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This paper studies the magnetization mechanism of a hybrid high temperature superconducting (HTS) trapped field magnet. To address the size limitation of traditional HTS bulk materials, hybridization between HTS-stacked ring magnets and HTS bulks is proposed here. A jointless HTS-stacked ring magnet is used to increase the trapped field area for HTS bulks. A hybrid HTS magnet with 90 mm in length and 60 mm in width was tested to provide a trapped field of 7.35 T in a field cooling magnetization. The paper focuses mainly on understanding the novel magnetization mechanism of this hybrid HTS trapped field magnet. A numerical model based on homogenized H formulation was used to compare with experimental results, and a good match was found. Our experimental and numerical study of the electromagnetic interaction between the HTS-stacked ring magnet and the HTS bulks reveals that there are two magnetization stages, and the magnetization speed differs in these two stages by a sing criterion: whether the HTS-stacked ring magnet is fully penetrated or not. This study confirms that hybridization helps to build large HTS trapped field magnets. [ABSTRACT FROM AUTHOR]

Trapped field high-temperature superconducting (HTS) magnets have zero resistance and can maintain strong magnetic fields without external power supplies once properly magnetized. HTS-stacked ring magnets fabricated with commercial HTS tapes have demonstrated the ability to trap large and stable fields with more flexible sizes. However, during field cooling (FC) magnetization, the Lorentz forces and corresponding mechanical stress may cause damage to the magnets. Therefore, in this study, 3D numerical models are established and verified to investigate the stress and strain in HTS-stacked ring magnets. The stress distribution in the HTS-stacked rings under FC magnetization is calculated and the influence of sample fixation methods on the stress concentration and strain is discussed. The study also reveals that HTS stack inserts, which enhance the central trapped field, are subjected to unbalanced Lorentz force during magnetization, causing asymmetric stress distribution in the HTS stacks due to the asymmetric trapped field of the HTS-stacked ring magnets. These findings offer important insights into the mechanical behaviour of HTS-stacked ring magnets, which can guide the optimization of their design for various applications, such as nuclear magnetic resonance, Maglev, and HTS machines. [ABSTRACT FROM AUTHOR]

Background: Given its narrow treatment window, high toxicity, adverse effects, and individual differences in its use, we collected and sorted data on tacrolimus use by real patients with kidney diseases. We then used machine learning technology to predict tacrolimus blood concentration in order to provide a basis for tacrolimus dose adjustment and ensure patient safety. Methods: This study involved 913 hospitalized patients with nephrotic syndrome and membranous nephropathy treated with tacrolimus. We evaluated data related to patient demographics, laboratory tests, and combined medication. After data cleaning and feature engineering, six machine learning models were constructed, and the predictive performance of each model was evaluated via external verification. Results: The XGBoost model outperformed other investigated models, with a prediction accuracy of 73.33%, F-beta of 91.24%, and AUC of 0.5531. Conclusions: Through this exploratory study, we could determine the ability of machine learning to predict TAC blood concentration. Although the results prove the predictive potential of machine learning to some extent, in-depth research is still needed to resolve the XGBoost model's bias towards positive class and thereby facilitate its use in real-world settings. [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 (HTS) trapped field magnets can generate and maintain stable, high magnetic fields without requiring external power supplies. Recently, HTS-stacked ring magnets have garnered significant attention due to their flexible geometry, robust mechanical strength, and proven trapped field performance. In this study, we examine the magnetization characteristics of HTS-stacked ring magnets and observed a trapped field higher than the applied field during field cooling magnetization. We also observed that by inserting HTS stacks into the hollow cavity of the HTS-stacked rings, the center field ceased to exhibit an increased center field. Our analysis revealed that the unique induced current distribution and the penetration sequence are the underlying causes. Inspired by the investigation results, we explored deeper into the magnetization properties and identified that a final trapped field higher than the applied field can be achieved through proper design and magnetization of the HTS-stacked ring magnets. However, even though the trapped central field experiences an increase, this does not translate into an increment in the total trapped flux. Instead, a redistribution of the flux is observed. These findings hold significant implications for the design and application of superconducting magnets. [ABSTRACT FROM AUTHOR]

To explore the effect of grass and shrub plant roots on the stability of soil slopes in rainy areas in the south, this article relies on the Longlang Expressway construction project. Cynodon dactylon and Magnolia multiflora were selected as research subjects. The plant distribution characteristics and mechanical properties are analyzed. This paper uses ABAQUS finite element software to construct a 3D model of the planted slope in the test section. The stress and strain on the root system and the soil were observed, and the variation law of slope stability before and after plant protection under different rainfall events was compared and analyzed. The test and simulation results show that the root content of Cynodon dactylon gradually decreases with increasing depth. Cynodon dactylon was mainly distributed in the 0–30 cm soil body, and its effect on improving the cohesion of the soil body reached 75%. Magnolia multiflora belongs to vertical roots and has a strong and longer main root with relatively developed lateral roots. Its root system passes through the sliding surface of the slope bottom, which reduces the maximum equivalent plastic stress generated inside the slope by 61%. When the total rainfall duration is unchanged, under the three rainfall intensities of small, medium, and large, herbaceous plants increase the safety factor of the soil by 1.33%, 2.08%, and 6.1%, respectively, and the roots of shrubs increase the safety factor of the soil by 3.29%, 4.08%, and 4.32%, respectively. When the rainfall intensity does not change, as the rainfall time increases, the effect of plants on the slope safety factor first gradually increases and eventually stabilizes. The research results provide a reliable theoretical basis for analyzing the effect of plant roots on soil consolidation and slope protection, and they also lay a technical foundation for the promotion and application of ecological slope protection technology. [ABSTRACT FROM AUTHOR]

The inconsistency in the magnitude and phase variations among the receiving array elements in multibeam soundings can seriously affect the beam pattern characteristics, which reduces the array gain, increases the sidelobe level, and deteriorates the direction-of-arrival (DOA) estimation. The accuracy of the beamforming result may be improved by correcting for magnitude and phase variations among the array elements. Therefore, a novel estimation and correction method based on near-field focused beamforming is proposed to overcome deficiencies of the conventional methods. The magnitude and phase variation model and the corresponding influence on the direction-finding accuracy are analyzed. The near-field focused beamforming model is established for multielement systems, and the root-mean-square error (RMSE) method is used to determine the ideal-source incident angle for correction. We construct the receiving signal covariance matrix in the frequency domain and further estimate the magnitude and phase variations in each array element. The performance and effectiveness of the proposed method are verified by simulations and small anechoic tank experiments. The proposed method requires the employment of a rotation platform that provides necessary rotation information and, thus, can accurately and effectively estimate and correct for variations in the magnitude and phase response of elements in the receiving array. The experimental results show that the sidelobe level can be reduced by approximately 3 dB after the array is corrected, and the angle deviation is reduced by approximately 1.0°. [ABSTRACT FROM AUTHOR]

Theoretical and experimental AC loss data on a superconducting pancake coil wound using second generation (2 G) conductors are presented. An anisotropic critical state model is used to calculate critical current and the AC losses of a superconducting pancake coil. In the coil there are two regions, the critical state region and the subcritical region. The model assumes that in the subcritical region the flux lines are parallel to the tape wide face. AC losses of the superconducting pancake coil are calculated using this model. Both calorimetric and electrical techniques were used to measure AC losses in the coil. The calorimetric method is based on measuring the boil-off rate of liquid nitrogen. The electric method used a compensation circuit to eliminate the inductive component to measure the loss voltage of the coil. The experimental results are consistent with the theoretical calculations thus validating the anisotropic critical state model for loss estimations in the superconducting pancake coil. [ABSTRACT FROM AUTHOR]

Growing electricity demand from a range of sources and the changes of the power grid structures open the possibility of more frequent and much higher fault current. Traditional solutions to the fault are difficult to satisfy the requirement of the new power grid due to many factors, such as high cost, additional impact to power grid in normal loading condition, which leads to the research for an efficient alternative solution of interest to both academia and industry: Superconducting fault current limiter (SFCL). In this paper, two types of low-inductance solenoidal coils, the braid type and the nonintersecting type, are built with 2G high-temperature superconductors. The current limiting performance, the recovery characteristics, and the ac losses of both types of coils are tested and compared in detail. Experimental results show that both types of coils can effectively limit fault current and recover in several seconds. Furthermore, comparison between the ac losses of both types of SFCLs shows that the ac loss of the braid type coil is lower than that of the single tape by about an order of magnitude in low-current regions. [ABSTRACT FROM PUBLISHER]

In this paper, a 220-V resistive superconducting fault current limiter (SFCL) prototype is built and tested under different prospective fault currents, which vary from 0.8 to 7.4 kA. A 2D superconductor model is integrated into an experimental circuit model in COMSOL to simulate the performance of the SFCL prototype in the experimental system in fault tests. In the simulation, a new E- J relationship is proposed to enhance the convergence of calculation. Comparison between simulation results and experimental results shows that the proposed model performs well in simulating current limiting performance of SFCL in experimental system in case of fault. [ABSTRACT FROM AUTHOR]

Since high temperature superconducting magnetic energy storage system (HT SMES) has attracted significant attention for their fast response in milliseconds, high efficiency (cyclic efficiency over 95%) and unlimited times of charging and discharging cycles, it can be used for system stabilizing – damping out low frequency power oscillations. A voltage source converter (VSC) based HTS SMES has been optimal designed for achieving a high efficiency and has been constructed by China Electric Power Research Institute (CEPRI). This SMES can store the maximum energy, while for the first time used two states of art high temperature superconductors, YBCO and BSCCO tapes. It has been tested in a 110 kV transmission power system by a dynamic power fluctuation compensation experiment using three different controlling strategies in CEPRI. The experimental output powers with these three strategies are compared and the results show that the SMES can trace the power variation and provide the required power to restrain the power fluctuation in milliseconds successfully. Finally, the application planning of SMES with the equivalent capacity in a practical renewable power system at Zhangbei wind power test base is evaluated by a case study based on the PSCAD/EMTDC simulation. An optimal switch time of the SMES in wind power system is presented using the real transmission parameters of Zhangbei power grid. This study can provide a reference for the demonstration of large-scale SMES systems in renewable power system. [ABSTRACT FROM AUTHOR]

In this paper, the use of magnetic materials to divert flux in high-temperature superconductor superconducting coils and reduce transport ac loss is investigated. This particular technique is preferred over other techniques, such as striation, Roebel transposition, and twisted wires because it does not require modification to the conductor itself, which can be detrimental to the properties of the superconductor. The technique can also be implemented for existing coils. The analysis is carried out using a coil model based on the \bf H formulation and implemented in comsol multiphysics. Both weakly and strongly magnetic materials are investigated, and it is shown that the use of such materials can divert flux and achieve a reduction in transport ac loss, which, in some cases, is quite significant. This analysis acts to provide a foundation for further optimization and experimental work in the future. [ABSTRACT FROM PUBLISHER]

This paper presents the design of an AC loss experiment using nitrogen boil-off method. This experiment is aimed at exploring the AC loss of HTS double race-track coils which will be installed on the rotor of a wind turbine generator. The operating environment is simulated by designing a cryostat with rotating magnetic field windings. Apart from the fact that the alternating magnetic field causes most of AC loss on the HTS coils, we also believe that the DC background field would be another important factor causing AC loss if the HTS coil is experiencing by both alternating magnetic field in the perpendicular direction and DC background field in the parallel direction. In order to perform the boil-off measurement, we present the method to estimate the heat leakage in the cryostat which might cause errors to the measurement . [ABSTRACT FROM PUBLISHER]

AC loss can be a significant problem for any applications that utilize or produce an AC current or magnetic field, such as an electric machine. The authors are currently investigating the electromagnetic properties of high temperature superconductors with a particular focus on the AC loss in coils made from YBCO superconductors. [ABSTRACT FROM AUTHOR]

This paper begins with introducing the winding techniques of two superconducting double-pancake coils wound using 2G coated conductors. These winding techniques are able to guarantee a good performance for the superconducting coils. Then the coil critical currents were measured and compared with a simulation model. The results were consistent. Finally the coil AC losses were measured using an experimental circuit including a compensation coil. The simulation results are close to the experiment results. [ABSTRACT FROM AUTHOR]

Abstract: This paper gives a introduction of a SMES unit using 2G HTS wires. A complete SMES system including both superconducting coils and control circuit has been designed to operate at 77K. Three single-phase H-bridge converters have been used in the control circuit. A loop control signal is sent out by using 32 fixed point Digital Signal Processor (DSP). The complete circuit has been both modelled in simulation and built experimentally. The results validate that this SMES successfully compensates a voltage sag in a power system. [Copyright &y& Elsevier]

Objective [ABSTRACT FROM AUTHOR]

Abstract: Purpose : In systemic lupus erythematosus (SLE), a disease of immune complex (IC) deposition, interleukin-10 (IL-10) is thought to promote B-lymphocyte hyperactivity and autoantibody production. Both ICs and Toll-like receptor (TLR) ligands have been shown to stimulate the production of IL-10 by human monocytes. Using an in vitro model, we studied how IC solubility, complement activation products, and TLR ligands could affect IL-10 production by human monocytes stimulated with ICs. Methods : Human monocytes were stimulated with soluble or insoluble heat-aggregated human IgG with or without TLR ligands or C5a. Cytokine levels in cell culture supernatants were measured by ELISA. To study cytokine signaling, cell lysates were analyzed by Western blot for total or tyrosine-phosphorylated STAT3. Results : Insoluble ICs were most effective at stimulating production of IL-10, and costimulation LPS enhanced synthesis of IL-10. In addition, stimulation with insoluble ICs together with C5a enhanced the production of IL-10 by 2–4 fold in either the presence or absence of TLR ligands. Increased STAT3 phosphorylation correlated temporally with enhanced IL-10 production and was reduced by an IL-10 receptor blocking antibody, suggesting that IL-10 was responsible for observed STAT3 phosphorylation. Conclusions : Because the immune deposits of SLE are, by definition, insoluble; and because IL-10 is thought to be important for B-cell hyperactivity and autoantibody production, these observations provide a critical link, bridging current views of B-cell hyperactivity with the early concept that SLE may arise from defective clearance of immune complexes. [Copyright &y& Elsevier]

To improve the ecological protection of coal gangue slopes, this work developed a polymer curing agent using a pure acrylic emulsion and cement as the main raw materials. By testing the workability, waterproofing, durability, and adhesion of the curing agent with different polymer-to-cement ratios, the optimum mixing ratio of the polymer curing agent was obtained, and the protection mechanism was analysed based on the test results and by scanning electron microscopy (SEM). Then, simulated slope and practical engineering applications were carried out. The results show that pure acrylic emulsion curing agent with a polymer-to-cement ratio of 6 : 5 is most suitable for the ecological protection of coal gangue slopes. The polymer curing agent can form a network structure film layer with a good waterproofing effect on the coal gangue surface. Simultaneously, the network structure film layer can reduce the influence of weathering and leaching on the coal gangue, prevent the heavy metal elements in coal gangue from entering the surrounding soil, improve the growth environment of plants, and improve the effect of ecological restoration. This research can be applied to the ecological protection of coal gangue slopes. [ABSTRACT FROM AUTHOR]

Second-generation high-temperature superconductors (2G HTS) have high current density in very high magnetic fields. They are good candidates for high field magnets, especially when the magnetic field exceeds the critical fields of low-temperature superconductors. However, the thin and flat geometry of these conductors allows persistent screening currents (or shielding currents) to flow in the conductors. The screening currents caused by the ramping of applied current to the coil is identified as the self-field screening effect. The screening-current-induced magnetic field changes the magnetic field distribution of the magnet, and it also generates drift. This paper employs both experimental and numerical methods to study the mechanism of self-field screening currents for 2G HTS magnets. A 2G HTS magnet was constructed and tested, and a finite element model was built based on the magnet. The comparison between calculation and measurement is presented with detailed analysis. Current distributions inside the HTS magnet are calculated to illustrate the effects of screening. The screening-current-induced magnetic field is quantified by comparing the magnetic field distribution with a baseline copper model. The model is also used to explain the mechanism of the current sweep strategy, which can be used to effectively eliminate screening currents. [ABSTRACT FROM AUTHOR]

This study examines the use of superconducting magnetic and battery hybrid energy storage to compensate grid voltage fluctuations. The superconducting magnetic energy storage system (SMES) has been emulated by a high-current inductor to investigate a system employing both SMES and battery energy storage experimentally. The design of the laboratory prototype is described in detail, which consists of a series-connected three phase voltage source inverter used to regulate ac voltage, and two bidirectional dc/dc converters used to control energy storage system charge and discharge. “DC bus level signaling” and “voltage droop control” have been used to automatically control power from the magnetic energy storage system during short-duration, high-power voltage sags, while the battery is used to provide power during longer term, low-power undervoltages. Energy storage system hybridization is shown to be advantageous by reducing battery peak power demand compared with a battery-only system, and by improving long-term voltage support capability compared with an SMES-only system. Consequently, the SMES/battery hybrid dynamic voltage restorer can support both short-term high-power voltage sags and long-term undervoltages with significantly reduced superconducting material cost compared with an SMES-based system. [ABSTRACT FROM AUTHOR]

Summary: The promotion of the heat transfer by ferro‐nanofluid under a magnetic field has caught more extensive attention in the field of nuclear industry and energy engineering. Firstly, a modified model based on the Buongiorno model was proposed to investigate the heat transfer considering the Kelvin force in the presence of an inhomogeneous magnetic field to elevate the heat transfer performance of nanofluid using thermomagnetic convection. Secondly, the influence of Kelvin force, thermophoresis, and Brownian motion of nanoparticles on the heat transfer at a moderate Reynolds number was investigated. The numerical results indicate that the chaotic convection induced by the Kelvin force and the thermophoretic effect are much important factors. Thirdly, the numerical results demonstrate that the NSN and NSN/SNS arrangements of magnets should be the preferential selection. Besides, the more powerful magnetic field and greater volume fraction of nanoparticle can produce better heat transfer performance. Finally, the discussions on the underneath mechanisms for heat transfer augment are conducted, and it can be concluded the thermomagnetic convection induced the combination of the magnetic effect and thermophoretic effect may be the key mechanism. [ABSTRACT FROM AUTHOR]

Flux-pinned interaction between high T superconductors (HTSs) and an applied magnetic field provides a new, no-contact interface approach that can be used in docking and assembling process of space module systems. Unlike operations on the Earth, the magnetization of the HTS happens in orbit which differs from the traditional field cooling (FC) magnetization, and the additional field has to be used to magnetize the HTS in advance and make it produce a self-stable force in the interacting process with the interfacing magnet. This paper presents a type of superconducting interface structure configuration consisting of bulk HTSs, actuation electromagnets and interfacing magnets, and discusses the effects of different magnetization conditions on the quasi-static force interaction between the HTS and the interfacing magnet. Primary experiments show that the HTS after pre-magnetization can show self-stable force behavior, which often happens in the traditional FC magnetization, and the self-stable force is further enhanced with the increase of the pre-magnetizing current. Multi-pulse field magnetization after the pre-magnetization is also applied to raise the trapped field strength ( B) of the superconductor. The results show that B is added with the increasing number of the pulsed field, and the corresponding self-stable force properties are also improved. Therefore, the pre-magnetization combined with the pulsed field magnetization can enhance the flux trapping in the HTS and bring more stable force for the superconducting interface structure. [ABSTRACT FROM AUTHOR]

In order to generate volumetric underwater acoustic images, planar arrays are often used to collect the signals coming from a 3-D scene in underwater environment. These acquired signals are commonly processed using the 2-D conventional beamforming method. The 2-D conventional beamforming is robust and the most commonly used method. However, the 2-D conventional beamforming suffers from fat beams and high-level sidelobes. High-resolution beamforming, based on the inverse of the signal covariance matrix, such as minimum-variance distortionless response, produces narrow beamwidth and low sidelobe levels but is sensitive to signal mismatch and requires many snapshots of data. In order to overcome the above-mentioned limitations, this paper applies a 2-D deconvolution algorithm to the 2-D conventional beamforming result of planar array in order to improve the beamwidth and suppress the high-level sidelobes. The 2-D deconvolved beam power produces narrow beams, and low sidelobe levels without compromising the robustness of 2-D conventional beamforming. The 2-D deconvolution algorithm provides higher output signal-to-noise ratio than the 2-D conventional beamforming for isotropic noise. The vector extrapolation method is improved to make it applicable on two-dimensional data. The detailed implementations of the original 2-D deconvolved beamforming and the efficient 2-D deconvolved beamforming are presented. Simulations and experiments are conducted to validate the performance of the proposed method. [ABSTRACT FROM AUTHOR]

The high critical current density of second-generation high-temperature superconducting (2G-HTS) tapes is the result of the systematic optimisation of the pinning landscape for superconducting vortices through careful engineering of the size and density of defects and non-superconducting second phases. Here, we use scanning Hall probe microscopy to conduct a vortex-resolved study of commercial GdBaCuO tapes in low fields for the first time and complement this work with "local" magnetisation and transport measurements. Magnetic imaging reveals highly disordered vortex patterns reflecting the presence of strong pinning from a dense distribution of nanoscale Gd2O3 second-phase inclusions in the superconducting film. However, we find that the measured vortex profiles are unexpectedly broad, with full-width-half-maxima typically of 6 μm, and exhibit almost no temperature dependence in the range 10–85 K. Since the lateral displacements of pinned vortex cores are not expected to exceed the superconducting layer thickness, this suggests that the observed broadening is caused by the disruption of the circulating supercurrents due to the high density of nanoscale pinning sites. Deviations of our local magnetisation data from an accepted 2D Bean critical state model also indicate that critical state profiles relax quite rapidly by flux creep. Our measurements provide important information about the role second-phase defects play in enhancing the critical current in these tapes and demonstrate the power of magnetic imaging as a complementary tool in the optimisation of vortex pinning phenomena in 2G-HTS tapes. [ABSTRACT FROM AUTHOR]

As air traffic has been increasing in recent years, the environmental impact of aviation is more obvious, forcing governments to impose stringent regulations on emissions. In order to meet these regulations, and reduce the carbon footprint, research has been directed towards the all-electric and hybrid aircraft, where the use of cryogenic HTS machines and cables has been proposed to reduce the overall size of the aircraft. With the cryogenic system already in place, research has been exploring the use of power electronics at lower temperatures in order to obtain systems with higher power densities and lower losses. In this paper several power semiconductor devices are tested at room and cryogenic temperature in order to evaluate their performance at lower temperature. One of the tested devices, a “CoolMOS” superjunction MOSFET, is used in a single voltage source phase-leg which is experimented with at room and cryogenic temperature to evaluate its efficiency as a primary indication of its usefulness in the All-Electric Aircraft. [ABSTRACT FROM AUTHOR]

One of the most promising applications for high temperature superconducting (HTS) material is magnet. HTS magnet is considered to be used in a wide range of applications including MRI, particle accelerator, electrical machine, and etc. HTS rotating machines are mainly utilized for cryo-electrification, i.e. application of superconductivity for modern electrification. One of the main aspects of cryo-electrification is electric aircraft application which is recently enabled by continuous progress in design development of superconducting magnets and HTS machines. This paper discusses the challenges facing a newly developed magnet type, i.e. HTS ring magnet, that being considered in superconducting rotating machine in future electric aircrafts. HTS ring magnet is compact, easy to develop, fault tolerant, and light in weight, and it recently reached to a high level of magnetic field. [ABSTRACT FROM AUTHOR]

It is of great industrial interest and academic importance to investigate current harmonics impacts on AC losses of superconductors, especially in large-scale power devices. However, only effect of amplitude of in-phase current harmonics on AC loss has been studied in the works of literature. We numerically characterized nonsinusoidal AC loss of superconducting tape carrying harmonic currents with orders below 20th versus phase angles. A drastic AC loss variation was found when phase angle was considered for harmonic components. We observed that different harmonic orders show different AC loss profile versus phase angle. [ABSTRACT FROM AUTHOR]

The second-generation high-temperature superconductor REBCO is one of the most valuable candidates that meet the requirements of future magnetic confinement fusion device. Quench behavior of an improved high-current REBCO composite conductor is simulated by a 1-D finite element method. Indium-tin alloy foil placed in the gap between stabilizer, jacket, and superconducting tape stacks can significantly reduce thermal contact resistance, which leads to an increase on the minimum quench energy of composite conductor. Short perturbations have a better response to this improvement than long perturbations, due to the low normal zone propagation velocity (NZPV) of REBCO conductor. For short perturbation (perturbation length ($l_{p}$  = 0.1 m), the peak temperature in cable and helium drops 12.76 and 17.99%, respectively, after soldered. Due to the change of heat transfer in a composite conductor caused by helium wave propagation, the development and maximum length of normal zone significantly decrease from 13.06 to 4.78 m under long perturbation ($l_{p}$  = 10 m) circumstance. High current REBCO composite conductor with proper indium-tin alloy soldered can enhance the stability and safety of composite conductors under severe working conditions, but it also slows down the NZPV and hinders the quench detection of high-temperature superconducting magnet. [ABSTRACT FROM AUTHOR]

Fully superconducting machines provide the high power density required for future electric aircraft propulsion. However, superconducting windings generate AC losses in AC electrical machine environments. These AC losses are difficult to eliminate at low temperatures, and they add an extra burden to the aircraft cooling system. Due to the heavy cooling penalty, AC loss in the HTS stator is one of the key topics in HTS machine design. In order to evaluate the AC loss of superconducting stator windings in a rotational machine environment, we designed and built a novel axial-flux high temperature superconducting (HTS) machine platform. The AC loss measurement is based on the calorimetric boiling-off of liquid nitrogen. Both total AC loss and magnetisation loss in the HTS stator are measured under the condition of a rotational magnetic field. This platform represents a key element in studying ways to minimise AC losses in an HTS stator, in order to maximise the efficiency of fully HTS machines. [ABSTRACT FROM AUTHOR]

Application of high-temperature superconducting devices become promising in power networks, and transportation, including ship, train, and electric aircraft propulsion systems, with the advantages of light weight, compact size, and high efficiency, compared to conventional devices. In reality, electric networks—either in grid or transportation propulsion system—are polluted with harmonics due to the widespread use of power electronic devices and nonlinear loads. It is essential to explore the dependency of harmonic ac losses of different coil configurations carrying nonsinusoidal current. We modeled and compared harmonic ac loss behaviors in three coil configurations, single pancake coil (SPC), double pancake coil (DPC), and solenoid coil (SNC), where SPC and SNC are wound by identical wire length and DPC has twice conductor number compared to SPC. The research work has been carried out by means of H-formulation finite element method in a 2-D axisymmetric modeling environment of COMSOL Multiphysics. We explored and reported ac losses in these three coil structures carrying nonsinusoidal current with the third and the fifth harmonic orders, respectively, under different total harmonic distortion (THD) and fundamental current levels. It has been concluded that ac loss in these coils first decreases with the increase of the third harmonic content, when THD of the third harmonic <0.2; and increase with the increase of the third harmonic when THD >0.2. AC loss in coils monotonically increases with the increase of the fifth harmonic, drastically. We found that ac loss in SPC carrying the third harmonic and the fifth harmonic at different THD are more than 3.8 times of that in DPC; ac loss in SPC carrying either third or fifth harmonics at different THD are around 4.5 times of that in SNC. [ABSTRACT FROM AUTHOR]

With significant interest in the use of high‐temperature superconducting (HTS) components in electric aircraft, there is a need for novel modelling techniques that allow architecture‐level studies of the electrical systems including HTS components. In this study, a simple electric network architecture, as proposed in the literature has been considered, which includes generators, dynamic propulsion load and cables. This electric network has been modelled considering conventional technology and using HTS cables by replacing the conventional copper cables, to evaluate the variations in the network performance. The network performance has been studied for the dynamically varying propulsion load, which is nearly equivalent to the aircraft load over the entire flight duration. Following this, electric faults have been applied at various locations, and the impact of HTS cables on the network fault levels has been evaluated. The fault current levels are compared using both conventional and HTS cables, due to the fault current limiting properties of the HTS cables, they are observed to offer lowered fault current values. [ABSTRACT FROM AUTHOR]

This paper presents the modeling of second generation (2 G) high-temperature superconducting (HTS) pancake coils using finite element method. The axial symmetric model can be used to calculate current and magnetic field distribution inside the coil. The anisotropic characteristics of 2 G tapes are included in the model by direct interpolation. The model is validated by comparing to experimental results. We use the model to study critical currents of 2 G coils and find that 100 μV/m is too high a criterion to determine long-term operating current of the coils, because the innermost turns of a coil will, due to the effect of local magnetic field, reach their critical current much earlier than outer turns. Our modeling shows that an average voltage criterion of 20 μV/m over the coil corresponds to the point at which the innermost turns' electric field exceeds 100 μV/m. So 20 μV/m is suggested to be the critical current criterion of the HTS coil. The influence of background field on the coil critical current is also studied in the paper. [ABSTRACT FROM AUTHOR]

Highlights • Experimental platforms for two kinds of charging methods are demonstrated. • Charging performance on different types of loads is analyzed. • The results show that charging NI HTS coil is much slower than charging INS HTS coil. Abstract How to charge high-temperature superconducting coils is a crucial problem for superconducting magnets. In recent years, flux pump is recommended as a promising method for current compensation since it can charge coils without electrical contact to current source. In this work, two types of charging methods, rotating magnet based flux pump and magnetically controlled persistent current switch, are discussed experimentally and numerically. Their output characteristics were tested and demonstrated. Charging performance on different types of loads including insulated HTS coil, no-insulation HTS coil and DC current source, is analyzed and compared. Results of this paper will prove the validity of those two charging methods in future superconducting magnet applications. [ABSTRACT FROM AUTHOR]

This study proposes a hybrid energy storage system (HESS) composed of the superconducting energy storage system (SMES) and the battery. The system is designed to compensate power fluctuations within a microgrid. A novel control method is developed to share the instantaneous power between the SMES and the battery. The new control scheme takes into account the characteristics of the components of the HESS, and the battery charges and discharges as a function of the SMES current rather than directly to the power disturbances. In this way, the battery is protected from the abrupt power changes and works as an energy buffer to the SMES. An new hardware-in-loop experiment approach is introduced by integrating a real-time digital simulator (RTDS) with a control circuit to verify the proposed hybrid scheme and the new control method. This paper also presents a battery lifetime prediction method to quantify the benefits of the HESS in the microgrid. A much better power sharing between the SMES and the battery can be observed from the experimental results with the new control method. Moreover, compared to the battery only system the battery lifetime is quantifiably increased from 6.38 years to 9.21 years. [ABSTRACT FROM AUTHOR]

Frequency dynamics, occurring due to the high penetration of the renewable energy in the microgrid (MG) are of great concern to the system dynamic stability. The battery energy storage systems are reported to have a good frequency regulating ability in the off-grid microgrid systems. However, to compensate the power irregularities, the battery is needed to charge and discharge at a high frequency, which degrades its lifetime significantly. In addition, in the primary frequency control (PFC) the battery needs to deal with the abrupt power changes, which will also accelerate the battery degradation process. In this regard, this paper presents a new concept of primary frequency control by integrating the superconducting magnetic energy storage (SMES) with battery, thus achieving the ability of not only performing a good frequency regulating function but also extending the battery service time. A novel power sharing method using the dynamic droop factors to control charge/discharge prioritization between the SMES and the battery is proposed and has been proved to have a better operation than the preceding droop control. A microgrid system based on the case of Uligam Island of Maldives is developed in the PSCAD, verifying the performance of PFC with the hybrid energy storage system (HESS) using the dynamic droop control. The results show that the HESSs have a better frequency regulating ability and the proposed dynamic droop control is capable of exploiting the different characteristics of both SMES and battery, forming a kind of complementary hybrid energy storage system. Moreover, the battery in the new control scheme is better protected from the short-term frequent cycles and abrupt currents, hence has been proved to have a longer lifetime extension. [ABSTRACT FROM AUTHOR]

An MJ-class superconducting magnetic energy storage (SMES) system has a wide range of potential applications in electric power systems. The composite high-temperature superconducting HTS conductor, which has the advantages of carrying large critical currents and withstanding high magnetic fields, is suitable for winding an MJ-class magnet coil. However, the Lorentz force of an HTS wire is so large that its induced mechanical stresses should be examined to ensure that the magnet is in good condition. By means of the equivalent material properties method and the sequential coupling method, this paper studies the mechanical properties of a three MJ toroidal SMES magnet wound by a composite HTS conductor. Based on the electromagnetic-structural coupling analysis, the Von-Mises stress, the radial stress, and the hoop stress of a magnet coil are calculated and employed to validate the stability of the MJ-class toroidal SMES magnet. [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]

Voltage source converter based HVdc (VSC-HVdc) systems are prone to high short-circuit current during transmission line faults. The situation for multiterminal HVdc (MTDC) systems is worse. The characteristics of superconducting material are ideal to limit the fault current in HVdc systems. This paper presents a novel use of the resistive type of superconducting fault current limiter (SFCL) in the MTdc network with the function of limiting the high current. The working principles of fault current limiter and a three-terminal HVdc system are modeled in detail using PSCAD/EMTDC software. The hybrid operation of the SFCL in the three-terminal HVdc system is tested in this paper for the fault response of the MTdc system. The performances of SFCL under different fault conditions are analyzed. The simulation results show that the fault current is effectively restrained and the SFCL can act as an efficient protective device for VSC-based multiterminal HVdc systems. [ABSTRACT FROM PUBLISHER]

A coaxial cable made out of helically wound 2G HTS tapes is being widely implemented based on its low critical bending radius, ease of manufacturing and installation. Though the design technique is mature, the cable still lacks standard Ic definition. With increased usage of such cables, robustness in its operation is expected. HTS tapes are highly sensitive to externally applied mechanical stress and strain values. These limitations force the coaxial cables to be operated at 50–75% of its rated capacity. One of the major problems in coaxial cable design is the contact resistance of the tapes with the terminal, which affects the current distribution among different tapes in the same layer. Further current redistribution at constant intervals helps the applied current in bypassing the localized faults in the individual HTS tapes, thus making efficient use of the major length of the tape. This paper proposes the use of voltage shunts between HTS layers at constant intervals for regular current redistributions along the length of the cable. This method significantly helps to sustain the Ic value of the cable, even if it has got several minor defects in the tapes. [ABSTRACT FROM PUBLISHER]

The energy balancing problem is the main challenge for the effective application of micro combined heat and power (m-CHP) in a residential context. Due to its high energy density and relative robustness, the lead-acid battery is widely used for power demand management to compensate the mismatch between the m-CHP electrical output and domestic demand. However, batteries are not suited to respond effectively to high frequency power fluctuations, but when coupled to the m-CHP, they experience frequent short-term charge/discharge cycles and abrupt power changes, which significantly decreases their lifetime. This paper addresses this problem by hybridising the lead-acid battery storage with superconducting magnetic energy storage (SMES) to form a hybrid energy storage system (HESS) that is coordinated by a novel sizing based droop control method. The control method for the first time considers both the capacity sizing of the HESS technologies and the droop control method of the battery and the SMES. A hardware in the loop test circuit is developed coupling with the real time digital simulator (RTDS) to verify the performance of the HESS with the new control algorithm. The experimental results show that control method is able to exploit the different characteristics of the SMES and the battery to meet the mismatch of m-CHP power generation and domestic demand. In addition, the lifetime analysis is implemented in this paper to quantify the battery lifetime extension in the HESS, which further proves the validity of the proposed control strategy. [ABSTRACT FROM AUTHOR]

A single pancake coil without turn-to-turn insulation was tested in this paper to investigate the transient responses under different situations. We performed charging and discharging test, AC current test, and regional quench emulation test on the non-insulated (NI) coil. The experimental test results show a significant time delay for charging and discharging characteristics of NI coil and can be validated by a simple proposed equivalent electrical circuit. Under the AC operating current, the NI coil can bypass nearly all the AC current from the coil spiral path to the radial path such that it is not possible for NI coil to store or be affected by the AC magnet field. Additionally, while carrying AC current, the AC loss dissipation of NI coil is inversely proportional to the frequency of the AC operating current. When a regional quench occurs, the NI coil can bypass the current in the regional quench zone to avoid further temperature accumulated and protect the NI coil itself. [ABSTRACT FROM AUTHOR]

High capacity energy storage units are desirable to maintain power system stability in the presence of power disturbances produced by renewable energy sources and fluctuating load profiles. Battery energy storage systems may be used to smooth power flow, however, the frequent, deep charge and discharge cycling required dramatically reduces battery service life. A hybrid energy storage system (HESS) using battery energy storage with superconducting magnetic energy storage (SMES) is proposed to mitigate battery cycling while smoothing power flow. A HESS power sharing control method based on the novel use of droop control is proposed. This is able to control charge/discharge prioritization and hence protect the battery from high power demand and rapid transient cycling. A sizing strategy is proposed for the battery and SMES which overcomes the oversizing problem. A hardware implementation is used to assess the control and SMES sizing methods for short time scale HESS operation. A dynamic off-grid sea-wave energy conversion system is simulated to assess the performance of the HESS over a longer time scale. A battery lifetime model which takes into account both battery life cycles and discharge current rate is used to estimate battery lifetime extension. A lifetime increase of 26% is obtained for the HESS design example investigated. [ABSTRACT FROM AUTHOR]

Electric Vehicles (EVs) have been suggested as alternatives to conventional vehicles for reducing petrol consumption and carbon dioxide (CO 2 ) emissions. When a large number of EVs connect to the grid, they can cause a large amount of power loss. Where to install multiple charge stations in the grid, so as to mitigate losses caused by EVs when providing energy to those EVs, is becoming vitally important. In this paper, a distribution test-network model is described. A new analytical method is proposed, using the stations’ cooperation in terms of optimal active and reactive power dispatch as well as power flow analysis for locating the optimal placement of charge stations, so as to reduce power losses. This method is compared with the previously developed current density method for single charge stations using system simulation results. It was demonstrated that the methods proposed in this paper are more accurate than the current density method, and that 17% of the average active power loss can be saved for three different types of load profile. In addition, 27% of the average active power loss was saved by installing two charge stations rather than no charge stations in the test-line. It is shown that this could represent a 2.6% annual yield above inflation for investing in installing and running such charge stations. [ABSTRACT FROM AUTHOR]

The magnetic AC losses of monofilament Sr 0.6 K 0.4 Fe 2 As 2 /Ag tapes are measured in the temperature range between 20 K and 30 K both in perpendicular and parallel field. The loss, measured by the standard magnetization technique, is determined from the area of the hysteresis loop using a vibrating sample magnetometer (VSM) in a cyclic field of amplitude up to 7 T. The results in perpendicular field are compared to that of the parallel-field loss and theoretical calculation of magnetization loss at various temperatures. There is a reasonable agreement between the theoretical model and the experimental results even in high field. The magnetic critical current density (  J c ) of the tape, obtained by the magnetic hysteresis measurements M ( H ), are investigated in two field directions and in the temperature range from 5 K to 30 K. The comparison between the magnetic J c in both field directions and the transport J c of the tape are also done at various temperatures and fields. The anisotropy of J c ( Γ = J c a b / J c c ) is very small. [ABSTRACT FROM AUTHOR]

In off-grid wind energy systems, batteries often undergo frequent charge/discharge cycles, which reduce battery service life. In addition, due to motor start and other high ‘inrush current’ loads batteries undergo high rates of discharge which also degrade battery life. In this paper, a superconducting magnetic energy storage and battery hybrid energy storage system is proposed, which is beneficial in reducing battery short term power cycling and high discharge currents. To demonstrate system performance, a representative off-grid wind power system model is described in detail which incorporates turbulent wind variations, load variations and energy storage systems. To estimate battery lifetime improvement, a novel battery lifetime model is described, which quantifies the impact of both the number of charge/discharge cycles and also the effect rate of discharge. The model is validated using previously reported data. This work advances previous studies by describing the estimated improvement in terms of battery life in a wind energy conversion application by use of superconducting energy storage and by presenting a novel method for doing so. In addition, the proposed battery lifetime model can be potentially used in other applications. [ABSTRACT FROM AUTHOR]

In the power grid, the cold dielectric hightemperature superconducting (CD HTS) cable frequently subjects to overcurrents caused by the shortcircuit fault. During the fault, a large amount of Joule heat is generated. The heat causes the temperature of the HTS cable to rise and leads to the transition of the HTS cable from superconducting state to normal state which would influence the current carrying capacity of the HTS cable seriously. An algorithm has been proposed to calculate the transient current distributions of superconducting layers in fault conditions. This method couples an equivalent circuit model and a thermal model. So the temperature distributions in HTS cable is obtained based on the heat generated by the fault current. Finally, the current and temperature distributions of a 110 kV/3 kA CD HTS cable are investigated with a fault current impact of 25 kA for 3 s. The results show that the currents of the conducting layers decrease while the temperature increases in the HTS cable and the former withstands most of the fault current impacts. The current in the former of the HTS cable changes from zero to about 90 % of the fault current. A current diversion effect in the HTS cable is obvious. The conclusions provide the basis for the protection strategy of superconducting cable considering fault current impact and will be a benefit to the stable operation of a superconducting transmission grid. [ABSTRACT FROM AUTHOR]

HTS cable is an emerging technology for electricity power transmission. It is very important to set up an accurate and easy-to-build measurement system to characterize HTS cables. In this paper, a novel measurement system has been developed to measure the ac losses for a prototype HTS cable using cancelation coil technique. This system is based on the National Instrument Data Acquisition card. It can also be used to measure the critical current and current distribution in the prototype cable. The prototype cable has been innovatively designed using an improved particle swarm optimization algorithm which is more computationally efficient than conventional methods. The measurement system will be improved further by introducing an elaborate pre-amplifier prior to data collection process and the result will be compared with theoretical calculations for validation. [ABSTRACT FROM PUBLISHER]

Abstract: High-temperature superconducting magnetic energy storage systems (HTS SMES) are an emerging technology with fast response and large power capacities which can address the challenges of growing power systems and ensure a reliable power supply. China Electric Power Research Institute (CEPRI) has developed a kJ-range, 20 kW SMES using two state of art HTS conductors, BSCCO and YBCO tapes. This SMES system is used to compensate a power drop and a fluctuation in order to damp low frequency oscillations to increase stability of a power system. This paper presents an optimized design of the SMES system to achieve a maximum energy capacity. A voltage source converter using IGBTs is built and can be used to control the power flow between the SMES system and external circuits. A control system using a digital signal processor (DSP) and micro-programmed control unit (MCU) is constructed. SVPWM pulse modulation is used as a control strategy. The whole system was experimentally tested for compensation of power fluctuation within milliseconds in a dynamic power system simulation laboratory. The result validates the design and control circuit, and more importantly, the application capability of SMES systems in a power grid. [Copyright &y& Elsevier]

A high temperature superconducting magnetic energy storage system (HT-SMES) is constructed using YBCO coated conductor and is integrated with a cryogenic system using sub-cooled LN2. A closed loop control algorithm, based on the digital signal processor (DSP) TMS320F2812, is proposed using the 2G HT-SMES to compensate dynamic voltage sag in power systems. A dynamic simulation experiment for compensation of instantaneous voltage sag is achieved. The experiment circuit is built using a signal conditioning circuit, a DSP controlling circuit, a power conversion circuit and a SMES unit. Analysis of the voltage waveforms before and after compensation validates that this SMES system is able to compensate instantaneous voltage sag. [ABSTRACT FROM AUTHOR]