1. Field of the Invention
The invention relates to an offshore power generation plant having the following features: an offshore power generation plant including: a power transducer driven by a fluid movement; an electric generator, which is at least indirectly driven by the power transducer; an electrical connection cable for power transmission; and a pile foundation, including a foundation pile, which extends under the ocean bed. The invention also relates to an installation method for the connection of an electrical connection cable for power transmission to an offshore power generation plant.
2. Description of the Related Art
Offshore power generation plants which use the kinetic energy of a fluid movement at an ocean location to obtain power are known in various embodiments. These can be ocean current power plants, in particular tidal power plants and wave power plants, wherein a rotating or oscillating power transducer on a freestanding plant is driven by an ocean current. Furthermore, offshore wind power plants are included in this plant type. One possible construction of plants according to the species is represented by horizontal rotor turbines mounted on a nacelle, which at least indirectly drive an electrical generator within the nacelle. The nacelle is typically placed on a tower of the plant, which rests on a foundation on the ocean bed. The present case relates to offshore power generation plants having a foundation in the form of a pile foundation, which comprises at least one foundation pile which extends below the ocean bed. A single foundation pile (monopile) can be used for a sufficiently compacted ocean floor. For this purpose, reference is made to DE 103 40 088 A1, for example. Alternatively, a pile foundation can have multiple foundation piles extending into the ocean floor. An example of such a foundation structure in the form of a tripod is disclosed by DE 10 2004 042 066 A1.
The electrical power generated by an offshore power generation plant is conducted away from the plant by means of an undersea cable. The cable can be led out from the nacelle along the outer side of the support structure. Pipes or trough-shaped receptacle systems are used to protect the cable, which ensure a cable deflection in the horizontal direction in the region of the ocean floor. These cable guiding systems are designated as J-tubes. DE 10 2008 020 964 A1 and WO 02/066828 A1 are mentioned as examples. Alternatively, the electrical connection cable for power transmission can be guided within a closed support structure. Reference is made for this purpose to EP 1 985 845 B1, which describes an undersea cable feedthrough on the tower, which is located in the range of 3.5-5 m above the ocean floor. Such cable feedthroughs on the tower are typically embodied as encapsulated watertight, as described in GB 2479771 A and WO 2009/000322 A1.
To protect the electrical connection cable extending away from the tower, embedding in the ocean floor can be performed. The induction of undersea cables by means of a high pressure water jet is known. Furthermore, cable laying by means of a milling tool is described by JP 06141430 A. An alternative for protecting an undersea cable between two offshore wind power plants of a park is disclosed by WO 2012/008833 A2. The cable guiding on the plants themselves is performed by means of J-tubes. Therefrom, the electrical connection cable extends in direct proximity to the plant on the ocean floor up to an inlet of a bore channel, which is provided by means of a horizontally controlled drilling method and extends from an apron of a first plant up to the proximity of a second plant. A drilling device lowered onto the ocean bed is used to execute the boreholes.
To introduce an electrical connection cable into an access opening in the tower of an offshore power generation plant, which lies below the water level and above the ocean bed, WO 2011/141494 A1 proposes the use of a diving robot (ROV—remotely operated vehicle) which firstly attaches an insertion and securing device in the region of the cable entry opening on the tower, by which device the actual connection cable is advanced into the interior of the tower, which is flooded with water.
Furthermore, storing an electrical connection cable for an offshore wind power plant on a cable drum in the tower or in the foundation is known from EP 1145397 B1. In order to produce an electrical connection to a neighboring plant of a park, the electrical connection cable is drawn out of an opening on the tower, which lies above the ocean bed, and brought by means of a dragline to the next plant.
The previously known devices and methods for installing and guiding an electrical connection cable from an offshore power generation plant to a feed point or transformer point or to an adjacent plant of a park have the disadvantage represented by the complex cable installation, which requires the use of divers or ROVs. Furthermore, in the event of a strong current in the body of water, the danger exists that the known external structures for cable securing, such as J-tubes or seal glands attached on the tower, have a limited lifetime because of the continuous load change caused by the varying incident flow.
The present invention is based on the problem of designing an offshore power generation plant having a pile foundation in such a manner that the electrical connection cable for power transmission is protected over the entire cable length. In particular, no cyclically alternating loads are to act on the electrical connection cable. Furthermore, a method for the electrical connection of an offshore power generation plant is to be specified, so that the laying of the electrical connection cable can be executed in a simpler and safer manner.
The present invention provides an offshore power generation plant including: a power transducer driven by a fluid movement; an electric generator, which is at least indirectly driven by the power transducer; an electrical connection cable for power transmission; and a pile foundation, including a foundation pile, which extends under the ocean bed; characterized in that a cable passage, which extends through an outer wall of the foundation pile and through which the electrical connection cable is guided, is arranged on the foundation pile below the ocean bed. The present invention also provides a method for the electrical connection of an offshore power generation plant, including: a power transducer driven by fluid movement; an electrical generator, which is at least indirectly driven by the power transducer; and a pile foundation, including a foundation pile, which extends under the ocean bed; characterized in that an electrical connection cable for power transmission is drawn below the ocean bed through a cable passage, which extends through an outer wall of the foundation pile.
The starting point of the solution of the above-mentioned problem is an offshore power generation plant having a pile foundation. Accordingly, at least one foundation pile is provided, which extends into the ocean floor. For a monopile, the entire plant rests on a single foundation pile. However, the use of multiple foundation piles connected to one another via the ocean floor or a combined foundation, for which, in addition to the foundation pile extending below the ocean floor, further support units, for example, gravity elements or cable anchors, are provided, is also conceivable.
According to the invention, the electrical connection cable, which transmits the power generated by an electric generator of the offshore power generation plant, is guided in the foundation pile up to a cable passage, which lies below the ocean bed. Accordingly, the electrical connection cable extends through the outer wall of the foundation pile at a predetermined depth in the ocean floor, so that a good protection of the cable is provided against current forces and further risks, such as anchor damage. The ocean bed at the foundation pile is understood as the mean level of the ocean floor, i.e., a positionally and chronologically averaged sediment level in a circle around the plant, which corresponds to the rotor diameter. Accordingly, the mean level of the ocean floor represents the height reference which is used to determine the penetration depth of the foundation pile below the ocean bed.
The cable passage, through which the electrical connection cable is guided on the foundation pile, preferably lies at a depth below the ocean bed such that stable soil conditions are provided and therefore in a region for which no sediment transport occurs because of the surrounding current. The selected exit depth of the cable passage below the ocean bed is dependent on the prevailing current and soil conditions. A cable passage is preferably created such that it lies at least 3 m below the ocean bed. In case of a rocky subsurface, the location of the cable passage can be created at a lesser depth under the ocean bed in comparison to a location having a sandy or clayey subsurface. Furthermore, it is preferable to arrange the cable passage such that it lies below the zone of higher notch load on the foundation pile. Therefore, a cable passage is advantageous which is located in the region of the lower two-thirds of the penetration depth of the foundation pile into the ocean floor. The lower third of the penetration depth of the foundation pile under the ocean bed is particularly preferably used for the creation of the cable passage.
For a preferred refinement, the electrical connection cable is guided within the foundation pile up into a dry inner region of the plant, in which a connection element for the electrical connection cable is arranged. The dry inner region is particularly preferably designed as a watertight closable compartment in the region of the foundation pile, which allows the access of service technicians. In addition to the connection element, at which the electrical connection cable can be contacted by simple terminals, the power electronics of the plant can be housed within the compartment. These can include rectifiers and a transformer. Furthermore, it is preferable to arrange further assemblies of the plant, in particular hydrostatic components, sensory components, and components used for the controller, within the dry inner region.
For a preferred embodiment, the cable passage opens outside the foundation pile into a cable tunnel, which also extends below the ocean bed. The cable tunnel is considered to be part of the offshore power generation plant. The cable tunnel is particularly preferably implemented as pressure resistant, liquid tight, and self-drying. For a further advantageous embodiment, the internal diameter of the cable tunnel is selected such that it is greater than the external diameter of the electrical connection cable laid therein. The dry-laid electrical connection cable can therefore be guided with a reduced cable capacitance.
For a preferred embodiment, it is provided that the cable tunnel is designed as traversable and/or a transport device is provided therein, for example, a carriage system for material and/or personnel transport. If the cable tunnel is connected up to a central entrance point of a park or to an access tunnel leading onto land, an access possibility to the plant exists. If such a cable tunnel is combined with a plant variant for which a dry inner region is provided in the interior of the foundation pile, an access possibility exists via a cable passage, which is implemented as correspondingly large for this case, so that installation and service measures can be carried out by human operating personnel.
For the case of a traversable cable tunnel or a cable tunnel equipped for personnel transport, it must have a watertight tunnel lining, for example, by steel pipe segments, for safety reasons. Furthermore, bulkheads for secure partitioning of individual cable tunnel sections and a ventilation system are provided.
For a simplified embodiment variant, the inner region of the foundation pile which adjoins the cable passage below the ocean bed is flooded. For this embodiment, a cable guiding device, which is arranged in the interior of the foundation pile, is preferably provided, which guides an electrical connection cable, which is inserted through the cable passage from outside into the plant, to a plug device. An embodiment is preferred for which the plugging-in procedure is executed by an automated or remote-controlled actuator, so that divers do not have to be used for the installation.
For the method according to the invention for preparing the electrical connection of an offshore power generation plant, an electrical connection cable for power transmission is drawn through a cable passage in the outer wall of the foundation pile, which is arranged under the ocean bed. Particularly preferably, the foundation pile is erected first and cemented in depending on the soil conditions. The cable passage is only opened under the ocean bed in a following method step.
The cable passage is particularly preferably created by means of a through borehole of the outer wall of the foundation pile. A through-drilling point can be provided on the foundation pile, which is created as a concrete wall without steel reinforcement, for example, which can be drilled by a standard drill head of a horizontal drilling machine. Furthermore, it is conceivable to create the foundation pile as a steel pipe and to provide a breakthrough of the steel external envelope for the through-drilling point and to provide a liquid-tight cover which can be drilled by means of a masonry drill, wherein a concrete inner lining can fulfill this purpose.
If a drilling method is used to open the cable passage after the erection of the foundation pile, this can be performed outward from the bored pile. For this purpose, a drilling device is lowered into the interior of the foundation pile or is preinstalled therein before the erection of the foundation pile. Alternatively, the possibility exists of docking the drilling device on the foundation pile, wherein it is advantageous for this embodiment to use a centering device within the foundation pile, in order to guide the drill bit to the through-drilling point located below the level of the ocean floor.
For a particularly preferred embodiment, after the erection of the foundation pile, horizontally controlled drilling is executed from the outside and the outer wall of the foundation pile is broken through at a through-drilling point provided for this purpose for the creation of the cable passage. The horizontally controlled drilling can be performed by a drilling device which is placed in the surrounding region of the offshore power generation plant on the ocean bed.
An embodiment is particularly preferred having a horizontally controlled borehole executed in the dry state. For this purpose, a tunnel extending up to land can be created for the park access, whose cross-section is selected as sufficiently large that a horizontal drilling machine can be constructed therein. It is conceivable to create expanded cavities in the tunnel at the operating regions of the drilling device, which allow the handling of the drill pipe. From these operating points, the application of horizontally controlled drilling in the dry state is performed, in order to advance cable channels up to the through-drilling points at a foundation pile of an offshore power generation plant and the cable passage adjoining thereon at the outer wall of the foundation pile. A liquid-tight tunnel lining for the existing pressure conditions is preferably created during the creation of the cable tunnel. This can be created in segments. The connection between the cable tunnel and the cable passage at the foundation pile is sealed accordingly.
For a simplified method for providing an electrical connection according to the invention of an offshore power generation plant, a cable passage is created on the foundation pile before the insertion into the ocean floor. The insertion of the foundation pile is performed with a penetration depth into the ocean floor and an orientation selected such that the cable passage which is already prefinished on the foundation pile aligns in the final installation position with a cable tunnel created below the ocean bed. The inner region of the foundation pile in the region of the cable passage and the cable tunnel extending away from the plant can be implemented as water-conducting. The laying of the electrical connection cable is then executed by diving robots.
The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein:
Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate embodiments of the invention, and such exemplifications are not to be construed as limiting the scope of the invention in any manner.
For the embodiment shown in
For the present exemplary embodiment, the offshore power generation plant 1 is constructed modularly. The nacelle 4 is placed on a tower 5 of the plant, which is used as a support structure. For this purpose, a tower adapter 22 adjoins the nacelle 4. This adapter has a complementary shape to a coupling device 6 on the tower, so that the nacelle 4 can be placed during the plant setup on the tower 5 and, secured during operation by its intrinsic weight, rests received in a formfitting manner in the coupling device 6 during operation. Further recovery of the nacelle 4 having the power transducer 2 for service purposes is possible by lifting it off of the tower 5.
The offshore power generation plant shown in
According to the invention, the offshore power generation plant 1 outlined in
The electrical components and preferably further supply units of the offshore power generation plant 1 are combined in the power and operating module 29. These typically include rectifiers and an electrical transformer. Furthermore, preferably hydrostatic or pneumatic assemblies of the offshore power generation plants are combined in this power and operating module 29, which is located in the dry state. These can be used, for example, for the operation of a braking device of the power transducer 2 or for a hydrostatic starting aid for its mount on the nacelle 4. The operating cable 25 is accordingly not only used to transmit the power generated by the electrical generator 3, but rather also for guiding operating media such as hydraulic oil, compressed air, or lubrication or flushing media. Furthermore, the control components used for processing sensory data and for the operational control are housed within the power and operating module 29 in the dry inner region 12. The operating cable 25 accordingly preferably additionally comprises signal and control lines.
A connection element 13 for the electrical connection cable 7 is arranged inside the dry inner region 12. Connection terminals for the electrical connection cable 7 are most simply provided on the connection element 13. Furthermore, there is an electrical connection between the connection element 13 and the power and operating module 29 for power transmission. The connection preferably additionally comprises signal and control lines, which, accommodated in the electrical connection cable 7, lead away from the offshore power generation plant 1.
Furthermore,
For the embodiment shown in
A tunnel connection 32 to the pressure resistant seal of the transition to the cable tunnel 14 is created in the region of the cable passage 10. Furthermore, the cable tunnel 14 has a liquid-tight tunnel lining 31 for the existing water pressure. This can be created in the form of tightly connected steel segments, for example, in the form of 120° partial arcs. A seawater-resistant, fiber-reinforced concrete inner wall can be used as an alternative tunnel lining 31, which is produced by means of a shotcrete method.
For the preferred embodiment shown in
After the preparation of the cable tunnel 14 and the cable passage 10 and the safety and sealing measures required for this purpose, the installation of the electrical connection cable 7 can be performed. For a preferred embodiment, a traction cable is output outward through the cable tunnel 14 up to the location of the cable drum on land or an offshore cavity on a cable retraction system 33, which is arranged in the region of the connection element 13 in the dry inner region 12. The electrical connection cable 7 can then be drawn in through the cable tunnel 14 up to the connection element 13 by means of the retraction movement of the traction cable. The electrical connection cable 7 is preferably mounted inside the cable tunnel 14 on cable mounts 30 at a distance to the inner wall of the tunnel lining 31.
The horizontally oriented borehole is guided up to a through-drilling point 21 on the foundation pile 9, which consists of a material which can be drilled through. An opening of the outer steel pipe 27 of the foundation pile 9 is preferably provided in the region of the through-drilling point 21. Furthermore, the reinforcement of the concrete inner jacket 28 is created in this region such that the drill head 37 can open the through-drilling point 21 to provide a cable passage 10. The above-described safety and sealing measures in the region of the cable tunnel 14 and the cable passage 10 are subsequently executed and the inlet chamber 48 located below the dry inner region 12 is drained. An access possibility to the dry inner region 12 then exists.
Furthermore, the cable connection device 43 preferably comprises an automatic plug device 19, in order to join together a seawater-tight plug on the electrical connection cable 7 and a complementary connection part on the operating cable 25 in the region of the cable connection device 43. In this manner, a connection can be provided underwater from the power and supply plug 24 in the region of the coupling device 6, via the operating cable 25 and the seawater-proof plug in the region of the cable connection device 43, to the electrical connection cable 7 in the cable tunnel 14. From the drilling outlet at the location of the horizontal drilling machine 35 on the ocean bed 20, the electrical connection cable 7 can be embedded in the ocean floor by known measures, for example, by means of a water plow.
For a simplified embodiment (not shown in detail), the cable tunnel 14 and the entire inner region of the foundation pile 9 are flooded, wherein the laying of the electrical connection cable is performed by means of a robot system. For this simplified embodiment, the sealing device 42 initially created in the cable tunnel 14 is only used as a protection for the cable passage and the cable tunnel during the cementing of the foundation pile 9. Alternatively, such a protection device can instead be created at the outlet of the cable tunnel 14 at the cable passage 10 of the foundation pile 9.
While this invention has been described with respect to at least one embodiment, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.
Number | Date | Country | Kind |
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10 2012 013 618.8 | Jul 2012 | DE | national |