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International audience; 2G HTS tapes are strong candidates for the de- velopment of future high magnetic field magnets. However, for such applications, field stability and quality are an issue due to the presence of Screening Current-Induced Field (SCIF) and the large magnetic field drift (FD). We propose here to model the screening currents induced during the ramping of a magnet composed of thousands of turns of 2G HTS tapes. The problem includes the strong coupling between the electromagnetic and mechanical model of the magnet through the critical current density. Thus, the latter does not only depend on the magnetic flux density and its orientation but on the local mechanical deformation as well. It is shown that the hysteresis loop shown by the central magnetic field is strongly dependent on the degradation of the critical current arising from mechanical deformation.

International audience; The high-Tc superconducting (HTS) dynamo is a promising device that can inject large DC supercurrents into a closed superconducting circuit. It could be used, for example, to energise rotor windings in superconducting rotating machines without the need for connection to a power supply via current leads. A number of different numerical models have now been developed as useful and cost-efficient tools to further examine and explain experimental results, as well as optimise and improve flux pump design. To adequately compare the different modelling tools available, we propose a new benchmark numerical model for the HTS modelling community: the HTS dynamo. In this work, this benchmark problem is implemented using several different methods: (1) coupled H-A formulation, (2) H-formulation + shell current, (3) segregated H-formulation, (4) Minimum Electromagnetic Entropy Production (MEMEP), (5) coupled T-A formulation, (6) integral equation and (7) volume integral equation-based equivalent circuit. These different techniques are used to solve the benchmark problem and compared in terms of computational requirements, ease of use and the solutions obtained with reference to each other, as well as experimental measurements.

International audience; High Temperature Superconducting (HTS) de- vices are taking an important role in electrical power systems. The Finite Element Method (FEM) often sim- ulates the device in itself, and some simplified models are applied to represent the equipment in electric grid studies, sometimes neglecting its physics. In this scenario, the development of models that can simulate the equipment integrated with the grid may be useful. Due to it, this paper presents a coupling method to link the superconducting de- vices modelled by 3D FEM to the power electrical system. This model enables an electromagnetic transient analysis. Moreover, by the FEM model, the critical current density of the tape can be examined in the transient period. A saturated iron-core superconducting fault current limiter (SIC-SFCL) will be modeled and connected to the power electrical grid as a study case. The simulation results are compared with experimental data to validate the model.

International audience; A finite-element model implemented in the open-source FreeFem++ program is presented, with the aim of introducing students to the calculation of AC losses in superconductors. With this simple approach, students can learn about the critical state model used to describe the macroscopic electromagnetic behavior of superconductors and the importance of several factors influencing the AC losses of superconductors.

International audience; The growing interest in modeling supercon- ductors has led to the development of increasingly effective numerical methods and software. Alongside this interest, the question of how to teach and to explain the operation of superconductors to students has arisen. EPFL and KIT have created a series of web applications based on COMSOL Multiphysics that are accessible through an open access web server called AURORA. This project allows users to dynamically change the parameters of the apps and observe their influence on the results, creating a vivid learning experience. The project is particularly directed to students. If, as Richard Feynman used to say “the questions of the students are often the source of new research,” why not stimulate students to ask questions on superconductivity?

International audience; Electric and hybrid-electric aircrafts with distributed propulsion have the potential to reduce commercial-flight emissions. REBCO full superconducting motors are very promising to achieve the required power- over-weight ratio. However, there are concerns about their possibly high AC loss in the stator. Computer modeling can provide design solutions for low AC loss, but these need to be fast and efficient. Here, we present two modeling methods to compute the AC loss in the stator of a 1 MW superconducting motor for aviation. One method combines a commercial Finite Element Method (FEM) with an in- house method based on a variational principle, while the second uses a novel variational method to model the whole motor that does not need meshing the air, avoiding moving mesh issues. Our results show that transposition is not required for distributed stator windings with multi-tape conductors. We also found promisingly low AC loss values for the stator winding, which require neither transposed nor striated tapes.

Afin de connaitre le courant nominal qu’un ruban supraconducteur haute température critique (HTc) puisse transporter, il est nécessaire de connaitre son courant critique Ic choisi habituellement pour un champ électrique égal à Ec=1µV/cm. Parce qu’au-dessus de Ic le supraconducteur risque de quencher, ce qui signifie une transition de l’état supraconducteur à l’état normal pouvant conduire à la destruction du ruban.La valeur du courant critique est obtenue à partir de mesures expérimentales faites à 77 K. Pour cela, nous relevons les caractéristiques U(I) aux bornes d’un échantillon en fonction de l’amplitude du champ magnétique appliquée (environ 5 champs) et de son orientation (environ 50 angles) car il dépend de ces deux paramètres.L’automatisation du processus d’une telle caractérisation permet de réduire les temps de mesures qui nécessitaient plusieurs jours (2-3 jours) manuellement à quelques heures (7h). Cette automatisation est pilotée par l’interface graphique LabVIEW, ce qui permet de communiquer avec les différents appareils comme les alimentations en courant, le moteur pas à pas pour la rotation, les dispositifs de mesures et d’ajuster divers paramètres.Ces données permettent de comparer la performance de chaque ruban HTc et de calculer pour une application précise le courant de fonctionnement du ruban supraconducteur.

For the minimization of AC-losses in a superconducting power cable their experimental determination is highly desirable with respect to the optimization of the design. However measurements on short samples are strongly hampered by the inhomogeneous current distribution between the superconducting tapes. A recently developed experimental setup gets rid of this problem by using a serial connection of the tapes with mutual field compensation of the backwards conductors.With this experimental method we now obtained first results of AC-losses in a one phase superconducting cable equipped with 22 YBCO-tapes (Superpower SCS 4050, width 4mm, Ic = 112 A). The losses were measured with an s-shaped voltage lead geometry and good reproducibility on the different tapes of the cable. Compared to the losses of a single tape, which are well described with the Norris-model (strip), the specific losses within the cable are reduced by a factor of about two, this in spite of the increased local field. This result is explained with the nearly perfect azimuthal direction of the local magnetic field. In additional experiments we studied the AC-losses for cases in which one or more tapes carry no current, a situation identic to application cases with damaged tapes. As a result the losses in the neighbouring tapes are increased by up to an order of magnitude, due to the increased vertical components of the self-field. This is confirmed by dedicated finite-element method simulations.Finally the experiments were compared to previous measurements on cables based on BSCCO 2223 tapes. The AC-losses for both materials are comparable, however the increased critical DC-current observed in the 1G – cable configuration could not be confirmed for 2G – cables.

International audience

International audience

International audience

International audience