Abstract:
The present invention relates to an arrangement for directing a lightning current within a wind turbine. The arrangement includes a first component, a second component, a contact element and a guideway. One of the two components is arranged moveably in relation to the other. The contact element is arranged in a way that the first component is electrically connected to the second component in order to direct a lightning current within the wind turbine. The contact element is guided moveably by the guideway. According to the invention, the guideway is at least partly integrated in the first component.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority of European Patent Office application No. 10157977.9 EP filed Mar. 26, 2010, which is incorporated by reference herein in its entirety. 
       FIELD OF INVENTION 
       [0002]    The present invention relates to an arrangement for directing a lightning current within a wind turbine and to a wind turbine comprising this arrangement. 
       BACKGROUND OF INVENTION 
       [0003]    Wind turbines are located in areas that are unprotected from meteorological conditions in order to tap the full potential of the wind. 
         [0004]    Due to this siting in exposed areas and due to the shape of wind turbines, there is a high probability of lightning strokes which may cause severe damage. For this reason, wind turbines are equipped with lightning protection systems for protecting their components against lightning impacts. 
         [0005]    As shown in the simplified schematical figure  FIG. 3 , wind turbines, generally, comprise a tower  23   d,  a nacelle and a rotor system  83 . 
         [0006]    The bed frame  103  of the nacelle is connected to the tower  23   d  via a yaw system for enabling movement of the nacelle on top of the tower  23   d.  The bed frame  103  further supports the drive train of the wind turbine which is installed inside of the nacelle. 
         [0007]    The rotor system  83 , comprising hub and rotor blades, is connected to the drive train. The drive train itself comprises at least a shaft  93 , a generator  113  and a braking system  13   c,    23   c  and may further comprise a gearbox  123 . The braking system comprises a brake calliper  13   c  and a brake disk  23   c.    
         [0008]    In case of a lightning stroke, significant parts of the lightning current may pass through or near all wind turbine components. Thus, the lightning current has to be directed over an electrically conducting path to ground in such a way that damages to the components are avoided. 
         [0009]    Some of the components on this conducting path have to be electrically coupled although they are moveable in relation to each other. 
         [0010]    Those interconnections are, beside the hub/nacelle interconnection, also the yaw clamp/tower interconnection  13   d,   23   d  on top of the tower and brake calliper/brake disk interconnections  13   c,   23   c,  wherein the brake calliper/brake disk interconnections  13   c,   23   c  may be located on the generator shaft or elsewhere in the wind turbine. 
         [0011]    In this context,  FIG. 4   a  and  FIG. 4   b  show a prior art realisation of a yaw system comprising a lightning current protection unit for transferring a lightning current from the nacelle  14  to the tower  24  of the wind turbine. 
         [0012]      FIG. 4   a  shows a cross-sectional view and  FIG. 4   b  shows a topview of this realisation. 
         [0013]    The realisation comprises basically a block-shaped conductive brush  44 , a spring  54  for pressing the brush  44  onto the yaw ring, a wire  144  for connecting electrically the brush  44  to the nacelle  14  and a bracket-shaped lightning brush casing  134  in which the brush  44  and the spring  54  are located. 
         [0014]    The parts of the unit are assembled in advance, and then, the entire assembly is mounted with bolts  154  between the yaw clamps  14   a,    14   b.    
       SUMMARY OF INVENTION 
       [0015]    A drawback of this realisation is the fact that a number of different parts has to be assembled in a confined space. 
         [0016]    Another drawback of this realisation is that free space near the components is required to mount the assembly. 
         [0017]    In addition, maintenance of the unit is difficult because the casing has to be detached or opened for exchanging parts or performing other maintenance measures. 
         [0018]    Moreover, this known arrangement does not function in an efficient way because the lightning current is not conducted the direct way. 
         [0019]    Concerning the lightning protection of braking systems of wind turbines, it is known to mount a number of brushes on a static part, which is a kind of brush holder. The brushes are in electrical contact with the static part and form an electrical connection to the brake disk. 
         [0020]    Disadvantageously, this known arrangement does not function in an efficient way because the lightning current is not conducted the direct way. 
         [0021]    Moreover, this known arrangement is complex because a number of parts have to be mounted. 
         [0022]    In addition, a certain space has to be provided for mounting these parts. 
         [0023]    Therefore, it is the aim of the present invention to provide an improved arrangement for directing a lightning current within a wind turbine which is space-saving as well as more efficient and less complex than lightning protection arrangements known in the art. 
         [0024]    The aim of the invention is achieved by the features of the independent claims. 
         [0025]    Further aspects of the invention are subject of the dependent claims. 
         [0026]    The present invention relates to an arrangement for directing a lightning current within a wind turbine. The arrangement comprises a first component, a second component, a contact element and a guideway. One of the two components is arranged moveably in relation to the other. The contact element is arranged in a way that the first component is electrically connected to the second component in order to direct a lightning current within the wind turbine. Moreover, the contact element is guided moveably by the guideway. According to the invention, the guideway is at least partly integrated in the first component. 
         [0027]    The inventive arrangement has the advantage that it consists of fewer parts and less complex parts compared to known lightning protection arrangements. Thus, the manufacturing and storage costs are reduced. 
         [0028]    Moreover, the arrangement as a whole is less complex and can be mounted more easily. 
         [0029]    Maintenance of the inventive arrangement is facilitated because the parts can be fitted and replaced in a simple manner. 
         [0030]    Even the adjustment of the resilient connection is easily possible. 
         [0031]    The inventive arrangement functions efficiently and the risk of failure is reduced because a lightning current is conducted over the shortest path between the components. 
         [0032]    In addition, it is no longer necessary to mount a lightning protection arrangement externally of the components. Thus, space is cleared which can be used otherwise, for instance for strenghtening structurally the yaw clamps. 
         [0033]    The invention will be described by way of example in more detail in the following. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0034]    The drawings  FIG. 1  and  FIG. 2  show preferred configurations and do not limit the scope of the invention. 
           [0035]      FIG. 1  shows a cross-sectional view of an arrangement according to an embodiment of the invention, 
           [0036]      FIG. 2  shows a cross-sectional view of an arrangement according to another embodiment of the invention, 
           [0037]      FIG. 3  shows a schematic represention of the basic components of a wind turbine as described above, and 
           [0038]      FIG. 4   a  and  FIG. 4   b  show the prior art as described above. 
       
    
    
     DETAILED DESCRIPTION OF INVENTION 
       [0039]      FIG. 1  shows a cross-sectional view of a part of a wind turbine comprising a yaw clamp  11  and a tower  21 . 
         [0040]    The yaw clamp  11  forms part of a yaw system which is mounted between the nacelle and the tower  21 . The nacelle and the yaw clamp  11  are able to move on top of the tower  21 . 
         [0041]    In order to achieve a lightning protection effect, a contact element  41  is installed between the yaw clamp  11  and the tower  21 . 
         [0042]    The contact element  41  is mounted at least partly integrated in the yaw clamp  11  in radial direction. For this reason, a guideway  31  is provided in the yaw clamp  11 . This guideway  31  is realised in form of a recess, for instance a radial hole. Alternatively, the guideway  31  may be constructed as a channel or as a groove. 
         [0043]    A first end of this contact element  41  is pressed onto the tower  21  to form a sliding contact. The contact element  41  is either resilient by itself or mounted resiliently. The first end of the contact element  41  may be pressed directly onto the surface of the tower  21  or onto a sliding element attached to the tower  21 . A second end of the contact element  41  is connected to the yaw clamp  11 . 
         [0044]    According to an embodiment of the invention the contact element  41  comprises a conductive rod. The conductive rod  41  is made of a material which is able to conduct and support a lightning current within a wind turbine like carbon, graphite, metal or a composite material comprising one or more of these materials. 
         [0045]    In a preferred embodiment of the invention, the rod is made of a graphite-copper composite material. Advantages of this material are a good conductivity and a low wear rate. An alternative material that could be used instead is a silver-graphite composite material. This material has an even better conductivity than a copper-graphite composite. 
         [0046]    The conductive rod  41  comprises a first end and a second end. According to another embodiment of the invention, the required pressing force of the conductive rod  41  is achieved by mounting an electrically conducting spring  51  tensely between the second end of the rod  41  and the yaw clamp  11 . Thus, a constant pressing force of the rod  41  is ensured in spite of wearing of the rod  41  over the time and unevennesses of the sliding surface of the tower  21  are compensated. Of course, different types of springs can be used. 
         [0047]    The rod  41  is connected via the spring  51  to the yaw clamp  11  in a firm but detachable manner. 
         [0048]    According to a further embodiment of the invention, this firm but detachable connection is achieved by a screw connection  61  at the outer end of the guideway  31 . 
         [0049]    In yet a further embodiment of the invention, this connection is realised by mounting a grub screw  61  in the guideway  31  which engages with a threading  71  provided at the outer end of the guideway  31 . This allows for easily changing the rod  41  or the spring  51  and it also allows for adjusting the spring force in a simple way by turning the grub screw  61 . Thus, maintenance of the arrangement is facilitated. 
         [0050]      FIG. 2  shows a cross-sectional view of a part of a braking system of the wind turbine comprising a brake disc  22  which is arranged rotatably within a double acting brake calliper  12 . The brake calliper  12  comprises a first calliper half  12   a  and a second calliper half  12   b.    
         [0051]    In order to achieve a lightning protection effect, a contact element  42  is arranged between the brake calliper  12  and the brake disc  22 . 
         [0052]    The contact element  42  is mounted at least partly integrated in the brake calliper  12 . For this reason, a guideway  32  is provided in the brake calliper  12 . This guideway  32  is realised in form of a recess, for instance a radial hole. Alternatively, the guideway  32  may be constructed as a channel or as a groove. 
         [0053]    In an embodiment of the invention, shown in  FIG. 2 , the guideway  32  is provided near the calliper set divide  12   a   12   b.    
         [0054]    As aforementioned, the brake calliper  12  comprises a first calliper half  12   a  and a second calliper half  12   b.  As shown in  FIG. 2 , the guideway  32  is arranged in the first calliper half  12   a.    
         [0055]    A first end of the contact element  42  is pressed onto the brake disk  22  to faun a sliding contact. The contact element  42  is either resilient by itself or mounted resiliently. The contact element  42  may be pressed directly onto the surface of the brake disk  22  or onto a sliding element attached to this brake disk  22 . 
         [0056]    The second end of the contact element  42  is connected to the first calliper half  12   a.    
         [0057]    According to an embodiment of the invention, the contact element  42  comprises a conductive rod. The conductive rod  42  is made of a material which is able to conduct and support a lightning current within a wind turbine like carbon, graphite, metal or a composite material comprising one or more of these materials. 
         [0058]    In a preferred embodiment, the rod is made of a graphite-copper composite material. Advantages of this material are a good conductivity and a low wear rate. An alternative material that could be used instead is a silver-graphite composite material. This material has an even better conductivity than a copper-graphite composite. 
         [0059]    The conductive rod  42  comprises a first end and a second end. According to an embodiment of the invention, the required pressing force of the rod  42  is achieved by mounting a conductive spring  52  tensely between the second end of the rod  42  and the first calliper half  12   a.  Thus, a constant pressing force of the rod  42  is ensured in spite of wearing of the rod  42  over the time, and unevennesses of the sliding surface of the brake disk  22  are compensated. Of course, different types of springs  52  can be used. 
         [0060]    The rod is connected via the spring  52  to the first calliper half  12   a  in a firm but detachable manner. According to an embodiment of the invention, this firm but detachable connection is achieved by a screw connection  62  at the outer end of the guideway  32 . 
         [0061]    In a preferred embodiment of the invention, this connection is realised by mounting a grub screw  62  in the guideway  32  which engages with a threading  72  provided at the outer end of the guideway  32 . This allows for easily changing the rod  42  or the spring  52 . It also allows for adjusting the spring force in a simple way by turning the grub screw  62 . Thus, maintenance of the arrangement is facilitated. 
         [0062]    In another embodiment of the invention, additional guideways  32  and contact elements  42  may be arranged in the brake calliper  12  in the first  12   a  and/or in the second half  12   b.    
         [0063]    In yet another embodiment of the invention, the above described braking system is located on the shaft near the generator and is used for securing the shaft, for instance for maintenance purposes. As a matter of course, the braking system may also be installed elsewhere in the wind turbine. 
         [0064]    The wind turbine can comprise an arrangement according to the invention either in a calliper brake or in one or more yaw clamps; and it can, of course, comprise such an arrangement in one or more calliper brakes as well as in at least one yaw clamp. 
         [0065]    It becomes clear to a person skilled in the art that the arrangement, according to the invention, can also be used to conduct a lightning current between other electrical conductive components in a wind turbine, in particular for directing a lightning current from a hub to a nacelle.