Lightning current transfer unit and wind turbine comprising same

Abstract

The present invention relates to a lightning current transfer unit for a wind turbine comprising: at least two contact means configured to connect two components of the wind turbine configured to rotate with respect to each other; and at least one electric conductor establishing an electrical connection between the at least two contact means, wherein the contact means and the electric conductor form a rolling bearing having a gear structure The present invention also relates to a wind turbine comprising one or more of such lightning current transfer units.

Description

[0001] Lightning current transfer unit and wind turbine comprising same

[0002] Technical Field

[0003] The invention relates to a lightning current transfer unit adapted for usage in a wind turbine. The invention also relates to a wind turbine in which the lightning current transfer unit is implemented.

[0004] Description of the Related Art

[0005] Due to their size, wind turbines are prone to lightning strikes. The height of wind turbines overshoots by far surrounding trees and buildings in order to efficiently convert wind power into electric energy. Without a lightning protection system, if lightning strikes the tip of a blade of a wind turbine, the current flows in an uncontrolled manner through the blade, the blade bearings, the hub, the hub bearings, the generator shaft, the generator and the tower into the ground. Due to the high current values, there is a high risk that the bearings and electrical generators are damaged by the high voltages and currents flowing through the bearings and the generators. Therefore, efforts have been made to avoid damages in the turbine generators and the generator shaft bearings by offering a current path with lower impedance around the sensitive areas.

[0006] Lightning current transfer units are commonly used in the state of the art to transfer lightning current from a blade to the nacelle of the wind turbine and to reduce and / or avoid damage in the turbine generators and the generator shaft bearings of wind turbines.

[0007] The lightning current transfer units for wind turbines known at the state of the art exploit sliding contacts between the various rotating components.

[0008] For example, document WO 2005 / 050008 A1 discloses a lightning current transfer system that uses sliding point contacts in order to transfer the lightning current from the blades of a wind turbine to a grounded nacelle, through a rotating hub.

[0009] However, sliding contacts are prone to wear and need to be serviced or replaced.

[0010] It is therefore an object of this invention to provide a lightning current transfer unit that avoids the problem of damaging point contacts due to electrical and mechanical wear and secures at the same time a defined lightning current path from a blade to a nacelle of a wind turbine. Summary of Invention

[0011] The present invention is based on the idea of replacing sliding contacts in a lightning current transfer unit with rolling contacts. This is achieved by providing the bearing used in a lightning current transfer unit with a gear structure.

[0012] According to a first aspect of the present invention, a lightning current transfer unit for a wind turbine is provided, the lightning current transfer unit comprising: at least two contact means configured to connect a first component and a second component of the wind turbine, the first component and the second component being configured to rotate with respect to each other; at least one electric conductor establishing an electrical connection between the at least two contact means, wherein the at least two contact means and the at least one electric conductor form a rolling bearing having a gear structure.

[0013] The advantage of this configuration is that the lifetime of the lightning current transfer unit is increased, since there are no, or minimal, mechanical loads transferred through the gear structure.

[0014] The contact means indicates any means configured to form contact areas facing the contact surfaces of the first and second components of the wind turbine. It is to be understood that the contact means form both a mechanical and an electrical connection between the contact areas and the contact surfaces.

[0015] The electric conductor indicates any element configured for establishing an electric connection between the contact means.

[0016] In the present invention, it is to be understood that the expression “rolling bearing” indicates a bearing comprising inner and outer gear racks between which one or more gear pinions can roll.

[0017] According to an embodiment of the first aspect of the present invention, the lightning current transfer unit is provided, wherein the at least two contact means are two mating gear racks and the at least one electric conductor is at least one gear pinion configured to roll between the mating gear racks, so that the two mating gear racks and the at least one gear pinion form the gear structure. The advantage of this configuration is that the lifetime of the lightning current transfer unit is increased, since there are no mechanical loads on the one or more pinions formed between the racks and they can roll freely. For example, the one or more pinions can last a turbine lifetime.

[0018] When the racks move with respect to each other, the one or more pinions roll in the process. When the lightning current reaches the surface of the first gear rack, it is transferred to the surface of the second gear rack via the pinions forming the electrical contact. In case of lighting, it is not necessary to have a stable and precise electrical contact, since a lightning current is capable of bridging small irregularities and gaps.

[0019] According to preferred configurations, each gear rack of the contact means may form a closed loop, or a closed ring. For example, each gear rack may be formed around the entire external perimeter of the main shaft.

[0020] According to alternative preferred configurations, each gear rack of the contact means may form an open loop or open structure. For example, each gear rack may be formed around a portion of the external perimeter of the blade root, such as a portion covering an angle of 90° or an angle of 180°

[0021] According to another embodiment of the first aspect of the present invention, a lightning current transfer unit is provided, wherein the two mating gear racks form two concentric rings.

[0022] The advantage of this configuration is that the gear structure is symmetric and rotation and rolling of the gear pinions along the gear racks are improved.

[0023] According to a preferred embodiment of the first aspect of the present invention, a plurality of pinions may be used in between the racks. Preferably, the plurality of pinions would all rotate the same way.

[0024] By use of multiple pinions, the current is distributed along various pinions and thus along various points of the gear racks. Hence, this configuration avoids concentration of a high lightning current in a single point. Accordingly, wear of the lightning current transfer unit is reduced.

[0025] According to another embodiment of the first aspect of the present invention, a lightning current transfer unit is provided, wherein the at least one gear pinion is rotatably fixed to the gear structure.

[0026] The advantage of this configuration is that sliding and friction between the gear components are reduced so that the expected life is higher. According to an alternative embodiment, the at least one gear pinion may be free to roll along the gear racks of the gear structure.

[0027] According to another embodiment of the first aspect of the present invention, a lightning current transfer unit is provided, wherein the gear structure is made of metal.

[0028] The advantage of this configuration is that, since the pinions are made of solid metal, they conduct lightning current quite efficiently.

[0029] According to a second aspect of the present invention, a wind turbine is provided which comprises: a tower; a nacelle mounted on the tower; a rotor rotatably connected to the nacelle, the rotor comprising a hub and a plurality of blades connected to the rotor hub; and one or more lightning current transfer units as the ones described above.

[0030] This wind turbine can be advantageously provided with one or more lightning current transfer units as the ones described above to transfer the lightning current from the blades to the rotor hub and / or between the rotor and the nacelle of the turbine.

[0031] Hereby, this system provides a simple and efficient connection between the components of the wind turbine.

[0032] Moreover, this configuration is advantageous because the lightning current transfer units are easy to integrate and install as a part of the wind turbine.

[0033] According to an embodiment of the second aspect of the present invention, a wind turbine is provided, wherein the one or more lightning current transfer units are configured to transfer current from the blades to the rotor hub or to the nacelle.

[0034] The advantage of this configuration is that the lightning current can be transferred from the blades to the hub or to the nacelle of the wind turbine by means of the lightning current transfer units, thus reducing or avoiding formation of electric arcs that could damage the mechanical bearings, such as the pitch bearings of the blades and / or main bearings in a power train of the wind turbine.

[0035] According to preferred configurations, the lightning current may be transferred from the blades to the hub directly by means of the lightning current transfer units. According to alternative preferred configurations, the lightning current may be transferred from the blades to the nacelle by means of the lightning current transfer units and electric cables connected to same.

[0036] According to another embodiment of the second aspect of the present invention, a wind turbine is provided, wherein the gear structure of the one or more lightning current transfer units is formed around a root portion of each blade and the wind turbine further comprises a connection element configured to establish an electrical connection between the gear structure and a rotor hub or the nacelle.

[0037] This configuration is advantageous because the lightning current transfer units can be easily integrated and installed on the blades and the rotor hub, and they can become stable parts of the wind turbine. In fact, the lightning current transfer unit configured as a rolling bearing is simply placed and fixed around the root portion of the blade and connected to the connection element, in order to establish a mechanical and electrical connection with the rotor hub.

[0038] Preferably, the lightning current transfer unit may be fixed to the root portion of the blade by means of fasteners such as screws or bolts.

[0039] According to preferred configurations, the connection element may be a connection bar or rod, such as a metal bar. These configurations are advantageous in establishing a reliable system, because they do not use cables to establish the connections between the lightning current transfer units and the components of the wind turbine.

[0040] According to alternative configurations, the connection element may comprise a connection rod and / or one or more cables, such as high voltage cables, for connecting the lightning current transfer units and the components of the wind turbine.

[0041] According to a preferred embodiment, a wind turbine is provided, which comprises one or more lightning current transfer units, wherein one of the mating gear racks forms an outer loop and the other mating gear rack forms an inner loop, and the outer loop is connected to the connection element and the inner loop is connected to one blade.

[0042] The advantage of this configuration is that the pitching mechanism of the blades is bypassed and is not mechanically connected to the lightning current transfer units. Hence, the possibility of damaging the pitching mechanism of the blades is reduced. Moreover, since the mating gear racks are formed on an external surface of the blade, they can be easily accessed from outside.

[0043] According to an alternative preferred embodiment, a wind turbine is provided, which comprises one or more lightning current transfer units within one or more blades, wherein one of the mating gear racks forms an outer loop and the other mating gear rack forms an inner loop, and the outer loop is connected to one blade and the inner loop is connected to the connection element.

[0044] The advantage of this configuration is that the lightning current transfer units are formed inside the corresponding blades, hence they are protected from external weather conditions.

[0045] According to another embodiment of the second aspect of the present invention, a wind turbine is provided, wherein the one or more lightning current transfer units are configured to transfer current from a main shaft of the wind turbine to the nacelle, the main shaft being electrically connected to the hub.

[0046] The advantage of this configuration is that the lightning current can be transferred from a main shaft of the wind turbine to the nacelle by means of the lightning current transfer units, thus reducing or avoiding formation of electric arcs that could damage the mechanical bearings placed around the main shaft.

[0047] According to another embodiment of the second aspect of the present invention, a wind turbine is provided, wherein the gear structure of the one or more lightning current transfer units is formed around the main shaft and directly contacts the nacelle.

[0048] This configuration is advantageous because the lightning current transfer units can be easily integrated and installed on the main shaft and on the nacelle, and they can become stable parts of the wind turbine. In fact, the lighting current transfer unit configured as a rolling bearing is simply formed and fixed around the main shaft and it directly establishes an electrical connection to the main shaft.

[0049] Preferably, the lightning current transfer unit may be fixed to the main shaft by means of fasteners such as screws or bolts.

[0050] According to a preferred embodiment, a wind turbine is provided, which comprises one or more lightning current transfer units, wherein one of the mating gear racks forms an outer loop and the other mating gear rack forms an inner loop, and the outer loop is directly connected to the nacelle and the inner loop is directly connected to the main shaft. In this way, a majority of a lightning current is diverted away from the power train.

[0051] According to another embodiment of the second aspect of the present invention, a wind turbine is provided, which comprises one lightning current transfer unit configured to transfer current from each blade to the rotor hub, and one lightning current transfer unit configured to transfer current from the main shaft to the nacelle. The advantage of this configuration is that the lightning current is transferred from the blades to the rotor and the nacelle, and then to the tower of the wind turbine in a simple and reliable way. Hence, the lifetime of the wind turbine components is increased.

[0052] According to preferred embodiments, the wind turbine comprises three blades and three lightning current transfer units are provided on the wind turbine (i.e. one lightning current transfer unit around each blade).

[0053] According to another embodiment of the second aspect of the present invention, a wind turbine is provided, further comprising at least one bearing formed around the main shaft so as to enable a rotation of the rotor relative to the nacelle.

[0054] Preferably the one or more lightning current transfer units formed around said main shaft are positioned between the hub and the least one bearing formed around the main shaft. In this way the bearing is ‘downstream’ in an electrical sense of the lightning current transfer unit, so that lightning current through the bearing is reduced or avoided.

[0055] Short description of the Figures

[0056] In the following, embodiments, examples, advantages and implementations of the invention will be explained in more detail by means of the accompanying figures, in which:

[0057] Fig. 1 schematically illustrates a front view of a wind turbine;

[0058] Fig. 2 schematically illustrates a cross-section of a portion of a wind turbine comprising lightning current transfer units, according to an embodiment of the present invention;

[0059] Fig. 3a schematically illustrates a front view of a lightning current transfer unit with a gear structure, according to an embodiment of the present invention;

[0060] Fig. 3b schematically illustrates an enlarged portion of the gear structure of the lightning current transfer unit of Fig. 3a;

[0061] Fig. 4 schematically illustrates a front view of a pinion and two portions of mating gear racks of a lightning current transfer unit according to an embodiment of the present invention.

[0062] Detailed Description of embodiments

[0063] In the following, the present invention is described with reference to particular embodiments, as is illustrated in the enclosed figures. However, the present invention is not limited to the particular embodiments described in the following detailed description and shown in figures. Instead, the described embodiments simply exemplify the different features of the present invention, the scope of which is defined in the claims. Further modifications and variations of the present invention will be clear to the skilled person.

[0064] Fig. 1 illustrates a wind turbine 1 with a tower 2, a wind turbine nacelle 3 positioned on top of the tower 2, and a wind turbine rotor 4. The wind turbine rotor 4 comprises a rotor hub 4a and three wind turbine blades 5. Each blade 5 is connected to the rotor hub 4a by means of a pitch bearing, or blade bearing (not visible in Fig. 1). The pitch bearing allows rotation of the blade 5 around the central axis passing through the center of the blade root, in order to control the loads and power of the wind turbine. Preferably, the pitch bearing allows a rotation of the blade 5 by at least 90°. The wind turbine rotor 4 is connected to a main shaft 4b, which is then connected to the generator of the wind turbine (not shown).

[0065] When a wind beyond a certain level hits the wind turbine 1 , the wind activates the rotor 4 due to the lift induced on the blades 5 and allows it to rotate in a perpendicular direction to the wind. The rotation movement is converted to electric power, which is then supplied to the utility grid.

[0066] Fig. 2 schematically illustrates a cross-section of a portion of the wind turbine 1 . As visible in Fig. 2, the wind turbine 1 comprises two lightning current transfer units 10a and 10b, i.e. one lightning current transfer unit 10a configured to transfer current from the blade 5 and the rotor hub 4a, and one lightning current transfer unit 10b configured to transfer current from the main shaft 4b and the nacelle 3.

[0067] Even if two lightning current transfer units 10a and 10b are shown in Fig. 2, it is to be understood that the wind turbine 1 may comprise any number of lightning current transfer units 10a and 10b, for example one, three, four, five, or more. For example, two lightning current transfer units 10b may be formed around the main shaft 4b and one lightning current transfer unit 10a and 10b may be formed around each blade. For instance, if the wind turbine comprises three blades 5, three lightning current transfer units 10a may be provided on the wind turbine 1 to transfer current away from the blades.

[0068] The lightning current transfer unit 10a is configured as a rolling bearing 11 with a gear structure, which is shown in detail in Fig. 3a. The rolling bearing 11 with a gear structure comprises two mating gear racks 14a, 14b, each forming a closed loop, and at least one gear pinion 12 configured to roll between the mating gear racks 14a, 14b. The two closed loops of the mating gear racks 14a, 14b are substantially concentric with respect to each other and extend around a root of the blade 5. The two mating gear racks 14a, 14b form an inner loop, or inner gear rack, and an outer loop, or outer gear rack, respectively. The inner gear rack 14a is directly in contact with the root of the blade 5. The outer gear rack 14b is directly in contact with a connection element 6, which is configured to connect the lightning current transfer unit 10a to the rotor hub 4a. Preferably, the connection element 6 is configured as a rod or shaft extending from the rotor hub 4a to the external surface of the lightning current transfer unit 10a.

[0069] According to an alternative configuration (not shown), the outer gear rack may be directly in contact with the root of the blade and the inner gear rack may be directly in contact with a connection element, such as a cable, which is configured to connect the lightning current transfer unit to the rotor hub.

[0070] Preferably, one or more down conductor cables 30 extend from the lightning current transfer unit 10a and are directed inside the blade 5, in order to provide an electrical connection between the lightning current transfer unit 10a and lighting receptors of the blade.

[0071] The lightning current transfer unit 10a allows transfer of current from the blade 5 to the rotor hub 4a, thus bypassing the pitch bearing 7 of the blade, which could be easily damaged in case of lightning.

[0072] The lightning current transfer unit 10b connects the different components of the wind turbine.

[0073] The lightning current transfer unit 10b is configured as a rolling bearing 1 T with a gear structure, which is shown in detail in Fig. 3a. The rolling bearing 1 T with a gear structure comprises two mating gear racks 14a’, 14b’, each forming a closed loop, and at least one gear pinion 12’ configured to roll between the mating gear racks. The two closed loops of the mating gear racks 14a’, 14b’ are substantially concentric with respect to each other and extend around the main shaft 4b. The two mating gear racks 14a’, 14b’ form an inner loop, or inner gear rack, and an outer loop, or outer gear rack, respectively. The inner gear rack 14a’ is directly in contact with the main shaft 4b. The outer gear rack 14b’ is directly in contact with the nacelle 3. In this way, the lightning current transfer unit 10b directly connects the main shaft 4b to the nacelle 3.

[0074] As the rotor hub 4a is connected to the main shaft 4b, the blade 5 and the nacelle 3 are also electrically connected to each other through the hub and the lightning current transfer units 10a and 10b. Accordingly, when a lightning hits a blade 5 of the wind turbine 1 , the current is transferred from the blade 5 to the nacelle 3 and then to the ground, via the lightning current transfer units 10a and 10b.

[0075] As also shown in Fig. 2, two bearings 20 are also formed around the main shaft 4b in order to provide a mechanical connection between the main shaft 4 and the nacelle 3. In the configuration of Fig. 2, the two bearings 20 are ‘downstream’ in an electrical sense of the lightning current transfer unit 10b, so that lightning current through the bearings 20 is reduced or avoided. Even if two bearings 20 are shown in Fig. 2, it is to be understood that the wind turbine 1 may comprise any number of bearings 20, for example one, three, four, five, or more, depending on the specific mechanical requirements.

[0076] The lightning current transfer unit 10b allows transfer of current from the main shaft 4b to the nacelle, thus bypassing the bearing 20 of the main shaft, which could be damaged in case of lightning.

[0077] As illustrated in Fig. 3a, in each lightning current transfer unit 10a and 10b, the gear structure 11 includes a rolling gear comprising two mating gear racks 14a, 14b, 14a’, 14b’ and a plurality of gear pinions 12, 12’. Preferably, the plurality of gear pinions 12, 12’ is symmetrically distributed along the gear racks 14a, 14b, 14a’, 14b’. Preferably, the gear pinions 12, 12’ are equally spaced from one another along the gear racks 14a, 14b, 14a’, 14b’. When the rack 14a, 14a’ rotates with respect to the mating rack 14b, 14b’, the pinion 12, 12’ rolls along with it. Since there is no or minimal mechanical load transferred through this gear structure, the gear pinion 12, 12’ and the gear racks 14a, 14b, 14a’, 14b’ are not prone to wear and their lifetime can be increased. The pinions 12, 12’ may be rotatably fixed to the gear structure 11. Alternatively, the pinions 12, 12’ may be free to rotate with respect to the gear structure 11.

[0078] With reference to Fig. 4, the working principle of the lightning current transfer units 10a, 10b is illustrated.

[0079] When a lightning hits the blade 5 of the wind turbine 1 , the lightning current reaches the root of the blade 5 and then the first lightning current transfer unit 10a. The lightning current is then transferred to the connection element 6 and to the second lightning current transfer unit 10b, which then transfers it to the nacelle 3. In this way, a transfer of current from the blade 5 to the nacelle 3 (then to the tower 2 and the ground) is ensured.

[0080] In the first lightning current transfer unit 10a, the lightning current flows from the inner gear rack 14a (in contact with the root portion of the blade 5) to the outer gear rack 14b through the gear pinion 12, in the directions E shown in Fig. 4. With continued reference to the preferred orientation of Fig. 4, the current flows from the inner gear rack 14a to the upper pinion tooth 16 (i.e. a pinion 12 directed towards the blade 5), then through the pinion body, and finally to the lower pinion tooth 16 (i.e. a pinion 12 directed towards the outside) and to the outer gear rack 14b. As the gear racks 14a and 14b move in opposite directions D1 and D2, the gear pinion 12 rotates around its central axis. In this way, the gear structure ensures that a pinion tooth 16 can always be inserted into a corresponding recess 18 of the gear racks and that the lightning current can be continuously transferred from the inner gear rack 14a to the outer gear rack 14b, and accordingly from the blade 5 to the rotor hub 4a. The same principle applies to the second lightning current transfer unit 10b. In the second lightning current transfer unit 10a, the lightning current flows from the inner gear rack 14a’ (in contact with the main shaft 4b) to the outer gear rack 14b’ through the gear pinion 12’, in the directions E shown in Fig. 4. With continued reference to the preferred orientation of Fig. 4, the current flows from the inner gear rack 14a’ to the upper pinion tooth 16 (i.e. a pinion 12’ directed towards the main shaft 4b), then through the pinion body, and finally to the lower pinion tooth 16 (i.e. a pinion 12’ directed towards the outside) and to the outer gear rack 14b’. As the gear racks 14a’ and 14b’ move in opposite directions D1 and D2, the gear pinion 12’ rotates around its central axis. In this way, the gear structure ensures that a pinion tooth 16 can always be inserted into a corresponding recess 18 of the gear racks and that the lightning current can be continuously transferred from the inner gear rack 14a’ to the outer gear rack 14b’, and accordingly from the main shaft 4b to the nacelle 3.

[0081] Even if the contact between the gear racks 14a, 14b, 14a’, 14b’ and the gear pinion 12, 12’ is not perfect, the lightning current can be easily transferred by means of flashovers through the free rolling metallic gear. Hence, a continuous current flow from the blade 5 to the nacelle 3 is ensured.

[0082] Even if the present invention has been described with reference to the embodiments described above, it is clear to the skilled person that it is possible to apply different modifications, variations and improvements of the present invention in light of the teachings described above and the field, and within the scope of the enclosed claims, without departing from the scope and purpose of the present invention.

[0083] Finally, those fields considered known to the skilled person have not been described to avoid unnecessarily covering the described invention.

[0084] REFERENCES:

[0085] 1 : wind turbine

[0086] 2: tower

[0087] 3: nacelle

[0088] 4: rotor

[0089] 4a: rotor hub

[0090] 4b: main shaft

[0091] 5: blade 6: connection element between blade and rotor

[0092] 7: pitch bearing

[0093] 10a: lightning current transfer unit from blade to rotor

[0094] 10b: lightning current transfer unit from rotor to nacelle 11: gear structure

[0095] 12, 12’: gear pinion

[0096] 14a, 14b, 14a’, 14b’: gear racks

[0097] 16: pinion tooth

[0098] 18: rack recess 20: bearing

[0099] 30: electrical cable

[0100] D1, D2: directions of rotation

[0101] E: direction of current propagation

Claims

Claims1 . A lightning current transfer unit (1 Oa, 10b) for a wind turbine comprising: at least two contact means configured to connect a first component and a second component of said wind turbine, said first component and said second component being configured to rotate with respect to each other; at least one electric conductor establishing an electrical connection between said at least two contact means, wherein said at least two contact means and said at least one electric conductor form a rolling bearing having a gear structure (11).

2. The lightning current transfer unit (10a, 10b) of claim 1 , wherein said at least two contact means are two mating gear racks (14a, 14b, 14a’, 14b’) and said at least one electric conductor is at least one gear pinion (12, 12’) configured to roll between said mating gear racks (14a, 14b, 14a’, 14b’), so that said two mating gear racks (14a, 14b, 14a’, 14b’) and said at least one gear pinion (12, 12’) form said gear structure (11).

3. The lightning current transfer unit (10a, 10b) of claim 2, wherein said two mating gear racks (14a, 14b, 14a’, 14b’) form two concentric rings.

4. The lightning current transfer unit (10a, 10b) of claim 2 or 3, wherein said at least one gear pinion (12, 12’) is a plurality of gear pinions.

5. The lightning current transfer unit (10a, 10b) of any of claims 1 to 4, wherein said at least one gear pinion (12, 12’) is rotatably fixed to said gear structure (11).

6. The lightning current transfer unit (10a, 10b) of any of claims 1 to 5, wherein said gear structure (11) is made of metal.

7. A wind turbine (1) comprising: a tower (2); a nacelle (3) mounted on said tower (2); a rotor (4) rotatably connected to said nacelle (3), the rotor comprising a hub (4a) and a plurality of blades (5) connected to said hub (4a);one or more lightning current transfer units (10a, 10b) according to any of claims 1 to 6.

8. The wind turbine (1) of claim 7, wherein said one or more lightning current transfer units (10a) are configured to transfer current from one or more of said blades (5) to said hub (4a) or said nacelle (3).

9. The wind turbine (1) of claim 8, wherein said gear structure (11) of said one or more lightning current transfer units (10a) is formed around a root portion of said one or more blades (5) and said wind turbine (1) further comprises a connection element (6) configured to establish an electrical connection between said gear structure (11) and said hub (4a) or said nacelle (3).

10. The wind turbine (1) of claim 9 comprising one or more lightning current transfer units (10a) according to any of claims 2 to 6, wherein one of said mating gear racks (14a, 14b) forms an outer loop and the other mating gear rack (14a, 14b) forms an inner loop, and said outer loop is connected to said connection element (6) and said inner loop is connected to one of said one or more blades (5).

11. The wind turbine (1) of claim 9 comprising one or more lightning current transfer units (10a) according to any of claims 2 to 6 formed inside a corresponding blade, wherein one of said mating gear racks (14a, 14b) forms an outer loop and the other mating gear rack (14a, 14b) forms an inner loop, and said outer loop is connected to one of said one or more blades (5), and said inner loop is connected to said connection element (6).

12. The wind turbine (1) of any of claims 7 to 11 , wherein said one or more lightning current transfer units (10b) are configured to transfer current from a main shaft (4b) to said nacelle (3), said main shaft (4b) being electrically connected to said hub (4a).

13. The wind turbine (1) of claim 12, wherein said gear structure (11) of said one or more lightning current transfer units (10b) is formed around said main shaft (4b) of said rotor (4) and directly contacts said nacelle (3).

14. The wind turbine (1) of claim 13 comprising one or more lightning current transfer units (10b) according to any of claims 2 to 6, wherein one of said mating gear racks (14a’, 14b’) forms an outer loop and the other mating gear rack (14a’, 14b’) forms an inner loop, and said outer loop is directly connected to said nacelle (3) and said inner loop is directly connected to said main shaft (4b).

15. The wind turbine (1) of any of claims 7 to 14 comprising one lightning current transfer unit (10a) configured to transfer current from each of said blades (5) to said hub (4a), and one lightning current transfer unit (10b) configured to transfer current from a main shaft (4b) to said nacelle (3).

16. The wind turbine (1) of any of claims 7 to 15 further comprising at least one bearing (20) formed around a main shaft (4b) so as to enable a rotation of said rotor (4) relative to said nacelle (3).

Images