Showing papers in "IEEE Transactions on Applied Superconductivity in 2009"
TL;DR: In this paper, the main issues involved in using superconductors for aeropropulsion are discussed. And the feasibility of superconducting electric propulsion is investigated for turbo-electric aircraft of the future.
Abstract: Sustainability in the aviation industry calls for aircraft that are significantly quieter and more fuel efficient than today's fleet. Achieving this will require revolutionary new concepts, in particular, electric propulsion. Superconducting machines offer the only viable path to achieve the power densities needed in airborne applications. This paper outlines the main issues involved in using superconductors for aeropropulsion. We review our investigation of the feasibility of superconducting electric propulsion, which integrate for the first time, the multiple disciplines and areas of expertise needed to design electric aircraft. It is shown that superconductivity is clearly the enabling technology for the more efficient turbo-electric aircraft of the future.
283 citations
TL;DR: In this article, a 2G HTS wire with an in-plane texture of 6 to 7 degrees with a uniformity of about 2% was reproducibly achieved in the kilometer-long fully buffered tapes.
Abstract: Tremendous progress has been accomplished in 2008 in key metrics of YBa2Cu3Ox (YBCO) second-generation (2G) HTS wires at SuperPower. Using improved precursor chemistry in our metal organic chemical vapor deposition (MOCVD) process, critical currents (Ic) as high as 813 A/cm were reached over meter-long lengths, representing the highest reported Ic in meter long 2G HTS. By use of Zr doping of (Gd,Y)Ba2Cu3Ox, strong enhancements were achieved in in-field performance over a wide angular range. A Ic of 229 A/cm was achieved at 77 K and 1 T perpendicular to the wire which is about a factor of 2.5 times better than that of standard MOCVD-derived films. At 65 K and 3 T, a Ic of 340 A/cm was demonstrated perpendicular to the wire. Kilometer lengths of 2G HTS have been demonstrated for the first time. Over 35 tapes 1,000 to 1,500 m in length with a complete 5-layer buffer stack have been routinely produced in our pilot-scale manufacturing facilities. An excellent in-plane texture of 6 to 7 degrees with a uniformity of about 2% was reproducibly achieved in the kilometer-long fully-buffered tapes. Using these high-quality buffers, the longest 2G wire length to date of 1,311 m was produced with a minimum Ic of 153 A/cm corresponding to a Ic times length value of 200,580 m. Also, an 1,030 m long complete 2G HTS wire has been demonstrated with a minimum Ic of 227 A/cm corresponding to a record Ic times length value of 233,810 A-m. Further, a 630 m long segment of the wire sustained a minimum Ic of 302 A/cm, the longest 2G wire reported to date with a Ic over 300 A/cm. Also, a Ic of 337 A/cm was achieved over a 540 m long segment. All these values represent a 2 to 3 fold improvement in length and Ic of 2G wires compared to our achievements in 2007. In 2008, a 30 m long 2G cable made with nearly 10,000 m of 2G wire previously delivered by SuperPower was successfully installed and energized in the grid of National Grid in downtown Albany, marking the world's first of 2G HTS device in the power grid.
184 citations
TL;DR: In this article, the ability of 2G HTS wire to operate under high stress levels has been demonstrated in both direct sample measurement and test coils, and the high winding current density that is available with SuperPower's thin 2GHTS wire was utilized in a high field insert coil demonstration generating central fields in excess of 26.8 T.
Abstract: Recent developments in 2G HTS coil technology are presented highlighting the ability of 2G HTS wire to function under difficult operating conditions without degradation. The challenges of use in various coil constructions and applications are discussed. Several applications where the conductor is subjected to high stress levels include high field insert coils and rotating machinery. While these applications present different challenges, the ability of the conductor to operate under high stress levels has been demonstrated in both direct sample measurement and test coils. The high winding current density that is available with SuperPower's thin 2G HTS wire was utilized in a high field insert coil demonstration generating central fields in excess of 26.8 T . The ability of the wire to be tailored (stabilization, insulation, ac losses) to fit various operating parameters will also be discussed.
173 citations
CERN1
TL;DR: This paper compares the most common parameterizations for the critical surface of A15 superconductors using consistent notation, and takes the various parameterizations as a basis for a generic scaling proposed for the characterization and production follow-up of the ITER strands.
Abstract: A number of models for the critical surface of Nb3Sn, and in general A15 superconductors, have been developed in the past years. This paper compares the most common parameterizations using consistent notation. Although the parameterizations appear dissimilar at first sight, they are in reality all based on a fit of the normalized pinning force vs. the reduced field, and have similar scalings for the critical field and critical temperature based on a Unified Scaling Law. In this paper we take the various parameterizations as a basis for a generic scaling proposed for the characterization and production follow-up of the ITER Nb3Sn strands. The accuracy of the scaling is estimated using the fitting residuals on various sets of IC(B,T,epsiv) data available in literature. We discuss the results, and give our view of the work towards a unified, practical parameterization.
139 citations
TL;DR: In this paper, the coordination between the SMES system for 100 MVA/2 GJ class load fluctuation compensating was conducted using IBAD/CVD-YBCO wire.
Abstract: YBCO superconducting wire has a relatively low decrease in power distribution at high temperatures and under a high magnetic field. A high-intensity substrate is used for the wire, so the wire has high machine characteristics. Therefore, it is expected that this wire can be used for large-scale high magnetic field coils. Here, coordination between the SMES system for 100 MVA/2 GJ class load fluctuation compensating was conducted using IBAD/CVD-YBCO wire. The SMES system includes a toroidal type YBCO coil consisting of 180 compact, high magnetic field multi-unit coils, a large coil cooling system that uses the conduction cooling method, which does not use a refrigerant medium, and a multi-cell power converter that achieves multi-unit coil connection with relatively low current and low voltage. Studies were conducted for each individual device and for the whole system. Based on the study plan in this paper, it has become possible to develop and coordinate each device of the 100 MVA/2 GJ class power system load fluctuation compensation SMES system using YBCO wire, which up until now had seem impossible as an actual system.
105 citations
Abstract: We designed superconducting nanowire single-photon detectors (SNSPDs) integrated with silver optical antennae for free-space coupling and a dielectric waveguide for fiber coupling. According to our finite-element simulation, (1) for the free-space coupling, the absorptance of the NbN nanowire for TM-polarized photons at the wavelength of 1550 nm can be as high as 96% by adding silver optical antennae; (2) for the fiber coupling, the absorptance of the NbN nanowire for TE-like-polarized photons can reach 76% including coupling efficiency at the wavelength of 1550 nm by adding a silicon nitride waveguide and an inverse-taper coupler.
105 citations
TL;DR: In this article, the first fully operational 1 V and 10 V programmable Josephson voltage standards with SINIS junctions that are suitable for a 70 GHz drive have been fabricated and tested.
Abstract: Programmable Josephson voltage standards (PJVSs) in combination with fast switchable DC current sources have opened up new applications in the field of low-frequency AC metrology. The growing interest in output voltages of up to plusmn10 V initiated efforts by several National Metrological Institutes to realize 10 V PJVSs. Presently, only 10 V PJVSs from PTB based on SINIS junctions have been successfully incorporated into existing setups for AC metrology. However, the fabrication of 10 V SINIS arrays that are driven at 70 GHz suffers from very low yield. The recent technological progress made at NIST enabled the drop-in replacement of the low-yield SINIS arrays by more robust SNS arrays. The N-material is an amorphous NbxSi1-x alloy near the metal-insulator transition and is deposited by co-sputtering. For the first time, fully operational 1 V and 10 V PJVSs with SNS junctions that are suitable for a 70 GHz drive have been fabricated and tested. This work was done in close cooperation between NIST and PTB.
104 citations
TL;DR: In this paper, the materials origins of dissipation and dephasing in superconducting qubits are discussed, which will guide the search for improved, low-noise materials and fuel continued progress in the field of quantum computing.
Abstract: Superconducting integrated circuits incorporating Josephson junctions are an attractive candidate for scalable quantum information processing in the solid state. The strong nonlinearity of the Josephson effect enables one to tailor an anharmonic potential and thus to realize an artificial quantum two-level system (ldquoqubitrdquo) from a macroscopic superconducting circuit. Josephson qubits can be made to interact strongly and controllably, and it should be straightforward to fabricate circuits incorporating hundreds or even thousands of Josephson qubits using standard thin-film processing techniques. Work over the last several years has shown that qubit performance is limited by spurious coupling of the qubit to microscopic defect states in the materials that are used to implement the circuit. Here we discuss the materials origins of dissipation and dephasing in superconducting qubits. A deeper understanding of the underlying materials physics that governs decoherence in superconducting quantum circuits will guide the search for improved, low-noise materials and fuel continued progress in the field of superconducting quantum computing.
91 citations
TL;DR: In this article, a hybrid superconducting fault current limiter (SFCL) is proposed for substation upgrade in the Korea Electric Power Corporation (KEPCO) grid and points at issue on the utility demands.
Abstract: This report presents efforts for introducing a hybrid superconducting fault current limiter (SFCL) associated with the substation upgrade in the Korea Electric Power Corporation (KEPCO) grid and points at issue on the utility demands. The substation upgrade includes replacement of 154 kV/22.9 kV main transformers and applying 22.9 kV/3 kA SFCLs to protect them. The SFCL is expected to meet not only the general requirements, but also such local conditions as (1) small size to be installed in an in-house substation, (2) sustainable current limitation without the power line breaking by circuit breakers (CB) for maximum 2 seconds. Optionally, recommended are (3) the reclosing capability and semi-active function. Different types of currently developed SFCLs have been examined associated with the conditions. We have proposed a hybrid SFCL of first peak non-limiting type, which potentially fulfills all the local conditions. As an intermediate step, a 22.9 kV/630 A hybrid SFCL was built. This SFCL meets the field requirements of the size limit, 1.5 seconds sustainability of current limitation, 0.3 s reclosing capability and semi-active function. The upgraded hybrid SFCL will be installed in the KEPCO's test line for operation tests. There are two major test targets; long term operation test of the SFCL and protection coordination test using artificial faults.
89 citations
TL;DR: The development of the generator is described and some key test results used to validate the design are presented, which indicate that the generator has a significant margin over the test points and that its performance is consistent with program specifications.
Abstract: General Electric, under contract with the Air Force Research Labs (AFRL), has successfully developed and tested a high speed, multimegawatt superconducting generator. The generator was built to demonstrate high temperature superconducting (HTS) generator technology for application in a high power density Multimegawatt Electric Power System (MEPS) for the Air Force. The demonstration tested the generator under load conditions up to 1.3 MW at over 10,000 rpm. The new MEPS generator achieved 97% efficiency including cryocooler losses. All test results indicate that the generator has a significant margin over the test points and that its performance is consistent with program specifications. This demonstration is the first successful full-load test of a superconducting generator for the Air Force. In this paper we describe the development of the generator and present some key test results used to validate the design. Extrapolation to a higher power density generator is also discussed.
85 citations
TL;DR: In this paper, the authors reported electrical measurements on samples of HTS Roebel cable and reported insulation which protects the assembled conductors from environmental degradation, and discussed manufacturing issues such as the long length registration of the strand crossovers and the maximum yield from wide strip.
Abstract: We have manufactured lengths of up to 10 m of Roebel cable from wide strips of second generation YBCO wire. The wide strips are first screened using magnetic scanning to check for superconductor defects to avoid incorporating poor quality wire into the cable. Manufacturing issues such as the long length registration of the strand crossovers and the maximum yield from wide strip is discussed. Differences in cutting and winding due to different tape substrate materials are shown to be minimal. We report electrical measurements on samples of HTS Roebel cable. Insulation which protects the assembled conductors from environmental degradation is reported.
TL;DR: The first long length, transmission level voltage, cold dielectric, high temperature superconductor power cable has been successfully installed in the Long Island Power Authority (LIPA) grid.
Abstract: The first long length, transmission level voltage, cold dielectric, high temperature superconductor power cable has been successfully installed in the Long Island Power Authority (LIPA) grid. The cable is capable of carrying 574 MVA at a voltage of 138 KV. Three 600 m long phase conductors were manufactured and shipped to the LIPA site. The installation process included pulling three cables through three separate 600 m long underground conduits and assembly of three terminations at each end. The project has been funded by the US Department of Energy and is led by American Superconductor. The project team is comprised of Nexans, Air Liquide and LIPA. This paper describes the cable system, installation process and an overview of various testing results before and after installation. In addition, details of an initial successful cool-down process are presented. It also includes the performance results in grid operation.
TL;DR: In this article, the authors describe the latest status of the Albany, NY HTS cable project, which was installed between two substations in National Grid's electric utility system and operated successfully in unattended condition through May 1, 2007.
Abstract: High-temperature superconducting (HTS) cable systems are expected to be a solution for improvement of the power grid and three demonstration projects in the real grid are underway in the United States. One of these is the Albany, NY HTS Cable Project, involving the installation and operation of a 350 meter HTS cable system with a capacity of 34.5 kV, 800 A, installed between two substations in National Grid's electric utility system. A 320 meter and a 30 meter cable are installed in an underground conduit and connected together by a joint, or splice in a vault. In Phase I of this project, the cables were fabricated with DI-BSCCO wire in a 3-core-in-one cryostat structure. After the installation of the HTS cable system, the in-grid operation began on July 20, 2006 and operated successfully in unattended condition through May 1, 2007. In Phase II, the 30 meter section was replaced by a 2G (YBCO) cable. The 2G cable was fabricated with SuperPower's YBCO coated conductors in a 3-core-in-one cryostat. After replacement of the 30 meter section, the joint and one termination were reassembled and the commissioning tests that included initial cooling, critical current measurement and DC withstand voltage test were completed successfully. After the commissioning tests, the HTS cable system with a 30 meter YBCO cable and a 320 meter DI-BSCCO cable was re-energized on January 8, 2008 and started again to operate in a live utility network. This paper describes the latest status of the Albany HTS cable project.
TL;DR: The method of linear programming, especially combining with genetic algorithm, reduces optimizing variables, which makes the design of a magnet feasible, and a full open MRI superconducting magnet is designed with maximum radii.
Abstract: An optimization design method of short-length actively shielded and open structure superconducting MRI magnets is suggested in the paper. Firstly, the section of the solenoid coil is simplified as a current loop with zero section to solve a linear programming problem. The position coordinates in the radius and axial, and current for the loop can be calculated by the linear programming method. Then, the cross-section of the coil is optimized with a genetic algorithm to get appropriate section size. The method of linear programming, especially combining with genetic algorithm, reduces optimizing variables, which makes the design of a magnet feasible. Based on the method, a full open MRI superconducting magnet is designed with maximum radii of 0.8 m and 1.2 m. In the paper, the detailed optimization technologies are presented.
TL;DR: The US Department of Homeland Security is currently funding the design, development and demonstration of an inherently fault current limiting HTS cable, called Secure Super Grids, under the Hydra project with Con Edison as discussed by the authors.
Abstract: The US Department of Homeland Security is currently funding the design, development and demonstration of an inherently fault current limiting HTS cable, called Secure Super Grids, under the Hydra project with Con Edison. The cable is 300 m long and is being designed to carry 96 MVA at a distribution level voltage of 13.8 kV. The cable will be built using cable system experience gained by AMSC and Ultera (a Southwire and nkt Cables joint venture) on previous projects. The underground cable will be permanently installed and energized in New York City in 2010. The project is led by American Superconductor who is teamed with Ultera and Con Edison. This paper describes the general goals and design criteria of the project. An overview of the concept of Secure Super Grids and advantages of this type of cable are presented in a grid-based network modeling. In addition, the design issues such as tailoring of the HTS wire to provide adequate thermal stability and electrical properties both under normal operation and during a fault are presented.
TL;DR: In this paper, a saturated iron-core type 35 kV/90 MVA superconductive fault current limiter was developed and installed in a transmission network at Puji substation of China Southern Power Grid for live-grid operation.
Abstract: We developed a saturated iron-core type 35 kV/90 MVA superconductive fault current limiter and installed the device in a transmission network at Puji substation of China Southern Power Grid for live-grid operation. Innovative design in the iron-core configuration ensures that the device has low impedance in normal power transmission and sufficiently high impedance for a fault current limiting action. A magnetization control circuit allows the iron-core to be saturated or de-saturated depending upon the functional requirements. An energy release and voltage-surge protection unit can promptly discharge the magnetic energy accumulated in the iron-core and suppress the induced and surge voltages of the dc circuit in a current limiting event. This device has been designed to reduce the magnitude of a fault current by about 50%, which will prevent the breaking capacity of the existing circuit breakers in the transmission network from being exceeded in the predictable future. This article presents structural and functional specifications and reports up-to-date live-grid operation data of the device.
TL;DR: In this paper, a 10 kW superconducting slow rotating generator was designed for demonstration in a small scale wind turbine, where the drive train only consisted of the turbine blades connected directly to the generator.
Abstract: We have performed a design study of a 10 kW superconducting slow rotating generator suitable for demonstration in a small scale wind turbine, where the drive train only consists of the turbine blades connected directly to the generator. The flux density in the superconducting rotor is chosen as B = 1 Tesla to be similar to the performance of permanent magnets and to represent a layout, which can be scaled up in future off-shore wind turbines. The proposed generator is a 8 pole synchronous machine based on race-track coils of high temperature superconducting tapes and an air cored copper stator enclosed in an iron shield.
TL;DR: 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 super Conductor (LTS/HTS), NMR magnet are presented.
Abstract: 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.
TL;DR: In this article, the performance of superconducting nanowire photon detectors fabricated from ultra-thin Nb is investigated, and it is shown that Nb detectors are significantly more susceptible than NbN to thermal instability (latching) at high bias.
Abstract: We investigate the performance of superconducting nanowire photon detectors fabricated from ultra-thin Nb. A direct comparison is made between these detectors and similar nanowire detectors fabricated from NbN. We find that Nb detectors are significantly more susceptible than NbN to thermal instability (latching) at high bias. We show that the devices can be stabilized by reducing the input resistance of the readout. Nb detectors optimized in this way are shown to have approximately 2/3 the reset time of similar large-active-area NbN detectors of the same geometry, with approximately 6% detection efficiency for single photons at 470 nm.
TL;DR: The optimal location determined by the proposed method is coordinated with the corresponding optimal resistive value of the SFCL to improve low-frequency oscillation damping performance of the system.
Abstract: This paper describes a study on the optimal location of a resistive superconducting fault current limiter (SFCL) applied to an electric power grid. The resistive SFCL, which is designed to provide the quick system protection in the event of a fault, can have different effects on the planning and operation of a power system depending on its location. To select the optimal location of the SFCL, the sensitivity analysis of power changes and/or power losses in the system with respect to its resistive value occurred in series with a transmission line during a fault is introduced. Moreover, the optimal location determined by the proposed method is coordinated with the corresponding optimal resistive value of the SFCL to improve low-frequency oscillation damping performance of the system. The IEEE benchmarked four-machine, two-area test system is used to evaluate the effectiveness of the proposed method with the case studies based on time-domain simulation.
TL;DR: In this article, a large bore Nb3Sn quadrupole with 15 T peak coil field is developed within the framework of the US LHC Accelerator Research Program (LARP).
Abstract: In support of the Large Hadron Collider luminosity upgrade, a large bore (120 mm) Nb3Sn quadrupole with 15 T peak coil field is being developed within the framework of the US LHC Accelerator Research Program (LARP). The 2-layer design with a 15 mm wide cable is aimed at pre-stress control, alignment and field quality while exploring the magnet performance limits in terms of gradient, forces and stresses. In addition, HQ will determine the magnetic, mechanical, and thermal margins of Nb3Sn technology with respect to the requirements of the luminosity upgrade at the LHC.
TL;DR: A new HTS cable project supported by Ministry of Economy, Trade and Industry (METI) and New Energy and Industrial Technology Development Organization (NEDO) has just started in Japan as discussed by the authors.
Abstract: A new HTS cable project supported by Ministry of Economy, Trade and Industry (METI) and New Energy and Industrial Technology Development Organization (NEDO) has just started in Japan. Target of this project is to operate a 66 kV, 200 MVA HTS cable in a real grid in order to demonstrate its reliability and stable operation. Tokyo Electric Power Company (TEPCO) provides the real grid and studies the impact of connecting the HTS cable to the existing conventional facilities in Yokohama. Sumitomo Electric Industries, Ltd. (SEI) designs and manufactures the HTS cable, terminations and joint. Mayekawa Mfg. Co. Ltd. provides a cooling system. Total project period is planned to be 5 years. In 2007, components of HTS cable system were studied and designed. In 2008 and early 2009, the pre-system with a 30-meter cable will be installed in the factory to demonstrate basic performance of the HTS cable and its accessories. Then the 200 MVA HTS cable will be manufactured in 2009 and installed and operated at the site in 2010 and 2011. One of the technical targets in this project is to reduce the AC loss of HTS cable. For this purpose, a new type DI-BSCCO wire with twisted superconducting filaments is planned to be applied in the cable. A 1-meter cable core manufactured with the new wires shows its AC loss as less than 1 W/m/ph at 2 kArms, which is 1/4 of AC loss with normal DI-BSCCO.
TL;DR: In this paper, a high rate reactive magnetron sputtering at transition mode was developed to deposit Al2O3 and Y 2O3 layers at a routine production speed of 750 m/h (all speeds in this paper are the equivalent speed of 4 mm wide tape.) with excellent process stability over kilometer length and from run to run, and with same texture and critical current as the ion beam sputtering process.
Abstract: High rate reactive magnetron sputtering at transition mode were developed to deposit Al2O3 and Y2O3 layers at a routine production speed of 750 m/h (all speeds in this paper are the equivalent speed of 4 mm wide tape.) with excellent process stability over kilometer length and from run to run, and with same texture and critical current as our previous ion beam sputtering process. For the IBAD MgO process, a reactive ion beam sputtering process with higher deposition rate and long time stability has been developed and routine production speed has been increased to 360 m/h. The tape driving system has been upgraded from 6 wraps to 11 wraps in our Pilot Buffer system. Homo-epitaxial MgO process has been re-tuned with the routine production speed increased to 340 m/h. The LaMnO3 routine process speed has been increased to 450 m/h by reactive sputtering of a La-Mn alloy target. Throughput was further improved by reducing total buffer process from 5 steps to 3 steps. The routine processing length of single pieces of buffer tape was increased to 1,400 m. The actual production capacity is 500 km/year now. We developed a new Direct LMO process with same Ic as our standard IBAD buffer stack and dramatically increased the yield which makes it a very promising manufacturing process.
TL;DR: In this paper, the authors compared the load side frequencies under the 1 MJ and 2.5 MJ superconducting magnetic energy storage connection, respectively, and concluded that the SMES is a very effective device for stabilization of power system and minimization of frequency fluctuations.
Abstract: WPGS (Wind Power Generation System) output fluctuates due to wind speed variations and PV power generation output is changed by sudden cloudy weather conditions. Hence, if a large number of wind and PV power generators are connected to power system, their output can cause a serious influence on the power system operation, that is, frequency and voltage fluctuations. In order to solve these problems, the control of generator output fluctuations is very important. With these points as background, Superconducting Magnetic Energy Storage (SMES) is probably a key technology to overcome these fluctuations. For stabilization of power, the SMES is connected to the terminal of the WPGS. The authors compared the load side frequencies under the 1 MJ and 2.5 MJ of SMES connection, respectively. From the simulation results, it can be concluded that the SMES is a very effective device for stabilization of power system and minimization of frequency fluctuations.
TL;DR: In this article, the authors proposed readout electronics using single-fluxquantum (SFQ) circuits to process a large number of output signals from an SSPD array.
Abstract: Superconducting single-photon detectors (SSPDs) based on NbN nanowires possess properties such as high counting rate, low dark count rate and small timing jitter, which are promising characteristics for a quantum key distribution system. An SSPD array has recently attracted attention, because it can provide a higher counting rate, and spatial and photon-number resolutions. We propose readout electronics using single-flux-quantum (SFQ) circuits to process a large number of output signals from an SSPD array. We designed and tested an interface circuit between an SSPD and SFQ circuit, and successfully observed SFQ pulse generation for an input pulse with a current amplitude of 17.4 ~ 36.4 muA , which is comparable with an output current amplitude of the SSPD. The interface circuit was also operational for an input pulse duration of 1.6 ns, which is shorter than the typical recovery time of the SSPD.
TL;DR: In this article, the minimum quench energy (MQE) and normal zone propagation velocity (NZPV) of short YBa2Cu3O7-x (YBCO) coated conductors are determined using voltage and temperature measurements.
Abstract: YBa2Cu3O7- x (YBCO) coated conductors (CCs) are now capable of carrying very high transport critical current density Jc over a broad range of magnetic field and temperature space, and as a result, they are receiving significant interest for a wide range of applications. While many of these applications take advantage of the high-temperature performance of YBCO CCs, because the YBCO CC is typically produced on a high-strength substrate and carries very high Jc at very high magnetic field, there is now growing interest in using YBCO CCs at 4.2 K to generate very high magnetic fields. The transition from high-field conductor to high-field superconducting magnet, however, requires that some challenging issues be addressed. One of the most important challenges remaining is to better understand the stability and quench behavior at 4.2 K, so that an effective quench protection system can be developed. Here, we report on measurements of the stability and quench behavior of short YBCO CC at 4.2 K by inducing a quench via a heat pulse from a heater mounted on the conductor surface. Through gradually increasing heater pulse amplitude, the transition from stable to unstable (i.e., recovery to quench) is observed through voltage and temperature measurements. Using these data, the minimum quench energy (MQE) and normal zone propagation velocity (NZPV) are determined. It is found that, for the same fraction of critical current (I/Ic), YBCO CCs have similar MQE and NZPV as Ag-alloy-clad Bi2Sr2CaCu2Ox wires and significantly higher MQE and lower NZPV than those of MgB2 round wires of similar Ic (4.2 K). Furthermore, the voltage and temperature versus time data are correlated to better understand the quench onset behavior at 4.2 K. It is determined that a normal temperature gradient exists from the CC surface to the YBCO layer within the conductor, as well as a directly measured longitudinal temperature gradient. After the heater pulse has ended but while the transport current continues, the temperature gradient along the length becomes dominant. Nevertheless, voltage and temperature measurements remain problematic for quench detection in large magnets because of the slow longitudinal propagation velocity. Thus, new approaches to quench detection and/or protection of high-field YBCO magnets are needed.
TL;DR: In this article, the authors investigated reliability enhancement of the fast switch (FS) by using power electronic switches such as integrated gate commutated thyristors (IGCTs) in the line commutation type hybrid superconducting fault current limiter (SFCL).
Abstract: We have investigated reliability enhancement of the fast switch (FS) by using power electronic switches such as integrated gate commutated thyristors (IGCT) in the line commutation type hybrid superconducting fault current limiter (SFCL). The FS utilizes a vacuum interrupter (VI) to open and close the primary power line. The operation of the FS highly relies upon the complete line breaking by the VI. Since the primary line resistance including the arc resistance may not be extremely high after the VI opens, there may be non-zero arc current in the VI, causing a failure in the line communication. The IGCTs are to completely remove the remanent current in the VI, guaranteeing the arc extinction and enhancing reliability in operation. We fabricated and successfully tested the SFCL which was equipped with the IGCT-assisted FS.
TL;DR: In this article, the critical current density (Jc) of Nb3Sn strand has been significantly improved over the last several years, reaching 1700 A/mm2 at 15 T.
Abstract: The critical current density (Jc) of Nb3Sn strand has been significantly improved over the last several years. For most magnet applications, high Jc internal tin has displaced bronze process strand. The highest Jc values are obtained from distributed barrier strands. We have continued development of strands made with Nb-47 wt%Ti rods to supply the dopant, and have achieved Jc values of 3000 A/mm2 (12 T, 4.2 K). Such wires have very good higher field performance as well, reaching 1700 A/mm2 at 15 T. To reduce the effective filament diameter in these high Jc strands, the number of subelement rods incorporated into the final restack billet has been increased to 127 in routine production, and results are presented on experimental 217 stacks. A new re-extrusion technique for improving the monofilament shape is also described. For fusion applications such as ITER, we have developed single-barrier internal tin strands having non-Cu Jc values over 1100 A/mm2 (12 T, 4.2 K) with hysteresis losses less than 700 mJ/cm3 over non-Cu volume. The Jc-strain behavior of such composites is also presented.
TL;DR: This paper describes a technique to superconductively splice multifilament MgB2 wires and has achieved joints capable of carrying a superconducting current of 200 A at 10 K in self field.
Abstract: This paper describes a technique to superconductively splice multifilament MgB2 wires. To date the technique has achieved joints capable of carrying a superconducting current of 200 A at 10 K in self field. Joints details, as well as testing methods and results are presented here.
TL;DR: The limiting capability of YBCO CCs has been investigated and was demonstrated in a successful laboratory test of a 2.2 MVA medium voltage FCL and the cooperation has entered a new DOE funded joint project that encompasses the design, construction and test of an 115 kV FCL for power transmission within a time frame of 4-5 years and additional partners.
Abstract: All over the world there is a growing need for current limiting devices in electrical networks with steadily increasing power demands and fault currents. Production of YBCO coated conductors (CCs) paves the way for the economic viability of superconducting fault current limiters (FCLs) both in power distribution and transmission networks. In a cooperation between AMSC and Siemens the limiting capability of YBCO CCs has been investigated and was demonstrated in a successful laboratory test of a 2.2 MVA medium voltage FCL. This device is based on bifilar coils as switching elements and corresponds to one phase of a 3-phase FCL designed for the 13 kV-class distribution voltage level. In more than 40 switching tests at voltages up to 7.7 kV the device showed excellent limiting performance. Presently this cooperation has entered a new DOE funded joint project that encompasses the design, construction and test of a 115 kV FCL for power transmission within a time frame of 4-5 years and additional partners. AMSC as the project leader is responsible for wire manufacturing, system integration and cryogenics. Siemens' main task is switching modules development, Nexans contributes the high voltage terminations and Los Alamos National Lab investigates AC losses. Installation and testing are planned for a Southern California Edison substation. A project overview and progress under the first phase will be reported.