Generation High Temperature Superconducting Research Articles

Design and Simulation Analysis of HTS Wind Generator

With the development of high temperature superconductor (HTS) material, countries all over the world have shown great attention in HTS generator over the theoretical research and application. In this paper, a 3MW high temperature superconductor wind generator has been designed by using the RM and Maxwell 2D module of FEM software Ansoft. This design use the second generation HTS material YBCO bulk to be the permanent magnet. It break through the capability limitation of the traditional permanent magnet generation. Based on the FEM simulating, calculating and changing the parameter, the data of the HTS wind generator has been shown, such as magnet line of force, magnetic-field distribution and so on. Compared with the traditional permanent magnet generation, the HTS wind generator has a strong superiority in various aspects.

Second Generation Wire Development at AMSC

AMSC has established a Second Generation (2G) High-Temperature Superconductor (HTS) wire manufacturing technology based on the Rolling Assisted Biaxially Textured Substrate and Metal Organic Deposition processes. AMSC's 2G wire (Amperium) has been used by a wide range of customers for development and testing of initial commercial HTS-based applications. Although the Amperium wire properties and quantities satisfy the requirements for these initial projects, improvements in critical current, field performance, and cost are beneficial for large-scale commercial and military applications. As Amperium wire manufacturing continues to ramp up, AMSC's R&D program has focused on increasing critical current, and the development of nonmagnetic substrates. The R&D process developed for a single-coat, 1.2 μm YBCO film has been transferred to production-scale equipment, resulting in the first Amperium wires with critical currents reaching 500 A/cm-w (77 K, self-field) in production length. A nonmagnetic substrate, which minimizes ferromagnetic substrate losses in ac cable applications, has been produced in R&D lengths and demonstrated in an Amperium cable wire.

초전도 한류기 설계 검증을 위한 초전도 한류 모듈 단락 특성 시험

KEPCO Research Institute has been researching a Superconducting Fault Current Limiter (SFCL) which is considered one of solutions of fault current problems with Korea Institute of Machinery & Materials (KIMM) and Hanyang University since 2011. In this paper, we fabricated a current limiting module and conducted electrical short circuit tests for checking the validity of the transmission level SFCL design. Based on the short circuit characteristics of the second generation High Temperature Superconductor (HTS), we analyzed the short circuit characteristics of 3 parallel connected superconducting wires. The structure of the HTS wire is as follows: the stainless steel stabilizer of <TEX>$100{\mu}m$</TEX> is laminated on the superconductor layer and under the substrate, both of which are electrically jointed with solder. We fabricated the current limiting module which has 40 series and 6 parallel connections and studied the short circuit characteristics of the module under various voltage levels.

Electrical Characteristics of 2G HTS Tapes Under DC Current With AC Ripple

Electrical behavior and AC losses of Second Generation High Temperature Superconducting (2G HTS) tape were characterized under AC ripple current superimposed on a DC offset current. The maximum safe transport current and ac losses were measured as functions of AC ripple current amplitude and frequency. It was observed that the frequency of ripple current does not significantly affect the maximum safe transport current. For total DC and AC current less than the critical current, the extent of AC loss does not depend on the magnitude of DC offset current. The losses, however, increase with DC offset current for total current value exceeding the critical current because of increased resistance caused by the onset of quench of the tape to normal state.

A Study on Recovery Characteristics of Joined Tapes From the View of Thermal and Electrical Variation for Superconducting Magnets

In order to assemble a magnet using second generation (2G) high temperature superconducting (HTS) tapes, one usually stacks the pancakes using the joint method. When joining the tape, it is important to keep the initial characteristics of the original tape. When two tapes are joined, appropriate pressure should be applied to each tape. The reason is that insufficient or excessive forces on the joined surface affect the inherent characteristics of each tape, such as the critical current and the n-value. The generated heat flux on the joined tapes is related to the quench occurrence when the magnet is affected by unexpected disturbance. In this study, the effect of the external disturbance on the joined tapes was examined. The experiments were carried out with a single tape and two kinds of joined tapes. The joints were exposed to various pressures. The stability and recovery characteristics of the experimental samples were analyzed and compared with each other.

Study of AC Losses in a 1-m Long, HTS Power Cable Made From Wide 2G Tapes

AC loss measurements were carried out on several model power cables fabricated with varying tape width of second generation (2G) high temperature superconductor. The total amount of superconducting tape used in all the cables was kept constant. The results of the measurements show that, contrary to many previous studies, the losses are not proportional to the number of tapes and the width of the gaps between tapes. The purpose of this study is to investigate the losses of a cable using 4 mm, 10 mm and 46-mm wide tapes made by American Superconductor Corporation, helically-wound around a former with minimal gap. Tests were performed in liquid nitrogen. Test results show that the AC losses for these different configurations are similar in magnitude and are in the range of ~25-50 mJ/cycle/m, or ~1.5-3 W/m at 60 Hz near the cable critical current.

Selection Criteria of High ${\rm T}_{\rm c}$ Superconducting Tapes for Superconducting Fault Current Limiter Applications

To establish a selection criterion of high temperature superconducting (HTS) tapes for their possible application in superconducting fault current limiters (SFCLs), it is required to have high critical current density, high `n' value, high normal state resistance, low AC losses, large heat transfer area, high thermal diffusivity and quick recovery against thermal instabilities for the HTS tapes. At present HTS tapes are categorized into two types namely Bi2223 based 1st generation (1G) HTS tape and YBCO based 2nd generation (2G) coated conductors (CCs). These 1G and 2G tapes are composite tapes. Hence, it is required to know their averaged material properties that can affect the performance of the SFCL during normal state operation. This paper deals with these issues along with DC characterization results to establish selection criteria of HTS tapes for SFCL applications.

Study of second generation, high-temperature superconducting coils: Determination of critical current

This paper presents the modeling of second generation (2 G) high-temperature superconducting (HTS) pancake coils using finite element method. The axial symmetric model can be used to calculate current and magnetic field distribution inside the coil. The anisotropic characteristics of 2 G tapes are included in the model by direct interpolation. The model is validated by comparing to experimental results. We use the model to study critical currents of 2 G coils and find that 100 μV/m is too high a criterion to determine long-term operating current of the coils, because the innermost turns of a coil will, due to the effect of local magnetic field, reach their critical current much earlier than outer turns. Our modeling shows that an average voltage criterion of 20 μV/m over the coil corresponds to the point at which the innermost turns’ electric field exceeds 100 μV/m. So 20 μV/m is suggested to be the critical current criterion of the HTS coil. The influence of background field on the coil critical current is also studied in the paper.

A Transverse Flux High-Temperature Superconducting Generator Topology for Large Direct Drive Wind Turbines

Abstract The cost and mass of an offshore wind turbine power-train can be reduced by using high-temperature superconducting generators, but for a successful commercial design the superconducting generator should be as reliable as its alternatives. In this paper, we present a novel transverse flux superconducting generator topology which is suitable for low-speed, high-torque applications. The generator is designed with a stationary superconducting field winding and a variable reluctance claw pole motor for simplified mechanical structure and maximum reliability. 3D FEA simulation results of a 70 kW prototype is presented.

New Material Requirements for Superconductor Grid Technology

Superconductor ac and dc cables, fault current limiters and wind turbine generators offer solutions to key challenges in modernizing electric power infrastructure around the world. High critical current Jc is an essential requirement for the practical commercial operation of such systems. High temperature superconductor (HTS) wires have met the basic Jc requirements, and some initial systems have been successfully installed in the power grid. From an applications perspective, further progress in increasing the superconductor critical temperature Tc and critical current Jc could open up an even broader impact. However, thermal fluctuations and the resulting flux creep depress critical current, creating a trade-off between higher temperature and higher critical current. The origins of this trade-off are discussed. The YBCO material used in today's second generation HTS wires strikes a good compromise between these competing effects, and because of the flux creep problem, applications needs call for further research to be focused more on increasing Jc than on increasing Tc.

Fast insertion impedance of 2G HTS superconductors for megawatt AC and repetitive pulsed power operation

Within the past few years a newer, more robust type of superconductor known as 2 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">nd</sup> Generation (2G) High Temperature Superconductors (HTS) wire capable to operate in LN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> has become available in sufficient quantity and lengths for developers to build prototype devices and test their capabilities. 2G HTS made possible to reduce size, weight and volume of electrical apparatus in few orders of magnitude and provide a fast switching power and energy transitions with negligible impedance in superconducting stage and fast transitions impedances in resistive stage. This transition is typically called quenching and is useful for driving high impedance loads, limiting fault currents and developing large steep insertion impedances useful in many pulsed power applications. Electrical equipments made out of copper or aluminum typically shows high current transitions, inrush and short circuiting faults currents that can reach 100's of kA. There is a need for having repeatable fast insertion impedance to transform high current transitions, useful for impedance matching, stabilization, robustness of large current transients and proper dielectric operation in Megawatt installations. Development of Superconducting Fault Current Limiters (SFCLs) has been pursued for decades and has been limited thermally and/or mechanically by the available superconducting materials performance characteristics. However, this new 2G material has re-invigorated the worldwide race to develop a successful SFCL device that meets the stringent demands of Megawatt power equipment. SuperPower is pursuing the development of modular SFCL based on its proprietary 2G HTS wire and SFCL technologies. We will discuss testing and improvements made to optimize Recovery Under Load (RUL) performance. We also discuss high power tests and the influence of the different variables that have an important impact in RUL. A wide operating RUL window has been tested in order to define where RUL is feasible. We will show the manufacturing and latest tests and capabilities of sub-cooled of the SFCL device and modules designed for distribution and transmission lines. We show the advantages and superior performance of the new 2 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">nd</sup> Generation HTS superconductors under sub-cooled liquid nitrogen operation when used in SFCL.

Full Vector Magnetic Field Critical Current Characterization of Coated Conductors Deposited on Solution Deposition Planarized IBAD Templates

Second generation high temperature super-conductor (HTS) wire consists of metal substrate tapes textured with intermediate buffer layers that are coated with a superconducting layer. The applications of these coated conductors require a high current in magnetic fields that are not restricted to a narrow range of angles. Ion beam assisted deposition (IBAD) template tilt, in combination with REBCO vapor deposition, results in asymmetric sample growth. This requires Vector Magnetic Field (VMF) measurement over 180 degrees to be fully described. We have developed a piece wise characterization and analysis method of the VMF using a number of Ic scaling models. Solution Deposition Planarization (SDP) permits REBCO film deposition on 100 nm rms roughness substrates. To test buffer layer effects on film growth, with and without SDP, superconducting films were deposited at Superconductor Technologies, Inc. by co-evaporation of REBCO on IBAD buffer layer templates from Los Alamos. Critical current measurements in VMF up to a magnitude of ~ 0.9 Tesla show behaviors traceable to the effects of buffer layer template on pinning. The ability to discriminate between buffer layers based on in-field Ic behavior is a useful technique for the optimization of buffer layers for future REBCO film deposition.

Second Generation HTS Quadrupole for FRIB

Quadrupoles in the fragment separator region of the Facility for Rare Isotope Beams (FRIB) will be subjected to very large heat loads (over 200 Watts) and an intense level of radiation (~10 MGy per year) into the coils of just the first magnet. Magnets made with High Temperature Superconductors (HTS) are advantageous over conventional superconducting magnets since they can remove these heat loads more efficiently at higher temperatures. The proposed design is based on second generation (2G) HTS which allows operation at ~50 K. 2G has been found to be highly radiation tolerant. The latest test results are summarized. The goal of this R&D program is to evaluate the viability of HTS in a real machine with magnets in a challenging environment where HTS offers a unique solution.

Design of a High Temperature Superconducting Generator for Wind Power Applications

High temperature superconducting (HTS) generator was promising in the wind power applications for its advantages in the weight, size and thermal stability against load fluctuations, especially in the “direct-driven” design. A 100 kW generator was proposed for the demonstration of the feasibility of using HTS in 10 MW wind turbine generators. The electromagnetic design and optimization of the rotor were done using finite element method (FEM). The excitation coil of the rotor was designed considering variable working conditions. According to the numerical results, a number of suggestions in the design and winding techniques of the superconducting rotor were proposed.

AC Loss Reduction in Filamentized YBCO Coated Conductors With Virtual Transverse Cross-Cuts

While the performance of 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-x</sub> (YBCO)-based coated conductors under dc currents has improved significantly in recent years, filamentization is being investigated as a technique to reduce ac loss so that the 2nd generation (2G) high temperature superconducting (HTS) wires can also be utilized in various ac power applications such as cables, transformers and fault current limiters. Experimental studies have shown that simply filamentizing the superconducting layer is not effective enough to reduce ac loss because of incomplete flux penetration in between the filaments as the length of the tape increases. To introduce flux penetration in between the filaments more uniformly and further reduce the ac loss, virtual transverse cross-cuts were made in superconducting filaments of the coated conductors fabricated using the metal organic chemical vapor deposition (MOCVD) method. The virtual transverse cross-cuts were formed by making cross-cuts (17 ~ 120 μm wide) on the IBAD (ion beam assisted deposition)-MgO templates using laser scribing followed by depositing the superconducting layer ( ~ 0.6 μm thick). AC losses were measured and compared for filamentized conductors with and without the cross-cuts under applied peak ac fields up to 100 mT. The results were analyzed to evaluate the efficacy of filament decoupling and the feasibility of using this method to achieve ac loss reduction.

Transport AC Loss Measurements in Superconducting Coils

Transport AC loss measurements were performed on several Second Generation (2G) High Temperature Superconducting (HTS) pancake coils. A good agreement was observed between the AC loss values of the coils obtained using two separate techniques. Self-field critical current density of the tape did not have direct effect on the AC losses in coils. Relative orientation of the tapes in 2-tape stack affects AC losses in coils using the stacked conductor. Losses scale with maximum perpendicular field seen by the conductor in the coil suggesting that the magnetization loss is the predominant component of coil losses. Absence of frequency dependence of the losses indicates that the eddy current losses are not significant in the coils up to 400 Hz.

Electrical Characteristics of Stacks of YBCO Tapes in Applied Magnetic Field

Stacks of Second Generation (2G) High Temperature Superconductor (HTS) tapes were characterized for critical current density and magnetization losses. Effect of external magnetic field on critical current density is studied as a function of number of tapes in the stack and the configuration of stack arrangement. Results of the measurements on stacks of IBAD and RABiTS showed interesting differences. The results suggest that the arrangement of tapes in fabricating high-current cables needs to consider self-field effects, critical current density in external magnetic field, and magnetization losses to optimize the cable configuration for specific applications.

${\rm YBa}_{2}{\rm Cu}_{3}{\rm O}_{7-\delta}$ Films Grown on Faceted Sapphire Fiber

There have been great advancements in the 2nd generation (2G) high temperature superconductors (HTS) wires termed coated conductors (CCs). Nevertheless, due to the high aspect ratio and the nature of metallic substrates, AC loss is a serious problem for the coated conductors. In this paper, we present a novel approach of fabrication of thin faceted sapphire fibers as substrates for YBCO film growth by laser heated pedestal growth (LHPG) technology. Single crystal sapphire fibers of about 100 μm in diameter with two r-plane facets on the sides have been successfully grown. By adjusting seed orientation and process optimization, the growth was tuned to the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">a</i> -axis growth with extremely smooth r-plane on the sides. A buffer layer of about 30 nm was then deposited by magnetron sputtering followed by the superconductor layer of YBCO film. A critical current density over 1 MA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> has been demonstrated at 77 K self-field. Experimental results shows that fiber orientation and surface smoothness are critical for the performance of YBCO films and that can be achieved by the technologies presented.

The Construction and Testing of YBCO Pancake Coils for a High Field Solenoid

Pancake coils are being fabricated using second generation (2G) High Temperature Superconductor (HTS) for a prototype 10 T solenoid. The length of conductor in each coil is 100 m and the inner diameter of the coil is 101 mm. The critical current of each coil was measured at 77 K in liquid nitrogen and down to ~20 K in helium gas. It has been observed that the effect of thermal shock during cool-down may cause coil performance to degrade irreversibly. The detailed results and the improvements to achieve 10 T will be discussed.

Optimization of 2G YBCO Wires for Resistive Fault Current Limiters

Recent progress increasing the critical current density of second generation (2G) high temperature superconductor (HTS) tapes seems also to increase the switching capacity per effective surface area. An optimized (as thin as possible, as thick as necessary) stabilization cap layer allows to maximize the switching capacity of tapes at an acceptable temperature rise and to minimize the overall tape length. We present the architecture of available 2G HTS tapes designed for FCL, address an approximate and a precise HTS model computation under full fault and moderate overload conditions and report on the set of experiments on short tape samples for identifying the optimal stabilized coated conductor according to the required specification of an FCL with large inrush current. As a result we present a tool to optimize the Ag cap layer in dependence on critical current density and limitation time.