J. Duron

University of Geneva, Genève, Geneva, Switzerland

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Publications (10)9.47 Total impact

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    ABSTRACT: We present the results of an advanced numerical model for fault current limiter (FCL) based on HTS thin films in which both thermal and electromagnetic aspects are taken into account. This model allows simulating the behavior of FCL in the over-critical current regime and we used it for studying strip lines of a YBCO/Au FCL on sapphire substrate. The electromagnetic and thermal equations have been implemented in finite-element method (FEM) software in order to obtain a model for investigating the comportment of the superconductor when the current exceeds I<sub>c</sub>. In particular, materials equations have been implemented in order to simulate the electrical behavior of superconducting devices with strong over-critical currents. We report results of simulations in voltage source mode where currents largely exceed I<sub>c</sub>. The global behavior of the FCL is compared with measurements, showing a good agreement. The use of FEM simulations offers the advantage to give access to local variables such as current density or temperature. Studies with this model can replace expensive experiments where very high current density might damage or destroy the FCL device.
    IEEE Transactions on Applied Superconductivity 07/2007; · 1.20 Impact Factor
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    ABSTRACT: The adjunction of constrictions along the meander of a superconducting fault current limiter (FCL) greatly improves its behavior thanks to a better distribution of the dissipative zones at the occurrence of a short circuit. This design works perfectly for symmetrical short circuit (i.e. short circuit at the maximum voltage). However for asymmetrical short circuits (at voltages close to 0), we are facing a problem due to the small number of the initially switched constrictions. To solve this problem, we test the possibility to speed up the transition into the normal state of the whole meander by heating it locally. This thermally assisted transition is realized by growing a gold layer on the backside of the substrate and by patterning it into a meander with its dissipative parts lying just underneath the constrictions of the FCL. This gold meander can be either connected in parallel with the superconducting meander or a capacitor bank can supply the current. In order to confirm the benefit of the thermally assisted transition we have carefully measured the behavior of the FCL during constant current and low voltage pulses as a function of the power injected into the gold line. We present results showing that the response of the FCL to the generated heat is very fast; typically less than 100 mus. Furthermore the distribution of the dissipated power across the wafer, during asymmetrical AC short circuit, is clearly improved.
    IEEE Transactions on Applied Superconductivity 07/2007; · 1.20 Impact Factor
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    ABSTRACT: In this paper we present a numerical model in which both the thermal and the electromagnetic aspects of the over-critical current regime of HTS materials are taken into account. The electromagnetic and thermal equations have been implemented in finite element method (FEM) software in order to obtain a novel, closer to reality model for investigating the behaviour of the materials when the current exceeds Ic. A thermal dependence of the electrical parameters, like the critical current density Jc, has been introduced. This model has been used to analyse the behaviour of strip lines of a YBCO/Au fault current limiter (FCL) on a sapphire substrate. Simulations with currents largely exceeding Ic have been performed, showing that the current limitation phase can be correctly reproduced. Such modelling can be used to study the influence of the geometry on the performance of the FCL. It is designed to replace experiments with currents far exceeding Ic which may damage or destroy HTS samples or devices.
    Superconductor Science and Technology 01/2007; · 2.76 Impact Factor
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    ABSTRACT: In this paper, we present a new numerical model, in which both the thermal and the electromagnetic aspects of the over-critical current regime of HTS materials are taken into account. The electromagnetic and thermal equations have been implemented in finite-element method (FEM) software in order to obtain a novel, closer to reality model for investigating the behaviour of the superconductor when the current exceeds Ic. This model has been applied for studying the behaviour of strip lines of an YBCO/Au FCL with a sapphire substrate. Simulations with currents largely exceeding Ic have been performed, showing that the total current limitation occurs only when the temperature dependence of the electrical parameters is taken into consideration. Such modelling can replace experiments with currents far exceeding Ic which may damage or destroy the studied sample or HTS device.
    Journal of Physics Conference Series 07/2006; 43(1):1076.
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    ABSTRACT: The magnetic field profile on the surface of Bi-2223/Ag tapes has been dynamically measured across the width of the samples. The experimental technique uses a Hall-probe array with 7 sensors connected to a multiple channel lock-in amplifier especially programmed for fast and synchronous data acquisition measurements. The speed of the system is high enough to measure real-time profiles with 7 probes and 50 Hz sine current through the sample. A numerical method to estimate the current distribution inside the tapes using the measured field profile data is proposed. The inverse problem has been solved using certain assumptions on the current distribution in the superconductor. Validation of the results has been done by comparison with finite element method simulations.
    IEEE Transactions on Applied Superconductivity 07/2005; · 1.20 Impact Factor
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    ABSTRACT: Geometrical aspects of the design of fault current limiters (FCL) have a great impact on their performances. Recently, the University of Geneva have made certain optimizations by splitting the FCL into many small dissipative lengths in order to achieve a distributed transition along the device. For this paper, we have performed new 3D finite element method (FEM) simulations for studying the behavior of strip lines of a YBCO/Au FCL in an AC nominal use (sinusoidal current at industrial frequency) up to 3 I<sub>c</sub>. The very large aspect ratio of the device needs a particular attention to the modeling and meshing process. The numerical results show that presence of sharp corners can influence the performance of the device. Due to the high value of the electric field in these areas, the local losses are much higher than in the case of smooth corners, and this may lead to burning and cracking the wafer. Irreversible damage experiments have confirmed these locations. In this paper we proposed new geometries, taking into account the length of the connecting path and the corners optimization in order to decrease the risk of very high localized losses in the meander.
    IEEE Transactions on Applied Superconductivity 07/2005; · 1.20 Impact Factor
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    ABSTRACT: For describing the E-J relation of high-Tc superconductors (HTS) in power applications, where the applied current I is generally limited by Ic, the critical state model, a piecewise linear generalization, or a simple power-law of the type E=Ec(J/Jc)^n are most often used. The power-law cannot be used for modelling the E-J relation with I>>I_c due to the unbound exponential increase of the electric field for currents above Ic, while in reality the non-linear HTS resistivity is limited by its normal state value. This paper presents a modified E-J model for describing the V-I characteristic of HTS tapes with applied currents largely exceeding Ic. This model is based on the power-law in combination with a parallel metallic branch and has a limited resistivity - the HTS one in the normal state. It can be used for black-box modelling of superconductors in a unlimited current range, as well as for numerical modelling of superconducting devices, which can be operated at currents far exceeding Ic; for example fault-current limiters or cables with over-critical current excursions. The model has been tested in a simple numerical implementation and the modified power-law has been implemented in finite element method simulations. It is shown that for bulk material with currents above 1.3-2Ic$ (depending on the n-value), the usual power-law results in excessive AC loss estimation.
    Physica C Superconductivity 01/2004; · 0.72 Impact Factor
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    M. Sjostrom, B. Dutoit, J. Duron
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    ABSTRACT: We propose an equivalent circuit model that describes the behavior of a superconductor viewed by an external user, for whom the global variables voltage and current are of interest. It is used in time-continuous simulations and it treats well both the subcritical and supercritical current regime. The model is based on Maxwell's equations, measurement results as well as on the physical structure of a superconducting tape. The incorporated circuit elements have been described in mathematical expressions: a nonlinear resistance and a nonlinear inductance (superconducting core) in parallel with a linear resistance and a linear inductance (silver sheath or by-pass material). The simplicity of the model makes it fast and easy to apply compared to existing numerical models of superconductors, based on finite element methods. Furthermore, it is wide-ranging and may represent a superconductor in many different applications depending on parameter values. Examples of applied voltage and current with nonstationary waveforms on a HTS tape are given. Calculated are the hysteresis losses (due to flux pinning) and resistive losses (due to flux creep and flux flow) in the tape in the range 0.1 to 1.8 I<sub>c</sub>.
    IEEE Transactions on Applied Superconductivity 07/2003; · 1.20 Impact Factor
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    Joseph Duron
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    ABSTRACT: This thesis is focused on the modelling of superconducting materials, and in particular, high-temperature superconducting materials. This work is divided in two parts: first, the dynamic magnetic field mapping obtained by measurements is used in order to reconstruct the dynamic current distribution inside a tape assuming a model describing its global behavior. In the second part, superconductors in over-critical regime have been both electrically and thermally modelized with a finite element method. Calculations have been applied on a current limiter and compared to a constructed and measured device at the University of Geneva. The first chapter is an introduction to high-temperature superconducting materials, where the main superconducting physical properties used are presented. Next, we introduce the different existing models which can be used for describing the behavior of a superconducting tape. With the help of the Bean model, a novel method to evaluate the current distribution in a mono-filamentary superconducting tape from surface magnetic field measurements is proposed. The obtained results are compared with more precise, but more complex, methods like finite element modeling, which will be used for the second part of this work. The last part is focused on the modelization of superconducting material in overcritical regime. To achieve this goal, we need to introduce a different expression than the usual Ec(J/Jc)n power-law for describing the electric behavior of the material in a much wider current range covering over-critical excursion. The original proposition we made is able to fit the measurements made on YBCO tapes, allowing to describe the transition from the superconducting to the normal state. Then, to taking into account the thermal phenomena, the temperature dependence of the electrical parameters has been introduced in order to solve a coupled electromagnetic and thermal problem: solving a time step of the electromagnetic part leads to the knowledge of the local losses. These losses are injected inside the thermal part. The resulting temperature computation is used to modify the electrical parameters for the next time step. Finally, this method has been applied in order to simulate a superconducting current limiter. The global behavior of the device can be reproduced by the implemented numerical model, which also allows the study of the local variables, like current density distribution or temperature profile. The obtained results can be used to optimize a device according to specific criteria. In particular, we have proposed geometric modifications for avoiding possible local thermal runaway, which can lead to the destruction of the device. This proposition has beeing inspired the new design, which is now tested. L'objectif principal de cette thèse est la modélisation de matériaux supraconducteurs, et plus particulièrement, de ceux dits à haute température critique. Ce travail est divisé en deux parties distinctes : dans un premier temps, nous nous intéressons à la reconstruction de la distribution dynamique du courant dans la section d'un ruban supraconducteur à l'aide d'un modèle décrivant son comportement global. Ensuite, nous nous focalisons sur la modélisation électromagnétique et thermique par éléments finis des supraconducteurs en régime sur-critique, c'est à dire au-delà du courant critique Ic. Une introduction à la supraconductivité est faite dans le premier chapitre de ce travail, présentant les propriétés physiques principales que possède un matériau supraconducteur. Ensuite, nous décrirons les différents modèles existants permettant de décrire le comportement d'un échantillon supraconducteur. En se basant sur le modèle de Bean, nous proposons une nouvelle méthode permettant d'évaluer la distribution du courant dans la section d'un ruban monofilamentaire à partir de la mesure du profil magnétique à sa surface. Les résultats obtenus sont comparés avec ceux données par une modélisation certes plus précise, mais aussi plus complexe : l'utilisation de la méthode des éléments finis. Cette dernière sera largement utilisée dans la seconde partie de ce travail, qui traite de la modélisation de matériaux en régime sur-critique. Ceci nécessite d'introduire une formulation différente de l'habituelle loi de puissance Ec(J/Jc)n pour décrire le comportement électrique du matériau dans une plage de courant plus importante, incluant les régimes sur-critiques. Pour cela, nous proposons une méthode originale, permettant d'approcher des mesures effectuées sur des échantillons d'YBCO et autorisant la description de la transition de l'état supraconducteur vers l'état normal. La dépendance en température a aussi été introduite afin d'étudier les phénomènes thermiques qui se produisent. Il est ainsi possible de résoudre de manière couplée les équations électromagnétiques et thermiques du problème : la résolution d'un pas de temps électromagnétique conduit à la connaissance des pertes locale. Ces pertes sont injectées dans le modèle thermique, et permet de calculer l'augmentation de température correspondante. Ce résultat est alors utilisé pour modifier les paramètres électriques en vue de la résolution du prochain pas de temps. Finalement, cette méthode a été utilisée afin de simuler le comportement d'un limiteur de courant supraconducteur. Le comportement global du système peut être reproduit par le modèle numérique implémenté, autorisant ainsi l'étude des variables locales, telles que la densité de courant ou le profil de température. Les résultats obtenus peuvent être utilisés afin d'optimiser les performances du dispositif selon des critères spécifiques. C'est ainsi que nous avons proposé une modification de la géométrie permettant d'éviter un possible emballement thermique qui pourrait conduire à la destruction du système. Sur la base de cette proposition, des modifications ont été apportées au design du dispositif, et sont actuellement testées.
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Geometrical aspects of the design of fault current limiters (FCL) have a great impact on their performance. Recently, the University of Geneva have presented optimized geometries obtained by splitting the FCL into many small dissipative lengths in order to distribute the power along the device. We have performed 3D finite element method (FEM) simulations for studying the behavior of strip lines of a YBCO/Au FCL in AC nominal use (sinusoidal current at industrial frequency) up to 3 Ic. Particular attention has been paid to the mesh, due to the very large involved aspect ratios. The numerical results show a concentration of the electric field in the sharp corners. This results in very large power dissipation, which has been experimentally confirmed by wafer cracks during over-Ic tests. A new geometry, taking into account the length of the connecting path and the corner optimization, has been proposed. Finally, simulations coupling electromagnetic and thermal equations show the behavior of the device when a default occurs on the electrical network. This work is supported by the Swiss National Science Foundation through the National Center of Competence in Research “Materials with Novel Electronic Properties – MaNEP”

Publication Stats

60 Citations
9.47 Total Impact Points

Institutions

  • 2007
    • University of Geneva
      • Department of Condensed Matter Physics
      Genève, Geneva, Switzerland
  • 2004
    • Eawag: Das Wasserforschungs-Institut des ETH-Bereichs
      Duebendorf, Zurich, Switzerland
    • École Polytechnique Fédérale de Lausanne
      • Institut de génie électrique et électronique
      Lausanne, VD, Switzerland
  • 2003
    • Mid Sweden University
      Härnösand, Västernorrland, Sweden