WO2020048572A1

WO2020048572A1 - Wind turbine tower and method of installing a wind turbine tower

Info

Publication number: WO2020048572A1
Application number: PCT/DK2019/050259
Authority: WO
Inventors: Gunnar K. Storgaard Pedersen; Gerner Larsen
Original assignee: Vestas Wind Systems AS
Current assignee: Vestas Wind Systems AS
Priority date: 2018-09-06
Filing date: 2019-09-02
Publication date: 2020-03-12
Anticipated expiration: 2021-03-06

Abstract

A wind turbine tower having a lower wind turbine tower member and an upper wind turbine tower member. The upper wind turbine tower member has a hollow body with a flange formed at its lower end which projects radially inwardly. The flange has an engaging portion configured to engage with the lower wind turbine tower member, and a first overhanging portion configured to extend outwardly beyond the lower wind turbine tower member when the engaging portion of the flange and lower member are engaged. A plurality of first tension stay connectors are located at the first overhanging portion of the flange which are configured to enable a plurality of first tension stays to be secured to the wind turbine tower from within the hollow body.

Description

WIND TURBINE TOWER AND METHOD OF INSTALLING A WIND TURBINE TOWER

FIELD OF THE INVENTION

The present invention relates to a wind turbine tower joint, a wind turbine tower comprising said joint and a method of installing the same.

BACKGROUND OF THE INVENTION

In order to meet global energy demands, renewable energy sources, such as wind turbines, are being placed under increasing pressure to increase power outputs, which is driving technology in the field. Due to space constraints and also due to the high costs associated with installing individual winds turbines, increasing power output by simply building and installing an increasing number of wind turbines is often not an economically viable solution to meet global demands.

Therefore, wind turbines are now being designed and manufactured to yield increased “per unit” power outputs. This is principally achieved in two ways, firstly, by increasing the size of the turbine blades and rotor to increase turbine capacity, and secondly, by placing the turbine blades higher in the atmosphere so that they are able to access a more steady supply of wind.

In order for these features to be implemented, modern wind turbines require increasingly tall support. In addition, towers can be made solely of steel, concrete or a combination of the two materials in what is known as a hybrid tower with a concrete lower region and a steel upper region. Towers may have a height ranging from 75m to 160m or more and this height can lead to issues with tower stiffness.

The concrete lower region of hybrid wind turbine support towers are typically stiffened by internal tension stays which ensures that the concrete is in compression at all times as concrete does not provide much structural integrity when under tension.

Moreover, tall towers may benefit from external tension stays at a stay cable angle of about 45° to improve the bending characteristics of the tower.

A compromise between the near vertical internal tension stay and the 45° external tension stay is disclosed in WO 2016/116645 A1 where external tension stays are provided at a shallow angle and replacing the internal tension stays. This construction provides both compression of the concrete lower region and stability of the tower. Tension stays may be joined to a region of a wind turbine tower using external fixings. However, external fixings are often difficult to access at the height at which they are located and require specialised equipment to enable access for installation and maintenance, thereby increasing installation and maintenance times and associated costs.

Furthermore, external fixings are often vulnerable to degradation due to adverse weather conditions and can therefore exhibit a reduced service life, which further impacts on maintenance costs.

Therefore, the aim of the present invention is to provide a way of alleviating at least some of the aforementioned issues.

SUMMARY OF THE INVENTION

A first aspect of the invention relates to a wind turbine tower joint comprising:

a hollow body with a flange formed at a lower end of the body and projecting radially inwardly the flange having an engaging portion configured to engage with an upper receiving face of a lower member of a wind turbine tower, and having a first overhanging portion configured to extend outwardly beyond the upper receiving face of the lower member when the engaging portion of the flange and upper receiving face of the lower member are engaged; and a plurality of first tension stay connectors located at the first overhanging portion of the flange, each configured to secure a first end of a first tension stay from within the hollow body.

The lower member of the wind turbine tower may form or be a modular component of a lower region of the wind turbine tower.

The joint is an upper member that is part of an upper region of the wind turbine tower. The upper member may form or be a modular component of the upper region of the wind turbine tower.

As such, the joint may alternatively be referred to as an upper wind turbine tower member of the wind turbine tower due to its relative location and relative engagement with the lower member of the wind turbine tower.

The term“modular component” is used herein to refer to a respective component of a plurality of constituent components which make up the upper and/or lower regions of the wind turbine tower.

A second aspect of the invention relates to a wind turbine tower comprising: a lower wind turbine tower member comprising an upper receiving face; and an upper wind turbine tower member comprising:

a hollow body comprising a flange, wherein the flange is formed at a lower end of the body and projects radially inwardly, and the flange comprises an engaging portion configured to engage with the upper receiving face of the lower member, and a first overhanging portion configured to extend outwardly beyond the upper receiving face of the lower member when the engaging portion of the flange and upper receiving face of the lower member are engaged, and

a plurality of first tension stay connectors located at the first overhanging portion of the flange, each being configured to secure a first end of a first tension stay from within the hollow body.

The term“tension stay” is used herein to refer to an anchoring tether, or tendon, having a high axial stiffness so as to induce a compressive load on the wind turbine tower structure to which it is attached. The term“tension stay” is well known in the art of wind turbine systems.

In an embodiment of the invention the turbine is located on-shore. The term“on-shore” is used herein to refer to a location situated on or near to the shore. This may include areas such as rivers or shorelines but will be considered to exclude any deep, open water areas such as locations in the middle of oceans or other comparable open water areas, such as large lakes.

The term“continuous” is used herein to refer to a flange which extends completely and continuously around the entirety of the lower end of the hollow body (i.e. without any gaps).

The provision of a plurality of first tension stay connectors located at the first overhanging portion of the flange, each configured to secure a first end of a first tension stay from within the hollow body enables easy access to the respective first tension stay connectors during installation and maintenance without the need for specialist external access equipment, such as abseiling equipment. This provides the advantage of improved installation and maintenance times, as well as reduced associated costs.

Furthermore, this provision also enables the tension stay connectors to be housed within the hollow body, thereby providing improved weather protection to these components. This provides the advantage of improved component service life, which helps to further reduce maintenance costs. The flange may further comprise a second overhanging portion configured to extend inwardly beyond the upper receiving face of the lower member when the engaging portion of the flange and upper receiving face of the lower member are engaged.

A plurality of second tension stay connectors may be located at the second overhanging portion of the flange, each configured to secure a first end of a second tension stay from within the hollow body.

The plurality of first tension stay connectors may comprise a first tension stay receiving aperture extending through the first overhanging portion of the flange, configured to receive a first end of a respective first tension stay such that the first end of the respective first tension stay extends into the hollow body.

The plurality of second tension stay connectors may comprise a second tension stay receiving aperture extending through the second overhanging portion of the flange, configured to receive a first end of a respective second tension stay such that the first end of the respective second tension stay extends into the hollow body.

The plurality of first tension stay connectors may further comprise a first key member locatable within the respective first tension stay receiving aperture from within the hollow body, configured to secure a respective first tension stay within the aperture.

The plurality of second tension stay connectors may further comprise a second key member locatable within the respective second tension stay receiving aperture from within the hollow body, configured to secure a respective second tension stay within the aperture.

The flange may extend circumferentially around the lower end of the hollow body. The flange may extend continuously around the lower end of the hollow body. Alternatively, the flange may be formed as a series of discrete tabs.

At least one flange connector may be configured to secure the engaging portion of the flange to the upper receiving face of the lower member from within the hollow body. The at least one flange connector may comprise at least one of fastener and at least one fastener receiving aperture configured to receive a respective fastener. The fastener may be a washer, nut and bolt arrangement. Alternatively, the fastener may be a screw or a G-clamp.

At least one reinforcer may be configured to reinforce the first and/or second tension stay connector, and/or the flange connector from within the hollow body. The hollow body may be a conical shape, widening towards the lower end of the body. Alternatively, the hollow body may be substantially cylindrical.

The hollow body may comprise a plurality of gusset plates to enhance the structural integrity of the hollow body.

The hollow body may comprise steel.

In a preferred embodiment of the invention the lower member of the wind turbine tower comprises concrete sections. In an alternative embodiment the lower member comprises steel and/or concrete substitute material.

The lower member may be a modular component of a modular lower region of the wind turbine tower. Alternatively, the lower member may be a single, unitary structure forming the lower region of the wind turbine tower.

The joint/upper member may be a modular component of a modular upper region of the wind turbine tower. Alternatively, the joint/upper member may be single, unitary structure forming the upper region of the wind turbine tower.

A third aspect of the invention provides a wind turbine comprising a wind turbine tower according to the second aspect of the invention and a plurality of first tension stays comprising respective first ends and second ends, wherein each of the respective first ends are secured within the hollow body by a respective first tension stay connector and/or a plurality of second tension stays comprising respective first ends and second ends, wherein each of the respective first ends are secured within the hollow body by a respective second tension stay connector.

The wind turbine may further comprise a tension stay foundation. The tension stay foundation may be integrally formed with a wind turbine tower foundation. Alternatively, the tension stay foundation may be formed separately from the wind turbine tower foundation as a plurality of separate tension stay foundation elements.

The respective second ends of the plurality of first tension stays may be secured to the tension stay foundation such that the plurality of first tension stays extend from the upper region of the wind turbine tower to the tension stay foundation, external to the lower member, to induce a compressive load on the lower member. The respective second ends of the plurality of second tension stays may be secured to the tension stay foundation such that the plurality of second tension stays extend from the upper region of the wind turbine tower to the tension stay foundation, internal to the lower member, to induce a compressive load on the lower member.

The first and/or second tension stays may be made from steel. Alternatively, the plurality of tension stays may comprise a composite material exhibiting a high tensile strength. The composite material may be a carbon fibre reinforced composite. Alternatively, the composite material may be a glass fibre reinforced composite and/or an aramid fibre reinforced composite. In a further alternative, the plurality of tension stays may be made from a high tensile strength polymer material, such as Nylon.

A fourth aspect of the invention relates to a method of installing a wind turbine comprising the steps of:

providing a lower wind turbine tower member comprising an upper receiving face;

providing an upper wind turbine tower member comprising a hollow body with a flange formed at a lower end of the body and projecting radially inwardly, the flange having an engaging portion and a first overhanging portion, and a plurality of first tension stay connectors located at the first overhanging portion of the flange; providing a plurality of first tension stays comprising respective first ends and second ends;

securing the respective first ends of the plurality of first tension stays within the hollow body to a respective first tension stay connector;

installing the engaging portion of the flange onto the upper receiving face of the lower member such that the engaging portion interfaces with the upper receiving face of the lower member and the first overhanging portion of the flange extends outwardly beyond the upper receiving face of the lower member, and subsequently securing the engaging portion of the flange to the upper receiving face of the lower member. If the upper member further comprises a second overhanging portion configured to extend inwardly beyond the upper receiving face of the lower member when the engaging portion of the flange and upper receiving face of the lower member are engaged, and a plurality of second tension stay connectors located at the second overhanging portion of the flange; the method may comprise providing a plurality of second tension stays comprising respective first ends and second ends, and securing the respective first ends of the plurality of second tension stays within the hollow body to a respective second tension stay connector.

The step of securing the respective first ends of the plurality of first tension stays to respective first tension stay connectors may be performed prior to the step of installing the engaging portion of the flange onto the upper receiving face of the lower member.

The step of securing the respective first ends of the plurality of first tension stays to respective first tension stay connectors may be performed after the step of installing the engaging portion of the flange onto the upper receiving face of the lower member.

The step of securing the respective first ends of the plurality of second tension stays to respective second tension stay connectors may be performed prior to the step of installing the engaging portion of the flange onto the upper receiving face of the lower member.

The step of securing the respective first ends of the plurality of second tension stays to respective second tension stay connectors may be performed after the step of installing the engaging portion of the flange onto the upper receiving face of the lower member.

If each of the first tension stay connectors comprise a first tension stay receiving aperture formed in the first overhanging portion of the flange and a first key member, the method may comprise the step of locating the first end of a respective first tension stay within the respective first tension stay receiving aperture of the respective first tension stay connector such that the first end of the first tension stay extends into the hollow body and applying the first key member in the first tension stay receiving aperture from within the hollow body so as to secure the first tension stay within the respective first tension stay receiving aperture. If each of the second tension stay connectors comprise a second tension stay receiving aperture formed in the second overhanging portion of the flange and a second key member, the method may comprise the step of locating the first end of a respective second tension stay within the respective second tension stay receiving aperture of the respective second tension stay connector such that the first end of the second tension stay extends into the hollow body and applying the second key member in the second tension stay receiving aperture from within the hollow body so as to secure the second tension stay within the respective tension stay receiving aperture.

The step of securing the engaging portion of the flange to the upper receiving face of the lower member may comprise providing at least one flange connector and applying the at least one flange connector from within the hollow body to secure the engaging portion of the flange to the upper receiving face of the lower member.

The method may comprise the further steps of providing a tension stay foundation and securing the second ends of the plurality of first tension stays and/or second tension stays to the tension stay foundation to induce a compressive load on the lower member.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described with reference to the accompanying drawings, in which:

Figure 1 illustrates a perspective view of a wind turbine according to one example of the present invention;

Figure 2 illustrates a perspective view of the upper member of the wind turbine according to the example illustrated in Figure 1 ;

Figure 3A illustrates a perspective view of the flange of the upper member according to the example illustrated in Figure 2;

Figure 3B illustrates a perspective view of the flange of the upper member according to an alternative example; and

Figure 4 illustrates a perspective view of a wind turbine tower according to the example of the present invention. DETAILED DESCRIPTION OF EMBODIMENT(S)

Figure 1 shows a wind turbine 1 utilising the wind turbine tower 2 according to an example of the present invention.

The wind turbine tower 2 comprises an upper region 2a and a lower region coupled together using a joint 2c. The upper region may be a modular upper region comprising a plurality of modular upper members 2c-2f as shown in the Figures 1 and 4. Alternatively, the upper region may be a unitary structure comprising a single upper member. Likewise, the lower region may be a modular lower region comprising a plurality of modular lower members as shown in Figure 4. Alternatively, the lower region may be a unitary structure comprising a single lower member 2b as shown in Figure 1.

Typically, the one or more lower members 2b is made from steel, concrete and/or concrete substitute material, although concrete or concrete substitute material is generally preferred due to their beneficial properties in compression. However, it shall be appreciated that any other suitable materials may be used.

The lower portion further comprises an access door 9 to enable internal access into the wind turbine tower 2 for installation and maintenance purposes.

In the example illustrated in Figure 1 , the upper region of the wind turbine tower 2 comprises a plurality of modular upper members including a joint module 2c and upper tower modules 2d-f. However, in other examples, it shall be appreciated that the upper region 2a may be a unitary upper member integrally comprising the joint 2c to couple the upper region and lower region of the wind turbine tower.

The wind turbine 1 further comprises a nacelle 3 supported on the upper member 2a of the wind turbine tower 2. The nacelle 3 supports a rotor 4 comprising a hub 5 to which three blades 6, 7, 8 are attached. It will be noted that the wind turbine 1 illustrated in Figure 1 is the common type of horizontal axis wind turbine (HAWT) such that the rotor 4 is mounted at the nacelle 3 to rotate about a substantially horizontal axis defined at the centre at the hub 5. However, it shall be appreciated that in an alternative example, the wind turbine 1 may be a vertical axis wind turbine (VAWT). As is known, the blades 6, 7, 8 are acted on by the wind which causes the rotor 4 to rotate about its axis thereby operating generating equipment through a gearbox (not shown) that is housed in the nacelle 3. The generating equipment is not shown in Figure 1 since it is not central to the examples of the invention. The wind turbine 1 further comprises a plurality of first tension stays 1 1-14 each having a first end 11 a-14a and a second end 1 1 b-14b. Each of the first ends 11 a-14a are secured to a respective first tension stay connector of the joint 2c located in the upper region 2a of the wind turbine tower (see Figure 2). Each of the second ends 11 b-14b are secured to a respective tension stay foundation 10 located on the ground. The first tension stays 11-14 extend from the joint 2c to the tension stay foundation, external to the lower region of the wind turbine tower 2. In the example illustrated in Figure 1 , the respective tension stay foundations are integrally formed with the wind turbine tower foundation to form the wind turbine foundation 10. However, it shall be appreciated that in other examples the tension stay foundations may be formed separately from the wind turbine tower foundation as a series of separate tension stay foundation elements. In one particular example, the separate tension stay foundation elements may be provided in the form of separate intermodal containers.

The first tension stays 11-14 are configured to induce a compressive load on the lower region once the wind turbine 1 has been installed and provide stability. This feature helps to improve tower stiffness.

A wind turbine 1 according to an example of the present invention typically comprises sixteen first tension stays. However, for clarity and conciseness, only four of the first tension stays 1 1-14 shall be referenced and described in this application. It shall also be noted that, in other examples, more than sixteen, or fewer than sixteen, first tension stays may be used, although the number of first tension stays will typically be no fewer than three. In embodiments the number of first tension stays are a multiple of three, for example three, six, nine, twelve, fifteen, eighteen, twenty-one or twenty-four. In other embodiments the number of tension stays are an uneven number from three and upwards, for example three, five, seven, nine, eleven, thirteen, fifteen, seventeen, nineteen, twenty-one or twenty-three.

The joint 2c of the upper region 2a is shown in greater detail in Figure 2. The joint 2c comprises a hollow body 20 with an upper end 21 , lower end 22 and internal surface 23. The hollow body 30 further comprises a flange 30 formed at its lower end 22.

The flange 30 projects radially inwardly towards a central axis (X) of the wind turbine tower 2 and extends circumferentially around the lower end 22 of the hollow body 20. In the example illustrated in Figure 2, the flange 30 extends continuously around the lower end 22 of the hollow body. However, the flange may alternatively be formed as a series of discrete tabs. The flange 30 comprises an engaging portion 31 , configured to engage with the upper receiving face 2b’ of the lower member 2b, and a first overhanging portion 32, configured to extend outwardly beyond the upper receiving face 2b’ of the lower member 2b when the engaging portion 31 and the upper receiving face 2b’ are engaged.

In the illustrated example, the hollow body 20 is made from steel. However, it shall be appreciated that other suitable materials may be used.

The hollow body 20 has a conical shape extending from an upper end 21 and widening towards the lower end 22. However, it shall be appreciated that the hollow body may alternatively comprise any other suitable shape, for example the hollow body may be substantially cylindrical.

The widened lower end 22 of the conical hollow body 20, in the region of the flange 30, allows for easy installation and internal accessibility during installation and maintenance of the wind turbine tower 2.

The upper end 21 of the joint 2c comprises a receiving face 25 which is configured to engage with a respective receiving face 26 of an upper tower module 2d to form part of the upper region 2a. However, in other examples, in which the joint 2c and upper tower sections 2d-f are formed as a unitary structure, the receiving face of the upper member 2a may instead be configured to engage with a respective receiving surface (not shown) of the nacelle 3 so as to couple the nacelle 3 to the upper member 2a.

The internal surface 23 of the hollow body 20 comprises a plurality of gusset plates 24a-d to enhance structural integrity. In the example depicted in the Figure 2, the gusset plates 24a-d formed thereon which extend from the flange 30 at the lower end 22 of the hollow body 20 and terminate at the upper end 21. The gusset plates 24a-d illustrated in Figure 2 are substantially triangular, although it shall be appreciated that the gusset plates 24a-d may alternatively comprise any suitable shape, and are joined to the internal surface via welding, or any other suitable joining means. The plurality of gusset plates 24a-d are typically made from steel, and typically match the material of the hollow body 20, although other like or dissimilar materials may be used. Furthermore, in another example, the gusset plates 24a-d may be integrally formed with the internal surface 23 of the joint 2c. It shall also be appreciated that in a further example, the gusset plates may be omitted. The plurality of gusset plates 24a-d enable stresses to be better transferred across the joint 2c of the upper region 2a and therefore provide the advantage of strengthening the upper region 2a.

The wind turbine tower 2 further comprises a plurality of flange connectors to securely couple the upper region 2a and lower region of the wind turbine tower. The plurality of flange connecters are configured to secure the engaging portion 31 of the flange 30 to the upper receiving face 2b’ of the lower member 2b from within the hollow body 20, as illustrated in Figure 3A. Although multiple flange connectors are shown in Figure 3A, for clarity and conciseness, only the first of these components shall be described in this application.

In the example illustrated in Figure 3A, the plurality of flange connectors each comprise a respective fastener receiving aperture 33 in the flange, a respective fastener receiving aperture 35 in the lower member 2b and a respective fastener 34. The respective fastener receiving apertures in both the flange and the lower member 2b are configured to receive the respective fastener 34. The fastener 34 is configured to be mounted in the fastener receiving apertures from within the hollow body and thereby secure couple the upper region 2a and lower region of the tower. In the example illustrated in Figure 3A, the fastener 34 is a washer, nut and bolt arrangement. However, in an alternative example, the fastener may be a screw, a G-clamp or any other suitable fastener type to secure the upper and lower portions of the tower from within the hollow body 20 of the joint 2c. Furthermore, in yet another alternative, the flange connector may be omitted with the engaging portion 31 being coupled to the upper receiving face 2b’ of the lower member 2b via bonding, co-curing or any other suitable means.

The provision of a flange connector configured to secure the engaging portion 31 of the flange 30 to the upper receiving face 2b’ of the lower member 2b from within the hollow body 20 is advantageous as it enables the upper region 2a and lower region of the tower to be secured from within the wind turbine tower 2, thereby reducing the need for specialist abseiling equipment, which is required when coupling the upper region 2a and lower region externally. This provides the benefit of reducing installation and maintenance times and associated costs.

It also has the further advantage of reducing curing times associated with adhesive or co-curing joining methods, thereby reducing overall wind turbine installation times. The provision of securing the engaging portion 31 of the flange 30 to the upper receiving face 2b’ of the lower member 2b via a flange connector 34 located within the hollow body 20 has the further advantage of providing weather protection to the flange connector components, since these components are housed within the hollow body 20 and so are protected from adverse weather conditions, such as rain, which can lead to corrosion and other effects which are detrimental to product life. This feature therefore also has the benefit of improving the wind turbine service life and subsequently reducing maintenance costs across the wind turbine’s lifespan.

The joint 2c further comprises a plurality of first tension stay connectors to connect a plurality of respective first tension stays 11 -14 to the upper region 2a of the wind turbine tower. The first tension stay connectors are located at the first overhanging portion 32 of the flange 30. Although multiple tension stay connectors are shown in Figure 3A, for clarity and conciseness, only the first of these components shall be described in this application.

The first tension stay connectors are configured to secure the first ends 11 a-14a of the first tension stays 1 1-14 from within the hollow body of the joint 2c. The first tension stay connector in the example illustrated in Figure 3A comprises a first tension stay receiving aperture 36 extending through the first overhanging portion 32 of the flange 30. The first tension stay receiving aperture 36 is configured to receive the first end 14a of the first tension stay 14 within the hollow body 20 such that the first end 14a of the first tension stay 14 extends into the hollow body 20. As such, the protruding first tension stays 11-14 can be accessed from within the tower 2. By providing internal accessibility to the first tension stays 1 1-14 within the hollow body, installation and maintenance is improved.

The first tension stay connector further comprises a first key member 37, which is locatable within the first tension stay receiving aperture 36 from within the hollow body 20 and is configured to secure the first end 14a of the respective first tension stay 14 within the respective first tension stay receiving aperture 36. The first key member 37 may be provided in the form of a conically shaped wedge, having a through-hole 37a for receiving and securing the first end 14a of the respective first tension stay 14. However, it shall be appreciated that in another example, any other suitable type of key member may be used. The first end 14a of the first tension stay 14 is secured by the key member 37 within the through hole 37a via an interference fit. However, it shall be appreciated that in another example, any other suitable securing means may be utilised.

Due to the configuration of the first overhanging portion 32 of the flange 30 being located outboard of the upper receiving face 2b’ of the lower member 2b, the tension stay connectors of the joint 2c are configured to secure the first ends 1 1a- 14a of the first tension stays 11-14 within the hollow body. Moreover, the configuration of the first overhanging portion allows the tension stays extend from the joint 2c towards the wind turbine foundation 10, whilst remaining external to the lower region of the wind turbine tower.

This feature negates the need for providing through holes in the lower member 2b to accommodate the passage of respective first tension stays and therefore simplifies the construction of the wind turbine tower and provides the advantage of reducing installation and maintenance time.

As shown in the example illustrated in Figure 3A, the wind turbine tower 2 further comprises at least one reinforcer 38 to reinforce a respective first tension stay connector. The reinforcer 38 may comprise a reinforcer body mountable from within the hollow body 20, the reinforcer body comprising a reinforcer aperture 38a configured to correspond and align with the first tension stay receiving aperture 36 of a respective first tension stay connector. As a consequence, the first end 14a of the first tension stay 14a protrudes through both apertures 36, 38a of the first tension stay connector and reinforcer 38 into the hollow body 20. The reinforcer 38 may further comprise a reinforcer key member which is locatable within the reinforcer aperture 38a from within the hollow body 20 and is configured to secure the first end 14a of the first tension stay within the reinforcer aperture 38a. The reinforcer key may be the first key member 37 of the first tension stay connector and may further extend into the respective first tension stay receiving aperture 36 from the reinforcer aperture 38a to simultaneously secure the first end 14a of the first tension stay within the reinforcer and the first tension stay connector. The at least one reinforcer may be configured to additionally or alternatively reinforce a respective flange connector. The reinforcer may comprise a reinforcer body mountable from within the hollow body 20, wherein the reinforcer body comprises an aperture 38b that is configured to correspond and align with the fastener receiving apertures 33, 35 of the respective flange connector. The respective fastener is thereby able to be mounted to protrude through all the apertures of the flange connector and reinforce from within the hollow body.

The provision of at least one reinforcer 38 provides improved strength at the joint, which enhances the overall coupling effect.

The at least one reinforcer 38 may be configured to reinforce both a respective tension stay connector and flange connector, for example when the tension stay connector and flange connector are adjacent as shown in Figures 3A and 3B.

Although multiple reinforcers are shown in Figure 3A, for clarity and conciseness, only the first of these components shall be described in this application.

In the illustrated example, the reinforcer 38 comprises a substantially rectangular body. However, it shall be appreciated that the reinforcer body may be any other suitable shape. The reinforcer 38 is typically made from steel or any other suitable material. In the example depicted in Figure 3A, the reinforcer 38 comprises a first aperture 38a configured to correspond and align with the tension stay receiving aperture 36 of the first tension stay connector and a second aperture 38b configured to correspond and align with the fastener receiving apertures 33, 35 of flange connector 34, when mounted on the inside surface of the flange 30 within the hollow body 20.

As shown in the illustrated example in Figure 3A, the first aperture 38a is configured to receive the first key member 37 from within the hollow body 20 so as to secure the first end 14a of the first tension stay 14 in the reinforcer. The first key member 37 comprise a through-hole 37a for receiving and securing the first end 14a of the first tension stay 14.

Similarly, the second aperture 38b is configured to receive the respective fastener 34 so that the fastener 34 is mounted from within the hollow body and extends into the fastener receiving apertures 33, 35 thereby securing the flange 30 to the lower member 2b. The wind turbine may 1 may further comprise a plurality of second tension stays 42 each having a first end 42a and a second end. The second tension stays 42 extend internally within the wind turbine tower between the joint 2c and a wind turbine tower foundation to provide additional compression and stability. Each of the first ends 42a are secured to a respective second tension stay connector of the joint 2c. Figure 3B illustrates an alternative example of a joint 2c that is suitable for securing the plurality of second tension stays 42 in addition to the plurality of first tension stays 1 1-14. Like reference numerals denote like parts with Figure 3A, and only the differences will be described here.

The joint 2c illustrated in Figure 3B further comprises a second overhanging portion 39 configured to extend inwardly beyond the upper receiving face 2b’ of the lower member 2b when the engaging portion 31 of the flange and upper receiving face 2b’ of the lower member 2b are engaged.

The joint further comprises a plurality of second tension stay connectors 40 to connect a plurality of respective second tension stays 42 to the upper region 2a of the wind turbine tower 2, although only the first of these components shall be illustrated and described in this application. The second tension stay connectors 40 are located at the second overhanging portion 39 of the flange 30 and are configured to secure the first ends 42a of the second tension stays 42.

The second tension stay connectors are configured to secure the first ends 42a of the second tension stays 42. The second tension stay connector 40 in the example illustrated in Figure 3B comprises a second tension stay receiving aperture 46 extending through the first overhanging portion 39 of the flange 30. The second tension stay receiving aperture 46 is configured to receive the first end 42a of the second tension stay 42 within the hollow body 20 such that the first end 42a of the second tension stay 42a extends into the hollow body 20. As such, the protruding second tension stays 42 can be accessed from within the tower 2. By providing internal accessibility to the second tension stays 42 from within the hollow body, installation and maintenance is improved. The second tension stay connector 40 further comprises a second key member 47, which is locatable within the second tension stay receiving aperture 46 from within the hollow body 20 and is configured to secure the first end 42a of the respective second tension stay 42 within the respective second tension stay receiving aperture 46. The plurality of second tension stay connectors 40 depicted in Figure 3B are substantially the same as the first tension stay connectors which have been previously depicted and described in relation to Figure 3A and shall therefore not be described in any further detail. However, it shall be appreciated that the different connector types may be used from the first and second tension stay connectors.

The provision of the second overhanging portion 39 having a plurality of second tension stay connectors 40 has the advantageous effect of better balancing the forces acting on the flange 30, thereby achieving a more even stress distribution over the upper receiving face 2b’ of the lower member 2b.

As shown in the example illustrated in Figure 3B, the reinforcer 38 may further comprise a third aperture 38c configured to correspond and align with the second tension stay receiving aperture 46 of a respective second tension stay connector 40. As a consequence, the first end 42a of the second tension stay 42 may protrude through both apertures 46, 38c of the second tension stay connector 40 and reinforcer 38 into the hollow body 20. The second key member 47 may act as a key in the third aperture 38c to secure the first end 42a of the second tension stay 42. However, in an alternative example, a separate reinforcer (not shown) may be provided to reinforce the second tension stay connector 40,

In a further alternative, the reinforcer may be omitted entirely.

The second tension stay connectors 40 of the joint 2c are configured so as to secure the first ends 42a of the second tension stays 42 within the hollow body 20. Moreover, due to the configuration of the second overhanging portion 39 of the flange 30 being located inboard of the upper receiving face 2b’ of the lower member 2b, the tension stays extend downwardly from the joint 2c in the upper region 2a of the wind turbine tower, whilst remaining internally within the lower region. The second ends (not shown) of the second tension stays 42 are secured internally within the wind turbine tower 2 to a respective wind turbine foundation 10.

In Figure 3B the second tension stay 42 is shown with an inclination. In an embodiment of the invention the second tension stay 42 is vertical or parallel to the internal surface (23) of the hollow body 20. A method of installing a wind turbine according to an example of the present invention shall now be described with reference to Figure 4.

A first step of the illustrated method involves installing a tension stay foundation. As has been discussed previously in the example illustrated in Figure 1 , the tension stay foundation is integrally formed with the wind turbine tower foundation to form the wind turbine foundation 10. However, it shall be appreciated that in other examples the tension stay foundations be formed separately from the wind turbine tower foundation as a plurality of separate tension stay foundation elements.

Once the tension stay foundation has been installed, the lower region of the wind turbine tower is provided. In the example illustrated in Figure 4, the lower region of the wind turbine tower is installed as a plurality of lower tower modules which are stacked on top of each other, via a crane (not show), or other suitable lifting means. However, it shall be appreciated that in alternative examples, such as the example depicted in Figure 1 , the lower region may be installed as a single unitary lower member 2b. Once the lower region has been installed, the upper region 2a can be provided. The upper member 2a is also typically installed as a plurality of modular components, comprising a joint module 2c and a plurality of upper tower modules 2d-f which are stacked on top of each other to form the upper region 2a. However, it shall be appreciated that the upper region 2a may alternatively be provided as a single, unitary component.

Prior to the engaging portion 31 of the joint 2c being installed onto the upper receiving face 2b’ of the lower member 2b, the respective first ends 1 1a-14a of first tension stays 11-14 are secured within the hollow body 20 of the joint 2c to a respective first tension stay connector. The step of securing the respective first ends 11 a-14a within a respective first tension stay connector involves locating the first ends 11 a-14a of each of the first tension stays 1 1-14 within a respective first tension stay receiving aperture 36 such that the first end 11 a-14a of each of the respective first tension stays 11 a-14a protrude through the first tension stay receiving aperture 36, through the first reinforcer aperture 38a and extend into the hollow body 20 of the joint 2c. Once the first ends of the first tension stays 11 a-14a have been located within the respective first tension stay receiving apertures 36a and first reinforcer aperture 38a, respective first key members 37 can be applied to each of the first reinforcer apertures 38a so as to secure the first tension stays 11-14. However, it shall be appreciated that in an alternative example, the first key members 37 may be applied to each of first tension stay receiving apertures 36, or extend into both apertures.

However, in another example, it shall be appreciated that the step of securing the first ends 1 1 a-14a of the first tension stays 1 1-14 within the hollow body 20 of the joint 2c may be performed after the step of installing the engaging portion 31 of the joint 2c onto the upper receiving face 2b’ of the lower member 2b.

It shall also be appreciated that during the assembly of the wind turbine tower 2 illustrated in Figure 3B, the respective first ends 42a of the plurality of second tension stays 42 are secured within the second tension stay connectors 40 in substantially the same manner as for the first tension stays 11-14 described previously. The plurality of second tension stays 42 may be secured as part of the same operation as for the first tension stays 11-14, or may be secured in a separate stage. Furthermore, the step of securing the first ends 42a of the plurality of second tension stays 42 within the hollow body 20 of the joint 2c may be performed prior to, or after, the step of installing the engaging portion 31 of the joint 2c onto the upper receiving face 2b’ of the lower member 2b. Once the first ends 1 1a-14a of the first tension stays 1 1-14 have been secured within the hollow body of the joint 2c, the engaging portion 31 of the flange 30 is installed onto the upper receiving face 2b’ of the lower member 2b such that the engaging portion 31 interfaces with the upper receiving face 2b’ and the first overhanging portion 32 extends outwardly beyond the upper receiving face 2b’ of the lower member 2b, and optionally, in the example depicted in Figure 3B, the second overhanging portion 39 of the flange 30 extends inwardly beyond the upper receiving face 2b’ of the lower member.

Once the engaging portion 31 interfaces with the upper receiving face 2b’, the plurality of fasteners 34 are applied from within the hollow body, extending through the fastener receiving apertures 33 of the flange 30 and into the fastener receiving apertures 35 of the lower member 2b to secure the engaging portion 31 of the flange 30 to the upper receiving face 2b’ of the lower member 2b.

Once the engaging portion 31 of the flange 30 has been secured to the upper receiving face 2b’ and the joint 2c is securely coupled to the lower region of the wind turbine tower, the second ends 1 1 b-14b of the first tension stays 1 1-14 may then secured to a respective tension stay foundation.

The lower region of the tower typically comprises fourteen modular lower tower modules and therefore, due to its height, typically requires additional support before the upper region 2a can be fully installed. Therefore, the second ends 11 b-14b of the first tension stays 1 1-14 may attached to the tower foundation 10 to provide a provisional stabilising effect during installation. The first tension stays 1 1-14 sufficiently stabilise the lower member 10b of the tower 10 to allow the upper member 10a to be installed, as shown in Figure 4. In the illustrated example, the first tension stays 11-14 are permanent tension stays which are left attached to the tower 2 during operation.

Once the first tension stays 11-14 have been installed, the upper region 2a of the tower 2 can be installed. In the examples depicted in the accompanying Figures, the upper region 2a is installed as a plurality of upper tower modules 2d-f which are stacked on top of each other, via a crane (not show), or other suitable lifting means. However, it shall be appreciated that in alternative examples, upper region may be installed as a single unitary upper region 2a. Once the upper region 2a has been installed, the second ends (not shown) of the second tension stays 42 and optionally the second ends (not shown) of additional first tension stays (not shown) may attached to respective wind turbine stay foundations to induce a compressive load on the lower region 2b of the wind turbine tower 2 and to provide stability during the operation of the wind turbine 1.

It shall be appreciated that the second ends 42a of the plurality of second tension stays 42 may be secured as part of the same operation as for the first tension stays, or may be secured as a separate stage.

However, in an alternative example, the first tension stays 11-14 may be subsequently detached and replaced by alternative tension stays (not shown) to provide the desired tension and stability during the operation of the wind turbine 1.

Once the tower 2 and its associated first and second tension stays have been installed, the nacelle 3, rotor 4 and other components of the wind turbine system 1 can be installed onto the upper region 2a of the tower 2 to complete the installation process. It shall be appreciated that the invention described herein primarily relates to an on shore wind turbine system with a wind turbine foundation being situated on, or proximal to, dry land.

Although the invention has been described above with reference to one or more preferred embodiments, it will be appreciated that various changes or modifications may be made without departing from the scope of the invention as defined in the appended claims.

Claims

1. A wind turbine tower comprising:

a lower wind turbine tower member comprising an upper receiving face; and an upper wind turbine tower member comprising:

a hollow body with a flange formed at a lower end of the body and projecting radially inwardly, the flange having an engaging portion configured to engage with the upper receiving face of the lower member, and having a first overhanging portion configured to extend outwardly beyond the upper receiving face of the lower member when the engaging portion of the flange and upper receiving face of the lower member are engaged; and

2. The tower according to claim 1 , wherein the flange further comprises a second overhanging portion configured to extend inwardly beyond the upper receiving face of the lower member when the engaging portion of the flange and upper receiving face of the lower member are engaged, and wherein the upper member further comprises a plurality of second tension stay connectors located at the second overhanging portion of the flange, each configured to secure a first end of a second tension stay from within the hollow body.

3. The tower according to claims 1 or 2, wherein each of the plurality of first tension stay connectors comprise a first tension stay receiving aperture extending through the first overhanging portion of the flange, configured to receive a first end of a respective first tension stay such that the first end of the respective first tension stay extends into the hollow body, and/or wherein each of the plurality of second tension stay connectors comprise a second tension stay receiving aperture extending through the second overhanging portion of the flange, configured to receive a first end of a respective second tension stay such that the first end of the respective second tension stay extends into the hollow body.

4. The tower according to claim 3, wherein each of the plurality of first and/or second tension stay connectors further comprises a respective first and/or second key member locatable within the respective first and/or second tension stay receiving aperture from within the hollow body and configured to secure a respective first and/or second tension stay within the respective first and/or second tension stay receiving aperture.

5. The tower according to any preceding claim, wherein the flange extends circumferentially around the lower end of the hollow body.

6. The tower according to any preceding claim, further comprising at least one flange connector configured to secure the engaging portion of the flange to the upper receiving face of the lower member from within the hollow body.

7. The tower according to any of claims 3 to 6, further comprising at least one reinforcer configured to reinforce the first and/or second tension stay connector, and/or the flange connector from within the hollow body.

8. The tower according to any preceding claim, wherein the hollow body is a conical shape, widening towards the lower end of the body.

9. The tower according to any preceding claim, wherein the body comprises a plurality of gusset plates.

10. The tower according to any preceding claim, wherein the lower member comprises concrete, steel and/or concrete substitute material and wherein the hollow body comprises steel.

11. A wind turbine comprising:

a wind turbine tower according to any preceding claim; and

a plurality of first tension stays comprising respective first ends and second ends, wherein each of the respective first ends are secured within the hollow body by a respective first tension stay connector and/or a plurality of second tension stays comprising respective first ends and second ends, wherein each of the respective first ends are secured within the hollow body by a respective second tension stay connector.

12. The wind turbine according to claim 11 , further comprising a tension stay foundation and wherein each of the respective second ends of the plurality of first tension stays are secured to the tension stay foundation such that the plurality of first tension stays extend from the upper member to the tension stay foundation, external to the lower member, to induce a compressive load on the lower member and/or wherein each of the respective second ends of the plurality of second tension stays are secured to the tension stay foundation such that the plurality of second tension stays extend from the upper member to the tension stay foundation, internal to the lower member, to induce a compressive load on the lower member.

13. A method of installing a wind turbine comprising the steps of:

providing a lower wind turbine tower member comprising an upper receiving face;

providing an upper wind turbine tower member comprising a hollow body with a flange formed at a lower end of the body and projecting radially inwardly, the flange having an engaging portion and a first overhanging portion, and a plurality of first tension stay connectors located at the first overhanging portion of the flange;

providing a plurality of first tension stays comprising respective first ends and second ends;

installing the engaging portion of the flange onto the upper receiving face of the lower member such that the engaging portion interfaces with the upper receiving face of the lower member and the first overhanging portion of the flange extends outwardly beyond the upper receiving face of the lower member; and subsequently securing the engaging portion of the flange to the upper receiving face of the lower member.

14. The method according to claim 13, comprising the further steps of:

providing a second overhanging portion configured to extend inwardly beyond the upper receiving face of the lower member when the engaging portion of the flange and upper receiving face of the lower member are engaged, and a plurality of second tension stay connectors located at the second overhanging portion of the flange; providing a plurality of second tension stays comprising respective first ends and second ends; and

securing the respective first ends of the plurality of second tension stays within the hollow body to a respective second tension stay connector.

15. The method according claim 13 or 14, wherein the step of securing the respective first ends of the plurality of first tension stays to the respective first tension stay connectors and/or the step of securing the respective first ends of the plurality of second tension stays to the respective second tension stay connectors is performed prior to, or after, the step of installing the engaging portion of the flange onto the upper receiving face of the lower member.

16. The method according to any of claims 13 to 15, wherein each of the plurality of first and/or second tension stay connectors comprise a tension stay receiving aperture formed in the first and/or second overhanging portion of the flange and a first and/or second key member; and the method further comprising the steps of:

locating the first end of a respective first tension stay within the respective first tension stay receiving aperture of the respective first tension stay connector such that the first end of the first tension stay extends into the hollow body and/or locating the first end of a respective second tension stay within the respective second tension stay receiving aperture of the respective second tension stay connector such that the first end of the second tension stay extends into the hollow body; and

applying the first and/or second key member in the first and/or second tension stay receiving aperture from within the hollow body so as to secure the first tension stay and/or second tension stay within the respective tension stay receiving aperture.

17. The method according to any of claims 13 to 16, wherein the step of securing the engaging portion of the flange to the upper receiving face of the lower member comprises:

providing at least one flange connector;

applying the at least one flange connector from within the hollow body to secure the engaging portion of the flange to the upper receiving face of the lower member.

18. The method according to any of claims 13 to 17, further comprising the steps of: providing a tension stay foundation;

securing the second ends of the plurality of first tension stays and/or second tension stays to the tension stay foundation to induce a compressive load on the lower member.

19. A wind turbine tower joint comprising:

a hollow body comprising a flange, wherein the flange is formed at a lower end of the body and projects radially inwardly, and the flange comprises an engaging portion configured to engage with an upper receiving face of a lower member of a wind turbine tower, and a first overhanging portion configured to extend outwardly beyond the upper receiving face of the lower member when the engaging portion of the flange and upper receiving face of the lower member are engaged; and a plurality of first tension stay connectors located at the first overhanging portion of the flange, each configured to secure a first end of a first tension stay from within the hollow body.

20. The joint according to claim 19, wherein the flange further comprises a second overhanging portion configured to extend inwardly beyond the upper receiving face of the lower member when the engaging portion of the flange and upper receiving face of the lower member are engaged; and wherein the joint further comprises plurality of second tension stay connectors located at the second overhanging portion of the flange, each configured to secure a first end of a second tension stay from within the hollow body.