Patent Description:
Due to their location in relatively unprotected sites, wind turbines often experience considerable exposure to environmental conditions during the turbine lifetime. Such exposure can often result in localised wearing or erosion of sections of the surfaces of the wind turbine blades, in particular along the blade leading edge. These eroded sections can result in fractures or cavities forming on the blade surface, which can impact upon the blade aerodynamic and noise performance, as well as upon the appearance of the blade. Accordingly, regular service inspection of blades in use can often reveal the need for localised blade surface repair operations.

Due to the considerable expense and difficulty involved in the demounting and subsequent transportation of blades installed on a wind turbine tower, such localised repair operations are often performed in the field, and in particular when the blade to be repaired is still mounted to the greater wind turbine structure. Such in-field repairs place substantial demands on the efficiency and ease-of-implementation of the repair procedure, to reduce the time and cost involved in carrying out the blade repair. Furthermore, as such repairs are carried out in the field, the difficulty in providing effective control of process variables such as air temperature, humidity levels, etc., can impact on the effectiveness of the repair performed. As a result, current blade repair solutions possess considerable limitations.

An example of a blade repair solution is the Alexit® BladeRep™ coating system, provided by Mankiewicz Gebr. , which provides for two-component polyurethane-based repair coating which can be applied to a section of a blade to be repaired. Another example of a blade repair solution is the Wind Blade Protection Coating W4600 from <NUM>™. However, such systems have the limitation of a very narrow process window, reducing effectiveness in relatively difficult repair conditions, e.g. in relatively hot or cold climates, or environments with a relatively high humidity level.

Alternatives include UV-light-based curing systems, such as the RENUVO™ system provided by Gurit Holding AG. , where a resin is applied which can be cured using a UV-light source. While such systems are generally not as sensitive to environmental conditions, such UV-based systems require the deployment of dedicated UV lamps for the curing process to work. In addition, UV-cured coatings often present reduced long-term performance as a cured coating, often requiring increased levels of maintenance and future repair operations when compared to polyurethane-based systems. Additionally, this type of material requires complicated and expensive packaging in order to protect it against UV light, which could thereby initiate the cure process prior to application. <CIT> discloses a method of repairing a section of the surface of a wind turbine blade, the method comprising the steps of applying a layer of viscous coating material to a section to be repaired such that said layer of viscous coating material is substantially flush with the surface of the wind turbine blade adjacent said section; providing a temporary coating shield adjacent the surface of the wind turbine blade in the region of said section to be repaired, said temporary coating shield defining a curing region adjacent said section to be repaired, wherein said temporary coating shield is arranged to partially seal or cover said curing region; curing said layer of viscous coating material to repair said section; and after said step of curing, removing said temporary coating shield.

It is an object of the invention to provide a wind turbine blade repair method and system which provides improved performance over existing repair solutions.

Accordingly, there is provided a method of repairing a section of the surface of a wind turbine blade as defined in claim <NUM>.

The use of a viscous coating material as a repair solution allows for a flexible and adaptive repair solution, and which does not require a large deal of surface preparation and treatment for use, nor does the repair solution have to be specifically constructed for the repair in question. It will be understood that the step of curing is intended to cover a hardening of the viscous coating material into a relatively solid coating layer on the wind turbine blade. The section of the surface of a wind turbine blade comprises a section of a blade leading edge.

It will be understood that the wind turbine blade preferably comprises a structure formed from fibre-composite material, e.g. glass fibres and/or carbon fibres suspended in a cured resin. It will be further understood that the wind turbine blade is an essentially massive structure, preferably of at least <NUM> metres in length.

Preferably, said viscous coating material comprises a polyurethane based material, preferably a polyurethane elastomer coating, preferably an aliphatic polyurethane. The polyurethane-based material may comprise an aliphatic or aromatic isocyanate, preferably an aliphatic isocyanate.

The use of such materials provides a subsequently-repaired surface which presents good durability and erosion-resistance.

Preferably, the method comprises the step of:.

Preferably, said step of preparing said section comprises at least one of the following: sanding, machining, grinding, polishing, cutting, abrading, scraping, melting, solvent wiping, and/or plasma-activated corona treatment.

Preferably, said step of preparing comprises applying a marking to define the edges of said section to be repaired.

The step of applying a marking helps to delimit the area to be treated by the repair operation.

Preferably, said step of applying a marking comprises applying an adhesive tape to the surface of the wind turbine blade around the perimeter of the section to be repaired.

The use of an adhesive tape can result in a clean transition between repaired and existing structures after the repair operation is completed, once the tape is removed.

Preferably, the method comprises the step of after said curing, smoothing the cured layer of viscous coating material.

Preferably, said step of smoothing comprises polishing the exterior of said cured layer of viscous coating material, and/or smoothing the edges of said cured layer of viscous coating material.

Preferably, the method further comprises the steps of:.

The use of the covering layer seals the viscous coating material from the environmental conditions, e.g. varying humidity levels, and prevents debris such as dust particles, insects, etc. from disturbing or impacting on the uncured coating. Furthermore, the use of a low surface energy material results in a film which can be easily removed from the surface of the wind turbine blade without disturbing the blade surface, leaving a smooth surface and without impacting on the cured or partially cured coating material.

Preferably, said layer of covering material is provided as a low-surface energy plastic or polymer material.

Preferably, said layer of covering material is a thin foil.

The use of a thin foil allows for the covering layer to be flexible to adapt to the blade surface, in particular to the curvature of a blade leading edge.

Preferably, said layer of covering material comprises a film of low surface energy material, wherein said material comprises a critical surface tension lower than approximately <NUM> mN/m, as measured by the Zisman method. The low surface energy allows the film to not adhere to the coating when cured.

Said layer of covering material may comprise any suitable material, preferably polymer films such as Low Density Polyethylene (LDPE), Polytetrafluoroethylene (PTFE), Polydimethylsiloxane (PDMS).

Preferably, said layer of covering material is provided with heating elements, preferably resistive heating elements incorporated into said layer of covering material. Preferably, the method comprises the step of applying heat to said layer of viscous coating material from said heating elements during said curing step. Applying this heat can allow for the acceleration of the curing process, and/or the use of the repair solution within a wider process window.

Preferably, said layer of covering material comprises a transparent foil.

If the foil is transparent, this allows for the visual inspection of the covered layer of coating material. It will be understood that an opaque or coloured foil may also be used.

Preferably, said layer of covering material is provided as a patch of greater size than that of the section to be repaired, the patch having an adhesive applied about the perimeter of patch to secure said patch to the surface of the wind turbine blade adjacent said section to be repaired.

Alternatively, the patch may be provided with an adhesive applied on the entire surface of the patch facing the surface of the blade.

The use of an adhesive-backed patch, with adhesive provided on either the patch perimeter or the entire rear surface of the patch, results in a single-step system which is simple to apply to the surface of the blade, and which presents considerable advantages in restricted work conditions, e.g. during field repairs of a blade mounted to a wind turbine.

Additionally or alternatively, the patch may be adhered to the blade by the adhesive properties of the layer of viscous coating material.

The patch may be provided without any adhesive on the entire surface facing the surface of the blade, thereby using the liquid coating as a way of fixating the patch to the blade. Alternatively, the adhesive properties of the liquid coating may improve the adhesive performance of any other adhesive provided to affix the patch to the blade.

In one aspect, the method comprises providing said marking tape as a double-sided adhesive tape, wherein a first adhesive surface of said adhesive tape is applied around the perimeter of the section to be repaired, and wherein a release liner is provided on an opposed second adhesive surface of said adhesive tape, and wherein the method comprises the step of removing said release liner to provide a bonding surface around the perimeter of the said section to be repaired, said bonding surface arranged to receive said foil.

In this case, the marking tape can fulfil a double purpose, being further used to secure the protective patch in place on the blade. Preferably, the adhesive used to bond to the foil is an adhesive suitable for bonding to an LSE material, e.g. <NUM> High-Strength Acrylic Adhesive 300LSE series.

In an additional or alternative aspect, the method comprises the step of securing said layer of covering material to said wind turbine blade by forming an adhesive bond between the layer of covering material and the surface of said wind turbine blade. Said adhesive bond may be in the form of an adhesive tape applied over the perimeter of said layer of covering material to bond said layer of covering material to the surface of the wind turbine blade adjacent the region to be repaired. Additionally or alternatively, said adhesive bond may be in the form of a separate adhesive material, e.g. a pressure-sensitive adhesive, provided between portions of said layer of covering material and the surfaces of the wind turbine blade to which it is desired to bond the said layer of covering material.

There is further provided a layer of covering material, as described, for use with the above-described method.

The use of a temporary coating shield next to the region to be repaired allows for further protection of the viscous material during curing. In addition, the definition of a partially sealed or covered curing region allows for the creation of an effective microclimate region adjacent the layer of viscous material during the curing step, allowing for the localized environment in the region of the layer of viscous material to be more effectively controlled, e.g. allowing for localized heating of the curing region and the contained viscous coating material to speed up the curing process. The temporary coating shield provides a buffer zone around the repair region.

The temporary coating shield is not completely sealed against the surface of the wind turbine blade, which distinguishes the invention from prior art repair systems utilising localised autoclaves. By contrast, the temporary coating shield can be relatively loosely held in place adjacent the repair region, allowing for ease of installation before, and removal after, a repair operation on a blade.

By allowing for such control of the environmental conditions adjacent the layer of curing viscous coating material, this allows the curing process of the coating material to be more effectively controlled, regardless of general environmental conditions, e.g. for a repair operation carried out in a relatively cold climate, where the relatively low temperature may impede the speed of the curing process, or in climates with relatively higher relative humidity, which could influence the end result of a polyurethane based coating system.

The temporary coating shield defines an open-ended chamber or channel at said curing region.

The temporary coating shield is arranged such that said open-ended chamber or channel extends along a portion of the leading edge of the wind turbine blade.

Preferably, the method comprises the step of providing an air cavity between the temporary coating shield and the curing region, preferably wherein said air cavity allows for the formation of a microclimate or microenvironment above or adjacent to said curing region.

The method comprises the step of heating said defined curing region.

Said step of heating may be provided through the actuation of at least one heating element which may be provided on or supported by said temporary coating shield. Additionally or alternatively, said step of heating may be provided by passing hot air through said curing region, between said temporary coating shield and the adjacent surface of the wind turbine blade.

Preferably, the method comprises the step of providing a hot air source arranged to conduct hot air into said defined curing region.

The hot air source may comprise a heater provided with a fan arranged to blow hot air into said curing region defined between said temporary coating shield and the surface to be repaired. Preferably, the method comprises the step of blowing air through the defined curing region. Preferably, said fan is coupled to said curing region via a hose coupled to an inlet nozzle provided connected to said temporary coating shield. Preferably, said nozzle is below <NUM> in diameter, preferably between approximately <NUM>-<NUM> in diameter.

Additionally or alternatively, the method comprises the step of reducing the relative humidity of said defined curing region.

By reducing the humidity in the air adjacent the section to be repaired, this results in an accelerated cure process, and prevents the occurrence of defects caused by a side reaction between isocyanates which may be present in the coating material and any moisture in the air. Said step of reducing the relative humidity may comprise conducting or blowing dry air into said defined curing region.

Preferably, said step of providing a temporary coating shield comprises:.

By providing a supporting arm to carry a separate shield member, the weight of the temporary coating shield can be reduced, as the separate shield member can be formed from a relatively lightweight material to be carried by the structural arm or bracket.

Preferably, said step of attaching comprises releasably securing said at least one supporting arm or bracket to a surface of the wind turbine blade.

Preferably, said releasably securing comprises providing at least one releasable securing means at one end of said at least one supporting arm or bracket, for example a vacuum cup, an adhesive tape, etc..

In a preferred embodiment, said at least one supporting arm or bracket is provided as an elongate member, preferably a relatively flexible member, which is releasably attachable at opposed ends of the elongate member to the surface of the wind turbine blade adjacent opposed sides of the region to be repaired.

It will be understood that the repair solution is used to repair localised sections of a blade leading edge, preferably sections less than <NUM> metres in length along the longitudinal direction of the blade, preferably less than <NUM> metres, further preferably less than <NUM> metres.

In a preferred embodiment, said at least one a temporary coating shield comprises a lightweight cover, preferably formed from a plastics or polymer material.

Preferably, said shield is formed from a relatively flexible material, such that the shield may be shaped to conform to the profile of the at least one supporting arm or bracket when mounted on the wind turbine blade.

Preferably, said shield is releasably attached to said at least one supporting arm or bracket. The shield may be attached using any suitable attachment method, preferably a reusable attachment method, e.g. a magnet attachment, a button or snap-fit attachment, an adhesive bond, etc..

There is further provided a system comprising a wind turbine blade and a temporary coating shield as described in claim <NUM>, for use with the above-described method.

An embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:.

It will be understood that elements common to the different embodiments of the invention have been provided with the same reference numerals in the drawings.

<FIG> illustrates a conventional modern upwind wind turbine <NUM> according to the so-called "Danish concept" with a tower <NUM>, a nacelle <NUM> and a rotor with a substantially horizontal rotor shaft. The rotor includes a hub <NUM> and three blades <NUM> extending radially from the hub <NUM>, each having a blade root <NUM> nearest the hub and a blade tip <NUM> furthest from the hub <NUM>. The rotor has a radius denoted R.

<FIG> shows a schematic view of a wind turbine blade <NUM>. The wind turbine blade <NUM> has the shape of a conventional wind turbine blade and comprises a root region <NUM> closest to the hub, a profiled or an airfoil region <NUM> furthest away from the hub and a transition region <NUM> between the root region <NUM> and the airfoil region <NUM>.

The diameter (or the chord) of the root region <NUM> is typically constant along the entire root area <NUM>. The transition region <NUM> has a transitional profile <NUM> gradually changing from the circular or elliptical shape <NUM> of the root region <NUM> to the airfoil profile <NUM> of the airfoil region <NUM>. The chord length of the transition region <NUM> typically increases substantially linearly with increasing distance r from the hub.

The airfoil region <NUM> has an airfoil profile <NUM> with a chord extending between the leading edge <NUM> and the trailing edge <NUM> of the blade <NUM>.

<FIG> shows a schematic view of an airfoil profile <NUM> of a typical blade of a wind turbine depicted with the various parameters, which are typically used to define the geometrical shape of an airfoil. The airfoil profile <NUM> has a pressure side <NUM> and a suction side <NUM>, which during use - i.e. during rotation of the rotor - normally face towards the windward (or upwind) side and the leeward (or downwind) side, respectively. The airfoil <NUM> has a chord <NUM> with a chord length c extending between a leading edge <NUM> and a trailing edge <NUM> of the blade. The airfoil <NUM> has a thickness t, which is defined as the distance between the pressure side <NUM> and the suction side <NUM>. The thickness t of the airfoil varies along the chord <NUM>. The deviation from a symmetrical profile is given by a camber line <NUM>, which is a median line through the airfoil profile <NUM>. The median line can be found by drawing inscribed circles from the leading edge <NUM> to the trailing edge <NUM>. The median line follows the centres of these inscribed circles and the deviation or distance from the chord <NUM> is called the camber f. The asymmetry can also be defined by use of parameters called the upper camber and lower camber, which are defined as the distances from the chord <NUM> and the suction side <NUM> and pressure side <NUM>, respectively.

Airfoil profiles are often characterised by the following parameters: the chord length c, the maximum camber f, the position df of the maximum camber f, the maximum airfoil thickness t, which is the largest diameter of the inscribed circles along the median camber line <NUM>, the position dt of the maximum thickness t, and a nose radius (not shown). These parameters are typically defined as ratios to the chord length c.

Wind turbine blades are generally formed from fibre-reinforced plastics material, e.g. glass fibres and/or carbon fibres which are arranged in a mould and cured with a resin to form a solid structure. Modern wind turbine blades can often be in excess of <NUM> or <NUM> metres in length, having blade root diameters of several metres. Wind turbine blades are generally designed for relatively long lifetimes and to withstand considerable structural and dynamic loading.

In the event of damage to a surface of the blade <NUM>, e.g. erosion damage or other impact damage, such a damaged area is identified during a turbine inspection. Additionally or alternatively, the wind turbine <NUM> may be provided with a sensor system operable to detect the occurrence of damage to a blade surface, e.g. through monitoring of blade vibration levels. Once a section of a blade to be repaired is identified, the wind turbine rotor is locked into position with the blade in question preferably arranged in a vertical orientation to allow for ease of access.

With reference to <FIG>, a series of steps of a repair method according to an embodiment of the invention are illustrated.

In <FIG>, a section of a leading edge <NUM> of a wind turbine blade <NUM> is illustrated. The leading edge of <FIG> comprises an erosion protection member indicated at <NUM>. The erosion protection member <NUM> may comprise any suitable layer of erosion-resistant material arranged at the leading edge <NUM> of the blade <NUM> along a portion of the length of the blade <NUM>, preferably as a coating applied to a surface of the blade structure. It will be understood however that the repair method of the invention may be performed on a wind turbine blade <NUM> without such a leading edge erosion protection member <NUM>, wherein the following operations may be performed directly on the surface of the blade structure.

At a point along the length of the blade <NUM>, a section of the blade <NUM> is identified which has experienced sufficient erosion or impact damage to merit a repair of the surface of the blade <NUM>, such a section indicated at <NUM> in <FIG>.

The section to be repaired <NUM> may be designated as a square or rectangular section centred on the damaged section of the blade <NUM>, and may be delimited through the use of a suitable marker, e.g. adhesive tape (not shown), around the periphery of such a section. The section <NUM> is then treated to remove the erosion protection member <NUM> in the area of the damaged section, <FIG>. Such treatment may include any suitable mechanical or thermal processing of the section of the erosion protection member <NUM>, preferably a sanding operation or a heating of the erosion protection member <NUM> above the melting point of the material before the material is scraped away. Other possible treatments may include for example machining, grinding, polishing, cutting, abrading, scraping, solvent wiping, and/or plasma-activated corona treatment. The treatment may be a multi-stage process, wherein successive operations increasing in granularity are performed, which results in the creation of a smooth surface for the section to be repaired <NUM>.

Once the section to be repaired <NUM> has been treated appropriately, a layer <NUM> of a coating material is applied to the section <NUM>, <FIG>. The layer is preferably applied as a viscous or liquid layer, which can be sprayed, rolled, brushed, or painted onto the surface of the blade <NUM> in the treated section <NUM>.

Preferably, the layer of viscous coating material comprises a polyurethane-based material, preferably a polyurethane elastomer coating, and preferably an aliphatic polyurethane. The polyurethane-based material may comprise an aliphatic or aromatic isocyanate, preferably an aliphatic isocyanate. The use of such materials, such as the W4600 coating solution from <NUM>™, can provide a surface layer which presents good durability and erosion-resistance. In one aspect, the layer of coating material <NUM> may be formed of the same material as the leading edge erosion protection member <NUM>. It will be understood that any suitable coating material may be used.

The layer <NUM> is applied to fill the section to be repaired <NUM>, the thickness of the layer <NUM> approximately equal to the depth of the section <NUM>, such that the outer surface of the layer <NUM> is substantially flush and in line with the surrounding exposed surface of the wind turbine blade <NUM>, additionally in this case in line with the surface of the leading edge erosion protection member <NUM>.

Once the layer of coating material <NUM> is applied to the section <NUM> of the blade <NUM>, a layer of covering material <NUM> is applied over the viscous coating material layer <NUM>, <FIG>. The layer of covering material is preferably provided as a thin foil <NUM>, which covers the external surface of the viscous material <NUM>. The covering material <NUM> acts to seal the external surface of the coating material <NUM> during the curing or hardening of the coating material <NUM>, preventing unwanted particles, e.g. dust, dirt, or insects from disturbing or impacting on the relatively viscous coating material <NUM>, and affecting the smoothness or composition of the subsequent surface. The foil <NUM> can also act to seal the coating material <NUM> from the environmental conditions, e.g. varying atmospheric humidity conditions, etc., which may affect the curing process of the coating material <NUM>.

The foil <NUM> is provided from a Low Surface Energy (LSE) material, preferably a low-surface energy plastic or polymer material. This results in a film which can be easily removed from the surface of the wind turbine blade without disturbing the blade surface, e.g. by peeling, leaving a smooth surface and without impacting on the cured or partially cured coating material. The foil <NUM> is preferably formed of material having a critical surface tension lower than <NUM> mN/m, preferably lower than approximately <NUM> mN/m, as measured by the Zisman method. The low surface energy allows the film to not adhere to the coating when cured.

The film <NUM> may be made from a transparent material, which allows the underlying layer <NUM> to be inspected through the film <NUM>, or the film may be formed from a relatively opaque material. Said layer of covering material may comprise any suitable material, preferably polymer films such as Low Density Polyethylene (LDPE), Polytetrafluoroethylene (PTFE), Polydimethylsiloxane (PDMS).

The film <NUM> may be attached to the surface of the blade <NUM> using any suitable method, e.g. an adhesive such as a pressure-sensitive adhesive may be applied to the blade-facing surface of the film <NUM>, preferably around the periphery of the film <NUM>. The film <NUM> may then be adhered to the surface of the blade adjacent the edges of the section to be repaired <NUM>. In an alternative aspect, an adhesive may be applied on the surface of the blade <NUM> adjacent the section to be repaired <NUM>, the film <NUM> applied to said adhesive. In a further alternative aspect, the marker used to delimit the edges of the section to be repaired may be provided in the form of a double-sided adhesive tape, with a first adhesive side used to secure the tape to the blade <NUM>, and a second adhesive side used to secure the film <NUM> to the tape. In an additional or alternative aspect, it will be understood that the layer of viscous coating material <NUM> may possess inherent adhesive properties to form a temporary bond with the film <NUM> on the blade <NUM>.

The layer of coating material <NUM> is allowed to cure or harden, at which point the thin foil layer <NUM> can be removed from the surface of the wind turbine blade <NUM> to reveal the repaired surface beneath, <FIG>. A further treatment may be performed on the cured layer of coating material <NUM> if required, e.g. a further mechanical polishing, in order to ensure an adequately smooth surface, and to provide a transition between the repaired section and the surrounding surface area, e.g. the pre-existing leading edge erosion protection member <NUM>.

By covering the layer of coating material <NUM> during the curing process with a removable film <NUM>, this results in an improved repair process, providing a repaired section <NUM> having a smooth and even surface, and which provides a faster and more controllable curing stage.

In a further embodiment of the invention, the removable film <NUM> may be provided with heating elements, preferably resistive heating elements incorporated into the film <NUM>. The presence of such heating elements allows for heat to be applied to the layer of coating material <NUM> during the curing process, thereby accelerating the curing process, or at least allowing for the use of the repair method within a wider process window. Preferably, the heating elements are operable to generate a <NUM>-<NUM> temperature increase. Preferably, the heating elements are operable to heat the layer of coating material <NUM> above at least <NUM>.

The heating elements may be provided as thin resistive wires embedded in the film <NUM>, and/or as a resistive coating applied to a surface of the film <NUM>. A current source or battery may be provided coupled to the heating elements, to provide a current to the heating elements during the curing process. Such a battery may be relatively small, due to the relatively minor heat change desired, and accordingly may be easily mounted to the surface of the blade <NUM> adjacent the film <NUM> during the curing process, e.g. by way of suitable adhesive bonding. Preferably, the removable film <NUM> is provided as a reusable component.

In an additional aspect, which may be used in combination with the removable film <NUM> or as a separate repair procedure, a temporary coating shield may be used adjacent the section to be repaired <NUM>, and in particular extending over the layer of coating material <NUM>. Such a shield can be used to create an effective microclimate region adjacent the curing material <NUM>, allowing for greater control of the curing process and a much wider process window for performing repairs than is provided by the prior art.

<FIG> illustrates a series of steps of a repair method which may be combined with the method steps illustrated in <FIG>, after the film <NUM> has been applied to the exterior of the layer of viscous coating material <NUM>.

In <FIG>, a series of supporting arms or brackets <NUM> are attached to the surface of the blade <NUM>, adjacent the section to be repaired <NUM>. Preferably, the brackets <NUM> are arranged to extend around the section to be repaired <NUM>, presenting a basic cage-like structure adjacent the section <NUM>.

With reference to <FIG>, a shield member <NUM> is coupled to said brackets <NUM>, the shield member <NUM> extending in an arcuate manner adjacent the section to be repaired <NUM>. The shield member <NUM> substantially covers the section to be repaired <NUM>, and partially seals or covers an area adjacent said section <NUM>, effectively defining a curing region <NUM> which is at least partially protected from the ambient environmental conditions. The shield member <NUM> may be provided as a lightweight cover, preferably formed from a plastics or polymer material, and may be opaque or transparent.

Once the curing region <NUM> is defined adjacent the section to be repaired <NUM>, a blower and/or heater device <NUM> may be coupled to the assembly, <FIG>. This allows hot dry air to be passed into the curing region <NUM>, and over the surface of the section to be repaired <NUM>, aiding in the curing of the layer of coating material <NUM>. By providing for effective control of the temperature and humidity levels adjacent the curing layer of coating material <NUM>, the curing process can be accelerated rapidly, even at relatively low temperatures, such as below <NUM>. This allows for the repair procedure to be effectively and quickly carried out for a wide range of temperatures and atmospheric conditions, widening the process window for the repair procedure.

The blower and/or heater device <NUM> may comprise a heater provided with a fan arranged to blow hot air into said curing region <NUM> defined between said temporary coating shield <NUM> and the surface to be repaired <NUM>. The blower and/or heater device <NUM> may comprise a hose coupled to an inlet nozzle provided connected to said temporary coating shield <NUM>, preferably below <NUM> in diameter, preferably between approximately <NUM>-<NUM> in diameter, such that the hot dry air can be conveyed directly to the curing region <NUM>, with minimal heat losses or changes in humidity level between the blower and/or heater device <NUM> and the curing region <NUM>.

After the curing process has effectively completed, the heater <NUM>, shield <NUM>, and brackets <NUM> can be removed from the blade <NUM>, with the thin foil layer <NUM> removed from the surface of the wind turbine blade <NUM> to reveal the repaired surface, as in <FIG>. Further surface treatment operations may be carried out at this point, as described above.

<FIG> illustrates in more detail an example of a supporting bracket <NUM> as used in <FIG>. <FIG> shows a plan view of a first bracket <NUM>. The bracket <NUM> is provided as an elongate member, preferably formed from a relatively flexible material, having attachment means <NUM> provided at opposite ends of the elongate member. In <FIG>, the attachment means <NUM> are provided as vacuum cups used to secure the ends of the bracket <NUM> to the surface of a wind turbine blade <NUM>, but it will be understood that any suitable attachment means may be used, e.g. double sided adhesive tape. Preferably, the attachment means provide for a releasable connection between the bracket <NUM> and the blade surface.

In use, the bracket <NUM> is attached to the surface of the blade <NUM> such that the attachment means <NUM> are affixed to the blade surface at opposite sides of the section to be repaired <NUM>, the bracket <NUM> forming a curved profile extending around the curvature of the leading edge <NUM> of the blade <NUM>. It will be understood that the bracket and shield assembly may also be used for the repair of sections of the blade not provided at the blade leading edge <NUM>. Furthermore, it will be understood that the blade may be positioned in any suitable orientation to facilitate repair, e.g. in a substantially horizontal or vertical alignment.

In one aspect, a plurality of further attachment elements <NUM> are provided along the length of the bracket <NUM>, the further attachment elements <NUM> used to couple the bracket <NUM> to the shield member <NUM>. In <FIG>, the further attachment elements <NUM> are provided in the form of magnetic strips provided on the bracket <NUM>, as shown in the side view illustrated in <FIG>.

With reference to <FIG>, the shield <NUM> is effectively wrapped around the exterior of the curved bracket <NUM>, wherein magnets <NUM> are applied to the exterior of the shield <NUM>, to hold the shield <NUM> in position between the magnets <NUM> and the magnetic strip or strips <NUM>, as shown in the side view illustrated in <FIG>.

The magnets <NUM> may be incorporated into the body of the shield <NUM>, or may be applied as separate elements to the exterior surface of the shield <NUM>. It will be understood that any suitable releasable attachment members may be used to couple the shield <NUM> to the brackets <NUM>, e.g. a snap-fit coupling, adhesive bonding, etc. In an alternative embodiment, it will further be understood that the shield <NUM> and the brackets <NUM> may be provided as a single integrated structure which can be applied to the blade surface. In a further alternative embodiment, the shield <NUM> may be provided as a sliding or rolling door or curtain-type member, which can be moved between a retracted position and a deployed position, where the shield <NUM> is supported by at least one bracket <NUM>.

In an additional or alternative embodiment, a flexible plastic sheet or panel may be relatively loosely wrapped around at least a portion of the periphery of a wind turbine blade in the region of a repair location, to provide a partial chamber above the repair region into which dry, heated air can be passed to improve the curing process of the repair. Such a flexible plastic sheet or panel may be attached to the blade using e.g. an adjustable strap or elasticated band which can be applied around the periphery of the blade.

The use of the repair method comprising the thin film <NUM> to protect the curing layer of coating material <NUM>, and/or the use of the temporary shield member <NUM> to control the curing environment adjacent the section to be repaired <NUM>, allows for a considerably improved repair solution, allowing for the undertaking of effective repair procedures with larger process windows compared to the prior art.

Claim 1:
A method of repairing a section (<NUM>) of the surface of a wind turbine blade (<NUM>), the method
comprising the steps of:
identifying a section (<NUM>) of the surface of a wind turbine blade (<NUM>) to be repaired;
applying a layer of viscous coating material (<NUM>) to said section (<NUM>) such that said layer of viscous coating material (<NUM>) is substantially flush with the surface of the wind turbine blade (<NUM>) adjacent said section (<NUM>);
providing a temporary coating shield (<NUM>) adjacent the surface of the wind turbine blade (<NUM>) in the region of said section (<NUM>) to be repaired, said temporary coating shield (<NUM>) defining a curing region adjacent said section (<NUM>) to be repaired, wherein said temporary coating shield (<NUM>) is arranged to partially seal said curing region, wherein said step of providing a temporary coating shield (<NUM>) comprises arranging said temporary coating shield (<NUM>) to define an open-ended chamber or channel at said curing region, said open-ended chamber or channel being arranged to extend along a portion of a leading edge of the wind turbine blade (<NUM>);
curing said layer of viscous coating material (<NUM>) to repair said section (<NUM>); and
after said step of curing, removing said temporary coating shield (<NUM>),
wherein the method comprises the step of heating said defined curing region.