DK202100544A1

DK202100544A1 - Tower deformation zone

Info

Publication number: DK202100544A1
Application number: DKPA202100544A
Authority: DK
Inventors: Sigfred Mortensen Peter
Original assignee: Vestas Wind Sys As
Priority date: 2021-06-28
Filing date: 2021-06-28
Publication date: 2022-06-16

Abstract

A tower for supporting a nacelle to form a wind turbine is provided. The tower comprises: a plurality of tower sections connected together to form the tower, wherein at least one tower section is a deformation tower section configured such that it is predisposed, relative to the remaining plurality of tower sections, to deform if the nacelle should be dropped onto the tower while being mounted thereon, such that energy transferred to the tower resulting from the impact of the nacelle on the tower can be absorbed by the deformation tower section in a predictable and controlled manner.

Description

DK 2021 00544 A1 1

TOWER DEFORMATION ZONE

FIELD OF THE INVENTION The present invention relates to wind turbines, including both offshore and onshore wind turbines, and more specifically to a wind turbine tower with a built- in safety feature.

BACKGROUND A typical wind turbine includes a tower, mounted upon which is a nacelle that houses a generator connected by a shaft to a drive hub, and rotor blades attached to the drive hub. To install the wind turbine onshore, the base of the tower is fixed to the ground, which provides a foundation. For an offshore wind turbine installation the foundation will usually be provided by the seabed or a floating foundation moored to the seabed. The tower is constructed from a plurality of tower sections, which are connected together one after the other. Lastly, the nacelle is lifted by crane and lowered onto the top of the tower, onto which it is mounted and physically secured by construction personnel. When the nacelle is initially mounted on top of the tower, there is a small risk that it may be accidentally dropped onto the tower during the installation process, which theoretically may lead to uncontrolled deformation or even collapse of the tower and injury to personnel. Therefore, it may be a requirement that the construction personnel are evacuated from the tower while this occurs and, once the nacelle is securely mounted, the evacuated personnel have to re-enter the tower and ascend to the top again to secure the nacelle to the tower. Such safety procedures can take a lot of time during the construction process. Indeed, if the nacelle was to be accidentally dropped onto the tower during mounting, the damage could potentially compromise the entire structure, which would likely result in the tower needing to be completely rebuilt due to the impact shock waves having a damaging effect on all parts of the tower. It is therefore desirable to provide a solution to allow personnel to remain in a wind turbine tower while the nacelle is being mounted that would overcome these problems.

DK 2021 00544 A1 2

SUMMARY OF THE INVENTION Described herein is a tower (e.g. a wind turbine tower) for supporting a nacelle for a wind turbine, comprising: a plurality of tower sections connected together to form the tower, wherein at least one tower section is a deformation tower section configured such that it is predisposed, relative to the remaining plurality of tower sections, to deform if the nacelle should be dropped onto the tower while being mounted thereon, such that energy transferred to the tower resulting from the impact of the nacelle on the tower can be absorbed by the deformation tower section in a predictable and controlled manner.

Advantageously, providing at least one tower section as a deformation tower section that is “predisposed...to deform” may allow construction personnel to remain safely inside the tower below that deformation tower section while the nacelle is being mounted onto the tower. This is because, in the unlikely event that the nacelle were accidentally to be dropped onto the tower while being mounted, the damage caused by the impact to the tower should be isolated to the at least one deformation tower section. In this way, construction time may be significantly reduced compared with the current situation where personnel have to vacate the tower while the nacelle is being mounted. Furthermore, the tower may be reused after only replacing the deformation tower section instead of having to replace the complete tower.

As used herein, the phrase “predisposed...to deform” preferable connotes that in the event where deformation is expected to occur somewhere within the tower structure (e.g. due to the energy of the nacelle impacting the tower structure if the nacelle should be dropped onto it during mounting thereon), the at least one deformation tower section should be the first, and preferably the only, tower section(s) to deform. In other words, the deformation tower section is configured to be more susceptible or inclined to deformation than the remaining tower sections in the structure, and thus any deformation to the tower structure will be initiated in the deformation tower section (e.g. in advance of the any deformation in the remaining plurality of tower sections, in the event that they should deform at all). It will be appreciated that the deformation tower section can be

DK 2021 00544 A1 3 configured to be predisposed to deform in a number of ways.

Furthermore, it will be appreciated that the tower may comprise more than one tower section that is predisposed to deform, i.e. the term “deformation tower section” does not limit the tower to only having one deformation tower section.

If multiple deformation tower sections are used, then any features described herein with reference to a singular deformation tower section may be applied to only one of the deformation tower sections, or can be applied to some or all of the deformation tower sections.

Preferably, the deformation tower section comprises a substantially tubular wall arranged to have a deformation zone comprising one or more features configured to deform if the nacelle should be dropped onto the tower while being mounted to the tower, such that the energy transferred to the tower resulting from the impact of the nacelle on the tower can be absorbed by the deformation zone in the wall of said tower section.

Advantageously, by providing deformation features on the deformation tower section, it should deform in a predictable and safe manner.

The design of the deformation features can be altered to suit any particular wind turbine tower and/or nacelle, so as to deform and safely absorb the impact from the dropped nacelle.

The deformation zone may be provided by at least a portion of the wall of the deformation tower section having a reduced thickness relative to the thickness of the wall of at least one of the remaining plurality of tower sections.

For example, said at least a portion of the wall of the deformation tower section may have a reduced thickness relative to the thickness of the wall of the tower section directly below the deformation tower section.

Advantageously, this reduced wall thickness selectively weakens the deformation tower section, thereby predisposing that tower section to deform, relative to the remaining tower sections, if the nacelle is dropped onto the tower.

Alternatively or additionally, the deformation zone may be provided by the wall of the deformation tower section including one or more ribs (e.g. or ridges / corrugations) extending circumferentially around at least a portion of the

DK 2021 00544 A1 4 deformation tower section. Advantageously, the ribs may help the deformation tower section to crumple vertically to absorb impact from a dropped nacelle. Alternatively or additionally, the deformation zone may be provided by at least a portion of the wall of the deformation tower section configured to bulge inwardly or outwardly from the plane of the wall. The portion of the wall may be constructed as a bulge or a bulb shape extending inwards or outwards relative to the tower. If the nacelle is dropped onto the tower the bulge portion may collapse inwards or outwards respectively thereby absorbing energy of the impact and/or the shockwave of the impact of the dropped nacelle.

Preferably the deformation tower section is an uppermost tower section. Advantageously, having the uppermost tower section being predisposed to deform maximises the number of the remaining plurality of tower sections that remain undamaged in the event of an accidental drop — and hence the height that personnel can remain within the tower, again saving time during construction. Furthermore, it may facilitate dispersing of the shockwave of the impact.

Preferably the deformation tower section comprises one or more features that are configured to be reinforced once the nacelle is mounted onto the tower. Advantageously, this ensures that the deformation tower section is no longer predisposed to deform once mounting of the nacelle is complete. This reduces the possibility that the deformation tower section will fail during routine use of the completed wind turbine tower.

A tower section positioned beneath the deformation tower section may be reinforced so as to be stronger than the deformation tower section. The tower section beneath the deformation tower section may be referred to as a “supporting” tower section. If that supporting tower section is reinforced or strengthened, it may also be referred to as a “reinforced” tower section. Advantageously, reinforcing a tower section beneath the deformation tower section may reduce the amplitude of any shockwave travelling past that reinforced tower section and may further, to some degree, reflect the shockwave

DK 2021 00544 A1 back up the tower, which helps isolate any damage to the deformation tower section, and reduces the chance of damage to any tower sections below the reinforced tower section.

Preferably, the reinforced tower section is connected directly to the deformation 5 tower section, such that it is positioned immediately beneath the deformation tower section (i.e. in the tower). Advantageously, this means that any reflection of the shockwave off the reinforced tower section travels directly into the deformation tower section, and maximises the number of the remaining plurality of tower sections that are protected from damage.

Atleast a portion of the wall of the reinforced tower section may be thicker than the wall of the deformation tower section. Advantageously, the thicker wall adds stiffness to the reinforced tower section in the longitudinal direction, which inhibits deformation of the reinforced tower section and helps reflect the impact shockwave back up the tower to the deformation tower section.

The reinforced tower section may for example be reinforced by one or more internal struts. Advantageously, the internal struts may inhibit deformation (e.g. buckling) of its wall.

The reinforced tower section may have ribs (or ridges / corrugations) extending longitudinally along its length. Advantageously, such ribs add stiffness to the reinforced tower section in the longitudinal direction, and thereby inhibit deformation (e.g. buckling) of its wall.

Preferably, the deformation tower section is configured to have sufficient strength to support the nacelle as part of the tower during normal use. Advantageously this ensures that the tower is able to support the nacelle during routine use of the wind turbine.

Also described herein is a wind turbine comprising a tower as defined above and herein.

DK 2021 00544 A1 6 Also described herein is a method of constructing a tower (e.g. a wind turbine tower) for supporting a nacelle, the method comprising: connecting together a plurality of tower sections to form a tower, wherein at least one tower section is a deformation tower section configured such that it is predisposed, relative to the remaining plurality of tower sections, to deform if the nacelle should be dropped onto the tower while being mounted thereon, such that energy transferred to the tower resulting from the impact of the nacelle on the tower can be absorbed by the deformation tower section in a predictable and controlled manner.

The method may further comprise reinforcing the deformation tower section after the nacelle is mounted onto the tower.

Advantageously, this ensures that the deformation tower section(s) are no longer predisposed to deform after installation of the nacelle.

This reduces the likelihood of the tower section being damaged during routine use of the fully installed wind turbine tower.

The method may further comprise reinforcing a tower section below the deformation tower section to form a reinforced tower section, and optionally removing reinforcement of the reinforced tower section below the deformation tower section once the nacelle is mounted onto the tower.

Advantageously, reinforcing a tower section beneath the deformation tower section may reduce the amplitude of any shockwave travelling past that reinforced tower section and may at least partially reflect the shockwave back up the tower, which helps isolate any damage to the deformation tower section, and reduces the chance of damage to any tower sections below the reinforced tower section.

While the present invention is susceptible to various modifications and alternative forms, specific embodiments have been shown by way of examples in the drawings and will be described in details herein.

It should be understood that the invention is not intended to be limited to the particular forms disclosed.

Rather, the invention is to cover all modifications, equivalents, and alternatives falling within the scope of the invention as defined by the appended claims.

DK 2021 00544 A1 7

BRIEF DESCRIPTION OF THE DRAWINGS One or more embodiments will now be described, purely by way of example, with reference to the accompanying figures, in which: Figure 1 is a schematic side view of a wind turbine, which includes a tower constructed from a plurality of tower sections; Figure 2 is a schematic view of a tower section in isolation; Figure 3 is a cross-sectional schematic view showing two tower sections according to a first embodiment; Figure 4 is an isometric schematic view showing two tower sections according to a second embodiment; Figure 5 is a schematic view of a tower section according to a third embodiment; and Figure 6 is a schematic side view of a tower section according to a fourth embodiment.

DETAILED DESCRIPTION Figure 1 depicts a modem utility-scale wind turbine 1, comprising a tower 10, and a wind turbine nacelle 20 positioned on top of the tower 10. A wind turbine rotor 30, comprising three wind turbine blades 40, is connected to the nacelle 20 though a low speed shaft (not shown) which extends out of the front of the nacelle 20. The different components of the wind turbine 1 are usually transported separately to the site and assembled there. To facilitate transportation, the tower 10 is constructed from a plurality of (e.g. generally cylindrical) tower sections 100. The way in which the tower sections 100 are connected together to construct the tower 10 can be understood with reference to the tower section 100 shown In Figure 2. Each tower section 100 comprises a plurality of shells 101, typically

DK 2021 00544 A1 8 formed from rolled steel plate and typically joined together by welding. For further ease of transportation, each of the shells 101 may be divided into three longitudinal segments 104 that combine to provide a substantially tubular wall 106 that forms the complete tower section 100. The longitudinal segments 104 are typically welded together to form the tower section 100, but may instead be bolted together using longitudinal flanges that extend the length of the section. Depending on the diameter of a section 100, it may be divided into more or less than three longitudinal segments 104, or may not be split into longitudinal segments 104 at all.

— Although not clearly visible in Figure 2, the tower sections 100 typically have a slight taper such that a lower end 100a of a tower section 100 has a greater diameter than an upper end 100b of said tower section 100. In this way, the wind turbine tower 10 narrows from its base to its top, onto which the nacelle 20 is mounted (see Figure 1). Due to the smaller diameter of the sections 100 near the top of the tower 10 they may not need to be segmented in order to facilitate transportation.

In order to facilitate connection of adjacent tower sections 100 in the tower 10, a flange 102 is provided at each end 100a, 100b of a tower section 100. The flanges 102 are welded to the ends of the tower sections 100. During assembly, the flanges 102 of adjacent tower sections 100 are mated together using lifting machinery, such as a tower crane, and the vertically orientated tower sections 100 are then secured together by bolts passing through bolt holes 103 in the flanges 102. Lifting machinery, such as a crane, is also used to install the nacelle 20 on top of the tower 10, where it will be bolted to the uppermost tower section 110 in a similar manner, via the uppermost flange 102 on the uppermost tower section 110.

To address the risk that the nacelle 20 may accidently be dropped onto the assembled tower 10 during installation (e.g. while being mounted thereon), at least one of the tower sections 100, typically the uppermost tower section 110, onto which the nacelle 20 is to be secured, may be configured to deform during an accidental drop of the nacelle 20 to absorb the majority, if not all, of the force

DK 2021 00544 A1 9 of the impact of the nacelle, such that none of the lower tower sections 100 are damaged, or significantly damaged.

For convenience, in the following explanation the uppermost tower section 110 will be referred to as the (at least one) tower section 100 configured to deform, though this disclosure is not limited to only that tower section 110 being configured to deform, or indeed the (at least one) tower section 10 that is configured to deform being the uppermost tower section 110. The at least one tower section 100 that is configured to deform will be hereafter referred to as the “deformation” tower section.

Thus, as will now be described, the deformation tower section 110 may be configured such that it is predisposed, relative to the remaining plurality of tower sections 100, to deform (at least in part) if the nacelle 20 should be dropped onto the tower 10 while being mounted thereon, such that energy (e.g. the impact force) transferred to the tower resulting from the impact of the nacelle 20 on the tower 10 can be absorbed by the deformation tower section 110 in a predictable and controlled (and therefore relatively safe) manner.

Furthermore, construction personnel can safely remain in the tower 10 while lifting equipment (e.g. a crane) lowers the nacelle 20 onto the top of the tower 10. The construction personnel may remain in a tower section 130 that is specifically adapted to house (or shelter) them, which is hereafter referred to as the “containment” section 130, and which may be additionally strengthened to protect the construction personnel against damage from falling or damaged debris, such as equipment or parts of the tower 10.

With the deformation tower section 110 configured to deform under a sudden impact force of the nacelle 20 being accidentally dropped onto the top of the tower 10, the mass of the nacelle 20 and the height from which it is dropped will affect the size of the impact force experienced by the tower 10. For any given wind turbine 1, the mass of the nacelle 20 and the installation method including the lifting height above the tower 10 will be known, so the maximum impact force can be calculated. With the deformation tower section 110 configured to deform

DK 2021 00544 A1 10 to (at least partially) absorb the impact force, the impact force that is transmitted to the remaining plurality of tower sections 100 beneath the deformation tower section 110 should be greatly decreased, if not entirely avoided so harm can be avoided or reduced.

With damage to the tower 10 due to the impact force of the nacelle 20 being dropped onto being controlled such that the impact force is absorbed by the deformation tower section 110, the remaining plurality of tower sections 100 positioned beneath it in the tower 10 should, ideally, remain undamaged. Thus, following an accidental drop of the nacelle 20 onto the tower 10, in the event that damage is limited only to the deformation tower section 110, it can potentially be replaced with a new deformation tower section 110, and a new nacelle 20 installed to the top of the tower 10. Some analysis will of course be required of the remaining plurality of tower sections 100 to ascertain whether any of them have sustained damage, before only replacing the deformation tower section

110.

Despite being configured to deform, the deformation tower section 110 is nonetheless configured such that it can provide the necessary strength and rigidity to support the weight of the nacelle 20 (and any tower sections 100 above it) during normal use of the wind turbine 1, i.e. once the nacelle 20 has been mounted to the tower 10. As will be explained further on, this may be achieved by reinforcing the deformation tower section 110 after mounting of the nacelle 20, for example. Or it may be that the deformation tower section 110 is configured to be slightly weaker in some way than the remaining plurality of tower sections 100, while still having the necessary strength and rigidity required ofit.

The initial force of the nacelle 20 impacting the top of the tower 10 would result in a shockwave that travels down the tower 10, typically at the speed of sound. In an ordinary wind turbine tower 10, such a shockwave may result in deformation or even buckling of the tower 10 at any point along its length, in one or more of the tower sections 100 in a completely unpredictable manner.

However, by configuring a deformation tower section 110 to deform, it may be

DK 2021 00544 A1 11 possible to isolate most, if not all, of the force of that shockwave to the deformation tower section 110. As mentioned above, in order to isolate the force of the shockwave to only the deformation tower section 110, it may be constructed to be weaker than the remaining plurality of tower sections 100 directly beneath it.

This can be achieved by weakening the deformation tower section 110, i.e. relative to the remaining plurality of tower sections 100, strengthening or reinforcing one or more of the remaining plurality of tower sections 100 beneath the deformation tower section 110, relative to the deformation tower section 110, or a combination of approaches.

The tower section 120 directly below the deformation tower section 110 may be referred to as the “supporting” tower section 120, and when this supporting tower section 120 is strengthened or reinforced, it may be referred to as the “reinforced” tower section 120. When the shockwave reaches a boundary between the deformation tower section 110 and the supporting tower section 120 beneath it, the difference in their relative strengths should cause most of the shockwave to be reflected back up into the deformation tower section 110, with any remaining shockwave travelling down the remaining plurality of tower sections 100 with a reduced amplitude.

The relative strength of the deformation tower section 110 and the remaining tower sections 100 may be configured specifically for the design of a particular wind turbine 1, in order to minimise downward transmission of the shockwave.

The physical properties of the deformation tower section 110 and the remaining tower sections 100 may not be uniform over their lengths.

For instance, the deformation tower section 110 may comprise bands of weaker material, or may be configured to have a gradient in the strength profile of the sections along their length, to provide a “deformation zone” in the wall 106 of the deformation tower section 110. These bands or strength gradients may be provided using shells of rolled steel plate, like the shells 102 described in relation to the tower section 100 in Figure 2. Furthermore, the strength of the deformation tower section 110 need not be uniform around the circumference of its wall 106. For instance a portion of the wall 106 of the deformation tower section 110 may be

DK 2021 00544 A1 12 stronger (e.g. on one side of the deformation tower section 110) to encourage off-axis deformation (e.g. crumpling), which would cause deflection of a dropped nacelle 20 to one side of the tower 10. This non-uniform strength may be provided, for example, by constructing the deformation tower section 110 from a number of different segments 104. Further ways in which the deformation tower section 110 may be constructed will now be described in more detail.

Figure 3 illustrates a cross section of one possible configuration for the deformation tower section 110. As previously discussed, the deformation tower section 110 and the remaining plurality of tower sections 100 are constructed from shells 111, 121 formed from rolled steel plate that have been fixed together by welding to form the wall 106 of each tower section 100. In the deformation tower section 110, however, the wall 106 is thinner than the wall of the supporting tower section 120 beneath it, to provide a “deformation zone”. The deformation zone may be a result of the supporting tower section 120 being reinforced to have a thicker wall 106, for example, or it may be that the wall 106 of the deformation tower section 110 is thinner than the wall 106 of each of the remaining tower sections 100. As with all of the tower sections 100, each tower section 110, 120 shown has a flange 112, 122 extending inwardly from the periphery of its ends.

The flanges 112, 122 each have a plurality of bolt holes (not shown) provided around their circumference and the adjacent tower sections 110, 120 are secured together with bolts 118 during assembly of the tower 10. The external diameters of both the deformation tower section 110 and the supporting tower section 120 are configured to provide a required external profile of the tower 10 such that the external surface of the tower 10 is continuous / smooth along its length.

In the example shown in Figure 3, a distance between the bolt holes (not shown) on the respective flanges 112, 122 of the tower sections 110, 120 and the interior surfaces of each tower section 110, 120 may be different for the deformation tower section 110 and the supporting tower section 120, so that the bolt holes line up between the tower sections 110, 120.

DK 2021 00544 A1 13 An optimum thickness of the wall 106 of the deformation tower section 110 and the supporting tower section 120 beneath it may be determined based on the design for a specific wind turbine 1 to minimise risk of damage to the tower 10. For a typical wind turbine 1, the thickness of the steel shells 101 may range between 20mm to 80mm, for example, depending both on the height of the tower 10 and on the mass of the nacelle 20, which can range anywhere from around 50 tonnes to 700 tonnes, or more.

In one example, a deformation tower section 110 may have a “deformation zone” configured to deform in a predictable and controlled manner, with the remaining plurality of tower sections 100 constructed in the usual way.

The deformation zone in the deformation tower section 110 may be provided by reinforcing part of its wall 106 by making it between around 2mm to around 8mm thicker in a “reinforced zone” of between around 3m to around 5m around the circumference of the deformation tower section 110, with the reinforced zone being arranged in the wall 106 to have an upper edge between about 2m to about 10m beneath the upper end 100b of the deformation tower section 110. This reinforcement of the wall 106 of the deformation tower section 110 thereby effectively creates a “deformation zone” in the wall 106 of the deformation tower section 110 above the “reinforced zone”, due to the relatively thinner wall 106 in the deformation zone.

This arrangement would allow the deformation zone to deform under the immediate shock wave of the impact of a nacelle 20 being dropped onto the tower 10 whereas the “reinforced zone” would withstand the shock wave.

The remaining (i.e. unreinforced) portion of the wall 106 of the deformation tower section 110, and also the remaining plurality of tower sections 100, should withstand the impact force due to weakening of the shock wave before it reaches them.

In other words, the relatively thicker wall 106 of the “reinforced zone” in the deformation tower section 110 will reflect at least some of the impact shockwave back up into the “deformation zone” or weaken the shockwave so that the remaining plurality of tower sections 100 beneath the deformation tower section

DK 2021 00544 A1 14 110 are not damaged. As a result, the deformation tower section 110 will deform to absorb the impact force. The shells 111, 121 do not need to have the same thickness throughout each tower section 110, 120. For example, only some of the shells 111 of the deformation tower section 110 may be constructed using thinner steel plates than the other steel plates in the deformation tower section 110. The remaining shells 111 of the deformation tower section 110 may be constructed with the same thickness as those in the remaining plurality of tower sections 100, or possibly using shells 111 of a greater thickness such that only part of the deformation tower section 110 is predisposed to deform if the nacelle 20 were accidentally dropped onto the tower 10 during construction. As previously discussed in relation to Figure 2, tower sections 100 may optionally be constructed using longitudinal segments 104 welded together or bolted together using longitudinal flanges. The deformation tower section 110 may also be constructed in this way using a plurality of longitudinal segments

104. The longitudinal segments 104 of the deformation tower section 110 may be constructed from steel plates with different thicknesses. In this way, the deformation can again be controlled to occur on one side of the tower 10, which will deflect the dropped nacelle 20 to one side. This may, for example, be utilised to ensure that the nacelle 20 would fall in a relatively safe direction such as away from the crane, personnel or vessels if the nacelle 20 is completely released from the crane when dropped. Figure 4 illustrates another possible configuration for the deformation tower section 110. Here, the deformation tower section 110 has a series of horizontal ridges and grooves (e.g. to form ribs) extending circumferentially around the deformation tower section 110 to form a “deformation zone” in its wall 106. In addition, (at least) the supporting tower section 120 may have ridges and grooves (e.g. to form ribs) extending longitudinally along the length of the tower section 120. In this way, if the nacelle 20 is dropped onto the top of the deformation tower section 110, the shockwave should travel down the deformation tower section 110, and be reflected back upwards due to the

DK 2021 00544 A1 15 increased stiffness of the supporting tower section 120 due to the longitudinal ribs.

Thereafter, when the shockwave initiates deformation of the deformation tower section 110, the circumferential ribs of the deformation tower section 110 should deform, which should safely decelerate the dropped nacelle 20 and/or absorb the energy of the impact.

In order to facilitate attachment of adjacent tower sections 100 together, and to the nacelle 20 at the top, the ribs do not necessarily extend all the way around or along each tower section 110, 120. Here, the upper portions 110a, 120a and lower portions 110b, 120b of each tower section 110, 120 are free of ribs.

The upper and lower portions of the tower sections 110, 120 can be welded to portions of their respective tower section 110, 120 having ribs.

Similar to the tower sections 100 described in relation to Fig. 2, the tower sections 110, 120 may be formed from a number of shells (not shown). The outer edges of the shell at the end of each tower section 110, 120 may have a flange (not shown) similar to the flanges 102 on the remaining tower sections 100. The ribs may also be formed from one or more shells welded together.

The number and size of the welded shells as well as the depth and spacing of the ribs can be determined based on the design for a specific wind turbine 1 to minimise risk of damage to the tower 10. The depth and spacing of the ribs may be varied between different shells that form the ribs on each tower section 110, 120. Alternatively, or additionally, each tower section 110, 120 may have several ribbed shells separated by shells that are free of ribs.

It will of course be appreciated that the tower may comprise only a deformation tower section 110 having circumferential ribs such that it is predisposed to deform without a supporting tower section 120 (or indeed any of the remaining tower sections 100) having ribs.

However, a supporting tower section 120 may be provided with longitudinal ribs to reinforce it relative to the deformation tower section 110. A combination of both is also possible, as discussed above.

Figure 5 illustrates another possible configuration for a deformation tower section 110. Here, a portion of the wall 106 of the deformation tower section 110 is configured to bulge outwards (e.g. from the vertical axis of the tower 10). In

DK 2021 00544 A1 16 this way, if the nacelle 20 is dropped onto the top of the deformation tower section 110, the bulging portion of wall 106 should collapse outwards and thereby absorb the impact force from the dropped nacelle 20. Alternatively, the wall 106 could bulge inwards towards the central longitudinal axis of the tower 10, and thereby collapse inwards due to the impact force of a nacelle 20. As with the remaining plurality of tower sections 100, the deformation tower section 110 may be formed by welding steel shells together. The upper shell of the deformation tower section 110 will have a flange 112 for connection with the nacelle 20. The lower shell of the deformation tower section 100 will have a flange (not shown) for connection with the supporting tower section 120 beneath it. The number and size of the welded shells as well as the extent of the bulge in the deformation tower section 110 can be determined based on the design for a specific wind turbine 1 to minimise risk of damage to the tower 10. Figure 6 illustrates another possible configuration for reinforcing a supporting tower section 120. Here, internal struts 125 are attached to the wall 106 of the tower section 120, connecting the flange 122 at one end 120a of the tower section 120, to the flange 122 at the other end 120b of the tower section 120. Dotted lines have been used to show the internal struts 125 through the solid wall 106 of the tower section 120. The internal struts 125 provide additional rigidity to the wall 106 of the tower section 120 and help prevent deformation if the nacelle 20 were dropped onto the tower 10. Internal struts 125 may be added to the tower section 120, whether or not the tower section 120 is split into separate segments 104. The internal struts 125 are, preferably, spaced apart at an equal distance around the circumference of the tower section 120. While in Figure 6 only four internal struts 125 are depicted, more or fewer internal struts 125 may be used to suit the required strength of the tower section

120. Additional bracing may be added between different internal struts 125 of the tower section 120, either between adjacent internal struts 125 or between

DK 2021 00544 A1 17 struts on opposite sides of the tower section 120. The bracing may further prevent inward buckling of the tower section 120. There may be additional ways to weaken the deformation tower section 110, such as through drilling holes, through heat treatment, introducing indentations or stress concentrations to the metal, or using a material with a lower stiffness.

Similarly, there may be additional ways to strengthen the supporting tower section 120, such as through heat treatment, using a material with a higher stiffness, or adding an internal wall.

These methods, together with the using different wall thickness, ribs, or bulging wall sections can be used simultaneously in any combination so that the deformation tower section 110 and the supporting section 120 have the desired characteristics.

Any configuration of deformation tower section 110 can be used with any configuration of supporting tower section 120. Alternatively, a deformation tower section 110 may be installed without first reinforcing the supporting tower section 120. Optionally the containment section 130 may be combined with the supporting tower section 120. The deformation tower section 110 described in the above embodiments may be strengthened / reinforced after the nacelle 20 has been successfully installed at the top of the tower 10. This may be done by adding additional an internal wall / wall portion and/or supports to the deformation tower section 110, or using any other suitable method, such as methods used to reinforce the supporting tower section 120. In another example, internal struts 125 may be installed into a deformation tower section 110 after installation of the nacelle 20 onto the tower 10, once it is no longer necessary for the deformation tower section 110 to be predisposed to deform.

The deformation tower section 110 may be placed at a position in the tower 10 that is not at the top of the tower 10. The deformation tower section 110 may be a different length to other sections 100 of the tower 10. The deformation tower section 110 may be formed of a plurality of sub-sections or shells for ease of transportation and/or construction.

The length of the deformation tower

DK 2021 00544 A1 18 section 110 may be varied for each specific design of wind turbine 1 to minimise risk of damage to the tower 10. The deformation tower section 110 described above can also be installed at the top of other types of tower 10 which are not otherwise constructed in separate tower sections 100. The deformation tower section 110 may be added to the top of a tower 10 with just a single (e.g. longer) supporting tower section 120 beneath it, which may therefore be mounted to the ground, and which may be constructed with shells of rolled metal sheets, or could be constructed from concrete or any other material.

Indeed, it will be appreciated that any of the embodiments described herein can be implemented alone, or together in any combination.

Moreover, any feature in a particular embodiment described herein may be applied to another embodiment, in any appropriate combination.

It should also be appreciated that particular combinations of the various features described and defined in any aspects described herein can be implemented and/or supplied and/or used independently.

Any apparatus feature described herein may also be incorporated as a method feature, and vice versa.

While the foregoing is directed to exemplary embodiments of the present invention, it will be understood that the present invention is described herein purely by way of example, and modifications of detail can be made within the scope of the invention.

Indeed, other and further embodiments of the invention will be apparent to those skilled in the art from consideration of the specification, and may be devised without departing from the basic scope thereof, which is determined by the claims that follow.

Claims

DK 2021 00544 A1 19 CLAIMS

1. A tower for supporting a nacelle for a wind turbine, comprising: a plurality of tower sections connected together to form the tower, wherein at least one tower section is a deformation tower section configured such that it is predisposed, relative to the remaining plurality of tower sections, to deform if the nacelle should be dropped onto the tower while being mounted thereon, such that energy transferred to the tower resulting from the impact of the nacelle on the tower can be absorbed by the deformation tower section in a predictable and controlled manner.

2. The tower of claim 1, wherein the deformation tower section comprises a substantially tubular wall having a deformation zone comprising one or more features configured to deform if the nacelle should be dropped onto the tower while being mounted to the tower, such that energy transferred to the tower resulting from the impact of the nacelle on the tower can be absorbed by the deformation zone in the wall of the deformation tower section.

3. The tower of claim 2, wherein the deformation zone is provided by at least a portion of the wall of the deformation tower section having a reduced thickness relative to the thickness of the wall of at least one of the remaining plurality of tower sections, preferably said at least a portion of the wall of the deformation tower section having a reduced thickness relative to the thickness of the wall of the tower section directly below the deformation tower section.

4. The tower of claim 2, wherein the deformation zone is provided by the wall of the deformation tower section including one or more ribs extending circumferentially around at least a portion of the deformation tower section.

5. The tower of claim 2, wherein the deformation zone is provided by at least a portion of the wall of the deformation tower section being configured to bulge inwardly or outwardly from the plane of the wall.

DK 2021 00544 A1 20

6. The tower of any of claims 2 to 5, wherein the deformation tower section is the uppermost tower section of the tower configured to receive the nacelle.

7. The tower of any of claims 2 to 6, wherein the deformation tower section comprises one or more features configured to be reinforced once the nacelle is mounted onto the tower.

8. The tower of any one of the preceding claims, wherein a tower section positioned beneath the deformation tower section is reinforced so as to be stronger than the deformation tower section, preferably wherein the reinforced tower section is connected directly to the deformation tower section, such that it is positioned immediately beneath the deformation tower section.

9. The tower of claim 8, wherein at least a portion of the wall of the reinforced tower section is thicker than the wall of the deformation tower section.

10. The tower of any of claims 7 to 9, wherein the reinforced tower section is reinforced by one or more internal struts.

11. The tower of any of claims 8 to 10, wherein the reinforced tower section has one or more ribs extending longitudinally along its length.

12. The tower of any preceding claim, wherein the deformation tower section is configured to support the nacelle, as one of said plurality of tower sections, once the nacelle has been mounted onto the tower.

13. A wind turbine comprising a tower according to any preceding claim.

14. A method of constructing a tower for supporting a nacelle, the method comprising: connecting together a plurality of tower sections to form a tower,

DK 2021 00544 A1 21 wherein at least one tower section is a deformation tower section configured such that it is predisposed, relative to the remaining plurality of tower sections, to deform if the nacelle should be dropped onto the tower while being mounted thereon, such that energy transferred to the tower resulting from the impact of the nacelle on the tower can be absorbed by the deformation tower section in a predictable and controlled manner.

15. The method of claim 14, further comprising reinforcing the deformation tower section once the nacelle is mounted onto the tower.

16. The method of claim 14 or 15, further comprising reinforcing a tower section below the deformation tower section to form a reinforced tower section, and optionally removing reinforcement of the reinforced tower section below the deformation tower section once the nacelle is mounted onto the tower.