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  Problemele energeticii regionale

E-Journal №2(37)2018



1 Mathematical Model of Electrical Line with Transposition of Phase Circuits
Authors: Berzan V., Patiuc V., Rybacova G. Institute of Power Engineering Kishinau, Republic of Moldova
  Abstract: The purpose of this paper is to elaborate the mathematical model and the method of calculation of the permanent regime in the line with many conductors with transposed phases. The mathematical model is based on the telegraph equations and takes into account the fact that the electric lines are lines with distributed parameters. As a subject of the study it is selected the 110 kV overhead power line with two compact circuits with the conductors placed horizontally and circularly transposed. The initial and boundary conditions are formulated for the case of two-circuit electric line and the adjustment of the phase angle of the voltages at the line input. In the transposition the values of the conductor parameters change by leap, which complicates the process of calculating the operating mode. The developed model and elaborated software include all these features. Based on the developed model, calculations of the operating mode of the two-circuit electric circuit and of the self-compensated line were performed. Numerical solutions have been obtained regarding the evolution of active and reactive power in the phases of the line in its various sections under regulation and non-regulation of the phase shift angle for the cases without and with the transposition of the phase conductors. The applicability of the model for studying power transfer processes in multi-conductor power lines has been demonstrated. There were obtained the numerical solutions useful for estimating the degree of mutual influence of phases on the ability to transfer power to load under the transposition of conductors.
  Keywords: electrical line, double circuit, adjustment, phase shift angle, active power, reactive power, magnitude, deviation.
2 Method of Parameters Determination for Multi-Winding Transformer Equivalent Circuit in the Form of Multi-Beam Star
Authors: Suslov V.M. Bosneaga V.A. Institute of Power Engineering Kishinau, Republic of Moldova
  Abstract: For the case of transformer with a number of windings four or more, the number of pair short-circuit impedances are more than the number of beams of the corresponding star, which makes it impossible to obtain a sufficiently correct equivalent scheme in the form of a multi-beam star without electromagnetic coupling between the elements of the beams. The scope of this paper is the elaboration of the technique for determining the elements of the equivalent circuit for the replacement of a multi-winding transformer in the form of multi-beam star with mutual electromagnetic coupling between the elements of the beams, with one magnetization branch. The scope of the article is achieved by application of the formula that connects the pair short-circuit impedance of the two windings with their total own and mutual impedance. Using the matrix pseudo-inversion procedure, a technique was developed for finding the own and mutual impedances, constituting the star's beams. The new results consist in the fact that this equivalent scheme is universal and did not depend on the specific mutual arrangement of the windings. Besides, it is possible to determine the parameters of the proposed multi-beam equivalent circuit in exact accordance with the values of the pair short-circuits impedances of the transformer and is a logical continuation of the conventional equivalent scheme of three-winding transformer. In addition, the proposed algorithm ensures the positive values of the own inductive resistances of the beams (windings).
  Keywords: equivalent scheme, multi-beam star, pair short-circuit windings impedances.
3 Sliding Mode Control Based Shunt Active Power Filter
Authors: Skuriatin Y.V., Belousov A.V., Denysevych N.A. Belgorod State Technological University named after V.G. Shukhov Belgorod, Russian Federation
  Abstract: The shunt active power filter (APF) is an effective device for reducing inactive components of the power consumed from the network. At the same time, the shunt APF being a nonlinear element is itself a source of higher harmonics, the suppression of which is imposed on the interface filter. When using a passive three-phase L-filter in this capacity, the higher voltage harmonics appear at the connection points to the network and the amplitude of these higher voltage harmonics depends on the ratio of the filter inductance and the network inductance. In this case, it is not always possible to ensure the proper quality of the voltage at the connection points to the network. In order to assess the efficiency of compensation for the inactive power components and the form of voltage at the points of connection to the network, this work considers the shunt APF with an interface three-phase LC-filter of the second order and with a sliding mode control. The synthesis of current loop control of the APF has been shown as well. A system with the shunt APF was simulated under the nonlinear unbalanced load conditions in Matlab software package. The simulation results presented in this work demonstrate the ability of the above-mentioned APF to provide radically high quality of voltage at the points of connection to the network and suppression of all inactive components of the power consumed from the network. In addition, the shunt APF has the property of slow response to disturbances from the load side.
  Keywords: active power filter, sliding mode, control, higher harmonics, semiconductor converter, inactive components of the power.
4 Electric Power Loss Minimization in Power Supply Systems for the Suburban Houses
Authors: Averbukh М.А., Zhilin Е.V., Prokopishin D.I. Belgorod State Technological University named after V.G.Shukhov. Belgorod, Russian Federation
  Abstract: The main purpose of the work is the development and improvement of methods for minimizing power losses for non-sinusoidal and asymmetric modes of operation of power supply systems for suburban houses. To achieve this goal, the analysis of existing methods and methods for reducing power losses during non-sinusoidal and asymmetric operation modes has been made. Proposition is to minimize power loss due to the installation of passive and active harmonic filters. The choice of the installation site and the type of the passive harmonic filter is made for the currents of the 3rd and 5th harmonics based on the solution of the two-criteria optimization problem. The currents of the 3rd and 5th harmonics are calculated, the method of nodal potentials, and the compensation currents are obtained, based on the solution of the first part of the optimization problem by the Lagrangian method. The solution of the problem of minimizing the reduced costs by the conjugate gradient method allows us to choose the type of the passive harmonic filter. Based on the solution of the two-criteria optimization problem, it is proposed to install resonant passive harmonic filters, on three supports, beginning with the final one, every 100 m. At the same time, the total harmonic current component, due to compensation of the 3rd and 5th harmonics, decreased to 5.49 %. The installation of four shoulder active harmonic filter on the low-voltage buses of the transformer substation allowed to reduce the total coefficient of harmonic current components to KI = 0.97%.
  Keywords: electric power losses, non-sinusoidal, asymmetry, optimization, active harmonic filter, passive harmonic filter, simulation modeling. harmonic components.
5 Research of the Changes in the Structural Group Composition of Transformer Oil During Operation
Authors: Kurakina O.E. 1, Kozlov V.K. 1, Turanova O.A. 2, Turanov A.N. 2 1Kazan State Power Engineering University, Kazan E.K. Zavoisky Physical-Technical Institute of the Kazan Scientific Center of the Russian Academy of Sciences, Kazan, Russian Federation
  Abstract: The actual issue of the electric power industry is the diagnostics of equipment to timely detection of emerging defects and their prevention. The aim of presented work is the development of a method for monitoring the state of transformer equipment based on the determination of structural-group composition of transformer oil. The goal is achieved by measuring spectra of oil in the near-IR (infrared) region. The method of investigation is approximation of obtained spectra of transformer oils on the basis of reference compounds spectra. A new method for determining the structural group composition of oils was proposed. It is distinguished by a significant simplicity and directly related to the characteristics of the molecules in comparison with the existing methods for determining the structural group composition from nomograms. Optical spectra in the near-IR range of fresh and used samples of GK transformer oil in the range of 10250-11750 cm-1 were recorded and analyzed. It was shown that during the aging transformer oil fraction of CH2-groups decreases, CH3-groups fraction increases somewhat, CH-groups fraction is significantly increased, thereby confirming the effect of increasing the proportion of aromatics in such systems reducing the amount of cycloalkanes, paraffins are most stable. This fact can be used to develop monitoring systems for power oil-filled transformers. Determination of the structural group composition of the oil and its changes during operation will allow monitoring the oil condition, the technical condition of the transformer and to determine the origin of thermal and discharge defects.
  Keywords: spectroscopy, infrared spectroscopy, transformer oil.
6 Estimation of Power Exchange through 110 kV Overhead Power Lines at the Interface of the Romanian and Moldovan Power Systems
Authors: 1Postolaty V., 1Berzan V., 1Bykova E.,1 Bosneaga V., 1Suslov V., 1Ermurachi Iu., 2Grigoras Gh., 2Gavrilas M., 2Istrate M. 1Institute of Power Engineering, Kishinau, Republic of Moldova 2Technical University "Gheorghe Asachi", Iasi, Romania
  Abstract: The purpose of this paper is to estimate the possibility of technical use of the 110 kV voltage lines (OPL) for the interconnection of the power systems of the Republic of Moldova and Romania, taking into account in the unified power system regime, which includes the power system of the CIS countries, of Moldova, Romania, Ukraine and other countries in the region. In the calculation scheme of the permanent synchronous regime of the integrated system, the interconnection zone of the Moldovan and Romanian systems was highlighted for the lines of 110 kV: Stanca-Costeşti, Ţuţora (Fai) - Ungheni and Hushi-Cioara. Transformer phase difference angle adjustment devices have been introduced in the 110 kV OPL to provide the bidirectional power shift regime. In the existing topology of electricity networks, power flows at the power system interface are directed from the Republic of Moldova to Romania. Changing the direction of the power flows is possible through the 110 kV OPL A when equipped with phase shift devices. The results of the calculations of the permanent regime have demonstrated the possibility of achieving the reciprocal power exchange regime between the interconnected power systems by adjusting the phase difference angle. It was shown the possibility of stable operation when using 110 kV overhead power lines as interconnection lines of the Moldovan and Romanian power systems. The issue of interconnection through the 110 kV lines is complex and requires an individual approach to how to achieve it.
  Keywords: interconnection, 110 kV lines, adjusting devices, phase difference angle, two-way exchange of active power, permanent mode.
7 Modes of the Reactive Power Source Controlled by the Phase-Shifting Transformer
Authors: Golub I.V., Zaitsev D.A., Tirsu M.S. Institute of Power Engineering Kishinau, Republic of Moldova
  Abstract: The purpose of this work is to develop a diagram version of the compensating device, and its control strategies using a phase-shifting transformer device. The purpose has been achieved performing a complex of research based on structural-simulation models both for the compensating device as a whole, and for the phase-shifting transformer. Based on the phase-shifting transformer model, calculation experiments in idle, short-circuit and under load conditions have been carried out. The obtained data allowed to determine the energy characteristics of the object of research and to perform analysis of its characteristics during the process of adjusting the angle of phase shift. The paper also provides the results of research in the regime's parameters issue of the device as a whole. The obtained data confirmed the functionality of the proposed reactive power source. The novelty of the work consists in the development of innovative circuit variant of controlled compensating device. Its component parts are susceptances, allowing carrying out a symmetrical adjustment of reactive power both consumed and offered to the network in a predetermined range. A control diagram for adjusting windings of a phase-shifting transformer has been proposed. The control's principle of power electronic keys provides control of the phase shift of the voltage at the output terminals of the device in the range from 0° to 60° at 15 switching positions. The proposed technical solution provides symmetrical smooth control of reactive power in a wide range at the point of connection of the device to the network.
  Keywords: reactive power source, phase-shifting transformer, susceptances, angle of phase shift, electronic power switches, control strategy.
9 Method for Burning Super-Poor Fuel Mixtures in the Combustion Chamber of the Energy Microturbine by Means of the Streamer Discharge
Authors: Grachev L.P.1, Bulat P.V.2,3, Esakov I.I.1, Bulat M.P.2, Volobuev I.A.3, Upyrev V.V.2 1Moscow Radiotechnical Institute of the Russian Academy of Sciences Moscow, Russian Federation, 2 Baltic State Technical University VOENMEH, Saint-Petersburg, Russian Federation 3 Saint-Petersburg National Research University of Information Technologies, Mechanics and Optics (ITMO University), Saint-Petersburg, Russian Federation
  Abstract: The paper considers the problem of increasing fuel efficiency and reducing emissions of gas turbine power plants. The aim of the work is to develop a method for burning extra-lean fuel mixtures. The method of ignition by a streamer high-frequency discharge was considered. The discharge was ignited in the presence of the resonator by a quasioptical beam of microwave radiation with a wavelength of 8.9 - 12.5 cm. The resonant ignition method was 20 to 100 times more energy efficient than laser and plasma ignition methods. The method combines an experiment and mathematical modeling of a streamer discharge. The result was the ignition of an extremely lean mixture with an air fuel rate of more than 30. A regime of flameless combustion was detected, when a flame wasn’t visible, but heat generation as a result of a chemical reaction has occurred. Stable combustion of the lean mixture was obtained at a flow rate of up to 30 m/s. These conditions simulated combustion in a tubular combustion chamber. A pulse with a wavelength of about 2.5 cm couldn’t create a streamer discharge and couldn’t be used for multi-point ignition. Burning front speed was 2-4 times higher than in spark ignition. Traditional low-emission combustion chambers have large dimensions and a very complex design. This makes it difficult to use them in microturbine. The application of the method described in the article makes it possible to create significantly more compact low-emission and highly economical combustion chambers for power gas turbine plants.
  Keywords: microturbine, lean burn, low-emission combustion chamber, microwave discharge, streamer discharge, non-equilibrium plasma.
10 Efficiency of the Operation of the Cogeneration Steam Turbine Plants at the Variable Heat and Electric Load Schedules
Authors: Tatarinova N.V., Suvorov D.M., Sushchikh V.M. Vyatka State University Kirov, Russian Federation
  Abstract: The urgency of the work is conditioned by the need to improve the management methods of the operation modes of the power plant by creating software tools for predicting the performance of equipment when the conditions of its operation change. In this regard, the aim of the study is to carry out a detailed calculation research of such modes using unique computational mathematical models based on the actual turbine power characteristics. Following tasks were set to achieve it: first, to calculate the limits of change for the main energy and economic indicators in real operating conditions on the example of the turbines T-50-130 of the Kirov CHP-4; secondly, to identify and describe the possible resources to increase the efficiency of the operation of the cogeneration turbine plants under conditions of variable heat and electric load schedules. The received results testify that at today's prices for energy carriers, additional power generation by the thermal cycle of CHP plants is economically feasible during all day. The low economic efficiency of some common methods of generating peak power is shown, in particular, by changing the degree of opening the sliding grids in the low-pressure section. The proposed approach can be implemented and used to optimize the operation of CHP plants in the Russian wholesale electricity and capacity market. The results of the study make it possible to conclude that most steam turbine CHP plants have significant reserves for saving fuel and energy resources, which can be realized by optimizing turbine operation modes.
  Keywords: CHP plant, cogeneration steam turbine, computational model, mathematical modeling, operating modes, optimization, power characteristics.
11 Increase of the Single-Shaft Power Microturbine Unit Capacity by Installing the Rotor on Hybrid Air Bearings
Authors: Volobuev I.A., Bulat P.V., Prodan N.V. Saint-Petersburg National Research University of Information Technologies, Mechanics and Optics (ITMO University) Saint-Petersburg, Russian Federation
  Abstract: The problem of increase of the unit power on the shaft of an energy microturbine is of current interest. One of the problems is the small single unit power of microturbines, limited by the low capacity of gas-dynamic air bearings. The problem could be solved by replacing gas-dynamic bearings with hybrid ones with a higher load-bearing capacity. Hybrid bearings use self-aligning turning segments and forcing gas into the lubricating layer. The scientific result of the work is the method of designing grooves that distributes gas, the shape of which repeats the pressure isoline on the segment’s surface when the microturbine is operating at the rated rotation speed. Method is based on solving Reynolds equations for a thin lubricating layer at the grooves. The developed system of grooves provides static stability of the segment in stationary modes and dynamic in transient modes, vibration suppression, automatic response to changes in load and speed. The calculation method allows finding the optimum thickness of the lubricant layer for a given accuracy of shaft and segment manufacture. It is shown that the load-bearing capacity is maximal when the resultant forces act on a segment, and not between segments. Numerical calculations and experiments have shown that the developed hybrid bearing has a maximum bearing capacity at a given air flow rate for the power range on the shaft from 200 kW to 2000 kW, with a load on the shaft up to 300 kg and a speed of up to 100.000 rpm.
  Keywords: microturbine power plant, pressurized gas bearing, hybrid gas bearing, gas-dynamic bearing, foil bearing.
13 Development of Efficiency Determination Methods of Automation Facilities in Sequential Areas of their Applications
Authors: Yakovlev A.I. National Technical University «Kharkov Polytechnic Institute» Kharkov, Ukraine
  Abstract: It is identified that the effect of high-quality innovations may not be over in the sphere of their direct use. The objective of the article is the development of theoretical and methodical propositions for the effect valuation of such development works according to the sphere of their final use by way of example electrotechnical means of workflow automation. The objective is attained as a result of the research carried out. It’s proved that under the valuation of the means of workflow automation for the output of the means of labor the effect valuation should be carried out for three levels: production of means of automation, their use, consumption of the means of labor, produced by the use of the means of workflow automation analyzed. Under valuation the effect of the means of labor aimed for production of objects of labor the level of manufacture of objects of labor which are produced on the certain equipment is added. The methodical recommendations for the determination of the size of needs for new items at different levels of consumption under the change in degree of qualitative characteristics with regard to stochastic nature of economic processes are introduced. These recommendations have the universal character and they enable their use under the estimation of the effect of other kinds of means of labor and objects of labor. The result of the research is the certain contribution to the improvement of the theory and practice for the determination of social and economic efficiency of innovations.
  Keywords: automation facilities, quality, effect, levels of effect calculation, final consumption, production volume, financial calculations.
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