Search

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]

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 Bi-2212 round wire has a multifilamentary structure, and the use of numerical method to study ac loss of such multifilamentary superconducting wire requires a long calculation time and large memory. Adopting a homogenization method at low frequency to study the ac loss of multifilamentary structural wire/tape has been proven to have high enough accuracy and can save a lot of calculation time. With the expansion of the application range of superconducting materials, however, superconducting power devices exceeding the frequency of tens of kHz have huge potential applications in the future such as wireless power transfer. Therefore, it is necessary to study the applicability of the homogenization model at high frequencies. This article mainly presents an ac loss numerical study of Bi-2212 round wire at wider frequency (50 Hz–500 kHz) by homogenization method. The homogenization is achieved by two different methods. The first method is to treat the superconducting bundle and the Ag matrix between the bundles as a superconducting domain (bundle-matrix homogenized model, BHM). The second method is to regard the Ag matrix between the superconducting filaments and the filaments as a superconducting domain (filament-matrix homogenized model, FHM). In order to evaluate the feasibility of the two different homogenization methods, we compare the calculation results of the two different homogenization models with the original model, OM. The results show that the FHM can effectively improve the calculation speed while satisfying the high calculation accuracy. This conclusion can be used to quickly evaluate the ac energy loss of large-scale superconducting devices at wider frequencies. [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]

For some high-temperature superconducting (HTS) devices, such as fusion magnet, fault current limiters (FCLs), and superconducting energy magnetic system, the ac loss of the HTS current leads is one of the most important heat sources in the cryogenic system. When HTS current lead is carrying alternating current, ac loss occurs. However, the HTS current leads of the above HTS devices usually carry the nonsinusoidal current, and the ac loss is difficult to be analyzed when the applied transport current is nonsinusoidal waveform. In this paper, we firstly proposed two kinds of structure of HTS current leads, and the ac losses of these two current leads with the specific current waveform were calculated subsequently by using finite element method software COMSOL. Furthermore, the ac losses of two structure current leads were measured by using the integral method, respectively. Finally, the ac loss results of these two structures of current leads were compared and analyzed theoretically and experimentally, which aims to select the preferred structure of current lead for HTS applications in terms of ac loss. [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 measurement and simulation of Alternating Current (AC) losses on the Stabilizer-free and Copper Stabilizer High Temperature Superconducting (HTS) Tapes: SuperPower SF12100 and SCS12050. The AC loss measurement utilised electrical method to obtain overall losses with AC transport currents. The 2D H -formulation by COMSOL Multiphysics has been used to simulate the real geometry and multi-layer HTS tapes. Ferromagnetic AC losses of substrate have been assumed to be ignored as the substrates of SF12100 and SCS12050 are non-magnetic. Hysteresis AC losses in the superconducting layer, and eddy-current AC losses in copper stabilizer, silver overlayer and substrate were concerned in this investigation. The measured AC losses were compared to the AC losses from simulation, with 3 cases of different AC frequency 10, 100, and 1000 Hz. The eddy-current AC losses of copper stabilizer at frequency 1000 Hz were determined from both experiment and simulation. The estimation of AC losses with frequency at 10,000 Hz was also carried out using simulation method. Finally, the frequency dependence of AC losses from Stabilizer-free Tape and Copper Stabilizer Tape were compared and analysed. [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]

• 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]

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]

• 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]