High-temperature Superconducting Windings Research Articles

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.

Optimization Study of Cooling Channel for the Oil Cooling Air Gap Armature in a High-Temperature Superconducting Motor

With the continuous advancement of science and technology, the application of high-temperature superconductivity has developed rapidly. The high-temperature superconducting (HTS) motor replacing the copper coil in the traditional motor with HTS winding is increasingly used in power equipment, and the effective thermal management of HTS winding is vital in ensuring the life and effective operation of the HTS motor. In this study, five enhancement structures of indirect oil cooling channels were designed to improve the heat dissipation capacity of the HTS motor winding, and the enhancement effects of the different structures were comprehensively evaluated through numerical simulation using Fluent software 2022R1. The best enhancement structure was selected through structural optimization. The results showed that the Nusselt number of the gap-type enhanced structure was higher than that of the V- and staggered-type structures at the same flow velocity and 68% higher than that of the bare pipe. At the same inlet flow velocity and with a pressure drop limit of 30 kPa, the performance evaluation criterion value of the gap-type structure was 39% and 63% higher than that of the staggered- and V-type structures, respectively. The gap type is the optimal enhancement structure and can effectively improve the heat dissipation of the HTS winding coil.

Influence of Copper Rings and Plates on Eddy Losses of No-Insulation High Temperature Superconductor Coil in Synchronous Machines

No-insulation (NI) high temperature superconducting (HTS) machine is a semi-superconducting machine with improved thermal-stability and power density, in which the rotor windings are replaced with NI HTS coils. However, the AC background field from stator windings leads to significant eddy current in NI HTS windings. The induced eddy current and loss affect the operating efficiency and safety of HTS machine. Traditionally, copper discs and rings are used for conduction cooling and mechanical support of NI HTS coil. In this paper, the influence of copper discs and rings on reducing the eddy current and loss of double pancake NI HTS coil is studied. Three structures of copper discs, copper ring, and both copper discs and ring are analyzed, by both simulation and experiment. The results show that all these three structures of copper shielding can effectively reduce the eddy loss on NI HTS coil within the HTS machine operating temperature of 20–30 K. The combination of copper discs and ring has the best shielding performance.

Reluctance-Based Circuit for High-Temperature Superconductor Generator Lumped-Parameter Model

The present work addresses the ongoing development of a mesh-based magnetic equivalent circuit (MEC) to estimate the magnetic flux distribution in a superconducting hybrid rotating synchronous machine, superconducting (SC) rotor, and conventional stator. The MEC is to be integrated in an existing thermoelectric lumped-parameter machine model for the transient simulation of High Temperature Superconductor (HTS) field coil synchronous generator (SG) in the dq0 frame of reference. It will allow the inclusion of the magnetic flux density inside the definition of the non-linear resistance of the superconductor in addition to the already-present temperature and current. The objective is to gain further accuracy on the coupled thermal and electromagnetic behavior of superconducting hybrid machines during partial or total loss of the superconducting state. In the present work, the MEC is benchmarked against a Finite Element Model (FEM). It is shown that the MEC can provide proper magnitude of the magnetic flux density over the HTS winding achieving a good estimation of the magnetic response of the field winding by taking into account the penetration of current within the superconductor. The case study is a 100-MVA hydroelectric HTS field coil SG considering a field current ramp.

Design and Analysis of Optimal Current Vector for HTS-Based Multi-Input Wireless Power Transfer Systems

This paper presents a newly-designed optimal current algorithm for high-temperature superconductor (HTS)-based multi-input wireless power transfer (WPT) systems. In this way, both high controllability and lower AC losses can be achieved in the proposed systems, and they are especially superior for long-range and long-time operations. Simplified AC loss modeling for HTS windings is developed for the designed transmitter coils. The accordant optimal current vector is derived and analyzed in order to achieve the highest output power and the lowest primary AC losses. With the proper current control of multiple transmitters and the use of a designed HTS coupler, the system controllability can be greatly improved compared with conventional WPT systems. Based on the information on the impedance characteristics on the primary side, the magnetic field generated by different transmitters can be maximized at the target position. Thus, the maximum output power tracking can be realized with a relatively long transmission distance and a low coupling coefficient. Both active and passive solutions are designed and presented to deal with the cross-coupling issue in multi-input WPT systems. For numerical validation, a practical prototype of the HTS couplers is fabricated. An experimental platform is established with a liquid nitrogen cooling system. The test results further validate the feasibility and the high controllability of the proposed system.

The calculation and measurement of electromagnetic energy flows for investigation of critical current estimation for high-temperature superconducting coil by means of pick-up coils

For practical operations of high-temperature superconducting (HTS) devices, we have proposed a monitoring and diagnosing system to detect the degradations of superconducting properties before normal transitions occur locally in the HTS winding. The proposed system estimates the distributions of critical current indirectly from measurement results of the active power components of the Poynting vector around the monitoring HTS devices conducting ac currents by means of pick-up coils pairs mounted surrounding the HTS devices. For this purpose, it is necessary to solve the inverse problem. In order to estimate the critical current distribution, therefore, it is first necessary to be able to calculate the measurement signal distribution from the critical current distribution of the monitoring coil. This paper first proposes the calculation method of signal distributions measured by our system, next reports the results of the experiments and analysis, which were carried out to verify the validity of the calculation method. A pancake coil wound with Bi-2223 multifilamentary tape exposed to a uniform AC magnetic field was assumed as a monitoring coil in the experiments and analyses. The good agreement between the measured signals obtained from the experiments and the numerical analysis demonstrates the effectiveness of the proposed calculation method of measured signals.

Experimental and numerical study on AC loss reduction in a REBCO coil assembly by applying high saturation field powder-core flux diverters

AC loss is one of the key issues need to be considered in designing high temperature superconducting (HTS) devices. An effective method for AC loss reduction is applying magnetic flux diverters (MFDs) in close proximity of the HTS coil windings. In this work, two types of low-loss powder-core MFDs − high flux (HF) and molypermalloy-powder (MPP) MFDs − were applied to a REBCO coil assembly for reducing the AC loss. The measured and simulated results show that both types of MFDs can significantly reduce the total loss (the summation of the losses in the HTS windings and the MFDs) in the coil assembly. At 77 K and 40 A coil current, compared with the coil assembly without MFDs, the total loss with HF and MPP MFDs was reduced by 77 % and 81 %, respectively. Although MPP MFDs show slightly better performance in reducing total loss in the coil assembly than HF MFDs at low coil current, HF MFDs are more obvious option for AC loss reduction in high magnetic field applications owing to their relatively high saturation magnetic field.

Influence of the HTS Winding Tape on Limiting the Transient Currents in Superconducting Transformers

The article presents an extended computer model of a HTS (high temperature superconducting) 21 MVA 70/10.5 kV transformer with severalfold compound windings, based on a verified PSpice model of 10 kVA transformer with single windings. Two superconducting tapes: SCS12050 (with a copper stabiliser layer) and SF12050 (without a stabiliser) were used in the windings. The circuit model of the transformer developed in the PSpice environment considers Rhyner’s power law and the Jiles–Atherton description of the magnetic hysteresis loop. Two types of transient states were analysed: switching on a superconducting transformer to the network and an emergency short-circuit of the secondary winding. For the first five unidirectional current pulses generated when connecting an unloaded transformer to the network, the values of the pulse duration (γ angle), the temperature increase in the primary winding as well as the mean and effective values of the switch-on current were calculated. The waveforms of currents, voltages, changes in resistance and temperature during the operation short-circuit were compared for the windings with both types of HTS 2G (high temperature superconductor second generation) tapes. The conducted analysis allowed us to determine the influence of electrical and thermal parameters of the tapes in question on the effective limitation of current in transient states and the possibility of their use in the construction of superconducting transformer windings.

Optimization study of the main parameters of different types of wind turbine generators * * This work was supported in part by the National Natural Science Fund under Grant 52071090, in part by the Doctoral Start-up and Postgraduate Fund under Grant R17062, and in part by the Young Innovative Talents in Colleges and Universities of Guangdong Province under Grant 2019KQNCX046.

The research and development of large-scale wind turbine generators have become a future trend in green renewable energy field from the dual perspectives of the environment and economics. In this work, an electrical design method is first proposed and applied to different types of wind turbine generators, including the high-temperature superconducting (HTS), the permanent magnet, and the traditional copper generators. The optimal electrical designs of the three types of 10 MW wind turbine generators are then created based on the developed design program. Second, the influences of the rated revolution on the basic performance parameters of the HTS generator are investigated, and the results are compared with those of the other two types of generators. It is found that the generator weight decreases with the increases of the rated revolution and the stator outer diameter, and the optimal rated revolution for a generator with a large stator outer diameter is determined to be 40 min−1. Moreover, the weight of the field parts is found to have the same regulation rule as the generator weight. Finally, the design results of the three types of wind turbine generators are comparatively discussed, and it is found that the HTS wind turbine generator is superior to its two counterparts.

Электротепловые переходные процессы в сети с высокотемпературным сверхпроводящим трансформатором с функцией токоограничения

The results of a study of thermal and electromagnetic transients in an electric power system containing a high-temperature superconducting (HTS) transformer with a current limiting function are presented. For carrying out the research work, an experimental HTS transformer sample with windings made of Y1Bа2Cu3O7 superconductor and with liquid nitrogen at an operating temperature of 77 K serving as dielectric medium was developed. It has been demonstrated, taking the experimental sample as an example, that transformers with HTS windings can be used to limit short-circuit currents in electrical systems. By using the developed mathematical model of a three-phase single-machine network containing an HTS transformer, it became possible to perform an in-depth analysis of electromagnetic transients in the current limiting mode and to study the thermal and electrodynamic effects produced by the short-circuit current in varying the short-circuit fault kind (single-phase, two-phase and three-phase short-circuit faults) and the type of connected load (active, active-inductive, and active-capacitive) on the current limiting degree. It has been determined that significant heat flows arise at the current limitation moment, which also should be limited. A positive effect of HTS transformers on the electric power system operating modes is shown. The obtained results of theoretical and experimental studies of HTS transformers prove a high efficiency of their current limiting function.

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

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.

Precise appraisement of the harmonic loads impact on hysteresis losses in a 3-phase HTS transformer

Nowadays, the application of non-linear loads such as, rectifiers, electronic phase control, PWM drives, gives rise to a vastly increased level of harmonics in the power network. As such, the transport currents of transformers are non-sinusoidal alternating currents. On the other hand, AC losses are one of the most critical characteristics for the design and operation of high-temperature superconducting (HTS) transformers. The amount of hysteresis losses is a key parameter for the design of HTS windings affecting equipment, cooling cost, efficiency, and transformer economic feasibility. The computation of AC losses by traditional techniques, is suitable for the sinusoidal current condition. While, non-linear loads brings about different number of peaks and amplitudes in the current waveform passing through the HTS transformer windings. So that, in addition to the major hysteresis loop, a number of minor hysteresis loops are also formed changing the hysterical nature of the AC losses.Hence, this paper proposes an accurate, yet efficient analytical algorithm, for calculating hysteresis losses in a three-phase HTS transformer's windings in the presence of the harmonic loads accounting for the AC losses estimation. This is accomplished by performing a numerical Finite Element Method to verify the analytical results. The analysis of the hysteresis losses in an exemplary 315 kVA three-phase HTS distribution transformer for different harmonic loads, is another object of this paper.

Design, Fabrication, and Testing of a Full-Scale HTS Coil for a 10 MW HTS Wind Power Generator

The authors have proposed a performance evaluation system (PES) for large-scale high temperature superconducting (HTS) wind power generators, which produces strong electromagnetic force and high torque due to the high excitation current and the high magnetic load of the machine, based on the computer simulation results. The PES can physically test the structural stability of HTS coils and armatures against high torque and the effect of the magnetic field before mounting the HTS coil on the generator. This paper deals with the design, fabrication, and performance testing of a full-scale HTS coil to be installed in the PES, a performance analysis system for a 10 MW HTS wind power generator. The HTS coil with metal-insulation consists of four racetrack-type single coils with 310 turns per layer. The manufactured HTS coil was tested at 77 K with and without an iron-core. As a result, the critical currents of the tested HTS coils with and without the iron-core were 90 A and 106 A, respectively. Compared to the simulation results, it was found that the magnitude of the magnetic field was the same. These results will be effectively used to study and fabricate high magnetic field coils for HTS applications, as well as the PES being fabricated.

Effects of stainless steel thickness and winding tension on electrical and thermal characteristics of metal insulation racetrack coils for 10-MW-class HTS wind generator

Experimental results on the electrical and thermal characteristics of GdBCO racetrack coils co-wound with stainless steel (SS) tapes of various thicknesses and winding tensions are presented in this paper. The SS thickness and winding tension are identified as the factors affecting the charging time and thermal stability of metal insulation (MI) coils. To verify these characteristics, three types of MI-SS racetrack coils were fabricated with various SS thicknesses and winding tensions: 100-μm SS thickness and 10-kgf winding tension; 100-μm SS thickness and 5-kgf winding tension; and 50-μm SS thickness and 10-kgf winding tension. Further, three MI-SS racetrack coils were characterized by sudden discharging, charging, and overcurrent tests. The sudden discharging and charging tests were performed in a steady state to investigate the decay time constant of the center magnetic field discharging the coils and the delay time of the magnetic field charging the test coils, respectively. To estimate the thermal stability of the three MI-SS coils, overcurrent tests were conducted in a transient state at 1.1 times the critical current (Ic) and 1.05 Ic. Based on the experimental results of three small-scale test coils, the total contact resistance between the layers of the test coils was calculated and applied to design a field winding using a second-generation high-temperature superconducting (HTS) tape for a 10-MW-class HTS generator used in an offshore wind turbine environment. Subsequently, an equivalent electrical circuit model was proposed to analyze the electromagnetic response and thermal stability characteristics of three HTS field coils of a 10-MW-class HTS generator with the key parameters of the HTS field coils, which were obtained using electromagnetic finite-element analysis. Finally, the charging delay time and thermal stability of the three HTS field coils were compared and analyzed in detail.

Transient Test and AC Loss Study of a Cryogenic Propulsion Unit for All Electric Aircraft

This paper reports a pioneering demonstration platform of a cryogenic propulsion unit at liquid nitrogen temperature. A high temperature superconducting (HTS) machine is connected with a cryogenic power rectifier in a generator mode to prove the feasibility of a cryogenic propulsion unit for electric aircraft propulsion applications. Machine operation was carried out with a special focus on the total heat dissipation inside the HTS AC windings. Different types of 2G HTS tapes were tested to provided data for stator coils’ design. The transient operation was carried out to represent a short-circuit failure in one of the power electronic devices. The test shows AC loss performance of the HTS windings using calorimetric method during the short circuit event, indicating the importance of developing protection schemes for the cryogenic propulsion units to prevent damage to the HTS components. The paper provides initial insights into the interaction between superconducting machines and cryogenic power electronics within a cryogenic propulsion unit. It is an important first step to understand and further develop cryogenic propulsion technology for future electric aircraft.

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.

Exploration of a Novel HTS Thin-Film Device Combined With Roles of Transformer and Overcurrent Limiter

A novel high-temperature superconducting (HTS) thin-film device based on double-sided YBa <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7-</sub> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> (YBCO) thin film, combined with roles of transformer and overcurrent limiter, is proposed and tested in this article. Due to the effective improvement on the power density, operating frequency, repeatability, functional integration, and low profile of the high-frequency converters, thin-film transformer (TFT) has been widely employed in power conversion fields. In contrast to the normal conductive materials, the surface resistance of the HTS materials is much smaller. Thus, the TFT fabricated by HTS thin film has lower Joule losses and higher power conversion efficiency. We designed the double-sided YBCO thin-film-based HTS-TFT and measured its parameters at liquid nitrogen (LN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ). As a comparison, we also developed the copper (Cu) based TFT and measured the same parameters at LN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> and room temperature. Besides, we also tested the overcurrent limiting performance of the HTS-TFT, which is based on the state change from superconductivity to normal state. It can be found from the contrastive experiments that the HTS-TFT has better operating parameters than the Cu-TFT; meanwhile, the overcurrent can be limited by the HTS winding effectively.

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.

General Design of a 300-Kvar HTS Synchronous Condenser Prototype

China Southern Power Grid Corporation has started a project to study the feasibility of large-scale high-temperature superconducting (HTS) dynamic synchronous condensers (DSC) in Ultra High Voltage Direct Current (UHVDC) transmission grid. To investigate some key technologies, a small-scale prototype of HTS DSC of 300 kvar/2 poles/3000 RPM is under development. The electromagnetic design, especially the critical current of REBCO rotor coils was discussed. Besides, the configuration and properties of the air-core stator, the damper and the rotor were also described. Water-cooled windings in the air-core stator have a rated current density of 9.55 A/mm 2 . Helium cooling pipes were embedded within REBCO rotor coils, and HTS windings will be cooled down to <; 30 K (<; 25 K for better) through conduction cooling. Two REBCO coil assemblies were manufactured and successfully tested in liquid nitrogen for several thermal cycles, which validated the manufacture techniques.