Finite element analysis of current flowing patterns and AC loss in the multifilament strand

• Published in: Physica. C, Superconductivity Vol. 495; pp. 118 - 125
• Main Authors: Ta, Wurui, Li, Yingxu, Gao, Yuanwen
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 15.12.2013; Elsevier
• Subjects: AC loss; Alternating current; Applied sciences; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Current flow pattern; Electrical engineering. Electrical power engineering; Electrical resistivity; Exact sciences and technology; Filaments; Finite element analysis; Finite element method; Granular, melt-textured, amorphous and composite superconductors; Inhomogeneous superconductors and superconducting systems; Materials; Mathematical analysis; Mathematical models; Multi-filament composite strand; Physics; Strands; Superconductivity; Three dimensional models; Multi-filament composite strand; Finite element analysis; Current flow pattern; AC loss; Electrical conductivity; Boundary conditions; Niobium alloys; Contact resistance; Finite element method; Field distribution; Multifilamentary superconductors; Composite superconductors; Transport processes; AC losses
• ISSN: 0921-4534; 1873-2143
• DOI: 10.1016/j.physc.2013.09.001

•We study current flow patterns and AC loss in the multifilament strand.•Transverse and longitudinal flows are considered separately.•Stationary and time-varying situations are involved.•The effect of various contact resistances and twist pitches is discussed. Intrinsic current flow and field distribution scheme under the imposed low current injection and the applied weak field is meaningful to interpret Ic degradation and AC loss in a strand that performs as a normal composite conductor. A 2D finite element (FE) transport model is built in COMSOL to identify the various transverse resistance components and reveal the interrelation among them. Then the transverse resistivity components are taken as the basic electrical components in a 3D composite strand model. The 3D model follows the realistic trajectories of twisted filaments in strand composite and experimental material properties. To address the potential/current map in the stationary transport, the FE model is thoroughly analyzed for the short-sample and long-sample strand, imposed by two in-plane steady current injections and a potential boundary condition at one strand end with the other end grounded, respectively. The results show that the short-sample longitudinal current is uniform with little resistivity loss, and flows from the positive source and converges to the negative one in the cross section with different paths and current proportions between filaments and matrix. However, for the long-sample, there is a serious reduction in electric potential along the strand axis and the currents mostly concentrate on filaments. The time-varying problem is also implemented by computing AC loss induced by a relatively far-away alternating line current. It is discussed where appropriate that the effect of the twist pitch and contact resistivity on the pattern and magnitude of the current flow and AC loss.