Taking a technology from the laboratory to industry is a long and resource-consuming process. Discovered more than a century ago, the phenomenon of superconductivity is testament to this process. ...Despite the promise of this technology, currently the only major use of superconductors outside the laboratory is in MRI machines. The advent of high-temperature superconductors in 1986 heralded a new dawn. Machines which do not require cooling with liquid helium are a very attractive target. A myriad range of different superconductors were rapidly discovered over the next decade. This process of discovery continues to this day with, most recently, a whole new class, the pnictides, being discovered in 2006. Many different usages have been identified, including in motors, generators, wind turbines, fault current limiters, and high-current low-loss cables. This Special Issue looks at some of the different factors which will help to realise these devices and thereby bring about a superconducting world
This paper reviews the modeling of high-temperature superconductors (HTS) using the finite-element method (FEM) based on the <inline-formula> <tex-math notation="LaTeX">\boldsymbol {H} ...</tex-math></inline-formula>-formulation of Maxwell's equations. This formulation has become the most popular numerical modeling method for simulating the electromagnetic behavior of HTS, especially thanks to the easiness of implementation in the commercial finite-element program COMSOL Multiphysics. Numerous studies prove that the <inline-formula> <tex-math notation="LaTeX">\boldsymbol {H} </tex-math></inline-formula>-formulation is able to simulate a wide scope of HTS topologies, from simple geometries such as HTS tapes and coils, to more complex HTS devices, up to large superconducting magnets. In this paper, we review the basics of the <inline-formula> <tex-math notation="LaTeX">\boldsymbol {H} </tex-math></inline-formula>-formulation, its evolution from 2D to 3D, its application for calculating critical currents and AC losses as well as magnetization of HTS bulks and tape stacks. We also review the use of the <inline-formula> <tex-math notation="LaTeX">\boldsymbol {H} </tex-math></inline-formula>-formulation for large-scale HTS applications, its use to solve multi-physics problems involving electromagnetic-thermal and electromagnetic-mechanical couplings, and its application to study the dynamic resistance of superconductors and flux pumps.
Abstract
When a type II superconductor carrying a direct current is subjected to a perpendicular oscillating magnetic field, a direct current (DC) voltage will appear. This voltage can either result ...from dynamic resistance effect or from flux flow effect, or both. The temperature variation in the superconductor plays an important role in the nature of the voltage, and there has been little study of this so far. This paper presents and experimentally verifies a 2D temperature-dependent multilayer model of the second generation (2G) high temperature superconducting (HTS) coated conductors (CC), which is based on H-formulation and a general heat transfer equation. The model has coupled the electromagnetic and thermal physics, and it can simulate the behavior of 2G HTS coated conductors in various working conditions where the temperature rise has a significant impact. Representative electromagnetic phenomena such as the dynamic resistance effect and the flux flow effect, and thermal behavior like quench and recovery have been simulated. This thermal-coupled model is a powerful tool to study the thermal-electromagnetic behaviors of 2G HTS coated conductors in different working conditions, especially when the impact of temperature rise is important. This multilayer model is also very useful in analyzing the impact of different layers in the 2G HTS CCs, especially the metal stabilizer layers. It has been proven to be a very powerful tool to help understand more complicated characteristics in the CCs which could not be accurately measured or simulated by previous numerical models. The work is indicative and very useful in designing ac magnetic field controlled persistent current switches and flux pumps, in terms of increasing the off-state resistance, analyzing different sources of losses, minimizing detrimental losses, and enhancing the safety and stability.
A rapiddevelopment of the permanent magnetic synchronous generator (PMSG)-based offshore wind farm has been witnessed in the past decade. To prevent the offshore wind farms from being disconnected ...during a fault, many countries have proposed specification requirements for the fault ride-through (FRT). Traditional FRT scheme Chopper circuit for PMSG needs to consume all the mismatching energy and the impulse current is too high during the fault, which will even affect the safe of the PMSG. In this paper, the superconducting fault current limiter (SFCL) is applied to enhance the ability of the FRT in the PMSG-based offshore wind farm. In the proposed scheme, the resistive SFCL can reduce the energy consumption and improve the working performance of the Chopper circuit by absorbing the power of the grid-side converter (GCS) during the fault. An offshore wind farm model is built through PSCAD/EMTDC software. The comparison simulation results validate the feasibility of the proposed scheme.
Superconducting flux pump is a wireless charging technique utilizing electromagnetic induction law for exciting the superconducting magnet by pumping the magnetic flux into the superconducting ...closed-loop circuit without any electrical contact in order to compensate current attenuation and ensure the stability of the magnetic field. The contactless flux pump not only charges the magnet, but also quantitatively compensates the current decay of the magnet, which makes it possible for superconducting coils to work in the persistent current mode. This method of magnetizing can effectively reduce contact losses and heat losses, making the whole magnet system more compact and effective. This paper introduces the working principle and research progress of the recent flux pumping technology, reviews different types of high temperature superconducting (HTS) flux pumps proposed during the last decade, summarizes the underlying physics as well as merits and drawbacks of each type, and finally gives a potential developing trend for the future flux pumps where power engineering is largely applied.
Flux pumps have attracted increasing attention due to its capability of energizing superconducting coil wirelessly and avoid thick current leads which cost huge power loss. The transformer-rectifier ...flux pump is one type of the most important pumps, which is promising in real application. It usually made up of two main parts, the transformer and the dynamic bridge. This paper will investigate the impact of the saturated transformer on working performance of the flux pump. Based on the working principle of the flux pump and the transformer, analysis and comparison on how the saturation degree of the transformer on the flux pump will be carried out. Simulation tests based on Simulink software package will be carried out to verify all the analysis in the paper.
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
-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.
The Health of the Nation Outcome Scales was developed to routinely measure outcomes for adults with mental illness. Comparable instruments were also developed for children and adolescents (the Health ...of the Nation Outcome Scales for Children and Adolescents) and older people (the Health of the Nation Outcome Scales 65+). All three are being widely used as outcome measures in the United Kingdom, Australia and New Zealand. There is, however, no comprehensive review of these instruments. This paper fills this gap by reviewing the psychometric properties of each.
Articles and reports relating to the instruments were retrieved, and their findings synthesised to assess the instruments' validity (content, construct, concurrent, predictive), reliability (test-retest, inter-rater), sensitivity to change, and feasibility/utility.
Mostly, the instruments perform adequately or better on most dimensions, although some of their psychometric properties warrant closer examination.
Collectively, the Health of the Nation Outcome Scales family of measures can assess outcomes for different groups on a range of mental health-related constructs, and can be regarded as appropriate for routinely monitoring outcomes.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
This article presents a novel all-superconducting propulsion and protection system for the high-temperature superconducting (HTS) Maglev. The HTS magnet is the key component in the HTS Maglev, as it ...is in charge of the most crucial works, the propulsion and levitation of the train, to realize the zero-friction and ultra-high-speed just above the ground. The HTS magnet can conduct massive electric current and generate extremely high magnetic field, but the HTS magnet is also relatively venerable compared to the conventional copper magnet, regarding the strict operating conditions of temperature, magnetic field and electric current. Therefore, we proposed a new all-superconducting propulsion and protection system, introducing the superconducting fault current limiter (SFCL) and superconducting magnetic energy storage (SMES) to be equipped into the HTS Maglev, which can protect the HTS magnet, but also ensure the safety and reliability of Maglev operation. The real size HTS magnet was modeled to check the magnetic requirements of HTS Maglev and determine the specifications of other superconducting devices. Then a scaled all-superconducting protection and energy compensation system with the scaled HTS magnet, SFCL and SMES was analyzed, and some components were verified by experiments. Future plans were proposed to merge the full size all-superconducting protection and protection system into an HTS Maglev prototype.
High-Tc superconducting (HTS) materials are extremely promising for high-field applications, due to their relatively high upper critical field. Flux pumps are a means of energizing closed ...superconducting magnets without electrical contact. The physics of these devices is also attractive. In this paper, we propose a simulation methodology for a transformer-rectifier HTS flux pump. A model is built, based on the electrical circuit. The simulation methodology opens up various opportunities for flux pump developers to design the whole superconducting magnet energizing system.
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