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ELECTRIC POWER ENGINEERING
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INVESTIGATION OF ASYMETRIC MODES OF THREE-PHASE THREE LEGS PHASE SHIFTING TRANSFORMER WITH CONNECTION IN DELTA AND TWO ADDITIONAL WINDINGS
Authors: Bosneaga V.A., Suslov V.M. Power Engineering Institute of the Academy of Sciences of Moldova
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Abstract: The model of power three-phase three legs phase-shifting transformer with connection in delta and two additional windings is realized. Calculations and research of steady state asymmetric modes particularities of given transformer with such windings connection were fulfilled, taking into account the electromagnetic coupling of the windings, located on different legs. Calculations and analysis were made using as an example the distribution transformer with 10 kV high voltages, including the most characteristic steady state asymmetric modes that occur during different short circuits and asymmetric no load modes, associated with the occurrence of zero sequence magnetic flux. For the considered modes vector diagrams for currents and voltages, as well as for the relative values of magnetic fluxes in legs were constructed, which in ensemble give clear idea about their particularities. |
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Keywords: Power three-phase three legs phase-shifting transformer model, asymmetric modes, three legs magnetic circuit, connection in delta with two additional windings, zero-sequence magnetic flux.
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FINITE VOLUME METHOD FOR THE CALCULATION OF ELECTROSTATIC FIELD OF THE 3-D SPHERE WITH A CUBIC CAVITY
Authors: Patsiuk V. Institute of Power Engineering of the Academy of Sciences of Moldova
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Abstract: The paper examines an approach to finite volume method which is used to calculate the electric field in three-dimensional environment. It is formulated the problem Dirichlet with building of the computational grid on base of space partition, which is known as Delaunay triangulation with the use of Voronoi cells. It is proposed numerical algorithm for calculating the potential, electric field strength and capacitance in the 3-d sphere with cubic cavity. There are presented results of calculations of distribution in the potential space, electric field strength, and capacitance of the 3-d sphere with cubic cavity. |
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Keywords: Electric field, potential, capacitance, numerical method.
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OPERATIONAL REGIMES OF MOLDAVIAN POWER SYSTEM UNDER DEVELOPMENT OF NETWORK INTERCONNECTIONS
Authors: Zaitsev D., Golub I., Kalinin L., Tirshu M. Institute of Power Engineering of the Academy of Sciences of Moldova
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Abstract: The paper discusses and analyzes the basic steady state regimes in accordance with various strategies Moldova's accession to ENTSO-E. The four strategies have been analyzed for the accession of Moldova to the ENTSO-E: 1-without Ukraine and Transnistria; 2-without Ukraine; 3-together with Ukraine and 4- currently existing schemes. Evaluation of the proposed options: the following parameters were considered as criteria for active losses in the power system as a whole, and also in the network elements by voltage grades, coefficients of static stability of active power and voltage, the assessment of import / export of electrical power. As a result of the comparative analysis have been selected the most effective strategies for the accession of Moldova to the ENTSO-E. |
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Keywords: Moldavian energy system, ENTSO-E, power system, active power losses, import, export of electricity.
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CALCULATION OF THREE-PHASE CIRCUIT WITH ARBITRARY NUMBER OF LOADS
Authors: Berzan V. Institute of Power Engineering of the Academy of Sciences of Moldova
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Abstract: An algorithm for calculating the normal and emergency modes of three-phase circuits with distributed loads is elaborated. We propose to divide the required unknown currents into two groups: load currents are considered as principal, and currents in the other circuit branches are considered as complementary. This approach allows calculating at the first phase the load currents, and then other currents using the first Kirchhoff's law. The form of the matrix equation and rules of matrix coefficients composition for each phase depends on the number of loads connected to the phases of the circuit. Matrix equation includes 3n unknown currents. The proposed method allows calculating both the symmetric and asymmetric modes in the three-phase unbalanced network, using the same calculation algorithm. The fault modes, such as a single-phase, two-phase, three-phase and phase-to-phase short-circuits as well as the open circuits with some phase loads (simulation of the no-load mode in any node and in any phase of the circuit), could be also calculated. |
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Keywords: Matrix method, three-phase circuit, symmetrical and non-symmetrical distributed load.
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Heat and Power Engineering
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SPECIFIC HEAT CAPACITY AND THERMAL CONDUCTIVITY OF HEAT STORAGE MATERIALS BASED ON PARAFFIN, BROWN-COAL WAX AND POLYETHYLENE WAX
Authors: Snezhkin Yu., Mykhailyk V., Korinchevska T., Vorobiev L., Dekusha L. Institute of Engineering Thermophysics of National Academy of Sciences of Ukraine
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Abstract: The present paper overviews heat storage materials (HSM) with phase change based on organic compounds. They consist of paraffin, brown-coal wax and polyethylene wax. These materials are produced on an industrial scale for the foundry work. It is shown that heat capacity of HSM in the solid and liquid states can be used for heat storage in addition to the heat of phase change. The results of investigations of phase change during heating and cooling HSM are presented. The studies are carried out by differential scanning calorimetry (DSC). The measurement techniques of the specific heat capacity and the coefficient of thermal conductivity are shown. Temperature dependences of the specific heat capacity of HSM in the solid and liquid states are researched by DSC. Values of the coefficient of thermal conductivity are determined by contact stationary technique of the flat plate over the entire temperature range of the operation of heat storage system. |
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Keywords: heat storage, phase change, heat capacity, thermal conductivity.
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HEAT PUMP GAS COOLER CONTROL USING CRITERION OF MINIMUM OF EXERGY LOSSSES
Authors: Sit M.L., Sit B.M., Burciu V.I., Ioişer A.M. Institute of Power Engineering of the Academy of Sciences of Moldova
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Abstract: This paper focuses on the development of the criterion of optimality of transients of the control system, based on the minimum of exergy losses in the gas cooler of carbon dioxide heat pump. It is noted that the exergy quality criterion has a clear physical meaning, as compared with the integral quadratic criterion in which the choice of the coefficients in the integrand is not justified. Mathematic model of heat exchanger is obtained using the method of solving differential equations, without going to the irrational transfer functions. The model is reduced to transfer functions of the first and second order with the delay. The continuous temperature control system of heat pump gas cooler is considered. It is shown, that one of the versions of the control system for the minimization of the proposed criterion can be a combined control system using both the principle of the negative feedback and the principle of the invariance related to a number of disturbances affecting the processes of heat transfer in the heat exchanger. |
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Keywords: heat pump, carbon dioxide, control system, gas cooler, exergy, heat exchanger.
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SPREADING OF A FLUID JET ON THE CORRUGATED SURFACE OF THE STRUCTURED PACKING OF WET SCRUBBERS
Authors: Gorodilov A.A.*, Pushnov A.S., Berengarten M.G. Moscow State University of Mechanical Engineering (MAMI), Russian Federation
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Abstract: The new packing for wet scrubbers for cooling exhaust gases of furnaces is presented. Spreading features of the fluid jet on the corrugated surface of the proposed packing have been studied. Flow rate of the liquid flowing through slits to the opposite side of the packing element was determined. Several regimes of a fluid flow on the surface of the proposed structured packing were determined. An optimal range of rational flow rates for more intense cooling of exhaust gases is proposed. It was discovered that the range of optimum flow rates may be extended if the surface of the packing element is pre-wetted. The way of increasing the rate of effective interfacial surface area for gas-liquid contact per unit volume of the packing of the scrubber is presented. |
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Keywords: structured packing, fluid film, heat and mass transfer, wet scrubber, exhaust gases, waves.
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SOLAR ABSORBING COOLING SYSTEMS BASED ON MULTISTAGE HEAT-MASS-TRANSFER DEVICES
Authors: Doroshenko A.V., Ludnitsky K.V. Educational and Research Institute of Refrigeration, Сriotehnology and Eco-Energetics Odessa National Academy of Food Technologies
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Abstract: The article presents the worked out schematics for the alternative refrigeration systems and of air-conditioning systems, based on the use of absorbing cycle and of the sunny energy for the regeneration (renewals) of absorbent solution. We use here the cascade principle of construction of all heat-mass-transfer apparatus with variation of both the temperature level and the growth of absorbent concentration on the cascade stages. The heat-mass-transfer equipment as a part of the drying and cooling units is standardized and is executed by means of multistage monoblock compositions from poly-meric materials. The preliminary analysis of possibilities of the sunny systems in application to the tasks of cooling of environment and air-conditioning systems is carried out. |
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Keywords: solar systems, drainage of air, cooling of environments, air-conditioning systems, heat-mass-transfer apparatus, absorption, desorption, evaporated cooling.
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ANALYSIS OF EXERGY PARAMETERS OF BIOGAS POWER PLANT
Authors: Denysova A.E., Ngo Minh Hieu Odessa National Polytechnic University, Ukraine
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Abstract: The techniques of an exergy analysis concerning various circuits of biogas units, which allows replacing traditional energy resources and improving environmental conditions, has been presented. The heat schemes of biogas units were proposed, and analysis of their effectiveness was made. The comparison of different cycle parameters of various biogas units (i.e. a combustion turbine unit, a combined cycle gas turbine unit with gas discharges into the boiler and a combined cycle gas turbine with a high-temperature vapor generator and a reheating stage) was made, and the comparison of their exergy characteristics was carried out. The results of exergy analysis had demonstrated that the cycle of biogas CCGT (combined cycle gas turbine) with a reheating stage and using a high-pressure steam generator is the most effective, that can be explained by the fact that the thermal energy proportions of combustion products, accounting for the steam cycle and the gas cycle are approximately equal, comparing to conventional combined cycle gas turbine units. |
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Keywords: exergy characteristics, biogas unit, combined cycle gas turbine, high-temperature steam generator, reheat of steam.
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ENERGY EFFICIENCY
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THEORETICAL AND EXPERIMENTAL STUDIES OF ENERGY-EFFICIENT GRINDING PROCESS OF CEMENT CLINKER IN A BALL MILL
Authors: Kuznetsova M.M., Ved V.E. National University of Civil Protection, National Technical University “Kharkiv Polytechnic Institute ”, Ukraine
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Abstract: The article presents results of theoretical and experimental research of grinding process of bulk materials in a ball mill. The new method of determination of energy efficiently mode of operation of ball mills in a process of a cement clinker grinding is proposed and experimentally tested. |
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Keywords: mechanical grinding processes, ball mills, grinding process parameters, energy efficiency, coefficient of efficiency.
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ENERGY EFFICIENCY OF ELECTRIC HEATING OF REACTORS IN THE MANUFACTURE OF VARNISHES AND PAINTS
Authors: Tovajniansky L.L., Ved V.E., Gurina G.I. National Technical University “Kharkiv Polytechnic Institute”, Ukraine
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Abstract: The drawbacks of the traditional design of the heaters, which make known imperfections in manufacturing processes, realized with the use of electric heating. This determines the need for a radically new design of the heating devices. Created by high-temperature ceramics, characterized by abnormally high thermal stability and clarified the parameters that allow a certain degree change its thermal conductivity. On this basis the contact type ceramic heaters that provide thermal flow direction using different materials in the body of the heater - of high thermal conductivity, the surface facing the heat transfer and low which differs opposite sides of the heater are designed to eliminate the dissipation of heat into the surrounding space. This made it possible to equip the modern production paint industry energy efficient heating equipment with explosion and fire heating system reactors. |
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Keywords: Heaters, ceramic, viscoplasticity, heat transfer, energy efficiency.
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