. For this purpose, a program was developed to determine the amount of heat generated by a short-circuit current flowing before it is disconnected. For a transformer with high-temperature superconducting winding with a capacity of 40 MVA, a short circuit must be eliminated after 0.1 seconds, without switching off the transformer. To limit the short-circuit current; it is intended to use a hybrid winding. The performed assessment showed that the return of the winding to the superconducting state, first, depends on the ratio of the short-circuit currents to the operating current. This is the criterion for the return/non-return to the superconducting state.
  Keywords: transformer, superconductor winding, energy efficiency, reactor, pre-emergency mode, power loss, limitation, short-circuit currents.
2 Nonlinear Control of an Open-Loop Open-Winding Motor System with Modulated Converters
Authors: Oleschuk V.I. Institute of Power Engineering of the Academy of Sciences of Moldova Kishinau, Republic of Moldova
  Abstract: Purpose of this work - to provide wider control opportunities for multiphase open-end winding motor drive by modification of basic scheme of space-vector pulse-width modulation (PWM). It has been shown, that the proposed development of basic PWM scheme insures available solutions for realization of specific control dependences and modes of operation of adjustable speed ac drives with different types and kinds of loads. Suitable algorithms of PWM of converters of multiphase drive have been analyzed and compared. Extensive simulation studies have been executed for evaluation of performance and effectiveness of the proposed control strategy. Assessment of harmonic composition of the phase voltages of drive system with modified scheme of space-vector modulation has been done. Results of the executed simulations proved the fact, that the developed techniques of space-vector pulse-width modulation allow providing quarter-wave or half-wave symmetry of waveforms of the output voltage of six-phase adjustable speed drive systems during the analyzed non-standard modes and regimes of its operation.
  Keywords: multiphase ac drives, power electronic converters, control and modulation strategies.
3 Optimization of Transformation Coefficients Using Direct Search and Swarm Intelligence
Authors: Manusov V.Z., Matrenin P.V., Orlov D.V. Novosibirsk State Technical University Novosibirsk, Russia
  Abstract: This research considers optimization of tap position of transformers in power systems to reduce power losses. Now, methods based on heuristic rules and fuzzy logic, or methods that optimize parts of the whole system separately, are applied to this problem. The first approach requires expert knowledge about processes in the network. The second methods are not able to consider all the interrelations of system’s parts, while changes in segment affect the entire system. Both approaches are tough to implement and require adjustment to the tasks solved. It needs to implement algorithms that can take into account complex interrelations of optimized variables and self-adapt to optimization task. It is advisable to use algorithms given complex interrelations of optimized variables and independently adapting from optimization tasks. Such algorithms include Swarm Intelligence algorithms. Their main features are self-organization, which allows them to automatically adapt to conditions of tasks, and the ability to efficiently exit from local extremes. Thus, they do not require specialized knowledge of the system, in contrast to fuzzy logic. In addition, they can efficiently find quasi-optimal solutions converging to the global optimum. This research applies Particle Swarm Optimization algorithm (PSO). The model of Tajik power system used in experiments. It was found out that PSO is much more efficient than greedy heuristics and more flexible and easier to use than fuzzy logic. PSO allows reducing active power losses from 48.01 to 45.83 MW (4.5%). With al, the effect of using greedy heuristics or fuzzy logic is two times smaller (2.3%).
  Keywords: optimization, smart grid, transformer, active power loss, directed search, swarm intelligence.
4 Distinctive Features of Faults for Use in Power Transformer Differential Protection
Authors: Glazyrin V.E., Litvinov I.I. Novosibirsk State Technical University Novosibirsk, Russian Federation
  Abstract: The aim of the work is to study the change in instantaneous values of the differential current in power transformer differential protection circuits under conditions of magnetizing inrush when the unloaded transformer is energized and under conditions of a fault within the protection zone. Saturation of measuring current transformers during the transient process leads to distortion of signals in their secondary windings, which can cause a long delay in the disconnection of the protected object and the development of an accident in the power system if traditional protective algorithms are used. Taking into account the peculiarities of the change in the instantaneous values of the differential current while developing the protection algorithm makes it possible to recognize faults with maximum speed before the moment of the first saturation of electromagnetic current transformers and thus avoid a delay in the operation of the protection. For quick and correct recognition of a fault within the protection zone authors proposed to monitor the maximum value of the derivative of the differential current and the duration of its monotonous change from the moment of the onset of the transient process. This is because the monitored parameters in the emergency and normal operation of the power transformer can vary significantly. Application of traditional protection algorithms together with proposed methods allows increasing the speed of differential protection response in different operation modes of the power system. Mathematical simulation has been used to study the magnetizing inrush and short circuits within the protection zone.
  Keywords: relay protection, power transformer differential protection, power transformer inrush current, transients, simulation, distinctive features of faults.
5 Identification of Synchronous Generator Electric Parameters Connected to the Distribution Grid
Authors: Frolov M. Yu., Fishov A. G. Novosibirsk State Technical University Novosibirsk, Russian Federation
  Abstract: According to modern trends, the power grids with distributed generation will have an open system architecture. It means that active consumers, owners of distributed power units, including mobile units, must have free access to the grid, like when using internet, so it is necessary to have plug and play technologies. Thanks to them, the system will be able to identify the unit type and the unit parameters. Therefore, the main aim of research, described in the paper, was to develop and research a new method of electric parameters identification of synchronous generator. The main feature of the proposed method is that parameter identification is performed while the generator to the grid, so it fits in the technological process of operation of the machine and does not influence on the connection time of the machine. For the implementation of the method, it is not necessary to create dangerous operation modes for the machine or to have additional expensive equipment and it can be used for salient pole machines and round rotor machines. The parameter identification accuracy can be achieved by more accurate account of electromechanical transient process, and making of overdetermined system with many more numbers of equations. Parameter identification will be made with each generator connection to the grid. Comparing data obtained from each connection, the middle values can be find by numerical method, and thus, each subsequent identification will accurate the machine parameters.
  Keywords: synchronous generator, parameter identification, distributed grid, digital modeling, analysis of oscillograms.
6 The Method of Optimization of Hydropower Plant Performance for Use in Group Active Power Controller
Authors: Glazyrin G.V. Novosibirsk State Technical University Novosibirsk, Russia
  Abstract: The problem of optimization of hydropower plant performance is considered in this paper. A new method of calculation of optimal load-sharing is proposed. The method is based on application of incremental water flow curves representing relationship between the per unit increase of water flow and active power. The optimal load-sharing is obtained by solving the nonlinear equation governing the balance of total active power and the station power set point with the same specific increase of water flow for all turbines. Unlike traditional optimization techniques, the solution of the equation is obtained without taking into account unit safe operating zones. Instead, if calculated active power of a unit violates the permissible power range, load-sharing is recalculated for the remaining generating units. Thus, optimal load-sharing algorithm suitable for digital control systems is developed. The proposed algorithm is implemented in group active power controller in Novosibirsk hydropower plant. An analysis of operation of group active power controller proves that the application of the proposed method allows obtaining optimal load-sharing at each control step with sufficient precision.
  Keywords: hydropower plant, active power, group controller, hydraulic turbine, water flow, trash screens.
8 Increase of Ecological Safety, Reliability and Efficiency of Coal-Fired Boilers
Authors: Volkov E.P.,1 Arkhipov A.M.,2 Prokhorov V.B.2, Chernov S.L.2 1Power Engineering Institute G.M. Krjijanovskogo, Moscow, Russia. 2Moscow Power Engineering Institute (MPEI, National Research University), Moscow, Russia
  Abstract: The changes of environmental legislation of the Russian Federation will lead to a drastic increase of the ecological payments for environmental pollution in excess of technological standards. Significant excess in relative emissions of nitrogen oxides take place in burning solid fuel with liquid slag-tap removal. The purpose of this article was to develop technical solutions for low-cost reconstruction of the boilers to ensure efficient combustion of the fuel and technological standards of emissions of nitrogen oxides. As shown the use of straight-flow burners with compulsory optimization of the aerodynamics of the furnace and the organization of staged combustion of fuel will provide low nitrogen oxide emissions and efficient fuel combustion. Research on physical models has demonstrated the feasibility of increasing the angle of the pulverized coal burners down to 65-70o, and also achieved a more uniform distribution and increase the speed of the jets coming from upper and lower tertiary air vertical compartments of nozzles through the installation of the vertical extra sheets, which guide the flow in a space between jets. The results obtained allow the transfer of existing boilers with slag-tag removal to a solid with the installation of direct-flow burners and optimization of the aerodynamics of the furnace, which provides regulations for energy efficiency and ecological safety corresponding to the best, achieved technologies, and dramatically reduces environmental payments. The proposed technology in boiler BKZ-210-140F allowed reducing emissions of nitrogen oxides by more than 2 times when burning highly reactive Kuznetsk coal, as shown as an example.
  Keywords: best available technologies, boilers, direct-flow burner, nitrogen oxides, coal burning.
9 Simulation of Working Processes in the Water-Tube Boiler Furnace with the Purpose of Reducing Emissions of Nitrogen Oxides
Authors: Redko A.A.,1 Davidenko A.V.,1 Pavlovskiy S.V.,1 Kulikova N.V.,1 Pavlovskaya A.A.,1 Redko I.A.2 1Kharkiv National University of Construction and Architecture, 2Kharkiv National University of Urban Economy by O.M. Beketov Kharkiv, Ukraine
  Abstract: A significant number of domestic and industrial boilers are in operation in Ukraine. Nitrogen oxides are the most dangerous among all combustion products that pollute the atmosphere, therefore, one should take some measures for decreasing the formation of nitrogen oxides during combustion. The studies were carried out at the boilers of low power (100 kW) with a tubular radiator and an open end. The studies in the furnaces of industrial steam boilers having a tubular radiator with a closed end have not been done. The numerical study results of the gaseous fuel combustion processes in the furnace of a DE-10/14 steam water-tube boiler are presented. The fuel-air mixture is formed by premixing the 15% part of the air with a primary burner twist factor n=2.4 and a secondary burner twist factor n=1.6, and an air excess factor αв=10. As a result of the studies, the temperature and velocity distributions of gases in the combustion chamber, the density of heat flows on the screen tubular surfaces, and the concentrations of the combustion components were determined. Flue gas recirculation in the volume of 80-100% is provided, and the reversible movement of combustion products towards the combustion front provides a reduction in the concentration of nitrogen oxides up to 123-125 mg/m3 at the furnace outlet. Disadvantages are the following: the formation of stagnant zones near the end of the secondary radiator. The optimum diameter of the tubular radiator equals to two burners diameters and tubular radiator is located at a distance of one meter from the burner cutoff.
  Keywords: water-tube boiler; furnace; nitrogen oxides; secondary emitter; numerical investigation.
10 Energy and Economic Efficiency of Gas Turbine Units and Heat Pumps in Power-supply Systems in the Arctic Regions of Russia
Authors: Suvorov D.M., Tatarinova N.V., Krupin D.F., Suvorova L.A., Baibakova T.V. Vyatka State University, Kirov, Russian Federation
  Abstract: Currently, in publications, there is some controversy about the efficiency of various power-supply systems operating in extreme climatic conditions. The need to dispel this controversy explains this study's relevance. The purpose of this study is to evaluate the feasibility of the use of cogeneration gas turbine and microturbine units as the heat-and-power source for a camp-like residential facility in the Arctic regions of Russia. A boiler plant and a heat pump system are analyzed as heat sources for the afore-mentioned camp. The authors used their own mathematical models of the units to do the study. The estimates were based on the annual facility-specific power and heat consumption data, additionally climatic conditions and fuel kind (natural gas) were taken into consideration. The study resulted in defining the plants' limits of equal fuel consumption, depending on the substituted power output efficiency and the power/heat production cost to the price of gas correlation. Another result was the evaluation of the power efficiency (by the natural gas consumption) and economic feasibility, as well as the payback term. We concluded that in case the natural gas was the only fuel available the ground source vapor-compressing heat pump systems were power-wise and economically unsound, provided they were operated under environmental conditions typical for the Russian North and according to the region-specific heat-supply schedule. The outcome of this study can be used when planning/designing the power-supply facilities in extreme climatic conditions, as well as in evaluating/estimating the power-supply systems' efficiency.
  Keywords: boiler plant, cogeneration, efficiency, gas turbine unit, heat pump, microturbine unit, payback term, power supply, production cost.
11 New Solutions for Solar Absorption Refrigeration Systems and Air Conditioning Systems
Authors: Doroshenko A.V., Antonova A.R., Liudnicky K.V., Ivanova L.V. Educational and Research Institute of Refrigeration, Сriotehnology and Eco-Energetics Odessa National Academy of Food Technologies, Odessa, Ukraine
  Abstract: The mission of the research includes the following objectives: the development of new circuit decisions for the alternate refrigerating systems based on the use of an open absorptive circuit and on the use of solar energy for absorbent solution regeneration; an assessment of the energy and environmental characteristics of the developed systems; obtaining of the experimental data for an assessment of the principal capabilities of the proposed new solar air-conditioning systems. The multistage principle of the creation of drying and cooling contours with the increase of concentration of absorbent on cooler steps is offered. The absorber with internal steam cooling allowing the improvement of the scheme of the alternate refrigerating system is developed. On the basis of the obtained experimental data the analysis of the main opportunities of the developed solar air-conditioning systems was made which showed that the created systems: provide the required comfortable parameters indoors without engaging of traditional refrigerating technics; allow to use only one - or two-stage option of refrigerating system for application in the conditions of Ukraine and of Europe. In comparison with traditional vapor-compression systems, the developed solar systems provide the considerable decrease in energy consumption (to 30%), their use leads to the decrease of exhaustion of natural resources, influences less global climate change.
  Keywords: solar systems, drying of air, heat-mass-transfer apparatus, film flow, absorption, desorption, evaporative cooling.
12 Automatic Pressure Stabilization in Front of the Evaporators in the Multifunctional Heat Pump
Authors: Sit M.L., Zhuravleov A.A. Institute of Power Engineering of the Academy of Sciences of Moldova Kishinau, Republic of Moldova
  Abstract: The aim of the article is to elaborate and to investigate the automatic control system of pressure in front of evaporators of the multifunctional heat pump, which has several condensers and several evaporators. The control system must reduce the value of pressure perturbations acting on evaporators and decrease the value of pressure pulsations before them. To solve this problem, a hydraulic scheme has been developed in which this parameter is stabilized by using fine and coarse adjustment valves in hydraulic circuits of condensers and compressors using a pressure control system for a static flow mixer. The system for control of the flow of the refrigerant consists of two groups of compressors with automatic control drives installed in the lines of each of the condensers. The pressure control system uses a model of control valve with proportional-integral – derivative (PID) controller in the direct line of the controller loop. This solution allowed simplifying the heat pump control system by eliminating the necessity of matching the pressure and flow control valves in each line and controlling the flow in the line over a wider range as well. A mathematical model of the static mixer of flows installed after the pressure control valves is obtained. The proposed pressure control system gives a possibility to reduce the amplitude of pulsations of pressure before the evaporators up to 14-16 times.
  Keywords: heat pump, static mixer, mathematical model, control system, pressure, control valve, simulation.
13 Technologies of Selective Energy Supply at Evaporation of Food Solutes
Authors: Burdo O.G., Burdo A.K., Sirotyuk I.V. 1, Pour D.R.2 1Odessa National Academy of Food Technologies Odessa, Ukraine 2”Davarrostamipour” firm Tehran, Iran
  Abstract: The aim of the research is to create innovative evaporating equipment that can produce concentrates with a high content of solids, with a low level of thermal effects on raw materials. The significance of the solution of technological problems of the key process of food technologies - concentration of liquid solutions (juices, extracts, etc.) is shown. Problems and scientific contradictions are formulated and the hypothesis on using of electromagnetic energy sources for direct energy transfer to solution’s moisture has been offered. The prospects of such an energy effect are proved by the energy management methods. The schemes of fuel energy conversion for the conventional thermal concentration technology and the innovative plant based on the electromagnetic energy generators are presented. By means of the similarity theory the obtained model is transformed to the criterial one depicted kinetic of evaporation process at the electromagnetic field action. The dimensionless capacity of the plant is expressed by the dependence between the Energetic effect number and relative moisture content. The scheme of automated experimental system for study of the evaporation process in the microwave field is shown. The experimental results of juice evaporation are presented. It has been demonstrated that the technologies of selective energy supply represent an effective tool for improvement of juice concentration evaporative plants. The main result of the research is design of the evaporator that allows reaching juice concentrates with °brix 95 at the temperature as low as 35 °С, i.e. 2…3 times superior than traditional technologies.
  Keywords: energy, food technologies, simulation, juice concentrating, evaporation, electromagnetic energy supply.
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