Wind turbine blade with lightning protection

Abstract

A method of making a wind turbine blade (10) having a metallic lightning receptor (110) is described. The method comprises configuring a wind turbine blade (10) mold assembly (100) such that a clearance region (120) is defined between a mold surface (116) of at least one mold half (112, 114) and a majority of a metallic lightning receptor component (110) when the mold assembly (100) is closed, such that contact between that mold half (112, 114) and the metallic lightning receptor component (110) is substantially avoided. In certain embodiments of the invention, one or both mold halves (112, 114) are truncated such that the metallic lightning receptor component (110) projects from the mold (100) when the mold (100) is closed.

Claims

1. A method of making a wind turbine blade, the method comprising: providing a mould assembly having first and second mould halves, each mould half comprising a mould surface, the mould assembly having an open position in which the mould halves are spaced apart, and a closed position in which the mould halves are brought together; making a first half shell of the wind turbine blade in the first mould half and making a second half shell of the wind turbine blade in the second mould half when the mould assembly is in the open position, each half shell comprising a composite material; integrating a metallic lightning receptor component with the first half shell such that when the mould assembly is in the open position, the entirety of the metallic lightning receptor component is provided to the first mould half and none of the metallic lightning receptor component is provided to the second mould half; configuring the mould assembly such that a clearance region is defined between the mould surface of the second mould half and the metallic lightning receptor component when the mould assembly is in the closed position, such that contact between the second mould half and the metallic lightning receptor component is substantially avoided; closing the mould assembly; and joining the first and second half shells together.

2. The method of claim 1, further comprising holding the metallic lightning receptor component in place with respect to the first half shell during closing of the mould assembly.

3. The method of claim 1, further comprising configuring the mould assembly such that the clearance region is also defined between the mould surface of the first mould half and the metallic lightning receptor component when the mould assembly is in the closed position.

4. The method of claim 1, wherein an end region of the second mould half is truncated, such that the metallic lightning receptor component projects from the truncated end region of the second mould half when the mould assembly is in the closed position.

5. The method of claim 1, wherein an end region of the first mould half is truncated, such that the metallic lightning receptor component projects from the truncated end region of the first mould half when the mould assembly is in the closed position.

6. The method of claim 1, wherein the step of integrating the metallic lightning receptor component with the first half shell comprises bonding the metallic lightning receptor component to the first half shell.

7. The method of any preceding claim 1, wherein the step of making the first half shell involves a curing process, and the step of integrating the metallic lightning receptor component with the first half shell occurs after the curing process.

8. The method of claim 1, wherein the metallic lightning receptor component is a metal blade tip.

9. The method of any of claim 1, wherein a metal blade tip is connected to the metallic lightning receptor component.

10. The method of claim 1, wherein one or both of the first and second mould halves comprises a removable tip portion, and the method comprises removing a corresponding tip portion from at least one of the first and second mold halves prior to closing the mould assembly.

11. The method of claim 1, wherein the first and second shell halves each include a leading edge portion and a trailing edge portion, and wherein joining the first and second half shells together further includes joining the leading and trailing edge portions of the first and second shell halves to form the leading and trailing edges of the wind turbine blade.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIGS. 1, 2, and 3A to 3C have already been described above by way of background to the present invention. In order that the invention may be more readily understood, specific embodiments of the invention will now be described, by way of example only, with reference to the following drawings, in which:

(2) FIG. 4 is a partial cross-sectional view of a wind turbine blade having a solid metal tip and being supported by a truncated mould assembly according to a first embodiment of the invention, the mould assembly being arranged in a closed position;

(3) FIG. 5 is a partial perspective view of a truncated tip region of a first mould half of the mould assembly of FIG. 4;

(4) FIG. 6A is a partial perspective view of the first mould half of the mould assembly of FIG. 4 when the mould assembly is in an open position, and before the turbine blade is fully formed, showing a first half shell of the blade arranged in the mould half and the solid metal tip integrated with the first half shell;

(5) FIG. 6B is a partial perspective view of the mould assembly of FIG. 4 when the mould assembly is in the closed position;

(6) FIGS. 7A to 7C illustrate a series of steps of a method of making a wind turbine blade in accordance with an embodiment of the present invention;

(7) FIG. 8 is a partial cross-sectional view of the mould assembly of FIG. 4 with the mould halves misaligned; and

(8) FIGS. 9A to 9C are partial cross-sectional views of alternative embodiments of a mould assembly according to the invention;

(9) FIG. 10A is a partial perspective view of the first mould half of the mould assembly in an open position, and before the turbine blade is fully formed, showing a first half shell of the blade arranged in the mould half;

(10) FIG. 10B is a perspective view of a solid metal tip.

DETAILED DESCRIPTION

(11) FIG. 4 shows a cross-sectional view of a mould assembly 100 according to an embodiment of the invention. Specifically, the mould assembly 100 is for moulding a wind turbine blade 102 that comprises an outer shell 104 formed from two half shells 106, 108, and a lightning receptor in the form of a solid metal tip (SMT) 110 integrated with the outer shell 104. Each half shell 106, 108 of the outer shell 104 is moulded from glass-fibre reinforced plastic (GRP).

(12) The mould assembly 100 comprises two mould halves: a first mould half 112 for moulding the first half shell 106, and a second mould half 114 for moulding the second half shell 108. The mould assembly 100 has an open position in which the two mould halves 112, 114 are spaced apart, and a closed position in which the two mould halves 112, 114 are brought together, as shown in FIG. 4.

(13) Each mould half 112, 114 extends along a longitudinal axis and comprises an inner mould surface 116 (FIG. 5) for moulding its respective half shell 106, 108. The mould surface 116 is substantially smooth and has a generally concave curvature. Each mould half 112, 114 extends along its longitudinal axis from a root end of the mould half 112, 114 towards a truncated tip end 118 of the mould half 112, 114.

(14) To make a wind turbine blade 102, each half shell 106, 108 is made in its respective mould half 112, 114 with the mould assembly 100 in its open position, as will be later described. Once the half shells 106, 108 have been cured to harden the resin, the SMT 110 is integrated with the first half shell 106. The mould assembly 100 is then moved into the closed position, the half shells 106, 108 are bonded together, and the SMT 110 is bonded to the second half shell 108.

(15) In the open position, the mould halves 112, 114 are arranged next to one another, with their longitudinal axes aligned and respective mould surfaces 116 facing upwards. To move the mould assembly 100 into the closed position, one of the mould halves 112, 114 is lifted and pivoted into place above the other, for example, by means of hydraulic pistons. In the example described above, where the SMT 110 is integrated with the first half shell 106, the second mould half 114 is typically pivoted into place above the first mould half 112, such that in the closed position the second mould half 114 is arranged above the first mould half 112, with its mould surface 116 facing downwards.

(16) As mentioned briefly above, each mould half 112, 114 has a truncated tip end 118 (FIG. 5). When the mould assembly 100 is in use and in the closed position, the SMT 110 protrudes from this truncated tip end 118, as shown in FIG. 6B. Accordingly, the SMT 110 projects clear of the mould surfaces 116 of the first and second mould halves 112, 114, or in other words a clearance region 120 is defined between the SMT 110 and the respective mould surfaces 116, such that contact between the first and second mould halves 112, 114 and the SMT 110 is substantially avoided. This clearance region 120 is particularly significant in the event that there is a misalignment of the mould halves 112, 114, as will be described later.

(17) The truncation of the tip end 118 of each mould half 112, 114 also provides a substantially flat end surface 122 of the mould half. A support 124 is mounted to the flat end surface 122 of the first mould half 112. The support 124 holds the SMT 110 in place during bonding of the SMT 110 to the first half shell 106, and subsequently during closing of the mould assembly 100, and joining of the half shells 106, 108. In the embodiment shown, the support 124 is in the form of a wedge having a vertical surface 126 that abuts the flat end surface 122 of the mould half 112, a supporting surface 128 that is substantially horizontal when the mould assembly 100 is in use, and a sloping surface 130 that extends between the vertical surface 126 and the supporting surface 128. In use, the supporting surface 128 supports the SMT 110. In other words, the support 124 acts as a jig for the SMT 110.

(18) To manufacture a wind turbine blade 102 using the mould assembly 100, the second and first shells 106, 108 are first moulded in the respective first and second mould halves 112, 114. Each half shell 106, 108 is laid up by arranging the various laminate layers of the half shells in the respective mould halves 112, 114, as will now be described.

(19) An outer skin in the form of a dry fibre material is first placed on the inner mould surface 116. A layer of structural foam is introduced into the mould half 112, 114, and an inner skin in the form of a dry fibre material is placed on the upper surface of the structural foam.

(20) Further components such as spar caps may also be incorporated into the shell, between the outer and inner skins. The various layers and components of the half shell 106, 108 extend up to the truncated tip end 118 of the mould half 112, 114, or stop shortly before the truncated tip end 118, such that the half shell 106, 108 is truncated in the same manner as the mould half 112, 114.

(21) The components are covered with an airtight bag to form an evacuation chamber that encapsulates all of the components. The chamber is then evacuated using a vacuum pump. With the pump still energised, a supply of liquid resin is connected to the chamber, and resin flows into the chamber through a plurality of resin inlets, which are longitudinally spaced along the mould half 112, 114. Resin infuses throughout the half shell 106, 108 in a generally chordwise direction, between the components in the half shell 106, 108.

(22) The pump continues to operate during a subsequent moulding operation in which the mould assembly 100 is heated so as to cure the resin, although during the curing process the vacuum pressure may be adjusted. The bags are then removed from the moulded half shells 106, 108.

(23) Because the components of each half shell 106, 108 are laid up to extend only as far as, or just short of, the truncated tip end 118 of the mould half 112, 114, each half shell 106, 108 is truncated in the same manner as the mould half 112, 114. The truncation of each half shell 106, 108 defines a substantially flat end surface 132 of the half shell 106, 108, as best shown in FIG. 7A, which receives the SMT 110.

(24) In the next step of the method, illustrated in FIG. 7B, an SMT 110 is integrated with the first half shell 106.

(25) The SMT 110 is made from copper, and is able to receive and conduct lightning, as previously described. The SMT 110 comprises a flat base 134, and a first half 136 of the flat base 134 abuts the flat end surface 132 of the first half shell 106. A second half 138 of the flat base 134 protrudes above the first half shell 106, to abut the flat end surface 132 of the second half shell 108 during subsequent stages of the process.

(26) A tongue 140 extends outwardly from the flat base 134 of the SMT 110 and into the first half shell 106, as shown in FIG. 6A. The tongue 140 may be coated with an insulating material prior to integration of the SMT 110 with the half shell 106, and the insulating material may be bonded to the first half shell 106, so as to secure the SMT 110 to the first half shell 106. FIG. 6A also shows a lightning down conductor 135 connecting the tongue 140 to ground potential. In the event of lightning hitting the SMT 110, which functions as a lightning receptor, the lightning current will flow through the SMT 110, the tongue 140 and the down conductor 135 to ground.

(27) During insertion of the SMT 110 into the first half shell 106, and during the subsequent forming process, the SMT 110 is held in place by the support 124. In this way, the SMT 110 is fixed in place, and movement of the SMT 110 is minimised. This helps to ensure a close fit between the half shells 106, 108 and the SMT 110, and therefore results in effective bonding between the SMT 110 and the outer shell 104 of the wind turbine blade 102. Holding the SMT 110 in place also helps to ensure that the outer shell 104 and the SMT 110 provide the correct blade profile and geometry.

(28) In the next step of the method, shear webs are attached to the inner skin of the first half shell 106, and the upper free ends of the webs are coated with respective layers of adhesive.

(29) As best shown in FIG. 7C, the second mould half 114 is then lifted and pivoted into position above the first mould half 112, such that the second mould half 114 is upturned and placed on top of the first mould half 112. The truncation of the second half shell 108 allows it to accommodate the SMT 110 that is arranged at the end of the first half shell 106. When the mould assembly 100 is closed, the flat end surface 132 of the second half shell 108 faces the second half 138 of the base 134 of the SMT 110. If the mould halves 112, 114 are accurately aligned, the flat end surface 132 of the second half shell 108 abuts the base 134 of the SMT 110. The SMT 110 is then fully integrated into the blade 102, such that an outer surface 142 of the SMT 110 is contiguous with the outer surfaces 144 of the first and second half shells 106, 108.

(30) Closing the mould assembly 100 also causes the inner skin of the second half shell 108 to adhere to the upper free ends of the shear webs, as is known in the art. The resilient nature of the webs gives rise to a biasing force of the webs against the second half shell 108, so as to ensure good adhesion.

(31) As previously described, and as shown particularly in FIGS. 6B and 7C, the first and second mould halves 112, 114 are truncated. In this way, when the mould assembly 100 is in the closed position, the SMT 110 projects from the tip ends 118 of the mould halves 112, 114 and a clearance region 120 is defined between the mould surfaces 116 of the first and second mould halves 112, 114 and a majority of the SMT 110; i.e. contact between the respective mould surfaces 116 and the SMT 110 is substantially avoided.

(32) FIG. 8 illustrates a mould assembly 100 according to the invention that has a misalignment between the first and second mould halves 112, 114. Specifically, the second mould half 114 lies rearward of the first mould half 112 to define an underbite. The truncated tip end 118 of the second mould half 114 ensures that contact between the mould surface 116 of the second mould half 114 and the SMT 110 is substantially avoided even in cases of misalignment.

(33) Thus, when using a mould assembly 100 or method according to the invention, a misalignment of the mould halves 112, 114 at the tip end 118 does not result in unacceptable clashing of the second mould half 114 with the SMT 110. Risk of damage to the SMT 110 as the mould assembly 100 is closed is therefore substantially avoided. Furthermore, the second half shell 108 can be properly lowered onto the first half shell 106 despite any misalignment, so that effective contact can still be made between the half shells 106, 108, and the required pressure can be applied during bonding.

(34) In the final step of the method, the mould assembly 100 is opened and the finished wind turbine blade 102 is lifted from the mould assembly 100. The resulting wind turbine blade 102 is then incorporated into a wind turbine by known methods.

(35) FIGS. 9A, 9B, and 9C show alternative embodiments of the invention in which the clearance region 120 is defined only between the second mould half 114 and the SMT 110. FIG. 9A illustrates an embodiment in which only the second mould half 114 is truncated, while the first mould half 112 is a complete (i.e. non-truncated) mould half that comprises a tip portion 146 at the tip end 118. In this embodiment a support 124 extends from a flat end surface 122 of the tip end 118 of the first mould half 112 to meet an upper surface 148 of the SMT 110, and holds the SMT 110 in place.

(36) FIGS. 9B and 9C illustrate embodiments in which the second mould half 114 is not truncated. Instead, the mould surface 116 of the second mould half 114 is shaped to define a cavity 150 adjacent the SMT 110 when the mould assembly 100 is closed. The cavity 150 defines the clearance region 120 between the mould surface 116 and the SMT 110 to avoid contact between the SMT 110 and the mould surface 116 of the second mould half 114 when the mould is closed.

(37) In the embodiment shown in FIG. 9C, a support 124 extends from an upper surface 152 of a tip end 146 of the first mould half 112 to an upper surface 148 of the SMT 110, and the support 124 holds the SMT 110 in place. The support 124 extends into the cavity 150 defined between the mould surface 116 of the second mould half 114 and the SMT 110. The mould surface 116 at the tip end 146 of the second mould half 114 is therefore shaped to accommodate the support 124, so as to avoid clashing between the second mould half 114 and the support 124.

(38) In a further embodiment as shown in FIGS. 10A and 10B, the SMT is not actually integrated with the mould halves 112, 114 when they are closed. Instead, the tip assembly has a modular construction and the SMT is connected to the blade after the blade shells have been bonded together. In this embodiment, an implant 160 which comprises an insulating plastic material such as polyurethane has a metallic lightning receptor component embedded within it. In this example, the metallic lightning receptor component is in the form of a metal plate 161. The metal plate 161 has a free end 162 which projects from the tip end of the implant 160. The implant 160 is positioned on the half shell 106 such that the free end of the plate 162 protrudes from the truncated tip end of the mould half 112. The implant 160 and plate 161 are maintained in position by the support 124 and located through holes 163 which are aligned with holes in support 124 so that the support acts as a jig. Bolts or similar are inserted through holes 163 so that the plate 161 is aligned with the support 124.

(39) The half shell 106 has already been cured and in this embodiment the implant 160 is bonded to the half shell 106 though adhesive, such as epoxy adhesive. The support 124 ensures accurate alignment of the implant 160 and the plate 161 in all three directions. The second mould half 114 is then lifted and pivoted into position on top of the first mould half 112adhesive placed on top of the implant 160 ensures that the implant is also bonded to the second half shell 108. Subsequently, the SMT 110 (which is shown in FIG. 10B) can be connected to the free end of the plate 162. As seen in FIG. 10B, the SMT has a recess 164 into which the free end of the plate 162 is received. The SMT can then be mechanically connected via bolts through holes 165 which are aligned with holes 163 in the free end of the plate 163.

(40) In this embodiment with a modular tip, the mould constructions shown in FIGS. 9A to 9C can also be implemented.

(41) Embodiments are also envisaged in which one or both mould halves comprises a removable end portion, which may be removable from the mould half to provide the truncation of the mould half or the cavity between the mould surface and the SMT, and thereby to define the clearance region. Such a removable end portion would allow for ongoing adaptability of the mould assembly. In other embodiments, the clearance region may be filled by a compressible material which is elastically deformable so as to accommodate any clashing between the mould half and the blade tip whilst cushioning the SMT, i.e. minimising any force exerted on the SMT when the mould is closed.

(42) Although in the embodiments described the support is attached to the first mould half, it will be appreciated that this need not be the case, and the support may instead be provided as a free-standing component.

(43) Many other modifications may be made to the embodiments described above without departing from the scope of the invention as defined in the following claims.