Development of YBCO power devices in Japan

Japanese efforts on coated conductor processing and its power applications: New 5 year project for materials and power applications of coated conductors (M-PACC)

In electrical power devices, ac losses from a superconductor is a primary factor which determines their usefulness as commercial power equipment. For this reason, extensive studies have been carried out on the losses of Bi{sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub 10}/Ag, [Bi(2223)/Ag], tapes. These studies were mostly limited to a single isolated tape. However, a conductor in a power device is surrounded by other conductors and the precise magnetic field distribution around it is very different from that for a single conductor carrying currents or in ac fields. Since the precise field distribution in and around a superconductor is critical in determining the losses, it is very important to measure and to understand the losses in Bi(2223)/Ag tapes which are surrounded by other tapes as in a power device. Taking this fact into consideration, recently the authors have studied ac losses in stacks of Bi(2223)/Ag tapes in parallel and perpendicular applied fields and shown that they can calculate the losses in these cases utilizing the critical state model if a number of appropriate factors about properties of the tape are taken into a consideration. However, in a power device such as a transformer, magnetic fields near the ends of a solenoid vary from parallel to perpendicular with the tape face. Thus, it is important to learn the behavior of the losses in the stacks of Bi(2223)/Ag tapes with respect to the variations in the angle between the applied field direction and the tape face. In order to accomplish this, they measured the angular dependence of the losses in the stacks which were made from two different Bi(2223)/Ag tapes. Here they report this result and discuss under what conditions they can calculate the losses with a reasonable accuracy. The angular dependence of the losses in ac applied fields were measured using a series of stacked Bi(2223)/Ag tapes having the angles with the direction of applied fields of 0, 7.5, 15, 30, 45, 60, and 90 degrees. The measured values of the losses were compared with the calculated values. The calculations were performed using the measured losses for the 0 and 90 degrees orientations and assuming the losses can be separated for the currents circulating in the plane of and across the tapes. It was shown that at very high fields, i.e., well above the full penetration fields, this assumption was justified by the observed good agreement between the measured and the calculated losses for both tapes. However, at the low fields, significant deviations between the calculated and the measured were seen for both of the tapes. One possible contributing factor to this discrepancy is the non-ideal shape of the tape cross sections. This can causes the field distribution near the edges of the slabs to deviate from that for an assumed uniform infinite slab. This makes the actual fields at the edge regions to be greater than the applied fields. Thus, the losses will be higher than those calculated. Although not having a full understanding of the losses at low fields is of concern, it will not be of a great importance in the designs of power devices in practice. This is due to the fact that the values of the losses at low fields are orders of magnitudes lower than those at high fields and thus the primary concern for the power device development is the reduction of the losses at high fields.

The demand for high-performance dielectrics has increased due to the rapid development of modern electric power and electronic technology. Composite dielectrics, which can overcome the limitations of traditional single polymers in thermal conductivity, dielectric properties and mechanical performance, have received considerable attention. In this study, we report a multifunctional nanocomposite material fabricated by blending fluorinated graphene (F-graphene) with epoxy resin. The F-graphene/epoxy composite exhibited a high thermal conductivity of 0.3304 W·m-1·K-1 at a low filler loading of 1.0 wt.%, which was 67.63% higher than that of pure epoxy. The composite dielectric also showed high breakdown strength (78.60 kV/mm), high dielectric constant (8.23), low dielectric loss (<0.015) and low AC conductivity (<10-11 S·m-1). Moreover, the composite demonstrated high thermal stability and strong mechanical strength. It is believed that the F-graphene/epoxy composite has outstanding performance in various aspects and can enable the development and manufacturing of advanced electric power and electronic equipment devices.

Study on AC loss of stacked REBCO cable wrapped with magnetic strip

Development of YBCO HTS cable with low AC loss

The assembly of meander shaped coated conductor tapes by the Roebel technique is apromising way to manufacture high current cables with low ac losses. The application oflongitudinal striations to the single strands can be an option to create a filament structurefor further possible reduction of the ac losses. Due to the complex Roebel strandgeometry, it was important to identify a reliable technique to produce such structuresusing a picosecond-infrared (IR) laser for the groove etching process. We analyzedthe effects of the filament structure on the magnetization ac loss behavior bycomparing the losses of a cable with striated strands with those of a reference one withnon-striated strands. The ac loss reduction in the Roebel cable with striated strandswas confirmed. The measured magnetization loss of the 125 mm striated singlestrand is five times lower than that of the non-striated one. In the case of thecable sample the loss reduced by a factor of three, but not in the whole intervalof amplitudes of the applied magnetic field. We also compared the results withthose for a cable with insulated striated strands: they seem to indicate that thecoupling currents occur mostly between the filaments, not between the strands.

In-situ exfoliation of hexagonal boron nitride during the forced flow of highly elastic polylactide to fabricate electrospun fibrous film with high thermal conductivity and low dielectric loss

This paper reviews the history, evolution, and applications of silicon microwave & RF power transistors and electric power devices. The current status of silicon microwave & RF power transistors (BJT, DMOSFET, SIT) and a new kind of electric power device - RSD in HSRI are mainly presented. Important techniques for manufacturing such power devices are introduced. Future trends of such power devices are given briefly.

AC loss test and analysis of the prototype CIC conductor joint for CFETR CSMC

Wounded with second-generation (2G) high temperature superconductors (HTS) tapes, the conductor on round core (CORC) coil exhibits notable benefits such as low AC loss, powerful current-carrying capability, and great mechanical properties, which makes it one of the optimal materials for high magnetic field generation in the engineering applications for fusion magnets. However, it is challenging for current manufacturing techniques to ensure the uniformity among the joint resistances of HTS tapes in CORC coils. And it will have a crucial impact on the electro-magnetic properties of CORC coils. Therefore, a three-dimension (3D) finite element model of CORC coils considering joint resistance is established, and the effects of joint resistance on the coils’ current distribution and AC losses are analyzed. Results show that during AC operation, uneven joint resistances and reactance arising from the coils’ helical winding structure will act together on the current among HTS tapes, causing non-uniform current distribution and increasing the total AC losses of CORC coils. Additionally, the uneven degree of the joint resistance raises the CORC coil’s overall AC loss.

For the use of silver or silver-alloyed Bi-2223 tapes in different applications of power engineering, very good electrical and mechanical properties are required. Besides high critical current densities of up to 100 kA/cm/sup 2/ the tapes have to cope with high mechanical stresses and strains and need low AC losses with respect to the variety of applications. At Vacuumschmelze we produce and develop different multifilamentary tapes with high strengthened matrix, low AC losses and high electrical performance. Overall critical current densities >7 kA/cm/sup 2/ and critical currents up to 80 A in lengths of up to 800 m have been measured in the production line. In short-samples current densities over 10 kA/cm/sup 2/ have been achieved, An overview of the fabrication process, the optimization of different process parameters, the microstructure of the filaments as well as the electrical performance of the multifilamentary tapes in different magnetic fields and at different temperatures are given. Also AC loss and mechanical measurements of different tapes will be shown.

Materials with high dielectric permittivity are important in electronic components such as capacitors, gate dielectrics, memories, and power-storage devices. Conventional highpermittivity materials such as barium titanate (BT) can be processed into thin films by using chemical solution deposition yielding a relative permittivity (er) of about 2500 and relatively low dielectric loss but require high-temperature sintering, which is not compatible with many substrate materials. Polymer-based dielectrics, such as biaxially oriented polypropylene (BOPP), have good processability with high dielectric strengths (∼ 640 V lm) suitable for high-energy-density capacitors, but the storage capacity (ca. 1–1.2 J cm) is limited by the low er (ca. 2.2) of these materials. [6] Various approaches to high-er materials based on nanocomposites containing metal particles or other conductive materials have been pursued. Such nanocomposites have afforded huge er values but the resulting materials are limited by the high-temperature processing required, high dielectric loss, or low dielectric strength. Polymer/ceramic nanocomposites in which high-er metal oxide nanoparticles such as BT and lead magnesium niobate–lead titanate (PMN–PT) are incorporated into a polymer host are of significant current interest. The combination of high-er nanoparticles with high-dielectric-strength polymer hosts offers the potential to obtain processable highperformance dielectric materials. Simple solution processing of BT particles in a polymer host generally results in poor film quality and inhomogeneities, which are mainly caused by agglomeration of the nanoparticles. Addition of surfactants, such as phosphate esters and oligomers thereof, can improve the dispersion of BT nanoparticles in host polymers and consequently the overall nanocomposite film quality. However, in such systems, residual free surfactant can lead to high leakage current and dielectric loss. Thus, approaches to bind surface modifiers to BT nanoparticles via robust chemical bonds are highly desirable. Ramesh et al. have reported on the use of trialkoxysilane surface modifiers for the dispersion of BT nanoparticles in epoxy polymer hosts resulting in nanocomposites with reasonably high er, up to 45. [12] With the objective of identifying ligands that can form stable bonds to a BT surface through coordination or condensation, we have investigated a series of different ligand functionalities. In this Communication, we report that phosphonic acid ligands effect robust surface modification of BT and related nanoparticles and that the use of particles modified with suitable phosphonic acid ligands leads to well-dispersed BT nanocomposite films with high er and high dielectric strength. We have investigated the binding of a variety of ligands to the surface of BT nanoparticles, as the stability of the binding on the surface is vital to effective surface modification. We examined the following set of ligands, each bearing an aliphatic octyl chain with a different terminal binding group: C8H17-X, where X = PO(OH)2 (OPA), SO2ONa (OSA), Si(OCH3)3 (OTMOS), and CO2H (OCA). Trialkoxysilanes are widely used surface modifiers for silicate, indium tin oxide, and other metal oxide surfaces. Phosphonic acids have been reported to modify TiO2, ZrO2, and indium tin oxide surfaces and are thought to couple to the surface of metal oxides either by heterocondensation with surface hydroxyl groups or coordination to metal ions on the surface. Carboxylic acid and sulfonic acid groups may also bind to the surface in a similar manner. A sample of each ligand was mixed with BT nanoparticles (30–50 nm, 0.5 mmol ligand/ g BT) in an ethanol/water solution and stirred at 80 °C, followed by extensive washing with ethanol or water and centrifugation to remove excess and/or physisorbed ligand. The treated BT nanoparticles were dried and characterized by using Fourier transform infrared (FTIR) spectroscopy and thermogravimetric analysis (TGA). Figure 1a shows a comparison of FTIR spectra in the C–H stretching region for the BT nanoparticles treated with the ligands described above, followed by washing. These results C O M M U N IC A IO N

The configuration and projected performance of a 15 kA monolithic superconductor designed for 0.36 to 72 GJ (0.1 to 20 MW-hr) SMES use for the Naval Surface Warfare Center is described. The conductor operates at 4.2 K and 1 atmosphere in a peak magnetic field of 5 T at 70% along the load line, which corresponds to a temperature margin of 1.7 K. The conductor consists of a Nb-Ti copper composite Rutherford cable soldered into a high purity aluminum stabilizer that has a nominal RRR of 1500. The conductor is cryogenically stable at the operating point. Pulsed devices and energy storage systems using superconductors require conductors with low AC losses. Internal eddy current barriers limit AC losses during a discharge. Extrapolation of the conductor configuration to further reduce AC losses is considered. A possible test configuration for the conductor is described as it is related to design specifications.

The novel RBB-BSCCO tape design resembling a Rutherford cable structure for low AC losses was improved with respect to the conductor geometry and the superconducting properties in combination with a low level of AC losses. The PITAR route (powder in tube assemble and react) allows economical preparation of a stranded conductor composite with techniques similar to standard BSCCO tapes. The advantage is a very effective twist application to the strands and low geometrical distortions to the filament cross sections. Data of the transport current anisotropy and current homogeneity (by MOI) for differently twisted conductors are presented. Transport currents up to 9 kAcm/sup -2/ were achieved. Filament twist pitches down to 3.4 mm were realized and the achieved effective decoupling of the strands shifts the maximum of the AC losses in perpendicular external AC fields to frequency values above 500 Hz. This was the first time realization for a BSCCO conductor.

The benefits that turboelectric propulsion may offer transport aircraft due to the flexibility of electrical distribution of power have been discussed by various authors and are briefly summarized. Estimates of the weights and efficiencies of the electric components, based on approximate sizing models for fully superconducting motors and generators and on aggressive estimates for cryocoolers and inverters, were presented at ASM2009 in a baseline turboelectric system study. An SBIR study has since predicted that the apparently aggressive cryocooler weight and performance estimates (5 lb/input-hp at 30% of Carnot efficiency) can be met. Another SBIR study has predicted that a cryogenically cooled inverter can exceed the 10 hp/lb specific power (including cooler) and the 98.8% efficiency (including cooler) that were assumed in the baseline study. The inverter with its cooler constituted half of the baseline electrical system weight. On the other hand, new estimates for the superconducting motors and generators, based upon inclusion of additional components in the sizing models and more complete ac loss models, predict somewhat heavier and slightly less efficient motors and generators. The lighter, more efficient inverter roughly offsets the adverse motor and generator changes for machines wound with a hypothetical future high temperature superconductor with low ac losses. For such a material, the weight of the entire electric system changes very little, and the already high efficiency improves slightly, from the ASM2009 estimates. For machines wound with the intermediate temperature superconductor MgB2, the system weight increases about 25%, because MgB2 must operate much colder. The modeling and performance estimates of each component are discussed and compared to the baseline estimates and to the current state-ofthe-art. The dependence of motor and generator weights and efficiencies upon some important design parameters are presented in an appendix. These results quantify the benefits of technology development of lighter cryocoolers and of superconductors with lower ac loss. A zero-th order estimate of the benefits of lower fan pressure ratio and of boundary layer ingestion, offset by the electric system weight and inefficiency penalties from the added components, gives a net fuel burn reduction of about 9%, before iterating and resizing.