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BACKGROUND 
       [0001]    Technical Field 
         [0002]    The present invention relates to a wind turbine tower and to a method for erecting a wind turbine tower. 
         [0003]    Description of the Related Art 
         [0004]    For towers of wind turbines, the construction of a durably stable and even foundation is of great importance. The foundation of a wind turbine is constructed by first creating, in a foundation bed, what is termed a blinding layer, that is to say a layer of cement or concrete which is as planar and as horizontal as possible. Then, anchor rods are fixed to the foundation segments, i.e., the lower segments of the tower consisting of multiple segments, by means of which anchor rods the foundation segment is positioned on the blinding layer. In order to even out unevennesses in the blinding layer and to orient the foundation segment as horizontally as possible, the anchor rods are screwed into the underside of the foundation segment to varying extents. To that end, the anchor rods have a threaded rod. 
         [0005]    DE 102 26 996 A1 describes a method for erecting a foundation of a wind turbine tower consisting of multiple segments. To that end, a foundation bed is excavated and a stable, essentially even and horizontal blinding layer is created. A foundation segment of the wind turbine is placed on the blinding layer, wherein at least three height-adjustable anchor rods are attached, by means of a supporting foot attached to the end of the anchor rod, to the foundation segments in a distributed manner such that only the anchor rods are established at predefined supporting points on the blinding layer. Then, a reinforcement is produced on the blinding layer and the remaining foundation is cast up to above the lower rim of the foundation segment using a foundation material such as concrete. 
         [0006]    In the German patent application forming the basis for priority, the German Patent and Trademarks Office has searched the following documents: DE 102 26 996 A1, DE 20 2010 001 337 U1, US 2013/0129525 A1 and WO 2012/168467 A2. 
       BRIEF SUMMARY 
       [0007]    The present invention is directed to a wind turbine tower and a method for erecting a wind turbine tower, which permits simple and exact orientation and/or levelling of the lower tower segment. 
         [0008]    Thus, provided is a wind turbine tower with a plurality of tower segments which are placed one on top of another so as to form the tower. A lower tower segment has a lower end face and in the lower region of the tower segment or in the region of the lower end face a plurality of cavities and through bores between the lower end face of the lower tower segment and a bottom of the cavity. The cavities are configured for receiving a levelling unit for levelling the lower tower segment. The cavities are preferably provided on the inside of the lower tower segment and represent an effective possibility for receiving levelling units. 
         [0009]    According to one aspect, a plurality of levelling units is placed in the cavities. Each of the levelling units has a supporting foot and/or a rod which can be inserted through the through bore into the cavity. The levelling unit is configured to set the length of the rod or the separation between the lower end of the supporting foot and the bottom of the cavity for levelling the lower tower segment. 
         [0010]    According to a further aspect, the levelling unit has a hydraulic unit for setting the length of the rod for levelling the lower tower segment. 
         [0011]    It is thus possible for the lower tower segment to be levelled in particular automatically and very precisely by means of the hydraulic unit. 
         [0012]    According to a further aspect, the levelling unit has a supporting frame with two sidewalls, a bottom and a cover as well as an intermediate bottom. The bottom and the intermediate bottom each have a cutout, such that the supporting frame can be inserted into the cavity if the rod and/or the supporting foot has been inserted through the through hole into the cavity. 
         [0013]    According to a further aspect, a nut is screwed onto the rod. For arresting the levelling of the lower tower segment, the nut is screwed onto the rod such that it bears beneath the intermediate bottom. 
         [0014]    According to a further aspect, the supporting foot and the (threaded) rod can be configured as one part or in two parts. 
         [0015]    The invention also relates to a method for erecting a wind turbine tower which has a lower tower segment that has a plurality of cavities in the lower region. The lower tower segment further has a plurality of through bores between a lower end face of the lower tower segment and a bottom of the cavity. One end of the supporting foot and/or of a rod is inserted through the through bore. A levelling unit is placed into the cavity and the lower tower segment is oriented and/or levelled using the levelling units by setting the separation between the lower end of the supporting foot and the bottom of the cavity or the cavity itself. 
         [0016]    The invention relates to the concept, of providing, in the lower region of the lowest tower segment of the tower of the wind turbine and on the inside of the tower, a plurality of cavities which are open inwards and which each have a through bore towards the underside of the lowest tower segment. A levelling unit is inserted into this cavity, wherein a (threaded) rod with a foot is pushed through the through bore from below, such that the tower segment rests on the feet. 
         [0017]    The height or the length of the (levelling) foot can optionally be set hydraulically. If, at this point, a plurality of cavities and levelling units is provided along the circumference of the lower tower segment, it is then possible, by controlling the hydraulics, to set the height of the levelling feet of the respective levelling units such that the lowest tower segment is levelled to horizontal. In order to check the horizontal levelling, optical measuring units such as lasers or the like can be used. 
         [0018]    The levelling unit has a (levelling) foot with a (threaded) rod which is provided through the through bore between the lower end face of the lowest tower segment and the bottom of the cavity. A nut is provided at the upper end of the threaded rod. Then, a levelling frame (e.g., in the form of a supporting frame) can be inserted into the cavity. The levelling frame has a bottom and an intermediate bottom, each with a cutout, such that the levelling frame can be introduced into the cavity after the threaded rod has been introduced through the through bore. The intermediate bottom of the levelling frame is then located above the nut. The frame can then be screwed upwards by actuating the nut, such that it bears against the underside of the intermediate bottom. In this case, the load exerted by the lower tower segment on the foundation, can be transmitted to the levelling foot via the intermediate bottom, the nut and the threaded rod. 
         [0019]    A plurality of cavities and/or recesses is provided on the inside and in the lower region of the lower tower segment. A through bore is provided between the cavity and the lower end face of the lower tower segment. The cavity and the through bore can subsequently be bored or milled into the lower tower segment. Alternatively, during production of the tower segment, which is typically a concrete tower segment, both the cavities and the through holes can be left free. 
         [0020]    Further configurations of the invention form the subject matter of the subclaims. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0021]    Advantages and exemplary embodiments of the invention are explained in more detail below with reference to the drawing. 
           [0022]      FIG. 1  shows a schematic representation of a wind turbine according to the invention, 
           [0023]      FIG. 2A  shows a schematic representation of a lower tower segment of a wind turbine tower according to a first exemplary embodiment, 
           [0024]      FIG. 2B  shows a schematic section view of a lower tower segment according to the first exemplary embodiment, 
           [0025]      FIG. 3  shows a schematic representation of a levelling unit for levelling a lower tower segment of a wind turbine tower according to a second exemplary embodiment, 
           [0026]      FIG. 4  shows a schematic plan view of the levelling unit of  FIG. 3 , 
           [0027]      FIG. 5  shows a schematic side view of the levelling unit of  FIG. 3 , 
           [0028]      FIG. 6  shows a schematic representation of a threaded rod of the levelling unit according to the second exemplary embodiment, 
           [0029]      FIG. 7  shows a view of a nut of a levelling unit according to the second exemplary embodiment, and 
           [0030]      FIGS. 8A-8B  respectively show a schematic section view A-B and A-A and B-B of the nut of  FIG. 7 . 
       
    
    
     DETAILED DESCRIPTION 
       [0031]      FIG. 1  shows a schematic representation of a wind turbine according to the invention. The wind energy  100  has a tower  102  and a nacelle  104  on the tower  102 . The tower  102  has a plurality of tower segments  102   a  which are placed one after another on a foundation  10  in order to form the tower  102 . On the nacelle  104  there is provided an aerodynamic rotor  106  with three rotor blades  200  and a spinner  110 . When the wind turbine is in operation, the aerodynamic rotor  106  is set in rotation by the wind and thus also turns a rotor of a generator, which is coupled either directly or indirectly to the aerodynamic rotor  106 . The electric generator is arranged in the nacelle  104  and generates electrical energy. The pitch angles of the rotor blades  200  can be changed by pitch motors at the rotor blade roots of the respective rotor blades  200 . 
         [0032]      FIG. 2A  shows a schematic representation of a detail of a lower tower segment of a wind turbine tower according to a first exemplary embodiment. A plurality of cavities  102   b  is provided in the lower tower segment  102   a.  The lower tower segment  102   a  has a (lower) end face  102   d.  In the lower tower segment  102   a  there is provided a plurality of through holes or through bores  102   c  which extend between the lower end face  102   d  and a bottom  102   e  ( FIG. 2B ) of the cavity  102   b.  A levelling unit  300  is provided in the cavity  102   b.  The levelling unit  300  has a supporting frame  310 , an intermediate bottom  311 , a hydraulic unit  320 , a threaded rod  330  and a supporting foot  350 . A levelling foot  360  is provided at the lower end of the supporting foot  350 . The supporting foot  350  and the levelling foot  360  can be configured as one component. The threaded rod  330  and the supporting foot  350  can be configured as one component (with the threaded rod above and the supporting foot below) or as separate components. A nut  340  is screwed on over the upper end of the threaded rod  330 . The supporting foot  350  with the levelling foot  360  is inserted into the through bore  102   c.  Then, the threaded rod  330  can be secured to (e.g., screwed onto) the supporting foot and the nut  340  can be screwed onto the threaded rod  330 . After this, a supporting frame  310  of the levelling unit  300  is introduced into the cavity  102   b.  To that end, in reference also to  FIG. 3 , the bottom  310   c  and the intermediate bottom  311  each have a cutout  310   f,    311   a,  ( FIG. 5 ) such that the frame  310  is pushed into the cavity  102   b  and the supporting foot  350  is accommodated in the two cutouts  310   f,    311   a.  The levelling unit  300  also has a hydraulic unit  320  with a hydraulic connection  321 . A hydraulic hose  321  can be connected to the hydraulic connection  321 , such that the hydraulic unit  320  can be activated. When the hydraulic unit  320  is activated, it can then press on the upper end of the threaded rod  330  and can thus raise or lower the lower tower segment  102   a.    
         [0033]      FIG. 2B  shows a schematic section view of a lower tower segment according to the first exemplary embodiment. The lower tower segment  102   a  has a lower end face  102   d  and a plurality of cavities  102   b.  Preferably, the cavities  102   b  are configured such that they are open towards the inside of the tower segment. The cavities  102   b  have a bottom  102   e.  Between the bottom  102   e  of the cavity  102   b  and the end face  102   d  of the lower tower segment there is provided a through bore  102   c.  A supporting foot  350  can be inserted (from below) into this through bore  102   c.  The supporting foot  350  can have a levelling foot  360 . Optionally, the supporting foot  350  and the levelling foot  360  can be configured as one component. After the supporting feet  350  have been introduced into the through bores  102   c,  a lower tower segment can be placed on a foundation  10  of the wind turbine. Optionally, a cutout  11  can be provided on the upper side of the foundation  10 . The supporting feet  350  and thus the lower tower segment or the lower end face  102   d  of the lower tower segment can be placed in the region of the cutout  11 . After the lower tower segment  102   a  has been oriented by means of the levelling unit  300 , the cutout  11  can be filled with Pagel mass or with a curable casting compound. This is advantageous because thus the weight of the lower tower segment and of the further tower segments and finally of the nacelle and of the rotor then rests not only on the supporting feet  350 , but is distributed by the Pagel mass  20 . 
         [0034]      FIG. 3  shows a schematic representation of the levelling unit according to a second exemplary embodiment. The levelling unit  300  has a (supporting) frame  310  with two sidewalls  310   a,    310   d,  a cover  310   b,  a bottom  310   c  and an intermediate bottom  311 . The bottom  310   c  and the intermediate bottom  311  can each have a longitudinal cutout  310   f,    311   a.  The levelling unit  300  further has a threaded rod  330 , a supporting foot  350  and a levelling foot  360  at one end of the supporting foot  350 . The nut  340  is screwed on over the other end of the threaded rod  330 . In the installed state, the second end of the threaded rod  330  projects beyond the intermediate bottom  310 . The supporting foot and the threaded rod  330  can be configured as separate components or as one component. 
         [0035]      FIG. 4  shows a schematic representation of a schematic cross section of a levelling unit according to  FIG. 3 . The levelling unit has a supporting frame with two sidewalls  310   d,    310   a.  Further, the levelling unit has an intermediate bottom  311  and a bottom  310   c.  A cutout  312  is provided in the bottom  310   c.  The same is true in corresponding fashion for the intermediate bottom  311 . The cutout  312  serves for receiving the threaded rod  350 ,  330 . 
         [0036]    The levelling unit further has a threaded rod  330  and a nut  340 . 
         [0037]      FIG. 5  shows a perspective side view of a levelling unit according to the second exemplary embodiment. The levelling unit  300  has a supporting foot  350  with a (levelling) foot  360 . The levelling unit  300  further has a supporting frame  310  with a bottom  310   c,  a cover  310   b,  two sidewalls  310   a,    310   d  and an intermediate bottom  311 . The intermediate bottom  311  and the bottom  310   c  each have a cutout such that the threaded rod can be received in the cutout. 
         [0038]      FIG. 6  shows a schematic representation of a threaded rod  330 . 
         [0039]      FIG. 7  shows a schematic representation of the nut  340 . The nut  340  has a plurality of holes  341  and optionally an internal thread. 
         [0040]      FIGS. 8A and 8B  respectively show a section view, along A-A and B-B, of the nut of  FIG. 7 . The nut  340  has a plurality of holes  341  on its outer side.

Summary:
A wind turbine tower is provided with a plurality of tower segment which are placed one on top of the other in order to form the tower. A lower tower segment has a lower end face, and in the lower region of the lower tower segment, the lower tower segment has a plurality of recesses and through-bores between the lower end face of the lower tower segment and a base of the recesses. The recesses are designed to receive a leveling unit for leveling the lower tower segment. The recesses are preferably provided on the inner face of the lower tower segment and provide an effective possibility for receiving leveling units.