Large Current Capacity Research Articles

Feasibility of large-current capacity YBCO conductors with on-demand transposition

Abstract We propose a new idea for fabricating a large-current capacity YBCO conductor having a Roebel-type transposition formed by joining tapes. If the joule heating generated by joints is smaller than other heat sources, such as AC losses, this type of conductor may work as a quasi-superconductor. We note that the Roebel-type transposition can be included on demand in coil windings, not over the whole conductor length but rather locally, such as at terminals and coil edges to secure uniform current distribution among tapes. We fabricated a 1.2 m-long conductor sample based on this idea using 20 YBCO tapes. The Roebel-assembled tapes having joints with a 600-mm pitch length for meandering were imbedded in a copper jacket and soldered. The sample was tested in liquid nitrogen under the self magnetic field and the critical current was measured. The joint resistance was evaluated and compared with the expected value.

Development of an ${\rm MgB}_{2}$ Coil Wound With a Parallel Conductor Composed of Two Tapes With Insulation

The MgB2 coil wound with a parallel conductor composed of two MgB2 tapes with insulation has been developed. The tape is obtained by the rolling process from the round wire which is fabricated by in-situ method. The performances of tapes, such as critical current density and ac losses, are higher than that of round wires in case that the transverse magnetic fields are applied to the tape in direction of the parallel to the flat face of the tape. We proposed as a candidate of applying the tape to a conductor with large current capacity that the parallel conductor is composed of insulated tapes. We fabricated a tape with aspect ratio of two from a round wire with diameter of 0.8 mm as a strand for the conductor. The coil is composed of two coils that are jointed each other in series. At the joint, two strands are transposed to be identical the inductances of two strands. The inner and outer diameters of the coil are 65 mm and 107 mm, respectively. The length of the coil is 53 mm. The total turn number is 540 turn. The magnetic flux density at the center in the coil is 1.31 T when the transport current is 200 A. In this paper, the design and the test results of the MgB2 coil wound with the conductor are shown and the critical current properties and ac loss properties of the coil are discussed.

Estimation of the Critical Current Density From the Measured Values of Perpendicular Magnetization Losses in HTS Coated Conductors

Stacking of conductors for large current capacity and striation for low loss are needed in large scale power applications of HTS superconductor. It, however, was difficult to measure superconducting properties of the HTS coated conductor non-destructively. Instead of direct measurement of the critical current of HTS coated conductor, indirect estimation from the measured magnetization loss can be used for the practical estimation of the critical current. The magnetization loss of a superconductor can be affected by the full penetrating magnetic field, and it tends to show an inflection point at the full penetrating magnetic field in the plot of magnetization loss vs. external magnetic field. The full penetrating magnetic field depends on the shape of the conductor and its critical current density, and so the effective critical current density can be estimated from the measured magnetization loss. In this paper, to prove the effectiveness of this indirect estimation of the critical current, we measured the perpendicular magnetization losses in short samples of 2G HTS coated conductors with different shapes which includes striated coated conductors were measured, and the estimated critical current densities were compared with those directly measured.

Long RE123 coated conductors with high critical current over 500 A/cm by IBAD/PLD technique

We have developed long RE1Ba2Cu3O7−X (RE123) coated conductors with large current capacity by the ion beam assisted deposition (IBAD) and the pulsed laser deposition using hot wall heating (HW-PLD) technique. As a result, we could fabricate an 8m-long Gd1Ba2Cu3O7−X (Gd123) coated wire with the minimum and maximum critical current (Ic) of 951A/cm-w and 1003A/cm-w at 77K, 0T, respectively, measured in 0.7m-long sections by the standard 4-probe technique. Furthermore, we succeeded in preparation of over 600m-long Gd123 coated wire with the uniform Ic distribution over 600A/cm-w. It had average, maximum and minimum Ic of 665, 698, 609A/cm-w, respectively. The n-values of the sample showed the maximum Ic and minimum Ic were 40 and 36, respectively. As a result, we set the new world record of Ic×L value as 374535Am (= 609A×615m). The in-field performance of this long wire was quite high as well; the minimum Ic exceeded 50A/cm-w at 77K, 3T.

An experimental analysis on the design of HTS current lead with respect to the arrangement of coated conductor and the shape of a current terminal

Many researches on the application of superconducting tapes for large current apparatus have been conducted because of their advantages of low resistance and high efficiency. In the applications, superconducting tapes which are available below a critical current density should be arranged in the stacking or parallel structure for increasing a current capacity. However it is difficult to achieve large current capacity in each structure as much as expected; a simple stacking structure has a current distribution problem due to contact resistance between superconducting tapes and a parallel structure has the spatial limitation. In order to reduce the contact resistance, superconducting tapes should be stacked vertically and these tapes are connected by solder; therefore large current capacity can be achieved. In this paper, a design of a copper terminal for HTS current lead using a stacked HTS tapes and a parallel arrangement of stacked HTS tapes were analyzed and the operating characteristics were proved by experimental analysis.

2A2-E07 大容量かつ信頼性・汎用性の高いモータドライバの開発(ロボカップ・ロボットコンテスト)

2A2-E07 大容量かつ信頼性・汎用性の高いモータドライバの開発(ロボカップ・ロボットコンテスト)

Technology Development Status of Yttrium Based Coil for SMES

A new Japanese national project has started in 2008 to develop high temperature superconducting electric power devices. In this project, we have developed a superconducting magnetic energy storage (SMES) system, which are highly expected as a stable power supply. Main issues are a large current capacity conductor made of YBCO-coated tapes and a compact coil wound the conductors. Aiming at the manufacturing of compact coil with higher energy density through the creation of higher magnetic field, we produced YBCO coil, and by carrying out hoop stress tests. Also, aiming at the development of 20 MJ class SMES component coils necessary for picturing the technological outlook of 2 GJ class SMES coil for power system control, we manufactured component coils (outer diameter 650 mm), adopting the bundled conductor that would enable the realization of high strength and low loss, proving that its current capacity was large enough to exceed 2.6 kA, through basic verification test for energization. In addition, we have challenged the development of high efficiency coil conduction cooling technology, stable manufacturing technology of coated conductors for SMES and the highly reliable/highly durable SMES coil component technology.

Improvement of Electromagnetic Properties of ${\hbox{MgB}}_{2}$ Filaments Due to Deformation to Tape Shape

We have proposed MgB2 multifilamentary tapes with high critical current densities and low ac losses under external magnetic fields which is parallel to the tape face. The purpose of this proposal is to develop the MgB2 new conductors composed of plural tapes as windings of superconducting coils with both large current capacities and low losses for fusion reactors, superconducting magnetic energy storage systems, and so on. Our MgB2 multifilamentary tapes are fabricated by rolling process from round wires. The tapes are fabricated by using in-situ method. The purpose of this paper is to clarify the effects of deformation to tape shape on the electromagnetic properties of MgB2 filaments in multifilamentary wires. For the purpose, measurements of both critical currents and magnetizations have been carried out on MgB2 fine single filament wires which have simulated a filament in multifilamentary wires. Measurements on wires with large diameter have been also carried out, in order to clarify the effect of diameters of original round wires. We prepared pure and SiC-added MgB2/Nb/Cu composite wires as the original round wires before rolling process. The diameters of round wires have been varied and then the aspect ratios of tapes have been varied. The observed critical current densities of the tapes are about 7 times larger than that of the original round wire at a maximum. The ratios of Jc of wires to tapes don't have dependence of the diameter of the original round wire. In addition, the results of measurements of magnetizations have shown that magnetization losses in MgB2 tapes decrease to 1/3 compared with original round wires.

A Conceptual Design for HTS Cable With Large Current Capacity Using Co-Axial Configurations

High temperature superconducting (HTS) cable is promising one of HTS power applications to be commercialized operation in 77 K in near future, particularly in the applications with short distance and large current. The magnetic field of cable seriously limits critical current of HTS superconductor and then the current capacity. A new conceptual design of cable is presented for minimizing the magnetic field as small as possible and increasing critical current by using co-axial configuration which is sandwich structure of interleaved winding, then the magnetic fields are opposite between the adjacent layers. Two configurations are suggested and the jointing technique between layers and terminal is also put forwarded in order to simplify jointing method. The magnetic field distributions, AC losses are calculated by numerically method. The results show that the new approaches can greatly reduce magnetic field and AC losses, then degrade critical current with minimum degree, highly improve efficiency and save HTS materials, which are potential for transmission HTS cable with large current in mid- and -low voltage applications.

High-speed deposition of RE123 film with large current capacity by hot-wall type PLD system

We have studied a hot-wall heating system to produce GdBa2Cu3Oy (GdBCO) films with large critical currents (Ic) at a high production rate by a pulsed-laser-deposition (PLD) method. GdBCO films fabricated at a production rate of 30m/h under the optimized conditions, especially a distance of 95mm between the target and the substrate (T–S), exhibited high critical current densities (Jc) of about 3MA/cm2 and Ic over 300A at a thickness of 1–2μm. Furthermore, long GdBCO tapes prepared by repeated depositions at each tape-passing speed of 80m/h showed uniform Ic distribution along the longitudinal direction, because the hot-wall system enabled to stabilize temperature within a few degrees at 800°C. A 170m long tape with Ic over 600A was successfully fabricated at a production rate of 16m/h using a laser power of 360W.

Indirect measurement of AC current distributions in HTS tapes by a pickup coil method

It is necessary to develop HTS conductors with a large current capacity and low AC loss characteristics for practical use of HTS power devices. For large capacity power applications, HTS tapes such as Bi-2223 tapes and YBCO coated conductors are assembled. So, it is important to evaluate the characteristics of current distributions in such assembled HTS tapes. However, an adequate measurement method has not been established. In this study, we have tried the development of an indirect measurement method to evaluate the current distributions in stacked HTS tapes. In this method, the current distributions are indirectly found from the results of the field distributions measured by a pickup coil located around the surface of the sample tapes. To confirm the accuracy and the sensitivity of this method, current distributions in a test conductor made of copper tapes are measured. Numerical and measured current distributions are compared. Using this method, the current distributions in stacked Bi-2223 tapes are measured at room temperature and 77K. On the basis of the obtained results, the characteristics of the AC current distributions in the HTS tapes are discussed.

Transient State Analysis of HTS Cable Using EMTP-RV

A high temperature superconducting power cable (HTS power cable) was applied large current capacity by no resistance in normal state. Fault state was risen out of over-current but, it was limited to resistance. this study was modeling equivalence, and unbalanced state analyzed operating charateristics of HTS power cable. The equivalence model was composed superconductor, shield, and former part. This model simulation was appeared conductor and shield current in normal state, but fault state was appeared former current as rise current by resistance. so it need to sufficiently influenced the quench characteristic when the former design.

Carbon Nanotube Interconnects

The performance and power dissipation of integrated circuits (IC) are largely affected by interconnects. Carbon nanotubes, which are rolls of one-atom-thick carbon sheets, show great potential in addressing some of the major interconnect challenges in future generations of technology, when copper conductivity will degrade substantially because of size effects. Some of the fascinating properties of carbon nanotubes include very large current conduction capacity, large electron mean free paths, high mechanical strength, and stability. In this article, the physical circuit models for carbon nanotubes are reviewed, and the potential performances of both single-wall carbon nanotube (SWNT) and multiwall carbon nanotube (MWNT) interconnects are benchmarked against their copper counterparts at a realistic operating temperature (100°C). The models capture various electron phonon scattering mechanisms and the dependency of quantum conductance on temperature and diameter. A hybrid system of copper/SWNTs/MWNTs offers the highest performance enhancement for interconnects.

Measurement of Transport Current Losses in HTS Conductors With Large Current Capacity by Using HTS Current Transformer

In order to evaluate the transport current loss characteristics in HTS conductors with large current capacity, we developed a new compact measurement system. This system enables us to measure the transport current losses electrically in the straight HTS conductors with the current capacity of 1 kA class by using the small capacity AC power supply of about 50 A. In this system, an HTS current transformer is used to feed current to the sample conductor for the measurement. The secondary current of this current transformer can be induced at about 1 kA at 77 K when the primary current is 40 A. The current transformer is made very compactly, and the externals size is 70 mm in diameter, and 110 mm in length. The sample conductor is connected with the secondary coil of this current transformer. The loss measurement is done by the Poynting vector method. The distribution of Poynting vectors around the sample conductor can be obtained by using many sets of both a potential lead and a pickup coil. To confirm the validity of this measurement system, we measured the transport current losses in an HTS conductor. As a sample conductor, we used a parallel conductor composed of 16 Ag-sheathed Bi-2223 multifilamentary tapes. The obtained results showed that this compact system was useful for measuring AC loss characteristics of large scale HTS conductors.

Fabrication and Properties of Bi2212 Rutherford Superconducting Cable

Bi2212/Ag round wire can be used as large current capacity conductor fabricated in the shape of Rutherford cable. We have fabricated 110 m long Bi2212 Rutherford cable of 20 strand and 10 m long Bi2212 Rutherford cable of 30 strand and 8 strand by using our own Rutherford cabling machine. The critical current (I c) of the reacted Rutherford cables have been measured at 4.2 K and 65 K, respectively. The magnetization (M) versus. magnetic field (H) and magnetic irreversibility (DeltaM) versus. magnetic field (H) have been measured at 5-40 K in background magnetic field up to 8 T using PPMS instrument. It is estimated from DeltaM that critical current density (J c) of 20 strand Rutherford cable is higher than that of 30 strand Rutherford cable.

Over-Current Characteristics of a 20-m-Long YBCO Model Cable

To achieve large current capacity and mechanical flexibility, high-temperature superconductor (HTS) power transmission cables consist of a number of YBCO coated conductors, which are assembled and wound spirally on a Cu former. In practical applications, superconducting cables might be subjected to short-circuit fault currents that are 10 to 30 times the operating current. Therefore, in order to ensure the stability and feasibility of HTS power cables and protect them from fault currents, it is important to estimate the redistribution of the transport current and electromagnetic coupling among the conductor layer, shield layer, and Cu former. In this study, we carried out experiments on a 20-m-long YBCO model cable, which was composed of two jointed 10-m-long YBCO model cables. Over-current with a peak of 31.8 kArms and a duration of 2.02 s was applied to the model cable. We performed numerical simulations using a newly developed computer program based on the 3D finite element method (FEM) in order to clarify the electromagnetic and thermal behaviors of the YBCO model cable in the presence of an over-current.

AC loss characteristics of a hex-cable in an azimuthal external AC magnetic field

Recently, power transmission cables made of a high temperature superconductor (HTS) are being developed, showing progress in field tests on a power network of distribution level. The HTS power cable consists of a conductor and a shield, which are composed of dozens of HTS tapes. In addition, the HTS cable with a large current capacity has a multi-layered structure in both the conductor and the shield. In such a complicated HTS cable with a multi-layered structure, the AC loss estimation is very difficult and thus not cleared yet. In this study, a hex-cable sample was prepared by arranging six Bi-2223(Bi 2Sr 2Ca 2Cu 3O 10) tapes on the surface of a normal copper-rod in order to experimentally investigate the AC loss characteristics of an HTS cable. The AC loss characteristics of the Bi-2223 tape in the hex-cable were estimated in different transport modes of the tape. The AC loss characteristics of the hex-cable were also examined in different cable transport modes in order to experimentally simulate the various transport situations of the conductor and the shield in an actual HTS cable. The measured AC loss of Bi-2223 tape in the hex-cable strongly depends on the transport mode. In particular, the measured AC losses for the simultaneous mode increase as the arrangement of tapes approaches a polygonal shape. The measured AC loss when the current of the same direction flows in the hex-cable and the copper-rod is about two times larger than the transport loss. On the contrary, it is almost half of the transport loss for the current flowing in the opposite direction, especially in the region of high currents.

Over-current characteristics of YBCO superconducting cable

To achieve large current capacity and high mechanical flexibility, YBa 2Cu 3O 7 (YBCO) superconducting cables consist of a number of YBCO coated conductors that are assembled and wound spirally on a Cu former. In practical applications, superconducting cables are vulnerable to short-circuit fault currents that are 10–30 times greater than the operating current. Therefore, in order to ensure the stability of YBCO superconducting cables in such a situation and to protect them from the fault currents, it is important to investigate the redistribution of the transport current and electromagnetic coupling between the conductor layer, shield layer, and Cu former. In this study, we carried out experiments on a 10-m-long YBCO model cable, which was manufactured by Furukawa Electric. An over-current with a peak of 31.8 kA rms and a duration of 2.02 s was applied to the model cable. We performed numerical simulations using a novel computer program developed using the 3D finite element method to elucidate the electromagnetic and thermal behavior of the YBCO model cable in the presence of an over-current.

Experimental verification of non-inductive wound solenoid coil for large transport currents

YBCO coated conductor (CC) wires has many advantages for resistive superconducting fault current limiters (SFCLs). Especially, the 344S manufactured by AMSC CC clad with stainless steel can reduce fault current to lower temperature because stainless steel stabilizer roles as higher resistant shunt. Multi parallel structure is inevitable for SFCLs with large current capacity. The two layered with four parallel paths non-inductive wound solenoid coils were fabricated. The inductances of inner and outer layers were calculated using finite element method (FEM) tool. These results were compared with measured values. In this paper, the current distribution characteristics of coils were measured when 240 A peak was applied. From the experiments, the results show that more large current flows into inner layers by difference in inductance. Therefore, the two solenoid coils was transposed to reduce of non-uniform current distribution between inner and outer layers by electrical inductance. The experimental results provide to suitable design parameters and showed technical feasibility of multi parallel structure.

Development of a high-temperature superconducting bus conductor with large currentcapacity

A high-temperature superconducting (HTS) bus conductor with a capacity of20 kA and 5 m long has been constructed. The HTS bus was wound by hermeticstainless-steel-reinforced multifilamentary Bi2223/Ag tapes. Its structure is multilayerby clockwise and anticlockwise winding with different winding spiral pitch andangle based on a conventional uniform current approach. The joint technologybetween HTS tapes and terminations is developed in order to ensure that theresistances between them are as small as possible. Fundamental characteristics ofthe HTS bus conductor are obtained at the liquid nitrogen temperature of 77 K.