U.S. patent application number 10/607945 was filed with the patent office on 2004-12-30 for novel superconducting articles, and methods for forming and using same.
This patent application is currently assigned to SuperPower, Inc.. Invention is credited to Lee, Hee-Gyoun, Xie, Yi-Yuan.
Application Number | 20040266628 10/607945 |
Document ID | / |
Family ID | 33540432 |
Filed Date | 2004-12-30 |
United States Patent
Application |
20040266628 |
Kind Code |
A1 |
Lee, Hee-Gyoun ; et
al. |
December 30, 2004 |
Novel superconducting articles, and methods for forming and using
same
Abstract
A superconducting tape is disclosed, including a substrate, a
buffer layer overlying the substrate, a superconductor layer
overlying the buffer layer, and an electroplated stabilizer layer
overlying the superconductor layer. Also disclosed are components
incorporating superconducting tapes, methods for manufacturing
same, and methods for using same.
Inventors: |
Lee, Hee-Gyoun;
(Guilderland, NY) ; Xie, Yi-Yuan; (Guilderland,
NY) |
Correspondence
Address: |
TOLER & LARSON & ABEL L.L.P.
5000 PLAZA ON THE LAKE STE 265
AUSTIN
TX
78746
US
|
Assignee: |
SuperPower, Inc.
|
Family ID: |
33540432 |
Appl. No.: |
10/607945 |
Filed: |
June 27, 2003 |
Current U.S.
Class: |
505/238 ;
257/E39.018 |
Current CPC
Class: |
H01L 39/143 20130101;
H01L 39/247 20130101; Y10S 428/93 20130101 |
Class at
Publication: |
505/238 |
International
Class: |
B32B 001/00 |
Claims
1. A superconducting article, comprising: a substrate; a buffer
layer overlying the substrate; a superconductor layer overlying the
buffer layer; and an electroplated stabilizer layer overlying the
superconductor layer.
2. The superconducting article of claim 1, wherein the
electroplated stabilizer layer comprises a non-noble metal.
3. The superconducting article of claim 2, wherein the non-noble
metal comprises a material from the group consisting of copper,
aluminum, and alloys thereof.
4. The superconducting article of claim 3, wherein the non-noble
metal comprises copper.
5. The superconducting article of claim 1, wherein the
electroplated stabilizer layer consists essentially of a non-noble
metal.
6. The superconducting article of claim 1, wherein the buffer layer
comprises a biaxially crystal textured film having generally
aligned crystals both in-plane and out-of-plane of the film.
7. The superconducting article of claim 1, wherein the buffer layer
comprises a barrier film.
8. The superconducting article of claim 1, further comprising a
noble metal layer provided between the electroplated stabilizer
layer and the superconductor layer.
9. The superconducting article of claim 8, wherein the noble metal
layer comprises silver.
10. The superconducting article of claim 1, wherein the
superconductor layer comprises a high temperature superconductor
material, having a critical temperature T.sub.c not less than about
77.degree. K.
11. The superconducting article of claim 1, wherein the
superconductor material comprises REBa.sub.2Cu.sub.3O.sub.7-x,
wherein RE is a rare earth element.
12. The superconducting article of claim 11, wherein the
superconductor material comprises YBa.sub.2Cu.sub.3O.sub.7.
13. The superconducting article of claim 1, wherein the
electroplated stabilizer layer has a thickness within a range of
about 1 to 1000 microns.
14. The superconducting article of claim 1, wherein the
electroplated stabilizer layer has a thickness within a range of
about 10 to 200 microns.
15. The superconducting article of claim 1, wherein the article is
in the form of a superconducting tape.
16. The superconducting article of claim 15, wherein the substrate
has an aspect ratio of not less than 10.sup.3.
17. The superconducting article of claim 15, wherein the substrate
has an aspect ratio of not less than 10.sup.4.
18. The superconducting article of claim 15, wherein the substrate
includes first and second opposite surfaces, and the electroplated
stabilizer layer includes first and second electroplated stabilizer
layers respectively overlying the first and second opposite
surfaces of the substrate.
19. The superconducting article of claim 18, wherein the first and
second electroplated stabilizer layers extend so as to define first
and second side surfaces of the superconducting tape and
encapsulate the superconducting tape.
20. The superconducting article of claim 19, wherein the first and
second electroplated stabilizer layers form a convex contour along
at least a portion of the side surfaces of the superconducting
article.
21. The superconducting article of claim 15, wherein the
superconducting article has a dual-sided structure, the substrate
having first and second surfaces that are opposite each other, the
buffer layer includes first and second buffer layers that
respectively overlie the first and second surfaces of the
substrate, the superconductor layer includes first and second
superconductor layers overlying the first and second buffer layers
respectively, and the electroplated stabilizer layer includes first
and second electroplated stabilizer layers respectively overlying
the first and second superconductor layers.
22. The superconducting article of claim 1, wherein the
electroplated stabilizer layer is adhered without incorporation of
a bonding layer.
23. The superconducting article of claim 1, wherein the
electroplated stabilizer layer is adhered without incorporation of
a solder layer.
24. The superconducting article of claim 1, wherein the article is
a power cable, the power cable including a plurality of
superconductive tapes, each tape comprising said substrate, said
buffer layer, said superconductor layer, and said electroplated
stabilizer layer.
25. The superconducting article of claim 24, further comprising a
conduit for passage of coolant fluid.
26. The superconducting article of claim 25, wherein the
superconductive tapes are wrapped around the conduit.
27. The superconducting article of claim 24, wherein the power
cable comprises a power transmission cable.
28. (withdrawn) The superconducting article of claim 24, wherein
the power cable comprises a power distribution cable.
29. The superconducting article of claim 1, wherein the article is
a power transformer, the power transformer comprising a primary
winding and a secondary winding, wherein at least one of the
primary winding and secondary winding comprises a wound coil of
superconductive tape, the superconductive tape comprising said
substrate, said buffer layer, said superconductor layer, and said
electroplated stabilizer layer.
30. The superconducting article of claim 29, wherein the secondary
winding has a fewer number of windings than the primary winding,
for reducing voltage.
31. The superconducting article of claim 29, wherein the primary
winding has a fewer number of windings than the secondary winding,
for increasing voltage.
32. The superconducting article of claim 1, wherein the article is
a power generator, comprising a shaft coupled to a rotor comprising
electromagnets containing rotor coils, and a stator comprising a
conductive winding surrounding the rotor, wherein at least one of
the winding and the rotor coils comprises a superconductive tape
comprising said substrate, said buffer layer, said superconductor
layer, and said electroplated stabilizer layer.
33. The superconducting article of claim 1, wherein the article is
a power grid, the power grid comprising: a power generation station
comprising a power generator; a transmission substation comprising
a plurality of power transformers for receiving power from the
power generation station and stepping-up voltage for transmission;
a plurality of power transmission cables for transmitting power
from the transmission substation; a power substation for receiving
power from the power transmission cables, the power substation
comprising a plurality of power transformers for stepping-down
voltage for distribution; and a plurality of power distribution
cables for distributing power to end users, wherein at least one of
the power distribution cables, power transmission cables,
transformers of the power substation, transformers of the
transmission substation, and the power generator comprises a
plurality of superconductive tapes, each superconductive tape
comprising said substrate, said buffer layer, said superconductor
layer, and said electroplated stabilizer layer.
34. A method for forming a superconducting tape, comprising:
providing a substrate; depositing a buffer layer overlying the
substrate; depositing a superconductor layer overlying the buffer
layer; and electroplating a stabilizer layer overlying the
superconductor layer, the stabilizer layer being electrically
conductive and functioning as an electrical shunt to bypass
current.
35. The method of claim 34, wherein electroplating is carried out
by passing the superconducting tape through an electroplating
solution, wherein the tape is biased to form a cathode, an anode is
provided in the solution.
36. The method of claim 35, wherein the stabilizer layer comprises
a non-noble metal.
37. The method of claim 36, wherein the non-noble metal comprises
copper.
38. The method of claim 37, wherein the solution comprises copper
sulfate.
39. The method of claim 35, wherein the superconducting tape is
passed through the solution by a reel-to-reel process.
40. The method of claim 34, wherein electroplating is carried out
such that the stabilizer layer overlies one side of the
substrate.
41. The method of claim 34, wherein electroplating is carried out
such that the stabilizer layer overlies first and second opposite
sides of the substrate.
42. The method of claim 34, wherein electroplating is carried out
such that the stabilizer layer encapsulates the substrate, buffer
layer, and the superconductor layer.
43. A method of laying power cable, comprising: providing a coil of
power cable, the power cable comprising a plurality of
superconductive tapes, each tape comprising a substrate, a buffer
layer overlying the substrate, a superconductor layer overlying the
buffer layer, and an electroplated stabilizer layer overlying the
superconductor layer; and unwinding the coil while inserting the
power cable into a conduit, wherein the conduit is an underground
utility conduit.
Description
CROSS-REFERENCE TO RELATED APPLICATION(S)
BACKGROUND
[0001] 1. Field of the Invention
[0002] The present invention is generally directed to
superconducting or superconductor components, and in particular, a
novel superconducting tape, power components incorporating same,
and methods for utilizing and manufacturing same.
[0003] 2. Description of the Related Art
[0004] Superconductor materials have long been known and understood
by the technical community. Low-temperature (low-T.sub.c)
superconductors exhibiting superconductive properties at
temperatures requiring use of liquid helium (4.2K), have been known
since about 1911. However, it was not until somewhat recently that
oxide-based high-temperature (high-T.sub.c) superconductors have
been discovered. Around 1986, a first high-temperature
superconductor (HTS), having superconductive properties at a
temperature above that of liquid nitrogen (77K) was discovered,
namely YBa.sub.2Cu.sub.3O.sub.7-x (YBCO), followed by development
of additional materials over the past 15 years including
Bi.sub.2Sr.sub.2Ca.sub.2Cu.sub.3O.sub.10+y (BSCCO), and others. The
development of high-T.sub.c superconductors has brought potential,
economically feasible development of superconductor components
incorporating such materials, due partly to the cost of operating
such superconductors with liquid nitrogen, rather than the
comparatively more expensive cryogenic infrastructure based on
liquid helium.
[0005] Of the myriad of potential applications, the industry has
sought to develop use of such materials in the power industry,
including applications for power generation, transmission,
distribution, and storage. In this regard, it is estimated that the
native resistance of copper-based commercial power components is
responsible for quite significant losses in electricity, and
accordingly, the power industry stands to gain significant
efficiencies based upon utilization of high-temperature
superconductors in power components such as transmission and
distribution power cables, generators, transformers, and fault
current interrupters. In addition, other benefits of
high-temperature superconductors in the power industry include an
increase in one to two orders of magnitude of power-handling
capacity, significant reduction in the size (i.e., footprint) of
electric power equipment, reduced environmental impact, greater
safety, and increased capacity over conventional technology. While
such potential benefits of high-temperature superconductors remain
quite compelling, numerous technical challenges continue to exist
in the production and commercialization of high-temperature
superconductors on a large scale.
[0006] Among the many challenges associated with the
commercialization of high-temperature superconductors, many exist
around the fabrication of a superconducting tape that can be
utilized for formation of various power components. A first
generation of HTS tapes includes use of the above-mentioned BSCCO
high-temperature superconductor. This material is generally
provided in the form of discrete filaments, which are embedded in a
matrix of noble metal, typically silver. Although such conductors
may be made in extended lengths needed for implementation into the
power industry (such as on the order of kilometers), due to
materials and manufacturing costs, such tapes do not represent a
commercially feasible product.
[0007] Accordingly, a great deal of interest has been generated in
the so-called second-generation HTS tapes that have superior
commercial viability. These tapes typically rely on a layered
structure, generally including a flexible substrate that provides
mechanical support, at least one buffer layer overlying the
substrate, the buffer layer optionally containing multiple films,
an HTS layer overlying the buffer film, and an electrical
stabilizer layer overlying the superconductor layer, typically
formed of at least a noble metal. However, to date, numerous
engineering and manufacturing challenges remain prior to full
commercialization of such second generation-tapes.
[0008] Accordingly, in view of the foregoing, various needs
continue to exist in the art of superconductors, and in particular,
provision of commercially viable superconducting tapes, methods for
forming same, and power components utilizing such superconducting
tapes.
SUMMARY
[0009] According to a first aspect of the present invention, a
superconducting article is provided, which includes a substrate, a
buffer layer overlying the substrate, a superconductor layer
overlying the buffer layer, and an electroplated stabilizer layer
overlying the superconductor layer. According to a particular
feature, the stabilizer layer may be formed principally of
non-noble metals, such as copper, aluminum, and alloys and mixtures
thereof. A noble metal cap layer may be provided between the
stabilizer layer and the superconductor layer. The electroplated
stabilizer layer may overlie one of the two opposite major surfaces
of the substrate, both major surfaces, or may completely
encapsulate the substrate, buffer layer, and superconductor layer.
The article may be in the form of a relatively high aspect ratio
tape.
[0010] According to another aspect of the present invention, a
method for forming a superconducting tape is provided, which
includes providing a substrate, depositing a buffer layer overlying
the substrate, and depositing a superconductor layer overlying the
buffer layer. Further, an electroplating step is carried out to
deposit a stabilizer layer overlying the superconductor layer.
[0011] According to another aspect of the present invention, a
power cable is provided including a plurality of superconductive
tapes, the superconductive tapes being provided in accordance with
the first aspect of the present invention described above.
[0012] According to yet another aspect of the present invention, a
power transformer is provided including primary and secondary
windings, at least one of the windings including a wound coil of
superconductive tape provided in accordance with the first aspect
of the present invention.
[0013] According to yet another aspect of the present invention, a
power generator is provided including a shaft coupled to a rotor
that contains electromagnets comprising rotor coils, and a stator
comprising a conductive winding surrounding the rotor. The rotor
coils and/or the conductive winding include a superconductive tape
generally in accordance with the first aspect of the present
invention described above.
[0014] According to yet another aspect of the present invention a
power grid is provided, which includes multiple components for
generation, transmission and distribution of electrical power.
Namely, the power grid includes a power generation station
including a power generator, a transmission substation including a
plurality of power transformers for receiving power from the power
generation station and stepping-up voltage for transmission, and a
plurality of power transmission cables for transmitting power from
the transmission substation. Distribution of the power is provided
by utilization of a power substation for receiving power from the
power transmission cables, the power substation containing a
plurality of power transformers for stepping-down voltage for
distribution, and a plurality of power distribution cables for
distributing power to end users. According to a particular feature
of this aspect of the present invention, at least one of the power
grid elements described above includes a plurality of
superconductive tapes, provided in accordance with the first aspect
of the present invention described above.
[0015] Still further, another aspect of the present invention
provides a method for laying power cable, sometimes also referred
to generically as "pulling" cable. The method calls for providing a
coil of power cable, and unwinding the coil while inserting the
power cable into a conduit, wherein the conduit is an underground
utility conduit. The structure of the power cable is described
above, namely, includes a plurality of superconductive tapes in
accordance with the first aspect of the present invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] The present invention may be better understood, and its
numerous objects, features, and advantages made apparent to those
skilled in the art by referencing the accompanying drawings.
[0017] FIG. 1 illustrates an HTS conductive tape according to an
embodiment of the present invention.
[0018] FIG. 2 illustrates a cross-section of a HTS tape according
to another embodiment of the present invention in which the entire
superconductive tape is encapsulated by electroplated
stabilizer.
[0019] FIG. 3 a cross-section of a dual-sided HTS conductive tape
according to another embodiment of the present invention.
[0020] FIG. 4 illustrates an electroplating process according to an
embodiment of the present invention.
[0021] FIG. 5 illustrates the results of a current overloading
test.
[0022] FIG. 6 illustrates the results of testing conducted to
evaluate the effect of overloading on the critical current of the
HTS tape.
[0023] FIGS. 7 and 8 illustrate power cables incorporating
superconductive tapes.
[0024] FIG. 9 illustrates a power-transformer according to an
aspect of the present invention.
[0025] FIG. 10 illustrates a power generator according to an aspect
of the present invention
[0026] FIG. 11 illustrates a power grid according to another aspect
of the present invention.
[0027] The use of the same reference symbols in different drawings
indicates similar or identical items.
DETAILED DESCRIPTION
[0028] Turning to FIG. 1, the general layered structure of an HTS
conductor according to an embodiment of the present invention is
depicted. The HTS conductor includes a substrate 10, a buffer layer
12a overlying the substrate 10, an HTS layer 14a, followed by a
capping layer 16a, typically a noble metal layer, and a stabilizer
layer 18a, typically a non-noble metal.
[0029] The substrate 10 is generally metal-based, and typically, an
alloy of at least two metallic elements. Particularly suitable
substrate materials include nickel-based metal alloys such as the
known Inconel.RTM. group of alloys. The Inconel.RTM. alloys tend to
have desirable thermal, chemical and mechanical properties,
including coefficient of expansion, thermal conductivity, Curie
temperature, tensile strength, yield strength, and elongation.
These metals are generally commercially available in the form of
spooled tapes, particularly suitable for HTS tape fabrication,
which typically will utilize reel-to-reel tape handling.
[0030] The substrate 10 is typically in a tape-like configuration,
having a high aspect ratio. For example, the width of the tape is
generally on the order of about 0.4-10 cm, and the length of the
tape is typically at least about 100 m, most typically greater than
about 500 m. Indeed, embodiments of the present invention provide
for superconducting tapes that include substrate 10 having a length
on the order of 1 km or above. Accordingly, the substrate may have
an aspect ratio which is fairly high, on the order of not less than
10.sup.3, or even not less than 10.sup.4. Certain embodiments are
longer, having an aspect ratio of 10.sup.5 and higher. As used
herein, the term `aspect ratio` is used to denote the ratio of the
length of the substrate or tape to the next longest dimension, the
width of the substrate or tape.
[0031] In one embodiment, the substrate is treated so as to have
desirable surface properties for subsequent deposition of the
constituent layers of the HTS tape. For example, the surface may be
lightly polished to a desired flatness and surface roughness.
Additionally, the substrate may be treated to be biaxially textured
as is understood in the art, such as by the known RABiTS (roll
assisted biaxially textured substrate) technique.
[0032] Turning to the buffer layer 12a, the buffer layer may be a
single layer, or more commonly, be made up of several films. Most
typically, the buffer layer includes a biaxially textured film,
having a crystalline texture that is generally aligned along
crystal axes both in-plane and out-of-plane of the film. Such
biaxial texturing may be accomplished by IBAD. As is understood in
the art, IBAD is acronym that stands for ion beam assisted
deposition, a technique that may be advantageously utilized to form
a suitably textured buffer layer for subsequent formation of an HTS
layer having desirable crystallographic orientation for superior
superconducting properties. Magnesium oxide is a typical material
of choice for the IBAD film, and may be on the order or 50 to 500
Angstroms, such as 50 to 200 Angstroms. Generally, the IBAD film
has a rock-salt like crystal structure, as defined and described in
U.S. Pat. No. 6,190,752, incorporated herein by reference.
[0033] The buffer layer may include additional films, such as a
barrier film provided to directly contact and be placed in between
an IBAD film and the substrate. In this regard, the barrier film
may advantageously be formed of an oxide, such as yttria, and
functions to isolate the substrate from the IBAD film. A barrier
film may also be formed of non-oxides such as silicon nitride and
silicon carbide. Suitable techniques for deposition of a barrier
film include chemical vapor deposition and physical vapor
deposition including sputtering. Typical thicknesses of the barrier
film may be within a range of about 100-200 angstroms. Still
further, the buffer layer may also include an epitaxially grown
film, formed over the IBAD film. In this context, the epitaxially
grown film is effective to increase the thickness of the IBAD film,
and may desirably be made principally of the same material utilized
for the IBAD layer such as MgO.
[0034] In embodiments utilizing an MgO-based IBAD film and/or
epitaxial film, a lattice mismatch between the MgO material and the
material of the superconductor layer exists. Accordingly, the
buffer layer may further include another buffer film, this one in
particular implemented to reduce a mismatch in lattice constants
between the HTS layer and the underlying IBAD film and/or epitaxial
film. This buffer film may be formed of materials such as YSZ
(yttria-stabilized zirconia) strontium ruthenate, lanthanum
manganate, and generally, perovskite-structured ceramic materials.
The buffer film may be deposited by various physical vapor
deposition techniques.
[0035] While the foregoing has principally focused on
implementation of a biaxially textured film in the buffer stack
(layer) by a texturing process such as IBAD, alternatively, the
substrate surface itself may be biaxially textured. In this case,
the buffer layer is generally epitaxially grown on the textured
substrate so as to preserve biaxial texturing in the buffer layer.
One process for forming a biaxially textured substrate is the
process known in the art as RABiTS (roll assisted biaxially
textured substrates), generally understood in the art.
[0036] The high-temperature superconductor (HTS) layer 14a is
typically chosen from any of the high-temperature superconducting
materials that exhibit superconducting properties above the
temperature of liquid nitrogen, 77K. Such materials may include,
for example, YBa.sub.2Cu.sub.3O.sub.7-x,
Bi.sub.2Sr.sub.2Ca.sub.2Cu.sub.3O.sub.10+y,
Ti.sub.2Ba.sub.2Ca.sub.2Cu.sub.3O.sub.10+y, and
HgBa.sub.2Ca.sub.2Cu.sub.- 3O.sub.8+y. One class of materials
includes REBa.sub.2Cu.sub.3O.sub.7-x, wherein RE is a rare earth
element. Of the foregoing, YBa.sub.2Cu.sub.3O.sub.7-x, also
generally referred to as YBCO, may be advantageously utilized. The
HTS layer 14a may be formed by any one of various techniques,
including thick and thin film forming techniques. Preferably, a
thin film physical vapor deposition technique such as pulsed laser
deposition (PLD) can be used for a high deposition rates, or a
chemical vapor deposition technique can be used for lower cost and
larger surface area treatment. Typically, the HTS layer has a
thickness on the order of about 1 to about 30 microns, most
typically about 2 to about 20 microns, such as about 2 to about 10
microns, in order to get desirable amperage ratings associated with
the HTS layer 14a.
[0037] The capping layer 16a and the stabilizer layer 18a are
generally implemented for electrical stabilization, to aid in
prevention of HTS burnout in practical use. More particularly,
layers 16a and 18a aid in continued flow of electrical charges
along the HTS conductor in cases where cooling fails or the
critical current density is exceeded, and the HTS layer moves from
the superconducting state and becomes resistive. Typically, a noble
metal is utilized for capping layer 16a to prevent unwanted
interaction between the stabilizer layer(s) and the HTS layer 14a.
Typical noble metals include gold, silver, platinum, and palladium.
Silver is typically used due to its cost and general accessibility.
The capping layer 16a is typically made to be thick enough to
prevent unwanted diffusion of the components from the stabilizer
layer 18a into the HTS layer 14a, but is made to be generally thin
for cost reasons (raw material and processing costs). Typical
thicknesses of the capping layer 16a range within about 0.1 to
about 10.0 microns, such as 0.5 to about 5.0 microns. Various
techniques may be used for deposition of the capping layer 16a,
including physical vapor deposition, such as DC magnetron
sputtering.
[0038] According to a particular feature of an embodiment of the
present invention, a stabilizer layer 18a is incorporated, to
overlie the superconductor layer 14a, and in particular, overlie
and directly contact the capping layer 16a in the particular
embodiment shown in FIG. 1. The stabilizer layer 18a functions as a
protection/shunt layer to enhance stability against harsh
environmental conditions and superconductivity quench. The layer is
generally dense and thermally and electrically conductive, and
functions to bypass electrical current in case of failure in the
superconducting layer. Conventionally, such layers have been formed
by laminating a pre-formed copper strip onto the superconducting
tape, by using an intermediary bonding material such as a solder or
flux. Other techniques have focused on physical vapor deposition,
typically, sputtering. However, such application techniques are
costly, and not particularly economically feasible for large-scale
production operations. According to a particular feature of the
embodiment, the stabilizer layer 18 is formed by electroplating.
According to this technique, electroplating can be used to quickly
build-up a thick layer of material on the superconducting tape, and
it is a relatively low cost process that can effectively produce
dense layers of thermally and electrically conductive metals.
According to one feature, the stabilizer layer is deposited without
the use of or reliance upon and without the use of an intermediate
bonding layer, such as a solder layer (including fluxes) that have
a melting point less than about 300.degree. C.
[0039] Electroplating (also known as electrodeposition) is
generally performed by immersing the superconductive tape in a
solution containing ions of the metal to be deposited. The surface
of the tape is connected to an external power supply and current is
passed through the surface into the solution, causing a reaction of
metal ions (M.sup.z-) with electrons (e.sup.-) to form a metal
(M).
M.sup.z-+ze.sup.-=M
[0040] The capping layer 16a functions as a seed layer for
deposition of copper thereon. In the particular case of
electroplating of stabilizer metals, the superconductive tape is
generally immersed in a solution containing cupric ions, such as in
a copper sulfate solution. Electrical contact is made to the
capping layer 16a and current is passed such that the reaction
Cu.sup.2++2e.sup.-.fwdarw.Cu occurs at the surface of the capping
layer 16a. The capping layer 16a functions as the cathode in the
solution, such that the metal ions are reduced to Cu metal atoms
and deposited on the tape. On the other hand, a copper-containing
anode is placed in the solution, at which an oxidation reaction
occurs such that copper ions go into solution for reduction and
deposition at the cathode.
[0041] In the absence of any secondary reactions, the current
delivered to the conductive surface during electroplating is
directly proportional to the quantity of metal deposited (Faraday's
Law of Electrolysis). Using this relationship, the mass, and hence
thickness of the deposited material forming stabilizer layer 18a
can be readily controlled.
[0042] While the foregoing generally references copper, it is noted
that other metals, including aluminum, silver, gold, and other
thermally and electrically conductive metals may also be utilized.
However, it is generally desirable to utilize a non-noble metal to
reduce overall materials cost for forming the superconductive
tape.
[0043] While the foregoing description and FIG. 1 describe
electroplating to form a stabilizer layer 18a along one side of the
superconductive tape, it is also noted that the opposite, major
side of the superconductive tape may also be coated, and indeed,
the entirety of the structure can be coated so as to be
encapsulated. In this regard, attention is drawn to FIG. 2.
[0044] FIG. 2 is a cross-sectional diagram illustrating another
embodiment of the present invention, in which the entire
superconductive tape is encapsulated with first stabilizer layer
18a, second stabilizer layer 18b disposed on an opposite major
surface of the superconductive tape, the first and second
stabilizer layers 18a, 18b, joining together along the side
surfaces of the superconductive tape, forming generally convex side
portions or side bridges 20a and 20b. This particular structure is
desirable to further improve current flow and further protect the
HTS layer 14a, in the case of cryogenic failure, superconductivity
quench, etc. By essentially doubling the cross-sectional area of
the deposited stabilizer layer by forming first and second
stabilizer layers 18a and 18b, a marked improvement in
current-carrying capability is provided. Electrical continuity
between stabilizer layers 18a and 18b may be provided by the
lateral bridging portions 20a and 20b. In this regard, the lateral
bridging portions 20a and 20b may desirably have a positive radius
of curvature so as to form generally convex surfaces, which may
further reduce build up of electrical charge at high voltages that
HTS electric power devices will experience. Additionally, to the
extent that a suitably electrically conductive material is utilized
for the substrate 10, further current-carrying capability can be
provided by encapsulation as illustrated in FIG.2. That is, the
bridging portions extending laterally and defining side surfaces of
the tape may provide electrical connection to the substrate itself,
which can add to the current carrying capability of the coated
conductor (tape).
[0045] While not shown in FIG. 2, it may be generally desirable to
deposit a noble metal layer along the entirety of the
superconductive tape, particularly along the side surfaces of the
superconductive tape, to isolate the superconductor layer 14a from
the material of the bridging portions 20a and 20b, which may be a
non-noble metal such as copper or aluminum as described above.
[0046] FIG. 3 illustrates yet another embodiment of the present
invention. The embodiment is somewhat similar to that shown in FIG.
2, but essentially forms a double-sided structure, including first
and second buffer layers 12a and 12b, respectively overlying first
and second surfaces 11a and 11b of the substrate 10. Further, first
and second superconductor layers 14a and 14b are provided, along
with first and second capping layers 16a and 16b. This particular
structure provides an advantage of further current-carrying
capability by utilizing both sides of the substrate for coating of
the superconductor layers 14a and 14b.
[0047] FIG. 4 schematically illustrates an electroplating process
according to an embodiment of the present invention. Typically,
electroplating is carried out in a reel-to-reel process by feeding
a superconductive tape through an electroplating solution 27 by
feeding the tape from feed reel 32 and taking up the tape at
take-up reel 34. The tape is fed through a plurality of rollers 26.
The rollers may be negatively charged so as to impart a negative
charge along the capping layer(s) and/or the substrate for
electrodeposition of the metal ions provided in solution. The
embodiment shown in FIG. 4 shows two anodes 28 and 30 for
double-sided deposition, although a single anode 28 may be disposed
for single-sided electroplating. As discussed above, the
electroplating solution 27 generally contains metal ions of the
desired species for electrodeposition. In the particular case of
copper, the solution may be a copper sulfate solution containing
copper sulfate and sulfuric acid, for example. The anodes 28, 30
provide the desired feedstock metal for electrodeposition, and may
be simply formed of high-purity copper plates. It is noted that
while the rollers 26 may be electrically biased so as to bias the
superconductive tape, biasing may take place outside of the
solution bath, to curtail unwanted deposition of metal on the
rollers themselves.
[0048] A particular example was created utilizing the
electroplating technique described above. In particular, samples
were subjected to DC magnetron sputtering of silver to form 3
micron-thick capping layers. Those samples were placed in a
copper-sulfate solution and biased such that the capping layers
formed a cathode, the anode being a copper plate. Electroplating
was carried out to form a copper layer having a nominal thickness
of about 40 microns. Testing of the samples is described
hereinbelow.
[0049] Namely, a sample that is 1 cm wide, 4 cm long and with 1.7
micron thick YBCO HTS layer having a critical current I.sub.c of
about 111 A was subjected to a current load of 326 A,. The sample
was overloaded and voltage data was gathered as illustrated in FIG.
5. The voltage recorded was 44.4 mV at 326 A, which corresponds to
heat dissipation of 3.6 W/cm--lower than the critical heat flux
density in LN.sub.2 cooling condition 5-20 W/cm.sup.2. This means
that this coated conductor with 50 micron stabilizer may carry a
current higher than 326 A in LN.sub.2 without experiencing burning
out. Without the stabilizer, the estimated power dissipation is
higher than 62.5 KW/cm.sup.2 at 326 A. The foregoing indicates that
the electroplated stabilizer layer acted as a robust shunt layer to
protect the superconducting film from burning out during the
overloading event.
[0050] Subsequently, the sample was then subjected to a second
load, following the overloading event. As illustrated in FIG. 6,
the curves show the same I.sub.c of about 111 A before and after
overloading. The foregoing indicates that the HTS tape retained its
critical current even after the overloading.
[0051] In order to provide adequate current-carrying capability in
the stabilizer layer, typically the stabilizer layer has a
thickness within a range of about 1 to about 1,000 microns, most
typically within a range of about 10 to about 400 microns, such as
about 10 to about 200 microns. Particular embodiments had a nominal
thickness at about 40 microns and about 50 microns.
[0052] Moving away from the particular structure of the
superconducting tape, FIGS. 7 and 8 illustrate implementation of a
superconducting tape in a commercial power component, namely a
power cable. FIG. 7 illustrates several power cables 42 extending
through an underground conduit 40, which may be a plastic or steel
conduit. FIG. 7 also illustrates the ground 41 for clarity. As is
shown, several power cables may be run through the conduit 40.
[0053] Turning to FIG. 8, a particular structure of a power cable
is illustrated. In order to provide cooling to maintain the
superconductive power cable in a superconducting state, liquid
nitrogen is fed through the power cable through LN2 duct 44. One or
a plurality of HTS tapes 46 is/are provided so as to cover the duct
44. The tapes may be placed onto the duct 44 in a helical manner,
spiraling the tape about the duct 44. Further components include a
copper shield 48, a dielectric tape 50 for dielectric separation of
the components, a second HTS tape 52, a copper shield 54 having a
plurality of centering wires 56, a second, larger LN2 duct 58,
thermal insulation 60, provided to aid in maintaining a cryogenic
state, a corrugated steel pipe 62 for structural support, including
skid wires 64, and an outer enclosure 66.
[0054] FIG. 9 illustrates schematically a power transformer having
a central core 76 around which a primary winding 72 and a secondary
winding 74 are provided. It is noted that FIG. 9 is schematic in
nature, and the actual geometric configuration of the transformer
may vary as is well understood in the art. However, the transformer
includes the basic primary and secondary windings. In this regard,
in the embodiment shown in FIG. 9, the primary winding has a higher
number of coils than the secondary winding 74, representing a
step-down transformer that reduces voltage of an incoming power
signal. In reverse, provision of a fewer number of coils in the
primary winding relative to the secondary winding provides a
voltage step-up. In this regard, typically step-up transformers are
utilized in power transmission substations to increase voltage to
high voltages to reduce power losses over long distances, while
step-down transformers are integrated into distribution substations
for later stage distribution of power to end users. At least one of
and preferably both the primary and secondary windings comprise
superconductive tapes in accordance with the foregoing
description
[0055] Turning to FIG. 10, the basic structure of a generator is
provided. The generator includes a turbine 82 connected to a shaft
84 for rotatably driving a rotor 86. Rotor 86 includes
high-intensity electromagnets, which are formed of rotor coils that
form the desired electromagnetic field for power generation. The
turbine 82, and hence the shaft 84 and the rotor 86 are rotated by
action of a flowing fluid such as water in the case of a
hydroelectric power generator, or steam in the case of nuclear,
diesel, or coal-burning power generators. The generation of the
electromagnetic field generates power in the stator 88, which
comprises at least one conductive winding. According to a
particular feature of the embodiment, at least one of the rotor
coils and the stator winding comprises a superconductive tape in
accordance with embodiments described above. Typically, at least
the rotor coils include a superconductive tape, which is effective
to reduce hysteresis losses.
[0056] Turning to FIG. 11, a basic schematic of a power grid is
provided. Fundamentally, the power grid 110 includes a power plant
90 typically housing a plurality of power generators. The power
plant 90 is electrically connected and typically co-located with a
transmission substation 94. The transmission substation contains
generally a bank of step-up power transformers, which are utilized
to step-up voltage of the generated power. Typically, power is
generated at a voltage level on the order of thousands of volts,
and the transmission substation functions to step-up voltages are
on the order of 100,000 to 1,000,000 volts in order to reduce line
losses. Typical transmission distances are on the order of 50 to
1,000 miles, and power is carried along those distances by power
transmission cables 96. The power transmission cables 96 are routed
to a plurality of power substations 98 (only one shown in FIG. 10).
The power substations contain generally a bank of step-down power
transformers, to reduce the transmission level voltage from the
relatively high values to distribution voltages, typically less
than about 10,000 volts. A plurality of further power substations
may also be located in a grid-like fashion, provided in localized
areas for localized power distribution to end users. However, for
simplicity, only a single power substation is shown, noting that
downstream power substations may be provided in series. The
distribution level power is then transmitted along power
distribution cables 100 to end users 102, which include commercial
end users as well as residential end users. It is also noted that
individual transformers may be locally provided for individual or
groups of end users. According to a particular feature at least one
of the generators provided in the power plant 90, the transformers
and the transmission substation, the power transmission cable, the
transformers provided in the power substation, and the power
distribution cables contain superconductive tapes in accordance
with the present description.
[0057] While particular aspects of the present invention have been
described herein with particularity, it is well understood that
those of ordinary skill in the art may make modifications hereto
yet still be within the scope of the present claims.
* * * * *