WIND TURBINE TOWER

Abstract

A wind turbine tower is tethered by a number of cables, each cable extending between a first end anchored to an anchoring element and a second end attached to the tower at an attachment element. Two cables extending from two different anchoring elements are attached to the tower such that projection lines from the second ends of the two cables converge at a point which lies inside the tower wall thickness or within a distance of three wall thicknesses from the wall inner surface. A method of erecting a wind turbine tower includes positioning a first tower section, attaching at least some tethering cables to a second tower section while the second tower section is on the ground, lifting the second tower section with the attached cables onto the first tower section, and joining the second tower section to the first.

Claims

1. A wind turbine tower configured to support a wind turbine nacelle and a rotor, comprising: a first elongate tower section having a first connection flange at an upper end thereof; a second elongate tower section having a second connection flange at a lower end thereof; a cable attachment section disposed between the first and second elongate tower sections and coupled to the first and second connection flanges, wherein the cable attachment section includes a plurality of attachment elements affixed to an outer surface of the cable attachment section, and wherein the cable attachment section has a length significantly shorter than a length of the first and second elongate tower sections; a plurality of anchoring elements disposed at a lower end of the wind turbine tower and radially outboard thereof; and two tethering cables extending from each of the plurality of anchoring elements to a respective one of the plurality of attachment elements on the cable attachment section.

2. The wind turbine tower of claim 1, wherein the cable attachment section has a length slightly greater than a length the attachment elements extend along the cable attachment section.

3. The wind turbine tower of claim 2, wherein the cable attachment section has a length less than about three times the length the attachment elements extend along the cable attachment section.

4. The wind turbine tower of claim 1, wherein two tethering cables extending from two different anchoring elements are attached to the cable attachment section of the tower such that longitudinal projection lines from the ends of the two cables converge at a convergence point.

5. The wind turbine tower of claim 4, wherein said convergence point lies at a location at a height and inside the tower within a distance of three wall thicknesses from the wall inner surface as measured at the height and in a direction perpendicular to a central longitudinal axis.

6. The wind turbine tower of claim 1, wherein the two tethering cables extending from each anchoring element diverge from each other in a direction toward the anchoring elements on the cable attachment section.

7. The wind turbine tower of claim 1, wherein the plurality of attachment elements forms an integral part of the cable attachment section.

8. The wind turbine tower of claim 1, wherein the two tethering cables anchored to the same anchoring element extend to different positions at the tower at essentially the same height of the tower.

9. A method of erecting a wind turbine tower configured to support a wind turbine nacelle and a rotor, comprising: providing a first elongate tower section having a first connection flange at an upper end thereof; providing a second elongate tower section having a second connection flange at a lower end thereof, providing a cable attachment section having a plurality of attachment elements affixed to an outer surface of the cable attachment section, wherein the cable attachment section has a length significantly shorter than a length of the first and second elongate tower sections; attaching each of a plurality of tethering cables to a respective one of the plurality of attachment elements on the cable attachment section while the cable attachment section is on the ground; attaching the cable attachment section to one of the first connection flange of the first tower section or the second connection flange of the second tower section while the respective first or second tower section is on the ground; erecting the tower by attaching a lower end of the first elongate tower section to a wind turbine structure; and further erecting the tower by attaching the cable attachment section to the other of the first connection flange of the first tower section or the second connection flange of the second tower section.

10. The method of claim 9, further comprising attaching each of the plurality of tethering cables to one of a plurality of anchor elements disposed at a lower end of the wind turbine tower and radially outboard thereof, wherein the plurality of tethering cables are arranged such that two tethering cables extend from each of the plurality of anchoring elements to a respective one of the plurality of attachment elements on the cable attachment section.

11. The method of claim 10, further comprising arranging the plurality of tethering cables such that two tethering cables extending from two different anchoring elements are attached to the cable attachment section of the tower such that longitudinal projection lines from the ends of the two tethering cables converge at a convergence point.

12. The method of claim 11, wherein said convergence point lies at a location at a height and inside the tower within a distance of three wall thicknesses from the wall inner surface as measured at the height and in a direction perpendicular to a central longitudinal axis.

13. The method of claim 10, further comprising arranging the plurality of tethering cables such that the two tethering cables extending from each anchoring element diverge from each other in a direction toward the anchoring elements on the cable attachment section.

14. The method of claim 10, further comprising arranging the plurality of cables such that the two tethering cables anchored to the same anchoring element extend to different positions at the tower at essentially the same height of the tower.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0040] In the following different embodiments of the invention will be described with reference to the drawings, wherein:

[0041] FIG. 1 shows a sketch of a wind turbine tower according to an embodiment of the invention,

[0042] FIGS. 2 and 3 show the attachment of cables to a tower section in a cross sectional view and an enlargement of a detail hereof, respectively,

[0043] FIGS. 4A and B show an embodiment of the cables attached to a tower section in two different views,

[0044] FIG. 5 shows an embodiment of an attachment element,

[0045] FIG. 6 shows a cross sectional view of a tower section with an attachment element,

[0046] FIGS. 7A and B show an attachment of a cable to an attachment element and to an anchoring element, respectively, and

[0047] FIG. 8 is a sketch of a wind turbine tower during erection as seen from above.

DETAILED DESCRIPTION OF THE DRAWINGS

[0048] FIG. 1 shows a sketch of a wind turbine tower 100 according to an embodiment of the invention. The wind turbine tower is configured to support a wind turbine nacelle and a rotor (not shown) and is tethered by a number of cables, 101. The tower extends in a longitudinal direction along and about a central vertical longitudinal axis 105. In the present embodiment, in total six different cables 101 extend between their first ends attached to in total three different anchoring elements 102 which here are on the ground and their second ends attached to attachment elements 103 at one tower section 104 of the tower. Two cables extend from each anchoring element and extend in different angles to two different attachment elements at the tower but at the same height. In this embodiment the anchoring elements 102 are placed at the same distance from the tower and at 120 degrees apart around the tower so that the cables tensioning is symmetrical. The cables here extend to the tower at an angle of approximately 45 degrees and are attached to the tower at a height just beneath the height of wind turbine blade tip when in its lowermost position. In this way the cables cannot under any weather conditions be hit by a blade.

[0049] FIG. 2 shows a cross sectional view of the wind turbine tower 100 of FIG. 1 and at the height where the cables 101 are attached to attachment elements 104. A part hereof is shown in an enlargement in FIG. 3. The six cables 101 are attached in pairs to three anchoring elements as shown in FIG. 1, and are attached to meet in other pairs at the tower. Hereby is obtained the symmetrical tethering of the tower as sketched in FIG. 2.

[0050] The longitudinal projection lines 201 from the second ends of a pair of cables 101 converge at a convergence point 300. The convergence point lies at a location at some height and in this embodiment inside the tower wall thickness 301 extending between the inner surface 202 and the outer surface 203 in a radial direction 204. The location of the convergence point 300 may in other embodiments lie inside the tower and within a distance of three wall thicknesses from the wall inner surface 201 as measured at the height of the location of the convergence point and in a direction perpendicular to said central longitudinal axis as indicated by the arrow 305 in FIG. 3.

[0051] The pair of cables with converging projection lines may be attached to two separate attachment elements 103 or to the same attachment element configured to receive two different cable ends.

[0052] In FIGS. 4A and B are shown an embodiment of the cables 101 attached to a tower section 104 of the wind turbine tower 100 in a perspective view and as seen from the side, respectively. The tower section 104 onto which the cable ends are attached is here reinforced by a larger wall material thickness in order to better withstand the forces from the cables. As can be seen from the figures the outer diameter of the tower section 104 is larger than the outer diameter of the neighbouring tower sections 401. The tower sections are here joined by flanges abutting inside the tower (not shown).

[0053] Preferable the attachment elements are shaped such that the cable projection lines of each cable go up to and through the middle height of the attachment element to obtain an even stress distribution in the welding of the attachment element to the tower wall.

[0054] FIG. 5 shows a sketch of an attachment element 103 as seen from above. The attachment element is configured to receive two cables 101 and is formed by a bended plate 501 with one eye or aperture 502 at each end. Nooses 503 at the cable ends can then be attached to the eyes 502 by bolts or pins. The attachment element 103 is attached to the tower for example by welding or by mechanical fastening members such as bolts, rivets or the like, or may form an integral part of the tower wall.

[0055] In FIG. 6 is shown an attachment element 103 as attached to a tower section 104 and as seen in a cross sectional view from a side. The attachment element 103 is here formed as a plate element with an opening 502 for receiving a cable end. The wall thickness of the tower section 104 with the attachment elements has an increased thickness 301 adjacent to the attachment element 103. The tower section 104 comprises flanges 601 at both ends for joining of the tower section to other tower sections. The flanges 601 are to be connected by bolts.

[0056] In FIG. 7B is shown in a top view an embodiment of the cable ends 101 as attached to an attachment element 103 at the tower section 104, and as attached in the other end to an anchor element 102. FIG. 7A shows the anchor element 102 from FIG. 7B in a side view. The cable can be tensioned by tensioning the bolts 701 appropriately at the anchor element 102.

[0057] FIG. 8 is a sketch of how the wind turbine tower can be erected and as seen in a top view. A first tower section 401 of the tower has been positioned and the cables 101 have been attached to the second tower section 104 optionally with a portion of the cables still being rolled onto cable drums 802. Here, the two cables to be attached to the same anchor element 102 are rolled onto the same cable drum 802. The set of cables may alternatively be rolled onto separate cable drums. In general the lengths of each of the cables in a set to be attached to the same anchor element are the same. Preferably, the anchor elements are all placed with the same distance to the wind turbine tower. However, even in that case the cable lengths may vary some length due to the possibility of level differences between the anchor elements. A crane 801 then lifts the second tower section 104 with the attached cables 101 onto the first tower section 401 and the tower sections are joined. The crane 801 may then advantageously be used to lift each cable drum 802 with the other cable ends out from the tower to the location of the anchoring elements 102 for attachment and tensioning of the cables. In this way the crane can lift the cables over trees or other types of vegetation or obstacles without having to clear a path on the ground.

[0058] While preferred embodiments of the invention have been described, it should be understood that the invention is not so limited and modifications may be made without departing from the invention. The scope of the invention is defined by the appended claims, and all devices that come within the meaning of the claims, either literally or by equivalence, are intended to be embraced therein.