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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.

High-temperature superconducting (HTS) magnets have found wide applications in high-field settings owing to their high current capabilities. Typically, these magnets are powered by high-current power supplies via current leads, which can complicate insulation between cryogenic and room temperature environments. However, new developments in flux pumps for HTS magnets have enabled charging of kA levels of current without power supplies. By combining flux pumps with HTS persistent current operation, it is possible to achieve accurate flux modulation and eliminate the need for power supplies and current leads. In this study, we report on a novel feedback-controlled flux modulation for HTS magnets in persistent current operations. This flux modulation is based on a flux pump mechanism that generates a DC voltage across the charging superconductor by applying a current higher than its critical current. With closed-loop feedback control, our flux modulation can achieve precise injection and reduction of HTS magnet current in increments of 0.5 A. This technology can lead to stable magnetic fields in HTS magnet designs. We anticipate that this work will enable future magnets to operate in a stable persistent current mode within a closed cryogenic chamber, significantly reducing the footprint and power demand of HTS magnets and opening up new opportunities for their applications.

Previous studies on magnetization AC loss of high temperature superconducting (HTS) coated conductors (CCs) taken into account the ideally sinusoidal external magnetic field, or non-sinusoidal by considering only the harmonics in phase with the fundamental component. However, realistically magnetic field often contains harmonics with different phase angles and amplitudes. In this paper, magnetization AC loss in HTS CC was studied, considering the phase angle $\varphi $ of each harmonic; assuming superconductor is subjected to external magnetic field which is distorted by the $3^{\mathrm {rd}}$ and the $5^{\mathrm {th}}$ harmonics. Phase angle of each harmonic was considered in the range of 0 to $\pi $ and amplitude of fundamental magnetic field, was assumed as 10, 20, 50, and 100 mT. Different distortion level of magnetic field was considered too. It is concluded that phase angle of field harmonic has a significant effect on magnetization loss of HTS CCs.

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.

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.

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.

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. 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.

We report here a record 4.6 T trapped field generated by high temperature superconducting (HTS) persistent current loops using a HTS ring structure. By stacking 200 HTS rings into a compact magnet 90 mm in diameter, we performed a field cooling magnetisation at 25 K. The main advantage of the new magnet compared to existing trapped field HTS magnets is that the magnetic field is in the parallel direction to the ab plane of the HTS, leading to higher critical currents in the same magnetic field. Therefore, compact HTS magnets can be developed based on this principle to achieve high magnetic fields. Experimental results show that the final trapped field distribution depends on the ring geometry. We developed a new three dimensional model to simulate the magnetic field distribution within the HTS ring magnet and good agreement between experiments and simulation have been found. The temperature dependency and ramping rate dependency have been studied numerically as potential factors to influence the magnet field. The proposed HTS ring magnet will have promising applications in medical imaging devices, e.g. MRI, as well as electrical machines.

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.

This research investigates the economic aspects of using superconducting magnetic energy storage (SMES) systems and high-temperature superconducting (HTS) transformers as reported by utilities and other projects. The focus is on producing a preliminary set of information that could form a guideline in estimating cost-benefit-related numbers for these technologies. In this paper, a literature review of studies using SMES systems and HTS transformers is presented and an effort is made to highlight major cost factors and drivers based on available information. In conclusion, it is evident that more utility scale studies need to be undertaken to have a comprehensive understanding of the economic benefits of SMES and HTS-based systems in addition to a thorough comparative assessment to prevalent and conventional options.

The magnetism of substrate has significant influence on the transport loss in high temperature superconducting (HTS) coated conductors (CCs). Taking three types of substrates (i.e., nonmagnetic, weakly magnetic, and strongly magnetic) into account, a study on the frequency dependence (in the range of 10–1000 Hz) of transport loss in HTS CCs with these substrates is performed numerically and experimentally. Different loss components and magnetic field profile are calculated individually to clarify the effect of substrate magnetism. Results show that HTS CCs with magnetic substrate exhibit higher transport loss than CCs with nonmagnetic substrate. Both hysteresis loss in HTS layer and eddy current loss in conventional metal increase with the enhancement of substrate magnetism.

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.

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.

AC losses in superconductors are essential for the design of cooling system for large scale power applications. Magnesium diboride (MgB 2 ) superconducting wires have been investigated and manufactured over the last decade due to cheap raw materials and flexibility for coil design. In addition, multifilamentary MgB 2 wires have been manufactured to reduce ac losses. In this paper, self-field ac losses of multifilamentary MgB 2 wires with magnetic barrier are investigated using both experimental and numerical methods. A short straight wire sample and a coil sample are tested under various temperatures and frequencies between 16-and 128-Hz. The test results show that the transportation loss is independent of the operating temperature. On basis of both theoretical and numerical study, it is found that hysteresis loss in superconductor accounts only for a small fraction of the transportation losses, ferromagnetic hysteresis loss in the magnetic barrier dominates when the transport current is low, whereas eddy current loss dominates when the transport current is close to the critical current.

ReBCO conductor-on-round-core (CORC) cable has become a promising candidate for high temperature superconducting (HTS) power applications, due to its great mechanical strength, high current carrying capacity, high flexibility, and low ac losses. However, ReBCO coated conductors are at risk of quenching, which significantly affects the thermal stability and reliability of the CORC cable. Three-dimensional (3-D) numerical study on the quench behavior of the CORC cable remains a challenge, for its complex geometry is difficult to cope with. In this paper, a 3-D time-dependent multi-physics quench model based on the T-A formulation has been developed. Three modules are coupled in this model; the T-A formulation model, a heat transfer model, and an equivalent circuit model. The quench behavior of a single-layer ReBCO CORC cable with non-uniform terminal contact resistances has been studied, when a hotspot is imposed on one of the tapes to induce a local quench. Results show that, the CORC cable has the highest MQE; in other words, it is the most stable situation, when the hotspot-induced quench occurs on the tape with the middle value of terminal contact resistance.

The increase in aircraft passengers and airfreight traffic has given rise to concerns about greenhouse gas emissions for traditional aircraft and the resulting damage to the environment. This has led several companies and organizations, including NASA, to set goals to enhance aircraft efficiency as well as reduce fuel burn, pollution, and noise for commercial aircraft. The most notable electric aircraft (EA) concept is the N3-X, which was developed by NASA to achieve environmental goals while maintaining the annual growth of the aviation industry. However, one of the main challenges that EA is facing is their overall weight. This paper proposes and explores an improved power system architecture for use in EA, based on the N3-X concept. The number of superconducting magnetic energy storage (SMES) and fault current limiter (FCL) devices required can be reduced by utilizing multifunctional superconducting devices that combine the functionalities of both a SMES and a FCL, thus reducing the weight and cost of the EA by eliminating a complete device. The proposed control technique offers greater flexibility in determining the appropriate size of coils to function as a FCL, based on the fault type. The proposed EA power system architecture including the SMES-FCL devices is modelled in Simulink/MATLAB to test the system performance under different failure scenarios.

Electric aircraft has already become a reality, with demonstration flights at power ratings of less than 1 MVA. Conventional machines and distribution technologies suffer from poor power densities when scaling to large power demands, leading to significant challenges in applying this technology from small (100-seater) planes. Superconducting devices could be an enabler for electric aviation due to their great potential for high efficiency and low weight. However, while the development of the superconducting components presents a significant challenge, the safe and effective combination of such components into a propulsion system also requires a significant area of research. For this purpose, a signal-based MATLAB-Simscape model for a dc network architecture in a turbo-electric aircraft has been established and the highly nonlinear models for the superconducting devices have been developed and integrated. This network model has been used to understand the fault current magnitude and rise time, as well as the stability behavior of the system utilizing the realistic electro-thermal models of superconducting devices in it. The derived network was investigated for a bus bar short circuit fault using both superconducting fault current limiter and fault current limiting high temperature superconducting (FCL HTS) cable. Based on the network characteristics, a fault tolerant dc network design was achieved by utilizing the FCL HTS cables. Similarly, the operation limits of the protection devices have been reduced greatly using superconducting components.

A Conductor on Round Core (CORC®) cable wound with a high temperature superconductor is an important cable concept for high current density applications. The design of a CORC cable makes understanding its electromagnetic performance—for example its AC losses—challenging. This paper presents a thorough study of CORC cables by combining experimental and numerical methods. In particular, it focuses on understanding how the cable structure influences the magnetization losses and on how these can be reduced. A novelty of this paper lies in the use of a new T-A formulation, which, for the first time, is employed for three-dimensional modelling of a CORC cable with real geometry. The use of the new T-A formulation in finite element software enables the study of how the winding direction and multiple-layer structure affect the magnetization losses of CORC cables. Moreover, influence of striation in CORC cables is studied as an effective way to reduce their losses. A CORC cable with striated tapes shows a significant magnetization loss reduction at high magnetic fields, in comparison to its counterpart without striated tapes. At low magnetic fields, tape striation leads to an increase in loss when the number of filaments is low, then the loss drops with a further increase in the number of filaments, but this loss reduction is much weaker than that at high fields. This paper provides an efficient tool for investigating the electromagnetic behaviour of CORC cables, which can provide valuable guidance in designing CORC cables with minimized losses for high energy physics and energy conversion applications.

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.

This paper investigates how the current distribution and ac losses of second-generation high-temperature superconducting (2G HTS) pancake coils are affected by the material anisotropy. The 2G HTS tape has a strong anisotropy, which means that its critical current densities are different at different magnetic field orientations. 2G HTS pancake coils with different anisotropies have different ac losses. We studies this phenomenon by both experimental and numerical methods. Three 2G HTS coils with different turns are fabricated and tested in liquid nitrogen. AC losses with different frequencies are measured and compared with simulation. We use the critical-state model to calculate the current distribution and ac losses. Our modeling results are well validated by experimental measurements. We apply this numerical model to pancake coils with different anisotropies and calculate the current distribution, magnetic field, and ac loss. We find that the anisotropy of 2G HTS affects the ac loss and current distribution. It is possible to decrease the ac loss by an advanced pinning technique.

This paper proposes a novel use of superconducting magnetic energy storage (SMES) hybridized with the battery into the electric bus (EB) with the benefit of extending battery lifetime. A new power control algorithm, which integrates a power grading strategy with the filtration control method, is introduced in this paper, achieving further improvement of battery lifetime. To demonstrate the performance of the SMES/battery hybrid energy storage system (HESS), a dynamic EB system is described with the advantage of considering more factors into the driving patterns. Simulation results show that the proposed HESS has successfully combined the SMES with the battery forming an optimal system that has the advantages of primary energy storage systems while complementing the disadvantages of each system. This paper also does the quantitative analysis of battery lifetime extension in the battery-only system, the filtration-based HESS, and the novel control-based HESS.

Growing electricity demand from a range of sources with higher loads and the industry structural changes open the possibility of more frequent and larger fault currents producible in liver power grids. Traditional solutions to the fault have difficulties in satisfying the requirement of the new power grid requirement due to many factors, such as high cost and 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). Critical current Ic is used to describe the maximum current that a superconductor can transport and is one of the most important parameters to be considered while designing a SFCL. Guaranteeing the homogeneous distribution of the critical current density flowing in a superconductor is not possible due to manufacturing process limitations. In this paper, the impact of critical current inhomogeneity of coated high temperature superconductors (HTSs) during the quench process is studied experimentally. The results show that both the amount of Ic degradation and the size of Ic degraded segments have a great impact on the maximum temperature generated in the quench process of HTSs when the prospective fault current is low ( 1.13Ic to 1.51Ic. Higher amount of localized Ic degradation allows higher maximum temperatures under low voltage fault. Additionally, smaller Ic degraded segment allows higher maximum temperatures.

This paper demonstrates an efficient method to calculate the ac losses in multipancake coils. We use the front track line to analyze stacked pancakes by assuming that the current fronts are straight lines and using the critical state model. The current distribution is solved by minimization of total magnetic energy. The calculated ac loss results are compared with the well-accepted H-formula in COMSOL. We further apply this model to the design of a SMES with 2 kJ, which is under construction. The object of the design is to maximize the stored energy and decrease the ac loss. We discuss the detailed geometry parameters and operation temperature with the validated numerical model. Our model provides a fast calculation method of ac loss in stacked (Re)BCO pancakes and is useful to HTS applications in high field magnets, energy storage devices, and electric machines.

This paper focuses on the 2G HTS armature winding design for fully HTS machines. The main challenge for HTS armature windings is the ac loss calculation. This paper proposes an effective way to estimate 2G HTS armature efficiency. The originality of ac loss calculation is effectively coupling a machine model with a HTS model using boundary conditions to simulate machine environment while considering material anisotropy. The paper then uses H formulation to estimation the total armature ac loss for a 1-MW propulsion motor. The ac loss is calculated for different electrical loadings and magnetic loadings. A new double-layer armature winding is proposed to reduce the spatial harmonics of HTS armature.

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 remove at low temperatures and they add an extra burden to the aircraft cooling system. Due to heavy cooling penalty, AC losses 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 calorimetrically boiling-off liquid nitrogen. Both total AC loss and magnetisation loss in HTS stator are measured in a rotational magnetic field condition. This platform is essential to study ways to minimise AC losses in HTS stator, in order to maximum the efficiency of fully HTS machines., Comment: 17 pages, 15 figures

Integrating permanent magnet synchronous generator (PMSG) wind turbines with DC microgrids have attracted a great attention due to the inherent merits of DC systems. However, under the fault conditions, the excessive energy during fault will be reflected on PMSG rotating parts causing overspeed, mechanical stresses, and fast aging. Also, large fault currents will force generator-side converter to disconnect making it not complied with grid codes. Accordingly, this paper aims to apply superconducting fault current limiter (SFCL) to enhance the performance of PMSG wind turbines with DC microgrids under the fault conditions. PSCAD/EMTDC software is used to build the system under study that includes PMSG, controlled AC/DC converter, SFCL, and DC bus. The behavior of SFCL in enhancing the DC output of the converter is first studied. Then, the impact of using SFCL on the speed, torque, and output current of PMSG is investigated and discussed. Finally, the suitable current limiting resistance is adopted considering DC output as well as PMSG speed.

High-temperature superconducting (HTS) triaxial conductor on round core (CORC) cable is a potential candidate for use in the transmission line of hybrid-electric aircraft because of its advantages in compactness, high power density, and reduced usage of HTS tapes. The harmonic currents generated by ac/dc converters, generators, and motors in the aircraft affect the ac loss of the transmission cable, thus influencing the efficiency of the cable. This paper analyzes the influence of harmonic current on the magnetization loss of a triaxial CORC HTS cable (10 MW, 3 kV/2 kA), which is designed for hybrid-electric aircraft. A finite element method model based on the T-A formulation has been developed for the HTS triaxial CORC cable, which calculates the losses induced both with and without applied harmonic currents. The results show that the magnetization loss has a significant nonuniform distribution among three phases even under a three-phase balanced rated load. The results also show that a small harmonic current (less than 10% of the rated load current) can lead to a considerable increase in the magnetization loss of the cable (up to 40%). In the triaxial CORC cable, harmonic currents lead to the highest increasing rate of magnetization loss with respect to frequency in the innermost phase.

This paper introduces a new scheme, which uses a multifunctional superconducting device that can be used as an energy storage and as a fault current limiter. It is denoted as a superconducting magnetic energy storage - fault current limiter (SMES-FCL) and is modeled as a number of pancakes. It is connected to a wind turbine power system via tertiary transformer and power converters. A complete control scheme is built to achieve effective power transfer between the superconducting coil and the power system during normal operation to smooth the wind turbine output power. The fault current limiting function is implemented using a new technique that inserts a few pancakes from the whole SMES coil into the main electrical system during the fault and isolates the remaining pancakes. The number of pancakes used to limit the fault is quenched and operates as a resistive fault current limiter. The whole system including the wind turbine, the SMES-FCL model, and the interface circuit are implemented using PSCAD/EMTDC computer package. Also, the control scheme of SMES-FCL is built based on a feedback current signal to enable its operation into the two modes.

This paper details the key outputs of the U.K.'s first feasibility study of implementing the high-temperature superconducting (HTS) cables in electricity distribution networks to solve capacity issues. This project is mainly aimed at studying the technical and economic aspects of using superconducting cables and comparing them with the existing approaches, to determine whether a demonstration project of the superconducting solution is feasible. The University of Bath in collaboration with Western Power Distribution (WPD) has conducted this study, considering a previous capacity issue in WPD's network using both conventional and superconducting solutions. The first part of the study investigated the different aspects (installation procedures, power capacity, capital, and operational costs, etc.) of superconducting cables, comparing them with conventional cables. This identified the unique benefit of the high power density of HTS cables, which could allow the usage of a low-voltage superconducting cable in place of a high-voltage conventional cable. In the second part of the study, a 132-kV site in WPD's network that required reinforcement has been chosen for performing the feasibility study. As part of this study, a detailed cost benefit analysis (CBA) was conducted, comparing the superconducting solution with the conventional solution. The outputs from the present value analysis that has been carried out as part of the CBA are discussed. The results of the CBA power system studies performed are presented, evaluating the impact that each solution has on the network power flows, losses, and fault levels. Finally, based on the outputs from the CBA and future projections in the costs of superconducting cables, recommendations were made for the usage of superconducting cables in U.K. electricity distribution networks to solve network capacity issues.

Superconducting devices have emerged in many applications during the last few decades. They offer many advantages, including high efficiency, compact size, and superior performance. However, the main drawback of these devices is the high cost. An option to reduce the high cost and improve the cost-benefit ratio is to integrate two functions into one device. This paper presents the superconducting fault current limiting transformer (SFCLT) as a superior alternative to normal power transformers. The transformer has superconducting windings and also provides fault current limiting capability to reduce high fault currents. The SFCLT is tested in two power system models: A 7 bus wind farm-based model simulated in PSCAD and on the 80 bus simplified Australian power system model simulated in real-Time digital simulator. Various conditions were studied to investigate the effectiveness of the fault current limiting transformer.

As the capacity of all-electric ships (AESs) increases dramatically, the sudden changes in the system load may lead to serious problems, such as voltage fluctuations of the ship power grid, increased fuel consumption, and environmental emissions. In order to reduce the effects of system load fluctuations on system efficiency, and to maintain the bus voltage, we propose a hybrid energy storage system (HESS) for use in AESs. The HESS consists of two elements: a battery for high energy density storage and a superconducting magnetic energy storage (SMES) for high power density storage. A dynamic droop control is used to control charge/discharge prioritization. Maneuvering and pulse loads are the main sources of the sudden changes in AESs. There are several types of pulse loads, including electric weapons. These types of loads need large amounts of energy and high electrical power, which makes the HESS a promising power source. Using Simulink/MATLAB, we built a model of the AES power grid integrated with an SMES/battery to show its effectiveness in improving the quality of the power grid.

The AC superconducting power transmission cable projects are being carried out around the world, while the DC superconducting cable is also proven to be very competitive for power transmission in electrical grid due to the negligible AC losses. The critical current and current distributions are two important factors to improve the performance of DC HTS cable for large transmission capacity. In this paper, we proposed an experimental method to investigate the behavior of critical current affected by various gap distances between the individual HTS tape and transverse tape width. The results show that the critical current of the HTS tape in the cable field can be increased by about 10% if the gap distance is less than 1 mm. Finite element method (FEM) is used to calculate the magnetic field distribution to verify the experimental results. A short HTS cable has been constructed to investigate the influence of contact resistance on the current distribution among the HTS tapes. The results show that the contact resistances have significant influence on the current sharing of each HTS wire in the cable structure.

Concept design and optimization for a high-temperature superconducting (HTS) rotor of a 100-kW generator is studied in this paper. The rotor has eight HTS magnets constructed by air-cored racetrack coils. The HTS magnets with a unique circular cross-sectional shape can produce a gap field over 2.0 T. The present design is based on a new graphical method developed to estimate the maximum operating current of an HTS magnet that takes both I c -B characteristics and angular dependence into consideration. The optimized stepped shape design saved more than 8% of the HTS material compared with the rectangular one without sacrificing the gap field.

Using a high-temperature superconducting (HTS) coil as the transmitting coil is an optional way to increase the efficiency and the distance of a wireless power transfer (WPT) system. In practical cases, receiving coils might be not only one, or not convenient to get a low-temperature environment, or not in the same sizes with the transmitting coil. Thus, we constructed a WPT system from one HTS coil to two copper coils, and one of the copper receiving coils had a different size from the HTS transmitting coil. In addition, we placed one HTS relaying coil between the transmitting coil and the receiving coils to increase the efficiency and the distance. Based on this system, we conducted several experiments and analyzed the results. We found that a denser coil could obtain more power in an HTS WPT system and that WPT from one HTS coil to two copper coils was more efficient than WPT from the same HTS coil to one of the two copper coils. We also demonstrated that an appropriate layout of the HTS relaying coil can increase the HTS WPT efficiency.

The second generation high temperature superconductor, specifically REBCO, has become a new research focus in the development of a new generation of high-field (>25 T) magnets. One of the main challenges in the application of the magnets is the current screening problem. Previous research shows that for magnetized superconducting stacks and bulks the application of an AC field in plane with the circulating current will lead to demagnetization due to vortex shaking, which provides a possible solution to remove the shielding current. This paper provides an in-depth study, both experimentally and numerically, to unveil the vortex shaking mechanism of REBCO stacks. A new experiment was carried out to measure the demagnetization rate of REBCO stacks exposed to an in-plane AC magnetic field. Meanwhile, 2D finite element models, based on the E–J power law, are developed for simulating the vortex shaking effect of the AC magnetic field. Qualitative agreement was obtained between the experimental and the simulation results. Our results show that the applied in-plane magnetic field leads to a sudden decay of trapped magnetic field in the first half shaking cycle, which is caused by the magnetic field dependence of critical current. Furthermore, the decline of demagnetization rate with the increase of tape number is mainly due to the cross-magnetic field being screened by the top and bottom stacks during the shaking process, which leads to lower demagnetization rate of inner layers. We also demonstrate that the frequency of the applied AC magnetic field has little impact on the demagnetization process. Our modeling tool and findings perfect the vortex shaking theory and provide helpful guidance for eliminating screening current in the new generation REBCO magnets.

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.

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.

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.

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.

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.

A heat-shrink tube insulation for second-generation high-temperature superconducting (2G HTS) coils is studied experimentally in this paper. The insulation can be used to prevent the delamination of 2G HTS due to epoxy impregnation. According to the experiment results, the insulated coil shows no degradation before and after the epoxy impregnation. To validate the performance of 2G HTS coils with the heat-shrink insulation, we measured the transport loss, magnetization loss and total loss of a 2G HTS coil. The study demonstrates the feasibility of the heat-shrink tube insulation method for electrical applications.

The high-temperature superconductor (HTS) (RE)Ba 2Cu 3O x (REBCO) conductor on round core (CORC) cable has great advantages with its high current capacity and power density. In REBCO CORC cables, current is redistributed among tapes through terminal contact resistance (TCR) when a local quench occurs. Therefore, its quench behavior is different from the single tape situation. To better understand the underlying physical process of local quenches in CORC cables, a new 3D multi-physics modeling tool for CORC cables is developed and presented in this paper. In this model, the REBCO tape is treated as a thin shell without thickness, and four models are coupled: a T-formulation model, an A-formulation model, a heat transfer model, and an equivalent circuit model. The T-formulation model is applied to the conductor shell only to calculate current distribution, which will be input into the A-formulation model; the A-formulation model is applied to the whole 3D domain to calculate the magnetic field, which is then fed back to the T-formulation model. The hot spot-induced quenches of CORC cables are analyzed. The results show that the thermal stability of the CORC cable can be considerably improved by reducing the TCR. The minimum quench energy (MQE) increases rapidly with the reduction of TCR when the resistance is in a middle range, which is about in this study. When the TCR is too low () or too high (), the MQE shows no obvious variation with TCR. With a low TCR, a hot spot in one tape may induce an overcurrent quench on other tapes. This will not happen in a cable with high TCR. In this case, the tape with a hot spot will quench and burn out before inducing a quench on other tapes. The developed modeling tool can be used to design CORC cables with improved thermal stability.

Most high-temperature superconducting (HTS) electric devices have been built by employing a superconducting composite cable. These HTS devices generally have large current-carrying capacities. Therefore, the electromagnetic characteristic of a composite superconducting cable with high current density becomes a key point for the application of these HTS devices. A helical superconducting cable and a Roebel cable consisted of YBCO-coated conductors with a critical current of 500 A @ 77 K in the self-field are both proposed in this paper. The helical superconducting cable that has two conductor layers and the structure parameters of the helical cable are given. The Roebel cable has four layers with a critical current of 500 A. Two 3-D models are built for a helical cable and a Roebel cable with variable geometries. Their magnetic flux distributions along the axis are presented based on the finite-element analysis method, and their electromagnetic characteristics are discussed as well. The analysis model can be further applied for the large-scale HTS electric device design with high current-carrying ability.

As we known, the high temperature (77 K) superconducting (HTS) motor is considered as a competitive electrical machine by more and more people. There have been various of designs for HTS motor in the world. However, most of them focus on HTS tapes rather than bulks. Therefore, in order to investigate possibility of HTS bulks on motor application, a HTS magnet synchronous motor which has 75 pieces of YBCO bulks surface mounted on the rotor has been designed and developed in Cambridge University. After pulsed field magnetization (PFM) process, the rotor can trap a 4 poles magnetic field of 375 mT. The magnetized rotor can provide a maximum torque of 49.5 Nm and a maximum power of 7.8 kW at 1500 rpm.

High-temperature superconductors have created the opportunity for a step change in the technology of power applications. Racetrack superconducting coils made from YBCO coated conductors have been used in several engineering applications including SMES, rotor or stator windings of electric machines. AC loss is one of the most important factors that determine the design and performance of superconducting devices. In this paper, a numerical model is developed to calculate the AC losses in superconducting racetrack coils in different magnetic conditions. This paper first discusses the AC losses of the coils in self-field or external field only. It then goes to investigate the AC losses of the coils being exposed to AC ripple field and a DC background field. Finally, the AC losses of the coils carrying DC current and being exposed to AC field are calculated. These two scenarios correspond to using superconducting coils as the rotor field winding of an electric machine.

YBaCuO-coated conductors offer great potential in terms of performance and cost-saving for superconducting fault current limiter (SFCL). A resistive SFCL based on coated conductors can be made from several tapes connected in parallel or in series. Ideally, the current and voltage are shared uniformly by the tapes when quench occurs. However, due to the non-uniformity of property of the tapes and the relative positions of the tapes, the currents and the voltages of the tapes are different. In this paper, a numerical model is developed to investigate the current and voltage sharing problem for the resistive SFCL. This model is able to simulate the dynamic response of YBCO tapes in normal and quench conditions. Firstly, four tapes with different Jc's and n values in E-J power law are connected in parallel to carry the fault current. The model demonstrates how the currents are distributed among the four tapes. These four tapes are then connected in series to withstand the line voltage. In this case, the model investigates the voltage sharing between the tapes. Several factors that would affect the process of quenches are discussed including the field dependency of Jc, the magnetic coupling between the tapes and the relative positions of the tapes.