WO2011080177A1 - Lightning protection of a wind turbine blade - Google Patents

Lightning protection of a wind turbine blade Download PDF

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Publication number
WO2011080177A1
WO2011080177A1 PCT/EP2010/070504 EP2010070504W WO2011080177A1 WO 2011080177 A1 WO2011080177 A1 WO 2011080177A1 EP 2010070504 W EP2010070504 W EP 2010070504W WO 2011080177 A1 WO2011080177 A1 WO 2011080177A1
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WO
WIPO (PCT)
Prior art keywords
blade
wind turbine
layer
lightning
electrically conductive
Prior art date
Application number
PCT/EP2010/070504
Other languages
French (fr)
Inventor
Marlon Rens
Original Assignee
Vestas Wind Systems A/S
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Vestas Wind Systems A/S filed Critical Vestas Wind Systems A/S
Publication of WO2011080177A1 publication Critical patent/WO2011080177A1/en

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Classifications

    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02G—INSTALLATION OF ELECTRIC CABLES OR LINES, OR OF COMBINED OPTICAL AND ELECTRIC CABLES OR LINES
    • H02G13/00—Installations of lightning conductors; Fastening thereof to supporting structure
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F03—MACHINES OR ENGINES FOR LIQUIDS; WIND, SPRING, OR WEIGHT MOTORS; PRODUCING MECHANICAL POWER OR A REACTIVE PROPULSIVE THRUST, NOT OTHERWISE PROVIDED FOR
    • F03D—WIND MOTORS
    • F03D1/00—Wind motors with rotation axis substantially parallel to the air flow entering the rotor 
    • F03D1/06—Rotors
    • F03D1/0608—Rotors characterised by their aerodynamic shape
    • F03D1/0633—Rotors characterised by their aerodynamic shape of the blades
    • F03D1/0641—Rotors characterised by their aerodynamic shape of the blades of the section profile of the blades, i.e. aerofoil profile
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F03—MACHINES OR ENGINES FOR LIQUIDS; WIND, SPRING, OR WEIGHT MOTORS; PRODUCING MECHANICAL POWER OR A REACTIVE PROPULSIVE THRUST, NOT OTHERWISE PROVIDED FOR
    • F03D—WIND MOTORS
    • F03D1/00—Wind motors with rotation axis substantially parallel to the air flow entering the rotor 
    • F03D1/06—Rotors
    • F03D1/065—Rotors characterised by their construction elements
    • F03D1/0675—Rotors characterised by their construction elements of the blades
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F03—MACHINES OR ENGINES FOR LIQUIDS; WIND, SPRING, OR WEIGHT MOTORS; PRODUCING MECHANICAL POWER OR A REACTIVE PROPULSIVE THRUST, NOT OTHERWISE PROVIDED FOR
    • F03D—WIND MOTORS
    • F03D80/00—Details, components or accessories not provided for in groups F03D1/00 - F03D17/00
    • F03D80/30—Lightning protection
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F05—INDEXING SCHEMES RELATING TO ENGINES OR PUMPS IN VARIOUS SUBCLASSES OF CLASSES F01-F04
    • F05B—INDEXING SCHEME RELATING TO WIND, SPRING, WEIGHT, INERTIA OR LIKE MOTORS, TO MACHINES OR ENGINES FOR LIQUIDS COVERED BY SUBCLASSES F03B, F03D AND F03G
    • F05B2230/00—Manufacture
    • F05B2230/30—Manufacture with deposition of material
    • F05B2230/31—Layer deposition
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F05—INDEXING SCHEMES RELATING TO ENGINES OR PUMPS IN VARIOUS SUBCLASSES OF CLASSES F01-F04
    • F05B—INDEXING SCHEME RELATING TO WIND, SPRING, WEIGHT, INERTIA OR LIKE MOTORS, TO MACHINES OR ENGINES FOR LIQUIDS COVERED BY SUBCLASSES F03B, F03D AND F03G
    • F05B2230/00—Manufacture
    • F05B2230/90—Coating; Surface treatment
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
    • Y02B10/00—Integration of renewable energy sources in buildings
    • Y02B10/30—Wind power
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/70—Wind energy
    • Y02E10/72—Wind turbines with rotation axis in wind direction
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
    • Y02P70/50—Manufacturing or production processes characterised by the final manufactured product

Definitions

  • the present invention relates to a wind turbine blade comprising a lightning protection system for conducting electrical currents induced by lightning from at least one reception area in a tip part of the blade to a root part of the blade.
  • the invention furthermore relates to a method for lightning protecting a wind turbine blade, and to a method for repairing a lightning protecting system of a wind turbine blade.
  • Lightning strikes in wind turbines is an increasing problem for one reason because of the increasing sizes of the wind turbines and of the length of the wind turbine blades. Lightning strikes may lead to unacceptable structural damage both in the blades where the lightning most often hits, and in the electrical components in the nacelle, if the lightning is not guided safely to the ground .
  • Lightning reception means comprising solid blade tips using pre-casted implants with one or more lightning receptors are known. It may however be difficult or even impossible to avoid air voids in such tip implants which may act as attractors to lightning and may cause the lightning receptor or the surrounding blade tip to be severely damaged under lightning.
  • lightning receptors comprising pre-manufactured Copper caps or solid blade tips of electrically conducting materials are known, which are to be retrofit on existing blades. Although such caps may provide better lightning capture than the relatively small receptors described above, the caps or solid tips may be expensive to prepare, and difficult to effectively install on and secure to the main blade structure. Furthermore, it has proven difficult to obtain the exact desirable final shape of the blade tip and perhaps especially along the trailing edge where it may be hard or even impossible to obtain any other shapes than relatively thick and blunted trailing edges.
  • a wind turbine blade comprising a lightning protection system for conducting electrical currents induced by lightning from at least one reception area in a tip part of the blade to a root part of the blade, the wind turbine blade comprising at least one blade shell at least partly forming an aerodynamical surface of the blade and at least partly enclosing a blade cavity.
  • the lightning protection system comprises a down conducting means placed in said cavity, extending between the root part and the tip part.
  • the reception area comprises at least one layer of an electrically conductive material coated onto the blade shell to act as an attractor for a lightning, and wherein at least one connector of an electrically conductive material is placed to electrically connect the electrically conductive material layer with the down conducting means, thereby forming a conductive path for electrical currents induced by lightning from the reception area to the root part of the wind turbine.
  • an effective lightning protective system where a lightning may be effectively attracted, received and guided safely from the outermost part of the wind turbine blade via the down conducting means placed in the interior of the blade to the root part of the blade, thereby avoiding that the lightning currents run in and potentially damage other parts of the wind turbine blade such as e.g. structural materials like carbon fibers in the blade shells or beams, electrical materials like copper or other conductive material used for wires , sensors or other electrical systems, or mechanical metal parts like hinges, brackets etc.
  • a lightning is most likely to strike one of the blades of a wind turbine in the outer part comprising the tip part of the blade, wherefore the lightning attractor is most effectively placed here.
  • the tip part may comprise any part of the blade further out towards the tip than the root part of the blade.
  • the tip part may for example comprise the outermost 30 m of the blade, or more specifically the outermost approximately 10 m or 3 m of a 55 m blade.
  • the reception area may cover the entire outermost blade tip portion or may cover a part hereof such as only a part of the pressure and suction side of the blade, or the trailing or leading edges as well.
  • the one or more layers of electrically conductive material coated onto the blade shell By the one or more layers of electrically conductive material coated onto the blade shell is obtained an effective lightning attractor and thereby a well defined attachment point of the lightning whereby may be controlled to a high degree of certainty where a possible lightning will strike. Further, the one or more layers of electrically conductive material coated onto the blade shell may act to protect the underlying parts of the wind turbine blade. This may for instance be advantageous in cases where the structural reinforcing beam or beams of the blade comprises a material of a certain electrically conductivity such as Carbon fibres.
  • an attractor which due to the coated layer of electrically conductive material is capable of following the overall shape of the blade tip part onto which the layer is coated.
  • the blade may be provided with enhanced lightning protection properties without altering the blade tip shape and thereby important blade properties such as the aerodynamical and noise characteristics of the blade tip.
  • the trailing edge shape may influence such properties, for which reasons a sharp and thin trailing may often be preferred. According to the present invention such trailing edge shape may be maintained by the application of the coated layer or layers of the attractor.
  • the coated material layer acting as an attractor is advantageous by its capability to be applied to advanced or complex surfaces such as e.g. double curved surfaces.
  • the coating may furthermore be applied such that a smooth and even surface of the blade tip part is achieved which may be advantageous out of aerodynamical and noise considerations for the blade, and in reducing the speed with which dirt particles settle on the blade surface.
  • the coated material layer may by the coated material layer be obtained a lighting attractor with good structural connection to the underlying blade shell thereby increasing the life time of the lightning protection system and reducing the risk of deterioration or damage caused by normal wear and/or lightning strokes.
  • the time where an operational wind turbine needs to be stopped for maintenance and repair is decreased, and expensive reparations of the lightning protection system, which otherwise for conventional lightning systems of e.g. blade tip implants and carbon structural spars could mean extensive blade repair or even blade exchange, may be reduced or even avoided.
  • the disclosed lightning protection system is advantageous in not requiring any semi-products customized to the specific blade type.
  • the same manufacturing method may hence be applied on any wind turbine blade regardless of its type, whereby the manufacturing costs may be reduced considerably.
  • the lightning protection system is advantageous in that the coating of the material layers acting as the attractor and the connection to the interior down conducting cable by means of the connector may be performed on the finished blade at least partly from the outside of the blade.
  • the manufacturing steps of integrating parts of the lightning protection system in the mould to be embedded or integrally moulded with the blade shells, which may be difficult and associated with higher manufacturing tolerances, may be avoided.
  • the lightning attractor according to the present invention comprising one or coated material layers, or some another type of attractor, such as metal blade tip cap, may be repaired or renewed on site in a simple yet effective and fast way by simply coating one or more new layers of an electrically conductive material on the whole or parts of the reception area.
  • the new material layer(s) may be coated to partly or wholly cover the old attractor or in direct electrical connection to the connector and thereby the down conducting means. In this way an old ineffective lightning attractor may be renewed or updated without the need to replace the whole blade or the blade tip.
  • the reception area may comprise a single layer of electrically conductive material coated onto the blade shell or may comprise several relatively thinner layers coated wholly or partly on top of each other, which may result in a better connection to the blade shell than the use of a single coated layer of the same total thickness.
  • the lightning reception system according to the invention may further be used in combination with one or more other lightning protection systems which may of the same or of different types.
  • the lightning protection system of a blade may comprise a first reception area comprising coated layer(s) of electrically conductive material near or on the tip end portion of the blade and a second reception area of coated layer(s) of electrically conductive material placed closer the root part of the wind turbine blade.
  • the coated layers may be electrically connected to the same or to different down conducting means.
  • the layer of an electrically conductive material is at least partly sprayed onto the blade shell by means of thermal spraying or metal spraying, where one or several molten metals are sprayed onto the blade shell to form a coating.
  • thermal spraying or metal spraying where one or several molten metals are sprayed onto the blade shell to form a coating.
  • This may be achieved by melting either pure or alloyed metals in a flam, where the molten metal is then subjected to a blast of compressed air which has the joint effect of creating tiny droplets of metal and projecting them towards the surface to be coated.
  • Thermal spraying techniques such as e.g. cold spraying, flame spraying, high-velocity oxy- fuel coating spraying (HVOF), plasma spraying, warm spraying, and wire arc spraying may be applied.
  • HVOF high-velocity oxy- fuel coating spraying
  • the one or more coating materials may be fed in powder or wire form, heated to a molten or semimolten state and accelerated towards substrates in the form of micrometer-size particles.
  • the resulting coatings are made by the accumulation of numerous sprayed particles.
  • Thermal spraying may provide coatings of approximate thicknesses ranging from a few microns to several mm, depending on the process and feedstock, and may be provided over a large area at high deposition rate as compared to other coating processes.
  • To create thin coatings one requires a very fine particle size, usually at sizes between 10 and 20 microns. Liquid spray processing is able to decrease the thickness even more.
  • a molten particle or a particle able to deform plastically is transported at high speeds within a heat source towards a surface upon which deposition occurs.
  • the droplet or particle undergoes spreading and may create a chemical bond with the underlying surface.
  • the substrate is roughened to create a mechanical bond.
  • Each droplet or particle impacts a roughened surface and mechanically interlocks with the asperities on the underlying surface.
  • the bond strength is dictated by the speed of the particle, temperature within the thermal spray plume, substrate roughness and reaction with the underlying substrate. Bond strength up to 60-80 MPa is not uncommon for thermally sprayed materials.
  • the bonding ability is material and process dependant.
  • the end result is a solid metal coating on the surface to be treated where the thickness of the coating may be dictated by the number of layers applied.
  • the coating technology of thermal spraying may further be advantageous by the ability to deposit high melting temperature materials, to obtain a fast coating deposition, and by the fast heating and cooling produced inequilibrium phases, which may result in a decomposition of certain materials being avoided. Normally, few or less volatile organics may be employed during the thermal spraying process as may otherwise be the case with many paints.
  • thermal sprayed layer may furthermore be obtained that the coating layer follows the often double curved or complex blade shell surfaces thereby not changing the aerodynamical properties of the blade.
  • metal sprayed coating may further be obtained, that a sharp and/or thin trailing edge of the wind turbine blade may be preserved on the same time as an effective lightning protection of the blade and with the same superior adhesion and connection to the blade shell.
  • a thermal sprayed coating may furthermore be advantageous in being possible to apply to the finished or nearly fully assembled wind turbine blade in a simple and fast manner in the same or completely individual way to all wind turbine blades regardless of the specific blade type and without the need for any blade type specific semi-products.
  • the layer of an electrically conductive material is at least partly painted onto the blade shell whereby the electrically conductive layer acting as the attractor for the lightning may be applied to the blade in a simple and relatively fast manner without the need for advanced production equipment.
  • the layer of an electrically conductive material comprises a metal or a metal alloy belonging to the group of Cu, Si, Au, Ag, Al, and bronze, whereby excellent electrical conductive properties may be obtained for the layer.
  • the blade tip part terminates in a tip end portion and the reception area covers said tip end portion, hereby yielding an effective protection of the part of the wind turbine blade which most often is hit by lightning.
  • the thickness of the at least one material layer may be substantially constant or may alternatively for instance decrease towards the edges of said layer thereby making a gradual transition from the metal coated reception area to the uncovered blade shell yielding optimal adhesion to the blade shell and at the same time ensuring a smooth and even blade surface. If the material layer is of a substantially constant thickness, the blade shell may be provided with a stepped surface such that the resulting blade surface after having applied the coating layer is even and smooth.
  • the at least one material layer is placed to at least partly fill out a recess in the blade shell whereby the resulting lightning protected blade surface remains smooth and even without any edges which may disturb the aerodynamical flow over the blade surface.
  • the material layer may cover at least a part of the trailing and/or leading edge of the blade, and the thickness of the layer may decrease in a direction towards the trailing and/or leading edge, respectively.
  • a relatively sharp and thin trailing edge may be obtained while on the same time ensuring an optimal lightning protection also close to the trailing edge and without jeopardizing the adhesion or connection of the material layer acting as the attractor for the lightning.
  • the exact geometrical airfoil parameters are upheld near the trailing or leading edge, which parameters influence significantly the aerodynamical characteristics of the blade.
  • an extra thick layer of electrical conductive material may be coated onto the central part of the blade away from the trailing and/or leading edges in the area where the lightning will most likely strike.
  • the down conducting means may comprise one or more cables or wires of an electrically conductive material such as e.g. a 50 mm2 cable.
  • the down conducting means may be of an electrically conductive material such as a metal or metal alloy comprising Cu, AU, Si, Au, Ag, Al, or bronze.
  • the down conducting means may be connected to further down conducting means in the blade root, inside the blade in the blade root part, or in the nacelle.
  • the down conducting means may run in the interior of the blade cavity alongside or attached to the one or inner structural beams of the blade thereby placed maximally away from the blade shells.
  • the down conducting means may in another embodiment be guided or attached to one or more interior surfaces of the blade shells.
  • the at least one connector of an electrically conductive material placed to electrically connect the electrically conductive material layer with the down conducting means may e.g. be of a large screw-like shape. This may be placed to extend through or traverse the blade shell and connect to the down conducting means optionally via a receptor house, thereby forming the conductive path for the electrical currents from the reception area on the exterior of the blade shell, and to the down conducting means placed internally in the blade cavity.
  • the connector may be of the same or another electrically conductive material as the down conducting means such as a metal or metal alloy comprising Cu, AU, Si, Au, Ag, Al, or bronze.
  • the connector may comprise an head of a larger cross sectional area than its screw- part going through the blade shell for increasing its contact surface and thereby the electrical connection to the reception area.
  • the connector may in extend through the thickness of the one or more coated material layers of the attractor or may alternatively or additionally be covered hereby.
  • the wind turbine blade according to any of the above may further comprise a receptor house connecting the down conducting means to the connector, hereby obtaining an enhanced electrical connection between the connector and the down conducting means.
  • the receptor house may also act to facilitate the connection of the connector to the down conducting cable in that an end of the cable may be received and secured in the receptor house at least during the blade manufacture.
  • the invention relates to a method for lightning protecting a wind turbine blade according to any of the above mentioned, the method comprising the steps of
  • the coating comprises thermal spraying the at least one layer of an electrically conductive material at least partly by a method belonging to the group of cold spraying, flame spraying, high-velocity oxy-fuel coating spraying (HVOF), plasma spraying, warm spraying, and wire arc spraying, which methods may result in a solid coated layer of high wear resistance and optimal adhesion to the underlying blade shell.
  • a method belonging to the group of cold spraying, flame spraying, high-velocity oxy-fuel coating spraying (HVOF), plasma spraying, warm spraying, and wire arc spraying which methods may result in a solid coated layer of high wear resistance and optimal adhesion to the underlying blade shell.
  • the method for lightning protecting may further comprise the step of assembling the blade shells prior to the step of coating the layer, whereby the coating may be applied onto the blade shells from the exterior yielding the best possible working conditions and allowing for the possibility to coat a material layer smoothly over the blade shell joining edges.
  • the at least one material layer may be coated onto the blade shell prior to the placing of the connector.
  • the connector may then be inserted to traverse the blade shell as well as the coated layer whereby the electrical connection between the connector and the coated layer is increased. More connectors may be applied thereby enhancing the electrical connection between the conductive material layer and the down conducting means.
  • the above described method may comprise a step of painting at least a part of the wind turbine blade for instance to obtain a desired specific coloring of the blade, to further improve the wear resistance, and to improve the characteristics of friction, corrosion, and erosion of the blade surface.
  • the invention relates to a method for repairing a lightning protecting system of a wind turbine blade according to any of the aforementioned, comprising the step of coating at least one further layer of an electrically conductive material onto the blade shell such that an electrical connection is established from the further layer to the down conducting means.
  • the above method for repair may further comprise the step of grinding the blade shell prior to coating the at least one further material layer and the in order to ensure an optimal electrical connection between the new and previously applied coating.
  • the method for repairing may comprise the step of placing one or more further connectors of electrically conductive material in electrically connection with the further material layer and the down conducting means for enhancing the electrical connection there between.
  • FIG. 1 shows a sketch of a wind turbine blade comprising a lightning protection system
  • Figs. 2 and 3 illustrate a wind turbine blade comprising a lightning protection system according to an embodiment of the invention as seen in a cross sectional view and from above, respectively,
  • Fig. 4 is a cross sectional view of a part of the blade tip part as seen from the trailing or leading edge illustrating a electrically conductive coated layer of stepwise increasing thickness
  • Fig. 5 is a cross sectional view of a part of the blade tip part comprising an electrically conductive coating of gradually increasing thickness
  • Fig. 6 shows an embodiment of a lightning protection system with a material coating covering part of the blade tip end portion.
  • Figure 1 shows a wind turbine blade 100 comprising a lightning protection system for conducting an electrical lightning current from a reception area 101, 106 in a tip part 102 of the blade to the ground via down conducting means 103 such as a cable of an electrically conductive material.
  • the down conducting means 103 are positioned in the interior of the blade in the blade cavity formed at least in part by the blade shells 104 forming the aerodynamical surface of the blade.
  • the down conductive means 103 are sketched to leave the blade in the root part 105 of the blade.
  • the down conducting means may be connected to further grounding means in or near the root part of the blade.
  • the wind turbine blade comprises two reception areas 101, 106 in the blade tip part 102 forming the outermost part of the turbine blade.
  • the outermost reception area 101 is placed where the risk of lightning strikes is the highest, and a second reception area may be placed additionally or alternatively with a view to protect a specific part of the blade from lightning currents, such as a structural beam of the blade comprising e.g. Carbon fibers.
  • a lightning protection system is illustrated in more details in figures 2 and 3 showing the blade tip part 102 as seen in a cross sectional view from the trailing edge 107 of the blade, and as seen from above from the pressure or suction side of the blade, respectively.
  • a reception area 101 may as shown in figures 2 and 3 cover the outermost tip part of the blade and comprises a layer 200 of an electrically conductive material coated onto the blade shell 104 thereby acting as an attractor for a lightning.
  • the blade may as illustrated in the figures 2 and 3 comprise a further reception area 106 and layer 206 of an electrically conductive material coated onto the blade shell 104 a distance from the first reception area 101.
  • the electrical current received by one or both of the coated layers is then guided via the connectors 201 traversing the blade shell and into the down conducting means 103.
  • Some or all of the connectors may as illustrated in figure 2 penetrate the entire blade thickness and traverse from the one side of the blade shell to the other, or may be connected from more connector parts.
  • the connectors may as illustrated in figure 2 comprise a head of a relatively large surface to ensure an optimal electrical connection to the surrounding reception area when placed in the blade shell.
  • the electrical connection of the connector to the down conducting means may be established by means of the connection to a receptor house 202 positioned in the blade cavity 205. If the lightning protection system comprises more than one reception areas 101, 106, these may be electrically connected to the same or different down conducting means 103.
  • the reception area may comprise a single or multiple layers 200, 206 of electrically conductive material such a metal or a metal alloy belonging to the group of Cu, Si, Au, Ag, Al, and bronze and coated onto the blade shell.
  • the one or more coated layers may further be covered by layers of paint.
  • the coating may be achieved by painting or thermal spraying of the metal.
  • thermal spraying is obtained an optimal adhesion of the electrically conductive material to the underlying blade shell which for instance may comprise a laminate of fiber-reinforced composite materials such as e.g. glassfiber/epoxy.
  • the coating may by thermal spraying be applied to the blade tip part in different thicknesses in different areas as considered optimal both with a view to ensure optimal attraction of the lightning and with a view to obtain the desired final aerodynamical shape of the blade tip. This is illustrated further in the figures 4-6.
  • the coated layer 200, 206 may be applied as an additional layer to the blade shell as sketched in figure 2, where there is a relatively sharp or clear transition 210 from the uncovered to the metal covered blade shell.
  • the coating 200, 206 may alternatively or additionally be applied to the blade shell 104 such that a gradual transition is obtained whereby a smooth outer blade surface may be obtained.
  • This may be obtained as illustrated in figure 4 by a stepwise 401 increasing thickness 400 of the coated layer 200.
  • the blade tip part is here seen in a cross sectional view as seen from the trailing or the leading edge, and the thickness of the blade shell 104 is decreased in a correspondingly stepwise manner whereby the resulting outer blade surface 402 may be smooth without any exposed edges of the coated layer 200.
  • more electrical conductive material may in this way be applied to the part of the blade shell most prone to lightning, or for instance closer to or surrounding the connector to increase the electrical connection hereto.
  • the blade shell may further be manufactured with recesses which may then be filled out by the coated material.
  • the blade tip part is seen in a cross sectional view as seen from the root of the blade and showing the blade shells 104 forming the aerodynamical surface of the blade and enclosing a blade cavity.
  • the blade shells are structurally reinforced by an inner beam 501.
  • the down conducting means 103 are placed in the blade cavity 205 and via a receptor house 202 electrically connected to the connectors 201 traversing the blade shell.
  • the layer of electrically conductive material is mainly coated onto the suction and pressure sides of the blade airfoil whereas both the trailing 503 and leading edges 504 of the blade are left uncovered.
  • the shape of the trailing edge has a high influence on the aerodynamically blade properties and on other parameters such as on the noise emitted from the blade during operation.
  • these regions may be coated by just a thin layer of material without altering the trailing edge properties significantly.
  • the coated part of the reception area 101 may be of any arbitrary shape not necessarily covering the entire blade tip part. Further is illustrated how more than one connector may be applied to enhance the electrical connection to the down conducting means 103 in some parts of the reception area also thereby in these parts decreasing the length of the conductive path for the electrical current to the ground.
  • the wind turbine blade comprising the described lightning protection system may be manufactured by first producing the blade shells e.g. by laminate lay-up and assembling the entire blade while placing the down conducting means in the blade cavity.
  • the down conducting means may be attached to an inner surface of a blade shell or to the reinforcing beam and may be secured in the blade tip region by means of the receptor house likewise placed in the interior of the blade.
  • one or more layers of the electrically conductive material may be coated onto the exterior of the blade surface in the reception area in the blade tip part.
  • the coating may be performed e.g. by painting or by thermal spraying of the material.
  • the position and the thickness of the material layers may be easily and well controlled during the application.
  • the exterior coated material layer is then electrically connected to the inner down conducting means by the placing of the connectors extending through the thickness of the blade shell and connected to the inner receptor house.
  • the connectors may for instance by screwed through the blade shell or entered trough holes of embedded bushings or nuts or the like.
  • the connectors may be positioned prior to the coating of the material layer whereby the electrical connection is established from the outer surface of the connector head to the underside of the coated material layer.
  • the manufacture may further comprise painting and/or polishing the wind turbine blade.

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  • Engineering & Computer Science (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Sustainable Development (AREA)
  • Sustainable Energy (AREA)
  • Chemical & Material Sciences (AREA)
  • Combustion & Propulsion (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Fluid Mechanics (AREA)
  • Wind Motors (AREA)

Abstract

Wind turbine blade (100) comprising a lightning protection system. The blade comprises a shell (105) at least partly enclosing a blade cavity in which a down conducting means (103) is placed extending between the root part and the tip part (101). The tip part comprises at least one layer of an electrically conductive material coated onto the blade shell and one or more connectors (201) placed to electrically connect the electrically conductive layer with the down conducting means, thereby forming a conductive path for electrical currents induced by lightning. The electrically conductive material may be coated onto the blade tip by thermal metal spraying or by painting.

Description

LIGHTNING PROTECTION OF A WIND TURBINE BLADE Field of the invention
The present invention relates to a wind turbine blade comprising a lightning protection system for conducting electrical currents induced by lightning from at least one reception area in a tip part of the blade to a root part of the blade. The invention furthermore relates to a method for lightning protecting a wind turbine blade, and to a method for repairing a lightning protecting system of a wind turbine blade.
Background
The risk of lightning strikes in wind turbines is an increasing problem for one reason because of the increasing sizes of the wind turbines and of the length of the wind turbine blades. Lightning strikes may lead to unacceptable structural damage both in the blades where the lightning most often hits, and in the electrical components in the nacelle, if the lightning is not guided safely to the ground .
There is therefore a need in designing wind turbines and wind turbine components to be able to control with high certainty where a lightning will hit, and to safely receive and guide the current to the ground without damaging any components or structural parts on the way.
Lightning reception means comprising solid blade tips using pre-casted implants with one or more lightning receptors are known. It may however be difficult or even impossible to avoid air voids in such tip implants which may act as attractors to lightning and may cause the lightning receptor or the surrounding blade tip to be severely damaged under lightning.
Further, lightning receptors comprising pre-manufactured Copper caps or solid blade tips of electrically conducting materials are known, which are to be retrofit on existing blades. Although such caps may provide better lightning capture than the relatively small receptors described above, the caps or solid tips may be expensive to prepare, and difficult to effectively install on and secure to the main blade structure. Furthermore, it has proven difficult to obtain the exact desirable final shape of the blade tip and perhaps especially along the trailing edge where it may be hard or even impossible to obtain any other shapes than relatively thick and blunted trailing edges.
Common to all known systems including the above mentioned is that damage to the lightning receptors or blade structure will require repair or in a significant number of cases replacement of the damaged blade, which needless to say is highly expensive also due to the downtime on the turbine. Description of the invention
It is therefore an object of embodiments of the present invention to overcome or at least reduce some or all of the above described disadvantages of the known lightning protection systems for wind turbines, and to provide a lightning protection system specifically for a wind turbine with improved connection to the blade shell structure and a reduced risk of being damaged upon lightning strikes, such as to avoid or reduce the need for repair or exchange of parts in the protection system.
It is a yet further object of embodiments of the invention to provide a lightning protection system which may be applied to wind turbine blades with no or only minimal changes to the aerodynamical shapes and surfaces and thereby aerodynamical properties of the blade.
It is a further object of embodiments of the invention to provide a method for lightning protecting a wind turbine which is effective both with respect to manufacturing quality and costs and durability of the obtained system.
It is a yet further object of embodiments of the invention to provide a method for effectively repairing or improving or updating an already existing lightning protection system which method may be performed on site without having to take down the wind turbine blade.
In accordance with the invention this is obtained by a wind turbine blade comprising a lightning protection system for conducting electrical currents induced by lightning from at least one reception area in a tip part of the blade to a root part of the blade, the wind turbine blade comprising at least one blade shell at least partly forming an aerodynamical surface of the blade and at least partly enclosing a blade cavity. The lightning protection system comprises a down conducting means placed in said cavity, extending between the root part and the tip part. The reception area comprises at least one layer of an electrically conductive material coated onto the blade shell to act as an attractor for a lightning, and wherein at least one connector of an electrically conductive material is placed to electrically connect the electrically conductive material layer with the down conducting means, thereby forming a conductive path for electrical currents induced by lightning from the reception area to the root part of the wind turbine.
Hereby is obtained an effective lightning protective system where a lightning may be effectively attracted, received and guided safely from the outermost part of the wind turbine blade via the down conducting means placed in the interior of the blade to the root part of the blade, thereby avoiding that the lightning currents run in and potentially damage other parts of the wind turbine blade such as e.g. structural materials like carbon fibers in the blade shells or beams, electrical materials like copper or other conductive material used for wires , sensors or other electrical systems, or mechanical metal parts like hinges, brackets etc. By the described lightning protection system is obtained a robust system with an increased chance of effectively down-conducting and grounding any lightning currents as opposed to the principle in some lightning systems primarily for aircrafts where the electrical currents are rather optimally diverted out as fast as possible and to as large an area as possible to reduce the damages.
A lightning is most likely to strike one of the blades of a wind turbine in the outer part comprising the tip part of the blade, wherefore the lightning attractor is most effectively placed here. The tip part may comprise any part of the blade further out towards the tip than the root part of the blade. For a wind turbine blade of 50-60 m in length the tip part may for example comprise the outermost 30 m of the blade, or more specifically the outermost approximately 10 m or 3 m of a 55 m blade. The reception area may cover the entire outermost blade tip portion or may cover a part hereof such as only a part of the pressure and suction side of the blade, or the trailing or leading edges as well.
By the one or more layers of electrically conductive material coated onto the blade shell is obtained an effective lightning attractor and thereby a well defined attachment point of the lightning whereby may be controlled to a high degree of certainty where a possible lightning will strike. Further, the one or more layers of electrically conductive material coated onto the blade shell may act to protect the underlying parts of the wind turbine blade. This may for instance be advantageous in cases where the structural reinforcing beam or beams of the blade comprises a material of a certain electrically conductivity such as Carbon fibres.
Further may be obtained an attractor which due to the coated layer of electrically conductive material is capable of following the overall shape of the blade tip part onto which the layer is coated. In this way the blade may be provided with enhanced lightning protection properties without altering the blade tip shape and thereby important blade properties such as the aerodynamical and noise characteristics of the blade tip. Especially the trailing edge shape may influence such properties, for which reasons a sharp and thin trailing may often be preferred. According to the present invention such trailing edge shape may be maintained by the application of the coated layer or layers of the attractor.
Further, the coated material layer acting as an attractor is advantageous by its capability to be applied to advanced or complex surfaces such as e.g. double curved surfaces. The coating may furthermore be applied such that a smooth and even surface of the blade tip part is achieved which may be advantageous out of aerodynamical and noise considerations for the blade, and in reducing the speed with which dirt particles settle on the blade surface.
Further, may by the coated material layer be obtained a lighting attractor with good structural connection to the underlying blade shell thereby increasing the life time of the lightning protection system and reducing the risk of deterioration or damage caused by normal wear and/or lightning strokes. Hereby, the time where an operational wind turbine needs to be stopped for maintenance and repair is decreased, and expensive reparations of the lightning protection system, which otherwise for conventional lightning systems of e.g. blade tip implants and carbon structural spars could mean extensive blade repair or even blade exchange, may be reduced or even avoided.
From a manufacturing view point the disclosed lightning protection system is advantageous in not requiring any semi-products customized to the specific blade type. The same manufacturing method may hence be applied on any wind turbine blade regardless of its type, whereby the manufacturing costs may be reduced considerably.
Further, the lightning protection system is advantageous in that the coating of the material layers acting as the attractor and the connection to the interior down conducting cable by means of the connector may be performed on the finished blade at least partly from the outside of the blade. Hereby the manufacturing steps of integrating parts of the lightning protection system in the mould to be embedded or integrally moulded with the blade shells, which may be difficult and associated with higher manufacturing tolerances, may be avoided.
Furthermore, if needed the lightning attractor according to the present invention comprising one or coated material layers, or some another type of attractor, such as metal blade tip cap, may be repaired or renewed on site in a simple yet effective and fast way by simply coating one or more new layers of an electrically conductive material on the whole or parts of the reception area. The new material layer(s) may be coated to partly or wholly cover the old attractor or in direct electrical connection to the connector and thereby the down conducting means. In this way an old ineffective lightning attractor may be renewed or updated without the need to replace the whole blade or the blade tip. The reception area may comprise a single layer of electrically conductive material coated onto the blade shell or may comprise several relatively thinner layers coated wholly or partly on top of each other, which may result in a better connection to the blade shell than the use of a single coated layer of the same total thickness. The lightning reception system according to the invention may further be used in combination with one or more other lightning protection systems which may of the same or of different types. As an example the lightning protection system of a blade may comprise a first reception area comprising coated layer(s) of electrically conductive material near or on the tip end portion of the blade and a second reception area of coated layer(s) of electrically conductive material placed closer the root part of the wind turbine blade. The coated layers may be electrically connected to the same or to different down conducting means.
According to one embodiment of the invention, the layer of an electrically conductive material is at least partly sprayed onto the blade shell by means of thermal spraying or metal spraying, where one or several molten metals are sprayed onto the blade shell to form a coating. This may be achieved by melting either pure or alloyed metals in a flam, where the molten metal is then subjected to a blast of compressed air which has the joint effect of creating tiny droplets of metal and projecting them towards the surface to be coated.
Thermal spraying techniques such as e.g. cold spraying, flame spraying, high-velocity oxy- fuel coating spraying (HVOF), plasma spraying, warm spraying, and wire arc spraying may be applied.
The one or more coating materials may be fed in powder or wire form, heated to a molten or semimolten state and accelerated towards substrates in the form of micrometer-size particles. Hereby the resulting coatings are made by the accumulation of numerous sprayed particles. Thermal spraying may provide coatings of approximate thicknesses ranging from a few microns to several mm, depending on the process and feedstock, and may be provided over a large area at high deposition rate as compared to other coating processes. To create thin coatings one requires a very fine particle size, usually at sizes between 10 and 20 microns. Liquid spray processing is able to decrease the thickness even more. A molten particle or a particle able to deform plastically is transported at high speeds within a heat source towards a surface upon which deposition occurs. The droplet or particle undergoes spreading and may create a chemical bond with the underlying surface. With materials that are not able to produce a chemical bond, the substrate is roughened to create a mechanical bond. Each droplet or particle impacts a roughened surface and mechanically interlocks with the asperities on the underlying surface. The bond strength is dictated by the speed of the particle, temperature within the thermal spray plume, substrate roughness and reaction with the underlying substrate. Bond strength up to 60-80 MPa is not uncommon for thermally sprayed materials. The bonding ability is material and process dependant.
The end result is a solid metal coating on the surface to be treated where the thickness of the coating may be dictated by the number of layers applied. By such a coating is obtained an effective attractor for a lightning with extremely good adhesion and connection to the underlying blade shell thereby reducing the risk of the electrical current damaging the attractor. Further is obtained good wear resistance.
The coating technology of thermal spraying may further be advantageous by the ability to deposit high melting temperature materials, to obtain a fast coating deposition, and by the fast heating and cooling produced inequilibrium phases, which may result in a decomposition of certain materials being avoided. Normally, few or less volatile organics may be employed during the thermal spraying process as may otherwise be the case with many paints.
By the use of a thermal sprayed layer may furthermore be obtained that the coating layer follows the often double curved or complex blade shell surfaces thereby not changing the aerodynamical properties of the blade. With the metal sprayed coating may further be obtained, that a sharp and/or thin trailing edge of the wind turbine blade may be preserved on the same time as an effective lightning protection of the blade and with the same superior adhesion and connection to the blade shell.
A thermal sprayed coating may furthermore be advantageous in being possible to apply to the finished or nearly fully assembled wind turbine blade in a simple and fast manner in the same or completely individual way to all wind turbine blades regardless of the specific blade type and without the need for any blade type specific semi-products.
According to an embodiment of the invention, the layer of an electrically conductive material is at least partly painted onto the blade shell whereby the electrically conductive layer acting as the attractor for the lightning may be applied to the blade in a simple and relatively fast manner without the need for advanced production equipment.
In a further embodiment of the invention, the layer of an electrically conductive material comprises a metal or a metal alloy belonging to the group of Cu, Si, Au, Ag, Al, and bronze, whereby excellent electrical conductive properties may be obtained for the layer. According to yet a further embodiment the blade tip part terminates in a tip end portion and the reception area covers said tip end portion, hereby yielding an effective protection of the part of the wind turbine blade which most often is hit by lightning.
The thickness of the at least one material layer may be substantially constant or may alternatively for instance decrease towards the edges of said layer thereby making a gradual transition from the metal coated reception area to the uncovered blade shell yielding optimal adhesion to the blade shell and at the same time ensuring a smooth and even blade surface. If the material layer is of a substantially constant thickness, the blade shell may be provided with a stepped surface such that the resulting blade surface after having applied the coating layer is even and smooth.
In a further embodiment of the wind turbine blade the at least one material layer is placed to at least partly fill out a recess in the blade shell whereby the resulting lightning protected blade surface remains smooth and even without any edges which may disturb the aerodynamical flow over the blade surface.
According to a further embodiment the material layer may cover at least a part of the trailing and/or leading edge of the blade, and the thickness of the layer may decrease in a direction towards the trailing and/or leading edge, respectively. Hereby a relatively sharp and thin trailing edge may be obtained while on the same time ensuring an optimal lightning protection also close to the trailing edge and without jeopardizing the adhesion or connection of the material layer acting as the attractor for the lightning. Further, in this way the exact geometrical airfoil parameters are upheld near the trailing or leading edge, which parameters influence significantly the aerodynamical characteristics of the blade. Further, an extra thick layer of electrical conductive material may be coated onto the central part of the blade away from the trailing and/or leading edges in the area where the lightning will most likely strike.
The down conducting means may comprise one or more cables or wires of an electrically conductive material such as e.g. a 50 mm2 cable. The down conducting means may be of an electrically conductive material such as a metal or metal alloy comprising Cu, AU, Si, Au, Ag, Al, or bronze. The down conducting means may be connected to further down conducting means in the blade root, inside the blade in the blade root part, or in the nacelle. The down conducting means may run in the interior of the blade cavity alongside or attached to the one or inner structural beams of the blade thereby placed maximally away from the blade shells. The down conducting means may in another embodiment be guided or attached to one or more interior surfaces of the blade shells.
The at least one connector of an electrically conductive material placed to electrically connect the electrically conductive material layer with the down conducting means may e.g. be of a large screw-like shape. This may be placed to extend through or traverse the blade shell and connect to the down conducting means optionally via a receptor house, thereby forming the conductive path for the electrical currents from the reception area on the exterior of the blade shell, and to the down conducting means placed internally in the blade cavity. The connector may be of the same or another electrically conductive material as the down conducting means such as a metal or metal alloy comprising Cu, AU, Si, Au, Ag, Al, or bronze. The connector may comprise an head of a larger cross sectional area than its screw- part going through the blade shell for increasing its contact surface and thereby the electrical connection to the reception area. The connector may in extend through the thickness of the one or more coated material layers of the attractor or may alternatively or additionally be covered hereby. Further still, the wind turbine blade according to any of the above may further comprise a receptor house connecting the down conducting means to the connector, hereby obtaining an enhanced electrical connection between the connector and the down conducting means. The receptor house may also act to facilitate the connection of the connector to the down conducting cable in that an end of the cable may be received and secured in the receptor house at least during the blade manufacture.
According to another aspect, the invention relates to a method for lightning protecting a wind turbine blade according to any of the above mentioned, the method comprising the steps of
- placing a down conducting means in a cavity of the wind turbine blade,
- coating at least one layer of an electrically conductive material onto the blade shell in a reception area, and
- placing a connector to electrically connect the electrically conductive material layer to the down connection means, thereby forming a conductive path for electrical currents induced by lightning from the reception area to the root part of the wind turbine.
The advantages of this method for lightning protection are as described above in relation to the wind turbine blade comprising a lightning protection device.
According to an embodiment of the method for lightning protecting, the coating comprises thermal spraying the at least one layer of an electrically conductive material at least partly by a method belonging to the group of cold spraying, flame spraying, high-velocity oxy-fuel coating spraying (HVOF), plasma spraying, warm spraying, and wire arc spraying, which methods may result in a solid coated layer of high wear resistance and optimal adhesion to the underlying blade shell.
The method for lightning protecting according may further comprise the step of assembling the blade shells prior to the step of coating the layer, whereby the coating may be applied onto the blade shells from the exterior yielding the best possible working conditions and allowing for the possibility to coat a material layer smoothly over the blade shell joining edges.
According to a further embodiment, the at least one material layer may be coated onto the blade shell prior to the placing of the connector. The connector may then be inserted to traverse the blade shell as well as the coated layer whereby the electrical connection between the connector and the coated layer is increased. More connectors may be applied thereby enhancing the electrical connection between the conductive material layer and the down conducting means.
Further, the above described method may comprise a step of painting at least a part of the wind turbine blade for instance to obtain a desired specific coloring of the blade, to further improve the wear resistance, and to improve the characteristics of friction, corrosion, and erosion of the blade surface.
According to a further aspect, the invention relates to a method for repairing a lightning protecting system of a wind turbine blade according to any of the aforementioned, comprising the step of coating at least one further layer of an electrically conductive material onto the blade shell such that an electrical connection is established from the further layer to the down conducting means. Hereby, an already existing lightning protection system on a wind turbine blade may be repaired or updated on site in a simple yet effective way without the need for down taking of the wind turbine blades, and with only minimal pause required in the wind turbine operation.
According to an embodiment the above method for repair may further comprise the step of grinding the blade shell prior to coating the at least one further material layer and the in order to ensure an optimal electrical connection between the new and previously applied coating. Further, the method for repairing may comprise the step of placing one or more further connectors of electrically conductive material in electrically connection with the further material layer and the down conducting means for enhancing the electrical connection there between. Brief description of the drawings
In the following different embodiments of the invention will be described with reference to the drawings, wherein :
Fig. 1 shows a sketch of a wind turbine blade comprising a lightning protection system, Figs. 2 and 3 illustrate a wind turbine blade comprising a lightning protection system according to an embodiment of the invention as seen in a cross sectional view and from above, respectively,
Fig. 4 is a cross sectional view of a part of the blade tip part as seen from the trailing or leading edge illustrating a electrically conductive coated layer of stepwise increasing thickness,
Fig. 5 is a cross sectional view of a part of the blade tip part comprising an electrically conductive coating of gradually increasing thickness, and
Fig. 6 shows an embodiment of a lightning protection system with a material coating covering part of the blade tip end portion.
Detailed description of the drawings
Figure 1 shows a wind turbine blade 100 comprising a lightning protection system for conducting an electrical lightning current from a reception area 101, 106 in a tip part 102 of the blade to the ground via down conducting means 103 such as a cable of an electrically conductive material. The down conducting means 103 are positioned in the interior of the blade in the blade cavity formed at least in part by the blade shells 104 forming the aerodynamical surface of the blade. In the figure the down conductive means 103 are sketched to leave the blade in the root part 105 of the blade. Alternatively the down conducting means may be connected to further grounding means in or near the root part of the blade. In the illustrated embodiment, the wind turbine blade comprises two reception areas 101, 106 in the blade tip part 102 forming the outermost part of the turbine blade. Here, the outermost reception area 101 is placed where the risk of lightning strikes is the highest, and a second reception area may be placed additionally or alternatively with a view to protect a specific part of the blade from lightning currents, such as a structural beam of the blade comprising e.g. Carbon fibers.
A lightning protection system according to an embodiment of the invention is illustrated in more details in figures 2 and 3 showing the blade tip part 102 as seen in a cross sectional view from the trailing edge 107 of the blade, and as seen from above from the pressure or suction side of the blade, respectively. A reception area 101 may as shown in figures 2 and 3 cover the outermost tip part of the blade and comprises a layer 200 of an electrically conductive material coated onto the blade shell 104 thereby acting as an attractor for a lightning. The blade may as illustrated in the figures 2 and 3 comprise a further reception area 106 and layer 206 of an electrically conductive material coated onto the blade shell 104 a distance from the first reception area 101. The electrical current received by one or both of the coated layers is then guided via the connectors 201 traversing the blade shell and into the down conducting means 103. Some or all of the connectors may as illustrated in figure 2 penetrate the entire blade thickness and traverse from the one side of the blade shell to the other, or may be connected from more connector parts. The connectors may as illustrated in figure 2 comprise a head of a relatively large surface to ensure an optimal electrical connection to the surrounding reception area when placed in the blade shell. The electrical connection of the connector to the down conducting means may be established by means of the connection to a receptor house 202 positioned in the blade cavity 205. If the lightning protection system comprises more than one reception areas 101, 106, these may be electrically connected to the same or different down conducting means 103. The reception area may comprise a single or multiple layers 200, 206 of electrically conductive material such a metal or a metal alloy belonging to the group of Cu, Si, Au, Ag, Al, and bronze and coated onto the blade shell. The one or more coated layers may further be covered by layers of paint.
The coating may be achieved by painting or thermal spraying of the metal. By thermal spraying is obtained an optimal adhesion of the electrically conductive material to the underlying blade shell which for instance may comprise a laminate of fiber-reinforced composite materials such as e.g. glassfiber/epoxy. Further, the coating may by thermal spraying be applied to the blade tip part in different thicknesses in different areas as considered optimal both with a view to ensure optimal attraction of the lightning and with a view to obtain the desired final aerodynamical shape of the blade tip. This is illustrated further in the figures 4-6. The coated layer 200, 206 may be applied as an additional layer to the blade shell as sketched in figure 2, where there is a relatively sharp or clear transition 210 from the uncovered to the metal covered blade shell. The coating 200, 206 may alternatively or additionally be applied to the blade shell 104 such that a gradual transition is obtained whereby a smooth outer blade surface may be obtained. This may be obtained as illustrated in figure 4 by a stepwise 401 increasing thickness 400 of the coated layer 200. The blade tip part is here seen in a cross sectional view as seen from the trailing or the leading edge, and the thickness of the blade shell 104 is decreased in a correspondingly stepwise manner whereby the resulting outer blade surface 402 may be smooth without any exposed edges of the coated layer 200. Further, more electrical conductive material may in this way be applied to the part of the blade shell most prone to lightning, or for instance closer to or surrounding the connector to increase the electrical connection hereto. The blade shell may further be manufactured with recesses which may then be filled out by the coated material.
These advantages mentioned above may likewise be obtained by gradually increasing the thickness 400 of the coated material layer as illustrated in figure 5. Here, the blade tip part is seen in a cross sectional view as seen from the root of the blade and showing the blade shells 104 forming the aerodynamical surface of the blade and enclosing a blade cavity. The blade shells are structurally reinforced by an inner beam 501. The down conducting means 103 are placed in the blade cavity 205 and via a receptor house 202 electrically connected to the connectors 201 traversing the blade shell. As illustrated in the figure, the layer of electrically conductive material is mainly coated onto the suction and pressure sides of the blade airfoil whereas both the trailing 503 and leading edges 504 of the blade are left uncovered. Hereby the relatively thin and sharp trailing edge may be maintained. The shape of the trailing edge has a high influence on the aerodynamically blade properties and on other parameters such as on the noise emitted from the blade during operation. Alternatively, these regions may be coated by just a thin layer of material without altering the trailing edge properties significantly.
In figure 6 is illustrated how the coated part of the reception area 101 may be of any arbitrary shape not necessarily covering the entire blade tip part. Further is illustrated how more than one connector may be applied to enhance the electrical connection to the down conducting means 103 in some parts of the reception area also thereby in these parts decreasing the length of the conductive path for the electrical current to the ground.
The wind turbine blade comprising the described lightning protection system may be manufactured by first producing the blade shells e.g. by laminate lay-up and assembling the entire blade while placing the down conducting means in the blade cavity. The down conducting means may be attached to an inner surface of a blade shell or to the reinforcing beam and may be secured in the blade tip region by means of the receptor house likewise placed in the interior of the blade. After assembly of the blade one or more layers of the electrically conductive material may be coated onto the exterior of the blade surface in the reception area in the blade tip part. As previously mentioned the coating may be performed e.g. by painting or by thermal spraying of the material. Hereby the position and the thickness of the material layers may be easily and well controlled during the application. The exterior coated material layer is then electrically connected to the inner down conducting means by the placing of the connectors extending through the thickness of the blade shell and connected to the inner receptor house. The connectors may for instance by screwed through the blade shell or entered trough holes of embedded bushings or nuts or the like. The connectors may be positioned prior to the coating of the material layer whereby the electrical connection is established from the outer surface of the connector head to the underside of the coated material layer. The manufacture may further comprise painting and/or polishing the wind turbine blade.
While preferred embodiments of the invention have been described, it should be understood that the invention is not so limited and modifications may be made without departing from the invention. The scope of the invention is defined by the appended claims, and all devices that come within the meaning of the claims, either literally or by equivalence, are intended to be embraced therein.

Claims

Claims
1. A wind turbine blade comprising a lightning protection system for conducting electrical currents induced by lightning from at least one reception area in a tip part of the blade to a root part of the blade, the wind turbine blade comprising at least one blade shell at least partly forming an aerodynamical surface of the blade and at least partly enclosing a blade cavity, the lightning protection system comprising a down conducting means placed in said cavity and extending between the root part and the tip part, the reception area comprises at least one layer of an electrically conductive material coated onto the blade shell to act as an attractor for a lightning, and wherein at least one connector of an electrically conductive material is placed to electrically connect the electrically conductive material layer with the down conducting means, thereby forming a conductive path for electrical currents induced by lightning from the reception area to the root part of the wind turbine.
2. A wind turbine blade according to claim 1, wherein said layer of an electrically conductive material is at least partly sprayed onto the blade shell by means of thermal spraying.
3. A wind turbine blade according to any of the preceding claims, wherein said layer of an electrically conductive material is at least partly painted onto the blade shell.
4. A wind turbine blade according to any of the preceding claims, wherein said layer of an electrically conductive material comprises a metal or a metal alloy belonging to the group of Cu, Si, Au, Ag, Al, and bronze.
5. A wind turbine blade according to any of the preceding claims, wherein the blade tip part terminates in a tip end portion and the reception area covers said tip end portion.
6. A wind turbine blade according to any of the preceding claims, wherein the thickness of said at least one material layer is substantially constant.
7. A wind turbine blade according to any of claims 1-5, wherein the thickness of said at least one material layer is decreasing towards the edges of said layer.
8. A wind turbine blade according to any of the preceding claims, wherein said at least one material layer is placed to at least partly fill out a recess in the blade shell.
9. A wind turbine blade according to any of the claims 1-5 or 7-8, wherein the material layer covers at least a part of the trailing edge of the blade, and wherein the thickness of said layer decreases in a direction towards the trailing edge.
10. A wind turbine blade according to any of the claims 1-5 or 7-9, wherein the material layer covers at least a part of the leading edge of the blade and wherein the thickness of said layer decreases in a direction towards the leading edge.
11. A wind turbine blade according to any of the preceding claims, further comprising a receptor house connecting the down conducting means to the connector.
12. A method for lightning protecting a wind turbine blade according to any of the claims 1- 11, comprising the steps of
- placing a down conducting means in a cavity of the wind turbine blade,
- coating at least one layer of an electrically conductive material onto the blade shell in a reception area, and
- placing a connector to electrically connect said electrically conductive material layer to said down connection means, thereby forming a conductive path for electrical currents induced by lightning from the reception area to the root part of the wind turbine.
13. A method for lightning protecting according to claim 12, wherein said coating comprises thermal spraying the at least one layer of an electrically conductive material at least partly by a method belonging to the group of cold spraying, flame spraying, high-velocity oxy-fuel coating spraying (HVOF), plasma spraying, warm spraying, and wire arc spraying.
14. A method for lightning protecting according to any of the claims 12-13 further comprising the step of assembling the blade shells prior to the step of coating the layer.
15. A method for lightning protecting according to any of the claims 12-14 where at least one material layer is coated onto the blade shell prior to the placing of the connector.
16. A method for lightning protecting according to any of the claims 12-15 further comprising a step of painting at least a part of said wind turbine blade.
17. A method for repairing a lightning protecting system of a wind turbine blade according to any of the claims 1-11, comprising the step of coating at least one further layer of an electrically conductive material onto the blade shell such that an electrical connection is established from the further layer to the down conducting means.
18. A method for repairing according to claim 17 further comprising the step of grinding the blade shell prior to coating said at least one further material layer.
19. A method for repairing according to any of the claims 17-18 further comprising the step of placing one or more further connectors of electrically conductive material in electrically connection with the further material layer and the down conducting means for enhancing the electrical connection there between.
PCT/EP2010/070504 2009-12-28 2010-12-22 Lightning protection of a wind turbine blade WO2011080177A1 (en)

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