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Artículos en revistas It is shown how a standard nonlinear programming approach can be applied to solve a sophisticated version of the static optimal mix problem in generation planning. The model presented includes technical minima of thermal capacity, detailed operating models of storage-hydro and pumped-hydro units, a realistic model of capital costs for hydro plants, operating reserve and minimum demand constraints, and capacity already in existence. The model formulation is in a format that can be directly handled by the well-known MINOS code and can be efficiently solved. The use of a general-purpose nonlinear optimization program results in a great flexibility, making it possible to modify the model formulation easily or to adapt it to the characteristics of a particular electric system. A realistic application to the Spanish generation system is presented info:eu-repo/semantics/publishedVersion

Abstract Protection devices are designed to provide high sensitivity to transients produced by undesirable conditions like lightning stroke, avoiding their operation under all tolerable events like switching operations. The problem of incorrect operation due to transient phenomena can be handled by two means, one is to allow the transients and provide additional logics in the relay, other means is to damp the oscillation from source side. Protection relays’ not always must trip or send a trip signal and sometimes, only an alarm is necessary. In this context, this research presents a fast and reliable formulation for transmission lines (TLs) switching operations and lightning strokes detection and identification. The proposed methodology is based on Principal Component Analysis (PCA) and Euclidean Norm (EN); by using PCA it is possible to determine that normal operation signals describe a very well defined Ellipsoidal Pattern (EP). In this manner, by calculating the Euclidean Norm (EN) among Principal Components (PCs) for each sample and the origin of the reference Ellipsoidal Pattern, switching operations and lightning strokes are detected and identified. Test results show that the proposed algorithm presents high success on phenomena detection and identification, presenting a high potential for online applications.

Micro hydro power plants (µHPP) are typically used to supply electric energy to microgrids outside the national power grids taking care of the frequency control of the isolated system. A conventional way to maintain the load balance in the system is to use thyristor switched AC-AC converters controlled dump loads. A disadvantage of the AC-AC converters is their reactive power consumption decreasing the power factor at the generator output. To avoid this problem the authors have earlier proposed two converter topologies utilizing symmetrical switching scheme resulting to zero reactive power consumption. The objective of this paper is to evaluate the frequency regulation loop performance of the dump load controlled single generator system by using the symmetrically switched converter structures. Evaluation is carried out by analyzing the performances of different converter structures in a simulator representing the operation of a Cuban µHPP “Los Gallegos”. The results showed that the frequency regulation loop performance using each proposed converter structure satisfied the Cuban standard of frequency regulation, but with the symmetrically switched structures reactive power consumption was reduced resulting to reduced losses and improved effective current delivery capacity of the generator.

The subject of the research is oriented to typical buildings, often critical from the energy standpoint, which are represented by social housings. The refurbishment target should be the NZEB model, even if it is very difficult to find suitable general solutions. As the renovation design process depends also on the sustainability of costs, an evaluation procedure, previously proposed, is widened to take into account this aspect, by considering characteristics and constraints, and assuring reasonable costs for the most suitable solutions. The methodology has been applied to a case study represented by a common building unit. The insulation improvement is made through a choice of the most suitable combination of material and thickness, with the aim not only of the energy saving, but also of the reduction of the risk of vapour condensation that depends, among other things, on the position of the insulating materials within the wall’s structure. Some combined refurbishment solutions for the building envelope are examined and the corresponding costs are evaluated. Moreover, to show the importance of the problem in mild and continental climates, a comparison of the results in different climatic conditions is presented.

Abstract Thermal energy storage with phase change materials (PCM) provides high storage capacities in small temperature intervals. For the design of storage systems, the enthalpy curve of the used PCM has to be known with high precision. The T-History method has evolved to a widely used method for the measurement of the enthalpy as a function of temperature of PCM because of its simplicity and the advantage to be able to investigate larger sample volumes than typically used for differential scanning calorimeters. In order to ensure isothermal specimen during the measurement a thermal insulation is often mounted around the sample holder, but this insulation material is not considered in the evaluation model. In this work a new evaluation model for insulated T-History setups is developed by an analytical heat balance. This model is validated by numerical simulations of insulated T-History measurements and experimentally. By the use of the new model for the evaluation of the enthalpy a significant increase of accuracy can be achieved.

The aim of the present work was to develop 3D discrete element models capable of simulating the observed flow of glass beads (simple glass spheres) and maize grains (represented as a combination of spheres) during their discharge from a small model silo. A preliminary model for each material was constructed based on values for variables measured in the laboratory or taken from the literature. The ability of the models to predict the flow of these materials was then tested by comparing their results with observed discharge flows. Three variables were recorded for this: the mean bulk density at the end of the filling phase, the discharge rate and the flow pattern. The comparison of the results for the last of these variables required the discharge process be filmed using a high speed camera in order to more easily recognise the details of the flow. The preliminary model for the glass beads made very reasonable predictions, but that for the maize grains required calibration. This involved modifying the values of the friction properties of the material until a model capable of making acceptable predictions was obtained. The results obtained highlighted the influence of friction properties on the characteristics of the discharge flow. Finally, some of the numerical results provided by the models were analysed in order to describe the flow characteristics and the behaviour of the discharge rate in more detail.

The recent advancements in Artificial Intelligence have paved the way for remarkable achievements in tasks that have traditionally posed challenges even for humans [...]

9 Figuras, 4 Tablas.-- Material suplementario disponible en línea en la página web del editor. Co-pyrolysis of grape seeds and polystyrene was conducted in a fixed-bed reactor, followed by an analysis of the organic phase for possible further application as a drop-in fuel. Significant positive synergistic effects were found with the addition of polystyrene (5–40 wt%) to the conventional pyrolysis of grape seeds. There was a considerable improvement in the organic phase yield, in particular, reaching values over 80 wt%, markedly higher than those obtained from conventional pyrolysis (61 wt%). Fuel properties of the bio-oil were also upgraded, with a decrease in oxygen content and an increase in the heating value. An organic bio-oil fraction with pH values ranging from 5.4 to 6.2 was obtained, reducing the issues associated with handling bio-oils obtained from common pyrolysis of lignocellulosic biomass, usually ranging pH between 2 and 3. Finally, an increment in the desired compounds, mainly aromatics, was also attained, while at the same time achieving a low content of undesired compounds, such as phenols. It was demonstrated that polystyrene can act as a H2-donor, favoring oligomerization, cyclation and hydrodeoxygenation reactions into aromatic compounds. The authors would like to thank MINECO and FEDER for their financial support (Project ENE2015-68320-R). O.S.P acknowledges the FPI fellowship (BES-2016-077750) funded by MINECO. The authors would also like to thank the Regional Government of Aragon (DGA) for the support provided under the research groups support programme. Peer reviewed