A method of filling a ballast tank within a wind turbine blade and associated wind turbine blade

Abstract

A method of filling a ballast tank (30) positioned within an interior of a wind turbine blade (20), the method comprising the steps of: providing a wind turbine blade (20), the wind turbine blade having a ballast tank (30) within an interior (42) of the blade; determining the location of the 5 ballast tank (30) in the blade (20); applying a visible position identifier (60) to an exterior surface (55) of the blade at a location corresponding to the position of the ballast tank (20); forming a hole (50) through the exterior surface (55) of the blade and into the ballast tank (30), at the location of the position identifier (60); introducing ballast material (48) through the hole (50) into the ballast tank (30)

Description

[0001] A Method of Filling A Ballast Tank Within a Wind Turbine Blade and Associated Wind Turbine Blade

[0002] Technical field

[0003] The present invention relates to balancing wind turbine blades. In particular the invention relates to a method of filling a ballast tank within an interior of a blade and the associated blade.

[0004] Background

[0005] A horizontal axis wind turbine comprises a number of blades, normally three blades, which rotate about the horizontal axis. It is important that these blades are balanced; if they are not balanced vibrations or other instabilities may be introduced into the drive train of the wind turbine.

[0006] Wind turbine blades are manufactured from composite materials, e.g. glass fibre reinforced plastic and carbon fibre reinforced plastic. The manufacturing process involves applying fabric reinforcing material in a mould and introducing resin into the mould, for example in a vacuum assisted resin transfer moulding (VARTM) system. Due to variabilities in the manufacturing process, not all blades will have the same mass and so blades are balanced together in a set. The balancing process comprises weighing the blades and adding ballast material to a ballast tank in the blade so that sets of blade can be provided where each blade has the same mass moment.

[0007] During the life of a wind turbine, it is sometimes necessary to service the blades. During servicing of a blade, material may be added to the blade, or even removed from the blade. This may be done up tower when the blades are mounted on the hub of the wind turbine. After the servicing of the blade, the blades on the turbine may be imbalanced and ballast material may need to be added to the ballast tank.

[0008] The ballast tank is located in an interior of the blade and it can be difficult to determine the location of the ballast tank from the exterior of the blade, especially when the blade is mounted to the hub of the wind turbine. It is an object of the invention to allow a technician to locate the position of the ballast tank from an exterior of the blade. Summary

[0009] According to the present invention, there is provided a method of filling a ballast tank positioned within an interior of a wind turbine blade, the method comprising the steps of: providing a wind turbine blade, the wind turbine blade having a ballast tank within an interior of the blade; determining the location of the ballast tank in the blade; applying a visible position identifier to an exterior surface of the blade at a location corresponding to the position of the ballast tank; forming a hole through the exterior surface of the blade and into the ballast tank, at the location of the position identifier; introducing ballast material through the hole into the ballast tank.

[0010] The provision of a visible position identifier on an exterior surface of the blade allows a technician to quickly and easily identify the position of the ballast tank within the interior of the blade. As the position identifier is a visible feature, the technician requires no tools to identify the position of the ballast tank.

[0011] The position identifier may include an attachable member which attaches to the exterior surface of the blade, and preferably the attachable member is a sticker. The use of a sticker is a simple way to provide a visible marking on the blade. If a hole is formed, e.g. by drilling, at the position of the sticker to introduce ballast into the ballast tank, a new sticker can easily be reapplied to the exterior surface after the hole is filled.

[0012] The position identifier may be a marking made by ink, paint or other marking medium. Forming the position identifier through ink or paint provides a flush surface to the exterior of the blade, which avoids negatively affecting the aerodynamic characteristics of the blade.

[0013] Preferably, the position identifier is a permanent marking on the exterior of the blade. It is desired for the position identifier to last for the life time of the wind turbine blade, e.g. 20 years or more. In this way, if ballast material needs to be added at any time during the life time of the blade, the position identifier will still be visible.

[0014] The position identifier may surround a perimeter of the ballast tank. The position identifier may mark a single point on the blade. Or it may surround an outline of the ballast tank. For example, if the ballast tank is rectangular, the position identifier will represent the rectangular shape on the exterior surface of the blade. In this way, from the outside of the blade, a technician will know the spanwise and chordwise extent of the ballast tank.

[0015] The step of determining the location of the ballast tank in the blade may comprises applying a marker in or on an outer skin of the blade during a moulding process of manufacturing the blade. During the moulding process of the blade, the marker can be positioned accurately for example by laser projection. In this way, the marker will accurately identify the position of the ballast tank.

[0016] The wind turbine blade may have multiple ballast tanks within the interior of the blade, and the exterior surface of the blade comprises separate position identifiers associated with each ballast tank.

[0017] The position identifier may be applied to the exterior surface of the blade in a factory, and the step of introducing ballast material takes place when the wind turbine blade is mounted on a hub atop a tower. Applying the position identifier in a factory allows it to be done in a controlled environment and by using jigs and specialist measuring tools, templates or the like so that the position identifier can be accurately placed. The step of introducing the ballast material may then take place at a later event in time when the blade is mounted on a turbine.

[0018] According to the present invention there is also provided a wind turbine blade comprising: a root end and a tip end, the blades extending in a spanwise direction from the root end to the tip end; a leading edge and a trailing edge, the blades extending in a chordwise direction along a chord from the leading edge to the trailing edge; a ballast tank located within an interior of the blade; a visible position identifier on an exterior surface of the blade at a location corresponding to the position of the ballast tank.

[0019] A wind turbine may comprise, a tower, a nacelle and a hub mounted atop the tower and a wind turbine blade as described above mounted to the hub.

[0020] Detailed Description

[0021] An example of the present invention will now be described, by way of non-limiting example only, with reference to the accompanying figures, in which:

[0022] Figure 1 shows a horizontal axis wind turbine; Figure 2 shows a schematic perspective view of a blade;

[0023] Figure 3 shows a schematic cross section of the blade through the cross section A-A in Figure 2;

[0024] Figure 4 shows a partial schematic cross section of the blade through the cross section A-A in Figure 2;

[0025] Figure 5 shows a schematic plan view of the blade.

[0026] Figure 6 is a flow chart of how the position identifier may be applied to the blade.

[0027] Figure 1 shows a wind turbine 10 including a tower 12 mounted on a foundation and a nacelle 14 disposed at the apex of the tower 12. A rotor 16 is operatively coupled to a generator (not shown) housed inside the nacelle 14. The rotor 16 includes a central hub 18 and a plurality of rotor blades 20, which project outwardly from the central hub 18. It will be noted that the wind turbine 10 is the common type of horizontal axis wind turbine (HAWT) such that the rotor 16 is mounted at the nacelle 14 to rotate about a substantially horizontal axis defined at the centre at the hub 18. While the example shown in Figure 1 has three blades, it will be realised by the skilled person that other numbers of blades are possible.

[0028] When wind blows against the wind turbine 10, the blades 20 generate a lift force which causes the rotor 16 to rotate, which in turn causes the generator within the nacelle 14 to generate electrical energy.

[0029] Figure 2 illustrates one of the wind turbine blades 20 for use in such a wind turbine. Each of the blades 20 has a root end 21 proximal to the hub 18 and a tip end 22 distal from the hub 18. The blade 20 is arranged to extend away from the hub 18 in a spanwise direction. A leading edge 23 and a trailing edge 24 extend between the root end 21 and tip end 22, and each of the blades 20 has a leeward side and a windward side extending between the leading and trailing edges of the blade.

[0030] Each blade has a cross section which is substantially circular near the root end 21 , because the blade near the root must have sufficient structural strength to support the blade outboard of that section and to transfer loads into the hub 18. The blade 20 transitions from a circular profile to an aerofoil profile moving from the root end 21 of the blade towards the tip end 22. The blade may have a "shoulder", which is the widest part of the blade where the blade has its maximum chord. The blade 20 has an aerofoil profile of progressively decreasing thickness towards the tip end 22. Figure 2 shows a ballast tank 30 within an interior of the blade 20. The ballast tank 30 defines an enclosed chamber in the blade for receiving ballast material.

[0031] Figure 3 shows a cross section through the blade shown in Figure 2 through the line A-A. Referring to Figure 3, the wind turbine blade comprises a first half shell 32 and a second half shell 34 which each extend in the spanwise direction from the root end 21 of the blade 20 towards the tip end of the blade 22. The blade 20 extends in a chordwise direction between the leading edge 23 of the blade 20 and the trailing edge 24 of the blade 20. The first and second blade half shells 32, 34 are joined together to form an enclosed blade shell which defines an aerodynamic contour for the blade 20. The blade 20 may be provided with opposed spar caps, 36, 38 each on a respective one of the leeward and windward sides of the blade, and a shear web 40 connecting the spar caps which together form a reinforcing structure along the spanwise length of the blade 20.

[0032] The blade shells 32, 34 define an internal blade volume, i.e. a blade interior 42 having an internal surface defined by respective internal skins of the first and second half shells 32, 34.

[0033] The ballast tank 30 is located within the internal blade volume 42. The ballast tank 30 has an outer surface 44 which provides a closed surface to the tank. The ballast tank 30 defines a ballast volume 46 which is configured to receive a ballast material. Each blade of the wind turbine is typically provided with a similar ballast tank so that any one or more of the blades can be filled with ballast material to the extent required. By adjusting the volume of ballast material within the ballast tanks, the masses of the blades can be adjusted and, hence, the mass moment of one blade relative to another can be adjusted to balance the blades.

[0034] During the manufacture of the blade, the ballast tank 30 is located in place and attached to an inner surface of one or both the shells. In particular, the ballast tank is adhesively bonded to the shells by adhesive (not shown). In other examples, the ballast tank could also be attached to the web 40.

[0035] The ballast tank is shown as being located between the web and the leading edge. However, the ballast tank could be located elsewhere in the blade, for example between the web and the trailing edge.

[0036] Figure 4 shows how ballast 48 can be filled in the ballast tank 30. From the outside of the blade, a hole 50 is formed (for example by drilling) through the shell and into the ballast tank. Then, as indicated by the arrow 52, ballast material 48 may be injected into the ballast tank 30. When the required amount of ballast material is in the ballast tank 30, the filling process stops and the hole in the blade shell is sealed.

[0037] The ballast material 48 may initially be injected into the ballast tank 30 in a liquid form (such as a polyurethane resin) for ease of insertion into the ballast tank, where it may then subsequently harden.

[0038] The ballast tank may have a volume of at least 25 litres for example, e.g. at least 50 litres, at least 75 litres or at least 100 litres. Multiple ballast tanks may also be in the blade, such as located in the spanwise direction.

[0039] During the lifetime of a wind turbine, the blades may need to be serviced or repaired. This could include, for example, adding new material to the blades to strengthen the blade in case of damage. If material is added to a blade, then its mass will change and the blades of the rotor on the wind turbine will need to be rebalanced. The amount of mass that needs to be added to one or more blades on the wind turbine can be established by the turbine controller, for example by sensing vibrations on the main shaft. A technician can then be informed how much mass to add to one or more blades of the rotor set.

[0040] The ballast material could be added to the blades when the blades are placed on the ground. However, this would entail an expensive process of removing the blades from the turbine with a crane, adding the ballast material, and then lifting the blades on to the turbine with a crane. It is much more cost effective to add the ballast material to the blades when the blades are in- situ on the turbine, mounted on the hub.

[0041] It is not possible to access the ballast tank on a wind turbine blade from the inside of the blade due to the confined space within the blade. Therefore, to add ballast material to a blade, a technician may abseil from the hub down the outside of the blade to fill the ballast tank from the outside. It should be noted that the ballast tanks are typically oversized so that additional ballast may be added during the life of the blades.

[0042] Modern wind turbine blades are in excess of 80 meters in length and the technician has to abseil down a majority of the length of the blade and then accurately locate the ballast tank within the blade and then drill through into the ballast tank. All of this takes place at a significant height, without a stable platform for the technician to work from. If the technician drills the hole in the wrong place it may have serious consequences. For example, drilling through a spar cap of the blade or some other critical component would necessitate a costly and time consuming repair to the damaged component. Such critical components may be part of a lightning system or an anti-icing system for example. The same issues may also take place in a factory environment if a technician were to drill a hole in the wrong place.

[0043] The technician will need to refer to drawings of the blade to establish where to drill the hole into the ballast tank. The technician will then have to measure from the root end of the blade to establish the spanwise position of the ballast tank. A measurement will also have to be taken from the leading edge or the trailing edge to establish the chordwise location of the ballast tank. As can be appreciated, this will be difficult to do when the technician is suspended by a rope from the hub. It is made more difficult because the trailing edge and especially the leading edge may not be clearly defined locations from which to take a measurement.

[0044] The present disclosure provides an effective solution for locating the position of the ballast tank from the outside of the blade. This is achieved as shown in Figure 5 by providing a position identifier 60 on the outside of the blade. The position identifier is a visible indication on an exterior surface 55 of the blade as to the position of the ballast tank. Thus a technician can identify the position of the ballast tank quickly and easily and without the risk of damaging critical components of the blade.

[0045] The position identifier 60 may be applied when the blade is manufactured in the factory. The position identifier 60 may be in the form of a sticker. After wind turbine blades have been manufactured, they are painted typically in a white colour. The position identifier 60 may be applied after the blade is painted. Alternatively, the position identifier 60 may be applied to the blade before the blade is painted and the position identifier is masked off so as not to be covered by the painting process. In other examples, the position identifier may itself be a paint marking.

[0046] It is necessary to accurately place the position identifier 60 on the blade so that the location of the ballast tank 30 can be determined from the outside of the blade. As the position identifier 60 is applied in a factory environment, it is possible to accurately determine the position of the ballast tank 30 by the use of laser projection, jigs, templates or other measurement tools.

[0047] Prior to the blade being painted, the outer skin of the blade may be translucent as the blade shell may be formed from glass fibre reinforced plastic. Thus, it may be possible to determine the position of the ballast tank 30 from the outside of the blade with the naked eye and then apply the position identifier prior to painting. Figure 6 is a flow chart which describes an example of how the position identifier 60 may be applied to the blade. As is known in the art, wind turbine blades are fabricated in shell moulds and the blade materials are laid up in the moulds. The blade materials may include fibre glass fabric, carbon fibre reinforced plastic and core material. Typically the process of laying up the blade material may start with applying a gel coat to the mould and then laying one or more layers of glass fibre fabric which will form the outer skin of the blade. In step 70 a first marker is applied to the blade layup and this may be applied on the gelcoat in the shell mould (if gel coat is used) or applied to one of the first layers of material laid up in the mould. In an example, the first marker is a sticker.

[0048] The first marker may be positioned at a predetermined position in the mould by use of a laser projection system. The position of the first marker will correspond to where the ballast tank 30 is subsequently placed in the build of the blade shell.

[0049] Via step 70, by applying the first marker to the blade layup, the marker is applied in or on an outer skin of the blade during the moulding process of manufacturing the blade. In this way, the location of the ballast tank in the blade can be determined.

[0050] After the blade shell has been fabricated, for example by the known method of VARTM, the blade is demoulded from the shell moulds. Step 71 shows that the first marker is visible from the outside of the blade shell after the demould process. This is because the first marker is at the outermost, or very close to the outermost layer of the blade and so can be seen by a technician.

[0051] At step 72 a second marker is applied at the position of the first marker. In an example, the second marker may be a sticker. The second marker is applied because the first marker, while being visible, may be rather faint if it is under a layer of blade material.

[0052] At step 73 the blade is painted, e.g. in the standard white colour of wind turbine blades. After the painting process, the second marker should be visible from the outside of the blade even though it has been painted. This may be achieved, for example, by the second marker having a thickness or texture so that it can be seen under the paint. Or, for example, the second marker may be formed from a material to which the paint does not adhere.

[0053] In step 74 the second marker is removed. For example, if the second marker is a sticker it can be peeled off the blade surface. In step 75 a paint stencil is applied to the blade at the position of the second marker. And, then at step 76, paint is applied to the paint stencil in order to paint onto the blade the position identifier 60. The method of this flow chart illustrates a preferred way of applying the position identifier to the blade. However, it will be appreciated that modifications can be made to this method. For example, it may not be necessary to apply the second marker to the blade. Instead, the position identifier 60 may be applied to the blade after step 71 , and then masked from the subsequent blade painting process.

[0054] Many modifications may be made to the examples described above without departing from the scope of the present invention as defined in the accompanying claims.

Claims

Claims1. A method of filling a ballast tank (30) positioned within an interior of a wind turbine blade (20), the method comprising the steps of: providing a wind turbine blade (20), the wind turbine blade having a ballast tank (30) within an interior (42) of the blade; determining the location of the ballast tank (30) in the blade (20); applying a visible position identifier (60) to an exterior surface (55) of the blade at a location corresponding to the position of the ballast tank (20); forming a hole (50) through the exterior surface (55) of the blade and into the ballast tank (30), at the location of the position identifier (60); introducing ballast material (48) through the hole (50) into the ballast tank (30).

2. A method according to claim 1 , wherein the position identifier includes an attachable member which attaches to the exterior surface of the blade, and preferably the attachable member is a sticker.

3. A method according to claim 1 , wherein the position identifier is a marking made by ink, paint or other marking medium.

4. A method according to any one of the preceding claims, wherein the position identifier is a permanent marking on the exterior of the blade.

5. A method according to any one of the preceding claims, wherein the position identifier surrounds a perimeter of the ballast tank.

6. A method according to any one of the preceding claims, wherein the step of determining the location of the ballast tank (30) in the blade (20) comprises applying a marker in or on an outer skin of the blade during a moulding process of manufacturing the blade.

7. A method according to any one of the preceding claims, wherein the position identifier is applied to the exterior surface of the blade in a factory, and the step of introducing ballast material takes place when the wind turbine blade is mounted on a hub atop a tower.

8. A wind turbine blade comprising: a root end and a tip end, the blades extending in a spanwise direction from the root end to the tip end;a leading edge and a trailing edge, the blades extending in a chordwise direction along a chord from the leading edge to the trailing edge; a ballast tank located within an interior of the blade; a visible position identifier on an exterior surface of the blade at a location corresponding to the position of the ballast tank.

9. A wind turbine comprising: a tower; a nacelle and a hub mounted atop the tower; a wind turbine blade according to claim 8 mounted to the hub.

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