WO2004101990A1

WO2004101990A1 - Method and device for erecting a steel tower

Info

Publication number: WO2004101990A1
Application number: PCT/NL2004/000319
Authority: WO
Inventors: Pieter Adriaan Oosterling; Fred Ernst Gardner
Original assignee: Swilion B.V.
Priority date: 2003-05-13
Filing date: 2004-05-11
Publication date: 2004-11-25
Also published as: NL1023402C2

Abstract

The invention relates to a method and device for erecting a steel tower comprising a conical steel shell. The steel tower is intended to support the machine housing of a wind turbine. The steel tower is erected by adding plating to the underside of a vertical top part, the top part being supported and held upright by a supporting and lifting device. The invention also comprises a steel tower for a wind turbine, with the diameter of the steel shell being greater than four metres in the vicinity of the foundation.

Description

METHOD AND DEVICE FOR ERECTING A STEEL TOWER

The invention relates to a method in accordance with the preamble of Claim 1. A method of this type is known. According to the known method, the tower is erected by continually placing successive parts of the tower on top of one another and joining them. The drawback of this method is that a crane with a large capacity and hoisting height has to be available for a prolonged period of time, and that the work is carried out at an ever greater height, which is disadvantageous .

To avoid this drawback, the method is carried out in accordance with the characterizing part of Claim 1. This allows the tower to be erected from below, with the work being readily accessible, and the prolonged availability of a large crane is not necessary during construction of the tower.

According to one refinement, the method is carried out in accordance with Claim 2. This makes it easy for the top part to be held upright while the steel tower is being erected.

According to a further refinement, the method is carried out in accordance with Claim 3. This allows the tower to be erected in layers or rings, with a new ring in each case being fitted beneath the top part.

According to a further refinement, the method is carried out in accordance with Claim 4. This allows the tower to be assembled in a continuous process, in which case it is possible for the additional parts to be supplied as a continuous strip which is fitted at a pitch beneath the top part.

According to a further refinement, the method is carried out in accordance with Claim 5. This allows the sheet material to be supplied as a coil with a small transport volume, so that transport costs can be saved.

According to a further refinement, the method is carried out in accordance with Claim 6. As a result, the desired helical joining seam can be obtained without the sides of the sheet material having to be cut in a corresponding way.

According to a further refinement, the method is carried out in accordance with Claim 7 or 8. This provides a fast method for erecting the steel tower.

The invention also comprises a device in accordance with the preamble of Claim 9. Devices of this type are known and generally comprise hoisting means and auxiliary means allowing work to be carried out at a great height. Devices of this type are expensive and in use require extensive safety measures, which is disadvantageous .

To avoid these drawbacks, the device is designed in accordance with the characterizing clause of Claim 9. A device of this type allows the steel tower to be erected from below and the work to be carried out at ground level.

According to a refinement, the device is designed in accordance with Claim 10. This makes it possible to correct any skew position of the top part continuously.

According to a further refinement, the device is designed in accordance with Claim 11. This allows the top part to be held upright in a simple and safe way.

According to a further improvement, the device is designed in accordance with Claim 12. This allows direct measurement of the direction and any skew position of the top part and allows the straightening means to apply corrections directly.

According to a further refinement, the device is designed in accordance with Claim 13. This enables the top part to rotate while it is being erected and allows the assembly and supply of material for the steel shell to be carried out at a single rotational position.

According to a further improvement, the device is designed in accordance with Claim 14. This allows the diameter to be increased while the top part is being erected, so that it is also possible to construct conical steel towers .

According to a further refinement, the device is designed in accordance with Claim 15. This allows the sheets required for the tower to be made available for assembly on site.

According to a further refinement, the device is designed in accordance with Claim 16. This enables the shape of the sheets to be made suitable for use as helically fitted plating for a conical tower without waste being produced.

According to a further refinement, the device is designed in accordance with Claim 17. This allows the steel wall of the tower to be reinforced, so that the sheet material of the metal wall can be made thinner.

The invention also comprises a steel tower in accordance with the preamble of Claim 18. Steel towers of this type are known' and have a limited diameter on account of the need for the components of the tower to be transported in part by road. On account of the strength required, it is therefore necessary for the wall thickness of the tower to be thickened, but the strength only increases to a limited extent and the tower remains weak, and moreover undesirable vibrations can occur on account of the low natural frequency of the steel tower.

To avoid this drawback, the steel tower is designed in accordance with the characterizing clause of Claim 18. This allows the construction of a steel tower with a high natural frequency, with the result that the level of vibrations will be reduced, while the possibility of using thinner plating makes it possible to limit costs. The foundation can also be of more lightweight design.

According to a refinement, the steel tower is designed in accordance with Claim 19. This allows the sheet material which is suitable for use throughout the entire tower to be supplied in the form of one or more coils, so that transport costs are saved.

According to a further refinement, the steel tower is designed in accordance with Claim 20. This allows the steel tower to be erected in a continuous process, which leads to savings.

According to a further refinement, the steel tower is designed in accordance with Claim 21, which limits the number of different types of sheet, with the result that the assembly equipment can be simpler, as can the logistics .

According to a further refinement, the steel tower is designed in accordance with Claim 22, which produces a stable steel tower in a simple way.

According to a further refinement, the steel tower is designed in accordance with Claim 23. As a result, the cross section of the steel tower retains its circular cross section even when thin sheet material is used, and therefore the steel tower retains its stability even when thin sheet material is used. The invention is explained below on the basis of a number of exemplary embodiments and with the aid of a drawing, in which: Figure 1 shows a side view of a wind turbine with a conical steel tower,

Figure 2 shows a side view of the structure of the steel tower from Figure 1,

Figure 3 shows a diagrammatic view of the underside of the steel tower during its erection in accordance with a first embodiment,

Figure 4 shows a diagrammatic side view of the underside of the tower in accordance with Figure 3,

Figure 5 shows a diagrammatic cross section through and side view of a rolling device used for the construction shown in Figure 3,

Figure 6 shows a diagrammatic cross section through the underside of the steel tower during its erection in accordance with a second embodiment, and Figure 7 shows a diagrammatic cross section v I-V I frorri Figure 6.

Figure 1 shows a wind turbine 3 with a steel tower 2 which is placed on a foundation 1. On top of the steel tower 2 there is a bearing 4 on which a machine housing 5 can rotate about the vertical centre axis 8 of the steel tower 2. The machine housing 5 is provided with vanes 6 which can rotate about an approximately horizontal axis of rotation 7 so as to drive a shaft in a known way. The height of the steel tower 2 is such that the horizontal axis of rotation 7 is at least forty to fifty metres above the ground, and the steel tower 2 has a mean diameter d, the height of the horizontal axis of rotation above the ground being more than ten times the mean diameter d. With a view to making the steel tower 2 strong, it is of conical design, with the wall forming an angle α with the vertical, a being greater than 2 degrees. The diameter of the steel tower 2 is at least four metres in the vicinity of the foundation 1. This avoids vibrations in the steel tower 2 and allows the steel tower 2 to be constructed with a thin wall; in the case of a fifty to a hundred metre high tower, consideration must be given to a wall thickness of 6-10 mm.

Figure 2 shows how the steel tower 2 can be erected. A supporting and lifting device 12 is placed onto the foundation 1. The supporting and lifting device 12 is used to hold a top part 11 of the steel tower 2 upright and to move it upwards, with control means (not shown) being present in order to control the supporting and lifting device 12. There is, inter alia, a sensor which can determine whether the centre axis 8 is sufficiently vertical; the sensor may for this purpose use a laser beam. A new part of the steel wall is constantly being added to the underside of the top part 11 by means of welding while the top part 11 is being lifted continuously or intermittently. The supply of new material for the steel wall, such as steel sheet material, is explained below. It will be clear to the person skilled in the art that after parts of the steel wall have been fitted it has to be treated to prevent corrosion.

In the exemplary embodiments described here, it is always assumed that the steel tower 2 is assembled by welding together sheet material. In addition to the sheet material being joined together by welding, there are numerous other known securing methods, such as riveting, adhesive bonding, flanging and other chipless deformation methods which can be used on the sheet material. These methods can be used in a comparable way to construct the steel tower 2 and will no longer be referred to separately in the text which follows.

If appropriate, cables 10 may be secured to the top side of the top part 11 and held under tension by winches 9. Paying out or tensioning the cables 10 allows the position of the top of the top part 11 to be fixed, thereby ensuring that the top part 11 remains upright. The cables can be secured to the wall at the top of the top part 11, for example using hoisting eyelets, or to the securing flange of bearing 4. When the bearing 4 has been fitted, it is also possible for the cables 10 to be secured to the rotatable part of bearing 4, with the result that it is possible to allow the top part 11 to rotate with taut cables 10. When the top part 11 is being lifted by the supporting and lifting device 12, the winches 9 are actuated in such a manner that the cables 10 are paid out uniformly and the top of the top part 11 remains fixed to a sufficient extent.

Figures 3, 4 and 5 diagrammatically depict the underside of the top part 11 of the steel tower 2 during its erection in accordance with a first embodiment. During erection, a removable auxiliary apparatus is placed on a centre support 27 and a rail foundation 18. Rail 17 is arranged in a circle and supported on the rail foundation 18. A turntable 29 is positioned on the centre support 27. The axis of rotation of the turntable 29 corresponds to the centre axis 8 of the steel tower 2 (cf. Figures 1, 2) . Twelve cylinder supports 26 are mounted on the turntable 29, inter alia by means of a bolt 28. The cylinder supports 26 are secured to one another by means of coupling plates 24 and coupling bolts 25. That end of each cylinder support 26 which is not mounted on the turntable 29 is provided with a wheel 19 which can rotate about a horizontal axis and can move along the rail 17 on a circular path. If the turntable 29 is rotated about its vertical axis of rotation with the aid of a drive (not shown) , the twelve cylinder supports 26 rotate synchronously with it. The cylinder supports 26 and the turntable 29 are designed in such a manner that they can easily be assembled and dismantled, so that after the steel tower 2 has been erected they can easily be dismantled and removed from under the steel tower 2 and reassembled and reused at a subsequent steel tower 2 which is to be constructed.

The cylinder supports 26 are each provided with an opening in which a hydraulic cylinder 22 can move in the radial direction, the cylinder being supported on the cylinder supports 26 by means of support journals 23. The radial movement of the hydraulic cylinder 22 can be effected automatically under the influence of a drive (not shown) if there is no load on the hydraulic cylinder 22. The hydraulic cylinder 22 is provided with a piston rod 21 with a clamp 35 at one end for clamping sheet material in place.

The conical wall of the steel tower 2 is formed from a strip of sheet material 20 with a width b. The material is supplied on a stock coil 13 placed on a turntable 14. The strip of sheet material 20 is stretched and rolled into a radius Ri in a rolling device 30 which is provided with four bending rolls 15 which are positioned next to one another, at a certain distance, alternately on either side of the sheet material 20. The radius Ri to which the sheet material 20 is rolled corresponds to the radius Ri of the underside of the top piece 11 of the steel tower 2. The sheet material 20 moves into adjacent turns in the outer wall of the steel tower 20. Since the steel tower 2 is conical, the edges of the sheet material 20 have to have a radius R₂ in the plane of the sheet material 20, as indicated in Figure 5. Suitable dimensioning of R₂ as a function of the radius Ri of the underside of the top part 11 of the steel tower 2 and the sheet width b ensures that the gap between adjacent edges of the sheet material 20 is minimal. To realize this radius R₂, the sheet material 20 is guided by a rolling device 31. In the rolling device 31, the sheet material 20 is passed between two rolling rolls 16 which are positioned on either side of the material 20. The distance between the rolling rolls 16 is ti at the top side and t₂ at the underside, t₂ being less than t_x and ti being less than or equal to the original thickness of the sheet material 20. As a result, the sheet material 20 is rolled out more at the underside than at the top side, and the sides of the sheet material 20 acquire a radius with the radii R₂ and (R₂+b) . In the embodiment shown, simple rolling rolls 16 are used. This is possible because the width b is limited to approximately 1.0 metre. For a greater width b of the sheet material 20, the rolling rolls 16 may have to be provided with support rolls.

The turntable 14, the rolling device 30 and the rolling device 31 are mounted on a support floor 32 which can be placed with an adjustable support 34 at a pitch angle φ with respect to the horizontal top surface of a foundation 33. The pitch angle φ is approximately equal to the pitch angle φ of the strips of sheet material 20 in the steel shell 2 and is approximately φ = arctan

(b/ (2 ^•Jt-Ri) ) . On account of the fact that the pitch angle op is dependent on the radius R , and this radius

Ri increases as the steel tower 2 becomes higher, the pitch angle φ will decrease as the height of the steel tower 2 increases.

The erection of the steel tower 2 using the device shown in Figures 3, 4 and 5 takes place as follows. A prefabricated top part 11 is placed onto the clamps 35. The underside of this top part 11 may have a pitch angle φ, with the sheet material 20 adjoining the top part 11 with a butt joint 36, and the side of the sheet material 20 being secured to the material which is already present. If the underside of the top part 11 is flat, the sheet material is made level with the side, in such a manner that it adjoins this flat underside of the top part 11. Then, the turntable 29 is rotated and the sheet material 20 is supplied by the rolling devices 30 and 31, so that it is rolled into the correct radii. In a joining region C, the top edge of the sheet material 20 supplied is secured to the bottom edge of the top part 11, for example by welding or another securing method. As soon as the sheet material 20 has been secured to the top part 11 and leaves the joining region C, the clamp 35 coupled to the bottom edge, as a result of the hydraulic cylinders 22 being tensioned, starts to support the top part 11, and will continue to do so until the associated hydraulic cylinder 22 has covered virtually a full revolution and has returned close to the joining region C. At the same time as the turntable 29 is rotating, the clamps 35 are moved upwards by the hydraulic cylinders 22, in such a manner that the centre axis 8 remains vertical and the coupling region C retains a more or less constant height. When a clamp 35, after virtually a complete revolution, returns close to and into the joining region, the clamp 35 is removed from the underside of the top part 11 and moved downwards. The hydraulic cylinder 22 is then displaced outwards on the cylinder support 26, in accordance with the angle of inclination α with the vertical. The clamp 35 is then moved upwards and secured to the underside of the sheet material 20, and the operations are repeated until stock coil 13 is empty. Then, a subsequent stock coil 13 is placed onto the turntable 14 and the strip of sheet material 20 is joined with a butt joint 36 to the top part 11 and the cycle is continued.

Preferably, at the same time as the plating of the wall of the top part 11 is being fitted, reinforcing rings 37 are being secured to the inner side of the wall. These reinforcing rings 37 ensure that the cross section of the steel tower always remains circular, and that local bending of the thin sheet material is prevented. The distance between these reinforcing rings is preferably no more ^■ than 1.0 metre and may, for example, be limited to 0.5 metre. One simple way of securing the sheet material 20 to the top part 11 is welding, in which case the more or less encircling seam is welded at one position, the joining region C, which makes it easy to automate the welding operation, in which case, by way of example, welding can be carried out from the outside and backing strips, support rolls or similar means can be applied to the inner side in the joining region C, allowing efficient automated welding from the side. It is also possible to carry out manual welding, since the weld seam is readily accessible to a number of people in the joining area C. If appropriate, the top part 11 and the sheet material are firstly coupled in a known way to coupling plates, in which case welding can be carried out over a large part of the circumference. Shrinkage between the clamps 35 and the top part which occurs during welding is detected as a result of the direction of the centre axis 8 of the tower changing, and this is automatically compensated for by adjusting the length in the hydraulic cylinders 22.

It would be clear to the person skilled in the art that the top part 11 of the steel tower 2 should be provided with a corrosion-limiting preservation treatment. It is preferable for this preservation treatment of the steel tower 2 to be carried out during erection, in the vicinity of the underside of the top part 11, since that is where the material which is to be protected is easiest to reach. The equipment required for this purpose can easily be positioned on the outer side next to the underside of the top part 11. Equipment required for the preservation treatment on the inner side of the steel tower 2 may if appropriate be secured to the turntable 29, in a manner which is not illustrated.

An electronic control system is used to keep the centre axis 8 of the steel tower 2 or the top part 11 vertical with the aid of sensors and to match the movement of the various components of the installation to one another. In this context, the operations required to keep the centre axis 8 upright with the aid of the hydraulic cylinders 22 and if appropriate the winches 9 will be fully automated, and the various processes can take place completely or partially automatically. It is preferable for there to be a direct coupling between the rotation of the turntable 29 and the driving of the sheet material by the rolling device 30 and the rolling device 31, and this may if appropriate be combined with the driving of the turntable 14. The adjustment and control of the rolling device 30 can also be automated, in which case there are sensors which are able to adjust and measure the radius Ri of the sheet material 20. The adjustment and control of the rolling device 31 can also be automated, likewise using sensors which measure the sheet thickness ti, t₂ or radius R₂.

To secure the sheet material 20 to the top part 1, it is possible to select an automated process or to use manual control. It is preferable for the clamp 35 to be fitted manually around the underside of the sheet material, while the repositioning of the hydraulic cylinder 22 on the cylinder support 26 may be manual or automatic.

Once the steel tower 2 has reached the required height, the outer wall of the steel tower 2 is secured to the permanent foundation, which is secured, for example, to the rail foundation 18, all the way around the outer side. After the steel tower 2 has been secured to the foundation, the clamps 35 can be removed and the hydraulic cylinders 22 can be lowered. The turntable 29, the cylinder supports 26 and the cylinders 22 can then be dismantled and removed from under the steel tower 2. Any surplus sheet material is removed, and if appropriate a door is made in the steel wall. The winches 9 can also be dismantled and the machine housing 5 can be placed onto the steel tower 2. Figures 6 and 7 diagrammatically depict the underside of the top part 11 of the steel tower 2 during its erection in accordance with a second embodiment. Beneath the centre axis 8 of the steel tower 2 there is a foundation 51 on which a centre support 50 is positioned. A foundation ring 49, on which a support 48 of a horizontal beam 38 can be supported, is arranged on the foundation 51. The other end of the horizontal beam 38 is supported on the centre support 50. A foot 39 can move in the horizontal direction over the horizontal beam 38, if appropriate under the influence of a drive system. An adjustable support 45 is secured to the foot 39 and a carriage 44 can be moved along this adjustable support in the vertical direction by a drive (not shown) ; this drive may be hydraulic or mechanical. Each carriage 44 is provided with a coupling piece 43 which can be coupled to a securing plate 42 which is secured to the inner side of the wall of the steel tower 2.

The steel tower 2 is constructed from conical steel rings. Figure 6 shows the top part 11 with a bottom ring 47 which has been secured to the top part 11 by means of a welded joining seam 52. Each conical steel ring is made from sheet material which is made suitable for assembly, for example, by rolling, as described above. Each conical ring has at least one butt joint 40 and is provided with reinforcing rings 37 for keeping the ring circular and/or preventing local bending of the slightly curved sheet. Six securing plates 42 are arranged around the inside, and the securing plates 42 may if appropriate form part of a reinforcing ring 37.

There are two groups of vertical supports 45. The first group of vertical supports 45 is coupled by the coupling pieces 43 to the securing plates of the bottom ring 47 and supports the top part 11. The carriages 44 are actuated by a control unit (not shown) so as to keep the centre axis 8 of the top part 11 vertical. With a view to achieving stability of support for the top part 11, there are preferably twelve or more vertical supports 45, so that each group comprises at least six vertical supports 45. The bottom ring 47 is moved upwards by the vertical supports 45 with the top part 11 while the cables 10 are being paid out by the winches 9. The bottom ring 47 is lifted sufficiently far for there to be space beneath it to assemble a subsequent ring 41 which is to be joined.

After the next ring 41 to be joined has been assembled, it is joined to the second group of vertical supports 45 after the latter have been moved to a larger diameter by the feet 39. Then, the next ring 41 to be joined is lifted by the vertical supports 45 until the joining seam 46 to be welded has become narrow enough to be welded, and then this joining seam 46 is welded mechanically or manually. Once this joining seam 46 is ready, the coupling pieces 43 can be removed from the bottom ring 47 and the corresponding decoupled carriages 44 can be moved downwards, and the carriages coupled to the ring 41 can be moved upwards, with the entire top part 11 moving upwards with it.

In this way, the steel tower 2 is erected from conical steel rings until the tower 2 has reached the required height. Then, the bottom ring is secured to a foundation and the vertical supports 45, the horizontal beams 38 and the other assembly means are removed.

The sheet material 20 used for this mode of erection may be the same as for the mode of erection described first of all. In this case too, the sheet material 20 will then have to be stretched and rolled into a radius Ri, and the edges of the sheet material will also have to acquire a comparable radius R₂. If appropriate, the edges can also be made suitable by removal of material.

Claims

Claims :

1. Method for erecting a steel tower (2) which comprises a conical steel shell that ends at the top side in a bearing (4) for supporting a machine housing

(5) of a wind turbine (3) , wherein a foundation (1) is put in place and the steel tower is erected on the foundation, characterized in that a supporting and lifting device (12) is placed on the foundation, after which the vertical top part (11) of the conical steel shell (2) , if appropriate together with the bearing (4), is placed onto the supporting and lifting device, and then additional parts of the conical steel shell are fitted to the underside of the vertical top part, and the vertical top part (11) is lifted upwards by the supporting and lifting device (12) .

2. Method according to Claim 1, in which the vertical top part (11) is held vertically by three or more cables (10), and the length of the cables is increased at the same time as the vertical top part is being lifted upwards.

3. Method according to Claim 1 or 2, in which the supporting and lifting device (12) comprises two groups of supports (45) which alternately lift the top part (11) upwards.

4. Method according to Claim 1 or 2, in which the supporting and lifting device (12) comprises supports

(22) which can rotate about a vertical axis (8) , and in which the top part (11) is lifted upwards by the supports synchronously with the rotation about the vertical axis.

5. Method according to one of the preceding claims, in which the steel shell (2) comprises sheet material (20) , and the additional parts, in the vicinity of the foundation (1), are rolled by a first rolling device (30) into a first radius (R_x) of the steel shell.

6. Method according to one of the preceding claims, in which the steel shell (2) comprises sheet material (20) with a constant thickness and parallel sides, and in which, before the additional parts are fitted, the sheet material is rolled by a second rolling device

(31) , in such a manner that a difference in thickness is produced over the width of the sheet and the sides of the sheet material acquire a second radius (R₂) which corresponds to the curvature of a helical line along the conical shell of the top part (11).

7. Method according to Claim 4, 5 or 6, in which the sheet material (20) is rolled while the supports (22) are rotating about the vertical axis (8) .

8. Method according to Claim 4, 5, 6 or 7, in which the sheet material (20) is secured to the top part (11) during the rolling and/or the rotation of the supports (22) .

9. Device for erecting a steel tower (2), which comprises a conical steel shell that ends at the top .side with a bearing (2) for supporting a machine housing (5) of a wind turbine (3), on a foundation (1), characterized in that there is a supporting and lifting device (12) for supporting a top part (11) of the conical steel shell on the underside, the supporting and lifting device (12) being provided with lifting means (22; 45) for moving the top part in the vertical direction.

10. Device according to Claim 9, in which there are straightening means for keeping the top part (11) straight in a vertical position.

11. Device according to Claim 10, in which the straightening means comprise at least three winches (9) with cables (10) secured to the top side of the top part (11).

12. Device according to Claim 10 or 11, in which the straightening means comprise sensors for measuring the direction of the centre axis (8) of the top part (11) .

13. Device according to one of Claims 9-12, in which the supporting and lifting device (12) comprises supports (22) that can rotate about the centre axis (8) of the steel tower (2) , and the height of each support can be adjusted separately.

14. Device according to Claim 13, in which for each support (22) there are adjustment means for manual or automatic adjustment of the support in the radial direction.

15. Device according to one of Claims 9-14, in which there is a first rolling device (30) for bending sheet material (20) supplied on a coil (13) into a first radius (RI) .

16. Device according to one of Claims 9-15, in which there is a second rolling device (31) for applying a thickness profile over the width of sheet material (20) supplied on a coil (13) .

17. Device according to one of Claims 9-16, in which there are welding means for securing reinforcements

(37) to the interior of the steel tower (2) .

18. Steel tower comprising a foundation (1) on which there is a conical steel shell (2) with a height of at least ten times the mean diameter (d) of the steel shell and, on the top side of the steel shell, a bearing (4) for supporting a machine housing (5) of a wind turbine (3), characterized in that the diameter of the steel shell is greater than four metres in the vicinity of the foundation (1) .

19. Steel tower according to Claim 18, in which the steel shell is made from sheet material (20) with a constant width (b) .

20. Steel tower according to Claim 18 or 19, in which the steel shell is made from sheet material (20) , and the joining seams between the edges of the sheet material form a pitch angle (φ) with the horizontal plane which is not a right angle.

21. Steel tower according to Claim 18, 19 or 20, in which the steel shell is made from sheet material (20), and the thickness of the sheet is approximately constant over the entire height of the tower.

22. Steel tower according to one of Claims 18-21, in which the wall of the conical steel shell forms an angle of inclination (α) with a vertical which is greater than 2 degrees.

23. Steel tower according to one of Claims 18-22, in which circular reinforcements (37) are arranged on the inner side of the steel shell, and the distance between the reinforcements is preferably less than 0.5-1.0 metre.