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This paper proposes a way to represent the anisotropic nonlinear superconducting properties using a discrete model for magnetization with the corresponding critical parameters, equivalent to the Power Law model for currents. This simplified model makes it possible to analyze magnetic systems with superconducting elements in a stationary mode, which reduces the calculation time. Using of proposed model is demonstrated by the calculation of force interactions between high-temperature superconducting (HTS) samples and permanent magnet in zero-field-cooling (ZFC) and field-cooling (FC) modes. HTS bulks in the form of a prism and stack made of HTS tape are considered. The calculation of the electromagnetic field was carried out using the method of integral equations for field sources. The data of calculations are compared with the results of experimental studies. [ABSTRACT FROM AUTHOR]

The main obstacle for the application of the high-temperature superconducting (HTS) coated conductors (CCs) in AC energy applications is the relatively large AC loss. To tackle this, several forms of HTS cables for AC applications have been invented and investigated, such as the HTS Roebel cable, Cable on Round Conductor (CORC), and Twisted Stacked Tape Cable (TSTC). In this paper, the possibility of encapsulating Roebel cables into a single HTS CC is investigated, from which a novel conception of a Roebel tape is proposed. Compared with the existing HTS cables, HTS Roebel tapes are more compact, more capable at carrying large current with minimised AC losses, and easier to manufacture. A 3D finite element method (FEM) model of the Roebel tape is built to optimise the structure and verify the performance. The results show that, compared with normal ReBCO CCs, Roebel tapes with optimum patterns can reduce AC transport losses by 60% through field-cancelling and can reduce magnetisation losses by the factor of the filament number through patterning. With excellent loss reduction performance and high current capability, the Roebel tape shows great potential to become a revolutionary HTS cable for high-current power transmission and AC machine applications. [ABSTRACT FROM AUTHOR]

The development of high-temperature superconducting (HTS) electrical machines results in applications of various fields, as they have higher efficiency and power density. Numerical modeling of superconducting electrical machines is usually performed by finite element method based their electrical behavior, and H-Formulation of the Maxwell's equations is one of the models that are used tremendously due to its high flexibility and simplicity. Axial field machine (AFM) is a machine topology with higher efficiency and power density, but with more complexity when modeling. This paper proposed a new 2D model for the superconducting AFM, where the superconducting coil is simulated with a 2D infinitely long model, this model also divides the electrical machine into two parts: the superconducting parts (HTS coils, bulks, etc.) and non-superconducting parts (e.g., conventional conductors, machine structure). This paper compares the results of H-A Formulation and T-A Formulation with this approach, which requires appropriate boundary conditions and continuity between the two regions, along with correct modeling of fixed and moving parts of the electrical machine, where the geometry of this model is based on a linear synchronous machine, which means the rotor is moving linearly instead of rotation. [ABSTRACT FROM AUTHOR]

This is a follow-up study of the cryogen-free superconducting prototype generator with YBCO field windings. The previous paper had introduced the design of the structure, cryogenic system and electromagnetic characteristics of the prototype machine, whose operating temperature was 30 K, maximum field current was 100 A and rotating speed was from 10 to 30 rpm. In this paper, the optimization of the airgap magnetic field and the stability of superconducting magnet have been carried out. For the purpose of increasing utilization of the magnetic field of superconducting windings, its support structure and vacuum chamber of the cryostat had been upgraded in order to reduce the physical airgap between the armature teeth and the vacuum chamber room temperature wall from 10 mm to 2 mm. In addition, a new coil curing method, vacuum impregnation process with paraffin, had been applied while the YBCO coil fabrication, to improve its stability. The performance properties of the optimized system as well as the comparison between FEM simulation and experimental results are finally presented. [ABSTRACT FROM AUTHOR]

High temperature superconductors have zero resistance under critical temperature and the HTS tapes have low thermal conductivity. The China Fusion Engineering Test Reactor(CFETR) project requires current leads with current carrying capacity up to 100 kA, making high temperature superconducting current leads the ideal choice. The main work of this paper is the theoretical analysis and optimization design of the 100 kA HTS current lead. Current leads are designed to minimize heat leakage to the cryogenic system and to reduce the mass flow of cooling gas. In this paper, some important design parameters are introduced firstly, and then one dimensional thermal analysis is carried out for the heat exchanger and high temperature superconductor parts. The LOFA time and overheating time of the current lead were calculated through simulation, and it was verified that the design meets the requirements of the project. Finally, the factors that have great influence on the performance of current leads are analyzed. In view of the four influencing factors, which are joint resistance, GHe inlet temperature, hPw and RRR, we respectively produced an optimized design. [ABSTRACT FROM AUTHOR]

This paper presents the DC fault transient study of a meshed DC grid with high-temperature superconducting (HTS) HVDC cables to integrate offshore wind power. A four-terminal meshed DC grid model with a ±100 kV DC voltage rating is developed. DC circuit breakers (DCCBs) are implemented in the DC grid to deal with DC cable faults. To conduct the fault transient study, the fault scenarios with different fault locations and protection delays are studied. The sensitivity study versus different DC fault locations reveals that the faults on the faulted cable will not cause the quenching of healthy cables. The sensitivity study considering different DC fault protection delays demonstrates that the HTS cables have a current-limiting effect and the long delay of DC fault protection does not result in large fault current and the quenching of healthy cables. Extensive simulations in PSCAD/EMTDC validate the founding. [ABSTRACT FROM AUTHOR]

High temperature superconducting generators (HTSGs) have great potential of high power density for future large direct-drive wind turbines. As synchronous machines, HTSGs have rapid rise of field currents during a sudden short circuit fault which cause AC losses in the HTS tapes. This paper applies H-A formulation of Maxwell equations for finite element simulation of electromagnetic behavior of a 10 MW, 9.6 rpm HTSGs. The model is integrated to a short circuit model to calculate the characteristics of the HTS field winding, such as field currents and AC losses during a three-phase no-load short circuit fault at the armature winding terminal. Two HTSG designs are compared. The $n$ value characterizing the sharpness of the superconducting-resistive state transition of the HTS tape and the number of armature winding segments are analyzed as key variables. The result indicates high AC losses are produced but more armature winding segments can effectively reduce the AC loss and the field current. A lower $n$ value can also lower the AC loss level but only for the non-magnetic rotor design. The field current is not affected by the $n$ value for both HTSG designs. [ABSTRACT FROM AUTHOR]

Spoke structure can increase the torque density of coaxial magnetic gear (CMG). However, the outer rotor can produce a large number of magnetic leakages. To improve the utility of PMs, a novel magnetic gear was proposed in this paper. The structure of the auxiliary flux modulator is a slotted iron yoke, and the slot angle is same as the stationary ring. Among, the permanent magnets (PMs) of inner rotor are adopted uneven block structure to improve air gap flux density. At the same time, the stationary ring adopts high-temperature superconducting (HTS) bulks, replacing the epoxy resin. In addition, Genetic algorithm (GA) is applied to calculate the optimal parameters of the proposed CMG. Finally, the air gap flux density and output torque of the magnetic gear a compared by the finite element method. The results show that the output torque of the proposed magnetic gear is effectively improved. [ABSTRACT FROM AUTHOR]

The performance of High Temperature Superconducting (HTS) tapes is strongly affected by the mechanical loadings they experience during manufacturing, cooldown and operation. Therefore, the development of HTS-based applications requires thorough investigations on the impact of these loadings on the critical current. In this work, a measurement procedure is applied to determine the critical current of a (Re)BCO tape at 77 K, after double bending at room temperature around a cylindrical mandrel. In this procedure, the tape is cooled down to cryogenic temperature, and the critical current is first measured on the straight sample. After warming the tape up to room temperature, a double bending around a cylindrical mandrel is applied in two opposite directions and the critical current is measured at the following cooldown. This analysis is repeated for different mandrel diameters in order to identify to study the impact of the curvature radius on the performance degradation. The application of one single bending at room temperature is compared to the results of the double bending procedure. The influence on the performance degradation of applying a known force to the tape during the double bending at room temperature is also experimentally analyzed. [ABSTRACT FROM AUTHOR]

Stress calculation is a key link in evaluating whether the structure of a superconducting magnet is safe. A 35-kV/3.5-MVA single-phase high temperature superconductivity-controllable reactor (HTS-CR) with the HTS winding wound by HTS double pancakes is being developed. The effect on the local stress and temperature rise of HTS double pancakes, which determines the design of the strengthening structure of the HTS double pancake, is studied in this paper. Furthermore, the multiprocess stress development for HTS double pancakes from manufacturing to power-on is also investigated, which discloses the model and the results of the stress calculation. This study can provide a reference for developing HTS-CR with large capacity in the future. [ABSTRACT FROM AUTHOR]

The high temperature superconducting (HTS) cable has shown promising prospects in megacities for the advantages of high transmission power density and low loss. However, when HTS cable is working on grid, various kinds of faults may cause irreversible damage, resulting in the failure of reclosing. In this paper, the resistive superconducting fault current limiter (R-SFCL) is introduced into the power system to cooperate with the HTS cable, so as to reduce the potential damage caused by fault current. Firstly, the equivalent circuit models are established, and then transient response of HTS cables under fault condition is analyzed, the recovery time of HTS tapes are used to define the design of R-SFCL. Finally, the operating reliability of HTS cable has been evaluated and measures about adaptive reclosing times were proposed under different fault currents. [ABSTRACT FROM AUTHOR]

High temperature superconducting (HTS) generators could enable a lightweight and cost-effective direct drive (DD) wind turbines with large power ratings. The EU-funded EcoSwing project successfully demonstrated the world's first full-scale MW-class HTS generator on a commercial DD wind turbine. This paper focuses on the commissioning of the EcoSwing HTS generator on the wind turbine. The commissioning campaigns, including the rotor cool-down, excitation of the HTS field winding, and the power production of the generator, are presented in the paper. In the testing period, the generator was grid-connected for more than 650 hours and accumulatively produced more than 600 MWh to the grid. The target output power of the 3 MW class was reached. Throughout the real-life testing on the wind turbine, the generator performed well from the electromagnetic, thermal, and mechanical perspectives. Moreover, the generator even sustained three sudden short circuits in the converter system. The work reported has shown that HTS generators are technologically feasible for wind turbine applications, and the technology readiness level of HTS wind turbine generators has been improved to 6 $\sim$ 7 for the first time. [ABSTRACT FROM AUTHOR]

When a high temperature superconductor (HTS) coated conductor carries a DC transport current within the background of an oscillating magnetic field, the effect of dynamic resistance takes place. Under the circumstance when the dynamic resistance effect is significant, heat dissipation will be generated to change the temperature of HTS tapes. The amplitude of the instantaneous dynamic resistance increases with time due to the rising temperature. The phenomenon is more obvious when it comes to the HTS stacks where superconducting tapes are assembled so close. This paper proposes a numerical model with electromagnetic and thermal coupling to study the dynamic resistance of the series-connected HTS stack. Experimental results have shown that the proposed numerical model can describe dynamic resistance more accurately than conventional models. Besides, investigations are carried out on how the insulation thickness in the stack and the frequency of AC magnetic fields impact the dynamic resistance of HTS stacks under the influence of Joule heat. This can provide a useful reference for the design of superconducting devices in which dynamic resistance occurs. [ABSTRACT FROM AUTHOR]

The realization and preliminary tests of a high temperature superconducting axial-field synchronous machine (HTS-AFSM) prototype are presented in this paper. The HTS machine consists of a 3-phase stator with HTS armature winding and a permanent magnet (PM) rotor. The HTS armature winding contains three pancake coils made of BSCCO tape forming a single layer nonoverlapping concentrated stator windings. The rotor is composed of four NdFeB permanent magnets. Several tests have been carried out such as voltage vs. currents curves of the HTS coils, static torque, back-EMF and load tests in generator mode. A 3D semi-analytical model, based on integral equations, has been used to check out the measured electromagnetic quantities. It has been shown that the measured and the calculated quantities are in satisfactory agreement. [ABSTRACT FROM AUTHOR]

Quench has always been an urgent problem for high temperature superconductor (HTS) magnets. Fast discharge of the coil current is an effective method to protect the HTS magnet from quenching. In HTS magnets, metal plates are originally used to provide conduction cooling and mechanical support for the coil. During fast discharging operations, the metal plates can rapidly absorb part of the magnetic energy stored in the HTS coils through electromagnetic coupling. Previous studies are based on copper plates. This paper studies the influence of several promising metal materials on the discharging process of the HTS coils coupled with metal plates by experiments and simulations. The results show that in the explored resistance range, the higher the electrical conductivity of the metal plates, the better the acceleration of the current attenuation of coil at the early stage of discharging process. The effects of different metal plates on accelerating current attenuation of the coil are ranked as follows: SS 304L < Al 6061-T6 < Al (RRR = 30) < Cu (RRR = 30) < Au < Cu (RRR = 300) < Ag. However, Cu (RRR = 300) plates can absorb more energy from the HTS coil than the Ag plates during the discharging process. Copper with higher purity (Cu (RRR = 300)) and silver are promising alternatives for metal plates of HTS magnets. Generally, a fast current drop is always the most effective method for avoiding tape turn-out during a local quench; therefore, silver with the highest electrical conductivity is the best choice in view of quench protection. [ABSTRACT FROM AUTHOR]

The high temperature superconducting (HTS) cable has shown promising prospects in megacities for the advantages of high transmission power density and low loss. However, when HTS cable is working on grid, various kinds of faults may cause irreversible damage, resulting in the failure of reclosing. In this paper, the resistive superconducting fault current limiter (R-SFCL) is introduced into the power system to cooperate with the HTS cable, so as to reduce the potential damage caused by fault current. Firstly, the equivalent circuit models are established, and then transient response of HTS cables under fault condition is analyzed, the recovery time of HTS tapes are used to define the design of R-SFCL. Finally, the operating reliability of HTS cable has been evaluated and measures about adaptive reclosing times were proposed under different fault currents. [ABSTRACT FROM AUTHOR]

In this work, we experimentally investigate the current carrying capacity of single REBCO tapes and stacks made 5 12 mm REBCO tapes with a 25 μm copper stabilizer in liquid helium in comparison with those made of bare tapes with no stabilizer at current ramp rates up to 55 kA/s. The motivation for the research was checking the usability of REBCO stacks as basic sub-elements for high current superconducting cables operating in fast cycling modes at 4.2 K. An original experimental technique was employed to induce the extremely high ramp rates. During the tests, one or 5-folded stacks curled into rings 95 mm dia with different types of joints were charged in the external magnetic field generated by an outer solenoid at ramp rates up to 1.6 T/s. The curled REBCO stacks were either soft-soldered over their entire length or contained local joints only. The maximum screening current induced in the samples during the outer solenoid charging Imax was registered. Our experiments showed that the current carrying capacity of the REBCO tapes and stacks was strongly affected by the absence or presence of the copper stabilizer as well as the type of the joint. The reasons for the Imax limitation for the copper stabilized and bare samples are also briefly discussed. [ABSTRACT FROM AUTHOR]

This paper reported the fabrication and the test results of the high temperature superconducting (HTS) magnet developed for the aluminum billet heater for aluminum extrusion processing. In this magnet, the HTS coils were combined with iron cores, because the required magnetic field in the working region was about 1T. Two HTS coils wound directly on the convex shape iron cores were fabricated. The HTS coils were made by the no-insulation winding of REBCO tape with the YOROI-coil technique. Each of them was separately installed in an individual cryostat. Two HTS coils with iron cores were disposed oppositely to each other and were magnetically connected by a C-shape yoke placed in room temperature. The HTS coil was cooled down to about 15 K by the GM cryocooler in the initial cooling. The magnetic field of 1.06 T at the center of the heating region was stably generated with the rated current of 200 A. It was also demonstrated that the HTS magnet could be charged up to 300 A without quench. According to the observation of the electromagnetic force direction from the outside of the cryostat, it was confirmed the validity of the force balance design of the magnet. [ABSTRACT FROM AUTHOR]

In recent years, the increase of microplastics (MPs) in ocean have been recognized as one of ocean pollution listed in Sustainable Development Goals (SDGs). Since MPs absorb harmful chemicals while floating in ocean, small fish which eats the absorbed MPs may fall into bad digestion and poor health condition. To solve the ocean pollution problem, a good MP collection method must be proposed with a high processing speed and a high MP collection ability. While, recently, the performances of 2nd generation high-temperature superconducting (HTS) magnets which can generate a field higher than 15 T have been improved. It is expected that MP collection performances are enhanced with such high field superconducting magnets. In this paper, we propose a conceptual design for MP collector from seawater using superconducting magnets. To evaluate the performances of the device, we developed a fluid simulation coupled with magnetic field simulation. The simulation results indicate that MPs can effectively be collected with a high magnetic field with a high processing speed. [ABSTRACT FROM AUTHOR]

The performance of High Temperature Superconducting (HTS) tapes is strongly affected by the mechanical loadings they experience during manufacturing, cooldown and operation. Therefore, the development of HTS-based applications requires thorough investigations on the impact of these loadings on the critical current. In this work, a measurement procedure is applied to determine the critical current of a (Re)BCO tape at 77 K, after double bending at room temperature around a cylindrical mandrel. In this procedure, the tape is cooled down to cryogenic temperature, and the critical current is first measured on the straight sample. After warming the tape up to room temperature, a double bending around a cylindrical mandrel is applied in two opposite directions and the critical current is measured at the following cooldown. This analysis is repeated for different mandrel diameters in order to identify to study the impact of the curvature radius on the performance degradation. The application of one single bending at room temperature is compared to the results of the double bending procedure. The influence on the performance degradation of applying a known force to the tape during the double bending at room temperature is also experimentally analyzed. [ABSTRACT FROM AUTHOR]

In this article, to accurately analyze the magnetic properties of high-temperature superconductor (HTS), a superconductor hysteresis model is proposed. Based on the physical mechanism, the hysteresis loop of HTS can be decomposed into an antimagnetic curve and a paramagnetic loop. The calculated and measured results of silver-sheathed Bi2223 superconducting tape samples under an external magnetic field are compared to show the effectiveness and accuracy of the presented method. [ABSTRACT FROM AUTHOR]

High temperature superconducting (HTS) technologies are expected to be a key enabler for lightweight and cost-effective direct-drive (DD) trains for large wind turbines. This paper reports the designing and basic experimental validation of the world's first full-scale DD HTS generator demonstrated on a commercial wind turbine. The HTS generator has its rotor with an HTS field winding working below 30 K, which is achieved by using off-the-shelf Gifford-McMahon cryocoolers. The stator of the generator is essentially conventional, except that the armature winding has four segments to limit fault torques in case of sudden short circuits due to converter failures. Compared to an existing DD permanent magnet generator on the turbine, the air gap shearing stress of the HTS generator is doubled, and the weight is reduced by 24%. The overall design requirements from the turbine integration perspective, as well as the topological considerations, are first described in this paper. The electromagnetic and cryogenic designs are then presented, followed by performance testing of HTS coils. The basic experimental validation shows that the cryogenic design is satisfactory and the measured no-load voltage matches the finite element calculation very well. [ABSTRACT FROM AUTHOR]

To enhance the operating security and stability of the cross-linked polyethylene power cable based urban distribution network due to conventional cable joint (CCJ) faults, this paper presents a novel superconducting fault current limitation scheme by using a superconducting cable joint (SCJ). The basic principle, circuit modeling, conceptual design and distribution network integrated with the SCJ are presented in detail. The comparative study without and with the proposed SCJ scheme and comprehensive evaluation are carried out. The simulation results obtained under symmetrical and asymmetrical CCJ faults show that the harmful large fault grid currents can be limited effectively and the fault grid voltage can be well improved. Thus the high temperature electric arc in the fault location caused by CCJ faults can be safely controlled. And large area power failure in actual power system can be avoided. [ABSTRACT FROM AUTHOR]

High temperature superconducting (HTS) no-insulation (NI) magnet excited by rotating flux pump has the characteristics of high current density, high field stability and small volume, which is in accordance with the development trend of MRI/NMR equipment for main magnet. In poor electromagnetic environment, however, quench detection of direct electrometric method based on threshold judgment is easily interfered by noise and severely disrupted quench signal may cause wrong quench determination and malfunction of quench protection, thereby resulting in unnecessary loss. To suppress the influence of the noises caused by current fluctuation and the rotation of motor on the correction of quench determination or accurate reading of data. Therefore, this paper compares and analyzes the experimental and filtering data detected by equipment based on wavelet de-noising algorithm, and verifies the necessity of using wavelet filtering data. [ABSTRACT FROM AUTHOR]

Once the miniaturization of high-performance magnetic resonance imaging (MRI) scanner was accomplished, extremely stringent indexes were needed for the magnetic field, the operational stability and mechanical strength. We adopted “No-insulation (NI) winding technology” to build high-temperature superconducting (HTS) magnets for 3-T grade MRI, in order to achieve these stringent indexes. To realize a compact size of 3-T MRI, the electromagnetic stress of HTS magnet becomes a technical challenge. In this paper, we investigated the construction of an electromagnetic stress reinforced structure for HTS magnets of 3-T MRI. First, the electromagnetic force was estimated, and the distributions of stress and strain induced by electromagnetic force in the winding part of the HTS magnet were reproduced using a finite element analysis. Meanwhile, the influences of the interlayers between sub-coils, shells and blind flanges on the stress property of HTS magnet were evaluated. Based on these results, the material and its consumed volume established the reinforced structure employed of the HTS magnet were also clarified. Finally, the utility of reinforced structure was verified for NI HTS magnets deployed in 3-T MRI. [ABSTRACT FROM AUTHOR]

For the design of superconducting magnets, the magnetic field and critical current distributions are usually calculated based on finite element software such as COMSOL, ANSYS, etc. These software are necessary for accurate structure modeling and field calculation, but they occupy large memory space and comsume long simulation time. Furthermore, they are not easy to use. To achieve an easy-to-implement solution for rapid magnet field and critical current calculations, this paper investigates three types of analytical calculating methods, and builds an autonomously-operated calculating application program (APP) for the uses in various superconducting magnets. [ABSTRACT FROM AUTHOR]

A simplified two-dimensional (2D) model, which takes the helical structure of the conductor on round core (CORC) cable into consideration, is utilized to analyze the electromagnetic and thermal properties of the cable. The model couples multi-physical fields through the JcBT(B,T) properties of the superconducting tape. We first introduced the modeling strategy and verified the validity of the 2D model. Then, considering the influence of thermal on the critical current of the tape, the cable loss under different conditions has been calculated. By changing the relative positions of the inner and outer conductor layers of the 2D model, the influence of the magnetic field on CORC cable loss can be obtained, and it can be extended to the periodic three-dimensional (3D) structure. [ABSTRACT FROM AUTHOR]

Based on existing quasi-isotropic strand (QIS) conductor and twisted stacked tape cable–cable in conduit conductor (TSTC-CICC), this paper proposed a novel QIS-CICC. The conductor was numerically modeled and the anisotropy of critical currents was analyzed. The simulations showed that although the critical currents of the QIS-CICC were worse than those of the TSTC-CICC for the self-field condition, the current decay of the QIS-CICC was far less than that of the TSTC-CICC under a 1 T external field, and the anisotropies of the two conductors were almost the same. [ABSTRACT FROM AUTHOR]

The Tri-axial high temperature superconducting (HTS) cable usually subjects to the impact of the fault currents in the power system. During the fault, a large amount of the Joule heat is generated, which may be damage cable. In this paper, an analysis model of electromagnetic thermal transient characteristics of the 10 kV/1 kA cable is built. The transient characteristics of the HTS cable are analyzed under a fault current of 15 kA rms lasting 0.14 s, and the current, resistance and temperature of the HTS cable are obtained. The maximum temperature of the HTS cable is 153.1 K under fault current. Meanwhile, the safe operating range of the HTS cable under the fault current of 15 kA to 25 kA is obtained. the analysis results will provide the theoretical basis for the quench protection and relay protection strategy of the tri-axial HTS cable in the Grid. [ABSTRACT FROM AUTHOR]

On the basis of 24 T magnet, the Institute of Plasma Physics, Chinese Academy of Sciences are developing 35 T all superconducting magnet. The magnet was designed as a combination of 20 T REBCO insert coil and a 15 T 150 mm low temperature superconductor background magnet. The 20 T insert coil consists of two coils nested together. NI winding technology is applied to coil 1 to increase its current density. The 50 μm thick Hastelloy tapes will be used to co-wind with REBCO tapes of the coil 2 to further improve its over-all mechanical strength. Electromagnetic analysis shows that the maximum ratio of operating current to the critical current of coil 1 and coil 2 is 0.63 and 0.37 respectively. A more accurate model for calculating strain considering screening current is under study. The inner joint is applied to the coil 1 to avoid in-plane bending of REBCO tape, and the detailed preparation method is given in the paper. The winding and preliminary testing of all double pancakes of coil 1 have been completed, and the winding of coil 2 is in progress. This magnet is planned to be assembled and tested in 2021. [ABSTRACT FROM AUTHOR]

Second-generation high-temperature superconductors, being brittle, need to be deposited on a substrate and converted to tapes with additional reinforcement layers. These tapes are wound on a core to make superconducting wires and cables. The mechanical loads during bending, twisting, winding, etc., can degrade the superconductor. It is necessary to determine the strain-induced during these processes. Variations in induced strain with bending of superconductors have been investigated analytically and numerically for various configurations of Rare-Earth Barium Copper Oxide (REBCO) tape. The numerical simulation has been carried out using COMSOL Multiphysics software; the analytical examination of the effect has been performed applying the Flexure formula. The geometrical configuration of the superconducting tape is varied in terms of the bending radius, the thickness of constituting layers made of Hastelloy and copper. The results showed that the variation in the thickness of the substrate has a large influence on the induced strain. Electrical performance analysis is also carried out using the power law of strain dependence and the 5% critical current degradation point is noted. Results of these numerical and analytical investigations are expected to help in finding out critical parameters to avoid degradation while being in use. [ABSTRACT FROM AUTHOR]

Glass Fiber Reinforced Plastic (GFRP) is usually employed as the insulator material of superconducting cable terminal, owing to its excellent mechanical properties and insulation strength at cryogenic temperature. However, in the presence of a void defect, both the insulation life span and mechanical strength of GFRP decrease significantly at superconducting temperature conditions. In this paper, efforts have been made to investigate the degradation process of GFRP at cryogenic temperature and give insight into its degradation mechanism. By comparing PD activities at 278.7 K, 223 K and 153 K in initial phase of aging, it is found that PDs are inclined to be inhibited at lower temperature. Experiments indicate that the deposited charge accumulation and mechanical properties degradation, instead of chemical aging and PD energy, play a crucial part in dielectric degradation. At cryogenic temperatures, the local heat accumulation brought by PDs increases the material internal mechanical stress, and the accumulation of deposited charges causes instantaneous energy release. On the basis of the decrease of the mechanical properties of the material, the crack expands rapidly, which leads to the dielectric failure of the material. In conclusion, the degradation of GFRP at cryogenic temperature is the result of the combined effects of deposited charge accumulation and mechanical properties decline. [ABSTRACT FROM AUTHOR]

A topological structure of 10 MW fully superconducting offshore wind turbine synchronous generator (FSWTG) is proposed, which stator and rotor windings are both composed with high temperature superconductors (HTS) in this paper. And an electrical design method is presented, which integrates the generator structure design, calculation analysis, and parameter optimization. It is all completed based on the electrical design method that the basic parameter design and the optimization of the number of poles, the pole pitch and the electrical load of the 10 MW FSWTG. Finally, the different design parameters are compared and analyzed for FSWTG, partial superconducting wind turbine synchronous generators (PSWTG: traditional armature winding + high temperature superconducting field winding) and the traditional wind turbine synchronous generators (WTG). The results show that the FSWTG has higher efficiency, lower weight and smaller size than those. [ABSTRACT FROM AUTHOR]

This paper analyses the current distribution in no-insulation (NI) coils in a layer-wound configuration. The investigation aims at comparing the electrical characteristic of two coils wound from the same BSCCO tape, with or without electrical insulation between turns. Both coils are characterized by a very similar geometry, with the same number of turns and layers. Both coils, cooled in liquid nitrogen bath, are charged until the tape critical current is exceeded. To interpret the measurements and analyze the current distribution within the winding, a lumped-parameter equivalent electrical circuit is developed and solved numerically in a time-varying regime. The model results are compared with the signals acquired through voltage taps soldered at the same locations in both coils. Finally, the model is applied to investigate the impact of the transverse contact resistance and to estimate the most stressed locations of the coil during charging, in terms of power produced by Joule effect. [ABSTRACT FROM AUTHOR]

Toward the practical development of high-voltage high-temperature superconducting (HTS) cables, high electrical insulation characteristics, and low dielectric loss become important. Dielectric loss drastically increases with the increase of operation voltage of HTS cables. Therefore, it is highly expected to find a novel insulating material with low dielectric loss for the high-voltage HTS cables. We have focused on Tyvek ^\circledR, polyethylene (PE) nonwoven fabric, and Tyvek ^\circledR/PE, a syntactic paper bonding PE-sheet on Tyvek^\circledR by heat, as low dielectric loss materials. In this paper, we investigated fundamental partial discharge inception characteristics and their mechanisms of Tyvek^\circledR immersed in liquid nitrogen (LN2).In addition, we compared the electrical insulation characteristics of Tyvek^\circledR, Tyvek ^\circledR/PE, and polypropylene laminated paper (PPLP^\circledR), and discussed their mechanisms. [ABSTRACT FROM PUBLISHER]

Critical current density is an important parameter reflecting power transmission capacity of HTS cable. Based on the superconducting energy pipeline, a tightly wound cable structure along arc of the pipeline is studied in this paper. Critical current density of electromagnetic thermal coupling is calculated and optimized superconducting cable structure is evaluated. Experimental results are useful to the design of high-temperature superconducting (HTS) cable in energy pipelines. [ABSTRACT FROM AUTHOR]

Trapped-flux magnets made of stacks of superconducting tapes are an interesting and important alternative to the application of rare-earth permanent magnets and trapping flux in bulk superconductors. Many applications, such as electric motors, can require the complex shapes of magnetic elements to combat issues such as demagnetization during the operation. Therefore, a reliable production technique of high temperature superconductor (HTS) stacks with different geometries is required to meet the needs of industry. In this article, a method of shaping the epoxy-glued stacks of superconducting tapes is proposed and investigated. The application of hot press allows to easily change the shape of the stack. The influence of shaping the stack on the density of trapped magnetic flux as well as critical current are presented. Experimental and numerical analyses are performed and their results are matched to find the change in the superconducting properties of the tapes. They show that with the proper process parameters the stacks can be shaped with only minor decrease of performance. However, strong degradation is observed if the applied force is too high. The observed problems are discussed and the possible solutions are proposed. [ABSTRACT FROM AUTHOR]

Presently, the high-speed electric machines with increased specific power are in the mainstream of research and are being developedworldwide. The high-temperature superconductor (HTS) machines allow improving the specific power even more significantly. The inductor generators are one of the perspective types of such machines. A new type of high-speed HTS electric machines is proposed in this paper. The proposed machine combines properties of generator with permanent magnets and inductor generator. In the rotor of this machine, permanent magnets are replaced by the stacks of HTS plates. In this case the HTS generator can be operated as an inductor iron-free HTS generator with combined excitation. This paper is devoted to the experiments and simulation of the proposed HTS generator. The experiment and simulation results prove the implementation of such design at three regimes: inductor, trapped-field, and combined excitation. The future development of the proposed HTS generators and perspectives of their application is discussed. [ABSTRACT FROM AUTHOR]

Flux pumps provide a contact-free method of energizing dc currents in superconducting coils. Since a predictive quantitative theory for dynamo-type flux pumps does not exist yet, the optimization of device designs must proceed through empirical experiment. In this paper, we investigate the effect of varying the annularwidth of the iron stator yokewithin a high-temperature superconducting dynamo. Reducing the dimensions of this iron yoke reduces the mass of cold iron within the dynamo, and hence has advantages in terms of weight, cryogenic efficiency, and eddy current losses. In this paper, we have investigated the dc output from an experimental high-temperature superconductor (HTS) dynamo in which the annular width of the iron yoke Δr is varied across a factor of four. Varying this dimension affects the reluctance of the magnetic circuit formed between the rotor and stator. We have shown that the dynamo output is surprisingly insensitive to the size of the iron yoke. The maximum current output (Isc ) is independent of Δr at all flux gaps. At the closest magnet-stator flux gap, a fourfold increase in Δr results in only a ~30% increase in the open circuit voltage (Voc ) and internal resistance (Rd) of the dynamo. Our results indicate that the smallest yoke studied (Δr = 6 mm) can be utilized with a 25.4-mm Nd-Fe-B rotor magnet, without adverse impact on the electrical performance of this type of HTS dynamo. [ABSTRACT FROM AUTHOR]

We have designed and built a novel high-temperature superconducting (HTS) flux pump device to charge a secondgeneration (2G) HTS double pancake coil (DPC). This device generates dc-biased ac travelling wave on sections of 2G HTS coated conductor (superconducting stator), which pumps flux into the superconducting closed loop formed by the DPC and superconducting stator. In this paper, we discuss the importance of the dc-biased field, ac travelling wave, and the travelling direction in the flux pump process, and how to control the magnetization of an HTS coil with the above factors. We have found that a pure ac travelling wave can only transport net flux into the superconducting closed loop in the presence of dc-bias field. The magnetization direction of the DPC can be reversed by reversing the dc-bias direction of the dc background field or travelling direction of the ac travelling wave. This paper shows the versatility and flexibility of this novel flux pump device in controlling the magnetization of the HTS coils, which will work as a wireless dc power source to help persistent current mode operation of a small-scaleMRI magnet built by HTS DPCs later in this project. [ABSTRACT FROM AUTHOR]

This paper reports the feasibility of the impregnation of no-insulation (NI) high-temperature superconducting (HTS) coils using solder. NI coils are widely studied and used in many situations. To utilize an HTS coil under high mechanical loads such as field coils for rotating machines, the HTS tapes must be stabilized mechanically. Epoxy impregnation is a common method to protect the HTS field from mechanical disturbances caused by the magnetic field and rotational vibration of the rotor to enhance the mechanical stability. However, traditional epoxy resins are electrical insulating materials which might cause the turn-to-turn contact resistance of NI coils to increase. Therefore, we proposed a new kind of impregnation method using the electrically conductive material, solder. Two coils were fabricated and tested for comparison. One is the NI coil without impregnation and the other is the NI coil impregnated with solder. The charge-discharge and sudden-discharge tests were performed in liquid nitrogen at 77 K. The experimental results were studied with equivalent circuit analyses. The results of this paper could provide useful data for the application of solder impregnated NI HTS coils. [ABSTRACT FROM AUTHOR]

Rare earth-based coated conductors have large ac magnetization losses, which hinder their use in a variety of applications. A common way to reduce these losses is by striating the superconductor into narrow filaments by means of laser ablation. Practical superconductors also need a sufficiently thick copper stabilization. The best way of creating copper-stabilized filamentized coated conductors is still to be found. In this paper, the ac magnetization losses of differently prepared 12 mm wide coated conductors manufactured by SuperOx were measured. The samples differ in terms of thicknesses of copper stabilization (5 and 10 \mu \textm), number of filaments (from 10 to 60), and order for copper deposition (filaments produced before or after electroplating the tape). The ac loss measurements were performed at 77 K in a wide range of frequencies of the external magnetic field, which allows determining the onset of coupling currents and the importance of the coupling losses. Complementary dc measurements of the transverse resistivity between filaments help to understand the path of the coupling currents. Thanks to the variety of tested samples and operating conditions, this paper provides a direct comparison of the two striation processes in commercially available high-temperature superconductor coated conductors. [ABSTRACT FROM PUBLISHER]

High-temperature superconducting (HTS) DC cables with the merits of light weight, large capacity and low loss provide a novel power transmission method for future utility grid. In this paper, the electromagnetic characteristics of unipolar and bipolar coaxial HTS DC cables are compared by finite element simulation. Besides, the 3D magnetic flux density distribution characteristics of HTS DC cable are obtained. The method to investigate the influence of winding angle on HTS DC cable magnetic flux density is also applied to 3D HTS DC analysis. [ABSTRACT FROM AUTHOR]

Modeling high temperature superconductor (HTS) motors remains challenging mainly due to the high aspect ratio of these conductors but also because of the properties of the magnetic materials. This article presents a 2-D time dependent model to assess the ac losses of superconducting motors based on the new T–A-formulation, which by using the finite-element method, allows its implementation in commercial software. The T–A-formulation computes the magnetic flux density with different Maxwell's equations depending on the areas of the motor and makes it possible to use the thin strip approximation i.e., the HTS tapes are modeled as infinitely thin lines. The model is then expected to tackle the high aspect ratio of the HTS as well as decreasing both the mesh complexity and the computing time. The first objective of the article is to validate the method in 2-D by evaluating the ac losses of a specific synchronous motor called superconducting torque motor; the computed results are compared with good agreements to those assessed with the minimum electromagnetic entropy production method, already validated. In a second part, the same losses are computed, taking into account the field anisotropy of Jc with the implementation of a dataset based on experimentally measured Ic at 65 and 77 K. With the model proposed in this article, it is possible to calculate the magnetic field of a whole electrical machine cross section and compute the ac losses in the individual tapes of its windings within the same numerical model. [ABSTRACT FROM AUTHOR]

The large magnetic fields that bulk high-temperature superconductors (HTS) can trap, enable us to develop high specific power electric machines. However, very few bulk HTS machine prototypes have been developed worldwide. To explore the potential of bulk HTS machines, we developed a 30-kW low speed radial-flux synchronous machine comprised of a conventional stator with ferromagnetic teeth. The rotor has four-field poles. Each pole is a rectangular array of QMG melt-growth GdBa2Cu3O7-δ bulk superconductors. The poles are cooled by a 150 W capacity neon thermosyphon, which maintains an operating temperature of around 30 K. The drawback of the ferromagnetic teeth, however, is their saturation and core losses under high and variable magnetic flux. Apart from high flux above 1 T, the trapped field profile of bulk HTS poles exhibits a nonsinusoidal shape, the harmonic components of which increase core losses. Such core losses are normally divided into hysteresis losses and eddy current losses, both of which depend on the magnitude and frequency of the trapped field. Hysteresis loss is associated with domain walls movement, while eddy currents are circulating currents induced in the core. In this paper, core losses in a ferromagnetic stator of the 30-kW machine are determined while the poles are magnetized to 2 and 3 T. The results show that core losses increase with increasing magnetic flux and rotor speed. Core losses due to rotor pole fields at the operating speed of 190 r/min were 1.2% and 1.9% of the machine rated output under 2 and 3 T magnetization, respectively. Finally, the harmonic content of the machine output voltage was obtained. [ABSTRACT FROM AUTHOR]

The YBa2Cu3O7-x (YBCO) coated conductor (CC) is one of the most promising superconducting materials because of their high critical current (Ic) and low dependency of the Ic on the external magnetic field. For superconducting applications, a large number of joints are required to join relatively short YBCO CC tapes. In this paper, we study the electromechanical behavior of lap-jointed YBCO CC tapes fabricated by etching Cu stabilizer at its service temperatures (77 K) under self-field. The effects of etching Cu stabilizer on Ic and joint resistance (Rj) of YBCO CC tapes were discussed. The Rj was reduced and the Ic values of the joints are consistent with the parent CCs tape by etching the Cu stabilizer. Preferable electrical properties under applying axial tension are achieved and proved by the axial tension tests and finite element simulations. This fabrication technique is a unique practicable solution to reduce joint resistance for YBCO CC tapes with thicker metal stabilizing layers and improving electromechanical performance in second generation high temperature superconductor (2G HTS) devices. [ABSTRACT FROM AUTHOR]

New technologies based on the use of High Temperature Superconductors (HTS) can lead to higher efficiency and more resilient energy systems. HTS applications are creating unique opportunities for promising commercial components that can enable the needed evolution of the energy system, such as high-capacity power cables, fault current limiters, high-efficiency generators for offshore wind turbines, energy storage, and innovative transformers. Not only do superconductor-based devices provide improvements over conventional electric grid technologies, they also offer unique alternatives to system challenges that cannot be addressed otherwise. This paper, developed by the International Energy Agency's Technology Collaborative Program on High Temperature Superconductivity, will explore the potential capabilities of HTS-based devices to advance the transformation of today's energy systems toward more a reliable, resilient, secure, affordable, flexible, and efficient regime. [ABSTRACT FROM AUTHOR]

Superconducting pulsed-power supply (SPPS) provides an efficient method for both high-density inductive energy storage and high current pulse generation. An SPPS consisting of eight high-temperature superconducting pulsed-power transformer (HTSPPT) modules with XRAM methodology was designed and simulated in preliminary studies. It recycled the leakage flux energy and reduced the voltage across the opening switch with a capacitor in primary. However, the SPPS with XRAM methodology has two problems. The first one is that it can provide high pulse amplitude, but cannot provide enough width. The other one is that the ratio of the maximum capacitive energy over the total inductive energy is relatively large, which cuts down the overall system energy density. This paper proposes a modified topology of SPPS with capacitor reuse methodology. Multiple HTSPPT modules are divided into several groups. Each group shares the same capacitor. The procedure of the modified SPPS is presented in detail. A 270-kJ SPPS with capacitor reuse methodology is designed and simulated to illustrate the modified topology. With the load parameters of a small railgun, the peak value of the load current is 207.15 kA and the pulse half-height width is 5.56 ms, the ratio of the maximum capacitive energy over the total inductive energy is 11%. The characteristics of the modified topology are also described in detail in this paper. [ABSTRACT FROM PUBLISHER]

AC losses in high-temperature superconductors are an important design parameter for large-scale power applications. It is often necessary to have a metallic containment vessel to house the superconducting element in a closed-loop cryogenic system. This, however, produces additional ac losses due to induced eddy currents in the walls of the vessel. This paper focuses on the investigation and understanding of the induced eddy current loss in the containment vessel. The total ac losses of a 1-m yttrium barium copper oxide coil were experimentally measured in three different containment vessels. The predicted eddy current loss from finite-element modeling combined with the measured superconductor hysteresis loss demonstrated good agreement with the experimental results. This paper also includes the implications for practical design of commercial cryostat containment vessel for superconductor power applications to minimize ac losses [ABSTRACT FROM PUBLISHER]

In this paper, the properties of current capacity and ac transport loss of striated high temperature superconductor (HTS) coil is compared with ordinary HTS coil by using both experimental and simulation methods. The measurements were carried out by transporting a sinusoidal varying current at 77 K, with an amplitude range of 10–50 A in frequency from 70 up to 300 Hz. Measurement facilities and methods are explained in more detail in the paper. The critical current of the 4-mm width multifilament coil made with four filaments at a spacing 0.03 mm was found to be lower than that of the nonstriated coil. The frequency dependent characteristics agreed well in both experimental and simulated results. Reducing ac loss of HTS is one enabling factor for widespread adoption of the technology, and therefore, understanding its characteristics is important and discussed in this paper. Future plans based on this preliminary work are the testing of multifilament tapes in an axial flux motor field environment. [ABSTRACT FROM PUBLISHER]