WIND TURBINE BLADE WITH LIGHTNING PROTECTION SYSTEM

There is provided a wind turbine blade having a root end, a tip end, a blade shell, a lightning protection system and an integrated web-down conductor. The integrated web-down conductor comprises: a down conductor forming part of the lightning protection system: electrical insulation surrounding the down conductor; and a web that surrounds the electrical insulation so as to enclose the down conductor and electrical insulation and is coupled to the blade shell.

FIELD OF THE INVENTION

The present invention is in the field of wind turbines, specifically wind turbine blade lightning protection systems.

BACKGROUND OF THE INVENTION

Wind turbines can be, and often are, struck by lightning, and typically include a lightning protection system. In a typical wind turbine blade construction, at the tip end of the blade, a down conductor will run parallel to the shear web which connects the blade shells. A wind turbine blade having one such lightning protection system is shown inFIG.2. The tip end of the blade has space constraints within its internal volume, which introduces manufacturing constraints and makes positioning of the lightning protection system components challenging. The parallel down conductor and web have a relatively high mass which introduces relatively high edgewise loads. As such, there is a need for an improved wind turbine blade.

SUMMARY OF THE INVENTION

It has been identified that known lightning protection systems can be improved by the following aspects of the invention, in which electricity passing from a tip of the blade passes through a lightning protection system having an integrated web-down conductor. In the following aspects of the invention, provision of an integrated web-down conductor, as opposed to a separate web and down conductor, benefits from at least some of the following advantages, which will be explained in more detail in relation to the figures:a) Improved performance of the blade resulting from an overall mass reduction, caused directly by providing fewer components and indirectly by a reduction in attachment means such as adhesive required;b) Better structural performance of the blade, due to a reduction in mass at the tip end;c) Improved lightning protection properties of the lightning protection system, due to improved accuracy in locating the down conductor of the integrated-web down conductor during manufacture;d) Reduced manufacturing complexity and reduced associated cost. This may be a direct result of fewer space constraints on fitting components within the tip end of the blade (as there are fewer individual components), or a result of ease of locating drill holes, as the integrated web-down conductor may be in a thin laminate region of the blade shell with no core; ande) Introduction of the possibility to use receptor bolts on windward and leeward sides of the blade that are aligned in a thickness direction of the blade, due to increased thickness of a receptor block of the integrated web-down conductor compared to a typical down conductor receptor block. In a typical blade, a receptor block, which is located on the down conductor, cannot be located at the maximum thickness location of the blade, as that space is occupied by a web. By the invention, a receptor block can be located at a maximum thickness location of the blade, because it is integrated with the web. As such, the receptor block can be thicker than those of known blade lightning protection systems.

A first aspect of the invention provides a wind turbine blade having a root end, a tip end, a blade shell, a lightning protection system and an integrated web-down conductor, the integrated web-down conductor comprising:a down conductor forming part of the lightning protection system;electrical insulation surrounding the down conductor; anda web that surrounds the electrical insulation so as to enclose the down conductor and electrical insulation and is coupled to the blade shell.

The wind turbine blade may have a blade section. The integrated web-down conductor may be at a maximum thickness of the blade section.

The blade may have a span extending in a span-wise direction from the root end to the tip end of the blade. The integrated web-down conductor may extend from adjacent the tip end of the blade up to a span-wise position. This extension may extend so as to terminate within 15% of the blade span away from the tip end. This extension may extend so as to terminate within 10% of the blade span away from the tip end. This extension may extend so as to terminate within 5% of the blade span away from the tip end.

The blade may comprise a secondary web and/or a secondary down conductor. The secondary web and/or secondary down conductor may be disposed inboard of the integrated-web down conductor. The secondary web and secondary down conductor may be provided as separate, not integrated, components.

The integrated web-down conductor may extend from adjacent the tip end of the blade up to a span-wise position at which it terminates. There may be no other web component disposed outboard of where the integrated web-down conductor terminates. There may be no other down conductor component disposed outboard of where the integrated web-down conductor terminates.

The web may define a filled tubular shape. The web may define a filled tubular shape in which the down conductor and electrical insulation are disposed.

The web may comprise a material laminate, preferably a fibre composite material laminate, preferably a glass fibre composite material laminate, preferably a biaxial glass fibre composite material laminate.

The integrated web-down conductor may comprise a filler component, such as a foam core. The filler component may be disposed around the electrical insulation between the electrical insulation and the web.

The lightning protection system may further comprise at least one lightning receptor. The at least one lightning receptor may be disposed near or at an outer surface of the blade shell. The at least one lightning receptor may be electrically connected to the down conductor.

The lightning receptor may be electrically coupled to the down conductor. The receptor may extend through the electrical insulation to a receptor block. The receptor block may have a width greater than a diameter of the down conductor. The receptor block may be electrically coupled to the down conductor. The filler component may be disposed around the electrical insulation and between adjacent receptor blocks. In this way the filler component may enable a constant section web around both the filler component and the receptor blocks.

A second aspect of the invention provides an integrated web-down conductor component for a wind turbine blade, the integrated web-down conductor component comprising:a down conductor for forming part of a lightning protection system of the wind turbine blade;electrical insulation surrounding the down conductor; anda web surrounding the electrical insulation so as to enclose the down conductor and electrical insulation and configured for coupling to a blade shell of the wind turbine blade.

A third aspect of the invention provides a method of forming an integrated web-down conductor, comprising:providing a down conductor,forming electrical insulation around the down conductor,forming a web around the electrical insulation so as to enclose the down conductor and electrical insulation.

Forming a web around the electrical insulation may comprise wrapping material around the electrical insulation and/or a filler component such as a foam core so as to form a material laminate web.

A fourth aspect of the invention provides a method of manufacturing a wind turbine blade, comprising:providing an integrated web-down conductor and a blade shell, the integrated web-down conductor having a down conductor, electrical insulation surrounding the down conductor and a web surrounding the electrical insulation so as to enclose the down conductor and electrical insulation,arranging the integrated web-down conductor relative to the blade shell, andfixing the integrated web-down conductor to the blade shell.

The blade shell may comprise first and second blade shell halves. The method of manufacture may comprise fixing the integrated web-down conductor to one of the first and second blade shell halves. The method of manufacture may then comprise fixing the second blade shell half to the first blade shell half and to the integrated web-down conductor.

The method of manufacture may further comprise electrically connecting one or more lightning receptors at or near the outer surface of the blade shell to the down conductor.

DETAILED DESCRIPTION OF EMBODIMENT(S)

In this specification, terms such as root end, tip end, span-wise, leading edge, trailing edge, and web, are used. While these terms are well known and understood to a person skilled in the art, definitions are given below for the avoidance of doubt.

The term “root” used herein in relation to a blade end, refers to an end of the blade at which the blade is attached to a hub18of a turbine10. The term “tip” used herein in relation to a blade end, refers to a blade end that is radially furthest away from the axis of rotation of the hub.

The term “leading edge” is used to refer to an edge of the blade which will be at the front of the blade as the blade rotates in the normal rotation direction of the wind turbine rotor.

The term “trailing edge” is used to refer to an edge of a wind turbine blade which will be at the back of the blade as the blade rotates in the normal rotation direction of the wind turbine rotor.

The term “span-wise” is used to refer to a dimension or direction from a root end of a wind turbine blade to a tip end of the blade, or vice versa. When a wind turbine blade is mounted on a wind turbine hub, the span-wise and radial directions of the wind turbine blade will be substantially the same.

A pressure side or surface (or windward side or surface) of a wind turbine blade is a side or surface between the leading edge and the trailing edge, which, when in use, has a higher pressure than a suction side or surface of the blade.

A suction side or surface (or leeward side or surface) of a wind turbine blade is a side or surface between the leading edge and the trailing edge, which will have a lower pressure acting upon it than that of a pressure side or surface, when in use.

The chord of a blade is the straight line distance from the leading edge to the trailing edge in a given cross section perpendicular to the blade span-wise direction.

The thickness of a wind turbine blade is measured perpendicularly to the chord of the blade and is the greatest distance between the pressure surface and the suction surface in a given cross section perpendicular to the blade span-wise direction.

The term “inboard” is used to refer to a portion of the blade closer to the root end than the tip end in the span-wise direction. The term “outboard” is used to refer to a portion of the blade closer to the tip end than the root end in the span-wise direction. The terms “inboard of” and “outboard of” when used to describe relative positions of components, means “closer to a root end than” and “closer to a tip end than”, respectively.

The term “web” (also known as a shear web) is used to refer to refer to a longitudinal, generally span-wise extending, reinforcing member of the blade that can transfer load from one of the windward and leeward sides of the blade to the other of the windward and leeward sides of the blade. The “web” may, together with spar caps, form part of a longitudinal reinforcing spar or support member of the blade. The spar caps may be embedded in the blade shell, or may be attached to the blade shell. The spar caps of the windward and leeward sides of the blade may be joined by the one or more webs extending through the interior hollow space of the blade.

The term “shell” is used to refer to an outer aerodynamic structure of the blade. The shell may be provided as two shell halves, which may be bonded together by an adhesive.

FIG.1shows a wind turbine10including a tower12and a nacelle14disposed at the apex of the tower12.

A rotor16is operatively coupled via a gearbox to a generator (not shown) housed inside the nacelle14. The rotor16includes a central hub18and a plurality of rotor blades20,220which project outwardly from the central hub18. While the example shown inFIG.1has three blades, it will be understood by the skilled person that other numbers of blades are possible.

When wind blows against the wind turbine10, the blades20,220generate a lift force which causes the rotor16to rotate, which in turn causes the generator within the nacelle14to generate electrical energy.

FIG.2illustrates a wind turbine blade20for use in such a wind turbine10. The wind turbine blade20has a root end21and a tip end22. The wind turbine blade20has a leading edge28and a trailing edge29.

The wind turbine blade20ofFIG.2has a known lightning protection system. This known lightning protection system comprises a tip down conductor110, a surface protection layer150and a root down conductor130. The tip down conductor110, surface protection later150, and root down conductor130are all configured to provide a path for electrical charge for lightning from the tip end22of the blade20to the root end21of the blade20. In this known lightning protection system, the tip down conductor110and root down conductor130are provided as a wire or cable. The surface protection layer150is an electrically conductive foil such as a metal foil, which may be covered by a layer of material, such as a glass layer. The surface protection layer150can have a mesh configuration or be an expanded metal foil.

As shown inFIG.2, the blade20having a known lightning protection system also has various structural components i.e. a first web141and a second web142. As shown inFIG.2, the first web141extends from proximate the root end21towards the tip end22. The second web142also extends from the root end21towards the tip end22. The first web141extends further towards the tip end22than the second web142. The first web141is arranged closer to the leading edge28than the second web142. The webs141,142of this known blade20are configured to provide structural support within the blade shell.

As a skilled person will appreciate, the webs141,142and the lightning protection system (tip down conductor110, surface protection layer150and root down conductor130) are separate components, having separate functions. At the tip end of the blade, outboard of the surface protection layer150, the tip down conductor110and first web141extend separately, alongside one another in a span-wise direction of the blade20.

In contrast to this known blade having a known lightning protection system, the present disclosure provides an integrated web-down conductor250.

A tip portion of a blade220including an example of an integrated web-down conductor250can be seen inFIG.3. Similar to the blade20ofFIG.2, the blade220has a tip end222, a leading edge228and a trailing edge229. The blade220also has a root end (not shown).

The integrated web-down conductor250is configured to conduct electrical charge from a tip end222of the blade, or from proximate a tip end222of the blade, towards a root end of the blade. The integrated web-down conductor250is also configured to transmit structural load between a windward side286and a leeward side285of the blade220. As best seen inFIG.5, the integrated web-down conductor250comprises a down conductor255, electrical insulation256and a web257.

The down conductor255forms part of the lightning protection system. The down conductor255is configured to carry electrical charge from at or proximate the tip end222of the blade towards the root end of the blade. As such, the down conductor255of the integrated web-down conductor250comprises or consists of an electrically conductive material such as a metal or alloy. The down conductor255may be provided as a cable, a wire or any other appropriate component.

The electrical insulation256surrounds the down conductor255. The electrical insulation256is configured to provide an electrically insulating barrier around the down conductor255. The electrical insulation256may also provide a barrier between the down conductor255and the web257. There may be provided a filler component258around the electrical insulation256, between the electrical insulation256and the web257, as will be described later.

The web257passes around the electrical insulation256so as to enclose, or encapsulate, the down conductor255and the electrical insulation256, and optional filler component258. By “enclosing”, the web may entirely surround the down conductor255and the electrical insulation256, and optionally the filler component258, in at least two dimensions. The web257may form or define a substantially continuous loop in transverse cross section, inside of which the down conductor255and/or the electrical insulation256and/or the filler component258may be disposed. The down conductor255and/or the electrical insulation256, and/or the filler component258may be wholly disposed within the web257. The web257may define a filled tubular shape, in which the down conductor255and electrical insulation256and optional filler component258are disposed. A tubular shape provides a particularly effective integrated web-down conductor, which is easy to manufacture and easy to assemble into a blade shell, while benefiting from good structural properties.

The web257is configured to act as a structural component that can, in conjunction with other components of the integrated web-down conductor250, convey loads between a windward side286and a leeward side285of the blade220. The web257may comprise a material laminate such as a fibre composite material laminate. Preferably, the web257comprises a glass fibre reinforced plastic (GFRP) composite material laminate, preferably a biaxial (GFRP) composite material laminate. Use of a material laminate provides a web257that is strong and easy to manufacture.

The arrangement and configuration of the integrated web-down conductor250may be best seen inFIGS.4and5. The integrated web-down conductor250has a root end251and a tip end252. The integrated web-down conductor250may be disposed, at a position within a cross-section of the blade shell, at a location of the highest second moment of inertia of the blade. The wind turbine blade220has a blade section, and the integrated web-down conductor250may be disposed at a maximum thickness of the blade section, i.e. at a location where there is the highest second moment of inertia of the blade. The integrated web-down conductor250may have a cross-sectional shape that varies along its length, i.e. from its tip end252to root end251, in a span-wise direction. The integrated web-down conductor250may have a cross-sectional shape that at least partially aligns with the blade shell. The integrated web-down conductor250may have a width that is substantially constant along its length, i.e. in a span-wise direction. The integrated web-down conductor250may have a height that varies along its length i.e. in a span-wise direction. The integrated web-down conductor250may have a height that increases along its length, such that it has a greater height at its root end251than at its tip end252. The integrated web-down conductor250may at least partly define a rounded square-shape in cross-section.

The integrated web-down conductor250may extend from the tip end222of the blade towards the root end of the blade. The blade220may have a span extending in a span-wise direction from its root end to its tip end222. The integrated web-down conductor250may extend from adjacent the tip end222of the blade220up to a span-wise position so as to terminate within 15% of the blade span away from the tip end222, optionally within 10%, optionally within 5%. The integrated web-down conductor250may extend from adjacent the tip end222of the blade220up to or proximate a most inboard receptor261,262. The integrated web-down conductor250may not extend towards the root substantially further than where receptors261,262are disposed. By not extending the integrated web-down conductor250further towards the root end221, i.e. by terminating the integrated web-down conductor250at one of the locations described herein, the overall weight of the blade is reduced, while benefitting from use of the integrated-web down conductor250at a location where its effects are the most beneficial. The integrated web-down conductor250may extend up to a secondary web240. The integrated web-down conductor250may be aligned with and/or connected to and/or fixedly attached to the secondary web240. There may be provided a secondary down conductor (not shown) provided inboard of the integrated web-down conductor250. The integrated web-down conductor250may be aligned with the secondary web240so as to define or form a continuous line. Aligning the integrated web-down conductor250with the secondary web240may ensure that blade loads are optimally supported. The blade220may be configured such that there is no other web component disposed outboard of where the integrated web-down conductor250terminates, i.e. outboard of the root end251of the integrated web-down conductor250. This has the advantage that all the shear load between the two blade shell halves is transferred by the integrated web-down conductor250. The blade220may be configured such that there is no other down conductor component disposed outboard of where the integrated web-down conductor terminates, i.e. outboard of the root end251of the integrated web-down conductor250. For example, with reference toFIG.3, the secondary web240does not extend past where the integrated web down conductor250terminates at root end251. InFIG.3, there is also no other down conductor component disposed outboard of where the integrated web down conductor250terminates at root end251.

The web257of the integrated web-down conductor250may be fixedly attached to the shell of the blade220by means of one or more attachment components, such as an adhesive, epoxy, or glue. There may be provided a first attachment component271on a leeward side of the web257configured to attach a side of the web257to the leeward side285of the blade220. There may be provided a second attachment component272configured to fixedly attach a side of the web257to a windward side286of the blade220. As noted above, the blade shell may comprise a first shell half285and a second blade shell half286. In this instance a first attachment component271may be configured to attach the web257to the first blade shell half285, and/or the second attachment component272may be configured to attach the web257to the second blade shell half286. As indicated inFIGS.4and5, the attachment component (i.e. adhesive) used may have a thickness greater than the thickness of the web257. The first and/or second attachment components271,272may be provided in sections along the length, i.e. in a span-wise direction, of the integrated web-down conductor250.

The lightning protection system may comprise at least one lightning receptor block260. The, or each lightning receptor block260may be electrically conductive. The, or each lightning receptor block260may comprise or consist of a metal or alloy. The, or each lightning receptor block260may be disposed substantially centrally within the blade shell, between windward and leeward sides of the blade, and is electrically connected to the down conductor255. There may be provided a plurality of receptor blocks260, for example as shown inFIGS.3and4. There may be provided one, two, three, four, five or more receptor blocks260within the integrated web-down conductor250. The, or each receptor block260may be substantially cuboidal or rectangular cuboidal shaped. The, or each receptor block260may have a width larger than the width of the down conductor255. This has the advantage that the receptor block260is easily connected to the one or more receptors261,262, i.e. when drilling through the blade shell to install receptors261,262, a drill can easily be positioned from outside the blade to drill into the receptor block260. As such, an effective connection between the one or more receptors261,262and the receptor block260can be established with reduced manufacturing accuracy, and in turn reduced manufacturing time and cost. The, or each receptor block260may have a depth larger than a corresponding depth of the down conductor255. The, or each receptor block260may be disposed within the integrated web-down conductor250so as to be enclosed or encapsulated by electrical insulation256and optionally the filler component258of the integrated web-down conductor250. The, or each receptor block260may also be disposed within the web257of the integrated web-down conductor250so as to be enclosed or encapsulated by the web257. The, or each receptor block260may be disposed centrally within the electrical insulation256and/or web257.

As shown inFIG.6, there may be provided a plurality of receptor blocks260spaced along the length of the down conductor255. A discussed previously the receptor blocks260may have a greater width than the down conductor255. Both the receptor blocks260and the down conductor260may be surrounded by the electrical insulation256which creates a generally stepwise profile of the electrical insulation256. It may be undesirable to increase the thickness of the electrical insulation256around the down conductor255between a pair of the receptor blocks260. However, it may also be undesirable to provide the web257having a stepwise profile to follow the stepwise profile of the electrical insulation. Accordingly, the filler component258may be provided surrounding the electrical insulation256between the pair of the receptor blocks260. The filler component258may have a thickness such that the web257may have a constant cross section tubular shape.

The or each receptor block260may be disposed centrally within the filler component258. The filler component258may be a foam core. The filler component258may substantially fill space between the electrical insulation256and the web257. As can be seen fromFIG.6, the filler component258can prevent stepwise changes in the cross-section of the integrated web-down conductor250, which has the advantage of improving the ease with which the integrated web-down conductor can be adhered to the blade shell. It also allows the down conductor255, receptors260and electrical insulation256to be easily surrounded by the web257, which may be a wrapped material.

There may be provided one or more receptors, which may be receptor bolts261,262. The, or each receptor bolt261,262may be configured and/or arranged and/or adapted to provide a lightning attachment point on the blade. The, or each receptor bolt261,262may be electrically connected or coupled to the down conductor255. This has the advantage that despite the down conductor255being surrounded by the web257, the benefits of electrically connecting the lightning receptors261,262to the down conductor255are still realised.

The, or each receptor bolt261,262is configured to extend between a side of the blade shell and a receptor block260. The, or each receptor bolt261is configured to be electrically conductive. The, or each receptor bolt261may comprise or consist of a metal or alloy and/or may comprise the same or a similar material to the, or each receptor block260. The, or each receptor bolt261,262may be electrically connected or coupled to the down conductor250by at least one receptor block260. For each receptor block260there may be provided a first receptor bolt261and a second receptor bolt262. The first receptor bolt261may extend from a windward surface of the blade shell to the receptor block260. The second receptor bolt262may extend from a leeward surface of the blade shell to the receptor block260. Where two receptor bolts261,262are provided for the, or each receptor block260, the receptor bolts261and262may be substantially aligned with one another in a thickness direction of the blade. In such a case, each first receptor bolt261may be aligned with a corresponding second receptor bolt262such that each first receptor bolt261and second receptor bolt262can occupy substantially the same position along a span-wise direction of the blade. Each first receptor bolt261and second receptor bolt262may have a length, and each first receptor bolt261and second receptor bolt262may be aligned so as to define a substantially straight line between their lengths. This has the advantage of permitting smaller receptor blocks260in a chord-wise and span-wise dimension than previously. The receptor blocks260can be made to substantially the same volume as prior receptor blocks but with a smaller chord-wise and span-wise dimension and a larger thickness dimension, which is accommodated by the integrated web-down conductor250being disposed at a maximum thickness location of the blade.

The integrated web-down conductor250may be formed by a method comprising:providing a down conductor255,forming electrical insulation around the down conductor256,forming a web257around the electrical insulation256so as to enclose or encapsulate the down conductor255and electrical insulation256.

Forming a web257around the electrical insulation256may comprise wrapping material around the electrical insulation256and/or a foam core so as to form a material laminate web. The resulting web257may comprise a structure indicative of having been manufactured by such a wrapping step, i.e. comprise layers of wrapped material.

The wind turbine blade220may be manufactured by a method, comprising:providing an integrated web-down conductor250and a blade shell, the integrated web-down conductor250having a down conductor255, electrical insulation256surrounding the down conductor255and a web257surrounding the electrical insulation256so as to enclose or encapsulate the down conductor255and electrical insulation256,arranging the integrated web-down conductor250relative to the blade shell, andfixing the integrated web-down conductor250to the blade shell.

Where the blade shell comprises first and second blade shell halves285,286, the method may comprise fixing the integrated web-down conductor250to one of the first and second blade shell halves285,286, and then fixing the second blade shell half286to the first blade shell half285and to the integrated web-down conductor250. This has the advantage of ease of manufacture, while providing a structurally reliable blade.

The method of manufacturing a blade220may further comprise electrically connecting one or more lightning receptors262,262at or near the outer surface of the blade shell to the down conductor250, which may be via a receptor block260. The method of manufacturing a blade220may further comprise inserting one or more receptor bolts261,262to provide an electrical connection from the or each receptor block260to the blade shell, through the or each receptor bolt261,262.

As the skilled person will appreciate, the integrated web-down conductor and its associated aspects disclosed herein have various advantages. Some of these advantages are noted above as a) to e) in the summary of the invention.

Firstly, as regards advantage a), the performance of the blade resulting from the use of an integrated web-down conductor is significantly improved. Instead of providing a separate down-conductor and web/spar component, each disposed at different locations and having different attachment means, for example as noted in relation toFIG.2, a single integrated web-down conductor component is provided. This provides a significant mass reduction overall, as there is no need for two separate components to be attached to the blade shell.

Secondly, as regards advantage b), a reduction in mass at the blade tip has a significant effect on load distribution within the blade during use. As the skilled person will appreciate, mass at the tip end of the blade contributes significantly to the mass moment of the blade. This mass reduction may result from a reduction in adhesive required compared to a separate web and down conductor of a known blade, in which adhesive is required to attach the down conductor to the blade shell and to attach the web to the blade shell. In contrast, with an integrated web-down conductor, adhesive may only be needed to attach the integrated web-down conductor to the blade shell. This mass reduction may also result from less overall components, and less associated mass of the integrated web-down conductor compared to a separate web and down conductor.

Thirdly, as regards advantage c), the integrated web-down conductor provides improved lightning protection properties. This results from improved accuracy during manufacture as the integrated web-down conductor can be more easily and more accurately attached to the blade shell, compared to a single down conductor such as the wire or cable. This results from the down conductor being integrated into the web, its resulting structure being stiffer than a down conductor provided as a separate component to the web, such as a flexible down-conductor wire.

Fourthly, as regards advantage d), manufacture simplicity and associated costs are significantly improved. There is a reduction in complexity and associated costs from reducing the overall number of components during manufacture that need to be assembled into the blade shell. In addition, the inventor has identified that the step of attaching and assembling a rigid integrated web-down conductor into the blade shell is easier than aligning and attaching a flexible down conductor independently of a web component. As such, less tooling may be required to align the integrated web-down conductor during manufacture, saving time, tooling and associated cost. As explained above, the manufacturing simplicity may also be a direct result of fewer space constraints on fitting components within the tip end of the blade (as there are fewer individual components), or a direct result of ease of locating drill holes, as the integrated web-down conductor may be in a thin laminate region of the blade shell with no core.

Fifthly, as regards advantage e), it is possible to use aligned receptor bolts261,262with the integrated web-down conductor. This can be seen, for example, inFIG.4, in which receptor bolts261,262are aligned in a thickness direction of the blade220, as described above. Such an alignment may not be possible where the down conductor and a web are provided as separate components, as any receptor block provided with a separate down conductor is likely to have a practical limit on its depth and thickness compared to those used with an integrated web-down conductor250.

Although a blade construction involving a blade shell or two blade shell halves has been shown in some of the figures and described, the skilled person would appreciate that the examples implemented may be implemented in other blade structures.

Although a web257having a tubular construction has been shown in some of the figures and described, the skilled person would appreciate that the web257may have a different configuration. For example, the web may be provided as discrete, sections assembled to form a tubular shape. The web257may be provided as a substantially continuous loop in two dimensions, or may contain one or more breaks or apertures.