TRANSITION PIECE FOR WIND TURBINE TOWER

Abstract

A transition piece for a wind turbine tower including a hollow frustoconical piece that is connected to an upper ring and a lower ring. The upper ring is connected to crossbars and the lower ring to radial columns. The transition piece also includes three connectors, each of them being connected to a crossbar, two radial columns and two connection profiles that keep the three connectors joined together, so that a pair of radial columns is arranged between a connector and the lower ring and the crossbars are arranged between the upper ring and a respective connector. The radial columns form an angle of between 65° and 75°, measured between the longitudinal axis of the corresponding radial column with the normal axis of the frustoconical piece.

Claims

1-13. (canceled)

14. A transition piece for a wind turbine tower with a nacelle and blades, the upper part of the tower being formed by tubular segments and the lower part by the connection of several lattice modules composed of columns, diagonal and horizontal ones, wherein the transition piece comprises a hollow frustoconical central piece connected to an upper ring and to a lower ring, said upper ring being connected to crossbars of the transition piece, and the lower ring connected to radial columns of the transition piece, and three connectors each of them being connected to a crossbar, two radial columns and two connection profiles that keep the three connectors joined together, so that a pair of radial columns is arranged between a respective connector and the lower ring and the crossbars are arranged between the upper ring and a respective connector, said radial columns forming an angle between 65° to 75°, measured between the longitudinal axis of the corresponding radial column and with the normal axis of the frustoconical piece.

15. The transition piece according to claim 14, wherein one radial column of the pair of radial columns arranged between a respective connector and the lower ring is compressed in use while the other radial column is elongated.

16. The transition piece according to claim 14, wherein each connector has an angled cylindrical configuration and two parts, preferably cylindrical, protrude from the angled area, each projecting part being adapted to cooperate with an end of a corresponding radial column, the ends of each connector being finished in flanges to complete their connection, for example, by a screwed connection, so that an upper end of the connector is fixed to a respective crossbar and a lower end is configured to be fixed to one of the columns of the tower.

17. The transition piece according to claim 14, wherein each radial column forms an angle of 25 to 35° with respect to the horizontal axis and each crossbar forms an angle of 55 to 65° measured from said horizontal axis.

18. The transition piece according to claim 14, wherein the upper ring is adapted to be connect, preferably by screwed connection, to the lower tubular segment of the tower.

19. The transition piece according to claim 14, wherein the crossbars comprise a length and a diameter equal to those of the columns of the lattice modules of the tower.

20. The transition piece according to claim 14, wherein the central frustoconical piece has an upper diameter of 4 to 4.5 m and a lower diameter of 3 to 4 m with a length of between 12 to 15 m which confers it a very lean design.

21. The transition piece according to claim 14, wherein the upper ring is modular and comprises several sectors that are joined together to form the upper ring, said sectors of the upper modular ring being preferably connected with flat bars overlapping said sectors.

22. The transition piece according to claim 14, wherein the upper ring comprises protrusions on its external contour that end in flanges, preferably with holes through which the connection means are inserted, which allow the connection to the corresponding crossbars.

23. The transition piece according to claim 14, wherein the lower ring consists of a single piece and comprises connection areas arranged peripherally to the lower ring itself, each connection area comprising two anchoring points so that from each anchoring point a radial column is fixed and extended leading to a different connector, preferably the connections between each anchoring point and its corresponding radial column located inside the connection area with access from inside the lower ring.

24. The transition piece according to claim 23, wherein two radial columns extend from each connector, said radial columns leading into anchoring points of different connection areas of the lower ring.

25. The transition piece according to claims 23, wherein a radial column fixed to an anchoring point of a connection area is compressed in use while the radial column fixed to the other anchoring point of the same connection area is elongated.

26. A wind turbine tower that comprises a nacelle and blades, said tower comprising an upper part formed by tubular segments and the lower part by lattice modules composed of columns, diagonal and horizontal ones, wherein the connection between the lower tubular segment and the upper lattice module is made through a transition piece according to claim

14.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Below, we will describe very briefly a series of drawings which will help us to better understand the invention and that expressly relate to an embodiment of said invention that is presented as a non-limiting example thereof.

[0015] FIG. 1 represents the entire wind turbine object of the invention.

[0016] FIGS. 2a, 2b and 2c show a perspective, plant and front view of the transition piece according to the Cartesian coordinates XYZ.

[0017] FIG. 3 shows the section AA with regards to the front view of FIG. 2c.

[0018] FIG. 4 shows a plant view with the angle formed by the radial columns arranged in pairs.

[0019] FIGS. 5a and 5b show an embodiment of the upper ring of the frustoconical piece and one of its sectors showing the modularity of the assembly.

[0020] FIG. 6 shows the lower ring of the frustoconical piece.

[0021] FIG. 7 shows a perspective view of one of the connectors.

DESCRIPTION IN DETAIL

[0022] As shown in FIG. 1, the assembly of the transition piece (1) is completed on the foundation (2) from which protrude the bolt cages (not detailed in the figure) which will first connect with the transition piece (1). Once the assembly of the transition piece (1) is completed, using a conventional 100 m high crane, the different parts of the monotubular tower (4) are assembled, and over them, the rotor (5) and its blades (6). At this point, we proceed with the self-lifting system that allows the assembly to be lifted and new lattice modules (3) to be introduced from the bottom until the entire assembly of the wind turbine is completed. Depending on the number of modules (3), a greater or lesser height will be reached in the final tower. These modules are formed by columns or legs (3′), some of which are diagonal (3″) and other horizontal (3′″). The maximum diameter of these elements is that of the columns (3′), with 1 m in diameter and with adjustable thicknesses depending on the height of the tower.

[0023] The transition piece (1), as shown in detail in FIGS. 2a, 2b and 2c, comprises a central frustoconical piece (7) that is hollow and mechanically welded, topped by an upper ring (8) and ended by a lower ring (9). Both rings are responsible for connecting the rest of the elements that make up the transition piece (1), such as crossbars (10), radial columns (11) and connection profiles (12). The tripod of the transition piece (1) is completed with three connectors (13) that combine the connection of crossbars (10), radial columns (11) and connection profiles (12) with the columns (3′) of the lattice modules (3) of the previous figure. Each connector (13) is connected to a crossbar (10), two radial columns (11) and two connection profiles (12) that keep the three connectors (13) joined together, so that a pair of radial columns (11) remains arranged between a connector (13) and the lower ring (9) and the crossbars (10) are arranged between the upper ring (8) and a respective connector (13), said radial columns (11) forming an angle between 65° and 75°, measured between the longitudinal axis of the corresponding radial column (11) and with the normal axis of the frustoconical piece (7).

[0024] In the preferred embodiment of the invention, the diameter and thickness of the crossbars (10) is the same as that of the columns (3′) of the lattice modules (3). So is their size, so that they can be transported in conventional trucks. The crossbars (10) and the radial columns (11) are preferably circular in shape and the connection profiles (12) preferably square in shape. The connection of all these mentioned elements, together with the connection with the connectors (13) and with the upper (8) and lower (9) rings are preferably carried out with screwed connections with maintenance-free screws.

[0025] The connectors (13) are connected through their lower end (17) to the columns (3′) of the lattice tower, as shown in section AA of FIG. 3 and in FIG. 1, from one of its sides they are connected together with the connection profiles (12) as shown, e.g., in FIG. 2a, through some parts (19) that protrude from an angled area towards the inside of the transition piece (1) they are connected with the corresponding radial columns (11) forming an angle of 25 to 35° with respect to the horizontal column, and through their upper end (18) they make change of direction towards the upper part of the transition piece (1) and they are connected with the corresponding crossbars (10) forming an angle of 55 to 65° from the horizontal column. This elongated connector (13) in its upper part and the downward-extended design of the upper ring (8) make the crossbars (10) to have a length of approximately 16 m so that they can be transported in conventional trucks.

[0026] In the preferred embodiment of the invention, the frustoconical piece (7) is formed by different rings (7′, 7″) welded at the factory in the same way as the ferrules of a tubular tower are welded, reaching a height of around 13 m, with further 2 m to be added for the upper (8) and lower (9) rings. All this gives it a high-rise design, between 12 and 15 m, compared to the upper diameter of 4.5 m and the lower diameter of 3.3 m. The total height of the transition piece (1) is around 15 to 20 m. The thicknesses of all the pieces is constrained as the weight cannot be high. If this is to happen, the tower's natural frecuency would decrease. The tower must be non-stiff soft-soft and for this, it must be operated within a natural frequency preventing to increase weight.

[0027] In finite-element models correlated on the transition piece (1), it can be seen that the bending moment has two paths: the crossbars (10) are the 30% and the central frustoconical body (7) and its radial columns (11) the 70%. To compensate for these loads, two technical transformations are carried out. The central frustoconical piece (7) is provided with great length, so that the torque acting on it is widely separated and balanced. And the radial columns (11) are arranged in pairs.

[0028] In FIG. 4 it is shown that the radial columns (11) connected almost tangentially between the corresponding connector (13) and the frustoconical central piece (7) form an angle of around 65° to 75°. It is the angle measured between the longitudinal axis of the corresponding radial column (11) and the normal axis of the frustoconical piece (7), that is, the Y axis according to the drawing of FIG. 2a. When torsioning the transition piece (1) in use, one of the radial columns (11) arranged between a respective connector (13) and the frustoconical piece (7) is compressed and the other radial column (11) arranged between the adjacent connector (13) and the frustoconical piece (7) is elongated, so both radial columns are offset. The rest of the radial columns act in the same way, compressing and elongating in pairs.

[0029] On the other hand, if the two radial columns (11) that emerge from the same connector (13) are taken, one of them is compressed and its partner is elongated. This behaviour multiplies the torsional stiffness by two and solves the problems presented at the critical stress concentration points of the transition piece during the working operation or in use of the wind turbine.

[0030] In the preferred embodiment of the invention, the upper ring (8) is adapted to connect, preferably by screw connection, to the lower tubular segment (4) of the wind turbine tower. It is a piece of 4 to 4.5 m in diameter, which by adding the protrusions (15) of the connections with the crossbars (10) increase its outer diameter, since said protrusions (15) are external. The protrusions (15) end in flanges with holes through which the connecting screws are inserted.

[0031] FIGS. 5a and 5b show another embodiment of the upper ring (8) wherein said upper ring (8) is modular, and as shown in FIG. 5a it can be manufactured in three parts or sectors that are connected together with flat bars (14) overlapping said pieces and screwed on. In this embodiment, the protrusions (15) also end in flanges with holes through which the connecting screws are inserted.

[0032] As shown in FIG. 6, the lower ring (9), in the preferred embodiment of the invention, is made of a single piece and comprises connecting areas that are peripheral to the lower ring (9) itself. Each connection area comprises two anchoring points (16) so that from each anchoring point (16) a radial column (11) is fixed and extended which leads to a different connector (13). The screwed connections between an anchoring point (16) and its corresponding radial column (11) are made from inside the connection area, accessing said point through the interior of the lower ring (9).

[0033] Likewise, as shown e.g., in FIG. 4, in the preferred embodiment of the invention from each connector (13) two radial columns (11) are extended, said radial columns (11) leading to anchoring points (16) of different connection areas of the lower ring (9).

[0034] FIG. 7 shows one of the three connectors (13) that is arranged in the lower part of the transition piece (1). They have a cylindrical shape that begins straight and ends at an angle. In the straight area, that is, at the lower end (17), it comprises a flange that cooperates with the self-lifting system that raises the completely assembled wind turbine and allows the introduction of modules (3) from the bottom. Said flange is reinforced by overlapping two flanges, one narrower and the other wider, forming a step. Two protruding sections (19), also cylindrical in shape, protrude from the angled area. All the cylindrical ends comprise flanges to complete their screw connection: the upper end (18) with the corresponding crossbar (10), the lower end (17) with the column (3′) of the corresponding modules (3) that make up the lattice tower and the protruding sections (19) of the angled area with the corresponding radial columns (11). In the lower part, two squares protrude (they could also have a cylindrical shape) perforated in their periphery and arranged to complete the screwed connection with the connection profiles (12).