DE3822685A1 - Electrical conductor in wire or cable form, consisting of at least two strands in the form of a sheathed wire or a multifilament conductor or a coaxial cable based on a ceramic high-temperature superconductor - Google Patents

Abstract

Electrical conductor in wire or cable form, consisting of at least two strands (single conductors) in the form of a sheathed wire or a multifilament conductor or a coaxial cable based on a ceramic high-temperature superconductor of the type REBa2Cu3O6.5+y, where RE = rare earth metal, 0 < y < 1, or of the type (La,Ba,Sr)2CuO4, the superconductor body (1) being arranged as a core or as a hollow cylinder in a metal sheath (3) as a mechanical support and standby current (emergency power) conductor, in such a way that the superconductor body (1) clad with the metal sheath (3) is embedded in an insulating material (4), adjacent strands alternately carrying currents of opposite direction for the purpose of mutual, at least partial, cancellation of their magnetic self-fields. <IMAGE>

Description

Technical field

Technology of electrical superconductors. Most recently takes on the importance of materials which are superconducting Properties have more and more too. The discovery of new superconducting materials, especially of the type Rare earth / Ba / Cu / O, led to a considerable expansion of possible uses for superconductors, as these Substances already superconducting at temperatures above 50 K. will.

The invention relates to the further development and improvement of components made of a ceramic high-temperature superconductor in wire form, the needs of large-scale industrial production to be taken into account. In particular, it relates to an electrical conductor in wire or cable form, consisting of at least two individual conductors in the form of a coated wire or a multiple filament _conductor or a coaxial cable based on a ceramic high-temperature superconductor of the type SEBa₂Cu₃O _{6.5+ y} , where SE is a rare earth metal and 0 < y <1 means, or of the type (La, Ba, Sr) ₂CuO₄ and said superconductor body is arranged as a core or as a hollow cylinder in a metal jacket serving as a mechanical support and emergency power conductor.

State of the art

It is known to produce superconductors of the type SEBa₂Cu₃O _6.5-7 by providing and mixing powders of the starting materials and subsequent heat treatment. Y₂O₃ / CuO and BaO or BaCO₃ are generally used as starting materials. In the case of BaCO₃, the CO₂ must be driven out by an additional calcination process (see T. Kawai and M. Kanai, "Preparation of high-Te Y-Ba-Cu-O Superconductor", Jap. Jour. Of Applied Physics, Vol. 26, No. 5, May 1987, pp. L736-L737; Y. Yamada, N. Fukuschima, S. Nakayama and S. Murase, "Critical current density of wire type Y-Ba-Cu-Oxide superconductor", Jap. Jour. Of Applied Physics, Vol. 26, No. 5, May 1987, pp. 2865-2866). It is sintered in an oxygen-containing atmosphere (air), that is, under a certain O₂ partial pressure. In this way, the surrounding sintering atmosphere contributes to the achievement of a slightly over-stoichiometric oxygen content of the compound. It has also been proposed to carry out the sintering process in a silver tube. Silver is permeable to elemental oxygen, so that the latter gets into the core material by diffusion (cf. H. Yoshino, N. Fukushima, M. Niu, S. Nakayama, Y. Aamada and S. Murase, "Superconducting wire and coil with zero resistance state at 90 K and current density of 510 A / cm² at 77 K ", Toshiba Corporation, R + D. Center, Saiwai-Ku, Kawasaki-City 210, Japan).

Ceramic high-temperature superconductors have a low critical current density based on their general use is a hindrance. Weak magnetic fields are sufficient to remove superconductivity. This includes the through the current-carrying conductor itself induced magnetic fields.

Presentation of the invention

The invention has for its object to provide an electrical conductor in wire or cable form based on a ceramic high-temperature superconductor, which has the highest possible current carrying capacity and in which the harmful influence of the magnetic field on the critical current density j _crit suppressed as much as possible is. The conductor should be easy to manufacture in large lengths and with reproducible physical properties.

This object is achieved in that mentioned in the beginning Conductor of the superconductor body provided with a metal jacket is embedded in an insulating material and that neighboring individual conductors alternating with currents of opposite ones Direction is applied so that cancel out their own magnetic fields at least partially.

Way of carrying out the invention

The invention is illustrated by the following figures described exemplary embodiments.

It shows

Fig. 1 shows a schematic cross section through the elemental form of a conductor (basic structure),

Fig. 2 is a diagrammatic cross section through a requirement of several anti-parallel coaxial cable superconductors

Fig. 3 shows a schematic cross section through an arrangement of several antiparallel multifilament superconductors (hexagonal honeycomb arrangement).

In Fig. 1 a schematic cross-section through the elemental form of a conductor (basic structure). The figure refers to the state of the final shape, ie after rolling (possibly forging), round hammers, drawing etc. 1 is the core made of superconducting material. 2 is a diffusion barrier made of tantalum, niobium, vanadium, nickel etc. or an alloy of at least two of these elements. It serves to prevent the migration of oxygen from the core material (superconductor body 1 ). 3 is a metal sheath (Cu, Ag) which serves as a mechanical support for stabilizing the geometric shape of the conductor. In addition, it takes on the function of an electrical emergency power conductor (normal conductor). 4 is an electrical insulating body made of plastic or a suitable composite insulating material, which is stable at low temperatures and insensitive to aging.

Fig. 2 relates to a schematic cross section through an arrangement of several anti-parallel coaxial cable superconductors. All individual parts of the coaxial cable consist of a cylinder and therefore coaxially arranged hollow cylinders. 1 a is a first superconductor body with a cylindrical cross section. The direction of the current is positive at a certain point in time (for example in the case of an alternating current), that is, for example, it is directed into the drawing plane. 1 b is a second superconductor body with a hollow cylindrical cross section. The current direction is negative at a certain point in time, ie directed out of the plane of the drawing. 1 a ' is a 3rd superconductor body with a hollow cylindrical cross section. The current direction is positive at some point. 1 b ' is a 4th superconductor body with a hollow cylindrical cross section. The current direction is negative at some point. The series of alternately positively and negatively charged hollow cylindrical superconductor bodies type 1 a ' and 1 b' can be continued arbitrarily according to increasing diameters. 2 is a diffusion barrier, the composition and function of which is explained in FIG. 1. 3 is a metal jacket (emergency power conductor) in a hollow cylindrical design. It generally consists of Cu or Ag. 4 is a hollow cylindrical electrical insulating body made of plastic or a composite material. Due to the coaxial arrangement, the self-generated magnetic fields cancel each other out.

In Fig. 3 is a schematic cross section of multiple antiparallel multifilament superconductor represented by an arrangement. It is a hexagonal honeycomb arrangement. The cross-sectional centers of the superconductor bodies 1 (see FIG. 1) each sit in the corners of seamlessly abutting hexagons. In the drawing, progressing from top to bottom, there are alternately negative [from the drawing level, indicated with ⊙] and positive (into the drawing level, indicated with ®) rows of superconductor bodies 1 . A negative conductor is always surrounded by 3 positive, symmetrically arranged conductors and vice versa. The effects of the magnetic self-fields cancel each other out. 2 is a diffusion barrier, 3 is a metal jacket (see FIG. 1). 4 is the insulating material that fills the entire space between the individual filaments, ie the coated superconductor bodies, and gives the whole shape and stability.

Embodiment 1 (See Figs. 1 and 2)

A composition was chosen for the superconductor body 1 , which has the formula

YBa₂Cu₃O₇

corresponded.

For this purpose, a hollow cylindrical metal jacket 3 in the form of a copper tube of 5 mm inside diameter and 8 mm outside diameter (1.5 mm wall thickness) was provided on the inside with a 200 μm thick nickel layer as a diffusion barrier 2 . The copper pipe was now filled with a powder mixture which had the following quantitative ratio:

1 mole of Y₂O₃
3 moles of BaO
1 mole of BaO₂
6 moles of CuO

The whole thing was now stretched into a zinc tube of 8 mm inside diameter and 9 mm outside diameter (0.5 mm wall thickness). Another metal jacket 3 in the form of a copper tube of 11 mm inside diameter and 13 mm outside diameter (1.0 mm wall thickness) was provided on the inside with a 150 μm thick nickel layer as a diffusion barrier 2 . This latter copper tube was then pushed over the rod sealed with the zinc tube, centered and the space (radial width 0.85 mm) filled with the above powder mixture and pounded. In this way, the procedure was continued so that a sequence of alternating powder mixture / diffusion barrier 2 / metal jacket 3 / zinc tube with a closure as a metal jacket 3 of approximately 21 mm outside diameter was formed. By caliber rolling and pulling, the cross-section of the rod was now reduced to approximately ½, so that the diameter was still approximately 5 mm. Now the whole thing was brought to about 500 ° C and the zinc layers were melted out. The rest of the zinc was removed in a bath of dilute hydrochloric acid. The spaces previously removed from the zinc were then filled with electrically insulating quartz powder (insulating material 4 ) and sintered in a plant for hot isostatic pressing under an argon pressure of 200 bar at a temperature of 950 ° C. for 5 hours. Then the coaxial conductor thus produced was cooled to room temperature at a rate of 25 ° C / h. The superconductor bodies 1 a , 1 a ' , 1 b , 1 b' etc. were formed by the annealing treatment (reactive sintering).

A comparison with a compact superconductor of equivalent Conductor cross section gave the following picture:

The current carrying capacity of the compact rod was approx. 20 A, which corresponded to a critical current density of approx. 500 A / cm². The current carrying capacity of the multiple coaxial cable with antiparallel single conductors, on the other hand, was approx. 100 A, which corresponded to a critical current density of approx. 2500 A / cm².

Recent research shows that the strong magnetic field dependence is a limiting factor of the critical current. The material loses its superconducting property when the intrinsic magnetic field H of the current exceeds a critical value, which is typically 20 Oe. From this it follows that the smaller the radius R is, the greater the current density j _crit that the filament can carry, because the maximum self-field is

This is found experimentally. A similar consideration shows that thin films too Can transport higher current densities than thick films.

Embodiment 2 (see Figs. 1 and 2)

For the superconductor body 1 , a composition was chosen as in Example 1, that of the formula

YBa₂Cu₃O₇

corresponded. This time, powder of the superconducting substance produced by reactive sintering of an oxide powder mixture was used. A hollow cylindrical metal jacket 3 in the form of a silver tube of 5 mm inside diameter and 6 mm outside diameter (0.5 mm wall thickness) was provided on the inside with a 150 μm thick nickel layer as diffusion barrier 2 . The powder mentioned above was filled into this silver tube. Now a second silver tube of 8 mm inside diameter and 9 mm outside diameter (0.5 mm wall thickness), which was provided with a 150 µm thick nickel layer on the inside, was pushed over the first silver tube and centered. The space between the two silver tubes was filled with Al₂O₃ powder. Then the same procedure was repeated with a third and fourth, inside with nickel-coated silver tube with an intermediate layer of Al₂O₃ powder with increasing diameter and so on until a multi-layered round rod of 30 mm outer diameter was formed. The rod was first rolled down to a diameter of 6 mm by caliber rolling and the wire thus formed was drawn down to a final diameter of 1.5 mm in several operations with intermediate annealing. After the final shaping, the wound wire was brought into a hot isostatic pressing plant and sintered under a pressure of 500 bar in an oxygen atmosphere for 10 hours at a temperature of 900 ° C. and then cooled to room temperature at a rate of 20 ° C./h.

A comparison with a compact conductor of equivalent Cross section gave the following picture:

The critical current density of the compact wire resulted in the Value of about 500 A / cm², while the coaxial cable with anti-parallel Individual conductors have a capacity of approx. 2200 A / cm² exhibited.

Embodiment 3 (see Figs. 1 and 2)

The superconductor body 1 consisted, as in Example 2, of pre-sintered powder of the substance YBa₂Cu₃O₇. First, analogously to Example 2, a hollow cylindrical metal jacket 3 , provided on the inside with a nickel layer 50 μm thick as a diffusion barrier 2 , was filled with powder of superconducting substance in the form of a silver tube with an outside diameter of 4 mm and an inside diameter of 3.2 mm (wall thickness 0.4 mm). Now a 20 µm thick layer of SiO₂ was applied as an insulating jacket 4 by sputtering on the silver tube. Then a 50 µm thick layer of superconductor body 1 was applied by the same method, followed by a nickel layer 20 µm thick as a diffusion barrier 2 and a 100 µm thick silver layer as a metal jacket 3 and a 20 µm thick layer of SiO₂ as an insulating jacket 4 . This process of applying said layer sequence was repeated about 50 more times until a rod of about 24 mm in diameter was formed. The bar was reduced to a diameter of 4 mm by caliber rolling and then pulling. Then the finished coaxial conductor was annealed for 10 h at a temperature of 920 ° C under a pressure of 1000 bar in an oxygen atmosphere and slowly (25 ° C / h) cooled to room temperature.

In the experiment, neighboring hollow cylindrical superconductor layers were used of the coaxial conductor alternately with positive ones and negative partial flows. there has been a critical current density of 3000 A / cm² determined.

Embodiment 4 (see Figs. 1 and 3)

For the substance of the superconductor body 1 , the following finished, reactive sintered and ground superconducting substance was selected.

YBa₂Cu₃O _{7+ x} with -0.5 < x <0.1

In the present case, x was approximately 0.05.

A metal jacket 3 in the form of a copper tube of 5 mm outside diameter and 4 mm inside diameter (0.5 mm wall thickness) provided on the inside with a 60 μm thick nickel layer as diffusion barrier 2 was filled with powder of superconducting substance. 6 filled copper tubes were placed with a center distance of 8 mm aligned in parallel in a thin-walled copper tube of 24 mm outside diameter and 21 mm inside diameter (1.5 mm wall thickness) that the centers of their cross sections formed an equilateral hexagon. The space was now filled with Al₂O₃ powder as insulating material 4 and pounded. The rod produced in this way was reduced to a wire of approximately 1.2 mm in diameter by caliber rolling and drawing. A large number of such wires was bundled into the thin spaces with Al₂O₃ powder in a thin-walled copper tube of about 15 mm outside diameter and the whole was reduced by caliber rolling and pulling to a final diameter of about 1.5 mm. The individual filament diameter was still approx. 30 µm.

Adjacent filaments of the multiple filament conductor were tested alternating with positive and negative partial flows acted upon. The critical current density was approx. 2600 A / cm².

The invention is not restricted to the exemplary embodiments. Basically, the electrical conductor in wire or cable form consists of at least two individual conductors in the form of a coated wire or a multiple filament _conductor or a coaxial cable based on a ceramic high-temperature superconductor of the type SEBa₂Cu₃O _{6.5+ y} , whereby SE is a rare earth metal and 0 < y <1 means, or of the type (La, Ba, Sr) ₂CuO₄ and said superconductor body is arranged as a core or as a hollow cylinder in a metal jacket serving as a mechanical support and emergency current conductor, the superconductor body provided with a metal jacket being embedded in an insulating jacket and in that adjacent individual conductors are alternately acted upon by currents of opposite directions, so that their own magnetic fields cancel out at least partially.

The individual conductors are advantageously in the form of multiple filament conductors in the form of a hexagonal honeycomb arrangement with constant distances between the individual superconductor bodies present and in a common body made of insulating material embedded in such a way that the magnetic self-fields completely cancel out in their entirety.

In another arrangement, the individual conductors are in the form of multiple coaxial cables in the form of nested cylindrical and hollow cylindrical superconductor body, wherein two adjacent superconductor bodies each with one coaxial Hollow cylinders made of insulating material are separated. Between Metal jacket and superconductor body is advantageous a diffusion barrier for oxygen is arranged.

The advantage of the invention is that it is unshielded wire or cable-shaped high-temperature superconductors critical critical current density increased by a factor of 4. Also the current carrying capacity in the case of AC operation is significantly increased by the magnetic shielding.

Claims (4)

1. Electrical conductor in wire or cable form, consisting of at least two individual conductors in the form of a coated wire or a multiple filament conductor or a coaxial cable based on a ceramic high-temperature superconductor of the type SEBa₂Cu₃O _{, 5 + y} , where SE is a rare earth metal and 0 < y <1 means, or of the type (La, Ba, Sr) ₂CuO₄ and said superconductor body ( 1 ) is arranged as a core or as a hollow cylinder in a metal jacket ( 3 ) serving as a mechanical support and emergency power conductor, characterized in that the one with a Metal jacket ( 3 ) provided superconductor body ( 1 ) is embedded in an insulating material ( 4 ) and that adjacent individual conductors are alternately acted upon by currents of opposite directions, so that their magnetic fields are at least partially canceled. 2. Electrical conductor according to claim 1, characterized in that the individual conductors are present as multiple filament conductors in the form of a hexagonal honeycomb arrangement with constant distances between the individual superconductor bodies ( 1 ) and are embedded in a common body made of insulating material ( 4 ) in such a way that completely cancel out the magnetic fields in their entirety. 3. Electrical conductor according to claim 1, characterized in that the individual conductors are designed as multiple coaxial cables in the form of nested cylindrical and hollow cylindrical superconductor bodies ( 1 ), two adjacent superconductor bodies ( 1 ) each having a coaxial hollow cylinder made of insulating material ( 4 ) are separated. 4. Electrical conductor according to claim 1, characterized in that a diffusion barrier ( 2 ) for oxygen is arranged between the superconductor body ( 1 ) and the metal jacket.