Rénovation complète d'une microcentrale électrique existante: étude de faisabilité

Le domaine viticole de Beudon possède une usine hydroélectrique. Cette dernière pourrait bénéficier d’une importante amélioration de sa capacité de production d’énergie électrique annuelle grâce à une rénovation complète de ses composants. Le but de ce projet était de réaliser une étude de faisabilité tenant compte des aspects techniques et financiers. Dans un premier temps, la collecte de tous les documents disponibles (anciens et récents) a été cruciale pour le bon déroulement du projet. Ensuite, je me suis concentré sur la spécification des paramètres nécessaires aux dimensionnements des turbines hydrauliques (dimensionnement confié à Mhylab), des alternateurs ainsi que de l’ingénierie civile. Après avoir dimensionné toutes les parties principales de l’aménagement hydroélectrique, je suis passé à la projection des coûts totaux d’une rénovation entière de l’usine, avec l’appui des professionnels des branches respectives. Ils ont su me fournir des offres détaillées selon mes besoins et mes dimensionnements

Nouvelles sources renouvelables réparties dans un réseau de distribution: travail de bachelor : diplôme 2016

La croissance du nombre d’installations réparties de production d’énergie renouvelable telles que le photovoltaïque ou l’éolien, dont le profil de production est de nature variable, représente un défi majeur pour les gestionnaires de réseaux électriques dont l’une des missions est d’en garantir au quotidien la stabilité. Pour le canton du Valais, de par son climat ensoleillé, il est évident qu’une des principales sources de renouvelable qui pourrait être exploitée sous la forme de petites installations réparties n’est autre que le photovoltaïque. De ce fait, il est important pour un gestionnaire de réseau actif en Valais de savoir comment le réseau pourrait réagir à une intégration à large échelle de production photovoltaïque décentralisée sur celui-ci. Cela afin de connaitre, si tel est le cas, les problèmes auxquels il risque d’être confronté au futur, et ainsi de pouvoir planifier les aménagements à apporter au réseau. Ce projet est réalisé avec la collaboration et sous mandat du groupe SEIC Télédis. Ce gestionnaire de réseau est actif notamment dans le Valais central et le Bas-Valais. L’objectif de ce projet est donc de développer un outil d’aide à la planification qui permette de favoriser la pénétration d’un maximum de sources de production photovoltaïque dans un réseau de distribution basse tension

Electromagnetic radiation from lightning return strokes to tall structures

The study of the interaction of lightning electromagnetic fields with electrical systems and the design of appropriate protection strategies are generally based on statistical distributions of the lightning current measured at the channel base using either instrumented towers or artificial initiation of lightning using rockets. Recent studies based both on numerical modeling and experimental observations have shown that the presence of the structure struck by (or used to initiate) lightning does affect the current measurement in a way depending upon the geometry of the structure itself, compromising therefore the reliability of the statistics adopted so far for lightning data. The aim of this thesis is to provide new elements (from both theoretical and experimental investigations) to improve the understanding of the electromagnetic consequences of the impact of lightning return strokes to tall structures. Chapter 2 introduces to the phenomenology of cloud-to-ground lightning and the importance of lightning return-stroke modeling. Among the different classes of return-stroke models existing in the literature, the attention is focused in this thesis on the so-called engineering models, which allow describing the current distribution along the channel as a function of the current at the channel base and the return-stroke speed, two quantities for which data can be obtained experimentally. After presenting a review of five engineering return-stroke models describing lightning strikes to ground, the extension of the engineering models to take into account the presence of an elevated strike object is presented and discussed. The original contributions of this thesis, consisting of both theoretical and experimental works, are presented in Chapters 3 through 6. Chapter 3 is devoted to the computation of the electromagnetic field produced by lightning return strokes to elevated strike objects, using the extension of the engineering models to include an elevated strike object presented in the previous chapter. It is shown, for the first time, that the current distribution associated with these extended models exhibits a discontinuity at the return-stroke wavefront which (although not physically conceivable) needs to be taken into account by an additional term in the equations for the electromagnetic field, the so-called "turn-on" term. A general analytical formula describing the "turn-on" term associated with this discontinuity for various engineering models is derived and simulation results illustrating the effect of the "turn-on" term on the radiated electric and magnetic fields are also presented. In the second part of the chapter, dedicated to the investigation of the propagation effects on lightning electromagnetic field traveling along a finitely-conducting ground, the commonly-used assumption of an idealized perfectly-conducting ground is relaxed in order to analyze, for the first time, how the electromagnetic field radiated by a tower-initiated strike is affected while propagating along a soil characterized by a finite conductivity. The results showed that the attenuation of the initial peak of the field radiated by a tower-initiated strike, resulting from the propagation over finitely conducting ground, depends strongly on the risetime of the current, the tower height and the ground conductivity and is, in general, much more important than the attenuation experienced, while propagating along the same finite ground, by the field produced by ground-initiated strikes. Chapter 4 presents a comparison among the predictions obtained using the five extended engineering return-stroke models for lightning strikes to tall structures described in Chapter 2. The spatial-temporal current profiles along the tower-channel axis predicted by the engineering models, as well as the respective predictions for the radiated electric and magnetic fields, calculated at different distances, are compared and discussed. It is shown that the computed electromagnetic fields associated with a strike to a tall tower are generally less model-dependent than those corresponding to a strike to ground, especially as far as the first-peak value is concerned, which is nearly model-insensitive in case of tall-tower strikes. A theoretical analysis is performed in the last part of the chapter with the aim to provide, for the same five engineering models extended to take into account the presence of the tower, expressions relating the return-stroke current and the associated distant radiated electric and magnetic fields. It is demonstrated, in addition, that only one model among the five presented is characterized by simple analytical formulas relating current-peak and far-field peak values, which (being the electromagnetic field peak value nearly independent of the adopted model) become general expressions applicable for any engineering return-stroke model in case of tower-initiated lightning. It was also shown that the peak amplitude of the electromagnetic field radiated by a lightning strike to a tall structure is relatively insensitive to both the values of the top reflection coefficient and the return-stroke speed. This latter result is important, in particular, because, unlike ground-initiated strikes, for which the far-field peak is strongly dependent on the return-stroke speed, far field peaks associated with strikes to tall structures are little sensitive to the return stroke speed. Since in most practical cases the value of the return-stroke speed is unknown, this interesting result suggests a possible calibration procedure for lightning detection systems by means of direct measurement of lightning currents on instrumented towers. Chapter 5 reports on the simultaneous measurements of the return-stroke current and of the electric and magnetic fields at three distances associated with lightning strikes to the Toronto CN Tower (553 m) that have been carried out during the summer of 2005. This is the first time ever that simultaneous records of lightning current and associated electric and magnetic fields at three distances have been obtained. Two propagation paths for the electromagnetic field to the first and to the second field measurement stations (located, respectively, 2.0 km and 16.8 km away from the CN Tower) were along the soil and through the Toronto city, whereas for the third location (50.9 km away) the propagation path was nearly entirely across the fresh water of Lake Ontario. It is shown that the waveforms of the electric and magnetic fields at 16.8 km and 50.9 km exhibit a first zero-crossing about 5 microseconds after the onset of the return-stroke, which is part of a narrow undershoot and which may be attributed to the transient processes along the tower. Effects of propagation (decrease of field amplitude and increase of its risetime) could also be observed in experimental records. It is shown that the fields at 50.9 km are less affected by such attenuation, compared to those at 16.8 km, presumably because the path of propagation was mostly across Lake Ontario. The measured waveforms are compared with the theoretical predictions obtained using five engineering return-stroke models, extended to include the presence of the strike object, finding a reasonable agreement for the magnetic field waveforms at the three considered distances. The overall agreement between the theoretically predicted and the experimentally observed field-peak-to-current-peak ratio is reasonable, although the theoretical expression appears to underestimate the experimentally measured ratio (by about 25 %). This may be due, at least in part, to the enhancement effect of the buildings on which the field measurement antennas were installed. Finally, the directly-measured lightning currents at the tower were correlated and compared with the current-peak estimations provided by the US National Lightning Detection Network (NLDN). It is shown that the NLDN-inferred values overestimate the actual current peaks because the presence of the tall struck object produces an enhanced radiated field at far distances (with respect to strikes to flat ground), which is not included in the algorithm used to infer lightning current peaks from remote field measurements. It is shown in this thesis that correcting the NLDN estimates using the correction factor introduced by the tower results in an excellent estimation of lightning current peaks. This is an important conclusion of this study showing that the estimation of lightning peak currents for tall towers can be greatly improved by considering the tower correction factor. Chapter 6 is devoted to the measurement of electromagnetic fields radiated by lightning. In its first part, the need for guidelines for reporting lightning data obtained experimentally is emphasized. The second part of the chapter presents the design, the construction and preliminary tests of a low-cost, multi-channel lightning field measuring system for the simultaneous measurement of three components of the electromagnetic field radiated by lightning. The proposed system uses one single optical link for the transmission of the three signals, appropriately digitized and multiplexed, lowering considerably the overall cost of the system itself

Evaluation de la fiabilité d'un algorithme de prévision de production photovoltaïque

Dans le cadre du présent travail de diplôme, la fiabilité d’un algorithme de prévision de production d’énergie photovoltaïque développé par l’eEnergy Center, est évaluée. Cet algorithme, conçu pour l’Energies Sion Région (ESR), se base essentiellement sur des prévisions météorologiques pour estimer la production d’énergie renouvelable d’un ensemble d’installations photovoltaïques raccordées au réseau du distributeur valaisan. Le but est, dans un premier temps, d’évaluer les enjeux liés aux prévisions de productions photovoltaïques pour un gestionnaire de réseau de distribution (GRD) tel que l’ESR dans le marché actuel de l’électricité. L’impact économique de la fiabilité des prévisions de production pour un GRD y est étudié. Dans un deuxième temps, il convient de présenter brièvement le fonctionnement de l’algorithme développé. L’analyse de l’historique du taux d’erreur de l’algorithme entre les données prédites et les mesures réelles issues d’une première année de fonctionnement permet, dans un troisième temps, d’identifier les facteurs ayant un impact sur la fiabilité des prévisions. Sur cette base, des solutions visant à améliorer les performances de l’algorithme peuvent être proposées et implémentées

eQE: An open‐source density functional embedding theory code for the condensed phase

AbstractIn this work, we present the main features and algorithmic details of a novel implementation of the frozen density embedding (FDE) formulation of subsystem density functional theory (DFT) that is specifically designed to enable ab initio molecular dynamics (AIMD) simulations of large‐scale condensed‐phase systems containing 1000s of atoms. This code (available at http://eqe.rutgers.edu) has been given the moniker of embedded Quantum ESPRESSO (eQE) as it is a generalization of the open‐source Quantum ESPRESSO (QE) suite of programs. The strengths of eQE reside in a hierarchical parallelization scheme that allows for an efficient and fully self‐consistent treatment of the electronic structure (via the addition of an additional DIIS extrapolation layer) while simultaneously exploiting the inherent symmetries and periodicities in the system (via sampling of subsystem‐specific first Brillouin zones and utilization of subsystem‐specific basis sets). While bulk liquids and molecular crystals are two classes of systems that exemplify the utility of the FDE approach (as these systems can be partitioned into weakly interacting subunits), we show that eQE has significantly extended this regime of applicability by outperforming standard semilocal Kohn–Sham DFT (KS‐DFT) for large‐scale heterogeneous catalysts with quite different layer‐specific electronic structure and intrinsic periodicities. eQE features very favorable strong parallel scaling for a model system of bulk liquid water composed of 256 water molecules, which allows for a significant decrease in the overall time to solution when compared to KS‐DFT. We show that eQE achieves speedups greater than one order of magnitude ( ) when performing AIMD simulations of such large‐scale condensed‐phase systems as: (1) molecular liquids via bulk liquid water represented by 1024 independent water molecules (3072 atoms with a 25.3× speedup over KS‐DFT), (2) polypeptide/biomolecule solvation via (gly)6 solvated in (H2O)395 (1230 atoms with a 38.6× speedup over KS‐DFT), and (3) molecular crystals via a 3 × 3 × 3 periodic supercell of pentacene (1940 atoms with a 12.0× speedup over KS‐DFT). These results represent a significant improvement over the current state‐of‐the‐art and now enable subsystem DFT‐based AIMD simulations of realistically sized condensed‐phase systems of interest throughout chemistry, physics, and materials science

Electromagnetic fields associated with the M‐component mode of charge transfer

In upward flashes, charge transfer to ground largely takes place during the initial continuous current (ICC) and its superimposed pulses (ICC pulses). ICC pulses can be associated with either M-component or leader/return‐stroke‐like modes of charge transfer to ground. In the latter case, the downward leader/return stroke process is believed to take place in a decayed branch or a newly created channel connected to the ICC‐carrying channel at relatively short distance from the tower top, resulting in the so‐called mixed mode of charge transfer to ground. In this paper, we study the electromagnetic fields associated with the M‐component charge transfer mode using simultaneous records of electric fields and currents associated with upward flashes initiated from the Säntis Tower. The effect of the mountainous terrain on the propagation of electromagnetic fields associated with theM‐component charge transfer mode (including classical M‐component pulses and M‐component‐type pulses superimposed on the initial continuous current) is analyzed and compared with its effect on the fields associated with the return stroke (occurring after the extinction of the ICC) and mixed charge transfer modes. For the analysis, we use a 2‐Dimentional Finite‐Difference Time Domain method, in which the M‐component is modeled by the superposition of a downward current wave and an upward current wave resulting from the reflection at the bottom of the lightning channel (Rakov et al., 1995, https://doi.org/10.1029/95JD01924 model) and the return stroke and mixed mode are modeled adopting the MTLE (Modified Transmission Line with Exponential Current Decay with Height) model. The finite ground conductivity and the mountainous propagation terrain between the Säntis Tower and the field sensor located 15 km away at Herisau are taken into account. The effects of the mountainous path on the electromagnetic fields are examined for classical M‐component and M‐component‐type ICC pulses. Use is made of the propagation factors defined as the ratio of the electric or magnetic field peak evaluated along the mountainous terrain to the field peak evaluated for a flat terrain. The velocity of theM‐component pulse is found to have a significant effect on the risetime of the electromagnetic fields. A faster traveling wave speed results in larger peaks for the magnetic field. However, the peak of the electric field appears to be insensitive to the M‐component wave speed. This can be explained by the fact that at 15 km, the electric field is still dominated by the static component, which mainly depends on the overall transferred charge. The contribution of the radiation component to the M‐component fields at 100 km accounts for about 77% of the peak electric field and 81% of the peak magnetic field, considerably lower compared to the contribution of the radiation component to the return stroke fields at the same distance. The simulation results show that neither the electric nor the magnetic field propagation factors are very sensitive to the risetimes of the current pulses. However, the results indicate a high variability of the propagation factors as a function of the branch‐to‐channel junction point height. For junction point heights of about 1 km, the propagation factors reach a value of about 1.6 for the E‐field and 1.9 for the H‐field. For a junction height greater than 6 km, the E‐field factor becomes slightly lower than 1. The obtained results are consistent with the findings of Li, Azadifar, Rachidi, Rubinstein, Paolone, et al. (2016, https://doi.org/10.1109/TEMC.2015.2483018) in which an electric field propagation factor of 1.8 was inferred for return strokes and mixed‐mode pulses, considering that junction points lower than 1 km or so would result in a mixed mode of charge transfer, in which a downward leader/return‐stroke‐like process is believed to take place. It is also found that the field enhancement (propagation factor) for return stroke mode is higher for larger ground conductivities. Furthermore, the enhancement effect tends to decrease with increasing current risetime, except for very short risetimes (less than 2.5 μs or so) for which the tendency reverses. Finally, model‐predicted fields associated with different charge transfer modes, namely, return stroke, mixed‐mode, classical M‐component, and M‐component‐type ICC pulse are compared with experimental observations at the Säntis Tower. It is found that the vertical electric field waveforms computed considering the mountainous terrain are in very good agreement with the observed data. The adopted parameters of the models that provide the best match with the measured field waveforms were consistent with observations. The values for the current decay height constant adopted in the return stroke and mixed‐mode models (1.0 km for the return stroke and 0.8 km for the mixed‐mode pulse) are lower than the value of 2.0 km typically used in the literature