Mitsuho Furuse

Feasibility study of low-Voltage DC Superconducting distribution system

This paper describes the advantages of using superconducting cables in low-voltage DC distribution systems, focusing on total cost reduction. Demand for DC electric power has been rapidly increasing, requiring reductions in total costs and power supply system losses. The effects of using superconducting cables were investigated by changing parameters such as the current and length of cables, and it is shown that DC superconducting distribution systems are feasible even for small-capacity power systems and savings can be obtained beyond the extra cost of the superconductors and refrigeration systems. In this study, a test model of a DC superconducting distribution system, constructed by modification of an AC superconducting power transmission system, is presented and evaluated.

Running Performance of a Pinning-Type Superconducting Magnetic Levitation Guide

A pinning-type superconducting magnetic levitation guide with bulk high-Tc superconductors was studied for use as a goods transportation system, an energy storage system, etc. A superconducting magnetic levitation running test apparatus with a circular track of ca. 38 m length, 12 m diameter, which comprises the magnetic rail constituted by Nd-B-Fe rare-earth permanent magnets and steel plates, was manufactured to examine loss and high-speed performance of the magnetic levitation guide. Running tests were conducted in air. These tests clarify that a vehicle supported by a superconducting magnetic levitation guide runs stably at speeds greater than 42 km/h above the circular track.

Copper stabilization of YBCO coated conductor for quench protection

The required amount of copper stabilizer to protect a YBCO conductor coil from damage caused by a hot spot due to a quench is studied in this paper. YBCO coated conductors which are made by deposition of thin YBCO film on high resistance metal substrates are highly resistive when they are quenched. Therefore, stabilization and quench protection are more important for YBCO conductors than Bi/Ag sheathed tapes which have low resistance silver matrix. In the work we numerically calculated maximum temperature rise of a YBCO conductor quenched by a local disturbance during the sequence of quench detection and energy dump. In the analysis, necessary amount of copper to keep the maximum temperature of the conductor below a threshold value is calculated for cases of conduction cooled coils of dry windings. Based on the analysis, optimum conductor design is discussed to protect the coil from a quench reliably.

High-power-density fault-current limiting devices using superconducting YBa2Cu3O7 films and high-resistivity alloy shunt layers

Switching of superconducting thin-film resistive fault-current limiting devices with alloy shunt layers was studied. Au–Ag alloy thin films, whose room-temperature resistivity is about six times higher than that of pure gold, were sputter deposited on YBa2Cu3O7 films on sapphire substrates with high critical current density of Jc=3.05±0.05MA∕cm2. A small sample, 5mm wide and 40mm long, had the capacity of a rated current of 32Arms in normal operation and withstood a high voltage of 107Vrms for 0.1s after switching, resulting in a very high switching power density of ∼1.7kVA∕cm2, which is more than four times higher than conventional devices using gold shunt layers.

AC loss measurement of HTS coils with ferromagnetic disks

Manufacturing techniques for low AC loss high-T/sub c/ superconducting coils are necessary to realize high efficiency superconducting power equipments. High-T/sub c/ superconducting tape conductors have anisotropic magnetic field dependence on critical current and AC magnetization loss. A magnetic field component perpendicular to the tape surface degrades HTS coil performance. We numerically investigated a magnetic field adjusting method and AC loss reduction effects by attaching ferromagnetic materials to both ends of HTS coils. We also measured total AC loss of an HTS coil comprising 10 HTS double pancake coils by the boil-off method. Total AC loss of the coil was dominated by mechanical loss due to vibration and movement of conductors and pancake coils. In this paper, methods to reduce total AC loss of HTS coils are discussed.

Fundamental Characteristics of Superconducting Fault Current Limiter Using LC Resonance Circuit

A new type of fault current limiter (FCL) utilizing series LC resonance circuit composed of a superconducting coil and a capacitor is proposed. The superconducting coil is wound by Bi-2223/Ag HTS tape conductor. The new FCL can suppress the rapid increase of a fault current by its energy storing capacity. Both theoretical analysis and experiments are carried out. The experimental result shows the current limiting ability of this FCL. The obtained experimental result agrees well with the theoretical one

Numerical evaluation of AC loss in high temperature superconducting coil

An approximated method to estimate the electro-magnetic AC loss in high temperature superconducting coil was proposed. We applied this method to estimate the AC loss characteristics of the high temperature superconducting coil made by stacking pancake coils which are wound by Bi2223/Ag tape. The analytical AC losses of the HTS coil were compared with the measured AC losses before and after impregnation by epoxy resin obtained in the previous work by National Institute of Advanced Industrial Science and Technology. The analytically estimated electro-magnetic AC losses in the HTS coil were much smaller than the measured AC loss of the coil. The AC loss characteristics could not be explained by the method proposed in this paper. The main reason of this discrepancy was considered that the measured AC losses in the HTS coil contained large amount of the mechanical AC loss due to the AC vibration of the winding even if the HTS coil was impregnated.

Design and Test of Filter of High Gradient Magnetic Separation System for Trapping Immunoglobulin in Serum

Recently, affinity magnetic beads have been widely used in immunomagnetic cell sorting (IMCS) technology. Today, we can easily sort and analyze DNA and antibodies (immunoglobulin) using various types of affinity magnetic beads available in the market. The diameters of these affinity magnetic beads used in immunomagnetic cell sorting are limited to above approximately 1 mum because of the low magnetic fields induced by permanent magnets. Now, nano-sized affinity magnetic beads are strongly desired to achieve high resolutions. We have been studying and attempting to develop a high-gradient magnetic separation (HGMS) system that employs a superconducting magnet to induce a considerably higher magnetic field than that induced by a permanent magnet in order to trap smaller nano-sized affinity magnetic beads by a filter made of fine stainless steel wool. In this study, we constructed a prototype of a desktop-type HGMS system using a cryocooler-cooled LTS magnet and conducted preliminary experiments on trapping the nano-sized magnetic particles. Furthermore, we investigated the magnetic field distribution and magnetic force around a magnetic wire in the filter by means of a numerical simulation.

Stability Analysis of HTS Power Cable With Fault Currents

We numerically calculated the transient temperature distribution of flowing subcooled liquid nitrogen in a high-Tc superconducting (HTS) model cable when faults occur. The coolant and cable core temperatures were calculated by numerically solving the heat equation using the finite difference method. In the calculation, we assume that the heat transfer coefficient between the flowing subcooled liquid nitrogen and the cable core surface is described by the Dittus-Boelter correlation. The calculation results reveal that the coolant temperature increases even after the fault has been removed and that it continues increasing until fresh coolant arrives from the inlet. The calculated temperature profile of the coolant agrees well with measured data obtained by conducting over-current tests on a model HTS cable. Using our computational code, we also evaluated the maximum HTS cable lengths that ensure that the coolant remains in the liquid phase for certain fault currents for an HTS model cable.

Experimental study on AC loss reduction of HTS coils by use of ferromagnetic disks

Manufacturing techniques suitable for fabricating low AC loss high-temperature superconductor (HTS) coils are necessary to realize high-efficiency power equipment. Usually, the AC magnetization loss of HTS tape conductors is anisotropically dependent on the magnetic field, with a magnetic field perpendicular to the tape surface degrading HTS coil performance. Therefore, decreasing the magnetic field perpendicular to the tape surface is an efficient method of reducing the total AC loss of HTS coils. In a previous study, the possibility of AC loss reduction through the use of ferromagnetic materials was shown numerically, and the total AC loss of HTS coils with and without attached ferromagnetic disks was measured. However, no obvious differences in AC loss were observed because the total AC loss was dominated by mechanical loss. In this study, a low mechanical loss, 30 A, 90 mH HTS coil is fabricated by winding with stainless-steel tape and employing epoxy impregnation. A clear reduction in AC loss is then observed by attaching the ferromagnetic disks.