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This paper proposes a way to represent the anisotropic nonlinear superconducting properties using a discrete model for magnetization with the corresponding critical parameters, equivalent to the Power Law model for currents. This simplified model makes it possible to analyze magnetic systems with superconducting elements in a stationary mode, which reduces the calculation time. Using of proposed model is demonstrated by the calculation of force interactions between high-temperature superconducting (HTS) samples and permanent magnet in zero-field-cooling (ZFC) and field-cooling (FC) modes. HTS bulks in the form of a prism and stack made of HTS tape are considered. The calculation of the electromagnetic field was carried out using the method of integral equations for field sources. The data of calculations are compared with the results of experimental studies. [ABSTRACT FROM AUTHOR]

On the basis of 24 T magnet, the Institute of Plasma Physics, Chinese Academy of Sciences are developing 35 T all superconducting magnet. The magnet was designed as a combination of 20 T REBCO insert coil and a 15 T 150 mm low temperature superconductor background magnet. The 20 T insert coil consists of two coils nested together. NI winding technology is applied to coil 1 to increase its current density. The 50 μm thick Hastelloy tapes will be used to co-wind with REBCO tapes of the coil 2 to further improve its over-all mechanical strength. Electromagnetic analysis shows that the maximum ratio of operating current to the critical current of coil 1 and coil 2 is 0.63 and 0.37 respectively. A more accurate model for calculating strain considering screening current is under study. The inner joint is applied to the coil 1 to avoid in-plane bending of REBCO tape, and the detailed preparation method is given in the paper. The winding and preliminary testing of all double pancakes of coil 1 have been completed, and the winding of coil 2 is in progress. This magnet is planned to be assembled and tested in 2021. [ABSTRACT FROM AUTHOR]

Second-generation high-temperature superconductors, being brittle, need to be deposited on a substrate and converted to tapes with additional reinforcement layers. These tapes are wound on a core to make superconducting wires and cables. The mechanical loads during bending, twisting, winding, etc., can degrade the superconductor. It is necessary to determine the strain-induced during these processes. Variations in induced strain with bending of superconductors have been investigated analytically and numerically for various configurations of Rare-Earth Barium Copper Oxide (REBCO) tape. The numerical simulation has been carried out using COMSOL Multiphysics software; the analytical examination of the effect has been performed applying the Flexure formula. The geometrical configuration of the superconducting tape is varied in terms of the bending radius, the thickness of constituting layers made of Hastelloy and copper. The results showed that the variation in the thickness of the substrate has a large influence on the induced strain. Electrical performance analysis is also carried out using the power law of strain dependence and the 5% critical current degradation point is noted. Results of these numerical and analytical investigations are expected to help in finding out critical parameters to avoid degradation while being in use. [ABSTRACT FROM AUTHOR]

Presently, the high-speed electric machines with increased specific power are in the mainstream of research and are being developedworldwide. The high-temperature superconductor (HTS) machines allow improving the specific power even more significantly. The inductor generators are one of the perspective types of such machines. A new type of high-speed HTS electric machines is proposed in this paper. The proposed machine combines properties of generator with permanent magnets and inductor generator. In the rotor of this machine, permanent magnets are replaced by the stacks of HTS plates. In this case the HTS generator can be operated as an inductor iron-free HTS generator with combined excitation. This paper is devoted to the experiments and simulation of the proposed HTS generator. The experiment and simulation results prove the implementation of such design at three regimes: inductor, trapped-field, and combined excitation. The future development of the proposed HTS generators and perspectives of their application is discussed. [ABSTRACT FROM AUTHOR]

The YBa2Cu3O7-x (YBCO) coated conductor (CC) is one of the most promising superconducting materials because of their high critical current (Ic) and low dependency of the Ic on the external magnetic field. For superconducting applications, a large number of joints are required to join relatively short YBCO CC tapes. In this paper, we study the electromechanical behavior of lap-jointed YBCO CC tapes fabricated by etching Cu stabilizer at its service temperatures (77 K) under self-field. The effects of etching Cu stabilizer on Ic and joint resistance (Rj) of YBCO CC tapes were discussed. The Rj was reduced and the Ic values of the joints are consistent with the parent CCs tape by etching the Cu stabilizer. Preferable electrical properties under applying axial tension are achieved and proved by the axial tension tests and finite element simulations. This fabrication technique is a unique practicable solution to reduce joint resistance for YBCO CC tapes with thicker metal stabilizing layers and improving electromechanical performance in second generation high temperature superconductor (2G HTS) devices. [ABSTRACT FROM AUTHOR]

In practical high-temperature superconducting (HTS) maglev systems, it was found that the levitation force of the onboard bulk superconductors may attenuate gradually under the inhomogeneous magnetic field. The corresponding phenomenon is that the levitation height will decay in the macroscopic and affects the long-term stability of the maglev vehicle. Thus, it is of great significance to study the dynamic levitation force of bulk superconductors under a varying external magnetic field and lay a foundation for the moderate and high-speed HTS maglev system application. In this paper, first, an experiment related to the dynamic levitation performance of YBCO bulks is carried out with a self-developed HTS maglev dynamic measurement system for the investigation of force attenuation. Then, a corresponding two-dimensional simulation model based on the finite element software of COMSOL Multiphysics 5.3 is built to research the dynamic levitation force of bulk superconductors moving above a nonuniform magnetic field. In the simulation, the electromagnetic properties are calculated using the H-formulation, and the moving mesh is employed to implement the relative movement between the bulk superconductors and permanent magnets. The experiment process is repeated in the simulation model, and the simulation results agree with the experimental results. [ABSTRACT FROM AUTHOR]

In this paper, an NbTi/BSCCO composite conductor made of NbTi/Cu wire and BSCCO/Ag wire cooled by cryocooler were investigated, extending the basic research on current distribution characteristics of low temperature superconductor and high temperature superconductor composite conductor and exploring its potential application. Current distribution characteristics with operating current, temperature, magnetic field, and current frequency were simulated and measured. Current-transfer characteristics between the two superconductors were also obtained. [ABSTRACT FROM AUTHOR]

This paper investigates the conditions of use and the equivalence of various constitutive laws used to model the electromagnetic behavior of high-temperature superconductors: two versions of the critical state model (CSM), the power law model, and a so-called percolation model. All these models can be used to represent the same superconducting material with some limit of accuracy. The CSM and the power law model are well known in the literature. The percolation model can be seen as a generalization of the power law model that includes also a CSM-like behavior at very low electric fields. The investigation has been carried out for three types of operating conditions: the sudden application of a dc excitation, a pure ac excitation, and combined dc and ac excitations. The equivalence between the different constitutive laws is shown to be a function of the magnitude of the electric fields and of the time scales involved. In the dc case, long time scales and very small electric fields are predominant; thus, the superconductor requires a model that is accurate at low electric fields, such as the percolation model. The losses then arise from the relaxation of the magnetic field in the sample. In the ac case, the power law and percolation models are nearly identical when considering power frequencies, so choosing the simpler power law model is fully acceptable in practice. In addition, the CSM coincidentally provides good predictions of the losses in the power frequency range. In the dc+ac case, when time scales in the range of minutes to hours are considered, it is shown that ac losses dominate over relaxation losses, and the same conclusions as for the ac case apply. [ABSTRACT FROM AUTHOR]

The YBCO Roebel cable is a promising option for the high-energy accelerator magnets and tokamak devices with high-current carrying capability and compactness. Referring to the complex current sharing and normal zone propagation, it is difficult to apply the traditional superconductor quench measurement methodology to such a long Roebel cable (2 m) in an adiabatic condition. An alternative method for the quench measurement is to make a Roebel pancake coil cowound with ribbon fiberglass. This paper starts reporting the methodology to wind the coil with impregnation process and the wire installment for the quenchmeasurement. Some initial performancemeasurements and a first trial of the quenchmeasurement were processed in LN2 at 77 K to show the robust performance of this Roebel cable at all the current contacts while maintaining the cable effectively adiabatic or similar to real magnets. [ABSTRACT FROM AUTHOR]

This paper proposes a new high-temperature superconductor (HTS) dual-rotor flux-switching machine for direct-drive wind energy conversion. The key is to adopt dual-rotor structure to improve utilizations of the HTS excitation field and the machine space, thus achieving a high power density. Also, the HTS excitation can easily achieve flexible flux regulation to keep armature voltage constant under time-varying wind speeds. The operation principle, with emphasis on the effect of relative position of both rotors on the magnetic circuits, is described in details. And the initial machine design, especially the split ratio optimization, has been done. By using the finite element analysis, the machine performances are analyzed, and its validity is verified. [ABSTRACT FROM PUBLISHER]

A superconducting magnetic bearing can levitate a rotor without contact. However, the rotor can whirl with large amplitude. To reduce the whirling amplitude, we focused on an electromagnetic shunt damper that is appliable to a rotor system. In this paper, an analysis considering influence of magnetic flux density distribution on dynamics of the rotor was carried out. From linearized and nondimensionalized governing equations, we obtained one parameter that determines the damper's effectiveness. Further, numerical calculation was performed and the optimum value concerning the dimensions of the electromagnetic shunt damper was obtained. [ABSTRACT FROM PUBLISHER]

With recent challenges in developing high-temperature superconductor coils using rare-earth barium copper oxide (REBCO) conductor, particularly critical current degradation in a fully wet wound coil using traditional epoxy, we present engineering stress analysis and new winding approaches in its coil fabrication in order to produce high quality coils. Its implementation, however, necessitates novel approaches and nonconventional considerations. This paper first calculates stress and analyzes stress concentration in the REBCO coil in processes of coil winding and thermal cycling. Thus, a thin film layer has been added to reduce the stress concentration on the coil winding. Second, it describes the critical current anisotropic properties and apply to a Helmholtz coil design to draw attentions to develop a full matrix of Ic(B, T, φ) data for various magnet designs. In the coil fabrication, it introduces a dry winding method with stainless steel cowind (metallic insulation) that has been applied and successfully delivers high quality high temperature superconductor (HTS) coils. Additionally, it tries a fully wet winding approach but employs alternative epoxy—Araldite and no degradation has been found after a few thermal cycles. [ABSTRACT FROM PUBLISHER]

Superconducting current-limiting transformers offer an effective current limitation and recovery-under-load characteristics; they are more compact and have a lightweight design and a reduced short-circuit impedance. Several designs for superconducting current-limiting transformers have been developed and proposed by researchers over the last two decades. However, less research work was devoted to effective current limitation of superconducting transformers in combination with recovery under full or under partial load. In this paper, we present the process of manufacturing a superconducting transformer demonstrator with current limitation and recovery-under-load capabilities. The demonstrator consists of a laminated iron core and a normal conducting 20-kV primary winding, both operated at the room temperature. 2G REBCO tapes are used for the secondary winding, which is operated at 1-kV nominal voltage. In order to keep the secondary winding at cryogenic operation conditions at 77 K, a vacuum insulated fiber reinforced plastics cryostat was designed and manufactured. [ABSTRACT FROM PUBLISHER]

This paper presents our new experimental facility and techniques to measure ac loss and current distribution between the layers for High Temperature Superconducting (HTS) cables. The facility is powered with a 45 kVA three-phase power supply which can provide three-phase currents up to 5 kA per phase via high current transformers. The system is suitable for measurements at any frequency between 20 and 500 Hz to better understand the ac loss mechanisms in HTS cables. In this paper, we will report techniques and results for ac loss measurements carried out on several HTS cables with and without an HTS shielding layer. For cables without a shielding layer, care must be taken to control the effect of the magnetic fields from return currents on loss measurements. The waveform of the axial magnetic field was also measured by a small pick-up coil placed inside a two-layer cable. The temporal current distribution between the layers can be calculated from the waveform of the axial field. [ABSTRACT FROM AUTHOR]

This paper presents the design and performance results of a pair of conduction-cooled brass current leads for a resistive superconducting fault current limiter (SFCL) system. The 24 kV class SFCL, which has been recently developed by the KEPRILSIS collaboration group in Korea, requires three pairs of conduction-cooled brass current leads operated continuously at 630 A. When the SFCL system is in the fault-mode, the current leads have experienced a 60-Hz fault current of ∼10 kA at 24 kV for 3–5 cycles. In this paper, we present the performance results of the conduction-cooled brass (commercial brass, 10% Zn) leads having a rated current of 667 A operated in a bath of liquid nitrogen. [ABSTRACT FROM AUTHOR]

Superconducting magnet systems operated at cryogenic temperature require high temperature superconducting (HTS) current leads to reduce the heat intrusion from the power supply at room temperature. However, some kinds of accidents, such as cryogenic failure, can cause a quench in the HTS current lead. Since the current conducting through the HTS current lead is very large, the quench in a HTS part can lead to a severe device failure. Therefore a study of a protection method for the HTS current lead is important. Generally, the HTS part of current lead used in large scale magnet systems has multiple separated HTS tape strands. They are electrically not connected or poorly connected. Therefore the quench in one strand affects other strands in current lead by applying additional loads for the other parts of the HTS current lead. In this paper, a strand-to-strand bridging method with HTS tapes is proposed as a quench protection method. Small scale HTS current leads with 2G HTS tapes and the suggested bridging method have been fabricated and tested. [ABSTRACT FROM PUBLISHER]

In this paper, the high temperature superconductor (HTS) winding and multitoothed structure are newly incorporated into the doubly salient (DS) and flux-switching (FS) machines, leading to create two new magnetless machines, namely the HTS-based multitoothed switched reluctance (HTS-MSR) and HTS-based multitoothed flux-switching (HTS-MFS) machines. Consequently, the design equations of the three machines, namely the MSR, HTS-MSR, and HTS-MFS, are formulated. The corresponding performances are analyzed by using the time-stepping finite element method (TS-FEM). By utilizing both torque-producing zones, the two HTS-based machines can achieve better performances than the MSR one. Moreover, the HTS-MFS can offer higher torque density than the HTS-MSR, but associated with larger torque ripple. [ABSTRACT FROM PUBLISHER]

In this paper, the use of magnetic materials to divert flux in high-temperature superconductor superconducting coils and reduce transport ac loss is investigated. This particular technique is preferred over other techniques, such as striation, Roebel transposition, and twisted wires because it does not require modification to the conductor itself, which can be detrimental to the properties of the superconductor. The technique can also be implemented for existing coils. The analysis is carried out using a coil model based on the \bf H formulation and implemented in comsol multiphysics. Both weakly and strongly magnetic materials are investigated, and it is shown that the use of such materials can divert flux and achieve a reduction in transport ac loss, which, in some cases, is quite significant. This analysis acts to provide a foundation for further optimization and experimental work in the future. [ABSTRACT FROM PUBLISHER]

This paper presents a high-temperature superconducting (HTS) planar balun. The balun exhibits an excellent amplitude and phase balance performance. The balun was fabricated using double-sided HTS YBCO films on a 0.5-mm-thick 3-in \LaAlO3 substrate. The balun demonstrates a wideband operation and a low insertion loss. The center frequency of the balun is 1.25 GHz. The return loss bandwidth of -18 dB is 1.02 GHz (the fractional bandwidth is 82%). The phase imbalance is less than 7^\circ. The amplitude imbalance is less than 0.7 dB, and the insertion loss is less than 0.31 dB over 0.69–1.77 GHz. [ABSTRACT FROM PUBLISHER]

We have developed a magnetic levitation system using a magnetic shielding effect of high temperature superconducting bulks. We have already succeeded to demonstrate principle of the levitation. In the paper, we tried to increase the levitation force. Firstly, when a ferromagnetic plate was put underside of a permanent magnet, the levitation force increased. And when the underside ferromagnetic plate was protruded from the magnet, the levitation force effectively increased furthermore. Lastly, the levitation force exceeded vehicle weight and the stable levitation became possible. [ABSTRACT FROM PUBLISHER]

This paper presents the design of an AC loss experiment using nitrogen boil-off method. This experiment is aimed at exploring the AC loss of HTS double race-track coils which will be installed on the rotor of a wind turbine generator. The operating environment is simulated by designing a cryostat with rotating magnetic field windings. Apart from the fact that the alternating magnetic field causes most of AC loss on the HTS coils, we also believe that the DC background field would be another important factor causing AC loss if the HTS coil is experiencing by both alternating magnetic field in the perpendicular direction and DC background field in the parallel direction. In order to perform the boil-off measurement, we present the method to estimate the heat leakage in the cryostat which might cause errors to the measurement . [ABSTRACT FROM PUBLISHER]

Now that ITER is entering construction, many of its systems are in the final stages of design and analysis. Among them the 31 feeders, which will be supplied in-kind by the Chinese ITER partner. The feeders supply the electrical power and cryogens through the warm-cold barrier to the ITER superconducting magnet systems. They are complex systems with their independent cryostats and thermal shields, densely packed with many components, such as the current feeds, the cryogenic valves and High-Voltage (HV) instrumentation hardware. Some of the feeder components are particularly critical and have been designed with great care. Among them the High-Temperature Superconductor (HTS) current leads, designed for unprecedented currents, the 30 kV class, Paschen-hard HV insulation and the bus bar support system, designed to react the multi-ton Lorentz-forces from the bus bars at minimal heat load. This paper discusses the design challenges for these (and other) key components of the ITER magnet feeders. [ABSTRACT FROM PUBLISHER]

This paper introduces the design methodology of HTS bulk generator for direct-driven wind turbine. The trap field capability of HTS bulks offer the potential of maintaining similar or even higher magnetic loading level without the iron circuit in the generator. This so-called air-cored design can reduce the weight and increase the power outing per volume of the machine. The detailed design method of the air-cored HTS bulk machine is presented; 3D modeling is applied to consider the total trapped field of bulk arrays; a case study is performed to demonstrate the advantages of air-cored HTS bulk machine over conventional permanent magnet machine. Our results show that the air-cored HTS bulk machine has the potential to maintain the same magnetic loading level as that of the conventional permanent magnet machine. More importantly, it can reduce the total machine weight by 30%. [ABSTRACT FROM PUBLISHER]

The knowing the critical current density JC is important to calculate AC losses in superconducting applications. Usually JC can be obtained from magnetization measurements or electric measurements based on global quantities as the magnetic flux or the voltage. In this paper a quick and direct magnetic method for determining JC is proposed. It is based on direct measurements of local magnetic field in the gap between two bulk HTS pellets. Field penetration measurements were carried out on HTS pellets at 77 K by applying increasing axial magnetic fields with a quasi constant sweep rate. This determination of JC is theoretically based on Bean model. JC is deduced from the complete penetration magnetic field BP. BP is deduced from the delay TP between the applied magnetic field Ba(t) and the magnetic field at the center between the two pellets B0(t). Numerical calculations allow deducing JC more precisely from theoretical calculations and measurements. The numerical calculations are made with the power law E=EC(J/JC)^{n}. For the determination of JC the influence of the gap due to Hall probe sensor and the applied magnetic field rise rate are taken into account. The influence of thermal is also studied. [ABSTRACT FROM PUBLISHER]

Our group has tried to introduce High Temperature Superconducting Technology to electric vehicle (EV) drive motor, and developed High Temperature Superconducting Induction-Synchronous Machine (HTS-ISM). In this paper, 20 kW class HTS-ISM were designed and manufactured with DI-BSCCO wires. First, we developed and tested partial superconducting HTS-ISM (HTS rotor windings with copper stator) for clarification of the performance. We could observe the efficiency at 92.3% even for the light load. Furthermore, we successfully fabricated and conducted no-load test for fully superconducting HTS-ISM. It was verified that stable synchronous rotation at 1200 rpm was succeeded, which is the world-first success of achieving the rotation at over 1000 rpm for fully superconducting motor. Our results are one of the big steps for realizing the HTS-EV. [ABSTRACT FROM PUBLISHER]

In the case of motors and generators, the benefits of using superconductors could be represented by the reduction of 50% in both losses and sizes compared to the conventional machines of the same rating. The high temperature superconducting (HTS) coils wound with HTS conductors have very low normal zone propagation velocity (NZPV) and complicated quench behaviors because the conductors have a low thermal conductivity and large specific heat. According to these reasons, in case of HTS coils and magnets, it is difficult to expect the self-protection like as low temperature superconducting (LTS) coils. In this paper, we suggest a method which inserts the Cu tape between turn-turn winding in the HTS coil instead of electrical insulation to improve the self-protection ability of HTS coils. Because the thermal and electrical contacts along the transverse direction are enhanced by inserted Cu tape instead of insulator and the whole thermal stability of HTS coils would be increased. To clarify the quench behavior of this suggested coil, we investigate the normal-zone propagation properties of the fabricated HTS pancake coils wound with 2G conductor and Cu tape under the cryocooled operation using GM cryocooler. The effects of inserted Cu tape and the improved the self-protection ability for the suggested HTS coil will be discussed. [ABSTRACT FROM PUBLISHER]

Among superconducting fault-current limiters (FCLs), the inductive type has some distinctive merits such as large design flexibility due to the turn ratio, isolation between a current-limiting device and a power transmission line, and low heat losses. This paper highlights the future perspective for an inductive-type superconducting fault-current limiter (LSFCL) by using an autotransformer (AT) in closed- and open-core schemes. These are considered technically feasible and economically viable alternative for the LSFCL in terms of compactness, efficient limitation, and lower alternating-current losses, which prove to be a construction cost-effective means of fault-current management. In the hybrid scheme, a diode-bridge-type SFCL is integrated with an AT-based LSFCL. The above is accomplished by advanced numerical techniques and, hence, simulation studies in a sample distribution system to realize the significant efficiency improvement of the superconductor-based technology. [ABSTRACT FROM AUTHOR]

In this paper we analyse numerically and experimentally the quench behavior of Cu-stabilized second-generation high temperature superconducting (2G HTS) wires at self-field and in adiabatic conditions. The electric field profiles along the superconductor after applying an energy pulse to the conductor have been obtained together with the parameters characterizing the quench: minimum quench energy (MQE) and the normal zone propagation velocity (NZPV). The analysis has been performed at different temperatures, T, between 72 K and 77 K, and at different applied currents, I/Ic(T)<1, Ic being the critical current. Our analysis shows that the numerical results obtained by finite element method (FEM) are closer to the experimental MQE values when the contribution of the thermal mass of the heater is taken into account. [ABSTRACT FROM AUTHOR]

High temperature superconductor (HTS) technology enables generators with one third the weight and one half the losses of conventional machines. These technologies enable a significant reduction in the size and weight of 10 MW-class generators for direct-drive wind turbine systems and reduce the cost of clean energy relative to conventional copper and permanent-magnet-based generators and gearboxes. With compact and light-weight 10 MW-class HTS generators, installation and low maintenance operation of high power wind turbine systems becomes practical and enable cost-effective access to wind resources. Under a program funded by the NIST-Advanced Technology Program, key generator technologies for a 10 MW class generator have been developed. This paper summarizes work under the NIST and internal programs. [ABSTRACT FROM AUTHOR]

Superconducting cables for power transmission usually contain two conductors for DC application, or three conductors for AC, with high voltage insulation. In contrast, for some applications related to accelerators it is convenient to transfer high currents via superconducting links feeding a number of circuits at relatively low voltage, of the order of a kilovolt, over distances of up to a few hundred meters. For power transmission applications based on cooling via sub-cooled liquid nitrogen, suitable HTS conductors are only available in the form of tape, and a multi-layer variant can be envisaged for the multi-circuit links. However, where cooling to temperatures of the order of 20 K is feasible, MgB2 conductor, available in the form of both tape and wire, can also be envisaged and in the latter case used to assemble round cables. There are, therefore, two distinct topologies—based on the use of wires or tapes—that can be envisaged for use in applications to multi-circuit link systems. In this paper the merits of the two approaches are compared, and case studies related to applications to the LHC are presented. [ABSTRACT FROM AUTHOR]

This paper investigates subharmonic resonance, one of typical nonlinear phenomena, appearing in a high-Tc superconducting bearing system. In such low-damping systems having noncontact support by magnetic force, complex dynamical behaviors can be caused by nonlinearity of the magnetic force. In this study, the magnetic rotor, supported by a high-Tc superconducting bulk, is bound to a D.C. motor with a universal joint. According to the equation of motion, caused by the quadratic term of the levitation force, subharmonic resonance of the rotor can occur when the rotor rotates, not at its critical speed, but at twice its critical speed. This analytical prediction was confirmed by our numerical and experimental results. Additionally, our study also found occurrence of internal resonance induced by this subharmonic resonance. These findings beyond linear regimes can be important for the design of high-Tc superconducting levitation systems. [ABSTRACT FROM AUTHOR]

The Karlsruhe Institute of Technology (which is a merger of former Forschungszentrum Karlsruhe and Karlsruhe University) is responsible for the design, construction and testing of the high temperature superconductor (HTS) current leads for the stellarator Wendelstein 7-X (W7-X) which is presently under construction at the Greifswald branch of the Max-Planck-Institute for Plasma Physics. The current leads are of the binary type, the HTS part covering the temperature range between 4.5 K and 60 K while the heat exchanger covers the range between 60 K and room temperature being cooled by 50 K He. In total 2 prototypes and 14 series current leads are required with a nominal current of 14 kA and a maximum current of 18.2 kA. The paper describes the design and first test results of the prototype HTS current leads. [ABSTRACT FROM AUTHOR]

Electric device applications of a high temperature superconducting (HTS) bulk magnet, having stable levitation and suspension properties due to their strong flux pinning force, has been proposed and developed. We have been investigating a three-dimensional (3-D) superconducting actuator using HTS bulks to develop a non-contract transportation device that moves freely in space. It is expected that our proposed 3-D superconducting actuator will be useful as a transporter used in a clean room where silicon wafers which dislike mechanical contact and dust are manufactured. The proposed actuator consists of an HTS bulk (trapped magnetic field by field cooling method) magnet for the mover and two-dimensional arranged multi-pole electromagnets as the stator. Up to now, the electromagnets consisted with ironed cores and copper coils were used as a stator, and each electromagnet was individually controlled using DC supplies. The movement of HTS bulk (mover) was not smooth because of the DC control. In this paper, the new electromagnets driven with AC control were proposed to improve the moving characteristics of the bulks. The characteristics of horizontal movement by newly proposed system will be presented. [ABSTRACT FROM AUTHOR]

This paper reports on the operation test of a 22.9 kV hybrid superconducting fault current limiter (SFCL) in the KEPCO test grid. The SFCL works at a rated voltage and current of 22.9 kV and 630 A, respectively. There are two major objectives of the operation test: (1) long-term operation and (2) fault tests for protection coordination study. The operation lasted for more than a year. We experienced several times of cryostat suspension due to blackouts and false alarms due to sensor failures during the operation. We also carried out short circuit tests in the test grid, equipped with circuit breakers and a recloser. An artificial fault generator was used to generate fault currents. The tests showed that the SFCL, together with the recloser, functioned reliably under repeated faults. We also confirmed the reclosing capability of the SFCL. We have presented herein the operation details, cost of operation, short-circuit test results, and our plans for further tests for protection coordination. [ABSTRACT FROM AUTHOR]

A conduction-cooled superconducting split magnet system with large crossing warm bore is designed and will be developed for material processing applications. The magnet is composed of eight coaxial coils and assembled in the form of split coil groups. Both the Bi2223/Ag HTS superconducting tape and NbTi LTS superconducting wires are used to generate a central magnetic field of 8 T, maximum of 11 T in the horizontal warm bore. The split gap between the coils is as large as 136 mm to accommodate the crossing warm bore of 100 mm in diameter. The superconducting split magnet will be conduction-cooled by two GM cryocoolers. The HTS coils and NbTi coils are to be operated in driven mode with two independent power supplies. The operation currents are 200 A (HTS) and 136 A (NbTi) respectively. Magnetic design, stress and strain analysis as well as magnet operation and protection are presented in this paper. [ABSTRACT FROM AUTHOR]

It is particularly attractive for High Temperature Superconductors (HTS), such as the melt-processed YBCO single-grain bulks, to trap strong magnetic fields at cryogenic temperatures. With the flux density orders of magnitude much greater than the rare earth magnets, the YBCO bulks can be formed as small and as compact as them. As a result, YBCO bulks are used as magnets in magnetic bearings, MRI scanners and motors, etc. The trapped field by the YBCO magnet is decided by the magnetization, which normally includes three different ways. However, the traditional ways to magnetize the YBCO will always need the applied field to be as high as the expected field on the superconductor or much higher than it. In this paper, we will describe a technique which facilitates the creation of the high magnetic field and utilize a normal permanent magnet in stead. By using this rare earth permanent magnet which is not as strong, this technique involves the superconducting flux pump concept, which means that a much larger field being trapped by the superconductor bulk is caused by a small field repeatedly applied to it. To achieve such pumping effect, an intermedia material is necessary and in the related experiments, Gadolinium is used as such an important thermally actuated material. Traveling magnetic field through it will magnetize the YBCO in such a way that the flux density will be accumulated step by step on the surface on the bulk. [ABSTRACT FROM AUTHOR]

In this paper, a novel coaxial magnetic gear (CMG) using bulk high temperature superconductors (HTS) is proposed. By substituting bulk HTS for ferromagnetic material, a novel stationary ring is resulted, which can not only provide the desired field modulation effect but also suppress the end-effects that commonly occurred in the traditionalCMG. The performance of the proposed bulk HTSCMGis assessed and then verified by using finite element analysis. [ABSTRACT FROM AUTHOR]

The insulation characteristics of high temperature superconducting (HTS) coil or winding are significant for their power application, which mainly includes partial discharging (PD), withstand voltage, breakdown voltage, flashover, fatigue effect through thermal cycles and lifetime. In this paper, we focused on investigation of the partial discharging of two HTS DP made of commercial multifilamentary Bi2223/Ag tapes and YBCO coated conductors. PD test was performed in order to ascertain the partial discharge inception voltage of DP in different conditions, which included static and quenching conditions. Experimental results revealed that PD density does not change obviously in different conditions. Useful results with combined conditions for PD characteristics were experimentally obtained. [ABSTRACT FROM AUTHOR]

High Temperature Superconductor (HTS) current leads provide the transition of the current transfer system from room temperature to the 4.5 K. For the ITER superconducting magnet system, a total of 60 HTS current leads are required, with a total nominal current capacity of 2.64 MA. By the use of HTS leads significant power savings can be achieved during the operation of the ITER magnet system. Based on the functional specification by the ITER Organization (IO), ASIPP manufactured and tested a first pair of trial HTS current leads for the ITER coils. The cryogenic test of these 68 kA and 52 kA trial HTS leads was performed at ASIPP using the cryo-plant and power supplies of the EAST Tokamak. The following paper presents the results of the tests and concludes with a discussion of the design features of the next generation prototype of the ITER HTS leads based on the results of the trial lead tests. [ABSTRACT FROM AUTHOR]

In this paper, we have studied the electromagnetic phenomenon and AC losses of assembled high-Tc superconductor (HTS) tapes using the finite element method (FEM) approach. The model cable is composed of several Bi-2223/Ag tapes with polygonal shape on the cylindrical former that was arranged in parallel along the conductor axis. The HTS tape usually shows complex material properties, which are described by the non-linear resistivity and the anisotropy against the external magnetic flux density as well as its angle. The numerical calculation was carried out considering the field dependence of critical current density and index value, which accounts for the anisotropy of the Bi-2223/Ag tape. The calculated AC losses were compared with the experimental results and with the theoretical values. It was observed that the analytic formulae are not proper to predict the AC loss of the multi-stranded conductor that is presented here. The adjacent tape's effect of the conductor on the AC loss was also investigated and discussed. [ABSTRACT FROM AUTHOR]

The superconductor-triggered type fault current limiter (STFCL), which was developed by Korea Electric Power Corporation (KEPCO) and LS Industrial Systems (LSIS), is under operation for the verification test at KEPCO's power testing center. The STFCL is composed of superconductor, fast switch and current limiting resistor. The fault current is suppressed after a half cycle by the method of a line commutation. In this paper, we investigated the empirical modeling of STFCL using principal components and auto-associative support vector regression (PCSVR) for the prediction and fault detection of the STFCL. Signals for the model are currents and voltages acquired from high-temperature superconductor (HTS), driving coil (DC) and current limiting resistor (CLR). After developing the empirical model we analyse the accuracy of the model. The results were compared with that of auto-associative neural networks (AANN). PCSVR showed much better performance in accuracy aspect. Moreover, this model can be used for the prognosis of STFCL system. [ABSTRACT FROM AUTHOR]

A permanent-magnet synchronous motor with high-Tc superconducting (HTS) armature operated at sub-cooled liquid nitrogen temperature has been designed. The prototype model has a ten-pole rotor and twelve sets of armature windings which are fabricated with BSCCO tapes, and its output power is 400 kW at the rated speed of 250 rpm. In order to decrease the AC loss of HTS coils to an appropriate level, the conventional stator iron cores are adopted. The coil design, behaviors of HTS conductors, even cooling system design will be proved in the armature case. And the prediction of AC loss in stacked tape conductor exposed to external magnetic fields with various directions have been carried out using FEA method. Based on the 3D magnetic field finite element analyses, this paper presents an AC loss analysis method for the armature winding and provides upper the limit of operating temperature for the cooling system. [ABSTRACT FROM AUTHOR]

This paper discusses the different possible designs of both cored and coreless superconducting synchronous generators using high-temperature superconducting (HTS) tapes, with particular reference to demonstrators built at the University of Southampton using BiSCCO conductors. An overview of the electromagnetic, thermal, and mechanical issues is provided, the advantages and drawbacks of particular designs are highlighted, the need for compromises is explained, and practical solutions are offered. The scalability of results obtained from small demonstrators is considered. [ABSTRACT FROM AUTHOR]

The crystal defects of the nano-scale, which are called artificial pinning centers (APCs), were successfully introduced into high-temperature superconductors (HTS) by nanotechnology, in order to strongly pin the quantized vortices. Critical current densities Jc of the HTS films were dramatically improved by APCs whose dimensions were controlled. By this method, the in-field Jc (77 K) of the high-quality, epitaxial films was improved by one order of magnitude or more compared with the values of the past. A current outline of the research is described in this paper. [ABSTRACT FROM AUTHOR]

In order to evaluate the stable operation of high temperature superconducting (HTS) power cable, the calculation of AC loss on HTS power cable is important factor. Because AC loss has a big effect on many superconducting equipments, which are fabricated using the HTS tape. In general, AC loss of the HTS tape can be calculated by using voltage variations of the tape with respect to the external magnetic field when AC current applied to the tape. In case of HTS power cable carrying AC current, however, because the magnetic field distribution in the cable is very complicated, it is hard to compute AC loss of the HTS cable directly using above method. In this paper, the stability evaluation of the HTS power cable was performed by the following procedures. Firstly, the voltage variations of the HTS tape carrying AC current in the external magnetic field with different field angle were measured and the magnetic field distribution of HTS power cable with AC current was analyzed. Then, AC loss of the HTS power cable was calculated by using the results of both the measurement and the analysis. The stable operation of the HTS power cable was evaluated on the basis of AC loss of the cable. [ABSTRACT FROM AUTHOR]

According to recent studies, economical feasibility of resistive superconducting fault current limiters (FCL5) in transmission and distribution power line is confirmed. Since the SFCL is operated under alternating current (AC), it causes power loss, so-called AC loss, during normal operation condition even though it is superconductor. Bifilar pancake winding with coated conductor (CC) is expected to reduce AC loss of the SFCL by canceling magnetic fields efficiently as compared with other type SFCLs using CC in the same length. AC loss characteristic of the bifilar pancake type coil for SFCL application was investigated in this paper. Two bifilar pancake coils were wound using CC with facing on high temperature superconductor (HTS) sides each other and substrate (Ni-W) sides each other, respectively. AC losses of the coils were measured at 77 K and theoretical analysis was performed by finite element method (FEM). The experimental results are compared with the Norris equations and numerical values using FEM. [ABSTRACT FROM AUTHOR]

YBCO tapes are expected to be used in future high temperature superconductor (HTS) applications as they have better Jc characteristics at high temperatures and in high magnetic fields. For power applications such as transmission cables, YBCO tapes and a copper former are connected in parallel and they might be subjected to a short-circuit fault current that is 10 to 30 times the normal operating current. Therefore, the over-current behavior, including the hot-spot and the distribution of transport current between the copper-laminated YBCO tapes and the copper former, is very important to examine the stability and feasibility of the cable. This paper describes the experimental results for over-current pulses of a 1-m single-layer cable fabricated with five copper-laminated YBCO tapes and a copper former. Further, we performed numerical simulations by using a newly developed computer program based on the 3D finite element method. [ABSTRACT FROM AUTHOR]

This paper describes a high power density high-temperature superconducting (HTS) electric machine topology that is scalable for marine propulsion and power generation. The design, currently being pursued for airborne applications, is based on homopolar inductor alternator (HIA) technology, which is new within HTS applications. The basic machine design configuration of the HTS HIA is based on a stationary HTS field excitation coil, a solid rotor, and an advanced but conventional stator comprising liquid-cooled air-gap armature winding and an advanced iron core. High power density is obtained by the enhanced magneto-motive force capability of the HTS coil, the increased airgap flux density and armature current loading, and the high tip velocity of the rotor. Preliminary scaled up designs look attractive for three marine applications: propulsion drive, primary ship power generation, and power generation modules. The generators are driven directly by the turbines without the additional complexity of a clutch and gear system. A conceptual design study of a 36-MW 3600-r/min generator, a 4-MW 7000-r/min auxiliary generator, and a 36-MW 120-r/min and 4-MW 132-r/min propulsion motor are summarized. [ABSTRACT FROM AUTHOR]

This paper reviews the application of trifluoroacetate (TFA)-based metalorganic deposition (MOD) for the production of thin film YBCO superconductors. A brief review of relevant studies leading to modern processing techniques is followed by a description of the present understanding of chemical and physical changes between decomposition and YBCO formation. [ABSTRACT FROM AUTHOR]

Since 2003, three years of the current 5-year national project for development of coated conductors using Y-system superconductors have passed and remarkable results have been achieved. In this paper, the current status and future prospects are reviewed. The group of Fujikura and SRL has worked on a long tape with high performance in the PLD-YBCO supercon- ducting tapes on the IBAD-GZO buffered substrates. The highest Ic × L value of the tape is over 50 k Am which is 212 m in length and 245 A of critical current (Ic). Additionally, a 500 m long IBAD-buffered tape with a reasonable in-plane texture was produced using a large scale IBAD apparatus by Fujikura. In the other group, long tape processing has been developed focusing on lowering production cost. An extremely high Ic value of 692 A was obtained in a short sample by the advanced TFA-MOD method on a CeO2 (PLD)/GZO(IBAD)/Hastelloy substrate. In the efforts for the long tape processing, a 25 m long tape with the Ic value of 100 A by a continuous reel-to-reel system and a 40 m long tape with 155 A by a batch system were realized. 100 m class long tapes were also obtained with the MOCVD and PLD-HoBCO processes. Both groups are aiming for 500 m long tapes with the high Ic value of 300 A/cm-w with a production rate of 5 m/h. Furthermore, feasibility studies for applications using coated conductors have already began due to the above mentioned success of long tape production. Several kinds of coils using the long coated conductors such as solenoid and pancake types and spiral shaped conductors for the cable were made. Reasonable high performance results were confirmed in the trials. New approaches on the preliminary studies for the applications of cables, transformers, motors and current limiters etc. are planned in this project. [ABSTRACT FROM AUTHOR]