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International audience; High-temperature mechanical tests coupled with Digital Image Correlation (DIC) on ceramics which exhibit rather low level of strain require to overcome extreme experimental conditions that usually can reduce significantly measurement accuracy. Thermal resistance of speckle pattern, black body radiation and heat haze are three main concerns, which should thus be taken into account while designing a high-temperature image acquisition setup. In this aim, an experimental procedure has been specifically designed in order to minimize the three above-mentioned disturbances. The main objective of this study is to select a suitable high-temperature resistant speckle pattern for mechanical characterization at 1200 °C (or above) on refractory ceramics. Most of tested speckle patterns were performed with white alumina adhesive and dark ceramic grains (silicon carbide or brown fused alumina). Different grain sizes of silicon carbide were tested. At first, different speckle patterns are compared in terms of DIC strain measurement uncertainty by discussing speckle features, some main DIC parameters and two image pre-treatments (low pass filter, image size reduction). Then, these speckle patterns are tested to analyse fracture behaviour of refractories through a Brazilian test. An enhanced digital image correlation technique (2P-DIC), dedicated to monitor the fracture behaviour, is applied to study the evolution of crack length. The best representation of crack progression has been achieved for sample surface covered with a fine SiC powder ranging from 50-100 µm. It is then possible to compare the fracture behaviour between 1200°C and 20°C and to show that the refractory exhibits more crack branching at 1200°C in comparison with behaviour at room temperature.

International audience

The religious education which prepares for Confirmation should be incessantly renewed. It results from the unprecedented pace of civilizational changes, on which the youth are exposed. They need reinforcement which the Sacrament of Confirmation brings. It also constitutes the unusual chance in the process of faith of the young man. Seeking the optimal model of the religious education for Confirmation, and more widely a youth chaplaincy, is an expression of care of the young man. Using mutual experience and learning from each other can bring new and valuable inspiration. One can see it on the example of compared organizational elements of the religious education which prepares for Confirmation in Poland and in Germany. Without their proper forming even the best selected content and methods of the transmission will not be able to bring full fruits.

For optimal coordination of directional overcurrent relay we propose to consider operation characteristics, pickup current and time multiplier setting of relays as optimization parameters. Each parameter is optimized independently with the aid of linear formulation of the coordination problem. First, optimal discrete values of pickup current are selected. Second, adequate operation time characteristics of relays are selected. Third, optimal discrete values of time multiplier setting are determined. The proposed method is tested on two networks: an 8-bus system and the IEEE 30-bus system. Its performances are evaluated and compared with those of the linear and nonlinear programming techniques.

International audience; Rare earth permanentmagnet synchronousmachines with the pulsewidth modulated supply are exposed to magnets'heating due to harmonic fields, which rotate in relation to rotor. In caseswhen skin effect is negligible, the corresponding eddy-current losses in magnets can be reduced by segmentation of magnets. In this paper, we propose an analytical method to evaluate the effect of both circumferential and axial segmentations on losses' reduction in various conditions, concerning the skin effect. With the skin effect operating, the magnets' division may lead to increase rather than decrease of the eddy-current losses. A criterion to determine range of parameters leading to this unexpected situation is presented. Finite-element calculation confirms the results of the analysis.

International audience

This article analyzes the drawbacks of linear programming methods to solve the directional over-current relay coordination problem. The solution infeasibility of these methods is due to selectivity constraints, which reduce the upper bound of the time multiplier setting of some relays. This infeasibility can be avoided by making the upper bound of the time multiplier setting insensible to selectivity constraints. With the proposed algorithm based on this idea, the constraints causing infeasibility are identified in order to change their position in relation to possible solution areas. This change is achieved by increasing the relay pickup currents. The proposed algorithm is tested and evaluated on the IEEE 14-bus and 30-bus networks. The results show that the previously infeasible solution of linear programming becomes feasible with high efficiency.

We think that strong capacitive currents, generating unfavorable conditions for traditional protection relays in compensated systems, can be exploited as carriers of relevant information. Whenever extremely rapid information is required, we can find it when treating the discharging currents as useful for treatment, at a price of higher sampling frequency. After fault inception we dispose of several tens of microseconds to get the data in wave propagation area. This can make sense in simple distribution systems, with single ramification per feeder and homogenous line impedance. We can also make useful the presence of strong capacitive currents in permanent fault regime, where these currents occult detection of faulty feeder. In such cases, the diagnosis based on phase advance of the faulty residual current over the sound residuals is better assured when tracing the corresponding apparent phase advance in transient regime. Both propositions need the current data be centralized; they work on few data points in a very short time span. These drawbacks are price for matching consequences of cable proliferation in resonant grounded distribution networks. When simulating the fault currents, we usually exploit large possibilities of dedicated packages like EMTP. However, in components in compensated distribution system these currents can be usefully analyzed also with aid of an equivalent circuit, which permits an evaluation of SLG fault distance. We have calculated fault position with several percent average errors, for fault resistance up to 3kin overhead lines or up to 200 in cables.

The PWM-supplied permanent magnet synchronous machines are exposed to magnets' heating due to harmonic fields which rotate in relation to rotor. The corresponding losses can be calculated by FE simulation for each frequency, with superposition of all components of the losses. In certain conditions three dimensional modelling is required to get enough precision. However, time-stepping 3D finite element methods coupled with motion equations can lead to excessive computational time. Then a locked rotor approach with current sheet rotating may be interesting. In this case however, the superposition doesn't really work unless special procedure is applied. Magnetic loss dissipation cannot be correctly calculated with simple superposition of individual fields, e.g. the 5th and 7th harmonic rotating in opposite direction. This is because the resulting field has an alternative component with dissipative effects depending on its position. They will be more important if the component oscillates in the middle of magnets and less important in the middle of gap between them.

Wave propagation laws are applied in MW cable networks in order to determine zone of constant polarity in after-fault transients. An “all current” polarity law permitting rapid fault detection is proposed and analysed using several EMTP cable models.

International audience

The integration of nonlinear VSC-HVDC transmission systems in power grids becomes very important for environmental, technical, and economic reasons. These systems have enabled the interconnection of asynchronous networks, the connection of offshore wind farms, and the control of power flow especially for long distances. This thesis aims the non-linear control and stabilization of VSC-HVDC systems, with two main themes. The first theme focuses on the design and synthesis of nonlinear control laws based on Variable Structure Systems (VSS) for VSC-HVDC systems. Thus, the Sliding Mode Control (SMC) and the Asymptotic Output Tracking (AOT) have been proposed to provide an adequate degree of stability via suitable Lyapunov functions. Then, the robustness of these commands has been studied in presence of parameter uncertainties and/or disturbances. The compromise between controller’s robustness and the system’s dynamic behavior depends on the gain settings. These control approaches, which are robust and can be easily implemented, have been applied to enhance the system dynamic performance and stability level in presence of different abnormal conditions for different DC link lengths. The second theme concerns the influence of VSC-HVDC control on improving the AC network dynamic performance during transients. After modeling the Single Machine via VSC-HVDC system in which the detailed synchronous generator model is considered, the conventional PI controller is applied to the converter side to act on damping the synchronous machine power angle oscillations. This simple control guarantees the reinforcement of the system dynamic performance and the power angle oscillations damping of the synchronous machine in presence of faults., L'intégration des liaisons à courant continu dans les systèmes électriques permet d’accroitre les possibilités de pilotage des réseaux, ce qui permet d’en améliorer la sûreté et de raccorder de nouveaux moyens de production. Pour cela la technologie VSC-HVDC est de plus en plus plébiscitée pour interconnecter des réseaux non synchrones, raccorder des parcs éoliens offshore, ou contrôler le flux d’énergie notamment sur des longues distances au travers de liaisons sous-marines (liaison NorNed). Les travaux de cette thèse portent sur la modélisation, la commande non-linéaire et la stabilisation des systèmes VSC–HVDC, avec deux axes de travail. Le premier se focalise sur la conception et la synthèse des lois de commandes non-linéaires avancées basées sur des systèmes de structures variables (VSS). Ainsi, les commandes par modes glissants (SMC) et le suivi asymptotique de trajectoire des sorties (AOT) ont été proposées afin d’assurer un degré désiré de stabilité en utilisant des fonctions de Lyapunov convenables. Ensuite, la robustesse de ces commandes face à des perturbations et/ou incertitudes paramétriques a été étudiée. Le compromis nécessaire entre la robustesse et le comportement dynamique requis dépend du choix approprié des gains. Ces approches robustes, qui sont facile à mettre en œuvre, ont été appliquées avec succès afin d’atteindre des performances dynamiques élevées et un niveau raisonnable de stabilité vis-à-vis des diverses conditions anormales de fonctionnement, pour des longueurs différentes de liaison DC. Le deuxième vise à étudier l’influence de la commande du convertisseur VSC-HVDC sur l'amélioration de la performance dynamique du réseau de courant alternatif en cas d’oscillations. Après une modélisation analytique d’un système de référence constitué d’un groupe connecté à un convertisseur VSC-HVDC via un transformateur et une ligne, un contrôleur conventionnel simple PI est appliqué au niveau du convertisseur du système pour agir sur les oscillations rotoriques de la machine synchrone. Cette commande classique garantie une amélioration acceptable des performances dynamiques du système; surtout pour l'amortissement des oscillations de l'angle de puissance de la machine synchrone lors de défauts.

In this thesis we present a study of high frequency rotor power losses in permanent magnet synchronous machines. In case of time harmonic fields we have shown by an analysis and confirmed by 3D finite element calculation an anomaly of the segmentation rule of the magnet. Consequently, we have proposed algorithms of optimization of the magnet segmentation aiming the minimization of eddy current losses, with a simple criterion on influence of the skin effect in losses calculation in high frequency. In the second part of the theses we have analyzed the rotor power losses dues to the stator slot harmonics. In case of homogeneous field we have proposed an analytical formulation taking into account machine’s geometrical parameters. We have then tested this model with aid of the finite element calculation. The analytical model gives acceptable results in absence of the skin effect in long magnets, but its application in laminated steels hasn’t proved successful., Dans cette thèse nous présentons une étude des pertes de puissance en haute fréquence dans les rotors des machines synchrones à aimants permanent. Dans le cas des champs harmoniques temporels au rotor, nous avons montré par calcul éléments finis en 3D que la règle de segmentation des aimants présente une anomalie. Par conséquent, nous avons développé une étude sur l’efficacité de la segmentation à deux dimensions des aimants permanents, avec l’optimisation de la de segmentation des aimants afin de minimiser les pertes par courants de Foucault. Un simple critère est proposé mettant en évidence l’influence de l’effet de peau dans le calcul des pertes à haute fréquence. En deuxième lieu nous avons étudié les pertes rotoriques dues à la modification du champ fondamental par la denture statorique, Dans ce but nous avons proposé un modèle analytique représentant cette modification par un champ homogène dans une maquette 2D/3D. Ce modèle met en évidence l’influence des paramètres géométriques de la machine sur les pertes de puissance dans le rotor. Il était validé par calcul en éléments finis dans une couche mince. Le modèle analytique a donné les résultats acceptables en absence de l’effet de peau dans le cas des aimants longs. Par contre il reste à améliorer pour le calcul de pertes par denture dans les tôles du rotor.

Liberalization of electricity markets has led to an economical (at least) separation between production and transmission utilities. So new interface rules have to be defined. This contribution tends to go further into a method to valorize reactive power production capacities on power grids in a competitive environment, which has been proposed by Xu, Kundur and da Silva. The method is based on the comparison between generators and static devices. Indeed, the generators are controlled by the producers whereas static devices are controlled by the Transmission System Operator. That's why this method tends to provide the technical value of the reactive power production for the TSO. In this work, the position of static devices is optimized tending to minimize their capacity with respect to the voltage bounds at each node while the reactive power output of a generator is decreased. The reactive power production can also be replaced by increasing reactive power production of generators where capacities are available. In this case generators located in parts of the grids which lack reactive power production capacities will have greater value tan those located in parts where capacities are numerous. This method has been successfully tested on the IEEE 118 bus benchmark grid and on a part of the French grid.; Dans le cadre de l'ouverture des marchés de l'électricité à la concurrence, de nouvelles règles doivent régir les relations entre producteur et transporteur d'électricité pour ce qui concerne les services au système tels que la fourniture de puissance réactive. Xu, Kundur et da Silva ont développé une méthode permettant d'évaluer le service rendu, et donc la valeur, d'un MVAr fourni par un générateur en calculant le nombre de MVAr qui doivent être fournis aux nœuds de charge pour maintenir leur tension lorsque le générateur réduit sa production. Nous avons amélioré cette méthode en optimisant l'emplacement et en minimisant la capacité de moyens de compensation permettant de remplacer la production réactive d'un générateur tout en maintenant la tension de chaque nœud dans sa plage acceptable. De plus les capacités de production réactives disponibles auprès d'autres générateurs sont mises à contribution, ce qui permet de prendre en compte la pénurie ou l'abondance de capacités de production. Cette méthode a été appliquée sur un réseau à deux nœuds, puis sur un réseau de test IEEE à 118 nœuds et enfin sur une partie du réseau électrique français. Les résultats obtenus permettent de valoriser chaque MVAr généré en fonction de la localisation du générateur sur le réseau, de l'état de charge du réseau, de la disponibilité des autres producteurs et du niveau de production du générateur. Ainsi les premiers MVAr fournis par un générateur sont difficilement remplaçables par des moyens de compensation et ont donc une valeur plus grande que les derniers qui eux sont facilement remplaçables.