Tape Wire Research Articles

Electromechanical Properties of Thin-Layer HTSC-2G Tape Wires at Helium Temperature and Tensile Stresses Above 1000 MPa

At present, HTSC-2G tape wires (hereinafter wires) are an uncontested basis for creating conductors for the magnetic system of a compact thermonuclear reactor. Since, according to calculations, the tangential mechanical stresses in the windings of its magnetic system can exceed 1000 MPa, the requirement for high electromechanical stability of the HTSC wire used comes first, which makes it possible to raise the constructive current density. In this work, comparative electromechanical test of HTSC-2G wires with different thicknesses of the superconducting layer, on a substrate made of AISI 310S stainless steel, at the temperature of liquid nitrogen and liquid helium were carried out. The factors leading to a decrease in the degradation of the critical current at high tensile stresses have been established. A new method for testing HTSC-2G wires at helium temperature and a simple method for preliminary assessment of their electromechanical properties at nitrogen temperature are proposed.

Superconducting state stability in second generation high-temperature superconducting wires with varying copper stabilizer thickness under AC overcurrent conditions

Superconducting state stability in high-temperature superconducting (HTS) wires is of great importance for the reliable operation of superconducting electric power equipment. To this end, a study was made of the steady state operation and transients under AC current overloading in second generation (2G) HTS tape wires with a copper stabilizing layer of varying thickness. The existence of a threshold stabilizer thickness has been found, such that determines the HTS tape I-V curve and transients when an overcritical current flows. If the current exceeds the critical value, primary instability takes place in a wire with no stabilizer layer as well as with a layer of any thickness. In a wire with the stabilizer thickness less than the threshold level, an irreversible superconducting-to-normal transition occurs. However, if the copper layer thickness exceeds the threshold thickness, the HTS wire stable overloaded state recovers after some transients that have an irregular oscillation shape. The recovery of the stable thermal state under overcurrent conditions in HTS wires with an over-threshold stabilizer thickness is applicable in a variety of superconducting electric power devices, such as transformers and current limiters with a high capability to withstand faults. The measurements also show that the loss of superconductivity under AC overcritical current is followed by the phase angle changing between voltage and current. This phenomenon could be used for fast response normal zone detection in current-carrying conductors of superconducting equipment.

Design and Development of Tape Applicator For Managing Wire Purposes

The project titled Design and Development of Tape Applicator for Managing Wire Purpose is a project that needs to be achieved by evaluate the users’ performance while using manual method when taping wires and design and developing a tape applicator. This project is focused on to make it easier for the workers to tape wires on the floor without have to bend their bodies. Primary and Secondary data is gathered for completing this project. Interview is done to determine the usual method applied by users in taping wires on the floor and the difficulties that users faced when using manual method. After data is collected, idea generation of concept and sketches are made manually by sketching. Several aspects are being considered to choose the final design which is the most suitable. The final design chosen for the tape applicator is designed by Computer Aided Drawing (CAD) using Solidwork Software. At the end of the project, fabrication process is done before the product is testing. As for the result, time consumed for taping wire cables by using product is shorter than the time consumed when manual method is applied. All of the objectives are achieved.

Theoretical evaluation of the screening-current-induced magnetic field in superconducting coils with tape wires

We theoretically investigate the physical mechanism of the screening-current-induced field (SCIF) in solenoid coils wound with superconducting tape wires. We derive the direct relationship between the SCIF and the magnetization of tape wires, and a scaling law for the SCIF and the coil dimensions is demonstrated. A simple analytical expression of the SCIF is obtained as functions of current load factor, tape wire width, and the coil dimensions. We verify that the published data for the precise numerical computation of SCIF are roughly fitted by our theoretical results for flat coils where the height is smaller than the outer diameter.

Development of a 3 T-250 mm Bore MgB2 Magnet System.

The authors had reported components' development of 3 T-250 mm bore MgB2 magnet system. Pre-reacted MgB2 tape wire with copper lamination had n-value related problem due to raw Boron particle size inequality, but it had been corrected. Long MgB2 wires over 3 km had been supplied. All six component coils were made with a wet winding procedure. They were tested individually with the same cooling scheme of conduction cooling as the actual magnet assembly. Though all coils could be ramped to some extent, some coils showed fairly large remnant voltage. Since the voltage distribution over the coil was not even, the uniformity along the wire length may not be good enough. The stability of the coil was verified by its no training performance even with fast ramping. The magnet assembly and its test with conduction cooling were planned. I c of the superconducting joint with this pre-reacted wire was doubled during past one year's development.

Temporal resistance variation of the second generation HTS tape during superconducting-to-normal state transition

BackgroundThe quench process in high-temperature superconducting (HTS) wires plays an important role in superconducting power devices, such as fault current limiters, magnets, cables, etc. The superconducting device should survive after the overheating due to quench.MethodsWe studied the evolution of the resistance of the YBCO tape wire during the quench process with 1 ms time resolution for various excitation voltages.FindingsThe resistive normal zone was found to be located in a domain of about 1-4 cm long. The normal state nucleation begins in 40-60 ms after voltage is applied across the HTS tape. In subsequent 200-300 ms other normal state regions appear. The normal domain heating continues in the following 5-10s that results in a factor of 2–3 increase of its resistance.ConclusionsFormation of the normal domain during the quench process follows the same stages for different excitation voltages. Characteristic domain sizes, lifetimes and temperatures are determined for all stages.

Normal domain temperature profile in second generation HTS tape wire

BackgroundStudies of the normal zone in high-temperature superconducting wires are extremely important for power applications, such as fault current limiters, motors, cables etc. We studied the temperature distribution and normal domain propagation in high-temperature superconducting YBCO tape with highly resistive substrate.FindingsFor applied voltages exceeding a certain threshold value the normal domain was found to become unstable and started to propagate along the tape.ConclusionsThe normal domain in superconducting tape with highly resistive substrate appears when voltage is applied to the sample.At voltages greater than the threshold value, the domain starts to move.This motion enables us to find the domain temperature and potential profile.

Influence of Repeated Shear Stresses on Critical Current and AC Losses in Multi-Filamentary Bi2223/Ag-Sheathed Wires

This paper investigates the influence of shear stresses on critical currents and characteristics of ac transport current losses in Bi2223/Ag-sheathed tape wires. Shear stresses are stresses applied to the flat face of the tape wire in the tangential direction. When an HTS potted and impregnated coil is cooled down, there are possibilities that wires peel off locally from the coil frame and other wires due to thermal contraction. This peeling-off occurs also due to electromagnetic force and external mechanical forces. The wires are released from the shear stresses where the wires peel off and the shear stresses to wires concentrate on areas where the wires are tightly bonded to the coil frame and other wires. This concentration of shear stresses may cause damages to the wire, degrades critical current and influence ac losses. In this paper, a method is presented to investigate the influence of the shear stresses on HTS tape, and data are given on the influence of shear stress to multifilamentary Bi2223/Ag-sheathed wires reinforced by copper alloy tapes. Also, aspects of defects caused by the shear stresses are studied by investigating the transport current loss characteristics.

Influence of Repeated Tensile Stresses in C-Axis Direction on AC Losses in Multi-Filamentary Bi2223/Ag-Sheathed Wires

The authors investigated influence of repeated and non-repeated c-axis tensile stresses on critical currents and AC transport losses in multi-filamentary Bi2223/Ag-sheathed tape wires reinforced by copper alloy tapes. Experimental results show that characteristics of the AC transport losses change and the manners of the changes are classified into three patterns, when the critical currents are degraded by the stresses. Features of defects caused in superconducting filaments by the stresses are discussed in relation to the three patterns of the transport loss characteristics.

The study on improving the self-protection ability of HTS coils by removing the insulation and lamination of the various metal tapes

The high temperature superconducting (HTS) coils have very low normal zone propagation velocity (NZPV) and complicated quench behaviors. Because of these reasons, it is difficult to expect the self-protection. In this paper, two methods are suggested to improve the self-protection ability of HTS coils. One is to remove the insulation between turn–turn winding in HTS coils to enhance the thermal and electrical contacts along transverse direction and to increase the whole thermal stability of them. The other is Cu or Brass tapes are wound with HTS tape wire instead of the insulation to improve the thermal, electrical and mechanical stability of the HTS coils. To clarify the quench behaviors of the suggested coils, the normal zone propagation properties of the fabricated non-insulated HTS pancake coils were shown by measured voltage and temperature traces during the quench as a function of the operating temperature. And the characteristics of the normal transition and amount of the shared current to adjacent layers were quantitatively measured by a Hall sensor located at the center of HTS coils to measure the change of the self-magnetic field by operating current. The current sharing behaviors in the non-insulated HTS coil and the coil with Cu tape inserted were observed. The minimum quench energy (MQE) of the HTS coil with Cu tape inserted was the largest in the tested coils. It means that the HTS coil with Cu tape inserted had the highest transient stability against the thermal disturbances among the tested coils and the improvement of self protection abilities was proved.

Critical Current and Electric Loss Under Magnetic Field at 30 K on Bi-2223 Superconducting Coil for Ship Propulsion Motor

We are currently under development of a 1 MW-class HTS ship propulsion motor, for which rotating HTS coil made of Bi-2223 tape wire has already been successfully cooled down to 30 K and attained the target performance. There, the electric loss estimation in the HTS tape wire is required under practical operation conditions. The magnetic field angle dependency on IC-B characteristics of Bi-2223 used for the field winding was measured at 40 K. Furthermore, the interlinkage flux density on HTS coils in the horizontal and vertical directions were calculated using three-dimensional magnetic field simulations. It was found that the estimated electric loss of the entire HTS coil using these measured and simulated results was about 9 W at the operating field current of 200 A, which was considerably small compared with 30 W at 215 A, and that the operating field current of 200 A was appropriate and desirable considering the required refrigerator capacity.

Development of REBCO Power Transformers

REBCO superconducting power transformers, which are incombustible, lightweight and compact, are expected to have practical applications in equipment for substations and office buildings in urban areas. In recent years, there have been remarkable improvements in the performance of REBCO tape wires, which have the characteristic of a large critical current in highly magnetic fields. Their use is expected to reduce AC loss through the application of slit processing on the tape wire. Based on these advantages, the authors have developed element and system technologies of REBCO power transformers. Wire-scribing technology, coil-winding technology (for example, short-circuit characteristics), cryogenic technology, fault current-limiting (FCL) technology and a design study of a 66 kV/6 kV, 20 MVA transformer are examined.

Effect of the hot pressing on the magnetic-field and temperature dependences of flux pinning for SiC-doped MgB 2 tape

To understand the effects of the hot pressing on the pinning behavior for the SiC doped MgB 2 tape wire, magnetic field and temperature dependences on a critical current density J c and the pinning force have been studied. The MgB 2 tapes were fabricated using an in situ powder-in-tube (PIT) method, the hot pressing process with nano-SiC powders and the carbon steel sheath. J c of the hot pressing processed wire is enhanced especially at low field compared with that of the no hot-pressed wire. It is suggested that the enhancement of J c is caused by the improvement of the MgB 2 grain connectivity came from the hot pressing. The pinning analysis using the pinning models of a surface pinning and a normal point pinning lead to that the scaled curve of the pinning force for the SiC-doped MgB 2 tape with the hot pressing process showed anisotropy in a lower field. This result suggests that the pinning center of the hot pressing processed MgB 2 wire forms into inequi-axial shape, which is different from that in the tape without the hot pressing having the equi-axial pinning center in our previous report. It was also found that the scaled pinning force of the SiC-doped MgB 2 tape with the hot pressing is larger than the surface pinning model in a higher field. This suggests that the pinning force was enhanced by the hot pressing in a higher field.

$J_{\rm c}$ Anisotropy and Pinning Behaviors of the In-Situ $\hbox{MgB}_{2}$ Wires With/Without SiC Addition

In an attempt to understand the effects of SiC addition on the pinning behavior for the in-situ PIT MgB2 tape wire, field and temperature dependencies on critical current density, Jc and the pinning force were studied by considering applied magnetic field direction for the rectangular-shaped wire. As a result, it was clarified that the SiC-doped wire has the equiaxial pinning center and the un-doped wire has the inequi-axial pining center. Taking the pinning scaling law into account, it is found that the SiC-doped MgB2 wire has two kinds of the pinning center and the dominant pinning center changes with temperature, that is, the pinning centers are the grain boundary and the precipitates at high and low temperatures, respectively. The un-doped MgB2 wire is assumed to have anisotropy of the pinning mechanism.

AC loss characteristics of Bi2223/Ag sheathed tape wires subjected to mechanical strainsand stresses

The influence of uniaxial tensile stress–strain on the AC loss characteristics ofmultifilamentary Bi2223/Ag sheathed tape wires was investigated. The uniaxial tensilestress–strain was applied to the sample wire in liquid nitrogen at atmospheric pressure, andthe AC losses (transport, magnetization and total losses) were measured by an electricmethod. Two kinds of wire, oxide-dispersion strengthened Ag-alloy sheathed and Ag-alloysheathed wires, were tested. The stress–strain curves of the tested wires were divided inthree regions, i.e. elastic deformation, continuous plastic deformation and serrated-likeplastic deformation regions, though the ranges of those regions were different for differentkinds of wire. In the elastic and continuous plastic regions, the stress–strain curvewas smooth and continuous, and in the serrated-like plastic region, the curvewas rough. In the serrated-like plastic region, the wires kept elongating, whileincrease of the tensile stress was suspended. Dependences of the critical currents onthe stress–strain were generally as follows. While decreases of the wire criticalcurrents were in the range of less than 4% of the original values of the no-stresscondition, the critical currents of the wires were reversible, that is, the criticalcurrents recovered the original values at zero stress when the stress were released,regardless of whether the wires were in the elastic or continuous plastic region. In thecontinuous plastic region, the critical currents decreased up to 10%–15% of the originalvalues and the critical currents were irreversible when the degradations of thecritical currents exceeded about 4%. In the serrated-like plastic regions, the criticalcurrents were more severely degraded. The AC loss characteristics of the wiresare different in those regions. In the elastic and continuous plastic regions, theabsolute values of AC losses were dependent on the stress–strain. However, thedependences of those normalized losses on the stress–strain are negligibly small when thelosses are properly normalized by the stress–strain-dependent critical currents.In the serrated-like plastic region, the AC loss characteristics are different fromthose in the elastic and continuous plastic regions and can be characterized bydefects grown almost tape wide, causing serious degradation of the critical currents.There are various origins of defects causing the degradations of the wire criticalcurrents. However, as a result of this investigation, the influence of the tensilestress–strain on the AC losses can be basically estimated by knowing the degrees of thedegradations of the wire critical currents caused by the stress–strain and in whichregions the stress–strain characteristics are, regardless of the origins of the defects.

A study for designing YBCO power transformer

It is highly expected that superconducting transformers, which are characterized by incombustibility, light weight, and compactness, will be used practically for equipment in substations and office buildings sited in urban areas. In recent years, remarkable improvements in the performance of YBaCuO (YBCO) tape wire have been seen. This kind of tape wire has the property that its critical current is large in a highly magnetic field; and, its use is expected to reduce AC loss by applying slit processing on the tape wire, contributing to future cost reductions. In addition, the development of efficient, economical cryogenic units is also expected. The authors have developed a conceptual design for a 66kV/20MVA power transformer using YBCO tape wires, or an YBCO power transformer. As a result, we were able to identify the transformer’s optimal system structure including coil winding comprised of coils and tape wires; and, we confirmed that the devised transformer can made to be both compact and highly efficient.

Numerical Evaluation of AC Loss Property in Bi-2223 Tapes Affected by Multifilament Structure

This paper describes the numerical results of AC losses in various types of non-twisted multifilamentary tapes that actual Bi-2223 Ag-sheathed wires are idealized. The penetration process of magnetic flux into the superconductor filaments subject to Bean's critical state model is simulated for the application of an external transverse magnetic field perpendicular to the broadest face of tape wire by means of energy minimization. The AC losses under cyclic fields are calculated from the distribution of a vector potential in an initial state. The influences of arrangements and shapes of the filaments on the losses are investigated as compared with those for a wire that the entire filamentary region is regarded as a homogeneous superconductor.

Current sharing among filaments for Bi-2223 Ag-sheathed tapes with inter-filament barrier

Current distribution in Bi-2223 multifilamentary tapes with inter-filament barrier is numerically evaluated for the application of an alternating transport current. In the case of barrier materials with an infinite resistivity, the current distribution can be determined with a lumped parameter circuit model including the inductances and resistances of all the filaments. The mutual inductance between a pair of filaments is obtained by estimating their geometric mean distance. The power-law model is also assumed to take into account the effect of resistance in each filament. The influences of the silver ratio and filament number in the tape wire on the current distribution are discussed systematically as well as the power index and frequency.

Fundamental Characteristics of a 200A-Class HTS Reactor

In order to develop a reactor for a LC resonance-type fault current limiter, we have been studying a pancake-type HTS coil with a low loss and a high current capacity. Double-pancake coils wound by Bi2223 tape wire are adopted as a unit coil for the reactor. In the double-pancake coil, two Bi2223 tapes are wound in parallel to each other to obtain a high current capacity. Besides, a stainless steel wire is co-wound with the Bi2223 tapes in order to increase the mechanical strength. The reactor is designed as an air-core type one to obtain a constant inductance. 12 unit double-pancake coils are manufactured. They are located in a toroidal shape in order to obtain symmetry. 12 unit coils are connected in 3-parallel/4-series mode. The critical current, the AC loss, and the current sharing ratio between the unit coils are measured. From the experimental results, it has been confirmed that the current sharing among the 3 parallel circuits is uniform, in spite of some deviations between the critical currents of each unit coil.

伝導冷却高温超電導コイルの交流電流通電時安定性解析

In our previous study, thermal runaway currents of a conduction-cooled single pancake coil wound with a Bi2223 tape wire were experimentally and numerically investigated and the relation between the cooling structure and the thermal runaway current was explained. On the basis of the results, we designed and fabricated a conduction-cooled HTS coil composed of 12 single-pancake coils and confirmed that the coil had a thermal stability as designed in DC operations. Secondly, the AC loss characteristics of the HTS coil were measured at 20-50 K and 0.05-2 Hz. Hysteresis losses of the coil were well explained using equations based on the Brandt model. As the result of the AC loss measurements, it was found that coupling losses were expressed as α(T)*(Bzf)2. Adopting the functions of hysteresis losses and coupling losses into the thermal stability analysis program developed in our previous study, the thermal stability of the conduction-cooled HTS coil was numerically investigated. In this paper, the thermal stability analysis results are described.