Conductor On Round Core Cable Research Articles

Fundamental study on performances of fiber-superconducting composite CORC cable: electromagnetic, thermal, mechanical and quench behaviors

Abstract Common terminal voltage measurement can be hardly applied to detect quenches in long high temperature superconducting (HTS) conductor on round core (CORC) cable because not only the HTS normal zone propagation velocity (NZPV) is low but also immobilizing a large number of voltage leads is inconvenient. Distributed optical fiber sensing (DOFS) technology is a promising method for quench detection of long superconductors. To sense the thermal changes of CORC cables during quenches more directly and prevent optical fibers from damages by external stress, a fiber-superconducting composite (FSC) CORC cable was fabricated. For this cable, three optical fibers were placed in three grooves of the copper core respectively, then three HTS tapes were spirally wound on the copper core in sequence. Comparing to a traditional CORC cable, obviously, the FSC CORC cable structure has been changed. To promote FSC CORC cable engineering applications, it is necessary to study the fundamental performance of the cable. In this paper, we investigated the electromagnetic, thermal and mechanical properties of the FSC CORC cable by comparing those with a common one. The results demonstrated that, compared to the common one, the magnetic distribution of the FSC CORC cable hardly changed, but the current distribution of the copper core in the FSC CORC cable slightly changed which led to decreases of transport AC loss, in addition, the thermal characteristics of the FSC CORC cable was slightly changed and the bending tolerance ability of the cables reduced within a bending diameter range of 15 cm. What’s more, the embedded optical fibers combined with DOFS system are successfully used to detect the temperature changes of the cable surface. Finally, to study the quench behaviors of the cable, we built a quench detection platform, which equips with a voltage acquisition system, a thermocouple temperature acquisition system and the DOFS system. By using the platform to detect the quenches of the FSC CORC cable, minimum quench energy of the cable and NZPV of the tape and cable at different currents was tested.

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.

Study on the response of the winding direction of multi-layer CORC cable to its electromagnetic characteristics

A Conductor on Round Core (CORC) cable wound with a high-temperature superconductor is an important cable concept for high-current density applications. It is widely used in large power systems because of its advantages of good flexibility and high engineering current density. However, the complex design structure of CORC cable makes it very difficult to understand its electromagnetic properties (such as AC loss). In particular, the different winding directions of each layer in multi-layer cable have a great influence on its electromagnetic characteristics. In this paper, the H-method is used to solve the electromagnetism and mechanics equations. The influence of the winding direction of CORC cable on its electromagnetic field distribution characteristics, AC loss, and mechanical variation under the action of external magnetic field is investigated. The AC loss study of single-layer cable reveals that when the applied magnetic field is increased from 0.01 to 0.02 and 0.03 T, the AC loss peak of the cable increases by 107 and 103 orders of magnitude, respectively, indicating that the effect of low applied magnetic field on the AC loss of the cable is more significant. For multi-layer cables, cables with opposite winding directions have a greater depth of current density penetration than cables with the same winding direction. In addition, the mechanical variations of multi-layer cables with different winding orientations are explored. The results show that the Mises stress in the cable with the same winding direction is about 32% higher than that of the cable with the opposite winding direction, which indicates that the method of winding the cable in the opposite direction between adjacent layers of tape can avoid excessive mechanical stress.

Mixed-mode fracture analysis of CORC cables with double-edge cracks under tension and torsion

The Conductor on round core (CORC) refers to a circular cable that is helically wound with rare-earth-barium-copper-oxide ((RE)BCO) high-temperature superconducting (HTS) tapes. This type of cable finds extensive applications in large superconducting magnets. However, the mechanical–electrical performance of CORC cables is hindered by microscopic edge cracks that occur during the mechanical slitting process of HTS tapes. In this paper, the mixed-mode stress intensity factor (SIF) of cracks in CORC cables under different loading conditions is investigated using the extended finite element method (XFEM). The design variables of CORC cables are optimized by considering the effect of various factors such as the crack parameter, the winding angle, the core radius, and the Poisson’s ratio of the winding core on the SIF. The results indicate that the impact of each factor on the mixed-mode SIF varies depending on the loading mode. Notably, the influence of the winding angle on the SIF is particularly significant and intricate. In the case of tensile loading, a smaller winding angle proves advantageous in impeding crack propagation. Conversely, the most dangerous winding angle for torsional loads is 45°. The divergence of these effects can be indirectly indicated by theoretical solutions regarding the tape strain along the helix direction. For the cases examined, the results have shown that the crack propagation path is independent of these factors, and the direction of propagation is perpendicular to the edge of the tape.

Mechanical behavior of multi-layer CORC cable in high external field with 3D numerical model

The degradation of critical current due to mechanical deformation in a high field has a profound impact on the performance of high-temperature superconducting (HTS) structures. The multi-layer conductor on round core (CORC) cable is a widely-applied HTS structure in engineering. Due to the complexity of the multi-layer CORC cable, the contact between the tapes should be considered when simulating the mechanical behavior in high field. In this paper, 3D electromagnetic and mechanical models were developed to investigate the mechanical behavior of the multi-layer CORC cable. Under the same electromagnetic force, the comparisons of mechanical models of a 5-layer CORC cable with different contact methods are presented. Subsequently, the effects of the loading path of the external magnetic field and transport current, the bending geometry of the CORC cable, the winding direction of the HTS tape in the CORC cable, and the shielding current on the mechanical behavior are discussed, respectively. The numerical results are useful for the design and operation of CORC cable in high field.

Numerical study on the transport current distribution in the multi-layer CORC coil

The conductor on round core (CORC) cable has attracted increasing attention due to its strong and high-efficient current carrying capacity. It is considered as one of ideal candidate cables for manufacturing nuclear fusion magncets. Under the circumstance, the transport current distribution of the coils wound by CORC cables has significant impacts on the operating performance of nuclear fusion magnets. Considering the difficulty in experimental tests, numerical model is an effective way to illustrate transport current distribution of the multi-layer CORC coil and provide further insights into its working performance. Therefore, in this work, A 3D finite element model based on the H formulation is proposed to simulate a single-turn and multi-layer CORC coil. The validity of the model has been verified by experimental results. Based on the proposed model, the transport current distribution of the multi-layer straight CORC cable and the multi-layer CORC coil is compared and discussed. In addition, the current density distribution on the superconducting tapes of the multi-layer CORC coil is also investigated. This work can provide an important reference for the design and practical application of multi-layer CORC coils.

Numerical study on the electromagnetic characteristics of multi-layer CORC cables

Due to the high isotropy and low AC losses, the multi-layer conductor on round core (CORC) cable is a good candidate for high field magnets, such as central solenoid magnets in fusion. Considering the difficulty in experimental measurement, numerical model is an effective way to illustrate the electromagnetic characteristics of the multi-layer CORC cable and provide further insights into its working performance. In this work, a 3D finite element model based on H formulation is proposed to simulate a CORC cable with as many as 18 layers considering electromagnetic coupling. The validity of the model has been verified by experimental results. Based on the proposed model, the DC transport current distribution characteristics and charge-discharge loss characteristics of multi-layer CORC cables wound in the same and opposite winding directions are investigated respectively. This work can provide an important reference for the design of multi-layer CORC cables for high-current or high-field application.

High temperature superconducting CORC cable with variable winding angles for low AC loss and high current carrying SMES system

Owing to the rising demand for enhanced high-current capacity within superconducting magnetic energy storage (SMES) system used in power grids, there is a growing focus on enhancing the current-carrying capability of SMES setups wound with conductor on round core (CORC) cables. However, it is crucial to note that the dissipation of AC losses in CORC cables during rapid charge and discharge cycles can substantially impact the safe operation of SMES. The CORC cable is crafted by spirally winding numerous ReBCO tapes around copper tubes. Even slight alterations in the winding angles of these tapes can result in shifts at current distribution across the ReBCO tapes, thus leading to differences in AC losses. Hence, the primary objective of this paper is to study the effect of varying winding angles of each ReBCO layer on AC loss. The adoption of variable angles results in the reduction of current flowing through the outermost tapes. And the AC losses in the outermost tapes happen to account for the majority of the total AC losses. Through simulations and experiments, it was observed that the AC loss in the CORC cable with variable angles (4 × 12, 25°–40°) was 25% lower than that in the case of fixed angles (3 × 11, 45°). These findings demonstrate a noteworthy downward trajectory in AC losses when variable angles are applied to the CORC cable. These insights hold significant value for the practical application of CORC cables within SMES systems.

Deformation and crack prediction of CORC cable induced by Poisson effect: Theoretical modeling and experimental validation

The conductor on round core (CORC) cable exhibits superior mechanical properties compared with single superconducting tape due to its unique twisted cable structure, which allows for expansion through spiral winding.However, the deformation characteristics have not yet been effectively elucidated during the winding process. Especially, the shapes and distributions of internal damaged cracks are difficult to predict resulting from the multilayer structure of the superconducting tape. In this work, the theoretical model considering the spiral winding of CORC cables has been established and the deformation characteristics caused by the Poisson effect have been elaborated. Meanwhile, the theoretical model was confirmed by comparing finite element simulations, the accuracy and reliability were also verified by the stereo digital image correlation (stereo-DIC) experiments. It is shown that this model can predict the distribution characteristics of damaged cracks inside the superconducting tape multilayer structure during the winding process, which was further checked by magneto-optical imaging (MOI) experiments. Furthermore, the effects of twisted cable parameters on the deformation characteristics of the superconducting tape have been elucidated. These findings contribute to a deeper understanding of deformation in CORC cables during the winding process and offer guidance for their preparation and application.

Numerical simulations of electromagnetic behavior in CORC cable based on a modified formulation

Alternating current (AC) losses have an important effect on the stable operation of high-temperature superconductors (HTSs). Researchers have proposed many formulations to estimate AC losses based on finite element methods, such as formulation, formulation and formulation. In this paper, in order to simulate complicated multi-layer conductor on round core (CORC) cable with transport current, a modified formulation is proposed to calculate AC losses in complicated HTS structures. The formulation, which is easy to implement and has fast computation speed, is verified by comparing the calculation results with the existing formulations and experiments. The electromagnetic behavior of CORC cables and a helical coil wound by a three-layer CORC cable is investigated with a modified formulation. The numerical results show the non-uniformity of the losses and currents in the different layers of the CORC cable. Furthermore, the effects of the external magnetic field on the distribution of the transport current are also discussed.

Effects of Winding Angle on Losses of CORC Cable—A Numerical Study

The conductor-on-round-core (CORC) cable made of high-temperature superconductors coated conductors possess advantages in current carrying capability, mechanical strength, and flexibility. Its relatively complicated structure raises interests in the losses during operation and the related stability. In this article, we investigated the effects of winding angle on CORC losses under various excitation conditions. The results show that the ac loss is positively related to the winding angle owning to the increased magnetic field component perpendicular to the tape which will reduce its critical current density ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$J_{c}$</tex-math></inline-formula> ). CORC cables with an even number of layers wound in reverse show a significant reduction of stray fields and hence diminish the ac loss. The magnetization loss depends on the magnitude of the external field. It is positively correlated with the winding angle under low fields and approaches a constant under high fields. The conclusions indicate that from the perspective of losses, a small winding angle is suggested which can be used as a reference for the commercialization and practical manufacturing of CORC cables.

Simulation of Dynamic Resistance and Total Loss of HTS CORC Cables

In some high temperature superconducting (HTS) applications, HTS coated conductors carry DC current under external AC magnetic fields. Dynamic resistance occurs when the amplitude of the magnetic field is greater than the threshold magnetic field of the coated conductors. The resulting AC loss, termed as total loss, consists of dynamic loss due to dynamic resistance and magnetization loss due to the shielding currents caused by the AC magnetic field. Conductor on round core (CORC) cables wound with HTS coated conductors have attracted broad attention due to their large current-carrying capability and mechanical flexibility for coil applications. However, there has been no report on dynamic resistance and total loss in CORC cables. In this work, we present 3D FEM simulation results on the dynamic resistance and total loss of a spiral tape and three CORC cables, based on the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\boldsymbol{T-A}}$ </tex-math></inline-formula> formulation. The number of layers of the CORC cables, the amplitude of the AC magnetic field and transport DC current levels have been varied to study the impact of those parameters on dynamic resistance and total loss of the three CORC cables. The simulation results show that magnetization loss without current in a spiral tape can be analytically estimated by Brandt and Indenbom’s theoretical equation for a superconducting strip under perpendicular AC magnetic field with a geometric coefficient 2/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\pi $ </tex-math></inline-formula> . Furthermore, dynamic resistance of the spiral tape and each tape in a single-layer cable can be predicted by the analytical equation for a strip carrying DC current under perpendicular AC magnetic field, also taking into account the geometric coefficient 2/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\pi $ </tex-math></inline-formula> . The simulation results also show that the difference of total loss values in the three CORC cables depends on the shielding effect: the more layers of CORC cables, the lower each loss component. The two-layer Cable with each tape in the outer layer sitting on top of the tape in the inner layer has the lowest loss and the highest threshold magnetic field.

Magnetization loss of CORC cables under axial tensile loading

As a highly flexible and fully isotropic cable structure, CORC (Conductor on Round Core) cable wound with high-temperature superconducting (HTS) tapes has promise for giant magnets, including fusion magnets, high-energy accelerator magnets, and nuclear magnetic resonance. CORC cables are subjected to mechanical, thermal, and electromagnetic loadings during preparation and operation. Axial tension is one of the basic deformation modes of CORC cables. To investigate the impact of axial tension loads on the electromagnetic performance of CORC cables, a mechanical-electromagnetic model is created in this study. A comparison of numerical simulations and experiments was first performed for single straight tape and single-layer CORC cables to verify the model's reliability, with particular attention to the critical current reduction and the variation of magnetization loss during axial tension. The model developed in this paper may evaluate electromagnetic performance under applied AC magnetic fields with small amplitudes and mechanical response to axial tension loads. On this basis, the strain distribution of CORC cables under axial tension and their magnetization loss characteristics under various strain states are presented. The effects of different cable design parameters on the critical current and magnetization loss are discussed. The results show that the strain affects the magnetization loss of CORC cable significantly, especially for ones with larger winding angles. The magnetization loss can be reduced by choosing a narrower tape, a smaller winding angle, or a cable core material with a higher Poisson ratio. This study can provide a theoretical basis for the structure optimization design and practical application of CORC cables.

Analysis on the transverse compression performance of the CORC cable

The conductor on round core (CORC) cable is considered as one of the best candidate cables for next generation fusion project due to its advantages of high current density, small cabling degradation and excellent magnetic field performance. Nevertheless, the CORC cable will be affected by huge transverse compression force during production and transportation, especially during operation in fusion project, which is the main reason that the current-carrying capacity of CORC cable will be irreversible degradation. There is little research on the transverse compression performance of CORC cables at present, and the influence rules of some cable parameters on its transverse compression performance are not yet clear. Therefore, in this paper, transverse compression tests are carried out on CORC cables of different former sizes, materials, and structures. The experimental results show that the larger the cable former size, the better its transverse compression performance. The transverse compression load limit of hollow tube former cable is larger than that of solid bar former cable. The performance of stainless steel bar former cable is similar to that of copper bar former cable. The limit value of transverse compression load of copper hollow tube former cable is larger than that of stainless steel hollow tube former cable. A 3D finite element model is also established to explain the internal reasons for the differences of current-carrying capacity decrease tendency of different CORC cables. The research results can provide theoretical basis for the selection of former of CORC cable in the future. In addition, the influence of load block structure on the CORC cable’s transverse compression load limit is also studied in this paper. The results show that the arc block can significantly increase the transverse compression load limit of CORC cable. The research results can provide a basis for the selection of the structure of support former when making cable in conduit conductor and the structure of coil former when winding CORC coil magnet.

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.

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.

Improved mechanical models and Ic estimation for the whole life cycle of high temperature superconducting coated conductors

To evaluate the effect of mechanical behaviors on the critical current (Ic) of superconducting conductors, this paper develops an improved modeling method at all the composite-layer, conductor, and cable levels, which provides a means to analyze the stress and strain for the whole manufacture process. First, a sandwich model based on composite shells was developed to calculate the residual thermal stress of coated conductors during the fabrication process. Then, the uniaxial tensile model was used to verify the loading method for applying the residual thermal stress to subsequent models as initial conditions. With the pre-stress loaded, mechanical behaviors of coated conductors under bending and torsion were analyzed. Further, an exponential function model was adopted to describe the relationship between the normalized critical current and longitudinal strain. Lastly, a series of numerical models were built to analyze the bending behavior of CORC (conductor on round core) cables. Combined with tests of a sample cable, the strain-dependent critical current predicted the Ic degradation under different bending radii. Calculation results show that the sandwich model is hundreds of times faster than other applicable finite element (FE) models. The loading method provides the initial stress for any geometry and software to precisely analyze the stress of coated conductors, especially the rare earth-barium-copper-oxide (ReBCO) layer with intrinsic compressive stress. The electromechanical behaviors of bending and torsion are in good agreement with experimental data, and the exponential mode obtained from conductor performance can estimate Ic degradation of the CORC cable within a relative error of 1.46 % in the reversible region.

Electromagnetic and mechanical properties of CORC cable due to screening current

With the development of type II high temperature superconducting (HTS) ReBCO tape, it has been widely used in high field magnets. Conductor on round core (CORC) cable is highly flexible and fully isotropic, making it one of the most important types of HTS cables. In the condition of high field and current, the electromagnetic and mechanical behaviors of CORC cable under screening current effect are not clear. In this paper, the behaviors of CORC cable under high field and current are studied for the first time by combining electromagnetic and mechanical simulation. A three-dimensional shell model and a three-dimensional solid element model of single-layer CORC cable are established by finite element software to study the electromagnetic and mechanical properties of CORC cable, respectively. Compared with the case without taking screening current into account, two current loops are induced within a pitch of the CORC cable due to the screening current, and the magnetic field homogeneity is significantly reduced. Meanwhile, two pairs of shear force are generated at the current loops meeting zones, it results in a certain degree of stress concentration. Fortunately, because the copper core provides stable mechanical support for the HTS tape, there is no significant difference of the maximum stress between two cases with and without screening current in the CORC cable.

Experimental Study On the Critical Current of CORC Cable Under Cyclic Bending-straightening

To develop the application potential of conductor on round core (CORC) cables in the next generation of fusion magnets and accelerator magnets, fully automatic mechanized winding technology is required for the long CORC cables manufacturing. Meanwhile, the manufacturing and usage of the CORC cable are both limited by the strain sensitivity of the wound ReBCO tape on the CORC cable, because the processes may cause the superconducting layer of the ReBCO tape damaged when the strain limit is exceeded. The strains can arise from the manufacturing, bending, cooling, and operation of the cable and magnet, especially for the needed cyclic bending-straightening procedure for a long and multilayer cable winding layer by layer. Thus in this manuscript, a 1-m-long 12-layer CORC cable was manufactured to study the influence of cyclic bending on the critical current carrying performance of the CORC cable. It is consisted of 28 ReBCO tapes from Fujikura with 4 mm width and 0.05mm substrate thickness. The central core has an outer diameter of 3.85 mm. The cyclic bending-straightening experiment was conducted with a bending diameter of 900 mm and 700 mm, the Ic was tested at 77 K and self-field. After the cyclic bending test, the sample was bended to a diameter of 95 mm, which is planned to be used for the following insert solenoid coil, and has been verified no influence on the critical current carrying performance if bended without cyclic bending-straightening treatment. The results show that the required diameter for the reel experiencing cyclic bending-straightening procedure for ReBCO cable winding is suggested to be larger than 700 mm, especially for the equipment used for multilayer cables winding.

Analysis on the Effect of Superconductor Layer Thickness on the AC Loss of Conductor on Round Core (CORC) Cables

Superconducting Conductor on Round Core (CORC) cables fabricated by several high temperature superconducting (HTS) tapes are able to carry enormous electrical current density, to be widely used in a variety of superconducting applications such as power transmission, fusion, and magnetic resonance imaging (MRI). However, the AC losses induced in the superconducting tapes under alternating current or magnetic field generate heat dissipation which can reduce the electric power efficiency. Therefore, it is essential to analyze the AC loss behavior of CORC cables as well as consider methods to reduce it. This paper presents an AC loss study of CORC cables with several different superconducting layer thicknesses. The CORC cable simulation model is built in a software suite named COMSOL Multiphysics utilising the finite-element method (FEM) solved by the three-dimensional (3-D) H-formulation. By implementing FEM simulations, the cases of increasing the degree of freedom of superconducting layers have been considered, and the AC losses of a single layer CORC cable model with three tapes mounted around the core have been calculated and analyzed for different layer thicknesses. Simulation results are verified with experimental results measured in previous literature.