High-temperature Superconducting Coil Research Articles

FPGA-Stabilized Magnetic Levitation of the APEX-LD High-Temperature Superconducting Coil

FPGA-Stabilized Magnetic Levitation of the APEX-LD High-Temperature Superconducting Coil

Performance evaluation of a racetrack high temperature superconductor winding in an HTS levitation platform

Abstract High temperature superconducting (HTS) is a key technology for next generation high-speed railway systems, which guarantees high current and highly efficient traction power supplies. HTS devices can reduce system weight and thus improve loads of vehicles. In high-speed maglev trains, HTS windings wound by second-generation HTS tapes play an important role in suspension and traction. However, in complex ferromagnetic environments, the performance of windings is notably influenced by the varying magnetic fields. In this paper, a new maglev platform is designed and comprised of a winding of six racetrack HTS coils, an E-shaped iron core and a magnetic guide rail. The air core structure of the winding is modeled and tested and the electromagnetic characteristics are analyzed for three dimensional finite element analysis of the platform. An A formulation is used to calculate magnetic vectors A and infer magnetic flux densities and current densities for the structures. After the winding is installed on the iron core and the magnetic guide rail is suspended above the iron core, the air gap between the iron core and the rail is varied from 0 mm to 20 mm in models and experiments. The magnetic fields, critical currents and losses of the winding in the cases of the air core and the iron core conditions are used for analysis. The comparison between the air core and the iron core conditions confirms the reliability of the proposed models. This study provides a means for the analysis of complex superconducting maglev systems.

Double-pancake superconducting coil integrated with DFIG-based wind power systems under voltage-dip events: Design and performance analysis study

The doubly fed induction generator (DFIG)-based wind turbine provides massive development in power generation. Uncertain power oscillations and voltage-dip events affect the stability of the DFIG. To mitigate the effect of voltage-dips in short period, superconducting magnetic energy storage (SMES), which possess rapid energy exchange and high power density, is integrated with large-scale renewable power systems. SMES is integrated at the DC link of the DFIG to ensure the power balance and fault ride-through (FRT) capability. During this operation, frequent current changes occur in the high-temperature superconducting (HTS) coil, which leads to an increase in AC losses. As a remedy, an additional power converter structure controlled with a model-predictive controller (MPC) is proposed. Firstly, a scale-down HTS double-pancake coil model is designed using a finite element model by which transport current loss and magnetic field formulation are studied. Additionally, the critical coil current is also verified through experimental studies. The effectiveness of the proposed MPC-based SMES integrated DFIG on DC link voltage and grid current under IEC-61000-4-11 standard, symmetrical and asymmetrical voltage-dip cases are investigated. The obtained results demonstrate that the proposed system effectively reduces transients in DC link voltage and improves the FRT capabilities of the grid.

Enhanced visualization of quench dynamics of HTS coils through embedded and distributed fiber optical sensing

The development of high-temperature superconducting (HTS) coils and magnets marks a significant advancement across various fields. To ensure their safety and reliability, thorough performance testing under extreme multi-field conditions is essential. This study introduces an innovative method that utilizes embedded and distributed fiber optical sensing (ED-FOS) in HTS pancake coils for precise real-time thermal monitoring and quench visualization. Incorporated during the manufacturing process, the ED-FOS sensors offer comprehensive and distributed measurements of thermal behavior during quenches. Our experiments demonstrate the ED-FOS effectively detects quenches caused by overcurrent and thermal issues. Unlike conventional techniques that rely on global voltage or magnetic field assessments, ED-FOS provides high spatiotemporal resolution and enhances temperature sensitivity. This capability allows for accurate, real-time identification and tracking of quench locations, which is essential for evaluating reliability and safety, as well as for improving performance. This advancement in HTS coil technology paves the way for wider application in critical fields and significantly enhances the design and management of superconducting coils.

Fast current discharging using self-coupling energy absorption for insulated high temperature superconductor magnets

Abstract Quench protection has always been challenging for high-temperature superconductor (HTS) coils. Fast current discharge after quench detection is important for a successful coil protection. The copper plates initially intended for cooling can significantly accelerate the discharging process for HTS coils through electromagnetic coupling between coils and copper plates. However, the underlying physical mechanism of this technique has not been studied thoroughly. Here we present a detailed study on the electromagnetic and thermal characteristics of HTS coils coupled with copper plates through experiments and simulations. The results show that a considerable current rebound occurs after an accelerating current drop in the early stage of the fast-discharging process. This coil current rebound is induced by temperature rise as well as the resistivity of copper plates, which are heated by induced eddy current. The heat transfer from copper plates can uniformly heat the whole coil rapidly, which speeds up the discharging process, meanwhile it can also induce overcurrent quench risk. A 30 T@20 K HTS magnet with 36 single pancakes (SP) is analyzed. The coupling copper plates can make the coil current drop to 36.9% within the initial 8 ms. The temperature rise induced by copper plates shows a considerable nonuniform distribution among the multiple coil systems. The protection can be enhanced by optimizing the resistivity of copper plates and magnetic coupling strength between plates and coils. This technique has great potential for the protection of insulated HTS magnets.

2D axisymmetric electromagnetic modeling of HTS coils based on T-A formulation with modified Newman boundary conditions

The T-A formulation based on thin film approximation has been widely used in electromagnetic modeling of high temperature superconducting (HTS) coated conductors (CCs). However, with the emergence of no-insulation (NI) HTS coils and its variant HTS coils, the electrical connection of HTS coils has become increasingly complex, and the traditional T-A formulation is challenging to handle the problems of conductors with non-negligible thickness and current sharing. This paper firstly describes the Neumann boundary condition of the T-A formulation under 2D axisymmetric symmetry in detail, as well as the conversion of different boundary conditions. And additional voltage variable is added to correct the Newman boundary condition from the perspective of circuit. Then, considering HTS CCs series or parallel stacking to carry current, the effectiveness of this method is verified by comparing with benchmark model. Finally, we extend the application range of the T-A formulation with modified Newman boundary conditions to simulate thick superconductors, and naturally process current sharing of azimuthal and radial current in circular NI HTS coils.

Overcurrent Quench Detection of Parallel-Wound No-Insulation High Temperature Superconductor Coil Based on Digital Twin Method

Overcurrent Quench Detection of Parallel-Wound No-Insulation High Temperature Superconductor Coil Based on Digital Twin Method

Current sharing in double-sided REBCO tapes

Current sharing between RE–Ba–Cu–O (REBCO, RE = rare earth) tapes within a high-temperature superconducting coil or cable is important to avoid damage from uncontrolled quench of superconducting devices operating at high currents. Current sharing between REBCO tapes is found to be limited by the contact resistivity between adjacent tapes, which is about 20x higher in the REBCO-facing-substrate (face-to-back) configuration that is commonly used in devices compared to a REBCO-facing-REBCO (face-to-face) configuration. Double-sided REBCO tapes always offer face-to-face contacts between adjacent tapes, and this benefit of excellent current sharing has been validated in experiments wherein an artificial defect is introduced in one tape in a 2-ply tape stack. Additionally, current sharing between the two REBCO layers within one double-sided REBCO tape has also been investigated. Slotting of the double-sided tapes, wherein slots through the insulating buffer stack are filled with a conductive material, has been found to significantly enhance the current sharing from one REBCO layer to the opposite layer.

Energization test apparatus of HTS coils cooled by liquid hydrogen and manufacture of split-type REBCO external field coil

Abstract Liquid hydrogen (LH2) is a potential coolant of high-temperature superconducting (HTS) devices. However, owing to the high flammability of hydrogen and the risk of hydrogen embrittlement in materials, studies on LH2-cooled superconducting devices are rare. We developed an LH2 test apparatus to analyze the basic characteristics of LH2 as a coolant and evaluate the energizing characteristics of LH2-cooled superconducting wires. A REBCO external field coil was designed and manufactured for conducting cooling stability tests on various HTS coils cooled by LH2. The field coil, comprising eight single pancake coils of 4 mm wide REBCO wires, with inner diameter 106 mm and outer diameter 250 mm was divided into upper and lower sections. The test coil was placed in the central space. A magnetic field perpendicular to the test coil’s wire surface was generated by running currents in opposite directions through the upper and lower sections. Each double pancake coil was securely placed in a stainless-steel housing to withstand repulsive electromagnetic forces. The manufactured field coil was cooled using LH2, energized to 150 A, and successfully generated the intended magnetic field of 1.75 T. No increase in voltage was observed in any of the double pancake coils, and there was no mechanical degradation due to electromagnetic forces. Subsequently, we initiated thermal runaway tests on various HTS coils using the manufactured field coil to assess the cooling stability of LH2-cooled HTS coils. The study will facilitate the development of explosion-proof designs and safety technologies for LH2-cooled superconducting devices and cooling systems.

The Interaction Between a High-Temperature Superconducting Coil and In-Series Permanent Magnets

The Interaction Between a High-Temperature Superconducting Coil and In-Series Permanent Magnets

Effect of local and global screening current on the current decay in closed-loop HTS coils

High-temperature superconducting (HTS) coils are generally operated in a closed-loop persistent current mode, which is crucial for ensuring long-term stability and minimizing heat generation in various applications. However, factors such as joint resistance, flux creep, and losses due to external fields can lead to accelerated decay of the coil’s current, making it challenging to achieve an effective persistent current mode. To gain insight into the current decay characteristics of HTS coils, we built a finite element method based model coupled with a lumped parameter electric circuit model. The model is initially verified against the experiment of an inductive magnetized HTS coil subject to a magnetic field perpendicular to the tape surface. The results indicate that the proposed model is highly effective in predicting the current decay behavior of this magnetized HTS coil and is able to provide high accuracy. With the help of this model, we have experimentally and numerically studied the behavior of a current-carrying closed-loop HTS coil subject to external alternating fields. The HTS coil is charged by a DC power supply and then shorted using a thermally-controlled persistent current switch. The current decay behavior of the HTS coil is examined under various scenarios. The simulation results show excellent agreement with experimental data, further validating the effectiveness and versatility of the modeling strategy. The influence of both local and global screening currents on the current decay performance of the closed-loop HTS coils has been investigated. For every case examined, rapid demagnetization occurred in the initial cycle of the applied alternating field. Furthermore, the current decay rate demonstrated a slight dependence on the frequency of the applied fields. Additionally, the resulting resistance has been thoroughly characterized. These insights contribute to the knowledge of the behavior and performance of closed-loop HTS coils, facilitating their practical application.

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.

Неизолированные сверхпроводящие обмотки: анализ методов описания электромагнитных процессов

Magnetic systems based on no-insulated high temperature superconductor coils (NI HTS) are finding increasingly practical applications. They became a scientific and industrial tool with enormous prospects. Their main advantage is that they are resistant to burnout due to protection in the form of a “built-in” shunt resistance. However, a serious disadvantage of NISO is the lack of a clearly defined current flow path, which makes it difficult to both describe the characteristics of such coils and predict their behavior under given conditions. This review shows the main methods for describing electromagnetic processes occurring in NI HTS and analyzes the limits of applicability of these methods.

Feasibility study on quench detection methods of Raman and Rayleigh scattering techniques in optical fiber encapsulated HTS coils

Quench detection is a key issue to be solved for safe operation of high temperature superconducting (HTS) magnets. Recently, distributed optical fiber sensors based on Raman and Rayleigh scattering techniques are proposed for quench detection in HTS applications. However, sensing and demodulating principles of these two techniques are different, and they may show different performances in quench detection. In this paper, a 13 m long optical fiber encapsulated HTS coil (OF-coil) was fabricated. Two sensing devices based on Raman and Rayleigh techniques, which are named Raman-device and Rayleigh-device, were prepared. Overcurrent and heater induced quench detection experiments in the OF-coil were carried out and the above two devices were used for quench detection. The results show that both Raman-device and Rayleigh-device can measure temperature changes of the OF-coil in the overcurrent experiment. And their quench response time is 36 s and 14 s, respectively. In heater induced quench detection experiment, Rayleigh-device can successfully acquire local temperature rise of the OF-coil, and the quench response time is 1.7 s. For Raman-device, its spatial resolution is too large to realize local quench detection.

A design study on 20 kW class axial flux motor with HTS field winding for 100 MPa liquid hydrogen pump

This paper presents a design study of a low-speed, high torque 20 kW class motor with a high-temperature superconductor (HTS) field coil for a liquid hydrogen centrifugal pump. The motor is designed based on three key concepts: 1) employing an axial-flux motor topology that can increase torque density by reducing the axial length together with a centrifugal pump; 2) using liquid hydrogen in a pump as a coolant for HTS coil; 3) adopting no-insulation (NI) YBCO solenoid coils as field coils of the motor to improve coil protection as well as mechanical stability. In the design process, first, an electromagnetic design of the axial type motor is obtained considering the required performance of previous commercial pumps. Considering the current and temperature margin to secure the HTS coils' stable operation, two types of HTS coils (solenoid type and triangle type) are designed and their performances are compared. Second, to evaluate validity of the electromagnetic designs, mechanical stresses in the HTS coils are estimated. By comparing the solenoid type and the triangle type, it is confirmed that the solenoid type has a distinct stress-reducing effect in terms of magnetic stress as well as rotational stress. Our design study results show the potential superior performance of the axial flux motor with HTS coils for several tens of kW applications with low speed and high torque loads such as liquid hydrogen pumps.

Study of the demagnetization behavior of no-insulation persistent-current mode HTS coils under external AC fields by 3D FEM simulation

The no-insulation (NI) winding technique is promising for applications in the persistent-current mode (PCM) operation of high-temperature superconducting (HTS) coils. To produce an NI PCM coil, it is essential to understand its demagnetization behavior (i.e. decay of persistent DC current) under an external AC field, which occurs in maglev trains, electric machines and other dynamic magnet systems. For this purpose, a 3D finite-element method (FEM) model, capturing the full electromagnetic properties of NI HTS coils is established. This work studied three kinds of AC fields, observing the impact of turn-to-turn contact resistivity on demagnetization rates, which is attributed to current distribution modulations. Under a transverse AC field, the lower contact resistivity attracts more transport current to flow in the radial pathway to bypass the ‘dynamic resistance’ generated in the superconductor, leading to slower demagnetization. Under an axial AC field, the demagnetization rate exhibits a non-monotonic relation with the contact resistivity: (1) the initial decrease in contact resistivity leads to a concentration of induced AC current on the outer turns, which accelerates the demagnetization; (2) the further decrease in contact resistivity makes the current smartly redistribute to avoid flowing through the loss-concentrated outer turns, thus slowing down the demagnetization. Under a rotating DC field, a hybrid of transverse and axial fields, the impact of contact resistivity on the demagnetization rate exhibits combined characteristics of the transverse and axial components. Additionally, quantitative prediction of the demagnetization rate of NI PCM coil under external AC field is instructive for practical designs and operations, which is tested by this 3D FEM model, and a comparison with experimental results is conducted.

A high-performance electromagnetic code to simulate high-temperature superconductors

Superconductivity is a physical phenomenon of some materials that allow them to conduct electrical current without resistance. This property has a wide range of applications. In particular, type-II high-temperature superconductors appear promising for building strong electromagnets carrying large amounts of current in the extreme conditions foreseen for future fusion reactors. However, their fabrication and related experiments are highly expensive and complex. Therefore, there is an increasing need for numerical models to guide the design optimization of superconducting cables and to predict their performance. In this work, we present a new code to simulate high-temperature superconductors (HTS) based on the edge finite element discretization of Maxwell’s equations in the time domain using the widely adopted H-formulation in the superconductor analysis community. This code is integrated in the High-Performance Computing (HPC) Alya suite and obtain an excellent performance up to 1024 processors in MareNostrum 4 supercomputer. This capacity allows to us to solve a wide variate of problems in big domains in relatively reduce amount of computer time, being a promising tool to aboard HTS coils design problems. Furthermore, validations against experimental data are presented and code results for superconducting tapes with different magnetic properties are analyzed.

Experimental study on AC loss of 1G and 2G HTS coils with an identical structure, geometry and number of turns

Devices made of High Temperature Superconductor (HTS) will suffer AC loss during AC operations, which has unnegligible influence on energy consumption, overall efficiency, cooling cost, and operational stability of the devices. In this study, comparative measurements on 1G and 2G HTS coil samples with an identical structure, geometry, and number of turns were systematically conducted with a calorimetric method at different current values (I rmss) and frequencies (fs). The AC loss characteristics of the HTS samples were analyzed and compared based on the experimental results. The results show that eddy current and coupling play a more dominant role than magnetic hysteresis in the total AC loss of coils made of HTS tapes. The AC loss of both samples increases with I rms and f, but the AC loss is more sensitive to I rms than to f. Under the same conditions, the 1G coil sample has a slightly larger AC loss than the 2G one.

A quench detection method for parallel co-wound HTS coils based on current redistribution

High-temperature superconducting (HTS) coated conductors (CCs) have become the preferred material for superconducting magnet applications due to their high engineering current density and high mechanical strength. However, due to the low quench zone propagation velocity of CCs, magnets wound with CCs suffer from severe quench risks. Therefore, a rapid, sensitive, and reliable quench detection method is crucial for the safe operation of such HTS magnets. In this paper, we propose a quench detection method based on current redistribution, in which two pieces of HTS CCs are soldered together at each end and insulated in the middle part, which are then parallel co-wound into a double-pancake coil. The two tightly coupled windings and low resistance joints form a very low inductance current loop, resulting in fast current redistribution between the two co-windings even at the inception of quench (with still low quench voltage). We deduced analytical solutions of the current redistribution process under different magnet operational scenarios, including constant current operation, charging and discharging, and proposed quench detection criteria. Corresponding quench tests were performed on a small scale co-wound HTS coil, and the results well verified the analytical solutions and the effectiveness of the quench detection method. Our work may be useful for lowering the risks in HTS magnet quench in various applications.

Enhancement of high-temperature superconducting coil stability using doped smart insulation materials for superconducting magnet applications

This study reports a high-temperature superconducting (HTS) coil containing molybdenum doped vanadium trioxide (V2O3:Mo) as turn-to-turn insulation material to ameliorate the electrical properties of both insulated and non-insulated (NI) coils. The electrical characteristics and thermal stability of the V2O3:Mo insulated coil against NI and V2O3 insulated coils were investigated through charge-discharge, over-current, and quench tests. The findings revealed that the V2O3:Mo and V2O3 insulated coils demonstrated a faster charge/discharge rate than the NI coil due to the high resistance of the V2O3: Mo or V2O3 insulator which obstructed the current to flow away from the azimuthal current path. In the over-current test at 160A, the V2O3:Mo insulated and NI coils exhibited higher electrical stability than the V2O3 insulated coil because the excessive currents above their critical values bypassed between the turn-to-turn contact. Moreover, the V2O3:Mo insulated coil demonstrated a 2.1times improvement in the minimum quench energy compared to the V2O3 insulated coil at 70 % of the coil's current-carrying capacity, which is an essential performance parameter for the operation of superconducting magnets.