High Temperature Superconducting Wire Research Articles

Utility applications and experience with resilient electric grid systems utilizing high temperature superconductor wires in Chicago

In spring 2020, Commonwealth Edison (ComEd) in Chicago, IL broke ground on Chicago's first permanent Resilient Electric Grid System utilizing high temperature superconductor (HTS) cable after successfully achieving the US Federal Energy Regulatory Commission (FERC) approval for the classification of this being a transmission asset. This permanent grid project, commissioned in August 2021, represents the first commercial adoption of the technology in North America, a major benchmark for the acceptance of HTS electric power applications.

A full-wave HTS flux pump using a feedback control system

Transformer-rectifier flux pumps are DC superconducting power supplies capable of charging superconducting magnets to high currents and stored magnetic energies. Here, we demonstrate a full-wave superconducting flux pump assembled from high-temperature superconducting (HTS) wire that utilizes superconducting switches controlled by applied magnetic field. A negative DC offset occurs in the superconducting secondary of the circuit during operation which is related to the output load current. A feedback control system is proposed and demonstrated to account for the negative DC offset. Increasing the primary current proportional to the load current during operation allowed for the maximum output of the flux pump to be increased from 35 A to more than 275 A. These results are reproduced using a coupled electrical- and magnetic–circuit model formulated in the MATLAB Simulink® package.

Improvement in Power Transmission Efficiency of Wireless Power Transfer System Using Superconducting Intermediate Coil

We have demonstrated that using a high-quality-factor intermediate (IM) coil with a high temperature superconductor (HTS) wire improves the power transmission efficiency (PTE) of a wireless power transfer (WPT) system for long-distance power transmission. The IM coil is placed at the center of Cu transmitting (Tx) and receiving (Rx) coils and consists of a previously developed double-sided HTS coated conductor (CC) wire. A WPT system with the HTS IM coil was designed on the basis of the design theory for a third-order bandpass filter. The measured PTE of the system was compared with that of one with a Cu IM coil. The resonant frequencies of the Tx, Rx, and IM coils in both systems were each about 9 MHz. When the distance between the Tx and Rx coils was 160 cm, the PTEs of the systems were 49.7% and 17.5%, respectively, demonstrating that the PTE of a WPT system can be greatly improved by using an HTS IM coil rather than a Cu one.

Influence of Shielding Currents in Coated Conductors on Field Quality of Iron-Dominated HTS Magnets Estimated by Numerical Analyses

Additional magnetic fields induced by shielding currents (persistent eddy current induced in superconductor) are called shielding-current induced fields (SCIFs). SCIFs are serious problem in magnets using tape-shaped high-temperature superconductor (HTS) wires, because it would worsen the accuracy and stability of the generated magnetic field of the magnets. In iron-dominated HTS magnets, magnetic field distribution at air gap between iron magnetic poles is dominated by poles' shape, so the influence of SCIFs on the quality of generated magnetic field is usually considered negligible. However, quantitative estimation of SCIFs is required to support this assumption. Therefore, we developed a practical method to estimate SCIF distributions in iron-dominated HTS magnets and use it to estimate temporal change of SCIF distribution in an iron-dominated HTS magnet. According to the analysis results, we confirmed relative error of magnetic field caused by SCIFs is in the order of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-4</sup> , which is negligible in many magnet applications.

Transport AC Losses in Multiple-Layer Roebel Tapes

The Roebel tape is a novel high-temperature superconducting (HTS) wire with a multiple superconducting layer structure. Adjacent layers are patterned into meander-shaped multifilaments in opposite directions so that the magnetic fields generated by each layer can be mutually cancelled. The Roebel tape can be regarded as an HTS Roebel cable encapsulated into a tape, and hence has exclusive advantages such as high engineering current density, small critical current degradation, low AC losses, and a simple manufacturing process. This paper focuses on the transport AC losses of the Roebel tape with a multiple-layer structure. 3-D finite element method (FEM) models for the Roebel tapes are built based on the T-A formulation. Current distribution and AC losses of the Roebel tapes with up to 10 ReBCO layers are obtained. The results show that the tapes with even numbers of layers generate lower losses than those with odd numbers, which indicates the superconducting layers should always appear in pairs. Increasing layers can increase the engineering current density of the tape, but the average loss per layer also rises. Therefore, we suggest increasing the distance between the layer pairs or using double-layer Roebel tape stacks instead. The results indicate that the multilayer Roebel tapes can be a promising cable solution for industry and fusion applications because of the high current density and low AC losses.

Investigation of HTS Coil Structure Robustness Against Misalignment Between Coils in a Wireless Power Transmission System for Railway Vehicles

A wireless power transmission (WPT) system using high-temperature superconducting (HTS) coils has been investigated. However, it is difficult to precisely match the positions of the primary and secondary coils. Thus, the HTS coil structure with high misalignment tolerance is required. In this paper, we investigated the non-circular HTS coil structure with a high quality factor for the WPT system, such as a rectangular coil and a racetrack coil. Also, we evaluated the power transmission characteristics of the WPT system using the non-circular HTS coils. As a result, the quality factor of the non-circular HTS coils was maximum when the radial gap between turns was almost the same as the HTS wire width, and increased with increasing coil length in a rail longitudinal direction. Also, the receiving power and the system efficiency using the non-circular HTS coils were more robust against misalignment between coils than those using the circular HTS coils. On the other hand, the receiving power decreased with increasing the coil length of the non-circular HTS coils in the rail longitudinal direction due to thermal radiation from normal temperature. From the above, the receiving power of the WPT system with small lateral misalignments can be improved by using the rectangular coils with a short coil length in the rail longitudinal direction in parallel. Moreover, the system efficiency of the WPT system with large lateral misalignments can be improved by using the rectangular coils or the racetrack coils with a long coil length in the rail longitudinal direction.

Limitation of Current Transport in Coated Conductors: Statistical Fluctuations or Weak Spots?

Traditionally, the critical current, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I_c</i> , of a superconducting wire, considered as the limit of DC operation, is experimentally verified on a sample few centimeters long. This approach could fail in case of high-temperature superconductor wires, where significant changes of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I_c</i> along the conductor length, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</i> , are commonly observed. Then, the quantity that could replace the uniform critical current as the entry data in designing of a superconducting device is to be found. We have analysed the properties of 6 coated conductor tapes provided by 4 different manufacturers. First, the overall critical current of the full tape length, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I_c_,ovrl</i> , has been evaluated from the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I_c(x</i> ) data. However, the dissipation in a non-uniform conductor with fluctuating critical current concentrates in the “weak spots” with the lowest <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I_c</i> values. Then, depending on the conditions of heat removal, thermal runaway in some location could happen before reaching <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I_c_,ovrl</i> during conductor testing or operation. Taking into account the conductor architectures and assuming the cooling in liquid nitrogen bath, we computed the thermal runaway current, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I_tr</i> , at which the weakest location in each of the analysed conductors would convert to a “hot spot” with rapid increase of temperature. Then, comparing <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I_tr</i> to <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I_c_,ovrl</i> one can identify which of these two values is lower, i.e., represents the upper limit of transportable current. We discuss how the result of such analysis would be influenced by a metallic stabilisation that exhibits significant impact on cooling.

Design and Characteristic Analysis of an Axial Flux High-Temperature Superconducting Motor for Aircraft Propulsion.

In line with global environmental regulations, the demand for eco-friendly and highly efficient aircraft propulsion systems is increasing. The combination of axial flux motors and superconductors could be a key technology used to address these needs. In this paper, an axial flux high temperature superconducting (HTS) motor for aircraft propulsion was designed and its characteristics were analyzed. A 2G HTS wire with high magnetic flux characteristic was used for the field winding of the 120 kW axial flux HTS motor, and the rotational speed and rated voltage of the motor were 2000 rpm and 220 V, respectively. The axial flux HTS motor implements a revolving armature type for solid cooling of the HTS field coil. The electromagnetic and thermal features of the motor were analyzed and designed utilizing a 3D finite element method program. The HTS coil was maintained at the target temperature by effectively designing the current lead and cooling system to minimize heat loss. These results can be effectively used in the design of propulsion systems for large commercial aircraft in the future as well as for the design of small aircraft with less than 4 seats.

Design and Analysis of Cryogenic Cooling System for Electric Propulsion System Using Liquid Hydrogen

As the demand for eco-friendly energy increases, hydrogen energy and liquid hydrogen storage technologies are being developed as an alternative. Hydrogen has a lower liquefaction point and higher thermal conductivity than nitrogen or neon used in general cryogenic systems. Therefore, the application of hydrogen to cryogenic systems can increase efficiency and stability. This paper describes the design and analysis of a cryogenic cooling system for an electric propulsion system using liquid hydrogen as a refrigerant and energy source. The proposed aviation propulsion system (APS) consists of a hydrogen fuel cell, a battery, a power distribution system, and a motor. For a lab-scale 5 kW superconducting motor using a 2G high-temperature superconducting (HTS) wire, the HTS motor and cooling system were analyzed for electromagnetic and thermal characteristics using a finite element method-based analysis program. The liquid hydrogen-based cooling system consists of a pre-cooling system, a hydrogen liquefaction system, and an HTS coil cooling system. Based on the thermal load analysis results of the HTS coil, the target temperature for hydrogen gas pre-cooling, the number of buffer layers, and the cryo-cooler capacity were selected to minimize the thermal load of the hydrogen liquefaction system. As a result, the hydrogen was stably liquefied, and the temperature of the HTS coil corresponding to the thermal load of the designed lab-scale HTS motor was maintained at 30 K.

Critical current asymmetry in HTS switches using iron-core electromagnets

Iron-core electromagnets are widely used as applied-field switches in high-temperature superconducting (HTS) flux pumps. It was recently reported that the critical current () of the HTS wire is suppressed by up to 45% in the air gap of the iron core. Here, it is reported that the self-field of a single tape (unifilar) is suppressed from 357 A to 195 A while in the air gap of an iron core, agreeing closely with the previous study. This is extended by showing that the response to a perpendicular magnetic field is asymmetric, with a peak of 249 A found to be at 0.16 T of applied magnetic field. This effect can be eliminated using an anti-parallel current configuration (bifilar), which is shown experimentally to recover close to the no-core self-field of 357 A with no observed asymmetry. The results of both types of switch configurations are closely replicated in finite-element modelling using COMSOL Multiphysics®. This is caused by the asymmetric interaction between the self-induced magnetic field of the HTS switch element and the magnetic circuit of the iron-core electromagnet.

A customized electric heater to mitigate screening current by optimal control on temperature distribution in a high-temperature superconductor coil

The so-called screening current in a high temperature superconductor (HTS) is a well-known phenomenon that has detrimental effects on performance of an HTS magnet. To date, many research efforts have been devoted to suppressing screening current in an HTS magnet. Here, we report a customized electric-heater, named “Thermal Eraser,” to mitigate the screening current. The key idea is to optimally control the spatial temperature distribution in an HTS magnet using the customized heater and the consequent temperature-dependent local critical current of HTS wires of the magnet. To validate the idea, a Thermal Eraser was designed, constructed, and installed in an actual single-pancake HTS coil. The Thermal Eraser with the test coil system was operated at temperatures ranging 7–40 K in our in-house conduction-cooling cryogenic facility. The feasibility of the Thermal Eraser was demonstrated in terms of two aspects: (1) creation of the designated spatial temperature distribution within the HTS test coil as designed and (2) quantitative evaluation of its effectiveness to mitigate screening current using both experimental and numerical results. We confirmed that the screening current induced field in the test coil was reduced by 0.6 mT after activation of the Thermal Eraser, which implies 60% reduction of screening current in the HTS test coil. The results demonstrate that the Thermal Eraser is a viable option to effectively reduce the screening current in an HTS magnet.

Study on the Magnetic Properties of Metal Substrates at Low Temperature by Fabricated Compact SST

In recent years, a development of a high magnetic field magnet using a high temperature superconducting (HTS) wire has been advanced. On the other hand, we are planning to use the HTS wires for superconducting applications cooled by cryocooler. So, it is necessary to measure the temperature dependence of the magnetic properties of the metal substrates (Hastelloy, stainless steel and NiW) for HTS wire under conduction cooling conditions. We have been developing a single sheet tester (SST) that can evaluate the magnetic properties of electromagnetic steel sheets and other materials. However, since the size of an excitation coil in the conventional SST is large, it is difficult to install them in the conduction cooling system. In this study, we fabricated the compact SST and its measurement accuracy was compared with the conventional SST. The magnetic properties of metal substrates were measured at room temperature and liquid nitrogen temperature (77 K). As a result, although the measurement accuracy of the compact SST was slightly reduced by decreasing the coil size, we found that the error of the magnetic field homogeneity of the compact SST was within 2&#x0025; at the center region of the 5 mm length. The magnetic properties of Hastelloy and stainless steel were almost unchanged at both room temperature and liquid nitrogen temperature. However, the magnetic properties of the NiW substrate changed significantly at liquid nitrogen temperature. The <i>B</i>-<i>H</i> characteristics of the NiW substrate in the rolling and transverse directions were clearly different, and the iron loss increased significantly at liquid nitrogen temperature.

Review on thermal-related measurement methods for superconducting devices and prospect for high-speed maglev transportation application

High-temperature superconducting (HTS) bulks can not only be self-stable when levitated above a permanent magnet (PM) but also can be used as quasi PM with higher magnetic energy product due to their magnetic flux pinning characteristics. Therefore, HTS bulks have wide application potentials in maglev trains, maglev bearings, flywheel energy storage, drug delivery, and high field magnets. In the external magnetic field of common application scenarios, HTS bulks have no external input current, so it is difficult to achieve the overall quench. However, local quenching in the bulk is still possible in the harsh fluctuating external field environment. Although it is difficult to reach the total quench, its critical parameters like Jc will inevitably deteriorate, which may collapse the application system. Therefore, in contrast to superconducting wires and tapes that are more concerned with quench detection, HTS bulks with a 3D volume effect are more focused on internal sensitive temperature locations, the impacts of volume and scale, and the coupling influence on application parameters such as magnetism and force. Therefore, for efficient thermal-related measurement of HTS bulk applications, this paper investigates and discusses 12 commonly-used temperature measurement or quench detection methods in all superconducting application fields. These methods primarily refer to the current quench detection technologies used in HTS tapes and wires. From the standpoint of practical temperature measurement requirements of HTS bulks and technological limitations of maglev application scenarios, working characteristics and service conditions of the 12 methods, and 4 temperature detection methods are selected through a comprehensive understanding and comparison of basic principles. They are expected to be used in real-time monitoring and early warning schemes for onboard superconducting levitation devices of HTS maglev transportation or other applications in the future.

High Efficiency Wireless Power Transmission System That Uses HTS Transmitting and Copper Receiving Coils With a Large Difference in Quality Factor

We developed an efficient wireless power transmission (WPT) system using a high-temperature superconductor (HTS) spiral coil with a high quality factor as the transmitting coil and a copper coil as the receiving coil. The HTS spiral coil was fabricated using double-sided HTS wire which we developed previously. The double-sided HTS wire consists of two conventional HTS coated conductor wires. The measured quality factor of the HTS spiral coil containing modified coil support was about 14 times higher than that of the copper coil. We designed the WPT system using the filter design theory. We measured the design parameters for a coupling coefficient and an external quality factor. We measured the power transmission efficiency (PTE) of the WPT in the facing direction, position misalignment, and angular misalignment. The PTE of the WPT system with the high quality factor HTS spiral coil showed significant improvements in all measurements compared to the system with copper coils.

절연파괴에 따른 2세대 고온 초전도선재의 열화특성에 관한 연구

2G high temperature superconducting (HTS) wires have been widely adopted to develop high voltage superconducting apparatuses such as a superconducting fault current limiter (SFCL), a superconducting cable, a superconducting transformer, and so on. A study on the dielectric degradation characteristics of 2G HTS wires due to electrical breakdown should be performed to enhance the stability and to accelerate the commercialization of high voltage superconducting apparatuses. In this study, the degradation characteristics of 2G HTS wires, SCN-04 made by SuNAM Co., Ltd. are analyzed by dielectric experiments with AC and lightning impulse voltage in saturated liquid nitrogen (LN2) of 77K. The 2G HTS wire used in this study has silver stabilizing layers on both sides of GdBCO layer. Also, the substrate is made with stainless steel and whole 2G HTS wire is surrounded by copper. It is verified that the degree of degradation of the 2G HTS wire is affected by the magnitude of the applied voltage and the type of voltage. Also, cracked GdBCO layer due to electrical breakdown is shown by scanning electron microscope (SEM) image. The degradation characteristics such as critical current and index n of 2G HTS wire due to electrical breakdown can be explained by mechanical cracked structure of a GdBCO layer.

Application of electron backscatter diffraction in the SEM to textural problems of coated high-temperature superconductors

Abstract YBa2Cu3O7– δ (YBCO) is a high-temperature superconductor (HTS) with unique characteristics for use in electrical engineering. The structure and the transport properties of the cuprate superconductor are reviewed. The key issues in HTS wire technology, viz. texture tailoring and grain boundary engineering of the polycrystalline material to be used in technical devices, are discussed. A production route is described to fabricate long lengths of highly aligned YBCO films on cube-textured nickel and nickel alloy substrates. Electron backscatter diffraction in the scanning electron microscope is used to control the process → texture relationship in developing the sheet material as well as the epitaxy and phase stability of the YBCO film.

Модернизация ионного источника нейтронного генератора ИПФ РАН

Using X-ray diffraction, there were determined the residual stresses on the surface of the AISI 310S stainless steel carrier tape used in manufacture of the second generation high temperature superconducting (2G HTS) wires at the National Research Center “Kurchatov Institute”, from delivery to deposition of the main buffer layer YSZ between the tape and the superconducting layer, and the residual stress in the buffer layer YSZ itself. The compressive stress of –0.8 GPa induced by rolling was found on the surface of the tape as-delivered. During processing, it varies from –0.5 to –1.1 GPa. At each stage, its depth distribution was found down to 10 μm, and the residual stresses caused by processing were determined. The residual stress in the YSZ layer deposited using the ABAD technology is compressive and amounts to –3.29 GPa. The layer has a defective single-crystal structure in type to radiation swelling with the unstressed lattice period of 5.1820 Å, 0.9% larger than in ordinary crystal. The results obtained are in agreement with the data of the earlier neutron diffraction study of residual stresses inside the carrier tape.

Residual stresses at the interface between carrier tape and YSZ layer in manufacture of 2G HTS wires

Using X-ray diffraction, there were determined the residual stresses on the surface of the AISI 310S stainless steel carrier tape used in manufacture of the second generation high temperature superconducting (2G HTS) wires at the National Research Center &amp;quot;Kurchatov Institute&amp;quot;, from delivery to deposition of the main buffer layer YSZ between the tape and the superconducting layer, and the residual stress in the buffer layer YSZ itself. The compressive stress of -0.8 GPa induced by rolling was found on the surface of the tape as-delivered. During processing, it varies from -0.5 to -1.1 GPa. At each stage, its depth distribution was found down to 10 μm, and the residual stresses caused by processing were determined. The residual stress in the YSZ layer deposited using the ABAD technology is compressive and amounts to -3.29 GPa. The layer has a defective single-crystal structure in type to radiation swelling with the unstressed lattice period of 5.1820 Angstrem, 0.9% larger than in ordinary crystal. The results obtained are in agreement with the data of the earlier neutron diffraction study of residual stresses inside the carrier tape. Keywords: residual stress, 2G HTS wires, AISI 310S tape, YSZ layer, YSZ crystal structure, X-ray diffraction.

Остаточные напряжения на интерфейсе между несущей лентой и слоем YSZ при изготовлении ВТСП проводов второго поколения

Using X-ray diffraction, there were determined the residual stresses on the surface of the AISI 310S stainless steel carrier tape used in manufacture of the second generation high temperature superconducting (2G HTS) wires at the National Research Center “Kurchatov Institute”, from delivery to deposition of the main buffer layer YSZ between the tape and the superconducting layer, and the residual stress in the buffer layer YSZ itself. The compressive stress of –0.8 GPa induced by rolling was found on the surface of the tape as-delivered. During processing, it varies from –0.5 to –1.1 GPa. At each stage, its depth distribution was found down to 10 μm, and the residual stresses caused by processing were determined. The residual stress in the YSZ layer deposited using the ABAD technology is compressive and amounts to –3.29 GPa. The layer has a defective single-crystal structure in type to radiation swelling with the unstressed lattice period of 5.1820 Å, 0.9% larger than in ordinary crystal. The results obtained are in agreement with the data of the earlier neutron diffraction study of residual stresses inside the carrier tape.

Fabrication and Critical Current Evaluation for HTS Twisted Cables Consisting of Soldered-Stacked-Square (3S) Wires

High temperature superconducting (HTS) conductors or cables can be considered as a significant candidate in various large-current HTS applications. To develop large-current HTS conductors or cables, HTS wires of small square dimension have been suggested and studied in our group, and the wire is named Soldered-Stacked-Square (3S) wires. Based on 3S (2+10c)-wires composed of two HTS tapes and ten copper tapes, a novel HTS twisted cable structure named “2mm-7-cable” including seven (2+10c)-wires was firstly proposed in this study. This structure is most similar to the cable in conduit conductor (CICC) structure of low temperature superconductor (LTS). To begin with, we introduced the fabrication process of the 2mm-7-cables, including preparation of soldered-stacked-square (3S) wire, winding copper wire process, twisting and cabling process. Then, their critical current performance was evaluated experimentally. The test results of critical current show that when the voltage-lead is directly connected to the surface of the (2+10c)-wire after removing the copper wires of both ends, the measured resistance of 2mm-7-cable will be greatly reduced. And the summation of the critical currents of seven (2+10c)-wires are almost identical to the one of the 2mm-7-cable. Thus, the feasibility of the fabrication method for the novel HTS twisted cable is partially verified in this study.