A superconducting magnetic energy storage-emulator/battery supported dynamic voltage restorer

This study examines the use of superconducting magnetic and battery hybrid energy storage to compensate grid voltage fluctuations. The superconducting magnetic energy storage system (SMES) has been emulated by a high current inductor to investigate a system employing both SMES and battery energy storage experimentally. The design of the laboratory prototype is described in detail, which consists of a series-connected three phase voltage source inverter used to regulate AC voltage, and two bidirectional DC/DC converters used to control energy storage system charge and discharge. 'DC bus level signaling' and 'voltage droop control' have been used to automatically control power from the magnetic energy storage system during short-duration, high power voltage sags, while the battery is used to provide power during longer-term, low power under-voltages. Energy storage system hybridisation is shown to be advantageous by reducing battery peak power demand compared with a battery-only system, and by improving long term voltage support capability compared with a SMES-only system. Consequently, the SMES/battery hybrid DVR can support both short term high-power voltage sags and long term undervoltages with significantly reduced superconducting material cost compared with a SMES-based system.</p

Not Just for Support: Companionship Activities in Healthcare Virtual Support Communities

The phenomenon of social support―aid and assistance exchanged through social relationships and interpersonal transactions―has been studied extensively for decades. In the context of healthcare virtual support communities, researchers have focused on exploring community members’ support behavior and its effects on individuals’ health outcomes. This emphasis, however, has led to the neglect of another type of social interaction that also promotes individual health―companionship activities. We argue that in order to gain a deeper insight into the online support phenomenon, the consideration of companionship activities, in addition to social support exchange, is necessary. To bridge this gap in the literature, this article attempts to contrast community members’ support behavior and companionship activities in two large healthcare virtual support communities―one for patients with breast cancer and the other for patients with prostate cancer. Based on the identification of the two types of social activities from the two cancer support communities, the relationship between individuals’ participation in these activities, and gender differences in their activity engagement are also hypothesized and tested. Our goal is to advance the understanding of online socio-behavioral dynamics of virtual support communities. We also wish to provide insights into the design of such communities and the delivery of patient-focused healthcare interventions

Total AC loss study of 2G HTS coils for fully HTS machine applications

The application of HTS coils for fully HTS machines has become a new research focus. In the stator of an electrical machine, HTS coils are subjected to a combination of an AC applied current and AC external magnetic field. There is a phase shift between the AC current and AC magnetic field. In order to understand and estimate the total AC loss of HTS coils for electrical machines, we designed and performed a calorimetric measurement for a 2G HTS racetrack coil. Our measurement indicates that the total AC loss is greatly influenced by the phase shift between the applied current and the external magnetic field when the magnetic field is perpendicular to the tape surface. When the applied current and the external magnetic field are in phase, the total AC loss is the highest. When there is a 90 degree phase difference, the total AC loss is the lowest. In order to explain this phenomenon, we employ H formulation and finite element method to model the 2G HTS racetrack coil. Our calculation agrees well with experimental measurements. Two parameters are defined to describe the modulation of the total AC loss in terms of phase difference. The calculation further reveals that the influence of phase difference varies with magnetic field direction. The greatest influence of phase difference is in the perpendicular direction. The study provides key information for large-scale 2G HTS applications, e.g. fully HTS machines and superconducting magnetic energy storage, where the total AC loss subjected to both applied currents and external magnetic fields is a critical parameter for the design.</p

Investigation of HTS cable impact on turboelectric aircraft performance

With significant interest in the use of high-temperature superconducting (HTS) components in electric aircraft, there is a need for novel modelling techniques that allow architecture-level studies of the electrical systems including HTS components. In this study, a simple electric network architecture, as proposed in the literature has been considered, which includes generators, dynamic propulsion load and cables. This electric network has been modelled considering conventional technology and using HTS cables by replacing the conventional copper cables, to evaluate the variations in the network performance. The network performance has been studied for the dynamically varying propulsion load, which is nearly equivalent to the aircraft load over the entire flight duration. Following this, electric faults have been applied at various locations, and the impact of HTS cables on the network fault levels has been evaluated. The fault current levels are compared using both conventional and HTS cables, due to the fault current limiting properties of the HTS cables, they are observed to offer lowered fault current values

Quench behavior of high temperature superconductor (RE)Ba2Cu3Ox CORC cable

High temperature superconductor (HTS) (RE)Ba2Cu3Ox (REBCO) conductor on round core cable (CORC) shows great advantages on high current capacity and power density. In REBCO CORC cables, current is redistributed among tapes through terminal contact resistances (TCR) when a local quench occurs. Therefore, its quench behaviour is different from single tape situation. To better understand the underlying physical process of local quenches in CORC cables, a new 3D multi-physics modelling 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: T-formulation model, A-formulation model, a heat transfer model and an equivalent circuit model. The T-formulation is applied to the conductor shell only to calculate current distribution, which will be input into A-formulation model; the A-formulation is applied to the whole 3D domain to calculate magnetic field, which is then fed back to the T-formulation model. The hot spot induced quenches of CORC cables are analysed. The results show that the thermal stability of CORC cable can be considerably improved by reducing TCR. The minimum quench energy (MQE) increases rapidly with the reduction of TCR when the resistance is in a middle range, which is about 5 μΩ ≤ Rt ≤ 200 μΩ in this study. When TCR is too low (Rt 50 μΩ), the MQE shows no obvious variation with TRC. With low TCR, a hot spot in one tape may induce an over-current quench on other tapes. This will not happen in a cable with high TCR. In this case, the tape with hot spot will quench and burn out before inducing a quench on other tapes. The modelling tool developed can be used to design CORC cables with improved thermal stability

Fully superconducting machine for electric aircraft propulsion : study of AC loss for HTS stator

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 eliminate at low temperatures, and they add an extra burden to the aircraft cooling system. Due to the heavy cooling penalty, AC loss 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 the calorimetric boiling-off of liquid nitrogen. Both total AC loss and magnetisation loss in the HTS stator are measured under the condition of a rotational magnetic field. This platform represents a key element in studying ways to minimise AC losses in an HTS stator, in order to maximise the efficiency of fully HTS machines

Study of the magnetization loss of CORC® cables using a 3D T-A formulation

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

Electromagnetic modelling using T-A formulation for high-temperature superconductor (RE)Ba2Cu3Oxhigh field magnets

Second generation (2G) high-temperature superconductor (HTS) (RE)Ba2Cu3Ox(REBCO) shows a great potential in building high field magnets beyond 23.5 T. The electromagnetic modelling is vital for the design of HTS magnet, however, this always suffers the challenge of huge computation for high field magnets with large number of turns. This study presents a novel electromagnetic modelling based on T-A formulation for REBCO magnets with thousands of turns. An equivalent turn method is proposed to reduce the number of turns in calculation, so that the computation cost can be reduced significantly, and meanwhile the key electromagnetic behaviour of HTS magnet can be simulated with enough accuracy. The ramping operation of a fully HTS magnet with 12,000 turns are analysed using both the original T-A model with actual turns and improved T-A model with equivalent turns. The two models show a good agreement on the key electromagnetic behaviours of the magnet: distribution of current density, magnetic fields, screen current induced field and magnetisation loss, so that this improved T-A model using equivalent turns is validated. The T-A modelling of REBCO magnet is a powerful tool for the electromagnetic analysis of industry-scale high field magnets

AC Loss Characterization of HTS Pancake and Solenoid Coils Carrying Nonsinusoidal Currents

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