Foundation for wind turbine tower

Abstract

Foundations for wind turbine towers of the kind used to support both metal and concrete towers of wind turbines use precast concrete or metal beams combined with small footings concreted in situ, the beams being structurally connected at the core of the foundation by connecting and supporting elements of the tower. The presented invention offers the main advantage that a significant reduction in the amount of material used, both concrete and rebar, is achieved, which greatly reduces erection time, resulting in considerable economic savings, as well as facilitating adaptation to various terrains.

Description

[Technical field]

[0001] This description, as indicated in the "Title of the Invention", relates to a foundation for a wind turbine tower, of the type used to support both metal and concrete towers of wind turbines, using precast concrete combined with small footings that are concreted in situ, with beams structurally connected at the center of the foundation by connecting and supporting elements of the tower.

[0002] The present invention relates to the field of foundations used as support for both metal and concrete towers of wind turbines. [Background technology]

[0003] Wind turbine towers are currently widely used, mainly for generating electrical energy. Due to their great height, they need to be firmly fixed to the ground and in most installations are constructed with mainly tapered foundations made of reinforced concrete. This is explained in the patent applications ES 2659523 "Method for erecting a wind turbine", ES 2685834 "A wind turbine tower and method for altering the natural frequency of a wind turbine tower" and ES 2347742 "Wind turbine foundation". ES 2571731 "Wind power plant foundation as well as wind power plant" includes in particular the reinforcement used for conventional foundations. This type of foundation brings about many disadvantages, of which the foundation requires a deep pre-excavation with a diameter of more than 18 meters and a depth of at least 4 meters, which requires a foundation with a depth of about 400 m. 3Large quantities of concrete, or more, are used, as well as some considerable amounts of heavy-section metal reinforcement or rebar, weighing more than 38,000 kg, all of which entails high economic costs and long construction times.

[0004] To partially circumvent these problems and to use less concrete and rebar, in some cases the mainly cylindrical structures are implemented with perimeter structural reinforcement in the form of radial ribs or braces, both concreted in situ. Examples of these structures can be found in patent documents WO2016116645 "Concrete Tower", WO2015185770 "Foundation system for towers and method for installing the foundation system for towers" and ES2524840 "Foundation system for towers and method for installing the foundation system for towers".

[0005] In other cases, these transverse reinforcements are in the form of precast concrete braces or metal bars or elements, as can be seen in patent documents ES 2 544 806 "Improved foundation for a wind turbine tower" or ES 2 601 232 "Foundation for wind power plants".

[0006] However, these embodiments do not address the major problems mentioned above, which are due to the large volumes of foundations that need to be concreted in situ, and the complexity and amount of reinforcement. Apart from these problems, the concrete application must be continuous without interruption to allow for hardening, which necessarily requires a constant supply of large amounts of concrete, which is difficult or impossible to obtain in many regions or countries. In many countries with poor economies, it is not easy to obtain the large amounts of rebar required for reinforcement.

[0007] Yet another problem is that in order to perform the required excavation, the depth required to do so requires the construction of a slope for the heavy equipment to descend, which increases the time required for the operation. Similarly, the bottom of the excavated hole needs to be level and smooth.

[0008] All of this means that typical mixing, concrete application, and curing times of around three or four weeks, when multiplied by the many wind turbines at each wind farm, entail significant economic costs.

[0009] A further drawback is that this type of foundation is difficult to adapt to heterogeneous or poor terrain, often requiring even larger investments or making the installation of wind turbines impossible in some terrains. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Spanish Patent Application Publication No. 2659523 [Patent Document 2] Spanish Patent Application Publication No. 2685834 [Patent Document 3] Spanish Patent Application Publication No. 2347742 [Patent Document 4] Spanish Patent Application Publication No. 2571731 [Patent Document 5] International Publication No. 2016116645 [Patent Document 6] International Publication No. 2015185770 [Patent Document 7] Spanish Patent Application Publication No. 2524840 [Patent Document 8] Spanish Patent Application Publication No. 2544806 [Patent Document 9] Spanish Patent Application Publication No. 2601232 Summary of the Invention [Problem to be solved by the invention]

[0011] To solve the problems currently existing in wind turbine foundations, a foundation for a wind turbine tower, which is the subject of the present invention, is envisaged, which combines at least three radially horizontally arranged precast beams with a small reinforced concrete footing constructed in situ, in the centre of which the concrete footing supports the outermost ends of the beams by means of supporting ball joints, either linear or spherical, which may or may not provide a displacement limit in one or more directions, thus allowing all supporting stresses to be equally distributed by the footing, the ends of which are also fixed between the ends of the beams and the footing by means of anchors, preventing the tower from tipping over. The different beams are rigidly fixed together in the centre of the foundation by means of connecting means. The precast beams can be made of concrete, metal or a combination of both concrete and metal.

[0012] Footings may take on different shapes and depths, even for the same foundation, to accommodate the particular characteristics of each terrain. [Means for solving the problem]

[0013] Preferably, three precast beams are used, one of which is approximately twice as long as the other two, with the inner end of the smaller beam being rigidly fixed to the center of the larger beam, forming a cross-plane structure. This structure has proven to be optimal in terms of ease of manufacture, transportation and performance. However, it is also possible to construct the foundation that is the object of the invention, which consists of alternating beams, more than two in number, of the same or different lengths, with the foundations joined to the inner ends of the beams, each of whose outer ends is likewise connected to a footing.

[0014] Two embodiment variants are described, one where the wind turbine tower is metal and another where the wind turbine tower is concrete at least in its lower portion, i.e., made entirely from precast concrete in either sections or segments, or the variant combines a mostly concrete lower tower portion with a metal upper tower portion.

[0015] If the wind turbine tower is metal, the means for rigidly fixing the beams also include concrete ball fillers located below ground level at the beam connections, across which there is an upper slab emerging above ground level for fixing the metal tower.

[0016] In case the wind turbine tower is concrete, the means for rigidly fixing the beams, at least in the lower part of the wind turbine tower, also include a hollow tension chamber closure, made by a precast concrete element with external circular sector or polygonal faces and walls, placed between the inner cross sections of the beams, and an upper slab with a circular crown surface, across the connection of the beams, for supporting the precast concrete tower and for fixing the vertical post-tensioning part of the tower, which in this case is supported on the upper slab, and which passes through the upper slab and through drillings or ducts to the hollow tension chamber, in which are located the means for post-tensioning and fixing of the cables that provide rigidity to the tower.

[0017] Preferably, the beams are of rectangular cross section, with greater height at the center cross section and lesser height at the ends. Because the greater height cross section is oriented vertically downwards, most of the foundation is buried below the ground level, with only a portion of the upper slab showing, minimizing the visual impact. However, where visual impact is not important and further savings are desired, it is possible to assemble beams with greater height cross sections oriented upwards that appear above the ground level together with the entire upper slab, together with some of the concrete ballast fill or precast concrete elements.

[0018] The disclosed foundation for a wind turbine tower requires a specific construction method including a first step of preparing the terrain, a second step of concreting the footing, a third step of curing the footing, a fourth step of assembling the precast beams, a fifth step of constructing the beam connections at the center, and a sixth step of filling the remaining space with the original ground surface. Effect of the Invention

[0019] The presented foundation for wind turbine towers offers many advantages over known technologies currently used, most importantly when using small footings, the foundation for wind turbine towers offers considerable savings in both the amount of concrete used and the amount of reinforcing steel, thereby implying both significant economic savings and high feasibility in regions or countries where there are problems regarding the supply or production of such quantities of concrete or steel.

[0020] As a result of the foregoing, problems associated with the need to dispense large volumes of concrete in an uninterrupted, continuous manner inherent in conventional large foundations to compensate for hardening are eliminated, and the need to fabricate costly specialized reinforcement in-situ prior to setting with concrete is eliminated, allowing for the use of conventional prefabricated steel reinforcement.

[0021] Another important advantage is that the need for excavation, both in terms of volume and depth, is significantly reduced and, as is the case for conventional foundations, typically several meters deep, there is no need to create slopes for heavy machinery to descend downwards, which results in significant savings in time and economic costs.

[0022] Another advantage of the present invention is that, unlike the prior art, the bottom surface of the footing does not need to be perfectly level or smooth, again resulting in further savings in time and financial costs.

[0023] Another important advantage that can be highlighted is that when using precast elements, the total construction time of the foundation is significantly reduced from the usual three or four weeks, using conventional techniques, to as little as one week.

[0024] Furthermore, another additional advantage is that the foundation can easily adapt to different types of ground (both homogeneous and heterogeneous or poor terrain), making it possible to install wind turbine towers in areas not possible with conventional foundations without any reduction in capacity.

[0025] In order to achieve a good understanding of the invention, in the attached drawings a practical preferred embodiment of a foundation for a wind turbine tower is shown by means of two embodiment variants, one variant relating to a metal tower and another variant relating to a tower having at least the lower part of the tower made from concrete. [Brief description of the drawings]

[0026] [Figure 1] 1 shows a cross-section and plan view of a foundation for a metal tower with the majority of the foundation below grade. [Figure 2a] 1 shows cross-sectional views of different variants of footings that can be used depending on the type of ground in the foundation for a metal tower with the majority of the foundation below grade. [Figure 2b] 1 shows cross-sectional views of different variants of footings that can be used depending on the type of ground in the foundation for a metal tower with the majority of the foundation below grade. [Figure 2c] 1 shows cross-sectional views of different variants of footings that can be used depending on the type of ground in the foundation for a metal tower with the majority of the foundation below grade. [Diagram 3] 1 shows cross-sections and plans of a foundation for a tower that is fully or partially concreted with the majority of the foundation below grade. [Figure 4a] 1 shows cross-sectional views of various variations of footings that can be used depending on the type of ground in a fully or partially concreted tower foundation with the majority of the foundation below grade. [Figure 4b] 1 shows cross-sectional views of various variations of footings that can be used depending on the type of ground in a fully or partially concreted tower foundation with the majority of the foundation below grade. [Figure 4c] 1 shows cross-sectional views of various variations of footings that can be used depending on the type of ground in a fully or partially concreted tower foundation with the majority of the foundation below grade. [Diagram 5]1 shows an elevation and a plan view of an upper slab for fixing a metal tower. [Figure 6] 1 shows elevation and plan views of a precast concrete element for closing a tension chamber for a tower that is fully or partially concreted. [Figure 7] 1 shows elevation and plan views of an upper slab for supporting a tower that is fully or partially concreted. [Figure 8] 1 shows a cross-sectional view of a foundation for a metal tower with a portion of the foundation above grade. [Figure 9] 1 shows a cross-section of a fully or partially concreted foundation for a tower with a portion of the foundation above grade. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] The structure and features of the present invention can be better understood in the following description taken in conjunction with the accompanying drawings.

[0028] Figures 1 and 3 show an example of a foundation for a wind turbine tower, which comprises at least three radially horizontally arranged precast beams (2a, 2b, 2c), the outermost end or ends of the beams are supported at the concrete footing (1) by a supporting ball joint (3) at the center of the footing and fixed by a number of anchors (4) between the ends of the beams (2a, 2b, 2c) and the footing (1), the different beams being rigidly fixed together at the center of the foundation by connecting means. The supporting ball joints (3) may be linear or spherical and may or may not provide displacement limitation in one or more directions.

[0029] In the preferred embodiment shown in figures 1 and 3, the beam (2a) is approximately twice as long as the beams (2b, 2c), whose inner ends are then rigidly fixed to the centre of the beam (2a) to form a cross-plane structure. This structure has proven to be optimal in terms of ease of manufacture, transport and performance. However, it is also possible to construct the foundation that is the object of the invention, which consists of alternating beams, more than three in number, of the same or different lengths, whose foundations are joined to the inner ends of the beams, each of whose outer ends is likewise connected to the footing (1).

[0030] The precast beams (2a, 2b, 2c) can be made from concrete, metal, or a combination of both concrete and metal.

[0031] In all cases, the means for rigidly fastening the beams (2a, 2b, 2c) include the use of conventional techniques for connecting precast concrete to other beams, tongue and groove joints, and threaded rods, brackets, reinforcing ends, etc. to concrete the cover of the post-tensioned helix.

[0032] Two embodiment variants are described. As shown in Figures 1, 2 and 5, in the first embodiment variant, it is mentioned that the wind turbine tower is metallic, in which case the means for rigidly fixing the beams (2a, 2b, 2c) further comprises a concrete ballast filling (5) located below the ground level (8) at the connection of the beams (2a, 2b, 2c), and across the connection of the beams (2a, 2b, 2c) there is an upper slab (6) emerging above the ground level (8) for fixing the metal tower (7).

[0033] The concrete ballast fill (5) can be constructed either from salvageable forms made from wood, metal, or a combination of both wood and metal, or from forms made from precast concrete elements.

[0034] FIG. 2 shows that the upper slab (6) for fixing the metal tower (7) preferably adopts a circular plan and its faces are polygonal, and may be preferably of reinforced concrete of at least HA-50 strength.

[0035] The fastening of the metal tower (7) to the upper slab (2) is accomplished using conventional techniques for fastening to a base such as threaded rods with nuts, bolts, and the like.

[0036] As shown in Figures 3, 4, 6 and 7, in a variant of the second embodiment, at least in the lower part of the wind turbine tower, reference is made to the case where the wind turbine tower is concrete, and the means for rigidly fixing the beams (2a, 2b, 2c) further comprise precast concrete elements (10) installed between the inner ends of the beams (2a, 2b, 2c) and defining a hollow tensile chamber (9), and an upper slab (11) for supporting the concrete tower (12) and for fixing the vertical post-tensioning part (13) of the tower across the connection of the beams (2a, 2b, 2c) and across the tensile chamber (9).

[0037] The precast concrete element (10) adopts a plane selected from the group formed by a circular sector whose angle is determined by the number of beams used and a polygon having a single vertical wall on the side or sides not adjacent to a beam. Figure 6 shows a precast concrete element (10) having a circular sector plane (90° angle in the case shown) and a single vertical wall at the curved end.

[0038] FIG. 7 shows that the upper slab (11) includes an access opening to the tensile chamber (9), and the upper slab (11) is preferably made from at least HP-50 strength prestressed concrete.

[0039] A precast concrete tower (12) is supported on an upper slab (11) with a vertical post-tensioned section (13) which passes through the upper slab (11) and reaches, through bores or ducts, into the hollow tension chamber (9) and in which are located means for post-tensioning and fixing of cables which provide stiffness to the tower, as is common practice for towers made from precast concrete sections or segments.

[0040] In both variants, it is possible to adopt different configurations regarding the shape, size and depth of all or any of the footings, to adapt the foundation to the respective particularities of the terrain on which the tower is to be installed, as shown in figures 2a, 2b, 2c, 4a, 4b and 4c. Thus, figures 2a and 4a show footings at the same depth, corresponding to homogeneous terrain; figures 2b and 4b show footings at different depths, corresponding to heterogeneous terrain or terrains of different heights; finally, figures 2c and 4c show deep pile foundation footings for poor terrain.

[0041] The beams (2a, 2b, 2c) are preferably of rectangular cross section, with greater height at the center cross section and lesser height at the ends. As shown in Figures 1, 2, 3, and 4, the greater height cross sections are oriented vertically downwards so that most of the foundation is buried below the ground level (8) to minimize visual impact. However, as shown in Figures 8 and 9, where visual impact is not important, it is possible to assemble alternating beams (2a, 2b, 2c) with greater height cross sections oriented upwards emerging from the ground level (8) together with the entire corresponding upper slab (6, 11) together with parts of concrete ballast fill (5) or precast concrete elements (10).

[0042] The proposed foundation for a wind turbine tower requires a specific construction method, which is: The first stage is to prepare the terrain, The second stage is to make the footing (1) out of concrete; A third stage is the hardening of the footing (1); A fourth step is to assemble the precast beams (2a, 2b); A fifth step of connecting the beams (2a, 2b) at the center; A sixth step is filling the remaining space to the original ground level (8); A method comprising:

[0043] The first stage of preparation of the terrain involves, as the case may be, the excavation of the grooves for the footings (1), the excavation of grooves between the footings (1) to accommodate the beams (2a, 2b), and the excavation of a central groove to connect the beams (2a, 2b) and for the concrete ballast fill (5) or precast concrete elements (10).

[0044] The second stage of concreting the footing (1) includes the steps of preparing the formwork, fitting the metal reinforcement, fitting the supporting ball joints (3) and anchors (4), and pouring the concrete.

[0045] The third stage, which involves hardening the footing (1), is carried out for a period appropriate to the shape and amount of concrete used.

[0046] The fourth stage of assembling the precast concrete beams (2a, 2b) comprises placing the beams by means of a crane in the channels with their outer ends at the supporting ball joints (3) and rigidly fastening the inner ends of the beams (2a, 2b) together by conventional techniques for connecting precast concrete elements or rigidly fastening the inner end of the beam (2b) to the middle part of the beam 2a if the beam (2a) is twice the length of the beam (2b) and rigidly fastening the outer ends to the footing (1) by means of anchors (4).

[0047] If the wind turbine tower is metal, the fifth stage of connecting the beams (2a, 2b) at the center includes placing a concrete ballast fill (5) and placing a top slab (6) over the connection of the beams (2a, 2b).

[0048] If the wind turbine tower is concrete at its bottom, the fifth step of connecting the beams (2a, 2b) at the core includes assembling a precast concrete element (10) in the remaining opening between the beams (2a, 2b, 2c) at the core by conventional techniques for connecting precast concrete elements, the precast concrete element (10) defining the hollow tensile chamber (9), and constructing an upper slab (11) over the connection of the beams (2a, 2b).

[0049] Those skilled in the art will readily understand that features of different embodiments can be combined with features of other possible embodiments, where such combination is technically possible.

[0050] All information referred to in the examples or embodiments forms part of the description of the invention.

Claims

1. 1. A foundation for a wind turbine tower, comprising at least three precast beams (2a, 2b, 2c) arranged horizontally in a radial pattern, the outermost ends of each of the precast beams (2a, 2b, 2c) being supported by a corresponding number of footings (1) by supporting ball joints (3) in the center of the concrete footings (1), and the outermost ends of the precast beams (2a, 2b, 2c) being fixed to the corresponding number of footings (1) by a plurality of anchors (4), and the precast beams (2a, 2b, 2c) being firmly fixed to each other in the center of the foundation by connecting means.

2. A foundation for a wind turbine tower as described in claim 1, wherein one of the precast beams (2a) is approximately twice the length of the other two precast beams (2b, 2c), and the inner ends of the other two precast beams (2b, 2c) are firmly fixed to the center of one of the precast beams (2a) to form a cross-plane structure.

3. 3. Foundation for a wind turbine tower according to claim 1 or 2, wherein the wind turbine tower is metal and the connection means for rigidly fixing the precast beams (2a, 2b, 2c) comprise concrete ballast fillings (5) located below the ground level (8) at the connections of the precast beams (2a, 2b, 2c) and wherein at the connections of the precast beams (2a, 2b, 2c) there is an upper slab (6) emerging above the ground level (8) for fixing a metal tower (7).

4. A foundation for a wind turbine tower as described in claim 3, wherein the connection means include the concrete ballast filling (5) and a formwork for precast concrete elements.

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