High Temperature Superconducting Cable Research Articles

Current sharing in double-sided REBCO tapes

Abstract Current sharing between RE-Ba-Cu-O (REBCO, RE=rare earth) tapes within a high-temperature superconducting (HTS) coil or cable is important to avoid damage from uncontrolled quench of superconducting devices operating at high currents. Current sharing between REBCO tapes is found to be limited by contact resistivity between the adjacent tapes, which is about 20x higher in the REBCO-facing-substrate (face-to-back) configuration that is commonly used in devices compared to a REBCO-facing-REBCO (face-to-face) configuration. Double-sided REBCO tapes always offer face-to-face contacts between adjacent tapes, and this benefit for excellent current sharing has been validated in experiments wherein an artificial defect is introduced in one tape in a 2-ply tape stack. Additionally, current sharing between the two REBCO layers within one double-sided REBCO tape has also been investigated. Slotting of the double-sided tapes, wherein slots through the insulating buffer stack are filled with a conductive material, has been found to significantly enhance the current sharing from one REBCO layer to the opposite layer.

Feasibility of high temperature superconducting cables for energy harvesting in large space-based solar power satellite applications: Electromagnetic, thermal and cost considerations

The aim of this paper is to present feasibility of application of High Temperature Superconducting (HTS) cables for Space-Based Solar Power (SBSP) application. SBSP is a promising technology that can deliver an infinite amount of clean and eco-friendly energy to the Earth. To deliver the harvested solar energy to the power systems on Earth, efficient energy transmission is critically important. To address the challenges of conventional transmission means, an ideal solution would be using HTS cables. In this research, the design procedure of a Direct Current (DC) HTS cable considering electromagnetic, thermal, and cost constraints is presented. The study considered a 2 MW bipolar DC HTS cable in five operational temperatures: 20 K, 30 K, 50 K, 65 K, and 77 K. The results were showed that the cost and weight of the designed HTS cables were increased by operational temperature increase. However, the cooling cost of HTS cable in higher temperatures, was less than lower temperatures. Also, the total efficiency of the HTS cable and cooling system were increased, when operational temperatures were changed from 20 K to 77 K, from 99.70% to 99.97%, respectively.

Оптимизация ВТСП кабелей постоянного и переменного тока с учетом эффекта продольного магнитного поля

It is known that in magnetic fields parallel to the transport current, an increase of the critical current is observed in most low-temperature and high-temperature superconductors — the effect of a longitudinal magnetic field (LMFE). LMFE has been theoretically predicted and experimentally confirmed in many studies. This article presents various methods for optimizing power coaxial cables based on high-temperature superconductors (HTS), considering LMFE. LMFE provides a higher current-carrying capacity of HTS DC cables and higher stability for HTS power AC cables, including lower AC losses. The results of optimization of HTS cables for both DC and AC applications with consideration of LMFE are presented and discussed. Two methods for calculating the magnetic field in coaxial HTS cables are presented: analytical and using the finite element method. The results of AC loss calculations and measurements for HTS cables are also presented.

Design and investigation of losses of a low-current HTS AC cable for a promising cryogenic generation system

Currently, there are a large number of projects dedicated to electric machines aimed at use in the field of transport and equipped with windings made of high-temperature superconductors (HTS). These machines in their majority have rated currents significantly less than 1kA, which is a too low value for AC HTS cables in the power industry, where current values can reach up to 10kA. On the other hand, connecting, for example, an electric generator with cryogenic cooling and its load (which, most likely, will also have cryogenic cooling) with copper wires on board of a vehicle does not look like an effective solution. This article is devoted to the development of the concept of an alternating current transmission system for machines with a rated current of less than 1 kA through HTS cable. In order to achieve a compact design, it was decided to use a cable consisting of stacks of second-generation (2G) HTS tapes. A series of experiments was carried out with different numbers of tapes and directions of current in them for stacks of 2, 4 and 6 the HTS tapes. The results were compared with finite element modeling. The article shows that when current flows in adjacent cable HTS tapes in opposite directions, like as in bifilar windings, it is possible to achieve a significantly lower level of losses per tape than when current flows in the cable tapes in one direction.

The Latest Progress in China's High-Temperature Superconducting Cable Industry

The Latest Progress in China's High-Temperature Superconducting Cable Industry

Transient research on distribution networks incorporating superconducting cables utilizing field–circuit coupling method

High temperature superconducting (HTS) cable represents a promising solution for fulfilling the power demands of cities with large loads and high density. However, due to their connection to the distribution network, HTS cables are vulnerable to fault currents exceeding ten times their rated current, which poses a serious threat to both the safety of the cable and the operation of the grid. Considering the highly nonlinear nature of superconducting conductivity, this study develops a field–circuit coupling model to investigate the transient characteristics of distribution networks incorporating superconducting cables (DNSC). Firstly, a finite element model based on the two-dimensional H formulation was built to calculate the electrical and thermal parameters of the HTS cable. Subsequently, an equivalent circuit model of the distribution network was employed to estimate the short-circuit currents. Communicating via a co-simulation server, the superconducting cable current and distribution network impedance were updated in each step. Further, based on an actual DNSC system in Shenzhen, China, the highest quenching temperature of the cable and the maximum fault current of busbars were assessed. Finally, by integrating current limiters into the system, the withstand capability of the cable and busbars was determined, which indicates that the improved protection configuration can effectively suppress fault currents and ensure safe operation. Successfully applied to an actual distribution network, the co-simulation model utilizing the field–circuit coupling method addresses the challenges of solving highly nonlinear and time-varying systems, enabling transient analysis and protection research for the integration of superconducting devices into the conventional grid.

Understanding ac losses in CORC cables of YBCO superconducting tapes by numerical simulations

Alternating current (ac) losses in conductor-on-rounded-core (CORC) cables of YBCO high-temperature superconducting (HTS) tapes are a significant challenge in HTS power applications. This study employs two finite element analysis (FEA) models to investigate the contributions from different ac loss components and provide approaches for reducing ac losses in cables. An FEA model based on the T-A formulation treats the cross section of thin superconducting layers as 1D lines and, therefore, only can predict the ac loss generated by the perpendicular magnetic field. In contrast, the model based on H-formulation can be performed on the actual 2D rectangular cross section HTS tapes to provide the total ac losses generated by magnetic fluxes penetrating from both the edges and surfaces of HTS tapes, although this model requires more computing time and memory. The 1D and 2D simulation models were validated by cross comparing the results from both models and by comparing sub-section and full cross section models. Subsequently, two models relate cable design and operational parameters to the surface and edge losses of a two-layer CORC cable by considering the (1) relative contributions of edge and surface losses to the overall ac losses; (2) effect of the current distribution between inner and outer HTS layers on ac losses; (3) impact of the tape alignment on ac losses in each HTS layer; (4) influence of the thickness of HTS layers on ac losses; (5) effect of size and number of inter-tape gaps on ac losses; and (6) contribution frequency on the ac losses. The research results given in this paper are therefore not only valuable to suggest strategies for reducing ac loss in multi-layer cables but also for developing more accurate and effective methods to calculate ac loss in CORC HTS cables.

BELFEM: a special purpose finite element code for the magnetodynamic modeling of high-temperature superconducting tapes

Predicting the performance and reliability of high-temperature superconducting (HTS) cables and magnets is a critical component of their research and development process. Novel mixed finite element formulations, particularly the h -φ-formulation with thin-shell simplification, present promising opportunities for more efficient simulations of larger geometries. To make these new methods accessible in a flexible tool, we are developing the Berkeley Lab Finite Element Framework (BELFEM). This paper provides an overview of the relevant formulations, discusses the current state of the art, and discusses the main aspects of the BELFEM code structure. We validate a first 2D thin-shell implementation in BELFEM against selected benchmarks computed in COMSOL Multiphysics and compare the performance of our code with a comparable formulation in GetDP. We also outline the next steps in the development process, paving the way for more advanced and robust modeling capabilities.

A Review on Insulation and Dielectrics for High- Temperature Superconducting Cables for Power Distribution: Progress, Challenges, and Prospects

The high temperature superconducting (HTS) AC and DC cables are gradually finding their way towards commercialization due to their ability to transfer bulk electric power with negligible dielectric loss. In this context, this paper critically reviews the different aspects of HTS cables used in various applications and related accessories. The operational, lab-scale, and prototype HTS cable projects are discussed in detail. Different dielectrics, electrical insulations, superconductors, cooling systems, cryogens, and upcoming projects of HTS cables are reviewed. The underlying challenges and future directions in AC and DC cables, electric aircraft and ships, associated costs, cryogenic insulation materials, cooling technologies, superconductors, and electrical insulations of HTS cables are discussed in detail. The space charge performance of presently-used polypropylene laminated paper (PPLP) insulation and future insulation, i.e., Kapton material, is experimentally analyzed, to show the future challenges in the insulation design. The technology readiness level, market trends, and relevant test standards are explored. The research and market trends suggest that HTS cables can replace conventional transmission methods. However, their consistent growth and adaptation of HTS cables will depend on design of cryocoolers, raw material cost of superconductors, and large-scale production.

AC Loss Analysis in Superconducting Cables Carrying Characteristic and Noncharacteristic Harmonic Currents

Harmonic distortions - especially in current waveform - are the inherent nature of any power system such as urban grids, wind farms, electric aircraft, and other electrified transportation units that could change the AC loss value in High Temperature Superconducting (HTS) cables. The aim is to investigate the impact of non-sinusoidal currents with different integer-harmonics, inter-harmonics, and sub-harmonics on the AC loss characteristics of a 22.9 kV, 50 MVA HTS cable. This was accomplished by using an Equivalent Circuit Model (ECM). To do so, current waveforms containing different harmonic components were passed to the ECM of HTS cable. For evaluating the impact of distorted current waveforms on the AC loss of the HTS cable, the ECM was validated by means of Finite Element Method (FEM) in tape level. The results of validation phase have shown a good agreement between the AC loss value derived by ECM and those calculated by FEM published in literature. The results showed that when current waveform was distorted by harmonics, the value of AC loss was changed significantly with respect to variations of harmonic phase angle, order, and amplitude. Results also indicated that 5 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sup> harmonic order has the highest impact on the AC loss value and could increase 6% to 80% of AC loss in comparison to pure sinusoidal current. Sub-harmonics and inter-harmonics could also increase the AC loss value to maximum 88% and 64% higher than that of sinusoidal condition.

Magnetization Loss Measurement of Twisted Stacked Tape Cable and Comparison With CORC

High Temperature Superconducting (HTS) cables for large current capacity are being studied in several forms for power device applications. Currently, the cables are being developed for DC applications rather than AC applications. However, if a technology for reducing AC loss is developed, it will be possible to apply HTS cables to various AC devices. Twisted Stacked-Tape Cable (TSTC) is one of the large current HTS cables. It is made by stacking and twisting multiple HTS tapes for large current capacity. The HTS tapes in TSTC should be twisted for the uniformity of current distribution in each tape. Since the HTS tape has a wide thin film shape, it is very difficult to twist itself. In this paper, we measured the magnetization losses of TSTC samples without the striations under AC magnetic fields that had peak values below 0.1 T. Several molds for the TSTC samples were made by using a 3D printer. TSTC samples had several numbers of stacked tapes and two kinds of the tape width. The magnetization losses of the samples in the molds were measured under uniform AC magnetic fields. The experimental results were compared to those of the straight HTS stacked cables and conductor on round core (CORC) cables.

Automatic Modeling of High-Temperature Superconducting Cable Using Reinforcement Learning

This paper proposes a technique of automatic modeling for high-temperature superconducting (HTS) cables. Reinforcement learning (RL), which is a representative methodology for automation and intelligence, is applied for the automation of the proposed modeling. To reflect the high-frequency characteristics of the HTS cables in the proposed modeling, reflectometry-based cable modeling is used. In addition, for agent training, an environment that combines simulation and experiment results is proposed, and detailed techniques for the process of the proposed RL model are introduced. The proposed technique is demonstrated by experiment using an actual HTS cable under 77 K and 300 K conditions. It is expected that the proposed technique will allow anyone without the related knowledge to perform the modeling of the HTS cables.

Aluminium-Stabilized High-Temperature Superconducting Cable for Particle Detector Magnets

Within the context of EP R&D, CERN is developing a high-temperature superconducting (HTS) conductor for future superconducting detector magnet projects. The conductor features a Rare-Earth Barium Copper Oxide (REBCO) tapes soldered to a copper-coated high-purity aluminium stabilizer. Critical currents of the 200 mm long straight cable samples measured with various numbers of REBCO tapes at 77 K are consistent with empirical scaling formulas for critical current within 10%. A few percent deviations are expected to arise from the critical current variation along the length of the HTS tape. No degradation was observed after multiple soldering and de-soldering cycles at 165 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^\mathrm{o}$</tex-math></inline-formula> C with Bi–Sn based solder and after thermal cycling between 77 K and room temperature. However, extreme bending (of 100 mm radius) of the already soldered HTS cable leads to failure of the cable. We repeated the critical current measurements with a 650 mm long cable loop sample with 85 mm bending radius, where the HTS tapes were soldered after the aluminium profile was bent. The critical current of the HTS cable loop was 7% lower than the prediction. Based on the first critical current measurements, the HTS cable preparation method presented in this work results in repeatable quality aluminium-stabilized HTS cable.

Anomaly Detection for HTS Cable Using Stacked Autoencoder and Reflectometry

Since a high–temperature superconducting (HTS) cable has a cooling process and the possibility of a quench, a real–time monitoring technique is essential than other conventional power cable. Conventional reflectometry–based monitoring parameters have inherent disadvantages in that the boundary between normal and abnormal cannot be determined and multiple baselines cannot be considered during the monitoring process. In this paper, a stacked autoencoder–based anomaly detection technique for HTS cable is newly proposed. The autoencoder monitors the condition of HTS cable in real–time by calculating an anomaly score from the input data. The proposed method can automatically set the boundary between normal and abnormal and has the advantage of using multiple baselines. The performance of the proposed method is verified by emulating a local quench in a testbed containing a commercial 22.9 kV HTS cable and compared with that of the conventional monitoring parameter. Based on the advantage of being able to set multiple baselines, it is expected that the proposed technique can be used for real–time monitoring of HTS cable to enhance the reliability of the systems.

Application of Enhanced Optimal-Detection of Time–Frequency Domain Reflectometry on HTS Cable With High-Resolution

Time–frequency domain reflectometry (TFDR) has been used for sensing various types of cables including high temperature superconducting (HTS) cables. Recently, the optimal-detection of time–frequency domain reflectometry (OD-TFDR) has been proposed and has better detection and localization performance than conventional TFDR. Additionally, OD-TFDR has provided a threshold that can distinguish detected signals from Gaussian noise. However, OD-TFDR does not provide a criterion for classifying the detected signals into fault signals and artifacts. Furthermore, the diagnosis result of OD-TFDR is not intuitive because an additional tool is needed to locate each fault. Thus, this paper proposes a new diagnosis algorithm that can provides a criterion for distinguishing between artifacts and faults by considering the propagation direction of the incident signal in the join time–frequency domain while preserving the detection and localization performance of OD-TFDR. Through a template matching process of generalized time–frequency cross-correlation (GTFCC), the core algorithm of OD-TFDR, a modified–generalized time–frequency cross-correlation (M–GTFCC) function is derived. Next, a modified–time–frequency cross-correlation (M–TFCC) function is derived by slicing the M–GTFCC function considering the propagation direction of signal. Finally, M–TFCC function is proposed as a new intuitive diagnosis result with artifact-free and high-resolution. The performance of the proposed algorithm is tested via experimental setup for a real-world single phase HTS cable with an emulated local quench by heating element, and the efficacy of the proposed algorithm is verified based on three performances: fault detection, locating accuracy, and resolution.

Integrated Operational Characteristic Simulations of a ±100 kV/1 kA Superconducting DC Energy Pipeline Based on Multi-Physics Field Interaction

The DC superconducting energy pipeline (DC SEP) is a promising technology, which has the ability to transmit electricity and fossil energy such as liquefied natural gas (LNG) at the same pipeline so that LNG could serve as the refrigerant for the high-temperature superconducting (HTS) cables. The collaborative transportation of electricity and LNG increases the efficiency while lowering the cost. However, the operation performance of the SEP, which is crucial for HTS cables and LNG, is of greater complexity on account of multi-physics interactions. Herein, a ±100 kV/1 kA SEP model with electric, magnetic, fluid and thermal fields is established in COMSOL Multiphysics to analyze the temperature distribution of SEP via parametric scanning on SEP heat leakage and LNG flow rate. Finally, the relationship between temperature rise and LNG flow rate of a SEP has been estimated based on the interactions of the multi-physics fields. The results indicate that the temperature rises by 11.6 K for every kilometer of SEP. Moreover, the influences of heat leakage and LNG flow on temperature rise are revealed. Temperature rise increases proportionally with heat leakage and it decreases not monotonously with LNG flow rate. This study validates the feasibility of SEP and provides the theoretical references for the demonstration of SEP.

Numerical and Experimental Design of the Former for TORT Cables

TORT (Tapes on Round Tube) cables, which implement high-temperature superconducting (HTS) tapes, offer additional benefit over other HTS cables, which is the internal cooling in the former itself. Up to now, the superconducting tapes of existing TORT cables have been wound on a copper tube of various diameters. However, in the alternating current (AC) mode, the high conductivity of the former causes undesirable eddy currents. Therefore, it is necessary to replace the copper with a less electrically conductive material. We designed a former from polyethylene terephthalate glycol-modified and reinforced with carbon fibers (PETG CF), polycarbonate (PC) and polycarbonate reinforced with carbon fibers (PC CF) materials in order to reduce the AC losses in TORT cables, using 3D printing technology. Because of the low thermal conductivity of polymers, the former must be specially designed to improve the cooling of the HTS tapes inside the former. Moreover, thermal deformation of the former during cooling from room temperature to liquid nitrogen temperature and resilience against low-diameter bending is another important issue that was taken into account. Detailed structural finite-element (FE) analysis was carried out using the FE modeling software ANSYS, in prototyping of the former. Based on the numerical models, formers differing in the materials used were fabricated, and subsequently a short TORT cable with wound HTS tape was electromagnetically characterized.

Degradation Characteristics of REBCO Tapes According to Electrical Breakdown

Second-generation (2G) high-temperature supercon-ducting (HTS) coated conductors are widely used to develop high-voltage superconducting apparatuses, such as HTS fault current limiters and HTS cables. In this study, experiments on electrical breakdown were performed in saturated liquid nitrogen (LN2) at a temperature of 77K to verify the relation between the applied voltage and electrically degraded characteristics of REBa2Cu3Ox (REBCO, RE: rear earth) tapes, such as the critical current (Ic) and index n. We used three types of REBCO tapes to determine the effect of the stabilizer material on the electrical degradation characteristics of silver, copper, and brass. A sphere electrode sys-tem was used to conduct electrical breakdown experiments under AC and lightning impulse voltages. Accordingly, we determined that the electrical degradation characteristics of REBCO tapes de-pend on the stabilizer material according to the applied voltage.

AC Loss Estimation Model for High-Temperature Superconducting Cables Derived From Experiments Simulating Electromagnetic Environments

In a previous study, the AC loss characteristics of each layer of a high-temperature superconducting (HTS) AC cable were experimentally investigated [1]–[3]. Based on these data, we modeled the AC loss in a superconducting cable by considering the maxi-mum and minimum values of the loss. A comparison between this model and the experimental data showed good agreement. Hence, it is possible to estimate AC loss under electromagnetic conditions in a high-temperature superconducting cable. This model makes it possible to determine the losses of each layer in the superconducting cable and to design the minimum AC loss load of the superconducting cable. This model estimates the AC losses of a three-layer twisted HTS cable.

Analytical Modeling of Magnetization Losses in Twisted Stacked HTS Conductors

The European post-ITER fusion demonstrator reactor (DEMO) design activities have been ongoing for several years in the framework of the EUROfusion Consortium. The designs proposed for the DEMOnstration Fusion Power Plants (DEMO) magnets include options based on high-temperature superconducting (HTS) technology, namely as an Insert in the Central Solenoid (CS). This work describes the development of tools for the calculation of magnetisation losses in a twisted-stacked HTS cable, which represents one of the most promising configurations of HTS fusion Cable-in-Conduit conductors (CICC). This geometry cannot be tackled with the straightforward application of 1D or 2D models, given their inability to describe the twisting of the tape stacks. However, the methodology proposed in this work allows one to treat the twisting of the conductors by discretizing them in a set of straight pieces. A set of analytical equations is developed to compute the instantaneous power losses in the slab approximation. This fast, easy-to-use, open-access tool, can be employed for the computation of AC losses in the central solenoid modules of a tokamak. In particular, we have applied the model to study the HTS insert of the DEMO central solenoid.