Lightning protection system

Abstract

A wind turbine blade having a blade shell with a lightning protection system; the lightning protection system comprising: a first metal layer; a second metal layer having an area no more than 10% of an area of the first metal layer; and a metal reinforcing disc formed across a portion of the second metal layer, wherein the metal reinforcing disc is fixed to the second metal layer so as to create an electrical connection with the second metal layer, and wherein a first portion of the first metal layer surrounds the second metal layer at an outer surface of the blade shell, and a second portion of the first metal layer overlaps the second metal layer and is in intimate electrical contact with the second metal layer.

Description

[0001] LIGHTNING PROTECTION SYSTEM

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to a wind turbine blade having a blade shell with a lightning protection system, a reinforcing patch for a lightning protection system of a wind turbine blade, and a method of manufacturing a wind turbine blade with a lightning protection system.

[0004] BACKGROUND OF THE INVENTION

[0005] Wind turbines are susceptible to lightning strikes, and the blades of wind turbines are particularly susceptible to lightning strikes.

[0006] As a result, it is common for a wind turbine blade to include a lightning protection system that electrically couples the wind turbine blade to ground. This lightning protection system may include lightning receptors and conductors that are electrically connected from the blade, through the tower and nacelle, to ground. The lightning protection system may also include a surface protection layer (SPL), for instance a metal mesh or foil surface protection layer, incorporated into the blade shell at the outer surface of the blade and extending along at least a portion of the blade. This surface protection layer typically covers a significant portion of the blade surface and intercepts lightning strikes before reaching conductive components of the blade. The surface protection layer is typically connected to the lightning protection system at numerous points so as to ensure a good electrical connection from the surface protection layer.

[0007] WO2015 / 055215 describes a wind turbine blade having a blade shell with a lightning protection system comprising a metal layer at the outer surface of the blade shell, wherein the metal layer is reinforced at the location of an electrically conductive pin, which extends through the metal layer, by a reinforcing metal disc.

[0008] Designing and manufacturing wind turbine blades comprising lightning protection systems increases complexity of the blade and manufacturing process. The present invention seeks to address this issue.

[0009] SUMMARY OF INVENTION A first aspect of the invention provides a wind turbine blade having a blade shell with a lightning protection system; the lightning protection system comprising: a first metal layer; a second metal layer having an area no more than 10% of an area of the first metal layer; and a metal reinforcing disc formed across a portion of the second metal layer, wherein the metal reinforcing disc is fixed to the second metal layer so as to create an electrical connection with the second metal layer, and wherein a first portion of the first metal layer surrounds the second metal layer at an outer surface of the blade shell, and a second portion of the first metal layer overlaps the second metal layer and is in intimate electrical contact with the second metal layer.

[0010] The first metal layer and the second metal layer are discrete and separate components when being laid up during manufacturing of the wind turbine blade. In this context ‘surrounds’ means that the first portion of the first metal layer encircles or fully surrounds the second metal layer. In this context the ‘area’ of the metal layers refers to the extent of the metal layer in the length and width dimensions perpendicular to the thickness dimension. The first metal layer and the second metal layer may each comprise a mesh or expanded metal foil. The metal reinforcing disc may be solid.

[0011] Providing the second metal layer with a metal reinforcing disc fixed to the second metal layer as a separate component to the first metal layer may improve ease of manufacture of the wind turbine blade comprising the lightning protection system. The larger first metal layer may be handled easily as it does not contain the metal reinforcing disc. In addition, the much smaller second metal layer may also be handled easily and positioned accurately despite containing the metal reinforcing disc. Positional accuracy of the metal disc in a mould for forming the blade shell is important. The metal layers may be fragile and so ease of handling is important to avoid handling damage so as to maintain good performance of the lightning strike protection system.

[0012] The second portion of the first metal layer may be located towards an inside of the blade with respect to the second metal layer. In this way, the second metal layer may be laid up first in a mould for forming the blade shell, and the first metal layer may be laid on top of the second metal layer. By locating the first metal layer towards an inside of the blade with respect to the second metal layer, a part of the first metal layer does not need to be removed to gain access to the disc from the outside of the blade. The second portion of the first metal layer may overlap the metal reinforcing disc.

[0013] Preferably, the metal reinforcing disc does not extend through the first metal layer.

[0014] The wind turbine blade may further comprise an electrically conductive pin which extends through the metal reinforcing disc.

[0015] The electrically conductive pin may be used to electrically connect the first metal layer one or more electrical components of the lightning protection system inside the blade shell, such as a down conductor cable or a tip array for example, to the first metal layer. The electrically conductive pin forms an intimate electrical connection to the first metal layer via the metal reinforcing disc. This enables lightning current to be conducted via the first metal layer to ground through the electrically conductive pin.

[0016] The electrically conductive pin may extend through the first metal layer. For example, an aperture may be formed through the first metal layer for receiving the electrically conductive pin. The aperture in the first metal layer may be formed simultaneously with forming an aperture through the metal reinforcing disc, during blade manufacture.

[0017] The wind turbine blade may further comprise an electrical component. The first metal layer may be electrically connected to the electrical component by the electrically conductive pin.

[0018] The electrical component may be a connector base for forming an electrical connection between the electrically conductive pin and one or more further electrical components of the lightning protection system. Alternatively, the electrical component may be a down conductor or tip array or other component of the lightning protection system, forming a direct electrical connection with the electrically conductive pin.

[0019] The electrical component may have a threaded aperture for receiving a threaded end of the electrically conductive pin for threadedly securing the electrically conductive pin to the electrical component. The electrical component may be fixed with respect to the inside of the blade shell. The electrically conductive pin may have a head. An underside of the head may face a surface of the metal reinforcing disc. This may form an intimate electrical connection between the pin head and the metal reinforcing disc.

[0020] The wind turbine blade may further comprise a recess in which the head of the pin is located.

[0021] The recess may be provided in the metal reinforcing disc.

[0022] The recess may be provided in a portion of a forming element around the metal reinforcing disc. The forming element may include a ramped section, e.g. a conical section, which deflects the first metal layer away from the outer surface of the blade towards the inside of the blade shell so as to enable the first metal layer to extend continuously over the recess.

[0023] The head of the pin may be substantially flush with the blade shell outer surface.

[0024] Providing a pin head that is substantially flush with the blade shell outer surface may reduce or negate the effect of the pin on aerodynamic performance of the wind turbine blade.

[0025] The metal reinforcing disc may extend through the second metal layer.

[0026] Providing a metal reinforcing disc that extends through the second metal layer may allow the metal reinforcing disc to be manufactured as part of the second metal layer such that the two are provided to the mould for forming the blade shell as a single component. This may improve ease of manufacture of the wind turbine blade. For example, the metal reinforcing disc may be a cast component, cast through the second metal layer. In the case that the second metal layer is a mesh or expanded metal foil, the metal reinforcing disc may be cast through the apertures of the mesh or foil. Alternatively, the metal reinforcing disc may be assembled to the second metal layer as two half discs, one on either side of the second metal layer, and fixed to the second metal layer, e.g. by soldering or welding for example.

[0027] Alternatively, the metal reinforcing disc may be provided on only one side of the second metal layer and fixed to the second metal layer. The second portion of the first metal layer may be in intimate electrical contact with the metal reinforcing disc. For example, the second portion of the first metal layer may extend over a surface of the metal reinforcing disc so as to create a direct electrical connection with the metal reinforcing disc, in addition to the indirect electrical connection with the metal reinforcing disc via the electrical connection between the overlapping first and second metal layers.

[0028] A further aspect of the invention provides a reinforcing patch for a lightning protection system of a wind turbine blade having a blade shell with a first metal layer, the patch comprising: a forming element; a second metal layer having an area no more than 10% of an area of the first metal layer; and a metal reinforcing disc formed across a portion of the second metal layer, wherein the metal reinforcing disc is located within the forming element and is fixed to the second metal layer so as to create an electrical connection between the metal reinforcing disc and the second metal layer, and wherein when the patch is incorporated into a wind turbine blade a first portion of the first metal layer surrounds the second metal layer at an outer surface of the blade shell, and a second portion of the first metal layer overlaps over the second metal layer and is in intimate electrical contact with the second metal layer.

[0029] Providing a reinforcing patch comprising a forming element, a second metal layer and a metal reinforcing disc allows these three parts of the lightning protection system to be provided as a single part. This may improve ease of manufacture of the wind turbine blade, rather than having to lay up each of the forming element, the second metal layer and the metal reinforcing disc separately. A reinforcing patch may further allow more modular design of different wind turbine blades, where a single common reinforcing patch can be used in multiple wind turbine blade designs and / or across multiple locations within each blade.

[0030] The forming element and the metal reinforcing disc may be separable prior to incorporation into the wind turbine blade.

[0031] A still further aspect of the invention provides a method of manufacturing a wind turbine blade with a lightning protection system, the method comprising: providing a mould surface; providing a reinforcing patch of a lightning protection system, the reinforcing patch including a metal reinforcing disc formed across a portion of a second metal layer, wherein the metal reinforcing disc is fixed to the second metal layer so as to create an electrical connection between the metal reinforcing disc and the second metal layer; providing a first metal layer of the lightning protection system, wherein the second metal layer has an area no more than 10% of an area of the first metal layer; arranging the first metal layer and the reinforcing patch on the mould surface; arranging one or more structural components on the first metal layer and the reinforcing patch; consolidating the structural components, the first metal layer and the reinforcing patch under vacuum to form a blade shell having a first portion of the first metal layer surrounding the second metal layer at an outer surface of the blade shell, and a second portion of the first metal layer overlaps the second metal layer and is in intimate electrical contact with the second metal layer.

[0032] The above method utilises a reinforcing patch comprising at least the second metal layer and the metal reinforcing disc, and optionally also a forming element, as described previously to simplify the manufacturing process.

[0033] The method may be used to construct a wind turbine blade according to the first aspect of the invention.

[0034] The reinforcing patch may further comprise a forming element and the metal reinforcing disc may be located within the forming element. The method may further comprise removing a portion of the forming element to reveal a surface of the metal reinforcing disc. The portion to be removed may be a disc. The disc portion to be remove may be a removable magnet used for locating the metal reinforcing disc after consolidating and curing the blade shell in the mould and de-moulding the blade shell. Locating the metal reinforcing disc may precede a step of forming an aperture through the metal reinforcing disc to accept an electrically conductive pin.

[0035] Removing a portion of the forming element may create a recess in the blade into which an electrically conductive pin is insertable.

[0036] The method may further comprise inserting an electrically conductive pin through the metal reinforcing disc to electrically connect an electrical component located adjacent an inner surface of the blade shell to the first metal layer via the metal reinforcing disc.

[0037] BRIEF DESCRIPTION OF THE DRAWINGS Embodiments of the invention will now be described with reference to the accompanying drawings, in which:

[0038] Figure 1 shows a wind turbine;

[0039] Figure 2 shows a wind turbine blade;

[0040] Figure 3 shows a planform view of a lightning protection system of a wind turbine blade including a metal layer in a blade shell of the blade;

[0041] Figures 4A-4G show a method of manufacturing a wind turbine blade including a lightning protection system;

[0042] Figure 5 shows a planform view of a portion of the lightning protection system;

[0043] Figures 6A-6I shows another method of manufacturing a wind turbine blade including a lightning protection system;

[0044] Figures 7A-7F show the methods of manufacturing a wind turbine blade including a lightning protection system from a different perspective;

[0045] Figures 8A-8D show another example of a reinforcing patch of a lightning protection system and its incorporation into a blade shell of a wind turbine blade;

[0046] Figures 9A-9B show a further example of a reinforcing patch of a lightning protection system and its incorporation into a blade shell of a wind turbine blade; and

[0047] Figures 10A-10B show a yet further example of a reinforcing patch of a lightning protection system and its incorporation into a wind turbine blade.

[0048] DETAILED DESCRIPTION OF EMBODIMENT(S)

[0049] In this specification, terms such as leading edge, trailing edge, pressure surface, suction surface, thickness, chord and planform are used. While these terms are well known and understood to a person skilled in the art, definitions are given below for the avoidance of doubt.

[0050] The term leading edge is used to refer to an edge of the blade which will be at the front of the blade as the blade rotates in the normal rotation direction of the wind turbine rotor.

[0051] The term trailing edge is used to refer to an edge of a wind turbine blade which will be at the back of the blade as the blade rotates in the normal rotation direction of the wind turbine rotor. The chord of a blade is the straight line distance from the leading edge to the trailing edge in a given cross section perpendicular to the blade spanwise direction. The term chordwise is used to refer to a direction from the leading edge to the trailing edge, or vice versa.

[0052] A pressure surface (or windward surface) of a wind turbine blade is a surface between the leading edge and the trailing edge, which, when the blade is in use, has a higher pressure than a suction surface of the blade.

[0053] A suction surface (or leeward surface) of a wind turbine blade is a surface between the leading edge and the trailing edge, which will have a lower pressure acting upon it than that of a pressure surface, when the blade is in use.

[0054] The thickness of a wind turbine blade is measured perpendicularly to the chord of the blade and is the greatest distance between the pressure surface and the suction surface in a given cross section perpendicular to the blade spanwise direction.

[0055] The term spanwise is used to refer to a direction from a root end of a wind turbine blade to a tip end of the blade, or vice versa. When a wind turbine blade is mounted on a wind turbine hub, the spanwise and radial directions will be substantially the same.

[0056] A view which is perpendicular to both of the spanwise and chordwise directions is known as a planform view. This view looks along the thickness dimension of the blade.

[0057] The term shear web is used to refer to a longitudinal, generally spanwise extending, reinforcing member of the blade that can transfer load from one of the windward and leeward sides of the blade to the other of the windward and leeward sides of the blade.

[0058] 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. The wind turbine 10 depicted here is an onshore wind turbine such that the foundation is embedded in the ground, but the wind turbine 10 may be an offshore installation in which case the foundation would be provided by a suitable marine platform.

[0059] A rotor 16 is operatively coupled to a generator (potentially via a gearbox) (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 12 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.

[0060] 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.

[0061] Figure 2 shows an example of one of the wind turbine blades 20 for use in such a wind turbine. The blade 20 has a root end 21 proximal to the hub 18 and a tip end 22 distal from the hub 18. The blade 20 includes a leading edge 23 and a trailing edge 24 that extend between the root end 21 and tip end 22. The blade 20 includes a suction surface 25 and a pressure surface 26. A thickness dimension of the blade extends between the suction surface 25 and the pressure surface 26.

[0062] The blade 20 has a cross section that may be substantially circular near the root end 21. The blade portion near the root must have sufficient structural strength to support the blade portion outboard of that section and to transfer loads into the hub 18. The blade 20 may transition from a circular profile to an aerofoil profile moving from the root end 21 of the blade towards a "shoulder" 28 of the blade, which is the widest part of the blade 20 where the blade 20 has its maximum chord. The blade 20 has an aerofoil profile of progressively decreasing thickness in an outboard portion of the blade, which extends from the shoulder 28 to the tip end 22.

[0063] The wind turbine blade 20 may include an outer blade shell 29 defining a hollow interior space with a shear web extending internally between upper and lower parts of the blade shell 29.

[0064] As shown schematically in Figure 3, the blade 20 may include one or more lightning receptors 36, such as a tip array, and one or more lightning down conductor cables 38 which form part of a lightning protection system 30 for the wind turbine. The lightning receptors attract the lightning strike and the down conductor cables 38, which run through the hollow interior of the blade, conduct the energy of the lightning strike down the blade 20 via the nacelle 14 and tower 12 to a ground potential. In addition, the lightning protection system 30 may include a surface protection layer 40 at the outer surface of the blade. The surface protection layer 40 may be electrically connected at each end to the down conductor cables 38.

[0065] The majority of the outer surface of the blade 20 may be covered with the surface protection layer 40, or only a portion of the outer surface of the blade 20 may be covered with the surface protection layer 40. The surface protection layer 40 serves to shield conductive material in the blade from a lightning strike, and may act as either a lightning receptor, a down conductor, or both. The down conductor may extend substantially the full length of the blade. In some examples, such as where the majority of the outer surface of the blade 20 is covered with the surface protection layer 40, the down conductor cable 38 may connect to the surface protection layer 40 adjacent the tip end 22 of the blade and adjacent the root end 21 of the blade, with no down conductor cable 38 along the majority of the length of the blade covered with the surface protection layer 40. The surface protection layer 40 may extend from root to tip in which case there may be no need for a down conductor cable 38. The surface protection layer 40 may extend in sections along the length of the blade with down conductor cable sections between the surface protection layer 40 sections. The down conductor cable 38 may alternatively extend under the surface protection layer 40 (inside the blade) so that the down conductor cable 38 and surface protection layer 40 are electrically connected in parallel.

[0066] At the root end 21 of the blade 20, the down conductor cable 38 may be electrically connected via an armature arrangement to a charge transfer route via the nacelle 14 or hub 18 and tower 12 to a ground potential. Such a lightning protection system 30 therefore allows lightning to be channelled from the blade to a ground potential safely, thereby minimising the risk of damage to the wind turbine 10.

[0067] The down conductor cable 38 and surface protection layer 40 may be connected by one or more connectors or receptors. The connectors may comprise an electrically conductive pin 60 that extends through the surface protection layer 40 and connects to the down conductor cable 38. Figure 3 shows five electrically conductive pins 60 connecting the down conductor cable 38 and the surface protection layer 40, although it will be understood that any suitable number of electrically conductive pin 60 may be used. The surface protection layer 40 may extend up to the leading edge 23 of the wind turbine blade 20 and / or extend up to the trailing edge 24 of the wind turbine blade 20. Alternatively, the surface protection layer 40 may be spaced from the leading and / or trailing edge of the blade 20.

[0068] Figures 4A to 4G show a method of manufacturing a wind turbine blade 20 having a blade shell 29 with a lightning protection system 30. Each figure shows a section view of a portion of the wind turbine blade 20 at different stages during its manufacture. Figure 4G shows the fully manufactured wind turbine blade 20. It will be appreciated that the wind turbine blade shell 29 comprises a structural component 48 not discussed in detail here. The structural component 48 may for example include fibre layers, such as glass fibre layers, core materials such as foam, and similar, as will be appreciated by the person skilled in the art.

[0069] The lightning protection system 30 comprises a first or main surface protection layer at an outer surface of the blade shell 29. The first surface protection layer is metal and may be referred to hereinafter as a first metal layer 42. The lightning protection system 30 also comprises a second surface protection layer. The second surface protection layer is metal and may be referred to hereinafter as a second metal layer 44. Both the first metal layer 42 and the second metal layer 44 are sufficiently thin that they may be considered two dimensional. The second metal layer 44 provides local reinforcement to the main surface protection layer in the vicinity of the electrically conductive pin 60. As such, the area of the second metal layer 44 (at each electrically conductive pin 60 location) is no more than 10% of an area of the first metal layer 42, such as illustrated by Figure 5.

[0070] The lightning protection system 30 also comprises a metal reinforcing disc 50 formed across a portion of the second metal layer 44. The metal reinforcing disc 50 has a diameter smaller than a diameter of the second metal layer 44. It will be appreciated that the second metal layer 44 may be non-circular and still have a diameter. The metal reinforcing disc 50 is fixed to the second metal layer 44 so as to create an electrical connection with the second metal layer 44. As such, the metal reinforcing disc 50 may be manufactured integral to the second layer 44 such that the metal reinforcing disc 50 and the second metal layer 44 are not readily separable. The metal reinforcing disc 50 may be a cast component, cast through the second metal layer 44. In the case that the second metal layer 44 is a mesh or expanded metal foil, the metal reinforcing disc 50 may be cast through the apertures of the mesh or foil. The metal reinforcing disc 50 may be solid. Alternatively, the metal reinforcing disc 50 may be assembled to the second metal layer 44 as two half discs, one on either side of the second metal layer, and fixed to the second metal layer, e.g. by soldering or welding for example. Alternatively, the metal reinforcing disc 50 may be provided on only one side of the second metal layer 44 and fixed to the second metal layer 44.

[0071] Since the area of the first metal layer 42 is greater than the area of the second metal layer 44, a first portion of the first metal layer 42 surrounds the second metal layer 44 at an outer surface of the blade shell 29. It will be appreciated that the first portion of the first metal layer 42 may alternatively be said to encircle or fully surround the second metal layer. A second portion of the first metal layer 42 overlaps the second metal layer 44 and is in intimate electrical contact with the second metal layer 44. The second portion of the first metal layer 42 may also overlap the metal reinforcing disc 50. In some cases, the metal reinforcing disc 50 does not extend through the first metal layer 42. The second portion of the first metal layer 42 may be located towards an inside of the blade 20 with respect to the second metal layer 44, e.g. as illustrated in Figure 4G. To allow any lightning current to be routed towards ground, the second portion of the first metal layer 42 is in intimate electrical contact with the second metal layer 44. This may be achieved by the second portion of the first metal layer being in physical contact with the second metal layer 44.

[0072] The larger first metal layer 42 may be handled easily as it does not contain the metal reinforcing disc 50. In addition, the much smaller second metal layer 44 may also be handled easily and positioned accurately within a mould for forming the blade shell 29 despite containing the metal reinforcing disc 50. Forming the metal reinforcing disc 50 across the smaller second metal layer 44 rather than across the larger first metal layer 42 makes handling of the metal layers easier.

[0073] Positional accuracy of the metal disc in a mould for forming the blade shell is important. The metal layers 42, 44 may be fragile and so ease of handling is important to avoid handling damage so as to maintain good performance of the lightning strike protection system. Blade moulds typically comprise a surface having double curvature. Laying metal sheet material onto a surface with double curvature can be difficult, particularly if multiple points of that metal sheet need to be in precise locations in the mould. This can lead to the metal sheet becoming wrinkled and / or stretched during lay-up. By providing a second smaller metal layer 44 having the metal reinforcing disc 50 separate to the main first metal layer 42, the smaller second metal layer 44 and metal reinforcing disc 50 can be precisely positioned with less chance of the second metal layer 44 becoming wrinkled and / or stretched. The larger first metal layer 42 may then be laid more easily to fit the double curvature of the mould without additional constraints of positioning a point, e.g. a metal disc location. This may reduce the likelihood of wrinkling and / or stretching in the first metal layer 42.

[0074] In some cases, the first metal layer 42 may be in intimate electrical contact with the metal reinforcing disc 50. In this case, the second portion of the first metal layer 42 may be in physical contact with the metal reinforcing disc 50.

[0075] A method of manufacturing the wind turbine blade 20 will now be described with reference to Figures 4A to 4G and Figures 7A to 7F. The second metal layer 44 and the metal reinforcing disc 50 may be provided as a single part (i.e. a unitary part), collectively referred to as a reinforcing patch 100 illustrated in Figure 4A. The reinforcing patch 100 may be referred to hereinafter as a patch 100.

[0076] The patch 100 may be incorporated into different lightning protection systems and / or different wind turbine blade designs. A common patch 100 comprising a metal reinforcing disc 50 and a second metal layer 44 each having set dimensions may be manufactured and used in multiple wind turbine blade designs. In this case, the first metal layer 42 in each blade may then be cut to size rather than needing bespoke positions for the reinforcing disc(s) as these are not within the first metal layer. This may reduce the cost of manufacture and design as a common patch 100 design can be used for multiple blades, and the first metal layer 42 can be cut from a simple roll of sheet material devoid of integral discs.

[0077] The patch 100 is first positioned over a mould surface 72 of a mould 70 for forming the blade shell 29 (or half shell) of a wind turbine blade. The mould surface 72 may comprise a marking 74 arranged to indicate a target position of the patch 100. The patch 100, e.g. the metal reinforcing disc 50, may comprise an alignment feature (not shown) to help align the patch with the marking 74. Once the patch 100 is positioned correctly, the first metal layer 42 is arranged over the mould surface 72 and the patch 100 as shown in Figures 4C and 7C. The metal reinforcing disc 50 may have chamfered edges facing the first metal layer 42 to avoid stress concentrations which may otherwise damage the first metal layer 42. The chamfered edges may also avoid stress concentrations in any surrounding blade material adjacent to the reinforcing disc. One or more structural components 48 are arranged on the first metal layer 42 as shown in Figures 4D and 7D. As described previously, it will be appreciated that the structural components 48 may include fibre layers, core materials such as foam, and similar.

[0078] The structural components 48, the first metal layer 42 and the patch 100 are consolidated under vacuum to form a blade shell 29. This may involve covering the mould 70, containing the structural components 48, the first metal layer 42 and the patch 100, in a vacuum bag 75 and applying a vacuum pressure through a valve 76 as shown in Figure 7E. The structural components 48 may subsequently be cured, e.g. under heat and / or pressure. In some examples, the structural components 48 may comprise fibre layers (not shown) which may be dry fibre preforms, or similar, requiring the addition of resin to the mould 70. Once consolidated, a blade shell 29 is formed comprising a lightning protection system 30 having a first portion of the first metal layer 42 surrounding the second metal layer 44 at an outer surface of the blade shell 29, and a second portion of the first metal layer 42 overlapping the second metal layer 44.

[0079] Once removed from the mould 70, a hole may be made through the metal reinforcing disc 50, the second metal layer 44, the first metal layer 42 and the structural components 48. This may be achieved using a drill 80 as shown in Figure 4F, however it will be appreciated that any suitable method of manufacture may be used.

[0080] The lightning protection system 30 may further comprise an electrically conductive pin 60 which extends through the metal reinforcing disc 50 as illustrated in Figure 4G. The electrically conductive pin 60 may be used to electrically connect the first metal layer 42 one or more electrical components of the lightning protection system 30 inside the blade shell 29, such as a down conductor cable or a tip array for example, to the first metal layer. The electrically conductive pin 60 forms an intimate electrical connection to the first metal layer 42 via the metal reinforcing disc 50. This enables lightning current to be conducted via the first metal layer 42 to ground through the electrically conductive pin 60. The electrically conductive pin 60 may extend through the first metal layer 42. For example, an aperture may be formed through the first metal layer 42 for receiving the electrically conductive pin 60. The aperture in the first metal layer 42 may be formed simultaneously with forming an aperture through the metal reinforcing disc 50, during blade manufacture. This may be achieved by drilling a hole through the blade shell 29 as described above and inserting the pin 60 into the hole.

[0081] The electrically conductive pin 60 may comprise a head 62 coupled to a shank 64. The shank 64 may extend through the metal reinforcing disc 50, the first metal layer 42, and the structural components 48. The head 62 may have an outer side 62a and an underside 62b. The underside 62b may face a surface of the metal reinforcing disc 50. The underside 62b may be adjacent the metal reinforcing disc 50. The underside 62b may be in contact with the metal reinforcing disc 50. This may create an intimate electrical connection between the electrically conductive pin 60 and the metal reinforcing disc 50. As illustrated in Figure 4G, the metal reinforcing disc 50 may be located towards an inside of the blade 20 with respect to the head 62. In such cases the outer side 62a of the pin 60 may be exposed to the environment outside the blade 20. The pin 60, e.g. the outer surface of the outer side 62a of the head 62, may be substantially flush with the blade shell 29 outer surface. Providing a substantially flush pin 60 and blade shell 29 outer surface may improve aerodynamic performance of the blade 20.

[0082] The wind turbine blade 20 may further comprise an electrical component 32 electrically connected to the first metal layer 42 as shown in Figure 4G. The electrical component 32 may be a connector base for forming an electrical connection between the electrically conductive pin 60 and one or more further electrical components of the lightning protection system 30. Alternatively, the electrical component may be a down conductor cable 38 or tip array 36 or other component of the lightning protection system 30, forming a direct electrical connection with the electrically conductive pin 60.

[0083] The electrical component 32 is electrically connected to the first layer 42 via the electrically conductive pin 60.

[0084] The electrical component 32 may have a threaded aperture for receiving a threaded end of the shank 64 of the electrically conductive pin 60 for threadedly securing the electrically conductive pin 60 to the electrical component 32. The electrical component 32 may be fixed with respect to the inside of the blade shell 29.

[0085] The pin head 62 may be located in a recess 97 within the wind turbine blade 20. This may assist with ensuring the pin head 62 does not sit proud of the outer surface of the blade shell 29.

[0086] The recess 97 may be provided in a portion of a forming element 90 around the metal reinforcing disc 50. The forming element 90 may be provided as part of the reinforcing patch 100. An example of a reinforcing patch 100 having a forming element 90, and a related method of manufacturing a blade shell with such a patch 100, is illustrated in Figure 6A to 6I. It will be appreciated that the example shown in Figures 6A to 6I shares many similarities with the example described above with reference to Figures 4A to 4G and Figures 7A to 7F described above.

[0087] The reinforcing patch 100 may therefore comprise a forming element 90; a second metal layer 44 having an area no more than 10% of an area of the first metal layer 42; and a metal reinforcing disc 50 formed across a portion of the second metal layer 44. The metal reinforcing disc 50 is located within the forming element 90 and is fixed to the second metal layer 44 so as to create an electrical connection between the metal reinforcing disc 50 and the second metal layer 44. When the patch 100 is incorporated into a wind turbine blade 20, a first portion of the first metal layer 42 surrounds the second metal layer 44 at an outer surface of the blade shell 29, and a second portion of the first metal layer 42 overlaps the second metal layer 44 and is in intimate electrical contact with the second metal layer 4. Once incorporated into a wind turbine blade, the second metal layer 44 of the reinforcing patch 100 may be located towards an outside of the blade 20 with respect to the first metal layer 42.

[0088] Alternatively, the forming element 90 and the metal reinforcing disc 50 may be separable prior to incorporation into the wind turbine blade 20. As such, the forming element 90 and the second metal layer 42 having the metal reinforcing disc 50 may be separate components of the patch 100 prior to lay up in the mould for forming the blade shell 29. The forming element 90 may be designed to create recess 97 such that an outer side 62a of the pin head 62 is substantially flush with the outer edge of forming element 90. As such, the forming element may be shaped as shown in Figure 6G to 6I to provide a smooth transition surface around the pin head 62 for the first metal layer 42 and / or the second metal layer 44.

[0089] The forming element 90 may comprise a first forming element 92 and a second forming element 94. The first forming element 92 may be designed to deform during manufacture, optionally during consolidation under vacuum as previously described. The first forming element 92 may comprise glass fibre material. The first forming element may be in the form of a wedge in cross section, so shaped as an annular conical section around the second forming element 94. The second forming element may be shaped as an annular disc. The second forming element 94 may comprise polyurethane (Pll) and may substantially not deform during consolidation in the mould, such that the recess 97 is correctly dimensioned to receive the pin 60. The recess 97 may be defined as a space within the second forming element 94 and bounded by the interior of the annular second forming element and the metal reinforcing disc 50. The metal reinforcing disc 50 may be securely held or fixed within the forming element 90, e.g. within the second forming element 90, so as to ease handling of the patch 100. The metal reinforcing disc 50 and the second forming element 90 may be coupled by friction or by adhesive for example. The first and second forming elements 92 and 94 may be securely held or fixed together, e.g. by friction or by adhesive. An example of a forming element 90 comprising a first forming element 92 and a second forming element 94 is illustrated in Figures 6B to 6I.

[0090] Where the patch 100 has the forming element 90 and the second metal layer 42 having the metal reinforcing disc 50 as separable parts prior to lay up in the mould, it will be appreciated that the forming element 90 then the second metal layer 44 having the metal reinforcing disc 50, and then the first metal layer 42 are arranged over the mould surface 72.

[0091] Figures 6B to 6F show an example of how the first forming element 92 may be shaped prior to consolidation under vacuum. Upon consolidation, the first forming element 92 may deform to match the profile of the mould surface 72 as shown in Figure 6G. As can be seen, the annular conical section of the first forming element 92 may initially have a shape in which the outer peripheral edge of the annular conical section is spaced away from the mould surface 72 and the first forming element 92 under consolidation deforms (Figure 6F to Figure 6G) such that the outer peripheral edge of the annular conical section is at the mould surface 72. After removal of the blade shell 29 comprising the reinforcing patch 100 from the mould, a portion of the forming element 90 may be removed to reveal a surface of the metal reinforcing disc. For example, the forming element 90 may comprise a non-deformable spacer 96 to maintain the recess 97 during manufacture of the blade shell 29. The non- deformable spacer 96 may be inserted into the recess 97 during layup of the blade shell 29 in the mould 70 as illustrated in Figure 6C. The spacer 96 may have the same dimensions as the pin head 62. The spacer 96 may be magnetic. Making the spacer magnetic aids in discovering the spacer 96 after de-moulding the cured blade shell 29, e.g. with a magnet detector. Once the spacer 96 is removed to reveal the recess 97, a hole may be made through the metal reinforcing disc 50, the second metal layer 44, the first metal layer 42 and the structural components 48. This may be achieved using drill 80 as shown in Figure 6H similar to the process shown in Figure 4F. Thereafter pin 60 may be inserted in the aperture and connected as shown in Figure 6I in a substantially identical manner to that previously described with reference to Figure 4G.

[0092] In a further example, the recess 97 may be provided entirely within the metal reinforcing disc 50. The metal reinforcing disc 50 may comprise a generally circular disc portion, again with chamfered edges towards the first metal layer 42, and an annular extension portion 52, extending from the circular disc portion, which forms the walls of the recess. As shown in Figure 8A, the annular extension portion 52 may extend around the entire periphery of the metal reinforcing disc 50. The metal reinforcing disc 50, such as shown in Figure 8A, may comprise the annular extension portion 52 but have no chamfered edge.

[0093] Where the patch 100 comprises the second metal layer 44 fixed to a metal reinforcing disc 50 comprising recess 97, a forming element 90 comprising a first forming element 92 only may be used without a second forming element. The first forming element 92 may be substantially as described above with reference to Figures 6B to 6I. The annular conical section of the first forming element 92 may have a maximum height substantially the same as the height of the annular extension portion 52 of the metal reinforcing disc 50. The first forming element 92 may be securely held of fixed to the metal reinforcing disc 50, e.g. by friction or adhesive for example. Alternatively, the first forming element 92 and the metal reinforcing disc 50 may be separable parts prior to lay up in the mould. As illustrated in Figures 8B to 8D, the first forming element 92 may be designed to deform during the consolidation step of manufacture of the blade shell 29 as previously described.

[0094] The metal reinforcing disc 50 having the integral recess 97 may be fitted with a spacer 96 in the same way as previously described, e.g. as shown in Figure 8C. The patch 100 may be laid up in the mould in the same way as described above with reference to Figures 6D to 6F and the blade shell components consolidated and cured. After removal of the blade shell 29 comprising the reinforcing patch 100 from the mould, a portion of the forming element 90, such as the spacer 96, may be removed to reveal a surface of the metal reinforcing disc 50. A hole may be made through the metal reinforcing disc 50, the second metal layer 44, the first metal layer 42 and the structural components 48. This may be achieved using drill 80 similar to the process shown in Figure 4F. Thereafter pin 60 may be inserted in the aperture and connected as shown in Figure 8D in a substantially identical manner to that previously described with reference to Figure 4G.

[0095] In a further example, the patch 100 may comprise a plurality of second metal layers 44a, 44b fixed to a single metal reinforcing disc 50. Although shown in Figure 9A as comprising two second metal layers 44a, 44b it will be appreciated that the patch 100 may comprise any number of second metal layers 44. Each second metal layer 44a, 44b may have the same area and optionally may be identical, or may be different. Each second metal layer 44a, 44b has an area no more than 10% of the area of the first metal layer 42. The patch 100 having the plural second metal layers 44a, 44b may be laid up in the mould during manufacture of the blade shell 29 in a substantially identical way to that described above with reference to Figures 4A to 4F, 6A to 6H, and 7A to 7F. Figure 9B shows an example of a completed blade shell 29 incorporating the plural second metal layers 44a, 44b.

[0096] A patch 100 comprising a plurality of second metal layers 44a, 44b may be more robust than a patch comprising a single second metal layer 44 only. This may beneficially reduce the risk of damage to the second metal layer during handling or incorporation into the blade. Additionally, providing a plurality of second metal layers 44a, 44b in electrical connection with the metal reinforcing disc may allow a greater current to be conducted in the event of a lightning strike upon the patch 100. This may enable the patch 100 to be more robust in the event of a lightning strike. In some examples, the metal reinforcing disc 50 extends through the second metal layer 44 as illustrated in Figures 4A to 4G, 6A to 6I, and 8A to 8D. Alternatively, in a further example, the metal reinforcing disc 50 extends up to the second metal layer 44 but not through it as shown in Figure 10A and 10B. It will be appreciated that where the patch 100 comprises a plurality of second metal layers 44a, 44b, the metal reinforcing disc 50 may extend up to at least one second metal layer 44 and through at least one further second metal layer 44. The metal reinforcing disc 50 may be fixed to the second metal layer 44, e.g. by welding or soldering. Alternatively, the metal reinforcing disc 50 may extend into the second metal layer 44 but not through the second metal layer 44 and may be formed by casting.

[0097] The patch 100 having the metal reinforcing disc 50 extending up to or into (but not through) the second metal layer 44 may be laid up in the mould during manufacture of the blade shell 29 in a substantially identical way to that described above with reference to Figures 4A to 4F, 6A to 6H, 7A to 7F, 8A to 8D or 9A to 9B. Figure 10B shows an example of a completed blade shell 29 incorporating the metal reinforcing disc 50 extending up to or into (but not through) the second metal layer 44.

[0098] Although the invention has been described above with reference to one or more preferred embodiments, it will be appreciated that various changes or modifications may be made without departing from the scope of the invention as defined in the appended claims.

Claims

CLAIMS1 . A wind turbine blade having a blade shell with a lightning protection system; the lightning protection system comprising: a first metal layer; a second metal layer having an area no more than 10% of an area of the first metal layer; and a metal reinforcing disc formed across a portion of the second metal layer, wherein the metal reinforcing disc is fixed to the second metal layer so as to create an electrical connection with the second metal layer, and wherein a first portion of the first metal layer surrounds the second metal layer at an outer surface of the blade shell, and a second portion of the first metal layer overlaps the second metal layer and is in intimate electrical contact with the second metal layer.

2. A wind turbine blade according to claim 1 , wherein the second portion of the first metal layer is located towards an inside of the blade with respect to the second metal layer.

3. A wind turbine blade according to claim 1 or claim 2, wherein the second portion of the first metal layer overlaps the metal reinforcing disc.

4. A wind turbine blade according to any preceding claim, wherein the metal reinforcing disc does not extend through the first metal layer.

5. A wind turbine blade according to any preceding claim, further comprising an electrically conductive pin which extends through the metal reinforcing disc.

6. A wind turbine blade according to claim 5, wherein the electrically conductive pin extends through the first metal layer.

7. A wind turbine blade according to claim 5 or claim 6, further comprising an electrical component, wherein the first metal layer is electrically connected to the electrical component by the electrically conductive pin.

8. A wind turbine blade according to claim 7, wherein the electrical component is a down conductor of the lightning protection system.

9. A wind turbine blade according to any of claims 5 to 8, wherein the electrically conductive pin has a head, and wherein an underside of the head faces a surface of the metal reinforcing disc.

10. A wind turbine blade according to claim 9, further comprising a recess in which the head of the pin is located.

11. A wind turbine blade according to claim 10, wherein the recess is provided in the metal reinforcing disc.

12. A wind turbine blade according to claim 10, wherein the recess is provided in a portion of a forming element around the metal reinforcing disc.

13. A wind turbine blade according to any of claims 9 to 12, wherein the head of the pin is substantially flush with the blade shell outer surface.

14. A wind turbine blade according to any preceding claim, wherein the metal reinforcing disc extends through the second metal layer.

15. A wind turbine blade according to any preceding claim, wherein the second portion of the first metal layer is in intimate electrical contact with the metal reinforcing disc.

16. A reinforcing patch for a lightning protection system of a wind turbine blade having a blade shell with a first metal layer, the patch comprising: a forming element; a second metal layer having an area no more than 10% of an area of the first metal layer; and a metal reinforcing disc formed across a portion of the second metal layer, wherein the metal reinforcing disc is located within the forming element and is fixed to the second metal layer so as to create an electrical connection between the metal reinforcing disc and the second metal layer, and wherein when the patch is incorporated into a wind turbine blade a first portion of the first metal layer surrounds the second metal layer at an outer surface of the bladeshell, and a second portion of the first metal layer overlaps over the second metal layer and is in intimate electrical contact with the second metal layer.

17. A reinforcing patch according to claim 16, wherein the forming element and the metal reinforcing disc are separable prior to incorporation into the wind turbine blade.

18. A method of manufacturing a wind turbine blade with a lightning protection system, the method comprising: providing a mould surface; providing a reinforcing patch of a lightning protection system, the reinforcing patch including a metal reinforcing disc formed across a portion of a second metal layer, wherein the metal reinforcing disc is fixed to the second metal layer so as to create an electrical connection between the metal reinforcing disc and the second metal layer; providing a first metal layer of the lightning protection system, wherein the second metal layer has an area no more than 10% of an area of the first metal layer; arranging the first metal layer and the reinforcing patch on the mould surface; arranging one or more structural components on the first metal layer and the reinforcing patch; consolidating the structural components, the first metal layer and the reinforcing patch under vacuum to form a blade shell having a first portion of the first metal layer surrounding the second metal layer at an outer surface of the blade shell, and a second portion of the first metal layer overlaps the second metal layer and is in intimate electrical contact with the second metal layer.

19. A method according to claim 18, wherein the reinforcing patch further comprises a forming element and the metal reinforcing disc is located within the forming element, the method further comprising removing a portion of the forming element to reveal a surface of the metal reinforcing disc.

20. A method according to claim 18 or claim 19, further comprising inserting an electrically conductive pin through the metal reinforcing disc to electrically connect an electrical component located adjacent an inner surface of the blade shell to the first metal layer via the metal reinforcing disc.

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