WO2021121500A1

WO2021121500A1 - Mitigation of nacelle drop by tension wire

Info

Publication number: WO2021121500A1
Application number: PCT/DK2020/050351
Authority: WO
Inventors: Julio Xavier Vianna NETO; Torben Ladegaard Baun; Jesper Lykkegaard NEUBAUER; Brian Jørgensen
Original assignee: Vestas Wind Systems A/S
Priority date: 2019-12-20
Filing date: 2020-12-11
Publication date: 2021-06-24

Abstract

A method of preventing nacelle drop in a multiple rotor (MR) wind turbine during mounting of a nacelle to the MR wind turbine, the MR wind turbine comprising a tower (2) extending in an upwards direction, a load carrying structure (3, 4) forming a first section (3) and a second section (4), the first and second sections extending in different directions away from the tower (2). To reduce the impact of a nacelle drop and therefore an abrupt change in the loading of the load carrying structure, the method comprises attaching at least one tension wire (20, 30, 60, 61) to one of the first section (3) and second section (4) such that vertical movement of an interface portion of the first section is reduced by the at least one tension wire, mounting the nacelle (5) to the first section (3), and subsequently removing the at least one tension wire (20, 30, 60, 61).

Description

MITIGATION OF NACELLE DROP BY TENSION WIRE

INTRODUCTION

The disclosure relates to a method of reducing impact of a sudden load on a multiple rotor (MR) wind turbine, e.g. caused by a nacelle drop during assembly of the MR wind turbine or caused by wind load during installation.

BACKGROUND

MR wind turbines typically comprise a tower extending in an upwards direction and one or more load carrying arm structures each forming two sections. A first section extends in one direction away from the tower and holds at least one nacelle, and a second section extends in another direction away from the tower and holds at least one nacelle.

For wind turbines, particularly of this kind, the risk of nacelle drop during installation needs to be considered as load during the design phase.

On MR wind turbines, the impact is potentially a large deflection of the load carrying structure caused by the mass of the nacelle hitting the load carrying structure during assembly. The interface is often in the range of approximately half a rotor diameter away from the tower, and the moments introduced in the interface between the tower and the load carrying structures can be large. As a result, the interface where the nacelle meets the load carrying structure may move several meters during deflection of the tower and the load carrying structure. If, by accident, the nacelle slides off and drops to, or towards the ground or sea, the load on the interface is suddenly released, causing an opposite reaction, i.e. upwards movement of the tower and load carrying structures.

To counteract such reactions, the tower and load carrying structures may be reinforced, and a potential nacelle drop in an MR wind turbine is therefore expensive.

SUMMARY

It is an object to reduce the impact of sudden release of load on the interface where the nacelle meets the load carrying structure, in the following referred to as "interface". According to this and other objects, the disclosure, in a first object provides a method comprising deflecting the first section in a vertically downwards direction while attaching a nacelle to the first section, or to the second section, and subsequently releasing the deflection of the first section.

The movement of the tower and load carrying structures is thereby limited by a counterforce if a nacelle drop occurs. This counterforce is applied by the tensioned wire, e.g. extending from below the interface of one of the first and second sections to a point on the tower, a point on ground, or a point on the sea or seabed. In case of nacelle drop, the downward movement of the load carrying structure is therefore limited thus also dampening the return movement and allowing the same safety with a lighter and cheaper wind turbine construction. In case of wind induced movement of the interface, the tensioned wire may limit the movement and therefore facilitate a safer and easier installation of the nacelle.

The tension wire may particularly be tensioned to a tension force corresponding to at least 10 percent of the weight of the nacelle, or at least 20 percent of the weight or 30 percent of the weight of the nacelle. If the weight of the nacelle is 100 tons, the tension force may at least correspond to the force of 10 tons.

The at least one tension wire may particularly be arranged such that it deflects the first section or the second section in a vertical direction, particularly a downwards direction, and thereby prevents an opposite movement of that section.

The at least one tension wire could be attached between the first or second section and: a foundation for the wind turbine, an on-shore point on the ground, an off-shore anchor point on the sea bed a part of the tower, a free hanging mass, e.g. provided by a heavy body suspended by the tension wire, a vessel floating on the sea, and/or a foundation or tower structure of an adjacent wind turbine.

In one embodiment the first section is deflected vertically downwards by suspending a first of the at least one tension wires between the first section and a low attachment point on the tower. The attachment point may particularly be at the base, or at least sufficiently low to establish an angle between the tension wire and the tower of not more than 45 degrees, and preferably not more than 30 degrees. The first section may be deflected vertically upwards by suspending a second one of the at least one tension wires between the second section and a low attachment point on the tower. The low attachment point may particularly be at the base, or at least sufficiently low to establish an angle between the tension wire and the tower of not more than 45 degrees, and preferably not more than 30 degrees.

The vertical movement of the interface portion of the first section is reduced by suspending a third one of the at least one tension wires between the first section and a high attachment point on the tower and on level with the nacelle or above the position of the nacelle when attached to the load carrying structure.

The vertical movement of an interface portion of the first section is reduced by suspending a fourth one of the at least one tension wires between the second section and a high attachment point on the tower and in height with or above the position of the nacelle when attached to the load carrying structure.

At least one dampening structure, e.g. a spring structure or a hydraulic or pneumatic damper may be inserted in at least one of the at least one tension wires to thereby absorb tension in the wire, and dampen oscillating elongation of the tension wire due to the tension and relaxation of the tension wire.

The at least one tension wire may be attached to a yawing assembly allowing the load carrying structure to rotate relative to the tower while the tension wire is attached. The yawing assembly may include a bearing assembly allowing the attachment point, i.e. one of the above mentioned low or high attachment points to rotate relative to the outer surface of the tower.

The tension wire may be attached at any position around the tower, i.e. anything from 0 to 360 degrees rotationally offset relative to load carrying position of the tower where the first or second section extends away from the tower. The position may particularly be between 0 and 90 degrees offset relative to the load carrying position of the tower. The position may e.g. be 45 degrees offset relative to the load carrying position of the tower, and in one embodiment, the at least one tension wire may be attached to the tower at an attachment point which is 90 degrees rotationally offset relative to a direction of the load carrying structure. Again, this may apply both to the low and to the high attachment points. In that way, the MR wind turbine may be yawed from side to side in a 180 degrees swing while the tension wire is relaxed and subsequently tensioned on an opposite side.

In a second aspect, the disclosure provides a multi rotor (MR) wind turbine comprising a tower extending in an upwards direction. A load carrying structure forms a first section and a second section. The first and second sections extend in different directions away from the tower, and at least one tension wire providing a downwards force on the first section.

Wherein at least one of the first section and the second section forms a nacelle mounting interface configured to receive a nacelle to be attached at the nacelle mounting interface. The wire may extend between one of the first section and second section to an attachment point, e.g. on the tower.

In this MR wind turbine, the attachment point is located below the load carrying structure and it is configured to reduce vertical movement of an interface portion of the first section.

The attachment point may be rotatable around the tower, and/or, the load carrying structure may extend in a first direction from the tower, and the attachment point may extend in a second direction from the tower such that the second direction is 90 degrees rotationally offset relative to the first direction.

In one embodiment, the tower comprises a plurality of attachment points configured for releasable attachment of the tension wire. These points can be at any position around the tower, i.e. anything from 0 to 360 degrees rotationally offset. This would enable a "walking line" solution where the tension wire is moved from point to point while the MR wind turbine is yawed e.g. during mounting of the nacelle to the interface.

LIST OF DRAWINGS

The disclosure will now be described in further detail with reference to the accompanying drawings in which:

Fig. 1 illustrates a front view of a MR wind turbine;

Fig. 2, 2a, and 2b illustrate a tension wire attached to the interface;

Fig. 3 illustrates the MR wind turbine with installation of an additional tension wire;

Fig. 4 illustrates the MR wind turbine with installation only of the additional tension wire 30; Fig. 5 illustrates a spring-damper 50 on the tension wire 20;

Fig. 6 illustrates a supplemental tension wire for each of the first and second sections; Figs. 7 and 8 illustrate the supplemental tension wire configuration in combination with the tension wire 20 and the additional tension wire 30;

Fig. 9 illustrates removal of the tension wire;

Fig. 10 illustrates the movement of the load carrying structure during attachment of the nacelle in case of nacelle drop;

Figs. 11-12 illustrate a method of enabling the wires to yaw along with the arms to avoid removing them when yawing during installation; and

Fig. 13 illustrates a 4T wind turbine with a tension wire.

DETAILED DESCRIPTION OF THE DRAWINGS

Fig. 1 illustrates a front view of a MR wind turbine 1 comprising a tower 2 carrying two load carrying structures 3. The illustrated MR wind turbine carries two nacelles. However, 3, 4 or more nacelles could be considered, e.g. in two rows of two nacelles, the rows being at different altitude, i.e. a so called 4T wind turbine.

The load carrying structures extend in different outwards directions away from the tower 2.

The load carrying structure comprises a first section 3', 3" and a second section 4', 4". Each section supports a nacelle 5, and each nacelle 5 forms an energy generating unit including a rotor 6 carrying three wind turbine blades 7, sweeping an area.

The load carrying structures 3', 3", 4', 4" are attached to the tower 2 via a yaw arrangement, allowing the entire pair of load carrying structures to perform yawing movements with respect to the tower 2 in order to direct the rotors 6 into the incoming wind.

When the multirotor wind turbine 1 is operational, the nacelles 5 are placed symmetrically around the tower 2 so that the multirotor wind turbine is balanced.

Each section of the load carrying structures 3, 4, includes a first part 3', 4' and a second part 3", 4". The first part 3', 4' acts as compression elements and it is supported by the second part 3", 4" forming a tension element in the form of two guy wires extending from a swivel arrangement on the tower. In the following description, we refer to first section as that section of the load carrying structure on which the nacelle is to be attached, and the second section as that section of the load carrying structure where there is either no nacelle, or where a nacelle is already attached.

Fig. 2 illustrates a tension wire 20 attached between the interface and an attachment point 21 on the tower 2. The tension wire could be made of various materials, e.g. steel wire rope, synthetic rope such as nylon rope. It may be an advantage if it floats if dropped into the water and a light-weight wire may also make it easier to handle.

The tension wire 20 extends from below the interface for the nacelle which is about to be mounted, and the other end of the tension wire is attached to the tower at a position as low as possible under the intersection between the tower and the load carrying structure. In case the nacelle which is about to be attached, drops and creates a swift change in the loading of the first section 3, the downward movement of the arm is limited by the pre-tensioning provided by the tension wire 20, and the tension wire 20 prevents a large return movement in upwards direction.

Fig. 2a illustrates the tension wire 20 attached between the interface and a load element. The tension wire 20 extends from below the interface for the nacelle which is about to be mounted and thereby displaces the interface vertically downwards.

Fig. 2b illustrates the tension wire 20 attached between the interface and a fixed anchor at ground. The tension wire 20 extends from below the interface for the nacelle which is about to be mounted and thereby displaces the interface vertically downwards.

Fig. 3 illustrates the MR wind turbine with installation of an additional tension wire 30 attached between the interface of the second section, i.e. opposite the first section of the load carrying structure where the nacelle is to be mounted. Also this additional tension wire extends from below the interface, in this case an interface where a nacelle is already mounted, and the other end of the additional tension wire is attached to the tower at a position as low as possible under the intersection between the tower and the load carrying structure. By the additional tension wire to the section opposite the one on which a nacelle is being installed, the downwards movement can also be limited, thereby further reducing also the return movement. Accordingly, this provides dampening in both directions.

Fig. 4 illustrates the MR wind turbine with installation only of the additional tension wire 30, i.e. without the tension wire 20 attached at the first section of the load carrying structure. By the additional tension wire 30 without the tension wire 20 on the first section, the downwards movement of the first section in case of nacelle drop can be limited, thereby reducing oscillation of the first section.

Fig. 5 illustrates a spring-damper 50 on the tension wire 20. The spring-damper reduces the force absorbed by the tension wire and could be used to also dampen sideways movement during installation.

Fig. 6 illustrates a supplemental tension wire 60, 61 for each of the first and second sections 3, 4. The supplemental tension wire extends from the interface to the tower in an essentially horizontal direction and may therefore also dampen the impact of nacelle drop. In this embodiment, the supplemental tension wire 60 on the first section reduces downwards movement of the interface of the first section and the supplemental tension wire 61 on the second section likewise reduces downwards movement of the interface of the first section.

Figs. 7 and 8 illustrate the supplemental tension wire configuration in combination with the tension wire 20 and the additional tension wire 30 as illustrated in the previous drawings.

Fig. 9 illustrates that the tension wire is only used during attachment of the nacelle to the interface of the load carrying structure. After the nacelle has been attached, the tension wire, in this case the tension wire 20 is removed and used when assembling a subsequent MR wind turbine.

Fig. 10 illustrates the movement of the load carrying structure during attachment of the nacelle in case of nacelle drop.

Fig. 11 illustrates a method of enabling the wires to yaw along with the arms to avoid removing them when yawing during installation.

Alternatively, the wires can be fixed 90 degrees rotationally offset relative to the direction of the load carrying structures to the points indicated at 110. In that way, the MR wind turbine may yaw 180 degrees. During this procedure the tension wire slackens and subsequently tensions again on the opposite side. The nacelle position is +/-90deg from tower attachment point.

Alternatively, the method may include the principle that the tension wire is shifted between two attachment points on the tower, i.e. "a walking wire". One attachment is removed and fixed 10-20deg further, then the 2nd one is removed and attached 10-20deg further, etc. An alternative to the method illustrated in Fig. 11 could be to attach the tension wires to the tower via a bearing allowing rotation relative to the tower.

Fig. 12 illustrates wires 121 connected in 45deg in this case, in order to allow the MR wind turbine may be yawed from side to side in an approximately 90 degrees swing while the tension wire is relaxed and subsequently tensioned on an opposite side. The approximately 90 degrees swing may be required during installation to avoid collision with the installation crane 122.

Fig. 13 illustrates a 4T wind turbine with two rows of two nacelles, the rows being at different altitude and each row defined by a load carrying structure (3,4) forming a first section (3) and a second section (4), the first and second sections extending in different directions away from the tower (2).

In this embodiment, the upper row and the lower row can be treated independently during mounting of the nacelles. In the illustrated stage of assembly, a tension wire 20 is attached between the first section 3 and a first low attachment point 21 on the tower 2. In this case, the low attachment point 21 on the tower could be a point above the lower row, i.e. as illustrated in Fig. 13, or it could be a point below the lower row. In that case, the wire may be suspended such that it can pass the lower load carrying structure without colliding with the lower load carrying structure or nacelles, or blades of the lower row.

Claims

1. A method of reducing impact of a sudden load on a multiple rotor (MR) wind turbine during mounting of a nacelle (5) to the MR wind turbine, the MR wind turbine comprising a tower (2) extending in an upwards direction, a load carrying structure (3,4) forming a first section (3) and a second section (4), the first and second sections extending in different directions away from the tower (2), the method comprising attaching at least one tension wire (20, 30, 60, 61) to one of the first section (3) and second section (4) such that vertical movement of an interface portion of the first section is reduced by the at least one tension wire, mounting the nacelle (5) to the first section (3), and subsequently removing the at least one tension wire (20, 30, 60, 61).

2. The method according to claim 1, wherein the first section is deflected vertically downwards by a first of the at least one tension wires attached to the first section.

3. The method according to any of the preceding claims, wherein the first tension wire (20) is suspended between the first section and a first low attachment point (21) on the tower (2).

4. The method according to any of the preceding claims, wherein the second section is deflected vertically downwards by a second of the at least one tension wires attached to the second section.

5. The method according to claim 4, wherein the second tension wire (20) is suspended between the second section and a second low attachment point (21) on the tower (2)

6. The method according to claims 3 or 5, wherein the first and second low attachment points are below the height of the nacelle when attached to the load carrying structure.

7. The method according to claims 3 and 5, wherein the first and second low attachment points are in the same level on the tower.

8. The method according to any of the preceding claims, wherein the vertical movement of the interface portion of the first section is reduced by suspending a third one of the at least one tension wires (60) between the first section and a high attachment point (62) on the tower (2), the high attachment point being in the same height as the nacelle or above the nacelle when attached to the load carrying structure.

9. The method according to any of the preceding claims, wherein the vertical movement of the interface portion of the first section is reduced by suspending a fourth one of the at least one tension wires (61) between the second section and a high attachment point (62) on the tower (2), the high attachment point being in height with the nacelle or above the nacelle when attached to the load carrying structure.

10. The method according to any of the preceding claims, comprising inserting at least one dampening structure (50) in at least one of the at least one tension wires.

11. The method according to any of the preceding claims, wherein the at least one tension wire is attached to a yawing assembly allowing the load carrying structure to rotate relative to the tower while the tension wire is attached.

12. The method according to any of the preceding claims, wherein the at least one tension wire is attached to the tower at an attachment point which is 90 degrees rotationally offset relative to a direction of the load carrying structure.

13. A multi rotor (MR) wind turbine comprising a tower (2) extending in an upwards direction, a load carrying structure (3,4) forming a first section (3) and a second section (4), the first and second sections extending in different directions away from the tower (2), and at least one tension wire (20, 30, 60, 61) providing a downwards force on the first section (3), wherein the first section (3) forms an nacelle mounting interface configured to receive a nacelle to be attached at the nacelle mounting interface.

14. The MR wind turbine according to claim 13, wherein the tension wire (20, 30, 60, 61) extends between the first section (3) and at least one attachment point (21) on the tower, the attachment point (21) being located below the load carrying structure.

15. The MR wind turbine according to claim 14, wherein the load carrying structure extends in a first direction from the tower, and wherein the attachment point (21) extends in a second direction from the tower, the second direction being between 0 and 360 degrees rotationally offset relative to the first direction.

16. The MR wind turbine according to claim 14, wherein the attachment point (21) is rotatable around the tower.

17. The MR wind turbine according to any of claims 14-16, wherein the tower comprises a plurality of attachment points configured for releasable attachment of the tension wire.