Conductor On Round Core Cable Research Articles

Magnetization Loss Characteristics in Superconducting Conductor on Round Core Cables With a Copper Former

The High Temperature Superconducting (HTS) Conductor on Round Core (CORC) cables have been widely utilized to fabricate various superconducting applications for power transmission, fusion, and magnets with high current density. Understanding the AC loss behavior of CORC cables during the cable design process is essential for analyzing its electromagnetic performance and evaluating its future industry potential. The aim of our research is to investigate the AC loss dependence caused by the magnitude and frequency of applied external variations to the magnetic field. This paper describes the simulation models of HTS CORC cables based on the finite-element method (FEM) by using an H-formulation in a commercial software named COMSOL Multiphysics. Three-dimensional (3-D) CORC models, with three HTS tapes wound around each layer, were built and analyzed. The 3-D CORC models, built using the FEM method, were then verified with published experimental results. AC losses dissipated in the CORC cables, resulting from applied external varying magnetic field, were calculated and examined.

Superconducting Conductor on Round Core (CORC) Cables: 2D or 3D Modeling?

The HTSConductor on Round Core (CORC) Cables have been widely recognized as the proper candidate for superconducting applications such as the high-field magnets and power transmission cables. This article presents the modeling of HTS CORC cables using the FEM H-formulation model merged into the package COMSOL Multi-physics. The 2D and 3D H-formulation models of HTS CORC cables were compared and analyzed. There were two important parameters in our CORC design: (1) the gap angle between the HTS tapes in a single layer, and, (2) the degree of twist for HTS tapes (normally identified as the pitch). The 2D CORC model has much faster solving speed over the 3D model and sometimes is able to model the AC loss in a reasonable range, while, the 3D CORC model has the advantages over 2D CORC model with respect to more information in each sector with the different conditions of two parameters above, and more realistic loss calculation.

A Simplified Model of the Field Dependence for HTS Conductor on Round Core (CORC) Cables

This article presents a simplified mathematical model the anisotropic magnetic field dependence (AMFD) for simulating the High-temperature superconducting (HTS) Conductor on Round Core (CORC) Cables. All these simulations of HTS CORC Cable were performed based on the finite-element method (FEM) <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</i> -formulation model merged into the numerical platform COMSOL Multi-physics. The simplified model of AMFD was implemented into both the 2D and 3D <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</i> -formulation models of HTS CORC cables. Their results were studied with different conditions, such as the increasing transport current, as well as the gap angle between the superconducting tapes in a single layer. This new simplified AMFD model can give a proper approximation of the actual electromagnetic behaviours of the HTS CORC, but also establish the upper limit of the AC loss calculation, which can be fairly useful for designing future HTS CORC cables.

Analysis of AC Transport Loss in Conductor on Round Core Cables

The conductor on round core (CORC) cable wound with second-generation high-temperature superconducting (HTS) tapes is a promising cable candidate with superiority in current capacity and mechanical strength. The composing superconductors and the former are tightly assembled, resulting in a strong electro-magnetic interaction between them. Correspondingly, the AC loss is influenced by the cable structure. In this paper, a 3D finite-element model of the CORC cable is first built, and it includes the complex geometry, the angular dependence of critical current and the periodic settings. The modelling is verified by the measurements conducted for the transport loss of a two-layer CORC cable. Subsequently, the simulated results show that the primary transport loss shifts from the former to the superconductors as the current increases. Meanwhile, the loss exhibited in the outer layer is larger than that of the inner layer, which is caused by the shielding effect among layers and the former. This also leads to the current inhomogeneity in CORC cables. In contrast with the two-layer case, the simulated single-layer structure indicates stronger frequency dependence because the eddy current loss in the copper former is always dominant without the cancellation of the opposite-wound layers. The core eddy current of the single structure is denser on the outer surface. Finally, the AC transport losses among a straight HTS tape, a two-layer cable and a single-layer cable are compared. The two-layer structure is confirmed to minimise the loss, meaning an even-numbered arrangement makes better use of the cable space and superconducting materials. Having illustrated the electro-magnetic behaviour inside the CORC cable, this work is an essential reference for the structure design of CORC cables.

Nonlinear contact behavior of HTS tapes during pancake coiling and CORC cabling

Both the pancake coiling and conductor on round core (CORC) cabling processes consist of winding second-generation high-temperature superconducting tape (REBCO) in a core. The contact behavior between the tape and the core during the winding process directly affects the critical current, cable flexibility, mechanical support and electrical contact resistance. Therefore, the winding process needs to be optimized to produce pancake coils and CORC cables with the desired electrical and mechanical properties. This paper comprehensively considers the role of the relaxation and Poisson effects. The theoretical model and the finite element model (FEM) for calculating the contact stress during the winding process are established, and a formula for the estimation of the contact force is proposed. The suitable winding pre-tension force, winding curvature radius of SCS2030 (2 mm width and 30 m substrate thickness) and SCS4050 (4 mm width and 50 m substrate thickness) of REBCO tapes are obtained and discussed by accounting for the relaxation effect and the critical current degradation limit. With consideration of the Poisson effect, the nonlinear contact behavior is investigated. In addition, the relaxation effect, Poisson effect and plasticity of the REBCO tape are taken into account in the FEM model. The results show that the axial strain in the REBCO layer during the winding process is related to the contact behavior. The greater the winding pre-tension force, the smaller the helical curvature radius, and the greater the contact force. The distribution of contact stress for several winding factors (winding pre-tension force, winding angle and the core radius) is divided into three contact types: the single-line contact, the double-line contact and the surface contact. The FEM model results are consistent with the theoretical evaluation and are more suitable for practical winding cases. This research is the basis for designing and optimizing pancake coils and CORC cables.

Calculation of CORC Cable Loss Using a Coupled Electromagnetic-Thermal T-A Formulation Model

High-temperature superconducting (HTS) potential solution of solving the urban demand of large load and high-density power. However, the ac loss within the cable body is one of the primary factors limiting the large-scale HTS cable application. Due to the complex spiral structure of CORC (conductor on round core) cable and the high aspect ratio of conductors, modeling and calculation of CORC cable are pretty challenging. To better assess the cable loss, this article illustrates an improved model based on T-A formulation. Combined with a low-dimensional thermal model, the J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">cBT</sub> (B,T) characteristics of HTS tape are applied in simulation. With a global parameter control equation, the current redistribution of the tape can be analyzed by the model. The loss of a three-phase coaxial (tri-axial) HTS cable under different electric and thermal conditions has been calculated. This article provides a method based on T-A formulation to study the current redistribution and quench process.

Study on Reducing Magnetization Loss in CORC Cables By Laser Cutting Technology

Conductor on round core (CORC) cables with the features of flexibility and a high engineering current density have been a potential candidate for high magnetic field magnets and accelerator magnets. In these applications, reducing the magnetization loss generated in superconductors is essential in the process of design. CORC cables fabricated by multifilament-coated conductor (CC) tapes have been proved to have a low magnetization loss. However, the degradation of the critical current (I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> ) and additional coupling losses significantly affects the performance of CORC cables. In this article, ultraviolet laser cutting technology is used to scribe both the superconducting layer and copper stabilization layers into narrow filaments. First, the magnetization loss of a single tape with different numbers of filaments was measured by a calibration-free method. Then, based on the testing results of a single tape, two typical CORC cables are wound by 10-mm-wide and 4-mm-wide CC tapes. The magnetization loss of cables made of striated tapes was discussed by both experimental and numerical methods. It is found that the magnetization loss significantly decreases with an increasing number of filaments under a high background magnetic field. The magnetization losses decrease in CORC cables made of striated CC tape. Due to the reduced coupling loss and attenuated shielding effect, there is not much difference between the two values of the magnetization loss reduction rates in CORC cables and single tapes. The conclusions obtained in this article will be instructive for the future design of CORC cables.

Numerical Study on Effect of Current Injection Methods on Terminal Resistance of Superconducting Compact Cables

Implement of low-resistive and compact terminal between superconducting cables and bus-bars is one of the most important challenges for industrial application of conductor on round core (CORC) cables. In this paper, a three-dimensional numerical model capable of simulating the terminal resistance and joint resistance of CORC cables is developed and validated by experimental data. On basis of this, the effect of different current injection methods on terminal resistance and the effect of trimming of HTS tapes on current distribution are discussed in this paper. Results shows a wide range of variation in terminal resistance and the homogeneity of current distribution. We expect conclusions obtained from this paper could provide guidelines for commercial and practical terminal fabrication of CORC cables.

Effect of Core Materials on the Electrical Properties of Superconducting Conductor on Round Core Cable

High temperature superconducting (HTS) conductor on round core (CORC) cable is considered as a potential technology for power applications, because of its high current-carrying capacity, compactness, and strong mechanical properties. As the main component of CORC cable, center core is used to support the HTS conductors. However, for metal center core, eddy current induced in the core under alternating electromagnetic field is unneglectable, which will lead to extra AC loss in power applications. This paper focuses on the selection of center core of CORC cable. AC losses of CORC cable using different core materials are evaluated by both numerical and experimental methods, in which copper, stainless steel, fiberglass epoxy and nickel have been chosen as the core. Results illustrate that AC loss of CORC cable has a correspondingly increase with the conductivity of core material. Significant frequency dependence of AC loss indicates that for single layer CORC cable, proper core material should be chosen to minimize the eddy current loss. Besides, CORC cable with core of nickel shows a quite different AC performance due to its ferromagnetic characteristics. Conclusions obtained from this paper will provide essential data for future optimization on the design of CORC cables.

Performance Evaluation of Conductor on Round Core Cables Used in High Capacity Superconducting Transformers

Conductor on Round Core (CORC) cables with scalability, flexibility, strong mechanical strength and high current density are of large potential for different power applications. In this paper, CORC Cables are proposed to be the secondary winding for high capacity superconducting transformer. In order to evaluate the working performance of CORC cable in HTS (high temperature superconductor) transformer, firstly, fundamental parameters of short CORC samples including self-field critical current and room temperature resistance were measured by experiments. Then, to represent the real working condition, both rated current tests and overcurrent tests were carried out to the CORC cable, respectively. In rated current test, magnetization and transport AC loss were discussed by both experimental and numerical method. It is found that AC loss of the CORC cable with double layers is much smaller than that of the CORC cable with single layer. In overcurrent tests, when the maximum value of current is 3588 A, 3.44 times of I c , resistance of CORC is 0.12 mΩ. The recovery time is used to evaluate the recovery-under-load capability, the peak-to-peak value of voltage becomes stable after 6 cycles. Conclusions obtained in this paper can verify the feasibility of this technique and also provide useful information for future design of HTS transformers.

Numerical Investigation of the Coupling Effect in CORC Cable With Striated Strands

Striation has been proved to be effective in reducing the magnetization losses of Conductor on Round Core (CORC) cables assembled with REBCO coated conductors. In this study, we present numerical models of CORC cable with striated strands considering the inter-filamentary coupling by using 3D T-A formulation. Calculated magnetization losses were compared against experimental data to confirm the validity of our models, including 3 × 2 CORC cables with straited and non-striated strands. Frequency dependence of magnetization losses and the electromagnetic coupling effect were demonstrated and analyzed. The coupling loss fits well with analytical function. And the coupling time constant characteristics was found almost in proportion to the square of pitch length.

Quench behavior of high-temperature superconductor (RE)Ba2Cu3Ox CORC cable

The high-temperature superconductor (HTS) (RE)Ba2Cu3Ox (REBCO) conductor on round core (CORC) cable has great advantages with its high current capacity and power density. In REBCO CORC cables, current is redistributed among tapes through terminal contact resistance (TCR) when a local quench occurs. Therefore, its quench behavior is different from the single tape situation. To better understand the underlying physical process of local quenches in CORC cables, a new 3D multi-physics modeling tool for CORC cables is developed and presented in this paper. In this model, the REBCO tape is treated as a thin shell without thickness, and four models are coupled: a T-formulation model, an A-formulation model, a heat transfer model, and an equivalent circuit model. The T-formulation model is applied to the conductor shell only to calculate current distribution, which will be input into the A-formulation model; the A-formulation model is applied to the whole 3D domain to calculate the magnetic field, which is then fed back to the T-formulation model. The hot spot-induced quenches of CORC cables are analyzed. The results show that the thermal stability of the CORC cable can be considerably improved by reducing the TCR. The minimum quench energy (MQE) increases rapidly with the reduction of TCR when the resistance is in a middle range, which is about in this study. When the TCR is too low () or too high (), the MQE shows no obvious variation with TCR. With a low TCR, a hot spot in one tape may induce an overcurrent quench on other tapes. This will not happen in a cable with high TCR. In this case, the tape with a hot spot will quench and burn out before inducing a quench on other tapes. The developed modeling tool can be used to design CORC cables with improved thermal stability.

Quench of a Single-Layer ReBCO CORC Cable With Non-Uniform Terminal Contact Resistance

ReBCO conductor-on-round-core (CORC) cable has become a promising candidate for high temperature superconducting (HTS) power applications, due to its great mechanical strength, high current carrying capacity, high flexibility, and low ac losses. However, ReBCO coated conductors are at risk of quenching, which significantly affects the thermal stability and reliability of the CORC cable. Three-dimensional (3-D) numerical study on the quench behavior of the CORC cable remains a challenge, for its complex geometry is difficult to cope with. In this paper, a 3-D time-dependent multi-physics quench model based on the T-A formulation has been developed. Three modules are coupled in this model; the T–A formulation model, a heat transfer model, and an equivalent circuit model. The quench behavior of a single-layer ReBCO CORC cable with non-uniform terminal contact resistances has been studied, when a hotspot is imposed on one of the tapes to induce a local quench. Results show that, the CORC cable has the highest MQE; in other words, it is the most stable situation, when the hotspot-induced quench occurs on the tape with the middle value of terminal contact resistance.

Influence of Harmonic Current on Magnetization Loss of a Triaxial CORC REBCO Cable for Hybrid Electric Aircraft

High-temperature superconducting (HTS) triaxial conductor on round core (CORC) cable is a potential candidate for use in the transmission line of hybrid-electric aircraft because of its advantages in compactness, high power density, and reduced usage of HTS tapes. The harmonic currents generated by ac/dc converters, generators, and motors in the aircraft affect the ac loss of the transmission cable, thus influencing the efficiency of the cable. This paper analyzes the influence of harmonic current on the magnetization loss of a triaxial CORC HTS cable (10 MW, 3 kV/2 kA), which is designed for hybrid-electric aircraft. A finite element method model based on the T-A formulation has been developed for the HTS triaxial CORC cable, which calculates the losses induced both with and without applied harmonic currents. The results show that the magnetization loss has a significant nonuniform distribution among three phases even under a three-phase balanced rated load. The results also show that a small harmonic current (less than 10% of the rated load current) can lead to a considerable increase in the magnetization loss of the cable (up to 40%). In the triaxial CORC cable, harmonic currents lead to the highest increasing rate of magnetization loss with respect to frequency in the innermost phase.

Numerical Study on Magnetization Characteristics of Superconducting Conductor on Round Core Cables

This paper presents numerical study on magnetization characteristics of conductor on round core (CORC) cable. Numerical models introduced in this paper are based on finite-element method (FEM) with simplified structure, optimized assumptions and settings. Magnetization performance of CORC cables is represented by both full coupled model and isolated model. These numerical models are verified by experiments on CORC cables made of commercial HTS tapes. On basis of this, two topics are discussed in this paper: one is the magnetic shielding effect of superconducting layers in CORC cables; the other one is the end effect of magnetization loss in short CORC cables. Conclusions obtained in this paper will be helpful to understand the working mechanism of CORC cable and also useful in design of large-scale magnets based on CORC cables.

Performance Test of an 8 kA @ 10-T 4.2-K ReBCO-CORC Cable

CERN is developing high-current ReBCO conductor on round core (CORC) cables for application in future detector and accelerator magnets. A characterization test on a ReBCO-CORC cable sample and its joints is performed in the 10-T FRESCA cable test facility at CERN. The sample is taken from the first 12-m-long CORC production. Key is the characterization of the field- and temperature-dependent critical currents of the CORC cable at 1.9 K and 4.2 K. Secondary objectives include evaluating the response of the CORC cable to quenches and the performance of cylindrical low resistive cable terminals especially designed and manufactured for use on CORC cables. The 7.6-mm CORC cable features 8 kA at 4.2 K and 10 T, and the joint terminals show a $25\pm 5-{n}\Omega$ resistance for 20-cm length.

Development of Joint Terminals for a New Six-Around-One ReBCO-CORC Cable-in-Conduit Conductor Rated 45 kA at 10T/4K

The European Organization for Nuclear Research (CERN) is developing a six-around-one conductor on round core (CORC)-strand-based cable-in-conduit conductor (CICC) for use in detector and other large magnet systems. The CICC comprises six ReBCO-CORC strands helically wound around a central tube or rod and inserted in a square aluminum jacket. A major design challenge is finding a simple yet low-resistive method of injecting current homogeneously into the CORC strands of the CICC. In the production of joints for single-CORC cables, we are currently pursuing a method in which the different ReBCO layers at both ends of the CORC cable are trimmed into a staircase-like geometry. A similar trimming method is developed for joint terminals for the ReBCO-CORC-based CICC. A demonstration joint terminal is made to test the various steps of the trimming and manufacturing process before fabricating a joint terminal with real CORC strands. This paper presents an overview of CIC-joint terminal design, simulation results, and the different steps in the manufacturing process.

Characterization of a high-temperature superconducting conductor on round core cables in magnetic fields up to 20 T** Partial contribution of NIST, not subject to US copyright.

The next generation of high-field magnets that will operate at magnetic fields substantially above 20 T, or at temperatures substantially above 4.2 K, requires high-temperature superconductors (HTS). Conductor on round core (CORC) cables, in which RE-Ba2Cu3O7−δ (RE = rare earth) (REBCO) coated conductors are wound in a helical fashion on a flexible core, are a practical and versatile HTS cable option for low-inductance, high-field magnets. We performed the first tests of CORC magnet cables in liquid helium in magnetic fields of up to 20 T. A record critical current Ic of 5021 A was measured at 4.2 K and 19 T. In a cable with an outer diameter of 7.5 mm, this value corresponds to an engineering current density Je of 114 A mm−2, the highest Je ever reported for a superconducting cable at such high magnetic fields. Additionally, the first magnet wound from an HTS cable was constructed from a 6 m-long CORC cable. The 12-turn, double-layer magnet had an inner diameter of 9 cm and was tested in a magnetic field of 20 T, at which it had an Ic of 1966 A. The cables were quenched repetitively without degradation during the measurements, demonstrating the feasibility of HTS CORC cables for use in high-field magnet applications.