Superconducting Winding Research Articles

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

Abstract High temperature superconducting (HTS) is a key technology of next generation high-speed railway systems, which guarantees high current and highly efficient traction power supply. HTS devices can reduce system weight and thus improve loads of vehicles. On high-speed maglev trains, HTS windings wound by second-generation (2G) HTS tapes play an important role in suspension and traction. However, in complex ferromagnetic environments, the performances of windings are 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 shape iron core and a magnetic guide rail. The air core structure of the winding is modeled，tested and the electromagnetic characteristics are analyzed for three dimensional (3D) 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 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 means for analysis of complex superconducting maglev systems.

Airplane motors employing superconducting DC field windings and conventional conductor AC windings

Many organizations are developing compact lightweight highly efficient rotating machines for airplane applications. These machines include permanent magnets for excitation and an iron-core with and without superconducting windings. Air-core (no magnetic iron) machines have the potential to be the most lightweight and efficient. Such machines can use superconductors for both DC excitation field coils and AC armature coils, which need conductors under development, like MgB2 and Bi2212. If liquid-hydrogen (LH2) is available on a plane and can be used as a coolant, it becomes feasible to develop machines with AC armature coils made from conventional conductors like copper, aluminium, and high-conductivity aluminium.This paper describes conceptual designs for a 3 MW, 4,500 RPM motor employing REBCO CORC conductor for the DC field coils and conventional conductor Litz cable for the AC armature coils cooled by LH2 available on the plane. Both rotor and stator coils are contained in separate cryostats. The DC excitation coils on the rotor are operated at 40 K to work successfully with a brushless flux pump exciter. Likewise, stator AC coils are cooled with available LH2 to take advantage of the lower resistivity of conventional conductors at cryogenic temperatures. Motor size, mass and losses are compared for stator windings employing copper, aluminium, and high-conductivity aluminium (Hyper-Al). Compared with copper and aluminium machines, the machine employing Hyper-Al has smaller size, mass and total losses.

High Temperature Superconducting Transformer Operating at an Increased Frequency of Alternating Current

The study's aim is to substantiate and employ materials with high technical characteristics for the active elements of a transformer, particularly in the context of increased operating frequencies. To accomplish this objective, the following tasks were addressed: An analysis and synthesis of the properties of a magnetic core composed of amorphous iron and superconducting windings in a high-temperature superconducting transformer (HST) were conducted. Dependencies and graphs illustrating the impact of frequency increase on heat losses related to hysteresis and eddy currents were derived. These losses occur within the magnetic circuit. The study also demonstrates the relationship between reducing size and weight parameters and material consumption of windings in high-temperature superconducting (HST) tapes. Current densities in these tapes can reach up to 500 A/mm². The most noteworthy outcome, taking advantage of superconductivity in the HST, is that HST acts as an ideal diamagnetic material. Additionally, the windings exhibit high electrical conductivity. This resolves issues related to current displacement to the conductor's surface, commonly known as the "skin effect," and effectively addresses concerns about increased resistance in transformers and electrical machines. The absence of the skin effect in HST conductors has been rigorously demonstrated using Bessel functions. The significance of these results is in enhancing the efficiency of transformers operating at high frequencies. This is achieved by synthesizing the properties of the transformer's active elements, which include an amorphous iron magnetic core, HST windings, and a dielectric medium utilizing liquid nitrogen.

Impact of Perlator on the cooling liquid flow and hottest point temperature of superconducting windings in HTS transformer

The generated heat by the superconducting windings and the other parts such as current leads in transformer increases the hottest point temperature (HPT) and causes the high temperature superconducting (HTS) windings to quench. Due to the properties of superconducting windings, reducing the HPT is of critical importance for the stable operation of the HTS transformer. The cooling system of HTS transformers, not only provides the cryogenic temperature for the proper operation of the superconductors but also is responsible for dissipating the generated heat by the windings. In this paper, the effect of the angle of inlet pipes in cooling system was investigated. This was a simple and effective solution which increases the heat transfer in liquid nitrogen. It was shown that inlet angle has a significant effect on the flow turbulence and the windings temperature. The Perlator is used as a lattice sheet which is installed inside the inlet valve and increases the turbulence of inlet flow of liquid nitrogen to increase heat transfer and reduce HPT. The thermal analysis is obtained by finite element method using ANSYS Fluent software. The influence of changing the inlet pipe angle and different structure of Perlator on heat transfer was investigated.

Technology Transition of Large Scale Wind Turbine System and Technology Status of High Temperature Superconducting Wind Turbine Generator

Technology Transition of Large Scale Wind Turbine System and Technology Status of High Temperature Superconducting Wind Turbine Generator

Development of the Test Bed for Experimental Investigation of Autonomous Current Supply System

The test bed is intended for investigations of autonomous current supply system and its individual units and testing of the correspondence of the system to the demands of the wind power alternator with high-temperature superconductive field winding. The test bed configuration is based on module principles thus accelerating the adapting of experimental equipment for quite definite tasks. The test bed contains serial equipment and a number of units specially developed for the definite test program. Some of specially developed modules are presented in the paper.

Modelling and experimental research of machine with annular HTS winding using equivalent magnetic permeability

The paper is devoted to the comparison of the results of finite element modelling and experimental research of the electrical machine with annular high temperature superconducting (HTS) windings. The method of equivalent magnetic permeability is used for determination of magnetic properties of armature HTS coils in the environment of electrical machine. The obtained results are discussed concerning influence of HTS coils properties on output machine parameters and AC losses.

‘Defect-irrelevant-winding’ no-insulation (RE)Ba2Cu3O7 − x pancake coil in conduction-cooling operation

This paper reports experiment and simulation results of a ‘defect-irrelevant-winding (DIW)’ no-insulation (NI) (RE)Ba2Cu3O7 − x pancake coil operated in a conduction-cooling environment at temperatures lower than 77 K. The key idea of the DIW high-temperature superconductor (HTS) winding technique, firstly proposed in 2016, is to wind an NI pancake coil with HTS tapes, on purpose, containing multiple ‘defects.’ Using the defect (flawed) HTS tapes, we expect to significantly lower the construction cost of a DIW HTS magnet in marginal sacrifice of the magnet performance. In this study, charging tests of a DIW coil were performed in a conduction cooling system by controlling the temperature of the second stage in a range of 20–65 K, to determine the maximum operable current that avoids thermal runaway of the test coil at a given temperature. Coil terminal voltages, center fields, local temperatures, and power supply currents were carefully monitored during the tests, and the trend for each parameter was obtained. Also, by use of an equivalent circuit model, the test results were numerically analyzed to evaluate the effect of local defects on the overall performance of the test coil in order to validate the feasibility of the DIW HTS coil in operation under the conduction-cooling environment at temperatures lower than 77 K.

Thermal-hydraulic analysis of Cable-In-Conduit Superconductor: A CFD approach

Superconducting (SC) magnets with Cable in Conduit Superconductor (CICSC) winding, cooled by helium at 4 K temperature are employed for many applications which require high magnetic field and high current densities. The construction of CICSC aims to maintain superconductivity state by optimization of various parameters, i.e., thermal stability, ratio of normal conductor to superconductor material, mechanical strength, low hydraulic impedance, current density, magnetic field, etc. The cryogenic thermal stability of the CICSC is of prime importance for the safe, stable and reliable operation of SC magnets. The prediction of thermal and hydraulic behaviour of CICSC in large SC magnets is difficult due to the complex geometry, variation of fluid properties, various heat in-flux incidences over the long length of CICSC and a complex heat transport phenomenon. Here we present a CFD approach for the thermal hydraulic analysis of a typical CICSC applying the porous media analogy and discuss the suitability for a wider range of operational scenario at higher Reynolds number and for various geometries.

Investigation on Key Parameters of NI HTS Field Coils for High Power Density Synchronous Motors

As global environment regulations are gradually strengthened, active research has been conducted on electric propulsion applications. High power density is one of the major research interests, as well as a machine's efficiency for a high-performance propulsion system. Among various electric propulsion technologies under development, a motor incorporating the no-insulation (NI) high-temperature superconducting (HTS) winding has the advantages of high current density and robustness to external disturbances, which are suitable for high specific power. However, still, there is little research on the motor with NI HTS coil. Therefore, as basic research, we investigated the potential application of the NI HTS motor, then derived required machine parameters and NI HTS coil designs in this paper. For that, first, basic parameters of the existing propulsion motors were investigated, then the target application and performance of the NI HTS motor were determined. Based on the target performance, conceptual designs of a motor with NI HTS coil were obtained by changing key design parameters including rated power, main dimensions, operating temperature, and width of air-gap. Calculated parameters were numerically compared, and expected design requirements and challenges were suggested.

Modelling and Fault Current Characterization of Superconducting Cable with High Temperature Superconducting Windings and Copper Stabilizer Layer

With the high penetration of Renewable Energy Sources (RES) in power systems, the short-circuit levels have changed, creating the requirement for altering or upgrading the existing switchgear and protection schemes. In addition, the continuous increase in power (accounting both for generation and demand) has imposed, in some cases, the need for the reinforcement of existing power system assets such as feeders, transformers, and other substation equipment. To overcome these challenges, the development of superconducting devices with fault current limiting capabilities in power system applications has been proposed as a promising solution. This paper presents a power system fault analysis exercise in networks integrating Superconducting Cables (SCs). This studies utilized a validated model of SCs with second generation High Temperature Superconducting tapes (2G HTS tapes) and a parallel-connected copper stabilizer layer. The performance of the SCs during fault conditions has been tested in networks integrating both synchronous and converter-connected generation. During fault conditions, the utilization of the stabilizer layer provides an alternative path for transient fault currents, and therefore reduces heat generation and assists with the protection of the cable. The effect of the quenching phenomenon and the fault current limitation is analyzed from the perspective of both steady state and transient fault analysis. This paper also provides meaningful insights into SCs, with respect to fault current limiting features, and presents the challenges associated with the impact of SCs on power systems protection.

Design and Property Analysis of a Performance Evaluation System for HTS Wind Power Generators

Large-scale High Temperature Superconducting (HTS) wind generators produce strong electromagnetic force and high torque due to the high magnetic load of the machines, which is produced by HTS coils with high excitation current. Therefore, in order to properly maintain the mechanical strength of the HTS coil part, the torque and Lorentz force of the HTS wind generator must be scrutinized and reflected in the design. The authors proposed a method for assessing mechanical and electrical stability of a large-scale HTS wind generator based on a Performance Evaluation System (PES) that has the same characteristics as some of the pole-pairs of the HTS generator. The generator and the PES were analyzed using 3D finite element method. The performance of the HTS coil was evaluated by comparing the tangential, radial force and magnetic field distribution of the 10 MW HTS generator with the PES. The tangential and radial forces of the 10 MW HTS generator were 73 kN and 11 kN, respectively. The tangential, radial forces and magnetic flux density of the HTS coils in the PES were equal to one pole in the 10 MW HTS generator. Therefore, the proposed PES-based generator characteristic evaluation method can be used to estimate the mechanical stability of the generator under a high magnetic field and high torque before manufacturing the HTS wind turbine.

Design and Analysis of a Magnetless Linear Variable Reluctance Motor With Modular Mover Units for Electric Propulsion

This paper proposes a magnetless linear variable reluctance motor (MLVRM) with modular mover units (MMUs) for electric propulsion. The proposed MLVRM adopts a doubly-salient structure with two sets of windings on mover, namely the ac armature windings, the dc field windings. In space, the two sets of windings are naturally isolated from each other due to the iron-core structure of the mover. Consequently, the space conflicts between the two sets of windings can be eliminated. To improve the force production capability, high-temperature superconducting (HTS) windings injected with large current are employed in the dc windings. The focus of this paper is to elaborate the method to adopt MMUs with equal clearance to suppress force ripple without weakening the back electromotive force (EMF). This paper also introduces the structure, working principle and choice of key parameters for the proposed MLVRM in detail. Moreover, MLVRMs with different number of MMUs are compared to MLVRM with only one MMU by finite element method (FEM) to verify the proposed method to suppress force ripple. The results show that the force ripple decreases significantly from 24.75% to 12.59% when the MLVRM adopts two MMUs.

Ground Testing of the World's First MW-Class Direct-Drive Superconducting Wind Turbine Generator

The EU-funded EcoSwing project addresses the world's first full-scale direct-drive (DD) high temperature superconducting (HTS) wind turbine generator. Before the generator was installed on a commercial wind turbine, the generator had been tested on the ground at the Dynamic Nacelle Testing Laboratory (DyNaLab) in Fraunhofer Institute for Wind Energy Systems (IWES), serving as an experimental validation of the generator design. This article is centered on the ground testing of the EcoSwing HTS generator, which includes corresponding tests for validating the generator's cryogenic design and electromagnetic performance. Despite one HTS coil with a defect limiting the operating current significantly, partial power production up to 1 MW at 14.5 rpm was reached. The critical auxiliary systems, i.e., vacuum system and rotary helium coupling, behaved as expected or even better than anticipated. The work reported in the article successfully validates the generator design, and also provides firsthand information prior to installing and testing the HTS generator on the wind turbine.

Experimental Validation of a Full-Size Pole Pair Set-Up of an MW-Class Direct Drive Superconducting Wind Turbine Generator

The article presents a full-size pole pair set-up of an MW-class direct drive (DD) high temperature superconducting (HTS) wind turbine generator. The set-up serves as a precursor to the world's first full-scale DD HTS generator developed within the EU-funded EcoSwing project. The set-up built for de-risking employs an HTS field winding in the rotor and a conventional copper armature winding in the stator, representing a minimum independent unit of the corresponding full generator. Such a prototyping approach well reflects the performance of the full generator at a low cost. The article first explains the main design considerations of the full generator, followed by designing and construction details of the set-up. Afterward, a number of tests for determining the key performance of the set-up are reported. The testing results showed that the HTS field winding ran stably at its rated current of 480 A and was well maintained below 30 K. Moreover, the tangential force in the set-up reached 29.8 kN, projecting the 2 MW target output power of the full generator. The set-up developed effectively validated the design ideas and engineering feasibilities of the full generator, leading to successful kick-off of the EcoSwing project.

Short-Circuit Characteristics of a High Temperature Superconducting Wind Turbine Generator Employing a Segmented Armature Winding

High temperature superconducting (HTS) wind turbine generators (WTGs) are expected to offer a compact and lightweight direct drive train for large offshore wind turbines. However, short circuits occurring at armature winding terminals can pose great challenges, such as high peak torques due to a large magnetic air gap in HTS generators, field current rise over the critical current that may cause a quench, and AC losses in HTS field windings that may cause local overheat. Segmentation of armature windings could be a solution to mitigate such challenges. In this paper, an optimized design of a 10-MW direct drive HTS generator using 2G HTS wires in the field winding is studied based on a well-verified generator topology. The generator design has two scenarios, i.e., without segmentation and with four segments in the armature winding. These two winding scenarios are compared through a phase-to-phase short circuit occurring at the terminals of the armature winding. The effects of segmentation are revealed on 1) electromagnetic torque, 2) current rise in the HTS field winding, and 3) AC losses in the HTS field winding after the short circuit occurs. The results show the great benefits of using segmented armature windings in an HTS WTG: the peak torque is reduced by a factor of 4, and the AC losses in the HTS field winding are nearly halved although the maximum field current is almost unchanged.

A volume integral approach for the modelling and design of HTS coils

PurposeThe purpose of this paper is to develop a rapid and realistic modelling approach for the design and characterization of high temperature superconducting (HTS) coils and windings carrying DC currents. Indeed, the strong dependence of the electromagnetic properties of such materials on the magnetic field makes the design and characterization of HTS systems a delicate operation where local quantities have to be evaluated.Design/methodology/approachA volume integral modelling approach has been developed taking into account the electric nonlinearity of the HTS material which is represented by power law. The variations of the characteristic quantities of the HTS (critical current density and power law exponent) with the magnetic flux density are also taken into account by using Kim’s law. The volume integral modelling allows to model only the active parts of the system and thus to overcome the difficulties linked to the multiscale dimensions.FindingsThe model has been tested in a case study in which simulation results were compared to measurements and to finite element analysis. A good agreement was found which validates the model as a rapid and efficient tool for HTS coils and windings design and modelling.Practical implicationsHTS coils are important elements of emerging superconducting devices which require a high level of reliability, such as generators or motors. The proposed approach is interesting to speed up the design and optimization procedures of such systems.Originality/valueAdvanced structures of the basic elements have been used in the volume integral modelling, which results in a considerable gain in computation time and in memory-space saving while keeping a high level of precision and realism of the modelling, which has been verified experimentally.

Design of a Combined Screening and Damping Layer for a 10-MW-Class Wind Turbine HTS Synchronous Generator

This paper is focused on the design of a single protection layer to cover both the screening and damping characteristics of a large-scale high-temperature superconducting (HTS) wind turbine synchronous generator under sudden short-circuit conditions. Due to small synchronous reactance of HTS generators, short-circuit condition causes substantial fault current in the stator windings, which produces high unbalance variable magnetic field as well as substantial mechanical fluctuations issues. The former one can lead to unstable condition for HTS field windings, due to induced ac loss and field overcurrent, and the latter one can produce large fluctuations on the generator rotational speed and rotor torque angle. The proposed protection layer is designed in a way that not only screening capability is provided for the HTS windings by preventing unbalance magnetic field penetration, but desirable damping ratio is also achieved so that the fluctuations are suppressed in a proper transient time. A 10-MW-class HTS synchronous generator is modeled and simulated using finite element method under different short-circuit conditions. The temperature variation study and field overcurrent analysis are provided to show the compatibility of the proposed model. In addition, magnetic force distribution and static eccentricity fault detection analyses are provided, which guarantee the proper dynamic performance of the studied generator using the proposed protection layer. Simulation results confirm that with the proposed protection layer, both the screening and damping characteristics of the 10-MW-class HTS generator are obtained and proper transient dynamic responses are deduced for wind power applications.

Electromagnetic Design of Superconducting Synchronous Motors for Electric Aircraft Propulsion

This paper evaluates the electromagnetic characteristics as to two types of superconducting motors: one is the superconducting motors adopting high-temperature superconducting field coils and copper armature windings; and the other is fully-superconducting motors, which have high-temperature superconducting field coils and MgB 2 superconducting armature windings. Analytical formulas and FEM are employed for the designs of 1.5-, 3.0-, and 5.0-MW motors. We consider how to reduce ac loss in MgB 2 winding structure as well. The analysis of our results, which was conducted mainly over output density and efficiency, suggests that the adoption of superconducting motors is more realistic in realizing electrical aircraft propulsion system in terms of higher output; the analysis results show that the fully-superconducting motors have a potential to reach over 16 kw/kg.

Comparative Study of 1-MW PM and HTS Synchronous Generators for Marine Current Turbine

Thanks to the high predictability and energy density of marine current, it can be utilized to generate electricity in an environmental and efficient form. However, placing a large-scale marine current turbine system is challenging, which requires a proper drive-train system to achieve high efficiency. In this paper, a conceptual structure of direct-driven marine current turbine generator (MCTG) is proposed. Then, the electromagnetic design method is developed, including the specifications, design, and optimization procedures. Two generator topologies using permanent magnets (PMs) and high temperature superconducting (HTS) windings in field poles are adopted for comparison. Design results demonstrate that it is feasible to design a 1-MW MCTG with HTS field winding at 77 K for the proposed structure. Furthermore, the optimum number of poles is found near 66 and 32 for PM and HTS topologies, respectively. Finally, it is found that the weight and efficiency for MCTG is around 17 ton, 89.6 % for the PM topology and 16 ton, 91.9 % for the HTS topology.