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ELECTROENERGETICS
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SIMULATION OF THE TRANSITIONAL REGIME OF THE MOLDOVAN POWER UNDER STATIC STABILITY
Authors: Vitaly Postolaty, Irina GolubInstitute of Power Engineering of Academy of Sciences of Moldova
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Abstract: The paper presents the outcome of the Moldovan power system static stability modeling and analysis, considering the operation in parallel with the Ukrainian power system and the established operation regimes. The analysis includes verification of the reserve of static stability and definition of the static stability limits for a given operation mode, and the determination of the power system stability domain of the controlled system nodes. Parameters used for the analysis are the active power flows via controlled sections and the voltage levels at the controlled system nodes. Two options of Moldovan power system scheme are considered: a single-circuit transit Dniester HPP - Balti - Straseni – Chisinau 330kV and a double-circuit transit. Studies have shown that the implementation of the double-circuit transit would lead to better static stability parameters and lower power system losses. The analysis has been carried out based on the power system stability. |
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Keywords: static stability, energy system regim.
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DISTRIBUTION ANALYSIS OF THE POWER SYSTEMS FAULTS
Authors: V.S. PopescuState Agrarian University of Moldova
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Abstract: In our days the significant number of power systems faults is taking place in power grids, being caused by various random factors. An in-depth analysis of these factors and of their distribution is needed in order to provide reliable forecasts and the desired degree of the power grids stability. The current study is aimed at assessing the distribution of the power system faults and defining factors that causes these faults, having a direct impact on the power grids operation. process. |
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Keywords: random faults, reliability indicators, influencing factors, power grids, distribution of faults.
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SYNCHRONOUS PWM CONTROL OF SYMMETRICAL DUAL THREE-PHASE DRIVE IN THE OVERMODULATION ZONE
Authors: V. Oleschuk, A. SizovInstitute of Power Engineering of the Academy of Sciences of Moldova Alexandr Sizov ,
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Abstract: . The analysis of operation of symmetrical six-phase (dual three-phase) ac drive system (which is a promising solution for the medium-power and high-power applications) with synchronized pulse-width modulation (PWM) during overmodulation has been performed. The induction machine of this system topology has two sets of windings spatially shifted by 60 electrical degrees with isolated neutral points, which are connected with two standard three-phase inverters. Algorithms of synchronized PWM provide continuous synchronization of the phase voltage of the system in the zone of overmodulation. Simulation results are given for dual three-phase systems with two discontinuous versions of synchronized PWM, and with combined synchronized scheme of pulsewidth modulation. |
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Keywords: symmetric six-phase induction motor, converter control, modulation strategy, phase voltage synchronization.
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MODELING OF OVER VOLTAGES IN 10 kV CABLE DISTRIBUTION NETWORK AT SINGLE-PHASE FAULTS TO GROUND WITH ARC
Authors: V.A. Bosneaga, V.M. Postolaty, V.M. Suslov (Institut of Power Engineering of the ASM), A.N. Klinduhov (state company „Dnestrenergo”)
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Abstract: The aim of the work is to study surges in the 10 kV cable distribution network in the presence (occurrence) of the intermittent arc, which could lead to significant damages in the network, including the failure of distribution transformers. Surge analysis is performed for single-phase to ground faults in the network. Surges’ levels in the 10 kV distribution network were determined for single-phase-to-ground faults and for HV winding inter-turn fault in the 10/0,4 kV distribution transformer. It is shown, that the maximum surge values are determined mainly by the functioning of installed surge arresters and are not directly related to the presence of the arc elimination reactor, which acts mainly as the current limiter in the place of short-circuit and only smoothes high-frequency oscillations. The elaborated model may be used for analyses of surges in the cable network, caused by short circuits via (due to) the intermittent arc. |
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Keywords: model, cable network, single-phase short-circuits, intermittent arc, transformer winding internal short-circuits.
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EXPERIENCE OF UTILIZATION OF CAPACITY BANKS AND SCHEMES OF FREQUENCY REGULATION IN MUNICIPAL CENTRALIZED HEATING SYSTEM OF CHISINAU
Authors: CHERNEI M., IARMOLICH A., LEU V.Stock Company „Termocom”, Kishinau
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Abstract: The current paper provides a brief summary of the district heating system of the municipality Chisinau, including heat power sources, heat distribution network, production and consumption development over the past two decades and other data. Also, the priority investment projects realized by JSC "Termocom" are being presented. The company had implemented an automated monitoring system for the heat power production, transportation and distribution. For many years, the company used bellows pipes with polyurethane insulation, ball valves and plate heat exchangers. 14 out of 21 district heating boiler stations were upgraded 10 were completely automated having as a result no further need in full-time duty personnel there. The experience gained in the implementation of capacity banks and frequency inverters, summarizing the benefits and achieved results, is also presented in the current paper. It is to be underlined that in 2011 the company achieved decrease in electricity consumption by about 30% in comparison with 2005. |
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Keywords: centralized heating system, capacity bank, schemes of frequency regulation.
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HEAT AND POWER ENGINEERING
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THE USE OF POROUS CERAMICS FOR EVAPORATIVE AND EVAPORATIVE – VAPOR –COMPRESSION SYSTEMS
Authors: Cheban D.N., Doroshenko A.V.Educational and Research Institute of Refrigeration, Сriotehnology and Eco-EnergeticsOdessa National Academy of Food Technologies
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Abstract: The use of natural evaporative cooling is one of technical solutions of problem of energy efficiency in air conditioning systems. The use of evaporative cooling in the first combined cooling stage allows reducing the load on the condenser of the cooling machine due to reducing of the condensing temperature. This combination allows the use of this type of system in any climatic conditions, including regions with small water resources. Multi-porous ceramic structure is used in evaporative air coolers and water coolers in this case. The objective of this paper is to show advantages of the using of porous ceramic as a working attachment, and to show advantages of the proposed scheme of compression-evaporation systems in comparison with standard vapor compression systems. Experimental research proved the fact, that in the film mode cooling efficiency of air flow is between EA=0,6÷0,7 and is slightly dependent of water flow. For countries with hot and dry climate where reserves of water are limited, it is recommended to use cyclical regime with EA≈0,65 value, or to use channel regime with a value of EA≈0,55. This leads to considerable energy savings. It has been determined, that combined air conditioning system is completely closed on the consumption of water at the parameters of the outside air equal to tA =32ºC and XA>13g/kg (in system with direct evaporative cooling machine), and tA=32ºC and XA>12g/kg (in system with indirect evaporative cooling machine). With these parameters, the cost of water in evaporative cooling stage can be fully compensated by condensate from the evaporator chiller. |
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Keywords: evaporative cooling, porous ceramics, combined refrigeration system.
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HEAT EXCHANGE AND AERODYNAMICS OF THE COMBINED TUBING BUNDLES WITH CROSS INCLINED FINS
Authors: Knyazyuk V. I., Lagutin A. E., Stoyanov P. F.Educational and Scientific Institute of Refrigeration Cryotechnologies Ecology and Energetic Odessa National Academy of Food Technologies
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Abstract: The paper presents results of experimental research and analyses air-side thermal performance of combined tube bundles with cross inclined fins. The empirical correlations for heat transfer and flow friction of tubes with inclined fins at different orientation finned tubes relatively of air flow are presented. The errors of thermal and aerodynamic tests are 3-5% and 9.2%, respectively. The proposed correlations describe an experimental data with a coefficient of determination about 0.979-0.998. The impact of tubes arrangement in a bundle on energy performance of heat exchanger were analyzed using complete and local heat modeling methods at a stationary heat flux. Experimental research indicates that efficiency of inclined fins can be calculated by using the equation for cross rectangular fins with average deviation of ±5 %. |
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Keywords: heat transfer, aerodynamics, finned tube, tube bundle, energy efficiency.
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AUTOMATIC CONTROL SYSTEM FOR THE HEAT PUMP EMBEDDED IN THE MILK PASTEURIZATION AND COOLING INSTALLATION, part II
Authors: Sit M.L., Sit B.M.Institute of Power Engineering of the Academy of Sciences of Moldova
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Abstract: The goal of the present work is to elaborate the scheme of the disturbance compensation system, which is influencing the level of refrigerant consumption in evaporators and gas coolers of the heat pump embedded in the milk pasteurization and cooling installation, as well as, to design the automatic control system for the heat-exchanger with two output parameters – the water temperature at the outlet of the primary and secondary heat-carrying agent circuits by adjusting the consumption level in the secondary heat-carrying agent circuit and by adjusting the heat exchange surface area. System structures are based on principles of the coordinated control and the multidimensional systems control. The proposed structural scheme of the coordinated system for control of the consumption in evaporators, both water heating and cooling segments, is more accurate in transient processes than alternative systems of non-integrated control of the working agent consumption in each evaporator. The heat exchanger control system with two controls controlling segments (controlling the heat exchange surface area and controlling the consumption level in the secondary coolant circuit) has proven to have good transient characteristics. |
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Keywords: milk pasteurization and cooling installation, control system, carbon dioxide.
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ENERGY PARADOXES IN ECONOMICS
Authors: Oleg BURDO Odessa National Academy of Food Technologies
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Abstract: The analysis of the energy situation in the world and in the Post-Soviet area was carried out. The main focus was on the energy problems in Ukraine. The current paper presents existing energy sector paradoxes. Issues of the comfort level and of the natural environment dependence on the energy resources consumption are being discussed. The relationship between the human life quality level and the level of energy consumption is shown. The analysis of the energy resources distribution in the world is provided. The likely review of the energy re-sources market is forecasted. State energy policies and strategies are being compared. The high profitability of the centralized energy supply management in municipalities is being underlined. Issues regarding the scientific poten-tial and the energy management development are considered. The compliance of energy resource prices with the level of thermal protection of buildings and with energy projects investment principles is being analyzed. The importance of the market-based choice of energy resources considering energy company mergers and decision power concentration is presented. The compliance between the energy policy of Ukraine and the obligations resulting from gas contract with Russia is being discussed. The role of energy in the agricultural processing chain is analyzed. |
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Keywords: energy resources, centralized management of energy supply.
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INFORMATION TECHNOLOGIES
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FORMAL CONDITIONS OF STEGANOGRAPHIC METHOD’S SUSTAINABILITY TO COMPRESSION ATTACKS AND THEIR IMPLEMENTATION IN NEW STEGANOGRAPHIC ALGORITHM
Authors: Kobozeva A.A., Melnik M.A.Odessa National Polytechnic University, Ukraine
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Abstract: The analysis of the current development and operation of information systems provided sufficient data for definition of sufficient conditions for a formal presentation steganographic transformation as a set of perturbations of singular values of the matrices (corresponding to the container) those ensure insensitivity (or low sensitivity) of formed steganographic message to compression attacks. The obtained sufficient conditions are independent of the confidential information that embedded to container (spatial or frequency) and specificity of stegano algorithm. The main mathematical tool is a matrix analysis. As the container is considered a digital image. New steganographic algorithm is developed and based on sufficient conditions that received in paper. The algorithm is stable to compression, including low compression rate. The results of computational experiments are presented. |
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Keywords: steganographic algorithm, compression attacks, digital image, singular values, matrix.
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