117 research outputs found

    Расчет емкости для работы мини-энергокомплекса на основе асинхронного генератора в автономном режиме

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    The article present the analysis of the operation of the mini-energy complex (MEC) based on alternative energy sources. An asynchronous generator (AG) was taken as energy source. The IEC operates independently with standard power parameters without the use of a frequency converter. To operate independently, AG needs a source of reactive excitation current. Based on the calculations carried out and the results obtained with the use of the experimental facility,the operating conditions of the MEC with standard parameters of electricity under varying load have been analyzed. A characteristic feature of the autonomous MEC is the commensurate capacity of the generating device and consumers. Therefore, any power consumer on/off leads both to significant changes of local electric system parameters and affects the operation of the generator itself. In this article, the main attention is paid to the influence of three-phase motor load on stable AG operation. When the MEC operates independently, reliable self-excitation of the asynchronous generator and the start-up of consumers whose power is commensurate with the generating unit must be ensured. It is also necessary to ensure the maintenance of voltage stability, the possibility of automatic operation of the generating unit, and the preservation of its integrity in emergency modes. Thus, for stable MEC-based AG operation the nature of the load should be taken take into account, the parameters of the of the local grid should be known as well as the exact availability of consumers and their characteristics, and also equivalent circuit parameters of asynchronous motors. In addition, it is necessary to accurately calculate the capacity when changing the parameters of the electrical system, so as not to lose the self-excitation of the asynchronous generator, which is equivalent to disconnecting the entire load of the generator and causes a sharp increase in speed. To solve these problems, it is necessary to create a high-speed MEC control system.В статье анализируется работа мини-энергокомплекса (МЭК) на базе альтернативных источников энергии. В качестве генерирующего устройства принят асинхронный генератор (АГ). МЭК работает в автономном режиме со стандартными параметрами электроэнергии без использования преобразователя частоты. Для работы в автономном режиме АГ необходим источник реактивного тока возбуждения. На основе проведенных расчетов и результатов, полученных с помощью экспериментальной установки, анализируются условия работы МЭК со стандартными параметрами электроэнергии при изменяющейся нагрузке. Характерной особенностью автономного МЭК является соизмеримость мощностей генерирующего устройства и потребителей. Включение и отключение любого потребителя существенно изменяют параметры локальной электрической системы и влияют на работу самого генератора. В данной статье основное внимание уделено влиянию трехфазной двигательной нагрузки на устойчивую работу АГ. При функционировании МЭК в автономном режиме должны быть обеспечены надежное самовозбуждение асинхронного генератора и запуск потребителей, мощность которых соизмерима с генерирующей установкой. Также необходимо обеспечить поддержку стабильности напряжения, возможность автоматической работы генерирующей установки, сохранение ее целостности в аварийных режимах. Таким образом, для устойчивой работы автономного МЭК на основе асинхронного генератора следует учитывать характер нагрузки, знать параметры локальной сети, точное наличие потребителей и их характеристики, параметры схем замещения асинхронных двигателей. Кроме того, необходим точный расчет емкости при изменении параметров электрической системы, чтобы не потерять самовозбуждение АГ, что равнозначно отключению всей нагрузки генератора и ведет к резкому увеличению скорости. Для решения данных проблем требуется создание быстродействующей системы управления МЭК

    Silver(I) sulfide: Ag2S Heat capacity from 5 to 1000 K, thermodynamic properties, and transitions

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    The heat capacity of Ag2S has been measured by adiabatic-shield calorimetry from 5 to 1000 K. The heat capacity increases regularly up to about 445 K where the pre-transitional contribution causes rapidly rising values. The [alpha]-to-[beta] transition of Ag2S occurs in the range 449.3 to 451.3 K, depending upon previous history of the sample. The enthalpy of transition [Delta]trsHm = (4058+/-26) J[middle dot]mol-1. A slightly decreasing heat capacity is observed for [beta]-Ag2S from 88.1 J[middle dot]K-1[middle dot]mol-1 at 460 K to 85.0 J[middle dot]K-1[middle dot]mol-1 at 850 K with a minimum of 84.6 J[middle dot]K-1[middle dot]mol-1 at 750 K. The transition of [beta]-Ag2S to [gamma]-Ag2S occurs at about 865 K with [Delta]trsHm = (784+/-5) J[middle dot]mol-1. Thermodynamic functions have been evaluated and the values of Cp,m, "Smo(T)-Smo(0)', and -"Gmo(T)-Hmo(0)'/T at 298.15 K are 75.31, 142.89, 85.43, and at 1000 K are 80.57, 253.28, 172.77 J[middle dot]K-1[middle dot]mol-1, respectively. No signs of further transitions were found, either in the stoichiometric compound, or in a sample with overall composition Ag2S1.0526. Thus, the present work does not support the hypothesis of Perrott and Fletcher concerning partial disordering of stoichiometric Ag2S around 600 K as opposed to complete disordering around 450 K in the presence of excess silver or sulfur. Subtraction of the estimated lattice heat capacity at constant pressure leaves a large transitional heat capacity for [beta]-Ag2S above 450 K. It is about 11 J[middle dot]K-1[middle dot]mol-1 at 500 K and decreases gradually to about 6 J[middle dot]K-1[middle dot]mol-1 at 850 K. Its origin is discussed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/26409/1/0000496.pd

    Determination of Alkali and Halide Monovalent Ion Parameters for Use in Explicitly Solvated Biomolecular Simulations

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    Alkali (Li+, Na+, K+, Rb+, and Cs+) and halide (F−, Cl−, Br−, and I−) ions play an important role in many biological phenomena, roles that range from stabilization of biomolecular structure, to influence on biomolecular dynamics, to key physiological influence on homeostasis and signaling. To properly model ionic interaction and stability in atomistic simulations of biomolecular structure, dynamics, folding, catalysis, and function, an accurate model or representation of the monovalent ions is critically necessary. A good model needs to simultaneously reproduce many properties of ions, including their structure, dynamics, solvation, and moreover both the interactions of these ions with each other in the crystal and in solution and the interactions of ions with other molecules. At present, the best force fields for biomolecules employ a simple additive, nonpolarizable, and pairwise potential for atomic interaction. In this work, we describe our efforts to build better models of the monovalent ions within the pairwise Coulombic and 6-12 Lennard-Jones framework, where the models are tuned to balance crystal and solution properties in Ewald simulations with specific choices of well-known water models. Although it has been clearly demonstrated that truly accurate treatments of ions will require inclusion of nonadditivity and polarizability (particularly with the anions) and ultimately even a quantum mechanical treatment, our goal was to simply push the limits of the additive treatments to see if a balanced model could be created. The applied methodology is general and can be extended to other ions and to polarizable force-field models. Our starting point centered on observations from long simulations of biomolecules in salt solution with the AMBER force fields where salt crystals formed well below their solubility limit. The likely cause of the artifact in the AMBER parameters relates to the naive mixing of the Smith and Dang chloride parameters with AMBER-adapted Åqvist cation parameters. To provide a more appropriate balance, we reoptimized the parameters of the Lennard-Jones potential for the ions and specific choices of water models. To validate and optimize the parameters, we calculated hydration free energies of the solvated ions and also lattice energies (LE) and lattice constants (LC) of alkali halide salt crystals. This is the first effort that systematically scans across the Lennard-Jones space (well depth and radius) while balancing ion properties like LE and LC across all pair combinations of the alkali ions and halide ions. The optimization across the entire monovalent series avoids systematic deviations. The ion parameters developed, optimized, and characterized were targeted for use with some of the most commonly used rigid and nonpolarizable water models, specifically TIP3P, TIP4PEW, and SPC/E. In addition to well reproducing the solution and crystal properties, the new ion parameters well reproduce binding energies of the ions to water and the radii of the first hydration shells

    Heats of formation of intermetallic compounds

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    The Temperature Dependence of the Properties of Electrolyte Solutions. III. Conductance of Various Salts at High Concentrations in Propylene Carbonate at Temperatures from − 45°C to + 25°C

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    Specific conductances of Et4NPF6, Pr4NPF6, Bu4NPF6, LiPF6, KPF6, LiClO4, and KSCN in propylene carbonate were studied at high concentrations in the temperature range from +25°C to -45°C. Data are fitted by a least-squares method to a four-parametric empirical equation, yielding the maximum specific conductance κmax and the corresponding concentration μ. Within the frame-work of a hydro-dynamic model the Stokes-radii of the ions and the solvent viscosity are found to be the most important conductance-determining parameters, affecting both κmax and μ Ionic association in solutions with propylene carbonate as the solvent is not of significant importance. Kinetic treatment of conductance yields temperature-dependent activation energies, but at any one temperature equal for all salts at concentration μ. Die spezifische Leitfähigkeit konzentrierter Lösungen von Et4NPF6, Pr4NPF6, Bu4NPF6, LiPF6, KPF6, LiClO4 und KSCN in Propylencarbonat wurde im Temperaturbereich zwischen +25°C und -45°C untersucht. Die Datenanalyse mittels eines Ausgleichs nach einer vier-parametrigen empirischen Gleichung liefert für jede Temperatur die maximale spezifische Leitfähigkeit kmax mit zugehörigem Konzentrationswert μ. Die Stokes-Radien der Ionen und die Viskosität des Lösungsimittels erweisen sich für ein hydrodynamisches Modell als die wichtigsten leitfähigkeitsbestimmenden Parameter zur Diskussion von κmax und μ. Ionenassoziation spielt in Propylencarbonat als Lösungsmittel keine hervorragende Rolle. Die Behandlung des Transportprozesses im Rahmen eines kinetischen Modells führt zu temperaturabhängigen Aktivierungsenergien, die aber bei jeder Temperatur für alle Salze bei der Konzentration μ gleich sind

    Electrical conductivity of the system stannic bromide-nitrobenzene

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