Generation High Temperature Superconducting Research Articles

Bending properties of solder joint of YBCO coated conductors by etching copper stabilizer

The YBa2Cu3O7−x coated conductor (YBCO CC) is one of the most promising superconducting materials for magnet applications because of its high critical current (Ic) and low dependency of the Ic on the external magnetic field. For magnet applications, plenty of joints are required to meet the connection of relatively short YBCO CC tapes. The bending properties of the joints inevitably become one of the critical factors that determine the performance of the superconducting magnet. In this paper, we fabricated the joints of YBCO CC tapes by etching Cu stabilizer and studied their bending properties under various bending diameter at 77 K and self-field. Compared with the soldering joint, lower joint resistance (Rj) and preferable electrical properties under applying various bending deformation were achieved and proved by the bending strain tests and finite element simulations. This fabrication technique is a unique practicable solution to reduce the Rj and improve the bending properties for the joints of YBCO CC tapes with thicker metal stabilizing layers in second generation high temperature superconductor (2G HTS) applications.

Design and Characteristics Analysis of a New High-Temperature Superconducting Composite Conductor

The second generation high-temperature superconducting (HTS)-coated conductors are increasingly used in power systems recently, especially in large-capacity superconducting magnetic energy storage. Some conceptual HTS composite conductors have been developed for large current-carrying capacities magnets with high field. In this paper, we propose a model of YBCO high-temperature superconducting composite conductor that may be applied to the large capacity superconducting energy storage magnets. The composite conductor that has three elliptical conductors on round core (CORC) cables, and the structure parameters of the composite conductor are given. We analyze the electromagnetic characteristics and ac loss of the HTS composite conductors during the charging process by the finite-element method. The magnetic flux density and current density distributions are presented, and the ac loss characteristic is discussed as well. The simulation date can be applied for analyzing the stability of composite conductors for future applications.

Angular Dependence of Twisted Soldered-Stacked-Square (3S) HTS Wire

Angular dependence of second generation (2G) high-temperature superconducting (HTS) tape is a crucial parameter for its industrial applications. Known as soldered-stacked-square (3S) HTS wire, a novel structure of HTS wire has been proposed in our previous research. In this paper, angular dependence of 1 mm HTS tape, 4 mm tape, 1 mm 3S HTS wire, and 1 mm 3S HTS twisted wire were measured in liquid nitrogen bath, respectively. It can be found that the 3S HTS wire would not enhance the critical current density under external magnetic field, while an isotropic angular dependence is obtained when 3S HTS wire is twisted. The test results obtained in this paper provides useful information for the future applications of 3S HTS wire.

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.

Three-Dimensional Numerical Study on Transport AC Loss of Soldered-Stacked-Square-Twisted (3S-T) Wire

High-temperature superconducting (HTS) soldered-stacked-square (3S) wire has been proposed as a novel potential structure for the second generation HTS wire. Twisted method is an available way to decrease the anisotropy and improve the performance of 3S wire in high field application. This paper presents a three-dimensional numerical model based on H-formulation for the 3S-twisted (3S-T) wire. AC loss is evaluated as an important parameter when 3S-T wire is applied in alternating current or magnetic field circumstances. Three different structures of 3S-T wires are considered, and the validity of the general model is verified by the corresponding experimental results. The results show that there is no significant eddy loss existing in the 3S-T wire. Moreover, if more HTS tapes are contained in 3S-T wires, the current distribution will be closer to elliptical shape and the current phase in different YBCO layers will be changed. The transport AC loss can be slightly reduced through the twisted method. The work in this paper will be helpful to understand the electromagnetic characteristics of 3S-T wire.

Performance comparison of 1X versus 4X HTS tapes toward the design a 10‐MW direct drive HTS generator for wind turbine applications

AbstractWith current developments underway at the University of Houston, 4× high‐temperature superconducting (HTS) yttrium barium copper oxide (YBCO) tapes are expected to reach a fourfold critical current density improvement at 30 K and 3 T as part of an Advanced Research Projects Agency‐Energy (ARPA‐E)‐sponsored project. The impetus for this project is to develop and deploy cost‐effective direct drive HTS generators for large offshore wind turbine generators. The improved conductor performance of 4× tapes over 1× tapes is projected to allow for a significant reduction in the amount of HTS tapes required to generate the excitation field and, thus, lead to a reduction of the overall generator cost. It was, however, deduced from simulation results that conventional methods of rotor field enhancement using rotor iron makes 1× conductor competitive enough compared with 4× conductors; hence, commercially available YBCO tapes can provide all the energy density requirements to make wind turbines a competitive energy resource based on energy forecasts. This paper is a presentation of design and optimization work to find the best generator topology from the point of view of both machine design and electricity supply. The generators are numerically modeled and simulated using 1× and 4× YBCO HTS conductors on either or of both the rotor and stator side of the generators.

Progress in fabrication of second generation high temperature superconducting tape at Shanghai Superconductor Technology

The development and application of second generation high temperature superconducting (2G-HTS) tapes have attracted much attention in China recently. Progress in upscaling high performance 2G-HTS tape production at Shanghai Superconductor Technology (SST) is reported in this paper. With ion beam assisted deposition, biaxially textured buffer layers with a configuration of CeO2/LaMnO3/MgO/Y2O3/Al2O3/C-276 have successfully been fabricated. In-plane and out-of-plane texture degrees of CeO2 films achieve 2°–4° and 2°, respectively. A multi-plume multi-turn pulsed laser deposition (PLD) system combined with the so-called ‘radiation assisted conductive heater’ has been proposed and further developed for REBCO layer deposition. Our effort was focused on minimizing the temperature variations in the deposition region by modifying the heating shield that assists the conductive heater of the drum-like cylinder. A tape travelling speed of 100–180 m h−1 can be achieved with a steady temperature profile when passing through the deposition zone, which is very beneficial for the growth of the REBCO layer. Taking advantage of the liquid phase growth mode, several compositions of superconducting films with a thickness in the range of 1–2.5 μm have been grown with high growth rates of over 40 nm s−1. Furthermore, the microstructures and superconducting performance were investigated in detail. Based on these studies, superconducting tapes with piece lengths of up to 500 meters have been developed. High Ic values at 77 K, self-field (over 520 A cm−1 width) or at low temperature, high magnetic field conditions (over 560 A/4 mm width at 4.2 K, 10 T, perpendicular field) have been achieved. Lamination and jointing techniques have also been developed by SST for power and magnet applications.

Process for scalable fabrication of low AC loss HTS conductors

A scalable process has been developed to fabricate low AC loss cable from second generation high-temperature superconducting (2G HTS) coated conductors with an emulated Rutherford twisted conductor topology. The process uses an indexed tape design to precisely align separate YBCO tapes to form a single tape structure making it compatible with a reel-to-reel production process and involves a combination of three methods: (1) the use of laser lithography to striate 2G HTS tapes into a pattern of isolated diagonal filaments, (2) the precise alignment and decal bonding of a pattern of solder preforms to the filament edge contact areas, and (3) the alignment and bonding of a top and bottom HTS tape with a thin intervening adhesive layer that provides mechanical adhesion and electrical isolation between adjacent bonds and the interior where filament transposition occurs. The observation of a resistive critical current transition in the fully fabricated transposed striated HTS conductor indicates that all bonds were well formed and the superconducting current path was restricted to the filaments.

Design of a Combined Screening and Damping Layer for a 10-MW-Class Wind Turbine HTS Synchronous Generator

This paper is focused on the design of a single protection layer to cover both the screening and damping characteristics of a large-scale high-temperature superconducting (HTS) wind turbine synchronous generator under sudden short-circuit conditions. Due to small synchronous reactance of HTS generators, short-circuit condition causes substantial fault current in the stator windings, which produces high unbalance variable magnetic field as well as substantial mechanical fluctuations issues. The former one can lead to unstable condition for HTS field windings, due to induced ac loss and field overcurrent, and the latter one can produce large fluctuations on the generator rotational speed and rotor torque angle. The proposed protection layer is designed in a way that not only screening capability is provided for the HTS windings by preventing unbalance magnetic field penetration, but desirable damping ratio is also achieved so that the fluctuations are suppressed in a proper transient time. A 10-MW-class HTS synchronous generator is modeled and simulated using finite element method under different short-circuit conditions. The temperature variation study and field overcurrent analysis are provided to show the compatibility of the proposed model. In addition, magnetic force distribution and static eccentricity fault detection analyses are provided, which guarantee the proper dynamic performance of the studied generator using the proposed protection layer. Simulation results confirm that with the proposed protection layer, both the screening and damping characteristics of the 10-MW-class HTS generator are obtained and proper transient dynamic responses are deduced for wind power applications.

Field Coil Optimization and Characteristics Contrastive Analysis for a High-Temperature Superconducting Generator Prototype

In this paper, a field coil is optimized for a kW-class high-temperature superconducting (HTS) generator prototype to decrease tape consumption and improve the use efficiency of the HTS tapes by increasing the operating current. First, the structure of the field coil is preliminarily designed based on a novel graphic method. Then, the field coil is optimized by using a genetic algorithm to decrease the tape consumption. Finally, the field coils are fixed in the finite element method generator prototype to study and compare the electromagnetic characteristics. The current distribution is calculated based on the J c -B-θ characteristics, and the minimum current to determine the operating current is also derived. After the optimization, the electromagnetic characteristics are improved and the operating current is increased.

Test in Strong Background Field of a Modular Element of a REBCO 1 MJ High Energy Density SMES

A superconducting magnetic energy storage (SMES) is a promising technology for pulse power current source. Nevertheless, they have modest specific energy. Taking advantage of new possibilities offered by the impressive performances of second generation high-temperature superconductors (HTS) tapes in liquid helium, the BOSSE project has the objective to build an SMES with a specific energy of 20 kJ/kg in the MegaJoule range (present world record is 13 kJ/kg). To reach such a high specific energy, high levels of stress and current density are required. A full-size prototype pancake, made of a 139-m-long insulated HTS conductor, has been tested in background magnetic field up to 8 T in Grenoble LNCMI. The objective was to test the mechanical limits of the pancake and to demonstrate the possibility to protect an HTS pancake at high current density, thanks to voltage measurement. A protection system dedicated to the experimental setup is described. It allows us the protection of the pancake at an overall current density of 691 A/mm 2 (i.e., 984 A/mm 2 bare tape engineering current density) and under noisy background field due to the resistive outer magnet. The analysis of the measured signals and mechanical performance of the pancake are presented.

Enhanced Magnetic Field Sensing Using Planar High-Temperature Superconductor Shields

Experimental and finite element model studies of magnetic shielding characteristics of one-side planar sheet structures of the second generation high-temperature superconducting (2GHTS) coated conductor tapes show that significant shielding can be achieved. The shields are shown to be useful for attenuating noise and enhancing the measurement accuracy of magnetic fields. The shields are particularly important for shielding the perpendicular component of the noise during the measurements. The location of the sensor with respect to the shield and the dimensions of the shield need to be designed appropriately to achieve the needed measurement accuracy. The number of superconducting layers in the shield is a design parameter that depends on the magnitude of the noise. The experimental results on shielding factor of a single layer sheet agree with the results of the finite element model.

2G HTS Magnet With Smart Insulation Method

This paper proposes an advanced method to satisfy both the stability and charging/discharging time constant requirements of second generation high-temperature superconductor (2G HTS) magnets. This novel method entails installing metal–insulator transition (MIT) material between the turns of the 2G HTS magnets. The MIT material acts as an insulator when the temperature is lower than a certain value. Above this temperature, the MIT material becomes a conductor. This transition can be used as a switch between the turns of the 2G HTS magnets. We refer to this temperature-dependent smart switch as “smart insulation.” Considering the operating temperature, we selected V2O3 as the material for smart insulation. We have experimentally verified that the advantages of both the insulation magnet (in the superconducting state) and no-insulation magnet (during quenching) can be simultaneously realized.

Design, Construction, and Test of HTS/LTS Hybrid Dipole

This paper presents the design, construction, and test results of a hybrid dipole magnet. The inner coils were of second generation (2G) high-temperature superconductor (HTS) ReBCO tape and the outer coils were of low-temperature superconductor (LTS) Nb3Sn Rutherford cable. The HTS and LTS coils were independently powered and protected using different power supplies. The HTS coils were quenched many times with no degradation in performance observed. The hybrid field reached ∼8.6 T, which is believed to be a record for a hybrid dipole. The maximum field was limited by the stable operation of the leads in the LTS coil at 8000 A. The HTS coils were independently ramped to 800 A, and the LTS coils to 10 000 A. With improved leads and instrumentation, this hybrid dipole is expected to produce over 13 T when the ReBCO tape in the HTS coil is aligned nearly parallel to the field. One major purpose of this program was to perform magnetization studies in the coils made with the HTS tape. Magnetization-induced field errors are expected to be small when the field is nearly parallel to the wide face of the tape. The magnetization measurements were performed at 77 K with the two racetrack coils in two orientations, with field predominantly either parallel or perpendicular to the wide face of the HTS tape. In addition, measurements were also performed at 4 K in different background fields provided by the outer Nb3Sn coils. This paper will summarize the magnetization measurements and present the quenching experience of the HTS coils in this hybrid magnet system.

Short-Circuit Fault Simulations in an HTS Wind Generator With Different Mechanical Conditions

The high-temperature superconducting (HTS) generators are proposed as a promising method to reduce the weight and size of the large-scale off-shore wind generators. However, the lower reactance of an HTS generator makes short-circuit faults heavier. The short-circuit fault problems of an HTS generator are complicated. A simulation is an effective way to study the generator's performances under fault conditions. However, different mechanical conditions affect the simulation results. In this paper, the performance of a 2.5 MW HTS wind generator under short-circuit fault conditions is studied by coupling the finite element method model and the equivalent circuit model. The mechanical conditions are set by three different methods that are the constant rotation speed method, the constant torque method, and the constant power method. The results in these three methods show similar peak values in transient processes, but different developing processes and different final states. The peak values of the electromagnetic torque, armature current, and field winding current appearing in the transient process should be considered when designing the HTS wind generators. This study provides a criterion to set mechanical conditions in the short-circuit fault model of an HTS wind generator, and also provides data for future work about the quench protection of the HTS field windings.

A Study on a Single-Phase HTS Transformer with a Cylindrical Central Iron Core

During the past decade, a number of high temperature superconducting (HTS) transformer prototypes have been designed, and the majority of them are full-core transformers and air-core transformers. However, in this study, we proposed a new type of HTS transformer, where the iron core is different in that the limbs and connecting yokes are absent. To investigate the performance of this type of HTS transformer, we design and fabricate a single-phase HTS partial core transformer prototype using the secondary generation (2G) HTS GdBCO wires. The iron core is at room temperature, and the windings are immersed in liquid Nitrogen. The structures of primary and secondary windings are three layers connected in series and nine double pancakes connected in parallel, respectively. Fundamental characteristics are obtained by standard short-circuit, no-load and load tests in liquid Nitrogen temperature of 77 K. In addition, an equivalent circuit of the HTS transformer is proposed to analyze the characteristic of the transformer. The calculated values based on the equivalent circuit are consistent with that of experiment. The detailed results about the design of the HTS partial-core transformer, the experiment, and the equivalent circuit are presented and discussed in this study.

Development of a 10 m quasi-isotropic strand assembled from 2G wires

Quasi-isotropic strands made of second generation (2G) high temperature superconducting (HTS) wires are attractive to applications of high-field magnets at low temperatures and power transmission cables at liquid nitrogen temperature in virtue of their high current carrying capability and well mechanical property. In this contribution, a 10 m length quasi-isotropic strand is manufactured and successfully tested in liquid nitrogen to verify the feasibility of an industrial scale production of the strand by the existing cabling technologies. The strand with copper sheath consists of 72 symmetrically assembled 2G wires. The uniformity of critical properties of long quasi-isotropic strands, including critical current and n-value, is very important for their using. Critical currents as well as n-values of the strand are measured every 1 m respectively and compared with the simulation results. Critical current and n-value of the strand are calculated basing on the self-consistent model solved by the finite element method (FEM). Effects of self-field on the critical current and n-value distributions in wires of the strand are analyzed in detail. The simulation results show good agreement with the experimental data and the 10 m quasi-isotropic strand has good critical properties uniformity.

Degradation of critical current in an HTS coated conductor considering curvature of ellipse for rotating flux pump

A rotating HTS flux pump is used to study the charging characteristics of superconducting synchronous motor. In order to design the rotating flux pump, the elliptical winding is essential. Numerous studies have been conducted on the degradation of the critical current with respect to the bending condition of the second generation (2G) high-temperature superconducting (HTS) tape. These studies focused on the same radius of curvature depending on the bending position. Therefore, in this paper, the critical current in a HTS coated conductor (CC) considering the curvature of elliptical shape is measured with regard to nine mandrels. These are a tall prolate ellipsoid, oblate ellipsoid and semicircle. In the tall prolate ellipsoid, the degradation of the critical current was the least. The diameters of each shape are 20, 30 and 40 mm, respectively. Finally, the experimental observations have been compared with the theoretical predictions.

Towards a 20 kA high temperature superconductor current lead module using REBCO tapes

Most of the large fusion devices presently under construction or in operation consisting of superconducting magnets like EAST, Wendelstein 7-X (W7-X), JT-60SA, and ITER, use high temperature superconductor (HTS) current leads (CL) to reduce the cryogenic load and operational cost. In all cases, the 1st generation HTS material Bi-2223 is used which is embedded in a low-conductivity matrix of AgAu. In the meantime, industry worldwide concentrates on the production of the 2nd generation HTS REBCO material because of the better field performance in particular at higher temperature. As the new material can only be produced in a multilayer thin-film structure rather than as a multi-filamentary tape, the technology developed for Bi-2223-based current leads cannot be transferred directly to REBCO. Therefore, several laboratories are presently investigating the design of high current HTS current leads made of REBCO. Karlsruhe Institute of Technology is developing a 20 kA HTS current lead using brass-stabilized REBCO tapes—as a further development to the Bi-2223 design used in the JT-60SA current leads. The same copper heat exchanger module as in the 20 kA JT-60SA current lead will be used for simplicity, which will allow a comparison of the newly developed REBCO CL with the earlier produced and investigated CL for JT-60SA. The present paper discusses the design and accompanying test of single tape and stack REBCO mock-ups. Finally, the fabrication of the HTS module using REBCO stacks is described.

Coupled Cryogenic Thermal and Electrical Models for Transient Analysis of Superconducting Power Devices with Integrated Cryogenic Systems

Benefits of an integrated high temperature superconducting (HTS) power system and the associated cryogenic systems on board an electric ship or aircraft are discussed. A versatile modelling methodology developed to assess the cryogenic thermal behavior of the integrated system with multiple HTS devices and the various potential configurations are introduced. The utility and effectiveness of the developed modelling methodology is demonstrated using a case study involving a hypothetical system including an HTS propulsion motor, an HTS generator and an HTS power cable cooled by an integrated cryogenic helium circulation system. Using the methodology, multiple configurations are studied. The required total cooling power and the ability to maintain each HTS device at the required operating temperatures are considered for each configuration and the trade-offs are discussed for each configuration. Transient analysis of temperature evolution in the cryogenic helium circulation loop in case of a system failure is carried out to arrive at the required critical response time. The analysis was also performed for a similar liquid nitrogen circulation for an isobaric condition and the cooling capacity ratio is used to compare the relative merits of the two cryogens.