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High-temperature superconductor (HTS) bulks have demonstrated extremely intriguing potential for industrial and commercial applications due to their capability to trap significantly larger magnetic fields than conventional permanent magnets. The magnetic field in electrical rotating machines is a combination of alternating and rotational fields. In contrast, all previous research on the characterization of electromagnetic properties of HTS have solely engrossed on the alternating AC magnetic fields and the associated AC loss. This research paper gives a thorough examination of the AC loss measurement under various conditions. The obtained results are compared to the finite element-based H-formulation. The AC loss is measured at various amplitudes of circular flux density patterns and compared with the AC loss under one-dimensional alternating flux density. The loss variation has also been studied at other frequencies. The findings in this research paper provide more insights into material characterization, which will be useful in the design of future large-scale HTS applications. [ABSTRACT FROM AUTHOR]

Over time, high-temperature superconductor (HTS)-coated conductors (CCs) have proven to be promising candidates for future high-efficiency and high-power density electrical machines. However, their commercialization is handicapped due to the AC dissipative loss that occurs upon exposure to external magnetic fields. In rotating electromagnetic devices, the external magnetic field is a combination of alternating and rotating magnetic fields. Most of the research is devoted to the effect of exposure of the superconductors to alternating magnetic fields only. This article presents an investigation to observe the behavior of HTSCCs under rotating magnetic fields, particularly the AC loss, using a finite-element-based homogeneous H-formulation technique. Our investigation shows that the AC loss could be considerably high when HTSCCs are exposed to rotating magnetic fields and, ultimately, could affect the cooling efficiency of future high-efficiency and high-power density electrical machines. [ABSTRACT FROM AUTHOR]

When the high-temperature superconducting (HTS) REBCO (rare-earth barium copper oxide) coil is applied in a power system, a large amount of heat may be generated due to the short-circuiting of the system, resulting in the thermal instability of the coil. Moreover, under complex working conditions, the oscillating external magnetic field will further aggravate the coil quench. In this paper, the electromagnetic–thermal coupling model is used to analyze the loss, current distribution and temperature distribution of the REBCO coil under short-circuit fault conditions and oscillating external magnetic fields. In order to get closer to the actual situation, the modeling of the superconducting tape adopts the real tape structure, and the resistivity of the superconductor is described by the modified E-J relationship. Four cases are considered for the oscillating external magnetic field, i.e., sine, triangle, sawtooth and square cases. This model has certain significance as a reference for understanding the thermal stability of coils in extreme cases. [ABSTRACT FROM AUTHOR]

High-temperature superconducting materials have shown great potential for the design of large-scale industry applications. However, they are complicated under AC conditions, resulting in penalties such as power loss or AC loss. This loss has to be considered in order to design reliable and efficient superconducting devices. Furthermore, when superconductors are used in rotating machines, they may be exposed to rotating magnetic fields, which is critical for the design of such machines. Existing AC loss measuring techniques are limited to measuring under one-dimensional AC magnetic fields or transport currents. Therefore, it is essential to develop and investigate robust experimental techniques to investigate the loss mechanism in HTS machines. In this paper, a new and novel experimental technique has been presented to measure AC loss in rotating magnetic field conditions. The loss under rotating magnetic fields is measured and compared by numerical modeling methods, and the results show a strong correlation with the numerical modeling and show the effectiveness of the experimental setup. [ABSTRACT FROM AUTHOR]

High-temperature superconductor (HTS) bulks have shown very promising potential for industrial applications due to the ability to trap much higher magnetic fields compared to traditional permanent magnets. In rotating electrical machines, the magnetic field is a combination of alternating and rotating fields. On the contrary, all studies on electromagnetic characterization of HTS presented in the literature so far have only focused on alternating AC magnetic fields and alternating AC loss due to the unavailability of robust experimental techniques and analytical models. This paper presents a numerical investigation on the characterization of HTS bulks subjected to rotating magnetic fields showing AC loss, current density distribution in three-dimensional axes, and trapped field analysis. A three-dimensional numerical model has been developed using H-formulation based on finite element analysis. An HTS cubic sample is magnetized and demagnetized with two-dimensional magnetic flux density vectors rotating in circular orientation around the XOY, XOZ, and YOZ planes. [ABSTRACT FROM AUTHOR]

The evolution from low-temperature superconductors (LTSs) to high-temperature superconductors (HTSs) has created a great amount of opportunities for superconducting applications to be used in real life. Dynamic voltage is a special superconducting phenomenon, and it occurs when the superconductor takes a DC transport current while simultaneously exposed to an AC magnetic field. The dynamic voltage is crucial for some superconducting applications as it is the energy source by which to energise the load, such as flux pumps. This article investigates the missing aspects that previous studies have not deeply exploited: the optimisation of energy efficiency for the dynamic voltage in an HTS tape with different working conditions (e.g., currents and magnetic fields). First, the mechanics of superconducting dynamic voltage were explicated by typical analytical solutions, and the modelling method was validated by reproducing the behaviours of the Bean model and analytical solutions of dynamic voltage. After the feasibility of the modelling was proved, in-depth modelling was performed to optimise the energy efficiency of an HTS tape with different DC transport currents and AC magnetic fields. Owing to the physical limitations of the superconducting tape (e.g., quench), a safe operating region was determined, and a more delicate optimisation was performed to discover the optimal operating conditions of the HTS tape. The novel conceptualisation and optimisation approaches for the superconducting dynamic voltage in this article are beneficial for the future design and optimisation of superconducting energy/power applications under complicated electromagnetic conditions. [ABSTRACT FROM AUTHOR]

Different from many superconducting magnet designs based on the analytical algorithm and finite element method (FEM), this article presents an intelligent design of the SMES and high-field magnet using the self-programmed graphical user interface (GUI). As the important basis, the analytical solutions of SMES magnet are developed for calculating the magnetic field, inductance and critical current, whose accuracies are also verified by the experiment. Then, the analytical solutions are merged into the GUI tool with multi-window interface based on the MATLAB. The new platform is built to offer scientists and engineers a smart tool to design and optimize SMES magnets to reach the maximum energy capacity. After the structural optimization of a MJ-class SMES magnet, the critical current and energy capacity improve by 20.46% and 38.67%, respectively. Compared to previous superconducting magnet designs, this new platform for the SMES and high-field magnet design has the advantages of diverse HTS tape/magnet structure selections, user-friendly interface, automatic optimization, and fast speed. [ABSTRACT FROM AUTHOR]

When a superconductor is exposed to an AC magnetic field whilst carrying a constant DC transport current, a DC electrical resistance can be observed, commonly referred to as “dynamic resistance”. This dissipative effect can play a critical role in many potential high-temperature superconducting (HTS) applications, especially for the AC-field-actuated HTS switch, which is the key component in the HTS transformer-rectifier flux pump (TRFP). The characteristics of the HTS switch determine the performance and reliability of TRFP. In this paper, we report a numerical study of a new HTS switch design made of series-connected YBCO stacks. This study aims to obtain insights into the characteristics of dynamic resistance and power loss, including their relationships with the amplitude and the frequency of the AC magnetic field. The energy conversion efficiency of the HTS switch is also investigated. This work will help design a high-performance AC-field-actuated HTS switch. [ABSTRACT FROM AUTHOR]

A comprehensive study of the quench properties of single laminated wires having a double-layered superconducting structure is presented. In particular, we have focused on the influence of the angle and intensity of an external magnetic field perpendicular to direction of the applied current on the minimum quench energy (MQE) and normal zone propagation velocity (NZPV) values. We conclude that strong changes on the NZPV are mainly determined by the intensity of the applied current, while the orientation and magnitude of the applied field have a less but not negligible impact on the resulting NZPV. The quench parameters are also reported for the case when the applied current is considered as a constant parameter in which case the MQE has been found to reach a maximum value when the in-field critical current is the largest. [ABSTRACT FROM AUTHOR]

Experimental and advanced superconducting Tokamak (EAST) was designed by the Institute of Plasma Physics Chinese Academy of Sciences. The magnet system of EAST includes poloidal field (PF) coils, central solenoid (CS) coils, and toroidal field coils. The heat generated by the ac losses of PF and CS coils increases the burden of the cooling system, which reduces the critical current of the superconducting cable. Once the superconducting magnet quenches, it will pose a serious threat to the stability of the whole device. In this paper, the piecewise linear method and the finite-element analysis were used to analyze the ac loss of the EAST PF and CS coils under the specific operating current. The whole calculation process is described in detail. The final results meet the stability margin of the design of the EAST device. Meanwhile, the ac losses of PF and CS coils for EAST are theoretically evaluated in terms of the structure of magnet, the simplified current, and the distribution of the coil. The results of this paper not only provide data support for the next design and experiment of the EAST device, but provide some references for similar calculation of other large nuclear fusion magnets. [ABSTRACT FROM AUTHOR]

High temperature superconductor (HTS) is becoming more and more attractive for the application in high field magnets, which can be utilized in the magnetic resonance imaging (MRI) and rotating machines. To charge the HTS magnets and operate them in persistent current mode, a persistent current switch (PCS) is very necessary. This paper will focus on how to build a fast persistent current switch controlled by ac magnetic field. The PCS can present a large resistance rapidly compared with conventional PCS and recover to zero-resistance in a short recovery time. Impacting factors and strategy to control the proposed PCS are discussed. An experimental system is built and tests are carried out to verify the practicality of the proposed PCS. [ABSTRACT FROM AUTHOR]

This paper presents the optimization on the strength and homogeneity of magnetic field from superconducting Halbach Array magnet. Conventional Halbach Array uses a special arrangement of permanent magnets which can generate homogeneous magnetic field. Superconducting Halbach Array utilizes High Temperature Superconductor (HTS) to construct an electromagnet to work below its critical temperature, which performs equivalently to the permanent magnet based Halbach Array. The simulations of superconducting Halbach Array were carried out using H -formulation based on B -dependent critical current density and bulk approximation, with the FEM platform COMSOL Multiphysics. The optimization focused on the coils’ location, as well as the geometry and numbers of coils on the premise of maintaining the total amount of superconductor. Results show Halbach Array configuration based superconducting magnet is able to generate the magnetic field with intensity over 1 Tesla and improved homogeneity using proper optimization methods. Mathematical relation of these optimization parameters with the intensity and homogeneity of magnetic field was developed. [ABSTRACT FROM AUTHOR]

This paper presents the design and modeling of a second-generation (2G) high-temperature superconducting (HTS) magnet, which is suitable for Lorentz force electrical impedance tomography (LFEIT). The concept of constructing a superconducting magnet using the configuration of a Halbach array is proposed, which can achieve a favorable thin geometry for the LFEIT system, and is able to build a homogeneous magnetic field with high intensity. The modeling of this superconducting Halbach array magnet has been executed by COMSOL Multiphysics. \boldsymbolH-formulation together with \boldsymbolB-dependent critical current density and bulk approximation are used as the basic tools for modeling. Results reveal that this magnet can achieve over 1-T magnetic field in the cross section required. The optimization of HTS coils' location and different numbers of coils are carried out to balance the strength and homogeneity of magnetic field. [ABSTRACT FROM PUBLISHER]

The dynamic voltage is a unique phenomenon of superconducting materials. It arises when the superconductor is carrying a DC transport current and spontaneously in subject to an AC magnetic field. This study excavates the aspects that previous studies have not comprehensively investigated: the dynamic voltage in a DC-carrying superconducting tape exposed to different oscillating AC magnetic fields. First, the fundamental physics of dynamic voltage/flux of superconductors is reviewed and further analysed in detail. We used the superconducting modelling method using the H-formulation merged into the finite-element method (FEM) software, to re-produce the typical dynamic voltage behaviour of a superconducting tape. The modelling was verified by both the analytical and experimental results, in order to precisely prove the reliability of the modelling. Afterwards, the modelling was performed for a DC-carrying superconducting tape under four different oscillating magnetic fields (sine, triangle, sawtooth and square), and their corresponding dynamic voltages and energy losses were analysed and compared. Results show the sinusoidal magnetic field can lead to the optimal combination of reasonable dynamic voltage but relatively lower loss, which is suitable for those superconducting applications requiring dynamic voltage as the energy source, e.g., flux pumps. This article presents novel investigation and analysis of the dynamic voltage in superconducting materials, and both the methodology and results can provide useful information for the future design/analysis of superconducting applications with DC transport currents and AC magnetic fields. [ABSTRACT FROM AUTHOR]

The high-temperature superconductor (HTS) has been recognised as one of the most up-and-coming materials thanks to its superior electromagnetic performance (e.g., zero resistance). For a high-speed maglev, the HTS magnet can be the most crucial component because it is in charge of both the levitation and the propulsion of the maglev. Therefore, a fundamental study of HTS magnets for maglev is crucial. This article presents the fundamental design and modelling of the superconducting magnet for a high-speed maglev, including mechanics, electromagnetics, and loss analysis during instability. First, the measurements of the superconducting wire were performed. The HTS magnet was primarily designed and modelled to fulfil the basic electromagnetic requirements (e.g., magnetic field) in order to drive the maglev at a high speed. The modelling was verified by experimental tests on a scale-down HTS magnet. A more professional model using the H-formulation based on the finite element method (FEM) was built to further investigate some deeper physical phenomenon of the HTS magnet (e.g., current density and loss behaviours), particularly in situations where the high-speed maglev is in the normal steady state or encountering instability. [ABSTRACT FROM AUTHOR]

When a type-II superconductor, exposed to a perpendicular alternating magnetic field, carries a direct current, a biased dc voltage response can occur. The response voltage can be classified into dynamic-resistance voltage and flux flow voltage according to its triggering mechanism. Experimental results for the phase differences of the two types of voltage have been provided in the paper. Harmonic analysis on the voltage response has been carried out to differentiate the two types of the response voltages. Based on analyzing the experimental data, a useful and flexible real-time method using the ratio of the dc component to the second harmonic component of the voltage response has been proposed to serve as a monitor indicating the state of dc-carrying HTS tapes subject to an ac magnetic field. The method is promising in the application of complex superconducting systems such as flux pumps, persistent current switches, superconducting cables and dc fault current limiters. [ABSTRACT FROM AUTHOR]

When a REBCO tape carrying DC transport current is exposed to a perpendicular AC magnetic field with amplitude above certain value, flux could be triggered to traversing the superconducting tape. During the process, a biased DC response voltage, called the dynamic resistance voltage will be induced. In the paper, the calculation on the time-dependent dynamic resistance voltage was carried out by the H -formulation model implemented in the finite-element method (FEM) software package COMSOL Multiphysics. Fourier analysis on the waveform of dynamic resistance voltage was utilized to figure out the main components of the response voltage. The DC component, second harmonic component and ratio of the two components can reflect how the instantaneous dynamic resistance responds to the applied AC magnetic field and the DC transport current. The findings in the paper can be used to monitor the state of DC-carrying REBCO tapes subject to an AC magnetic field. [ABSTRACT FROM AUTHOR]

• A numerical model of periodically arranged HTS tapes using the finite element method (FEM). • Distributions of the magnetic field and current of HTS tapes by periodical arrangements. • Differences between the FEM results and analytical models from periodically arranged HTS tapes. • Mathematical models for the AC loss in periodically arranged HTS tapes. • An effective method to optimize the electromagnetic environment for periodically arranged HTS tapes and estimate the AC loss. The practical operation of a high-temperature superconducting (HTS) tape to form a HTS device is strongly related to the HTS tape electromagnetic environment in the device. With regard to the HTS tapes commonly stacked for practical applications, it is necessary to study the electromagnetic interaction of the proximity HTS tapes to design and optimize the HTS tapes and devices. This paper presents a numerical model of periodically arranged HTS tapes using the finite element method (FEM). The numerical method has been developed to build the equivalent periodical arrangement of infinite HTS tapes and applied to simulate two basic arrangements, horizontal and vertical periodical arrangements. The magnetic field and current distributions of HTS tapes by periodical arrangements have been investigated. The effects on critical current with different arrangements have been illustrated. It is found that the Y-stack can reduce the current carrying capacity while the X-array can increase that in comparison to a single tape. The differences between the FEM results and analytical models have been analysed and also compared with the Norris model. The two mathematical models derived for AC loss prediction have shown higher accuracy than the existing analytical models. This study presents an effective method to optimize the electromagnetic design by considering favorable structure or environment for the stacked HTS tapes and estimate the AC loss, shows the phenomenon of central tapes in an HTS array, which could be further used in performance analysis of superconducting devices, e.g. HTS transformers. [ABSTRACT FROM AUTHOR]