Equipotential bonding of wind turbine rotor blades

Abstract

A wind turbine rotor blade portion has a root end, a tip end, and a blade shell defining a suction side, a pressure side, a leading edge, and a trailing edge of the blade portion. The blade shell comprises a lightning lead comprising a first conductive material and at least one spar cap associated with the blade shell and comprising a second conductive material different from the first conductive material. An equipotential bonding element electrically bonds the lightning lead to the spar cap. The equipotential bonding element includes: a first end having a first metallic material adjacent to the first conductive material of the lightning lead; a second end opposite the first end and having a second metallic material adjacent a second conductive material of the spar cap; and an intermediate portion in which the first metal material is joined to the second metal material at a joint, and which has an insulator that encapsulates the joint for preventing exposure of the joint to the electrolyte material.

Description

[0001] The present invention relates to a wind turbine rotor blade, in particular to equipotential bonding in a wind turbine rotor blade, and to a method for manufacturing a wind turbine rotor blade. Background Art

[0002] A wind turbine converts the kinetic energy of the wind into electrical energy. A generator converts the wind energy captured by a rotor having one or more rotor blades into electrical energy that is typically provided to a utility grid. The generator is housed in a nacelle along with various components required to operate and optimize the performance of the wind turbine. The tower supports the loads provided by the nacelle and the rotor. In a horizontal axis wind turbine (HAWT), the rotor blades extend radially outward from a central hub that rotates about a longitudinal axis that is generally aligned horizontally. In operation, the blades are configured to interact with the passing air flow to generate lift that causes the rotor to rotate in a plane substantially perpendicular to the direction of the wind.

[0003] A conventional rotor blade is made of a shell and a spar structure. The spar structure is used to transfer the loads from the rotating blades to the hub of the wind turbine. Such loads include tensile and compressive loads along the length of the blade caused by the circular motion of the blade and loads along the thickness of the blade caused by the wind, i.e. from the windward side to the leeward side of the blade. The spar structure includes one or more shear webs extending between the spar caps. The spar caps may be incorporated into the shell or may be attached to the shell.

[0004] The spar caps may comprise strips of pultruded fibre material. Pultrusion is a continuous process similar to extrusion in which fibres are pulled through a liquid resin source and then heated to cure the resin. The resulting cured fibre material has a constant cross-section, but because the process is continuous, the material once formed can be cut to any length.

[0005] WO2013 / 087078 describes a wind turbine blade having an elongated reinforcement structure comprising a stack of pultruded fiber composite strands. The pultruded fibers are carbon fibers and extend nearly the entire length of the blade from root to tip.

[0006] Wind turbines are susceptible to lightning strikes. Wind turbines typically include a lightning protection system that electrically couples wind turbine components to the ground. The blades may include a metal foil or surface protection layer (SPL) that is incorporated into the housing near the outer surface of the blade. The metal foil may cover only a portion of the blade outer surface or substantially the entire blade outer surface. The metal foil is electrically connected to the ground through the tower and the nacelle.

[0007] Although lightning strikes have a natural tendency to travel along the outer surface of a structure (e.g., a rotor blade) due to their high frequency, the presence of the conductive fibers in the blade shell may result in undesired discharges when a lightning strike occurs, which may result in damage to the blade shell. This problem may be exacerbated in cases where the conductive fibers are continuous and extend along a substantial length of the rotor blade, particularly for long blades. Summary of the invention

[0008] A first aspect of the invention provides a wind turbine rotor blade section having a root end and a tip end, the wind turbine rotor blade section comprising: a wind turbine blade shell defining a suction side, a pressure side, a leading edge and a trailing edge of the blade section, wherein the blade shell comprises a lightning lead comprising a first electrically conductive material; and at least one spar cap associated with the blade shell and comprising a second electrically conductive material different from the first electrically conductive material; an equipotential bonding element electrically bonding the lightning lead to the spar cap, wherein the equipotential bonding element comprises: a first end having a first metallic material adjacent to the first electrically conductive material of the lightning lead; a second end opposite to the first end having a second metallic material adjacent to the second electrically conductive material of the spar cap; and a middle section in which the first metallic material is joined to the second metallic material at a joint, and the middle section has an insulator encapsulating the joint for preventing the joint from being exposed to an electrolyte material.

[0009] Another aspect of the invention provides a method of manufacturing a wind turbine rotor blade section having a root end and a tip end, the method comprising: laying up a shell of a wind turbine rotor blade, the shell defining a suction side, a pressure side, a leading edge and a trailing edge of the blade section, the shell comprising a lightning lead, the lightning lead comprising a first conductive material; laying up a spar cap so that the lightning lead extends over the spar cap, wherein the spar cap comprises a second conductive material; and providing an equipotential bonding element to electrically bond the lightning lead to the spar cap, the equipotential bonding element comprising: a first end having a first metallic material adjacent to the first conductive material of the lightning lead; a second end opposite the first end and having a second metallic material adjacent to the second conductive material of the spar cap; and a middle portion in which the first metallic material is joined to the second metallic material at a joint, and the middle portion having an insulator encapsulating the joint for preventing the joint from being exposed to an electrolyte material.

[0010] By preventing the joint from being exposed to the electrolyte material, a current path may be prevented from forming between the first metallic material and the second metallic material other than via the joint. Avoiding such a current path or arc helps prevent galvanic corrosion of the first metallic material or the second metallic material, where the metallic materials are dissimilar metals, such as two metallic materials that are distant from each other in terms of their standard electrode potentials, such as copper and aluminum. The use of dissimilar metallic materials may be preferred to prevent: i) galvanic corrosion between the first conductive material of the lightning lead and the first metallic material of the equipotential bonding element; and ii) galvanic corrosion between the second conductive material of the spar cap and the second metallic material of the equipotential bonding element.

[0011] The presence of electrolyte material in the vicinity of the equipotential bonding element within the blade shell is unavoidable, for example ionized water from the natural environment when the wind turbine rotor blade section is operating normally as part of a wind turbine.

[0012] Preferably, the insulator covers only a small portion of the equipotential bonding element.The insulator may extend a sufficient distance on either side of the joint to prevent a current path from forming between the first and second metallic materials instead of through the joint.

[0013] The first metal material and the second metal material may be mechanically and electrically joined together at the joint.

[0014] The equipotential bonding element can be formed as a strip or a ribbon.

[0015] The first metallic material and the second metallic material may each have a form configured to accommodate, without yielding, an observed strain greater than a yield strength of a solid straight form of the corresponding material.

[0016] The first metallic material may have a different form than the second metallic material.

[0017] The first metal material and / or the second metal material may be formed as a porous foil or mesh.

[0018] The aspect ratio of the pores of the first metal material may be different from the aspect ratio of the pores of the second metal material.

[0019] The first metal material and / or the second metal material may be formed as lines on a substrate.

[0020] The lines may have an undulating form with undulations in a plane parallel to the substrate.Preferably, the pitch of the undulating lines of the first metallic material is different from the pitch of the undulating lines of the second metallic material.

[0021] The blade shell may comprise a plurality of fibre ply stacks.The equipotential bonding element may extend between an edge of one stack and an edge of an adjacent stack, the edge of one stack and the edge of the adjacent stack overlapping to define an overlapping edge region extending across the spar cap.

[0022] A middle portion of the equipotential bonding element may be located in the overlapping region, away from the spar cap and the lightning conductor.

[0023] Each fiber ply stack may have an inner edge towards the root end of the blade, an outer edge towards the tip end of the blade, a leading edge towards the leading edge of the blade and a trailing edge towards the trailing edge of the blade. The equipotential bonding element may extend between the outer edge of one stack and the inner edge of an adjacent stack, the outer edge of one stack and the inner edge of the adjacent stack overlapping.

[0024] The first end of the equipotential bonding element may be attached to the lightning conductor and in electrical contact with the lightning conductor.The second end of the equipotential bonding element may be attached to the spar cap and in electrical contact with the spar cap.

[0025] The spar cap may have an outer side and an inner side proximate to an inner portion of the blade, and the equipotential bonding element may be attached to and in electrical contact with the outer side of the spar cap.

[0026] The spar cap may comprise a stack of multiple layers of the second conductive material, preferably a carbon fiber material, preferably a pultruded carbon fiber composite material.

[0027] The first metallic material may have a standard electrode potential similar to that of the first conductive material of the lightning lead, and the second metallic material may have a standard electrode potential similar to that of the second conductive material of the spar cap. The standard electrode potentials may be similar so that galvanic corrosion may be minimal even in the presence of an electrolyte. In this context, "similar" may mean that the standard electrode potential (E 0 ) is of the same order of magnitude relative to the standard electrode potential of hydrogen.

[0028] Overlapping edges of adjacent fiber ply stacks may be formed by successively terminating the individual plies in the stack to form a step or ramp.

[0029] The lightning lead may be a metal foil of a lightning protection system.

[0030] The lightning conductor may be located at or near an outer surface of the blade.

[0031] The wind turbine rotor blade may further comprise a plurality of said equipotential bonding elements. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Embodiments of the present invention will now be described with reference to the accompanying drawings, in which:

[0033] Figure 1 A wind turbine is shown;

[0034] Figure 2 A wind turbine blade is shown;

[0035] Figure 3 shows a schematic plan view of a wind turbine blade having lightning protection features;

[0036] Figure 4a The hollow blades are shown along Figure 3 The cross-sectional view of AA in FIG. Figure 4b Shows Figure 4a Detailed view of the shell, spar caps and shear web at B in the figure;

[0037] Figure 5 A schematic diagram showing the chordwise layup of the shell in the mould;

[0038] Figure 6 shows a schematic spanwise cross section of a ply stack of an outer shell, showing the overlapping edges of the ply stack;

[0039] Figure 7 shows a schematic spanwise cross section of a pair of adjacent ply stacks of a skin, wherein equipotential bonding elements extend from the surface protection layer through the overlapping edges of the ply stacks to the spar cap;

[0040] Figure 8 An example is shown in which equipotential bonding elements are laid between the ply stacks;

[0041] Fig. 9 A bimetallic equipotential bonding element is shown;

[0042] Fig.10 Another bimetallic equipotential bonding element is shown;

[0043] Fig.11 The ends of two metal materials in an equipotential bonding element are shown;

[0044] Fig.12 A) to C) show various joints between two metal materials in an equipotential bonding element;

[0045] Fig.13 A) and B) show another joint between two metal materials in an equipotential bonding element;

[0046] Fig.14shows a further joint between two metallic materials in an equipotential bonding element; and

[0047] Fig.15 Another bimetallic equipotential bonding element is shown. DETAILED DESCRIPTION

[0048] In this specification, terms such as leading edge, trailing edge, pressure surface, suction surface, thickness, chord length and planform are used. Although these terms are well known and understood by those skilled in the art, for the avoidance of doubt, definitions are given below.

[0049] The term "leading edge" is used to refer to the edge of the blade which will be at the front of the blade when the blade is rotating in the normal direction of rotation of the wind turbine rotor.

[0050] The term "trailing edge" is used to refer to the edge of a wind turbine blade which will be located behind the blade when the blade is rotating in the normal direction of rotation of the wind turbine rotor.

[0051] The chord length of a blade is the straight-line distance from the leading edge to the trailing edge in a given cross section perpendicular to the spanwise direction of the blade.

[0052] The pressure surface (or windward surface) of a wind turbine blade is the surface between the leading edge and the trailing edge which, in use, has a higher pressure than the suction surface of the blade.

[0053] The suction surface (or leeward surface) of a wind turbine blade is the surface between the leading edge and the trailing edge which, in use, will have a lower pressure than the pressure acting on the pressure surface.

[0054] The thickness of a wind turbine blade is measured perpendicular to the chord of the blade and is the maximum distance between the pressure surface and the suction surface in a given cross section perpendicular to the spanwise direction of the blade.

[0055] The term "spanwise" is used to refer to the direction from the root end of a wind turbine blade to the tip end of the blade, or vice versa. When the wind turbine blade is mounted on a wind turbine hub, the spanwise and radial directions will be substantially the same.

[0056] The view perpendicular to the spanwise and chordwise directions is called the plan view. This view is along the thickness dimension of the blade.

[0057] The term "spar cap" is used to refer to the longitudinal (substantially spanwise extending) reinforcing members of the blade. The spar caps may be embedded in the blade shell, or may be attached to the blade shell. The spar caps on the windward and leeward sides of the blade may be joined by one or more shear webs extending through the internal hollow space of the blade. The blade may have more than one spar cap on each of the windward and leeward sides of the blade. The spar caps may form part of the longitudinal reinforcing spar or support member of the blade. In particular, the spar caps may form part of a load-bearing structure extending in the longitudinal direction, which carries the flapping direction bending loads of the blade.

[0058] The term "shear web" is used to refer to a longitudinal (generally span-wise extending) stiffening member of a blade capable of transferring loads from one of the windward and leeward sides of the blade to the other of the windward and leeward sides of the blade.

[0059] Figure 1 A wind turbine 10 is shown comprising a tower 12 mounted on a foundation and a nacelle 14 disposed at the apex of the tower 12. The wind turbine 10 shown here is an onshore wind turbine, such that the foundation is embedded in the ground, but the wind turbine 10 may be an offshore installation, in which case the foundation would be provided by a suitable offshore platform.

[0060] The rotor 16 is operatively coupled to a generator (not shown) housed within the nacelle 14 via a gearbox. The rotor 16 includes a central hub 18 and a plurality of rotor blades 20 extending outwardly from the central hub 18. It should be noted that the wind turbine 10 is a conventional type of horizontal axis wind turbine (HAWT) such that the rotor 16 is mounted at the nacelle 12 to rotate about a substantially horizontal axis defined at the center of the hub 18. Although Figure 1 The example shown has three blades, but those skilled in the art will recognize that other numbers of blades are possible.

[0061] When wind blows against wind turbine 10 , blades 20 generate lift, which causes rotor 16 to rotate, which in turn causes a generator within nacelle 14 to generate electrical energy.

[0062] Figure 2One wind turbine blade 20 for use in such a wind turbine is shown. Each blade 20 has a root end 22 proximate to the hub 18 and a tip end 24 distal to the hub 18. A leading edge 26 and a trailing edge 28 extend between the root end 22 and the tip end 24, and each blade 20 has a corresponding aerodynamic high pressure surface (i.e., pressure surface) and an aerodynamic low pressure surface (i.e., suction surface) extending between the leading edge and the trailing edge of the blade 20. The pressure surface is located on the pressure side of the blade, and the suction surface is located on the pressure side of the blade. The blade may be split in the spanwise direction to form a segmented blade comprising a plurality of blade sections, each blade section having a root and a tip, or alternatively, the blade may be continuous from the root end 22 to the tip end 24, thereby forming one blade section.

[0063] Each blade has a generally circular cross-section near the root end 22, because the blade near the root must have sufficient structural strength to support the blade outside of this cross-section and transfer loads into the hub 18. The blade 20 transitions from a circular profile to an airfoil profile, moving from the root end 28 of the blade toward the "shoulder" 30 of the blade, which is the widest part of the blade where the blade has its maximum chord length. The blade 20 has an airfoil with a gradually decreasing thickness at the outer portion of the blade, which extends from the shoulder 30 to the tip end 24.

[0064] like Figure 3 As schematically shown in Figure 1, the blade 20 includes one or more lightning receptors and one or more lightning "down conductors" that form part of a lightning protection system for a wind turbine. The lightning receptors attract the lightning strike, while the down conductors conduct the energy of the lightning strike down along the blade 20, via the nacelle 14 and the tower 12 to ground potential. The lightning conductor can take a variety of forms, such as a surface metal foil 32 on the outer surface of the blade and / or a cable 38 that runs through the interior of the hollow blade, for example. The lightning conductor includes a first conductive material. The lightning receptor may include a metal foil 32 mounted on the outer surface of the blade and / or a discrete lightning receptor 34, or, for example, a solid metal tip 36 or a metal-coated laminate (e.g., a copper cap) that conforms to the shape of the blade closest to the tip end 24 may be provided. The discrete lightning receptor 34 and the metal tip 36 may be electrically connected to the lightning conductor.

[0065] A large portion of the outer surface of the blade 20 may be covered with a metal foil 32. The metal foil 32 may be used as a lightning receptor, a down conductor, or both. The down conductor may extend substantially the entire length of the blade. In the case where a large portion of the outer surface of the blade 20 is covered with the metal foil 32, a cable 38 may be connected to the metal foil 32 near the tip end 24 of the blade and near the root end 22 of the blade, while there is no cable 38 along the majority of the length of the blade covered with the metal foil 32. The metal foil 32 may extend from the root to the tip, in which case no cable 38 is required. The metal foil 32 may extend in sections along the length of the blade, with cable sections between the metal foil sections. Alternatively, the cable 38 may extend below the metal foil 32 (inside the blade) so that the cable 38 and the metal foil 32 are electrically connected in parallel. Alternatively, the blade may have a greater number of discrete lightning receptors on the blade surface, which are electrically connected by a down conductor cable extending substantially along the entire length of the blade, without having a metal foil.

[0066] At the root end 22 of the blade 20, the down conductor 38 may be electrically connected by an armature arrangement to a charge transfer line to ground potential via the nacelle 14 or the hub 18 and the tower 12. Thus, such a lightning protection system allows lightning to be safely directed from the blade to ground potential, minimizing the risk of damaging the wind turbine 10.

[0067] like Figure 4a As shown, the wind turbine blade 20 includes a blade shell 40 defining a hollow interior space 42, wherein a shear web 44 extends internally between an upper portion and a lower portion of the blade shell 40. The blade shell 40 may include two half shells 40a, 40b that are molded separately before being joined together (at the leading edge 26 and the trailing edge 28) to form the blade 20. It should be understood that the blade shell 40 need not be formed as two half shells that are subsequently joined together, but may be formed as a unitary shell structure together with the shear web 42 in a "one shot" single shell process.

[0068] Figure 4b A detailed view of the area where the shear web 44 meets the blade shell 40 is shown. The spar caps 46 may be incorporated into the shell 40, such as Figure 4b As shown, or may be attached to the outer shell 40. The spar cap 46 is an elongated reinforcing structure extending from the root end 22 to the tip end 24 along substantially the entire length of the blade 20. The spar cap 46 includes a second conductive material, such as carbon fiber. For example, the spar cap may include pultruded fiber strips of a material such as a pultruded carbon fiber composite or other carbon fiber reinforced polymer material.

[0069] Back to Figure 3, the blade 20 may have more than one spar cap 46 that is incorporated in or attached to the upper and lower portions of the blade shell 40. In the example shown, the blade 20 has main spar caps 46a having shear webs 44 extending therebetween and rear spar caps 46b (also referred to as stringers) that may or may not have shear webs extending therebetween.

[0070] Each spar cap 46 may include a stack of layers of a second conductive material. The shear web 44 may be adhesively bonded to an inner surface 48 of the spar cap 46. An outer surface 50 of the spar cap 46 may be located adjacent to a lightning receptor in an outer surface of the blade shell 40. Figure 4b As shown, the lightning receptor may be in the form of a metal foil 32 separated from the outer surface 50 of the spar cap 46 by one or more insulating material (e.g., glass fiber reinforced polymer) layers 52. One or more additional glass fiber reinforced polymer layers 52 may be provided on the outside of the metal foil 32. The layers 52 together form an outer skin of the blade shell 40. The one or more additional glass fiber reinforced polymer layers provide an inner skin 54 of the blade shell 40, with a core material 56 between the outer skin 52 and the inner skin 54. The core material may be a lightweight structural foam, although other core materials (such as wood, particularly balsa wood) may also be used to provide a lightweight core material. It will be appreciated that an almost identical connection is formed between the shear web 44 and the other side of the blade shell 40.

[0071] The structure of the blade shell 40 (particularly the outer skin) and its manufacturing method will now be described in detail. Figure 5As shown, the fiberglass reinforced fabric layer 52 is laid in the mold 60 as a fiber ply stack 70. The fiber ply stack 70 may include a plurality of fiber plies sewn or otherwise attached together as a kit. The fiber ply stack 70 may be pre-cut to fit the shape of the mold 60 so that the fiber ply stack 70 easily conforms to the shape of the mold 60 and a plurality of plies may be laid in the mold 60 easily and in a short time, preferably without any cutting or detailed shaping of the plies once in the mold 60. Alternatively, the plies may be cut in the mold 60. The fiber ply stack 70 may include dry fibers that are subsequently infused with resin, or alternatively, the fiber plies may be wet or semi-dry fiber plies that do not require or only require partial infusion of resin before consolidation and curing in the mold 60. Alternatively, the fiber ply stack 70 may be laid layer by layer in the mold 60. The fiber ply stack 70 may be prepared outside the mold 60 on a flat or nearly flat surface outside the mold, so that the fiber ply stack 70 assumes its form or shape when placed in the mold 60. Alternatively, the fiber ply stack 70 may be laid up on a suitably shaped surface outside the mold, so that the fiber ply stack 70 assumes its (near final) form or shape outside the mold before being laid up in the mold 60. In the following, a fiber ply stack laid up on any surface outside the mold is referred to as a "preform".

[0072] Each fiber ply stack 70 may have an inboard edge 71 toward the root end 22 of the blade 20 , an outboard edge 72 toward the tip end 24 of the blade, a leading edge 73 toward the leading edge 26 of the blade, and a trailing edge 74 toward the trailing edge 28 of the blade.

[0073] The fiber ply stacks 70 are arranged such that an inboard edge 71 of one of the stacks 70 and an outboard edge 72 of an adjacent stack 70 overlap to define an overlap region 75 that extends generally transversely across the location of the spar cap 46. This is generally referred to as a "chord-wise layup" of the preform or fiber ply stacks 70. Each fiber ply stack 70 may extend across the entire chord-wise width of the mold 60 such that a leading edge 73 of each fiber ply stack 70 is at the leading edge 26 of the blade, and a trailing edge 74 of each fiber ply stack 70 is at the trailing edge 28 of the blade. Typically, the length of each fiber ply stack 70 between the leading edge 73 and the trailing edge 74 is greater than the width of the stack between the inboard edge 71 and the outboard edge 72. Note that this "chord-wise layup" does not refer to any fiber orientation of any ply making up the fiber ply stack 70, and any individual ply may have a fiber orientation.

[0074] In order to avoid the risk of arc discharge between the second conductive material of the spar cap 46 and the first conductive material of the metal foil 32 or other lightning conductor, an equipotential bonding element 58 is used to equipotentially bond the lightning conductor to the second conductive material of the spar cap 46, such as Figure 7By electrically coupling the lightning lead 32 to the spar caps 46 , the spar caps 46 may be maintained at the same electrical potential as the lightning lead, so that undesirable discharges or arcs between the lightning lead 32 and the spar caps 46 may be avoided in the event of a lightning strike.

[0075] The overlapping edges of adjacent fiber ply stacks 70 may be formed by continuously terminating the individual plies in the stack to form a step or slope. Advantageously, such continuous termination of the individual plies in the stack at the overlap region 75 may create a stepped path between the outboard edge 72 of one stack 70 and the inboard edge 71 of the adjacent stack 70 through which the equipotential bonding element 58 may extend to electrically bond the metal foil 32 or other lightning conductor to the spar cap 46.

[0076] The second conductive material of the spar cap 46 can be different from the first conductive material of the lightning lead 32. For example, as described above, the spar cap 46 can include carbon fibers used as the second conductive material. In contrast, the metal foil of the lightning lead 32 can typically be a metal mesh or expanded metal foil made of, for example, aluminum. Carbon and aluminum have very different standard electrode potentials. For example, carbon (graphite, in solution) has a standard electrode potential of +0.13 V relative to a standard hydrogen electrode, while aluminum has a standard electrode potential of -2.31 V relative to a standard hydrogen electrode. The aluminum of the first conductive material can be away from the carbon of the second conductive material, such as Figure 7 As shown in the exemplary arrangement of , even in the presence of electrolyte material, the risk of galvanic corrosion is not significant due to the relatively large physical distance between the two materials.

[0077] However, the equipotential bonding element 58 is used to equipotentially bond the first conductive material of the lightning conductor 32 to the second conductive material of the spar cap 46. Figures 7 to 9 As shown, the equipotential bonding element 58 has a first end 58a of a first conductive material adjacent to the lightning conductor (e.g., metal foil 32), a second end 58b of a second conductive material opposite to the first end and adjacent to the spar cap 46, and a middle portion 58c. The first end 58a has a first metal material 59a, and the second end 58b has a second metal material 59b.

[0078] By providing the equipotential bonding element 58 as a bimetallic component, the standard electrode potentials of the first conductive material of the adjacent lightning lead 32 and the first metallic material of the equipotential bonding element 58 can be closely matched; and the standard electrode potentials of the second conductive material of the adjacent spar cap 46 and the second metallic material of the equipotential bonding element 58 can be closely matched.

[0079] The first metallic material may have a standard electrode potential similar to the first conductive material of the lightning lead, and the second metallic material may have a standard electrode potential similar to the second conductive material of the spar cap. The standard electrode potentials may be similar so that galvanic corrosion may be minimized even in the presence of an electrolyte. In this context, "similar" may mean that the standard electrode phase (E0) is of the same order of magnitude relative to the standard electrode potential of hydrogen.

[0080] Referring to the example above (wherein the first conductive material is aluminum and the second conductive material is carbon), the first metal material of the equipotential bonding element 58 can be aluminum and the second metal material can be copper. In the case where the first conductive material and the first metal material are both aluminum, the standard electrode potentials of the two conductive materials can be matched substantially identically, and there should be no problem of galvanic corrosion when the two components are adjacent. In the case where the second conductive material is carbon and the second metal material is copper, the standard electrode potentials of the two conductive materials can be similar but not identical. For example, carbon has a standard electrode potential of +0.13V relative to a standard hydrogen electrode, while copper has a standard electrode potential of +0.1V relative to a standard hydrogen electrode. Although these values ​​are not the same, they are of the same order of magnitude, so the risk of galvanic corrosion at the proximity of these materials is significantly reduced to the extent that any galvanic corrosion can be safely ignored during the working life of the component.

[0081] Although the equipotential bonding element 58 may be formed as a bimetallic component, this shifts the galvanic corrosion problem from the ends 58a and 58b of the equipotential bonding element adjacent to the first and second conductive materials to the middle portion 58c of the equipotential bonding element 58. In order to function as an equipotential bonding element to equipotentially bond the first conductive material of the lightning lead 32 to the second conductive material of the spar cap 46, the first metallic material is joined to the second metallic material at a joint within the middle portion 58c. Fig. 9 As shown, insulator 59c encapsulates the joint to prevent exposure of the joint to the electrolyte material.

[0082] The presence of electrolyte material in the vicinity of the equipotential bonding element 58 within the blade shell 40 is unavoidable, for example, ionized water from the natural environment when the wind turbine rotor blade 20 or blade portion is operating normally as part of the wind turbine 10 .

[0083] By using an insulator 59c to prevent the joint from being exposed to the electrolyte material, a current path can be prevented from forming between the first metal material 59a and the second metal material 59b instead of through the joint. Avoiding such a current path or arc helps prevent galvanic corrosion of the first metal material or the second metal material that is close to each other in the case of dissimilar metals, such as two metal materials that are far away from each other in terms of their standard electrode potential, such as copper and aluminum, as in the example above.

[0084] The first metallic material 59a may be attached to and in electrical contact with the first conductive material of the metallic foil 32 or other lightning conductor. The second metallic material 59b may be attached to and in electrical contact with the second conductive material of the spar cap 46. These electrical contacts may be achieved by vacuum pressure on the blade layup prior to resin injection to form the blade shell. Conductive fleece may be added to help form these electrical contacts if desired.

[0085] The insulator 59c may cover only a small portion of the equipotential bonding element 58. The insulator 59c may extend a sufficient distance on either side of the joint to prevent a current path from being formed between the first metal material 59a and the second metal material 59b instead of through the joint.

[0086] The first metal material 59 a and the second metal material 59 b may be mechanically and electrically joined together in the middle portion 58 c of the equipotential bonding element 58 , and the joint is encapsulated by the insulator 59 c .

[0087] The equipotential bonding element 58 may be formed as a strip or a ribbon. Before being installed in the blade shell 40, the equipotential bonding element 58 may be substantially rectangular. The equipotential bonding element 58 may be substantially thin and flexible. This enables the equipotential bonding element 58 to be deformed during the manufacture of the blade shell, for example in the above-mentioned stepped manner. Figure 7 As shown, the spar cap 46 has an outer side 46a closest to the outer surface 29 of the blade 20 and an inner side 46b closest to the hollow interior 42 of the blade 20. The second metallic material 59b of the equipotential bonding element 58 can be attached to and in electrical contact with the outer side 46a of the spar cap 46. By "stepping" the flat tape between the edges of adjacent fiber ply stacks 70, the tape is kept as flat as possible.

[0088] The first metal material 59a and / or the second metal material 59b of the equipotential bonding element 58 can each be formed as a conductive layer, such as a conductive mesh, such as a metal mesh or foil; or, the first metal material 59a and / or the second metal material 59b may include conductive material lines (e.g., metal wires) woven into a fabric material (e.g., a glass fiber fabric).

[0089] The glass fiber material of the fiber ply stack 70 between the spar cap 46 and the lightning lead 32 primarily distributes mechanical loads, but the glass fiber also helps to avoid galvanic response between the carbon (second conductive material) of the spar cap and the aluminum (first conductive material) of the metal foil 32. Of course, it should be understood that the lightning lead 32 can be formed of other suitable materials (e.g., copper), and the selection of the first metal material 59a and the second metal material 59b for the equipotential bonding element 58 can be selected based on other material selections.

[0090] The spar caps 46 may be arranged to equipotentially bond between the conductive material layers in the spar caps. The spar caps 46 may include a stack including a plurality of conductive material layers. The conductive material may include a pultruded fiber composite material, such as a carbon fiber reinforced polymer. The pultruded fibers may be oriented in a longitudinal direction of the spar caps 46 that is aligned with the longitudinal direction or span direction of the blade 20. By equipotentially bonding adjacent conductive material layers 80, undesirable discharges or arcs from the spar caps 46 may be avoided in the event of a lightning strike to the blade 20.

[0091] The spar cap 46 may extend substantially the entire length of the blade 20 and have a first end 82 closest to the root end 22 of the blade 20 and a second end 84 adjacent the tip end 24 of the blade. The spar cap 46 has a thickness that may vary along the length of the spar cap 46 in the stacking direction of the conductive material layers 80.

[0092] Back to Figure 3 , it can be seen that the metal foil 32 type lightning conductor can extend substantially over the entire blade surface. A plurality of equipotential bonding elements 58 can be connected to the spar cap 46 at different locations along the length of the blade. In particular, a first equipotential bonding element 58 can be connected to the spar cap 46 at the tip end 84 of the spar cap 46, and a second equipotential bonding element 58 can connect the metal foil 32 to the first (root) end 82 of the spar cap 46. Additional intermediate equipotential bonding elements 58 connect the metal foil 32 type lightning conductors to the mid-span region of the spar cap 46, respectively.

[0093] By means of the electrical connection provided by the equipotential bonding elements 58 at the root and tip ends of the blade, there will be a voltage drop between the first end 82 and the second end 84 of the spar cap 46. Depending on the length of the blade 20, and in particular the length of the longest conductive material layer 80 in the spar cap 46, the value of the voltage drop between the first end 82 and the second end 84 of the spar cap 46 will vary. If this voltage drop is below a threshold at which arcing from the lightning lead to one or more conductive material layers 80 may occur, it may be sufficient to provide the equipotential bonding elements 58 only at the ends 82, 84 of the spar cap 46. However, if the voltage drop between the ends 82, 84 of the spar cap 46 is above a threshold, one or more additional equipotential bonding elements 58 may be required to electrically bond the metal foil 32 to an intermediate point between the first end 82 and the second end 84 of the spar cap 46.

[0094] Fig. 9 An example is shown in which both the first metal material 59 a and the second metal material 59 b are formed as a porous foil or mesh.

[0095] The joint between the first metal material 59a and the second metal material 59b is encapsulated by an insulator 59c to prevent the joint from being exposed to the electrolyte material. The insulator 59c may have a known dielectric strength. The insulator may be a polymer. Preferably, the polymer may be a thermoplastic material. The thermoplastic material may have a high surface tension, so the resin injection injected into the adjacent fiber layer stack 70 may adhere to the polymer. The polymer may be polyethylene (PE), or polyester terephthalate (PET), or other suitable polymers. The polymer may be corona treated on the outer surface to improve adhesion to the resin injection (e.g., epoxy resin).

[0096] The mesh strips of the first metallic material 59a and the second metallic material 59b may be approximately 50 mm wide. The insulator 59c may form an encapsulation area of ​​approximately 60 mm×60 mm in area and approximately 2 mm thick. The encapsulation area of ​​the equipotential bonding element 58 may be located between the fiberglass fabric layers of the fiber ply stack 70 and not in direct contact with the first conductive material of the lightning lead 32 and the second conductive material of the spar cap 46. The insulator 59c preferably covers only a relatively small portion of the length of the equipotential bonding element 58.

[0097] As described above, the first metal material 59a and the second metal material 59b are dissimilar metals, such as copper and aluminum. When dissimilar metals are used for the first metal material 59a and the second metal material 59b of the equipotential bonding element 58, each dissimilar metal material may have a different yield strength. It is important to consider the yield strength of these materials because the blade shell may experience significant flapwise bending deflections during use, i.e., the blades bend out of the rotor plane in the spanwise direction. It is necessary to accommodate the strains acting on the blades to prevent degradation due to strain hardening, leading to potential fatigue failure. In the case where the equipotential bonding element 58 has a length extending in the spanwise direction of the blade (such as Figure 8 ), which may be of particular concern because these strains are greater than the strains when the equipotential bonding element 58 extends in the chordwise direction of the blade. It should be noted that the chordwise extending equipotential bonding element 58 may be suitable for the fiber ply stack 70 to extend in the spanwise direction rather than in the spanwise direction. Figure 5 The chordwise laying situation is shown.

[0098] In the case where the equipotential bonding element 58 has a length extending in the span direction of the blade, both the first metal material 59a and the second metal material 59b need to be able to withstand the strain acting in the blade. The first metal material 59a and the second metal material 59b may be in a form with an elastic or "stretchable" design to reduce the strain absorbed in the metal material. Therefore, a "stretchable" metal mesh, braid or metal wire with a zigzag path may be preferred to avoid the first metal material and / or the second metal material absorbing all the blade strain.

[0099] To accommodate the different yield strengths of the dissimilar first and second metal materials 59a, 59b, the first and second metal materials 59a, 59b can have different forms. The first and second metal materials 59a, 59b can each have a form configured to accommodate observed strains without yielding, which is greater than the yield strength of a solid straight shape of the corresponding material.

[0100] The equipotential bonding element 58 is an internal electrical structure and may be located in one of the highest strain areas of the blade structure. It is important to avoid fatigue of the equipotential bonding element 58, otherwise it may cause arcing and impacts to the main structure of the blade.

[0101] Fig.10An example is shown where the first metal material 59a has a lower Young's modulus than the second metal material 59b, and where the mesh pattern of the first metal material 59a has a mesh (or "eye") aspect ratio that is higher than the aspect ratio of the mesh pattern of the second metal material 59b. The aspect ratio is considered to be the width / length of the hole "eye" in the width and length directions of the strip (equipotential bonding element 58).

[0102] In one example, the first metal material 59a comprises a stretchable aluminum mesh having an aspect ratio (AR) of 0.5 for the holes "eyes", and the second metal material 59b comprises a stretchable copper mesh having an AR of 0.4. The smaller the aspect ratio, the smaller the stiffness of the mesh in the short axis direction (i.e., the length dimension of the equipotential bonding element 58). The metal mesh can also withstand greater strains in this direction without fatigue. Aluminum has a lower Young's modulus than copper. The elastic modulus of aluminum is about 70GPa and the elastic modulus of copper is 125GPa. In the blade, the strain can reach 4000 microstrains, and the stress applied to the aluminum is 280MPa and the stress applied to the copper is 500MPa. For these solid forms of metal (i.e., without holes), this stress would be too high. By configuring the metal materials 59a, 59b as a stretchable mesh or foil, and then adapting the AR of the mesh's hole "eyes" to the specific material selected, the form of the metal material allows the metal to be prevented from seeing the full amount of strain, and therefore prevents the lower stress from being seen.

[0103] If the equipotential bonding elements 58 are oriented spanwise rather than chordwise, ie the fiber ply stack 70 is laid spanwise rather than chordwise, the mesh aspect ratio may need to be oriented to accommodate spanwise blade strains.

[0104] To simplify manufacturing, it may be desirable for the first metal material 59a and the second metal material 59b to have the same form, for example, both are "stretchable" meshes with the same AR but dissimilar metal materials. For example, if aluminum and copper are selected as previously described, a lower AR of 0.4 may be selected for the first metal material 59a and the second metal material 59b.

[0105] Now looking at the electrical connection between the first metal material 59a and the second metal material 59b in the middle portion 58c, the electrical joint can be formed by welding or casting. At least one of the first metal material 59a and the second metal material 59b may need to be processed for welding. For example, the aluminum mesh should be processed for welding. Zinc-coated aluminum is easy to weld. Copper is easy to weld. Tinning copper can provide additional corrosion protection. The treatment can be applied only to the end closest to the joint of the first metal material 59a or the second metal material 59b. However, it may also be desirable to apply the treatment to the end of the second metal material 59b adjacent to the second conductive material. The entire area of ​​the first metal material 59a and the second metal material 59b can be treated.

[0106] As an alternative to solder, a casting (eg, tin or zinc) may be used to connect the first metal material 59a and the second metal material 59b in the middle portion 58c.

[0107] For welding aluminum and copper, exemplary solders may be 98% zinc / 2% AL alloy or 88AL / 12Si alloy. Zinc alloy solders may provide good strength because the melting point (about 420°C) is farthest from the melting point of the aluminum mesh and therefore the welding process has less risk of overheating the aluminum. Aluminum alloy solders may provide good corrosion resistant joints but have a higher melting point of about 577°C. Both solders provide acceptable electrochemical response and are relatively corrosion resistant.

[0108] Another suitable solder may be 78% Zn / 22% Al. This product has a low melting point, so it is particularly suitable for soldering mesh. The mesh has a thin cross section and a large surface, so it is prone to overheating, so a low melting point alloy is preferred. Before encapsulating the joint, it may be necessary to remove the flux residue.

[0109] The solder metal may be selected to provide good mechanical and electrical strength. The solder itself is not particularly susceptible to galvanic corrosion since it will reside within the insulator 59c.

[0110] To facilitate the joining of the first metal material 59a and the second metal material 59b in the middle portion 58c, the joining may not be mesh to mesh but sheet to sheet. The mesh is formed of sheet material and the starting point may have a portion of sheet before forming the mesh.

[0111] Fig.11 An example is shown in which the first metal material 59a is formed as a mesh except for the end regions at the middle portion 58c which are formed as strips 59d. Similarly, the second metal material 59b is formed as a mesh except for the end regions at the middle portion 58c which are formed as strips 59d. Having strips on the ends of the first metal material 59a and the second metal material 59b allows the joint to be sheet-to-sheet.

[0112] Fig.12 A) shows a side view of an example joint between a first metal material 59a and a second metal material 59b in an intermediate portion 58c, wherein a strip 59c of the first metal material 59a is simply overlapped with a strip 59d of the second metal material 59b to form a lap joint ready for welding or casting or otherwise joining the first metal material 59a and the second metal material 59b.

[0113] Fig.12 B) shows an alternative side view of another example joint between first metal material 59a and second metal material 59b in middle portion 58c, wherein each of strips 59c and 59d is bent to form a return or "hook." The hook on strip 59c of first metal material 59a is mechanically engaged with the oppositely handed hook on strip 59d of second metal material 59b to form a double hook joint ready for welding or casting or otherwise joining first metal material 59a and second metal material 59b.

[0114] Fig.12 C) and Fig.13 A) and B) of FIG. 5 show another alternative example joint between first metal material 59a and second metal material 59b in middle portion 58c. Although first metal material 59a is again formed as a mesh except for the end regions at middle portion 58c formed as strips 59e, and second metal material 59b is formed as a mesh except for the end regions at middle portion 58c formed as strips 59f, strips 59e and 59f differ in that they have respective tabs 59g and grooves 59h. Fig.13 As shown in A), before forming the joint, the strips 59e and 59f are initially substantially planar. Strip 59e has at least one tab 59g protruding from the edge closest to strip 59f, and strip 59f has at least one corresponding slot 59h, which is sized to receive the corresponding tab 59g. During the formation of the joint, the tab 59g is received by the slot 59h and then bent to form a return or "hook". The completed single hook joint is Fig.13 B) is shown, the side view is Fig.12 C) shows that the first metal material 59a and the second metal material 59b are prepared for welding or casting or otherwise joining.

[0115] Fig.14Yet another alternative example joint between the first metal material 59a and the second metal material 59b in the middle portion 58c is shown, wherein the joint is mesh-to-mesh without any end plates. The mesh of one of the first metal material and the second metal material is cut through the "eyes" to provide forked barbs that will fit through the "eyes" of the other mesh material. The two mesh materials are brought together to provide an overlap area 59i, for example, about 3 checkerboard rows of eyes; the forked barbs 59j of the one mesh are then passed through the eyes of the other mesh material and bent to form a return or "hook" fixed around the node between adjacent eyes of the one mesh. The overlap may be important because the extent of the barbs alone may provide insufficient area (i.e., metal around the eye) for welding. Preferably, the AR and spacing of the two meshes are the same to increase the overlap area of ​​the two meshes. Once the return is formed, the joint is ready to weld or cast or otherwise join the first metal material 59a and the second metal material 59b.

[0116] In each case (lap joint, double hook joint or single hook joint), the joint is based on welding or casting the metals together to achieve complete mechanical and electrical contact. Fig.12 A) Lap joints are the simplest and should be clamped during welding or casting. Fig.12 B) The double hook joint may hold itself together during welding or casting and requires a forming tool to bend the return portion. Fig.12 C) The single hook joint requires a punching tool and may hold itself together. Fig.14 The mesh-to-mesh joints with equal hole spacing can be positioned on each other to allow welding, which allows the strip to be supported without solid plate ends. The absence of plate ends may also provide a smaller increase in stiffness and therefore may be less sensitive to fatigue from strain peaks caused by stiffness jumps.

[0117] Preferably, the length of the joint area should be as short as possible. This can help reduce strain peaks, for example at the transition from plate to mesh. The length of the joint area may be about 10 mm. A glass fiber reinforcement mat may be added to provide some strain relief over the joint area.

[0118] Fig.15Another example of an equipotential bonding element 58 used in exactly the same manner as the above example is shown. The equipotential bonding element 58 shown has a first end 58a of a first conductive material adjacent to a lightning conductor (e.g., a metal foil 32), a second end 58b of a second conductive material opposite the first end and adjacent to the spar cap 46, and a middle portion 58c. The first end 58a has a first metallic material 59a and the second end 58b has a second metallic material 59c. The first metallic material is joined to the second metallic material at a joint within the middle portion 58c. An insulator 59c encapsulates the joint to prevent exposure of the joint to the dielectric material. The key difference from the previous embodiment is that the first metallic material and / or the second metallic material is provided as a wire rather than a mesh.

[0119] The metal wire can be arranged on a substrate 59k (e.g. a fabric material, in particular a glass fiber fabric) so that it can be incorporated into the glass fiber fabric ply stack 70 without using additional components and injected with resin without gaps during the manufacture of the blade shell 40. The metal wire can be sewn onto the surface of the substrate 59k. The equipotential bonding element 58 is arranged as a strip or a belt in the same manner as in the previous example. The material selection of the first metal material 59a and the second metal material 59b can be the same as in the previous example.

[0120] The metal wire can have an undulating form across the surface of the substrate 59k, such as a zigzag pattern, wherein the pitch extends approximately over the length dimension of the equipotential bonding element 58. As previously described, the undulations in the metal wire can accommodate blade strain without degradation due to fatigue, since the pitch of the undulations can lengthen and shorten with blade strain, with a corresponding increase or decrease in the amplitude of the undulations. The nominal pitch of the undulations can be selected so that at the maximum expected strain, the wire does not deform, causing the wire to straighten and become over-strained in the straightened state, otherwise they will observe that all blade strain and fatigue of the wire may occur. The nominal pitch of the undulating wire of the first metal material can be different from the pitch of the undulating wire of the second metal material. The differential pitch can be selected based on the material selection of the first metal material and the second metal material.

[0121] Although the invention has been described above with reference to one or more preferred embodiments, it will be appreciated that various changes or modifications may be made without departing from the scope of the invention as defined in the appended claims.

Claims

1. A wind turbine rotor blade section having a root end and a tip end, the wind turbine rotor blade section comprising: a wind turbine blade shell defining a suction side, a pressure side, a leading edge and a trailing edge of said blade portion, wherein said blade shell comprises a lightning lead comprising a first electrically conductive material; and at least one spar cap associated with the blade shell and comprising a second electrically conductive material different from the first electrically conductive material; An equipotential bonding element, which electrically bonds the lightning lead to the spar cap, wherein the equipotential bonding element comprises: a first end portion having a first metallic material adjacent to a first conductive material of the lightning lead; a second end opposite the first end and having a second metallic material adjacent to a second conductive material of the spar cap; and An intermediate portion in which the first metal material is joined to the second metal material at a joint and has an insulator encapsulating the joint for preventing the joint from being exposed to an electrolyte material.

2. The wind turbine rotor blade according to claim 1, wherein: The first metal material and the second metal material are mechanically and electrically joined together at the joint.

3. A wind turbine rotor blade according to claim 1 or 2, wherein: The equipotential bonding element is formed as a strip or a ribbon.

4. A wind turbine rotor blade according to any one of the preceding claims, wherein: The first metallic material and the second metallic material each have a form configured to accommodate, without yielding, an observed strain greater than a yield strength of a solid straight form of the respective material.

5. The wind turbine rotor blade of claim 4, wherein: The first metallic material has a different form than the second metallic material.

6. A wind turbine rotor blade according to any one of the preceding claims, wherein: The first metal material and / or the second metal material is formed into a porous foil or mesh.

7. A wind turbine rotor blade according to claims 5 and 6, wherein: The aspect ratio of the pores of the first metal material is different from the aspect ratio of the pores of the second metal material.

8. A wind turbine rotor blade according to any one of claims 1 to 5, wherein: The first metal material and / or the second metal material are formed as lines on a substrate.

9. The wind turbine rotor blade of claim 8, wherein: The lines have an undulating form with undulations in a plane parallel to the substrate, preferably wherein the pitch of the undulating lines of the first metallic material is different from the pitch of the undulating lines of the second metallic material.

10. A wind turbine rotor blade according to any one of the preceding claims, wherein: The blade shell comprises a plurality of fiber ply stacks, and the equipotential bonding element extends between an edge of one stack and an edge of an adjacent stack, the edge of one stack and the edge of the adjacent stack overlapping to define an overlapping edge region extending across the spar cap.

11. The wind turbine rotor blade of claim 10, wherein: The middle portion of the equipotential bonding element is located in the overlapping region, away from the spar cap and the lightning conductor.

12. A wind turbine rotor blade according to claim 10 or 11, wherein: Each fiber ply stack has an inner edge towards the root end of the blade, an outer edge towards the tip end of the blade, a leading edge towards the leading edge of the blade and a trailing edge towards the trailing edge of the blade, and wherein the equipotential bonding element extends between the outer edge of one stack and the inner edge of an adjacent stack, the outer edge of one stack and the inner edge of the adjacent stack overlapping.

13. A wind turbine rotor blade according to any one of the preceding claims, wherein: A first end of the equipotential bonding element is attached to and in electrical contact with the lightning conductor, and a second end of the equipotential bonding element is attached to and in electrical contact with the spar cap.

14. A wind turbine rotor blade according to any one of the preceding claims, wherein: The first metallic material has a standard electrode potential similar to that of a first conductive material of the lightning lead, and wherein the second metallic material has a standard electrode potential similar to that of a second conductive material of the spar cap.

15. A wind turbine rotor blade according to any one of the preceding claims, wherein: The lightning lead is the metal foil of the lightning protection system.

16. A method of manufacturing a wind turbine rotor blade section having a root end and a tip end, the method comprising: laying a shell of a wind turbine rotor blade, the shell defining a suction side, a pressure side, a leading edge and a trailing edge of said blade portion, said shell comprising a lightning lead, the lightning lead comprising a first electrically conductive material; Laying a spar cap so that the lightning lead extends over the spar cap, wherein the spar cap comprises a second conductive material; and An equipotential bonding element is provided to electrically bond the lightning conductor to the spar cap, the equipotential bonding element comprising: a first end portion having a first metallic material adjacent to a first conductive material of the lightning lead; a second end opposite the first end and having a second metallic material adjacent to a second conductive material of the spar cap; and An intermediate portion in which the first metal material is joined to the second metal material at a joint and has an insulator encapsulating the joint for preventing the joint from being exposed to an electrolyte material.

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