Patent Description:
Depending on the weather conditions at a specific wind turbine site, icing of the rotor blades of the wind turbine may occur. A rotor blade which is partially or entirely covered with ice is generally undesired by the wind turbine operator for various reasons. First, the aerodynamic efficiency of the rotor blades and, hence, of the wind turbine may be reduced due to the icing. This is due to the fact that the shape and geometry of the rotor blade is carefully optimized and any deviation of the shape, e.g. by an additional layer of ice or by irregularities of the surface, generally impairs the aerodynamic efficiency. Second, a layer of ice on the surface of the rotor blade adds weight to the rotor blade, which, if unevenly distributed over the rotor of the wind turbine, may create imbalances of the rotor. Third, parts of the ice may be thrown from the rotor blades during operation of the wind turbine, i.e. during rotation of the rotor, which may create damages to people and objects being located in the reach of the wind turbine.

In summary, the build-up of ice on a wind turbine blade is preferably avoided. In the case of a blade which is already partly or entirely covered by ice, means to deice the blade are preferably provided.

One approach to avoid the build-up of ice and to eliminate existing ice on the surface of a wind turbine blade is the provision of an electro-thermal system. In this approach, an electrically conductive heating mat is used as an electrical resistance. The heating mat is usually laminated on the outer surface of the rotor blade after the rotor blade has been casted and before the top coat and paint is applied to the blade.

A problem of using heating mats on the surface of the rotor blade is that the heating mats may represent a preferred attachment area for a lightning leader (or streamer). In other words, there is a non-negligible likelihood that a lightning strike hits the heating mat instead of a lightning receptor of the rotor blade and afflicts damage to the rotor blade.

A document representing the prior art is e.g.: <CIT>.

The present invention seeks for a solution to this problem.

A solution thereof is disclosed by the independent claims.

Advantageous modifications and embodiments are disclosed in the dependent claims.

According to the invention, there is provided a rotor blade of a wind turbine comprising a leading edge section with a leading edge and a trailing edge section with a trailing edge, wherein the leading edge and the trailing edge divide the surface of the rotor blade into a suction side and a pressure side. The rotor blade further comprises a blade shell for defining the outer shape of the rotor blade, and a heating mat for anti-icing and/or deicing purposes which is arranged upon the blade shell. Furthermore, the rotor blade is characterized in that in the outboard region of the rotor blade, the heating mat is substantially or completely covered by a protective shield made of an electrically non-conductive polymer material.

Particularly, the outboard region of the rotor blade is defined by the outmost fifteen per cent of the rotor blade in spanwise direction. The spanwise direction of the rotor blade is defined as the direction of a straight line which extends from the root to the tip of the rotor blade.

The protective shield is made of an electrically non-conductive polymer material. The protective shield is destined for protection of at least a part of the leading edge section against erosion. Therefore, the protective shield is also referred to as a "leading edge protection" (LEP) shield. The LEP shield is also known as a LEP shell. Depending on the design of the protective shield, the shield may either be referred to as a "hard shell" or as a "soft shell". A soft shell features a certain flexibility and may cling to the contour of the surface of the rotor blade.

A key aspect of the present invention is that a protective shield, which is primarily known for protecting the leading edge section of a rotor blade of a wind turbine against erosion, is taken and modified in order to insulate a heating mat of the rotor blade against lightning strikes.

In one embodiment of the invention, at least ninety per cent, in particular at least nine-five per cent, even more particularly at least ninety-nine per cent of the heating mat in the outboard region of the rotor blade is covered by the protective shield.

In other words, the main part or the entire area where the heating mat is exposed to lighting strikes is insulated by the electrically non-conductive shield. A high degree of coverage is necessary as otherwise the lightning strike may just hit the heating mat in those areas which are uncovered by the insulating protective shield and may cause the damages to the blade shell there.

Exemplarily, the heating mat comprises carbon. Carbon has been proven to be a well suited material for a heating mat of a rotor blade of a wind turbine.

Typically, the heating mat does not extend until the very tip of the rotor blade. One reason therefore is that the chord lengths of a rotor blade decrease considerably at the tip section of the rotor blade. As for production and manufacturing reasons, it may be cost efficient to provide the heating mat in one distinct width, i.e. in one distinct chordwise extension when mounted to the rotor blade, the heating mat may only be applied until the last <NUM>-<NUM> meter of the rotor blade, as seen in spanwise direction.

Preferably, however, the spanwise extension of the heating mat in the outboard region of the rotor blade is greater than five per cent, in particular greater than seven per cent of the length of the rotor blade.

As the outboard region of the rotor blade is defined by the outmost fifteen per cent of the rotor blade in spanwise direction, this means that at least one third, preferably approximately half of the outboard region of the rotor blade are covered by the heating mat.

Such a spanwise extension of the heating mat in the outboard region is advisable as icing of the rotor blade occurs particularly in the outboard region of the rotor blade due to, inter alia, the high circumferential velocity of the rotor blade in that section.

Preferably, the rotor blade comprises a lightning protection system with at least one lightning receptor in the outboard region of the rotor blade.

In an embodiment of the invention, the heating mat is placed adjacent to the lightning receptor. In other words, the heating mat "encircles" or "surrounds" the lightning receptor, as seen in a top view onto the surface of the rotor blade.

Advantageously, the electrical insulation of the heating mat is sufficiently good that lightning strikes attach at the lightning receptor of the lightning protection system and not at the heating mat.

In the following, three concrete embodiments of protective shields are disclosed. Obviously, these embodiments represent examples only and are not to be construed to limit the scope of protection claimed by this patent application.

According to the invention, the protective shield comprises a curved unit which covers at least partially the leading edge of the rotor blade. Furthermore, the protective shield comprises a first panel which is substantially flat and arranged at the suction side of the rotor blade adjacent to a first rim of the curved unit, and a second panel which is substantially flat and arranged at the pressure side of the rotor blade adjacent to a second rim of the curved unit. The curved unit, the first panel and the second panel are configured as separate pieces.

In other words, a known protective shield such as leading edge protection shell is supplemented with a first and a second panel. Advantageously, the first and second panel is made of the same or a similar material as the protective shield. The advantage herein is that the way of manufacturing the panels and its properties are known.

According to the invention the first and second panel substantially or completely cover the heating mat, at least in the outboard region of the rotor blade. The supplement of the first and second panel is advantageous compared to the provision of the protective shield alone, as thus the area of the heating mat which is insulated, i.e. covered by a non-conductive material, may be reduced.

In an embodiment of the invention, the curved unit covers, in the outboard region of the rotor blade, substantially or completely the heating mat.

In other words, a known protective shield such as leading edge protection shell is extended over the substantial or complete surface of the heating mat. Thus, the area of the heating mat which is uncovered by an insulating material is significantly reduced, if not avoided at all.

An advantage of providing one single protective shield of which the area extended is that no joints between the shield and any flat panels are needed. Any joints between the shield and adjacent panels could be critical for both leading edge erosion (if the joint is close to the leading edge) and for lightning (as the lightning will target the weakest spot, i.e. the region with discontinuities or reduced thickness, at the surface of the rotor blade).

According to the invention, the rotor blade comprises a further protective shield, and wherein the further protective shield is arranged on top of at least a part of the protective shield.

The protective shield, which is between the surface of the rotor blade and the further protective shield is advantageously extended such that it substantially or completely covers the heating mat in the outboard region of the rotor blade. It can, however, in principle also be divided into a central piece and a first and second substantially flat panel, respectively.

In a variant, the thickness of the further protective shield is reduced in the area where the further protective shield overlaps with the protective shield. Also the thickness of the protective shield may be decreased in that area. As a result, the combined thickness of the protective shield and the further protective shield may be designed to be substantially constant and equal compared to the thickness of the protective shield alone, wherein no further protective shield is placed upon the protective shield.

Advantageously, the further protective shield covers at least a part of the leading edge of the rotor blade.

The invention is also directed towards the use of a protective shield made of electrically insulating polymer material for electrical insulation of a heating mat, in particular against lightning strikes, wherein the protective shield is destined for protection of at least a part of the leading edge section against erosion, the heating mat is arranged upon a blade shell of a rotor blade of a wind turbine and is destined for anti-icing and/or deicing purposes, and in the outboard region of the rotor blade, the heating mat is substantially or completely covered by the protective shield.

Embodiments of the invention are now described, by way of example only, with the help of the accompanying drawings, of which:.

Note that the drawings are in schematic form. Furthermore, similar or identical elements may be referenced by the same reference signs.

<FIG> shows a perspective view of a prior art rotor blade <NUM> of a wind turbine. The rotor blade <NUM> comprises a root section <NUM> with a root <NUM> and, at its opposite end, a tip section <NUM> with a tip <NUM>. The spanwise direction <NUM> of the rotor blade <NUM> is defined as the direction of a straight line extending from the root <NUM> to the tip <NUM> of the rotor blade <NUM>. The rotor blade <NUM> further comprises a leading edge section <NUM> with a leading edge <NUM> and a trailing edge section <NUM> with a trailing edge <NUM>. The leading edge <NUM> and the trailing edge <NUM> divide the surface of the rotor blade <NUM> into a suction side <NUM> and a pressure side <NUM>. <FIG> shows a view onto the suction side <NUM> of the rotor blade <NUM>.

The trailing edge section <NUM> is defined as that section which is adjacent to the trailing edge <NUM> and extends until ten percent in chordwise direction. Likewise, the leading edge section <NUM> extends until ten percent in chordwise extension away from the leading edge <NUM>.

The rotor blade <NUM> is constructed with a blade shell <NUM> which surrounds and defines a cavity inside. The cavity which can be understood as the hollow inside area of the rotor blade <NUM> has the function that material and weight of the rotor blade is minimized.

The rotor blade <NUM> is divided into an inboard region <NUM>, a mid-board region, and an outboard region <NUM>. The inboard region <NUM> is defined as the inner most fifteen percent of the blade length, the mid-board <NUM> region is defined as the seventy percent of the blade length which is located between the inboard region <NUM> and the outboard region <NUM>. Consequently, the outboard region <NUM> is defined as the outer most fifteen percent of the blade length. The wording "inner most" and "outer most" relate to the situation that the rotor blade <NUM> is mounted and attached to a hub of a wind turbine. Then, during rotation of the rotor of the wind turbine the rotor blade travels across a swept area wherein the circumferential velocity of the tip, and generally of the outboard region <NUM>, is highest.

The rotor blade <NUM> as illustrated in <FIG> also comprises a heating mat <NUM> for preventing the build-up of ice on the surface of the rotor blade <NUM>. Another purpose of the heating mat <NUM> is to melt, i.e. to eliminate, already existing ice on the rotor blade <NUM>. The heating mat <NUM> extends along the major part of the outboard region <NUM> and the major part of the mid-board region <NUM> of the rotor blade <NUM>. Note that the extension of the heating mat <NUM> in chordwise direction, i.e. its width, is substantially constant along its lengthwise extension. This leads to the situation that the heating mat <NUM> does not extend until the very tip <NUM> of the rotor blade <NUM>, but finishes a few meters before. The heating mat is not covering the leading edge section <NUM> in the inboard region <NUM> of the rotor blade <NUM> because the build-up of ice in the inboard region <NUM> is less likely than in the outboard region <NUM> of the rotor blade <NUM>.

The rotor blade <NUM> also comprises a protective shield <NUM> for protecting the leading edge <NUM> of the rotor blade <NUM> against erosion. Erosion typically occurs due to small particles of dust and dirt and may also occur due to insects. Over the years and under harsh conditions, the leading edge <NUM> and adjacent areas around the leading edge <NUM> are typically damaged. This generally decreases the aerodynamic efficiency of the rotor blade <NUM>. Therefore, provision of a protective shield <NUM>, such as a leading edge protection soft shell or leading edge protection hard shell is recommendable. Such a protective shield <NUM> can either be retro-fitted on an already operating wind turbine or can be provided on a newly manufactured rotor blade. Note, that in the example of <FIG>, the protective shield extends over the complete outboard region <NUM>, but only extends over a relatively small part of the leading edge section <NUM>. This is due to the fact that leading edge erosion mainly occurs at the leading edge <NUM> and in close vicinity to the leading edge <NUM>.

<FIG> shows a top view onto a part of the suction side <NUM> of the prior art rotor blade as illustrated in <FIG>. Here, it can be seen that the heating mat <NUM> does not extend until the tip <NUM> of the rotor blade <NUM>, while the protective shield <NUM> covers and protects the tip <NUM> of the rotor blade <NUM>.

Finally, <FIG> shows another view of the same rotor blade, namely a top view onto a part of the leading edge <NUM> of the rotor blade <NUM>. In <FIG>, it can be seen that both, the heating mat <NUM> and the protective shield <NUM>, extend symmetrically around the leading edge <NUM>.

<FIG> shows a perspective view of an inventive rotor blade <NUM> of a wind turbine. The rotor blade <NUM> as shown in <FIG> is similar to the rotor blade <NUM> as shown in <FIG>. However, this time, the protective shield <NUM> is designed differently. The main difference between the protective shield <NUM> of the rotor blade as illustrated in <FIG> compared to the protective shield <NUM> as illustrated in the <FIG> is that the protective shield <NUM> now covers the entire chordwise extension of the heating mat <NUM> in the region where the protective shield against erosion of the leading edge <NUM> is provided for. The chordwise extension of the protective shield <NUM> is still relatively small in the tip section <NUM> of the rotor blade <NUM> as in the tip section <NUM> of the rotor blade <NUM> there is not provided any heating mat. However, at that point where the heating mat <NUM> is arranged, the protective shield <NUM> ensures that it covers the surface of the heating mat <NUM> such that the heating mat <NUM> is electrically insulated and is not attracting lightning strikes. Thus, lightning only strikes and attaches in the lightning receptors and corresponding elements of the lightning protection system of the rotor blade.

<FIG> show similar views on the rotor blade <NUM> compared to <FIG>. Here again, it can be seen how the protective shield <NUM> effectively covers the surface of the heating mat <NUM> in the entire outboard region <NUM> and in parts of the mid-board region <NUM> of the rotor blade <NUM>. This effectively minimizes the risk of damages to the blade shell laminate of the rotor blade in the section of the rotor blade which is most sensible and most probable to be hit and damaged by lightning strikes not attaching to the lightning receptors of the lightning protection system.

<FIG> shows a first concrete embodiment of the invention. A cross-sectional view of the rotor blade in the outboard region of the rotor blade is shown. Only the leading edge section <NUM> and adjacent parts of the suction side <NUM> and the pressure side <NUM> are shown in <FIG>. First, the blade shell <NUM> of the rotor blade <NUM> can be discerned. The blade shell <NUM> is designed as a laminate comprising a fiber reinforced plastic material attached to balsa wood. The thickness of the blade shell <NUM> varies and is typically thinnest in the leading edge section <NUM> and at the leading edge <NUM>. In contrast, it becomes typically thicker towards the mainboard or main chordwise area of the blade shell <NUM>. This is due to the fact that in the mainboard part the spar caps and the beam (or: web) of the rotor blade naturally and typically are arranged. Here, the structural loads are often times highest and, thus, the blade shell <NUM> is designed thicker.

On top of the blade shell <NUM>, there is provided the heating mat <NUM> which is covering the leading edge <NUM> and a considerable part from the leading edge <NUM> towards the suction side <NUM> and towards the pressure side <NUM>. As the heating mat <NUM> is in principle electrically conductive, the heating mat <NUM> is in the example of <FIG> fully covered by a protective shield which comprises a curved unit <NUM> with a first rim <NUM> and a second rim <NUM>, and a first panel <NUM> and a second panel <NUM>. The first panel <NUM> is relatively flat and arranged adjacent to the first rim <NUM> of the curved unit <NUM>. Likewise, the second panel <NUM> is also relatively flat and is arranged at the second rim <NUM> of the curved unit <NUM>. The joints at the first rim <NUM> and the second rim <NUM> needs to be designed and constructed with utmost care in order to avoid any aerodynamic losses at the joints.

An advantage of providing three separate pieces, namely the curved unit <NUM>, the first panel <NUM> and the second panel <NUM>, is that first the curved unit <NUM> can be designed as a conventional hard shell or soft shell for LEP (leading edge protection). Secondly, the segmentation into three separate pieces has the advantage that the pieces can be handled easier, in particular if the mounting of the protective shield <NUM> takes place on site without dismounting the rotor blade. Such a mounting is known as a retro-fit of the rotor blade or the entire wind turbine.

<FIG> shows a second embodiment of the invention. Again, a cross-sectional view of a part of the leading edge section <NUM> with the leading edge <NUM> and a part of the suction side <NUM> and the pressure side <NUM> of the rotor blade is illustrated. Again, a heating mat <NUM> is arranged upon the blade shell <NUM>. The heating mat <NUM>, as it is electrically conductive and thus, prone to lightning strikes, is in this embodiment fully covered by one single piece, namely, a curved unit <NUM>. The curved unit <NUM> is not only extending over the leading edge section <NUM> but also extending substantially on the pressure side <NUM> and the suction side <NUM>, namely extending over the entire extension of the heating mat <NUM>.

This has the advantage that no joints need to be connected. However, the challenge is that the piece can be become relatively large, depending on the size of the rotor blade and the size of the heating mat at this section of the rotor blade. Also note, that in general the heating mat and, in particular the protective shield, can well be segmented into individual segments, each segment comprising a length of, for example, one to ten meter.

Finally, <FIG> shows a third concrete embodiment of the invention. This third embodiment resembles the second embodiment but it has additionally a further protective shield <NUM> which covers the leading section <NUM> of the rotor blade. This has the advantage of further protection again electrical conductivity, i.e. against lightning strikes and also against erosion. For example, the further protective shield <NUM> could be designed similar to conventional leading edge protection shells (soft shells or hard shells).

Claim 1:
Rotor blade (<NUM>) of a wind turbine comprising a leading edge section (<NUM>) with a leading edge (<NUM>) and a trailing edge section (<NUM>) with a trailing edge (<NUM>), wherein the leading edge (<NUM>) and the trailing edge (<NUM>) divide the surface of the rotor blade (<NUM>) into a suction side (<NUM>) and a pressure side (<NUM>), wherein the rotor blade (<NUM>) further comprises a blade shell (<NUM>) for defining the outer shape of the rotor blade (<NUM>), and a heating mat (<NUM>) for anti-icing and/or deicing purposes which is arranged upon the blade shell (<NUM>), wherein
in the outboard region (<NUM>) of the rotor blade (<NUM>), the heating mat (<NUM>) is substantially or completely covered by a protective shield (<NUM>) made of an electrically non-conductive polymer material,
wherein the protective shield (<NUM>) comprises a curved unit (<NUM>) which covers at least partially the leading edge (<NUM>) of the rotor blade (<NUM>), and
wherein the protective shield (<NUM>) further comprises
- a first panel (<NUM>) which is substantially flat and arranged at the suction side (<NUM>) of the rotor blade (<NUM>) adjacent to a first rim of (<NUM>) the curved unit (<NUM>), and
- a second panel (<NUM>) which is substantially flat and arranged at the pressure side (<NUM>) of the rotor blade (<NUM>) adjacent to a second rim (<NUM>) of the curved unit (<NUM>),
wherein the curved unit (<NUM>), the first panel (<NUM>) and the second panel (<NUM>) are configured as separate pieces, and
wherein the rotor blade (<NUM>) comprises a further protective shield (<NUM>), wherein the further protective shield (<NUM>) is arranged on top of at least a part of the protective shield (<NUM>).