UNDERWATER POWER CABLE COMPRISING NANOPARTICLES

RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No. 60/833,196, filed on July 25, 2006 and U.S. Provisional Application No.60/835,759, filed on August 4, 2006. The entire teachings of the above apρlication(s) are incorporated herein by reference.

BACKGROUND

Power cables for moveable underwater power generating turbines must be capable of carrying high levels of electrical power, and at the same time, should be flexible enough to allow repositioning of the turbines. In addition, the power cable must withstand the exposed underwater environment.

SUMMARY

The present invention provides power cable that is suitable for use with underwater turbines. The present invention provides a flexible underwater power cable including a generally flat flexible insulative jacket of polymeric material. At least one flexible electrical conductor is positioned within the insulative jacket. Insulative nanoparticles can be dispersed within the polymeric material of the insulative jacket. In particular embodiments, the insulative nanoparticles can include material which enhances the electrical breakdown strength of the polymeric material of the insulative jacket, can include material that increases dielectric constant £ of the polymeric material of the insulative jacket by about € > 7, can include a material that increases mechanical abrasion resistance of the polymeric material of the insulative jacket, can include resonant particles, and/or can provide visual identifiers to the insulative jacket. The insulative nanoparticles can comprise spherical Si. The at least one electrical conductor can include a series of flat conductive ribbons lying on one another. A lubricant can surround the at least one electrical conductor and

facilitate sliding of the flat conductive ribbons of the at least one electrical conductor. Nonconductive flexible reinforcement members can be positioned within the insulative jacket. The flexible reinforcement members can include a series of carbon fibers and can be in bundles. At least two electrical conductors and at least two carbon fiber bundles can be positioned side by side in an alternating arrangement. The insulative jacket can be extruded over the electrical conductors and carbon fiber bundles in an encapsulating manner.

The present invention also provides a flexible underwater power cable having a generally flat flexible insulative jacket of polymeric material. At least two flexible electrical conductors means for conducting electricity can be positioned within the insulative jacket, each including a series of flat conductive ribbon means lying on one another. At least two flexible reinforcement member means for reinforcing the cable can be included. The electrical conductor means and the reinforcement member means can be positioned laterally spaced apart from each other generally along a laterally bending axis. Insulative nanoparticle means can be dispersed within the polymeric material of the insulative jacket.

The present invention also provides an underwater power generation apparatus including an underwater turbine for generating electrical power. A flexible underwater power cable can be connected to the underwater turbine for conveying power generated by the underwater turbine. The cable can include a generally flat flexible insulative jacket of polymeric material. At least one flexible electrical conductor is positioned within the insulative jacket. Insulative nanoparticles can be dispersed within the polymeric material of the insulative jacket. The present invention also provides a method of forming an underwater power cable including forming a flat flexible insulative jacket of polymeric material. Insulative nanoparticles can be dispersed within the polymeric material. Flexible electrical conductors can be positioned within the insulative jacket.

In particular embodiments, the insulative nanoparticles can include a material that enhances the electrical breakdown strength of the polymeric material of the insulative jacket, can include a material that increases dielectric constant €. of the polymeric material of the insulative jacket by about £ > 7, can include a material that increases mechanical abrasion resistance of the polymeric material of the insulative

jacket, can include resonant particles, and/or can provide visual identifiers to the insulative jacket. The irisulative nanoparticles can include spherical Si. The at least one electrical conductor can include a series of flat conductive ribbons lying on one another. The at least one electrical conductor can be surrounded with a lubricant that facilitates sliding of the flat conductive ribbons of the at least one electrical conductor. Nonconductive flexible reinforcement members can be positioned within the insulative jacket. The flexible reinforcement members can be formed from a series of carbon fibers and can be arranged in bundles. At least two electrical conductors and at least two carbon fiber bundles can be positioned side by side in an alternating arrangement. The insulative jacket can be extruded over the electrical conductors and carbon fiber bundles in an encapsulating manner. The cable can be cut from a cable assembly in which multiple individual cables are cut from the cable assembly at selected laterally spaced parallel locations. The cable assembly can be formed from a flexible bottom sheet and a flexible top sheet which are combined with a series of the flexible electrical conductors. A series of reinforcement members can be combined within the cable assembly. The cable assembly can be at least 10 meters wide and at least 100 individual cables can be cut from the cable assembly.

The present invention also provides a method of conveying power from an underwater power generation apparatus including generating electrical power with an underwater turbine. A flexible underwater power cable can be connected to the underwater turbine to convey the electrical power from the underwater turbine. The cable can include a generally flat flexible insulative jacket of polymeric material. At least one flexible electrical conductor is positioned within the insulative jacket. Insulative nanoparticles can be dispersed within the polymeric material of the insulative jacket.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing will be apparent from the following more particular description of example embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts

throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating embodiments of the present invention.

FIG. 1 is a cross sectional view of an embodiment of a power cable in the present invention. FIG. 2 is a perspective view of the power cable of FIG. 1 connected to a submersible underwater turbine.

FIG. 3 is a schematic drawing of a method of manufacturing the power cable of FIG. 1.

FIG.4 is a schematic drawing of two extruded polymeric layers being combined.

DETAILED DESCRIPTION

Referring to FIGs. 1 and 2, cable 10 can be suitable for underwater use, for example, for conveying electrical power generated by an underwater ox submersible turbine 9. Cable 10 is elongate and can have a generally flat rectangular cross section with a central lateral axis, a large width W ₅ and a small thickness or height H. This generally flat shape allows cable 10 to bend in a flexible manner along the lateral axis X, and can be bent into a helix 10a to provide slack for underwater turbine 9 to allow movement of the turbine 9. Since water currents can shift position, the underwater turbine 9 can be periodically moved to be repositioned in the optimum position of a water current for generating power. The cable 10 can be long enough to reach desired locations, for example, on land, and miles away.

The cable 10 can have a water tight flexible electrically insulative jacket, cover or layer 12 surrounding longitudinally extending parallel electrical conductors 18, and electrically insulating the electrical conductors 18 from each other and from the surrounding environment. The insulative jacket 12 can be formed of flexible polymeric material and can have a first or bottom half portion 12a, and a second or top half portion 12b, which can be sealed together to surround, encase or encapsulate the conductors 18. The cable 10 can be strengthened by flexible reinforcement members 16 extending longitudinally along the cable 10, which can include a series of fibers 16a. The reinforcement members 16 can be formed, for example, from fiber materials such as bundles of carbon fibers. The reinforcement members 16 can

have a rectangular cross section, or can have other suitable cross sections, for example round. The reinforcement members 16 can be spaced and positioned on each side of a conductor 18, in parallel manner, and can also separate adjacent conductors 18 from each other. Additional components can be included for example, one or more optical or signal transmitting cables 15. FIG. 1 depicts cable 10 having three conductors 18 and four reinforcement members 16. It is understood that the number of conductors 18 and reinforcement members 16 can be greater or less, varying depending upon the situation at hand. The conductors 18 and reinforcement members 16 can be positioned in parallel manner laterally side by side along the lateral axis X which can also serve as a bending axis for cable 10. The bottom half portion 12a and/or the top half portion 12b can be contoured, or include grooves or indentations to facilitate the positioning of the conductors 18, reinforcement members 16, and cable 15.

Each conductor 18 can have a generally rectangular cross section and can include a series of flat parallel conductor ribbons or strips 18a which lie or are positioned on top of each other, with the flat surfaces against or adjacent to each other in a stack or an assembly. The flat conductor ribbons 18a can be oriented so that the flat surfaces of the conductor ribbons 18a are parallel to the plane of axis X. This can allow or facilitate bending of the conductors 18 along axis X. In addition, each conductor 18 can include a lubricant 20 such as an insulating lubricant surrounding the conductor 18, and can surround each conductor ribbon 18a. This can allow or facilitate sliding of the conductor ribbons 18a relative to each other and the insulative jacket 12 during bending along axis X. The lubricant 20 can be, for example, highly insulating transformer oil or grease, and can be encapsulated around the conductors 18 by the insulative jacket 12. The insulating oil or grease lubricant 20 can disable or prevent corona discharges from forming between and at the edges of the conductor ribbons 18 a.

The conductor ribbons 18a can be formed of ribbons of conductive metal, for example, aluminum. In other embodiments, other suitable materials can be used, including copper, etc. The flat geometry of the cable 10 provides an increased heat transfer surface area in comparison to round cables, for dissipating heat generated in the conductors 18 by electrical resistance. In addition, the flat geometry of the cable

10 positions opposite sides of the conductors 18 close to opposite flat surfaces of the cable 10, for efficient heat dissipation on opposite sides of the cable 10. When the cable 10 is submersed in water, the surrounding water can also act as a coolant.

By employing flexible polymeric material for the insulative jacket 12, and positioning the parallel conductors 18, reinforcement members 16 and signal transmitting cable 15 side by side along the plane of the lateral axis X, the cable 10 can be flexible and bend about the axis X. In addition, when employing aluminum ribbons for the conductors 18, carbon fibers for the reinforcement members 16, and polymeric material for the insulative jacket 12, the cable 10 can be light weight, allowing the cable to be suitable to be connected to a moveable buoyant underwater turbine 9, including those disclosed in U.S. Patent Application No. 11/709,308, filed February 21, 2007, the contents of which are incorporated herein by reference in its entirety.

The insulative jacket 12 can include nanoparticles 14 dispersed within the polymeric material to enhance or enrich properties of the polymeric material. The nanoparticles can be highly dielectric and can improve the insulative properties and electrical breakdown strength of the polymeric material. This can allow high levels of power to be carried by the conductors 18. For example, cable 10 can be employed to convey 500 MW. Also, by laterally spacing the conductors 18 from each other along axis X, the conductors 18 can spaced apart from each other in parallel manner the appropriate distance and separated by insulating polymeric material to carry high power levels. The nanoparticles 14 can in some embodiments, increase the dielectric constant £ of the polymeric material by several or more times, for example, £ > 7. The nanoparticles 14 can also increase the mechanical abrasion resistance of the insulative jacket 12. If desired, the nanoparticles 14 can add color or fluorescence to the visual appearance of the cable 10. The nanoparticles 14 can be resonant and can be stimulated by an appropriate frequency, to aid finding and/or identifying particular cables 10. In one embodiment, the nanoparticles 14 can be spherical silicon (Si) particles and can have a size of about 25μm. In other embodiments, the nanoparticles 14 can be 75-100 μm. The nanoparticles 14 can also include particles having a core of silicon dioxide, polymer or glass, with an outer cover or coating of zirconium nitride, hafnium nitride, or titanium nitride. In

addition, different selected materials or combinations can be chosen to obtain the desired properties.

FIG. 3 depicts a method of manufacturing cable 10. A wide polymeric base sheet 34 formed by an extruder 32 can be combined at station 36 with a series of components 36a across the width of the base sheet 34 to form assembly 40. A slitting station 38 can then cut the width of the assembly 40 into individual cables 10 in parallel. The base sheet 34 can be extruded from polymeric material containing the desired nanoparticles 14. In some embodiments, the base sheet 34 can be previously formed and unrolled from an unwind stand. The desired components 36a can include the conductors 18, the reinforcement members 16, and any signal transmitting cables 15. The desired components 36a can also include a top sheet 34 of polymeric material. The lubricant 20 can be injected or applied at station 36. The base sheet 34 can be combined with the desired components 36a, including the top sheet 34, at station 36 (FIG. 4) while the sheets 34 are in a molten state. The station 36 can include a combining apparatus 42 which can include combining rollers. Alternatively, if the sheets 34 are preformed, the combining apparatus 42 can include a mechanical, ultrasonic, or heat sealer for combining the sheets 34 together. The sheets 34 can be formed with grooves indentations, or otherwise contoured for accepting the conductors 18, reinforcement members 16, and signal transmitting cables 15, as well as to mate with each other in a desired fashion.

The slitting station 38 can include suitable slitting devices, for example, mechanical slitting blades, rotary dies, ultrasonic slitters, etc. The sheets 34 can be formed with longitudinal parallel indentations 44 having reduced thickness, or the indentations 44 can be formed at station 36. The longitudinal indentations 44 can provide the assembly 40 with lines of reduced cross section, thereby allowing the slitting station 38 to cut or slit the assembly 40 more easily along the longitudinal indentations 44, to obtain the individual cables 10. If the sheets 34 are still soft from being extruded, longitudinal indentations 44 might be unnecessary. In addition, heaters and/or heated slitting blades can be employed if desired.

In some embodiments, the insulative jacket 12 can be made of ethylene propylene rubber (EPR). Alternatively, other suitable materials can be employed for

the insulative jacket 12. If desired, the insulative jacket 12 can also include fibers or fibrous material, other than or in addition to reinforcement members 16. The conductors 18 can have a rectangular or square cross section with a width and height of about 25mm, and can be formed of about 250 conductor ribbons 18a. The conductor ribbons 18a can have a thickness of about 0.1 mm and a width of about 25mm. The reinforcement members 16 can have a width of about 5mm, and can include about 25 fibers 16a having a diameter of 0. lmm. The conductors 18 can be spaced apart from each other by a distance of about 100mm, with the reinforcement members 16 being a distance of about 50mm from each conductor 18. The assembly 40 can be 10 meters wide or greater, for example, 12 meters wide. Each cable 10 that is cut can be about 10 cm wide (about 4 inches). As a result, for an assembly 40 that is 10 meters wide, 100 cables 10 can be cut across the width, and 120 cables 10 can be cut from an assembly 40 that is 12 meters wide. It is understood that the width of assembly 40 and cable 10, as well as the dimensions, shape, and number of the components therein can vary depending upon the situation at hand. The individual cables 10 can be wound up on spools, and if desired, can be spliced together. By forming multiple cables 10 simultaneously in parallel, the cost of the cable 10 can be reduced in some embodiments by as much as a factor of about five in comparison to round cables having comparable power carrying capabilities. While this invention has been particularly shown and described with references to example embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims.

For example, although conductors 18 have been shown and described to be formed from flat conductor ribbons 18a, the conductors 18 can be of other suitable configurations and constructions, for example round. In addition, flat conductor ribbons 18a in a conductor 18 can be of varying widths to result in a conductor of a desired shape. Also, in some embodiments, the insulative jacket 12 can be formed in an unitary manner. The outer surfaces of cable 10 can have grooves, curves or ridges, etc., and still be considered generally rectangular, or generally flat.