AC Loss Research Articles

Probing Evolution of the Flux-Pinning Landscape in REBCO Coated Conductors Caused by Gamma Irradiation Using DC and AC Magnetometry: A Novel Approach to Tokamak Magnet Material Development

Optimisation of REBCO coated conductor tapes specifically for use in nuclear fusion will help improve the magnet component lifetimes in future tokamak reactor power plants. The focus of this work was exploration of a novel approach to irradiation studies on REBCO tapes, utilising multiple magnetic measurements to probe evolution of the REBCO flux-pinning landscape more deeply than reported in other studies, for the purpose of identifying primary limiting factors affecting performance. Gamma irradiation experiments were conducted, and pre-/post-irradiation results from DC and AC magnetic measurements using a Physical Property Measurement System (PPMS) are discussed. Magnetisation critical current density (Jc) decreased in all samples with increasing dose, except for the silver overlayer-only samples which did not contain artificial pinning centres (APCs), where Jc increased with dose. Removal of the copper stabiliser coupled with the presence of APCs allowed gamma irradiation to induce pinning force maximum peak shifts, from above 14 T before irradiation to below 9 T afterwards. Flux creep rate varied with the evolving pinning landscape, and the degree of Jc degradation directly correlated with creep rate fluctuations post-irradiation. Changes in critical temperature and diamagnetic saturation also corresponded with changes in Jc and flux creep rate. The major conclusion from this study was that minimisation of flux creep rate is the key to maintenance of performance under fusion-relevant operating conditions. Flux creep manifests as problematic AC losses in all high-temperature superconducting machines; therefore, future work will focus on reduction/prevention of the phenomenon to enhance longevity of performance in any application.

Calculation of Losses in a Motor Fed by a Conventional Inverter and a Battery Distributed Inverter

In the past decade, car manufacturers have started electrifying the traction chain of their vehicles. Although these vehicles attract more and more drivers, most of them have a limited range and are prohibitively expensive. Manufacturers must therefore offer high-performance conversion chains (particularly in terms of efficiency) while controlling costs. The power converter is a particularly crucial element of the conversion chains: it supplies the traction motor, and its structure and the way it is controlled can greatly influence the overall efficiency of the drive train. This paper studies two conversion structures that can be used as vehicle power converters, which are modeled and associated with an electric machine. The first is a classical three-phase inverter, and the second is a breakthrough architecture called IBIS (Intelligent Battery Integrated System). This battery integrates the conversion function directly into the battery, which reduces material costs. Two loss phenomena are also studied and modeled (with the help of finite element methods): iron losses in the electrical machine (magnetic losses in the ferromagnetic material used) and copper losses in the conductors (AC and DC losses in the conductors). The impact of the architecture is evaluated on a set of operating points from a road cycle standardized by the WLTP procedure.

Striating of REBCO-Coated Conductors for AC Loss Reduction

Striating of REBCO-Coated Conductors for AC Loss Reduction

Optimization of REBCO Tapes through Division and Striation for Use in Superconducting Cables with Low AC Losses

This study aimed to enhance the performance of Ag-stabilized high-temperature superconducting (HTS) tapes with a focus on reducing magnetization losses. Two approaches were employed: dividing the tapes into narrower widths and introducing striation at the level of the superconducting layer. The process of laser ablation proved to be an effective method for implementing these modifications. The quality of the cut edges and grooves was assessed using scanning electron microscopy. To evaluate the electrical properties, measurements were conducted on the critical current and magnetization loss in samples at different stages: in their initial state, after cutting, and after the striation process. Of the two modifications, the striation process more effectively reduced the AC losses in the HTS tapes, approximately by one order of magnitude. The retention of critical current remained high after cutting, but varied with the number of created filaments after the striation process. Subsequently, a short cable was wound from the cut and striated HTS tape. This cable demonstrated a remarkable sixfold reduction in AC losses compared to the initial HTS tape.

Ic measurement of twisted multifilamentary MgB2 wires with non-magnetic sheath over a wide range of temperatures and fields

All-superconducting rotating machines have the potential for meeting the high power density and high efficiency required for electrical aircraft applications. However, very high AC loss encountered in superconducting armature windings could hinder their development. Multifilamentary MgB2 wires are one of the promising candidates for the stator windings, due to their potentially low AC loss properties with small filament size and twist pitches. As the first step, the dependence of critical current and n-value on magnetic fields and temperatures Ic(B, T) and n(B,T), which are basic input parameters for AC loss simulation, needs to be measured. In this work, we present transport Ic measurements in three non-magnetic multifilamentary MgB2 wires (MgB2/Nb/CuNi/CuZn): one large wire with a 0.70 mm diameter and 25 mm twist pitch, and two small wires with a 0.48 mm diameter each and a 10 mm and 30 mm twist pitch respectively. A four-probe direct current method is used to measure Ic of the MgB2 wires with variations in temperature (15 – 35 K) and magnetic field (0 – 5.5 T). Full Ic data for the small wire with 10 mm twist pitch was obtained, and the n-values were mostly less than 20. While the Ic data for the large wire at low fields was more limited due to heating, the n-values were higher and could be up to around 100. The difference is attributed to the different filament sizes. Experiments also found that there is no significant hysteresis in the transport critical current measured by decreasing or increasing magnetic fields due to the non-magnetic sheaths. This non-hysteretic characteristic is critical for lowering AC loss because the additional losses from magnetic sheaths can be eliminated. From the magnetic-field dependence of critical current density, an empirical expression has been developed that provides suitable extrapolations to lower fields for the large wire.

Experimental and Numerical Investigations on the Parameters of a Synchronous Machine Prototype with High-Temperature Superconductor Armature Windings

In their applications in electrical machines, high-temperature superconductors (HTSs) are mainly used as inductors in synchronous machines due to the AC losses which can lead to high cryogenic costs. In this work, we show the possibility of their use as armature windings, handling some precautions. The approach is based on the combined use of modeling and measurements. The construction and the preliminary tests of a handmade prototype of an axial field HTS synchronous machine are presented. Several tests have been conducted at liquid nitrogen temperature. The measurements have been confirmed by modeling results. The preliminary tests on the prototype, in both modeling and measurements, are very promising.

Enhancing the optical, electrical, dielectric properties and antimicrobial activity of chitosan/gelatin incorporated with Co-doped ZnO nanoparticles: Nanocomposites for use in energy storage and food packaging

The solution casting method was utilized to produce a brand of new nanocomposites made of chitosan (Cs), gelatin (Ge), and co-doped ZnO nanoparticles (NPs). The physicochemical characteristics of these nanocomposites were examined using a variety of methods. The doped samples' XRD patterns clearly demonstrated changes in the structural features of the Cs/Ge host polymer, with the widening of the peak at 2θ = 20.31 becoming more prominent as Co-doped ZnO NPs concentration increased. Tauc's relation was utilized to describe the direct and indirect bandgap energies using UV–Vis analysis. By including 3.5 wt% of Co-doped ZnO NPs, the optical energy gap direct and indirect of pure Cs/Ge was reduced from 5.22 to 4.92 eV to 4.90 and 4.42 eV, respectively. Co-doped ZnO NPs reinforcing has a significant impact on the in ac conductivity, dielectric constant and loss tangent values. An ionic conductivity of 1.089 × 10−7 S/cm at Cs/Ge-3.5 wt% Co-doped ZnO NPs was observed. The nanocomposites' antimicrobial effect on bacteria and fungi was tested. The adding of 3.5 %Co-doped ZnO NPs improved the activity against S. aureus (22 mm), E. coli (13 mm), A. niger (29 mm), and C. albicans (27 mm) despite the fact that the investigated pure mix had no effect on the microbiological strains. The current research's remarkable findings in terms of optical, dielectric, electrical, and antimicrobial effects indicate that Cs/Ge-coated ZnO film will have significant uses in both food packaging and energy storage devices.

Equivalent 2-D FEA Modeling Method for AC Loss Analysis of High-Speed Electrical Machines With Litz Winding Considering Incomplete Transposition

In high-speed electrical machines, litz wire shows great performance on reducing the AC loss under complete transposition, which is well-known. However, due to technological limitation, its pitch cannot be made to match the stack length in small aspect ratio machines, bringing significant AC loss. And 3D FEA modeling method is too complicated for its twisted structure and time-consuming. This paper proposed an equivalent 2D FEA modeling method for high-speed electrical machines with litz winding. The machine is divided into several parts along the axial equally, and each part is established by a 2D FEA model approximatively in which litz winding transposition is considered. All 2D models are connected in series in field-circuit coupling model. The influences of structural parameters on AC loss are also analyzed, providing guidance for the optimal design of litz winding in high-speed electrical machines.

Design of Axial Flux HTS Machine Prototype and AC Losses Calculation

Design of Axial Flux HTS Machine Prototype and AC Losses Calculation

Pulsed Field Stability and AC Loss of ITER PF Joints by Detailed Quantitative Modeling

Pulsed Field Stability and AC Loss of ITER PF Joints by Detailed Quantitative Modeling

AC losses calculation of parallel multi‐strand flat wire windings for automotive drive motor

AbstractAutomobile drive motor with flat wire winding has improved the slot fill factor and efficiency. However, under the current environment of drive motors development to high frequency and voltage, the increase in winding AC loss has weakened those advantages. Accurate analysis of AC loss and the design of high‐performance windings have become the key issues and difficulties in the design process of drive motors. Based on the winding AC loss generation mechanism, the authors propose a winding AC loss analysis method, which can effectively separate DC loss, eddy current loss, and circulating current loss. The method is used to analyse winding AC loss of 60 kW flat wire winding permanent magnet synchronous motor (PMSM). In addition, parallel multi‐strand flat wire windings are proposed to reduce the winding AC loss and eliminate the limitation of the magnetic load of the motor on the selection of winding layers. The AC loss of the parallel multi‐strand flat wire windings at different frequencies is calculated, which demonstrates the effectiveness of the proposed winding topology in reducing the winding AC loss. In addition, the correctness of the simulation model was verified through experiments, and the loss calculation method was verified through finite element analysis.

Winding Loss Suppression in Inverter-Fed Traction Motors via Hybrid Coil Materials and Configurations

In a typical inverter-fed AC drive system, the stator windings carry a current with a large harmonics content, resulting in an increased AC loss. In this paper, the additional copper losses caused by non-sinusoidal currents are investigated for different magnet wire topologies, including the flat conductor, stranded, and litz wires. Also, a two-slot simplified model is introduced for accurate prediction of the AC losses at high frequency. It is found that one of the major issues of the conventional copper coil is that the losses are not uniformly distributed across the slot, and over 70% of the losses are concentrated near the slot opening. Moreover, using the transient finite element method, different winding topologies and arrangements are simulated at the stranded level to evaluate the losses and current density for each strand under highly distorted currents. Furthermore, different coil samples are prototyped for the same slot geometries to compare their performance under the same pulse-width modulation (PWM) waveforms for a wide range of frequencies. Finally, new hybrid coil topologies are proposed, which employ different magnet wires or materials within the same slot. The results demonstrate that utilizing a mixed wire configuration can effectively mitigate the adverse effects of eddy current losses. This approach can yield up to 16–41% lower losses while also achieving a weight savings of 36–70%.

Analysis of AC Loss Characteristics in Stacked Superconducting Strips in Complex Environments

Analysis of AC Loss Characteristics in Stacked Superconducting Strips in Complex Environments

High temperature superconducting CORC cable with variable winding angles for low AC loss and high current carrying SMES system

Owing to the rising demand for enhanced high-current capacity within superconducting magnetic energy storage (SMES) system used in power grids, there is a growing focus on enhancing the current-carrying capability of SMES setups wound with conductor on round core (CORC) cables. However, it is crucial to note that the dissipation of AC losses in CORC cables during rapid charge and discharge cycles can substantially impact the safe operation of SMES. The CORC cable is crafted by spirally winding numerous ReBCO tapes around copper tubes. Even slight alterations in the winding angles of these tapes can result in shifts at current distribution across the ReBCO tapes, thus leading to differences in AC losses. Hence, the primary objective of this paper is to study the effect of varying winding angles of each ReBCO layer on AC loss. The adoption of variable angles results in the reduction of current flowing through the outermost tapes. And the AC losses in the outermost tapes happen to account for the majority of the total AC losses. Through simulations and experiments, it was observed that the AC loss in the CORC cable with variable angles (4 × 12, 25°–40°) was 25% lower than that in the case of fixed angles (3 × 11, 45°). These findings demonstrate a noteworthy downward trajectory in AC losses when variable angles are applied to the CORC cable. These insights hold significant value for the practical application of CORC cables within SMES systems.

Understanding ac losses in CORC cables of YBCO superconducting tapes by numerical simulations

Alternating current (ac) losses in conductor-on-rounded-core (CORC) cables of YBCO high-temperature superconducting (HTS) tapes are a significant challenge in HTS power applications. This study employs two finite element analysis (FEA) models to investigate the contributions from different ac loss components and provide approaches for reducing ac losses in cables. An FEA model based on the T-A formulation treats the cross section of thin superconducting layers as 1D lines and, therefore, only can predict the ac loss generated by the perpendicular magnetic field. In contrast, the model based on H-formulation can be performed on the actual 2D rectangular cross section HTS tapes to provide the total ac losses generated by magnetic fluxes penetrating from both the edges and surfaces of HTS tapes, although this model requires more computing time and memory. The 1D and 2D simulation models were validated by cross comparing the results from both models and by comparing sub-section and full cross section models. Subsequently, two models relate cable design and operational parameters to the surface and edge losses of a two-layer CORC cable by considering the (1) relative contributions of edge and surface losses to the overall ac losses; (2) effect of the current distribution between inner and outer HTS layers on ac losses; (3) impact of the tape alignment on ac losses in each HTS layer; (4) influence of the thickness of HTS layers on ac losses; (5) effect of size and number of inter-tape gaps on ac losses; and (6) contribution frequency on the ac losses. The research results given in this paper are therefore not only valuable to suggest strategies for reducing ac loss in multi-layer cables but also for developing more accurate and effective methods to calculate ac loss in CORC HTS cables.

Numerical modelling of HTS tapes under arbitrary external field and transport current via integral method: review and application to electrical machines *

Superconductors in practical use can be subjected to spatially non-uniform and time-varying external magnetic field as well as carrying a transport current, for example, in an electrical machine. This paper verifies that the integral method can be used in situations in which the external field is spatially non-uniform, by providing both theoretical reasoning and simulation results. Variations in the integral method are reviewed, such as how to impose transport current. Further, the integral method is applied to calculate ac loss in superconducting tapes in an air-cored electrical machine in a two-stage process: the external field is calculated in a COMSOL model without superconducting tapes, and exported into the integral method model that consists of the tapes only. The time taken by the integral method is a small fraction of the time taken by the full machine model in COMSOL, which uses the T-A formulation. There are good agreements between the full COMSOL model and two-stage method incorporating the integral method.

Risk reduction by means of FLEX strategies in pressurized water reactors

One of the key lessons learned from the Fukushima Dai-ichi accident was the importance of the challenge presented by the loss of safety-related systems after a Beyond Design-Basis External Event (BDBEE). In particular, Extended Loss of AC Power (ELAP) or Loss of Ultimate Heat Sink (LUHS) can severely compromise key safety functions associated with core cooling and containment, ultimately leading to reactor core damage. Because of that the so-called Diverse and Flexible Coping Strategies (FLEX) were designed.These aforementioned FLEX strategies are also useful to avoid core damage in sequences due to internal events. Therefore, these FLEX strategies should be incorporated in the Level 1 Probabilistic Safety Assessment (L1PSA) to analyse their impact on core damage frequency (CDF). This work quantifies the impact of FLEX strategies by using a generic model (3 loops, PWR-WEC) developed by the Universidad Politécnica de Madrid (UPM) in collaboration with the Spanish Nuclear Regulatory Body (CSN). As a result, a decrease of the CDF at power for internal events is observed and, therefore, indicates that these FLEX strategies have a positive impact on the plant safety not only for BDBEE but also for other accidental conditions.

Material Tradeoff of Rotor Architecture for Lightweight Low-Loss Cost-Effective Sustainable Electric Drivetrains

The art of the successful design of high-speed electrical machines comes with many challenges in the mass, size, reliability, and energy efficiency. Material engineering of electrical machines has been identified as a key solution for higher power dense electric drivetrains. One of the main challenges at high speed is the eddy-current losses in the active electromagnetic parts, especially magnetic materials and permanent magnets (PMs). This study is devoted to the selection of PM rotor materials using multidisciplinary design optimization for a high-speed electric drivetrain. Beside AC loss minimization, more disciplines are considered, such as the minimization of weight, and cost. Different laminations are investigated with different magnetic properties as well as cost. Additionally, different PMs are optimized considering low-cost ferrite and high-coercivity permanent magnets (HCPMs). Moreover, the optimal materials are identified which have the best balance between loss, weight, cost, ripples. Finally, different rotor designs are prototyped, assembled, and tested using the same stator configuration. Also, the best rotor design is selected, and the electromagnetic performance is measured and compared with conventional designs. The optimal design results in 8% extra torque with at least 20% weight reduction.

AC Loss Analysis in Superconducting Cables Carrying Characteristic and Noncharacteristic Harmonic Currents

Harmonic distortions - especially in current waveform - are the inherent nature of any power system such as urban grids, wind farms, electric aircraft, and other electrified transportation units that could change the AC loss value in High Temperature Superconducting (HTS) cables. The aim is to investigate the impact of non-sinusoidal currents with different integer-harmonics, inter-harmonics, and sub-harmonics on the AC loss characteristics of a 22.9 kV, 50 MVA HTS cable. This was accomplished by using an Equivalent Circuit Model (ECM). To do so, current waveforms containing different harmonic components were passed to the ECM of HTS cable. For evaluating the impact of distorted current waveforms on the AC loss of the HTS cable, the ECM was validated by means of Finite Element Method (FEM) in tape level. The results of validation phase have shown a good agreement between the AC loss value derived by ECM and those calculated by FEM published in literature. The results showed that when current waveform was distorted by harmonics, the value of AC loss was changed significantly with respect to variations of harmonic phase angle, order, and amplitude. Results also indicated that 5 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sup> harmonic order has the highest impact on the AC loss value and could increase 6% to 80% of AC loss in comparison to pure sinusoidal current. Sub-harmonics and inter-harmonics could also increase the AC loss value to maximum 88% and 64% higher than that of sinusoidal condition.

Multifilament HTS Cables to Reduce AC Loss: Proof-of-Concept Experiments and Simulation

Reducing AC losses of HTS is essential for AC application since it can lower the constraint on the cryogenic cooling demand. Several studies have reported that the manufacturing of multi-filament HTS cables can reduce AC loss. However, large coupling losses were identified in the existing cables, due to the existence of coupled copper or soldering layers. We report in this paper a novel way to develop multi-filament HTS cables, mainly focusing on suppressing the coupling losses by reducing the contact resistivity within the HTS cables. Heat shrink tubes are used to directly insulate narrow HTS filaments into a cable structure. Sample cables were made with 4 mm and 2 mm wide HTS strips. Both transport losses and total AC losses in a rotational magnetic field were measured to quantify the AC loss reduction for the multi-filament HTS cables. The measurements were used to validate the modelling results, and to predict AC loss reduction for 1 mm wide HTS cable. The results showed loss reduction up to around 90% in the 1mm wide HTS cable compared with 4 mm cable. As a result, the proposed multi-filament HTS cables will have promising applications in reducing AC loss.