High-temperature Superconductor Technology Research Articles

Novel gases as electrical insulation and a new design for gas-cooled superconducting power cables

High Temperature Superconducting (HTS) power cables are being developed for a variety of applications including the electrical power grid, electrification of transportation, and high energy physics. The appeal of superconducting technology is its high current density — generally greater than 100 A/mm2 — compared with conventional copper and aluminum conductors, which generally do not support greater than 5 A/mm2. Thus, HTS wires and cables support high power ratings even at low and medium voltages, which reduce the size and weight of the electrical power systems. The size and weight reductions are essential to realize large all-electric ships and electric aircraft. HTS devices must be operated within the boundary of their respective critical temperature, critical current, and critical magnetic field [1]. Second generation HTS materials possess critical temperatures of ∼90 K. However, operating temperatures in the range of 50–70 K are typically required for HTS cables to support the desired operating current of many power-dense systems and to have a sufficient temperature margin to tolerate unexpected heat loads and fault currents. When a superconductor exceeds any of its three critical parameters, a quench will occur. A quench causes the HTS cable to transition to its normal state where it starts to display its high electrical resistance. The interdependency of the electrical and thermal properties of HTS materials also depends on the cryogen used to achieve the desired operating temperature. There are only a few cryogens compatible with the desired operating temperatures of 2 ) being the most commonly used for HTS cable applications for the electric power grid due to its abundance, low cost, and good electrical insulation and heat transfer properties. LN 2 -cooled HTS cables have been successfully demonstrated in the electrical power grid operating at 10–200 kV [2], [3]. The LN 2 -cooled 10 kV AC HTS cable installed as part of the Ampacity project in Essen, Germany demonstrated the potential of HTS technology to be economically feasible in urban areas. Installing the 10 kV HTS cable instead of a conventional 110 kV cable to supply the downtown area of Essen allowed for 4 out of 10, 110/10 kV transformer substations located in the center of Essen to be decommissioned and removed [2].

Trapped field potential of commercial Y-Ba-Cu-O bulk superconductors designed for applications

Bulk high-temperature superconductors (HTSs) that act as a trap field magnet establish a novel type of magnetic field source, which is significantly different from that of a permanent magnet or solenoid; therefore, they can be potentially used in magnetic-force-based applications. However, the primary issues related to the commercial use of the bulk HTS technology are established on the enhancement of trapped magnetic fields, as well as their reliability and reproducibility at temperatures achievable with off-the-shelf cryocoolers. This study presents experimental investigations on the strong trapped magnetic fields observed in commercial Y-Ba-Cu-O bulk HTSs produced as a double-sample stack, a cylindrical bulk, and a ring-shaped bulk. Consequently, a reliable and reproducible magnetic field of 9.5 T at 50 K was trapped in commercial Y-Ba-Cu-O assembled as a double-sample stack. In this case, shrink-fit encapsulation with either aluminum or stainless steel tube ensured equally effective reinforcement. Higher magnetization, although accompanied with partial flux jumps, yielded a trapped field of 16.85 T at 30 K, which is comparable to the reported record trapped fields. Finally, a maximum trapped field of 9.78 T - the strongest trapped field reported to date - was attained in the 6 mm hollow space of the ring-shaped bulk HTS.

Manufacture and Performance Test of 3.5 T High Temperature Superconducting Coils for the Magnetic Separation

With the development of the high temperature superconducting (HTS) materials technology, the manufacturing process of the HTS tape has been further improved and hundreds of meters of HTS tapes have been applied in industry. In beneficiation field, the magnetic separation facility of using HTS technology can not only improve the work efficiency of the material purification and separation, but solve the problem that some weak magnetic materials are difficult to separate due to the high magnetic intensity and gradient. Today, a 3.5 T HTS magnetic separation facility cooled by a cryocooler was manufactured in China. This paper focuses on the manufacturing process and performance test of the HTS magnet. Some new structure was adopted in the design and manufacture of the magnet and verified in the magnet performance test. Test results indicated that the magnet could be cooled below 20 K by the direct heat conduction, the center magnetic field could reach 3.57 T and the center axis uniformity of the magnetic field was better than 95% in the range of ±100 mm from the mid-plane. In short, the magnet design is reasonable and it is likely to be applied on other similar magnet in future.

Present and future of high-temperature superconductor quantum-based voltage standards

This paper presents a brief overview of the current state-of-the-art of Josephson junctions for Quantum-based Voltage Standards fabricated with High-Temperature Superconductors (HTS). A short introduction on the history and technical evolution of Low Temperature Superconductors (LTS) technology is provided for non-specialists. Then HTS technology is summarized and discussed in the context of quantum voltage standard applications. Finally, the two most promising technologies: bicrystal and Focused Helium-Ion Beam junctions are discussed with more detail, analyzing strength, limitations and perspectives in both cases.

Electromagnetic Design of 1.5 T No-Insulation REBCO Coil System Charged by Multiflux Pumps for Dedicated MRI

This paper presents an electromagnetic design of a 1.5 T REBCO magnet for dedicated orthopedic magnetic resonance imaging (MRI). This design makes MRI portable as well as cheaper. Due to the application of no-insulation high temperature superconductor (HTS) technology, the magnet composed of double-pancake coils (DPC) is highly compact; its outer diameter and axial length are both less than 300 mm, diameter of room-temperature bore of the magnet is 200 mm. On the other hand, we used multiflux pumps to charge the DPCs separately to reduce tape consumption and costs of power sources. In our optimized magnet, four HTS flux pumps were designed to charge the MRI magnet, while the overall tape consumption was decreased by 29.7% compared to that charged by a single dc current source. This multiple dc current sources method avoids the current limiting effect of the DPCs located at the end of the magnet, which has the highest field normal to the surface of the 2G HTS wire. Moreover, by using the HTS flux pump, the current leads which cause heat leakage were eliminated, while the HTS magnet was operated in a persistent mode, with its decayed current been constantly fed by the HTS flux pump. Although the whole cost is not able to compete with LTS MRI, high-field portable MRI are in great demand.

Electromechanical Properties of 1-mm-Wide Superconducting Cables Comprised of Exfoliated YBCO Filaments

Development of multifilament YBCO cables is an important step toward the manufacture of practical superconducting magnets based on second generation high-temperature superconductor technology. Currently, magnets manufactured from wide 2G tapes suffer from high magnetization loss and poor reliability. The presence of an insulation substrate is to insulate YBCO layers from each other, which allows only lateral (along the tape face) current sharing. Here we present an exfoliated multilayer cable with electrically coupled (1 mm wide) filaments that permit normal (across the tape) current sharing within the cable. This development can potentially enable fast ramping and stable high-field magnets for applications in fusion, energy storage, and transportation.

Tunable Stopband HTS Josephson Junction Left-Handed Transmission Line With Independently Biasable Unit Cells

A practical coplanar Josephson junction left-handed transmission line based on a step-edge junction technique is proposed in high-temperature superconductor technology and analyzed by electromagnetic simulations. The layout is designed for monolayer Yttrium Barium Copper Oxide thin film fabrication process. The propagation stopbands are tunable by controlling bias currents of Josephson junction arrays acting as parallel inductors for unit cells of the transmission line. Unlike the reported designs, each unit cell of our left-handed transmission line is independently biasable due to dc isolation of the unit cells along the transmission line. Being individually biasable is practically important for cancelling out junction critical current nonuniformities originated from the fabrication process. Tunability of the onset frequency of the left-handed propagation regime, and the propagation stopband separating the left- and right-handed propagation regimes of the proposed device has been demonstrated by simulations, is in good agreement with theory, and is predicted to be above 15%.

Some possible fields of utilization of high-temperature superconductivity in lunar exploration program

The article presents possible options to solve problems characteristic of the lunar program using devices with elements of high-temperature superconductivity technology (HTSC). Both the general state of work on high-temperature superconductivity technologies and types of HTSC products and their main characteristics are considered preliminarily. According to foreign information materials, the possible options are described to use HTSC assemblies for solving tasks on the lunar surface. It is shown that conditions on the lunar surface are more attractive for operation of HTSC devices than on the surface of the Earth. Combining HTSC and lunar technologies is related to the purpose of reducing the mass and dimensions and increasing the service life of the equipment for operation on the Moon. The main attention in the article is paid to devices with bulk HTSC and, above all, taking into account the possible wide use on the lunar surface – to magnetic HTSC bearings, including for the kinetic energy storage, a telescope. The list of devices with HTSC assemblies that can be efficiently used for the optimal solution of many urgent tasks is given and their features are described. Key words: high-temperature superconductivity, bulk HTSC, magnetic HTSC bearing, lunar surface, kinetic energy storage, telescope.

Development and testing of a 1 G based high temperature superconducting (HTS) double pancake coil for HTS synchronous machines

High Temperature Superconducting (HTS) synchronous machines are highly efficient, compact, lighter, low noise, high output power to weight ratio and better dynamic response machines compared to conventional copper conductor based machines. HTS synchronous machines are used worldwide for various strategic and critical industrial applications, because of the above mentioned advantages. Successful development of HTS synchronous machine requires HTS, electrical, mechanical, cryogenic and vacuum technologies. The major components of a HTS rotor and copper winding stator topology synchronous machine are air gap copper winding stator, HTS rotor, excitation system, cryogenic cooling and vacuum systems. HTS rotor consists of HTS tape wound pole coils, which generate DC magnetic field when DC current passes through them. There will be no joule heat in the HTS pole coils due to superconductivity. Each pole coil consists of few numbers of field coils (in the form of double pancake coils) which are stacked to form a pole. One of the main technical challenges for manufacturing HTS rotor is development of HTS field coil. The development of a HTS field coil involves the selection of HTS tape, winding technique, handling of the HTS tapes while winding and testing of the HTS coil at cryogenic temperatures of 77 K and 35 K. In the present work, a HTS racetrack double pancake coil using 1 G HTS tapes was fabricated and tested. The details of design, development and cryogenic testing of 1 G HTS tapes wound double pancake coil are presented in this paper.

Effects of flux pinning on the DC characteristics of meander-shaped superconducting quantum interference filters with flux concentrator

Superconducting quantum interference filters, or SQIFs, are a promising class of highly sensitive magnetometers benefiting from a highly peaked and symmetric magnetic response at zero-input flux. They can be used in magnetometry, e.g., in wideband applications. A simple solution to increase further their sensitivity is to add a superconducting flux concentrator (SFC) to their design. Using the ion irradiation process, we designed a meander-shaped SQIF enhanced with an SFC. The SFC improved the SQIF transfer factor by a factor of 8.4. However, high temperature superconducting (HTSc) devices are vulnerable to flux pinning, which can severely hinder their response. On the one hand, HTSc technologies alleviate the burden of cryogenics. On the other hand, applications that use SFCs in noisy and unshielded environments will become possible only if a better understanding of how this flux impacts the device’s properties is achieved. We studied the relationship between the field present during the cooling process of the SQIF antenna (thereafter called “cooling field”) and the evolution of its DC response. We developed a simple and phenomenological model and were able to reproduce the degradation of the SQIF response. This work demonstrates the usability of SFC-enhanced SQIFs based on ion irradiated junctions in rather harsh conditions, in particular, an unshielded environment, and also gives an insight into the implications that such conditions cause on the application of SFCs in general.

Evaluation of Josephson Junction Parameter Dispersion Effects in Arrays of HTS SQUIDs

We report on the experimental evaluation of dispersion effects on superconducting quantum interference device (SQUID) arrays made with high-temperature superconductor technology. The dispersion of Josephson junction parameters not only results in different operational temperature ranges but also in a flux shift of the voltage versus flux response of the SQUID. Another contribution to the phase shift originates from unbalanced inductances of each branch of the SQUID loop. Measurements show that both contributions can be discriminated. Optimal operation of SQUID arrays is obtained in principle only when these self-induced fluxes are negligible. Degradation of the response is more important when the involved currents are larger, i.e., at lower temperature. We compensated these phase shifts for an array of a few SQUIDs connected in series by direct current injection in one of the branches of each SQUID, thereby recovering the characteristic “antipeak” response. This demonstrates that in the lower temperature range of SQUID operation, phase shifts are mainly responsible for the degradation of the SQUID array response.

Reconfigurable MEMS-Based BPF for Manifold-Coupled-Superconducting Triplexers

This paper presents two configurations for manifold-coupled triplexers implemented using high-temperature superconductor (HTS) technology. The first configuration offers a bandpass function while the other offers an absorptive bandstop function. Each triplexer configuration offers eight states. Both simulation and experimental results are presented for the two HTS reconfigurable triplexers. Switching between the eight states can be implemented using switches strategically integrated within the filter resonators. Integration of commercial microelectromechanical systems switches with resonators of the HTS filters is demonstrated experimentally to illustrate the concept. The proposed reconfigurable triplexer can be extended to include more than three channels for high Q multifunction filter applications.

Recent Status and Progress on HTS Cables for AC and DC Power Transmission in Korea

The direction of the development of large-scale electric power networks has very much coincided with the history of increasing voltage values ever since the advent of Joule heat loss. However, a high-temperature superconducting (HTS) technology has changed the direction of that history. Furthermore, the HTS technology will rapidly accelerate the speed of such change due to its extremely high current density with no Joule heat loss. For these reasons, many different types of HTS electric power transmission applications have been being discussed, and selected items have been developed. Within a few decades, the technology of HTS ac and dc power transmission applications had already been developed and close to the required level for industrialization. Moreover, some of these applications have been installed, energized, and are operating within real power networks. In this paper, we report on the current status and progress in HTS applications of ac and dc power transmission. In particular, this paper focuses on the application field of superconducting cable among various HTS power applications. In South Korea, the Korea Electric Power Corporation, Naju, aims to introduce more new technologies in order to develop the Korean power network, and it believes that an HTS is a key factor in the development of the next generation of power grid, which will be discussed in detail in this paper.

Miniaturized Multiband HTS Bandpass Filter Design Using a Single-Perturbed Multimode Resonator With Multitransmission Zeros

This paper presents a miniaturized quint-band high-temperature superconducting (HTS) bandpass filter (BPF) based on a single-perturbed multimode resonator (PMMR). By properly adjusting the lengths and the position of the perturbation line in a PMMR, the intrinsic resonance modes can be controlled, which is advantageous for multiband design. The source-load coupling, spurlines, and matching stubs on feedlines are introduced to improve impedance matching and to generate multi transmission zeros, so that enhanced isolation and harmonics suppression can be realized. A low insertion loss (IL) within each band is obtained by using an HTS technology. The filter is fabricated on an MgO substrate with the YBCO thin films, and measured at the temperature of 77 K. The passband measurement is consistent with the simulation, which verifies five passbands located at 0.56, 1.52, 3.8, 4.7, and 5.3 GHz, respectively. A low-measured IL with less than 0.2 dB level is obtained due to the application of a superconducting technology. The proposed HTS BPF owns the great merits of a simple structure, a miniature size (0.008λ g 2 ), an enhanced upper stopband, and a low IL.

Technology Collaboration Programme on High-Temperature Superconductivity (HTS): HTS A pplications and the Need for International Standardization Activity

Electric power systems' application of high-temperature superconductivity (HTS) is the main focus of the HTS Technology Collaboration Programme (TCP) of the International Energy Agency. Through its nine active contracting parties and two sponsors, the HTS TCP fosters the penetration of HTS applications in electric power grids. HTS TCP activities facilitate information exchange among the most important HTS actors worldwide. As a common platform to prompt HTS applications, the HTS TCP also paves the way for progress in international standardization. Information exchange within the HTS TCP is often the starting point for developing standards that influence present and future power systems design. Recent activities demonstrate the trend toward collaborative outcomes in standardization; examples include the liaisons between the International Electrotechnical Commission's (IEC's) Technical Committee on superconductivity (TC 90) and CIGRE; Project Team 63075, launched in the framework of the IEC's Technical Committee on electric cables (TC 20); and two round robin tests on MgB2 conductors.

AC Loss Measurements in a Hybrid REBCO/BSCCO Coil Assembly

Wire cost and ac loss are paramount issues for the future uptake of high-temperature superconductor (HTS) ac machines. In particular, new approaches which reduce the total manufacturing cost of HTS coils are critical to the future commercial uptake of HTS technology. Here, we present the results of ac loss measurements of a hybrid HTS coil assembly comprising end windings (EWs) wound with BSCCO wire and a central winding (CW) wound with REBCO wire. As a cost mitigation measure, we have chosen to use REBCO wire which possesses a relatively low self-field $I_{{\rm{c}}}$ at 77 K, equating to approximately half that of the BSCCO wire. Transport ac loss measurements were made on the total coil assembly at both 77 K and 65 K, using a recently developed lock-in amplifier approach. We show the ac losses in the assembly at these temperatures scale with the overall transport critical current threshold of the hybrid coil assembly. The results are then compared with a reference coil assembly having similar geometrical dimensions, and in which both the EWs and CW were wound with identical BSCCO wire. Surprisingly, we observe that the ac loss of the hybrid coil is lower than that of the BSCCO coil, despite the CW of the hybrid coil employing wire a lower overall average $I_{{\rm{c}}}$ . We attribute this effect to the lower ac loss of coated conductor REBCO wire under parallel field, which is the dominant field orientation in the CW region. Based on this observation, we conclude that the hybrid assembly design is a good design strategy for HTS coil assemblies, enabling both wire cost and ac loss to be balanced.

Development of a single-phase 330kVA HTS transformer using GdBCO tapes

With the mature of manufacture process and technology of high temperature superconductors, the critical current and stability are gradually increased. High temperature superconductors could be used in transformer, current limiter, generator, magnet and etc. This paper focuses on development and characteristic tests of a single-phase high temperature superconducting (HTS) power transformer with capacity of 330 kVA by using GdBCO tapes, which is 1/3 model of a 1 MVA / 10kV / 0.4kV HTS transformer. The specifications of iron core, HTS windings and cryostat are described in detail. The iron core is made of silicon steel plate. The arrangement of HTS windings are based on experimental and simulated results. The cryostat with a room temperature bore is manufactured using nonmetallic materials. Several characteristic tests and insulation tests are performed in liquid nitrogen of 77K. The efficiency and AC loss at rated load is 99.90% and 243.7W, respectively. In addition, an overload test was also performed.

Design of a 10-MW-Class HTS Homopolar Generator for Wind Turbines

High-temperature superconductor (HTS) technology has been studied recently for the use with superconducting high-power transmission and distribution, motors, generators, and fault-current-limiting devices such as cables and transformers. HTS technology, which can provide a large electromotive force in a small area owing to its large current density compared to that of a normal conductor, can reduce the weight and loss of a generator when compared to the attributes of a conventional machine. Moreover, once the HTS conductor has stabilized, the challenge of cooling the windings in large-scale generators can be resolved. Therefore, the technology has been studied for application with 10-MW-class superconductor wind-turbine generators. Although an HTS conductor generator offering a higher torque density, lower weight, and higher efficiency than a conventional generator can be designed, the design must satisfy the requirements of the critical magnetic field, critical current, and critical temperature of the superconducting winding. The HTS homopolar superconducting synchronous generators have a simple structure with a fixed HTS conductor and are one of the most suitable types of generator that is able to satisfy these requirements more easily. In this paper, we propose a 10-MW homopolar-type wind-turbine generator.

High-Temperature Superconductivity: A Roadmap for Electric Power Sector Applications, 2015–2030

A roadmap document for high-temperature superconductivity (HTS) in the electric power sector, 2015–2030, was developed by the signatories to an International Energy Agency (IEA) Technology Collaboration Program for “Assessing the Impacts of High Temperature Superconductivity on the Electric Power Sector” to outline the current state of the industry development of HTS devices and what steps could be taken to reach market maturity. The document highlights trends and drivers in the electric power industry that could potentially enable HTS devices to be energized in the grid. Challenges and needs are discussed for wire, cryogenics, cables, fault current limiters, transformers, superconducting magnetic energy storage, generators, and transformers. The roadmap also outlines technology readiness levels for electric grid applications. While the roadmap serves as a useful document to help inform the industry, it is a living document that will be regularly updated due to the continuous HTS technology progress/development.

Experimental Research and Analysis of AC Critical Current in HTS Tapes

High-temperature superconductor (HTS) has found its way into both ac and dc transmission; yet HTS technology was not specially designed for either transmission type. Now critical current of HTS in dc circumstance is defined, while research on ac current-carrying capability of HTS is still scarce. A new critical current criterion of the ac condition should be established for further studies. In the paper, different dc critical current measurement methods were applied to analyze ac critical current. The E–I curves were obtained by the four-probe method and the frequency ranges from 30 to 540 Hz. The ac current carrying capacity of the superconductors is discussed and analyzed by the RMS method, virtual n value method, and the loss concept method. A criterion of ac critical current was proposed. The RMS method and the virtual n value method are no longer applicable in broad frequency band. While the loss concept method is still applied to explain the theory of critical current which varies with frequency; therefore, an ac critical current calculation method is obtained and the calculative equation at different frequencies is established.