Xie, Yi-yuan (22C Meadowbrook Ct, Guilderland, New York, 12084, US)
|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 nonnoble metal comprises a material from the group consisting of copper, aluminum, and alloys thereof.|
|4.||The superconducting article of claim 3, wherein the nonnoble metal comprises copper.|
|5.||The superconducting article of claim 1, wherein the electroplated stabilizer layer consists essentially of a nonnoble metal.|
|6.||The superconducting article of claim 1, wherein the buffer layer comprises a biaxially crystal textured film having generally aligned crystals both inplane and outofplane 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 Te not less than about 77 °K.|
|11.||The superconducting article of claim 1, wherein the superconductor material comprises REBa2Cu307 x, wherein RE is a rare earth element.|
|12.||The superconducting article of claim 11, wherein the superconductor material comprises YBazCu307.|
|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 103.|
|17.||The superconducting article of claim 15, wherein the substrate has an aspect ratio of not less than 104.|
|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 dualsided 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.||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 steppingup 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 steppingdown 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.|
|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 nonnoble metal.|
|37.||The method of claim 36, wherein the nonnoble 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 reeltoreel 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.|
BACKGROUND ART Superconductor materials have long been known and understood by the technical community. Low- temperature (low-Tc) 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-Te) 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 YBa2Cu307 x (YBCO), followed by development of additional materials over the past 15 years including Bi2Sr2Ca2Cu3Oio+y (BSCCO), and others. The development of high- Te 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.
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.
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.
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.
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.
DISCLOSURE OF INVENTION 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.
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.
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.
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.
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.
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 transmission9 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.
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 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.
FIG. 1 illustrates an HTS conductive tape according to an embodiment of the present invention.
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.
FIG. 3 a cross-section of a dual-sided HTS conductive tape according to another embodiment of the present invention.
FIG. 4 illustrates an electroplating process according to an embodiment of the present invention.
FIG. 5 illustrates the results of a current overloading test.
FIG. 6 illustrates the results of testing conducted to evaluate the effect of overloading on the critical current of the HTS tape.
FIGs. 7 and 8 illustrate power cables incorporating superconductive tapes.
FIG. 9 illustrates a power-transformer according to an aspect of the present invention.
FIG. 10 illustrates a power generator according to an aspect of the present invention
FIG. 11 illustrates a power grid according to another aspect of the present invention.
The use of the same reference symbols in different drawings indicates similar or identical items.
MODES FOR CARRYING OUT THE INVENTION 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.
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 group of alloys. The Inconel 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.
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 100m, most typically greater than about 500m. Indeed, embodiments of the present invention provide for superconducting tapes that include substrate 10 having a length on the order of km or above.
Accordingly, the substrate may have an aspect ratio which is fairly high, on the order of not less than 103, or even not less than 104. Certain embodiments are longer, having an aspect ratio of 105 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.
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.
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 Elm, 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 US Patent 6,190, 752, incorporated herein by reference.
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.
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.
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.
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, YBa2Cu307 x, Bi2Sr2Ca2Cu301o+y, Ti2Ba2Ca2Cu30lo+y, and HgBa2 Ca2Cu3 O8+y. One class of materials includes REBa2Cu307 x, wherein RE is a rare earth element. Of the foregoing, YBa2Cu307 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.
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.
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°C.
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) with electrons (e) to form a metal (M).
M'+ ze-= M 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 Cu2++2e~e 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.
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.
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.
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.
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).
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.
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 1 la and 1 lb 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.
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.
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.
Namely, a sample that is lcm wide, 4cm long and with 1.7 micron thick YBCO HTS layer having a critical current Ie 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 44.4mV at 326 A, which corresponds to heat dissipation of 3.6 W/cm2--lower than the critical heat flux density in LN2 cooling condition 5-20 W/cm2. This means that this coated conductor with 50 micron stabilizer may carry a current higher than 326A in LNZ without experiencing burning out. Without the stabilizer, the estimated power dissipation is higher than 62.5 KW/cm2 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.
Subsequently, the sample was then subjected to a second load, following the overloading event. As illustrated in FIG. 6, the curves show the same Ic of about 111 A before and after overloading. The foregoing indicates that the HTS tape retained its critical current even after the overloading.
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.
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.
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.
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.
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.
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.
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.