Abstract

When exposed to time-dependent magnetic fields, REBCO Roebel cables generate AC loss resulting from both magnetic hysteresis and induced inter-strand coupling currents. Until now, the AC loss has been computed in a two-dimensional approximation assuming fully coupled or decoupled strands, and a finite inter-strand resistance could be simulated only with three-dimensional models. In this work, we propose a homogenization procedure that reduces the three-dimensional geometry of the Roebel cable to two dimensions, without ignoring connections between the strands. The homogenized cable consists of two parallel ‘monoblocks’ with an anisotropic resistivity. The proposed model enables computation of AC coupling loss without the need for complex three-dimensional simulations. For experimental validation, a Roebel cable with soldered strands was prepared. The inter-strand resistance was determined by applying a transverse current and measuring the voltage profile. Additionally, the AC magnetization loss of the cable was measured in fields of 1 to 50 mT with frequencies of 1 to 2048 Hz using a calibration-free technique. With the measured inter-strand resistance as input parameter, the monoblock model gives a good estimate for the AC loss, even for conditions in which the coupling loss is dominant.

Highlights

  • The Roebel cable is a way to make fully transposed cables of REBCO coated conductors [1] (REBCO = rare-earth metal barium copper oxide)

  • When exposed to time-dependent magnetic fields, REBCO Roebel cables generate AC loss resulting from both magnetic hysteresis and induced inter-strand coupling currents

  • We propose a homogenization procedure that reduces the three-dimensional geometry of the Roebel cable to two dimensions, without ignoring connections between the strands

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Summary

Introduction

More advanced three-dimensional models exist [19,20,21,22] None of these models take into account a finite resistance between the strands, and cannot predict coupling losses. A network model developed by van Nugteren et al simulates the three-dimensional cable taking into account coupling between the strands [23]. To our knowledge this is the only numerical model for Roebel cables that can predict AC coupling losses. We aim to compute the magnetization AC loss in a Roebel cable with finite inter-strand resistance using a two-dimensional model, and evaluate it with an experiment. Due to limitations of the set-up, we have not been able to validate the model for higher amplitudes

Monoblock model
Sample preparation
Inter-strand resistance between adjacent and non-adjacent strands: ρa lt 2Ns
AC loss measurement
Summary and outlook
Full Text
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