Calculating transport AC losses in stacks of high temperature superconductor coated conductors with magnetic substrates using FEM

In this paper, the authors investigate the electromagnetic properties of stacks of high temperature superconductor (HTS) coated conductors with a particular focus on calculating the total transport AC loss. The cross-section of superconducting cables and coils is often modeled as a two-dimensional stack of coated conductors, and these stacks can be used to estimate the AC loss of a practical device. This paper uses a symmetric two dimensional (2D) finite element model based on the H formulation, and a detailed investigation into the effects of a magnetic substrate on the transport AC loss of a stack is presented. The number of coated conductors in each stack is varied from 1 to 150, and three types of substrate are compared: non-magnetic weakly magnetic and strongly magnetic. The non-magnetic substrate model is comparable with results from existing models for the limiting cases of a single tape (Norris) and an infinite stack (Clem). The presence of a magnetic substrate increases the total AC loss of the stack, due to an increased localized magnetic flux density, and the stronger the magnetic material, the further the flux penetrates into the stack overall. The AC loss is calculated for certain tapes within the stack, and the differences and similarities between the losses throughout the stack are explained using the magnetic flux penetration and current density distributions in those tapes. The ferromagnetic loss of the substrate itself is found to be negligible in most cases, except for small magnitudes of current. Applying these findings to practical applications, where AC transport current is involved, superconducting coils should be wound where possible using coated conductors with a non-magnetic substrate to reduce the total AC loss in the coil.

[1]  Francesco Grilli,et al.  Magnetization AC losses of stacks of YBCO coated conductors , 2006 .

[2]  F. Gomory,et al.  Theoretical and experimental study of AC loss in high temperature superconductor single pancake coils , 2008, 0808.0061.

[3]  J. H. Claassen,et al.  AC losses in a finite Z stack using an anisotropic homogeneous-medium approximation , 2007, 0708.4024.

[4]  T. A. Coombs,et al.  Numerical solution of critical state in superconductivity by finite element software , 2006 .

[5]  T. A. Coombs,et al.  Comparison of first‐ and second‐order 2D finite element models for calculating AC loss in high temperature superconductor coated conductors , 2011 .

[6]  Comparison of AC losses, magnetic field/current distributions and critical currents of superconducting circular pancake coils and infinitely long stacks using coated conductors , 2010 .

[7]  Mawatari.  Critical state of periodically arranged superconducting-strip lines in perpendicular fields. , 1996, Physical review. B, Condensed matter.

[8]  Alexander Otto,et al.  AC loss and critical current characterization of a noninductive coil of two-in-hand RABiTS YBCO tape for fault current limiter applications , 2011 .

[9]  K. Müller,et al.  Self-field hysteresis loss in periodically arranged superconducting strips , 1997 .

[10]  Norio Takahashi,et al.  Measurement of magnetic properties of Ni-alloy substrate of HTS coated conductor in LN2 , 2008 .

[11]  Francesco Grilli,et al.  A new finite-element method simulation model for computing AC loss in roll assisted biaxially textured substrate YBCO tapes , 2010 .

[12]  Mark D. Ainslie,et al.  An improved FEM model for computing transport AC loss in coils made of RABiTS YBCO coated conductors for electric machines , 2011 .

[13]  W. T. Norris,et al.  Calculation of hysteresis losses in hard superconductors carrying ac: isolated conductors and edges of thin sheets , 1970 .

[14]  T. A. Coombs,et al.  Numerical Modelling of AC Loss in Coated Conductors by Finite Element Software Using H Formulation , 2010 .

[15]  T. A. Coombs,et al.  Numerical analysis and finite element modelling of an HTS synchronous motor , 2010 .

[16]  T. A. Coombs,et al.  A model for calculating the AC losses of second-generation high temperature superconductor pancake coils , 2009 .

[17]  Luciano Martini,et al.  AC losses in thin superconductors: the integral equation method applied to stacks and windings , 2009 .

[18]  Francesco Grilli,et al.  Measuring transport AC losses in YBCO-coated conductor coils , 2007 .

[19]  W. Yuan,et al.  ac losses and field and current density distribution during a full cycle of a stack of superconducting tapes , 2010 .

[20]  Enric Pardo,et al.  Modeling of coated conductor pancake coils with a large number of turns , 2008 .

[21]  L. Martini,et al.  Modeling High-Temperature Superconducting Tapes by Means of Edge Finite Elements , 2007, IEEE Transactions on Applied Superconductivity.

[22]  Weijia Yuan,et al.  Modeling and Electrical Measurement of Transport AC Loss in HTS-Based Superconducting Coils for Electric Machines , 2011, IEEE Transactions on Applied Superconductivity.

[23]  Leonid Prigozhin,et al.  Computing AC losses in stacks of high-temperature superconducting tapes , 2011 .