Wind turbine blade with lightning receiver

Abstract

The invention provides a wind turbine blade shell portion for a wind turbine blade, the blade shell portion comprising: a structural element providing structural strength to the blade shell portion and comprising carbon fibers embedded in a polymer matrix; a lightning receiver exposed at an outer surface of the blade shell portion and extending toward the structural element; and a conductive adhesive to attach the lightning receiver to the structural element. A method for manufacturing such a blade shell portion is also provided.

Description

Background Art

[0001] As the size of wind turbines and wind turbine blades increases, the risk of wind turbines being struck by lightning also increases. Therefore, there is an increasing interest in providing wind turbines, and in particular wind turbine blades, with lightning protection measures.

[0002] Lightning protection measures in wind turbine blades typically include metal lightning receptors exposed at the outer surface of the blade to attract lightning in the event of a lightning strike. The lightning receptors are typically grounded via a metal conductor to prevent lightning current from flashing between less conductive parts, causing heating and possible damage to parts. Typically, the blade includes a downconductor cable that extends substantially the entire length of the blade. The downconductor cable is typically connected to several lightning receptors arranged along the length of the blade to reduce the risk of flashover during a lightning strike.

[0003] As blade sizes increase, there is also a need to manufacture blades with increased stiffness and relatively little weight gain. One way to achieve these properties is to combine various types of fibers in the laminate of the blade. For example, combining glass fibers and carbon fibers or manufacturing certain components solely from carbon fiber composites is an option. However, large amounts of carbon fibers in composite structural elements (such as spar caps) increase the risk of flashovers because carbon fibers are sufficiently conductive that lightning currents will flow in the carbon spar caps during a lightning strike, which can cause significant heating and lead to structural damage to the carbon fiber composite and surrounding parts. It may also cause delamination between different types of composites, such as the interface between a carbon fiber composite and a glass fiber composite, due in part to their different mechanical, thermal, and electrical properties.

[0004] Therefore, it is increasingly important to provide lightning protection measures that reduce the risk of flashover of lightning current into conductive materials such as carbon fiber composites within wind turbine blades. Furthermore, it is desirable that such measures are relatively easy to implement. Summary of the invention

[0005] The present invention aims to alleviate one or more of the above problems.

[0006] In a first aspect, the invention provides a wind turbine blade shell portion for a wind turbine blade, the blade shell portion comprising: - a structural element which provides structural strength to the blade shell portion and which comprises carbon fibres embedded in a polymer matrix, a lightning receptor exposed at the outer surface of the blade shell portion and extending towards the structural element, and - An electrically conductive adhesive which attaches the lightning receptor to the structural element.

[0007] The present invention reduces the risk of lightning current flashing over to conductive materials, such as carbon fiber composites within a wind turbine blade, in the event of a lightning strike on the blade.

[0008] In some embodiments, the conductive adhesive adhesively attaches the lightning receptor to the structural element, rather than the conductive adhesive holding the lightning receptor, for example by using threads. This can provide a secure bond between the lightning receptor and the structural element.

[0009] In some embodiments, the structural element is a spar cap.In some embodiments, the spar cap is in contact with a shear web, such as a shear web extending between the spar cap and another spar cap located in another part of the blade shell portion.

[0010] In some embodiments, the structural element comprises one or more pultrusions comprising carbon fibers embedded in a polymer matrix, and a conductive adhesive attaches the lightning receptor to the carbon fibers in one or more of the pultrusions. This provides electrical contact from the outer surface of the blade and the pultrusions, reducing the risk of flashover into the pultrusions.

[0011] In some embodiments, the structural element comprises: - one or more pultrusions comprising carbon fibres embedded in a polymer matrix, and one or more fiber layers comprising carbon fibers, the one or more fiber layers being positioned between the outer surface of the blade shell portion and one or more of the pultrusions and being adhesively attached to and in electrical contact with at least one of the one or more pultrusions, The conductive adhesive attaches the lightning receptors to the carbon fibers in one or more of the fiber layers.

[0012] In such embodiments, electrical contact between the outer surface of the blade and the pultrusion is provided via the one or more fiber layers.As further described below in relation to the second aspect, the one or more fiber layers partially act as sacrificial layers which introduce tolerances when the recess is then formed.

[0013] In some embodiments, the structural element comprises two or more pultrusions, and the one or more fiber layers provide potential equalization between at least two of the pultrusions. When the one or more fiber layers extend across several pultrusions, the potential between the pultrusions is equalized, which reduces the risk of flashover between the pultrusions and reduces resistance by ensuring that the current is distributed across multiple pultrusions.

[0014] In some embodiments, the structural element comprises: - one or more pultrusions comprising carbon fibres embedded in a polymer matrix, and a metal element, such as a metal mesh, positioned between the outer surface of the blade shell portion and one or more of the pultrusions and in electrical contact with at least one of the one or more pultrusions, The conductive adhesive attaches the lightning receptor to a portion of the metal element.

[0015] In such embodiments, electrical contact between the outer surface of the blade and the pultrusion is provided by a metal element, such as a metal mesh, such as a copper mesh. Similar to the one or more fiber layers described above, the metal element may partially act as a sacrificial layer that introduces tolerance when the recess is then formed.

[0016] In some embodiments, the metal element further extends to one or more other sides of the pultrusion. In some embodiments, the metal element also surrounds all sides of the pultrusion. In all cases, the contact area between the pultrusion and the metal element is increased to provide more electrical connection between the pultrusions, which provides further potential equalization between the pultrusions. This further reduces the risk of damage to the pultrusion by lightning current in the event of a lightning strike.

[0017] In some embodiments, the structural element comprises two or more pultrusions and the metal element provides potential equalization between at least two of the pultrusions. When the metal element extends across several pultrusions, the potential between the pultrusions is equalized, which reduces the risk of flashover between the pultrusions and also reduces resistance by ensuring that the current is distributed across multiple pultrusions.

[0018] In some embodiments, the lightning receptor adjoins a lightning shunt forming part of an outer surface of the blade shell portion.The connection between the lightning shunt and the lightning receptor and the connection between the lightning receptor and the structural element reduces the risk of flashover from the lightning shunt to the structural element.

[0019] In some embodiments, the lightning receptor is located at a first distance from the lightning shunt. This ensures that the lightning shunt is not damaged when the lightning receptor is inserted. This is described in more detail in relation to the second aspect of the invention.

[0020] In some embodiments, the first distance is at most 20 mm, such as at most 10 mm, such as at most 5 mm. In some embodiments, the first distance is in the range of 2-20 mm, such as in the range of 2-15 mm, such as in the range of 3-12 mm, such as in the range of 3-10 mm. This distance provides a good compromise between ease of insertion of the lightning receptor and ease of allowing the lightning current from the lightning shunt to jump from the lightning shunt to the lightning receptor connecting the outer surface to the structural element.

[0021] In some embodiments, the lightning diverter is a segmented lightning diverter.

[0022] In some embodiments, the conductive adhesive material has a conductivity less than 1.0 10 -5 Ohm-meter, such as less than 7.0 10 -6 Ohm-meter, such as less than 5.0 10 -6 Ohm-meter, such as less than 3.0 10 -6 Resistivity in ohm-meters.

[0023] In some embodiments, the conductive adhesive material has a thermal conductivity of at least 0.5 10 -6 Resistivity in ohm-meters.

[0024] In some embodiments, the conductive adhesive material has a relative humidity of 1.0 10 -6 Ohm-meter to 1.010 -5 Ohm-meter range, such as 2.0 10 -6 Ohm-meter to 6.0 10 -6 Such values ​​have been found to provide a good compromise between the resistivity of the conductive adhesive and its bond strength.

[0025] Adhesives such as Loctite Ablestik 57C or Loctite Ablestik 8200C offer a good balance between adhesion and conductivity.

[0026] In some embodiments, the perimeter of the lightning receptor is surrounded by a sealant at the outer surface. This protects the structural element from water.

[0027] In some embodiments, the area of ​​the lightning receptor at the outer surface of the blade shell portion is at least 5 cm 2 .

[0028] In some embodiments, the area of ​​the lightning receptor at the outer surface of the blade shell portion is at most 50 cm 2 .

[0029] In some embodiments, the area of ​​the lightning receptor at the outer surface of the blade shell portion is 10-30 cm 2 within the range.

[0030] The area of ​​the lightning receptor at the outer surface defines a cross-sectional area of ​​the lightning receptor. In some embodiments, the lightning receptor has a cross-sectional area at the outer surface that is less than the cross-sectional area of ​​the first recess in which the lightning receptor is placed. This embodiment intentionally provides space for an adhesive for sealing the outer surface around the lightning receptor. In some embodiments, the ratio between the cross-sectional area of ​​the receptor at the outer surface and the cross-sectional area of ​​the first recess is less than 0.95, such as less than 0.9, such as less than 0.8. In some embodiments, the ratio between the cross-sectional area of ​​the receptor at the outer surface and the cross-sectional area of ​​the first recess is in the range of 0.8-0.95.

[0031] In some embodiments, the structural element is a spar cap.

[0032] In some embodiments, the fibers in the pultrusion are substantially only carbon fibers. In some embodiments, the pultrusion includes both carbon fibers and other types of fibers, such as glass fibers and / or steel fibers.

[0033] In some embodiments, the blade shell portion comprises a wind turbine blade pressure side shell half and / or a wind turbine blade suction side shell half.In some embodiments, the blade shell portion is a complete wind turbine blade shell comprising a pressure side and a suction side.

[0034] A second aspect of the invention provides a method of attaching a lightning receptor to a wind turbine blade shell portion of a wind turbine blade to provide electrical contact between an outer surface of the blade shell portion and a structural element in the blade shell portion. The method comprises: - providing a blade shell portion comprising a structural element comprising carbon fibres embedded in a polymer matrix, - providing a first recess extending from the outer surface of the blade shell part towards the structural element, - applying a conductive adhesive into the recess, - inserting the lightning receptor into the recess so that the conductive adhesive attaches the lightning receptor to the structural element, and - Curing of adhesive.

[0035] The method makes it relatively easy to provide electrical connections from the outer surface of the blade shell portion and the structural element.

[0036] In some embodiments, the structural element comprises one or more pultrusions comprising carbon fibers embedded in a polymer matrix, and providing the recess exposes a portion of one or more of the pultrusions without extending into any of the pultrusions.

[0037] In some embodiments, the structural element comprises: - one or more pultrusions comprising carbon fibres embedded in a polymer matrix, and one or more fiber layers comprising carbon fibers, the one or more fiber layers being positioned between the outer surface of the blade shell portion and one or more of the pultrusions and being adhesively attached to and in electrical contact with at least one of the one or more pultrusions, The recess extends into one or more of the fiber layers, but not into any of the one or more pultrusions, and the conductive adhesive attaches the lightning receptor to the carbon fibers in the one or more of the fiber layers.

[0038] In some embodiments, the structural element comprises: - one or more pultrusions comprising carbon fibres embedded in a polymer matrix, and a metal element, such as a metal mesh, positioned between the outer surface of the blade shell portion and one or more of the pultrusions and in electrical contact with at least one of the one or more pultrusions, The recess exposes a portion of the metal element without extending into any of the one or more pultrusions, and the conductive adhesive attaches the lightning receptor to the exposed portion of the metal element.

[0039] In some embodiments, the lightning receptor, after insertion, abuts a lightning diverter forming part of the outer surface of the blade shell portion.

[0040] In some embodiments, the blade shell portion complies with the IEC 61400-24 standard (2019 edition).

[0041] In some embodiments, the lightning receptor and the conductive adhesive can withstand a lightning current of at least 10 kA when they are attached to the structural element, such as a rating in the range of 10-300 kA, such as in the range of 10-200 kA, such as in the range of 10-100 kA. In some embodiments, the blade shell portion complies with the IEC 61400-24 standard (2019 edition).

[0042] In some embodiments, the lightning receptor and the conductive adhesive can withstand a lightning strike of at least 50 coulombs of charge when they are attached to the structural element, such as a charge in the range of 50-1000 coulombs, such as a charge in the range of 50-300 coulombs, such as a lightning strike in the range of 100-200 coulombs. In some embodiments, the blade shell portion complies with the IEC 61400-24 standard (2019).

[0043] In some embodiments, the lightning receptor is located at a first distance from the lightning shunt after insertion, wherein the first distance is at most 20 mm, such as in the range of 2-20 mm, such as in the range of 3-10 mm.

[0044] In some embodiments, after inserting the lightning receptor into the first recess, there is a second recess at the outer surface around the lightning receptor, and the method further includes filling the second recess around the lightning receptor with a sealant.

[0045] In some embodiments, the conductive adhesive material has a relative humidity of less than 1.0 10 -5 Ohm-meter resistivity, such as less than 7.0 10 -6 Ohm-meter, such as less than 5.0 10 -6 Ohm-meter, such as less than 3.0 10 -6 Ohm-meter, such as less than 2.0 10 -6 Ohm-meter, such as less than 1.0 10 -6 Resistivity in ohm-meters.

[0046] In some embodiments, the structural element is a spar cap.

[0047] In some embodiments, the fibers in the pultrusion are substantially only carbon fibers. In some embodiments, the pultrusion includes both carbon fibers and other types of fibers, such as glass fibers and / or steel fibers.

[0048] In some embodiments, the blade shell portion comprises a wind turbine blade pressure side shell half and / or a wind turbine blade suction side shell half.In some embodiments, the blade shell portion is a complete wind turbine blade shell comprising a pressure side and a suction side.

[0049] The advantages of various features of embodiments of the second aspect are described in conjunction with the first aspect.Other features from embodiments of the first aspect of the invention may be included in embodiments of the second aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] The present invention will be explained in detail below with reference to the embodiments shown in the drawings.

[0051] Figure 1 A wind turbine is shown.

[0052] Figure 2 A wind turbine blade is shown.

[0053] Figure 3 A cross section of a wind turbine blade including structural elements is shown.

[0054] Figure 4 A top view of a blade shell section of a wind turbine blade comprising structural elements is shown.

[0055] Figure 5AA top view of a blade shell portion with a lightning receptor according to the invention is shown.

[0056] Figure 5B Shows Figure 5A Detail of the top view shown in .

[0057] Figure 5C-5E A cross section of a blade shell portion according to the invention is shown.

[0058] Figures 6A-6D A method according to the invention is shown.

[0059] Figures 7A-7D A method according to the invention is shown.

[0060] Fig. 8A A top view of a blade shell portion with a lightning receptor according to the invention is shown.

[0061] Figure 8B Shows Figure 5A Detail of the top view shown in .

[0062] Figure 8C A cross section of a blade shell portion according to the invention is shown. DETAILED DESCRIPTION

[0063] Embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. The same reference numerals may refer to the same elements throughout. The accompanying drawings illustrate selected ways of implementing the present invention and should not be interpreted as limiting the scope of the claims. The accompanying drawings are not necessarily drawn to scale.

[0064] Figure 1 A conventional modern upwind wind turbine 2 according to the so-called "Danish concept" is shown, having a tower 4, a nacelle 6 and a rotor with a substantially horizontal rotor axis. The rotor comprises a hub 8 and three blades 10 extending radially from the hub 8, each blade 10 having a blade root 16 closest to the hub and a blade tip 14 farthest from the hub 8.

[0065] Figure 2 A schematic diagram of a wind turbine blade 10 is shown. The wind turbine blade 10 has the shape of a conventional wind turbine blade and includes a root region 30 closest to the hub, a profile or airfoil region 34 farthest from the hub, and a transition region 32 between the root region 30 and the airfoil region 34. The blade 10 includes a leading edge 18 facing the direction of rotation of the blade 10 when the blade is mounted on the hub, and a trailing edge 20 facing the opposite direction of the leading edge 18. The outermost point of the blade 10 is the tip end 15, which is located opposite the root end 31 attached to the wind turbine hub 8.

[0066] The airfoil region 34 (also referred to as the profile region) of the wind turbine blade has an ideal or nearly ideal blade shape with respect to generating lift, while the root region 30 has a substantially circular or elliptical cross section for structural considerations, for example, which makes it easier and safer to mount the blade 10 to the hub. The diameter (or chord) of the root region 30 may be constant or may vary along the root region 30. The transition region 32 has a transition profile that gradually changes from the circular or elliptical shape of the root region 30 to the airfoil profile of the airfoil region 34. The chord length of the transition region 32 typically increases with increasing distance from the hub. The airfoil region 34 has an airfoil profile with a chord extending between the leading edge 18 and the trailing edge 20 of the blade 10. The chord generally decreases with increasing distance from the hub.

[0067] The shoulder 40 of the blade 10 is defined as the location where the blade 10 has its maximum chord length. The shoulder 40 is typically located at the boundary between the transition region 32 and the airfoil region 34. Figure 2 Also shown is the longitudinal extension L of the blade 10 B .L B The longitudinal axis of the blade 10 is also represented.

[0068] The blade is typically made of a pressure side shell portion 36 and a suction side shell portion 38 that are glued to each other along a join line at the leading edge 18 and the trailing edge 20 of the blade 10 .

[0069] Figure 3 A cross section II of a wind turbine blade 10 is schematically shown (see Figure 2 ). Cross section II shows Figure 2 The suction side shell portion 38, the pressure side shell portion 36, the leading edge 18 and the trailing edge 20 of the wind turbine blade 10 are shown in FIG. In addition, the wind turbine blade 10 includes a structural element 45 (such as a spar cap) located in the suction side portion 38 of the shell and a spar cap 41 located in the pressure side portion 36 of the blade 10. The shear web 55 extends between the two spar caps 41, 45 and provides resistance to shear forces. The following is further described in detail in conjunction with different embodiments of the present invention. Figure 3 The portion indicated in 65. Figure 3 An outer surface 39 of the suction side portion 38 is also indicated.

[0070] Carbon fiber composites are used in wind turbine blades in part because they are lighter and stiffer by volume than glass fiber composites. Structural elements, such as spar caps, often include carbon fiber composite materials, which can improve the overall mechanical properties of the blade. However, carbon fiber composites can conduct current during a lightning strike, albeit poorly, and are therefore more susceptible to flashover than, for example, glass fiber composites. Flashover causes heating that can damage the carbon fiber composite and other nearby parts, such as glass fiber composite materials.

[0071] Figure 4 A portion of a suction side blade shell 38 of a wind turbine blade is schematically shown. Figure 4 The outer surface 39 of the blade shell 38 facing the suction side (see Figure 3 ). A structural element 45, such as a spar cap, is located below the outer surface 39 of the suction side shell portion 38. In some embodiments, the structural element 45 is separated from the outer surface 39 by a gel coating, and in some embodiments, by a composite material and / or one or more metal elements. The present invention provides electrical contact between the outer surface 39 and the structural element 45, thereby reducing the risk of a lightning strike causing the structural element 45 to flash over and damage the wind turbine blade.

[0072] Figure 5A A portion of a blade shell portion 11 according to the invention is shown, in this example a portion of a suction side blade shell 38. A lightning receptor 53 is exposed at the outer surface of the blade. In this example, the lightning receptor 53 is located above a spar cap 45 which is located on the outer surface 39 of the suction side blade shell 38 (see FIG. Figure 3 ) below. The lightning receptor 53 attracts lightning in the event of a lightning strike, thereby at least reducing the risk of lightning causing a flashover near the lightning receptor 53. Figure 5A The area 56 indicated in Figure 5B , which is shown enlarged in FIG. 5 , shows a lightning receptor 53 arranged above the spar cap 45 located in the suction side blade shell 38 .

[0073] Figure 5C Shows Figure 5A The portion 65 of the cross section of the blade shell portion 11 shown in FIG. Figure 3 ). Portion 65 includes structural element 45, a portion of shear web 55, outermost gel coat 50, outer fiberglass composite layer 48, core material 47 (such as foam) and inner fiberglass composite layer 46. Figure 5C As can be seen in FIG. 5 , the lightning receptor 53 extends from the outer surface 39 toward the structural element 45 and contacts the structural element 45. According to the present invention, Figure 5C As shown in , the lightning receptor 53 is adhesively attached to the structural element 45 using a conductive adhesive 52 .

[0074] A method of manufacturing such a blade shell portion 11 will be described in more detail further below. The different structures shown in the figures should not be construed as limiting the scope of the claims.

[0075] Figure 5DAnother embodiment of the present invention is shown. In this example, the structural element 45 includes (six) pultrusions 44 that provide strength and rigidity to the blade. This embodiment also includes a material portion 49 positioned between the pultrusions 44 and the outer surface 39, in this example a gel coating 50. The additional material 49 partially acts as a buffer, which means that it is easier to provide electrical contact to the pultrusion without damaging the pultrusion 44. The buffer can be provided as adhesively attached to the pultrusion before the laying of the blade shell part 11, or it can be laid separately in the blade shell part mold before the pultrusion 44 is added to the ply. Subsequent resin infusion then bonds the buffer 49 to one or more pultrusions 44. The buffer may, for example, include one or more fiber layers, such as a fiber layer including carbon fibers, such as a fiber layer in which the fibers are made only of carbon.

[0076] Figure 5E Another embodiment of the present invention is shown. In this example, the buffer 49 positioned between the outer surface 39 and the pultrusion 44 includes one or more carbon fiber layers 49 and a metal element 60, which is made of, for example, copper, or aluminum, or brass, or tungsten, or titanium, or stainless steel, or gold, or an alloy of one or more of these. In some embodiments, the metal element is a mesh. Figure 5D Similar to one or more fiber layers 49 in the embodiment of FIG. 4 , the copper mesh is electrically connected to the carbon pultrusion 44 and thereby equalizes the potential across the pultrusions. This allows the lightning current to be distributed across the different pultrusions, reducing resistance and, in turn, reducing heating caused by a lightning strike. The metal element 60 may be provided adhesively attached to one or more of the pultrusions 44 prior to layup of the blade shell portion (optionally together with the fiber layer 49 or other material positioned between the metal mesh 60 and the pultrusion 44), or it may be laid up separately prior to adding the pultrusion 44 to the blade shell portion layup.

[0077] Figures 6A-6D A method according to the invention is shown. These steps provide an electrical contact between the outer surface of the blade shell part 11 and the structural element 45 in the blade shell part 11 .

[0078] Fig. 6A With the above Figure 5E Similar, but showing the blade shell portion before the addition of the lightning receptor.

[0079] like Figure 6BAs shown in , after providing a blade shell portion 11 including a pultrusion 44 and a buffer (comprising a carbon fiber layer 49 and a copper mesh 60 in this example), a first recess 51 is formed in the blade shell portion 11. In this example, the first recess 51 extends from the outer surface 39 of the blade shell portion through one or more fiber layers 49 and ultimately exposes a portion of the metal element 60. The first recess 51 does not extend into any of the one or more pultrusions, as this would weaken the strength of the pultrusion. The buffer makes it easier to form the recess 51 without damaging the pultrusion 44. In a sense, it partially acts as a sacrificial layer and provides some tolerance when the recess 51 is formed.

[0080] Figure 6C 1. A step is shown in which a conductive adhesive 52 is applied in the first recess 51 in such a way that when the lightning receptor 53 is inserted, the conductive adhesive 52 can then adhesively attach the exposed portion of the metal element 60 to the lightning receptor 53. For example, the conductive adhesive 52 has a maximum of 1.0 10 -5 This ensures a sufficiently high electrical conductivity between the lightning receptor 53 and the metal element 60. Loctite offers a resistivity of less than 1.010 -5 The resistivity of the bonding material in ohm-meters.

[0081] Next, if Fig.6D As shown in FIG. 5 , the lightning receptor 53 is inserted into the first recess 51 so that it becomes adhesively attached to the metal member 60 via the conductive adhesive 52 , thereby being electrically connected to the copper mesh 60 with low resistance.

[0082] Preferably, the conductive adhesive effectively seals the layers below the gel coat 50 from any water seal external to the blade shell portion 11. If desired, a sealant may be applied to completely seal the outer surface 39 from any water seal external to the blade shell portion 11.

[0083] Finally, the adhesive 52 and sealant cure. This results in Figure 5E The blade shell section shown in .

[0084] Figures 7A-7D Another method according to the present invention is shown. Figures 6A-6D The methods described are similar. However, the method described below provides an improved seal around the lightning receptor.

[0085] Fig. 7A Corresponds to Figure 6B , shows a blade shell portion in which a first recess 51 has been formed to expose the metal element 60 . Figure 7B Corresponds to Figure 6C, showing the application of a conductive adhesive 52 in the first recess 51 .

[0086] This method differs from the method described above in that a different lightning receptor 73 is used. The lightning receptor 73 is formed so that when inserted into the first recess 51, there is a significant second recess 71 around the lightning receptor 73 at the outer surface of the blade shell part 11. This Figure 7C The lightning receptor 73 has a cross-sectional area at the outer surface that is smaller than the cross-sectional area of ​​the first recess 51. For example, the ratio between the cross-sectional area of ​​the receptor 73 at the outer surface and the cross-sectional area of ​​the first recess 51 may be less than 0.95, such as less than 0.9, such as less than 0.8.

[0087] Fig.7D The second recess 71 is shown sealed by filling the second recess 71 with a sealant 72 around the lightning receptor 73. Fig.6D This more effectively seals the outer surface from any water outside the blade shell portion than the lightning receptor 53 shown. Fig.6D The lightning receptor 53 shown fits tightly, but is more difficult to seal for this reason. In this example, the sealant 72 extends onto the outer surface 39, wherein the sealant 72 is preferably rounded and thin so as not to affect the aerodynamic properties of the blade. By extending the sealant 72 onto the outer surface 39, the seal becomes very strong. If a conductive adhesive (such as Loctite) is exposed to moisture, an oxidation process begins, which adversely affects both its mechanical properties and its electrical properties of the conductive adhesive.

[0088] Alternatively, sealant 72 may be flush with exterior surface 39, but this may result in a less effective seal with a shorter useful life. If the seal is breached, oxidation of the conductive adhesive will occur as described above, and the mechanical and electrical properties of the conductive adhesive will deteriorate.

[0089] Finally, the adhesive and sealant are allowed to cure.

[0090] Figures 8A-8C Another embodiment of the present invention is shown. Figure 5E However, as shown in Fig. 8A As shown in FIG. 8 , the outer surface 39 includes a lightning diverter 81 , such as a segmented lightning diverter. In this example, the segmented lightning diverter is positioned proximate to the lightning receptor 53 , but not adjacent to the lightning receptor 53 . Fig. 8A The area 86 indicated in Figure 8B As shown in more detail, Figure 8BAlso shown is the distance between the lightning diverter 81 and the receptor 53. The segmented diverter may for example be provided when manufacturing the blade shell section, or it may be added after embedding the fibre layers, pultrusions and one or more metal elements in resin.

[0091] like Fig. 8A As shown in FIG, the blade shell portion may include a plurality of lightning receptors 53, 82 and 84. Fig. 8A In the embodiment of FIG. 8 , there are corresponding lightning shunts 81 , 83 and 85 combined with respective lightning receptors 53 , 82 and 84 .

[0092] An advantage of placing the lightning receptor 53 at a distance from the lightning shunt 81 is that, when providing the recess 51 , the lightning shunt 81 is not damaged, which could occur if the recess 51 is provided adjacent to the lightning shunt 81 or even forms an overlap with the lightning shunt 81 .

[0093] Reference Mark List 2 Wind Turbines 4 Tower 6 Cabin 8 hub 10 blades 11, 12 blade shell part 14 Leaf Tips 15 distal end 16 Blade root 18 Front Edge 20 Back Edge 30 Root Zone 31 root end 32 Transition Area 34 Airfoil area 36 Pressure side shell part 38 Suction side shell part 39 The outer surface of the blade shell portion 40 Shoulders 41, 45 Structural elements / load bearing structures / spar caps 44 Pultrusion parts including carbon fiber materials 46 fiber composite layers 47 core material 48 fiber composite layers 49 Additional materials, buffer 50 gel coats 51 recess 52 Conductive Adhesive 53 Lightning Receiver 55 Shear web 56 Blade shell area 60 metal components, copper mesh 65 Blade shell area 71 Recess surrounding lightning receptor 72 Adhesive surrounding the lightning receptor at the outer surface 73 Lightning Receiver 81, 83, 85 lightning diverters, segmented lightning diverters 82, 84 lightning receiver 86 Blade shell area L B Length of blade / longitudinal axis

Claims

1. A wind turbine blade shell portion (11, 12) for a wind turbine blade (10), the blade shell portion comprising: - a structural element (45) which provides structural strength to the blade shell portion and comprises carbon fibres embedded in a polymer matrix, a lightning receptor (53) exposed at the outer surface (39) of the blade shell portion and extending towards the structural element (45), and - An electrically conductive adhesive (52) which attaches the lightning receptor to the structural element.

2. A blade shell portion according to claim 1, wherein the structural element comprises one or more pultrusions (44), the pultrusions comprising carbon fibers embedded in a polymer matrix, and wherein the conductive adhesive attaches the lightning receptor to the carbon fibers in one or more of the pultrusions.

3. The blade shell portion of claim 1 , wherein the structural element comprises: - one or more pultrusions (44) comprising carbon fibres embedded in a polymer matrix, and - one or more fiber layers (49) comprising carbon fibers, said one or more fiber layers being positioned between the outer surface of said blade shell portion and one or more of said pultrusions and being adhesively attached to and in electrical contact with at least one of said one or more pultrusions, The conductive adhesive attaches the lightning receptor to carbon fibers in one or more of the fiber layers.

4. The blade shell portion of claim 1 , wherein the structural element comprises: - one or more pultrusions (44) comprising carbon fibres embedded in a polymer matrix, and a metal element (60), such as a metal mesh, positioned between the outer surface of the blade shell portion and one or more of the pultrusions and in electrical contact with at least one of the one or more pultrusions, The conductive adhesive attaches the lightning receptor to a portion of the metal element.

5. A blade shell portion according to any one of claims 3 to 4, wherein the structural element comprises two or more pultrusions, and wherein the one or more fiber layers or the metal element provides potential equalization between at least two of the pultrusions.

6. A blade shell part according to any one of the preceding claims, wherein the lightning receptor adjoins a lightning diverter (81 ) which forms part of an outer surface of the blade shell part.

7. The blade shell portion according to claim 5, wherein the lightning receptor is located at a first distance from a lightning diverter (81) forming part of an outer surface of the blade shell portion.

8. A blade shell portion according to claim 7, wherein said first distance is at most 20 mm, such as at most 10 mm, such as at most 5 mm.

9. A blade shell portion according to claim 7, wherein the first distance is in the range of 2-20 mm, such as in the range of 2-15 mm, such as in the range of 3-12 mm, such as in the range of 3-10 mm.

10. The blade shell part according to any one of claims 6 to 9, wherein the lightning diverter (81) is a segmented lightning diverter.

11. A blade shell section according to any one of the preceding claims, wherein the conductive adhesive material has a relative humidity of 1.0 10 -6 Ohm-meter to 1.0 10 -5 Ohm-meter range, such as 2.0 10 -6 Ohm-meter to 6.010 -6 Resistivity in the range.

12. A blade shell part according to any one of the preceding claims, wherein the periphery of the lightning receptor (73) is surrounded by a sealant (72) at the outer surface.

13. A blade shell portion according to claim 12, wherein the lightning receptor (73) has a cross-sectional area at the outer surface that is smaller than the cross-sectional area of ​​the first recess (51), and the ratio between the cross-sectional area of ​​the receptor (73) at the outer surface and the cross-sectional area of ​​the first recess (51) is less than 0.95, such as less than 0.9, such as less than 0.

8.

14. A blade shell portion according to any one of the preceding claims, wherein the structural element is a spar cap.

15. A blade shell portion according to any of the preceding claims, wherein the blade shell portion comprises a wind turbine blade pressure side shell half and / or a wind turbine blade suction side shell half.

16. A method of attaching a lightning receptor to a wind turbine blade shell portion (11, 12) of a wind turbine blade (10) to provide electrical contact between an outer surface (39) of the blade shell portion and a structural element (45) in the blade shell portion, the method comprising: - providing a blade shell part (11, 12) comprising a structural element (45) comprising carbon fibres embedded in a polymer matrix, - providing a first recess (51) extending from the outer surface (39) of the blade shell portion towards the structural element (45), - applying an electrically conductive adhesive into said recess, - inserting a lightning receptor (53) into the recess so that the conductive adhesive attaches the lightning receptor to the structural element, and - Curing the adhesive.

17. A method according to claim 16, wherein the structural element (45) comprises one or more pultrusions (44), the pultrusions comprising carbon fibers embedded in a polymer matrix, and wherein the recess is provided to expose a portion of one or more of the pultrusions without extending into any of the pultrusions.

18. The method according to claim 16, wherein the structural element (45) comprises: - one or more pultrusions (44) comprising carbon fibres embedded in a polymer matrix, and - one or more fiber layers (49) comprising carbon fibers, said one or more fiber layers being positioned between the outer surface of said blade shell portion and one or more of said pultrusions and being adhesively attached to and in electrical contact with at least one of said one or more pultrusions, The recess extends into one or more of the fiber layers, but not into any of the one or more pultrusions, the conductive adhesive attaching the lightning receptor to carbon fibers in one or more of the fiber layers.

19. The method of claim 16, wherein the structural element (45) comprises: - one or more pultrusions (44) comprising carbon fibres embedded in a polymer matrix, and a metal element (60), such as a metal mesh, positioned between the outer surface of the blade shell portion and one or more of the pultrusions and in electrical contact with at least one of the one or more pultrusions, The recess exposes a portion of the metal element without extending into any of the one or more pultrusions, and the conductive adhesive attaches the lightning receptor to the exposed portion of the metal element.

20. Method according to any one of claims 16 to 19, wherein the lightning receptor after insertion abuts a lightning diverter (81) forming part of the outer surface of the blade shell part.

21. The method according to any one of claims 16 to 19, wherein the lightning receptor after insertion is located at a first distance from the lightning shunt (81), wherein the first distance is at most 20 mm, such as in the range of 2-20 mm, such as in the range of 3-10 mm.

22. The method according to any one of claims 16 to 21, wherein after inserting the lightning receptor (73) into the first recess (51), there is a second recess (71) around the lightning receptor (73) at the outer surface (39), and wherein the method further comprises filling the second recess (71) around the lightning receptor (73) with a sealant (72).

23. The method of any one of claims 16 to 22, wherein the conductive adhesive material has a relative humidity of less than 1.0 10 -5 Ohm-meter, such as less than 7.0 10 -6 Ohm-meter, such as less than 5.0 10 -6 Ohm-meter, such as less than 3.0 10 -6 Ohm-meter, such as less than 2.0 10 -6 Ohm-meter, such as less than 1.0 10 -6 Resistivity in ohm-meters.

24. A method according to any one of claims 16 to 23, wherein the structural element is a spar cap.

25. The method according to any one of claims 16 to 24, wherein the blade shell portion is a wind turbine blade pressure side shell and / or a wind turbine blade suction side shell.

26. A blade shell portion according to any one of claims 1 to 15 or a method according to any one of claims 16 to 25, wherein the lightning receptor and the conductive adhesive are capable of withstanding a lightning current of at least 10 kA when they are attached to the structural element, such as in the range of 10-300 kA, such as in the range of 10-200 kA, such as in the range of 10-100 kA.

27. A blade shell portion according to any one of claims 1 to 15 or a method according to any one of claims 16 to 25, wherein the lightning receptor and the conductive adhesive when they are attached to the structural element are capable of withstanding a lightning charge of at least 50 coulombs during a lightning strike, such as a lightning charge in the range of 50-1000 coulombs, such as a lightning charge in the range of 50-300 coulombs, such as a lightning charge in the range of 100-200 coulombs.

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