Can Resistive-Type Fault Current Limiter Operate in Cryogen-Free Environment?

Superconducting fault current limiters are unique devices that offer fast response to fault without need of an external triggering system. Therefore, they are interesting for industrial use, although their price is high. The principle of the resistive fault current limiter is based on the steep current-voltage characteristic of superconductors. When the current rises over the critical one, voltage on the superconductor rises steeply, and this mechanism blocks the increase of the current. Simultaneous appearance of voltage and current during this limiting period of operation generates a substantial amount of heat that is dissipated in the superconducting wire causing a rapid increase of its temperature. In this contribution, we further develop the idea that, during a limiting period, there is only a small difference between cooling by liquid nitrogen and adiabatic conditions. Using this approach, one can think about a current limiter free from a liquid coolant using a cryocooler. In this contribution, we discuss main differences in cooling conditions and test the idea on a short sample of the high-temperature superconductor REBCO conductor. We compare the behavior of identical samples cooled to the same temperature by liquid nitrogen and conduction cooled. If the realization can be achieved, the huge benefit would be an FCL with a tunable triggering current via its operating temperature.

Design and manufacture of 20 kA HTS current leads for a hybrid magnet system

Pierluigi Bruzzone, Stephen Alfred March, Martin Vogel, Rainer Wesche

A new series connected 25 T hybrid magnet system is being developed by the Helmholtz Zentrum Berlin (HZB) for neutron scattering experiments. In collaboration with CRPP, high temperature superconducting (HTS) current leads have been developed for the powering of the outer superconducting coil. These HTS current leads, with a nominal current rating of 20 kA, have been designed and are being manufactured by CRPP, based on the design of the 18 kA EDIPO leads. Each of the two current leads consists of an HTS module cooled only by heat conduction from the cold end and a copper part actively cooled by helium gas of 44 K inlet temperature. To reach a temperature of 53.7 K at the warm end of the HTS a helium mass flow rate of 1.37 g/s per lead is required at a current of 20 kA. The estimated heat leak at the 4.5 K level caused only by heat conduction is as low as 1.4 W. The evolution of the temperatures in the case of a loss of flow has been calculated. In addition to the design, the main fabrication steps are described. (C) 2012 Published by Elsevier B. V. Selection and/or peer-review under responsibility of the Guest Editors.

Elsevier Science Bv2012

Heat transfer monitoring between quenched high-temperature superconducting coated conductors and liquid nitrogen

Daniele Colangelo, Bertrand Dutoit

High-temperature superconducting coated conductors (HTS-CCs) are good candidates for resistive superconducting fault current limiter (RSFCL) applications. However, the high current density they can carry and their low thermal diffusivity expose them to the risk of thermal instability. In order to find the best compromise between stability and cost, it is important to study the heat transfer between HTS-CCs and the liquid nitrogen (LN2) bath. This paper presents an experimental method to monitor in real-time the temperature of a quenched HTS-CC during a current pulse. The current and the associated voltage are measured, giving a precise knowledge of the amount of energy dissipated in the tape. These values are compared with an adiabatic numerical thermal model which takes into account heat capacity temperature dependence of the stabilizer and substrate. The result is a precise estimation of the heat transfer to the liquid nitrogen bath at each time step. Measurements were taken on a bare tape and have been repeated using increasing Kapton® insulation layers. The different heat exchange regimes can be clearly identified. This experimental method enables us to characterize the recooling process after a quench. Finally, suggestions are done to reduce the temperature increase of the tape, at a rated current and given limitation time, using different thermal insulation thicknesses.

2015

Computer Modeling of YBCO Fault Current Limiter Strips Lines in Over-Critical Regime With Temperature Dependent Parameters

Joseph Duron, Bertrand Dutoit, Francesco Grilli

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_{c}

. 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_{c}

. 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.

2007

Computer Modeling of YBCO Fault Current Limiter Strips Lines in Over-Critical Regime With Temperature Dependent Parameters

Joseph Duron, Bertrand Dutoit, Francesco Grilli

I_{c}

I_{c}

2007