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This paper describes new kind of HTS (High Temperature Superconducting) element for current leads, which can transfer large electric current in the nuclear fusion system. Since the HTS tapes have no resistance and the generated Joule heat is also very small compared to the conventional current leads, cooling costs of the current leads can be reduced. For this reason, the various feasibility researches for HTS current leads have been promisingly progressed in the superconducting power applications. However, there is a limitation on the capability of current carrying for single HTS tape. In addition, the cross-sectional area of the current leads should be small enough to minimize the heat conducted through the HTS current leads. In order to improve the current carrying capacity of the current leads, multiple HTS tapes are required. In this paper, we proposed several structures of compact HTS current leads and compare them other 2 kA class current leads. We report on the calculated characteristics of stabilized HTS current leads and on the performance measured during critical current measurement tests. [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]

Mechanical stresses of magnetically induced origins are becoming more serious with the trend of high-temperature superconductor (HTS) heavy-current transformer (HCT) applications. Mechanical forces in HTS HCTs that act on the transformer windings are generated by the interaction between the current density and the leakage flux density. This paper presents the calculation of leakage flux and mechanical force distribution in high-current HTS transformer windings. This requires the need for advanced numerical techniques for simulation studies using finite-element method by adapting two auxiliary windings for the leakage flux mitigation and, thereby, mechanical forces within the main windings. A model is developed for the calculation of mechanical force considering nonuniformity of both field and current distributions in the windings, which is the main motivation for initiating this paper. [ABSTRACT FROM AUTHOR]

This paper deals with design and operating test of a novel hybrid FCL. The FCL system consists of a coil, a fast switch and a resistor for bypassing the fault current. The switch is driven by novel non-inductive coil suggested in this paper but an extra driving coil is required for fast switch in existing hybrid FCL. We used two kinds of HTS wire for the coil. The impedance of the coil was negligible in normal operation. But different quench characteristics of HTS wires caused asymmetric current distribution which induced effective magnetic flux in the coil during faults. The switch was opened by repulsive force from this magnetic flux in fast response to the fault. Then, all current were flew through the normal conductive bypass resistor connected in parallel to both the coil and the switch. Electromagnetic analysis of the coil based on finite element method was performed. Also, a small-scale asymmetric non-inductive coil was designed, fabricated and tested. The proposed hybrid FCL system showed fast and efficient current limiting characteristic. [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]

This paper deals with feasibility of fault current limiter (FCL) by using Bi-2223 high temperature superconducting (HTS) wire. The FCL using HTS wire has some advantages of stability, flexibility of structure and cost compared with existing superconducting FCLs using bulk or thin film. Even if the FCL using HTS wire has zero resistance in normal state, it needs to be wound as a bifilar winding for non inductance. In this paper, four types of FCL module with bifilar winding were suggested, manufactured and experimented with short circuit tests in 77 K. The FCL modules have different fault current limiting characteristic and stability respectively. These types of module are solenoid, pancake, solenoid impregnated with epoxy resin and pancake impregnated with epoxy resin. The FCL module was applied by controllable AC bias during fault duration, 0.1 s, from 0.5 V to 22 V. A process of fault occurrence in this test is very similar to a fault occurrence in real system. In results of tests, the pancake type was more effective to limit a fault current than the solenoid type. Also modules impregnated with epoxy resin showed more efficient current limiting characteristics than nonimpregnated modules. The solenoid type has better characteristic of stability. The feasibility of the FCL by using HTS wire was verified by this paper. [ABSTRACT FROM AUTHOR]

A further development of the high temperature superconducting (HTS) mini power plant (MPP) concept designed earlier by one of the authors is presented in the paper. HTS fault current limiters (FCL) will be inserted at the terminals of the synchronous generator. Joint operation of HTS generators (including fully superconducting generators) and HTS FCL's provide additional benefits viz. a significant increase of the generator's unit power rating as well as of its dynamic stability, shown in the paper. A three-phase inductive HTS FCL designed and built for the protection of a generator is made up of three one-phase units, each containing YBCO rings as secondary "windings." A new design idea was applied for the primary winding to further reduce the leakage reactance of the FCL resulting in low reactive power consumption. Simulations of the electromagnetic processes in the HTS FCL are shown. Theoretical studies on the joint operation of a fully superconducting generator and an HTS FCL are presented. [ABSTRACT FROM AUTHOR]

ASIPP will supply for ITER all the current leads. There are three types of high temperature superconducting (HTS) current leads designed to carry 68 kA, 55 kA, or 10 kA to the ITER magnets. Different from the trial leads manufactured and tested in Institute of Plasma Physics, Chinese Academy of Sciences (ASIPP), some critical technologies were qualified before the manufacturing of the ITER leads could commence, including: 1) welding, brazing, and soldering qualification; 2) fin type heat exchanger (HEX) with tight assembly tolerance; 3) low temperature superconducting (LTS) linker with cables soldered to the 5 K copper terminal; 4) instrumentation mock-up for the temperature and voltage test. In this paper, the outcome of these qualification activities will be reported together with the plans for the series production planning and development. [ABSTRACT FROM PUBLISHER]

In this paper we extend the recently developed CtFD strategy for the analysis of the thermal-hydraulics of a meander flow type heat exchanger, validated against the Wendelstein7-X (W7-X) High Temperature Superconductor (HTS) current lead prototype experiment, to the case of a heat exchanger for a 68 kA HTS current lead. We aim to assess the optimized operative conditions and the influence of different geometrical configurations on the performance of the heat exchanger. [ABSTRACT FROM PUBLISHER]

This paper aims to study the feasibility of improving pulsed current output by using High temperature superconducting (HTS) air-core transformer. Based on the theoretical analysis, the simulations are done. Results of the simulations indicate that the HTS air-core pulse transformer can magnify the output current magnitude and accelerate the velocity of discharge. However, when a series of inductor modules use the same one HTS air-core transformer, the residual current may influence the discharging waveform. To eliminate residual current, self-coupling discharging model is proposed. The simulated and experimental results illustrate that a self-coupling model can eliminate the residual current effectively. The results of this analysis contribute to the research of superconducting inductor pulsed current output. [ABSTRACT FROM PUBLISHER]

MRI magnets and other magnets that have a low current and high self-inductance are passively quench-protected with a system that includes sub-divided coils with resistors and diodes that are in parallel with sections of the coils. The primary purpose of coil sub-division is to protect the coil from the high voltages that can occur during a quench. In the event of a lead failure (conventional or superconducting) between the coil and its power supply or its persistent switch, the total current in the coil flows through the diodes and resistors in parallel with the coil. When a lead fails, the current decay time constant for the coil current can be quite long. It is desirable that the coil quench in a time that is short compared to the coil current decay time constant. Experience shows that the heating from the resistors and diodes will eventually quench the magnet. This paper presents methods for shortening the time between a lead failure or a persistent switch failure and the eventual magnet quench. [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]

We developed a non-destructive and contactless system for measuring the critical current (Ic) in YBa2Cu3O7-\delta (YBCO)-coated conductors by using a permanent magnet (Sm2Co17). This Ic measurement method is based on the repulsive force (Fr) between the magnet and the shielding current in high-temperature superconductor-coated conductors. We measured Fr using a high-resolution load sensor and found that accurate Fr could be determined without the effect of thick copper film on the YBCO thin film and Hastelloy tape of the substrate. We can determine Ic from Fr0, which is the maximum repulsive force determined from an extrapolated value of the Fr vs. L curve for L=0\ \ mm, described in our previous paper [1]. We show that the permanent magnet method can be used to determine the longitudinal Ic distribution and large-scale defects in YBCO-coated conductors. In addition, it turned out from this experiment that the permanent magnet method was effective to rapidly measure the longitudinal Ic distribution of long-scale coated conductors. [ABSTRACT FROM AUTHOR]

In order to limit fault current from an accident in power grid, many research groups have developed resistive superconducting fault current limiters (SFCLs) with a bifilar solenoid and a bifilar pancake types. Comparing with a bifilar solenoid type, a bifilar pancake type has the advantage of its volume, but it has problems such as recovery and insulation of SFCLs. To eliminate the drawback of these two types, in this paper, a new type of coil that is an oval-shaped SFCL, have proposed. This type consists of inner and outer layers which are connected in parallel. A small-scale sample coil was fabricated and experiments for both a short circuit test and recovery characteristic test were performed in liquid nitrogen. Experimental results were compared with two types of coils; the bifilar solenoid and bifilar pancake coil. Consequently, we confirmed the feasibility of an oval-shaped type. [ABSTRACT FROM AUTHOR]

The ITER Organization (IO) and the Institute of Plasma Physics at the Chinese Academy of Sciences (ASIPP) are jointly developing the design of the 10 kA Current Leads (CL) using High Temperature Superconductors (HTS) for the Correction Coil (CC) Magnet System of the International Thermonuclear Experimental Reactor, ITER. The proposed design combines a conventional helium cooled heat exchanger operating between 65 K and 300 K with a HTS module covering the low temperature end using Bi-2223 tapes. The details of the design and test results obtained on a first prototype lead will be discussed in this paper. [ABSTRACT FROM AUTHOR]

High-Tc superconducting (HTS) wires have showed good capabilities as an alternative conductor for superconducting magnet. The HTS wires have more current carrying capability within high external magnetic field and its stability against external disturbance is much higher than the low temperature superconducting (LTS) wires. But the HTS wire has slower normal zone propagation (NZP) velocity which makes HTS magnets hard to be protected from unexpected hot spot. This paper presents experimental test and numerical analysis about the relation between transport current and rate of temperature rise in a hot spot. A sample which contained a HTS wire, a heater, and temperature sensor was fabricated and an experimental test on measuring normal zone propagation and temperature of the HTS wire was conducted. A numerical model was also built to estimate transient temperature rise of a winding pack model which was representing practical winding of HTS magnets. The numerical model and its numerical estimation results are expected to be a guideline about designing proper protection technique and operating current for HTS magnets. [ABSTRACT FROM AUTHOR]

Underground high temperature Superconductor (HTS) power cables have attracted extensive interest in recent years due to their potential for high power density. With funding support from the United States Department of Energy (DOE), the world's first transmission voltage level HTS power cable has been designed, fabricated and permanently installed in Long Island Power Authority (LIPA) grid. The HTS cable was successfully commissioned on April 22, 2008. In 2007, a new DOE Superconductor Power Equipment (SPE) program to address the outstanding issues for integrating HTS cables into the utility grid was awarded to the current project team (LIPA II). The goal of the LIPA II is to develop and install a replacement phase conductor manufactured using AMSC's second generation wire. In addition to the replacement of the phase conductor, the team will also address the outstanding components development necessary for full scale integration into a power grid including integral management of thermal shrinkage of the cable conductor, optimization of the cryostat design to mitigate the implications of potential cable damage, and the development and demonstration of a field splice in the operating utility grid and modular higher efficiency refrigeration system. This paper will report on the progress and status of LIPA II program. In addition, in-grid operation experience of existing 1G HTS Power cable is presented. [ABSTRACT FROM AUTHOR]

The behavior HTS materials and devices at overload currents is determined in a very high level by cooling, particularly, by the transient heat transfer from HTS device to liquid nitrogen. Recently we observed sharp peaks in the voltage during rectangular current pulse. In the present paper we explain these peaks by analysis of transient regimes in liquid nitrogen. The sharp peak in the voltage is occurring after temperature exceeds certain level before nucleate boiling starts. Basing on measurements of the voltage and temperature of HTS tapes during current overload and numerical analysis of the process we estimated overheat temperatures of nitrogen in transient regimes. Influence of covers of HTS tapes on overheat temperature of nitrogen is discussed. Experimental data and theoretical calculations' are compared. [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 multi-laminated HTS tape conductor has been recently developed to fabricate large double pancake coils. If the HTS tapes are simply laminated to form the conductor, the current distribution in the laminated tape conductor of the coil is unbalanced because of different inductances of all tapes. It is very important to analyze current distributions in the multi-laminated tape conductor used for the double pancake coil for SMES. In this paper, we analyze the current distribution in the tape conductor by using electrical circuit model, and then discuss how to obtain the homogeneous current distribution. One way is to transpose the tape position at both ends of pancake coil so as to arrange the tapes symmetrically. However, this method is not perfectly geometrical symmetry for more than 3 laminated tapes in the conductor. We propose new method to obtain homogeneous current distribution by adjusting gaps between HTS tapes in the conductor. Finally we numerically demonstrate the homogeneous current distribution in the 4-laminated tapes with inserting additional thickness among tapes. [ABSTRACT FROM AUTHOR]

This paper presents the goal and status of the high field High Temperature Superconductor (HTS) solenoid program funded through a series of SBIRs. The target of this R&D program is to build HTS coils that are capable of producing fields greater than 20 T when tested alone and approaching 40 T when tested in a background field magnet. The solenoid will be made with second generation (2G) high engineering current density HTS tape. To date, 17 HTS pancake coils have been built and tested in the temperature range from 20 K to 80 K. Quench protection, high stresses and minimization of degradation of conductor are some of the major challenges associated with this program. [ABSTRACT FROM AUTHOR]

Superconducting fault current limiting transformers (SFCLT) in electrical power systems offer the possibility to have both high short-circuit power during normal operation and limited short-circuit currents under fault conditions. During the current limitation, the temperature of the superconductor increases because of the resistive losses until the short-circuit is switched off. After the current limitation, the superconductor has to cool down to become superconducting again. Recovery under load is a very important requirement for superconducting current limiting transformers because in many applications it is not allowed to interrupt the power supply. In this case the superconductor has to cool down under regular load conditions. This paper presents the test results of a 60 kVA current limiting transformer demonstrator with full recovery under load. The design and the test results of the demonstrator are shown in detail and the test results confirm that full recovery under load can be achieved. [ABSTRACT FROM AUTHOR]

KEPCO decided to apply the HTS FCL and cable in real substation in 2009. This is the first commercial demonstration case and starting point of the HTS equipment in South Korea, even though this is not a general perfect commercialization. For a successful application on this commercialization preliminary, it is quite important to design the HTS-FCL specification with regard to the current status of the application site (for example, the existence of NGR (Neutral Grounding Reactor), 3-winding low% impedance and so on). This paper evaluates the necessary and sufficient design specifications of the 22.9 kV HTS-FCL to fulfill the real power system conditions. It investigates the detailed design criteria, short circuit capacity, FCL impedance, protection scheme, fault limiting type and other design parameters to learn the real status of ICHEON substation which will be using the HTS- FCL. [ABSTRACT FROM AUTHOR]

This paper presents a design concept of a planar-type superconducting undulator (SCU) using YBCO high-temperature superconductor (HTS) tapes. The SCU has a period length of 15 mm, and the tape conductor has dimensions of 4-mm width and 0.1-mm thickness. It has been shown that the conductor transition from one coil groove to the one in the next period is possible by making a semi-circular concave loop of the tape for continuous winding in the same direction. Non-uniform current distribution in the tape may cause field quality degradation. Assuming a uniform current density in the tape, the engineering critical-current density of the HTS in the coil for the design and the corresponding achievable on-axis peak field at 4.2 K were calculated. [ABSTRACT FROM AUTHOR]

The electrical resistivity of coated conductors is strongly related to the inter-dependent set of parameters (J, H, T), respectively current density, magnetic field and temperature. On the one hand, it is difficult to isolate the contribution of each of these parameters on the resistivity measured experimentally. On the other hand, numerical methods, which may allow this separation, require a good knowledge of the fundamental laws governing the superconducting transition which are, up to now, derived from curve fitting with experimental data. In this paper, we investigate the influence of phenomenological formulas on the outputs of a recently developed finite element model. The outputs are compared against experimental voltage curves, which have been obtained under pulsed transport currents between 80 and 160 A and external magnetic fluxes of 0 to 350 mT. The comparisons indicate that the numerical models may reproduce well the measurements, using the right set of phenomenological laws parameters. Nevertheless, the solution may still be inaccurate at low field values and high current amplitudes, where the curvature of the simulated E–J curves is more pronounced, indicating that further refinement is required in order to obtain models valid over a wider range of parameters. [ABSTRACT FROM AUTHOR]

A method for estimating the current distribution on the HTS strands which is composed of the HTS power cable was developed. A group of hall sensors which are well-arranged around the HTS cable were used in measuring the circumferential magnetic field. The current distribution can be calculated by solving a matrix equation which contains the measured magnetic field values as its elements. The contribution of the magnetic field generated by each strand in each hall sensor should be known to solve the matrix equation. The contribution can be calculated by FEM analysis simulating the HTS cable or can be measured using a duplicated short HTS cable of which current terminals are modified to apply the current to each strand independently. A simple computer simulation was performed to investigate the feasibility of the method and the performance characteristics of the method was examined for the HTS cable which is composed of several HTS strands. In this paper, a simple mathematics for estimating the current distribution and the results of experiment using the designed and manufactured measuring apparatus will be introduced. [ABSTRACT FROM AUTHOR]

The current decay of High temperature superconducting (HTS) magnet is larger than that of low temperature superconducting (LTS) magnet due to its lower n-value and higher joint resistance. To compensate the current decay in HTS magnet, various power supplies have been required. From this reason, as an option of power supply for HTS magnet, we have proposed a flux pump with heater trigger switch. In this paper, a performance and experimental analysis on a transformer type flux pump were presented. Characteristics of pumping rates with respect to change in the temperature and sequential timing of the heater-triggered switch were investigated. As well as, the pumping rates were carried out in the charging mode. Furthermore, the compensating actions were carried out in the persistent current mode using a feedback control unit. [ABSTRACT FROM AUTHOR]

This paper presents a new numerical method based on finite elements finite volumes (FE-FV) for solving 2-D diffusion problems in high temperature superconductors (HTS). The approach does not involve directly the resistivity term (p), generally used to model the E(J) characteristic as a power law, i.e E(J) = p(J)J, with p(J) α Jn-1 Instead, we use a J(E) constitutive law J α E(1/n) with →E= E→e z (a single component), which leads to a scalar non-linear differential equation. After presenting in details the developments, the method is tested in the case of a superconducting cylinder submitted to a transverse magnetic field. The current density obtained is compared to another numerical technique (the semi-analytical method) in order to validate the results. Although not fully optimized yet, it appears that the proposed method is very stable, especially for large n-values (greater than 100). [ABSTRACT FROM AUTHOR]

This paper presents experimental and simulation results of a screening current induced magnetic field (SCF) in a high temperature superconductor (HTS) insert that constitutes a low-/high-temperature superconductor (LTS/HTS) NMR magnet. In this experiment, the HTS insert, a stack of 50 double-pancake coils, each wound with Bi2223 tape, was operated at 77 K. A screening current was induced in the HTS insert by three magnetic field sources: 1) a self field from the HTS insert; 2) an external field from a 5-T background magnet; and 3) combinations of 1) and 2). For each field excitation, which induced an SCF, its axial field distribution and temporal variations were measured and compared with simulation results based on the critical state model. Agreement on field profile between experiment and simulation is satisfactory but more work is needed to make the simulation useful for designing shim coils that will cancel the SCF. [ABSTRACT FROM AUTHOR]

It is well known that HTS (high temperature superconductor) is promising for magnet applications, but it has been almost impossible so far to apply them to magnets in persistent current mode because of poor qualities of their superconducting joints at higher current as well as their lower index values. To get rid of the non-superconducting joints from an HTS superconducting magnet, a wind-and-flip technique for demonstrating a persistent current mode operation of HTS magnet using YBCO coated conductors had been suggested. This paper presents experimental results of measured drift of a persistent current in the YBCO pan. cake coil which was made by using the wind-and-flip technique. The pancake coil was wound by YBCO coated conductor with a width of 12 mm, which was slit longitudinally at the center of the conductor along the conductor by a specially designed slitter. A stainless steel heater was attached on the one end of the YBCO conductor as a persistent current switch to energize the pancake coil. A temporal stability of the magnetic field was analyzed by monitoring the long-term drift of the magnetic field at 77.3 K by hall sensors. [ABSTRACT FROM AUTHOR]

Superconducting Fault Current Limiters (SFCLs) are regarded as key components for modern power systems. The progress in the development of YBCO thin films opens new perspectives in the design of these devices. In this paper, the quenching phenomenon in YBCO thin films is investigated experimentally, in order to gain the proper technical know-how suitable for the design of resistive type SFCLs. In particular, the origin of the quenching, as well as the propagation dynamics within a YBCO tape, is investigated for different input current waveforms. The role of a parallel-connected protective resistance on the quench dynamic is also studied. [ABSTRACT FROM AUTHOR]

Currently produced and available HTS tapes with increased resistivity, like 2nd generation YBCO 344S tape made by American Superconductors, have enough parameters, e.g., resistivity, critical current density, to build inductive type current limiters to limit faults in medium-voltage power grid. The paper describes the assumption for 6,9 kV/1.15 kA superconducting fault current limiter with superconducting secondary winding made of high resistivity HTS tape as well as the results of numerical analysis. [ABSTRACT FROM AUTHOR]

We have been developing Superconducting Fault Current Limiting Transformer (SFCLT) as a superconducting transformer with current limiting function. As the Step-5 of the SFCLT project for the up-graded ratings of current and voltage, in this paper, we focused on the up-grading of current by parallel-connected YBCO coated conductors. Based on the asymmetric configuration of coated conductors, different parallel connections were tested and evaluated in terms of critical current level and current limiting characteristics under large ac current at 77 K in liquid nitrogen. [ABSTRACT FROM AUTHOR]

One of the most important issues in the design of a HTS power cable is the induced current between conducting and shield layers under fault condition. The current distribution of conducting and shield layers is changed due to the fault current. Conducting and shield layers are coupled magnetically. The analysis of current distribution in HTS power cable requires understanding of the magnetic coupling between the conducting and shield layers. In order to study the phenomenon mentioned above, a solenoid type of HTS power cable model which includes both conducting and shield layer is actually manufactured in this paper. The current distribution of conducting and shield layers is evaluated by real manufactured solenoid type of HTS power cable model. The results obtained through the experiment and analysis would provide important data for the design of HTS power cables and valid information for their installation in power system. [ABSTRACT FROM AUTHOR]

For the superconducting magnet system of the International Thermonuclear Experimental Reactor, ITER, 60 current leads for a total current of more than 2500 kA are needed. The use of High Temperature Superconductor current leads (HTS-CL) will reduce the resultant large refrigerator load considerably. Within the EU Fusion Technology Programme, the Forschungszentrum Karlsruhe and CRPP have developed and built a 70 kA HTS-CL demonstrator optimized for 50 K Helium operation. In 2004-2005, the CL was successfully tested with 50 K as well as 80 K Helium, and finally with LN2. In the meantime, ITER has decided to use HTS-CLs for the magnet system and China has taken the responsibility to provide the sc feeders for ITER including the current leads. In this paper, the performance of a 70 kA HTS-CL in fault conditions will be analysed using the FZK-CRPP demonstrator as a model. In particular, the quench performance and the safety behavior in case of a loss-of-flow accident (LOFA) will be described and an extrapolation of the leads performance in real ITER conditions will be given. Finally the effect of different shunt materials is discussed. [ABSTRACT FROM AUTHOR]

HTS pancake windings have been commonly used for the insert coil of high field magnets. All pancake windings have been connected in series and excited by a single power source. In that case, currents of the whole pancake windings were limited by the minimum current of the top and the bottom pancake windings where maximum perpendicular magnetic field was applied. This paper proposed the multiple power excitation of the HTS magnet which consists of pancake windings. It was able to increase the magnetic field of the magnet by conducting critical currents to all pancake windings. Results of calculation by using a model BSCCO magnet shows that proposed method was able to generate higher magnetic field comparing with the conventional single power excitation. [ABSTRACT FROM AUTHOR]

When the HTS magnet consisting of pancake windings is excited by a single power source, most of the pancake windings operate under their critical currents because currents of the entire pancake windings are limited by the critical current of the pancake winding which has the lowest critical current. By using multiple power sources, all pancake windings are able to conduct their critical currents. This paper describes the HTS magnet with pancake windings which are excited by multiple power sources. Critical current of each pancake winding is determined by using optimization technique. Fabrication of the BSCCO magnet consisting of 10 pancake windings is described and test results of the BSCCO magnet are given. The magnetic field and the perpendicular magnetic field of the magnet excited by multiple power sources are compared with those of the magnet excited by a single power source. [ABSTRACT FROM AUTHOR]

The superconducting magnet system of the W7-X stellarator presently under construction at the Max-Planck-Institute for Plasmaphysics in Greifswald, Germany, requires 7 pairs of current leads for a maximum current of 18.2 kA. The Forschungszentrum Karlsruhe is responsible for construction, manufacturing and performance testing of the current leads prior to installation in the W7-X machine. To reduce the overall cooling power for the refrigerator as well as the free convection problem due to the upside-down orientation of the leads, it was decided to use HTS material in the temperature range between approx. 5 K and 60 K. The optimization of the HTS part requires to know exactly the electrical, mechanical and thermal parameters of the HTS material. Actually two suppliers, EHTS and Sumitomo offer such Bi-2223/AgAu material. Single tapes as well as stacks were used to measure the critical current as a function of applied magnetic field for various temperatures. The thermal conductivity, the stress-strain dependence and the thermal contraction were also measured. In the paper the electrical, mechanical and thermal performance of different tapes and stacks will be described and discussed. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the electrodynamical properties of YBa2Cu3O7-x strip-shaped films, which were locally modified by confined heavy-ion irradiation. The irradiations were made by means of 4.2 GeV gold ions. Quantitative magneto-optical imaging as well as in-field transport characterizations show how the irradiated regions locally react to an external electromagnetic perturbation, thus allowing its localization and measurement. Aiming at future applications, the main issues about the detector sensitivity, such as the role of interfaces between irradiated and pristine regions, are addressed. [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]

According to the recent design of an HTS (High Temperature superconducting) power application whose capacity is hundreds MVA, the rated current is over thousand amps. Considering the performance of the recent HTS tapes, it is inevitable to use several HTS tapes in parallel for high capacity current. In this paper, we have investigated the influence of current distribution on the AC loss in the multi-stacked superconducting wire. The dependence of AC loss and critical current on the current distribution in multi-stacked wires was discussed. We fabricated multi-stacked wires and measured the current distribution at 77 K. The current distribution was indirectly found from the self-field distribution. The magnetic field was measured by an array of hall sensors located around the HTS superconducting wires. In the case of non-uniform distribution of current, the performance of multi-stacked HTS wires is worse than that of uniform current distribution. [ABSTRACT FROM AUTHOR]

Residual magnetic field in a high temperature superconductor (HTS) magnet is a factor which should be avoided when the field of the magnet is being operated under a high uniformity and high accurate control. In this paper, the residual field in a Bi2223/Ag pancake magnet at 77 K is systematically studied. The amplitude of the residual field as a function of maximum charging current and the relaxation of the residual field are measured. For a magnet with an inner diameter of 60 mm, an outer diameter of 80 mm and a height of 30 mm, the maximum residual field is about 14.5 G after ramping the charging current up to 15 A, followed by dropping the current to zero. A simple model is proposed, from which the residual field can be estimated as along as the configurations of the magnet and the critical current (Ic) of the original short sample are given. [ABSTRACT FROM AUTHOR]

For full cryogenic test of CERN 600 A High Temperature Superconducting (HTS) current leads prior to integration into the Large Hardron Collider (LHC), a dedicated facility has been designed, constructed and operated at the University of Southampton. The facility consists of purpose-built test cryostats, 20 K helium gas supply, helium gas flow and temperature control systems and quench protection system. Over 400 such leads have already been successfully tested and qualified for installation at CERN. This paper describes various design and operation aspects of the test facility and presents the detailed cryogenic test results of the CERN 600 A current leads, including steady state 20 K flow rates. [ABSTRACT FROM AUTHOR]

High-temperature superconductor (HTS) technology has been used to develop an advanced high Q resonant power electronic circuit and its special device. With HTS techniques, a very high Q circuit can be achieved; consequently special aspects such as high voltage generation and current control can be practically realized. Theoretical study has been carried out with regard to this HTS high Q resonant method, as well as a prototype device has been made for experimental verification of the voltage generation and current control, as details described in this paper. [ABSTRACT FROM AUTHOR]

As high temperature superconducting (HTS) power cables have some merits over conventional cables, several demonstration projects on the HTS cable system are presently under way around the world. Korea Electric Power Corporation (KEPCO) also initiated an HTS cable project in 2002 with the Korean government's support. A three phase 100 m HTS cable system with a capacity of 50 MVA has been installed at Gochang test yard, located in Chonnbuk province, Korea. The HTS cable system is composed of a 100 m-long cable, two terminations and a cooling system. The rated current is 1,250 Arms and the rated voltage is 22.9 kV considering compatibility with the conventional power distribution system in Korea. Main purposes of this project are to verify the performance of an HTS cable system and to evaluate the potential of the HTS cable system from the viewpoint of power utilities. The real grid application of the HTS cable system requires the demonstration of system reliability, accumulated operation experiences, and it has to meet the practical needs of the utilities. In such a meaning, this project provides various challenges for KEPCO, and the feedback will be delivered to cable manufacturers. This user initiative test will facilitate the introduction of HTS cable systems into a real grid network. The installation process of the HTS cable system and some results of the preliminary test were presented in this paper. [ABSTRACT FROM AUTHOR]

An 8 MVAR, 13.8 kV Superconducting Dynamic Synchronous Condenser (SDSC) prototype was tested on the Tennessee Valley Authority (TVA) grid for about a year. It shared a bus with an arc furnace. The SDSC was subjected to transient currents and harmonics created by the arc furnace, which consisted of up to 50 % negative sequence and 20% zero sequence components. The SDSC operated successfully in the presence of such high transient/harmonic currents. It provided cycle by cycle correction of voltage during operation. The benefits of voltage correction were observed both at the local bus and at the generator bus of a power generation station several miles away. Currently two commercial units rated 12 MVAR, 13.8 kV, are on order by TVA and are scheduled for delivery in December 2006 and March 2007. These units will be skid-mounted for easy installation on site. This paper discusses test results of the prototype unit operation on the grid and describes its potential applications for voltage support in wind farms. [ABSTRACT FROM AUTHOR]

In this paper, we report the results from evaluation on the use of 2nd generation high-temperature superconducting wires, or 2G HTS conductors, as elements for superconducting fault current limiter (SFCL). The unique features of 2G HTS conductors such as high N-values, superior electromechanical performance, large surface area available for cooling, and their availability in long-lengths that could be produced by high-throughput and low-cost manufacturing, may provide advantages for SFCL applications. We tested SuperPower's standard ion-beam-assisted-deposition based 2G HTS conductors under various conditions. First, individual conductors 10–20 cm long with dc critical current (Ic) ranging from 180 amps to 277 amps were tested at prospective fault current up to 3 kA (peak). 2G HTS conductors demonstrated good fault current limiting performance, including first peak limitation. Quench current was in the range of 1.8 to 3 times Ic, and the response time was within 1 ms. Secondly, 3–5 conductors in parallel connections demonstrated uniform current sharing and fast recovery under no-load condition. Finally, an assembly consisted of 12 elements in series connection was tested at high-power condition at KEMA PowerTest. Each element had four 40 cm long conductors with Ic ∼120 A in parallel connection. With 1080 V supply voltage and 90 kA prospective fault peak current, the fault current was limited to 32 kA at the 1st peak with 3.2 kA in the HTS elements. The response time was less than 1 ms. All these testing results indicate that our 2G HTS conductors are promising for practical SFCL applications. [ABSTRACT FROM AUTHOR]

This paper describes numerical analysis of current limiting characteristics of YBCO thin film with inhomogeneous superconducting properties. The analysis tool uses a finite element method (FEM) based on current vector potentials. First, the validity of the analysis tool was verified by comparing with experimental results using small samples. Then we analyzed large-size meander-shaped thin films and discussed the influence of inhomogeneous superconducting properties of YBCO thin film on current limiting characteristics. [ABSTRACT FROM AUTHOR]

During the operation of a HTS power cable in a real grid, large fault current can be introduced to the HTS power cable by several accidents. Large heat is generated until the circuit breaker operates and severe performance degradation or even burn-out can occur within the HTS power cable. Especially, the temperature rise of the HTS power cable should be limited to suppress the bubble generation, which induces partial discharge and it reduces the life time of the HTS power cable. Stabilizer is applied to the cable core to limit the temperature rise when the fault current is introduced. This paper describes the fault current experiment with a sample cable and the results are used to verify the simplified analysis model. Through the analysis results, the amount of the stability is determined for the successful operation of Korean HTS power cable. [ABSTRACT FROM AUTHOR]

AC loss is one of the major topics in large AC power applications using high temperature superconductor such as power transformers, transmission cables and fault current limiters because it is closely related to operation efficiency. Multi-stacked tape conductors should be used to transport the large current in those power applications. A research of various arrangements of HTS tapes for multi-stacked tapes has been performed to increase the capacity of transport current in HTS power applications. In this paper, we studied magnetization loss and shield effect from several different arrangements of BSCCO tapes such as Face-to-Face type, regular matrix type (m × 2) and irregular matrix type. The results show that the magnetization loss of the Face-to-Face arrangement was lower than those of the other matrix types for the same stacking numbers. We think that the result was due to the shield effect by demagnetization of adjacent HTS tapes which were located as face to face. [ABSTRACT FROM AUTHOR]