Development of design for large scale conductors and coils using MgB2 for superconducting magnetic energy storage device

MgB₂ wires are commercially available, and their superconducting characteristics have been continuously developed in the last decade. The relatively high critical temperature of these wires has attracted the attention of researchers, especially in the field of superconducting magnetic energy storage (SMES) coil applications in terms of its relatively high critical temperature, as it enables the use of liquid hydrogen for cooling the coils. The sensitivity of multi-filament MgB₂ wires to bending strain makes the design of large-scale conductors and coils for an SMES system technologically difficult, and the careful investigation of the applied strains during manufacturing is required. Two-conventional methods have been introduced for the fabrication of the coils: wind-and-react (W&R) and react-and-wind (R&W). These methods have been demonstrated to be suitable for the production of large-scale MgB₂ magnets to maximize the coil performance. The W&R and R&W methods have been successfully applied to the designs of conductors and coils, and small W&R test coil fabrication, as well as stability demonstrations are performed in this study. Our study is the first to demonstrate the feeding of hundreds of amperes of transport current using multifilamentary MgB₂ wires at around liquid hydrogen temperature in the practical background magnetic field of 2 T. The minimum quench energy and normal zone propagation velocity are also experimentally investigated for the protection of the actual coils for SMES application.     

Influence of the measuring-circuit configuration on the time-dependent flux-flow voltage

The instantaneous voltage generated by multiquantum flux tubes moving through a superconducting specimen depends upon both the instantaneous flux-flow velocity and the spatial configuration of the measuring circuit. For the case of two different voltage lead arrangements, for the first time the different temporal voltage profiles along constricted type I superconducting films have been recorded, using a highly sensitive signal-averaging technique. All experimental results were in good agreement with theoretical model considerations.     

Development of a 3 MJ/750 kVA SMES system

Research and development on superconducting magnetic energy storage (SMES) system have been carried out to realize efficient electric power management for several decades. Korea Electrotechnology Research Institute (KERI) has developed a 3 MJ/750 kVA SMES system to improve power quality in sensitive electric loads. It consists of an IGBT based power converter, NbTi mixed matrix Rutherford cable superconducting magnet and a cryostat with HTS current leads. A computer code was developed to find the parameters of the SMES magnet which used minimum amount of superconductors for the same energy storage capability, and the 3 MJ SMES magnet was designed based upon that. This paper describes the fabrication and experimental results of the 3 MJ/750 kVA SMES system.     

Design and manufacture of a toroidal-type SMES for combination with real-time digital simulator (RTDS)

The authors designed and manufactured a toroidal-type superconducting magnetic energy storage (SMES) system. The toroidal-type SMES was designed using a 3D CAD program. The toroidal-type magnet consists of 30 double pancake coils (DPCs). The single pancake coils (SPCs), which constitute the double pancake coils, are arranged at an angle of 6° from each other, based on the central axis of the toroidal-type magnet. The cooling method used for the toroidal-type SMES is the conduction cooling type. When the cooling method for the toroidal-type SMES was designed, the two-stage Gifford–McMahon (GM) refrigerator was considered. The Bi-2223 HTS wire, which was made by soldering brass on both sides of the superconductor, is used for the magnet winding. Finally, the authors connected the toroidal-type SMES to a real-time digital simulator (RSCAD/RTDS) to simulate voltage sag compensation in a power utility.     

Development of 3kA conduction cooled HTS current lead system

The research and development of superconducting magnet energy storage (SMES) system, a national project, began in 1999. One of the purposes of this project is investigation concerning the application of high-temperature superconducting (HTS) SMES. As a part of this project, the 3 kA class HTS small model coil was manufactured in order to verify the possibility of realizing conduction cooled HTS SMES. Therefore, it is important to develop the conduction cooled current lead system for applying this coil. We developed a kA class conduction cooled HTS current lead system. This current lead system consists of the copper current lead and the YBaCuO (YBCO) HTS current lead. The YBCO bulk manufactured by Nippon Steel Corporation was applied to the HTS current lead. The YBCO bulk keeps high critical current density (J_c > 10,000 A/cm²) in the magnetic field (1 T) at 77 K compared with Bi2223 superconductor. The experiment of this HTS current lead system was carried out, and rated current of 3000 A was achieved successfully.     

Quench detection system for twin coils HTS SMES

The quench detection and protection system is a critical element in superconducting magnets. After a short summary of the quench detection and protection issues in HTS magnets, an original detection system is presented. The main feature of this system is an active protection of the detection electronics during the discharges, making it possible to use standard electronics even if the discharge voltage is very high. The design of the detection system is therefore easier and it can be made very sensitive. An implementation example is presented for a twin coil HTS SMES prototype, showing the improvements when compared to classical detection systems during operation.     

Current status of SMES in Korea

The first superconducting magnetic energy storage (SMES) in Korea was fabricated in 1987. During 15 years after this, several SMES projects were carried out and many improvements were made. Presently, two main SMES projects are undergoing in Korea. One is low T_c SMES commercialization project and the other is HTS SMES design project. This paper describes a brief history of SMES development and the two main undergoing SMES projects in Korea.     

高温超导带材低/变温疲劳性能测试系统的研制

实用化高温超导带材(如Bi系与ReBCO高温超导复合带材)在高磁场下拥有较高的临界电流密度、宽泛的温度裕度、较强的抗粒子辐照能力及良好的机械特性,因此这类材料在加速器超导磁体系统、高场超导磁体、超导电力等方面表现出巨大的应用潜力。而作为典型的多层功能复合性材料,虽然高强度的基底层增强了高温超导带材拉伸强度,使其在强磁场、高载流条件下可以承受很高的应力,在其加工与运行过程中,不可避免地受到多种疲劳载荷的作用,从而其临界载流能力会显著地降低,进一步,会造成相应高温超导装置功能性难以达到设计标准等。该文介绍一种自主研制的高温超导带材低/变温疲劳性能测试系统,基于该测试系统:一方面,可以实现对高温超导材料在低/变温、疲劳载荷等环境下力学、热学等宏观参数的实验表征研究;另一方面,可以对高温超导材料开展低温疲劳载荷环境下力-电弱化等临界特性的实验研究。利用所研制的低/变温疲劳性能测试系统,对受拉-压疲劳荷载下的YBCO超导带材的力学行为、载流特性开展了初步的实验研究,并分析了应力比、温度等外部环境因素对实验结果的影响规律等。结果表明:在相同的疲劳次数的情况下,YBCO超导带材的力学性能及载流特性与其应力比成明显的非线性关系。该测试系统的成功研制将为中国粒子加速器用高温超导磁体的设计与研发提供基础测试平台。     

Superconducting magnetic energy storage

The author presents the rationale for energy storage on utility systems, describes the general technology of SMES (superconducting magnetic energy storage), and explains the chronological development of technology. The present ETM (Engineering Test Model) program is outlined. The impact of high-T_c materials on SMES is discussed. It is concluded that SMES is marginally competitive with other storage technologies and is likely to remain so     

超导线材短样测试装置测量系统

介绍了自行研制的超导线材短样测试装置的实时测量系统,包括温度、压力、液位、电流、电压降测量5个方面.该系统基于计算机和MCGS组态软件,选用合适的传感器和测量方法,采用A/D数据采集卡实现超导线材短样测试装置数据的实时显示和记录.测量系统具有操作简便、运行可靠等优点,已经通过与超导线材短样测试和超导磁体失超等实验,给出实验结果.这些结果表明,测量系统能满足超导线材短样测试装置的各项数据测量要求.该系统实现了低温测量和电量测量的有机结合,其成功研制为应用超导低温制冷系统的数据采集提供了参考.     

超导电力装置失超检测的基础研究

超导电力装置的失超会影响超导电力设备的运行和安全，是超导电力设备技术实用化有待深入研究的一个重要问题。对国内外通用的超导装置失超检测方法进行了分析，并根据电力系统中超导装置失超检测的特点，对高温超导线材在不同幅值的动态电流作用下的失超特性进行了试验研究，通过对试验数据的分析，对高温超导线材的失超特性有了较精细的理解，并在此基础上提出了超导电力装置失超先兆检测及其失超保护设计的新概念。     

Record‐High Superconductivity in Niobium–Titanium Alloy

The extraordinary superconductivity has been observed in a pressurized commercial niobium–titanium alloy. Its zero‐resistance superconductivity persists from ambient pressure to the pressure as high as 261.7 GPa, a record‐high pressure up to which a known superconducting state can continuously survive. Remarkably, at such an ultra‐high pressure, although the ambient pressure volume is shrunk by 45% without structural phase transition, the superconducting transition temperature (T_C) increases to ≈19.1 K from ≈9.6 K, and the critical magnetic field (H_C2) at 1.8 K has been enhanced to 19 T from 15.4 T. These results set new records for both the T_C and the H_C2 among all the known alloy superconductors composed of only transition metal elements. The remarkable high‐pressure superconducting properties observed in the niobium–titanium alloy not only expand the knowledge on this important commercial superconductor but also are helpful for a better understanding on the superconducting mechanism.     

Model calculations of the time-dependent flux-flow voltage in a thin-film type I superconductor

The temporal structure of the flux-flow voltage is calculated in the current-induced dissipative state of a thin-film type I superconductor. The instantaneous voltage generated by multiquantum flux tubes moving through a superconducting specimen depends upon both the instantaneous velocity and a geometry-dependent function of the position of the flux tube relative to the measuring circuit. The flux-tube velocity is strongly affected by the transport-current distribution, by the short-range edge-pinning effect, and by the repulsive interaction of simultaneously moving flux tubes. For a measuring circuit with leads kept far from the specimen surface, both nonuniform contributions due to the flux-flow velocity and the geometry-dependent function simultaneously cause the instantaneous voltage to peak when flux tubes nucleate and annihilate at the sample edges. Our model calculations reproduce reasonably well the experimental results obtained from signal averaging measurements.     

Field test of 70 MW class superconducting generator

Super-GM and the Kansai Electric Power Co., tested a 70 MW class model superconducting generator in actual power system. The model machine, operated as a rotary condenser, was connected to a 77 kV commercial power grid through 77/6.6 kV transformers. It supplied 40 MVar of leading reactive power to the electric power system. The model machine showed an ability to operate steadily through all the tests and various load changes in the commercial electric power system. The test results proved that the small synchronous reactance of the superconducting generator enhances voltage stabilization and their leading reactive capacity is larger, compared with conventional generators.     

Electrical parameter evaluation of a 1 MW HTS motor via analysis and experiments

A 1 MW class HTS (high-temperature superconducting) synchronous motor has been developed. Design concerns of the developed motor are focused on smaller machine size and higher efficiency than conventional motors or generators with the same rating simultaneously reducing expensive Bi-2223 HTS wire which is used for superconducting field coil carrying the operating current around 30 K (−243 °C). Influence of an important parameter, synchronous reactance, has been analyzed on the machine performances such as voltage variation and output power during motor and generator operation. The developed motor was also analyzed by three-dimensional electromagnetic FEM (finite element method) to get magnetic field distribution, inductance, electromagnetic stress and so forth.This motor is aimed to be utilized for industrial application such as large motors operating in large plants. The HTS field coil of the developed motor is cooled by way of Neon thermosiphon mechanism and the stator (armature) coil is cooled by water through hollow copper conductor. This paper also describes evaluation of some electrical parameters from performance test results which were obtained at steady state in generator and motor mode of our HTS machine.     

超导磁储能系统在舰船电力系统中的应用前景及其关键课题

现代舰船电力系统容量急剧增大，全电力舰船的实现、敏感负荷和新概念武器的引入使舰船电力系统面临着一系列挑战。介绍了超导磁储能系统（SMES）作为一种新型储能设备的应用研究进展，分析了SMES在舰船电力系统中的潜在应用，最后提出了舰船电力系统中应用SMES的关键课题。     

FPAA-based MHO distance relay considering CVT transient supervision

Present-day numerical relays provide remarkable capabilities such as monitoring, recording and communication. These capabilities are considered as secondary priority whereas speed and reliability are the two most important characteristics of a protective relay. Even though present-day numerical relays have provided considerable capabilities and advantages, they have not improved speed of operation in comparison to their solid-state counterparts. The idea of applying mixed signals processing using advanced analogue and digital technology in several applications has started. Use of advanced programmable analogue technology, which is known as field programmable analogue arrays (FPAAs), seems to have the potential to be used in protective relays. Hybrid hardware using both digital signal processor (DSP) and FPAAs is proposed to implement mho distance relay considering capacitor voltage transformer (CVT) transient supervision for low and high system impedance ratio (SIR) systems. Test results are reported and compared with a commercial relay test results.     

Analysis of observations during operation of the NHMFL 45-T hybrid magnet system

The NHMFL hybrid magnet system, which was designed to produce steady field in excess of 45 T in a 32-mm, room-temperature bore, was first tested in December 1999. Since then, the system has served users of the NHMFL at the full design currents in both the superconducting outsert (10 kA) and the resistive insert (67 kA), reaching a combined field of 45.2 T. This magnet system combines both superconducting and resistive magnet technologies, which, whether taken together or separately, define new states of the art. Operating alone, the superconducting outsert has been charged repeatedly to 10 kA, corresponding to a maximum field of nearly 16 T at its 710-mm winding i.d. More recently, operation of the outsert has been limited to 8 kA as a consequence of degradation suffered during an “unprotected” quench, but insert upgrades and higher-current operation (up to 74 kA) have allowed the system to provide 45 T to users still. Because the system was designed from the outset as a facility rather than an experiment, there is a minimum of instrumentation––in fact there is none internal to the steel vessel housing the superconducting magnet. Therefore, projections of internal conditions in the superconducting magnet are deduced from detailed analysis of observations from coil voltage taps and various external temperature sensors and pressure transducers. We present these with comments regarding their value in future magnet design as well as an introduction for more complete analysis by complex computer codes.     

Cryogen-Free Superconducting and Hybrid Magnets

The first practical cryogen-free superconducting magnets using a GM-cryocooler and high temperature superconducting current leads have been demonstrated successfully at the High Field Laboratory for Superconducting Materials (HFLSM). Easy-to-operate cryogen-free 10–15 T superconducting magnets have been used to provide access for new research areas in fields of magneto-science. The HFLSM has started construction projects for new high field cryogen-free superconducting and hybrid magnets.     

High-Voltage Superconducting Fault Current Limiters Based on High-Diffusivity Dielectric Substrates

High-temperature superconducting (HTS) tapes currently used for the manufacture of resistive fault current limiters use metallic substrates upon which the HTS film is grown. Because the alloys used for these substrates, such as Hastelloy, have a rather high resistivity and low thermal conductivity, the HTS film must be protected by a more conducting metallic layer acting as a shunt to avoid burn out during a fault. This shunt layer limits severely the electric field generated during the fault to values smaller than 100 V/m. A long length of tape is then necessary to achieve the desired high voltage. We show here that by using a high thermal diffusivity dielectric substrate such as sapphire, it is possible to obtain much higher electric fields of up to several kilovolts per meter.