METHOD OF INSTALLING A TRANSMISSION CABLE ARRANGEMENT

Abstract

Provided is a method of installing a transmission cable arrangement of an offshore wind turbine, including step of providing a cable protection assembly, wherein provision of the cable protection assembly includes the steps of installing an outer protective pipe at a marine foundation, which outer protective pipe is realized to extend from a cable hang-off to the seabed; and laying an inner protective pipe through the outer protective pipe to extend from the cable hang-off to a further destination; and wherein the method of installing a transmission cable arrangement further includes a step of loading the transmission cable arrangement into the inner protective pipe towards the further destination. A cable protection assembly and a wind turbine assembly are also provided.

Claims

1. A method of installing a transmission cable arrangement of an offshore wind turbine, comprising a step of providing a cable protection assembly, wherein provision of the cable protection assembly comprises the steps of installing an outer protective pipe at a marine foundation, which outer protective pipe is realized to extend from a cable hang-off to the seabed; and laying an inner protective pipe through the outer protective pipe to extend from the cable hang-off to a further destination; and wherein the method of installing a transmission cable arrangement further comprises a step of loading the transmission cable arrangement into the inner protective pipe towards the further destination.

2. The method according to claim 1, wherein the marine foundation is a monopile foundation, and the step of installing the outer protective pipe comprises a step of guiding the outer protective pipe through an aperture at the base of the monopile foundation.

3. The method according to claim 1, wherein the step of installing the outer protective pipe is facilitated by a messenger wire and a winch assembly provided at the cable hang-off.

4. The method according to claim 1, wherein the step of installing the inner protective pipe comprises pushing the inner protective pipe from an installation vessel into the outer protective pipe.

5. The method according to claim 1, wherein the step of installing the transmission cable arrangement comprises pushing the transmission cable arrangement into the inner protective pipe at the cable hang-off.

6. The method according to claim 1, comprising a step of filling water into a space between the transmission cable arrangement and the inner protective pipe.

7. A cable protection assembly for a transmission cable arrangement of an offshore wind turbine, comprising an outer protective pipe suspended from a cable hang-off of a marine foundation and extending to the seabed; and an inner protective pipe extending between that offshore wind turbine and a further destination, which inner protective pipe is suspended from the cable hang-off and extends through the outer protective pipe to the seabed.

8. The cable protection assembly according to claim 7, wherein the outer protective pipe comprises a HDPE pipe.

9. The cable protection assembly according to claim 7, wherein the inner protective pipe comprises a HDPE pipe.

10. The cable protection assembly according to claim 7, wherein the dimensions of the outer protective pipe are chosen to achieve a bending radius that exceeds the minimum bending radius of the transmission cable arrangement.

11. The cable protection assembly according to claim 7, wherein a protective pipe comprises embedded armoring.

12. The cable protection assembly according to claim 7, comprising a device for filling water into a space between the transmission cable arrangement and the inner protective pipe.

13. A wind turbine assembly comprising an offshore wind turbine mounted on a marine foundation, a transmission cable arrangement for exporting power, and further comprising the cable protection system according to claim 7 to protect the transmission cable arrangement.

14. The wind turbine assembly according to claim 13, wherein the marine foundation is a monopile foundation comprising a vertical hollow transition piece mounted on a monopile and comprising an aperture near the seabed.

15. The wind turbine assembly according to claim 13, wherein the outer protective pipe extends from a cable hang-off in the interior of the transition piece through the aperture to the seabed.

Description

BRIEF DESCRIPTION

[0023] Some of the embodiments will be described in detail, with reference to the following figures, wherein like designations denote like members, wherein:

[0024] FIG. 1 shows a marine foundation for an offshore wind turbine;

[0025] FIG. 2 shows a stage in the inventive method of installing a cable protection assembly for a wind turbine transmission cable arrangement;

[0026] FIG. 3 shows another stage in the inventive method of installing a cable protection assembly for a wind turbine transmission cable arrangement;

[0027] FIG. 4 shows another stage in the inventive method of installing a cable protection assembly for a wind turbine transmission cable arrangement;

[0028] FIG. 5 shows another stage in the inventive method of installing a cable protection assembly for a wind turbine transmission cable arrangement;

[0029] FIG. 6 shows a cross-section through an embodiment of the inventive cable protection assembly;

[0030] FIG. 7 shows a cross-section through a further embodiment of the inventive cable protection assembly;

[0031] FIG. 8 shows a cross-section through a further embodiment of the inventive cable protection assembly; and

[0032] FIG. 9 shows part of an offshore wind turbine array.

DETAILED DESCRIPTION

[0033] FIG. 1 shows a marine foundation 3 for an offshore wind turbine. In this exemplary embodiment, the marine foundation 3 is a monopile foundation comprising a monopile 30 that is driven partially into the seabed B, and a hollow vertical transition piece 31 mounted on the foundation 30. The wind turbine tower 20 will be mounted to the transition piece 31. The transmission cables 4 or power export cables 4 of the wind turbine 2 will be protected by a cable protection assembly 1 that is suspended from a cable hang-off 33 in the interior of the transition piece 31 and that extends down towards the monopile 30, exiting the transition piece 31 through an aperture 32 to reach the seabed B. The installation of the inventive cable protection assembly 1 can be done prior to installation of the wind turbine, and the tower 20 is shown here only for the purpose of illustration.

[0034] FIG. 2 shows a first stage in the installation of a cable protection assembly for a wind turbine transmission cable arrangement. The diagram shows a messenger wire 6 connected to a winch 60 inside the transition piece 31. The other “exterior” end of the messenger wire 6 has been brought out through the aperture 32 at the base of the foundation 3 and back up to an upper level, for example to the level of a working platform 34, where it is temporarily secured. To lay the messenger wire 6 in this manner, a remotely operated underwater vehicle (ROV) may be used. The ROV can be controlled from a host ship such as an installation vessel, for example, as will be known to the skilled person.

[0035] FIG. 3 shows a subsequent stage in the installation of the cable protection assembly. Here, an outer protective HDPE pipe PP0 is being installed. The “exterior” end of the messenger wire 6 has been retrieved and brought to the deck of an installation vessel 7. The installation vessel 7 carries a drum 70 loaded with the outer protective HDPE pipe PP0. The messenger wire 6 is secured to one end of the HDPE pipe PP0. To guide the HDPE pipe PP0 into the transition piece 31, the winch 60 is operated to retract the messenger wire 6 and, at the same time, a set of roller wheels 71 on the installation vessel 7 can act to “push” the required length of HDPE pipe off the installation vessel 7. The length of the outer protective HDPE pipe PP0 can be about twice the height of the transition piece 31, for example. After this stage in the installation process, the “outer” end of the outer protective HDPE pipe PP0 is temporarily secured at the working platform 34 of the monopile foundation 3 in readiness for the next stage.

[0036] FIG. 4 shows the next stage in the installation of the cable protection assembly. The “outer” end of the outer protective HDPE pipe PP0 has been brought to an installation vessel 7, which carries a drum 70 loaded with the inner protective HDPE pipe PP 1. One end of the inner protective HDPE pipe PP1 is pushed into the outer protective HDPE pipe PP0 until it reaches the level of the cable hang-off 33 in the interior of the transition piece 31. The installation vessel 7 can then proceed to move away, and the outer protective HDPE pipe PP0, now loaded with a section of the inner protective HDPE pipe PP1, is allowed to descend to the level of the seabed B. As the installation vessel 7 moves away, it continues to pay out the inner protective HDPE pipe PP 1. The inner protective HDPE pipe PP1 can be air-jetted, water-jetted or ploughed into the seabed B, or may be allowed to rest on the seabed B. The cable protection assembly 1 is now complete and can receive a transmission cable arrangement.

[0037] FIG. 5 shows a subsequent stage. Here, an installation vessel 7 is loaded with a transmission cable arrangement 4. The transmission cable arrangement 4 can be provided as a cable bundle enclosed in an outer sheath, for example, and may comprise power cables to transport power from the wind turbine, communication cables to exchange data between a park controller and the wind turbine, etc. The transmission cable arrangement 4 is fed into the inner protective HDPE pipe PP1, commencing at the level of the cable hang-off 33. Because the cable protection assembly 1 is already installed, the transmission cable arrangement 4 is protected from the outset. In particular, damage to the transmission cable arrangement 4 at the critical passage through the aperture 32 to the seabed B is prevented by the pipe-in-pipe assembly PP0, PP 1.

[0038] The transmission cable arrangement 4 can be fed into the inner protective HDPE pipe PP1 using a water-jetting apparatus similar to the apparatus used in a fiber optic cable installation, as will be known to the skilled person. This can be augmented by a roller-wheel system 71 on the installation vessel 7, to feed or push the transmission cable arrangement 4 into the inner protective HDPE pipe PP1 until the leading end of the transmission cable arrangement 4 has reached its destination (for example a neighboring wind turbine foundation, a substation, etc.).

[0039] In one exemplary embodiment, as shown in FIG. 6, the outer protective pipe PP0 is made of HDPE, and has an outer diameter DOA measuring 36 cm and an inner diameter DOB measuring 27 cm; the inner protective pipe PP1 is also made of HDPE, and has an outer diameter DIA measuring 22 cm and an inner diameter D1B measuring 20 cm. A three-core transmission cable arrangement 4 may have a diameter in the region of 16 cm. The bending radius of such an embodiment of the cable protection assembly 1—in this example 2.4 m or more—is therefore greater than the transmission cable's minimum bending radius, and ensures that the transmission cable arrangement 4 cannot be bent to within this favorably large bending radius.

[0040] The space between the inner protective pipe PP1 and the transmission cable arrangement 4 is filled with water W, so that the transmission cable arrangement 4 is water-cooled. FIG. 7 shows an exemplary cross-section through the inventive cable protection assembly 1, showing the outer protective pipe PP0, the inner protective pipe PP1, and the transmission cable arrangement 4 in the interior, with water filling the space between the inner protective pipe PP1 and the transmission cable arrangement 4.

[0041] The inner protective pipe PP1 and the outer protective pipe PP1 can simply comprise HDPE without any additional material, i.e. the inner and outer protective pipes PP1, PP0 can be unarmored. The inherent strength of the HDPE material and a suitable wall thickness can be sufficient to provide adequate protection to the transmission cable arrangement 4. In an alternative embodiment, one or both of the protective pipes PP0, PP1 can incorporate additional strengthening elements. FIG. 8 shows a cross-section through an armored outer protective HDPE pipe. The diagram shows steel wires 11 embedded in the pipe wall. These can be embedded during the HDPE extrusion process. With an armored outer protective HDPE pipe PP0, for example, it may no longer be necessary to bury the cable assembly under the seabed.

[0042] FIG. 9 shows two wind turbines 2 of an offshore array. A transmission cable arrangement extends between adjacent wind turbines 2 of the array, and also to an offshore or onshore substation (not shown). Each transmission cable arrangement is protected over its entire length by an embodiment of the inventive cable protection assembly 1. Particularly at the critical passages at the apertures of the transition pieces, the cable protection assemblies 1 ensure that the transmission cable arrangements are not damaged when the seabed is scoured from the base of the foundation 3.

[0043] Although embodiments of the present invention have been disclosed in the form of embodiments and variations thereon, it will be understood that numerous additional modifications and variations could be made thereto without departing from the scope of embodiments of the invention. For example, the cable protection assembly may be used in any application requiring telecommunications cables or power cables to be arranged underwater and is not restricted to the protection of a wind turbine transmission cable arrangement. For example, the inventive cable protection assembly may be used for other offshore installations such as oil rigs and gas rigs, or for any installation requiring a submerged interface at the seabed.

[0044] For the sake of clarity, it is to be understood that the use of “a” or “an” throughout this application does not exclude a plurality, and “comprising” does not exclude other steps or elements.