

EJournal №2(34)2017
"PROBLEMS of the REGIONAL ENERGETICS"
CONTENTS
0 
ELECTROENERGETICS

1 
Impact of Measuring Part Elements of Transformer Differential Protection on Input Signal Processing
Authors: Andreev M.V., Borovikov Yu.S., Gusev A.S., Ruban N.Yu., Suvorov A.S., Sulaymanov A.O., Ufa R.A. National Research Tomsk Polytechnic University Tomsk, Russian Federation


Abstract: The electric power system (EPS) is a large, multiparameter, nonlinear and dynamic system. The problem of calculation of relay protection (RP) settings has become more urgent nowadays. The situation is exacerbated by the active implementation of renewable energy sources, FACTS, etc., which significantly change the “traditional” EPS and their operating modes. The problem can be solved by deep analysis of functioning of main elements of RP devices in the specific operating conditions and revision of coefficients used in settings calculation. That can be done using RPs detailed mathematical models and modern EPS simulators. The results of the analysis will make it possible to formulate a new methodology for setting up RP. That is a final goal. In the framework of solving this problem, the novel approach for developing RPs’ detailed mathematical models is formulated and theoretically proved. On the basis of this approach, mathematical models of the system “instrumental transformer  auxiliary transformer  analog filter” (measuring part of digital transformer differential protection) for different types of auxiliary current transformers (active and passive) and filters (Butterworth, Chebyshev, Bessel) are developed. A comparative numerical analysis of their frequency and phase responses is carried out, including taking into account the magnetization of instrumental current transformers. Summarizing, the theoretical and practical studies presented in the article allows formulating requirements for RPs’ detailed mathematical models, which will be used in the further research. 

Keywords: mathematical simulation, flow graph, settings, relay protection.
DOI: 10.5281/zenodo.1188814

2 
Processes of SelfHealing in Film Capacitors in Overload Mode
Authors: Belko V.O., Emelyanov O.A., Ivanov I.O. Peter the Great St. Petersburg Polytechnic University St. Petersburg, Russian Federation


Abstract: The advantage of modern metallized film capacitors is high reliability caused by socalled ability to selfhealing. Application of such capacitors in overload modes (at short lifetimes) can significantly improve their technical and volumetric characteristics. In spite of the fact that selfhealing had been investigated over the last decades, the existing theoretical notions and the reported experimental results did not led to the commonly accepted model of the process of selfhealing. Moreover, there is no information on film capacitors performance in overload modes in the literature. In this paper, we present the results of experimental and theoretical study on processes of selfhealing of film capacitors in overload modes. The capacitors’ testing method is proposed. The method allows to record events of selfhealing over a wide range of voltages and times. It is shown that capacitors are able to operate at voltages 46 times higher than nominal value. The capacitors’ degradation mechanism is caused by multiple selfhealing events that lead to the gradual accumulation of highly conducting zones near the breakdown channels. Model of single event of selfhealing is developed. This allows estimating the energy of selfhealing for different levels of applied voltage. It is suggested to use the value of cumulative energy of selfhealing as a parameter for estimating the rate of degradation and predicting the film capacitor’s lifetime. 

Keywords: electrical capacitors, dielectric breakdown, selfrecovery, overload modes.
DOI: 10.5281/zenodo.1188819

3 
Numerical Method for Calculating Nonstationary Processes in the Nonhomogeneous Electric Circuit. Direct and Reverse Problem
Authors: Berzan V., Patsiuk V., Rybakova G. Institute of Power Engineering of the Academy of Sciences of Moldova Chisinau, Republic of Moldova


Abstract: In the paper has been proposed the conservative numerical scheme of the calculation of dynamic processes in nonhomogeneous electric circuits until reaching the phase of the stationary process. The numerical calculation scheme ensures the accuracy of the solution also in the case of the process analysis in the circuits with significant loss and dissipation of energy. The proposed method is also robust to solve the inverse problem in the field of mathematical physics, thus restoring the initial parameters of the nonstationary process based on the knowledge of the distribution of the voltage and current waves in the circuit. The results of the numerical solution were compared with those obtained by the finite difference of time method (FDTD) and the Godunov scheme. Calculations of the nonstationary process were performed in the partially homogeneous circuit with energy losses and high variability of linear parameters. The circuit under consideration is similar to the stator winding of a high power generator. It has been demonstrated the possibility of restoring the initial excitation parameters, for example, due to partial discharges or a short pulse. It has been found that the proposed numerical method can be used for purposes of increasing the precision of diagnosing the current state of insulation of high power rotating electric machines as a result of solving the inverse problem of the propagation of current and voltage waves in the nonhomogeneous circuit. 

Keywords: nonhomogeneous circuits, distributed, variability of linear parameters, numerical method, losses, solves the telegraph equations, diagnostic.
DOI: 10.5281/zenodo.1188832

4 
Statistical Analysis of Partial Discharge Characteristics in Transformer Oil at the “PointPlane” Electrode at Alternating Voltage
Authors: Korobeynikov S.M., Bychkov A.L., Chimitova E.V., Demin V.A. Novosibirsk State Technical University Novosibirsk, Russian Federation


Abstract: In this paper, we consider the problems related to measuring and analyzing the characteristics of partial discharges which are the main instrument for oilfilled highvoltage electrical equipment diagnosing. The experiments on recording of partial discharges in transformer oil have been carried out in the “pointplane” electrode system at alternating current. The instantaneous voltage and the apparent charge have been measured depending on the rootmeansquare voltage and the phase angle of partial discharges. This paper aimes at carrying out a statistical analysis of the obtained experimental results, in particular, the construction of a parametric probabilistic model of the dependence of the partial discharge inception voltage distribution on the value of the rootmeansquare voltage. It differs from usual discharges which occur in liquid dielectric materials in case of sharp inhomogeneous electrode system. It has been suggested that discharges of a different type are the discharges in gas bubbles that occur when partial discharges in a liquid emerge. This assumption is confirmed by the fact that the number of such discharges increases with increasing the rootmeansquare voltage value. It is the main novelty of this paper. This corresponds to the nature of the occurrence of such discharges. After rejecting the observations corresponding to discharges in gas bubbles, a parametric probabilistic model has been constructed. The model obtained makes it possible to determine the probability of partial discharge occurrence in a liquid at a given value of the instantaneous voltage depending on the rootmeansquare voltage. 

Keywords: partial discharge, transformer oil, bubble, energy, phase, apparent charge, cavity, statistical analysis, probability, distribution function.
DOI: 10.5281/zenodo.1188834

5 
Mathematical Model of Electromagnetic Transient for Superconducting ShortCircuit Current Limiter
Authors: Manusov V.Z., Pavlyuchenko D.A., Miheev P.A. Novosibirsk State Technical University Novosibirsk, Russian Federation


Abstract: At present on the basis of significant achievements in the field of hightemperature superconductivity more and more applications of this phenomenon appear in the electric power industry, in particular superconducting current limiters. To investigate current limitation process in electrical networks containing superconducting current limiter it is extremely important to evaluate the electrodynamic and thermal effects of the shortcircuit current at any time. The existing superconducting current limiters mathematical models don't consider the inertia of the device transition from the superconducting state to the conducting one. It is necessary to develop the mathematical model for the electromagnetic transient process that can adequately simulate the superconducting current limiter at any time point, taking into account its parameters in the normal and emergency modes and also to describe these parameters dynamics during the process of current limitation. The proposed mathematical model allows to simulate the changing inertia of the superconducting current limiter inductive reactance, to analytically describe the electromagnetic transient process, and also to evaluate the electrodynamic and thermal effects of shortcircuit current in networks with superconducting current limiter. The important feature of the mathematical model is the consideration of the increase rate (inertia) of the inductive reactance with respect to the external network. Also the model allows taking into account the initial and final values of the inductance of a superconducting current limiter before and after the end of the electromagnetic transient respectively. 

Keywords: hightemperature superconductivity, superconducting inductive current limiter, electromagnetic transient, short circuit currents.
DOI: 10.5281/zenodo.1188836

6 
Analysis of Electrical Safety Conditions Taking into Account Soil Conductivity Determined on the Basis of Fuzzy Logic
Authors: Manusov V.Z. 1, Zaytseva N.M. 2 1Novosibirsk State Technical University, Novosibirsk, Russian Federation, 2Innovative Eurasian University, Pavlodar, Republic of Kazakhstan


Abstract: The goal of this work is to prove a possibility of determining soil parameters that influence its conductivity being the basis of grounding, step voltage and touch voltage calculation. This in its turn increases the safety level of electric equipment operation. The article is devoted to development of new, no conventional models of soil conductivity using the theory of fuzzy sets and fuzzy logic. The description of the solution includes the following sections: fuzzy models of specific electrical resistance of different soil types depending on their salinity and moisture content at positive temperatures; dependences between ρ and negative temperature values for different types of soil and different moisture contents; fuzzy climatic soil models for a specific location in order to determine soil ρ deep into the earth throughout the year. Uncertainty of soil properties is a reason why calculations of grounding devices are very liberal with plenty to spare, and calculations of touch voltages and step voltages in the period of active snow melting or abundant rains give erroneous results. Since soil parameters are described by linguistic variables: humidity, salinity, and temperature etc., soil layers should be considered as overlapping fuzzy sets. Membership functions of the main components of the “soil conductivity” concept were formed on this basis. The new scientific result we obtained makes it possible to formalize natural language of the experts in the field of climatic factors influence on soil resistivity in order to represent this information with the help of computer algorithms for optimum design of energy supply security and step voltage and touch voltage calculation. 

Keywords: electrical safety specific, soil resistivity, modeling, fuzzy logic, membership functions, multiparameter dependence, touch voltage, stepbystep pressure.
DOI: 10.5281/zenodo.1188838

7 
HEAT POWER ENGINEERING

8 
Modeling of Frost Formation on FinandTube Surface of Air Cooler
Authors: Lagutin A. E., Kozachenko I. S., Zheliba U. A. Educational and Scientific Institute of Refrigeration Cryotechnologies Ecology and Energetic of the Odessa National Academy of Food Technologies Odessa, Ukraine


Abstract: The aim of this paper is to present a new method of modeling of frost predicting process on the surface of the fineandtube air cooler. The advantage in comparison with existing similar models is a significant reduction in the number of operations performed to determine the optimal geometrical parameters of the heat exchange surface. In this paper presented structural scheme of mathematical model, described benefits and usage area. The study present the results of numerical modeling for ammonia air cooler with staggered tube bank and injection molding round fins. The model tested on range of values: coolant temperature (t0= –20, –27°C), temperature difference between coolant and ambient air (θ=7, 10°C), relative humidity (φ=90…98%), air velocity (w=3, 5, 7 m/s). Fin spacing permitted δ=10mm. The result of study shows the effect of the above parameters on the frost formation dynamic and frost distribution on tube rows along air flow. Presented program application allows providing improving of finand tube air cooler due to fin spacing optimization. Consequently heat exchange surface redistribute and increase on the area of maximum efficiency. 

Keywords: mathematical model, frost formation, prediction, air cooler, optimization.
DOI: 10.5281/zenodo.1188844

9 
Numerical Investigation of the LowCaloric Gas Burning Process in a Bottom Burner
Authors: Redko A.,1, Redko I.2 1Kharkiv National University of Construction and Architecture 2O.M. Beketov National University of Urban Economy in Kharkiv Kharkiv, Ukraine


Abstract: The use of lowgrade gases in the fuel and energy balance of enterprises makes it possible to increase the energy efficiency of technological processes. The volumes of lowgrade gases (blast furnace and coke oven gases, synthesis gas of coal gasification processes, biogas, coal gas, etc.) that are utilized more significant in technological processes but their calorific value are low. At the same time artificial gases contain ballast gaseous (СО2, H2O) and mechanical impurities that are harmful gas impurities. Their use requires technological preparation. Thus coal methane is characterized of high humidity, coal dust and drip moisture, variable composition. Thus was effective burning of coal methane it is required the development of constructive and regime measures that ensure a stable and complete burning of gaseous fuels. In this article it is presented the results of computer simulation of a stationary turbulent diffusion flame in a restricted space in the process of burning natural gas and coal methane in a bottom burner. The calculation results contain the fields of gear, temperature, concentration of CH4‚ CO‚ H2O‚ CO2 and nitrogen oxides. The structural elements of the flame (recirculation zone, hot "dome", mixing layer and far trace) are determined. It has been established that complete combustion of coal methane in a modified bottom burner is ensured and the numerical values of nitrogen oxide concentrations in the flame are consistent with the literature data. 

Keywords: bottom burner, coal methane, diffusion flame, nitrogen oxides.
DOI: 10.5281/zenodo.1188850

10 
Estimation of the Influence of Operational Factors on the Oxygen Content of the Turbine Condensate at the Outlet from the Condenser of Steam Turbine
Authors: Shempelev A. G., Iglin P. V., Sushchikh V. M. Federal State Budgetary Educational Institution of Higher Education «Vyatka State University», Kirov, Russian Federation


Abstract: The aim of the article is to analyze the influence of different factors on the oxygen content in the condensate using the example of the condenser of the steam turbine unit T110/120130. For the first time, the authors of the article analyze in details how the basic parameters of the condenser's operation (the condenser heat load, the flow and temperature of the cooling water, the air inflow in the condenser, the condition of the heat exchange surface) influence the oxygen content of the condensate. The authors come to the conclusion that with standard air inflow in the vacuum system, the equilibrium oxygen content, which corresponds to the norms in the condensate at the condenser outlet, is only possible in its operation modes when the steam flow to the condenser is more than 50% of the nominal flow and cooling water temperatures are equal to or greater than calculated for this type of condenser. The conclusions are confirmed by the experimental material. The results of the research are the basis for the development of measures aimed to increase the deaerating capacity of condensers depending on specific operating conditions. 

Keywords: condenser, aggressive gases, oxygen, deaeration, steam turbine plant, mathematical model.
DOI: 10.5281/zenodo.1188854

11 
MultiTemperature Heat Pump with Cascade Compressor Connection
Authors: Sit M.L.1, Starikov A.V.2, Zhuravleov A.A.1, Timchenko D.V.1 Institute of Power Engineering of the Academy of Sciences of Moldova1, Kishinau, Republic of Moldova Samara State Technical University2, Samara, Russian Federation


Abstract: Object of the study is a multifunctional heat pump with several evaporators and condensers designed for simultaneous provision of technological processes with heat and cold. The aim of the work is the development and study of the scheme for this type of heat pumps, which ensures minimum irreversibility in the "compressorgas coolers" chain, without the use of adjustable ejectors installed after evaporators and used as flow mixers. Obtained technical solution ensures the stabilization of heat pump coefficient of performance (COP) and prescribed thermal regimes of heat exchangers at a variable flow rate of the refrigerant. The novelty of the elaboration is inclusion of a compressor of the first stage with a serially connected intermediate heat exchanger and a control valve that are located before the compressor inlet of the second stage of the heat pump, which allows establishing rational pressure after the first stage of compressors. A scheme for the temperature regulation at the inlet of first stage compressors by regulating the flow through the primary circuits of the recuperative heat exchangers has been proposed. Control system of first stage compressor allows providing the required modes of operation of the heat pump. Exergetic analysis of the sections of the hydraulic circuit of heat pump located between the evaporators and gas coolers established that reduction of irreversible losses in the heat pump could be ensured due to optimal choice of the superheat value of gas after the evaporators. 

Keywords: heat pump, simulation, control system, flow rate control, compressor, irreversibility.
DOI: 10.5281/zenodo.1189318

12 
Determining the Conditions for the Hydraulic Impacts Emergence at Hydraulic Systems
Authors: Mazurenko A.S., Skalozubov V.I., Chulkin O.A. , Pirkovskiy D.S., Kozlov I.L. Odessa National Polytechnic University Odessa, Ukraine


Abstract: This research aim is to develop a method for modeling the conditions for the critical hydraulic impacts emergence on thermal and nuclear power plants’ pipeline systems pressure pumps departing from the general provisions of the heat and hydrodynamic instability theory. On the developed method basis, the conditions giving rise to the reliabilitycritical hydraulic impacts emergence on pumps for the thermal and nuclear power plants’ typical pipeline system have been determined. With the flow characteristic minimum allowable (critical) sensitivity, the flow velocity fluctuations amplitude reaches critical values at which the pumps working elements’ failure occurs. The critical hydraulic impacts emergence corresponds to the transition of the vibrational heathydrodynamic instability into an aperiodic one. As research revealed, a highly promising approach as to the preventing the critical hydraulic impacts related to the foreground use of pumps having the most sensitive consumption (at supply network) performance (while other technical characteristics corresponding to that parameter). The research novelty refers to the suggested method elaborated by the authors’ team, which, in contrast to traditional approaches, is efficient in determining the pump hydraulic impact occurrence conditions when the vibrational heathydrodynamic instability transition to the aperiodic instability. 

Keywords: critical hydraulic impact, pressure pump, pipeline system.
DOI: 10.5281/zenodo.1189324

13 
Determination of the Quantitative Characteristics of the Engine of a Household Power Plant when Using Generator Gas as an Alternative Fuel
Authors: Plotnikov S. A., Buzikov Sh. V., Kartashevich A. N., Zubakin A. S. Federal state budgetary educational institution of higher professional education "Vyatka state University" Kirov, Russian Federation


Abstract: The relevance of the study is due to the need to study the feasibility of replacing traditional fuel with alternative types (generator gas) when using a household power plant. The purpose of the study is to obtain the value of a smalldisplacement engine GG2700 with a working volume of 1563 cm3 when it works on commercial fuel (gasoline) and generator gas. For this purpose, the authors developed an experimental setup on the basis of a smallsized household power station with fixation of variable parameters on a personal computer and a graphical representation of the measurement results. The records of the indicator diagrams allowed determining the burning time of various fuels. As a result, for the first time, there were obtained quantitative indicators of fuel efficiency and toxicity of exhaust gases of the smalldisplacement engine GG2700 with a working volume of 1563 cm3 when using commercial fuel (gasoline) and generator gas. The analysis of the data showed an increase in the specific consumption of generator gas in comparison with gasoline from 34.6% to 50.4% and a decrease in the content of toxic components in the exhaust gases: carbon monoxide (CO) – in 1.05 ... 1.25 times, hydrocarbons (CxHy )  in 1,1 ... 1,39 times, nitrogen oxides (NOх)  in 3,9 ... 5,7 times. The obtained results prove the expediency of using generator gas as an alternative fuel for the engine of a household power plant. 

Keywords: engine, power system, test bench, diesel, gaseous fuel, producer gas, alternative fuels.
DOI: 10.5281/zenodo.1189326

14 
Increase of Ship Power Plants GasAir Cooler Efficiency
Authors: Dymo B.V.1, Voloshyn A.Y.2, Yepifanov A.E.1, Kuznetsov V.V.1 1Admiral Makarov National University of Shipbuilding 2State Research & Design Shipbuilding Center Mykolaiv, Ukraine


Abstract: Results of theoretical and experimental study of a gasair cooler used to reduce the temperature of the exhaust gases of engines and boilers of ship power plants and the heat radiation of the chimney are presented in this paper. A Computational Fluid Dynamic (CFD) model of the gasair cooler designed as an inhomogeneous ejector with a nozzle apparatus was developed. As a result of numerical simulation, the fields of temperature, pressure and velocity distributions along the gasair cooler crosssections were obtained. An experimental study of working model of the gasair cooler at a scale of 1:5 was carried out. In the selfsimilarity region, characterized by Reynolds numbers (3.03.8)•105, the values of the resistance coefficient of the gasair cooler model in the confidence interval ± 4.4 % fit on the line ςм = 2.52. A comparative analysis of the characteristics of gasair flow, obtained during numerical simulation, with the results of thermal testing of working model of the gasair cooler is given. The error in calculating of gasair mixture temperature at the exit section of the gasair cooler at 100 % load is 4.6 %. The CFDmodeling allows making calculations and optimization of new designs of the gasair cooler at the design stage without carrying out thermal engineering tests both in the main and partial modes of operation. 

Keywords: gasair cooler, exhaust gases, mixing, selfsimilarity, experimental research, CFDmodeling.
DOI: 10.5281/zenodo.1189332

15 
RENEWABLE ENERGY SOURCES

16 
Modeling the Mixing of Components in a Rotary Kiln While Burning Municipal Waste to Ensure Rational Use of Energy
Authors: Krot O.P.,1 Rovenskyi O.I.2 1Kharkov National University of Civil Engineering and Architecture 2North–East Scientific Center of the National Academy of Sciences of Ukraine Kharkov, Ukraine


Abstract: In Ukraine municipal waste is collected and delivered to a landfill. Municipal waste can be used as fuel to generate additional heat and electricity. The primary advantages of incineration are that waste volumes are reduced by an estimated, and the need for land and landfill space is greatly reduced. The plant has been designed by North–East Scientific Center using a thermocatalytic waste gas purification system with highly efficient dioxins reduction and heat energy recovery system. The technology of waste neutralization includes: a rotary kiln, an afterburner chamber, a new catalytic technologies for the treatment, a heat exchanger for heating combustion air, supply of alkali solution into the gasescape channel, a carbon fiber adsorption filter. The organization of the right process of waste mixing in the rotary kiln allows increasing the efficiency of combustion, to equalize the combustion temperatures of the components of the waste and the completeness of the burning out of hazardous substances, which reduces the risk of their getting into the ash. The goal of the research is to build an analytical mathematical model of mixing of components in a rotary kiln. The model is based on the mathematical apparatus of Markov chains. The model allows to determine the concentration of the key component in any elementary volume of material circulating in the rotary kiln at any time and to calculate the statistical characteristics of the homogeneity of the mixture. The model will be used to research new designs of the equipment with rotary kilns. 

Keywords: waste incineration, rotary kiln, Markov chain, waste to energy, Energy efficiency, heat treatment.
DOI: 10.5281/zenodo.1189355

17 
Statistical analysis of energy indices of solar radiation (Based on the data of Tokmak Solar Power Station)
Authors: Kuznetsov N., Institute of Renewable Energy, National Academy of Sciences of Ukraine Kyiv, Ukraine Lysenko O., Tavria State Agrotechnological University Melitopol, Ukraine


Abstract: Average daily or monthly data of solar radiation are often used in statistical analysis and in development of mathematical models for predicting energy generation. However, this can have a negative impact on the accuracy of forecasting. The authors carried out the statistical analysis of solar radiation based on the data obtained from the Tokmak SPS of the Zaporizhia region, Ukraine during 2016. The data were collected with a 30minute interval in measurement. The analysis indicates close values of winter and summer insulation indices (direct and scattered), where the difference is approximately double. The mathematical expectation of the power surges is close to zero, and their distribution has signs of symmetry. The results of actual data calculation indicate that values of the elementary power surges of the SPS are a bit higher than the normal distribution calculated. Thus, the actual distribution corresponds to the normal one in the parameter of symmetry, but does not correspond to the parameters of kurtosis. If the time range is doubled from 30 minutes to 1 hour, the range of power changes slightly increases. In addition, the analysis of meteorological data showed that the probability of a prolonged growth or decline in power is not high, i.e. a change in power as a random process can be considered close to the stationary one. The performed analysis estimates the power supply possibilities for the region’s consumers by the solar power plant, and creates a mathematical model for operation of the combined energy system that uses solar energy. 

Keywords: solar radiation, power surges, statistical analysis of meteorological data, renewable energy sources.
DOI: 10.5281/zenodo.1189379

18 
ENERGY ECONOMICS

19 
Economic and Energy Security Impact of Interconnection Power Systems of Republic of Moldova and Western Europe
Authors: Comendant I. Institute of Power Engineering of Academy of Science of The R. of Moldova Chisinau, Republic of Moldova


Abstract: It is known, by implementing asynchronous interconnections with ENTSOE () the Republic of Moldova expects to reach the goals it has tended for more than 25 years: to have both a competitive electricity market and a decent energy security. In this paper, we try to evaluate whether this scenario can achieve those objectives. Based on a model created, which considers all possible power sources development scenarios and which permit to determine the tariffs applied to final consumers based on the costs the scenarios bear, it was shown that the implementation of asynchronous scenario, most likely will not be recovered economically, will not lead to creation of energy flows eastwest and vice versa from which the country stakes to obtain benefits and, will not get expected balancing power from the west to cover the appropriate needs in the wind and solar energy sources promotion projects. Thus, asynchronous project becomes only one to achieve the objective of energy security. But for this it is expected to pay too much, about 0.5 billion USD. The article suggests that this goal may be achieved by a scenario that would require much smaller financing and that justifies an investment portfolio in which Moldova share would not exceed 2030% of total investments asynchronous scenario needs for implementation. The originality of the results consists in: establishing the price difference of the competitive power markets that justifies economically the implementation of the asynchronous scenario of connecting the Moldovan power system to the Romanian one; The use of average tariffs applied to endusers  as a method to achieve the objective. 

Keywords: power system, scenarios, electricity market, investment recovery, energy security.
DOI: 10.5281/zenodo.1189432

20 
JUBILEE

21 
80th Anniversary of the academician V.M. Postolaty!

22 
70th Anniversary of Dr.Habilitat Valentin Oleschuk




