WO2017215718A1

WO2017215718A1 - A wind turbine tower and a method for erecting a wind turbine tower

Info

Publication number: WO2017215718A1
Application number: PCT/DK2017/050176
Authority: WO
Inventors: Casper LYNGSØ
Original assignee: Vestas Wind Systems A/S
Priority date: 2016-06-14
Filing date: 2017-05-30
Publication date: 2017-12-21

Abstract

A wind turbine tower(8) comprisinga plurality of tower sections (1, 3, 6) arranged along a longitudinal direction defined by the wind turbine tower(8) is disclosed. A lower tower section (3) and an upper tower section(6) define a pair of tower sections. At least one pair of tower sections in the wind turbine tower (8) comprises an intermediate flange (4) arranged between the lower tower section (3) and the upper tower section (6). The intermediate flange (4) isprovided with at least one assembly means (9) arranged to receive an assembly truss (7), the intermediate flange (4) thereby being connectable to a crane (5) via the assembly means (9) and at least one assembly truss(7). The intermediate flange (4) is further provided with a plurality of through-going holes(10). The lower tower section(3), the intermediate flange (4) and the upper tower section (6) are interconnected by means of a plurality of bolts (12), each bolt (12) extending through a portion of the lower tower section (3), one of the through-going holes (10) of the intermediate flange (4) and a portion of the upper tower section (6). A crane (5) can be tied to the wind turbine tower (8) without requiring additional bolt connections or adjustments to standard tower sections (1, 3, 6).

Description

A WIND TURBINE TOWER AND A METHOD FOR ERECTING A WIND TURBINE TOWER

FIELD OF THE INVENTION

The present invention relates to a wind turbine tower comprising a plurality of tower sections. The wind turbine tower of the invention is arranged to have a crane tied thereto during erection of the wind turbine. The invention further relates to a method for erecting such a wind turbine tower.

BACKGROUND OF THE INVENTION

When erecting wind turbines, a crane is often used for lifting various components of the wind turbine into position. For instance, the tower of the wind turbine may comprise two or more tower sections, which are assembled to form the tower. Such tower sections are often lifted into position using a crane. Furthermore, a number of other wind turbine components, such as nacelle, hub, wind turbine blades, etc., may be lifted into position once the wind turbine tower has been erected, also by means of the crane.

An unsupported crane, i.e. a crane which is not tied to another structure, normally has a maximum lifting height, which is determined by the height of the crane. Extending the height of the crane in order to obtain a higher maximum lifting height will result in the crane becoming unstable. Thus, the maximum lifting height of available cranes defines an upper limit for the height of wind turbines being erected using a crane.

WO 2012/163906 Al discloses a method for constructing a wind turbine comprising a tower structure. The tower structure comprises at least two sections. A supporting head element is placed on top of the first section, and pre-fabricated parts of the first section are connected to each other, to the supporting head element and to a supporting base element of a foundation of the wind turbine. Once the first section has been connected, a rotating tower crane is horizontally anchored to the supporting head element and a second section of the tower structure is subsequently mounted with the aid of the rotating tower crane.

DESCRIPTION OF THE INVENTION

It is an object of embodiments of the invention to provide a wind turbine tower with improved capabilities of having a crane tied thereto. It is a further object of embodiments of the invention to provide a method for erecting a wind turbine tower, in which a crane can be tied to the wind turbine tower.

According to a first aspect the invention provides a wind turbine tower comprising :

- a plurality of tower sections arranged along a longitudinal direction defined by the wind turbine tower, wherein two adjacent tower sections of the plurality of tower sections define a pair of tower sections comprising a lower tower section and an upper tower section, wherein at least one pair of tower sections in the wind turbine tower comprises:

- an intermediate flange arranged between the lower tower section and the upper tower section of the pair of tower sections, the intermediate flange being provided with at least one assembly means arranged to receive an assembly truss, the intermediate flange thereby being connectable to a crane via the assembly means and at least one assembly truss, the intermediate flange further being provided with a plurality of through-going holes, wherein the lower tower section, the intermediate flange and the upper tower section are interconnected by means of a plurality of bolts, each bolt extending through a portion of the lower tower section, one of the through-going holes of the intermediate flange and a portion of the upper tower section.

According to the first aspect, the invention relates to a wind turbine tower. In the present context the term 'wind turbine tower' should be interpreted to mean a tower structure used in a wind turbine, and being arranged to carry a nacelle of the wind turbine. The wind turbine tower defines a longitudinal direction which normally extends substantially vertically from a foundation of the wind turbine to the top of the tower, where the nacelle is normally mounted. The wind turbine tower comprises a plurality of tower sections arranged along the

longitudinal direction defined by the wind turbine tower. In the present context, the term 'tower section' should be interpreted to mean a component forming a part of the wind turbine tower, the component covering the full periphery of the wind turbine tower. Since the tower sections are arranged along the longitudinal direction defined by the wind turbine tower, they are arranged one above the other along the length of the wind turbine tower, and thereby the plurality of tower sections essentially form the wind turbine tower. Two adjacent tower sections of the plurality of tower sections define a pair of tower sections. In the present context the term 'adjacent tower sections' should be interpreted to mean two tower sections arranged in the wind turbine tower with no other tower section there between. Accordingly, a pair of tower sections comprises a lower tower section and an upper tower section, the lower tower section being arranged below the upper tower section in the wind turbine tower.

At least one pair of tower sections in the wind turbine tower comprises an intermediate flange arranged between the lower tower section and the upper tower section. Thus, along the longitudinal direction of the wind turbine tower, the lower tower section is arranged at the lowest position, with the intermediate flange arranged above the lower tower section and the upper tower section arranged above the intermediate flange. Accordingly, the intermediate flange also forms part of the wind turbine tower.

The intermediate flange is provided with at least one assembly means arranged to receive an assembly truss. Thereby the intermediate flange is connectable to a crane via the assembly means and at least one assembly truss. Since the intermediate flange forms part of the wind turbine tower, the wind turbine tower thereby allows a crane to be tied thereto. As described above, this allows the maximum lifting height of the crane to be increased, because the crane structure is further stabilised and strengthened by the tower structure, thus thereby allowing higher wind turbine towers to be erected by means of the crane. The intermediate flange is further provided with a plurality of through-going holes. The lower tower section, the intermediate flange and the upper tower section are interconnected by means of the plurality of bolts, each bolt extending through a portion of the lower tower section, one of the through-going holes of the intermediate flange and a portion of the upper tower section. Accordingly, the lower tower section, the intermediate flange and the upper tower section are interconnected essentially in the same manner, except for possibly requiring longer bolts, as the lower tower section and the upper tower section would normally be interconnected if the intermediate flange had not been arranged between the lower tower section and the upper tower section. Thereby the intermediate flange, and thereby the capability of the tower to have a crane tied thereto, can be provided without requiring additional bolt assemblies of the wind turbine tower, and without requiring adjustments of the design of the tower sections forming the wind turbine tower. This is an advantage, because thereby standard tower sections can be used for forming the wind turbine tower and the erection of the wind turbine tower is not more complicated than erection of a similar wind turbine tower without the capability of having a crane tied thereto. The tower sections may be made from steel. According to this embodiment, the wind turbine tower is a steel tower. Alternatively, the tower sections could be made from concrete, or some of the tower sections could be made from steel and some of the tower section could be made from concrete. In the latter case the wind turbine tower is a hybrid tower. The lower tower section may be provided with an upper flange and the upper tower section may be provided with a lower flange, and each of the bolts may interconnect the upper flange of the lower tower section, the intermediate flange and the lower flange of the upper tower section, via a through-going hole of the intermediate flange. According to this embodiment, the lower tower section and the upper tower section are both provided with connecting flanges allowing them to be connected to another tower section. The flanges of the tower sections are arranged with the intermediate flange there between, and the three flanges are interconnected by means of the plurality of bolts, and via the through-going holes of the intermediate flange. The upper flange of the lower tower section and the lower flange of the upper tower section may also be provided with through-going holes. In this case, the through-going holes of the upper flange, the intermediate flange and the lower flange may be aligned, and each bolt may extend through an aligned set of through-going openings.

The assembly means may be mounted on the intermediate flange in a detachable manner. For instance, the assembly means may be mounted on the intermediate flange via a threaded connection, via a split connection, or in any other suitable manner which allows the assembly means to be detached from the intermediate flange. According to this embodiment, the assembly means may be mounted on the intermediate flange during erection of the wind turbine tower, in order to allow a crane to be tied to the wind turbine tower. However, when the erection of the wind turbine tower has been completed, the assembly means may be detached from the intermediate flange. Thereby a more smooth wind turbine tower is obtained.

For instance, the intermediate flange may be configured with attachment means for attachment of the at least one assembly means to the intermediate flange, e.g. in the form of a threaded hole arranged to engage a mating outer thread on the assembly means.

As an alternative, the assembly means may be permanently mounted on the intermediate flange. For instance, the assembly means may form an integral part of the intermediate flange.

The intermediate flange may be provided with at least two assembly means, and two of the assembly means may be arranged along a periphery of the intermediate flange with an angular distance which is equal to or smaller than 180°. According to this embodiment, the at least two assembly means may advantageously be arranged on a side of the wind turbine tower which faces the crane. Thereby the crane can easily be tied to the assembly means via assembly trusses. This embodiment is especially advantageous when configured for a crane, where, in the plane of the intermediate flange, the diameter of a circumscribed circle about the crane is equal to or smaller than the diameter of the tower.

The angular distance between the assembly means may advantageously be arranged for a given crane, such that the angle between the radial towards the respective assembly means and the respective truss when installed is equal to or exceeds 90°. The assembly trusses interconnecting the assembly means and the crane will thus be arranged substantially tangentially to the periphery of the wind turbine tower. The truss is thus arranged such that the forces applied to the assembly means apply a shear force to the assembly means that may have a component acting in the direction of the radial towards the centre of the tower. Thereby the risk of the assembly means being accidentally pulled out of the intermediate flange while the crane is tied to the wind turbine tower is minimised. This enables an embodiment where the assembly means are mounted detachably on the intermediate flange.

Accordingly, the angular distance between the two assembly means may be within the interval 90° to 180°, such as within the interval 120° to 175°, such as within the interval 150° to 170°. The optimum angular distance depends on the relationship between the

aforementioned diameter of the circumscribed circle about the crane and the diameter of the tower in the plane of the intermediate flange. With smaller diameters of the circumscribed circle about the crane the angular distance may decrease and vice versa.

At least one assembly means may be selected among eye bolts, hooks or lugs. Such assembly means are all very suitable for receiving an assembly truss, thereby connecting the assembly truss to the intermediate flange. Assembly means in the form of eye bolts, hooks or lugs may advantageously be mounted on the intermediate flange in a detachable manner, as described above. However, it is not ruled out that such assembly means form an integral part of the intermediate flange.

As an alternative, other suitable kinds of assembly means may be used.

The wind turbine tower may further comprise at least one further pair of tower sections each having an intermediate flange arranged between a lower tower section and an upper tower section of the at least one further pair of tower sections. According to this embodiment, at least two intermediate flanges comprising assembly means as described above are arranged in the wind turbine tower. Since the intermediate flanges form part of two different pairs of tower sections, they are displaced relative to each other along the longitudinal direction defined by the wind turbine tower. Accordingly, the crane may, in this case, be tied to the wind turbine tower at at least two different positions along the longitudinal direction defined by the wind turbine tower. This further stabilises the crane and allows the maximum lifting height of the crane to be increased even further. The intermediate flange may comprise fixing means for attachment of the intermediate flange to a portion of the lower tower section or a portion of the upper tower section.

According to this embodiment, the intermediate flange may be at least temporarily fixed to the lower tower section before the lower tower section is erected or to the upper tower section before the upper tower section is lifted and placed on top of the lower tower section. In this respect the term "on top of" refers to the position of the upper tower section above the lower tower section with the intermediate flange in between the pair of tower sections, i.e. the upper tower section is not in direct contact with the lower tower section.

In an embodiment of the invention the intermediate flange may be fixed completely relatively to the lower tower section. Alternatively, the intermediate flange may be fixed in a radial direction relative to the lower tower section, but may be allowed to perform axial movement relative to the lower tower section. In this case, fixing the intermediate flange to the lower tower section may ensure proper alignment of the through-going holes of the intermediate flange with respect to the lower tower flange, e.g. with respect to through-going holes formed in an upper flange of the lower tower section. By fixing the intermediate flange to the lower tower section, it is obtained that the lower tower section and the intermediate flange can be handled as one unit during erection of the wind turbine tower.

The fixing means may, e.g., be selected among pins extending into apertures in the intermediate flange and a portion of the lower tower section or bolts extending through the intermediate flange and into a portion of the lower tower section.

In another embodiment of the invention the intermediate flange may be fixed to the upper tower section with proper alignment of the through-going holes of the intermediate flange with respect to the upper tower flange, e.g. with respect to through-going holes formed in lower flange of the upper tower section. By fixing the intermediate flange to the upper tower section, it is obtained that the upper tower section and the intermediate flange can be handled as one unit during erection of the wind turbine tower. The fixing means may be bolts extending into apertures in the intermediate flange and a portion of the upper tower section.

According to a second aspect the invention provides a method for erecting a wind turbine tower, the method comprising the steps of: - providing a lower tower section, an upper tower section and an intermediate flange, the intermediate flange being provided with at least one assembly means arranged to receive an assembly truss, and the intermediate flange being provided with a plurality of through-going holes,

- erecting the lower tower section at an installation site, - arranging the intermediate flange, such that it is positioned between the pair of tower sections when installed in the wind turbine tower,

- arranging the upper tower section on top of the lower tower section, interconnecting the lower tower section, the intermediate flange and the upper tower section by means of a plurality of bolts, each bolt extending through a portion of the lower tower section, one of the through-going holes of the intermediate flange and a portion of the upper tower section, and

- connecting the assembly means of the intermediate flange to a crane via at least one assembly truss.

The method according to the second aspect of the invention may advantageously be used for erecting a wind turbine tower according to the first aspect of the invention. The person skilled in the art would therefore readily recognise that any feature described in combination with the first aspect of the invention could also be combined with the second aspect of the invention, and vice versa. Accordingly, the remarks set forth above are equally applicable here. According to the method of the second aspect of the invention, a lower tower section, an upper tower section and an intermediate flange are initially provided. The lower tower section and the upper tower section are arranged to define a pair of tower sections of the resulting wind turbine tower, in the manner described above with reference to the first aspect of the invention. The intermediate flange is provided with at least one assembly means arranged to receive an assembly truss, and with plurality of through-going holes. This has already been described above.

The tower is erected at an installation site, and the intermediate flange is arranged, such that it is positioned between the pair of tower sections when installed in the wind turbine tower. This will be described in further detail below.

The lower tower section may be erected first. Then the intermediate flange may be arranged on top of the lower tower section, or the intermediate flange may be arranged on top of the lower tower section before the lower tower section is erected. In any event, when these two steps have been completed, the lower tower section is in its final position in the wind turbine tower, with the intermediate flange arranged on top.

Alternatively, the lower tower section is erected as a first step. Then, the intermediate flange is fixed to the upper tower section. The upper tower section including the intermediate flange is lifted into position above the lower tower section and placed on top of the lower tower section.

Thereby the lower tower section, the intermediate flange and the upper tower section are arranged relatively to each other in such a manner that the lower tower section is arranged at a lowermost position, the intermediate flange is arranged above the lower tower section, and the upper tower section is arranged above the intermediate flange. In other words, the intermediate flange is arranged between the lower tower section and the upper tower section.

As a final step in the process of erecting the pair of tower sections, the lower tower section, the intermediate flange and the upper tower section are interconnected. This is performed using a plurality of bolts, and each bolt extends through a portion of the lower tower section, one of the through-going holes of the intermediate flange and a portion of the upper tower section. This has already been described in detail above with reference to the first aspect of the invention.

Finally, the assembly means of the intermediate flange is connected to a crane via at least one assembly truss. Thereby, the intermediate flange allows the crane to be tied to the wind turbine tower during erection of the wind turbine tower, and the maximum lifting height of the crane can thereby be increased, as described above. Furthermore, this is obtained without having to increase the number of bolt assemblies of the wind turbine tower, and using standard tower sections.

The step of arranging the intermediate flange on top of the lower tower section may be performed prior to the step of erecting the lower tower section, and the method may further comprise the step of fixing the intermediate flange to the lower tower section. According to this embodiment, the intermediate flange is arranged on top of the lower tower section and fixed thereto before the lower tower section is erected. Thus, in this case the lower tower section and the intermediate flange are handled as one component during erection of the wind turbine tower, i.e. when the lower tower section is erected; the intermediate flange is erected along with it. Since the intermediate flange is fixed to the lower tower flange, it is prevented that the lower tower section and the intermediate flange move relative to each other during erection of the lower tower flange and the intermediate flange.

As an alternative, the step of erecting the lower tower section may be performed prior to the step of arranging the intermediate flange on top of the lower tower section. According to this embodiment, the lower tower section and the intermediate flange are handled separately during erection of the wind turbine tower, and the intermediate flange is lifted onto the erected lower tower section.

Also the intermediate flange can be connected to the upper tower section prior to it being lifted into position on top of the lower tower section. It is herewith achieved that the lifting of the tower sections can be performed without having to accommodate the intermediate flange in a lifting tool or lifting yoke.

The step of connecting the assembly means of the intermediate flange to a crane may be performed prior to the step of arranging the upper tower section on top of the intermediate flange. According to this embodiment, the crane is already tied to the intermediate flange when the second tower section is lifted into position on top of the intermediate flange.

Thereby the crane is already stabilised when it is used for lifting the upper tower section.

As an alternative, the step of connecting the assembly means of the intermediate flange to the crane may be performed after the step of arranging the upper tower section on top of the intermediate flange. The method may further comprise the step of detaching the assembly means from the intermediate flange when erection of the wind turbine has been completed. According to this embodiment, when erection of the wind turbine tower has been completed, and it is therefore no longer required to tie the crane to the wind turbine tower, the assembly means can be detached from the intermediate flange. Thereby a more smooth wind turbine tower is obtained, even though the intermediate flange forms part of the resulting wind turbine tower.

The method may further comprise erecting one or more further tower sections, i.e. adding one or more further tower sections to the wind turbine tower. The method may further comprise adding one or more further intermediate flanges to the wind turbine tower, essentially in the manner described above. This will allow the crane to be tied to the wind turbine tower at at least two different positions along the longitudinal direction defined by the wind turbine tower.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described in further detail with reference to the accompanying drawings in which

Figs. 1-5 illustrate various steps of a method for erecting a wind turbine tower according to an embodiment of the invention,

Fig. 6 is a cross sectional view of a wind turbine tower according to an embodiment of the invention, and

Fig. 7 is a cross sectional view of a bolt connection of a wind turbine tower according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

Figs. 1-5 illustrate various steps of a method for erecting a wind turbine tower according to an embodiment of the invention.

In Fig. l a first tower section 1 has been mounted on a foundation 2 of the wind turbine tower at an installation site of the wind turbine. A lower tower section 3 and an intermediate flange 4 have been provided, and are ready to be erected at the installation site. The intermediate flange 4 is provided with at least one assembly means, see fig. 7 and with a plurality of through-going holes, see fig. 7.

In Fig. 2 the intermediate flange 4 is in the process of being arranged on top of the lower tower section 3 by means of a crane, see fig. 3-6. The lower tower section 3 is provided with guide pins 15 arranged to mate with holes or openings formed in the intermediate flange 4. Thereby the intermediate flange 4 is fixed to the lower tower section 3, at least in a radial direction, once the intermediate flange 4 has been arranged on top of the lower tower section

3. This prevents relative movements of the lower tower section 3 and the intermediate flange

4, thereby allowing the lower tower section 3 and the intermediate flange 4 to be handled as a single unit subsequently.

In Fig. 3, by using a crane the lower tower section 3 has been lifted onto the first tower section 1, along with the intermediate flange 4, and using a crane 5. The lower tower section 3 and the intermediate flange 4 are still connected to the crane 5. Once the lower tower section 3 is in place on top of the first tower section 1, as shown in Fig. 3, the first tower section 1 and the lower tower section 3 can be bolted together.

It should be noted, that the lower tower section 3 could, alternatively, be lifted onto the first tower section 1 without the intermediate flange 4 arranged thereon. In this case the intermediate flange 4 is subsequently lifted separately onto the lower tower section 3.

In Fig. 3 an upper tower section 6 has further been provided. In Fig. 4 the crane 5 has been connected to at least one assembly means, see fig. 7 of the intermediate flange 4, by means of at least one assembly truss 7. Accordingly, the crane 5 is tied to the wind turbine tower, via the intermediate flange 4, and the crane 5 is thereby stabilised, allowing the maximum lifting height of the crane 5 to be increased.

Furthermore, in Fig. 4 the upper tower section 6 is in the process of being lifted to a position on top of the intermediate flange 4, by means of the crane 5.

In Fig. 5 the upper tower section 6 is arranged on top of the intermediate flange 4. Thereby the lower tower section 3 and the upper tower section 6 forms a pair of tower sections arranged along a longitudinal direction of the wind turbine tower, with the intermediate flange 4 arranged there between. The lower tower section 3, the intermediate flange 4 and the upper tower section 6 can now be interconnected by means of a plurality of bolts. Each bolt extends through a portion of the lower tower section 3, e.g. an upper flange of the lower tower section 3, one of the through- going holes of the intermediate flange 4 and a portion of the upper tower section 6, e.g. a lower flange of the upper tower section 6. Accordingly, the intermediate flange 4 is included in the wind turbine tower, between the lower tower section 3 and the upper tower section 6, by means of a single set of bolts, which would also be required in the case that the lower tower section 3 and the upper tower section 6 were connected directly to each other. Accordingly, the capability of tying the crane 5 to the wind turbine tower is obtained without requiring additional bolt assemblies, and without requiring adjustments to the standard tower sections 1, 3, 6 forming the wind turbine tower.

Further tower sections and/or further intermediate flanges may be mounted on top of the upper tower section 6, using the crane 5, thereby completing the wind turbine tower. Once erection of the wind turbine tower has been completed, the crane 5 may further be used for lifting a nacelle, a hub and/or one or more wind turbine blades to the top of the wind turbine tower.

In another embodiment (not shown) in fig. 2-3 the lower tower section 3 is lifted on top of the first tower section 1 without the intermediate flange 4 being located on the lower tower section 3. In fig. 4 before the upper tower section 6 is lifted too far off the ground the intermediate flange 4 is attached to the bottom of the upper tower section 6 and lifted into position on top of the lower tower section 3. In this case the assembly truss 7 cannot be connected to the intermediate flange 4 before the upper tower section 6 is lifted. Thus the assembly truss 7 is connected after tower sections have been interconnected in fig. 5.

Fig. 6 is a cross sectional view of a wind turbine tower 8 according to an embodiment of the invention. An upper surface of an intermediate flange 4 is shown. The intermediate flange 4 is arranged between a lower tower section and an upper tower section of the wind turbine tower 8, essentially in the manner illustrated in Figs. 1-5. The intermediate flange 4 is provided with two assembly means 9 in the form of lugs. Each assembly means 9 is connected to a crane 5 via an assembly truss 7. Accordingly, the crane 5 is tied to the wind turbine tower 8 in the manner described above. The assembly means 9 may be mounted on the intermediate flange 4 in a detachable manner, e.g. by means of a threaded connection or by means of a split connection. Alternatively, the assembly means 9 may form an integral part of the intermediate flange 4.

The assembly means 9 are arranged along a periphery of the intermediate flange 4 with an angular distance which is smaller than, but relatively close to, 180°. This allows the assembly trusses 7 to be easily connected to the assembly means 9, while it is prevented that the assembly means 9 are accidentally detached from the intermediate flange 4 due to a pull from the crane 5.

The intermediate flange 4 is further provided with a plurality of through-going holes 10. Each through-going hole 10 is arranged to receive a bolt in order to interconnect the intermediate flange 4 with a lower tower section and an upper tower section, as described above. This will also be described in further detail below with reference to Fig. 7.

The intermediate flange 4 further comprises a plurality of fixing means 11 for attaching the intermediate flange 4 to a portion of a lower tower section. The fixing means 11 could, e.g., be in the form of guiding pins or in the form of bolts.

Fig. 7 is a cross sectional view of a bolt connection of a wind turbine tower according to an embodiment of the invention. A lower tower section 3, an intermediate flange 4 and an upper tower section 6 are interconnected by means of a plurality of bolts 12, one of which is shown.

The bolt 12 extends through an upper flange 13 of the lower tower section 3, a through- going hole 10 of the intermediate flange 4 and a lower flange 14 of the upper tower section 6.

An assembly means 9 of the intermediate flange 4 is shown by a dotted line in order to illustrate that the assembly means 9 may be detached from the intermediate flange 4.

The bolts 12 in the joint between the pair of tower sections 3, 6 that includes an intermediate flange 4 may be longer compared to bolts applied in a joint between tower sections without the intermediate flange.

Claims

1. A wind turbine tower (8) comprising :

- a plurality of tower sections (1, 3, 6) arranged along a longitudinal direction defined by the wind turbine tower (8), wherein two adjacent tower sections (3, 6) of the plurality of tower sections (1, 3, 6) define a pair of tower sections comprising a lower tower section (3) and an upper tower section (6), wherein at least one pair of tower sections in the wind turbine tower (8) comprises:

- an intermediate flange (4) arranged between the lower tower section (3) and the upper tower section (6) of the pair of tower sections, the intermediate flange (4) being provided with at least one assembly means (9) arranged to receive an assembly truss (7), the intermediate flange (4) thereby being connectable to a crane (5) via the assembly means (9) and at least one assembly truss (7), the intermediate flange (4) further being provided with a plurality of through-going holes (10), wherein the lower tower section (3), the intermediate flange (4) and the upper tower section (6) are interconnected by means of a plurality of bolts (12), each bolt (12) extending through a portion of the lower tower section (3), one of the through-going holes (10) of the intermediate flange (4) and a portion of the upper tower section (6).

2. A wind turbine tower (8) according to claim 1, wherein the tower sections (1, 3, 6) are made from steel.

3. A wind turbine tower (8) according to claim 1 or 2, wherein the lower tower section (3) is provided with an upper flange (13) and the upper tower section (6) is provided with a lower flange (14), and wherein each of the bolts (12) interconnects the upper flange (13) of the lower tower section (3), the intermediate flange (4) and the lower flange (14) of the upper tower section (6), via a through-going hole (10) of the intermediate flange (4).

4. A wind turbine tower (8) according to any of the preceding claims, wherein the assembly means (9) is/are mounted on the intermediate flange (4) in a detachable manner.

5. A wind turbine tower (8) according to any of the preceding claims, wherein the

intermediate flange (4) is provided with at least two assembly means (9), and wherein two of the assembly means (9) are arranged along a periphery of the intermediate flange (4) with an angular distance which is equal to or smaller than 180°.

6. A wind turbine tower (8) according to any of the preceding claims, wherein at least one assembly means (9) is selected among eye bolts, hooks or lugs.

7. A wind turbine tower (8) according to any of the preceding claims, further comprising at least one further pair of tower sections having an intermediate flange (4) arranged between a lower tower section (3) and an upper tower section (6).

8. A wind turbine tower (8) according to any of the preceding claims, wherein the

intermediate flange (4) comprises fixing means (11) for fixing of the intermediate flange (4) at least radially in relation to the lower tower section (3) or the upper tower section.

9. A wind turbine tower (8) according to claim 8, wherein the fixing means (11) is selected among pins extending into apertures in the intermediate flange (4) and a portion of the lower tower section (3) or bolts extending through the intermediate flange (4) and into a portion of the lower tower section (3) or the upper tower section, respectively.

10. A method for erecting a wind turbine tower (8), the method comprising the steps of:

- providing a lower tower section (3), an upper tower section (6) and an intermediate flange (4), the intermediate flange (4) being provided with at least one assembly means (9) arranged to receive an assembly truss (7), and the intermediate flange (4) being provided with a plurality of through-going holes (10), - erecting the lower tower section (3) at an installation site,

- arranging the intermediate flange (4) , such that it is positioned between the pair of tower sections (3, 6) when installed in the wind turbine tower,

- arranging the upper tower section (6) on top of the lower tower section (3),

- interconnecting the lower tower section (3), the intermediate flange (4) and the upper tower section (6) by means of a plurality of bolts (12), each bolt (12) extending through a portion of the lower tower section (3), one of the through-going holes (10) of the intermediate flange (4) and a portion of the upper tower section (6), and - connecting the assembly means (9) of the intermediate flange (4) to a crane (5) via at least one assembly truss (7).

11. A method according to claim 10, wherein the step of arranging the intermediate flange (4) is performed prior to the step of erecting the lower tower section (3), by arranging the intermediate flange (4) on top of the lower tower section (3), and wherein the method further comprises the step of fixing the intermediate flange (4) to the lower tower section (3).

12. A method according to claim 10, wherein the step of arranging the intermediate flange is performed prior to the step of arranging the upper tower section (6) on top of the lower tower section (3), by fixing the intermediate flange to the bottom of the upper tower section (6).

13. A method according to claim 10-12, wherein the step of connecting the assembly means (9) of the intermediate flange (4) to a crane (5) is performed prior to the step of arranging the upper tower section (6) on top of the intermediate flange (4).

14. A method according to any of claims 10-13, further comprising the step of detaching the assembly means (9) from the intermediate flange (4) when erection of the wind turbine has been completed.