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In calculations for predicting the performance of high-temperature superconducting (HTS) cables, uniform physical and geometrical properties of the tapes are usually assumed. However, commercially available coated conductor tapes present a certain nonuniformity of their transport capability—namely their critical current—along the length. In addition, when coated conductor strands are compactly assembled to form a Roebel cable, their arrangement is far from the ideal one. In this work, we calculate the influence of Ic nonuniformities and of nonperfect strand alignment on the critical current of Roebel cables made of an HTS-coated conductor tape. For this purpose, we perform a statistical analysis using a recently developed and freely available open-source code to calculate the critical current of Roebel cables. We find that, for the considered cases, the nonuniformity of the strands’ Ic can have a significant impact on the final critical current of the cable, whereas the influence of the misalignment of the strands is rather low. [ABSTRACT FROM PUBLISHER]

In this paper, we derive integral equations for radially and polygonally arranged high-temperature superconductor thin tapes, and we solve them by finite-element method. The superconductor is modeled with a nonlinear power law, which allows the possibility of considering the dependence of the parameters on the magnetic field or the position. The ac losses are computed for a variety of geometrical configurations and for various values of the transport current. Differences with respect to existing analytical models, which are developed in the framework of the critical state model and only for certain values of the transport current, are pointed out. [ABSTRACT FROM PUBLISHER]

In this paper we present a new model for computing the current density and field distributions in superconductors by means of a finite element (FE) periodic space-time (PST) formulation. By considering the time as a space dimension, and considering periodic excitations for the applied field or transport current, we can use a static model to solve this time dependent problem. This approach has the potential to overcome one of the major problems of FE modeling of superconductors: the length of simulations, even for relatively simple cases. In this paper we show our first results for different cases of superconductors with AC magnetic fields and currents. Results are compared with those of standard time-dependent methods and analytical solutions. [ABSTRACT FROM AUTHOR]

In this paper we present a new model to compute the current density distribution and the AC losses in multiple YBCO coated conductors by means of coupled integral equations implemented in a finite-element (FE) environment. The model considers the superconducting tapes as 1D objects and allows overcoming the problem of the mesh of conductors of large aspect ratio, typical of 2D implementations; as a result, it is also much faster. The interaction between the different conductors is taken into account by means of a coupling of the electromagnetic variables. The magnetic field distribution in the space between the conductors is computed by coupling the 1D model with a standard 2D magnetic model, which uses the computed current density distributions as sources for the magnetic field. Results are compared with those obtained with standard 2D implementations and with experimental results. [ABSTRACT FROM AUTHOR]

In order to successfully integrate superconducting fault current limiters (SFCL) into electric power system networks, accurate and fast simulation models are needed. This led us to develop a generic electric circuit model of an inductive SFCL, which we implemented in the EMTP-RV software. The selected SFCL is of shielded-core type, i.e. a HIS hollow cylinder surrounds the central leg of a magnetic core, and is located inside a primary copper winding, generating an AC magnetic field proportional to the line current. The model accounts for the highly nonlinear flux diffusion phenomenon across the superconducting cylinder, governed by the Maxwell equations and the non-linear E-J relationship of HIS materials. The computational efficiency and simplicity of this model resides in a judicious 1-D approximation of the geometry, together with the use of an equivalent electric circuit that reproduces accurately the actual magnetic behavior for the flux density (B) inside the walls of the HTS cylinder. The HTS properties are not restricted to the simple power law model, but instead, any resistivity function depending on J, B and T can be used and inserted directly in the model through a non-linear resistance appearing in the equivalent circuit. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the influence of various numerical parameters on the precision and the speed of ac loss computations in high-temperature superconductors using the finite-element method. The case considered here is an infinite slab subjected to an external ac magnetic field. This problem can be modeled by a 1-D partial differential equation (diffusion equation). This relatively simple case allowed investigating the influence of the various parameters in a reasonable time. The findings of this work can be used as a starting point for optimizing the numerical settings of more complex models. As the main results, it is shown that choosing first-order elements for approximating the flux density (13) is the most stable option, and that using high order adaptive time-stepping methods provides good accuracy and fast simulations. A new and simple self-check test for validating the computed ac losses is also proposed. Finally, a detailed analysis about the behavior of the numerical solution near flux/current fronts is provided. [ABSTRACT FROM AUTHOR]

Coated conductors (CCs) are very promising for the design of novel and efficient resistive fault current limiters (FCLs). However, a detailed knowledge about their thermal and electromagnetic behaviors in the presence of over-critical currents is crucial for their improvement. In this context, we performed finite-element magneto-thermal modeling of CCs under over-critical current on several geometries. Accordingly, we have investigated the influence of the physical properties of stabilizer and substrate on the thermal stability to improve the high-temperature superconductor (HTS)-FCL design. All simulations were performed using COMSOL Multiphysics, a commercial finite-element package, which has a built-in coupling between the thermal and electrical equations, allowing us to compute both quantities simultaneously during the solving process. Our results allow us to determine the current threshold to achieve thermal stability of HTS FCLs made with CCs. [ABSTRACT FROM AUTHOR]

In superconducting coils tapes are often closely packed in a configuration similar to a ‘z-stack’, which strongly influences the AC losses with respect to when tapes can be considered as separate objects: losses are reduced in the presence of externally applied AC magnetic field, but are increased in the presence of AC transport current. In this paper, we quantify the magnitude of the tape interaction and the AC losses of these two cases, both experimentally and by means of finite-element method simulations. We also discuss the experimental issues arisen with the utilized AC loss measurement technique. [ABSTRACT FROM AUTHOR]

In this paper we present a new 2D numerical model for AC loss computation in high-temperature superconductors, based on the use of edge finite elements. These elements are curl conforming by construction and involve the continuity of the tangential component of the magnetic field between adjacent elements. In this way they do not require the imposition of the zero divergence of the magnetic field at each time step, which, with standard nodal elements, increases the null space of the matrix and the risks of divergence of the algorithm. The model, implemented in the software package COMSOL, uses the two magnetic field components as state variables. It has been tested for computing the losses of YBCO coated conductor tapes in two cases of practical interest, which cannot be investigated by analytical models. [ABSTRACT FROM AUTHOR]

In this paper we present initial results on growing YBCO/IBAD-MgO/YBCO stacks. Amorphous Y2O3 layers, deposited by sol-gel, are used to level the YBCO surface. Since the YRCO films prepared by pulsed laser deposition are relatively rough, preparing a smooth surface on top of YBCO for IBAD texturing is a major challenge for this structure. For all substrates studied-polished and unpolished metal tape and YBCO—we were able to reduce the roughness of the substrate using the sol-gel layer, with multiple coatings being more effective. First it is demonstrated that high quality YBCO films can be deposited on sol-gel-Y2 O3/IBAD-MgO templates. Second it is shown that the sol-gel and the IBAD process do not affect the superconducting properties of the underlying YBCO film. Finally, a superconducting YBCO bilayer stack is demonstrated. Improvements in the properties of the top YBCO layer is expected when the surface roughness is reduced further for deposition of subsequent IBAD-textured layers. This new technology should enable novel designs of coated conductors for reduced AC losses and increased Je. [ABSTRACT FROM AUTHOR]

The performance of HTS devices is strongly influenced by local values of the current and field distributions. In this paper, we investigate the influence of the magnetic field and the geometrical configuration on the loss behavior of a 200 kVA FCL prototype, composed by 111-2223/Ag tapes wound around a cylindrical support. The investigation is performed by means of finite element computations, with the use of an axisymmetric 2D A-V formulation for taking into account the cylindrical geometry. The electrical behavior of the superconductor is described by means of a B-dependent E-J power-law relation, derived from experimental measurements with a field of different orientation. Several geometrical configurations are analyzed and compared, in order to find the ones with the lowest AC loss. [ABSTRACT FROM AUTHOR]