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In this article, a novel non-uniform gap optimization method was proposed for high-current stacked HTS conductors. The proposed configuration was easy for fabrication, but also resulted in good electromagnetic performance. The experiment matched the modeling regarding the critical currents of different stacked HTS conductors, and they presented the optimal critical currents was by the non-uniform gap optimization. After proving the reliability of modeling, the zero gap and non-uniform gap stacked conductors with 15 HTS tapes were comprehensively evaluated with respect to the critical current, AC loss, and fault tolerance. Compared with zero gap stacked HTS conductor, the critical current of the stacked HTS conductor by the non-uniform gap optimization increased by 5%, while the AC loss was reduced by 30%, and the temperature rise due to fault was reduced by 50%. Overall, the stacked HTS conductors with novel non-uniform gap optimization can carry reasonably high currents, with less loss and better fault tolerance. [ABSTRACT FROM AUTHOR]

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]

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]

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]

Benefiting from the high critical temperature and high critical current, the second-generation high-temperature superconducting (HTS) tape is widely used in various large-scale magnet applications. Due to the length limitation of producing superconducting tapes, the joints between superconducting tapes are inevitable for large-scale high-field magnets. The joule loss from the joint resistance under over-current conditions is even larger, which will cause a sharp temperature rise, and will also decay the critical current of the superconducting tape. In this paper, 3 configurations of HTS joints are adopted to model the joint resistance characteristics using new methods, whose joint resistance model is coupled with the real-time operating temperature. The results show that the proposed temperature-dependent HTS joint resistance model well matches the experiment and analytical solution. Therefore, both the experiment and novel modeling investigation can provide useful and accurate references for the superconducting joints in real devices, and the temperature-dependent HTS joint resistance model can play an important role in giving early warnings of the over-current for HTS tapes and high-field magnets. [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 conductor on round core (CORC) cable wound with second-generation high-temperature superconducting (HTS) tapes is a promising cable candidate with superiority in current capacity and mechanical strength. The composing superconductors and the former are tightly assembled, resulting in a strong electro-magnetic interaction between them. Correspondingly, the AC loss is influenced by the cable structure. In this paper, a 3D finite-element model of the CORC cable is first built, and it includes the complex geometry, the angular dependence of critical current and the periodic settings. The modelling is verified by the measurements conducted for the transport loss of a two-layer CORC cable. Subsequently, the simulated results show that the primary transport loss shifts from the former to the superconductors as the current increases. Meanwhile, the loss exhibited in the outer layer is larger than that of the inner layer, which is caused by the shielding effect among layers and the former. This also leads to the current inhomogeneity in CORC cables. In contrast with the two-layer case, the simulated single-layer structure indicates stronger frequency dependence because the eddy current loss in the copper former is always dominant without the cancellation of the opposite-wound layers. The core eddy current of the single structure is denser on the outer surface. Finally, the AC transport losses among a straight HTS tape, a two-layer cable and a single-layer cable are compared. The two-layer structure is confirmed to minimise the loss, meaning an even-numbered arrangement makes better use of the cable space and superconducting materials. Having illustrated the electro-magnetic behaviour inside the CORC cable, this work is an essential reference for the structure design of CORC cables. [ABSTRACT FROM AUTHOR]

With regard to the state-of-the-art technologies in the fields of applied superconductivity and electromagnetic devices, research and development highlights are presented. The recent progress and achievement described with principle and technical details include mainly i) applied superconducting materials; ii) superconducting magnets and their applications such as in ITER and Tokamaks; iii) high Tc superconducting (HTS) magnetic levitation and applications; iv) HTS smart grids; v) superconducting and electromagnetic material modelling and characterization; and vi) advanced electromagnetic devices. The applied superconductivity technology and availability are especially focused and verified with the trend of development prospection. [ABSTRACT FROM AUTHOR]

Taking the advantage of quench behavior, high-temperature superconductors (HTS), such as YBCO tapes, are gradually used in the resistive superconducting fault current limiters (RSFCLs) for the direct current power system. However, due to the high cost, as well as the mechanical vulnerability, the complexity of HTS still remains. In this article, first YBCO tapes were sustained under different pressures, and then the transient characteristics of the tapes were tested under a huge pulsed current. Results show that while applying pressures on YBCO tapes, the resistance would increase significantly. Thus, a new approach to increase the quench resistance of RSFCLs was proposed, which could potentially reduce the consumption of YBCO tapes and cut down the cost. [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 concept of using horizontally parallel HTS tapes with AC loss study, and the investigation on possible wireless power transfer (WPT) applications. An example of three parallel HTS tapes was proposed, whose AC loss study was carried out both from experiment using electrical method; and simulation using 2D H -formulation on the FEM platform of COMSOL Multiphysics. The electromagnetic induction around the three parallel tapes was monitored using COMSOL simulation. The electromagnetic induction and AC losses generated by a conventional three turn coil was simulated as well, and then compared to the case of three parallel tapes with the same AC transport current. The analysis demonstrates that HTS parallel tapes could be potentially used into wireless power transfer systems, which could have lower total AC losses than conventional HTS coils. [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]

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]

• Economic and cashflow analysis of HTS SMES and hydrogen in smart grids. • Energy storage fleet run using novel algorithm with maximal time to fail. • Time evolution, reliability and capacity credit using Monte Carlo model. • Results show a capacity credit and reliability improvement of 30 % and 9 %. High Temperature Superconducting (HTS) Magnetic Energy Storage (SMES) devices are promising high-power storage devices, although their widespread use is limited by their high capital and operating costs. This work investigates their inclusion in smart grids when used in tandem with hydrogen fuel cells and other energy storage devices using a novel two-stage model. The first stage presents a stochastic allocation algorithm to optimally size the smart grid assets with the maximum expected profit. The next stage models the time system evolution with these optimal capacities using a dynamic Monte Carlo model to investigate the system reliability, capacity credit and loss of load expectation. A novel energy management algorithm is also presented that maximises the time with which a fleet of energy storage devices can fulfil a stochastically unknown power request. The analysis shows that from a purely economic standpoint, HTS SMES and hydrogen energy do not achieve high penetration levels (up to 10 %) due to their high costs, although the penetration levels can be improved with higher power imbalance penalties in day ahead markets. The novel capacity credit and reliability investigation shows that they can improve the reliability and capacity credit of wind turbines by approximately 30 %, thereby improving potential wind penetration levels. The optimal energy management algorithm improves the fleet lifespan and reliability by up to 9 % depending on the connected capacity. [ABSTRACT FROM AUTHOR]

• Numerical modeling of HTS stacked conductors with defective tapes. • Effects of various defective tapes on critical currents and AC losses. • Conductors with defects need proper redundancy and safety allowance. The numerical modeling of HTS stacked conductors was performed with different quantities and locations of defective tapes. The effects of various defective tapes on the overall critical currents, current distributions, and AC losses were studied. Results show the more defective tapes and the higher defect grades were, the larger degradations of critical currents would be. If the quantity of defective tapes was 10, compared with the non-defect case, the AC loss increased by 62% in Scenario A (defective tapes increasing from outside to inside), increased by 24% in Scenario B (defective tapes increasing from inside to outside), and increased by 48% in Scenario C (defective tapes increasing from top to bottom). Therefore, to overcome the issues on current-carrying capability and AC loss, adding reasonable redundancy and safety allowance for HTS tapes, overall critical currents and cryogenic systems is necessary. Overall, this article presents novel analysis and results, which are useful for the future designs of HTS high-current stacked conductors/cables. [ABSTRACT FROM AUTHOR]

• At a high fault current, the transport current in the tape will be shunted. • The losses of the two kinds of structural tape under different fault currents show obvious differences. • The temperature rise of type B tape is smaller at same fault current, and it has a relatively better fault tolerance. In this paper, the electromagnetic-thermal coupling numerical model is used to study the loss and temperature distribution of two typical high temperature superconducting (HTS) coated conductors (CCs) under short-circuit fault, as well as the dynamic evolution law with time. The electromagnetic module adopts the widely used H -formulation, and the thermal module adopts the general form of heat conduction equation. The coupling between the two module is realized by using the loss calculated by the electromagnetic module as the heat source of the thermal module and combining the J c0 ( B , T) relationship. A modified E - J relation suitable for any current density range is used to describe the resistivity of superconductors. Due to the difference of magnetic and thermal properties of the two kinds of structural tape substrate materials and geometric dimensions of copper stabilized layer, the losses of the two kinds of structural tape under different fault currents show obvious differences. At low fault transport current, the magnetic substrate of type B tape (NiW substrate) will obviously make the magnetic flux density perpendicular to the superconducting layer greater than that of type A tape (Hastelloy substrate), thus making the loss of type B tape greater. Under the condition of high fault transport current, the fault current will be shunted between different layers of the tape. Type B tape has a thicker copper stabilizer, which makes the current density of type B tape copper layer lower than that of type A tape, and the temperature rise and loss of type B tape are lower. Specifically, when I p / I c0 is less than about 0.65, the total loss of type A tape is less than that of type B tape. When I p / I c0 is greater than about 0.65, the total loss of type A tape is greater than that of type B tape. [ABSTRACT FROM AUTHOR]

• The total AC loss of the coil assembly of the coupled iron core is greater than that of the uncoupled iron core coil. • At a lower transport current, the iron loss introduced by the flux diverter will increase the AC loss of the coil assembly. • At a higher transport current, the flux diverter plays a positive role in reducing the AC loss of the coil assembly. High temperature superconducting (HTS) coil coupled with iron core can be widely used in superconducting power equipment such as superconducting motor, superconducting current limiter, superconducting transformer and so on. The AC loss of HTS coil decreases the efficiency and reliability of superconducting machines, and also brought severe challenges to the cryogenic system. The introduction of iron core will have a negative impact on the AC loss of superconducting coil, and the iron core itself will also produce iron loss, which will affect the overall efficiency of the system. It is considered that the additional flux diverter at the end of the coil can effectively reduce the AC loss of the coil. However, whether this method is effective for the HTS coil coupled with iron core has not been studied. Therefore, this paper focuses on the influence of flux diverter on the AC loss of HTS coil coupled with iron core by H -formulation. The results show that the iron loss of flux diverter plays a leading role in the coil assembly at low transport current, and the introduction of flux diverter plays a positive role in reducing the total AC loss of coil assembly at high transport current. [ABSTRACT FROM AUTHOR]

With the rapid global developments of digital economy and internet-based technologies, the ultra-dense high-efficiency energy distribution and supply are becoming urgently essential for the data centers that contain large amounts of information-technology (IT) equipments. Considering the limitation of current-carrying capacity and huge ohmic loss of the conventional copper busbars, this paper presents a novel solution using high-temperature superconductor (HTS) DC busbars for data centers with the ultra-high current-carrying capacity and compact size. The full layouts of 3-grade HTS busbars are designed in accord with the industrial standards of date centers. The economic analysis on different busbar schemes for a 10 MW class data center is carried out. For the 100 V/100 kA scheme, the ratio of total operating cost (HTS busbars/copper busbars) can be down to 0.11. With the consideration of the power supply unit (PSU) conversion efficiency, the benefit-turnover period can be reduced from approximately 23 to 17 years. A general design guideline (technical design and economic analysis) is made for building HTS busbar networks in high-dense data centers. Overall, the novel design, technical evaluation and economic analysis of the superconducting DC busbar network can provide useful information and potential solutions for the future high-dense data centers. • High-temperature superconductor (HTS) busbars for high-power data centers. • HTS busbars with ultra-high current-carrying capacity and compact size. • Full layouts of 3-grade HTS busbars in accord with data center standards. • Economic analysis on different busbar schemes for a 10 MW class data center. • General design guideline of HTS busbar networks for high-dense data centers. [ABSTRACT FROM AUTHOR]

In order to fabricate high-current superconducting conductors for engineering applications, the configuration of stacked high-temperature superconductor (HTS) strips is one of the most popular choices. AC losses in HTS stacks have been vastly studied, but the economic study towards the AC losses with respect to the capital investment and operating costs of HTS stacks is still missing. First, the modelling strategy using the finite element method (FEM) based on the H -formulation is explained, and the basic AC loss simulation of a single strip is verified by the Norris analytical methods. The HTS stack (16 strips) is used as an example, and the corresponding current distribution and magnetic field are analyzed. The relationship between the AC loss and current-carrying capability is studied for multiple stacks with different numbers of strips. Economic analysis is performed with regard to the relationship between the AC losses and investment/operating costs of multiple stacked HTS strips. In this article, the numerical modeling together with the economic analysis of stacked HTS strips bring new visions, which can be beneficial for the future designs of high-current superconducting conductors and cables. [ABSTRACT FROM AUTHOR]

• A new vision of loss measurement and modelling for superconducting coils for high-frequency operations. • The temperature and time dependence of AC loss in the HTS coil in a power electronic circuit. • Both the short-time and long-time loss tests for the HTS coil by a commercial power analyzer. • A new time-dependent analytical model for accurately modelling the real-time loss in the HTS coil. • Prediction of the real-time performance for numerous HTS devices during practical AC operations. This paper provides a new vision of loss measurement and modelling for superconducting coils, with both the short-time test and long-time test, as the behaviour of the AC loss in superconductors is actually a dynamic process with the temperature and time dependence, particularly for the medium-to-high frequency AC operation. A single-pancake High temperature superconducting (HTS) coil was tested in a power electronic circuit (DC-AC inverter). The operating current was from 15 A to 50 A, and the operating frequency was from 1 kHz to 5 kHz. The AC loss measurements were carried out using the function of fully decoupling power by a commercial power analyzer. This method was able to measure the real-time AC loss, and the loss measuring process is much easier than the conventional electrical and magnetic method. As expected, for short-time loss tests, the experiment, the FEM H -formulation model, and the conventional analytical model agree with each other. However, the AC losses in long-time tests are found having power-law relations with the operating time (above kHz level). As the accumulated heat in the HTS coil as well as the interrelation between the critical current and temperature, the real-time AC losses are strongly time-dependent. A new time-dependent analytical model is developed, for the purpose of accurately modelling the real-time loss in the HTS coil. The new analytical model well matches the AC loss tests over both the long and short testing time. The experimental method and new analytical model offer a new sight at the AC loss of superconducting coil for both the short-time and long-time operation in a power electronic circuit, which is able to explore more reasonable guidelines of safe operating area (SOA) during the practical AC operation of superconducting applications. [ABSTRACT FROM AUTHOR]