Patent Publication Number: US-2012027594-A1

Title: Arrangement for lightning protection

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority of European Patent Office application No. 10171592.8 EP filed Aug. 2, 2010, which is incorporated by reference herein in its entirety. 
     FIELD OF INVENTION 
     The invention relates to an arrangement for a lightning protection of a wind turbine blade. 
     BACKGROUND OF INVENTION 
     Document U.S. Pat. No. 7,540,716 B2 describes a rotor blade, which is shaped in a specific way to reduce sound emissions. The shape of the tip end of the blade is curved or angled in the direction of the pressure side of the blade. For this purpose a so called “edge arc”-component is used. The component is arranged at the tip end of the blade. The shaped tip might comprise metal and thus might be used as lightning conductor, too. 
     The configuration described above is expensive, if the tip end is made of metal instead of glass-fiber, which is commonly used for wind turbine blades. 
     Even when the tip end is designed to act as lightning conductor the metal-made blade-extension might not prevent other parts of the blade to be hit by lightning strikes. 
     SUMMARY OF INVENTION 
     It is therefore the aim of the invention to provide an improved arrangement for a lightning protection of a wind turbine blade. 
     This aim is achieved by the features of the independent claim. Preferred configurations of the invention are object of the dependent claims. 
     According to the invention the blade of the wind turbine is extended by a shaped winglet. The blade contains a lightning receptor, which is arranged at the tip end region of the blade. The winglet contains an additional lightning receptor. 
     Preferably the winglet is arranged at or even close to the tip end region of the blade. 
     Preferably the winglet is shaped in a way that a lift/drag-ratio of the blade is optimized. Due to the winglet the turning blade show less resistance in view to its turning moment thus the efficiency of the wind turbine is increased. 
     According to the invention a lightning receptor or a number of lightning receptors is/are placed at the tip end region of the blade. This region is the most relevant part of the blade in view to lighting strikes. 
     According to the invention an additional lightning receptor or a number of additional lightning receptors is/are arranged asides the winglet, as the winglet affects the tip end region of the blade too. 
     Preferably the lightning receptor is placed at the winglet at a specific region where so called “negative pressure-vortexes” are generated. 
     “Negative pressure-vortexes” are vortexes which are generated asides the suction side of the winglet or blade for example. 
     Preferably the position of the lightning receptors of the blade and the position of the lightning receptors of the winglet are jointly optimized. 
     For example the lightning receptors of a first blade, which is designed for a use without a winglet, are arranged at the same position as the lightning receptors of a second blade, which is designed for a use with a winglet. 
     Thus already mounted blades can be retrofitted by winglets if this is issued by the specific situation of the wind turbine site. 
     The lightning receptors ensure that the lightning current, being issued by the lightning strike, gets a hold without damaging the surround part of the blade. 
     Preferably the lightning receptors are attached to a lightning conductor, which leads the lightning current to the ground. 
     The positions of the lightning receptors, especially the position of the lightning receptors of the winglet part, are optimized by help of well-known computer-simulations. 
     These simulations are based on pressure conditions, which results along the blade due to the shaped winglet and due to the shaped blade itself. 
     It has to be noticed that for this invention each lightning receptor may be placed preferably into an opening of the winglet/blade. 
     The opening may be introduced into the blade/winglet after the manufacturing process of the blade. Thus the winglet/blade may be retrofitted with the receptor if needed within the appropriate opening. 
     The opening itself may also be arranged or provided asides the blade/winglet during the manufacturing process. 
     It is also possible that each lightning receptor may be cast into the winglet/blade during the manufacturing of the blade/winglet. Thus the receptor is an integrated part of the wind turbine after the manufacturing of the blade/winglet. 
     Even combinations of these two arrangements are within the scope of the invention. 
     Additionally it has to be noticed that for this invention the lightning receptor penetrates the blade/winglet. Thus the lightning receptor of the blade/winglet contains a first and a second surface, while the first surface of the lightning receptor is arranged at a first surface of the blade or winglet and while the second surface of the lightning receptor is arranged at a second surface of the blade or winglet. 
     Both surfaces of the lightning receptor are designed and arranged in a way, that each surface is able to withstand an incoming lightning strike and to pass on the resulting lightning energy towards an electric ground of the wind turbine. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is described in more detail now by help of some figures. 
       The figures show preferred configurations and are not intended to limit the scope of the invention. 
         FIG. 1  shows a lightning protection according to the invention for a first winglet-type, 
         FIG. 2  shows a lightning protection according to the invention for a second winglet-type, 
         FIG. 3  shows a lightning protection according to the invention for a third winglet-type, 
         FIG. 4  shows a cross section of a tip end of a blade, which is connected with a one-sided winglet, while the winglet is oriented in an upstream direction of the blade, 
         FIG. 5  shows a cross section of a tip end of a blade, which is connected with a two-sided winglet, while the winglet is asymmetric and is oriented in an upstream direction of the blade, 
         FIG. 6  shows a cross section of a tip end of a blade, which is connected with a one-sided winglet, while the winglet is oriented in an downstream direction of the blade, 
         FIG. 7  shows a cross section of a tip end of a blade, which is connected with a two-sided winglet, while the winglet is symmetric and is oriented in an upstream direction of the blade, and 
         FIG. 8  shows a cross section of a tip end of a blade, which is connected with a two-sided winglet, while the winglet is asymmetric and is oriented in an downstream direction of the blade. 
     
    
    
     DETAILED DESCRIPTION OF INVENTION 
     For the figures the phrase “upstream” or “upwind” refers to the direction of the incoming wind. Thus a pointer of this direction would point against the incoming wind. 
     For the figures the phrase “downstream” or “downwind” refers to the direction of the wind, passing the blade. Thus a pointer of this direction would point along and in line with the wind passing the blade. 
       FIG. 1  shows a lightning protection according to the invention for a first winglet-type. 
     The blade BL turns around the hub HB of the wind turbine WT. 
     The blade BL is extended by a winglet WL 1 , which is arranged close to the tip end region TER of the blade BL. 
     The winglet WL 1  is shaped as a one-sided winglet. 
     The winglet WL 1  is oriented into the incoming wind-direction of the wind turbine WT, thus the winglet WL 1  is called “one sided upstream winglet”. 
     A lightning receptor LR 11  is arranged close to the tip end region TER of the blade BL. 
     An additional lightning receptor LR 12  is arranged asides the winglet WL 1 . 
     The position of this lightning receptor LR 12  might be even close to the tip end region TER of the winglet WL 1 . 
     The lightning receptors LR 11  and LR 12  are connected with a lightning conductor, which leads the lightning current to the ground. 
       FIG. 2  shows a lightning protection according to the invention for a second winglet-type. 
     The blade BL turns around the hub HB of the wind turbine WT. 
     The blade BL is extended by a winglet WL 2 , which is arranged close to the tip end region TER of the blade BL. 
     The winglet WL 2  is shaped as a so called “two-sided winglet”. The winglet WL 2  is thus oriented into two directions: into the upstream (that is the direction of the incoming wind) and into the downstream (that is the direction of the wind after it passed the blade). 
     The winglet WL 2  might be shaped asymmetric or symmetric. 
       FIG. 2  shows the symmetric version. 
     A lightning receptor LR 21  is arranged close to the tip end region TER of the blade BL. 
     Two additional lightning receptors LR 22  and LR 23  are arranged asides the winglet WL 2 . 
     The position of the lightning receptors LR 22  and LR 23  might be even close to the tip end regions TER 1  and TER 2  of the winglet WL 2 . 
     The lightning receptors LR 21 , LR 22  and LR 23  are connected with a lightning conductor, which leads the lightning current to the ground. 
       FIG. 3  shows a lightning protection according to the invention for a third winglet-type. 
     The blade BL turns around the hub HB of the wind turbine WT. 
     The blade BL is extended by a winglet WL 3 , which is arranged close to the tip end region TER of the blade BL. 
     The winglet WL 3  is shaped as a one-sided winglet. 
     The winglet WL 3  is oriented into the downwind-direction of the wind turbine WT, thus the winglet WL 3  is called “one sided downstream winglet”. 
     A lightning receptor LR 31  is arranged close to the tip end region TER of the blade BL. 
     An additional lightning receptor LR 32  is arranged asides the winglet WL 3 . 
     The position of this lightning receptor LR 32  might be even close to the tip end region TER of the winglet WL 3 . 
     The lightning receptors LR 31  and LR 32  are connected with a lightning conductor, which leads the lightning current to the ground. 
       FIG. 4  shows a cross section CS of a tip end of a blade BL, which is connected with a one-sided winglet WL 4 . 
     The winglet WL 4  is oriented in an upstream direction of the blade BL, thus for  FIG. 4  reference is made to FIG  1 . 
     Preferably the winglet WL 4  shows one dedicated lightning receptor LR. 
       FIG. 5  shows a cross section CS of a tip end of a blade BL, which is connected with a two-sided winglet WL 5 . 
     The winglet WL 5  is asymmetric and is oriented due to its shape more into the upstream direction than into the downstream direction of the blade BL. 
     Thus for  FIG. 5  reference can be made to  FIG. 2  correspondingly. 
     Preferably each portion (side) of the winglet WL 5  show one dedicated lightning receptor LR. Thus a number of two lightning receptors LR are used and are arranged asides the winglet WL 5 . 
       FIG. 6  shows a cross section CS of a tip end of a blade BL, which is connected with a one-sided winglet WL 6 . 
     The winglet WL 6  is oriented in a downstream direction of the blade BL. 
     Thus for  FIG. 6  reference is made to  FIG. 3 . 
     Preferably the winglet WL 6  shows one dedicated lightning receptor LR. 
       FIG. 7  shows a cross section CS of a tip end of a blade, which is connected with a two-sided winglet WL 7 . 
     The winglet WL 7  is symmetric and is oriented due to its shape into the upstream direction as well as into the downstream direction of the blade BL. 
     Thus for  FIG. 7  reference is made to  FIG. 2 . 
     Preferably each portion (side) of the winglet WL 7  show one dedicated lightning receptor LR. Thus a number of two lightning receptors are used and are arranged asides the winglet WL 7 . 
       FIG. 8  shows a cross section CS of a tip end of a blade BL, which is connected with a two-sided winglet WL 8 . 
     The winglet WL 8  is asymmetric and is oriented due to its shape more into a downstream direction of the blade BL than into the upstream direction of the blade BL. 
     Thus for  FIG. 8  reference can be made to  FIG. 2  correspondingly. 
     Preferably each portion (side) of the winglet WL 8  show one dedicated lightning receptor LR. Thus a number of two lightning receptors are used and are arranged asides the winglet WL 8 .