Patent Application
20230016436
The present invention relates to a reinforcing structure for a wind turbine blade and to a wind turbine blade reinforced with such a reinforcing structure.
Wind power is a clean and environmentally friendly source of energy. Wind turbines usually comprise a tower, generator, gearbox, nacelle, and one or more rotor blades. The wind turbine blades capture kinetic energy of wind using known airfoil principles. Modern wind turbines may have rotor blades that exceed 90 meters in length.
Wind turbine blades are usually manufactured by forming two shell parts or shell halves from layers of woven fabric or fibre and resin. Spar caps or main laminates are placed or integrated in the shell halves and may be combined with shear webs or spar beams to form structural support members. Spar caps or main laminates may be joined to, or integrated within, the inside of the halves of the shell.
As the size of wind turbine blades increases, various challenges arise from such blades being subject to increased forces during operation, requiring improved reinforcing structures. The manufacturing of large reinforcing structures, such as spar caps or spar beams, is likewise challenging, in particular when pultruded carbon fibre reinforced composite spar caps are used as the reinforcing members. Carbon fibres are typically lighter than glass fibres by volume. Carbon pultrusion lay-up thus often results in slight overlap and/or misplacement of carbon pultrusion layers, which may introduce gaps. Further, pultrusions do not line up completely, and thus gaps between individual pultrusions is a problem.
Gaps between carbon fibre reinforced composite pultrusions make the structure susceptible to flashover between pultrusions in case lightning strikes the blade and a current rushes through the blade. Such flashovers can be detrimental to the mechanical integrity of the blade.
It is therefore an object of the present invention to provide a reinforcing structure for a wind turbine blade, where the risk of flashover within the reinforcing structure is reduced or even eliminated.
The present invention provides a reinforcing structure for a wind turbine blade, where the risk of internal flashover as a result of a lightning strike is mitigated or even eliminated.
In a first aspect, the invention provides a reinforcing structure comprising:
The reinforcing structure may for instance be a structure for reinforcing a wind turbine blade.
In the reinforcing structure, two carbon fibre reinforced composite elements in the first composite element layer are in electrical connection via the conduction portion. This reduces or eliminates the problem of flashover occurring within the reinforcing structure during a lightning strike.
It is important that the conductive portion does not extend throughout an interlayer, but only contacts two carbon fibre reinforced composite elements in a layer, and preferably extends only enough to establish the desired conductance between those two elements. The reason is that the conductive portions may comprise a material that is not easily permeable to liquid resin. It can therefore be difficult during an infusion process for creating a composite reinforcing structure to force the liquid resin into all voids between the carbon fibre reinforced composite elements, especially near the conductive portions. By reducing the extent of conductive portions, this problem is reduced. However, the dimensions of the conductive portion should not be so small that the conductance is insufficient to prevent flashover. The person skilled in the art will, with the knowledge provided in this specification, recognize that this is a matter of design and that the size of the conductive portion depends for instance on the electrical resistivity of the material or materials chosen for the conductive portion. A higher resistivity will require a larger conductive portion to achieve sufficient conductance.
One or more, such as all, of the carbon fibre reinforced composite elements have a fibre content of at least 50%, such as at least 60%, such as at least 65%, determined by weight % or by volume %.
One or more, such as all, of the carbon fibre reinforced composite element may comprise materials other than carbon, such as glass, such as glass fibres.
In some embodiments, a conductivity of the conductive portion is at least 0.03 S/m, such at least 0.0375 S/m, such as at least 0.05 S/m, such as at least 0.1 S/m.
In some embodiments, the conductive portion further abuts exactly two carbon fibre reinforced composite elements comprised in the second composite element layer. In this way, a conductive portion provides electrical contact between four carbon fibre reinforced composite elements. Such embodiments may further reduce the risk of flashover.
In some embodiments, the conductive portion abuts exactly two of the carbon fibre reinforced composite elements comprised in the first composite element layer and abuts exactly one carbon fibre reinforced composite element comprised in the second composite element layer. This may be the case in a part of a reinforcing structure where one element, not two or more, in the second composite element layer overlaps with two elements in the first composite element layer.
In some embodiments, all carbon fibre reinforced composite elements in the reinforcing structure are electrically interconnected via conductive portions configured as described above. This ensures that there is a conductive path from any one carbon fibre reinforced composite element to any other carbon fibre reinforced composite element in the reinforcing structure via the conductive portions.
The interlayer may have multiple conductive portions, arranged to conduct current between two elements at more than one point. The conductance from one carbon fibre reinforced composite element to another can be increased in this way.
In some embodiments, all carbon fibre reinforced composite elements in a layer, such as in all layers, are connected as described above. In some embodiments, a conductive portion connects four carbon fibre reinforced composite elements where possible, as described above. This is not possible on an edge of a carbon fibre reinforced composite element that is not adjacent to another carbon fibre reinforced composite element in the same layer. For instance, in two adjacent stacks of three carbon fibre reinforced composite elements, a conductive portion can only be in contact with exactly four carbon fibre reinforced composite elements between the two stacks. On the free sides of each stack, a conductive portion may only provide electrical connection between two carbon fibre reinforced composite elements in adjacent layers.
In some embodiments, a thickness of the conductive portion is within 50-150% of a thickness of the non-conductive portion, such as within 80-120% of a thickness of the non-conductive portion. When the conductive portion and the non-conductive portion have approximately the same thickness, the strain in the abutting carbon fibre reinforced composite elements is minimized. In some embodiments, the thickness of the conductive portion is substantially identical, such as identical, to the thickness of the non-conductive portion.
In some embodiments, the conductive portion is attached to an anchor element extending from the conductive portion and in between the two carbon fibre reinforced composite elements that are comprised in the first composite element layer and abut the conductive portion. Such an anchor element may aid in keeping the conductive portion aligned so that during layup, the conductive portion does not shift, potentially ending up not connecting two carbon fibre reinforced composite elements in a layer as intended. In some embodiments, a thickness of the anchor element is in the range 0.05 to 2 mm, such as in the range 0.05 to 1.5 mm, such as in the range 0.05 to 1 mm, such as in the range 0.1 to 0.5 mm. This allows for controlling how close the respective carbon fibre reinforced composite elements get.
The anchor element can be made for instance of fibre reinforced composite material or metal. Dry fibre may also be used, for instance stitched to the conductive portion. The conductive portion and anchor element may also be provided by folding fibre, such as fibre mat material, to form a T-shaped element, the stem of the T providing the anchor element and the cross bar providing the conductive portion.
In some embodiments, the non-conductive portion is made at least partly of a polyester material, such as a polyester veil, such as a non-woven polyester veil. In some embodiments, the entire non-conductive portion is made of polyester, such as of a polyester veil. In some embodiments, the non-conductive portion is made at least partly of glass, such as glass fibre. In some embodiments, the non-conductive portion is made at least partly of polymeric filament. Any combination of such materials may be used for the non-conductive portion.
The non-conductive portion may be woven or non-woven.
In some embodiments, the conductive portion is made at least partly of carbon fibres. In some embodiments, the conductive portion comprises a woven carbon fibre material. In some embodiments, the conductive portion comprises a carbon fibre veil. Such materials allow conduction of lightning current while also allowing resin to pass.
In some embodiments, the conductive portion is stitched into a corresponding hole in the non-conductive portion. The conductive portion may alternatively or additionally be stapled and/or glued and/or bonded together with the non-conductive portion.
In some embodiments, the conductive portion is made of metal, such as solid metal or a metal mesh. The metal may for instance be copper or aluminium.
In some embodiments, the composite element layers and the interlayer have been bonded together in a liquid resin infusion and curing process.
In some embodiments, the reinforcing structure is part of a wind turbine blade main laminate or is a wind turbine blade main laminate.
In some embodiments, the reinforcing structure is part of a spar structure for a wind turbine blade or is a spar structure for a wind turbine blade.
In some embodiments, one or more of the carbon fibre reinforced composite elements, such as all of the carbon fibre reinforced composite elements, are at least partly or wholly made by pultrusion.
In some embodiments, a largest dimension of the conductive portion is less than 300 mm, such as less than 100 mm, such as in the range 10-60 mm, such as in the range 30-60 mm. As discussed above, the dimension must allow both sufficient conductance while not being so large that more than two carbon fibre reinforced composite elements in a layer are connected by the same conductive portion. Also, if it is too large, it will significantly, even critically, alter the resin flow, resulting in defects/infusion failure.
In some embodiments, a largest dimension of the conductive portion is equal to or less than a width of a carbon fibre reinforced composite element abutting the conductive portion, such as equal to or less than half a width of a carbon fibre reinforced composite element abutting the conductive portion.
A second aspect of the invention provides a wind turbine blade reinforced with a reinforcing structure in accordance with an embodiment of the first aspect.
The reinforcing structure may for instance be a spar cap or a main laminate or other spar structure. In some embodiments, the reinforcing structure comprises a spar beam. The reinforcing structure may for instance extend along the blade in a spanwise direction. Typically, the reinforcing structure will extend over 60-95% of a length of the blade, but in the present context this is a matter of design.
A third aspect provides a method for manufacturing a reinforcing structure in accordance with the first aspect or a wind turbine blade in accordance with the second aspect. The method comprises:
The method may further comprise adding one or more additional interlayers and composite element layers.
The method may further comprise a step of infusing liquid resin and curing the resin to bond the carbon fibre reinforced composite elements and the interlayer(s) together. This can, for example, be done using vacuum-assisted resin transfer moulding.
In some embodiments, exactly one carbon fibre reinforced composite element in the second composite element layer abuts the conductive portion.
In some embodiments, exactly two carbon fibre reinforced composite elements in the second composite element layer abut the conductive portion.
For conciseness, known steps in the process of manufacturing a wind turbine blade are not recited.
The invention is explained in detail below with reference to embodiments shown in the drawings.
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.
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.
It should be noted that the chords of different sections of the blade normally do not lie in a common plane, since the blade may be twisted and/or curved (i.e. pre-bent), thus providing the chord plane with a correspondingly twisted and/or curved course, this being most often the case in order to compensate for the local velocity of the blade being dependent on the radius from the hub.
The blade is typically made from a pressure side shell part 36 and a suction side shell part 38 that are glued to each other along bond lines at the leading edge 18 and the trailing edge of the blade 20.
The spar cap 41 of the pressure side shell part 36 and the spar cap 45 of the suction side shell part 38 are connected via a first shear web 50 and a second shear web 55. The shear webs 50, 55 are in the shown embodiment shaped as substantially I-shaped webs. The first shear web 50 comprises a shear web body and two web foot flanges. The shear web body comprises a sandwich core material 51, such as balsawood or foamed polymer, covered by a number of skin layers 52 made of a number of fibre layers. The blade shells 36, 38 may comprise further fibre-reinforcement at the leading edge and the trailing edge. Typically, the shell parts 36, 38 are bonded to each other via glue flanges.
The carbon fibre reinforced composite elements 301-304 may for instance be pultruded elements, such as planks, that are stacked to form a reinforcing structure. Stackable shapes are typically used, as they are easier to handle when laying up the reinforcing structure. However, other shapes may be used.
A conductive portion 311 made for instance of a carbon fibre material may, as discussed previously, impede the flow of liquid resin during an infusion process meant to bond all the carbon fibre reinforced composite elements and the interlayer together to form a reinforcing structure. Thus, the size of the conducting portion is such that it provides sufficient conductance between the carbon fibre reinforced composite elements 301-304, while not significantly impeding the flow of liquid resin during an infusion process.
The conductive portion 311 is thus embedded into the non-conductive portion 421, which may for instance be a polyester material. A polyester veil allows liquid resin to relatively easily flow between the composite element layers. As described above, the conductive portion 311 may somewhat impede flow of liquid resin, but because it extends over a relatively small area, it does not significantly affect the process of infusing liquid resin in between the carbon fibre reinforced composite elements.
The conductive portion 311 abuts all four carbon fibre reinforced composite elements 301-304, thereby allowing lightning current to flow between all the carbon fibre reinforced composite elements, as illustrated by the dashed lines in
For simplicity and generality, the figures do not show any resin between the carbon fibre reinforced composite elements. It is to be understood that the structure will be reinforcing once resin has been infused to bond the elements together. However, this step may take place before the reinforcing structure is applied to the part to be reinforced, or the infusion may only take place as a step that at the same time forms the part to be reinforced, bonding the carbon fibre reinforced composite elements together and bonding the carbon fibre reinforced composite elements to the part to be reinforced.
As in
The first composite element layer is separated from the second composite element layer by interlayer 831. The second composite element layer is separated from the third composite element layer by interlayer 832. The third composite element layer is separated from the fourth composite element layer by interlayer 833.
Interlayer 831 comprises a non-conductive portion 821 and conductive portions 811-813. Similarly, interlayer 832 comprises a non-conductive portion 822 and conductive portions 814-815. Interlayer 833 comprises a non-conductive portion 823 and a conductive portion 816. Widths W1 and W2 represent the width of the first and the second composite element layer, respectively, and will be referred to in the description of
The conductive portion 811, as an example, electrically connects carbon fibre reinforced composite elements 803 and 804 of the first composite element layer and carbon fibre reinforced composite element 807 of the second composite element layer. Similarly, conductive portion 814 electrically connects carbon fibre reinforced composite elements 806 and 807 of the second composite element layer and carbon fibre reinforced composite elements 808 and 809 of the third composite element layer. Conductive portion 816 electrically connects carbon fibre reinforced composite elements 808 and 809 of the third composite element layer and carbon fibre reinforced composite element 810 of the fourth composite element layer. As a result, lightning current can be conducted without flashover from element 804 to element 810 via conductive portions 811, 814 and 816, and via carbon fibre reinforced composite elements 807 and 809, as illustrated by the dashed line. In fact, in the embodiment in
In the exemplary embodiment 800, each conductive portion is attached to a respective anchor element, such as anchor element 861, which assists in maintaining conductive portion 815 aligned with carbon fibre reinforced composite elements 805 and 806, ensuring a high conductance between the two carbon fibre reinforced composite elements as well as carbon fibre reinforced composite element 808. In a more complex structure such as structure 800 in
Similarly, anchor element 862 maintains conductive portion 812 in the correct place relative to carbon fibre reinforced composite elements 802 and 803, thereby ensuring that the conductive portion 812 performs the function of allowing electrical current to be relatively easily conducted between those carbon fibre reinforced composite elements, as well elements 806-807, which also abut conductive portion 812.
The same applies to the other conducting portions and respective anchor elements shown in
The interlayer has a length, L1, which corresponds to the length of the reinforcing structure 800 and to the length of the carbon fibre reinforced composite elements. This length depends on the length of the blade. The length, L1, may for instance be in the range 60-95 m for a blade having a total length of 100 m.
The width W1 of the interlayer 831 corresponds to the width W1 of the first composite element layer illustrated in
In
Detail 960 of
Similarly to
In
The structure in
Next, the second composite element layer, consisting of carbon fibre reinforced composite elements 805-807, is arranged on the interlayer 831 as per
This results in the reinforcing structure 800 shown in
Infusion and curing can then be performed in order to bond the carbon fibre reinforced composite elements together to form a single reinforcing unit.
The invention is not limited to the embodiments described herein and may be modified or adapted without departing from the scope of the present invention.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2020/060552 | 4/15/2020 | WO |
