Publications by Bertrand Dutoit

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This paper focuses on the experimental determination of the electrical resistance (R) of commercial high temperature superconductor (HTS) coated conductors (CCs) at currents well above the critical current. The major novelty of this work rests on the unique experimental capability of applying constant current pulses in the sample (up to 1000 A) for durations as short as 15 mu s, which allows very precise control of the amount of energy dissipated in the sample (the Joule effect), as well as the resulting te

This paper presents a quantitative comparison of the AC loss performance of two BSCCO and two YBCO conductors, characterized by the same self-field critical current of 150 A. In particular, compared are a 37-filamentary BSCCO tape, a 16-filamentary BSCCO s ...

The current repartition inside a HTS cable is very important for determining its AC losses and can be influenced by the uniformity of several parameters, either linked to the physical properties of the individual tapes (critical current Ic and power index n) or due to the manufacturing process (contact resistance). This work investigates the importance of the non-uniformity of these parameters for a manufactured 16-tape straight superconducting cable by means of finite element method (FEM) simulations. The

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 ...

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 finit ...

Coated conductors are very promising for the design of novel and e±cient Fault Current Limiter (FCL). However, before considering using them in a power grid, their thermal and electromagnetic behaviors in the presence of over-critical currents need to be i ...

The a.c. self-field loss in Bi-2223 Ag and Ag-alloy sheathed tapes with different number of filaments has been measured in the range 59-2500 Hz by means of a dual lock-in amplifier technique. We have been able to dissociate quantitatively the different self-field loss contributions: hysteretic, eddy current and flux-creep resistive loss (near Ic) due to their different frequency dependence and the wide frequency range of the measurements. The relative weight of eddy current losses is found to be inversely p

A round-robin of self-field ac loss measurements on Bi-2223 tapes has been performed for the first time, under the Brite EuRam research programme SACPA. Excellent agreement on loss data has been obtained by the four measurement partners. This further confi ...

Transient stability investigations consist of studying the rotor oscillations of generators (electro-mechanic oscillations, 0.1-2 Hz) after the occurrence of a fault of large amplitude, e.g. short circuit. The goal is to indicate if the generators are capable to stay synchronous after a fault has occurred. The fault duration is one of the most important factors to be determined. In fact, the shorter the fault, the more the maintaining of synchronisation can be guaranteed. Now in case of a fault, a fault cur

The E-J power law as electric characterization of the HTS material in Finite Element computations has shown good agreement with measurements of field-dependent crtical current density and losses due to transport current. We use this technique to investigate the loss caused by Ac transport current in self-field and in applied AC magnetic field in both elliptical monocore and multicore tapes, where the current is generated by means of a voltage source. The current density is first kept constant and then varie

We use a dual channel digital lock-in to perform electrical measurement of AC losses at power frequencies. A DC magnetic field between 2 and 400 mT is applied with a varying angle from parallel to perpendicular to the tape surface, thus having a complete view of the loss behavior under DC applied field. Furthermore, the same experimental layout is used to acquire time series of current and voltage across the sample. Using a triangular input current, we measure and average the voltage, which then is fitted t

This paper presents results from numerical modelling of non-twisted multifilamentary Bi-2223/Ag conductors with various geometry and filament arrangement. New anisotropic models of Jc(B) and n(B) have been employed in finite element method simulations under different operating conditions – with applied AC transport current, in external parallel and perpendicular AC magnetic field, and with combined current and field of varying orientation. AC losses, as well as current and magnetic flux densities in square

High voltage direct current super-grids are one attractive solution for the transmission of bulk power of renewable electricity over long distances. Their protection is still an issue and superconducting fault current limiters (SCFCL) offer attractive pers ...

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 prog ...

This paper presents results from numerical modeling of non-twisted multifilamentary Bi-2223/Ag conductors with various geometry and filament arrangement. Anisotropic models of Jc(B) and n(B) have been employed in finite element method simulations under different operating conditions – with applied ac transport current, in external parallel and perpendicular ac magnetic field, and with combined current and field of varying orientation. AC losses and current distributions in square and round Bi-2223/Ag wires

Using 3D finite element modelling, the present work investigates the coupling effect between superconducting filaments induced by an externally applied varying magnetic field. The considered geometry consists of two superconducting filaments separated by a resistive matrix. The shape of the conductors, which strongly influences the magnetic field profiles inside the conductors and the degree of coupling, has been varied to take into account very different cases: in particular, the slab, square and strip geo

The performance of HTS devices is strongly influenced by local values of the current/field distributions. In this paper, we investigate the influence of the magnetic field and of the geometrical configuration on the loss behaviour of a 200kVA FCL prototype ...

A good knowledge of material properties is a critical aspect for modeling high-temperature superconductor (HTS) devices. However, the knowledge of the electrical resistivity of coated conductors above the critical current is limited. The major challenge in ...

A fast hotspot detection technique has been implemented and patented at ecole Polytechnique Federale de Lausanne (EPFL) under the European Union project FastGrid. The optical fibre sensing based technique uses the Mach-Zehnder Interferometer (MZI) and can ...

The a.c. self-field loss in Bi(2223)Ag sheathed tapes with different number of filaments has been measured between 59 and 2500 Hz by means of a dual lock-in amplifier. Due to the wide frequency range of the measurements we have been able to dissociate quantitatively the different self-field loss contributions: hysteretic, eddy current and resistive loss (near Ic). This is an important advantage compared to single frequency measurements where such loss dissociation is only qualitative. The hysteresis losses

Bertrand Dutoit

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Characterization of the electrical resistance of high temperature superconductor coated conductors at high currents using ultra-fast regulated current pulses

Comparison of the AC losses of BSCCO and YBCO conductors by means of numerical analysis

Numerical modelling of a HTS cable in AC regime

3D Finite Element Simulations of strip lines of a YBCO/Au Fault Current Limiter

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

Magneto-thermal finite element modeling of 2nd generation HTS for FCL design purposes

Eddy current self-field loss in Bi-2223 tapes with ac transport current

A series of round-robin measurements of the self-field ac loss of Bi-2223 tapes

Enhancement of power system transient stability using superconducting fault current limiters

Losses in HTS Tapes due to AC External Magnetic Field and AC Transport Current

Bi(2223) Ag sheathed tape Ic and exponent n characterisation and modelling under DC applied magnetic field

Numerical modelling and AC losses of multifilamentary Bi-2223/Ag conductors with various geometry and filament arrangement

Status of the European Union Project FASTGRID

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

AC Losses of Multifilamentary Bi-2223/Ag Conductors with Different Geometry and Filament Arrangement

Finite element method study of the coupling effect between superconducting filaments in varying magnetic field

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

Optimization Method for Extracting Stabilizer Geometry and Properties of REBCO Tapes

Fast Quench Detection in SFCL Pancake Using Optical Fibre Sensing and Machine Learning

Frequency dependence of A.c. loss in Bi(2223)Ag sheathed tapes