WO2012130292A1

WO2012130292A1 - Wind turbine tower and method of fabricating a wind turbine tower

Info

Publication number: WO2012130292A1
Application number: PCT/EP2011/054847
Authority: WO
Inventors: Markus Krause
Original assignee: AMSC Windtec GmbH
Current assignee: AMSC Windtec GmbH
Priority date: 2011-03-29
Filing date: 2011-03-29
Publication date: 2012-10-04
Anticipated expiration: 2013-09-29

Abstract

A wind turbine tower and a method of fabricating a wind turbine tower are provided. The wind turbine tower comprises a hollow body (B) formed of a plurality of stacked segmented rings (SR1, SR2, SR3) of wooden panels (S11-S16; S11'-S16'), said hollow body (B) having a channel (CH) formed therethrough; a support profile (PS; PS') disposed below the hollow body (B); a top profile (PT) disposed above the hollow body (B); and a tensioning mechanism (C; C) guided through the channel (CH) and attached under tension to said support profile (PS; PS') and to said top profile (PT) to pretension said stacked segmented rings (SR1, SR2, SR3).

Description

PATENT APPLICATION

Wind Turbine Tower and Method of Fabricating a Wind Turbine Tower

The present invention relates to a wind turbine tower and to a method of fabricating a wind turbine tower.

Various different kinds of wind turbine towers have been proposed during the last decade. The most common types are steel-shell towers designed with flanges and both longitudinal and transversal welds, steel-shell towers with bolted friction joints, concrete towers with pre- tensioned steel tendons, hybrid towers with a lower concrete part and an upper part built as a steel shell, lattice towers and wooden towers.

Today the welded steel shell tower dominates the wind turbine market. However, for road transportation there are limitations due to the width of bridges, tunnels and other obstacles which limit the base diameter approximately to 4.5 metres.

When diameter restrictions tend to make steel-shell welded towers uneconomical, the next option is steel-shell towers with bolted friction joints. Such a tower can be transported as separate cut, bent, drilled and painted steel plates which are assembled at the turbine site.

Also pre-tensioned concrete towers have a long history in wind power generation.

Conventional concrete towers are generally assembled from pre-fabricated elements, cast in sizes allowing road transportation. Concrete towers are capable of absorbing large moments in an economical way.

As a compromise between weight and stability, hybrid towers are appearing on the market with a concrete part for the lower section and a steel-shell tower part for the upper section. This solution also provides the designer with some freedom regarding both the design of the concrete tower and placement of the eigenfrequencies of the tower.

Due to the very large base width, lattice towers provide lower weights and costs as other towers. The tallest wind turbines generally use lattice towers. However, their dynamic properties are hard to control and in conditions large where freezing occurs accumulations of ice may endanger the turbine.

Wood has been used as a construction material for wind turbine blades for decades, but only recently considered for wind turbine towers. Wood is generally known to be an economical construction material resistant to fatigue and buckling. Moreover, wood has much better damping properties than steel.

Therefore, greater attention is paid to wooden towers featuring laminated panels that are stacked crosswise and glued together. The crosswise layering of the longitudinal and transversal laminated panels greatly reduces swelling and shrinking in the panel plane and greatly increases static ability to withstand stress as well as form stability. The panels are assembled on-site to form an enclosed polygonal hollow body that contains all the wiring and ladder and lift systems. With this design fasteners are integrated into the tower components, and at the top of the tower there is a round, steel adaptor, connecting the tower to the turbine nacelle. Hub heights of up to 200 m seem to be technically and economically feasible. The mass of wooden towers is comparable to some made of steel. The base diameter is almost unlimited because wooden towers can be mounted of transportable parts on the construction site.

Today, mobile cranes are generally used to lift tower segments and turbines. However such cranes are typically limited to lifting tower components to heights of 125 to 150 m. Raising tower components beyond that can be achieved with lifting towers, however, use of lifting towers can be quite expensive.

US 2010/0192503 HI discloses a wind turbine tower comprising a hollow body of stacked segmented modules constructed from timber panels. The cross section of the modules decreases from bottom to top of the tower. The modules are of a polygon cross-section and are interconnected by adhesive or bolting together.

WO 2005/028781 A2 discloses a composite tower for a wind turbine. The tower comprises several nested power sections that can telescope to increased heights. Each section may be formed from two or more composite panels connected by two or more connectors, the sections comprising any of a plurality of polygonal shapes. The panels may further comprise tough-tips form-core panels that have great strength properties.

DISCLOSURE OF THE INVENTION

The present invention provides a wind turbine tower according to claim 1 and to a method of fabricating a wind turbine tower according to claim 12.

The idea underlying the present invention is to provide an effective pretensioning of the wooden panels. This is achieved by guiding the tensioning mechanism through one or more channels in the wooden panels and attaching the tensioning mechanism under tension to a support profile and to a top profile by tensioning fasteners such that said tensioning mechanism centrally pretension said stacked segmented rings in their interior. Among other advantages, the pretensioning is homogeneous and the tensioning mechanism are well protected against external influences.

Preferred embodiments are listed in the dependent claims.

According to a preferred embodiment the segmented rings include aligned through-holes to form the channel.

According to another preferred embodiment said tensioning mechanism comprise cables. These cables can be stranded in order to enhance their stability.

According to another preferred embodiment said tensioning fasteners comprise nut and/or wedge fasteners. These type of fasteners are stable and can withstand high tensions.

According to another preferred embodiment support profile and/or said top profile are ring shaped. Thus the geometry of the support profile and/or said top profile can be adapted to the geometry of the stacked segmented rings in order to facilitate the mounting process.

According to another preferred embodiment the lowest one of said stacked segmented rings includes inner threaded sleeves for attaching the lowest one of said stacked segmented rings to the support profile. Thus, additional stability can be provided against external influences such as heavy winds or storms.

According to another preferred embodiment said wooden panels within said segmented rings are horizontally connected by tongue and groove connectors. Thus, an exact alignment can be achieved.

According to another preferred embodiment said wooden panels are made of cross-laminated wood elements and have angled and/or curved and/or straight shape. Thus, polygonal, curved or mixed geometries of the hollow body can be formed.

According to another preferred embodiment said top profile includes press studs for connecting to the uppermost one of said stacked segmented rings. Thus, greater stability of the top profile can be achieved.

According to another preferred embodiment said tensioning mechanism include external extensions which together with said tensioning mechanism serve as lightning conductors, wherein said tensioning mechanism and said external extensions are electrically isolated from the wooden panels.

According to another preferred embodiment neighbouring segmented rings are connected by vertical panel connections which include adjacent step profiles of the rings and at least one fixing screw screwed through a edge of the adjacent step profiles.

In the following preferred embodiments of a wind turbine tower and a method of fabricating a wind turbine tower according to the present invention are described with reference to the enclosed Figures, wherein

Fig. 1 a,b show an embodiment of a wind turbine according to the present invention, namely Fig. la in vertical cross-section and Fig. lb in horizontal cross-section along line AA' in Fig. la; Fig. 2 shows a horizontal cross-section along line AA' in Fig. 1 a for illustrating another embodiment of panels and horizontal panel connections within a segmented ring;

Fig. 3 shows a top view of the top profile of Fig. 1 a;

Fig. 4 shows a partial enlarged cross-section of Fig. la for illustrating an example of the tensioning fastener at the support profile of Fig. la;

Fig. 5 shows a partial enlarged cross-section of Fig. la for illustrating another

embodiment of the tensioning fastener at the support profile of Fig. la;

Fig. 6 shows a partial enlarged cross-section of Fig. la for illustrating still another embodiment of the tensioning fastener at the support profile of Fig. la;

Fig. 7 shows a partial enlarged cross-section of Fig. la for illustrating an example of the tensioning fasterer at the top profile of Fig. la;

Fig. 8 shows a partial enlarged cross-section of Fig. la for illustrating another

embodiment of the tensioning fasterer of Fig. 1 a;

Fig. 9 shows a partial enlarged vertical cross-section in a plane perpendicular to the plane of Fig. la for illustrating vertical panel connections between

neighbouring segmented rings; and

Fig. 10 shows another embodiment of a wind turbine according to the present

invention in vertical cross-section.

BRIEF DESCRIPTION OF THE DRAWINGS

In the Figures, the same reference signs denote the same or equivalent components. Fig. 1 a,b show an embodiment of a wind turbine according to the present invention, namely Fig. la in vertical cross-section and Fig. lb in horizontal cross-section along line A A¹ in Fig. la.

In Fig. 1 a reference sign F denotes a reinforced concrete foundation as installation site for the wind turbine tower 1 according to this embodiment of the present invention.

A ring-shaped hexagonal support profile PS is attached by a fastening mechanism Fl in form of screws to the concrete foundation F. The cross section of the support profile in this example is of u-shape, however, may vary along its length in order to make parts to be explained later accessible for workers. The support profile PS is preferably made of steel or a single metal or metal alloy which exhibits good mechanical stability.

On the support profile PS there is provided a hollow body B of stacked segmented rings SRI, SR2, SR3 of wooden panels SI 1-S16 of straight shape which also exhibit hexagonal cross- section as is hown in Fig. lb. A top profile PT also made of a hexagonal steel ring SE welded to a cylindrical part CY is provided above the uppermost ring SR3 of the stacked segmented rings SRI, SR2, SR3. The cylindrical part CY which is welded to the ring of the top profile serves to support the bearing and nacelle of the wind turbine (not shown here).

The segmented rings SRI, SR2, SR3, the support profile PS and the top profile PT include aligned through-holes TH which form channels CH that start from the support profile PS and end at the top profile PT.

A tensioning mechanism C in the form of stranded cables are provided through the channels CH and attached under tension to the support profile PS and to the top profile PT by tensioning fasteners TF such that the tensioning mechanism C pre-tensions the stacked segmented rings SRI, SR2, SR3 along the height direction. The tensioning fasteners TF, shown schematically in Figure la, however, will be explained greater detail below.

Still with reference to Fig. la, the support profile PS is connected to the lowest one of said stacked segmented rings SRI by a fastener F2, here screws. Each screw is screwed through corresponding holes of the support profile PS. Referring to Fig. lb, the stacked segmented rings SRI, SR2, SR3 are also of hexagonal shape with decreasing diameter such that the diameter of the hollow body decreases from the support profile PS to the top profile PT.

As may be further seen from Fig. lb, each wooden panel SI 1 to S16 includes two through- holes TH for forming corresponding channels for the tensioning mechanism C. The wooden panels SI 1 to S 16 are horizontally connected by tongue and groove connectors NF formed in the panels SI 1 to S16 so as to form stable segmented rings. The tongue and groove connectors NF are formed by extensions and grooves of the wooden panels S 11 to S 16 and may be fixed either by an adhesive or by other fasteners, e.g. screws.

In order to achieve the diminishing diameter from the bottom to the top, the wooden panels SI 1 to S 16 have a trapezoidal shape. Each wooden panel is on the order of several metres wide, is several metres high and has a thickness of 0.1 to 0.6 metres. The wooden panels are made of cross-laminated wood elements in order to achieve a high stiffness and endurability.

The construction of the embodiment shown in Fig. 1 a, b provides a stable wooden tower which is light weight relative to concrete towers and can be used to achieve tower heights of up to about 200 metres.

In particular, the use of the tensioning mechanism in form of pre-tensioned cables allows the use of a wooden tower construction as a substitute for a concrete or steel tower, conventional structures known for their capability of withstanding relatively high fatigue loads that the tower for supporting the wind turbine is subjected. A wooden tower with pre-tensioned cables C is less expensive, easier to manufacture and easier to transport than a conventional steel or concrete tower.

Fig. 2 shows a horizontal cross-section along line AA' in Fig. la for illustrating another embodiment of panels and horizontal panel connections within a segmented ring.

In the example of Fig. 2, the wooden panels do not have a straight shape as in Fig. lb, but are angled shape, and the tongue and groove connectors NF', which may be glued together, are not provided at the vertices of the panels; instead they are provided along the length, e.g. in the middle, of each straight section. Apart from this constructional difference, the shape of the segmented rings of this example is the same as the shape of the segmented rings of the example of Fig. lb.

Fig. 3 shows a top view of the top profile of Fig. la. As may be seen from Fig. 3, the hexagonal steel ring SE and the cylindrical part CY are welded together along a weld seam WR. The pitch and shape of the throughholes TH of the hexagonal steel ring SE correspond to the ones of the stacked segmented rings SI, S2, S3.

Fig. 4 shows a partial enlarged cross-section of Fig. la for illustrating an example of the tensioning fastener at the support profile of Fig. la.

As may be seen from Fig. 4, the tensioning fasteners TF of this embodiment comprise wedges WD for clamping the pre-tensioned cable C as well as a nut NU screwed to a threaded sleeve SL provided at the end of the cable C. By such a combination of wedge clamping and notch tensioning, easy adjustment and re-adjustment of the tension of the cable C is possible. In genera, the stress in the cable or the cables depends on the type of cables, e.g. cross-section, size of the tower and occurring loads, and e.g. be controlled every six months.

Fig. 5 shows a partial enlarged cross-section of Fig. la for illustrating another embodiment of the tensioning fastener at the support profile of Fig. 1 a.

Referring to Fig. 5, the details of the fastener F2 for connecting the lowest one SRI of the segmented rings to the support profile PS is shown. In particular, the segmented ring SRI includes inner threaded sleeves G which are used for attaching the segmented ring SRI to the support profile PS by means of screws SC which are screwed through through-holes T of the support profile PS.

This additional stabilization allows that bending moments of 100,000 kN and more which occur very rarely in the lifetime of wind turbine towers to be sustained. The threaded sleeves G typically are located 30 to 60 cm above the support profile PF in the interior of the wooden panels of the segmented ring SRI . It should be noted that the cross-section of the support profile PS varies in order to make the fixing screws SC accessible for workers as well as the tensioning fasteners TF.

Fig. 6 shows a partial enlarged cross-section of Fig. la for illustrating still another embodiment of the tensioning fastener at the support profile of Fig. 1 a.

In this embodiment, the concrete foundation F' is obliquely arranged. The lower support profile PS' has a double-t structure which is more easily accessable for the mounting and/or repair process. The remaining parts are the same as in Fig. 4 and 5, respectively. Particularly, a nut NU is screwed to a threaded sleeve SL provided at the end of the cable C as tensioning fastener TF.

Fig. 7 shows a partial enlarged cross-section of Fig. la for illustrating an example of the tensioning fastener at the top profile of Fig. la.

In the example of Fig. 7, the top profile PT includes press studs D disposed on the portion of the top profile that contacts the uppermost segmented ring SR3 and which are pressed in the wood of the segmented ring SR3 at the time of pre-tensioning the cable C. This arrangement ensures that there is no horizontal movement of the top Profile PT relative to the segmented ring SR3. Of course, additional fasterners such as screws or screws in connection with threaded sleeves as used for the support profile PS can also be used for connecting of the top profile PT to the uppermost segment ring SR3. However, the pre- stressing cables should be strong enough to take the full load under any load condition.

Moreover, in Fig. 7 reference sign NSV schematically denotes a tension control and adjustment mechanism for monitoring the tension in the cable C and for providing an indication of deviations by a corresponding indicator.

Fig. 8 shows a partial enlarged cross-section of Fig. la for illustrating another embodiment of the tensioning fasterer of Fig. la. The tensioning fastener of Fig. 8 which can also be used for the support profile PS and the top profile PT includes a steel plate SK with four holes HI to H4. Cables CI to C4 are led through each channel CH and pre-stressed by appropriate tensioning. The pre-stressed cables CI to C4 are then fixed by means of wedges WD in their respective pre-stressed positions.

Fig. 9 shows a partial enlarged vertical cross-section in a plane perpendicular to the plane of Fig. l a for illustrating vertical panel connections between neighbouring segmented rings.

As shown in Fig. 9, neighbouring segmented rings SRI, SR2 are connected by vertical panel connections VC which include adjacent step profiles ST provided in the rings SRI , SR2 and aligned to each other. A fixing screw SF is screwed through an edge K of the adjacent step profile ST. Thus, a precise and stable alignment of neighbouring segmented rings SRI , SR2 may be achieved. Optionally, the head of the fixing screw SF can be provided in a pocket of the wooden panels such that a smooth outer surface is provided. Optionally, one ore more additional fixing screws SF' may be used for this connection.

Because the horizontal connection gaps are pre-stressed loads from normal operation typically do not cause tension forces in the screws SF. The screws SF will only become stressed if objected to abnormal loads. Tension force in the screws SF is then the difference of abnormal loads minus the loads which the pre-stressing cables can absorb.

Fig. 10 shows another embodiment of a wind turbine according to the present invention in vertical cross-section.

In Fig. 10 reference sign F denotes a reinforced concrete foundation as installation site for the wind turbine tower 1 ' according to this embodiment of the present invention.

The tensioning mechanism C of the embodiment shown in Fig. 10 includes external extensions CV which are electrically connected to the cables C by means of the tensioning fasteners TP', The cables C are electrically isolated from the wooden panels by means of an appropriate plastic mantle. Preferably the tensioning fasteners TF' also insulate the cables C and the extensions CV electrically form the top profile PT. By such a construction, the extensions CV together with the isolated cables C may serve as lightening conductors providing an electrically conductive path from the upper end of the extensions CV to the ground. Additional ground connections (not shown) may be provided in electrical contact with the support profile PS.

In this case of construction, the cables C fulfil both the function of pretensioning as well as an electrical ground-path function thereby enhancing the cost effectiveness of the wind turbine power of this embodiment.

Although detailed explanations of wind turbine towers have been provided with reference to particular embodiments, the invention is not restricted thereto and various modifications can be made by the average person skilled in the art without departing from the scope of the invention. In particular, the various explained embodiments may be arbitrarily combined with each other.

Moreover, the shape of the segmented rings is not limited to the illustrated hexagonal shape but can be of arbitrary shape such as curved shape, polygonal shape or combinations thereof.

Also the type of the tensioning mechanism is not limited to stranded cables, but can be also rigid rods or combinations of rods and cables or multiple rods and / or cable within each channel.

The shape of the support profile is not restricted to the ring shape but the support profile can also be constituted of a plurality of profile elements which are separately fixed to the foundation.

Also the type of the horizontal connection between the individual panels and the vertical connections between the individual rings is not limited to the examples shown here.

Claims

1. A wind turbine tower comprising: a hollow body (B) formed of a plurality of stacked segmented rings (SRI , SR2, SR3) of wooden panels (SI 1 -SI 6; SI l'-S16'), said hollow body (B) having a channel (CH) formed therethrough; a support profile (PS; PS') disposed below the hollow body (B); a top profile (PT) disposed above the hollow body (B); and a tensioning mechanism (C; C) guided through the channel (CH) and attached under tension to said support profile (PS; PS') and to said top profile (PT) to pretension said stacked segmented rings (SRI, SR2, SR3).

2. The wind turbine tower of claim 1, wherein the segmented rings (SRI, SR2, SR3) include aligned through-holes (TH) to form the channel (CH).

3. The wind turbine tower of claim 1 or 2, wherein wherein said tensioning mechanism (C; C) comprise cables (C; C).

4. The wind turbine tower of claim 1, 2 or 3, wherein said tensioning fasteners (TF; TF, TF') comprise nut (NU) and/or wedge (WD) fasteners.

5. The wind turbine tower according to one of the preceding claims, wherein support profile (PS; PS') and/or said said top profile (PT) are ring shaped.

6. The wind turbine tower according to one of the preceding claims, wherein the lowest one (SRI) of said stacked segmented rings (SRI , SR2, SR3) includes inner threaded sleeves (G) for attaching the lowest one (SRI) of said stacked segmented rings (SRI, SR2, SR3) to the support profile (PS; PS').

7. The wind turbine tower according to one of the preceding claims, wherein said wooden panels (SI 1-S16; SI l'-S16') within said segmented rings (SRI, SR2, SR3) are horizontally connected by tongue and groove connectors (NF; NF').

8. The wind turbine tower according to one of the preceding claims, wherein said wooden panels (SI 1 -SI 6; SI l'-S16') are made of cross-laminated wood elements and have angled and/or curved and/or straight shape.

9. The wind turbine tower according to one of the preceding claims, wherein said top profile (PT) includes press studs (D) for connecting to the uppermost one (SR3) of said stacked segmented rings (SRI , SR2, SR3).

10. The wind turbine tower according to one of the preceding claims, wherein said tensioning mechanism (C; C) include external extensions (CV) which together with said tensioning mechanism (C; C) serve as lightning conductors, and wherein said said tensioning mechanism (C; C) and said external extensions (CV) are electrically isolated from the wooden panels (SI 1 -SI 6; SI l'-S16').

1 1. The wind turbine according to one of the preceding claims, wherein neighbouring segmented rings (SRI, SR2) are connected by vertical panel connections (VC) which include adjacent step profiles (ST) of the rings (SRI, SR2) and a fixing screw (SF, SF') screwed through a edge (K) of the adjacent step profiles (ST).

12. A method of fabricating a wind turbine tower comprising the steps of: forming a hollow body (B) by stacking a plurality of segmented rings (SRI , SR2, SR3) of wooden panels (SI 1-S16; Sl l '-S16'); forming a channel (CH) through said hollow body (B); and pretension said stacked segmented rings (SRI, SR2, SR3) by means of a tensioning mechanism (C; C) extending through the channel (CH).

13. The method of claim 12, wherein a lowest one (SRI) of said stacked segmented rings (SRI, SR2, SR3) includes inner threaded sleeves (G), further comprising the step of attaching the lowest one (SRI) of said stacked segmented rings (SRI, SR2, SR3) to a support profile (PS; PS') by screwing screws (SC) through throughholes (T) of the support profile (PS; PS') into the inner threaded sleeves (G).

14. The method of claim 12 or 13, wherein said wooden panels (SI 1 -SI 6; SI l'-S16') within said segmented rings (SRI, SR2, SR3) are horizontally connected by tongue and groove connectors (NF; NF').

15. The method of claim 12, 13 or 14, wherein a top profile (PT) including press studs (D) is provided, further comprising the step of connecting to the uppermost one (SR3) of said stacked segmented rings (SRI, SR2, SR3) to said top profile (PT) by pressing said press studs (D) into the uppermost one (SR3) of said stacked segmented rings (SRI, SR2, SR3).

16. The method of one of claims 12 to 15, wherein neighbouring segmented rings (SRI , SR2) are connected by vertical panel connections (VC) which include adjacent step profiles (ST) of the rings (SRI, SR2) and at least one fixing screw (SF, SF') screwed through a edge (K) of the adjacent step profiles (ST).