Steve Stavrev

Publications (36) View all

• Article: Finite-element modelling of superconductors in over-critical regime with temperature dependent resistivity

  J Duron, F Grilli, L Antognazza, M Decroux, S Stavrev, B Dutoit, Ø Fischer
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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.
• Source

  Available from: epfl.ch

  Article: Dynamic field mapping for obtaining the current distribution in high-temperature superconducting tapes

  B. Dutoit, J. Duron, S. Stavrev, F. Grilli
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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 Appiled Superconductivity 07/2005; · 1.04 Impact Factor
• Source

  Available from: Roberto Brambilla

  Article: Analysis of magnetic field and geometry effects for the design of HTS devices for AC power applications

  F. Grilli, L. Martini, S. Stavrev, B. Dutoit, R. Brambilla
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  ABSTRACT: The performance of HTS devices is strongly influenced by local values of the current and field distributions. In this paper, we investigate the influence of the magnetic field and the geometrical configuration on the loss behavior of a 200 kVA FCL prototype, composed by Bi-2223/Ag tapes wound around a cylindrical support. The investigation is performed by means of finite element computations, with the use of an axisymmetric 2D A-V formulation for taking into account the cylindrical geometry. The electrical behavior of the superconductor is described by means of a B-dependent E-J power-law relation, derived from experimental measurements with a field of different orientation. Several geometrical configurations are analyzed and compared, in order to find the ones with the lowest AC loss.
  IEEE Transactions on Appiled Superconductivity 07/2005; · 1.04 Impact Factor
• Source

  Available from: epfl.ch

  Article: 3-D finite element Simulations of strip lines in a YBCO/Au fault current limiter

  J. Duron, L. Antognazza, M. Decroux, F. Grilli, S. Stavrev, B. Dutoit, O. Fischer
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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_c. 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 Appiled Superconductivity 07/2005; · 1.04 Impact Factor
• Article: Finite-element method modeling of superconductors: from 2-D to 3-D

  F. Grilli, S. Stavrev, Y. Le Floch, M. Costa-Bouzo, E. Vinot, I. Klutsch, G. Meunier, P. Tixador, B. Dutoit
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  ABSTRACT: A three-dimensional (3-D) numerical modeling technique for solving problems involving superconducting materials is presented. The model is implemented in finite-element method software and is based on a recently developed 3-D formulation for general electromagnetic problems with solid conductors. It has been adapted for modeling of superconductors with nonlinear resistivity in 3-D, characterized by a power-law E-J relation. It has first been compared with an existing and verified two-dimensional (2-D) model: Compared are the current density distribution inside the conductors and the self-field ac losses for different applied transport currents. Second, the model has been tested for computing the current distribution with typical 3-D geometries, such as corner-shaped and twisted superconductors. Finally, it has been used with two superconducting filaments in the presence of external magnetic field for verifying the existence of coupling currents. This effect deals with the finite length of the conductors and cannot be taken into account by 2-D models.
  IEEE Transactions on Appiled Superconductivity 04/2005; · 1.04 Impact Factor