Validation of Homogenized Filament Bundle Model in AC Loss Computations

Abstract

In high current ac applications, such as CERN and ITER magnets, superconducting cables are used. These cables typically consist of several individual strands and therefore have very complex geometries. Even a single NbTi strand designed for ac applications may consist of tens of thousands of filaments embedded in a normal conducting matrix. It is not practical to numerically model the cable or the strand at the filament level in the ac loss analysis due to extremely long computation times. However, an approximation for the ac losses can be computed if the filament zones or bundles are considered as a homogeneous mixture of superconducting filaments and matrix metal. This means, for example, substantial savings in the computation times of optimization procedures where hundreds of geometries are analysed. In this paper we compare the ac losses computed with both a homogenized bundle model and a detailed model (all or some of the bundles are modeled at the filament level) for different NbTi strand geometries to benchmark the accuracy of the bundle approximation. The results show that the bundle model is a suitable approximation, especially for certain bundle geometries.

Numerical Investigation on the Thermo-Mechanical Behavior of HTS Tapes and Experimental Testing on Their Critical Current

“…Given the high aspect ratio of the tape sample -with a length of 300 mm and a thickness of 0.139 mm -and the thinness of the (Re)BCO layer, an effective finite element discretization operated by means of 3D continuum elements would require millions of elements, thus resulting in millions of degrees of freedom. To avoid this, homogenization procedures could be used [10]- [13]. On the other side, HTS tapes can be considered thin-walled structures where in-plane components of the strain and stress fields play a major role.…”

3D simulation of AC loss in a twisted multi-filamentary superconducting wire

“…Due to the advantages of H-formulation, it has become a powerful tool to study the superconductor's behaviors [15,21,[33][34][35][36]. Several numerical models are available for studying the behaviors subject to transport current or exposed to transverse magnetic field [15,27,31,37]. Amemiya [38] et al analyze the AC loss of the twisted filament bundle in multi-filamentary high T c superconducting tapes by treating the tapes as a homogeneous mixture of superconductor and matrix.…”

Suitability of Bundle Approximation in AC Loss Analysis of NbTi Wires: Simulations and Experiment

“…Particularly, we consider the usability of the filament bundle approximation and the time-harmonic approach in the R&D process of the NbTi wires. In the filament bundle approximation, the filament bundles are considered as a homogenous domain instead of individual filaments and matrix [8], [9]. The time-harmonic approach is used to approximate the losses in the matrix due to the interbundle coupling currents [10].…”