2G High Temperature Superconducting Wire Research Articles

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.

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.

Experimental Study on Quasi-Isotropic Critical Current of an HTS Conductor With High Engineering Current Density

It is well known that the critical current of the second generation (2G) high temperature superconducting (HTS) wire strongly depends on magnetic field and its orientation. An HTS conductor with high engineering current density considering the effect of quasi-anisotropy of critical current has been proposed, and its configuration is a combination of a quasi-isotropic strand (Q-IS) on which winding HTS wires similar with winding method of cable layer. In this paper, the dependence of the critical current density of inner Q-IS on twisting pitch of Q-IS and winding pitch of cable layer was analyzed by both of simulation and experiment. Experimental results are good agreement with the simulation ones, and show that the critical current density of Q-IS increases as decreasing winding pitch of cable layer and twisting pitch of Q-IS. The achieved maximum critical current density is about 7%more than the one of Q-IS in self-field. It is predicted that the critical current density of inner Q-IS will increase further if the 2G HTS wire is narrower or the current in outer cable layer bigger. The variation of n-value of inner Q-IS with winding pitch of cable layer and twisting pitch of Q-IS is also measured, and the trend of n-value is similar to the trend of critical current density.

Short-Circuit Characteristics of a High Temperature Superconducting Wind Turbine Generator Employing a Segmented Armature Winding

High temperature superconducting (HTS) wind turbine generators (WTGs) are expected to offer a compact and lightweight direct drive train for large offshore wind turbines. However, short circuits occurring at armature winding terminals can pose great challenges, such as high peak torques due to a large magnetic air gap in HTS generators, field current rise over the critical current that may cause a quench, and AC losses in HTS field windings that may cause local overheat. Segmentation of armature windings could be a solution to mitigate such challenges. In this paper, an optimized design of a 10-MW direct drive HTS generator using 2G HTS wires in the field winding is studied based on a well-verified generator topology. The generator design has two scenarios, i.e., without segmentation and with four segments in the armature winding. These two winding scenarios are compared through a phase-to-phase short circuit occurring at the terminals of the armature winding. The effects of segmentation are revealed on 1) electromagnetic torque, 2) current rise in the HTS field winding, and 3) AC losses in the HTS field winding after the short circuit occurs. The results show the great benefits of using segmented armature windings in an HTS WTG: the peak torque is reduced by a factor of 4, and the AC losses in the HTS field winding are nearly halved although the maximum field current is almost unchanged.

Probing the Irradiation Defects in Enhanced 2G High Temperature Superconducting Wire

Probing the Irradiation Defects in Enhanced 2G High Temperature Superconducting Wire

R&D of No-Insulation HTS Magnets Using 2G Wires in a Prototype for Maglev Applications

Superconducting magnetic levitation (Maglev) is developing rapidly in recent decades. Compared to traditional railways, superconducting Maglev is superior in aspects such as faster speed, less pollution, and safer operation. The development of second generation (2G) high-temperature superconducting (HTS) wires, which have higher in-field critical current density and mechanical strength, has also improved the design performance of the superconducting Maglev. This paper presents design and optimization processes of no-insulation magnets using 2G HTS wires for a prototype of linear propulsion system in the Maglev. According to the design results, one of the coils in the magnets are manufactured for routine test including <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I_C</i> measurement and Maglev-related tests including field quality comparison, charging characters like delay and loss, over-MMF test and mechanical vibration test simulating the running conditions of the Maglev. The coil has no degradations or obvious changes of performances after the tests. And the test results meet the expected requirements of the prototype.

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.

Analysis on Critical Current Density of an HTS Conductor With Quasi-Isotropic and High Engineering Current Density

A high-temperature superconducting (HTS) conductor with quasi-isotropic and high engineering current density is proposed. The HTS conductor consists of inner quasi-isotropic strand and outer power cable. The inner quasi-isotropic strand, equivalent to a former, is a twisted quasi-isotropic conductor made from four components stacked by the second generation (2G) HTS wire with symmetrical arrangement. The outer conductor is made by winding the 2G wire on the inner conductor that is equivalent a power cable. Simply speaking, the HTS conductor is a power cable with replacing the copper former by HTS quasi-isotropic strand so that its engineering critical current is high. The HTS conductor has quasi-isotropic critical current density, since it is a combination of a quasi-isotropic strand and an isotropic power cable. The engineering current density is improved by changing twisting pitch of inner quasi-isotropic conductor and pitch of outer power cable, the conductor is also of benefit to mechanical flexibility and quasi-isotropic critical current density. Additionally, the critical current density of inner quasi-isotropic strand is higher than the one in self-field by considering the effect of longitudinal magnetic fled taking into account.

Measurement of the Current in 2G HTS Coil With Rogowski Coil in Cryogenic Environment

This paper presents a Rogowski coil that can be used to measure the current in second-generation (2G) high-temperature superconducting (HTS) coils in a cryogenic environments. We describe the key materials involved in building the coil and its structure and then report on experiments that were carried out to assess its potential. To ensure the accuracy of current measurements in cryogenic temperatures, the coil was given a closed and rigid shape and foamed plastic was used to fix a 2G HTS wire in the center of the coil. Silicon nitride ceramic was chosen to build the winding holder because of its thermodynamic stability and mechanical strength in cryogenic environments. The performance of the Rogowski coil was evaluated in a liquid nitrogen bath at 77 K. The results confirmed the stability of the coil and the accuracy of its current measurements, underscoring its viability for 2G HTS applications.

An effective way to reduce AC loss of second-generation high temperature superconductors

Second-generation (2G) high temperature superconducting (HTS) devices have high power density and efficiency for energy applications. However, in alternative current conditions, the vortex movement in 2G HTS leads to energy dissipation at low temperatures, which significantly affects efficiency and adds an extra burden to cooling systems. This energy dissipation is identified as AC loss. Reducing AC loss to improve efficiencies of 2G HTS devices, e.g. HTS machines, cables and fault current limiters, has become a key research focus. We report here on an effective way to reduce AC losses by using a new 2G HTS wire. The principle is to stack narrow 2G HTS tapes into a wire structure, which is called a soldered-stacked-square (3S) wire. Our experiments on solenoid coils have proved that the 3S wire helps to reduce the AC loss by 80%. Moreover, the critical current of the 3S wire can be easily adjusted for various applications. It is envisioned that the 3S wire will become a powerful technology enabling the development of 2G HTS power devices with high efficiency.

Design of a high temperature superconducting magnet for a single silicon crystal growth system

This paper presents a study on the design of a high-temperature superconducting (HTS) magnet for a Czochralski single silicon-crystal growth system by evaluating the temperature and flow distributions of silicon melt at the cusp magnetic field. A two-dimensional finite element method (FEM) simulation model was built to determine the effects of the magnetic field on the temperature and flow distributions in the silicon melt. The characteristics of the HTS magnet were analyzed using a three-dimensional FEM model. The HTS magnet was designed using 2G HTS wire and the magnet was validated through FEM simulation. The simulation results showed that the melt convection was significantly suppressed by the Lorentz force, and that the temperature distribution was uniform in the silicon melt under the cusp magnetic field. The shape of the HTS magnet was determined as a magnet ring with a magnetic flux density of 0.35 T at the center of the crucible bottom. The fundamental design specifications and the data obtained from this study can be applied to the development of a real silicon-crystal growth system.

2G HTS wires made on 30 μm thick Hastelloy substrate

REBCO (RE = rare earth) based high temperature superconducting (HTS) wires are now being utilized for the development of electric and electromagnetic devices for various industrial, scientific and medical applications. In the last several years, the increasing efforts in using the so-called second generation (2G) HTS wires for some of the applications require a further increase in their engineering current density (Je). The applications are those typically related to high magnetic fields where the higher Je of a REBCO wire, in addition to its higher irreversibility fields and higher mechanical strength, is already a major advantage over other superconducting wires. An effective way to increase the Je is to decrease the total thickness of a wire, for which using a thinner substrate becomes an obvious and attractive approach. By using our IBAD-MOCVD (ion beam assisted deposition-metal organic chemical vapor deposition) technology we have successfully made 2G HTS wires using a Hastelloy® C276 substrate that is only 30 μm in thickness. By using this thinner substrate instead of the typical 50 μm thick substrate and with a same critical current (Ic), the Je of a wire can be increased by 30% to 45% depending on the copper stabilizer thickness. In this paper, we report the fabrication and characterization of the 2G HTS wires made on the 30 μm thick Hastelloy® C276 substrate. It was shown that with the optimization in the processing protocol, the surface of the thinner Hastelloy® C276 substrate can be readily electropolished to the quality needed for the deposition of the buffer stack. Same in the architecture as that on the standard 50 μm thick substrate, the buffer stack made on the 30 μm thick substrate showed an in-plane texture with a Δϕ of around 6.7° in the LaMnO3 cap layer. Low-temperature in-field transport measurement results suggest that the wires on the thinner substrate had achieved equivalent superconducting performance, most importantly the Ic, as those on the 50 μm thick substrate. It is expected the 2G HTS wires made on the 30 μm thick Hastelloy® C276 substrate, the thinnest and with the highest Je to date, will greatly benefit such applications as high field magnets and high current cables.

Conceptual Design of a Resistive 154-kV/2-kA Superconducting Fault Current Limiter

The expansion of electric capacity is inevitable to satisfy the demands of rapid economic growth. An increase in electricity load causes a decrease in load impedance. As a result, the fault current would exceed the capacity limit for the short-circuit breaker installed in a power system. Fault current that exceeds the rating of a conventional circuit breaker will degrade the stability of the power grid system. Many types of high-temperature superconducting (HTS) fault current limiters (FCLs) have been developed to enhance the stability and reliability of a power grid system. In this paper, a resistive HTS FCL using 2G HTS wires is designed, taking into consideration the demand quantity of 2G HTS wires, the winding type of the coils, the number of series and parallel connections, electrical insulation, and mechanical stability in the fault state. The length of the superconducting coils and the number of series and parallel connections are calculated. A finite-element method is used to perform dielectric and mechanical design analysis.

Development of a Quasi-Isotropic Strand Stacked by 2G Wires

This paper presents a concept of quasi-isotropic high-temperature superconducting (HTS) strands with round and square cross sections made from REBa2Cu3O7-x (RE=rare earth, REBCO) coated conductor, the so-called second-generation (2G) HTS wires under development at North China Electric Power University. Considering several key issues for fabricating the quasi-isotropic strands, for instance, in-plane bending performance of 2G wire, isotropic-strand bending performance, strand termination method, and critical current in liquid nitrogen (LN2 ) temperature and self-field, a feasible manufacturing method by using mature laser welding is suggested and investigated experimentally. After fabricating several short-length strand samples consisting of 72 REBCO wires with an outer diameter of 7.5 mm, critical currents in straight and bending and under direct current (DC) magnetic fields with different orientations were tested in LN2 temperature. The critical current in straight strand is in agreement with the simulated one; the anisotropy of the critical current is less than 8% in the orientation range of $0^{\circ}{-}90^{\circ}$ with a DC magnetic field of 0.5 T. After successfully finishing a 10-m-length strand, it was demonstrated that the laser welding technique is an attractive and feasible method for manufacturing practical long strands which have potential applications in large-scale high-field magnet and energy transmission.

A Study on Critical Current and AC Loss Characteristics of Novel 2G HTS Narrow Wires

In high-temperature superconducting (HTS) applications, the external magnetic field affects the performance of the critical current and the ac loss. In this study, to improve the performance, narrowing and twisting processes are first suggested for the second-generation (2G) HTS wires: the original wire with 4-12-mm width is incised into several narrow wires with the same width under 2 mm, and narrow wires are twisted around each other as tight as possible. Using the narrow wires, we prepared various types of novel wire samples with stacking and twisting structures. The main results show that the feasibility of the narrow wires with stack and twist structures is confirmed from both critical current and ac loss points of view.

Development and Characterization of a 2G HTS Roebel Cable for Aircraft Power Systems

Lightweight megawatt-range power cables in electric aircraft propulsion systems will allow reducing fuel consumption by more than a half. Taking into account the low voltage limitations for onboard use, superconductivity providing high current-carrying capacity becomes an enabling technology for this application. In the frame of a preliminary study of an onboard superconducting power distribution grid, we fabricated and tested a high-temperature superconducting (HTS) Roebel cable. The work was done by a consortium of institutions and supported by Airbus Group Innovations. SuperOx provided a 400 A-class 12-mm-wide 2G HTS wire. The team at the Karlsruhe Institute of Technology prepared 5.5-mm-wide Roebel strands with a transposition length of 226 mm and assembled the strands into a 6-m-long Roebel cable. The team at the Russian Scientific Research and Development Cable Institute performed characterization of the cable. Short samples of the cable were tested to determine their critical currents, mechanical properties, and stability during thermal cycling. For a 4-m-long section of the cable, we measured the critical current, as well as the transport ac losses at frequencies in the range from 50 to 400 Hz. This paper presents the cable design and test results. The feasibility of using 2G HTS Roebel cables in electric aircraft systems is discussed.

Hysteresis Losses Analysis in 2G HTS Cables

The Russian Scientific R&D Cable Institute is involved in many projects on R&D high-temperature superconducting (HTS) power cables including those made of modern second generation (2G) HTS wires. Evaluation of ac losses and methods for the reduction of the ac losses are important in the design of the cables. A fine experimental technique has been developed and implemented to measure ac losses in representative cable models with a length of ~5 m. However, only calculation can provide ac loss prediction in cases when it could be difficult to make measurements. Thus, we need a comprehensive simulation model to calculate ac losses. In HTS cables made of 2G wires, the main ac loss is a hysteresis loss, which only numerical simulation can predict for full-size 2G cables. We develop a finite-element method model to solve the electromagnetic problem for the calculation of ac losses. The model takes into account the strong nonlinear resistivity of the HTS materials, the hysteresis behavior of the magnetic substrate, the nonuniformity of critical current density across the tapes of the cable, and the possible ferromagnetism of a substrate. The model also takes into account any geometrical aspect of the 2G HTS cables. The details of the model and comparisons of calculations with our measurements of the ac losses are presented.

A study on the required performance of a 2G HTS wire for HTS wind power generators

YBCO or REBCO coated conductor (2G) materials are developed for their superior performance at high magnetic field and temperature. Power system applications based on high temperature superconducting (HTS) 2G wire technology are attracting attention, including large-scale wind power generators. In particular, to solve problems associated with the foundations and mechanical structure of offshore wind turbines, due to the large diameter and heavy weight of the generator, an HTS generator is suggested as one of the key technologies. Many researchers have tried to develop feasible large-scale HTS wind power generator technologies. In this paper, a study on the required performance of a 2G HTS wire for large-scale wind power generators is discussed. A 12 MW class large-scale wind turbine and an HTS generator are designed using 2G HTS wire. The total length of the 2G HTS wire for the 12 MW HTS generator is estimated, and the essential prerequisites of the 2G HTS wire based generator are described. The magnetic field distributions of a pole module are illustrated, and the mechanical stress and strain of the pole module are analysed. Finally, a reasonable price for 2G HTS wire for commercialization of the HTS generator is suggested, reflecting the results of electromagnetic and mechanical analyses of the generator.

Analysis on the electrical degradation characteristics of 2G HTS wires with respect to the electrical breakdown voltages

Abstract Recently, the electrical insulation design for electrical apparatuses is important to cope with the tendency of high voltage.The degradation characteristics of a superconducting coil due to an electrical breakdown should be considered to design a high voltage superconducting coil. In this paper, the degradation characteristics of 2G high temperature superconducting (HTS) wires are studied with respect to electrical breakdown tests. To analyze the dependency of the degradation characteristics of 2G HTS wires, the electrical breakdown tests are performed with AC(alternating current) and DC(direct current) voltage. All tests are performed by applying various magnitudes of AC and DC breakdown voltages. To verify the degradation characteristics of 2G HTS wires, the tests are performed with various 2G HTS wires with respect to stabilizer materials. The degradation characteristics of 2G HTS wires, such as Ic(critical current) and index number are measured by performing electrical breakdown tests. It is found that the characteristics such as Ic and index number can be degraded by an electrical breakdown. Moreover, it is concluded that the degradation characteristics of 2G HTS wires are affected by the stabilizer material and applied voltag es. The cross -sectional view of 2G HTS wires is observed by using a scanning electron microscope (SEM).As results, it is found that the degradation characteristics of 2G HTS wires are concerned with hardness and electrical conductivity of stabilizer layers.

Development of toroid-type HTS DC reactor series for HVDC system

This paper describes design specifications and performance of a toroid-type high-temperature superconducting (HTS) DC reactor. The first phase operation targets of the HTS DC reactor were 400mH and 400A. The authors have developed a real HTS DC reactor system during the last three years. The HTS DC reactor was designed using 2G GdBCO HTS wires. The HTS coils of the toroid-type DC reactor magnet were made in the form of a D-shape. The electromagnetic performance of the toroid-type HTS DC reactor magnet was analyzed using the finite element method program. A conduction cooling method was adopted for reactor magnet cooling. The total system has been successfully developed and tested in connection with LCC type HVDC system. Now, the authors are studying a 400mH, kA class toroid-type HTS DC reactor for the next phase research. The 1500A class DC reactor system was designed using layered 13mm GdBCO 2G HTS wire. The expected operating temperature is under 30K. These fundamental data obtained through both works will usefully be applied to design a real toroid-type HTS DC reactor for grid application.