WO2011056121A1

WO2011056121A1 - Wind turbine with turbine blades

Info

Publication number: WO2011056121A1
Application number: PCT/SE2010/051050
Authority: WO
Inventors: Staffan ENGSTRÖM
Original assignee: Ägir Konsult AB
Priority date: 2009-10-02
Filing date: 2010-09-30
Publication date: 2011-05-12
Also published as: SE0950727A1

Abstract

The invention regards a wind turbine comprising a least one turbine blade attached to a hub 10. The turbine blade comprises an inner part 2, comprising a load carrying structure 6 with a longitudinal axis 21 and aerodynamically active surfaces 7, which wholly or partly enclose the structure, joined to an outer part 3 by means of a joint 19. The joint 19 comprises a ring shaped bearing 8 and a blade pitch mechanism 9, which enables the outer part 3 to rotate in relation to the inner part 2 around the longitudinal axis 21. Furthermore the joint 19 is situated at a distance from the rotational centre 22 of the wind turbine of between one eighth and half of the total length of the turbine blade from the rotational centre 22 of the wind turbine to the outer end 23 of the outer part and where the load carrying structure 6 stretches from the hub 10 to the joint 19. The invention also regards a wind power plant comprising such a wind turbine.

Description

Wind turbine with turbine blades

Field of invention

This invention regards a wind turbine according to the preamble of Claim 1.

The invention also regards a wind power plant comprising such a wind turbine.

The background of the invention

Wind turbines for wind power plants and other purposes extract energy from the wind by braking it to a lower speed. Generally a wind turbine comprises two or three turbine blades with aerodynamically active surfaces that are mounted on a turbine hub and rotating around an axis which for this type of wind turbine mainly is horizontal. Also one bladed wind turbines exist. The extracted mechanical torque is further transferred for use e.g. via a gearbox in an electrical generator or directly in a generator. For power control and for facilitating start and stop, each blade is mostly made in a way that enables rotation (pitching) around its own axis of roughly 90 degrees.

The blades preferably are made of a composite material, which may consist of a plastic material reinforced with fibres of glass, carbon or other materials. Composites partly consisting of wood also exist. The mobility between blade and hub is commonly achieved by connecting the blade to the hub by means of o single rolling bearing. The hub normally consists of a steel construction, often of cast nodular iron.

For control purposes it is normally sufficient to rotate the outer part of the turbine blade. It is commonly known to achieve the mobility between inner and outer parts according to the principle of a sleeve gliding on a pin, see e.g. US-4,575,309. Another well-known solution applied is a pin supported by two rolling bearings. These solutions only enable rotation of a short section of the turbine blade, since the stress acting on the pin otherwise gets too large. The short height of the profile in the outer parts of the blade obstructs access for inspection and maintenance.

In order to enable larger energy production, wind turbines and their turbine blades have grown larger. Today wind turbines with diameters of 125 m and more are produced. Turbine blades for such large turbines are not possible to transport onshore on ordinary roads, and the use of such turbines has thus, mainly been limited to offshore wind power plants. Thus, limited capacity of public roads is an obstacle against this development. With respect to the transport limitations onshore it is desirable to be able to divide the blades in parts.

Examples of solutions for making the turbine blades transportable in parts are revealed in the patent document EP- 1 ,561 ,947, which depicts a solution aiming to lead a lightning conductor through the joint between the sections. It however does not pay attention to where the point of division is situated and thus neither on how this influences the aerodynamically active surfaces. The turbine blade is put together by means of a metal plate.

Furthermore documents US 2009/0148291 and US 2009/0148285 disclose that the inner and outer parts of the turbine blades are attached to each other by means of a bearing, but none of them reveal what type of bearing is used.

The aim of this invention is to create a turbine blade with a design that pays attention to the aerodynamically active surfaces and the need for rotating the blade, and that is easy to transport onshore and offshore.

Summary of the invention

The above mentioned purposes of the invention are achieved by the invention according to the independent patent claim. Preferred embodiments are defined by the dependent claims.

Thus the invention covers a wind turbine comprising at least one turbine blade attached to a hub. The turbine blade comprises an inner part, comprising a load carrying structure with a longitudinal axis and

aerodynamically active surfaces that wholly or partly enclose the structure, joined to an outer part by means of a joint. The joint is situated at a distance from the rotational centre of the wind turbine of between one eighth and half of the total length of the turbine blade from the rotational centre of the wind turbine to the outer end of the outer part, and where the load carrying structure covers the distance from the hub to the joint.

Furthermore, the joint comprises a bearing and a pitch mechanism, which enables rotation of the outer part in relation to the inner part around the longitudinal axis. The bearing is ring shaped and enables rotation around the longitudinal axis, and where the load carrying structure reaches from the hub to the joint.

When using a generator according to the preferred embodiment, the hub and the inner part of the load carrying structure will be relieved from the driving torque, which enables smaller dimensions of these parts. Since the joint between the inner and outer part is situated at some distance from the rotational centre of the wind turbine, the moment acting on the bearing and the blade pitch mechanism will decrease considerably. Thus also the bearing and the blade pitch mechanism will be possible to manufacture and maintain at a lower cost than according to previous art.

The bearing and the blade mechanism will be easily accessible for maintenance, compared to if only the outermost part of the blade is possible to rotate. When the blade is positioned horizontally, a person may walk upright out to the bearing, for wind turbines of a size where application of the invention is of interest. Making a larger part of the blade possible to rotate will also benefit the aerodynamics.

The ring shaped form of the bearing is also advantageously since this is an economical way to design a bearing that shall absorb a large moment. It is a especially economical to use when the structure is wide enough, as in this case. Furthermore, this type of bearing is compact and easy to connect to the inner and outer load carrying structures of the blade. It also provides easy connection of the pitch mechanism.

The design of a wind turbine will also be more economical than according to previous art, since it is considerably cheaper to absorb the large moments close to the hub with a steel construction than with an equivalent design of composite material.

In summary, the invention means that the transportation problem of large wind turbine blades will be solved without having to create joints between composite parts. Furthermore, the wind power plant in total will be more economical than according to previous art.

Summary of enclosed drawings

The invention is further explained with reference to drawings, where;

Figure 1 depicts a principal drawing of a wind power plant with a wind turbine where the joint between the inner and outer parts is indicated,

Figure 2 depicts a cross section of a wind power plant, where the figure to the left is a side view and the figure to the right is a front view,

Figure 3 depicts a cross section according to the line A-A in figure 2 where the outer and inner parts of a turbine blade are joined,

Figure 4 depicts a perspective view of the separate components that are part of the joint at the cut A-A, and

Figures 5 - 6 depict principal designs for the separate parts in the inner parts and how they are joined together.

Detailed description of the invention

The invention is hereafter described with reference to a direct drive generator which e.g. is depicted in the European patent application

EP- 1.657.437. The application may also be applied on other technical solutions, e.g. with a gearbox and a generator with a high rotational speed.

In the figures 1 and 2 may be seen a wind power plant furnished with a machinery 1 that carries a wind turbine. Figure 2 depicts to the left a side view of the wind power plant and to the right a front view of the same. The wind turbine consists of at least one turbine blade attached to a hub 10. The machinery is supported by a tower 4, which is connected to a foundation in the ground 5. The turbine blade comprises an inner part 2, comprising a load carrying structure 6 with a longitudinal axis 21 and aerodynamically active surfaces 7 which enclose the structure 6 as depicted in e.g. figures 3 and 4. The inner part 2 is connected to an outer part 3 by means of a joint 19. The joint 19 comprises a bearing 8 and a blade pitch mechanism 9, which enables rotation of the outer part in relation to the inner part 2 along a longitudinal axis 21. Furthermore the joint 19 is situated at a distance from the

rotational centre 22 of the wind turbine amounting to between an eighth and half of the total length of the turbine blade from the rotational centre 22 of the wind turbine to the outer end 23 of the outer part, as e.g. shown in figures 1 and 2, and where the load carrying structure 6 stretches from the hub 10 to the joint 19. According to a preferred embodiment the joint 19 is situated at a distance from the rotational centre 22 of the wind turbine amounting to between a fourth and half of the total length of the turbine blade from the rotational centre 22 to the outer end 23 of the outer part.

Figure 5 reveals a cross section of a preferred embodiment of the turbine blade at the joint 19. It depicts the load carrying structure 6 in the inner part 2 of the blade. The load carrying structure 6 is designed as a tube which in preferred embodiments has a circular, cylindrical cross section. Also other geometrical shapes of the cross section are possible, such as elliptical or oval and adapted according to the desired aerodynamically shape according to figure 6. The load carrying structure also may be composed by several elements. The structure also may possess a cross section that varies with the distance from the hub and e.g. is conical. This structure is preferably manufactured in steel or other material.

The structure is preferably manufactured in steel while the shell around it does not carry any loads except for those that are created locally. As depicted in figures 5 and 6 the aerodynamically active surfaces 7 are joined from a number of panels, here exemplified by an aft upper panel 7A and an aft lower panel 7B together with a front panel 7C. These panels are adapted for joining with the load carrying structure 6, e.g. by means of a screw joint 24. The aerodynamically active surfaces may be manufactured in a composite material or metal, e.g. aluminium.

In an alternative embodiment the load carrying structure 6 is designed in a way that wholly or partly makes it into an aerodynamically active surface. E.g. the front panel 7C may be left out or the two aft panels 7A, 7B may have another geometrical shape as described above, see figure 6.

The bearing 8 is ring shaped and enables rotation of the load carrying structure 6 around the longitudinal axis 21. Furthermore it is suitable that the bearing 8 has a large diameter and a short length. Preferably the diameter of the bearing 8 is at least five times larger than its length and may e.g. consist of a rolling or a sliding bearing. It is the bearing 8 that together with the blade pitch mechanism 9 creates the mobility between the inner and outer parts 2, 3 of the blade.

The bearing 8 is connected to the load carrying structure 6 of the inner part 2 and the outer part 3. The bearing may be connected by means of screw joints. It is preferably designed as a ring which is consisting of two rings. The forces between the rings are transferred by the rolling elements or the sliding surfaces respectively. Preferably on the inner side of the bearing 8 a gear rim or similar is arranged for the blade pitch mechanism 9 to interact with. The blade pitch mechanism may be electric or hydraulic. Also other types are conceivable. The blade pitch mechanism 9 enables the outer part 3 to rotate about 90 degrees around its own axis.

The outer part 3 is preferably manufactured in a composite material, e.g. glass fibre reinforced plastic, but also other materials are conceivable.

The wind turbine is preferably used in a wind power plant as depicted in figures 1 and 2.

As revealed in figure 2 the inner part 2 of the turbine blade together with the load carrying structure 6 is attached to the hub 10, which by means of a bearing 1 1 is connected to a generator 12 and a machinery bed 13. The aerodynamically active parts 7 in the inner part 2 constitute preferably at most three fourths of the length of the load carrying structure 6, stretching from the joint 19 to the hub 10 and thus also inside a spinner 17. The aerodynamically active parts 7 in the inner part 2 stretch from the joint 19 to the spinner 17. The machinery bed 13 is furthermore connected to the tower 4 by means of a bearing 14 and one or several yaw mechanisms 15.

The driving torque of the turbine is preferably transferred directly from the load carrying structure 6 to the rotor of the generator 12 by means of flexible elements for transfer of torque 16. In a more conventional design of the wind power plant the torque may be transferred through the hub 10. The rotor is preferably arranged on the outside of the generator 12, but also other solutions are possible.

Besides the mentioned details of the design, the hub 10 and the machinery 1 are surrounded by the spinner 17 and a nacelle cladding 18, the purpose of which is mainly to provide a weather protection for equipment and personnel.

A wind power plant where the wind turbine according to the present invention is especially useful typically has a turbine diameter of 100 - 200 meters or more. This implies a length of the turbine blades of roughly 50 - 100 meters. In the inner part of the blade the load carrying structure of an embodiment with a circular cross section may possess a diameter of roughly 2 - 6 meters. The height to the rotational centre of the wind turbine is typically roughly the same as the turbine diameter.

The present invention is not limited to the preferred embodiments as described above. Various alternatives, modifications and equivalents may be used. The embodiments mentioned above therefore shall not be assumed to limit the protection provided by the invention, which is defined by the patent claims enclosed.

Claims

1. Wind turbine comprising at least one turbine blade attached to a hub (10), where the turbine blade comprises an inner part (2), comprising a load carrying structure (6) with a longitudinal axis (21) and aerodynamically active surfaces (7), which wholly or partly enclose the structure (6), joined to an outer part (3) by means of a joint (19), where the joint (19) is situated at a distance from the rotational centre (22) of the wind turbine of between one eighth and half of the total length of the turbine blade from the rotational centre (22) of the wind turbine to the outer end (23) of the outer part,

characterised in

that the joint (19) comprises a bearing (8) and a blade pitch

mechanism (9), which enable the outer part (3) to rotate in relation to the inner part (2) along the longitudinal axis (21), where the bearing (8) is ring shaped and enables rotation around the longitudinal axis (21), and where the load carrying structure (6) stretches from the hub (10) to the joint (19).

2. Wind turbine according to claim 1 , characterised in that the diameter of the bearing (8) is at least five times the length of the bearing.

3. Wind turbine according to any of the previous claims, characterised in that the bearing (8) is a rolling bearing.

4. Wind turbine according to claim 1 or 2, characterised in that the

bearing (8) is a gliding bearing.

5. Wind turbine according to any of the previous claims, characterised in that the bearing (8) is attached to the load carrying structure (6) of the inner part (2) and of the outer part (3).

6. Wind turbine according to claim 5, characterised in that the bearing (8) is attached to the inner and outer parts (2, 3) by means of screw joints.

7. Wind turbine according to claim 1 , characterised in that the blade pitch mechanism (9) preferably is electric or hydraulic.

8. Wind turbine according to claim 1 , characterised in that the load carrying structure (6) of the inner part (2) is designed as a tube.

9. Wind turbine according to claim 8, characterised in that the load carrying structure (6) of the inner part (2) is designed with a circular cross section.

10. Wind turbine according to claim 1 , characterised in that the

aerodynamically active surfaces (7) of the inner part (2) constitute a number of separate panels (7A - 7C), adapted to be joined to each other and to the load carrying structure (6).

1 1. Wind turbine according to any of the previous claims, characterised in that the aerodynamically active surfaces (7) of the inner part (2) preferably constitute three fourths of the length of the load carrying structure (6) at most.

12. Wind turbine according to claim 1 , characterised in that the outer part (3) is manufactured of composite material.

13. Wind power plant comprising a wind turbine according to any of the previous claims.