Local electromagnetic properties and hysteresis losses in uniformly and non-uniformly wound superconducting racetrack coils
A noteworthy physical dependence of the hysteresis losses with the axial winding misalignment of superconducting racetrack coils made
with commercial second generation high temperature superconducting (2G-HTS) tapes is reported. A comprehensive study on the influence
of the turn-to-turn misalignment factor on the local electromagnetic properties of individual turns is presented by considering six different
coil arrangements and ten amplitudes for the applied alternating transport current, Ia, together with an experimentally determined function
for the magneto-angular anisotropy properties of the critical current density, Jc(B, θ), across the superconducting tape. It has been found
that for moderate to low applied currents Ia 0:6 Ic0, with Ic0 the self-field critical current of individual tapes, the resulting hysteretic losses
under extreme winding deformations can lead to an increase in the energy losses of up to 25% the losses generated by a perfectly wound
coil. High-level meshing considerations have been applied in order to get a realistic account of the local and global electromagnetic properties of racetrack coils, including a mapping of the flux front dynamics with well defined zones for the occurrence of magnetization currents,
transport currents, and flux-free cores, which simultaneously has enabled an adequate resolution for determining the experimental conditions when turn-to-turn misalignments of the order of 20–100 μm in a 20 turns 4 mm wide racetrack coil can lead not only to the increment
of the AC losses but also to its reduction. In this sense, we have shown that for transport current amplitudes Ia . 0:7 Ic0, a slight reduction
in the hysteresis losses can be achieved as a consequence of the winding displacement, which is at the same time connected with the size
reduction of the flux-free core at the coil central turns. Our findings can be used as a practical benchmark to determine the relative losses
for any 2G-HTS racetrack coil application, unveiling the physical fingerprints that possible coil winding misalignments could infer.
Funding
The authors acknowledge the use of the High Performance Computing Cluster Facilities (ALICE) provided by the University of Leicester. This work has been supported by the EPSRC (Grant No. EP/S025707/1). H.S.R. has led the team and contributed toward the analysis and writing of the paper. B.C.R. acknowledges the Niger Delta Development Commission for their funding support and has contributed toward the model’s development, analysis and plotting of results, and writing of the paper. M.U.F. acknowledges the College of Science and Engineering Scholarship Unit of the University of Leicester and has contributed toward some of the computational tasks derived from this paper.
History
Citation
Journal of Applied Physics 126, 123902 (2019); https://doi.org/10.1063/1.5100223Author affiliation
/Organisation/COLLEGE OF SCIENCE AND ENGINEERING/Department of EngineeringVersion
- VoR (Version of Record)