Round Core Cable Research Articles

AC Losses Properties of Optical Fiber Encapsulated High Temperature Superconducting Conductor on Round Core Cable

AC Losses Properties of Optical Fiber Encapsulated High Temperature Superconducting Conductor on Round Core Cable

The dynamic resistance of muti-layer conductor on round core cables for SMES systems

The conductor on round core (CORC) cables with multi-layer structure show great potential for superconducting magnetic energy storage (SMES) because of their low AC losses and large current carrying capacity. The dynamic resistance is an important electro-magnetic property of CORC cables for SMES. Considering that experimental results of multi-layer CORC cables are usually difficult to obtained, numerical model is an efficient method to demonstrate their electro-magnetic properties. In the work, a numerical model is proposed to illustrate the dynamic resistance of the multi-layer CORC cables. Then, an analytical model using method of rotating magnetic field is proposed to provide mathematical expressions for computing the dynamic resistance, which verifies the numerical model. According to the numerical model, the impacts of DC current and AC magnetic field on dynamic resistances of the multi-layer CORC cables are investigated respectively. The simulation clearly illustrates the dynamic resistance characteristics of CORC cables, showing dynamic resistances and currents in individual layers. This study can serve as a valuable guidance for the implementation of multi-layer CORC cables in SMES systems.

Numerical simulation of the mechanical behavior of superconducting tape in conductor on round core cable using the cohesive zone model

Numerical simulation of the mechanical behavior of superconducting tape in conductor on round core cable using the cohesive zone model

Research on a novel HTS double pancake coil based on CORC: used for kA-level SMES of accelerator

Large-scale complex needs high performance SMES system with 5 kA-level current carrying and kA s−1 current ramping rate (such as particle accelerator complex), the inductance of which should be as small as possible (≪1 H) to reduce the terminal voltage and realize ideal energy evacuation. This paper introduces the world’s first application of double pancake (DP) coil with conductor on round core cable (CORC) cable, which can be a unit of MJ-level SMES system with a total inductance of 125 mH and 4 kA current carrying (@30 K, 4 T). The combination of low inductance and high current capacity guarantee the safety during kA s−1 operating condition. The CORC wound with highly anisotropic YBCO tape can realize quasi-isotropy with critical properties. The performance of the CORC with 11 layers and three tapes in each layer has been fully validated with excitation test at 77 K and the critical current can reach 2906 A at 77 K, self-field. The skeleton of the DP coil is specially designed with semi-circular spiral groove and the climbing-layer area is supported by two symmetrical blocks, which can provide reasonable support to the CORC cable. The measured critical current of DP coil can realize 1750 A at 77 K (theoretical value is 1800 A). It means that the coil winding method is feasible to avoid performance degradation during winding. The DP coil based on CORC cable is fully suitable for the SMES system which needs to realize ∼4 kA current carrying and fast energy conversion. It also provides a good practice for the engineering application of CORC cable.

Investigating the effect of transverse compressive loads on the electromagnetic performance of superconducting CORC® cables

High-temperature superconductor (Re)Ba2Cu3O x (ReBCO) conductor on round core cable (CORC®) has a large current carrying capacity for high field magnets. Lorentz forces acting on CORC conductors, cause a reduction of the critical current, or even permanent degradation of their performance when exceeding critical values. Transverse compressive stress is one of the principal mechanical stresses when CORC cables are bundled to cable-in-conduit conductors (CICC) conductors capable of operating at currents up to 100 kA in magnetic fields of up to 20 T. In this research, a mechanical-electromagnetic model is developed to study the effect of transverse compressive loads on the electromagnetic performance of CORC cables. A mechanical transverse load on the cable is implemented to simulate the electromagnetic force. A comparison of numerical simulations with experiments for a three-layer CORC cable is first performed to validate the model’s reliability, with particular attention to critical current reduction during the transverse compression process. A novel feature of this paper is that the model developed can analyze both mechanical response under transverse compressive loads and electromagnetic performance under applied AC magnetic fields with low amplitudes. On this basis, the model investigates the effects of winding parameters on the axial strain and critical current reduction of the ReBCO layer in a single-layer CORC cable. The numerical analysis shows that increasing the winding angle can reduce the axial strain and critical current reduction of the ReBCO layer in the contact area. Subsequently, a detailed comparative study is carried out studying the axial strain of the ReBCO layer in the non-contact area with and without taking the winding core into account. In addition, a sudden increase in the magnetization loss is explained when the transverse compressive load reaches a certain level. Finally, a six-layer CORC cable’s electromagnetic analysis is performed, and each tape layer’s critical current reduction is investigated and discussed. The comparison of magnetization loss and current density between six- and single-layer CORC cables in the no-strain case is also given. This finite element model can guide optimizing a cable design for specific application conditions.

Study On Torsion Behavior of Superconducting Conductor On Round Core Cable

With high current-carrying capacity and strong mechanical properties, conductor on round core (CORC) cable is widely adopted in high-field magnet applications, for instance, in the form of solenoids, double pancakes and canted cosine theta coils. However, CORC cable may be twisted in the fabrication of magnet with complex structure, as well as suffering huge Lorentz force in the operation process, which could pose unpredictable strain on helical superconducting tape, arousing secondary damage. In this paper, single layer and double layer CORC samples were fabricated to test their torsion performance through both numerical and experimental methods. Critical twisting angle would be analyzed from the aspect of critical current degradation. Result shows that, compared to additional strain on tape, geometric distortion due to multi-layer structure of CORC cable is more harmful to current-carrying performance of cable. Conclusion obtained from this paper could provide important data for future optimization.

Numerical Study on AC Loss Characteristics of Conductor on Round Core Cables Under Transport Current and Magnetic Field

Conductor on round core (CORC) cables wound by high-temperature superconducting (HTS) tapes have received much attention due to the advantages in power capacity and mechanical flexibility. This paper first developed a 3D model for a CORC cable through the finite-element method (FEM). Next, the total AC loss caused by transported current only was investigated, revealing the eddy current loss in the tube former contributes to the cable loss. The numerical CORC model was validated by published measurements. Moreover, the AC loss that resulted from a simultaneous presence of transport current and magnetic field was explored. With the induced current, the magnetisation loss generated in superconductors can increase the total loss. It is concluded that the addition of a magnetic field can result in a surge in the total loss of a current-carrying cable.

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.

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.

Numerical Study on Mechanical Properties of Conductors on Round Core Cables

The unique structure of conductors on round core (CORC) cable leads to symmetrical electromagnetic properties and excellent mechanical performance. However, it is quite a big challenge to analyze the mechanical properties of CORC cables, due to the unpredictable initial residual stress generated during the fabrication process of both tape and cable. In this paper, the mechanical model of CORC cable consists of several individual models representing the tape fabrication, cable fabrication, CORC cable bending and cooling process. The numerical model is verified by experimental results of both superconducting tapes and CORC cables. On basis of this, the numerical model is used to explain the mechanism of performance degradation during bending process. Moreover, the effects of winding angle on critical bending diameter are analyzed from the aspect of critical current degradation and physical extrusion. And simulation results are used to determine the principle critical bending diameter of CORC cable. Conclusions in this paper can be useful for design of CORC cables in applications where small bending diameter is needed.

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.

Finite-Element Analysis of the Strain Distribution Due to Bending in a REBCO Coated Conductor for Canted Cosine Theta Dipole Magnet Applications

High-current cables using REBCO tapes can be used to develop high-field dipole magnets. However, the strain accumulated during cable fabrication and coil winding may reduce the critical current of the conductor. Therefore, it is important to properly consider the strain when designing high-field magnets. In this paper, we used structural finite-element analysis (FEA) to predict the strain experienced by a REBCO tape during bending in configurations relevant to the fabrication of high-field accelerator magnets, in particular, the mechanical strain generated during cable fabrication and winding in a canted-cos θ dipole configuration. We considered two different cable options: (A) Flat tape that lay in the mandrel channel and (B) a REBCO tape helically wound around a circular copper core, the typical configuration of the conductor in round core cable (CORC). Strain accumulated during tape winding is studied for different core diameters and winding tilt angles. FEA longitudinal strain results were compared with the simulations for configuration A, where higher strain was observed experimentally. Configuration B was verified indirectly by comparing experimentally measured Ic with the one predicted (based on the longitudinal strain) as a function of the bending diameter. Good agreement was found up to a bending diameter of 30 mm. The presented results will help to understand the impact of bending on REBCO tapes and CORC wires to develop high-field magnets.

The winding mechanical behavior of conductor on round core cables

In the process of the HTS cable structure cabling, the HTS tape is subjected to the combined deformation caused by tension, bending, and torsion. The electro-mechanical behaviors and the degradation mechanism of HTS cable are remain elusive. In the present paper, a numerical model is built in ABAQUS software to analyze the winding mechanical behavior of the CORC cable. Then, the critical current degradation is calculated and the effects of the tape width, substrate thickness, pre-stress, winding pitch and helix angle are investigated. The results show that it should be avoid selecting a roller with a much small radius to produce a large strain. The critical current degradation of the cable is minimal when the helix angle equals to 45°, which is the best choice to winding the tape to form the CORC cable. A smaller winding radius can be choose when the thickness of the substrate is in the small strain region of 10–20 µm. This study helps understand the deformation of the HTS tape during the winding process and provides a winding optimization for the CORC cable.

Electro-mechanical behavior of single twisted high-temperature superconducting tape under transverse Lorentz force

In recent years, several cabling methods of high temperature superconducting (HTS) cable have been proposed; e.g., the conductor on a round core cable (CORC), the Roebel assembled coated conductor cable, the helical twisted stacking-tape cable (TSTC) and the twisted-stack slotted core HTS cable (TSSC). These cabling methods allow the high temperature superconducting tapes widely used in the high-field magnets. The single superconducting tape performance under applied loads directly relates to the transport performance of the cable and the choice of the cabling method. In this paper, we investigate the effect of twisting morphology on the electro-mechanical properties of HTS tapes. Particular attention is given to the transverse Lorentz force of a pre-twisted HTS tape. The analytical solution of the deflection of the HTS tape under transverse Lorentz force is derived. Then, the current distribution and AC loss of the tape are calculated by using H-formulation. The effects of twist angle and loading conditions are examined for different HTS tape lengths. The results show that the stiffness resistance ability to Lorentz force of the HTS tape can be increased in several ranges by increasing the twist angle. The twisting structure can also reduce current degradation and AC loss, and thus enhance the transport capacity of HTS tape. This study helps understand the electro-mechanical properties of pre-twisted HTS tapes and provides theoretical reference for the design of novel HTS cable structures.

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.

Stability and normal zone propagation in YBCO CORC cables

In this work, a two layer conductor on round core cable was tested for stability and normal zone propagation at 77 K in a liquid nitrogen bath. The cable was instrumented with voltage taps and wires on each strand over the cable’s central portion (i.e. excluding the end connections of the cable with the outside world). A heater was placed in the central zone on the surface of the cable, which allowed pulses of various powers and durations to be generated. Shrinking (recovering) and expanding (not recovering) normal zones have been detected, as well as stationary zones which were in thermal equilibrium. Such stationary thermal equilibrium zones did not expand or contract, and hit a constant upper temperature while the heater current persisted; they are essentially a form of Stekly stability. Overall, the cable showed a high degree of stability. Notably, it was able to carry a current of 0.45Ic cable with maximum temperature of 123 K for one minute without damage.

Behavior of a high-temperature superconducting conductor on a round core cable at current ramp rates as high as 67.8 kA s−1 in background fields of up to 19 T

High temperature superconducting (HTS) conductor-on-round-core (CORC®) cables have been developed for use in power transmission systems and large high-field magnets. The use of high-current conductors for large-scale magnets reduces system inductance and limits the peak voltage needed for ramped field operation. A CORC® cable contains a large number of RE-Ba2Cu3O7−δ (RE = rare earth) (REBCO) coated conductors, helically wound in multiple layers on a thin, round former. Large-scale applications, such as fusion and accelerator magnets, require current ramp rates of several kilo-Amperes per second during pulsed operation. This paper presents results that demonstrate the electromagnetic stability of a CORC® cable during transient conditions. Measurements were performed at 4.2 K using a 1.55 m long CORC® cable in background fields of up to 19 T. Repeated current pulses in a background field of 19 T at current ramp rates of up to 67.8 kA s−1 to approximately 90% of the cable’s quench current at that field, did not show any sign of degradation in cable performance due to excessive ac loss or electromagnetic instability. The very high current ramp rates applied during these tests were used to compensate, to the extent possible, the limited cable length accommodated by the test facility, assuming that the measured results could be extrapolated to longer length cables operated at proportionally lower current ramp rates. No shift of the superconducting transition to lower current was measured when the current ramp rate was increased from 25 A s−1 to 67.8 kA s−1. These results demonstrate the viability of CORC® cables for use in low-inductance magnets that operate at moderate to high current ramp rates.

Twisting Characteristics and Tensile Effects of aQuasi-isotropic Strands made of Coated Conductors

With the development of second generation (2G) high-temperature superconducting (HTS) tapes, several cabling configurations, such as twisting stacked-tapes cable and conductor on round core cables, have been proposed, and some prototypes were developed. Alternating current (ac) losses arise in HTS tapes in ac operations, and those losses are an important consideration for applications since they influence the stability and operating cost. Conventionally, a twisting technique is used to effectively reduce the ac losses. This paper presents the twisting properties and tensile properties of a quasi-isotropic (QI) strand made from 2G tapes. The strand consists of 2G tapes, aluminum foil, and a metal sheath. A twisting apparatus was designed and demonstrated to research the characteristics of the strands in twisting situations. The critical currents and strain of a single CC were tested for different twist pitches in self-field and at 77 K. The results show that the critical twist pitch of the QI strand is higher than that of a single tape. The critical current of the QI strand was also measured at 77 K after the application of different tensile stresses at room temperature.

Temperature- and field-dependent characterization of a conductor on round core cable

The conductor on round core (CORC) cable is one of the major high temperature superconductor cable concepts combining scalability, flexibility, mechanical strength, ease of fabrication and high current density; making it a possible candidate as conductor for large, high field magnets. To simulate the boundary conditions of such magnets as well as the temperature dependence of CORC cables a 1.16 m long sample consisting of 15, 4 mm wide SuperPower REBCO tapes was characterized using the ‘FBI’ (force—field—current) superconductor test facility of the Institute for Technical Physics of the Karlsruhe Institute of Technology. In a five step investigation, the CORC cable’s performance was determined at different transverse mechanical loads, magnetic background fields and temperatures as well as its response to swift current changes. In the first step, the sample’s 77 K, self-field current was measured in a liquid nitrogen bath. In the second step, the temperature dependence was measured at self-field condition and compared with extrapolated single tape data. In the third step, the magnetic background field was repeatedly cycled while measuring the current carrying capabilities to determine the impact of transverse Lorentz forces on the CORC cable sample’s performance. In the fourth step, the sample’s current carrying capabilities were measured at different background fields (2–12 T) and surface temperatures (4.2–51.5 K). Through finite element method simulations, the surface temperatures are converted into average sample temperatures and the gained field- and temperature dependence is compared with extrapolated single tape data. In the fifth step, the response of the CORC cable sample to rapid current changes (8.3 kA s−1) was observed with a fast data acquisition system. During these tests, the sample performance remains constant, no degradation is observed. The sample’s measured current carrying capabilities correlate to those of single tapes assuming field- and temperature dependence as published by the manufacturer.