To this date, the characterization of Non-Insulated HTS coils for parameter estimation has been conducted using relatively slow current ramps. In the present work, a methodology based on AC signals is proposed to get additional parameters to refine the model of such coils and to improve on the existing lumed-parameter models for DC applications under dynamic responses. In that regard, two sets of sequential characterizations were conducted in liquid nitrogen at 77.3 K. First, a classical U(I) characterization in DC and different ramp tests were carried out to deduce the critical current ICC and the self-inductance of the NI coil. Second, AC measurements are performed at different frequencies and current magnitudes. From these last measurements, it was found that the lumped-parameter model best agreeing with experimental data is serial and not parallel as usually considered in DC. Thus, it further simplifies the equivalent electrical circuit of the NI HTS coils with a serial resistance RS connected in series with a serial inductance XS. Both electrical parameters can be directly obtained from voltage measurements and strongly depend on frequency but not the current amplitude in subcritical conditions. Ultimately, a lumped-parameter model is a useful approach to understand the behavior of NI HTS coils interacting with a more complex system or to study their response to transients in DC or DC+AC conditions.

The present paper deals with the development of a costumed-made system and techniques to address the challenges of the magnetization and characterization of bulk superconductors as large as 100 mm in diameter. The system is composed of a dry superconducting magnet capable of producing a field variation up to 18 T and a measurement setup relying on an advanced field mapping arrangement made of a 10 & times; 10 Hall sensor matrix for rapid magnetic field acquisition under 0.5 s. To achieve the desired accuracy, the experimental setup incorporates precise thermal management and calibration. Its purpose is to investigate strategies to enhance the stability, structural integrity, and overall performance of superconducting bulk materials magnetized in high magnetic fields. The goal is to promote scientific collaborations through a dedicated experimental facility for forthcoming magnetization and fast field-mapping studies, thereby supporting the development of bulk superconductors.

The design of a superconducting armature is currently one of the major challenges for the development of a cryogenic turboelectric chain for aeronautics. To limit the voltage rise in aircraft, HTS coils are designed with parallel strands and must withstand both thermal constraints related to the presence of AC losses and mechanical constraints during operation. In this study, the AC losses of an impregnated 3-parallel strands racetrack double pancake HTS coil were investigated for currents and frequencies ranging from 30 to 150 A and from 40 to 440 Hz, respectively. Experimental results show that despite an overall hysteresis loss behavior, mechanical losses of vibrational origin seem to be part of the loss balance, particularly at low current and high frequency where they appear to be preponderant.

This paper presents a fast-integral modeling approach for the design and characterization of large-scale non-inductive high temperature superconducting (HTS) coils made of first-generation HTS tape. The integral modeling is combined with a strategy of far tape approximation allowing to model a reduced set of consecutive tapes instead of the entire coil. It makes it possible to estimate the losses and the current density distribution in the coil, under different current supply. This leads to a considerable reduction in the computation time. The calculated AC losses show a good agreement with the Norris ellipse formula and measurements, highlighting the importance of considering the elliptical section of the superconductor in the tape, in the modeling. The developed modeling approach is in particular useful in the AC + DC mode, where Norris’s formulas cannot be used to determine the losses. Besides, some interesting phenomena have been observed, related to the current distribution in the tapes at different AC and DC current values.

Flux-Pinning Docking Interfaces (FPDI) in satellite systems were developed using bulk superconductors and permanent magnets in previous works. However, such FPDIs have limited magnetic field strength, consist of heavy-weight material, and can only be used with a single purpose, i.e., as chasing or docking satellite. Replacing the magnetic material in the FPDI by a trapped field (TF)-magnet would enable the interface to operate for both purposes, i.e., generating a (stronger) magnetic field and trapping it. We show the requirements for such a system and discuss the possible gains when using a TF-FPDI in satellites. To reduce the system weight, the use of superconducting foams as superconducting material is discussed in detail. Furthermore, the use of superconducting foams, the size of which can be easily upscaled, may also comprise the function of the damping material, so even more weight could be saved for the payload.

This article presents an integral modeling approach for computing ac losses in high-temperature superconductors near magnetic materials. The current density and magnetic field distributions are calculated by solving Maxwell's equations in integral form in the active parts. Equivalent surface and interface current densities are considered in the magnetic material to take into account its magnetic field-dependent relative permeability. The proposed approach is applied to compute ac losses in a second-generation high-temperature superconducting tape with a magnetic substrate. The obtained results are compared with the finite element method using H formulation to check the validity and performances of the proposed integral approach.

In this work, a novel superconducting (SC) inductor topology for an axial flux synchronous machine is presented and tested. The proposed device combines HTS YBaCuO bulks and coils supplied with DC current to create a variable air gap flux density distribution. In fact, the two SC bulks modulate and redirect the flux lines produced by the coil thanks to their magnetic field shielding property. This results in a periodic space variation of the axial component of the flux density. A 3D electromagnetic modeling based on a finite element solution is developed to demonstrate the relevance of using the magnetic shielding properties of SC bulks. In order to verify the screening properties of the SC bulk, a prototype of the proposed inductor was constructed and tested in the laboratory.

The realization and preliminary tests of a high temperature superconducting axial-field synchronous machine (HTS-AFSM) prototype are presented in this paper. The HTS machine consists of a 3-phase stator with HTS armature winding and a permanent magnet (PM) rotor. The HTS armature winding contains three pancake coils made of BSCCO tape forming a single layer nonoverlapping concentrated stator windings. The rotor is composed of four NdFeB permanent magnets. Several tests have been carried out such as voltage vs. currents curves of the HTS coils, static torque, back-EMF and load tests in generator mode. A 3D semi-analytical model, based on integral equations, has been used to check out the measured electromagnetic quantities. It has been shown that the measured and the calculated quantities are in satisfactory agreement.

Superconducting YBa2Cu3Oy (YBCO) foams were prepared using commercial open-cell, polyurethane foams as starting material to form ceramic Y2BaCuO5 foams which are then converted into superconducting YBCO by using the infiltration growth process. For modelling the superconducting and mechanical properties of the foam samples, a Kelvin-type cell may be employed as a first approach as reported in the literature for pure polyurethane foams. The results of a first modelling attempt in this direction are presented concerning an estimation of the possible trapped fields (TFs) and are compared to experimental results at 77 K. This simple modelling revealed already useful information concerning the best suited foam structure to realize large TF values, but it also became obvious that for various other parameters like magnetostriction, mechanical strength, percolative current flow and the details of the TF distribution, a refined model of a superconducting foam sample incorporating the real sample structure must be considered. Thus, a proper description of the specific microstructure of the superconducting YBCO foams is required. To obtain a set of reliable data, YBCO foam samples were investigated using optical microscopy, scanning electron microscopy and electron backscatter diffraction (EBSD). A variety of parameters including the size and shape of the cells and windows, the length and shape of the foam struts or ligaments and the respective intersection angles were determined to better describe the real foam structure. The investigation of the foam microstructures revealed not only the differences to the original polymer foams used as base material, but also provided further insights to the infiltration growth process via the large amount of internal surface in a foam sample.

Stability issues exist in embedded electrical grids, mainly due to power electronics. One of the solutions is to use a superconducting power filter (SPF), made of a non-inductive superconducting coil. The DC losses are close to zero, the coil being in its superconducting state. The AC losses, proportional to the frequency, are weak but still exist and can be used to increase the stability of the DC grid. In this paper, different SPF prototypes are presented and experimental characterizations are exposed: measurements of the critical current, measurements of AC losses and measurements of AC+DC losses. This AC+DC loss measurement is unusual, tricky and especially developed for SPF application. Experimental results are discussed and compared to calculations obtained with the analytical Norris formulas. Strip model formula underestimates losses and elliptical section formula overestimates losses but both formulas give good approximation of the losses and are therefore useful tools to design a SPF.

In the process of manufacturing products from high-temperature superconductors (HTS), quality control must be carried out. Traditionally, for HTS coils, electrical tests are carried out to determine critical current. In the case of an unacceptable result, it is necessary to determine the cause. Therefore, it is necessary to develop nondestructive testing methods. This article proposes a technology for manufacturing quality evaluation. It is based on determining the actual location of the tape and the gaps between the turns and rows of the coil and analyzing these values. For this purpose, samples were scanned using computed tomography (CT) with a Nordson Dage XD7600NT X-ray inspection system with a μCT module. The obtained data were analyzed using VolumeGraphics VGStudio 2.2 software. Furthermore, the proposed technology can be used as part of a predictive analysis of the state of HTS coils in the windings of electrical machines.

The electromagnetic properties of high temperature superconductors (HTS) are characterized with the explicit intent to improve their integration in electric power systems. A tape and a coil made of Bismuth Strontium Calcium Copper Oxide (BSCCO) are considered in the presence of electromagnetically active materials in order to mimic properly the electromagnetic environment typical of electrical machines. The characterization consists of the determining the critical current and the AC losses at different values of the frequency and the transport current. The effects induced by the proximity of the active materials are studied and some related experimental issues are analyzedc.

In manufacturing high-temperature superconductor (HTS) devices, outgoing control of their quality must be carried out. Conventionally, for coils made of HTS, electrical tests are carried out to determine the critical current. In case of an unsatisfactory result, the reason why the critical current is below its expected value should be determined. The HTS tape coil manufacturing quality should be checked on the basis of non-destructive test methods. The article proposes an HTS coil examination technology, according to which the actual locations of the tape and gaps between the coil turns and rows are determined with subsequently analyzing the obtained values. To this end, the samples were scanned using the computed tomography method on the Nordson Dage XD7600NT X-ray machine with the μCT module, and the data obtained were processed using the VolumeGraphics VGStudio 2.2 visualization software. The proposed technology can be used as part of a predictive analysis of the state of the HTS coils of electrical machine windings.

In this article, the inductance variation with the current in high-temperature superconducting (HTS) pancake coils is investigated numerically and experimentally. Both dc and ac modeling approaches are developed. The results show that the dc modeling approach, even though it considers the non-uniformity of the current density distribution using a power minimization criterion, is not sufficient to characterize the inductance variation, which is affected by the dynamic behavior of HTS coils. The ac modeling approach reproduces a variation of the inductance similar to the experimental results.