Lightning protection in a segmented wind turbine blade

Abstract

The present disclosure relates to a segmented wind turbine blade comprising a first blade shell segment joined with a second blade shell segment via attachment means. A fairing element is provided that comprises fibre-reinforced composite material and a metal element attached to the fibre-reinforced composite material. The fairing element is fastened to the first and second shell segments using fasteners. The fairing element covers the attachment means at least partly and forms part of an aerodynamic profile of the wind turbine blade. The metal element of the fairing element is configured such that the metal element of the fairing element provides electrical contact between a first metal element in the first shell segment and a second metal element in the second shell segment. A composite fairing element and a method for manufacturing a segmented wind turbine blade are also provided.

Description

[0001] Title

[0002] Lightning protection in a segmented wind turbine blade

[0003] Technical field

[0004] The present invention relates to lightning protection in segmented wind turbine blades, particularly to lightning protection measures in the vicinity of segment joints in segmented wind turbine blades.

[0005] Background of the invention

[0006] As wind turbines and wind turbine blades increase in size, the risk of lightning striking the wind turbine blades increases. It is therefore of increasing interest to provide wind turbine blades with lightning protection measures.

[0007] Lightning protection measures in a wind turbine blade typically include metal lightning receptors exposed at the outer surface of the blade to attract lightning in a controlled manner in case of a lightning strike. The lightning receptors are typically connected to ground through metal conductors in order to prevent lightning current from flashing over between less conductive parts of the blade, which would cause heating and potentially damage to those parts. Typically, blades include a downconductor cable extending substantially the entire length of the blades. The downconductor cable is typically coupled to several lightning receptors arranged along the length of the blade to reduce the risk of flashovers into the blade during a lightning strike.

[0008] As blade sizes increase, it may also be advantageous to manufacture blades in several blade shell segments which, when assembled, form the entire blade shell. The individual segments are shorter and lighter and thus easier to handle individually and easier to transport from the manufacturing site to the deployment site. Once the shell segments have arrived at the deployment site, they are assembled into the final blade shell.

[0009] In a segmented blade, a very strong structure is needed to join the segments, as the centrifugal force acting on the blade is very high and increasingly so with increasing rotation speed. Attachment means for joining segments are integrated into each segment; different solutions exist for joining shell segments. In all cases, attachment means are substantially metallic since metallic attachment means are relatively easy to work with and provide the most secure joints at the present time. Materials such as composite materials are not at present desirable for joining segments because they do not have the required mechanical properties, such as sufficient strength. However, when segments are joined using metallic attachment means, there is an increased risk that lightning strikes at the joint. Further, existing solutions use metal fairings to cover the joints, which further increases the risk that lightning will strike at the joint via the metal fairing, potentially weakening it and increasing the risk that the joint fails.

[0010] Thus, there is a need to reduce the risk that a lightning strike damages the joint between two wind turbine blade shell segments in a segmented wind turbine blade.

[0011] Summary of the invention

[0012] A first aspect of the invention provides a wind turbine blade comprising a first wind turbine blade shell segment having first attachment means, the wind turbine blade further comprising a second wind turbine blade shell segment having second attachment means engaged with the first attachment means, thereby rigidly joining the first shell segment to the second shell segment, the first shell segment further comprising a first metal element, the second shell segment further comprising a second metal element, the wind turbine blade further comprising one or more fairing elements covering the first and second attachment means and forming a part of an aerodynamic profile of the wind turbine blade, wherein at least a first fairing element of the one or more fairing elements comprises fibre-reinforced composite material and a metal element attached to the fibre- reinforced composite material of the fairing element, the first fairing element being fastened to the first shell segment using a first set of one or more fasteners, such as rivets and / or screws, the first fairing element being fastened to the second shell segment using a second set of one or more fasteners, such as rivets and / or screws, wherein the metal element of the first fairing element provides electrical contact between the first metal element in the first shell segment and the second metal element in the second shell segment.

[0013] Metal elements in wind turbine blades are usually connected to a downconductor, and in segmented blades, metal elements that have a lightning-protecting function are usually attached to a downconductor with a separate electrical conductor. In the present invention, an electrical connection is provided between metal elements in two segments using a metal element that is part of a first fairing element comprising fibre-reinforced composite material. The metal element in the first fairing element is configured such that when the first fairing element is fastened to the two segments, an electrical connection is established between the metal element of the first shell segment and the metal element of the second shell segment. Depending on the embodiment and the specifics of the metal element in the first fairing element, especially the geometry of the metal element, the sets of fasteners must be placed in specific positions. For instance, the metal element may be a mesh, and in some embodiments, the fasteners must be electrically conductive and be placed such that they are in electrical contact with the mesh.

[0014] As a result of the configuration of wind turbine blades according to the invention, the metal elements in the two shell segments have the same potential. This reduces the risk of flashover within the wind turbine blade. Another advantage is that any other metal elements electrically connected to the metal element of the first shell segment and any other metal elements electrically connected to the metal element of the second shell segment will have the same potential, thus further reducing the risk of flashover between more or less conductive elements in the blade, including elements such as metal elements and carbon fibre composite elements.

[0015] Also, if each of the metal elements in the first and second shell segments are individually connected to a downconductor, lightning current will be conducted to ground in parallel, reducing the current in each metal element.

[0016] The present invention provides electrical connection between two metal elements in two respective wind turbine blade shell segments that have been joined together. However, the number of shell segments can be three or higher. The principles of the invention are applicable at each joint between two segments.

[0017] Each of the first and second sets of fasteners preferably comprises at least two fasteners. This leads to a more secure fastening of the first fairing element to the first and second shell segments.

[0018] The first fairing element comprises composite material in addition to a metal element. In case the metal element is a metal mesh, the first fairing element can be lighter compared to pure metal fairings. Further, a first fairing element in accordance with the invention reduces the risk that lightning attaches to it. If a lightning strike occurs near the attachment means joining the shell segments, there is a risk that the attachment means become damaged and thus an increased risk that the joint between the first and second shell segments fails. Therefore, the first fairing element reduces the risk that the joint between two wind turbine blade shell segments fails. In addition, composite materials of the type normally used in wind turbine blades have a lower thermal expansion coefficient than metals such as steel, aluminium, and copper. Therefore, the interfaces between the shell segments and the composite first fairing element may experience less fatigue than when metal fairings are used. In some embodiments, the one or more fairing elements completely enclose the first and second attachment means and complete the entire aerodynamic profile at the joint where the first shell segment and the second shell segment are joined to one another.

[0019] In some embodiments, all of the one or more fairing elements are composite elements, like the first fairing element. The composition of one fairing element may differ from the composition of other fairing elements. Further, the shape of the fairing elements may differ from each other, for instance because they combine to form the shape of the airfoil, which is usually nonsymmetric.

[0020] In some embodiments, the first shell segment comprises an electrically conductive suction side spar cap and an electrically conductive pressure side spar cap, and the first metal element of the first shell segment is arranged in direct contact with either the suction side spar cap of the first shell segment or the pressure side spar cap of the first shell segment; and the second shell segment comprises an electrically conductive suction side spar cap and an electrically conductive pressure side spar cap, and the second metal element of the second shell segment is arranged in direct contact with one of the suction side spar cap of the second shell segment and the pressure side spar cap of the second shell segment. (It is implied in this embodiment that the metal elements of the two segments are located on the same side of the blade, i.e. the metal elements of the shell segments are both in the pressure side or in the suction side of the shell segments, as this is a requirement for the composite fairing element to provide electrical connection between the metal elements of the two shell segments via the conductive fasteners and the metal element of the first fairing element.)

[0021] In some embodiments, the first shell segment comprises an electrically conductive suction side spar cap and an electrically conductive pressure side spar cap and the first metal element of the first shell segment is arranged adjacent to and in direct contact with one of: the suction side spar cap of the first shell segment and the pressure side spar cap of the first shell segment; and the second shell segment comprises an electrically conductive suction side spar cap and an electrically conductive pressure side spar cap and the first metal element of the second shell segment is arranged adjacent to and in direct contact with one of: the suction side spar cap of the second shell segment and the pressure side spar cap of the second shell segment; and the first and second sets of fasteners fastening the first fairing element to the first shell segment and to the second shell segment without engaging the spar caps.

[0022] This allows equipotentialisation between spar caps in two adjacent wind turbine blade segments. In some embodiments, the first shell segment further comprises a third metal element arranged adjacent to and in direct contact with the other of the suction side spar cap and the pressure side spar cap of the first shell segment, whereby both the suction side spar cap and the pressure side spar cap of the first shell segment are adjacent to and in direct contact with a respective one of the first and third metal elements in the first shell segment; and the second shell segment further comprises a fourth metal element arranged adjacent to and in direct contact with the other of the suction side spar cap and the pressure side spar cap of the second shell segment, whereby both the suction side spar cap and the pressure side spar cap of the second shell segment are adjacent to and in direct contact with a respective one of the second and fourth metal elements in the second shell segment, the third metal element and the fourth metal element being electrically connected by a second fairing element, the second fairing element comprising fibre-reinforced composite material and the metal element that electrically connects the third metal element and the fourth metal element.

[0023] This allows equipotentialisation between spar caps in two adjacent wind turbine blade segments, both on the pressure side and on the suction side.

[0024] In some embodiments, the first shell segment comprises an electrically conductive suction side spar cap and an electrically conductive pressure side spar cap and the first metal element of the first shell segment is separated from the suction side spar cap of the first shell segment and from the pressure side spar cap of the first shell segment by non-conductive material, such as by non-conductive composite material, such as by non-conductive fibre-reinforced composite material; and the second shell segment comprises an electrically conductive suction side spar cap and an electrically conductive pressure side spar cap and the second metal element in the second shell segment is separated from the suction side spar cap of the second shell segment and the pressure side spar cap of the second shell segment by non-conductive material, such as by non-conductive composite material, such as by non-conductive fibre-reinforced composite material; and the first and second sets of fasteners fastening the first fairing element to the first shell segment and to the second shell segment without engaging the spar caps.

[0025] This electrically connects metal elements that act as Faraday cages in two adjacent segments.

[0026] In some embodiments, the first shell segment further comprises a third metal element separated from the suction side spar cap of the first shell segment and from the pressure side spar cap of the first shell segment by non-conductive material, such as by non-conductive composite material, such as by non-conductive fibre-reinforced composite material; and the second shell segment further comprises a fourth metal element separated from the suction side spar cap and the pressure side spar cap of the second shell segment by non-conductive material, such as by non-conductive composite material, such as by non-conductive fibre-reinforced composite material, the third metal element and the fourth metal element being electrically connected by a second fairing element, the second fairing element comprising fibre-reinforced composite material and the metal element that electrically connects the third metal element and the fourth metal element.

[0027] This electrically connects metal elements that act as Faraday cages in two adjacent segments, both on the pressure side and on the suction side.

[0028] In some embodiments, the metal element of the first fairing element is adjacent to and in direct contact with the first metal element in the first shell segment and adjacent to and in direct contact with the second metal element in the second shell segment.

[0029] This results in a relatively low resistance between the first metal element and the second metal element.

[0030] In some embodiments, the first set of fasteners is a set of electrically conductive fasteners that engage with one or more flanges of the first shell segment and wherein the second set of fasteners is a set of electrically conductive fasteners that engage with one or more flanges of the second shell segment, the one or more flanges of the first shell segment comprising part of the first metal element and part of the third metal element of the first shell segment, the one or more flanges of the second shell segment comprising part of the second metal element and part of the fourth metal element of the second shell segment, whereby the first and second set of fasteners establish electrical connection between the first metal element in the first shell segment and the metal element in the first fairing element, and between the second metal element in the second shell segment and the metal element in the first fairing element.

[0031] Such flanges make it easier to install a fairing element providing a low resistance between metal elements in the two respective segments.

[0032] In some embodiments, one or more of, such as all of, the metal elements are respective layers made of one or more of: copper, copper alloy, aluminium, aluminium alloy.

[0033] In some embodiments, one or more of, such as all of, the metal elements are respective layers comprising a metal mesh, such as a copper mesh or a copper alloy mesh. In some embodiments, the first fairing element is arranged on a suction side of the blade, the one or more fairing elements further including a second fairing element comprising fibre-reinforced composite material and a metal element, the second fairing element being arranged on a pressure side of the blade, the second fairing element being fastened to the first shell segment and the second shell segment using a third set of fasteners, wherein the second fairing element is arranged and fastened such that the metal element of the second fairing element provides electrical contact between the third metal element in the first shell segment and the fourth metal element in the second shell segment.

[0034] In some embodiments, the first attachment means comprises a first set of bushings and the second attachment means comprises a corresponding second set of bushings, and the first shell segment and the second shell segment are joined by metal rods engaging bushings in the first set of bushings and opposing bushings in the second set of bushings, at least one of the metal rods comprising: a first conductive element, such as a conductive rubber ring, that provides electrical contact between the metal rod and a spar cap in the first shell segment, and a second conductive element, such as a conductive rubber ring, that provides electrical contact between the metal rod and a spar cap in the second shell segment.

[0035] In some embodiments, the first fairing element is premanufactured either: by sandwiching the metal element of the first fairing element between at least two non- conductive fibre material layers; infusing liquid resin into the at least two fibre material layers; and curing the resin, or

[0036] . by sandwiching the metal element of the first fairing element between at least two non- conductive fibre material layers; infusing liquid resin into the at least two fibre material layers; and curing the resin; and subsequently removing at least part of one of the non-conductive fibre material layers to expose at least part of the metal element, or by arranging the metal element adjacent to at least one non-conductive fibre material layer; infusing liquid resin to the metal element and the at least one non-conductive fibre material layer; and curing the resin.

[0037] In some embodiments, each of the spar caps is either a carbon spar cap or a hybrid spar cap comprising carbon fibres and fibres other than carbon fibres. In some embodiments, each of the spar caps is either a carbon spar cap or a hybrid spar cap comprising carbon fibres and fibres other than carbon fibres. Spar caps comprising carbon fibre material are somewhat electrically conductive and as such, they attract lightning more than composite spar caps made purely with glass fibre material. At the same time, carbon spar caps have a significant resistivity, which causes them to heat in case of a lightning strike. Placing the metal elements in direct contact with the spar caps is therefore particularly advantageous when the spar caps comprise a significant amount of carbon fibre material, such as at least 10 % by weight compared to the entire weight of fibre material. The carbon spar caps can be made for instance from fibre mats or by pultrusion.

[0038] A second aspect of the invention provide a method for manufacturing a wind turbine blade, comprising: providing a first wind turbine blade shell segment having first attachment means and providing a second wind turbine blade shell segment having second attachment means, engaging the first attachment means with the second attachment means to rigidly join the first shell segment to the second shell segment, fastening one or more fairing elements to the first and second shell segments such as to cover the first and second attachment means, the one or more fairing elements further being configured to form a part of an aerodynamic profile of the wind turbine blade, at least a first fairing element of the one or more fairing elements comprising fibre-reinforced composite material and a metal element attached to the fibre-reinforced composite material, wherein the first fairing element is fastened to the first shell segment using a first set of one or more fasteners and the first fairing element is fastened to the second shell segment using a second set of one or more fasteners, wherein the metal element of the first fairing element, when fastened, provides electrical contact between a first metal element in the first shell segment and a second metal element in the second shell segment.

[0039] In some embodiments of the second aspect: the first shell segment comprises: i. an electrically conductive suction side spar cap, the first metal element of the first shell segment being arranged in direct contact with the suction side spar cap of the first shell segment, ii. an electrically conductive pressure side spar cap and a third metal element arranged in direct contact with the pressure side spar cap of the first shell segment, and the second shell segment comprises: i. an electrically conductive suction side spar cap, the second metal element of the second shell segment being arranged in direct contact with the suction side spar cap of the second shell segment, ii. an electrically conductive pressure side spar cap and a second metal element arranged in direct contact with the pressure side spar cap of the second shell segment.

[0040] In some embodiments of the second aspect, the first set of fasteners engage with one or more flanges of the first shell segment and the second set of fasteners engage with one or more flanges of the second shell segment, the one or more flanges of the first shell segment comprising part of the first metal element and part of the second metal element of the first shell segment, the one or more flanges of the second shell segment comprising part of the first metal element and part of the second metal element of the second shell segment.

[0041] In some embodiments of the second aspect: the first set of fasteners and the second set of fasteners comprise rivets and / or screws, the first fairing element comprising fibre-reinforced composite material is premanufactured, the one or more fairing elements comprise a second premanufactured fairing element comprising fibre-reinforced composite material and a metal element, the first fairing element being arranged on a suction side of the blade, the second fairing element being arranged on a pressure side of the blade, the second fairing element being fastened to the first shell segment and the second shell segment using electrically conductive fasteners such that the second metal element of the first shell segment is electrically connected to the second metal element of the second shell element via the metal element of the second fairing element.

[0042] In some embodiments, one or more of, such as all of, the metal elements are respective layers made of one or more of: copper, copper alloy, aluminium, aluminium alloy. Layers, such as metal plates or foils, can be incorporated into wind turbine blade shells.

[0043] In some embodiments, one or more of, such as all of, the metal elements are respective layers comprising or being made of a metal mesh, such as a copper mesh or a copper alloy mesh. Metal meshes are lighter and more flexible than metal plates, while providing sufficient conductance. Also, resin bonds the metal elements more strongly to the surrounding fibre material.

[0044] In some embodiments, the first fairing element is premanufactured. This ensures that the first fairing element has the desired shape and size to complete the aerodynamic profile and also results in a first fairing element having high mechanical strength and stability.

[0045] In some embodiments, the first fairing element is arranged on a suction side of the blade, and the one or more fairing elements further include a second premanufactured fairing element comprising fibre-reinforced composite material and a metal element, similar to the first fairing element. The second fairing element is arranged on a pressure side of the blade and fastened to the first shell segment and the second shell segment on the pressure side using electrically conductive fasteners such that the second metal element of the first shell segment is electrically connected to the second metal element of the second shell element via the metal element of the second fairing element and the fasteners with which the second fairing element is attached to the first and second shell segments on the pressure side. Such embodiments provide the advantages described above, but on both sides of the wind turbine blade.

[0046] In some embodiments, the fasteners, including the first and second sets of fasteners, comprise rivets and / or screws.

[0047] As mentioned above, the first and second fairing elements may be premanufactured before being fastened to the first and second shell segments. This ensures that they have the desired shape to complete the aerodynamic profile. Each composite fairing element may be premanufactured for instance by sandwiching a metal element between at least two fibre material layers and infusing liquid resin and curing the resin. The fairing elements can be tailored as desired. For instance, the fibre materials on the sides may be different. It may be advantageous that fibre material facing the attachment means inside the blade comprises carbon fibre material that is in contact with the metal element of the fairing element, as this will improve the conductivity of the fairing element. Several metal layers can be used in the composite fairing elements. This may increase the conductivity of the composite fairing element.

[0048] In some embodiments, a first fairing element covers the first attachment means on the suction side; a second fairing cover the second attachment means on the pressure side; a third fairing element extends from an edge of the first fairing element, over the leading edge of the blade, and ends at an edge of the second fairing element; and a fourth fairing element extends from an edge of the first fairing to an edge of the second fairings, but covers the trailing part of the blade. These four fairing elements enclose the attachment means and complete the aerodynamic profile of the blade. In some embodiments, one or more of the fairing elements consists of several sub-elements.

[0049] In some embodiments, a width of the first and / or second fairing element is in the range 1 cm to 100 cm, such as in the range 10 cm to 100 cm, such as in the range 20 cm to 100 cm, such as in the range 40-60 cm, such as about 48-52 cm. Although this depends on the precise joint design and joint dimensions, these values are advantageous due to the mechanical and electrical properties of the first and / or second fairings. Different fairing elements at the joint may have different widths.

[0050] In some embodiments, a length of the first and / or second fairing element is between 20 cm and 200 cm, such as in the range 20 cm to 150 cm. Although this depends on the precise joint design and dimensions, these values are advantageous due to the mechanical and electrical properties of the first and / or second fairings.

[0051] Preferably, a thickness of one or more of the fairing elements is in the range 2-15 mm, such as in the range 2-10 mm. In some embodiments, one or more of the fairing elements have a uniform thickness.

[0052] In a second aspect, the invention provides a method for manufacturing a wind turbine blade. The method comprises: providing a first wind turbine blade shell segment having first attachment means and providing a second wind turbine blade shell segment having second attachment means, engaging the first attachment means with the second attachment means to rigidly join the first shell segment to the second shell segment, fastening one or more fairing elements to the first and second shell segments to cover the first and second attachment means, the one or more fairing elements further being configured to form a part of an aerodynamic profile of the wind turbine blade, at least a first fairing element of the one or more fairing elements comprising fibre-reinforced composite material and a metal element, wherein the first fairing element is fastened to the first shell segment using a first set of one or more fasteners and the first fairing element is fastened to the second shell segment using a second set of one or more fasteners, the first and second sets of fasteners being electrically conductive, the first set of fasteners being fastened so as to establish electrical connection between the metal element of the first fairing element and a first metal element of the first shell segment, the second set of fasteners being fastened so as to establish electrical connection between the metal element of the first fairing element and a first metal element of the second shell segment, whereby the first metal element of the first shell segment is electrically connected to the first metal element of the second shell segment via the first and second sets of fasteners and via the metal element of the first fairing element.

[0053] The advantages and features described in relation to the first aspect generally apply to the second aspect. For instance, in some embodiments,

[0054] - the first shell segment comprises: i. an electrically conductive suction side spar cap, the first metal element of the first shell segment being arranged in direct contact with the suction side spar cap of the first shell segment, and ii. an electrically conductive pressure side spar cap and a second metal element arranged in direct contact with the pressure side spar cap of the first shell segment,

[0055] - the second shell segment comprises: i. an electrically conductive suction side spar cap, the first metal element of the second shell segment being arranged in direct contact with the suction side spar cap of the second shell segment, and ii. an electrically conductive pressure side spar cap and a second metal element arranged in direct contact with the pressure side spar cap of the second shell segment.

[0056] In some embodiments, the first set of fasteners engage with one or more flanges of the first shell segment and the second set of fasteners engage with one or more flanges of the second shell segment, the one or more flanges of the first shell segment comprising part of the first metal element and part of the second metal element of the first shell segment, the one or more flanges of the second shell segment comprising part of the first metal element and part of the second metal element of the second shell segment.

[0057] In some embodiments, the first set of fasteners and the second set of fasteners comprise rivets and / or screws, the first fairing element comprising fibre-reinforced composite material is premanufactured, the one or more fairing elements comprise a second premanufactured fairing element comprising fibre-reinforced composite material and a metal element, the first fairing element being arranged on a suction side of the blade, the second fairing element being arranged on a pressure side of the blade, the second fairing element being fastened to the first shell segment and the second shell segment using electrically conductive fastening elements such that the second metal element of the first shell segment is electrically connected to the second metal element of the second shell element via the metal element of the second fairing element.

[0058] A third aspect provides a wind turbine blade manufactured using a method in accordance with embodiments of the second aspect of the invention.

[0059] A fourth aspect provides a fairing element for covering first attachment means and second attachment means in a segmented wind turbine blade comprising a first wind turbine blade shell segment and a second wind turbine blade shell segment, the first shell segment comprising the first attachment means, the second shell segment comprising the second attachment means, the first shell segment being joined to the second shell segment by engaging the first attachment means with the second attachment means, the fairing element being configured to form a part of an aerodynamic profile of the wind turbine blade, wherein the fairing element comprises fibre-reinforced composite material and a metal element attached to the fibre-reinforced composite material, the metal element being dimensioned such that the fairing element can be attached to the first shell segment using a first conductive fastener and to the second shell segment using a second conductive fastener in such a way that the metal element is in electrical contact with the first fastener and the second fastener, whereby the metal element in the fairing element electrically connects the first fastener with the second fastener.

[0060] In some embodiments, the fairing element is a layered structure comprising a metal layer and a fibre material layer. In some embodiments, the metal layer is sandwiched between two layers of fibre material.

[0061] In some embodiments, the metal element is a mesh structure. This reduces the weight of the metal element while maintaining sufficiently low electrical resistance.

[0062] In some embodiments, the fairing element is curved, i.e. non-planar. Brief description of the drawings

[0063] The invention is explained in detail below with reference to the embodiments shown in the drawings.

[0064] Fig. 1 is a schematic view illustrating an exemplary wind turbine.

[0065] Fig. 2 is a schematic view illustrating an exemplary wind turbine blade.

[0066] Fig. 3 illustrates two shell sections of two shell segments of a segmented wind turbine blade, adapted for the invention.

[0067] Fig. 4a and 4b illustrate details of regions around suction side spar caps in two shell segments adapted for the invention.

[0068] Figs. 5a-5d illustrate cross-sections of shell segments adapted for the invention.

[0069] Figs. 6a-6d illustrate cross-sections of shell segments adapted for the invention and use of a composite fairing in accordance with the invention.

[0070] Figs. 7 and 8 illustrate views of the suction side surfaces of two shell segments joined by attachment means and with covering fairing elements.

[0071] Detailed description of selected embodiments

[0072] Embodiments of the invention will be described in more detail in the following with reference to the accompanying drawings. Similar reference numbers generally refer to similar elements throughout. The drawings show selected ways of implementing the aspects of the present invention and are not to be construed as limiting. Unless otherwise indicated, the drawings are not necessarily drawn to scale. The relative size of the different elements and their shape may have been chosen to make different elements or details clearly discernible.

[0073] Fig. 1 illustrates a conventional modern upwind wind turbine 2 according to the so-called "Danish concept" with a tower 4, a nacelle 6 and a rotor with a substantially horizontal rotor shaft. The rotor includes a hub 8 and three blades 10 extending radially from the hub 8, each blade having a blade root 16 nearest the hub and a blade tip 14 with a tip end 15 furthest from the hub 8. The invention is not limited to wind turbines of this type.

[0074] Fig. 2 shows a schematic view of an exemplary wind turbine blade 10. The wind turbine blade 10 has the shape of a conventional wind turbine blade with a root end and a tip end 15 and comprises a root region 30 closest to the hub, a profiled or airfoil region 34 having an aerodynamic profile, and a transition region 32 between the root region 30 and the airfoil region 34. The blade 10 comprises 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.

[0075] The airfoil region 34 (also called the profiled region) preferably has an ideal shape with respect to generating hub rotation, whereas the root region 30 due to structural considerations has a substantially circular or elliptical cross-section, which for instance makes it easier and safer to mount the blade 10 to the hub. The diameter of the root region 30 may be constant along the entire root region 30 or may taper. The transition region 32 in the wind turbine blade 10 in this example has a transitional profile gradually changing from the circular shape of the root region 30 to the airfoil profile of the airfoil region 34. The chord length in the transition region 32 typically increases in an outward direction 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 length in the airfoil region typically decreases in the direction of the tip end 15.

[0076] Different sections of the blade normally do not have a common plane, since the blade may be twisted and / or curved (i.e. pre-bent) along a direction from the root region to the tip, this being most often the case, for instance to more or less compensate for the local velocity of the blade being dependent on the distance from the hub.

[0077] The wind turbine blade 10 comprises a blade shell which may for instance comprise two blade shell parts, a first blade shell part 36 and a second blade shell part 38, for instance made at least partly of fibre-reinforced polymer. The first blade shell part 36 may for instance be part of a pressure side or upwind blade part. The second blade shell part 38 may for instance be part of a suction side or downwind blade part. The first blade shell part 36 and the second blade shell part 38 are typically joined together, such as glued together, along bond lines or glue joints extending along the trailing edge 20 and the leading edge 18 of the blade 10.

[0078] The blade 10 in Fig. 2 is a segmented blade made of a first shell segment 35a and a second shell segment 35b. The suction side surface 38a of the first shell segment 35a and the suction side surface 38b of the second shell segment 35b are indicated in Fig. 2. The two segments 35a and 35b are joined to one another by joining first attachment means in the first shell segment 35a with second attachment means in the second shell segment 35b. After the two segments 35a and 35b have been joined, the first and second attachments means are covered with one or more fairings. In the example in Fig. 2, the fairing on the suction side 38b comprises three fairing elements: Fairing element 85 is arranged near the leading edge 18 of the blade 10, fairing element 74 is arranged above the first and second attachment means on the suction side, and fairing element 81 is arranged towards the trailing edge 20 of the blade 10. The fairing elements 74, 81, and 85 are fastened to the first and second shell segments 35a and 35b using fastening means, for instance rivets. Leadingedge fairing element 85 typically covers both part of the suction side and part of the pressure side near the leading edge 18, as this leads to a smoother surface than if separate fairing elements were used, one for each side near the leading edge. The same may apply to the trailing-edge fairing element 81. That is, at the trailing edge 20, a single fairing element covers both a part of the suction side and part of the pressure side near the trailing edge. This is the configuration illustrated in Fig.

[0079] 2 (for the suction side).

[0080] A downconductor (not shown) is also included in blades, typically in the form of a cable placed inside the blade shell. Lightning receptors (not shown) are placed on the surface of the blade shell and are connected to the downconductor, whereby lightning current from a lightning strike can be conducted to ground. Each lightning receptor may be connected to the downconductor by a separate conductor, whereby different lightning receptors are essentially coupled to the downconductor in parallel. Lightning receptors are often placed close to structural elements, such as spar caps, which may cause flashover of lightning from a lightning receptor to a structural element, which can cause damage to the structural element. The invention provides an additional electrical path between a metal element in one shell segment and a metal element in another shell segment of a segmented wind turbine blade. This causes lightning further distribution of lightning current, resulting in less heating in specific elements in the blade in case of a lightning strike.

[0081] The fairing elements 74, 81, and 85 also complete the aerodynamic profile of the suction side surface 38a and 38b of the blade. In this example, the fairing elements 74, 81, and 85 are flush with the suction side surface 38a of the first shell segment 35a and the suction side surface 38b of the second shell segment 35b. Corresponding fairing elements are located on the pressure side 36 of the blade to protect the attachment means, as indicated by dashed lines representing the edges of one or more fairing elements arranged on the pressure side 36 of the blade 10. The trailing-edge fairing element 81 may extend from the suction side 38 to the pressure side 36 as one piece, which may improve the structural properties and reduce the number of interfaces between fairing elements, thereby requiring less filling for sealing any gaps. The same possibility is available for the leadingedge fairing element 85.

[0082] The fairing elements 74, 81, and 85 and the fairing elements of the pressure side protect the attachment means from the environment, preventing rain, snow, and dust from getting inside the blade. Thus, they completely enclose the first and second attachment means. In Fig. 2, a shell section 37a of the first shell segment 35a and a shell section 37b of the second shell segment 35b are indicated. These shell sections are discussed in detail below in order to illustrate the invention.

[0083] Fig. 3 illustrates the two shell sections 37a and 37b of the first and second shell segments 35a and 35b, respectively, in a perspective view. The first shell segment 35a, represented by shell section 37a, comprises a pressure side spar cap 52a and core material 51a as part of the first shell segment 35a. The first shell segment 35a further comprises an outer skin 64a on the pressure side 36 of the first shell segment 35a. Further, a copper mesh 56a is arranged between the outer skin 64a and the pressure side spar cap 52a and core material 51a on the pressure side 36 of the shell segment 35a. In this example, the copper mesh is wider than the spar cap 52a as shown in the following. Depending on its use, the copper mesh may for instance end at a nearest receptor and be relatively short, such as for instance 2-10 m long. It can also extend substantially all the way to the root of the blade to form a full Faraday cage to protect whole blades or to act as a downconductor. In the example in Fig. 3, the copper mesh 56a is adjacent to and in direct contact with the pressure side spar cap 52a in the first shell segment 35a and provides equipotentialisation along the corresponding part of the pressure side spar cap 52a. The core material may for instance be Polyethylene terephthalate (PET) or similar material, or balsa or similar material.

[0084] In the example in Fig. 3, the outer skin 64a of the first shell segment 35a has a flange 63a to which the fairing element(s) will be attached to cover the attachment means and to complete the aerodynamic profile of the blade 10 at the joint. This is illustrated further in Figs. 7 and 8.

[0085] To join the two shell segments 35a and 35b, attachment means in the form of bushings 67a in the first shell segment 35a will be engaged with attachment means in the second shell segment 35b, which in this example are corresponding bushings 67b. The bushings are joined using metal rods that engage with opposing bushings in the two segments, as illustrated for instance in Fig. 5a. This method for joining wind turbine blade segments is known. In some embodiments, conductive elements, such as O-rings 70 shown in Fig. 5c, are arranged on opposite ends of each metal rod 68 and in contact with the spar caps and electrically couple the metal rod to the spar caps, in this case spar caps 62a and 62b. This results in equipotentialisation of the two spar caps 62a and 62b. The same can readily be done on the pressure side of the shell segments.

[0086] As shown in Fig. 3, the reference number 63a is used to refer to both the flange surface and to the layer(s) that define the flange relative to the outer skin 64a. The flange 63a may be formed for instance by providing a recess in the outer layers, either during material layup before infusion or by removing part of the outer skin 64a after infusion and curing of the shell segment 35a. The outer skin 64a and the layer(s) defining the flange 63a may for instance be made of composite material, such as for instance glass fibres and / or carbon fibres embedded in a polymer matrix.

[0087] Similarly, the suction side of the first shell segment 35a comprises a suction side spar cap 62a and core material 61a as part of the first shell segment 35a to the outer skin 64a on the suction side 38 of the first shell segment 35a. In the example, a copper mesh 66a is arranged between the outer skin 64a and the suction side spar cap 62a and core material 61a on the suction side 38 of the shell segment 35a. The copper mesh 66a extends along at least a part of the suction side spar cap 62a in the first shell segment 35a and, being adjacent to and in direct contact with the suction side spar cap 62a, provides equipotentialisation along that part of the suction side spar cap 62a. The pressure side spar cap 52a and the suction side spar cap 62a typically extend along most of the first shell segment 35a and carry the bending load experienced during rotation of the wind turbine blade.

[0088] The second shell segment 35b, represented by shell section 37b, is constructed similarly to shell section 37a of the first shell segment 35a. Since wind turbine blades typically taper in the direction towards the tip end 15 (as shown in Fig. 1), the dimensions of the shell section 37b are typically slightly smaller than those of the shell section 37a, which is closer to the root. For simplicity, this is not illustrated, as this is not essential to the invention; the invention is also applicable to a blade having a portion with a fixed airfoil profile or a blade where the section nearer the tip is generally larger than the section nearer to the root.

[0089] Similarly to shell section 37a, shell section 37b of the second shell segment 35b comprises a pressure side spar cap 52b and core material 51b inside the shell section 37b, and an outer skin 64b on the pressure side of the second shell segment 35b. In the example, a copper mesh 56b is arranged between the outer skin 64b and the pressure side spar cap 52b and core material 51b on the pressure side of the second shell segment 35b. The copper mesh 56b extends along at least part of the pressure side spar cap 52b in the second shell segment 35b and provides equipotentialisation along that part of the pressure side spar cap 52b. In this example, the outer skin 64b of the second shell segment 35b has a flange 63b to which the fairing element(s) are attached in order to cover and protect the attachment means and to complete the aerodynamic profile of the blade 10. When the one or more fairings are secured, partly via the flange 63a of the first shell segment 35a and the flange 63b of the second shell segment 35b, for instance using rivets, the attachment means are covered and protected from the outside environment and the aerodynamic profile is completed in the area of the joint. As shown in Fig. 2, several fairing elements are used to completely cover the attachment means and to complete the aerodynamic profile at the joint between the first shell segment 35a and the second shell segment 35b. Specifically, three fairing elements 74, 81, and 85 are used on the suction side 38 of the blade 10 in the example in Fig. 2. Similarly, one or more fairing elements are needed on the pressure side 36 of the blade 10 to ensure that the attachment means are completely covered.

[0090] As shown in Fig. 3, the reference number 63b is used to refer to both the flange of the shell segment 35b and to the layer(s) that define the flange 63b relative to the outer skin 64b of the second shell segment 35b. The flange 63b may be formed as described in relation to flange 63a, for instance by providing a recess in the outer skin 64b, either during material layup before infusion or by removing part of the outer skin 64b after infusion and curing. The outer skin 64b and the layer(s) defining the flange 63b may be made of composite material, such as for instance glass fibres and / or carbon fibres embedded in a polymer matrix.

[0091] Similarly, the suction side 38 of the second blade shell segment 35b comprises a suction side spar cap 62b and core material elements 61b attached inside the shell section 37b to the outer skin 64b on the suction side 38 of the second shell segment 35b. In this example, a copper mesh 66b is arranged between the outer skin 64b and the suction side spar cap 62b and core material elements 61b on the suction side 38 of the second shell segment 35b. The copper mesh 66b provides equipotentialisation along the suction side spar cap 62b.

[0092] Similarly to spar caps 52a and 62a in the first shell segment 35a, the pressure side spar cap 52b and the suction side spar cap 62b in the second shell segment 35b typically extend along a substantial part of the second blade shell segment 35b to carry the bending load experienced during operation of the wind turbine. The spar caps 52b and 62b in the second shell segment 35b typically do not extend all the way to the tip end 15 because the bending loads are lower near the tip end 15. Copper meshes 56b and 66b extend along the pressure side spar cap 52b and the suction side spar cap 62b, respectively, in this example adjacent to and in direct contact with the pressure side spar cap 52b and the suction side spar cap 62b, respectively, to provide equipotentialisation along these spar caps.

[0093] Region 65a, indicated in Fig. 3, of the suction side of the shell section 37a in the area of the suction side spar cap 62a is illustrated and described in more detail below. Similarly, the region 65b, also indicated in Fig. 3, of the suction side of the shell section 37b in the area of the suction side spar cap 62b is illustrated and described in more detail below.

[0094] One or more shear webs connect the spar cap 52a with spar cap 62a and space cap 52b with spar cap 62b to add strength to the blade. To simplify the drawings, and since shear webs are not an essential part of the invention, such shear webs are not shown in the drawings. Figs. 4a and 4b illustrate in more detail the regions 65a and 65b indicated in Fig. 3.

[0095] The view in Fig. 4a is into the shell section 37a in a direction along the suction side spar cap 62a. Thus, the view in Fig. 4a (and also Fig. 4b) is not a cross-section. Nevertheless, the different parts in the region 65a are shown hatched to make it easier to distinguish between them.

[0096] Fig. 4a shows the outer skin 64a (made for instance of composite material including for instance gel and glass fibres), the flange 63a, the copper mesh 66a, the suction side spar cap 62a, and the core material 61a. As seen in Fig. 4a, the copper mesh 66a is arranged in direct contact with the suction side spar cap 62a whereby it causes the abovementioned equipotentialisation along the suction side spar cap 62a. In other examples, for instance as illustrated in Figs. 5c-5d, the copper mesh is separated from the spar cap, for instance by a non-conductive composite material.

[0097] It is further seen in Fig. 4a that the copper mesh 66a also extends beyond the suction side spar cap 62a in the chordwise direction, both towards the leading edge (LE) and towards the trailing edge (TE) of the shell segment 35a. In this example, this assists in providing the electrical connection between the copper mesh 66a in the first blade shell segment 35a and the copper mesh 66b in the second blade shell segment 35b, as will be described below.

[0098] Similarly, Fig. 4b illustrates the region 65b in more detail, including the outer skin 64b (made for instance of composite material including for instance glass fibres and / or carbon fibres), the flange 63b, the copper mesh 66b, the suction side spar cap 62b, and the elements 61b. As seen in Fig. 4b, the copper mesh 66b is arranged in direct contact with the suction side spar cap 62b whereby it provides equipotentialisation along the suction side spar cap 62b. Further, it is seen that the copper mesh 66b, like copper mesh 66a, extends beyond the suction side spar cap 62b in the chordwise direction, both towards the leading edge (LE) and towards the trailing edge (TE). Together with the copper mesh 66a in the first shell segment 35a, this feature assists in establishing the electrical connection between copper mesh 66a in the first blade shell segment 35a and the copper mesh 66b in the second blade shell segment 35b. As will be described below, a composite fairing element completes the electrical connection. The electrical connection can conduct lightning current between the second shell segment 35b and the first shell segment 35a, for instance from a lightning strike on a lightning receptor arranged in the second shell segment 35b, or vice versa.

[0099] Corresponding elements may be provided on the pressure side 36 in a similar manner. For brevity, this is not illustrated in detail. Figs. 5a illustrates the shell section 37a of the first shell segment 35a attached to the shell section 37b of the second shell segment 35b using the respective attachment means, including bushings 67a and 67b and a metal rod 68 joining the opposing bushings 67a and 67b.

[0100] Section A-A in Fig. 5a, this section being indicated in Fig. 4a, is a cross-section along the shell section 37a through the middle of the suction side spar cap 62a and layers 63a and 64a. Similarly, Section C-C in Fig. 5a, this section being indicated in Fig. 4b, is a cross-section along the shell section 37b through the middle of the suction side spar cap 62b and layers 63b and 64b. A fairing is later attached between outer layers 64a and 64b. The fairing will be supported by the flanges 63a and 63b of the shell sections 37a and 37b, respectively. As described above, a fairing in accordance with the invention will protect the attachment means 67a, 67b, and 68 and complete the aerodynamic profile of the blade at the joint. As described above and as shown also in Fig. 5a, the copper meshes 66a and 66b are in direct contact with the respective suction side spar caps 62a and 62b to provide equipotentialisation along the respective spar caps 62a and 62b. The cross-sections A-A and C-C are at essentially the same chordwise position in the respective shell sections 37a and 37b and the bushings 67a and 67b in the respective shell segments 35a and 35b pairwise oppose each other to allow them to be connected pairwise using respective metal rods 68.

[0101] Similarly to Fig. 5a, Section B-B in Fig. 5b, this section being indicated in Fig. 4a, is a cross-section along the shell section 37a through the core material 61a. Similarly, Section D-D in Fig. 5b, this section being indicated in Fig. 4b, is a cross-section along the shell section 37b through the core material 61b. The composite fairing, discussed in more detail below, will extend also to the chordwise position corresponding to Section B-B of the shell section 37a and Section D-D of the shell section 37b. The composite fairing thus covers the attachment means 67a, 67b, and 68 also at these positions.

[0102] As mentioned above, Sections B-B and D-D go through the core material 61a and 61b, not through the suction side spar caps 62a and 62b. The copper meshes 66a and 66b extend beyond the suction side spar caps, including to the positions of sections B-B and D-D. In this example, the copper meshes 66a and 66b extend outside the suction side spar caps 62a and 62b also in the direction of the leading edge 18. As will be illustrated below, this allows fastening of the fairing element on both the leading-edge side and the trailing-edge side of the suction side spar caps 62a and 62b.

[0103] Contrary to the Sections A-A and C-C, the fairing can be riveted to the shell sections 37a and 37b at Sections B-B and D-D. Provision of rivets at Sections A-A and C-C would damage the suction side spar caps 62a and 62b, reducing their strength. Therefore, the fairing is fastened to the shell sections 37a and 37b in one or more positions a distance from the spar caps 62a and 62b where the fastening means, such as rivets, will extend through the copper mesh, but not through the spar caps 62a and 62b. This is shown in more detail below.

[0104] Figs. 5c and 5d illustrate an example of a wind turbine blade in which the copper meshes 66a and 66b are separated from the spar caps 62a and 62b by a non-conductive layer, such as non- conductive composite layers 69a and 69b. This makes the copper meshes 66a and 66b act as Faraday cages around the spar caps 62a and 62b, protecting them from lightning current in case of a lightning strike. The present invention is equally applicable when the copper meshes are separated from the spar caps in this way as when they are in direct contact with the spar caps. Fig. 5c corresponds to cross-sections A-A and C-C indicated in Figs. 4a and 4b, and Fig. 5d corresponds to cross-sections B-B and D-D, also indicated in Figs. 4a and 4b. That is, Fig. 5a shows the cross-section through the spar cap 62a and 62b, and Fig. 5d illustrates a cross-section through core material 61a and 61b, outside the region of the spar caps 62 and 62b.

[0105] Figs. 6a and 6b are similar to Figs. 5a and 5b, respectively, but include a composite fairing element 74 in accordance with the invention. As shown in Fig. 6b, the fairing element 74 at least partially completes the aerodynamic profile in the vicinity of the joint. Further, the fairing element 74 covers the attachment means 67a, 67b, and 68 at least partially, providing at least partial protection of the attachment means from the environment as mentioned above. As also mentioned above, and as illustrated for instance in Fig. 2 and below in Figs. 7 and 8, further fairing elements are used in this example to complete the aerodynamic profile around the joint and to completely protect the attachment means 67a, 67b, and 68 from the environment.

[0106] The fairing element 74 may be premanufactured, made of a fibre-reinforced composite material and a metal element 72, such as a metal mesh layer or metal plate or metal foil, sandwiched between fibre layers 71 and 73 and infused with resin to form the premanufactured fairing element 74. The fairing element is preferably shaped to follow the shape of the flanges 63a and 63b, whereby the flange element 74, when fastened to the flanges 63a and 63b, experiences as little bending load as possible.

[0107] Fig. 6a corresponds to Fig. 5a, i.e. to the Sections A-A and C-C illustrated in Figs. 4a and 4b, respectively, but with the composite fairing attached. As mentioned above, fastening means, for instance rivets, cannot be provided in these regions since they would damage the spar caps 62a and 62b, thereby reducing the strength of the spar caps 62a and 62b. Instead, as illustrated in Fig. 6b, rivets 75a and 75b are provided a distance from the spar caps, but in regions to which the copper meshes 66a and 66b extend.

[0108] The rivets 75a and 75b may be electrically conductive, if needed. As a result, as can be seen from Fig. 6b, the rivet 75a establishes an electrical connection between the copper mesh 66a in the shell section 37a and the copper mesh layer 72 in the fairing element 74. The copper mesh layer 72 in the fairing element 74 extends to the shell section 37b where an electrically conductive rivet 75b establishes an electrical connection between the copper mesh layer 72 in the fairing element 74 and the copper mesh 66b in the shell section 37b. In case of a lightning strike, the fairing element 74 together with the rivets 75a and 75b ensure equipotentialisation between the suction side spar caps 66a and 66b, thus allowing lightning current to be discharged through both a downconductor attached to the copper mesh 66a in the shell segment 35a and through a downconductor attached to the copper mesh 66b in the shell segment 35b. The electrical connection also provides equipotentialisation between any receptors attached to the copper meshes 66a and 66b. At the same time, the fairing element 74, being made of a metal layer 72 covered by composite material, is less susceptible to a lightning strike than is a fairing made entirely of metal. Accordingly, the fairing element 74 itself also reduces the risk that lightning strikes at the joint in the first place.

[0109] By providing more rivets, which will be illustrated below and in Figs. 7 and 8, the electrical resistance between the copper meshes 66a and 66b can be reduced and the fairing element 74 is also held more securely.

[0110] Fig. 6c represents another embodiment of the invention. It is essentially the structure shown in Fig. 5c, but the copper meshes 66a and 66b are exposed, for instance by removing material, such as by grinding material away. For instance, parts of layers 63a and 63b shown in Fig. 5c has been removed. In a sense, Fig. 5c shows the structure in Fig. 6c when only part of the outer layer(s) 64a and 64b (including layer(s) 63a and 63b) has been removed at the position where the fairing element will be placed, whereas Fig. 6c illustrates the segments after those remaining parts have been completely removed. As a result, flanges 63a' and 63a' are formed with upper surfaces that comprise copper mesh.

[0111] A different fairing element 74' is used in this embodiment. The fairing element 74' consists of a composite portion 71 and a copper mesh portion 72 and can be made for instance similarly to the fairing element 74 shown in Fig. 6a, after which the composite layer 73 facing the attachment means is removed at least partially. In the example in Figs. 6c-6d, the layer is completely absent. Alternatively, only material corresponding to, or at least substantially corresponding to, the flanges 63a' and 63b', is removed from the layer 73. This saves time compared to removal of the entire layer 73. It also results in a fairing element having a higher mechanical strength. In addition, especially in case the composite material is non-conductive, the presence of the composite material on part of the inside of the fairing element between the flanges 63a' and 63b' reduces the risk that lightning flashes over to the attachment means 67a, 67b, and 68.

[0112] Fig. 6d illustrates the sections 37a and 37b with the fairing element 74' attached. Similarly to the embodiment in Fig. 6b, the fairing 74' is attached to the sections 37a and 37b a distance from the spar caps 62a and 62b. However, due to the direct contact between the copper mesh 72 in the fairing element 74' and the copper meshes 66a and 66b in the respective sections 37a and 37b, the fasteners, such as rivets, need not be electrically conductive. Thus, fasteners made of plastic can be used instead or in addition. In the embodiment in Fig. 6b, the fasteners are electrically conductive in order to provide electrical connection between the copper mesh 72 in the fairing element 74 and the copper meshes 66a and 66b in the segments 35a and 35b.

[0113] The embodiment in Figs. 6d has the advantage that the copper meshes 66a and 66b in the first and second segments 35a and 35b are in direct contact with the copper mesh in the fairing element 74' over larger areas 63a and 63b. This results in a relatively low resistance between the metal meshes 66a and 66b in the two segments 35a and 35b.

[0114] Figs. 7 and 8 illustrate the shell sections 37a and 37b in a direction towards the suction side surfaces 38a and 38b of the two shell sections 37a and 37b. Fig. 7 is without reference to the spar caps 62a and 62b and the copper meshes 66a and 66b to simplify the view. Fig. 8 illustrates the same view, but with indications of the edges of the spar caps 62a and 62b and the copper meshes 66a and 66b.

[0115] The example in Fig. 7 corresponds to the blade 10 in Fig. 2, which comprises, on the suction side 38, three fairing elements 74, 81, and 85. The fairing element 81 is closer to the trailing edge 20, the fairing element 85 is closer to the leading edge 18, and the fairing element 74 is located above the attachment means that join the shell segment 35a to the shell segment 35b. The fairing element 74 comprises a composite material with a metal element as described above, such as a copper mesh 72 sandwiched between two layers 71 and 73 made of fibre material, such as glass fibre material and / or copper fibre material.

[0116] Rivets 82 attach the fairing element 81 for instance to flanges 63a and 63b. The fairing 81 may have a width different from the width of the fairing element 74 and it may be attached to the shell sections 37a and 37b in another way than via the flanges 63a and 63b. Adjacent fairing elements may also be joined together, such as with rivets. Similarly, rivets 84 attach the fairing element 85 to the shell sections 37a and 37b. The fairing may have a width different from the width of the fairing element 74 and the fairing element 81.

[0117] Finally, and in accordance with the invention, the composite fairing element 74 is attached to the flange 63a of the shell section 37a using a first set of rivets 75a and to the flange 63b of the shell section 37b using a second set of rivets 75b. The rivets 75a and 75b engage with the flanges 63a and 63b, respectively, including the respective copper meshes 66a and 66b, thereby providing electrical connection between the copper meshes 66a and 66b. This provides the advantages already described in detail above.

[0118] Fig. 8 is essentially identical to Fig. 7, but Fig. 8 further includes outlines of the spar caps 62a and 62b as well as the copper meshes 66a and 66b and indicates the sections A-A, B-B, C-C, and D-D (with the fairing element 74 attached as in Figs. 6a and 6b).

[0119] As discussed above, and as illustrated in Fig. 8, the copper meshes 66a and 66b, the edges of which are indicated with same reference numbers 66a and 66b, are wider than the respective spar caps 62a and 62b, the edges of which are indicated with same reference numbers 62a and 62b. The extent of the flanges 63a and 63b of the respective shell sections 37a and 37b is also indicated. As seen for instance from Fig. 5a and 5b, the flanges 63a and 63b comprise a part of respective copper meshes 66a and 66b.

[0120] As shown in Fig. 6a sections A-A and C-C are through the middle of the respective spar caps 62a and 62b. Similarly, sections B-B and D-D run through respective core material 61a and core material 61b (outside the spar caps 62a and 62b). As also shown in Fig. 6b, the sections B-B and D-D run through two rivets 75a and 75b, one in each of the shell sections 37a and 37b. As shown in Fig. 8, the rivets 75a and 75b are located away from the spar caps 62a and 62b, but in regions that contain the copper meshes 66a and 66b. This provides the desired electrical connection between the spar caps 62a and 62b without damaging the spar caps. Further, the rivets 75a go through the flange 63a in the shell section 37a, and the rivets 75b go through the flange 63b in the shell section 37b. As discussed above, the copper meshes 66a and 66b extend into the flanges (as shown for instance in Fig. 5a), whereby the rivets 75a and 75b are in electrical contact with the copper meshes 66a and 66b, respectively, in the shell sections 37a and 37b.

[0121] The description above related to the suction side of the blade 10 applies equally to the pressure side of the blade. In some embodiments, only the suction side or the pressure side are adapted in accordance with the invention and uses a composite fairing element in accordance with the invention. In other embodiments, both sides are adapted in accordance with the invention and use one or more composite fairing elements in accordance with the invention. The composite fairing elements is preferably adapted to provide optimal aerodynamic properties of the final blade shell. The curvature of the suction side and the pressure side are not necessarily the same, and thus a composite fairing element for the suction side is likely shaped differently from a composite fairing element for use on the pressure side.

[0122] List of references

[0123] 2 wind turbine

[0124] 4 tower

[0125] 6 nacelle

[0126] 8 hub

[0127] 10 blade

[0128] 14 blade tip

[0129] 15 tip end

[0130] 16 blade root

[0131] 18 leading edge

[0132] 20 trailing edge

[0133] 30 root region

[0134] 32 transition region

[0135] 34 airfoil region

[0136] 35a first blade shell segment

[0137] 35b second blade shell segment

[0138] 36 pressure side shell portion of blade

[0139] 37a section of first blade shell segment

[0140] 37b section of second blade shell segment

[0141] 38 suction side shell portion of blade

[0142] 38a suction side surface of first blade shell segment

[0143] 38b suction side surface of second blade shell segment

[0144] 40 blade shoulder

[0145] 51a core material in first blade shell segment

[0146] 51b core material in second blade shell segment

[0147] 52a pressure side spar cap of first blade shell segment

[0148] 52b pressure side spar cap of second blade shell segment J

[0149] 56a third metal element in first blade shell segment

[0150] 56b fourth metal element in second blade shell segment

[0151] 57a bushings in first shell segment

[0152] 57b bushings in second shell segment

[0153] 61a core material in first blade shell segment

[0154] 61b core material in second blade shell segment

[0155] 62a suction side spar cap of first shell segment

[0156] 62b suction side spar cap of second shell segment

[0157] 63a flange on first shell segment, flange layers in first blade shell segment

[0158] 63a' flange on first shell segment, flange layers in first blade shell segment

[0159] 63b flange on second shell segment, flange layers in second blade shell segment

[0160] 63b' flange on second shell segment, flange layers in second blade shell segment

[0161] 64a outer skin of first blade shell segment

[0162] 64b outer skin of second blade shell segment

[0163] 65a detail of suction side spar cap of first blade shell segment

[0164] 65b detail of suction side spar cap of second blade shell segment

[0165] 66a first metal element in first blade shell segment

[0166] 66b second metal element in second blade shell segment

[0167] 67a bushings in first shell segment

[0168] 67b bushings in second shell segment

[0169] 68 metal rod connecting opposing bushings

[0170] 69a non-conductive composite layer

[0171] 69b non-conductive composite layer

[0172] 70 conductive O-ring

[0173] 71 composite, such a fibre-reinforced composite

[0174] 72 fairing copper mesh

[0175] 73 composite, such a fibre-reinforced composite

[0176] 74 first fairing element

[0177] 74' first fairing element

[0178] 75a first set of electrically conductive fasteners

[0179] 75b second set of electrically conductive fasteners

[0180] 76a first set of fasteners

[0181] 76b second set of fasteners

[0182] 81 trailing-edge fairing element

[0183] 82 fasteners fasteners leading-edge fairing element longitudinal axis of blade

Claims

Claims1. A wind turbine blade (10) comprising a first wind turbine blade shell segment (35a) having first attachment means (57a, 67a), the wind turbine blade further comprising a second wind turbine blade shell segment (35b) having second attachment means (57b, 67b) engaged with the first attachment means, thereby rigidly joining the first shell segment (35a) to the second shell segment (35b), the first shell segment (35a) further comprising a first metal element (66a), the second shell segment (35b) further comprising a second metal element (66b), the wind turbine blade further comprising one or more fairing elements (74, 74', 81, 85) covering the first and second attachment means and forming a part of an aerodynamic profile of the wind turbine blade (10), wherein at least a first fairing element (74, 74') of the one or more fairing elements comprises fibre-reinforced composite material (71, 73) and a metal element (72) attached to the fibre-reinforced composite material (71, 73) of the fairing element, the first fairing element (74, 74') being fastened to the first shell segment (35a) using a first set of one or more fasteners (75a), such as rivets and / or screws, the first fairing element (74, 74') being fastened to the second shell segment using a second set of one or more fasteners (75b), such as rivets and / or screws, wherein the metal element (72) of the first fairing element (74, 74') provides electrical contact between the first metal element (66a) in the first shell segment (35a) and the second metal element (66b) in the second shell segment (35b).

2. A wind turbine blade in accordance with claim 1, wherein: the first shell segment (35a) comprises an electrically conductive suction side spar cap (62a) and an electrically conductive pressure side spar cap (52a) and the first metal element (66a) of the first shell segment (35a) is arranged adjacent to and in direct contact with one of: the suction side spar cap (62a) of the first shell segment (35a) and the pressure side spar cap (52a) of the first shell segment (35a), and the second shell segment (35b) comprises an electrically conductive suction side spar cap (62b) and an electrically conductive pressure side spar cap (52b) and the second metal element (66b) of the second shell segment (35b) is arranged adjacent to and in direct contact with one of: the suction side spar cap (62b) of the second shell segment (35b) and the pressure side spar cap (52b) of the second shell segment (35b), the first and second sets of fasteners fastening the first fairing element to the first shell segment and to the second shell segment without engaging the spar caps (52a, 52b, 62a, 62b).

3. A wind turbine blade in accordance with claim 2, wherein:The first shell segment (35a) further comprises a third metal element (56a) arranged adjacent to and in direct contact with the other of the suction side spar cap (62a) and the pressure side spar cap (52a) of the first shell segment (35a), whereby both the suction side spar cap (62a) and the pressure side spar cap (52a) of the first shell segment (35a) are adjacent to and in direct contact with a respective one of the first and third metal elements (56a, 66a) in the first shell segment (35a), and the second shell segment (35b) further comprises a fourth metal element (56b) arranged adjacent to and in direct contact with the other of the suction side spar cap (62b) and the pressure side spar cap (52b) of the second shell segment (35b), whereby both the suction side spar cap (62b) and the pressure side spar cap (52b) of the second shell segment (35b) are adjacent to and in direct contact with a respective one of the second and fourth metal elements (56b, 66b) in the second shell segment (35b), the third metal element and the fourth metal element being electrically connected by a second fairing element, the second fairing element comprising fibre-reinforced composite material (71, 73) and the metal element (72) that electrically connects the third metal element and the fourth metal element.

4. A wind turbine blade in accordance with claim 1, wherein: the first shell segment (35a) comprises an electrically conductive suction side spar cap (62a) and an electrically conductive pressure side spar cap (52a) and the first metal element (66a) of the first shell segment (35a) is separated from the suction side spar cap (62a) of the first shell segment (35a) and from the pressure side spar cap (52a) of the first shell segment (35a) by non-conductive material (69a), such as by non- conductive composite material, such as by non-conductive fibre-reinforced composite material, and the second shell segment (35b) comprises an electrically conductive suction side spar cap (62b) and an electrically conductive pressure side spar cap (52b) and the second metal element (66b) in the second shell segment (35b) is separated from the suction side spar cap (62b) of the second shell segment (35b) and the pressure side spar cap (52b) of the second shell segment (35b) by non-conductive material (69b), such as by non-conductive composite material, such as by non-conductive fibre-reinforced composite material,the first and second sets of fasteners fastening the first fairing element to the first shell segment and to the second shell segment without engaging the spar caps (52a, 52b, 62a, 62b).

5. A wind turbine blade in accordance with claim 4, wherein: the first shell segment (35a) further comprises a third metal element (56a) separated from the suction side spar cap (62a) of the first shell segment (35a) and from the pressure side spar cap (52a) of the first shell segment (35a) by non-conductive material, such as by non-conductive composite material, such as by non-conductive fibre- reinforced composite material, and the second shell segment (35b) further comprises a fourth metal element (56b) separated from the suction side spar cap (62b) and the pressure side spar cap (52b) of the second shell segment (35b) by non-conductive material, such as by non-conductive composite material, such as by non-conductive fibre-reinforced composite material, the third metal element and the fourth metal element being electrically connected by a second fairing element, the second fairing element comprising fibre-reinforced composite material (71, 73) and the metal element (72) that electrically connects the third metal element and the fourth metal element.

6. A wind turbine blade in accordance with one of claims 2-5, wherein the metal element (72) of the first fairing element (74) is adjacent to and in direct contact with the first metal element (66a) in the first shell segment (35a) and adjacent to and in direct contact with the second metal element (66b) in the second shell segment (35b).

7. A wind turbine blade in accordance with any of claims 2-6, wherein the first set of fasteners (75a) is a set of electrically conductive fasteners that engage with one or more flanges (63a, 63a') of the first shell segment (35a) and wherein the second set of fasteners (75b) is a set of electrically conductive fasteners that engage with one or more flanges (63b, 63b') of the second shell segment (35b), the one or more flanges (63a, 63a') of the first shell segment (35a) comprising part of the first metal element (66a) and part of the third metal element (56a) of the first shell segment (35a), the one or more flanges (63b, 63b') of the second shell segment (35b) comprising part of the second metal element (66b) and part of the fourth metal element (56b) of the second shell segment (35b), whereby the first and second set of fasteners establish electrical connection between the first metal element (66a) in the first shell segment (35a) andthe metal element (72) in the first fairing element, and between the second metal element (66b) in the second shell segment (35b) and the metal element (72) in the first fairing element.

8. A wind turbine blade in accordance with any of the preceding claims, wherein one or more of, such as all of, the metal elements (56a, 66a, 56b, 66b, 72) are respective layers made of one or more of: copper, copper alloy, aluminium, aluminium alloy; and wherein one or more of, such as all of, the metal elements (56a, 66a, 56b, 66b, 72) are respective layers comprising a metal mesh, such as a copper mesh or a copper alloy mesh.

9. A wind turbine blade in accordance with any of the preceding claims, wherein the first fairing element (74, 74') is arranged on a suction side (38) of the blade, the one or more fairing elements further including a second fairing element comprising fibre-reinforced composite material and a metal element, the second fairing element being arranged on a pressure side (36) of the blade, the second fairing element being fastened to the first shell segment (35a) and the second shell segment (35b) using a third set of fasteners, wherein the second fairing element is arranged and fastened such that the metal element of the second fairing element provides electrical contact between the third metal element (56a) in the first shell segment (35a) and the fourth metal element (56b) in the second shell segment (35b).

10. A wind turbine blade in accordance with any of the preceding claims, wherein the first attachment means (67a) comprises a first set of bushings and the second attachment means (67b) comprises a corresponding second set of bushings, and wherein the first shell segment and the second shell segment are joined by metal rods engaging bushings in the first set of bushings and opposing bushings in the second set of bushings, at least one of the metal rods comprising: a first conductive element, such as a conductive rubber ring, that provides electrical contact between the metal rod and a spar cap (62a, 52a) in the first shell segment (35a), and a second conductive element, such as a conductive rubber ring, that provides electrical contact between the metal rod and a spar cap (62b, 52b) in the second shell segment (35b).

11. A wind turbine blade in accordance with any of the preceding claims, wherein the first fairing element (74, 74') is premanufactured either:by sandwiching the metal element (72) of the first fairing element (74) between at least two non-conductive fibre material layers (71, 73); infusing liquid resin into the at least two fibre material layers; and curing the resin, or. by sandwiching the metal element (72) of the first fairing element (74) between at least two non-conductive fibre material layers (71, 73); infusing liquid resin into the at least two fibre material layers; and curing the resin; and subsequently removing at least part of one of the non-conductive fibre material layers to expose at least part of the metal element (72), or by arranging the metal element (72) adjacent to at least one non-conductive fibre material layer; infusing liquid resin to the metal element and the at least one non- conductive fibre material layer; and curing the resin.

12. A method for manufacturing a wind turbine blade, comprising: providing a first wind turbine blade shell segment (35a) having first attachment means (57a, 67a) and providing a second wind turbine blade shell segment (35b) having second attachment means (57b, 67b), engaging the first attachment means with the second attachment means to rigidly join the first shell segment (35a) to the second shell segment (35b), fastening one or more fairing elements (74, 74', 81, 85) to the first and second shell segments such as to cover the first and second attachment means (67a, 67b), the one or more fairing elements further being configured to form a part of an aerodynamic profile of the wind turbine blade (10), at least a first fairing element (74, 74') of the one or more fairing elements comprising fibre-reinforced composite material (71, 73) and a metal element (72) attached to the fibre-reinforced composite material (71, 73), wherein the first fairing element (74, 74') is fastened to the first shell segment (35a) using a first set of one or more fasteners (75a) and the first fairing element (74, 74') is fastened to the second shell segment (35b) using a second set of one or more fasteners (75b), wherein the metal element (72) of the first fairing element (74, 74'), when fastened, provides electrical contact between a first metal element (66a) in the first shell segment (35a) and a second metal element (66b) in the second shell segment (35b).

13. A method in accordance with claim 12, wherein:the first shell segment (35a) comprises: i. an electrically conductive suction side spar cap (62a), the first metal element (66a) of the first shell segment (35a) being arranged in direct contact with the suction side spar cap (62a) of the first shell segment (35a), ii. an electrically conductive pressure side spar cap (52a) and a third metal element (56a) arranged in direct contact with the pressure side spar cap (52a) of the first shell segment (35a), the second shell segment (35b) comprises: i. an electrically conductive suction side spar cap (62b), the second metal element (66b) of the second shell segment (35b) being arranged in direct contact with the suction side spar cap (62b) of the second shell segment (35b), ii. an electrically conductive pressure side spar cap (52b) and a second metal element (56b) arranged in direct contact with the pressure side spar cap (52b) of the second shell segment (35b).

14. A method in accordance with claim 13 or 14, wherein: the first set of fasteners and the second set of fasteners comprise rivets and / or screws, the first fairing element (74, 74') comprising fibre-reinforced composite material is premanufactured, the one or more fairing elements comprise a second premanufactured fairing element comprising fibre-reinforced composite material and a metal element, the first fairing element (74, 74') being arranged on a suction side (38) of the blade, the second fairing element being arranged on a pressure side (36) of the blade, the second fairing element being fastened to the first shell segment (35a) and the second shell segment (35b) using electrically conductive fasteners such that the second metal element (56a) of the first shell segment (35a) is electrically connected to the second metal element (56b) of the second shell element (35b) via the metal element of the second fairing element.

15. A fairing element (74, 74') for covering first attachment means (57a, 67a, 68) and second attachment means (57b, 67b, 68) in a segmented wind turbine blade (10) comprising a first wind turbine blade shell segment (35a) and a second wind turbine blade shell segment (35b),the first shell segment (35a) comprising the first attachment means (57a, 67a), the second shell segment (35b) comprising the second attachment means (57b, 67b), the first shell segment (35a) being joined to the second shell segment (35b) by engaging the first attachment means with the second attachment means, the fairing element (74, 74') being configured to form a part of an aerodynamic profile of the wind turbine blade (10), wherein the fairing element (74, 74') comprises fibre-reinforced composite material (71, 73) and a metal element (72) attached to the fibre-reinforced composite material (71, 73), the metal element (72) being dimensioned such that the fairing element can be attached to the first shell segment (35a) using a first conductive fastener and to the second shell segment (35b) using a second conductive fastener in such a way that the metal element (72) is in electrical contact with the first fastener and the second fastener, whereby the metal element (72) in the fairing element electrically connects the first fastener with the second fastener.

16. A fairing element in accordance with claim 15, wherein the fairing element is a layered structure and wherein the metal element is a metal layer forming part of the layered structure, the layered structure further comprising a fibre material layer.

17. A fairing element in accordance with claim 16, wherein the metal layer is sandwiched between two layers comprising fibre material.

18. A fairing element in accordance with any of claims 15-17, wherein the metal element is a mesh structure.

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