Abstract:
Some general aspects of the invention provide a foundation fixing unit ( 202, 204, 400 ) for fixing a tower ( 108 ) of a wind energy converter ( 100 ) onto a foundation ( 110 ). The unit comprises a fixation plate ( 202 ) fixable to the foundation ( 110 ), walls forming at least one tower fixation hole ( 300 ) in the intermediate plate ( 202 ) for passing a tower fixation bolt ( 220 ) through the fixation plate ( 202 ) in order to fix the tower ( 108 ) to the fixation plate ( 202 ), a tower fixation nut ( 400 ) arranged below the at least one tower fixation hole ( 300 ) for receiving a threaded portion of the tower fixation bolt ( 220 ) and a nut cage ( 204 ) holding the tower fixation nut ( 400 ), the nut cage ( 204 ) being attached to a bottom surface ( 222 ) of the fixation plate ( 202 ). Under further aspects, the invention provides a wind energy converter tower comprising the foundation fixing unit ( 202, 204, 400 ) and a method for fixing a wind energy converter tower onto a foundation.

Description:
BACKGROUND 
       [0001]    The present invention relates to a foundation fixing unit for fixing a tower of a wind energy converter onto a foundation, to a corresponding method for fixing a tower of a wind energy converter onto a foundation, and to a wind energy converter. 
         [0002]    Wind energy can be converted into useful forms, such as electricity, by a wind energy converter that generally includes a rotor, e.g. a low-speed propeller, coupled to a generator. Typically, wind energy converters include a tower comprising a tubular steel, concrete or mixed construction, which is fixed to an associated foundation, and, on the upper end of the tower, a rotary arrangement such as a nacelle, which bears the rotor and generator and is configured for rotation into the respective wind direction. 
         [0003]    For towers of wind energy converters it is common to use anchor bolt connections for the fixation of the tower at the foundation. For example, when casting a concrete foundation, bolts are partially embedded in the wet concrete as cast-in-place anchor bolts, a threaded end of each anchor bolt left protruding upwardly from a top surface of the foundation. After the concrete has hardened, the threaded ends are guided through corresponding fixing holes formed in a flange at a bottom end of the tower. Then, washers and nuts are attached to the threaded ends of the anchor bolts in order to rigidly connect the tower to the foundation. 
         [0004]    For towers subjected to high loads at the tower bottom, as in wind energy converters of high energy generating capacity, anchor bolt connections that provide the fixation of the tower to the foundation are subject to high fatigue loads, which may shorten the lifespan of the tower foundation, requiring the tower to be dismantled or placed on a new foundation at high cost. 
       SUMMARY 
       [0005]    One general aspect of the invention relates to a foundation fixing unit for fixing a tower of a wind energy converter onto a foundation. The unit comprises a fixation plate fixable to the foundation, walls forming at least one tower fixation hole in the fixation plate for passing a tower fixation bolt through the fixation plate in order to fix the tower to the fixation plate, a tower fixation nut arranged below the at least one tower fixation hole for receiving a threaded portion of the tower fixation bolt, and a nut cage holding the tower fixation nut, the nut cage being attached to a bottom surface of the fixation plate. 
         [0006]    Because the tower is fixable to the fixation plate, and the fixation plate is fixable to the foundation, the inventive tower fixation unit enables fixation of the tower onto the foundation via the fixation plate. Because the tower fixation bolt that effects the fixation of the tower is received in the tower fixation nut below the fixation plate, which is held inside the nut cage, the tower fixation bolt may be removed, inspected and/or replaced even after erection of the tower when the underside of the intermediate plate is no longer accessible, thus enabling safe operation and maintenance over a long time even under very high fatigue load conditions typically observed in high-power wind energy converters. 
         [0007]    Embodiments of this foundation fixing unit may include one or more of the following features. 
         [0008]    The fixation plate comprises walls forming a plurality of foundation fixing holes for fixing the fixation plate onto the foundation. This enables e.g. to guide a corresponding plurality of protruding threaded ends of anchor bolts that are partially embedded in the foundation through the foundation fixing holes, such that the fixation plate can be fixed with great rigidity on top of the foundation. The fixation plate is in this way enabled to function as an intermediate plate arranged between the tower and the foundation. 
         [0009]    For towers subjected to high loads at the tower bottom, as in wind energy converters of high energy generating capacity, it is desirable to distribute the load to avoid excessive pressure on the foundation. Commonly, this is achieved by using a T-flange, which extends both towards the outside and the inside of the tower. Two corresponding rows of anchor bolts, one inside and one outside the tower provide the fixation of the T-flange to the foundation. 
         [0010]    For tubular towers, generally a higher strength-to-weight ratio, which leads to lower material cost, can be achieved by increasing the diameter at the tower bottom. However, the maximum outside diameter is limited by transportation issues in the typical case where prefabricated tower segments have to be transported from a manufacturing site to the erection site of the wind energy converter. For a tower equipped with a T-flange, the outward-extending portion of the T-flange defines the maximum outside diameter of the tower. The outside diameter of the tubular tower walls could in principle be increased by replacing the T-flange with an L-flange that from the lower end of the tubular tower walls extends only inwardly. However, a single row of anchor bolts positioned along the inside of the tower walls and guided through fixing holes in the L-flange would place the concrete foundation under excessive pressure. 
         [0011]    By enabling to arrange the fixation plate as an intermediate plate between the tower and the foundation, the tower fixation bolt does not directly act on the foundation such as placing it under pressure when mechanical load is transferred by the tower e.g. due to wind. 
         [0012]    Because the tower fixation bolt does not act directly on the foundation, arrangements of tower fixation bolts along a single row is enabled without causing excessive pressure on the foundation. For example, use of a flange such as an L-flange is enabled, which comprises only a single row of holes for guiding the tower fixation bolts through the flange. Consequently, a higher weight-to-strength ratio of the tower is achievable by choosing a larger tower diameter without exceeding a predetermined size restriction imposed e.g. by transportation. 
         [0013]    Typically a size restriction imposed by transportation issues applies to a maximum value for the smallest of the three dimensions of an object along three orthogonal axes in space. Because the intermediate plate is plate-shaped, implying a thickness of the plate that is substantially less than its dimensions in the horizontal plane, the horizontal dimensions of the intermediate plate may be chosen to be greater than the predetermined size restriction. Thus, the intermediate plate may be dimensioned such that its fixation to the foundation distributes the load transferred by the tower, preventing excessive pressure on the foundation. 
         [0014]    In some embodiments, the fixation plate comprises a plurality of tower fixation holes arranged along a substantially arc-shaped row. This enables to fix the fixation plate to a tower having a substantially tubular shape with particularly favorable strength-to-weight ratio. 
         [0015]    The plurality of foundation fixing holes can be arranged along inner and outer rows that enclose in-between them the row of tower fixation holes. In other words, the inner row and the outer row are disposed on either side of the row of tower fixation holes. In this way, particularly strong fixation of the tower to the foundation is achieved. 
         [0016]    In some embodiments, the intermediate plate comprises an annular or annular-section like shape. This enables the fixation plate to support a tower having a substantially tubular shape with particularly favorable strength-to-weight ratio with little material requirement due to the cut-out interior of the annulus. An annular-section shape enables a tower of substantially tubular shape to be supported by a combination of two or more such fixation plates arranged to combine into an annulus while enabling easy transportation of each fixation plate due to small size. 
         [0017]    The nut cage can comprise a nut tube having a non-circular interior profile or cross section, which blocks rotation while permitting vertical translation of the nut. This enables the nut to move vertically while being held when the tower fixation bolt is screwed into the nut. 
         [0018]    In some embodiments, the nut tube comprises a height 1.2 to 2 times greater than a height of the nut, e.g. about 1.5 times greater. This enables the tower fixation bolt, when chosen to have a suitable length that slightly exceeds the nut in fixed position, to reach the nut through the tower fixation hole when the nut is disconnected from the tower fixation bolt and rests at the bottom of the nut cage. 
         [0019]    The interior cross section of the nut tube can comprise a pair of opposing walls separated by a distance that corresponds to a wrench size of the nut. That is, an imaginary line orthogonal to both walls and extending between them has a length that corresponds to the wrench size of the nut. This enables the nut tube to securely and precisely hold the tower fixation nut through surface-to-surface contact when receiving the tower fixation bolt and/or in case of removal of the tower fixation bolt, acting as a wrench of appropriate wrench size that exerts a torque on the nut for preventing it from rotating with the tower fixation bolt. 
         [0020]    In some embodiments, the interior profile of the nut tube is rectangular. This enables cost-effective production of the foundation fixing unit due to a simple geometric shape having only four walls. 
         [0021]    In some embodiments, the nut tube and the nut have the same profile. That is, the nut comprises an exterior profile corresponding to an interior profile of the nut tube, the exterior profile of the nut being slightly smaller than the interior profile of the nut tube to allow the nut to be located within the nut tube. This enables the nut tube to hold the tower fixation nut particularly securely and precisely when receiving the tower fixation bolt and/or removing the tower fixation bolt because surface-to-surface contact is established over a particularly large area along the circumference of the tower fixation nut. 
         [0022]    In some embodiments, the interior profile of the nut tube is hexagonal in correspondence with a hexagonal exterior profile of the nut. This advantageously enables to use a conventionally available type of nut at low cost. 
         [0023]    The nut cage can comprise a cover disc that covers a bottom end of the nut tube. This prevents undesired material such as water and/or grout from entering the nut tube, thus preventing corrosion and ensuring free movability of the tower fixation nut in the nut cage. 
         [0024]    In some embodiments, the foundation fixing unit further comprises a washer held in the nut cage above the nut. This enables a particularly even load distribution between the tower fixation nut and the intermediate plate, such that damage to the tower fixation nut and the fixation plate is avoided and a particularly secure fixation achieved. 
         [0025]    In some embodiments, the washer has an outer profile exceeding the interior profile of the nut tube, while the nut cage further comprises a washer tube above the nut tube for holding the washer. In this way, the washer is enabled to have a particularly large size and corresponding favorable load distribution. Furthermore, the washer is prevented from entering the nut tube and getting jammed within. 
         [0026]    The nut cage can have an exterior sheathing comprising an elastomeric material, e.g. rubber or a rubber-like material. In this way, deformation and damage through exterior pressure on the nut cage by material such as grout or concrete surrounding the nut cage is prevented. Also, tension and cracks in the grout or concrete, which otherwise might arise from differences in temperature and ensuing differences in the thermal expansion state between the tower and the foundation, are prevented. 
         [0027]    Another general aspect of the invention provides a wind energy converter comprising a foundation, the foundation fixing unit of any one of the preceding embodiments and a tower fixed onto the foundation using the foundation fixing unit. 
         [0028]    Embodiments of this aspect may include one or more of the following features. 
         [0029]    In some embodiments, the wind energy converter furthermore comprises anchor bolts, which fix the fixation plate as an intermediate plate onto the foundation. In this way, particularly strong fixation of the intermediate plate is enabled, while stresses on the foundation concrete are avoided. 
         [0030]    The wind energy converter can further comprise an anchor plate embedded in the foundation, such that stresses are distributed also within the foundation, thus further avoiding excessive pressure. 
         [0031]    The anchor plate may have an exterior shape substantially identical to the intermediate plate, resulting in distribution of stresses in the foundation over the entire area of the intermediate plate with minimal material requirement. 
         [0032]    In some embodiments, the wind energy converter further comprises a layer of grout between the foundation and the intermediate plate. This enables to equalize unevenness in a foundation top surface and to adjust the position of the intermediate plate above the foundation such that a top Surface of the intermediate plate lies within a horizontal plane. Furthermore, accommodation of the nut cage within the grout layer is enabled, such that e.g. special preparation of an opening etc. to accommodate the nut cage in the foundation is unnecessary. 
         [0033]    Another general aspect of the invention provides a method for fixing a tower of a wind energy converter onto a foundation. The method includes fixing a fixation plate having at least one tower fixation hole to the foundation. In further steps, a nut cage holding a tower fixation nut is attached to a bottom surface of the intermediate plate below the at least one tower fixation hole, a tower fixation bolt is passed through the tower fixation hole into the nut cage, and the tower is fixed to the fixation plate using the tower fixation bolt and the tower fixation nut. 
         [0034]    Embodiments of this aspect may include one or more of the following features. 
         [0035]    The fixing of the tower to the fixation plate is performed by screwing the tower fixation bolt into the tower fixation nut, providing a reliable and easily removable fixation between tower and fixation plate. 
         [0036]    fixation plate to the foundation can be performed before the fixing of the tower to the fixation plate. In this way, the intermediate plate can be precisely aligned to the horizontal without the tower. This saves time for the tower erection. 
         [0037]    In some embodiments, the fixing of the fixation plate onto the foundation is performed after the fixing of the tower to the fixation plate. This means that the fixation plate is pre-assembled to the tower and later on the tower with the already connected fixation plate is assembled to the foundation. 
         [0038]    Other features and advantages are illustrated in the accompanying drawings and described in detail in the following part of the description. 
     
    
     
       FIGURES 
         [0039]    In the Figures: 
           [0040]      FIG. 1  is a schematic illustration of a wind energy converter according to an embodiment of the invention, the wind energy converter having a tower fixed onto a foundation via a tower fixation unit including an intermediate plate with nut cages; 
           [0041]      FIG. 2  is a cross-sectional detail view of the wind energy converter of  FIG. 1 , showing the fixation of the tower onto the foundation by means of a tower fixation unit according to an embodiment and a method according to embodiment; 
           [0042]      FIG. 3  is a schematic cross-section detailing a nut cage of a tower fixing unit according to an embodiment, comprising a tower fixation nut at rest in the nut cage; 
           [0043]      FIG. 4  is a schematic cross-section of the nut cage of  FIG. 3 , with a tower fixation bolt screwed into the tower fixation nut; 
           [0044]      FIG. 5  is a schematic top view of a foundation fixing unit according to an embodiment, for fixing a tower of a wind energy converter onto a foundation; and 
           [0045]      FIG. 6  is a cross-sectional detail view showing the fixation of a tower of a wind energy converter onto the foundation by means of a tower fixation unit according to a further embodiment. 
       
    
    
       [0046]    Throughout the figures, the same reference numbers indicate the same or functionally equivalent means. 
       DETAILED DESCRIPTION 
       [0047]      FIG. 1  is a schematic illustration of a wind energy converter  100 , which includes a rotor  114  having a number of rotor blades  106  that extend radially from a hub  104 . The hub  104  is rotatably mounted on a nacelle  102 , which houses a generator  120  for generating electricity, when driven by the rotor  114  directly or via a gear train  121 , shown as an example. 
         [0048]    The nacelle  102  is rotatably mounted on a tubular steel tower  108  that is fixed onto a concrete foundation  110 , which is embedded in soil  112  in order to transfer loads received from the tower  108  to the earth. The tower  108  is of approximately conical outward shape centered on a vertical symmetry axis  116 , its outer diameter gradually tapering off from a maximum diameter  118  close to the foundation  110  to a minimum diameter  119  close to the nacelle  102 . For optimum strength-to-weight ratio of the tower  108 , a large value of the maximum diameter  118  is desirable. For ease of transportation to the erection site of the wind energy converter  100 , the tower  108  may be divided horizontally into two or more segments of tubular shape. In order to enable economical transportation of the tubular segments of the tower by conventional means of transportation such as roads, railways, etc., the maximum diameter  118  of the tower  108  is configured to correspond to a size limit imposed by the chosen means of transportation, e.g. 4.3 m in case of conventional road transportation that involves passage below bridges. 
         [0049]    The tower  108  is fixed onto the foundation  110  by means of a foundation fixing unit that includes a fixation plate provided as an intermediate plate  202  arranged horizontally between the tower  108  and the foundation  110 . The intermediate plate  202  is fixed onto the foundation  110 , an adjustment gap  224  filled with a layer of grout  218  being provided between the foundation  110  and the intermediate plate  202 . The adjustment gap  224  enables horizontal alignment of the intermediate plate  202  on the top surface of the foundation  110 , which after casting may not be sufficiently even and horizontal to directly support the intermediate plate  202 . The tower  108  is fixed onto the intermediate plate  202 , thus resulting in indirect fixation of the tower  108  onto the foundation  110  via the intermediate plate  202 . 
         [0050]    The fixation of the tower  108  onto the foundation  110  shall now be explained in further detail by making reference to  FIG. 2 , which shows a cross-section taken along the symmetry axis  116  of the tower  108 , detailing a bottom portion of the tower  108 , the intermediate plate  202 , the grouting layer  218 , and a top portion of the foundation  110  of  FIG. 1 . The tower  108 , i.e. a bottom segment of the tower  108  in case of a horizontally segmented tower, is shown to comprise at its lower end an inward-facing L-flange  200 . Because the L-flange  200  is facing inwards, its horizontal width does not add to the maximum diameter  118  of the tower  108 . In the L-flange  200 , vertically extending through-holes  226  are formed in regular intervals  228  along the diameter of the tower  108  within its tubular walls. 
         [0051]    The intermediate plate  202 , which has a constant thickness  228 , is preferably formed of steel. As can be seen in  FIG. 2 , a bottom side of the L-flange  200  rests on the intermediate plate  202 , with tower fixation holes  300  for fixing the tower  108  onto the intermediate plate  202  extending vertically through the intermediate plate  202 , coinciding with the through-holes  226  that are formed in the L-flange  200 . In the horizontal plane, i.e. when viewed from above in the direction of the tower axis  116 , the intermediate plate  202  exhibits an annular shape, each of the tower fixation holes  300  being equally distanced from an inner  314  and outer  316  radius of the annulus. 
         [0052]    Centered below each tower fixation hole  300 , a nut cage  204 , which encloses an associated tower fixation nut  400  and washer  408 , is attached to a bottom surface  222  of the intermediate plate  202 . The intermediate plate  202  together with the attached nut cages  204  and the associated tower fixation nuts  400  and washers  408  contained therein form a foundation fixing unit  202 ,  204 ,  400 ,  408  by means of which the tower  108  is fixed onto the foundation  110 . 
         [0053]      FIG. 3  shows an enlarged cross section through a portion of the intermediate plate  202 , which includes the opening of one of the tower fixation holes  300  into the bottom surface  222  of the intermediate plate  202 , and the corresponding nut cage  204  attached to the intermediate plate  202  below the tower fixation hole  300 . 
         [0054]    The nut cage  204  includes a washer tube  406  of cylindrical shape in which the washer  408  is contained. The washer tube  406  is attached, e.g. by welding, to the bottom surface  222  of the intermediate plate  202 , centrally positioned on a symmetry axis  429  of the tower fixation hole  300 . The washer  408  is a thin, disc-shaped plate with a circular hole  430  in the middle. The washer tube  406  has an inner diameter  426  that is larger than an outer diameter  428  of the washer  408  by such an amount of clearance that the washer  428  is allowed to slightly move horizontally in the washer tube  406  while being sufficiently restricted to ensure that the washer hole  430  substantially overlaps the tower fixation hole  300 . Similarly, the washer tube  406  has an inner height W that is larger than a thickness w of the washer  408  by such an amount of clearance that the washer  428  is allowed to slightly move horizontally in the washer tube  406  while being sufficiently restricted to ensure that the washer hole  430  substantially overlaps the tower fixation hole  300 . 
         [0055]    The nut cage  204  further includes a nut tube  404  of hexagonal inner and outer profiles, centered on the symmetry axis  429  of the tower fixation hole  300 , in which the tower fixation nut  400  is contained. The inner hexagonal profile of the nut tube  404  is chosen to be slightly wider than a hexagonal outer profile of the tower fixation nut  400 , such that the nut  400  is easily movable within the nut tube  404  in the vertical direction along the symmetry axis  429  while being prevented from rotation and tilting with respect to the symmetry axis  429 . In other words, the distance of diametrically opposing walls  410  of the inner hexagonal profile of the nut tube  404  corresponds to a wrench size of the tower fixation nut  400 . The nut tube  400  has a height H that is about 1.2 to 2.0 times higher than a height h of the tower fixation nut  400  and is closed off at its bottom end by a welded-on lid  402 . 
         [0056]    At its top end, the nut tube  404  is welded to the bottom end of the washer tube  406 . The welding connections between the intermediate plate  202 , the washer tube  406 , the nut tube  404 , and the lid  402  are performed without gaps such that the nut cage  204  is open only to the tower fixation hole  300 . The outer diameter  428  of the washer  408  is chosen such that the washer  408  is prevented from entering the nut tube  404 . For example, the outer diameter  428  of the washer  408  is configured to be greater than the distance  432  between opposing corners of the inner profile of the nut tube  404 , preferably by at least half the difference between the outer diameter  428  of the washer  408  and the inner diameter  426  of the washer tube  406 . 
         [0057]    At its outside, the nut cage  204  comprises a rubber armoring  414 , which provides an elastic buffer zone between the nut cage  204 , which is made e.g. of steel, and surrounding material such as the grout layer  218  shown in  FIG. 2 . 
         [0058]      FIG. 5  shows is a schematic top view of a foundation fixing unit, which includes an intermediate plate  202  having an annular shape with an inner radius  314  that is smaller than a bottom radius of a corresponding tower to be fixed onto a foundation, and an outer radius  316  that is larger than the bottom radius of the tower. A plurality of equally spaced tower fixation holes  300  is formed in a central circular row  310  around the annulus, which runs midway between the inner  314  and outer  316  radii. Hexagonal nut cages  204  containing nuts and washers (not shown) are attached to the intermediate plate  202  below each tower fixation hole  300 . 
         [0059]    Furthermore, a plurality of inner  301  and outer  302  foundation fixing holes are formed in the intermediate plate  202 , the inner  301  and outer  302  foundation fixing holes each being equally spaced along corresponding inner  311  and outer  312  circular rows. All three circular rows  310 - 312  are concentric around the symmetry axis  116  of the intermediate plate  202 , which coincides with the symmetry axis of the tower to be fixed. 
         [0060]    The fixation of an intermediate plate  202  such as shown in  FIG. 5  to a foundation  110  shall now be explained by making reference again to  FIG. 2  wherein an intermediate plate  202  is shown that, apart from having fewer tower fixation holes  300  and foundation fixing holes  301 ,  302  than the intermediate plate  202  of  FIG. 5 , is of substantially equivalent design. 
         [0061]    Within the foundation  110 , two concentric rows of inner  206  and outer  207  anchor bolts are partially embedded in the concrete, threaded portions thereof projecting vertically from a top surface  270  of the concrete foundation  110 . For additional strength, an annular anchor plate  216  made from steel is embedded in the foundation, having substantially half the thickness and identical inner  314  and outer  316  radii as the intermediate plate  202 . In the anchor plate  216 , through holes  272  are formed coincidently with the foundation fixing holes  301 ,  302  in the intermediate plate  202 . 
         [0062]    When preparing the foundation  110 , each anchor bolt  206 ,  207  is guided, bolt head  208  facing downward, through an associated washer  210  and one of the through holes  272  formed in the anchor plate  216 . Afterwards, and possibly after additional steel reinforcements have been positioned, the concrete of the foundation  110  is cast. After hardening of the concrete foundation  110 , the threaded ends of the anchor bolts  206 ,  207  are each guided through a corresponding one of the foundation fixing holes  301 - 302  of the intermediate plate  202 . The intermediate plate  202  is then supported in horizontal alignment above the foundation  110 , leaving a gap  224  between its bottom surface  22  and the foundation, the nut cages  204  being suspended in the gap  224  without touching the foundation  110 . 
         [0063]    After aligning the intermediate plate  202 , the gap  214  is filled with grouting concrete, creating a grouting layer  218  in which each nut cage  204  is immersed. After the grouting layer  218  has hardened, the intermediate plate  202  is fixed to the inner  207  and outer  206  anchor bolts by screwing corresponding inner  213  and outer  212  anchor bolt nuts equipped with associated anchor bolt nut washers  214  onto the threaded ends of each anchor bolt  206 - 207 . 
         [0064]    The fixation of the tower  108  to the intermediate plate  102  may be performed either before or after fixing the intermediate plate  202  to the foundation  110 . After the tower  108 , or the bottommost tower segment in case of a segmented tower, has been brought into contact and alignment with the intermediate plate  202  such that each through hole  226  formed in the L-flange  200  coincides with a corresponding tower fixation hole  300  formed in the intermediate plate  202 , for each tower fixation hole  300  a tower fixation bolt  220  is guided first through an associated tower fixation bolt washer  221 , then through an associated through hole  226  formed in the L-flange, and finally through the tower fixation hole  300  into the associated nut cage  204  attached to the intermediate plate below the tower fixation hole  300  until a threaded portion at the tip of the tower fixation bolt  220  contacts the tower fixation nut  400  contained in the nut cage  204 . 
         [0065]    Then, the tower fixation bolt  220  is screwed by turning its head  219 , using a suitable wrench, into the tower fixation nut  400 . The nut  400 , which is blocked from rotation by the surrounding nut tube  404 , gradually rises from the bottom lid  402  of the nut cage  204  towards the intermediate plate  202 , eventually partially entering the washer tube  406  and pressing the washer  408  against the bottom surface  222  of the intermediate plate  202 . The resulting positions of the tower fixation bolt  220 , tower fixation nut  400  and tower fixation nut washer  430  in a state where the tower is fixed to the intermediate plate  202  are shown in  FIG. 4 . 
         [0066]      FIG. 6  illustrates the fixation of a tower of a wind energy converter onto its foundation by means of a further tower fixation unit  600 ,  204 ,  400 , which includes a fixation plate  600  formed as an anchor plate  600  with nut cages  204  attached to a bottom surface thereof, below tower fixation holes  300  formed in the fixation plate  600 . The fixation plate  600  is fixed to the foundation  110  by embedding in the wet concrete during foundation  110  casting. Furthermore embedded in the foundation  110  are tower fixation bolt pipes  602 , which extend upwardly from the openings of the tower fixation holes  300  through the foundation  110  and a grout layer  218  formed on top of the foundation  110 . The tower fixation bolt pipes  602  comprise an interior width approximately corresponding to the interior width of the tower fixation holes  300 . The tower fixation bolt pipes  602  may be welded to the fixation plate  600 . 
         [0067]    The tower  108  includes an annular T-flange  604  welded  606  to a bottom end thereof. In the T-flange, the annular shape of which corresponds to an annular shape of the fixation plate  600 , two rows of through-holes  226  are formed to coincide with the tower fixation holes  300 . In order to attach the tower  108  to the foundation  110 , tower fixation bolts  200  have each been guided through an associated washer  221 , one of the through-holes  226  formed in the T-flange, a tower fixation bolt pipe  602 , and a tower fixation hole  300  into one of the nut cages  204 , and subsequently screwed into the nut  400  held therein. 
         [0068]    The embodiments described above can be varied in multiple ways. For example, the embodiments of  FIG. 2  and  FIG. 6  may be combined by adding nut cages to the anchor plate  216 , forming the connection between the anchor plate  216  and the intermediate plate  202  substantially like the connection between the fixation plate  600  and the flange  604  in the embodiment of  FIG. 6 . Also, a nut tube may be provided having a quadrangular, in particular rectangular cross section, wherein the smaller inside diameter of the nut tube is slightly bigger than the wrench size of the tower fixation nut and the larger inside diameter is slightly bigger than the width across corners of the nut. Or, a nut cage may be provided that does not contain a washer. The nut tube may be connected directly to the fixation plate without a washer tube being present in-between. Generally, the nut cage may be constructed monolithically without welding connections, or from an arbitrary number of parts. Also, instead of being shaped as a full annulus, the intermediate plate may be configured in two or more sectional parts. Other embodiments are within the scope of the following claims.