Applications Of High Temperature Superconductors Research Articles

Low resistance splices for HTS devices and applications

This paper discusses the preparation methodology and performance evaluation of low resistance splices made of the second generation (2G) high-temperature superconductor (HTS). These splices are required in a broad spectrum of HTS devices including a large aperture, high-field solenoid built in the laboratory to demonstrate a superconducting magnetic energy storage (SMES) device. Several pancake coils are assembled in the form of a nested solenoid, and each coil requires a hundred meters or more of 2G (RE)BCO tape. However, commercial availability of this superconductor with a very uniform physical properties is currently limited to shorter piece lengths. This necessitates us having splices to inter-connect the tape pieces within a pancake coil, between adjacent pancake coils, and to attach HTS current leads to the magnet assembly. As a part of the optimization and qualification of splicing process, a systematic study was undertaken to analyze the electrical performance of splices in two different configurations suitable for this magnet assembly: lap joint and spiral joint. The electrical performance is quantified in terms of the resistance of splices estimated from the current-voltage characteristics. It has been demonstrated that a careful application of this splicing technique can generate lap joints with resistance less than 1nΩ at 77K.

Development of a Novel Soldered-Stacked-Square (3S) HTS Wire Using 2G Narrow Tapes With 1 mm Width

Based on the pre-existing assembled, stacked, or twisted structures of high temperature superconducting (HTS) wires, a novel soldered-stacked-square (3S) HTS wire is suggested and developed through narrowing, stacking, and soldering processes in this study. For the fabrication processes of the 3S wire, a narrow 2G tape with 1 mm width is applied, and the stacking and soldering processes are completed simultaneously. To confirm the performance of the 3S HTS wire, several 3S samples are fabricated. For the 3S HTS samples, we evaluate typical electrical and mechanical properties, and investigated for the feasibility of the 3S HTS wire in the HTS applications. The test results show that measured critical currents of two 3S wire samples are 170 and 255 A, and their curves are typical ones of HTS tapes. The measured self-field ac loss is also reasonable, which is analyzed from both theoretical models of the elliptical and thin strip equations. Moreover, the minimum bending diameter for the 3S samples is approximately 60 mm, and the allowable axial tensile force is 350 N. These mechanical properties of 3S wire are satisfied for the HTS applications significantly. Finally, the smallest round structure of the HTS wire is conceptually suggested for the 3S HTS wire.

Heating and Loading Process Improvement for Indium Inserted Mechanical Lap Joint of REBCO Tapes

A mechanical lap joint of REBCO high-temperature superconducting (HTS) tapes with an indium foil inserted between joint surfaces has been proposed for segment-fabrication of HTS magnet of an advanced fusion reactor and various HTS applications. In a previous study, we successfully achieved a joint resistivity of about 3.5 pΩm 2 by heat treatment during fabrication of the joint. In this study, improved heat treatment method was developed by controlling contact pressure and combining bake-out process. We evaluated joint resistance and critical current of the joint depending on the heating condition and bake-out condition. The joint resistivity after heat treatment was 2.5 pΩm 2 without decreasing critical current with conditions of heating temperatures of 90-140 °C, a heating time of 30 min, a contact pressure of 100 MPa, a bake-out time of 30 min, and a bake-out temperature of 150 °C. Owing to applying the contact pressure when the indium becomes softer, the true area of contact increased and the thickness of the indium decreased greater than those in the previous method. In addition, it was shown that voids appearing by heating were removed by bake-out process from thermal desorption spectroscopy test.

Significant flux trapping in single grain GdBCO bulk superconductor under off-axis field cooled magnetization

A single grain bulk high-temperature superconductor (HTS) exhibits intensified flux trapping performance upon field cooled magnetization. The world record of trapped flux is 17.6 T achieved by using stacked two-fold GdBCO bulks. However, the majority of magnetization studies focused on the magnetization along the crystallographic c-axis. In the present study, we clarify the flux trapping performance under field cooled magnetization using an off-axis magnetic field with respect to the c-axis. The results show that the trapped flux is almost polarized along the applied field as expected. This tendency remains up to a high off-axis angle θ around 60°. It is worth mentioning that, with θ of 30°, the maximum trapped flux component B//max parallel to the c-axis significantly remains more than 96% of 1.6 T which occurs under on-axis magnetization. Meanwhile, the angular dependence of the c-axis parallel component exhibits that observed flux density is higher than that expected from 1.6 cosθ. In addition, to visualize the flux line upon magnetization at θ of 90°, we successfully demonstrate the continuous flux line trace using steel wires; different trapped flux behaviour appears when applied field penetrates the bulk through the growth sectors centre and along the growth sector boundary, respectively. We interpret these results may come from the microstructure as a result of melt growth. It is highly emphasized that the off-axis magnetization with the finite inclination angle is quite useful for introducing into the design of HTS applications.

Modelling of 3D temperature profiles and pressure drop in concentric three-phase HTS power cables

To meet the increasing power demand in cities under the spatial constraints for cable channels, the application of high temperature superconducting (HTS) cables cooled with liquid nitrogen offers an increasingly attractive alternative to conventional cable solutions. This paper presents a differential equation model for three-phase concentric HTS cables, describing the temperature distribution in the various cable layers and in the liquid nitrogen flow. The design of the 1km long AmpaCity cable is used as a reference, which presently is the longest HTS cable installation in the world. The model considers the AC losses in the superconducting phases in addition to the external thermal load, as well as pressure losses in the coolant flow. The integrity of the algorithm is verified through energy conservation, yielding negligible numerical solver errors. The model is then applied to the operation of the AmpaCity cable. The monitoring of its operating range is explained, based on electrical and coolant properties measured at the cable end. The final application study shows options for extending the cable length up to factor five, using a second cooling unit in combination with a mixed coolant.

HTS Applied to Power System: Benefits and Potential Analysis for Energy Conservation and Emission Reduction

Energy conservation and emission reduction is a critical task for power systems. Innovative technology such as applied superconductivity has great potential. With the rapid advances in high temperature superconducting (HTS) technology, various HTS power applications, such as HTS cables, HTS transformers, HTS generators, HTS fault current limiters, and superconducting magnetic energy storage can be of great help for energy conservation and emissions reduction in modern power systems. A brief review of energy losses and CO 2 emissions in power systems is first presented with various currently existing solutions and techniques analyzed and compared. After analysis of the inherent characteristics of HTS applications, the potential and possible benefits of HTS power applications for energy conservation and emission reduction are studied in detail. In addition, the technical and economic challenges for HTS power applications are also discussed. It is obvious that HTS power applications have great potential and extensive direct and indirect benefits for energy conservation and emissions reduction in the future power systems, after some challenges for HTS power applications have been solved.

Fabrication of YBa2Cu3O7−x (YBCO) superconductor bulk structures by extrusion freeforming

Practical applications of high temperature superconductors may require them to be processed into complex geometries. In this work, slurry-based extrusion freeforming coupled with high temperature treatment was attempted for the fabrication of bulk YBa2Cu3O7−x (YBCO) superconducting structures. YBCO parts with approximately 93% of the theoretical density were successfully fabricated after sintering at 940°C for 60h, with the obtained constituent phases strongly dependent on the heat treatment temperature and duration. A high critical transition temperature (TC=92K) and good magnetic levitation ability could be obtained after optimization of the heat treatment conditions. Overall, the experimental results demonstrate that extrusion freeforming is a feasible and effective technique for fabricating YBCO superconductors that have desirable configurations and good superconductivity properties.

Axial Tension and Overcurrent Study on a Type of Mass-Producible Joint for ReBCO Coated Conductors

Given the limited length of ReBCO coated conductors (CCs), a large number of joints is necessary in high-temperature superconducting (HTS) applications. The quality of joints largely determines the stability of the HTS applications, because joints are usually weaker than ReBCO CCs themselves concerning mechanical and electrical characteristics. To address this problem, a novel type of CC joint, which employs a fabrication process similar to CC lamination, is developed (named after “lamination joint” for convenience). In this paper, the behaviors of the lamination joints under axial tension loads and dc/ac overcurrent are investigated. Single fully laminated CCs and joints fabricated by a conventional soldering method are also studied for comparison. The lamination joints exhibit similar critical axial tensile forces (around 700 N) to the single fully laminated CCs, which are much larger than that of the conventional soldering joints. Moreover, overcurrent tests show that the lamination joints have smaller possibilities to burn out than the single fully laminated CCs. Moreover, the lamination joints are much more stable in quality and are mass producible since they are automatically fabricated by a lamination system. Furthermore, a joint resistance of several <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{n}\Omega$</tex-math></inline-formula> can be achieved by simply extending the splicing length to several meters.

Dynamic Analysis of Transformers With Second-Generation High-Temperature Superconductors

The high-temperature superconducting (HTS) transformer is one of the potential applications of high-temperature superconductors. When a HTS transformer was put into the power grid, the fault current at the secondary winding loads or the fault passing through current of the power grid may occur. During this transient process, the voltage, current, magnetic field, and temperature distribution would take great changes. Not only it affects the power grid but also the HTS transformer. This paper investigated the dynamic analysis of transformers with secondary-generation high-temperature superconductors based on COMSOL Multiphysics simulation software. Combining the electric circuit, magnetic field, and heat transfer, the factors that influenced the magnitude of fault current, temperature distribution were concluded.

Investigation on AC Losses of a Quasi-Isotropic Strand Made From REBCO Coated Conductors

With the development of REBCO coated conductor (REBCO CC), high-temperature superconducting (HTS) strand with high current capacity and quasi-isotropic performance is expected to have widely potential applications. The alternating current (AC) loss is always one of the most important characteristics in AC HTS applications. This paper aims to perform research of AC losses of quasi-isotropic strand consisting of REBCO CCs by theoretical analysis and experiment. The electromagnetic characteristic of the strand is simulated. Then, the finite-element method is used to calculate AC losses. Based on the analysis of magnetic field distributions of the REBCO CCs, different theoretical models are introduced to calculate AC losses of the strand. To verify this model, AC losses of the strand are calculated and compared with the measured results.

Commercial Pulse Tube Cryocoolers Producing 330 W and 1000 W at 77 K for Liquefaction

Fabrum Solutions and Callaghan Innovation have been developing large pulse tube cryocoolers based on Callaghan Innovation's diaphragm pressure wave generators (DPWGs). The pulse tube's lack of moving parts in combination with the DPWG's metal diaphragms produces a cost-effective, long-life, and robust cryocooler. The DPWG has had ten years of development, resulting in a series of DPWGs ranging in input powers from 0.5 to 30 kW that have been coupled to a variety of inline and coaxial pulse tubes. Two DPWGs have each had in excess of 7000 h running to date. A 330-cc DPWG was designed and manufactured to run with an inline pulse tube with a target refrigeration power of 330 W at 77 K. Absolut System carried out the pulse tube design, and manufacture was done by Fabrum Solutions, with integration and testing by Callaghan Innovation. Over 450 W of cooling power at 77 K was achieved from the cryocooler. A sealed condensation chamber was added to the cold head and connected to a Dewar via vacuum insulated lines for nitrogen liquefaction. Three such pulse tubes were combined on a single 1000-cc DPWG to produce over 1000 W at 77 K. This paper details the development of the PTC330 and PTC1000 cryocoolers from initial laboratory prototypes to commercial products, integrated into liquefiers and ready for use in applications such as liquid nitrogen production, reliquefaction of storage tank boiloff, or cooling of high-temperature superconductor applications.

Numerical modeling of HTS applications

High-temperature superconductor applications have reached a mature status, with several prototypes and devices in precommercial stage installed around the world. Following this development, numerical models able to simulate their electromagnetic and thermal behavior have become indispensable tools to improve their design and predict their performance. In this paper, I show how numerical models have evolved from simple models able to calculate the current distribution in one individual tape to powerful instruments able to simulate complex geometries, material properties, and operating conditions. Then, I focus on the state of the art of numerical modeling of specific applications, such as cables, magnets, and electrical machines. Finally, I indicate the challenges that are still open and the possibility of establishing a collective effort to speed up the advance of this important research topic.

Fracture problem for an external circumferential crack in a functionally graded superconducting cylinder subjected to a parallel magnetic field

In this study, the multiple isoparametric finite element method (MIFEM) is used to investigate external circumferential crack problem of a functionally graded superconducting cylinder subjected to electromagnetic forces. The superconducting cylinder is composed by Bi2223/Ag composite with material parameters varying. A crack reference region is defined to reflect the effects of crack on flux and current densities, and the magnetically impermeable crack surface condition and the generalized Irie–Yamafuji critical state model outside the crack region are adopted. The distributions of magnetic flux density in the superconducting cylinder are obtained analytically for both the zero-field cooling (ZFC) and the field cooling (FC) activation processes. Based on the MIFEM, the stress intensity factors (SIFs) at crack fronts in the process of field ascent and/or descent are then numerically calculated. It is interesting to note from numerical results that for the present crack model in the ZFC activation process, the crack is easily propagate and grow with the applied field increases, and that in the field descent process of either the ZFC case or FC case, the crack generally does not propagate. In addition, in the field ascent process of the ZFC case, the SIFs depend on not only the crack depths and model parameters but also the applied field. The present study should be helpful to the design and application of high-temperature superconductors with external edge cracks.

Peculiarities of simulation of magnetic field in electromechanical nodes of magnetic-levitation transport system by the method of secondary sources

In recent years increasingly discusses the prospects of application of high-temperature superconductors (HTS) as the winding current-carrying elements of magnetic systems for various purposes. It seems particularly attractive possibility of such systems at liquid nitrogen temperature. The article describes the prototype of module of the magnetic system which is made on the basis of high-temperature superconducting tapes, designed for the installation and testing on a working model of a static levitation. In the working model levitation of the platform carried by the interaction of the magnetic field of the assembly of permanent magnets mounted on the platform with a field similar to assemblies located in the track structure. Compact HTS module replaces the two assemblies of permanent magnets mounted on the platform. Each block of the module represents HTS racetrack coil with current inputs, power structure, positioning system and bracing which is placed in a cryostat, providing at minimum wall thickness of the required mechanical strength and thermal insulation at liquid nitrogen temperature. The prototype of unified superconducting module successfully passed preliminary tests.

Enhanced critical current density in the pressure-induced magnetic state of the high-temperature superconductor FeSe.

We investigate the relation of the critical current density (Jc) and the remarkably increased superconducting transition temperature (Tc) for the FeSe single crystals under pressures up to 2.43 GPa, where the Tc is increased by ~8 K/GPa. The critical current density corresponding to the free flux flow is monotonically enhanced by pressure which is due to the increase in Tc, whereas the depinning critical current density at which the vortex starts to move is more influenced by the pressure-induced magnetic state compared to the increase of Tc. Unlike other high-Tc superconductors, FeSe is not magnetic, but superconducting at ambient pressure. Above a critical pressure where magnetic state is induced and coexists with superconductivity, the depinning Jc abruptly increases even though the increase of the zero-resistivity Tc is negligible, directly indicating that the flux pinning property compared to the Tc enhancement is a more crucial factor for an achievement of a large Jc. In addition, the sharp increase in Jc in the coexisting superconducting phase of FeSe demonstrates that vortices can be effectively trapped by the competing antiferromagnetic order, even though its antagonistic nature against superconductivity is well documented. These results provide new guidance toward technological applications of high-temperature superconductors.

Commercialisation of Pulse Tube cryocoolers to produce 330 W and 1000 W at 77 K for liquefaction

Fabrum Solutions in collaboration with Callaghan Innovation has been developing large pulse tube cryocoolers based on Callaghan Innovation's diaphragm pressure wave generators (DPWG). The pulse tube's lack of moving parts in combination with the DPWG's metal diaphragms produces a cost-effective, long life and robust cryocooler. The DPWG has had 10 years of development, resulting in a series of DPWGs ranging in input powers from 0.5 kW to 30 kW that have been coupled to a variety of in-line and coaxial pulse tubes. Two DPWGs have had in excess of 7000 hours running to date. The PTC330 cryocooler is based on a new 330 cc DPWG and has produced 480 W of cooling at 77 K during testing. The PTC1000 combines three such pulse tubes on a single 1000 cc DPWG to produce 1270 W at 77 K. This paper details the development of the PTC330 and PTC1000 cryocoolers from initial lab prototypes through to commercial products, integrated into liquefiers and ready for use in applications such as: Nitrogen liquefaction, re-liquefaction of boil-off from storage tanks, or cooling of cryostats for High Temperature Superconductor applications.

Influence of Substrates in HTS Wires on AC Loss Characteristics of Cylindrical Single Layer Conductors

Substrates of high temperature superconductor (HTS) wires can change the magnetic field distribution of the wires, with the consequence that they can affect AC losses of the HTS wires, which is a critical issue in HTS applications. In this study, in order to investigate the effects of the substrates on the AC losses of cylindrical single layer conductors which are usually used in HTS power cables, we first experimentally and numerically evaluated self-field losses of the HTS wires and investigated the influence of the substrates on their self-field losses. Next various HTS cylindrical single layer conductors were prepared using different HTS wires and their AC loss characteristics were discussed from the perspective of magnetic substrate. The main results show that the magnetic materials in HTS wires do affect their losses and the magnetic field distribution. For our pentagonal conductors, magnetic flux does not exist outside of the conductor when the magnetic substrates are located outside. Moreover, the AC losses of the bismuth strontium calcium copper oxide (BSCCO) and yttrium barium copper oxide (YBCO) conductors are quite similar and the AC losses of the NY and YN conductors are larger than the losses of the other two conductors. Especially, the AC loss of the YN conductor is the greatest in the low current region.

Robust critical current density in applied magnetic fields in 5 μm thick, SmBa2Cu3O7−δ based superconducting wires

We report the magnetic field and temperature dependence of the critical current density {Jc(H) and Jc(T)} flowing in a 5μm thick sample of SmBa2Cu3O7−δ (SmBCO) film. The film is a coated conductor (CC) deposited on an IBAD-MgO textured metallic template. For a range of intermediate fields, we find JcαH-α with values of α between 0.44 and 0.49. These values are lower than those reported for other CC in the literature. The sample has a Jc of 13.6MA/cm2 at 5K and self-field. Such high-Jc wires should find applications in large-scale energy applications of high-temperature superconductors. The temperature dependence of Jc at self-field and different applied fields is also analyzed.

Quench Characteristic and Minimum Quench Energy of 2G YBCO Tapes

Due to a much extended current sharing regime and to the power law like E-J characteristics instead of the critical state, the quench characteristics of high temperature superconductors (HTSs) potentially differs from LTS. The understanding of thermal stability is therefore of crucial importance to meet the performance requirements set up by applications. In this work the quench characteristic and MQE measurements were carried out on 2G YBCO tape in self-field and field (0.1 T) scenario, in a wide range of temperature (40-80 K), where the conductors have a modest power exponent n ~ 20-30. The study focuses in particular on high current in the vicinity of Ic (j = I/Ic ~ 1), where power law current sharing dominates. Instead of vanishing with (1 - j), as expected for the critical state, the measured MQE is much higher near Ic. The high MQE and the heat generation of a non-(1 - j) scaling were constantly found in the temperature range 40 K-80 K of measurements. Such an enhanced MQE in the high current regime could be significant for HTS applications and suggests the possibility of sufficient stability very close to Ic. We show that the results can be explained by approximating the non-linear current sharing power-law heat generation with temperature by an equivalent critical state at a higher current sharing temperature. While the power-law and critical state converge at low j regions, the non-linear temperature dependence of thermal properties needs to be considered due to elevated quench/current sharing temperatures.

Device for Measuring the Thermal Cycling Degradation in 2G Tapes for Electrical Power Applications

The standard electrical engineering applications of high-temperature superconductors (HTSs) as coils (SMESs), motors, power cables, fault current limiters (SFCLs), etc., usually involve operating conditions under which the critical current of HTS tapes might be degraded. The dependence of such magnitude on mechanical properties, frequency variations, or thermal changes is a key concern for the accurate design of those devices. Two of the parameters affecting the critical current when the superconductor operates in broad temperature ranges are the number and the speed of transitions from the superconducting to the normal state. In order to determine how these parameters affect the critical current, we have designed an automated dipping setup in liquid nitrogen to reproduce heating and cooling cycles on superconducting tapes. In this paper, this device is described, and several tests on a short sample of YBCO coated conductor are reported and analyzed.