An Offshore Wind Turbine Installation with a Concrete-Cast Transition Piece Between the Wind Turbine Tower and its Support

Abstract

An offshore wind turbine installation comprising a wind turbine on a support structure. A concrete-cast transition piece is provided in between the tower of the wind turbine and a tower support of the support structure. Flanges of the tower and the tower support are either bolted to each other, sandwiching the transition piece in between, or bolted into the transition piece for fixation.

Claims

1. An offshore wind turbine installation, comprising: a wind turbine comprising a tower having a tower flange at a lower end of the tower; a support structure for supporting the wind turbine in offshore conditions, the support structure comprising a tower support having a support flange; a concrete-cast transition piece between the support flange and the tower flange, the transition piece on its lower side in mechanical contact with the support flange and supported by the support flange, and the tower flange on its lower side in mechanical contact with an upper side of the transition piece and supported by the transition piece; wherein the support flange is at an upper end of the tower support, and the support flange and the tower flange each comprise holes for bolts extending therethrough, the bolts directly or indirectly holding the tower flange to the tower support flange with the transition piece in between; wherein (A) each of the bolts extends through both the support flange and the tower flange for pulling the support flange and the tower flange towards each other by the bolts with the transition piece sandwiched in between or (B) a first number of the bolts extends through the tower flange into first threaded bushings embedded inside concrete of the transition piece and a second number of the bolts extends through the support flange into second threaded bushings embedded inside concrete of the transition piece, thereby bolting the tower flange and the support flange to opposite sides of the transition piece.

2. The installation according to claim 1, wherein at least some of the bolts also extend through holes in the transition piece.

3. The installation according to claim 1, wherein the support flange and the tower flange each extend radially in a plane perpendicular to a central longitudinal axis of the tower.

4. The installation according to claim 1, wherein the bolts, which extend through the holes in the flanges, are oriented with their longitudinal axes parallel to a central axis of the tower.

5. The installation according to claim 1, wherein in (B) the tower has a first diameter Dt and the support structure has a support diameter Ds, wherein Ds is different from Dt, wherein the tower flange comprises a first number of holes along a first circle, and the support structure comprises a second number of holes along a second circle with a second diameter, which is different from the first diameter, and wherein the first number of bolts extends from below the support flange through the first number of holes and into a first cooperating number of bushings inside the transition piece, and wherein the second number of the bolts extends from above the tower flange through the second number of holes and into a second cooperating number of bushings inside the transition piece.

6. The installation according to claim 1, wherein the support structure is formed as a tetrahedron with a triangular base to which the tower support is fixed and with diagonal braces extending from the triangular base inclined upwards to form a tetrahedral structure with the tower support.

7. The installation according to claim 6, wherein the diagonal braces are embedded in concrete in a volume contained in the upper end of the tower support, and each of the diagonal braces extends with one of its ends into the volume through an opening in the tower support.

8. The installation according to claim 1, wherein the transition piece is located entirely above a water surface.

9. The installation according to claim 1, wherein the transition piece comprises a platform for workers.

10. The installation according to claim 1, wherein the tower support and the tower are steel columns to which the support flange and the tower flange are welded, respectively.

11. The installation according to claim 1, wherein the transition piece extends over no more than a height H, when measured in a direction parallel to the central axis of the tower, wherein H is less than half of a diameter Dt of the tower.

12. The installation according to claim 11, wherein H is in a range of 1-3 meters, and wherein a distance between the support flange and the tower flange with the transition piece therebetween is in a range of 1-3 meters.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The systems and methods will be explained in more detail with reference to the drawings, wherein:

[0026] FIG. 1 illustrates a semisubmersible wind turbine installation, according to an embodiment;

[0027] FIG. 2 illustrates a transition piece between a support structure and a tower of equal diameter, according to an embodiment;

[0028] FIG. 3 illustrates a transition piece for a support structure having a smaller diameter than the tower, according to an embodiment;

[0029] FIG. 4 illustrates a transition piece for a support structure having a larger diameter than the tower, according to an embodiment;

[0030] FIG. 5A illustrates a transition piece with lateral support bars for the platform and FIG. 5B is a top view of a transition piece, according to an embodiment;

[0031] FIG. 6A illustrates diagonal braces inserted into the tower support for a grout connection, and FIG. 6B shows details thereof, according to an embodiment.

DETAILED DESCRIPTION

[0032] FIG. 1 illustrates an offshore wind turbine installation 1. The installation 1 comprises a wind turbine 2 and an offshore support structure 3, on which the wind turbine 2 is mounted and by which it is supported in offshore conditions. The wind turbine 2 comprises a rotor 5 and a tower 7 and nacelle 6 that connects the rotor 5 with the tower 7.

[0033] The offshore support structure 3 is exemplified as a semisubmersible structure with mooring lines 13 and buoyancy tanks 12 that keep the structure 3 floating half-way submersed under water. Alternatively, the structure could be a tension leg platform (TLP) with a fully submerged floating support structure or a bottom supported platform, for example a monopile.

[0034] The exemplified semisubmersible structure 3 comprises buoyancy tanks 12 that are interconnected in a triangular shape where the triangular base is formed by side braces 10A and radial braces 10B. The side braces 10A form a triangle by interconnection at corners 10C. The radial braces 10B connect the corners 10C to the tower support 8.

[0035] The tower support 8 is exemplified as a support column. On top of the support column 8, there is provided a transition piece 9, which optionally also comprises a workers' platform 15 that is accessible for workers when inspecting the wind turbine 2 and entering the tower 7.

[0036] In order to provide increased mechanical stability between the support column 8 and the triangular base, formed by the side braces 10A and the radial braces 101B, there are provided diagonal braces 11, which extend from the corners 10C to the upper portion of the support column 8, thereby forming a tetrahedron.

[0037] As illustrated, the tower support 8 extends to a position above the water surface 4, and correspondingly, also the transition piece 9 with the workers' platform 15 is located entirely above the water surface 4. The fact that the transition piece 9 is located above the water surface 4 reduces risk for wear and corrosion.

[0038] FIG. 2 illustrates a transition piece 9 between the tower support column 8 and the tower 7. Integrated in the transition piece 9 is the workers' platform 15 where workers can stand for inspection, as already mentioned. For safety, it is surrounded by a fence 14.

[0039] The transition piece 9 comprises a connector segment 16 and a platform support 17, which supports the workers' platform 15. The connector segment 16 is provided between a flange 19 of the tower 7 and a flange 20 of the support column 8. The flanges 19 and 20 are arranged parallel to each other and oriented perpendicular to a central longitudinal axis of the tower 7. The flanges 19, 20 are connected to each other by bolts 18 that extend vertically in corresponding holes 28 through the connector segment 16.

[0040] Alternatively, the flanges 19 and 20 are screwed by bolts 18 into corresponding threaded bushings embedded in the connector segment 16. Examples thereof will be given in the following.

[0041] FIG. 3 illustrates a transition piece 9 between the tower support 8 and the tower 7 where the tower support 8 has a diameter Ds that is smaller than the diameter Dt of the tower. In this case, the flange 19 of the tower 7 is fastened to the transition piece 9, in particular to the connector segment 16, by bolts 18 that extend vertically through holes in the tower flange 19 from above and into corresponding threaded bushings in the connector segment 16. Correspondingly, the flange 20 of the support column 8 is fixed to the connector segment 16 by bolts 18 that extend vertically through holes in the flange 20 from below and into threaded bushings in connector segment 16. Typically, the bushings are integrated in the connector segment 16 of the transition piece 9 when it is cast in concrete.

[0042] FIG. 4 illustrates an embodiment where the support column 8 has a diameter Ds that is larger than the diameter Dt of the tower 7. Also, in this case, the corresponding flanges 19 and 20 are fixed to the connector segment 16 by bolts 18 that are fastened in threaded bushings.

[0043] And advantage of the principle of providing a transition piece 9 in the described manner is great flexibility in the shaping and in the production, which can be easily customized to the various sizes of support columns 8 and towers 7. In particular, for a certain support column 8 of fixed diameter Ds, it is possible to mount various wind turbine towers 7 with different diameters Dt by providing corresponding transition pieces 9. The transition pieces 9 are cast in enforced concrete and can even be prepared in stock for certain sizes and shapes of tower supports 8, be it in the form of a column or another shape, when the tower diameters Dt in question are already known, for example because there are standard diameters for towers 7 of different wind turbine brands.

[0044] The fact that the transition piece 9 is provided between the flanges 19 and 20 has an advantage of the height H of the transition piece 9 being relatively small, for example in the range of 1-3 meters, or even only in the range of 1-2 meters, and the corresponding requirements for material in the transition piece 9 is correspondingly small.

[0045] This is in contrast to the prior art, where transition pieces embrace a substantial portion of the upper part of the tower support, which necessitates casting of a hollow tubular structure with a cavity into which the upper portion of the tower support and/or a lower portion of the tower is accommodated.

[0046] As illustrated in FIG. 4, the platform support 17 is cast as part of the transition piece 9 and integral with the connector segment 16. However, this is not strictly necessary.

[0047] FIG. 5A in cross sectional view and FIG. 5B in top view illustrate an alternative embodiment in which the platform support 17 is provided by using bars 21 that are embedded in the connector segment 16 but extend therefrom, for example extend radially from the connector segment 16. In the illustrated case of FIG. 5A, these bars 21 are in practical embodiments covered by a platform surface. As compared to the integrally cast platform support 17 of FIG. 4, the platform structure in FIG. 5A results in a more lightweight arrangement. Illustrated in FIG. 5B are also the holes 28 for the bolts 18.

[0048] For example, the diameter Dt of the tower 7 is in the range of 6-10 m and diameter Ds of the support column in the range of 8-10 m. Examples of combinations of these are exemplified in the drawings. However, dimensions given in the drawings are exemplary and not limiting.

[0049] FIG. 6 illustrates an arrangement in which diagonal braces 11 are embedded in the tower 8 with one of their ends. For this type of attachment, the tower 8 is provided with three openings 23 into each of which one end of one of the diagonal braces 11 is inserted. The volume 25 into which the ends of the diagonal braces 11 are inserted is delimited by a bottom plate 26 that extends across the support column 8 laterally relatively to the central axis of the support column 8. For example, the bottom plate 26 is welded to the inner wall of the metallic support column 8. The volume 25 between the bottom plate 26 and the flange 20 of the support column 8 is filled with concrete after the insertion of the ends of the diagonal braces 11.

[0050] Advantageously and as exemplified, in order for the diagonal braces 11 to be held securely inside the concrete in the volume 25, the ends of the diagonal braces 11 are provided with sheer keys 24.

[0051] In practice, the diagonal braces 11 are inserted with their ends into the volume 25 after which the volume 25 is filled with concrete from above, for example before the transition piece 9 is placed and fixed onto the support column on top of the volume 25. Alternatively, the transition piece 9 is fastened to the tower 8 on the flange 20 prior to filling the volume 25 with concrete. This is possible because the transition piece 9 has a central opening through which concrete can be inserted into the volume 25 from above.