WO2022122102A1

WO2022122102A1 - Drop release for a nacelle in a wind turbine

Info

Publication number: WO2022122102A1
Application number: PCT/DK2021/050355
Authority: WO
Inventors: Peter BØTTCHER; Jesper Lykkegaard NEUBAUER; Søren DALSGAARD; Torben Ladegaard Baun
Original assignee: Vestas Wind Systems A/S
Priority date: 2020-12-11
Filing date: 2021-12-07
Publication date: 2022-06-16

Abstract

A method of assembling an MR wind turbine, the method comprising the steps of: - providing a tower structure comprising a tower (2) holding a load carrying structure (3, 4), the load carrying structure forming a load carrying structure interface (35); - providing a nacelle (5) having a mass and forming a nacelle interface (34); - carrying the mass by a crane which exerts a lifting force while connecting the load carrying structure interface to the nacelle interface by a quick release structure (32) which is only able to maintain the position of the nacelle interface on the load carrying structure interface when supported by the lifting force; - reducing the lifting force; -connecting the load carrying structure interface to the nacelle interface by a fixation structure (33) which can maintain the position of the nacelle interface on the load carrying structure interface without support from the lifting force; and - removing the lifting force.

Description

DROP RELEASE FOR A NACELLE IN A WIND TURBINE

INTRODUCTION

The present disclosure relates to a method of assembling a wind turbine, and particularly to a method of assembling a multiple rotor (MR) wind turbine. The disclosure further relates to a wind turbine structure for an improved assembly procedure.

BACKGROUND

MR wind turbines typically comprise a tower structure comprising a tower extending in an upwards direction and one or more load carrying 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 a different direction away from the tower and holds at least one nacelle.

For wind turbines, particularly of this kind, the load carrying structure may move unintentionally, e.g. in case of being hit by a nacelle which is accidentally dropped during installation.

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.

Because of risk of faults in lifting gear during assembly of the wind turbine, the interface where the nacelle meets the tower structure is dimensioned stronger than necessary considering the daily operation of the wind turbine.

Competition amongst producers of renewable energy systems applies pressure on prices, delivery schedule, quality, and safety. Accordingly, there is a constant desire for optimization. SUMMARY

It is an object to reduce the required strength of a tower structure for a wind turbine, and particularly for an MR wind turbine. It is a further 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, embodiments of the disclosure provide a method of assembling a wind turbine. The method comprises the steps of:

- providing a tower structure comprising a tower holding a load carrying structure, the load carrying structure forming a load carrying structure interface; providing a nacelle having a mass and forming a nacelle interface;

- carrying the mass by a crane which exerts a lifting force while connecting the load carrying structure interface to the nacelle interface by a quick release structure which is only able to maintain the position of the nacelle interface on the load carrying structure interface when supported by the lifting force; reducing the lifting force;

- connecting the load carrying structure interface to the nacelle interface by a fixation structure which can maintain the position of the nacelle interface on the load carrying structure interface without support from the lifting force; and removing the lifting force.

Since the light fixation structure has a strength which is insufficient to hold the position of the nacelle relative tower structure if the lifting force is removed, the light fixation structure would release the nacelle e.g. if the full load of the nacelle is suddenly applied on the tower structure. Accordingly, sudden mass transfer and thus heavy loading caused by a nacelle drop is prevented.

When used herein, the term "nacelle" may include the machine housing typically referred to as a nacelle and optionally including also the rotor, i.e. what is sometimes referred to as a rotor-nacelle-assembly (RNA). The MR wind turbine may e.g. carry two nacelles, or 3, 4 or more nacelles, e.g. in two rows of two nacelles, the rows being at different altitude, i.e. a so called 4T wind turbine. The wind turbine could be upwind or downwind.

The connection of the load carrying structure interface to the nacelle interface by the quick release structure may be obtained unattended, i.e. an un-manned operation. That may increase safety during the installation. The connection of the load carrying structure interface to the nacelle interface by the fixation structure may be obtained attended by personnel.

The lifting force may be reduced while the load carrying structure interface is connected to the nacelle interface by the fixation structure, e.g. reduced in steps alternately stepwise connecting the load carrying structure interface to the nacelle interface by the fixation structure. In that way, a part of the load carried by the crane is released from the crane while the fixation structure is defined.

In one embodiment, the fixation structure comprises flanges joined by a plurality of bolts. In this embodiment, a number of bolts may be attached, and the crane lifting force is released, subsequently another number of bolts is attached followed by a subsequent further release of lifting force from the crane etc. until all bolts are connected.

The lifting force may be monitored, and a power driven release structure may be operated to release the nacelle from the load carrying structure based on the lifting force.

The monitored lifting force may be used by personnel working with manually connecting the load carrying structure interface to the nacelle interface by the fixation structure. In one example, the lifting force may be communicated wireless to the personnel.

A set of instructions for guiding the personnel how to amend the fixation structure and thereby prepare the fixation structure to carry the full load may be generated. Herein, we refer to an amending-instruction for the personnel. These instructions could be prepared by a computer system based on the lifting force, and they may specify a stepwise connection of the load carrying structure interface to the nacelle interface by the fixation structure while the lifting force is reduced.

In a second aspect, the disclosure relates to an MR-wind turbine tower structure comprising an upright tower and a load carrying structure extending transverse to the tower structure and being carried by the tower, the load carrying structure defining a load carrying structure interface for receiving a complementary nacelle interface of a nacelle during an assembly procedure and an assembly structure configurable between an initial state in which it is only able to maintain the position of the nacelle interface on the load carrying structure interface when supported by a lifting force acting on the nacelle, and a final state in which it is capable of maintaining the position of the nacelle interface on the load carrying structure interface without support from the lifting force. The initial state could be provided by a quick release structure which is insufficient to carry a mass of the nacelle and the final state could be provided by a fixation structure providing a final strength which is sufficient to hold the mass of the nacelle.

The fixation structure may comprise a plurality of bolts arranged to assemble a flange of the nacelle to a flange of the tower structure, and wherein the quick release structure is constituted by a subset of a total number of bolts. I.e. the subset is not sufficiently strong to carry the full weight of the nacelle, and should the lifting force from the crane fail, the nacelle will be released with less or no damage to the structure of the tower or load carrying structure.

Bolts in excess to the subset of bolts may be added while the lifting force is reduced until the total number of bolts are attached and the lifting force can be removed.

The fixation structure may comprise a plurality of bolts assembling a flange of the nacelle to a flange of the tower structure, and the quick release structure may be constituted by a body fixed to the load carrying structure interface or to the nacelle interface and having a beveled surface configured to slide on the other one of the load carrying structure interface or nacelle interface. In this embodiment, the nacelle can be released by the sliding if the lifting force disappears.

The initial state may provide an initial weight balance which depends on the lifting force to maintain the nacelle on the tower and the final ability provides a final weight balance which is independent on the lifting force to maintain the nacelle on the tower. Accordingly, the nacelle will tilt in the initial state and thereby become released.

A first interface section may be attached between the load carrying structure and the nacelle. The first interface section may e.g. be formed by a nacelle support casting, i.e. a casted component inserted between the load carrying structure and the nacelle as illustrated in the drawings pertaining to the different embodiments.

The first interface section may define a first split line against the load carrying structure and a second split line against the nacelle, the second split line extending closer to vertical than the first split line, wherein the fixation structure defines an assembly in the second slit line. The more vertical, second, split line, facilitates easier release of the nacelle and allows the nacelle to be released with less impact on the tower and load carrying structure. The wind turbine may comprise a second interface section attached between the load carrying structure and the nacelle. The second interface section may e.g. be formed by a nacelle support casting.

The second interface section may define a first split line against the load carrying structure and a second split line against the nacelle. The first split line may extend closer to vertical than the second split line, wherein the fixation structure defines an assembly in the first split line. The more vertical, first, split line, facilitates easier release of the nacelle and allows the nacelle to be released with less impact on the tower and load carrying structure.

The wind turbine may comprise a power driven release structure configured to release the nacelle from the load carrying structure in response to receiving a release signal, e.g. as controlled by a force sensor arranged to sense the lifting force from the crane.

LIST OF DRAWINGS

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

Fig. la and lb illustrate an MR wind turbine;

Fig. 2 illustrates a situation where a nacelle 5' is lowered down onto the load carrying structure;

Figs. 3-5 illustrate a method according to a first embodiment;

Figs. 6-8 illustrate a method according to a second embodiment;

Figs. 9-10 illustrate details of a quick release mechanism; and

Figs 11-15 illustrate examples of quick release mechanisms.

DETAILED DESCRIPTION OF THE DRAWINGS

Figs, la and lb illustrate 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. The load carrying structure 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 structure 3', 3", 4', 4" are attached to the tower 2 via a yaw arrangement, allowing the load carrying structure sections 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 situation where a nacelle 5' is lowered down onto the load carrying structure 3. During this procedure, a nacelle drop onto the load carrying structure may create a momentary increased load. Herein we refer to this load as "a drop load". The drop could be caused by errors in the lifting gear etc. For safety reasons, the load may be defined e.g. as two times the load caused by the weight of the nacelle including the rotor. This drop load is a driver for the design of the wind turbine and triggers a strength requirement which is much higher than required for the subsequent daily operation. It also increases the weight of the wind turbine and thereby increases not only the costs of making the wind turbine but also the costs of making the foundation and transporting the wind turbine components.

Figs. 3-5 illustrate in a sequence of illustrations, a method for assembling a wind turbine by use of a vertical split line.

In Fig. 3, a nacelle support casting 31 is mounted with a quick release mechanism 32 and/or by use of only a few bolts constituting a part of a fixation structure 33. The number of bolts is insufficient for carrying the weight of the nacelle. If the full nacelle mass is transferred to the support casting 31, the quick release mechanism 32 and/or the few bolts 33 will fail, and the nacelle and the nacelle support casting will fall from the load carrying structure and to the ground or into the ocean. The nacelle interface 34 is a part of the nacelle and the load carrying structure interface 35 is a part of the nacelle support casting. The nacelle and load carrying structure interfaces could typically be constituted by flanges with bolt assembly structures.

In Fig. 4, the nacelle and rotor are placed on the nacelle support casting 31 with as little clearance as possible and the mass of the mass transfer from the crane to the load carrying structure is slowly increased. As the mass transfer progresses, the number of bolts is increased. For that purpose, personnel 41 inside the load carrying structure attends the operation.

At approximately 50% mass transfer all bolts are installed between the nacelle support casting and the load carrying structure. Alternatively, the period of the first 50% load transfer is performed by a quick release mechanism, e.g. in the form of a number of retractable pistons or pins or similar. Different release mechanisms are illustrated in Figs. 9- 15.

In Fig. 5 the weight of the nacelle is completely transferred, and the personnel can move into the nacelle support casting and bolt the nacelle to the nacelle support casting, depicted by the bolts 51.

By the illustrated method, it is not necessary to work under suspended load, and the method increases the safety and may reduce the necessary drop load design criteria.

Since the nacelle is not standing on a horizontal assembly split line, the method allows for a quick release mechanism to be implemented, e.g. as illustrated in Figs. 11-14.

Figs. 6-8 illustrate in a sequence of illustrations another method for assembling a wind turbine by use of a vertical split line.

In Fig. 6, the nacelle support casting 31 is pre-mounted on the nacelle and lifted together with the nacelle. The nacelle interface 34 is a part of the nacelle support casting 31, and the load carrying structure interface 35 is an end part of the arm 61 forming a primary part of the load carrying structure. Typically, the load carrying structure interface 35 is constituted by a flange welded onto a steel structure of the arm and having a bolt assembly structure. The nacelle support casting is lifted horizontally onto the quick release mechanism interface. The procedure is like that described relative to Figs. 3-5 and may include mounting of a few bolts with insufficient strength for carrying the weight of the nacelle. In this way the full mass of the nacelle mass cannot be transferred to the load carrying structure in case of a nacelle drop. Instead, the nacelle and the support casting will fall to the ground or into the ocean.

In Fig. 7, the nacelle and nacelle support casting 31 is fixed in a preliminary way to the load carrying structure by use of the quick release mechanism and a few bolts and the mass transfer is started.

The number of bolts is increased as the mass transfer progresses and at approximately 50% mass transfer, all bolts are installed between the nacelle support casting and the load carrying structure.

In Fig. 8, the fixation is completed and if a quick release tool has been used this is removed and reused in a later wind turbine installation.

Figs. 9 and 10 illustrate details of the load carrying structure interface 35, the nacelle interface 34, and an example of a quick release mechanism 32.

The load carrying structure interface 35 is formed by a flange 32 welded onto an arm structure and thereby forms the end part of the load carrying structure. The flange has a plurality of bolt holes or prefixed bolts 33 and extends circumferentially about an opening into an inner space withing the load carrying structure. During the assembly procedure, personnel can access the bolt structure via a space in the nacelle support casting 31.

The quick release mechanism 32 is detachably attached to the flange 35 e.g. by bolts and can therefore be reused for assembly of different wind turbines. During the interim stages of the nacelle mounting procedure, the nacelle interface 34 is lifted onto the quick release mechanism 32. The quick release mechanism has a beveled upper surface 101, e.g. having a 1-2 degrees angle to horizontal. The nacelle interface may rest with a relatively low weight on the quick release mechanism. If the weight increases above a limit, e.g. 20-30 percent of the weight of the nacelle, the nacelle interface will slide of the quick release mechanism due to the beveled angle. The personnel may increase the ability of the load carrying structure interface to hold the nacelle interface by adding bolts between the interfaces while the crane stepwise or continuously reduces the lifting force.

Figs. 11-12 illustrate a quick release mechanism comprising a retractable cylinder structure

110 with a piston 111 movable between a forward position illustrated in Fig. 11 and a rearward position illustrated in Fig. 12. In the forward position, the piston supports the lower edge of the projection 112 of the support casting 31. When the piston moves backwards, it releases the support casting and the impact of the nacelle on the load carrying structure is released. Figs. 13-15 illustrate another example of a quick release mechanism 131. Fig. 13 illustrate that the location and general principle is like the embodiment in Figs. 11-12, i.e. to hold or release the support casting 31.

In the example in Figs. 13-15, however, the mechanism uses a spring pre-loaded lock. Figs. 14-15 illustrate the lock and spring in an enlarged view of the quick release mechanism. When load is transferred from the edge of the projection 112 onto the arm structure, the pretensioned spring 141 in the release mechanism starts to compress. Before the full load is transferred, e.g. until 50% load is transferred, the edge of the flange 112 is not behind the shoulder 142 of the release mechanism. After the 50% load transfer the edge of the flange 112 is compressing the pretensioned spring enough to move down behind the shoulder 142 of the release mechanism and the mechanism is no longer able to release the load of the nacelle if a nacelle drop should occur.

Claims

1. A method of assembling an MR wind turbine, the method comprising the steps of:

- providing a tower structure comprising a tower (2) holding a load carrying structure (3, 4), the load carrying structure forming a load carrying structure interface (35); providing a nacelle (5) having a mass and forming a nacelle interface (34);

- carrying the mass by a crane which exerts a lifting force while connecting the load carrying structure interface to the nacelle interface by a quick release structure (32) which is only able to maintain the position of the nacelle interface on the load carrying structure interface when supported by the lifting force; reducing the lifting force;

- connecting the load carrying structure interface to the nacelle interface by a fixation structure (33) which can maintain the position of the nacelle interface on the load carrying structure interface without support from the lifting force; and removing the lifting force.

2. The method according to claim 1, wherein the connection of the load carrying structure interface to the nacelle interface by the quick release structure is obtained unattended.

3. The method according to claim 1 or 2, wherein the connection of the load carrying structure interface to the nacelle interface by the fixation structure is obtained attended by personnel.

4. The method according to any of the preceding claims, wherein the lifting force is reduced while connecting the load carrying structure interface to the nacelle interface by the fixation structure.

5. The method according to claim 4, wherein the lifting force is reduced in steps alternately stepwise connecting the load carrying structure interface to the nacelle interface by the fixation structure.

6. The method according to any of the preceding claims, wherein the lifting force is monitored, and a power driven release structure is operated to release the nacelle from the load carrying structure based on the lifting force.

7. The method according to claim 6, wherein the monitored lifting force is used by personnel working with manually connecting the load carrying structure interface to the nacelle interface by the fixation structure.

8. The method according to claim 7, wherein an amending-instruction for the personnel is prepared by a computer system based on the lifting force, the amending-instruction specifying a stepwise connection of the load carrying structure interface to the nacelle interface by the fixation structure while the lifting force is reduced.

9. An MR-wind turbine comprising an upright tower and a load carrying structure extending transverse to the tower and being carried by the tower, the load carrying structure defining a load carrying structure interface for receiving a complementary nacelle interface of a nacelle during an assembly procedure and an assembly structure configurable between an initial state in which it is only able to maintain the position of the nacelle interface on the load carrying structure interface when supported by a lifting force acting on the nacelle, and a final state in which it is capable of maintaining the position of the nacelle interface on the load carrying structure interface without support from the lifting force.

10. The wind turbine according to claim 9, wherein initial state is provided by a quick release structure which is insufficient to carry a mass of the nacelle and the final state is provided by a fixation structure providing a final strength which is sufficient to hold the mass of the nacelle.

11. The wind turbine according to claim 10, wherein the fixation structure comprises a total number of bolts assembling a flange of the nacelle to a flange of the tower structure, and wherein the quick release structure is constituted by a subset of the total number of bolts.

12. The wind turbine according to claim 10, wherein the fixation structure comprises a plurality of bolts assembling a flange of the nacelle to a flange of the tower structure, and wherein the quick release structure is constituted by a body fixed to the load carrying structure interface or to the nacelle interface and having a beveled surface configured to slide on the other one of the load carrying structure interface or nacelle interface.

13. The wind turbine according to any of claims 10-12, comprising a first interface section attached between the load carrying structure and the nacelle, the first interface section defining a first split line against the load carrying structure and a second split line against the nacelle, the second split line extending closer to vertical than the first split line, wherein the fixation structure defines an assembly in the second slit line.

14. The wind turbine according to any of claims 10-13, wherein the wind turbine comprises a second interface section attached between the load carrying structure and the nacelle, the second interface section defining a first split line against the load carrying structure and a second split line against the nacelle, the first split line extending closer to vertical than the second split line, wherein the fixation structure defines an assembly in the first split line.

15. The wind turbine according to any of claims 10-14, comprising power driven release structure configured to release the nacelle from the load carrying structure in response to receiving a release signal.