The high-temperature superconducting (HTS) conductors composed of REBCO tapes have great potential in the field of superconducting applications due to their high critical current density and good mechanical properties. From the safety perspective, research on quench protection of HTS conductors is a key issue for their widespread application. This paper investigates the thermal stability of the superconducting conductor woven by 3 REBCO tapes, using the simply stacked conductor with the same number of tapes for comparison. Three-dimensional (3D) electromagnetic-thermal coupled models are established for the two types of conductors. An experimental platform is constructed to measure the critical current of both conductors. The critical current of the woven conductor reaches a maximum at the transposition length of 95 mm, and this conductor is used to study thermal stability. For normalized currents from 0.6 to 0.9, the minimum quench energy (MQE) and quench propagation velocity (QPV) of both woven and stacked conductors are calculated and experimentally verified using the developed platform. The results show that the MQE of the woven conductor is 1.5 to 2 times higher than that of the stacked conductor, despite its 19% higher critical current. This work demonstrates that the woven conductor exhibits better thermal stability while maintaining a higher current-carrying capacity, making it a promising candidate for reliable power transmission. It also provides important guidance and theoretical benchmarks for quench protection.

Although the ripple loss of self-shielding high-temperature superconducting (HTS) DC cables have been studied previously, their thermal stability in comparison with conventional coaxial bidirectional DC cables has not been systematically analyzed. For further investigating the operation stability of self-shielding HTS cables, a three-dimensional (3D) coupled electromagnetic‑thermal model is established to compare the thermal stability characteristics of the two configurations. Both cables have a four‑layer structure and are wound with 48 HTS tapes, each 2 mm wide, 0.1 mm thick, and with the critical current of 80 A at 77 K. The results indicate that the self‑shielding cable not only exhibits a higher overall critical current (e.g., 1700 A for self‑shielding cable and 1600 A for conventional cable), but also shows higher minimum quench energy (e.g., at 1350 A, its MQE is about 12.5% higher than that of the conventional cable) and slower quench propagation velocity (e.g., at 1350 A, its QPV is about 35.3% lower), thus exhibiting a clear advantageous trend in thermal stability. This work provides critical technical insights for designing and optimizing high-stability, high-safety HTS DC cables, addressing a key need in the field.

Superconducting strands need to be connected together for practical applications, so the connection method is crucial. Quasi-isotropic superconducting strands (Q-IS) made from second-generation REBCO high-temperature superconducting (HTS) tapes hold broad application prospects in high-power transmission and other fields, where the interstrand connection is a crucial link for their engineering application. Addressing the research gap that existing studies have not involved the current transfer length (CTL) between two Q-IS strands, this paper proposes two novel connection methods: copper ring connection and stepwise lap connection. A three-dimensional electromagnetic simulation model based on the H-formulation is established and verified by experiments to systematically investigate the CTL and Joule loss characteristics of the joints under different connection methods. The simulation and experimental results indicate that different connection methods exert a significant influence on the CTL of superconducting strands.

As the development of superconducting materials reaches the bottleneck, it is worth exploring new method to obtain superconducting tapes with better performance through the composite method. In this article, BSCCO tape and REBCO tape are composited. The current distribution of the hybrid superconducting tape is investigated based on the percolation flow model, and the corresponding experiments are also carried out. The current transfer process of the hybrid superconducting tape is also simulated with the change of current and temperature. The results show that the hybrid superconducting tape has a wider temperature range and can still carry large current above the temperature of 100 K.

This paper proposes a method for manufacturing high-temperature superconducting (HTS) cables woven by three or more rare-earth barium copper oxide (REBCO) tapes. The REBCO tapes exhibit complete transposition, with each tape occupying an equivalent position and thus achieving excellent symmetry. This design ensures uniform distribution of the operating current among all REBCO tapes, thereby maximizing their collective utilization efficiency. In addition, this transposition enables all tapes to reach the critical state simultaneously, thereby significantly enhancing the overall critical current of the cable. Moreover, the proposed weaving method allows for the fabrication of cables using a variable number of REBCO tapes, making it suitable for high-current applications, such as nuclear fusion and high-capacity power delivery. The weaving process follows clear and repeatable patterns, facilitating the development of specialized equipment for industrial-scale manufacturing. Experimental results demonstrate that cables woven by REBCO tapes attain superior critical currents relative to Roebel cables. Additionally, a finite element model (FEM) based on the H-formulation illustrates the distribution of the operating current and magnetic fields within HTS cables woven by REBCO tapes.

A novel method for weaving a high-temperature superconducting (HTS) cable is proposed. Two REBCO tapes are stacked to form a subunit, and several such subunits are woven into the cable. This method reduces the complexity of the weaving process while improving mechanical stability compared with weaving with individual tapes. Finite element models of cables with 6, 8, and 10 HTS tapes are established. The simulation results show that the woven structure significantly improves the distributions of current density, magnetic flux density, and electromagnetic stress, reducing their maximum values and making them more uniform compared with the conventional stacked cable. In addition, the critical currents of the woven cables with 6, 8, and 10 tapes are measured experimentally using the four-probe method at 77 K under self-field. For the cable with 6 tapes, the critical currents at varying transposition lengths are obtained, and the results show that the optimal transposition length is 100 mm. Compared with stacked cables with the same number of tapes, the woven cables exhibit critical current enhancements of 21%, 26%, and 32% for 6, 8, and 10 tapes, respectively. The advantage of the woven cable grows with tape number because transposition effectively mitigates the self-field non-uniformity that increasingly penalizes stacked cables. Therefore, this novel cable offers a promising route for high-current HTS applications.

The high-temperature superconducting (HTS) flux pump is a charging device that can achieve contactless excitation and pro-vide stable current compensation for superconducting magnets without increasing the refrigeration burden of the system. Com-pared with the traditional excitation method through current leads, the HTS flux pump has the advantages of high safety per-formance, high excitation efficiency, and high stability, making it an effective solution for the stable operation of superconducting magnets. This article provides a detailed analysis of the working principle of the transformer-rectifier HTS flux pump based on dynamic resistance. A finite element simulation model of the su-perconducting bridge is established and a formula for calculating the dynamic resistance is obtained. Also, a measurement system for the dynamic resistance of a single superconducting tape under a composite magnetic field is constructed. Subsequently, a circuit model of the transformer-rectifier HTS flux pump is built in MATLAB Simulink and the output characteristics of the flux pump are analyzed. The results indicate that the excitation speed of the load magnet and the final saturation current are mainly affected by the amplitude, frequency, phase difference of the composite magnetic field, and the magnitude of the charging cur-rent, but are independent of the frequency of the charging cur-rent. The study also shows that the output efficiency of the flux pump peaks with a 60 degrees phase difference of the parallel field com-ponent over the perpendicular field.

BSCCO/REBCO hybrid superconducting cables integrate the high critical temperature of BSCCO and the strong magnetic field tolerance of REBCO, exhibiting great application potential in high-current DC power transmission. A 2D electromagnetic finite-element model based on the H-formulation and E–J power law is established to investigate the critical current characteristics, current redistribution behavior, and ripple-loss performance of the proposed cables. Comparison between the two proposed BSCCO/REBCO hybrid cable structures shows similar maximum magnetic fields. Therefore, one structure is selected for the subsequent investigations. Critical current and its degradation rate under different temperatures and external magnetic fields are calculated and compared with those of single BSCCO and single REBCO cables. Current redistribution between superconducting tapes and copper formers is investigated with increasing temperature and operating current, and ripple loss is computed. Results show that the self-shielding composite cable achieves balanced high temperature tolerance and magnetic field resistance. Its critical current at all temperatures is higher than that of single REBCO cables, while its degradation rate under external magnetic fields is lower than that of single BSCCO cables. With increasing temperature, current transfers from REBCO to BSCCO and then to the copper former. The ripple loss of this hybrid cable is lower than that of the BSCCO cable. This study provides data and design support for the engineering application of hybrid superconducting power transmission cables.

The circular electron positron collider (CEPC) represents a major international scientific project, with its detector magnet proposing the use of the aluminum-stabilized stacked REBCO tapes cable (ASTC) in its high-temperature superconducting (HTS) design. To ensure the long-term stable and safe operation of this magnet, a thorough investigation on the quench behavior of the ASTC is imperative. This article presents a comprehensive 3-D quench simulation model for the ASTC, incorporating coupled electromagnetic-thermal analysis. The model is employed to simulate the global quench characteristics of the cable under liquid nitrogen immersion cooling, explicitly accounting for internal electrical contact resistance and thermal contact resistance. Key quench parameters, namely, the minimum quench energy (MQE) and quench propagation velocity (QPV), are investigated under varying operational currents, with particular emphasis on performance under adiabatic conditions representing the worst-case scenario. Simulation results demonstrate the significant role of the aluminum stabilizer in current sharing and heat conduction, contributing to the cable's stability and recoverability. The study confirms that the ASTC exhibits robust operational stability, where local quenches are unlikely to propagate into global quench events under effective cooling, thereby validating its suitability for the CEPC detector magnet application. The developed multiphysics model and simulation methodology provide a valuable framework for subsequent quench analysis of superconducting magnets.

Compared to conventional cables, high-temperature superconducting (HTS) dc cable offers numerous benefits, such as low loss, high transmission current, and small volume. The self-shielding structure allows HTS dc cables to carry a larger critical current and smaller leakage magnetic field. In the event of a short-circuit fault, the current through the cable will increase several times instantaneously, and the electromagnetic force on the cable will also be greater. Therefore, it is necessary to study the electromagnetic force and current change of HTS dc cable under short-circuit current. Based on the finite element method (FEM), this article establishes a 3-D model to simulate the short-circuit electromagnetic force and current evolution of three kinds of HTS dc cables with different structures, and analyzes the changes of electromagnetic force and fault current under different structures, which is crucial for the design and operation of HTS dc cables.

Liquid hydrogen energy pipelines combine the transmission of electrical energy with hydrogen. Liquid hydrogen can not only be used as a cooling medium for superconducting dc cables but can also be used as a clean energy source for delivery, realizing highly efficient transmission of energy. Self-shielding superconducting dc cables (SSDCCs) have the advantages of no magnetic leakage and small critical current attenuation. This article presents a study of the application of the SSDCC in a liquid hydrogen energy pipeline. The critical current, magnetic field, and ripple loss of the cables at the temperature of liquid hydrogen are investigated by the T-A formulation. The findings indicate that the SSDCC can make the liquid hydrogen energy pipeline achieve more efficient transmission, which provides a novel perspective for the research of liquid hydrogen energy pipelines.

A fully high-temperature superconducting (HTS) magnet capable of operating in persistent current mode (PCM), assembled with a closed-loop superconducting sheet featuring single-connected double holes (CLSSSCDHs), is expected to create high magnetic field above 20 T at low temperature by amplifying magnetic flux density and magnetic flux accumulating so that it could be potentially used in practical industrial applications. Recognizing the constrained magnetic field produced by an individual sheet, in this paper, we have improved its capabilities by arranging multiple sheets in diverse configurations. This study verified the effect of magnetic flux density amplification and magnetic flux accumulation within four different arrangements through experiments and simulations, based on which the conceptual configuration of a fully HTS magnet above 20 T at 4.2K is proposed, laying a feasibly revolutionary foundation for achieving high magnetic field at larger scales and lower temperatures.

The critical current of a REBCO tape is a crucial factor in describing its quality. The orientation of applied field has a significant impact on it which is different under different temperatures and amplitudes of applied field. In this paper, we construct a cryogen-free I-c measurement system with a wide range of temperature (20-100 K), magnetic field (0-3 T), angle of the magnetic field (0(degrees)-360(degrees)), and current (0-875 A). The results of the measurements demonstrate that the system can accurately measure the critical current. The magnetic field angle dependency curves of three types of REBCO tapes (MOCVD, MOD, and PLD) are measured. The offset angles near theta = 0(degrees) and 180(degrees), impact of the parallel field's direction, and uplifts near theta = 90(degrees) appear in all REBCO tapes. The effect of temperature and magnetic field on these characteristics depends on the tape's technique. These features are essential in the selection of REBCO tapes for different applications and the structure design of HTS facilities.

This paper presents a gourd-shape closed loop with double circular configurations at different diameters, which is arranged by slitting second-generation high-temperature superconducting (2G HTS) tape along its length direction. The flux density amplification and flux accumulation mechanisms of this architecture with closed-loop HTS coils using both experimental and numerical methods were performed. Flux density amplification and flux accumulation in small circular configuration was observed by using field-cooling (FC) method in LN2 temperature. The mechanisms of flux density amplification and flux accumulation can be understood by the flux conservation law in superconducting closed loop. Three types of arrangements were carried out to confirm the principles of flux density amplification and flux accumulation. Compared with existing HTS magnetic magnets by winding on former, this gourd-shape HTS coil is more compact and operates in persistent current mode (PCM). Besides, it can be particularly generalized to big dimensional size permanent HTS magnet by stacking gourd coils if 2G tape with large width can be prepared for industrial application. Our results show that the proposed gourd-shape HTS coil is very promising in full HTS magnet with higher magnetic field in low temperature and has the potential to provide much stronger magnetic fields relative to existing permanent magnets.

Compared with high temperature superconducting (HTS) ac cable, HTS dc cable has the advantages of large transmission capacity, low ac loss and strong controllability. Self-shielded HTS dc cables with different current directions in adjacent layers can reduce the magnetic field interaction between layers, so as to increase the critical current of the cables and reduce ripple loss. In this paper, a novel self-shielded dc cable is proposed, which is made of REBCO tapes with different widths. The magnetic field distribution, ac ripple loss of the novel cable and Ampere force are studied based on T-A formula. The results show that the wider outer tapes can counteract the magnetic field in the inner tapes, and the novel self-shielded dc cable has smaller magnetic field between layers, lower ripple loss and smaller Ampere force than the previous self-shielded dc cable made by tapes with the same width. This novel self-shielding structure provides a new idea for the design of dc cable for large dc applications.

High temperature superconducting (HTS) magnet is promising in many applications due to its advantages of high upper magnetic field at low temperature compared with conventional magnet. In this paper, a RE-Ba-Cu-O (REBCO, RE is rare earth) plate consisting of several holes with different diameters made from the second-generation high temperature superconducting (2G HTS) tape is proposed. An exciting coil with iron core is located in one hole with the biggest diameter and then excites the HTS coil by the field cooling (FC) method. Based on the law of flux conservation, the principle of excitation and multistage magnetic field generation of HTS ring is presented. Numerical analyses by finite element method (FEM) are performed to verify the feasibility of the HTS magnet at 77 K. The results show that the permanent magnet model can be excited to generate a stepwise amplified magnetic field by the FC method and has the ability of long-term stable operation with persistent current mode (PCM), which can possibly be extended to practical HTS permanent magnets stacked by REBCO plates with multi- holes and magnetic fields.

A preliminary design of a Rutherford cable (Rfc) consisting of a copper core and 10 Quasi-isotropic Strands (Q-ISs) with symmetrical geometry is proposed. The current sharing temperature (Tcs), minimum quench energy (MQE), and normal zone propagation velocity (NZPV) are significant for determining the thermal stability performance of the superconducting cable. Firstly, an electric model of the conductor equivalent circuit is established, and the algebraic equations are derived. The model is validated with the empirical formula by calculating the Tcs of a single Q-IS. Using the validated model, the Tcs of Rfc fabricated by Q-ISs operating in liquid helium temperature at different magnetic fields are obtained. Then, to quantitatively characterize the effect of Q-ISs located at different positions on Rfc after a heating disturbance, the MQE and NZPV of Rfc are numerically simulated by the finite element method, which uses a 3-D thermal model with a homogenization procedure and coupled with the previous electrical model. The analyzed results provide a preliminary assessment of the thermal stability of the high-current superconducting cable and provide important guidance for subsequent experiments and prospective engineering applications.

This paper presents a new method to improve both the critical current and the uniformity of current distribution in a high-temperature superconducting (HTS) cable. The proposed method involves weaving the cable using transpositional REBCO tapes. To establish a three-dimensional (3D) finite element model (FEM) in the proposed approach, the H formula is used. Numerical methods are used to analyze the current distribution and critical current at 77 K. The E - I curve is obtained through experimentation. The results indicate that the novel HTS cable has several favorable characteristics compared to the cable simply stacked by REBCO tapes, including a larger critical current and a more uniform current distribution.

For self-shielded HTS DC cable, fault current characteristics is an urgent research domain. Since the use of parallel conductors is a common method to protect HTS tapes, fault current characteristics of REBCO tape in parallel with several different metal materials are analyzed in this paper. The REBCO tape in parallel with stainless steel tape is designed into self-shielded HTS DC cable for its ascendant current limiting ability. Then a 2D simulation model is established based on coupling electric, magnetic and thermal fields to simulate the current-temperature variations of cables. At last, the influence of thickness of the stainless steel variation on the surge withstand capability of cable is summarized. It is of important referential value for self-shielded HTS DC cable and other cables.

HTS transformers can provide lower loss and higher efficiency with smaller size and lighter weight compared with traditional transformers. In this paper, we designed a 500 kVA HTS transformer and developed its simulation using finite element software based on the H-formulation, and the simulation incorporates a heat model and E-J power law. The simulation shows that there is a large radial flux leakage at the end of the low-voltage (LV) windings (superconducting windings), leading to a reduction in critical current density and an associated increase in joule loss in the LV winding. In order to reduce joule loss, various LV winding structures were designed. The results demonstrate that either increasing the axial distance between the coils at the LV winding end or installing a flux diverter outside the LV windings can effectively diminish the radial flux leakage at the LV winding end, consequently reducing joule loss in the LV winding. The impact of the size, position and relative permeability of the flux diverter on radial flux leakage and joule loss are also studied. These structure optimizations and the corresponding effects have important significance to the design of HTS transformers.