High Temperature Superconducting Wire Research Articles

Superconducting state stability in second generation high-temperature superconducting wires with varying copper stabilizer thickness under AC overcurrent conditions

Superconducting state stability in high-temperature superconducting (HTS) wires is of great importance for the reliable operation of superconducting electric power equipment. To this end, a study was made of the steady state operation and transients under AC current overloading in second generation (2G) HTS tape wires with a copper stabilizing layer of varying thickness. The existence of a threshold stabilizer thickness has been found, such that determines the HTS tape I-V curve and transients when an overcritical current flows. If the current exceeds the critical value, primary instability takes place in a wire with no stabilizer layer as well as with a layer of any thickness. In a wire with the stabilizer thickness less than the threshold level, an irreversible superconducting-to-normal transition occurs. However, if the copper layer thickness exceeds the threshold thickness, the HTS wire stable overloaded state recovers after some transients that have an irregular oscillation shape. The recovery of the stable thermal state under overcurrent conditions in HTS wires with an over-threshold stabilizer thickness is applicable in a variety of superconducting electric power devices, such as transformers and current limiters with a high capability to withstand faults. The measurements also show that the loss of superconductivity under AC overcritical current is followed by the phase angle changing between voltage and current. This phenomenon could be used for fast response normal zone detection in current-carrying conductors of superconducting equipment.

The influence of BaSnO3 artificial pinning centres on the resistive transition of 2G high-temperature superconductor wire in magnetic field

In this work, we present a study of the resistive transition in magnetic field of 2G high-temperature superconductor wire samples with BaSnO3 (BSO) artificial pinning centres (APCs) in a GdBa2Cu3O7−x (GdBCO) superconductor. The GdBCO layer was fabricated by pulsed laser deposition, using production equipment to obtain samples with varied concentrations of APC: 0, 6, 12 and 18 mol% of BSO. Resistive transition curves were measured in the magnetic field range from 0 to 9 T, and magnetic field orientations from B∣∣c (θ = 0°) to B∣∣ab (θ = 90°) with an angle step of 15°. We observed an irreversibility temperature peak at the B∣∣ab orientation. We determined the angular regions where correlated pinning centres dominated and found them to expand with the increase of BSO concentration. The activation energy (Ua) obtained from the lg(ρ/ρ0) against the 1/T plots was almost constant in the whole angular range, with a small peak at B∣∣ab. The activation energy as well as the irreversibility temperature decreased with the increasing doping level, but the Ua(θ) curves looked similar for all samples with APCs. The logarithmic resistivity plot of the undoped sample looked substantially different from those of the APC samples, with a kink and two different slopes corresponding to two regions with different Ua. We discuss that this difference is related to the different pinning landscapes in samples with and without APCs.

전기추진 항공기를 위한 10 MW급 공심형 초전도 발전기의 설계 타당성 연구

In this paper, a study on the design feasibility of superconducting electric machine using HTS(High Temperature Superconducting) wire for electric propulsion aircraft was carried out. NASA(National Aeronautics and Space Administration) is developing electric propulsion aircraft and electric machine for electric propulsion aircraft and aims at 41.4kW/kg specific power by 2035. Based on research trends, this paper proceeds with the design of superconducting electric machine using fully air-cored superconducting field coil to achieve high power density. Electromagnetic design was performed for fully air-cored machine. Also, the superconducting field magnet and armature rotor design were performed to satisfy the generator requirements. The analysis result confirmed that the design target 10MW output was satisfied. The results of this study can be applied to the design and research of superconducting electric machine for electric propulsion aircraft.

Practical Design and Experimental Test of MgB2 Magnets for 300 kW-Class Superconducting Induction Heater

A shape and characteristics of Superconducting magnets used in superconducting applications are effected by purposing of a device and these coils are wound with various superconducting wires such as high temperature superconducting (HTS) wire and low temperature superconducting (LTS) wire. MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> wire is the one of the wires which can compensate the disadvantages of each wire. Therefore, if we adopt MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> wire to superconducting applications, we get advantages such as operating temperature with cryogen free cooling system and wire's price. In this paper, the author designs, fabricates and tests MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> magnet for a 300 kW-class DC superconducting induction heater. Firstly, MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> magnet is designed and analyzed using finite elements method for a 300 kW-class superconducting induction heater. Secondly, the magnet is fabricated using dry-winding and metal insulation method. Finally, MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> magnet is stacked and assembled into conduction cooling property measurement system for evaluate its performance and characteristics. As a result, MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> magnet guaranties a satisfactory performance with low price and highest critical temperature among LTS wires. The low temperature as 10 K, which is the operating temperature of the MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> magnet, can be achieved by a conduction cooling system. This study will be effectively utilized for a 300 kW-class superconducting induction heater and other superconducting magnet applications.

Effect of Dynamic Resistance on AC loss in Stacked superconducting tapes

High temperature superconductors (HTS) are promising candidate conductors for multiple applications, such as superconducting magnets and electric machines. However, these superconductors are normally faced with significant AC loss under a certain alternating magnetic field. Dynamic resistance occurs in a superconductor which carries DC current and experiences an AC magnetic field that exceeds the threshold value. In order to understand the mechanisms and magnitudes of AC loss and dynamic resistance for each tape which is stacked in z -arrays, the equation of dynamic resistance for stacked HTS wires in a perpendicular field was modified based on the formula for a single coated conductor. Analytical predictions were compared with experimental results. It is shown that analytical expressions modified by the external susceptibility and Kim model are available for predicting the dynamic resistance of stacked superconducting tapes.

Analysis application possibilities of high-temperature superconductors in electric networks

In the article the technical analysis of existing constructive decisions concerning use of high-temperature superconducting cables is carried out. The features of the use of superconductors in electrical distribution networks are analyzed. The advantages of using high-temperature superconductors in comparison with low-temperature superconductors are established. It is determined that the use of high-temperature superconductors, due to the increased critical parameters, provides an increase in the power of transmission lines and energy saving. From the analysis it follows that high-temperature superconductor wires of 2G generation have better operational characteristics, respectively, their use is more efficient compared to wires of 1G generation. A scheme of a three-phase high-temperature superconducting power transmission network with a neutral wire is considered. The working conditions of a three-phase power network with high-temperature superconducting cables are analyzed. It is determined that the use of two cores of a high-temperature superconducting cable of a distributed power transmission system provides an increase in the throughput of electric power in distribution electric networks. Accordingly, the efficiency of electric power transmission is increased, as well as the loss of AC power and operating costs are reduced. It is shown that the use of the reactor reduces the requirements for protection devices, facilitates the operation of electrical installations, including generators of power plants, and also reduces the cost of distribution networks equipment. It is indicated that the smallest power loss in a three-phase distributed power transmission system using high-temperature superconducting cables can be achieved with a symmetrical load operation mode. The results of technical analysis can be used to develop recommendations for improving the characteristics of cable power lines.

Stable Overload Operation of High-Temperature Superconductor Protective Resistors

The use of high-temperature superconductor (HTS) resistors to protect electrical equipment and ac networks from emergency short-circuit currents and single phase-to-ground faults has been considered. It has been proposed to use a stable overload operation in HTS composite wires to enhance the speed of response and thermal stability of HTS current-limiting devices. Design solutions for the use of stabilized low-resistance HTS wires in protective resistors for ac networks have been developed that increase the resistance inserted in the circuit by several orders of magnitude. The characteristics of first-generation HTS wires with high critical parameters in the resistive state have been measured in a wide current overload range. Prototypes of instantaneous thermally stable current-limiting devices with HTS protective resistors have been fabricated and tested. The design parameters of HTS protective resistors for use in electric power networks have been calculated.

Analytical Model for the Magnetic Field Distribution in a Flux Modulation Superconducting Machine

This article presents a theoretical analysis of an axial field machine using high-temperature superconductors (HTSs) wires and bulks. The air-gap magnetic field obtained with the HTS coil and modulated by the HTS bulks is predicted by two 2-D axisymmetric models. Analytical models are based on the solution of Laplace’s equation by the separation of the variable method. The torque is obtained by a quick numerical integration of the Laplace force that acts on the armature winding. The proposed model is compared with 3-D finite-element simulations and good agreement is obtained. This model can be used with an optimization design procedure with a large reduction of the computational time.

The Influence of the Voltage Rise Time on Transient Processes during Current Overload in Stabilized Second-Generation HTSC Wires

The effect of spontaneous reverse transition of a stabilized high-temperature superconductor (HTSC) tape from the normal to resistive state during rapid (jumplike) voltage application and alternating current overload has been observed. It is established for the first time that, at a stabilizing layer thickness above 13 μm, the main heat evolution takes place in the copper stabilizer and this heat is effectively removed to the refrigerant, which significantly decreases the HTSC layer’s overheating. This is accompanied by a drop in the resistance of the secondary resistive state and increase in the duration of its existence. These data allow using the observed effect to increase the time of current limitation and improving reliability of HTSC current limiters.

Energy dependent structure of Xe ion tracks in YBCO and the effect on the superconductive properties in magnetic fields

The morphology and structure of damaged regions (tracks) produced by swift heavy 167, 77, and 46 MeV 132Xe23+ ions in YBCO-based second generation industrial high temperature superconductors wires (2G HTS) were studied using transmission electron microscopy. It was shown that ions produce tracks aligned along the ion trajectory but of morphology depending on their energy: continuous, nearly continuous, or discontinuous tracks like prolate ellipsoids of 10–15 nm in length and spheroids of 5 nm in diameter. The damaged regions of about 5 nm in diameter contain an amorphous material with a lower density compared to the pristine YBCO. The material density drops from 6300 kg m−3 for YBCO matrix to 3600 kg m−3 inside the tracks. Barium enrichment was found in the vicinity of the track at a distance of about 10 nm from the center of the defect. Ion damage tracks with different morphologies showed different effectivenesses as pinning centers. Tracks composed of discontinuous pinning centers—spheroids of about 5 nm in diameter—bring the best enhancement of the critical current density. It occurs for the lowest ion energy (46 MeV) in the range of energy loss of 8.9 keV/nm–4.7 keV/nm for Xe ions. The samples showed highest critical current densities of 56 MA/cm2 (4.2 K) and 3 MA/cm2 (77 K) in self-field, while in magnetic fields of 8 T, the values of 17 MA/cm2 (4.2 K) and 1.6 MA/cm2 (77 K) were achieved. The reduction of the superconducting volume corresponding to the amorphous radiation defects did not exceed 4% from the total sample volume.

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.

AC Loss Measurement in HTS Coil Windings Coupled With Iron Core

Utilizing high temperature superconducting (HTS) magnets coupled with iron core on the rapid cycling synchrotrons is considered as an effective way to reduce their construction and running costs. However, the heat generation by ac loss in HTS wires is a critical obstacle for the application, and prediction and reduction of ac loss in HTS magnets coupled with iron core are essential. In this work, we built one HTS double pancake coil (DPC), a stack of two DPCs, and an iron core comprising laminated steel to couple with the coil windings. The HTS-coated conductors are 200 A-class 4-mm–wide Shanghai Conductors. We report the ac loss measurement results on the coil windings with/without the iron core at three different frequencies. The ac loss in the HTS windings was significantly increased due to the existence of the iron core. Increasing the number of stack of the DPCs may help reduce the difference in ac loss values in the coil windings with/without iron cores.

R&amp;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.

Charging Characteristics of Rotary HTS Flux Pump With Several Superconducting Wires

High-temperature superconducting (HTS) flux pumps are used to charge HTS coils at cryogenic temperatures without thermal and mechanical contact with the power supply at room temperature. We found that the larger the alternating magnetic field (AMF) penetrating into the HTS wire, the faster is the current charge rate in the HTS coil and the larger will be the amount of charge. AMF causes vortex pinning of the HTS wire to move, resulting in dynamic resistance ( R dyn) and electromotive force (EMF). Charging characteristics are determined by R dyn and EMF which are generated by effective internal resistance ( R eff) and open-circuit voltage (OCV), respectively. Even if AMF of the same magnitude penetrates the wires, the size of R eff and EMF generated will vary depending on the characteristics of the HTS wires. Therefore, in this study, R eff and OCV of a HTS wire are measured and compared with the results of HTS coil charging using a flux pump.

Magnetic Design of a Half-Size 5 T High-Temperature Superconducting Coil for MRI

We have been developing a liquid-helium-free magnet using High-Temperature Superconducting (HTS) wire for MRI. The aim of this research and development is to commercialize a 3-T HTS magnet for whole body MRI which has the characteristics of being liquid-helium-free, small, and light-weight. HTS coil requires tolerance of a high magnetic field, 7 T, and it must have high current density, 200 A/mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , for developing a small and light weight magnet used for 3-T MRI. A half-size 5-T HTS magnet will be manufactured in order to demonstrate the tolerance of high magnetic field and high current density of the coil, which are equivalent to a whole-body 3-T MRI magnet in a half-size HTS magnet. In this paper, we have investigated the arrangement of coils of a half-size 5-T coil. The designed coil consists of 124 double-pancake coils, whose inner diameter is 560 mm, outer diameter is 1200 mm, and axial length is 1100 mm. The uniformity of designed magnetic field is under 2.0 ppm (250 mmDSV).

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.

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

3-D Numerical Modeling for the Magnetization of Superconductors Using a Local Discontinuous Galerkin Finite Element Method

A numerical methodology is proposed to discretize a nonlinear low-frequency approximation to Maxwell’s equations using a local discontinuous Galerkin (DG) finite element method, with an upwind-like numerical flux, for modeling superconductors. In this paper, we focus on high-temperature superconductors (HTS) and the electrical resistivity is modeled using a power law. Nodal elements and the Whitney element are used. Numerical studies have been performed to verify the proposed methodology: a problem with a manufactured solution, the nonlinear magnetic front problem, and the magnetization of HTS wires. Based on the final time that can be reached for a given time-step size, the proposed strategy is compared with the $\mathbf {H}$ formulation discretized using the Galerkin finite element method with the Whitney element for the magnetic front problem. The proposed local DG strategy allows the use of a larger time-step size over a longer time interval, particularly, when we use the Whitney element. The proposed methodology can also capture sharp gradients of the current density with limited spurious oscillations. The numerical results are in agreement with Bean’s model for large values of power-law’s exponent. The proposed local DG strategy could be generalized to more complex electrical resistivity models, including multiphysics models.

Superconductive REBCO Thin Films and Their Nanocomposites: The Role of Rare-Earth Oxides in Promoting Sustainable Energy

The lossless transmission of direct electrical currents in superconductors is very often regarded as an ‘energy superhighway’ with greatly enhanced efficiency. With the discovery of high temperature superconductors (HTS) in the late eighties, the prospect of using these materials in efficient and advanced technological applications became very prominent. The elevated operating temperatures as compared to low temperature superconductors (LTS), relaxing cooling requirements and the gradual development of facile synthesis processes raised hopes for a broad breakthrough of superconductor technology. The impact of superconductor technology on the economy and energy sectors is predicted to be huge if these are utilized on a large scale. The development of superconducting tapes with high critical current density (Jc) is crucial for their use in transmission cables. Many countries these days are running projects to develop wires from these HTS materials and simultaneously field trials are being conducted to assess the feasibility of this technology. These HTS wires can carry electrical currents more than 100 times larger than their conventional counterparts with minimum loss of energy. The increased efficiency of HTS electric power products may result in greatly reduced carbon emissions compared to resulting from using the conventional alternatives. In order to use the thin films of YBa2Cu3O7- (YBCO) and REBCO [RE (rare-earth) = Sm, Gd, Eu etc.], the members of the HTS family, for future technological applications, enhancement of Jc over wide range of temperatures and applied magnetic fields is highly desired. The enhancement of Jc of YBCO and REBCO films has been successfully demonstrated by employing different techniques which include doping by rare earth atoms, incorporating nanoscale secondary phase inclusions into the REBCO film matrix, decoration of the substrate surface etc. which generate artificial pinning centers (APCs). In this review, the development of the materials engineering aspect that has been conducted over the last two decades to improve the current carrying capability of HTS thin films is presented. The effect of controlled incorporation of APCs through various methods and techniques on the superconducting properties of YBCO and REBCO thin films is presented, heading towards superior performance of such superconducting thin films.