Electricity: conductors and insulators – Conduits – cables or conductors – Superconductors
Reexamination Certificate
1998-11-09
2001-08-07
Paladini, Albert W. (Department: 2841)
Electricity: conductors and insulators
Conduits, cables or conductors
Superconductors
C505S230000, C505S231000, C505S431000, C505S887000
Reexamination Certificate
active
06271474
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to techniques for manufacturing stranded wires and cable conductors using oxide superconductor, and more particularly, to techniques for providing an electrically insulating material suitable for the step of sintering oxide superconductor, and providing a stranded wire and a cable conductor which have high critical current, using such an electrically insulating material.
2. Description of the Background Art
Since the oxide superconducting wire exhibits superconductivity at liquid nitrogen temperature, its application to superconducting cables and the like has been expected and its development has been ongoing. Since a wire having a bismuth-based 2223-phase oxide superconductor sheathed with silver in particular can be readily formed long, and a relatively high critical current density (Jc) results, the research and development is proceeding.
When an oxide superconducting wire is directed to alternating current (ac) application, a problem of ac losses is encountered. Particularly when such a wire is applied to a power cable, a loss by a self-magnetic field is problematic. It is known that the loss by self-magnetic field is effectively reduced by employing the structure in which wires that form the power cable are translocated. Translocation of the wires may be achieved by twining the wires. In the process of twining the wires, however, great bending strain is loaded upon the wires, and therefore it has been quite difficult to twine the wires having relatively fragile oxide superconductor, without reducing the superconducting property. In order to obtain significant effects by twining the wires, it is also important to provide the wires with electrical insulation. In a stranded wire using a metal-based superconductor, for example, the strands are coated with enamel. In the field of Nb
3
Sn application, glass is used as an insulating material. When a Nb
3
Sn superconducting coil is manufactured by the wind-and-react process, for example, wires coated with glass are wound into a coil and heat-treated.
The cable conductor in which tape-shaped silver-sheathed bismuth-based superconducting wires are spirally wound on a former in layers is generally known. Such a structure, however, can easily generate current drift.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a technique for manufacturing a stranded wire and a cable conductor having good superconducting property, using an oxide superconducting wire.
Another object of the present invention is to find a preferable electrically insulating material and to provide an oxide superconducting stranded wire and an oxide superconducting cable conductor using such a material.
Yet another object of the present invention is to provide an oxide superconducting stranded wire and an oxide superconducting cable conductor having good superconducting property and reduced ac losses.
A still further object of the present invention is to provide a structure with reduced ac losses in an oxide superconducting cable conductor.
Provided according to the present invention is a method of manufacturing a stranded wire using wires comprising an oxide superconducting material and a matrix covering the material and consisting essentially of silver or a silver alloy. The method includes the steps of applying a paint containing, as an essential component, boron nitride or a compound which thermally decomposes at a temperature equal to or lower than the temperature necessary for sintering the oxide superconducting material and generates an electrically insulating ceramics onto the surface of the matrix of the wire comprising the oxide superconducting material and the matrix covering the material and consisting essentially of silver or a silver alloy, baking the paint at a temperature equal to or lower than the temperature necessary for sintering the oxide superconducting material, preparing a plurality of such wires having the baked paint, twining the obtained plurality of wires, and heating the resulting stranded wire up to the temperature necessary for sintering the oxide superconducting material.
In the manufacturing method according to the invention, a paint containing an organometallic polymer such as a silicon-based organometallic polymer as a main component, a paint containing aluminum phosphate as a main component or the like may be applied to the wires. The shape of a cross section perpendicular to the longitudinal direction of the wires to form the stranded wire is preferably a circle or a polygon substantially in rotation symmetry. In the manufacturing method according to the present invention, the oxide superconducting material inside is preferably densified by subjecting the wires to a plastic working before applying the paint. Furthermore, in the manufacturing method according to the invention, after twining the wires, the resulting stranded wire may be shaped to have a sectoral cross section. Alternatively, after twining the wires, the resulting stranded wire may be shaped into a flat form. Subsequently, the shaped stranded wire is heated up to the temperature necessary for sintering the oxide superconducting material. The sintering after the shaping reduces or cancels the influence at the time of the shaping, and results in a shaped stranded wire having a high critical current and a high critical current density. The shaped stranded wire is useful in forming a more compact cable conductor.
According to the invention, a method of manufacturing a superconducting cable conductor which includes the step of winding a plurality of the stranded wires obtained by the above manufacturing method on a cylindrical or spiral former is provided.
According to the invention, coated wires which can be used for manufacturing an oxide superconducting stranded wire is provided. The coated wire includes a filament portion consisting essentially of an oxide superconducting material, a matrix covering the filament portion and consisting essentially of silver or a silver alloy, and a coating layer produced by baking at 200° C. to 800° C. a paint containing, as a main component, boron nitride or a compound which thermally decomposes at a temperature equal to or lower than the temperature necessary for sintering the oxide superconducting material to generate an electrically insulating ceramics.
In the coated wire according to the invention, the coating layer may be composed of a material produced by baking an organometallic polymer such as a silicon-based organometallic polymer at a temperature in the range from 200° C. to 800° C. The coating layer may also be composed of a material produced by baking aluminum phosphate at a temperature in the range from 500° C. to 800° C.
According to the invention, an oxide superconducting stranded wire produced by twining a plurality of the above-described coated wires and subjecting the twined wires to a heat-treatment necessary for sintering the oxide superconducting material is provided. According to the present invention, an oxide superconducting stranded wire produced by twining a plurality of the coated wires described above, shaping a resulting stranded wire to have a sectoral cross section or into a flat form, and performing a heat-treatment necessary for sintering the oxide superconducting material is provided. In these stranded wires, the strand includes a filament consisting essentially of an oxide superconductor, a stabilizing matrix covering the filament and consisting essentially of silver or a silver alloy, and an electrically insulating ceramic film covering the stabilizing matrix. The electrically insulating ceramics film can have a dense structure and a substantially even thickness along the longitudinal direction of the wire. The strand is preferably a multifilamentary wire having a plurality of filaments. A cross section of the strand is preferably a circle, an ellipse or a substantially regular polygon. According to the present invention, an oxide superconducting cable conductor produced by winding a pluralit
Fujikami Jun
Hahakura Shuji
Honjo Shoichi
Ishii Hideo
Iwata Yoshihiro
Foley & Lardner
Paladini Albert W.
Sumitomo Electric Industries Ltd.
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