Study Of AC Losses Research Articles

Numerical study of AC loss and H-formulation for high temperature superconductors

Abstract The high-temperature superconductor (HTS) plays a crucial role in power grids due to its ability to carry high current densities and withstand strong magnetic fields, making it ideal for applications like superconducting magnetic energy storage (SMES). However, integrating SMES systems with the grid introduces challenges, particularly regarding the generation of AC losses during cyclic operations, which can lead to temperature increases in HTS tape. This article presents a method for calculating AC losses and determining the magnetic field formulation at the critical state of HTS using numerical techniques. The study focuses on analyzing the charging and discharging operations of a grid-integrated SMES system based on silicon-controlled rectifiers. Additionally, the critical current of the HTS tape is determined using the four-probe method to characterize its I-V characteristics.

AC Loss Study in REBCO HTS Tape and Four-Tape Stack Carrying AC Current With DC Offset

AC Loss Study in REBCO HTS Tape and Four-Tape Stack Carrying AC Current With DC Offset

Study on the response of the winding direction of multi-layer CORC cable to its electromagnetic characteristics

A Conductor on Round Core (CORC) cable wound with a high-temperature superconductor is an important cable concept for high-current density applications. It is widely used in large power systems because of its advantages of good flexibility and high engineering current density. However, the complex design structure of CORC cable makes it very difficult to understand its electromagnetic properties (such as AC loss). In particular, the different winding directions of each layer in multi-layer cable have a great influence on its electromagnetic characteristics. In this paper, the H-method is used to solve the electromagnetism and mechanics equations. The influence of the winding direction of CORC cable on its electromagnetic field distribution characteristics, AC loss, and mechanical variation under the action of external magnetic field is investigated. The AC loss study of single-layer cable reveals that when the applied magnetic field is increased from 0.01 to 0.02 and 0.03 T, the AC loss peak of the cable increases by 107 and 103 orders of magnitude, respectively, indicating that the effect of low applied magnetic field on the AC loss of the cable is more significant. For multi-layer cables, cables with opposite winding directions have a greater depth of current density penetration than cables with the same winding direction. In addition, the mechanical variations of multi-layer cables with different winding orientations are explored. The results show that the Mises stress in the cable with the same winding direction is about 32% higher than that of the cable with the opposite winding direction, which indicates that the method of winding the cable in the opposite direction between adjacent layers of tape can avoid excessive mechanical stress.

Parametric AC Loss Study on 7 MW Fully Superconducting Direct-Drive Wind Turbine Generators With Concentrated Stator Winding

Parametric AC Loss Study on 7 MW Fully Superconducting Direct-Drive Wind Turbine Generators With Concentrated Stator Winding

Experimental AC loss study on REBCO coil assemblies coupled with an iron cylinder

In high-temperature superconducting (HTS) power devices, the presence of iron cores changes the magnetic field profile around the HTS coil windings, potentially affecting their AC loss characteristics. AC loss measurements for HTS coil windings coupled with an iron core using the electrical method can lead to a significant error, owing to the indirect estimation of the iron core loss through using a copper test coil. To investigate the cause of the experimental error and the influence of an iron core on coil AC losses, transport AC losses of REBCO double pancake coil (DPC) assemblies coupled with an iron cylinder were measured. A 40-turn 1DPC and an 80-turn 2DPC assembly wound with 4 mm SuperPower wire were employed in the measurements. To ensure the same iron core loss using the HTS coil assembly and the copper coil, 2D finite element method simulations were conducted iteratively to design the iron core and the copper coil to get the same local magnetic field distributions in the designed iron core for the two cases. The main cause of the error is due to the difference in local magnetic flux densities in the iron core generated by the HTS coil assembly and the copper coil even when the ampere-turns of the coils are identical. We showed that the simulation-guided measurement method can assure accurate AC loss measurement in the HTS coil assemblies coupled with iron cores. Compared with the AC losses in the 1DPC and 2DPC coil assemblies without the iron cylinder, the presence of the iron cylinder significantly increases the coil losses. Frequency dependence is observed in the coil AC losses of the 1DPC and 2DPC assemblies when coupled with the iron cylinder. This is due to the eddy current induced in the iron cylinder generating a magnetic field, which influences the coil AC loss.

AC loss study on a 3-phase HTS 1 MVA transformer coupled with a three-limb iron core

High-temperature superconducting (HTS) technology provides an alternative approach to achieve compact transformers. Addressing AC loss in the HTS winding is crucial for HTS transformer applications. Most numerical AC loss studies on HTS transformers have neglected the influence of iron cores. This work carries out an AC loss study to explore the impact of an iron core on the HTS windings in a 3-phase HTS 1 MVA transformer coupled with it. AC loss simulations for the transformer winding both with and without the iron core are conducted by adopting the three-dimensional (3D) T-A homogenization method. When the iron core is incorporated, the saturation magnetic fields of iron materials, flux diverters (FDs) with different geometries, and variations in turn spacings in the LV winding composed of Roebel cables are considered to investigate their influence on the AC loss of the transformer winding. The inclusion of the iron core leads to a 1.2% increase in AC loss for the transformer winding while simulating at the rated current. We attribute this slight difference to the non-inductive winding structure of the transformer winding, where a strong magnetic field generated in the space between the LV and HV windings effectively shields the influence of the iron core.

AC loss study of high-temperature superconducting stacked conductors based on parameter identification method

Fusion magnets generate significant AC loss during the processes of excitation and demagnetization. The electrical measurement was predominantly employed as the method for estimating the AC loss. However, the phase-locked amplifier method and integral method (IM) can access the average power across one or multiple current cycles but leave the instantaneous power value unrecorded. In this study, the AC loss of two types of high-temperature superconducting (HTS) stacked conductors composed of REBCO and Bi-2223 were measured. An AC loss analysis method based on parameter identification method is employed to study AC loss in REBCO and Bi-2223 stacked conductors by identifying their instantaneous inductance and instantaneous resistance. Unlike the integral method, the AC loss analysis method based on parameter identification method can analyze the average power, and also the instantaneous power at any given time using a fixed forgetting factor which can affect the accuracy of the calculation. The experimental data suggest that, under identical frequency and current, the AC loss of the REBCO stacked conductor is approximately three times that of the Bi-2223 stacked conductor.

Experimental and Numerical Study of AC Losses in HTS Coils of AC Electric Machines

Experimental and Numerical Study of AC Losses in HTS Coils of AC Electric Machines

Experimental and numerical study of AC losses in HTS coils of AC electrical machines

Experimental and numerical study of AC losses in HTS coils of AC electrical machines

Effects of Noncharacteristic Harmonics on AC Losses of High-Temperature Superconducting Coils

Superconductivity is a remarkable state of matter exhibited by some materials, which is characterized by the vanishing of electrical resistivity at cryogenic temperatures, among other phenomena. However, the prospective economical viability of superconducting devices relies heavily on an efficient cooling system to remove the heat generated during operation. Although this would be meaningless in conventional devices, it occurs at cryogenic temperatures, impacting the efficiency and cost of the whole system. Thus, it is necessary to predict the losses of, e.g., superconducting coils in power systems. This article presents a study of ac losses in superconducting coils due to noncharacteristic current harmonics. These harmonic components are typical in electromechanical drives like the one presented in this article. A computational model of high-temperature superconducting coils and the numerical procedure used to solve the problem are described in this article. The contribution of the noncharacteristic harmonic components in these ac losses will be presented. These results, obtained by computational analysis, were validated in experimental tests that assessed the power dissipated due to triangular waveforms currents.

Analysis on the Effect of Superconductor Layer Thickness on the AC Loss of Conductor on Round Core (CORC) Cables

Superconducting Conductor on Round Core (CORC) cables fabricated by several high temperature superconducting (HTS) tapes are able to carry enormous electrical current density, to be widely used in a variety of superconducting applications such as power transmission, fusion, and magnetic resonance imaging (MRI). However, the AC losses induced in the superconducting tapes under alternating current or magnetic field generate heat dissipation which can reduce the electric power efficiency. Therefore, it is essential to analyze the AC loss behavior of CORC cables as well as consider methods to reduce it. This paper presents an AC loss study of CORC cables with several different superconducting layer thicknesses. The CORC cable simulation model is built in a software suite named COMSOL Multiphysics utilising the finite-element method (FEM) solved by the three-dimensional (3-D) H-formulation. By implementing FEM simulations, the cases of increasing the degree of freedom of superconducting layers have been considered, and the AC losses of a single layer CORC cable model with three tapes mounted around the core have been calculated and analyzed for different layer thicknesses. Simulation results are verified with experimental results measured in previous literature.

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.

AC losses in horizontally parallel HTS tapes for possible wireless power transfer applications

This paper presents the concept of using horizontally parallel HTS tapes with AC loss study, and the investigation on possible wireless power transfer (WPT) applications. An example of three parallel HTS tapes was proposed, whose AC loss study was carried out both from experiment using electrical method; and simulation using 2D H-formulation on the FEM platform of COMSOL Multiphysics. The electromagnetic induction around the three parallel tapes was monitored using COMSOL simulation. The electromagnetic induction and AC losses generated by a conventional three turn coil was simulated as well, and then compared to the case of three parallel tapes with the same AC transport current. The analysis demonstrates that HTS parallel tapes could be potentially used into wireless power transfer systems, which could have lower total AC losses than conventional HTS coils.

Study on AC loss measurements of HTS power cable for standardizing

High-temperature superconducting power cables (HTS cables) have been developed for more than 20 years. In addition of the cable developments, the test methods of the HTS cables have been discussed and proposed in many laboratories and companies. Recently the test methods of the HTS cables is required to standardize and to common in the world. CIGRE made the working group (B1-31) for the discussion of the test methods of the HTS cables as a power cable, and published the recommendation of the test method. Additionally, IEC TC20 submitted the New Work Item Proposal (NP) based on the recommendation of CIGRE this year, IEC TC20 and IEC TC90 started the standardization work on Testing of HTS AC cables. However, the individual test method that used to measure a performance of HTS cables hasn’t been established as world’s common methods. The AC loss is one of the most important properties to disseminate low loss and economical efficient HTS cables in the world. We regard to establish the method of the AC loss measurements in rational and in high accuracy. Japan is at a leading position in the AC loss study, because Japanese researchers have studied on the AC loss technically and scientifically, and also developed the effective technologies for the AC loss reduction. The JP domestic commission of TC90 made a working team to discussion the methods of the AC loss measurements for aiming an international standard finally. This paper reports about the AC loss measurement of two type of the HTS conductors, such as a HTS conductor without a HTS shield and a HTS conductor with a HTS shield. The AC loss measurement method is suggested by the electrical method..

Experimental and theoretical study of AC losses in variable asymmetrical magnetic environments

Measurements of AC losses in a HTS-tape placed in between two bulk magnetic shields of high permeability were performed by applying calorimetric techniques for various asymmetrical shielding arrangements. The experiment was supported by analytical calculations and finite-element simulations of the field and current distributions, based on the Bean model of the critical state. The simulated current and field profiles perfectly reproduce the analytic solutions known for certain shielding geometries. The evaluation of the consequent AC losses exhibits good agreement with measurements for the central position of the tape between the magnets but have increasing discrepancy when the tape is approaching the shields. This can be explained by the increasing contribution of the eddy currents and magnetic hysteresis losses in the conducting shields.

Investigation of AC losses in horizontally parallel HTS tapes

This paper presents an AC loss study of horizontally parallel HTS tapes. We proposed to use three parallel HTS tapes as an example. The AC losses of the middle and end tape of three parallel tapes have been measured using the electrical method and compared to those of an individual tape. The effect of the interaction between tapes on AC losses has been analysed, and compared with finite-element method (FEM) simulations using the 2D H-formulation implemented in COMSOL Multiphysics. By using FEM simulations, the cases of increasing number of parallel tapes have been considered, and the normalised ratio between the total average AC losses per tape and the AC losses of an individual single tape has been calculated for different gap distances. We proposed a new parameter, Ns, a turning point for number of tapes, to divide Stage 1 and Stage 2 for the AC loss study of horizontally parallel tapes. For Stage 1, N < Ns, the total average losses per tape increased with the increasing number of tapes. For Stage 2, N > Ns, the total average losses per tape decrease with the increasing number of tapes. The analysis demonstrates that horizontally parallel HTS tapes could be potentially used in superconducting devices like HTS transformers, which could retain or even reduce the total average AC losses per tape with large number of parallel tapes.

Numerical study of AC loss of two-layer HTS power transmission cables composed of coated conductors with a ferromagnetic substrate

This work includes the simulation of hysteretic AC losses in two-layer HTS power transmission cables made of second-generation high-temperature superconducting tapes with a ferromagnetic substrate subject to an oscillating AC transport current, calling upon the COMSOL Multiphysics finite-element software program and exploiting an AC/DC module. How the AC transport loss is influenced by the arrangement of tapes, as well as the optimized design of superconducting power cables based on YBCO-coated conductors, are investigated. According to the radial arrangement of the tapes, four different orientations of ferromagnetic substrate are considered: 1) out-in (substrate of inner/outer layer facing outward/inward), 2) in-out (substrate of inner/outer layer facing inward/outward), 3) in-in (substrates of both inner and outer layers facing inward), and 4) out-out (substrates of both inner and outer layers facing outward). We found that the AC loss of the superconducting layer for the out-in arrangement is the lowest. We also compare our calculations with experimental results.

Investigation of the hysteresis losses in CC tapes after laser filamentation

Study of AC loss has been conducted on the 4 mm wide CC-tapes manufactured by SuperOx. Filamentation was carried out by laser cutting of the commercially available tapes with a copper coating. Also for comparison, original tapes and commercial multifilament tapes (manufactured by SuperOx by using chemical etching method) were studied. Losses were obtained from the magnetization curves measured on a vibration sample magnetometer in the temperature range from 4 K to 77 K. In addition, the current carrying characteristics of tapes were studied, and the effect of filamentation on the critical current value were examined. We present an analysis of the experimental results, as well as a comparison of data for different types of samples. The possibility of decreasing the energy losses due to filamentation tapes was demonstrated.

Study of AC Loss and Temperature Distribution of a BSCCO Coil Cooled in Liquid Nitrogen or Using a Cryocooler

The prediction of critical current of the HTS coil is necessary in the HTS coil applications. This paper focuses on the AC loss and the temperature distribution of a BSCCO coil, based on the electro-thermal coupling of the AC loss and the environment, with an emphasis on the cooling boundary. The major concern of this paper is the balance between the AC loss and the cooling efficiency of the environment. This paper first provides a 2-D axisymmetric model based on the resistivity-adaption algorithm method and heat conduction equations. Then, the BSCCO coil with different thermal contact conditions and cooling methods are discussed. A 52-turn Bi2223/Ag double-pancake coil is tested. The measurement of surface temperature is compared with the model result, showing good consistency. The critical current decreasing with the increasing frequency was observed. In the cryocooler cooled situation, the coil stability might be achieved with a more economic cryocooler through operating at a lower temperature.

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.