Numerical models for ac loss calculation in large-scale applications of HTS coated conductors

Abstract

Numerical models are powerful tools to predict the electromagnetic behavior of superconductors. In recent years, a variety of models have been successfully developed to simulate high-temperature-superconducting (HTS) coated conductor tapes. While the models work well for the simulation of individual tapes or relatively small assemblies, their direct applicability to devices involving hundreds or thousands of tapes, as for example coils used in electrical machines, is questionable. Indeed the simulation time and memory requirement can quickly become prohibitive. In this article, we develop and compare two different models for simulating realistic HTS devices composed of a large number of tapes: 1) the homogenized model simulates the coil using an equivalent anisotropic homogeneous bulk with specifically developed current constraints to account for the fact that each turn carries the same current; 2) the multi-scale model parallelizes and reduces the computational problem by simulating only several individual tapes at significant positions of the coil's cross-section using appropriate boundary conditions to account for the field generated by the neighboring turns. Both methods are used to simulate a coil made of 2000 tapes, and compared against the widely used Hformulation finite element model that includes all the tapes. Both approaches allow speeding-up simulations of large number of HTS tapes by 1-3 orders of magnitudes, while keeping a good accuracy of the results. Such models could be used to design and optimize large-scale HTS devices. I.

Real-time simulation of large-scale HTS systems: multi-scale and homogeneous models using the T–A formulation

“…Since the new approaches rely on the characteristics of the T-A formulation, they are suitable for cases where the 1D approximation is meaningful and the influence of the parallel component of the field is negligible. At the same time, these new approaches also inherit the limitations of the multi-scale and the homogeneous models previously described in [20,33], thus they require less computational resources, but at the price of a lower accuracy than that of the full models. The full models should be applied in the cases where the best possible accuracy is required, if the size of the system and the available computational resources allows it.…”

“…The multi-scale method, as presented in [20,35], uses two different submodels, single tape and coil. The single tape submodel uses the H formulation and computes the J distribution in the analyzed tapes.…”

“…Nevertheless, they have specific characteristics that should be considered in order to successfully address the modelling task [18][19]. For a deeper review of numerical models, the reader is referred to [5,20]. Among the available methodologies suitable for the analysis of large-scale HTS systems, one should also mention the Minimum Magnetic Energy Variation (MMEV) method introduced in [21][22].…”

“…The resulting magnetic field is subsequently used as boundary condition to solve the current density in the analyzed tapes. This method was proposed in [34], with later refinements added in [20]. The last version of the method incorporates an iterative process to improve the accuracy of the current density in the analyzed tapes and, consequently, of the losses [35].…”

Exploiting asymmetric wire critical current for the reduction of AC loss in HTS coil windings

“…Furthermore, intensive AC loss analysis of HTS coils has been carried out both experimentally and numerically [14][15][16][17][18][19][20]. However, there has been no report to date on the influence of asymmetric wire critical current on coil AC loss.…”