LIGHTNING PROTECTION SYSTEM FOR A WIND TURBINE BLADE

Abstract

The present invention relates to a wind turbine blade having a lightning protection system. The blade includes a pressure side shell part and a suction side shell part. The pressure side shell part or the suction side shell part comprises a blade component extending along a longitudinal axis of the blade and comprising one or more carbon fibre structures. The blade component is at least partially embedded in the shell part. An elongate metallic element is arranged in direct contact with the blade component, and at least part of the elongate metallic element is positioned between the blade component and an outer surface of the shell part. A lightning receptor is arranged in electrical contact with the elongate metallic element and extends to or near an outer surface of the blade shell part. The lightning receptor does not extend through the blade component.

Claims

1-22. (canceled)

23. A wind turbine blade (300) comprising a first blade shell part (36), such as a pressure side shell half, and a second blade shell part (38), such as suction side shell half, wherein the first blade shell part (36) comprises: a first blade component (306) extending along a longitudinal axis of the blade and comprising one or more first carbon fibre structures, the first blade component being at least partially embedded in the first blade shell part, a first elongate metallic element (308) arranged in direct contact with the first blade component, at least part of the first elongate metallic element being positioned between the first blade component and an outer surface of the first blade shell part, and a first lightning receptor (304a, 304b, 304c) arranged in electrical contact with the first elongate metallic element and extending to or near an outer surface of the first blade shell part, wherein the first lightning receptor does not extend through the first blade component, and/or wherein the second blade shell part (38) comprises: a second blade component (406) extending along the longitudinal axis of the blade and comprising one or more second carbon fibre structures, the second blade component being at least partially embedded in the second blade shell part, a second elongate metallic element (408) arranged in direct contact with the second blade component, at least part of the second elongate metallic element being positioned between the second blade component and an outer surface of the second blade shell part, and a second lightning receptor (1104) arranged in electrical contact with the second elongate metallic element and extending to or near an outer surface of the second blade shell part, wherein the second lightning receptor does not extend through the second blade component.

24. A wind turbine blade in accordance with claim 22, wherein the first lightning receptor (304a, 304b, 304c) does not extend into the first blade component (306), and/or wherein the second lightning receptor (1104) does not extend into the second blade component (406).

25. A wind turbine blade in accordance with claim 22, wherein the first elongate metallic element is at least partially embedded in the first blade shell part, and/or wherein the second elongate metallic element is at least partially embedded in the second blade shell part.

26. A wind turbine blade in accordance with claim 22, wherein the first elongate metallic element along its entire length is embedded in the first blade shell part, and/or wherein the second elongate metallic element along its entire length is embedded in the second blade shell part.

27. A wind turbine blade in accordance with claim 22, wherein the first lightning receptor is arranged between an outer surface of the first blade shell part and the first blade component, and/or wherein the second lightning receptor is arranged between an outer surface of the second blade shell part and the second blade component.

28. A wind turbine blade in accordance with claim 22, wherein the first lightning receptor extends at least from the first elongate metallic element to or near an outer surface of the first blade shell part, and/or wherein the second lightning receptor extends at least from the second elongate metallic element to or near an outer surface of the second blade shell part.

29. A wind turbine blade in accordance with claim 22, wherein a length of the first elongate metallic element is at least 50% of a length of the blade, such as at least 60% of the length of the blade, such as at least 75% of the length of the blade.

30. A wind turbine blade in accordance with claim 22, wherein a ratio between a length of the first elongate metallic element and a length of the first blade component is in the range 0.8 to 1.2, such as in the range 0.9 to 1.1, such as substantially equal to 1, and/or wherein a ratio between a length of the second elongate metallic element and a length of the second blade component is in the range 0.8 to 1.2, such as in the range 0.9 to 1.1, such as substantially equal to 1.

31. A wind turbine blade in accordance with claim 22, wherein the first blade component and the first elongate metallic element are in contact with one another substantially along an entire length of the first blade component or an entire length of the first elongate metallic element, whichever is shorter.

32. A wind turbine blade in accordance with claim 22, further comprising a first electrical connector (321) electrically connecting the first elongate metallic element and the second elongate metallic element to one another at distal ends of the first elongate metallic element and the second elongate metallic element.

33. A wind turbine blade in accordance with claim 22, wherein the first blade component and/or the second blade component is a spar cap comprising carbon fibre material, such as a spar cap formed by pultrusion.

34. A wind turbine blade in accordance with claim 22, wherein the one or more first carbon fibre structures and/or the one or more second carbon fibre structures comprise carbon fibre mats or carbon fibre reinforced composite planks.

35. A wind turbine blade in accordance with claim 22, wherein the first metallic conductor and/or the second metallic conductor is made of copper or a copper alloy.

36. A wind turbine blade in accordance with claim 22, wherein the first metallic conductor and/or the second metallic conductor has a cross-sectional area of at least 50 mm.sup.2, such as in the range 50-100 mm.sup.2, such as in the range 60-90 mm.sup.2, such as in the range 70-80 mm.sup.2.

37. A wind turbine blade in accordance with claim 22, wherein the first elongate metallic element is a metal strip, wherein at least part of the metal strip has a rectangular cross-section along the longitudinal axis of the blade, a height of said part of the first elongate metallic element being in the range 1-5 mm, such as in the range 2-4 mm, such as being a height of 3 mm, and a width of said part of the first elongate metallic element is in the range 5-30 mm, such as in the range 10-30 mm, such as in the range 20-30 mm, such as being a width of 25 mm.

38. A wind turbine blade in accordance with claim 22, further comprising a downconductor arranged between the first blade shell part and the second blade shell part and extending to a root end of the wind turbine blade, the downconductor being electrically connected to the first elongate metallic element and/or the second elongate metallic element, wherein a length of the downconductor is at most 0.5 times a length of the blade, such as at most 0.3 times the length of the blade, such as at most 0.2 times the length of the blade, such as at most 0.02 times the length of the blade

39. A wind turbine blade in accordance with claim 22, wherein the wind turbine blade further comprises a downconductor arranged between the first blade shell part and the second blade shell part and extending to a root end of the wind turbine blade, the downconductor being electrically connected to the first elongate metallic element and/or the second elongate metallic element, wherein a length of the downconductor is at most 0.5 times a length of the blade, such as at most 0.3 times the length of the blade, such as at most 0.2 times the length of the blade, such as at most 0.02 times the length of the blade, and wherein the first lightning receptor is arranged between an outer surface of the first blade shell part and the first blade component, and/or wherein the second lightning receptor is arranged between an outer surface of the second blade shell part and the second blade component.

40. A wind turbine blade in accordance with claim 22, wherein the wind turbine blade further comprises a downconductor arranged between the first blade shell part and the second blade shell part and extending to a root end of the wind turbine blade, the downconductor being electrically connected to the first elongate metallic element and/or the second elongate metallic element, wherein a length of the downconductor is at most 0.5 times a length of the blade, such as at most 0.3 times the length of the blade, such as at most 0.2 times the length of the blade, such as at most 0.02 times the length of the blade, and wherein the first lightning receptor extends at least from the first elongate metallic element to or near an outer surface of the first blade shell part, and/or wherein the second lightning receptor extends at least from the second elongate metallic element to or near an outer surface of the second blade shell part.

41. A premanufactured elongate fibre-reinforced composite element (414) for being incorporated into a wind turbine blade shell, comprising: a blade component (306) extending along a longitudinal axis of the premanufactured composite element, the blade component comprising one or more carbon fibre structures, and an elongate metallic element (308) arranged in direct contact with the blade component.

42. A premanufactured elongate fibre-reinforced composite element in accordance with claim 41, wherein the blade component is a spar cap for a wind turbine blade shell and the elongate metallic element is a metal strip extending substantially along an entire length of the spar cap.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0040] The invention is explained in detail below with reference to embodiments shown in the drawings.

[0041] FIG. 1 is a schematic view of a wind turbine.

[0042] FIG. 2 is a schematic view of a wind turbine blade.

[0043] FIG. 3 illustrates a wind turbine blade in accordance with an embodiment of the invention.

[0044] FIG. 4A illustrates a cross-section of a wind turbine blade in accordance with an embodiment of the invention.

[0045] FIGS. 4B and 4C illustrate a detail of a cross-section of a wind turbine blade in accordance with an embodiment of the invention.

[0046] FIG. 4D illustrates a premanufactured elongate fibre-reinforced composite element in accordance with an embodiment of the invention.

[0047] FIG. 5A illustrates a cross-section of a wind turbine blade in accordance with an embodiment of the invention.

[0048] FIG. 5B illustrates a detail of a cross-section of a wind turbine blade in accordance with an embodiment of the invention.

[0049] FIG. 6A illustrates a cross-section of a wind turbine blade in accordance with an embodiment of the invention.

[0050] FIG. 6B illustrates a detail of a cross-section of a wind turbine blade in accordance with an embodiment of the invention.

[0051] FIG. 7A illustrates a cross-section of a wind turbine blade in accordance with an embodiment of the invention.

[0052] FIG. 7B illustrates a detail of a cross-section of a wind turbine blade in accordance with an embodiment of the invention.

[0053] FIG. 8 illustrates a wind turbine blade in accordance with an embodiment of the invention.

[0054] FIG. 9 illustrates a cross-section of a wind turbine blade in accordance with an embodiment of the invention.

[0055] FIG. 10 illustrates a wind turbine blade in accordance with an embodiment of the invention.

[0056] FIG. 11 illustrates a cross-section of a wind turbine blade in accordance with an embodiment of the invention.

DETAILED DESCRIPTION OF SELECTED EMBODIMENTS

[0057] In the following, selected embodiments of the invention are described with reference to the attached drawings. The examples shall not to be construed as limiting the scope of protection as defined by the claims. The dimensions in the drawings are for exemplification only and shall not be construed as limiting, unless otherwise indicated.

[0058] 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 having a blade root 16 nearest the hub and a blade tip 14 farthest from the hub 8. The rotor has a radius denoted R.

[0059] FIG. 2 shows a schematic view of a wind turbine blade 10. The wind turbine blade 10 has the shape of a conventional wind turbine blade and comprises a root region 30 closest to the hub, a profiled or an airfoil region 34 farthest away from the hub 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. The outermost point of the blade 10 is the tip end 15. The blade 10 comprises a pressure side shell part 36 and a suction side shell part 38. Together, they form the shell of the wind turbine blade 10.

[0060] The airfoil region 34 (also called the profiled region) has an ideal or almost ideal blade shape with respect to generating lift, 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 (or the chord) of the root region 30 may be constant along the entire root area 30. The transition region 32 has a transitional profile gradually changing from the circular or elliptical shape of the root region 30 to the airfoil profile of the airfoil region 34. The chord length of the transition region 32 typically increases with increasing distance r 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 width of the chord decreases with increasing distance r from the hub.

[0061] A shoulder 40 of the blade 10 is defined as the position where the blade 10 has its largest chord length. The shoulder 40 is typically provided at the boundary between the transition region 32 and the airfoil region 34. FIG. 2 also illustrates the longitudinal length Z of the blade.

[0062] FIG. 3 illustrates an embodiment of a blade 300 in accordance with the first aspect of the invention. The blade is shown from a pressure side shell part 36 of the blade 300. A first wind turbine blade component 306, such as a carbon fibre spar cap, is at least partially embedded in the pressure side shell part 36, positioned below an outer surface of the pressure side shell part 36. A conductive element 308, such as a metal strip, such as a copper strip, is in direct contact with the carbon fibre spar cap component 306 along the length of the carbon spar cap 306. The copper strip 308 is also located below the outer surface of the pressure side shell part 36. The copper strip 308 is arranged between the spar cap 306 and the outer surface of the pressure side shell part 36. That is, the copper strip 308 is closer to the outer surface of the pressure side shell part 36 than the spar cap 306. The pressure side shell part 36 of the blade 300 further comprises a number of one or more lightning receptors, including receptors 304a, 304b, 304c, and 310. The lightning receptors 304a, 304b, and 304c are in contact with the copper strip 308 and extend from the copper strip 308 to or near the outer surface of the pressure side shell part 36 to provide lightning attraction. The lightning receptor 310 near the tip of the blade is not in direct contact with the copper strip 308. In other embodiments, all lightning receptors are in direct contact with the copper strip 308. In the present example, the receptor 310 must be coupled to ground another way, such as by a separate conductor 302 coupled to the copper strip 308.

[0063] FIG. 3 further illustrates a connector element 321 that connects the copper strip 308 in the pressure side shell part 36 to a corresponding copper strip (not shown in FIG. 3) in the suction side shell part 38. The example also includes a second connector element 322 that connects the copper strip 308 with the copper strip in the suction side shell part 38. This is illustrated below.

[0064] FIG. 4A illustrates a cross-sectional view A-A as indicated in FIG. 3. The cross-section is through receptor 304c, as seen in FIG. 3 and FIG. 4A. The carbon fibre spar cap 306 is embedded in the pressure side shell part 36. A copper strip 308 is positioned in direct contact with the carbon spar cap 306. The lightning receptor 304c extends between the surface of the pressure side shell part 36 and the copper strip 308. The lightning receptor does not extend into the carbon spar cap 306, as this would compromise the integrity of the carbon spar cap 306. Thus, the lightning receptor extends only through non-carbon material, such a glass fibre material. The copper strip aids in distributing the current received at the relatively small receptor 304c across a relatively large area of the carbon spar cap 306. This prevents high local currents in the carbon spar cap that may cause severe damage to the carbon spar cap due to its relatively poor conductivity.

[0065] FIG. 4B illustrates the area encircled in FIG. 4A in more detail, showing more clearly the copper strip 308 in contact with the carbon spar cap 306, and the receptor 304c in contact with copper strip 308.

[0066] The region 414 indicated with a dashed line in FIG. 4B can advantageously be provided as a premanufactured composite element as shown in FIG. 4D. During manufacturing of the pressure side shell part 36, the premanufactured composite element is laid up in the shell part mould where needed, and other elements of the shell part are added, before and/or after. Lightning receptors such as lightning receptor 304c can be added during manufacturing of the blade shell part or after. Appropriate coupling means are included, as required. The premanufactured composite element may combine the carbon spar cap 306 with glass fibre material 416 to produce a robust element that is relatively easy to handle and arrange in the shell part mould together with other fibre material before resin infusion.

[0067] FIG. 4C illustrates an alternative embodiment compared to the cross-section illustrated in FIGS. 4A and 4B. Instead of being entirely embedded in the pressure side shell part 36 at cross-section A-A, the spar cap 306 forms an inner surface of the pressure side shell part 36, at least in the vicinity of the cross-section A-A.

[0068] Similarly, the suction side shell part 38 may include a carbon fibre spar cap 406, and a copper strip 408 may be positioned in direct contact with the carbon spar cap 406. The lightning receptor 404c extends between the surface of the suction side shell part 38 and the copper strip 408. As described above in relation to lightning receptor 304c, the lightning receptor 404c does not extend into the carbon spar cap 406, as this would compromise the integrity of the carbon spar cap 406. Thus, the lightning receptor extends only through non-carbon material, such as a glass fibre material. The copper strip 408 aids in distributing the current received at the receptor 404c across a relatively large area of the carbon spar cap 406, preventing high local currents in the carbon spar cap that may cause severe damage to the carbon spar cap due to its relatively poor conductivity.

[0069] FIG. 5A illustrates a cross-sectional view B-B as indicated in FIG. 3. The cross-section is closer to the tip of the blade 300, and it does not intercept a lightning receptor. Thus, the pressure side shell part comprises only the carbon spar caps 306 and 406 and associated copper strips 308 and 408. This is illustrated in more detail in FIG. 5B. For simplicity, a shear web is not illustrated.

[0070] FIG. 6A illustrates a cross-sectional view C-C as indicated in FIG. 3. This cross-section is yet closer to the tip of the blade 300 compared to cross-section B-B, and like cross-section B-B, it does not intercept a lightning receptor. Instead, the cross-section coincides with the end of the copper strip 308 in the pressure side shell part 36. A connector element 321 connects the copper strip 308 in the pressure side shell part to the copper strip 408 in the suction side shell part. In this example, as illustrated in FIG. 6B, the conductive element extends into the shell part 36 in order to connect to the copper strip 308. As will be described below, this connection reduces the heating generated in the blade from a lightning strike.

[0071] FIG. 7A illustrates an alternative embodiment compared to the cross-section illustrated in FIG. 6A. Instead of being embedded in the pressure side shell part 36 at cross-section C-C, the copper strip 308 has instead been adapted to form part of an inner surface of the pressure side shell part 36, at least in the vicinity of the cross-section C-C. The copper strip at cross-section B-B may still look as shown in FIGS. 5A and 5B, but transitions towards the inner surface of the shell parts 36 and 38 towards the cross-section C-C. This can be achieved during layup in a blade mould or during premanufacturing of a portion similar to portion 414 shown in FIG. 4D.

[0072] FIG. 8 indicates another cross-section, D-D, in the blade 300. The cross-section intersects the carbon spar caps 306 and 406, but not the copper strips 308 and 408 and the lightning receptors.

[0073] FIG. 9 illustrates cross-section D-D defined in FIG. 8. It shows the copper strips 308 and 408 arranged in contact with the carbon spar caps 306 and 406 along a longitudinal axis of the blade.

[0074] The example in FIG. 9 illustrates an example of grounding of the copper strips. In this example, conductive element 321, mentioned earlier, connects the copper strips 308 and 408 electrically to one another near a tip end of the blade 300, and similarly, conductive element 322, also mentioned earlier, connects the copper strips 308 and 408 electrically to one another near a root end of the blade 300. Contact elements 631 and 931 connect the conductive element 321 to the copper strips which, in this example, are embedded in the shell parts and therefore not readily accessible. A contact element 631 for the copper strip 308 may for instance be provided by drilling a hole from an inside surface of the blade shell to the copper strip 308 and inserting a conductive element into the hole in electrical contact with the corresponding copper strip 308. The contact element 631 may for instance be a cylindrical metal piece that fits the hole, such as a copper piece. In view of this disclosure, the person skilled in the art can easily envision various other ways of providing the connection between the copper strips 308 and 408 at the tip end. The same applies to connection via conductive element 322, where contact elements 932 and 933 provide electrical connection between the copper strips 308 and 408 and the conductive element 322.

[0075] Finally, the example in FIG. 9 illustrates the actual grounding, which in this example is by electrical connection to a downconductor 302 arranged only near the root end of the blade 300. It is seen that the copper strips 308 and 408 can replace a downconductor arranged inside the shell made up of the pressure side shell part and the suction side shell part, between the pressure and suction side shell parts 36 and 38. Such a downconductor involves a number of mechanical issues associated with attachment of the downconductor to shear webs or the like, as well as the need to couple individual lightning receptors, such as receptors 304a, 304b, and 304c, to the downconductor running inside the shell along most of the length of the blade.

[0076] The connection 321 at the tip has the advantage that a parallel circuit is achieved, which reduces the resistance between any one lightning conductor and ground by providing two current paths from the lightning receptor to ground rather than just one, as would be the case in the absence of the connection provided by conductive element 321.

[0077] The downconductor 302 is typically connected to ground through the hub. Connection of a downconductor to ground is well known in the art and will therefore not be addressed in further detail.

[0078] FIG. 10 indicates another cross-section, E-E, in the blade 300. The cross-section E-E intersects the carbon spar caps 306 and 406, the copper strips 308 and 408, and the lightning receptors.

[0079] FIG. 11 illustrates cross-section E-E defined in FIG. 10. It shows the copper strips 308 and 408 arranged in contact with the carbon spar caps 306 and 406 along a longitudinal axis of the blade, and it further illustrates lightning receptors, including receptors 304a, 304b, 304c, and suction side receptors (some of which are pointed to by reference 1104), arranged in contact with respective copper strips 308 and 408, without interfering with the carbon spar caps 306 and 406. Due to the geometry selected for this example, conductive elements 321 and 322, contacts 631, 931, 932, and 933 are also intersected and illustrated as such. The person skilled in the art will readily appreciate that the exact positions of the various elements are a matter of design. However, the example illustrates the contact between the conductive elements 321 and 322 on the one hand and contacts 631, 931, 932, and 933 on the other hand, and the contact between the contacts 631, 931, 932, and 933 on the one hand, and the copper strips 308 and 408 on the other hand, allowing lightning current to be conducted to ground in the event of a lightning strike.

[0080] The invention is not limited to the embodiments described herein and may be modified or adapted without departing from the scope of the claimed invention.

LIST OF REFERENCE NUMERALS

[0081] 2 wind turbine [0082] 4 tower [0083] 6 nacelle [0084] 8 hub [0085] 10 blades [0086] 14 blade tip [0087] 15 tip end [0088] 16 blade root [0089] 18 leading edge [0090] 20 trailing edge [0091] 30 root region [0092] 32 transition region [0093] 34 airfoil region [0094] 36 pressure side shell part [0095] 38 suction side shell part [0096] 40 blade shoulder [0097] 300 wind turbine blade [0098] 302 downconductor [0099] 301a-304c lightning receptors on pressure side [0100] 306 carbon spar cop [0101] 308 copper strip [0102] 310 lightning receptor on pressure side [0103] 321, 322 connector element [0104] 404c lightning receptor on suction side [0105] 406 carbon spar cap [0106] 408 copper strip [0107] 414 premanufactured portion [0108] 416 glass fibre material [0109] 631 contact element [0110] 931-933 contact element [0111] 1104 lightning receptors on suction side [0112] L longitudinal length of the blade