Lightning electromagnetic flux density reduction in wind turbines

Abstract

The present disclosure relates to reducing the electromagnetic flux density of lightning in a wind turbine. A nacelle (14) for a wind turbine (10) comprises: an outer surface (40) exposed to magnetic flux induced by lightning; a generator (15) rotating about a rotation axis (Y), the generator (15) comprising a rotor (4), a stator (3), an air gap (5) separating the rotor (4) and the stator (3), and a plurality of electrical conductors (24) wound in the rotor (4) or the stator (3) near the air gap (5); a lightning protection device (100) comprising at least one waveguide (110) located between the rotor (4) and the stator (3) and inserted between the outer surface (40) and the air gap (5) for providing protection for the electrical conductors (24) from the magnetic flux induced by lightning.

Description

Technical Field

[0001] The present invention relates to a lightning protection device for a wind turbine. The purpose of the device is to avoid critical magnetic flux densities in electrically critical components of the wind turbine. Background Art

[0002] The magnetic field is a vector field that describes the magnetic influence of relative motion and electric charges in magnetized materials. Wind turbines are therefore subject to electric and magnetic fields, for example, there are designed electromagnetic fields in wind turbines due to the presence of complex electrical systems or natural electromagnetic fields determined by lightning strikes.

[0003] Wind turbines typically have a shape and size that make them good recipients of lightning strikes. The magnetic field generated by a lightning strike can reach a strength of about 90,000 A / m. Such strong magnetic fields can generate electromagnetic interference and may damage electrical or electronic components of the wind turbine. Considering that the magnetic field is generated in a direction perpendicular to the electric field, when the lightning current flows through the down conductor of the lightning protection system and other grounding paths, a burst of electromagnetic fields is generated in the turbine. Although these electromagnetic fields are short-lived, they may generate induced voltages in various components of the wind turbine (especially in the air gap between the rotor and the stator), which is likely to produce flashovers. These events may damage critical components installed near the air gap. Such components include generator electrical windings and generator permanent magnets, which are accommodated in slots of the stator or rotor. The generator permanent magnets may be at least partially demagnetized, thereby reducing the overall efficiency of the wind turbine.

[0004] Therefore, the lightning protection system must be carefully designed, especially considering the induced voltage generated on the generator coil due to this magnetic field. Overvoltage protection devices can be further provided on the generator windings to protect them from the induced voltage of lightning. However, such devices increase the cost.

[0005] Therefore, the scope of the present invention is to provide a wind turbine having features allowing to reduce the electromagnetic fields induced by lightning at the air gap between the stator and the rotor. Summary of the invention

[0006] This scope can be achieved by the subject matter according to the independent claims. Advantageous embodiments of the invention are described by the dependent claims.

[0007] According to the present invention, a nacelle for a wind turbine is provided. The nacelle comprises:

[0008] an outer surface, said outer surface being exposed to a magnetic flux induced by lightning,

[0009] a generator rotating about a rotation axis, the generator comprising a rotor, a stator, an air gap separating the rotor and the stator, and a plurality of electrical conductors wound in the rotor or the stator near the air gap,

[0010] The cabin further comprises:

[0011] A lightning protection device comprises at least one waveguide located between the rotor and the stator and inserted between the outer surface and the air gap for providing protection for the electrical conductor from magnetic flux induced by lightning.

[0012] As "waveguide", it refers to an electromagnetic feed line. A waveguide consists of a rectangular or cylindrical metal channel in which the electromagnetic field propagates longitudinally or is blocked, depending on the size of the waveguide. The waveguide designed according to the present invention allows the restricted passage of the magnetic field generated during a lightning event.

[0013] When an external surface (e.g., the external surface of a nacelle) is subjected to an electromagnetic field, any opening provided on the surface may cause the electromagnetic field to leak into the internal volume of the nacelle, and the larger the opening, the greater the possible leakage. According to the present invention, a waveguide is provided between the surface opening and the air gap to reduce or eliminate electromagnetic leakage. The waveguide may have the same width as the opening. This allows the electromagnetic field of lightning inside the nacelle (particularly at the air gap between the rotor and the stator) to be conveniently reduced.

[0014] This design can provide further key advantages in that overvoltage protection is no longer required and other voltage isolation features on the cable insulation and windings can be reduced.

[0015] According to an embodiment of the invention, the waveguide may be arranged at an opening separating the rotor from the stator.The invention may be applied to a wind turbine having an inner stator and an outer rotor, or to a wind turbine having an inner rotor and an outer stator.

[0016] According to an embodiment of the invention, the lightning protection device comprises a stationary plate fixed to the stator and a rotating plate fixed to the rotor, the waveguide is arranged between the stationary plate and the rotating plate, and the stationary plate or the rotating plate is exposed to the magnetic flux induced by lightning. In a specific embodiment of the invention in which the rotor is outside the stator, the rotating plate comprises an outer surface, which is exposed to the magnetic flux induced by lightning. Such a rotating plate may comprise a brake disc of the rotor.

[0017] According to an embodiment of the present invention, the lightning protection device comprises a structural element connected to the stator and extending along the rotation axis, and the static plate protrudes at the axial end of the structural element. The structural element connected to the stator can have a hollow cylindrical structure coaxial with the rotation axis, and the static plate can protrude radially from the rotation axis, for example in the form of a radially outer flange attached at the axial end of the structural element.

[0018] According to an embodiment of the invention, the waveguide may be tilted relative to the rotation axis at an angle comprised between 0 and 90 degrees. More particularly, the waveguide may be tilted relative to the rotation axis at an angle comprised between 45 and 90 degrees. The waveguide may have a width comprised between 1 and 15 mm. More particularly, the waveguide may have a width comprised between 8 and 12 mm.

[0019] The waveguide may have a length comprised between 200 and 700 mm, more particularly between 400 and 500 mm. Higher values ​​of the length of the waveguide allow for a higher magnetic field attenuation, lower values ​​may be chosen to adapt to nacelle constraints.

[0020] The aspects defined above and further aspects of the invention are apparent from the examples of embodiment to be described hereinafter and are explained with reference to these examples of embodiment.The invention will be described in more detail hereinafter with reference to examples of embodiment but to which the invention is not limited. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 A schematic side view of a wind turbine is shown, the wind turbine comprising a nacelle according to the invention.

[0022] Figure 2 Shows Figure 1 A first schematic cross-sectional view of a wind turbine.

[0023] Figure 3 Shows Figure 1 and Figure 2 A second more detailed schematic cross-sectional view of a wind turbine.

[0024] Figure 4 Shows Figure 1 , Figure 2 and Figure 3 An enlarged view of a component of a wind turbine. DETAILED DESCRIPTION

[0025] The drawings are schematic. Similar or identical elements are denoted by the same or different reference numerals.

[0026] Figure 1A direct drive wind turbine 10 for generating electricity is shown. The wind turbine 10 comprises a tower 11 which is mounted at one bottom end on the ground 9. A nacelle 14 is mounted at an opposite top end of the tower 11. The nacelle 14 is typically mounted so as to be rotatable relative to the tower 11 about a yaw axis Z which is substantially perpendicular to the ground 9. The nacelle 14 houses a generator (at Figure 1 Furthermore, the wind turbine 10 comprises a hub 13, which is rotatably attached to a nacelle 14 for rotation about an axis of rotation Y, which is a longitudinal axis of the nacelle 14. When not specified differently, the terms axial or longitudinal, radial and circumferential are conventionally used hereinafter with reference to the longitudinal rotor axis Y. The hub 13 is connected to a generator in the nacelle 14 so as to receive rotational energy from the hub 13.

[0027] The wind turbine 1 further comprises at least one blade 17 mounted on the hub 13 (at Figure 1 In the embodiment of FIG. 1 , the wind rotor comprises three blades 17 , of which only two blades 17 are visible). The blades 17 extend along respective blade longitudinal axes X which are oriented substantially radially with respect to the rotation axis Y.

[0028] Reference Figure 2 The nacelle 14 comprises a base frame 22 having a flange for rotatably connecting the nacelle 14 to the tower 11 to allow the nacelle to rotate about the yaw axis Z. The nacelle also comprises a hollow fixed shaft 20 extending coaxially with respect to the rotation axis Y. The hollow fixed shaft 20 extends coaxially along the rotation axis Y between two longitudinal ends, one of which is rigidly attached to the base frame 22. A main bearing 21 of the wind turbine 10 is mounted on the other longitudinal end of the hollow fixed shaft 20. The hub 13 is connected to the main bearing 21 so as to allow the hub 13 to rotate about the rotation axis Y.

[0029] The nacelle 14 includes a generator 15 extending along a rotation axis Y between a drive end adjacent to the hub 13 and a non-drive end adjacent to the base frame 22. The generator 15 includes an outer rotor 4 and an inner stator 3 separated by an air gap 5. According to other embodiments of the present invention (not shown), the generator 15 includes an inner rotor and an outer stator separated by an air gap. The stator 3 is rigidly supported by a hollow fixed shaft 20. The stator 3 includes two stator support plates 33, which are respectively arranged at the axial ends of the stator 3 for radially supporting a stator body 34. Two annular spaces are defined between each stator support plate 33 and the rotor 4, namely a front annular space 25 close to the hub 13 and an axially opposite rear annular space 26 close to the base frame. The stator 3 includes a plurality of electrical conductors 24 in the form of windings, which are accommodated in a plurality of stator slots (not shown) provided in the stator body 34. The winding includes an end winding for connecting the windings in two different slots of the stator 3, and the end winding protrudes axially at the axial end of the stator body 34. During operation, the outer rotor 4 is rotated about the rotation axis Y in order to convert mechanical energy into electrical energy. The rotor 4 comprises an outer rotor housing 45 extending coaxially along the rotation axis Y between a hub interface 42 and an opposite axial end 41. According to the embodiment of the figures, the axial end 41 is shaped as an annular radially oriented end plate, which may have the function of a reinforcement or a brake disc. The outer rotor housing 45 comprises an outer surface 40, which is exposed to the magnetic flux induced by lightning. The rotor 4 also comprises a plurality of permanent magnets 43, which radially face the stator 3 at the air gap 5. The hub interface 42 is rigidly connected to the hub 13 and rotationally connected to the main bearing 21, so as to allow the assembly comprising the hub 13 and the rotor housing 45 to rotate about the rotation axis Y. When required by the operating conditions, the end plate 41 locks the rotation of the rotor 4 relative to the stator 3. An opening 47 is provided between the end plate 41 and the hollow fixed shaft 20 for providing the necessary distance between the stationary part and the rotating part of the nacelle 14. The opening 47 may be annular.

[0030] In the rear annular space 26, the nacelle 14 further comprises a lightning protection device 100, which comprises a waveguide 110 located between the rotor 4 and the stator 3. The waveguide 110 is inserted between the outer surface 40 and the air gap 5 for providing protection for the electrical conductor 24 from the magnetic flux induced by a lightning strike hitting the outer surface 40. The waveguide 110 can also provide protection for the permanent magnet 43 to prevent demagnetization. According to other embodiments of the present invention (not shown), more than one waveguide 110 can be inserted between the outer surface 40 and the air gap 5 for providing protection for the permanent magnet 43.

[0031] Reference Figure 3 and Figure 4, the waveguide 110 is disposed at the opening 47 of the outer surface 40, separating the rotor 4 from the stator 3. According to other embodiments of the present invention (not shown), the magnetic waveguide 110 may be disposed at any other opening exposed to the magnetic flux induced by lightning.

[0032] The lightning protection device 100 includes a stationary plate 120 fixed to the stator 3 and a rotating plate 130 fixed to the rotor 4. The stationary plate 120 and the rotating plate 130 may be made of a conductive material, in particular a metal material. The waveguide 110 is disposed between the stationary plate 120 and the rotating plate 130. Figure 3 and Figure 4 In the embodiment of the invention, the rotating plate 130 includes the end plate 41 and is exposed to the magnetic flux induced by lightning. According to other embodiments of the invention (not shown), such as embodiments with an inner rotor and an outer stator, the stationary plate 120 may be exposed to the magnetic flux induced by lightning.

[0033] The lightning protection device 100 comprises a structural element 140 connected to the stator support plate 33 at the rear end of the stator 3. The structural element 140 stator extends along the rotation axis Y, and the stationary plate 120 protrudes at the axial end of the structural element 140. Figure 3 and Figure 4 In a particular embodiment of the present invention, the structural element 140 has a hollow cylindrical structure coaxial with the rotation axis Y, from which the stationary plate 120 radially protrudes in the form of a radially outer flange attached at the axial end of the structural element 140. According to other embodiments of the invention (not shown), for example embodiments with an inner rotor and an outer stator, the structural element 140 can be used to connect the rotating plate 130 to the rotor.

[0034] exist Figure 3 and Figure 4 In an embodiment of the invention, the waveguide 110 is radially oriented. According to other embodiments of the invention (not shown), the waveguide 110 may be inclined at an angle between 45 and 90 degrees relative to the rotation axis Y. The waveguide 110 has a width 113 comprised between 1 and 15 mm, i.e. the distance between the stationary plate 120 and the rotating plate 130. More particularly, the waveguide 110 has a width comprised between 8 and 12 mm. According to an embodiment of the invention, the width of the waveguide 110 may be equal to the width of the opening 47. The waveguide extends perpendicularly to its width between the two longitudinal ends 111, 112. The waveguide 110 may have a length 114 measured between the longitudinal ends 111, 112, which is comprised between 200 and 700 mm, more particularly between 400 and 500 mm. Figure 3 and Figure 4 In the embodiment of FIG. 1 , the length of the waveguide 110 corresponds to the radial extension of the stationary plate 120 .

[0035] When magnetic flux is induced by lightning on the outer surface 40, the waveguide 110 disposed at the opening 47 or in the magnetic path between the opening 47 and the air gap 5 can significantly reduce the magnetic flux reaching the air gap 5, for example, from 13000 A / m (without the waveguide 110) to about 2500 A / m (with the waveguide 110). This reduction in magnetic field is acceptable because it does not have any significant effect on the induced voltage in the winding or the magnetostriction of the permanent magnet.

Claims

1. A nacelle (14) for a wind turbine (10), comprising: An outer rotor (4) and an inner stator (3), wherein the rotor (4) comprises an outer rotor housing (45) extending coaxially along the axis of rotation (Y) of the rotor (4) between a hub interface (42) and an opposite axial end, the axial end being formed as a radially oriented end plate (41), wherein the outer rotor housing (45) comprises an outer surface (40) exposed to magnetic flux induced by lightning, wherein an opening (47) is provided between the end plate (41) and the hollow fixed shaft (20) such that the opening (47) separates the rotor (4) from the stator (3); A generator (15) rotating about a rotation axis (Y), the generator (15) comprising a rotor (4), a stator (3), an air gap (5) separating the rotor (4) and the stator (3), and a plurality of electrical conductors (24) wound in the rotor (4) or the stator (3) near the air gap (5), Wherein, the cabin (14) further comprises: The lightning protection device (100) comprises at least one waveguide (110), the at least one waveguide being located between the rotor (4) and the stator (3), the waveguide (110) being arranged between the opening (47) and the air gap (5) for providing protection for the electrical conductor (24) from magnetic flux induced by lightning; and A stationary plate (120) and a rotating plate (130), wherein the stationary plate (120) is fixed to the stator (3), the rotating plate (130) is fixed to the rotor (4) and includes the end plate (41), the waveguide (110) is arranged between the stationary plate (120) and the rotating plate (130), and the stationary plate (120) or the rotating plate (130) is exposed to magnetic flux induced by lightning, wherein the stationary plate (120) and the rotating plate (130) are made of conductive materials.

2. The nacelle (14) according to claim 1, wherein: The opening (47) is annular.

3. The nacelle (14) according to claim 1 or 2, wherein: The plurality of electrical conductors include a plurality of end windings (24), and the waveguide (110) is inserted between the opening (47) and the end windings (24).

4. The nacelle (14) according to claim 1 or 2, wherein: The rotor comprises a plurality of permanent magnets (43) which radially face the stator (3) at the air gap (5), the waveguide also providing protection for the permanent magnets (43) from magnetic flux induced by lightning.

5. The nacelle (14) according to claim 1 or 2, wherein: The lightning protection device (100) comprises a structural element (140) for connecting the stationary plate (120) to the stator (3) or the rotating plate (130) to the rotor (4).

6. The nacelle (14) according to claim 5, wherein: The structural element (140) extends parallel to the rotation axis (Y).

7. The nacelle (14) according to claim 1 or 2, wherein: The waveguide (110) is inclined relative to the rotation axis (Y) at an angle comprised between 0 and 90 degrees.

8. The nacelle (14) according to claim 1 or 2, wherein: The waveguide (110) is tilted relative to the rotation axis (Y) at an angle comprised between 45 and 90 degrees.

9. The nacelle (14) according to claim 1 or 2, wherein: The waveguide (110) has a width (113) comprised between 1 and 15 mm.

10. The nacelle (14) according to claim 1 or 2, wherein: The waveguide (110) has a width (113) comprised between 8 and 12 mm.

11. The nacelle (14) according to claim 7, wherein: The width (113) of the waveguide (110) is equal to the width of the opening (47) of the outer surface (40).

12. The nacelle (14) according to claim 1 or 2, wherein: The waveguide (110) has a length (114) comprised between 200 and 700 mm.

13. The nacelle (14) according to claim 1 or 2, wherein: The waveguide (110) has a length (114) comprised between 400 and 500 mm.

14. The nacelle (14) according to claim 1 or 2, wherein: The lightning protection device (100) comprises a structural element (140) connected to the stator (3) and extending along the rotation axis (Y), and the stationary plate (120) protrudes at an axial end of the structural element (140).

15. A wind turbine (10), comprising: Wheel hub (13), at least one blade (17), the at least one blade (17) being fixed to the hub (13), A nacelle (14) on which the hub (13) is rotatably mounted for rotation about an axis of rotation (Y), the nacelle (14) being a nacelle according to any one of the preceding claims.

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