Wind turbine blade for a wind turbine and method of manufacturing a wind turbine blade

Abstract

A wind turbine blade (1) for a wind turbine, the wind turbine blade (1) comprising: a first element (2) comprising carbon fibers, the first element (2) being surrounded by a first metal cover (3) so as to form a Faraday cage around the first element (2); a second element (4) comprising carbon fibers, the second element (4) being surrounded by a second metal cover (5) so as to form a Faraday cage around the second element (4); and an electrical connection (6) connecting the first metal cover (3) and the second metal cover (5). Elements comprising carbon fibers can be protected against lightning strikes, thereby allowing such elements to be placed further towards the tip, thereby making the entire blade lighter and allowing the shape of the tip to be better adjusted.

Description

Technical Field

[0001] The invention relates to a wind turbine blade for a wind turbine and a corresponding method of manufacturing a wind turbine blade. Background Art

[0002] Carbon fiber reinforced polymer (CFRP), due to its high strength-to-weight ratio, is rapidly replacing glass fiber based structural components to obtain enhanced performance from wind turbine rotor blades, particularly as a material for spar caps or beams.

[0003] The rotor blades of wind turbines are often subject to lightning strikes. Lightning protection of rotor blades generally relies on providing a device that intercepts and transfers large lightning currents by using a metallic receptor (i.e., air terminal) and an internally laid cable (i.e., a down conductor that transfers the lightning current to the ground).

[0004] Since carbon fibers are conductive, carbon components may be subject to lightning strikes, which may damage their structure and thus cause the blade and turbine to fail without warning. To avoid lightning attachment, the use of carbon components is limited in the outermost parts of wind turbine blades (i.e., the tip region), which adversely affects the weight advantages and design flexibility that CFRP may otherwise provide. For the same reason, air terminations are avoided adjacent to carbon components.

[0005] Furthermore, the CFRP spar caps extending parallel to the metal down conductors in the spanwise direction behave like a set of parallel conductors with a short distance, and therefore, when lightning is intercepted by the air terminal and transferred via the down conductors, mutual inductance will establish current in the parallel CFRP spar caps.

[0006] In addition, the material properties of the down conductor combined with the waveform parameters of the lightning current result in a potential drop of approximately several million volts along the down conductor, forcing a flashover (i.e. arc) between the down conductor and the CFRP spar cap, which may lead to structural damage to the wind turbine blade.

[0007] To mitigate this risk, the prior art proposes to provide equipotential bonding at regular intervals along the length of the CFRP spar caps. Due to the anisotropy of CFRP and the difference in properties relative to metallic down conductors, passing current between them is challenging, resulting in sparks and hot spots.

[0008] Finally, at high currents, there is the challenge of Joule heating, which can cause thermal damage leading to delamination and burning, severely degrading the performance of structural elements such as spar caps. Summary of the invention

[0009] It is an object of the present invention to provide an improved wind turbine blade which facilitates a less restrictive use of carbon elements while providing adequate protection against lightning strikes.

[0010] According to a first aspect, there is provided a wind turbine blade for a wind turbine. The wind turbine blade comprises: a first element comprising carbon fibers, the first element being surrounded by a first metal cover so as to form a Faraday cage around the first element; a second element comprising carbon fibers, the second element being surrounded by a second metal cover so as to form a Faraday cage around the second element; and an electrical bond connecting the first metal cover and the second metal cover.

[0011] By forming a Faraday cage around the element including carbon fibers, lightning current can be effectively transferred while shielding the element from electromagnetic fields. At the same time, by connecting the first metal cover and the second metal cover to each other via an electrical connection, equipotentialization between the covers is obtained. Therefore, due to the high conductivity of the metal cover, an external lightning strike can be intercepted and safely conducted via the metal cover.

[0012] Furthermore, because the elements comprising carbon fibers are protected, they can be placed further towards the tip of the wind turbine blade, making the wind turbine blade lighter and allowing for better adjustment of the shape of the tip. By limiting the metal cap to only the elements comprising carbon fibers rather than the entire blade, weight and cost savings can be achieved.

[0013] Additionally, structural repairs and lightning-related repairs are decoupled, resulting in fast and efficient repairs, especially since repairs to the Faraday cage are relatively simple and involve only fabricating a new metal cover and optionally checking the electrical connections with an ohmmeter. This is the case since the carbon fiber-containing element no longer acts as an electrical conductor in the lightning protection system circuit. Furthermore, due to the protection provided by the metal cover, repairs can usually be performed by rope access or crane, making it unnecessary to lower the blade to the ground.

[0014] An electrically isolating cover such as fiberglass may be placed between the first metal cover and the first element, and / or an electrically isolating cover such as fiberglass may be placed between the second metal cover and the second element. This may improve the Faraday effect obtained for the respective elements.

[0015] According to an embodiment, the wind turbine blade further comprises an air termination point arranged on the metal cover and electrically connected to the metal cover.

[0016] Since the elements comprising carbon fibres are protected by means of the metal cover, lightning currents can be intercepted in areas of the wind turbine blade which could not be properly protected before.

[0017] According to a further embodiment, the wind turbine blade further comprises an air termination point which is arranged in a region of the wind turbine blade remote from the first and second elements and which is electrically connected to the metal cover, eg by means of a conductor, eg a cable.

[0018] Thus, an air termination point can be provided, for example towards the tip of a wind turbine blade, without the need for a down conductor extending through the entire horizontal cross-section of the wind turbine blade. In regions of elements comprising carbon fibers, such as spar caps, the component taking on the function of a down conductor is instead realized by means of a metal cover.

[0019] According to another embodiment, the electrical connection is a metal conductor, in particular a metal cable.

[0020] Due to their high electrical conductivity, metallic conductors provide rapid equipotentialization in the event of a lightning strike.

[0021] According to another embodiment, end portions of the first and / or second metal cover are bundled in order to form a connection interface for the electrical coupling.

[0022] In this way, an easy, efficient and safe interface with the rest of the lightning protection system may be provided, in particular since the number of additionally required components is reduced.

[0023] According to another embodiment, the first and / or second metal cover is at least one of a sheet, a mesh, a foil, a paint, and a coating.

[0024] The Faraday cage formed around the carbon fiber containing element may also be formed by a variety of methods, such as using a cabled mesh only at locations that serve as the connection interface for the electrical coupling, and using a coating elsewhere.

[0025] The mesh size of the Faraday cage can range from zero (i.e., continuous foil) to many millimeters for a mesh, wherein different areas of the element containing carbon fibers also use meshes of different mesh sizes. The mesh size can also be higher (i.e., greater than 1 cm), for example for areas with a low probability of lightning strikes or for areas primarily used for voltage equalization (such as the electrical connection connecting the first metal cover and the second metal cover).

[0026] According to another embodiment, the first and / or second element comprising carbon fibers is a carbon fiber reinforced polymer.

[0027] Carbon fiber reinforced polymers offer significant weight advantages and design flexibility in the design of wind turbine blades and must be protected against lightning strikes due to their electrical conductivity.

[0028] According to another embodiment, an end portion of each of the first and second metal covers is bundled and connected to each other in one piece so as to form an electrical connection.

[0029] Thus, the first and second metal covers are integrally formed from a single piece of material, such as a mesh, for protecting the first and second elements comprising carbon fibers.

[0030] According to another embodiment, the first element is a first spar cap and / or the second element is a second spar cap.

[0031] Since the spar caps are structural components and typically comprise carbon fiber, there is a great need to protect the spar caps.

[0032] According to another embodiment, the first and second spar caps extend spanwise and parallel to each other, wherein the electrical connection is the only conductor in the chordwise gap between the first and second metal caps.

[0033] This has the advantage that it is no longer necessary to position a down conductor between the two spar caps, since the metal cover surrounding the spar caps takes over the function of the down conductor. Thus, a significant simplification of the design and assembly of the wind turbine blade can be achieved.

[0034] According to another embodiment, an electrical coupling is provided between spanwise end portions of the first and second metal covers, wherein the electrical coupling is electrically connected to a down conductor of the wind turbine.

[0035] By providing electrical couplings only at lateral end portions of the first and second metal covers, ie at lateral end portions of the respective spar caps, no electrical connection needs to be located in the chord-wise space between the spar caps, which results in additional constructional simplification of the wind turbine blade.

[0036] According to a particularly preferred embodiment, the electrical connection is provided in a discontinuous manner, for example by providing a spark gap instead of a continuous connection.

[0037] The electrical couplings provided at the lateral end portions of the first and second metal covers may further be connected to an existing lightning protection system of the wind turbine, for example by means of a root terminal.

[0038] For the metal cover, conductive materials such as metals and alloys can be used as long as they pose a minimal risk of electrochemical corrosion (e.g. copper, bronze). Alternatively, non-metals (e.g. carbon) and / or their composites coated with metallic materials, such as metallized fibers, can also be used.

[0039] Any embodiment of the first aspect may be combined with any embodiment of the first aspect to obtain another embodiment of the first aspect.

[0040] According to a second aspect, the invention relates to a wind turbine comprising at least one wind turbine blade according to the first aspect.

[0041] According to a third aspect, there is provided a method of manufacturing a wind turbine blade for a wind turbine. The method comprises the steps of: surrounding a first element comprising carbon fibers with a first metal cover so as to form a Faraday cage around the first element; surrounding a second element comprising carbon fibers with a second metal cover so as to form a Faraday cage around the second element; and connecting the first metal cover and the second metal cover using an electrical connection.

[0042] The embodiments and features described with reference to the apparatus of the invention apply mutatis mutandis to the method of the invention.

[0043] Other possible implementations or alternative solutions of the present invention also cover combinations of features described above or below with respect to the embodiments not explicitly mentioned herein. Those skilled in the art may also add separate or independent aspects and features to the most basic form of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Other embodiments, features and advantages of the present invention will become apparent from the following description and the dependent claims, taken in conjunction with the accompanying drawings, in which:

[0045] Figure 1 shows a wind turbine blade according to a first embodiment in cross-section;

[0046] Figure 2 A first element comprising carbon fibres of a wind turbine blade according to a first embodiment is shown in cross-section;

[0047] Figure 3 showing in perspective a spar cap surrounded by a metal cover, wherein end portions of the metal cover are bundled to form a connection interface;

[0048] Figure 4 Shown in perspective are two spar caps surrounded by metal covers which are bundled and connected to each other in one piece so as to form an electrical connection;

[0049] Figure 5 Two embodiments of spar caps surrounded by metal covers are shown in perspective view, wherein the metal covers are connected to air termination points in different ways;

[0050] Figure 6 Another embodiment of an air terminal base is shown, the air terminal base including a retaining portion by means of which a metal cover is connected;

[0051] Figure 7 shows in cross-section a tip portion of a wind turbine blade including two air terminations; and

[0052] Figure 8A method of manufacturing a wind turbine blade for a wind turbine is shown in a flow chart.

[0053] In the drawings, like reference numbers indicate identical or functionally equivalent elements unless otherwise indicated. DETAILED DESCRIPTION

[0054] Figure 1 A wind turbine blade 1 according to a first embodiment is shown. The wind turbine blade 1 comprises a first element 2 comprising carbon fibres, the first element 2 being surrounded by a first metal cover 3 in order to form a Faraday cage around the first element 2. Furthermore, the wind turbine blade 1 comprises a second element 4 comprising carbon fibres, the second element 4 being surrounded by a second metal cover 5 in order to likewise form a Faraday cage around the second element 4. In the present case, the first element 2 is a first spar cap and likewise the second element 4 is a second spar cap.

[0055] Furthermore, an electrical connection 6 is provided connecting the first metal cover 3 and the second metal cover 5. Figure 1 In the embodiment, the corresponding metal covers 3 and 5 are metal meshes. Figure 1 This is particularly evident in the upper and lower enlarged parts.

[0056] Although three electrical couplings 6 are shown in this embodiment, it may be sufficient to provide only two electrical couplings 6 to connect the first metal cover 3 and the second metal cover 5. In detail, omitting the metal couplings 6 in the area between the spar caps will simplify the overall construction of the wind turbine blade 1.

[0057] The wind turbine blade 1 further comprises an air terminal point 7 arranged on the respective metal cover 3, 5, said air terminal point 7 being electrically connected to the respective metal cover. Furthermore, an additional air terminal point 7 may be arranged in a region 8 of the wind turbine blade 1 remote from the first and second elements 2, 4 (i.e. the spar caps) and electrically connected to the metal covers 3, 5. Figure 1 As is evident in FIG. 1 , the respective air termination point 7 penetrates an outer layer 9 of the wind turbine blade 1 , which surrounds the wind turbine blade.

[0058] The metal covers 3, 5, the electrical coupling 6 and the air terminal point 7 form a lightning protection system for a wind turbine blade 1. In order to transfer the lightning current to the ground after a lightning strike, the system may be connected by means of a root terminal 10 to a down conductor of the wind turbine.

[0059] The metal cover 3 may be provided by attaching metal wires to each other using retaining portions, crimping, welding, soldering, bundling or tying (eg, with conductive and non-conductive materials, etc.) so as to form a Figure 1 Alternatively, the metal cover 6 may be as follows: Figure 1A (eg, woven) metal mesh (without distinct nodes) is shown in the lower enlarged view of FIG.

[0060] Figure 2 A first element 2 of a wind turbine blade 1 according to a first embodiment is shown in cross section.

[0061] In the present case, the first element 2 comprising carbon fibers is a spar cap, which comprises, for example, a carbon fiber reinforced polymer. Since the first element 2 is surrounded by a metal cover 3, for example a metal mesh, it is protected against lightning strikes. This is the case because the metal cover 3 forms a Faraday cage around the first element 2, which serves to carry the lightning current.

[0062] Figure 3 A first element 2 comprising carbon fibres in the form of a spar cap is shown in a perspective view, which is surrounded by a metal cover 3. In it, end portions 11 of the metal cover 3 are bundled so as to form a connection interface 12.

[0063] The metal cover 3 has a transition 13, which may also be referred to as a "conductive bundle", from the Faraday cage surrounding the first element 2 to the connection interface 12. The connection interface 12 may be arranged towards the tip and / or the root of the wind turbine blade 1, which allows for an easy, efficient and safe interface with the rest of the lightning protection system, for example using the electrical coupling 6.

[0064] In the metal mesh including nodes (according to Figure 1 In the case where a metal cover 3 is used as the metal cover 3, bundling at the end portion (i.e. the root or tip) of the wind turbine blade is achieved by removing and / or untying metal nodes, clamps, crimps, knots, etc. from the metal mesh and bundling the metal wires into cables. Alternatively, the metal mesh may be bundled including the nodes after straightening the metal wires.

[0065] Figure 4 A first and a second element 2, 4 (e.g. spar caps) comprising carbon fibres are shown in perspective view, which are surrounded by metal caps 3, 5 respectively, wherein the metal caps 3 are bundled between the spar caps 2, 4 in order to form an electrical connection. Since only one piece of material is used to form the connection interface 12 for the two spar caps 2, 4, the number of required parts is reduced overall, and thus possible vulnerabilities such as loose connections can be avoided. In detail, it is no longer necessary to provide additional means for connecting the first metal cap 3 with the second metal cap 5, because the electrical connection is achieved by the bundled portion of the metal caps 3, as is apparent from the transition 13.

[0066] In the case where a metal mesh including a node is used as the metal cover 3 , bundling in the center of the beam may be achieved by including a third metal wire in the metal mesh (or metal node) or the metal mesh.

[0067] Figure 5 The element 2 comprising carbon fibres is shown in a perspective view, which is surrounded by a metal cover 3 which is directly connected to the air terminal point 7 according to the first embodiment and which is connected to the air terminal point 7 using a conductor 14 according to the second embodiment.

[0068] The conductor 14 may also be provided by means of a conductive bundle by bundling the ends of the metal cover 3 so as to form the conductor 14 connected to the base 15 of the air terminal point 7 .

[0069] Figure 5 The embodiment shown on the left shows an air terminal point 7 arranged directly on a first element 2 (e.g. a spar cap) comprising carbon fibers. In detail, a base 15 of the air terminal point 7 is electrically connected to the metal cover 3, while an air terminal 16 of the air terminal point 7 penetrates an outer layer 9 (not shown) of the wind turbine blade 1.

[0070] on the contrary, Figure 5 The embodiment shown on the right corresponds to an air termination point 7 which is arranged in a region of the wind turbine blade 1 remote from the second element 4 and is electrically connected to the metal cover 5 using a conductor 14. The conductor 14 may be, for example, a metal cable.

[0071] Figure 6 Another embodiment of an air terminal base 15 is shown, which comprises a retaining portion 17 by means of which the metal cover 3 is connected.

[0072] Before assembly, the retaining portion 17 may extend vertically from the bottom of the air terminal base 15. After the metal cover 3 has been inserted into the retaining portion 17, the retaining portion 17 is bent to clamp or crimp the metal cover 3. Advantageously, the retaining portion 17 clamps or crimps the metal cover 3 in the area where the different lines of the metal cover 3 are connected via the node 18, which is Figure 6 is shown on the left.

[0073] Figure 7 A tip portion of a wind turbine blade 1 is shown in cross section, comprising two air terminations 16. Each air termination 16 penetrates an outer layer 9 of the wind turbine blade 1, which surrounds the wind turbine blade 1. The air terminations 16 are connected to an air termination base 15, which in turn is connected to a conductor 14. Instead of connecting the conductor 14 to a down conductor which may extend in the wind turbine blade 1 in the span direction, the conductor 14 is connected to the first and / or second metal cover 3, 5.

[0074] Figure 8A flow chart is shown which illustrates a method of manufacturing a wind turbine blade 1 for a wind turbine. In step S1, a first element 2 comprising carbon fibers is surrounded by a first metal cover 3 so as to form a Faraday cage around the first element 2. In step S2, a second element 4 comprising carbon fibers is surrounded by a second metal cover 5 so as to also form a Faraday cage around the second element 4. In step S3, the first metal cover 3 and the second metal cover 5 are connected using an electrical connection 6.

[0075] Although the invention has been described in terms of preferred embodiments, it will be apparent to those skilled in the art that modifications may be made in all embodiments.

Claims

1. A wind turbine blade (1) for a wind turbine, the wind turbine blade (1) comprising: a first element (2) comprising carbon fibers, said first element (2) being surrounded by a first metal cover (3) so as to form a Faraday cage around said first element (2); a second element (4) comprising carbon fibers, said second element (4) being surrounded by a second metal cover (5) so as to form a Faraday cage around said second element (4); as well as An electrical connection portion (6), wherein the electrical connection portion (6) connects the first metal cover (3) and the second metal cover (5).

2. The wind turbine blade according to claim 1, further comprising an air termination point (7) arranged on the metal cover (3, 5) and electrically connected to the metal cover (3, 5).

3. The wind turbine blade according to claim 1 , further comprising an air termination point ( 7 ) which is arranged in a region ( 8 ) of the wind turbine blade ( 1 ) remote from the first element ( 2 ) and the second element ( 4 ) and is electrically connected to the metal cover ( 3 , 5 ).

4. The wind turbine blade according to claim 1 or 2, wherein: The electrical connection part (6) is a metal conductor.

5. The wind turbine blade according to claim 1 or 2, wherein: The electrical connection part (6) is a metal cable.

6. The wind turbine blade according to claim 1 or 2, wherein: The end portions (11) of the first metal cover (3) and / or the second metal cover (5) are bundled to form a connection interface (12) for the electrical connection portion (6).

7. The wind turbine blade according to claim 1 or 2, wherein: The first metal cover (3) and / or the second metal cover (5) is at least one of a sheet, a mesh, a foil, a paint and a coating.

8. The wind turbine blade according to claim 1 or 2, wherein: The first element (2) and / or the second element (4) comprising carbon fibers is a carbon fiber reinforced polymer.

9. The wind turbine blade according to claim 1 or 2, wherein: The end portion (11) of each of the first metal cover (3) and the second metal cover (5) is bundled and connected to each other in one piece to form the electrical coupling portion (6).

10. The wind turbine blade according to claim 1 or 2, wherein: The first element (2) is a first spar cap and / or the second element (4) is a second spar cap.

11. The wind turbine blade of claim 10, wherein: The first spar cap and the second spar cap extend in the span direction and are parallel to each other, wherein the electrical connection (6) is the only conductor in the chord-wise gap between the first metal cover (3) and the second metal cover (5).

12. The wind turbine blade of claim 10, wherein: The electrical connection portion (6) is provided between spanwise end portions of the first metal cover (3) and the second metal cover (5), wherein the electrical connection portion (6) is electrically connected to a down conductor of the wind turbine.

13. A wind turbine comprising at least one wind turbine blade (1) according to one of claims 1 to 12.

14. Method for manufacturing a wind turbine blade (1) for a wind turbine, the method comprising the steps of: Surrounding (S1) a first element (2) comprising carbon fibers with a first metal cover (3) so as to form a Faraday cage around said first element (2); surrounding (S2) a second element (4) comprising carbon fibers with a second metal cover (5) so as to form a Faraday cage around said second element (4); and The first metal cover (3) and the second metal cover (5) are connected (S3) using an electrical connection portion (6).

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