Lightning protection system

Abstract

A wind turbine blade having a blade shell with a lightning protection system. The lightning protection system includes a first metal layer, a metal plate configured to electrically connect to one or more electrical components, and a plurality of metal rods secured to the metal plate and arranged to extend therefrom. The plurality of metal rods extend over and contact the first metal layer such that the first metal layer is electrically connected to the metal plate via the plurality of metal rods.

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 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 intercepts lightning strikes before reaching conductive components of the blade.

[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] It is desired to improve the distribution of current to / from the surface protection layer.

[0009] SUMMARY OF INVENTION

[0010] According to a first aspect of the invention, there is provided a wind turbine blade having a blade shell with a lightning protection system, wherein the lightning protection system comprises: a first metal layer; a metal plate configured to electrically connect to one or more electrical components; and a plurality of metal rods secured to the metal plate and arranged to extend therefrom; wherein the plurality of metal rods extend over and contact the first metal layer such that the first metal layer is electrically connected to the metal plate via the plurality of metal rods.

[0011] Advantageously, the metal rods have a higher current carrying capacity compared to the first metal layer, thereby making a better transfer of current from the metal plate to the first metal layer.

[0012] The metal plate may be electrically connected to an electrical component of the lightning protection system by a pin. The pin may pass through an aperture in the metal plate.

[0013] Preferably, the plurality of metal rods are discrete from the metal plate. The plurality of metal rods are not integrally formed with the metal plate. The plurality of metal rods may be mechanically secured to and electrically bonded with the metal plate. Separate rods allow the metal plate and the rods to be pre-assembled or adjusted independently, simplifying manufacturing and reducing a risk of wrinkling or distortion compared to an integral component.

[0014] Each metal rod may be a separate component from the metal plate. They may be secured to the metal plate by e.g. soldering, clamping, or looping, such that the rods are not integral extensions of the metal plate.

[0015] Optionally, the blade defines a root end, a tip end, and a chordwise axis extending between a leading edge and a trailing edge of the blade. The plurality of rods may extend over the first metal layer so as to define a first angle relative to the chordwise axis, said first angle being non-perpendicular and non-parallel relative to the chordwise axis.

[0016] Advantageously, the plurality of rods can provide effective electrical contact between the first metal layer and the metal plate. The angled orientation of the rods reduces current concentration or hot spot generation compared to rods that are parallel with the chordwise axis or perpendicular to the chordwise axis. This occurs because each of the metal rods will create multiple electrical paths with the first metal layer between the metal plate and ground. Ground will normally be reached via the root end of the wind turbine blade with current passing along the blade in a generally spanwise direction. By aligning the rods at the first angle and towards the root end of the blade, current will be encouraged to flow along the rod and exit into the first metal layer at multiple points along the rod, distributing the current into a wide area of the first metal layer. If the rod were aligned in the blade chordwise direction (or extending towards the tip end of the blade), the shortest path for the current to follow towards ground would generally be from the rod into the first metal layer adjacent the metal plate, creating a hot spot adjacent the metal plate. If the rod were aligned in the blade spanwise direction, perpendicular to the blade chordwise direction, and towards the root end of the blade, the shortest path for the current would be along the rod to exit from a distal end of the rod, creating a hot spot at the distal end of the rod. Moreover, the present arrangement is advantageous compared with arranging the rods to extend in the spanwise direction), since these rods may fatigue due to high strain in the blade material. Moreover, the ends of spanwise rods may introduce high stress points.

[0017] Optionally, the first angle is in the range of 20° to 40°.

[0018] Advantageously, this angle has been found to reduce high stress points and electrical hot spots, whilst improving contact area between the rods and the first metal layer.

[0019] Optionally, the plurality of rods extend generally parallel to one another.

[0020] The plurality of metal rods may each have a substantially uniform cross-section along their length. In other words, the rods do not widen or taper and maintain consistent geometry for reliable electrical contact. A uniform cross-section ensures consistent current carrying capacity and avoids localised resistance changes that could cause hotspots. In addition, a substantially uniform cross-section allows for a stable contact area with the metal layer even if rods twist during manufacture of the blade.

[0021] Advantageously, the parallel rods remove a strain differential acting on the first metal layer as the blade bends, reducing the risk of damage to certain areas of the metal layer. The parallel rods facilitate a flexible connection that can conform to the shape of a blade while providing a robust electrical contact between the metal plate and the first metal layer.

[0022] Optionally, the first metal layer is a mesh or apertured foil having a mesh pattern, wherein the plurality of rods generally align with a direction of the mesh pattern. Advantageously, the rods follow the mesh pattern to increase the contact area between the rods and the mesh and thereby improve the effectiveness of the lightning protection system.

[0023] In some arrangements, the rods have a generally circular cross-section. Generally circular rods provide manufacturing robustness compared to e.g. flattened rods, which may twist during manufacture of the blade. If a flattened rod becomes twisted the contact patch between the rod and the first metal layer may change as compared with the design intent. By contrast, if a circular rod becomes twisted the contact patch between the rod and the first metal layer does not change and so the design intent is assured.

[0024] Optionally, the plurality of rods are spaced apart and have a pitch that is substantially the same as a pitch of the mesh pattern.

[0025] Advantageously the rods are positioned at the same intervals as the mesh, increasing the contact area between the rods and the mesh and thus improving the effectiveness of the lightning protection system.

[0026] Optionally, the lightning protection system comprises a second metal plate and a second plurality of rods extending from the second metal plate. The second plurality of metal rods may extend over and contact the first metal layer such that the first metal layer is electrically connected to the second metal plate via the second plurality of metal rods.

[0027] Advantageously, a second metal plate can provide increased contact with one or more electrical components, improving the effectiveness of the lightning protection system.

[0028] Optionally, the metal plate is spaced from the first metal layer.

[0029] Advantageously, the metal plate is spaced apart from the first metal layer while still maintaining an electrical connection therebetween via the rods. In this way, the metal plate can connect the first metal layer to electrical components without impacting the integrity of the first metal layer, e.g. in contrast to locating the metal plate over the first metal layer where a connection point (e.g. bore for receiving a pin) may have to be machined into the metal layer, reducing its integrity. Moreover, spacing the metal plate from the first metal layer can simplify the positioning of the components of the lightning protection system during manufacture. The metal layer may be fragile and so ease of handling during manufacture is important. This is made easier by the spaced metal plate. Avoiding damage is important so as to maintain good performance of the lightning protection system.

[0030] Optionally, the metal rods follow an S-shaped curve between the first metal layer and the metal plate. The metal plate may be disposed further from an exterior surface of the blade shell than is the first metal layer.

[0031] Advantageously, the rods can provide a continuous electrical connection between the metal plate and the first metal layer, while facilitating the metal plate being submerged deeper into the blade shell, e.g. for locating closer to the one or more electrical components inside the blade shell.

[0032] Optionally, at least one of the plurality of rods may be crimped to follow an S-shaped curve.

[0033] Optionally, the lightning protection system comprises a second metal layer having an area greater than the first metal layer. The first metal layer is arranged to define an overlap region between the first and second metal layers.

[0034] Instead of the rods directly contacting a metal layer providing significant coverage over the blade, the first metal layer may be provided as a patch or smaller area metal layer in contact with a second metal layer having a larger area. The second metal layer provides significant coverage over the blade. The electrical connection from the metal plate is provided via the plurality of rods and the first metal layer. The metal layers may be thin and therefore fragile and so improving ease of handling is important to avoid damage and maintain good performance of the lightning protection system. The smaller first metal layer may facilitate an improved flexibility regarding the position of the metal plate relative to the second metal layer, especially when the rods are secured to the first metal layer prior to handling the metal plate relative to the second metal layer when manufacturing the blade. The first metal layer and the second metal may be discrete and separate components when being laid up during manufacturing of the wind turbine blade. 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.

[0035] The first metal layer and / or the second metal layer may each comprise a mesh or expanded metal foil. The metal plate may be solid.

[0036] Optionally, the metal rods are sandwiched between the first metal layer and the second metal layer in the overlap region.

[0037] Advantageously, the electrical contact is increased (e.g. effectively doubled), as the rods contact the first metal layer and the second metal layer respectively on two opposite sides of the rods. This can facilitate a reduction in the length of the rods without impacting the electrical contact between the metal layers and the metal plate.

[0038] Optionally, a pair of the rods extending from the metal plate are formed from a single part looped around the metal plate.

[0039] Advantageously, this provides for a simpler means of manufacturing the blade. The looped rods can provide a compact connection that increases the structural integrity of the metal plate, reducing the risk of the rods becoming loose.

[0040] Optionally, the plurality of metal rods make electrical contact with the first metal layer at multiple points along the length of the rods.

[0041] Advantageously, the contact area between the rods and the metal layer is increased, improving the effectiveness of the electrical connection therebetween.

[0042] Optionally, the plurality of metal rods follow a contour of the first metal layer in a region where the metal rods make contact with the first metal layer.

[0043] Advantageously, contact between the metal rods and the first metal layer is maintained irrespective of the contour of the metal layer, thereby improving the electrical connection. The contour of the metal layer is defined by the contour in the outer surface of the blade shell which is defined by the aerodynamic profile of the blade. Optionally, the metal rods and the first metal layer and / or the metal plate comprise the same material.

[0044] Advantageously, using the same material removes the risk of galvanic corrosion.

[0045] Optionally, the plurality of rods each have a distal end furthest from the metal plate, and the distal ends of the rods terminate over the first metal layer in a staggered array.

[0046] Advantageously, the staggered array of distal ends of the rods may distribute the current into the metal layer over a wider area.

[0047] Optionally, the distal end of the plurality of rods may be aligned along a chordwise direction and / or the chordwise axis.

[0048] Optionally, the rods each have a diameter of 1 mm to 3 mm.

[0049] Optionally, the rods have a length of between 5 cm to 50 cm.

[0050] Optionally, the plurality of rods is between 5 to 15 rods.

[0051] Optionally the rods have a circular, ovoid, rectangular or square cross section.

[0052] Optionally, the metal plate does not locate on, over or extend through the first metal layer.

[0053] Optionally, the metal plate does not locate on, over or extend through the second metal layer.

[0054] Optionally, the lightning protection system further comprises an electrically conductive pin which extends through a bore of the metal plate.

[0055] Optionally, the lightning protection system further comprises an electrical component. The metal plate may be electrically connected to the electrical component by the electrically conductive pin. 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.

[0056] 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.

[0057] Optionally, the electrical component includes a down conductor of the lightning protection system.

[0058] The electrically conductive pin may be used to electrically connect the first metal layer to 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. The electrically conductive pin forms an intimate electrical connection to the first metal layer via the metal plate and rods. This enables lightning current to be conducted via the first metal layer to ground through the electrically conductive pin.

[0059] Optionally, the metal plate and / or the first metal layer and / or the plurality of rods are formed from aluminium.

[0060] Optionally, the plurality of rods are soldered to the metal plate. Optionally, the plurality of rods are soldered to the metal plate using a zinc solder.

[0061] Optionally, the metal plate is formed from two parts which sandwich the rods.

[0062] According to a further aspect of the invention, there is provided a method of manufacturing a blade shell of a wind turbine blade with a lightning protection system, the method comprising: providing a mould surface; providing an electrical connection assembly of the lightning protection system, comprising a first metal layer, a metal plate, and a plurality of metal rods secured to the metal plate and arranged to extend therefrom, the plurality of metal rods extending over and contacting the first metal layer; providing a second metal layer of the lightning protection system, the second metal layer having an area greater than the first metal layer; arranging the second metal layer and the connection assembly on the mould surface such that the first metal layer and the second metal layer overlap in an overlap region; providing a plurality of fibre composite layers; and consolidating the fibre composite layers, the second metal layer and the electrical connection assembly under vacuum in the mould to form a blade shell of a wind turbine blade.

[0063] Optionally, the electrical connection assembly is positioned between spanwise ends of the second metal layer.

[0064] Optionally, the plurality of metal rods are secured to the first metal layer prior to arranging the electrical connection assembly on the mould surface.

[0065] Optionally, the plurality of metal rods are secured by an adhesive or by stitching.

[0066] Optionally, the plurality of metal rods are secured to the metal plate prior to arranging the electrical connection assembly on the mould surface.

[0067] Optionally, the plurality of rods are soldered to the metal plate. Optionally, the plurality of rods are soldered to the metal plate using a zinc solder.

[0068] Optionally, the method further comprises introducing a resin to infiltrate the consolidated fibre composite layers, the second metal layer and the electrical connection assembly under the vacuum.

[0069] Advantageously, the reliability of lightning protection system is improved as the risk of the metal rods disconnecting from the first metal layer is reduced.

[0070] Preferably the adhesive is different than the resin material.

[0071] Optionally, at least one of the plurality of rods may be crimped to follow an S-shaped curve.

[0072] Optionally, the method further comprises bending the plurality of metal rods and / or the first metal layer to follow a contour of the mould surface, preferably prior to securing the plurality of metal rods to the first metal layer. Optionally, the method further comprises inserting an electrically conductive pin through a bore in the metal plate to electrically connect an electrical component located within or on an inner surface of the blade shell to the second metal layer via the first metal layer, plurality of rods and metal plate.

[0073] The method may be configured incorporate any or all of the features of the wind turbine blade of the previous aspect.

[0074] A further aspect of the invention provides an electrical connection assembly for a lightning protection system of a wind turbine blade, the electrical connection assembly comprises a first metal layer, a metal plate configured to electrically connect to one or more electrical components, and a plurality of metal rods secured to the metal plate and arranged to extend therefrom, wherein the plurality of metal rods extend over and contact the first metal layer such that the first metal layer is electrically connected to the metal plate via the plurality of metal rods.

[0075] The electrical connection assembly may incorporate any or all of the features of the first metal layer, metal plate, and metal rods outlined in relation to the previous aspects.

[0076] BRIEF DESCRIPTION OF THE DRAWINGS

[0077] Embodiments of the invention will now be described with reference to the accompanying drawings, in which:

[0078] Figure 1 shows a wind turbine;

[0079] Figure 2 shows a wind turbine blade;

[0080] 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;

[0081] Figure 4 shows a planform view of a portion of a lightning protection system according to an embodiment;

[0082] Figure 5 shows a planform view of a portion of a lightning protection system according to an embodiment;

[0083] Figure 6 shows a planform view of a portion of a lightning protection system according to an embodiment;

[0084] Figure 7 shows a cross-sectional view of a portion of an electrical connection assembly according to an embodiment; Figure 8 shows a cross-sectional view of a portion of an electrical connection assembly according to an embodiment;

[0085] Figure 9 shows a plan view of an electrical connection assembly;

[0086] Figure 10 shows a plan view of an electrical connection assembly;

[0087] Figure 11 shows a plan view of a portion of an electrical connection assembly;

[0088] Figure 12 shows a cross-sectional view through a wind turbine blade;

[0089] Figures 13A-13E show the methods of manufacturing a wind turbine blade including a lightning protection system.

[0090] DETAILED DESCRIPTION OF EMBODIMENT(S)

[0091] 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.

[0092] 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.

[0093] 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.

[0094] 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.

[0095] 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.

[0096] 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. 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.

[0097] 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.

[0098] 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.

[0099] 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.

[0100] 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.

[0101] 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.

[0102] 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. 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. The blade 20 defined a chordwise axis 27 extending between the leading edge 23 and the trailing edge 24, e.g. in a chordwise direction.

[0103] 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.

[0104] 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.

[0105] As shown schematically in Figure 3, the blade 20 may include one or more lightning receptors 36, such as a tip receptor, 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.

[0106] 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.

[0107] 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.

[0108] 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 blade shell 29 and connects to the down conductor cable 38. Figure 3 shows two 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 pins 60 may be used.

[0109] 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.

[0110] The lightning protection system 30 includes a first surface protection layer at or toward an outer surface of the blade shell 29. In some arrangements, the lightning protection system 30 is separated from the outer surface of the blade shell 29 by a thin skin of material and / or a gel coat. The first surface protection layer is metal and may be referred to hereinafter as a first metal layer 42. The first metal layer 42 is sufficiently thin that it may be considered two dimensional. For example, the first metal layer 42 may have a thickness of less than 1 mm, preferably between 0.25 mm to 0.5 mm. The lightning protection system 30 also includes a metal plate 50 configured to electrically connect to one or more electrical components 32. For example, the metal plate 50 may be electrically connected to an electrical component 32 of the lightning protection system by an electrically conductive pin 60. The pin 60 may pass through an aperture in the metal plate 50. In this way, the metal plate 50 may be electrically connected to an electrical component 32 via the electrically conductive pin 60 passing therethrough. The metal plate 50 may be a metal disc in some arrangements. The metal plate 50 may have an area smaller than an area of the first metal layer 42.

[0111] The lightning protection system 30 includes a plurality of metal rods 52. The metal rods 52 are secured to the metal plate 50 and are arranged to extend therefrom. The plurality of metal rods 52 extend over and contact the first metal layer 42 such that the first metal layer 42 is electrically connected to the metal plate 50 via the plurality of metal rods 52. The provision of the metal rods 52 improves the transfer of current between the metal plate 50 and the first metal layer 42, e.g. compared to prior art systems in which current is transferred between the first metal layer 42 and the metal plate 50 solely via direct contact therebetween. The metal rods 52 have a higher current carrying capacity compared to the first metal layer 42. In this way, the plurality of metal rods 52 provide an improved pathway for electric current to / from first metal layer 42 to the metal plate 50. The plurality of rods 52 may include between 3 to 20 rods. In some arrangements, between 5 to 15 rods may be provided.

[0112] The first metal layer 42 may extend over a significant area of the wind turbine blade 20, e.g. generally between the tip end 22 and the root end 21 , as is shown in Figure 3. In this way, the first metal layer 42 may define substantially all of the surface protection layer 40 of the lightning protection system 30. In alternative arrangements, instead of the rods 52 directly contacting the metal layer that provides significant coverage over the blade 20, the first metal layer 42 may be provided as a patch or a smaller area metal layer in contact with a second metal layer 44 having a larger area. An example of such an arrangement is shown in Figure 4. In this arrangement, the lightning protection system 30 includes a second surface protection layer. The second surface protection layer is metal and may be referred to hereinafter as a second metal layer 44. The second metal layer 44 is sufficiently thin that it can be considered two dimensional. The second metal layer 44 may be referred to as the main surface protection layer and may provide the majority of the surface area of the surface protection layer 40. The first metal layer 42 may be arranged to define an overlap region 54 between the first and second metal layers 42, 44. In the overlap region 54, the first metal layer 42 may be in intimate electrical contact with the second metal layer 44 so as to transfer current therebetween. In this arrangement, the electrical connection between the second metal layer 44 and the metal plate 50 is provided via the plurality of rods 52 and the first metal layer 42. The first metal layer 42 may be arranged to extend over one or more edges of the second metal layer 44 to define the overlap region 54. In this way, the overlap region 54 is not surrounded by the second metal layer 44. The first metal layer 42 and the overlap region 54 may be located on the blade 20 proximal a metal plate 50 and electrically conductive pin 60. The overlap region 54 region may have an area equivalent to at least 10%, optionally at least 20%, optionally at least 30%, optionally at least 40%, optionally around 50% of the area of the first metal layer 42.

[0113] The first metal layer 42 and the second metal layer 44 are discrete and separate components when being laid up during manufacturing of the wind turbine blade 20. The provision of the larger, second metal layer 44 may provide a lightning protection system 30 that is easier to assemble. For example, the metal layers 42, 44 are typically thin and fragile and so improving ease of handling the layers is important. The second metal layer 44 is not connected to any other components and so can be simply positioned in a mould during assembly. The first metal layer 42 may be secured to the rods 52 prior to assembly and so having this layer be smaller and easier to handle can improve the ease of installation while maintaining good performance of the lightning protection system. This is particularly advantageous in a wind turbine blade mould with complex curvatures.

[0114] In example arrangements, two first metal layers 42 are provided, one proximal an electrically conductive pin 60 proximal the tip end 22 of the blade 20 and another proximal an electrically conductive pin 60 proximal the root end 21 of the blade 20. The second metal layer 44 extends generally between the first metal layers 42. In alternative arrangements, only one first metal layer 42 may be provided. The second metal layer 44 has an area greater than that of the first metal layer 44. For example, the area of the or each first metal layer 42 may be no more than 10% of the area of the second metal layer 44. 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 42, the metal plate 50 and the plurality of metal rods 52 may be provided as a single component prior to assembly of the wind turbine blade 20. In this way, the first metal layer 42, metal plate 50 and metal rods 52 may be referred to as an electrical connection assembly 100.

[0115] Referring to Figure 4 to 6, various example arrangements of the electrical connection assembly 100 can be seen. In these figures, the lightning protection system 30 includes the first and second metal layers 42, 44 with an overlap region 54 therebetween. It will be appreciated that the second metal layer 44 may be omitted in alternative arrangements. The electrical connection assembly 100 of these figures is shown proximal the root end 21 of the blade 20. It will be appreciated an electrical connection assembly 100 may be positioned alternatively or additionally proximal the tip end 22 of the blade 20. In some arrangements, one or more electrical connection assemblies 100 may be positioned in various positions along the blade 20. For example, one or more assemblies 100 may be positioned between spanwise ends of the second metal layer 44, for example to provide attachment points for additional electrical connection points to the main surface protection layer.

[0116] The plurality of rods 52 may extend over the first metal layer 42 to define a first angle 56 relative to the chordwise axis 27 of the blade 20. The first angle 56 may be nonperpendicular and non-parallel relative to the chordwise axis 27. In the illustrated arrangement, the rods 52 extend generally toward the tip end 22 to define the first angle 56. In arrangements in which the assembly 100 is located toward the tip end 22 of the blade 20, the rods 52 may extend generally toward the root end 21 to define the first angle 56. The angled orientation of the rods 52 can provide effective electrical contact between the first metal layer 42 and the metal plate 50 without introducing electrical hot spots or high stress points into the metal layer 42. The first angle 56 may be an acute angle. The first angle 56 may be in the range of 10° to 60°, preferably 10° to 50°, preferably 20° to 50°, preferably 20° to 40, preferably 25° to 35°, preferably about 30°. The plurality of rods 52 may extend generally parallel to one another. In this way, each rod of the plurality of rods 52 may define the same angle, e.g. the first angle 56, relative to the chordwise axis 27 of the blade 20. The parallel arrangement of the rods 52 may reduce or remove a strain differential acting on the first metal layer 42 as the blade 20 bends, and may facilitate the conforming of the rods to the shape of the blade 20. The first metal layer 42 may be a mesh or apertured foil having a mesh pattern. The mesh pattern may be defined for example by an arrangement of strands that intersect each other. The mesh pattern may be described as a grid or lattice-like pattern. The strands of the mesh pattern may have a width in the range of 0.5 mm to 5 mm, optionally in the range of 1 mm to 3 mm, optionally in the range of 1.5 mm to 2 mm. The plurality of rods 52 may generally align with a direction of the mesh pattern. For example, as can be seen in Figure 4, the rods 52 may align with a plurality of strands of the mesh pattern that extend in the same direction. Arranging the rods 42 to follow the mesh pattern increases the contact area between the rods 42 and the mesh, thereby improving the effectiveness of current transfer between the first metal layer 42 and the plurality of rods 52.

[0117] The plurality of rods 52 may be spaced apart from one another. In some arrangements, the plurality of rods 52 may have a pitch that is substantially the same as a pitch of the mesh pattern of the first metal layer 42. Put another way, the rods 52 may be spaced apart to match the spacing between adjacent strands of the mesh pattern. The rods 52 may be spaced by the same intervals as strands of the mesh or apertured foil, increasing the contact area between the rods 52 and the mesh and thus improving current transfer between the first metal layer 42 and the plurality of rods 52. The pitch of the rods 52 may be in the range of 1 to 5 mm, optionally 2 mm, optionally 3 mm.

[0118] The plurality of metal rods 52 may make electrical contact with the first metal layer 42 at multiple points along the length of the rods 52. In this way, contact area is increased between the rods 52 and the first metal layer 42, improving the effectiveness of the lightning protection system. In some arrangements, the plurality of metal rods 52 follow a contour of the first metal layer 42 in a region where the metal rods 52 make contact with the first metal layer 42. Contact between the metal rods 52 and the first metal layer 42 is maintained irrespective of the contour of the metal layer 42, improving the electrical connection. The contour of the metal layer 42 may be defined by the contour in the outer surface of the blade shell 29 which is defined by the aerodynamic profile of the blade 20, e.g. the aerofoil shape.

[0119] The plurality of metal rods 52 each have a distal end 52a furthest from the metal plate 50. The distal ends 52a of the plurality of rods 52 may terminate over the first metal layer 42. In this way, the rods 52 do not extend beyond the overlap region 54 onto the second metal layer 44 in arrangements with the second metal layer 44. The distal ends 52a of one or more rods may not extend into the overlap region 54 in some embodiments, e.g. the distal ends 52a may terminate before extending into the overlap region 54. The rods 52 may define a length between the metal plate 50 from which they extend from and the distal end 52a. The length of the rods 52 may range between 5 cm to 50 cm. The distal ends 52a of the plurality of rods 52 may terminate over the first metal layer 42 in a staggered array, for example as can be best seen in Figures 4 to 6. In this arrangement, the lengths of the rods 52 decrease progressively from a longest rod to a shortest rod. The rods 52 may terminate in the staggered array such that the distal ends 52a of each rod 52 are generally aligned in a chordwise direction / along the blade chordwise axis 27 (e.g. are equidistant from the root end 21 and / or the tip end 22). The aligned distal ends 52a of each rod 52 may result in varying rod lengths when the rods 52 are parallel and at an angle to the blade chordwise di recti on / axis 27.

[0120] In alternative arrangements, the longest rod of the plurality of rods 52 may terminate furthest from the root end 21 of the blade 20 when the plurality of rods 52 are parallel and at an angle to the blade chordwise direction / axis 27. The shortest rod of the plurality of rods 52 may terminate closest to the root end 21 of the blade 20 in this arrangement. In arrangements in which the assembly 100 is positioned proximal the tip end 22 of the blade, the longest rod may terminate furthest from the tip end 22 of the blade, while the shortest may terminate closest to the tip end 22.

[0121] The staggered termination of the rods 52 may serve to distribute the current between the rods 52 and the metal layer 42 over a wider area, thereby reducing hot spots of current between the rods 52 and the first metal layer 42.

[0122] The metal plate 50 may be spaced from the first metal layer 42. The rods 52 extend between the spaced apart metal plate 50 and first metal layer 42 to maintain an electrical connection therebetween. The metal plate 50 does not locate on, over or extend through the first metal layer 42. The metal plate 50 can connect the first metal layer 42 to an electrical component 32 of the blade 20 without impacting the integrity of the first metal layer 42. Locating the metal plate 50 over the first metal layer 42 can reduce its integrity, e.g. since a connection point such as a bore for receiving a pin 60 may need to be machined into the metal layer. Spacing the metal plate 50 from the first metal layer 42 can simplify the positioning of components of the lightning protection system 30 during manufacture, since the metal layer 42 is easier to handle without the metal plate 50 located thereon. In addition, having the metal plate 50 spaced apart from the metal layers 42 can improve the accuracy of positioning the metal plate 50 in a mould for forming the blade shell 29.

[0123] In arrangements in which the second metal layer 44 is provided, the metal plate 50 may be spaced from the second metal layer 44. For example, the metal plate 50 does not locate on, over or extend through the second metal layer 44. Blade moulds typically have a surface having double curvature. Laying metal sheet material (i.e. the metal layer) 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, e.g. to align with one or more electrical components 32. This can lead to the metal sheet becoming wrinkled and / or stretched during lay-up. By providing a spaced apart metal plate 50 and / or a smaller metal layer 42 connected to the metal plate 50 via the rods 52, the smaller metal layer 42 and metal plate 50 can be precisely positioned with less chance of the first metal layer 42 becoming wrinkled and / or stretched. The larger second metal layer 44 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 plate. This may reduce the likelihood of wrinkling and / or stretching in the metal layers 42, 44.

[0124] The arrangement of Figure 4 includes one metal plate 50 provided adjacent a first metal layer 42. The plurality of rods 52 extend in a parallel direction from the metal plate 50 along the first metal layer 42 to provide an electrical coupling between the metal plate 50 and the first metal layer 42.

[0125] In alternative arrangements, for example as shown in Figure 5, the lightning protection system 30 may include a second metal plate 150 and a second plurality of rods 152 extending from the second metal plate 150. The second metal plate 150 may be provided proximal the first metal layer 42. The second plurality of metal rods 152 may extend over and contact the first metal layer 42 such that the first metal layer 42 is electrically connected to the second metal plate 150 via the second plurality of metal rods 152. The second metal plate 150 may be substantially the same as the first metal plate 52, for example the second metal plate 150 may be electrically coupled to an electrical component 32 of the lightning protection system 30, e.g. via an electrically conductive pin 60 extending therethrough. In some arrangements, the second metal plate 150 and the second plurality of rods 152 are positioned such that the second plurality of rods 152 are generally parallel with the plurality of rods 52. In alternative arrangements, e.g. as illustrated in Figure 5, the second metal plate 150 and the second plurality of rods 152 are positioned such that the second plurality of rods 152 are generally perpendicular to the plurality of rods 52. In this way, the second plurality of rods 152 may define the first angle 56 relative to the chordwise axis 27 in the opposite direction to the plurality of rods 52. Such an arrangement is advantageous when the mesh pattern of the first metal layer 42 includes perpendicularly extending strands, such that both sets of rods 52, 152 follow the mesh pattern of the first metal layer 42.

[0126] Referring to Figure 6, the lightning protection system 30 may include a first set of rods 52b and a second set of rods 52c that extend from the metal plate 50. The first set of rods 52b may include a plurality of rods that are generally parallel to one another. The second set of rods 52c may include a plurality of rods that are generally parallel to one another. The rods of the first set 52b may be generally perpendicular to the rods of the second set 52c. Put another way, the first set of rods 52b may extend in a direction that is generally perpendicular to a direction in which the second set of rods 52c extend. In this arrangement, the first and second set of rods 52b, 52c may each define the first angle 56 in opposite directions relative to the chordwise axis 27. This arrangement may improve the contact area between the metal plate 50 and the first metal layer 42, for example, the sets of rods 52b, 52c may be arranged to follow the mesh pattern. The rods of the first and second sets 52b, 52c may terminate such that the distal ends 52a of the rods in both sets 52b, 52c are generally aligned in a chordwise direction / along the blade chordwise axis 27 (e.g. are equidistant from the root end 21 and / or the tip end 22).

[0127] It will be appreciated that the arrangements discussed in relation to Figures 4 to 6 may be utilised in combination with one another, or in some cases, different arrangements of the electrical connection assembly 100 may be utilised in different locations along the blade 20.

[0128] Figure 7 shows a cross-sectional view of the plurality of rods 52 extending over the first metal layer 42. The rods 52 may define any cross-section, for example the rods 52 may have a circular, ovoid, rectangular or square cross-section. The rods 52 may define a generally uniform cross-section, e.g. the diameter of the rods 52 may be generally constant along their length. In some arrangements, the rods 52 may define a non- uniform cross-section. In the figures, the rods 52 have a generally circular cross- section. Generally circular rods provide for manufacturing robustness compared to, e.g. flattened rods, which may twist during manufacture. The contact area between the rods 52 and the first metal layer 42 may be reduced if a flattened rod becomes twisted. In contrast, if a rod 52 with a circular cross-section becomes twisted, the contact area between the first metal layer 42 and the rod 52 does not change and so effective electrical contact can be maintained. The rods 52 may each have a diameter in the range of 1 mm to 5 mm, optionally in the range of 1.5 to 3 mm, optionally around 2 mm. In the illustrated arrangement, the plurality of rods 52 all have substantially the same cross-section, e.g. the same shape and dimensions. In alternative arrangements, one or more of the plurality of rods 52 may define a different cross-section. In arrangements in which the second metal layer 44 is omitted. The rods 52 may be arranged to extend over an underside of the first metal layer when the assembly 100 is incorporated in the blade shell 29 (i.e. towards the inside of the blade with respect to the first metal layer). It will be appreciated that the rods 52 may be arranged differently in alternative arrangements, e.g. the rods 52 may overlay the first metal layer 42.

[0129] Figure 8 provides a cross-sectional view of an example arrangement of the overlap region 54 in the case that the first and second metal layers 42, 44 are provided. In this example, the rods 52 have been arranged to extend into the overlap region 54. The metal rods 52 may be sandwiched between the first metal layer 42 and the second metal layer 44 in the overlap region 54. Such an arrangement increases (e.g. effectively doubles) electrical contact between the rods 52 and the metal layers 42, 44, since the rods 52 contact the first metal layer 42 and the second metal layer 44 on two opposite sides of the rods 52. In this arrangement, the length of the rods 52 may be reduced without impacting the electrical contact between the metal layers 42, 44 and the metal plate 50, increasing the compactness of the assembly 100. In the illustrated arrangement, the rods 52 are arranged to overlay the first metal layer 42 and the rods 52 are arranged to extend beneath second metal layer 44 when incorporated into the blade shell 29. It will be appreciated that the rods 52 may be arranged differently in alternative arrangements, e.g. the rods 52 may overlay the second metal layer 44 and extend beneath the first metal layer 42.

[0130] The plurality of rods 52 may be secured to the first metal layer 42. In some arrangements, the plurality of metal rods 52 may be secured to the first metal layer 42 prior to providing the electrical connection assembly 100 to a mould. In some arrangements, the plurality of metal rods 52 may be secured to the first metal layer 42 by stitching 66, for example as shown in Figure 9. The stitching 66 may generally follow the mesh pattern of the first metal layer 42. The stitching 66 may be provided by a thread, e.g. a non-conductive material, such as yarn. In alternative arrangements, the plurality of metal rods 52 may be secured to the first metal layer 42 by an adhesive 68, for example as shown in Figure 10. In either case, the plurality of metal rods 52 may be positioned over the first metal layer 42 at the desired orientation, before adhesive 68 or stitching 66 is applied. In some arrangements, both stitching and adhesive may be utilised to ensure a highly robust connection. Connecting the rods 52 to the first metal layer 42 prior to manufacturing the blade 20 can improve the ease of handling of the electrical connection assembly 100, ensuring the components are in their desired position prior to laying up in a mould. In arrangements in which the second metal layer 44 is provided, the rods 52 may not be secured relative to the second metal layer 44. In this way, the electrical connection assembly 100 can be moved relative to the second metal layer 44 during assembly of the blade 20, e.g. to allow the electrical connection assembly 100 to be easily positioned as desired. In this case, the rods 52 may contact the second metal layer 44 as shown in Figure 8, but no fixed connection may be in place.

[0131] A pair of the plurality of rods 52 extending from the metal plate 50 may be formed from a single part looped around the metal plate 50. For example, Figure 11 shows a plurality of metal parts that have been looped or bent around an aperture or bore 50a of the metal plate 50 so as to provide a plurality of pairs of rods 52 that extend from the metal plate 50. The looped rods 52 are arranged to contact a face of the metal plate 50 to provide the electrical connection therebetween. Arranging the rods 52 in such a way can provide for a simpler means of manufacturing the electrical connection assembly 100. The looped rods 52 can provide a compact connection point to the metal plate 50, increasing the structural integrity of the plate 50 itself.

[0132] In some arrangements, the metal plate 50 is formed from two parts 50b, 50c which sandwich the rods 52, for example as can be seen in the cross-sectional view of Figure 12. The sandwiching of the rods 52 between two parts 50b, 50c can increase the contact area between the rods 52 and the metal plate 50, thereby increasing the effectiveness of the lightning protection system 30. In some arrangements, the looped portion of the rods 52 are arranged to contact the two parts 50b, 50c on opposing sides of the rods 52. The two parts 50b, 50c of the metal plate 50 may be generally disc shaped. The rods 52 are arranged to contact the generally planar surface of the two parts 50b, 50c of the metal plate 50.

[0133] The plurality of metal rods 52 and / or the first metal layer 42 and / or the metal plate 50 (e.g. both parts 50b, 50c) and / or the second metal layer 44 (if present) may be formed from the same material as one another. This mitigates the risk of galvanic corrosion occurring. In some arrangements, one or more of the metal rods 52, the first metal layer 52, the metal plate 50 and the second metal layer 44 are formed from aluminium. It will be appreciated that the metal rods 52 and / or the first metal layer 42 and / or the metal plate 50 (e.g. both parts 50b, 50c) and / or the second metal layer 44 (if present) may be formed from a different conductive material in alternative arrangements.

[0134] The plurality of rods 52 may be soldered to the metal plate 50. For example, the rods 52 may be soldered between the two parts 50b, 50c of the metal plate 50. In some arrangements, the looped portion of the rods 52 is soldered to the metal plate 50. The plurality of rods 52 may be soldered to the metal plate 50 using a zinc solder. The use of a zinc solder is particularly effective when the metal plate 50 and the rods 52 are formed from aluminium, e.g. since zinc reduces the risk of galvanic corrosion of aluminium. The plurality of rods 52 may be soldered to the metal plate 50 prior to manufacture of the blade 20. In some examples, the rods 52 are secured to the metal plate 50 prior to securing to the first metal layer 42. In alternative arrangements, the rods 52 may not be looped and soldered to the metal plate 50 and may instead be clamped between two parts of the metal plate 50 which may then be secured together, e.g. via one or more fasteners.

[0135] Figure 12 shows an example cross-section of a wind turbine blade 20 having an electrical connection assembly 100 in the blade shell 29. It will be appreciated that the wind turbine blade shell 29 is formed from structural components 48 not discussed in detail here. The structural components 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. The blade shell 29 includes an exterior surface 29a and an interior surface 29b. The exterior surface 29a of the blade shell 29 defines an outer surface of the blade 20.

[0136] The electrically conductive pin 60 may be arranged to extend through an aperture or bore 50 of the metal plate 50. The electrically conductive pin 60 may comprise a head 62 coupled to a shank 64. The shank 64 may extend through the metal plate 50 and the structural components 48. The head 62 may have an underside that is in contact with the metal plate 50. This may create an intimate electrical connection between the electrically conductive pin 60 and the metal plate 50.

[0137] As illustrated in Figure 12, the metal plate 50 may be located towards an inside of the blade 20 (e.g. toward the inside surface 29b of the blade shell 29) with respect to the first metal layer 42. Put another way, the metal plate 50 may be disposed further from the exterior surface 29a of the blade shell 29 than is the first metal layer 42. In the figure, the first metal layer 42 is provided adjacent the external surface 29a of the blade shell 29. In the figures, a portion of the metal rods 52 contact an underside of the first metal layer 42 (i.e. the rods are nearer the inside of the blade than the metal layer). The metal rods 52 may follow an S-shaped curve between the first metal layer 42 and the metal plate 50. In this way, the rods 52 may each include a first portion, and a second portion located at different locations relative to the exterior surface 29a of the blade shell 29. The first portion of the respective rod 52 may include the end fixed to the metal plate 50. The second portion of the respective rod may include the distal end 52a. The second portion of the rods contacts the first metal layer 42. The first portion of the respective rod 52 may be located further from the exterior surface 29a than the second portion. Put another way, the first portion of the respective rod 52 may be located closer to the inside surface 29b of the blade shell 29 than the second portion. The rods 52 may each include a bent or curved portion between the first and second portion so as to transition therebetween, e.g. to define the S-shape. The S-shaped rods 52 can provide a continuous electrical connection between the metal plate 50 and the first metal layer 42 while facilitating the metal plate 50 being submerged deeper into the blade shell 29, e.g. for locating closer to the one or more electrical components 32 inside the blade shell 29. At least one of the plurality of rods 52 may be crimped to follow the S-shaped curve. The rods 52 may be arranged to define any suitable shape to facilitate a continuous electrical connection between the metal plate 50 and the first metal layer 42.

[0138] The wind turbine blade 20 includes an electrical component 32 electrically connected to the first metal layer 42. 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 32 may be a down conductor cable 38 or receptor or other component of the lightning protection system 30, forming a direct electrical connection with the electrically conductive pin 60. The electrical component 32 is electrically connected to the first metal layer 42 via the electrically conductive pin 60, the metal plate 50 and the plurality of metal rods 52. 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 surface 29b of the blade shell 29.

[0139] Figures 13A to 13E show a method of manufacturing a wind turbine blade 20 having a blade shell 29 with a lightning protection system 30. The first metal layer 42, plurality of rods 52 and metal plate 50 may be provided as a single component, collectively referred to as an electrical connection assembly 100. The assembly 100 may be incorporated into different lightning protection systems 30 and / or different wind turbine blade 20 designs. A common assembly 100 comprising a metal plate 50, a plurality of rods 52 and a first metal layer 42 each having set dimensions may be manufactured and used in multiple wind turbine blade designs.

[0140] The method of Figures 13A to 13E includes the provision of a second metal layer 44 that has an area greater than that of the first metal layer 42. In this case, the second metal layer 44 may be cut to size rather than needing bespoke positions for the metal plate(s) 50 as these are not within the second metal layer. This may reduce the cost of manufacture and design as a common assembly 100 design can be used for multiple blades, and the second metal layer 44 can be cut from a simple roll of sheet material devoid of integral plates 50. It will be appreciated that in alternative examples, the second metal layer 44 may be omitted. In this case, the first metal layer 42 may have a greater area.

[0141] The connection assembly 100 and the second metal layer 44 are arranged on a mould surface 72 of a mould 70 for forming the blade shell 29 (or half shell) of a wind turbine blade. The connection assembly 100 and second metal layer 44 are positioned on the mould surface 72 such that the first metal layer 42 and the second metal layer 44 overlap in the overlap region 54.

[0142] As shown in Figures 13A to 13E, the second metal layer 44 is first positioned on the mould surface 72 as shown in Figure 13A. In this case, the second metal layer 44 may be provided closer to an exterior surface 29a of the resulting blade shell 29 than the first metal layer 42. In these figures, the second metal layer 44 is provided as a single layer. However, it will be appreciated that the second metal layer 44 may be provided as a plurality of second metal layer portions having an overlap to create electrical connection between them.

[0143] Once the second metal layer 44 is positioned correctly, the connection assembly 100 is positioned thereover as shown in Figure 13B. The assembly 100 may be oriented in the mould 70 such that the plurality of rods 52 extend between the first metal layer 42 and the second metal layer 44, e.g. such that the rods 52 are proximal the mould surface 72 relative to the first metal layer 42. In this way, the rods 52 may extend to be sandwiched between the first and second metal layers 42, 44 in the overlap region 54. In the illustrated method, only one assembly 100 is provided. It will be appreciated that a plurality of assemblies 100 may be provided in alternative arrangements. For example, at least one assembly may be provided at opposite ends of the second metal layer 44, e.g. such that one located proximal each of the root end 21 and the tip end 22 of the resulting blade 20.

[0144] The assembly 100 may also be positioned between the spanwise ends of the layer 44 to provide attachment points for additional electrical connection points to the main surface protection layer 44.

[0145] In alternative arrangement without a second metal layer, the connection assembly 100 comprises the plurality of rods 52 and metal plate 50. The first metal layer 42 (main metal layer) is laid up as on the mould and then the connection assembly 100 is positioned thereover, similar to the steps shown in Figures 13A and 13B.

[0146] One or more structural components 48 are provided. The structural components 48 are arranged on the electrical connection assembly 100 and the second metal layer 44 as shown in Figure 13C. As described previously, it will be appreciated that the structural components 48 may include fibre composite layers, core materials such as foam, and similar.

[0147] The structural components 48 (e.g. the fibre composite layers), the second metal layer 42 and the electrical connection assembly 100 are consolidated under vacuum in the mould 70 to form a blade shell 29 of a wind turbine blade 20. This may involve covering the mould 70, containing the structural components 48, the second metal layer 44 and the assembly 100, in a vacuum bag 75 and applying a vacuum pressure, for example through a valve 76 as shown in Figure 13D. The structural components 48 may subsequently be cured, e.g. under heat and / or pressure. Once consolidated, a blade shell 29 is formed comprising a lightning protection system 30 having an electrical connection assembly 100 and a second metal layer 44 that overlaps the first metal layer 42 to define an overlap region 54 as shown in Figure 13E. In some examples, the structural components 48 may comprise fibre layers (not shown) which may be dry fibre preforms, or similar. In this case the method may include introducing a resin to the mould 70 to infiltrate the consolidated fibre composite layers, the second metal layer 44 and the electrical connection assembly 100 under vacuum.

[0148] The plurality of metal rods 52 may be secured to the first metal layer 42 prior to arranging the electrical connection assembly 100 on the mould surface 72. The plurality of metal rods 52 may be secured by an adhesive 68 and / or by stitching 66 to the first metal layer 42, as discussed in reference to Figures 9 and 10. The adhesive 68 may be different than the resin material. The plurality of metal rods 52 may be fixed to the metal plate 50 prior to arranging the electrical connection assembly 100 on the mould surface 72, for example via looping the rods 52 around the plate 50 and soldering the rods 52 to the plate 50 as described above. The electrical connection assembly 100 may be completely connected to transfer electrical current between the metal plate 50 and the first metal layer 42 prior to arranging the assembly 100 on the mould surface 72. The risk of the rods 52 disconnecting after manufacture is therefore reduced. Alternatively, the rods 52 and / or the first metal layer 42 and / or the metal plate 50 may be separable prior to incorporation into the mould 70. As such, one or more of the rods 52, the first metal layer 42 and the metal plate 50 may be separate components of the assembly 100 prior to lay up in the mould for forming the blade shell 29. The components of the assembly 100 may be connected in-situ in the mould 70.

[0149] In some arrangements, the bore or aperture 50a of the metal plate 50 may be provided prior to laying the assembly 100 up in the mould 70. For example, the metal plate 50 may be cast with a bore 50a or a bore 50a may be machined therethrough. In this case, a hole may be made through the structural components 48 to align with the bore 50a after removal of the blade shell 29 from the mould 70. A hole may also be made through the electrical component 32. After forming the hole, an electrically conductive pin 60 can be inserted therethrough to provide electrical contact between the plate 50 and the electrical component 32. In this way, the electrically conductive pin 60 serves to electrically connect the electrical component 32 to the second metal layer 44 via the first metal layer 42, plurality of rods 52 and the metal plate 50. In some arrangements, the metal plate 50 may be provided in the assembly 100 without an aperture. In this case, once removed from the mould 70, a hole may be made through the metal plate 50, the structural components 48 and optionally the electrical component 32. This may be achieved using a drill, however it will be appreciated that any suitable method of manufacture may be used.

[0150] The method may include bending the plurality of metal rods 52 and / or the first metal layer 42 to follow a contour of the mould surface 72. The contour of the mould surface 72 may define a generally aerofoil profile. The rods 52 and / or the first metal layer 42 may be bent to follow the contour of the mould surface prior to securing the rods 52 to the first metal layer 42. Such an arrangement ensures the assembly 100 follows the contour of the blade shell 29, improving the ease of manufacture of the shell 29 and reducing the risk of components being misaligned. Bending the rods 52 prior to manufacture of the blade 20 is particularly important as the rods 52 may be formed of a rigid material that will not conform during manufacture of the blade 20 without an external force. The first metal layer 42 may be substantially thin so as to conform with the curvature of the rods 52 once the rods 52 are secured thereto.

[0151] 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, wherein the lightning protection system comprises: a first metal layer; a metal plate configured to electrically connect to one or more electrical components; and a plurality of metal rods secured to the metal plate and arranged to extend therefrom; wherein the plurality of metal rods extend over and contact the first metal layer such that the first metal layer is electrically connected to the metal plate via the plurality of metal rods.

2. A wind turbine blade according to claim 1 , wherein the blade defines a root end, a tip end, and a chordwise axis extending between a leading edge and a trailing edge of the blade, and wherein the plurality of rods extend over the first metal layer so as to define a first angle relative to the chordwise axis, said first angle being nonperpendicular and non-parallel relative to the chordwise axis.

3. A wind turbine blade according to any claim 1 or claim 2, wherein the plurality of rods extend generally parallel to one another.

4. A wind turbine blade according to any preceding claim, wherein the first metal layer is a mesh or apertured foil having a mesh pattern, wherein the plurality of rods generally align with a direction of the mesh pattern.

5. A wind turbine blade according to claim 4, wherein the plurality of rods are spaced apart and have a pitch that is substantially the same as a pitch of the mesh pattern.

6. A wind turbine blade according to any preceding claim, wherein the lightning protection system comprises a second metal plate and a second plurality of rods extending from the second metal plate, preferably wherein the second plurality of metal rods extend over and contact the first metal layer such that the first metal layer is electrically connected to the second metal plate via the second plurality of metal rods.

7. A wind turbine blade according to any preceding claim, wherein the metal plate is spaced from the first metal layer.

8. A wind turbine blade according to any preceding claim, wherein the metal rods follow an S-shaped curve between the first metal layer and the metal plate, preferably wherein the metal plate is disposed further from an exterior surface of the blade shell than is the first metal layer.

9. A wind turbine blade according to any preceding claim, further comprising a second metal layer having an area greater than the first metal layer, wherein the first metal layer is arranged to define an overlap region between the first and second metal layers.

10. A wind turbine blade according to claim 9, wherein the metal rods are sandwiched between the first metal layer and the second metal layer in the overlap region.

11. A wind turbine blade according to any preceding claim, wherein a pair of the rods extending from the metal plate are formed from a single part looped around the metal plate.

12. A wind turbine blade according to any preceding claim, wherein the plurality of metal rods make electrical contact with the first metal layer at multiple points along the length of the rods.

13. A wind turbine blade according to any preceding claim, wherein the plurality of metal rods follow a contour of the first metal layer in a region where the metal rods make contact with the first metal layer.

14. A wind turbine blade according to any preceding claim, wherein the metal rods and the first metal layer and / or the metal plate comprise the same material.

15. A wind turbine blade according to any preceding claim, wherein the plurality of rods each have a distal end furthest from the metal plate, and the distal ends of the rods terminate over the first metal layer in a staggered array.

16. A method of manufacturing a blade shell of a wind turbine blade with a lightning protection system, the method comprising: providing a mould surface; providing an electrical connection assembly of the lightning protection system, comprising a first metal layer, a metal plate, and a plurality of metal rods secured to the metal plate and arranged to extend therefrom, the plurality of metal rods extending over and contacting the first metal layer; providing a second metal layer of the lightning protection system, the second metal layer having an area greater than the first metal layer; arranging the second metal layer and the connection assembly on the mould surface such that the first metal layer and the second metal layer overlap in an overlap region; providing a plurality of fibre composite layers; and consolidating the fibre composite layers, the second metal layer and the electrical connection assembly under vacuum in the mould to form a blade shell of a wind turbine blade.

17. A method according to claim 16, wherein the electrical connection assembly is positioned between spanwise ends of the second metal layer.

18. A method according to claim 16 or claim 17, wherein the plurality of metal rods are secured to the first metal layer prior to arranging the electrical connection assembly on the mould surface, preferably wherein the plurality of metal rods are secured by an adhesive or by stitching, and preferably wherein the method further comprises introducing a resin to infiltrate the consolidated fibre composite layers, the second metal layer and the electrical connection assembly under the vacuum.

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