Lightning protection system for wind turbine

Abstract

Provided is a wind turbine including a generator enclosed in a generator housing, the generator housing including a rotating housing and a stationary housing, whereby the rotating housing is separated from the stationary housing by a first gap; a canopy mounted on a tower and including an electrical connection to a down conductor of the tower, wherein the canopy is separated from the generator housing by a second gap; a lightning current path provided by a plurality of brush assemblies mounted on the stationary housing, wherein a brush assembly includes a brush holder mounted on the stationary housing such that a carbon brush extends across the first gap to make electrical contact with the rotating housing; and an electrical connector extending across the second gap to electrically connect the brush holder to the canopy. Also provided is a method of providing a lightning current path for such a wind turbine.

Claims

1. A direct-drive wind turbine comprising: a generator enclosed in a generator housing, the generator housing comprising a rotating housing and a stationary housing, and whereby the rotating housing is separated from the stationary housing by a first gap; a canopy mounted on a tower and comprising an electrical connection to a down conductor of the tower, wherein the canopy is separated from the generator housing by a second gap; and a lightning current path provided by a plurality of brush assemblies mounted on the stationary housing, wherein a brush assembly comprises: a brush holder mounted on the stationary housing such that a carbon brush extends across the first gap to make electrical contact with the rotating housing; and an electrical connector extending across the second gap to electrically connect the brush holder to the canopy.

2. The direct-drive wind turbine according to claim 1, wherein the carbon brush bridges the first gap of at least 5 mm.

3. The direct-drive wind turbine according to claim 1, wherein the electrical connector bridges the second gap of at least 10 cm.

4. The direct-drive wind turbine according to claim 1, wherein the electrical connector is flexible, and wherein a length of the electrical connector exceeds a width of the second gap by at least 5%.

5. The direct-drive wind turbine according to claim 1, wherein the electrical connector is a ribbon cable.

6. The direct-drive wind turbine according to claim 1, further comprising at least 30 brush assemblies mounted in an annular arrangement on the stationary housing.

7. The direct-drive wind turbine according to claim 1, wherein the stationary housing comprises an EMC shielding plate for the generator.

8. The direct-drive wind turbine according to claim 1, further comprising a turner ring for turning a generator rotating component, and a further lightning current path provided by a brush assembly arrangement comprising at least one brush assembly arranged to provide an electrical connection between the turner ring and a stationary supporting structure.

9. The direct-drive wind turbine according to claim 8, wherein the stationary supporting structure is an annular plate arranged about a main shaft of the direct-drive wind turbine.

10. The direct-drive wind turbine according to claim 8, further comprising an annular arrangement of a plurality of brush assemblies between the turner ring and the stationary supporting structure.

11. The direct-drive wind turbine according to claim 1, wherein the direct-drive wind turbine is a direct-drive outer-rotor wind turbine.

12. The direct-drive wind turbine according to claim 1, wherein the generator rotating component is a generator field.

13. A method of providing a lightning current path for a direct-drive wind turbine comprising a generator enclosed in a generator housing, the generator housing including a rotating housing and a stationary housing, and whereby the rotating housing is separated from the stationary housing by a first gap, and a canopy mounted on a tower and comprising an electrical connection to a down conductor of the tower, wherein the canopy is separated from the generator housing by a second gap, the method comprising: providing a plurality of first brush assemblies, wherein a first brush assembly comprises a brush holder containing a carbon brush, and an elongated electrical connector originating in the brush holder and terminating at an outer end; mounting each brush holder on the stationary housing such that the carbon brush extends across the first gap to make electrical contact with the rotating housing; and securing the outer end of the electrical connector to the canopy.

14. The method according to claim 13, further comprising mounting a plurality of second brush assemblies between a turner ring and a stationary supporting structure.

15. The method according to claim 13, further comprising providing a down conductor arrangement in an aerodynamic rotor of the direct-drive wind turbine and electrically connecting the down conductor arrangement to the rotating housing.

Description

(1) Some of the embodiments will be described in detail, with references to the following Figures, wherein like designations denote like members, wherein:

(2) FIG. 1 shows an embodiment of a wind turbine;

(3) FIG. 2 shows an enlarged detail of the embodiment of FIG. 1;

(4) FIG. 3 shows an enlarged detail of the embodiment of FIG. 1;

(5) FIG. 4 shows a further embodiment of the wind turbine;

(6) FIG. 5 shows a further embodiment of the wind turbine; and

(7) FIG. 6 shows a detail of a further embodiment of the wind turbine.

DETAILED DESCRIPTION

(8) FIG. 1 shows a direct-drive outer-rotor wind turbine of the type described above. The wind turbine 1 has a generator 10 that is enclosed in a generator housing 10R, 10S. A rotating housing 10R encloses the outer rotor, and a stationary housing 10S encloses the stator. The rotating housing 10R is separated from the stationary housing 10R by a housing gap G1 of a few mm. The circular shape of the rotor housing 10R may be maintained by an anti-ovalisation ring mounted to the exterior of the rotor housing 10R so that the housing gap G1 may be expected to remain essentially constant.

(9) In the usual design manner, the wind turbine 1 further comprises a canopy 11 mounted on a tower 12, and the canopy 11 is separated from the generator housing 10R, 10S by a canopy gap G2, which may be several cm in width.

(10) The wind turbine has a lightning protection system (LPS) with down conductors arranged in the rotor blades 13 and extending into the hub. This lightning protection system LPS.sub.13 of the aerodynamic rotor 13 is electrically connected to the rotor housing 10R. The rotor housing 10R may be assumed to be made partially or completely of steel or a similar metal, and is therefore electrically conductive.

(11) The canopy also includes down conductors of a canopy lightning protection system LPS.sub.11 that are electrically connected to down conductors of a lightning protection system LPS.sub.12 of the tower 12.

(12) The wind turbine has a first lightning current path P2 that is provided by a plurality of brush assemblies 2 mounted on the stationary housing 10S. Each of these brush assemblies 2 comprises a brush holder 20 that is mounted on the stationary housing 10S such that a carbon brush 21 extends across the housing gap G1 to make electrical contact with the rotating housing 10R. This is shown in the enlarged view given by FIG. 2. The actual number of brush assemblies 2 is determined according to the current-carrying capacity of the brush assembly type, and on the LPS requirements. For example, a circumferential arrangement of 50 or more brush assemblies 2 may be sufficient to ensure that the voltage between rotor and stator does not exceed 2 kV during a 200 kA lightning strike (for the sake of clarity, only two brush assemblies 2 are shown in FIG. 1). The brush assembly 2 has a spring-loaded mechanism, as will be known to the skilled person, which acts to press the carbon brush 21 against the body of the rotor housing 10R. This ensures that the carbon brush 21 will maintain contact with the rotor housing at all times, even as the brush wears down over time, and even if there are slight variations in the width of the housing gap between rotor housing 10R and stator housing 10S due to ovalization of the rotor. The spring-loaded mechanism ensures that the brush 21 continually bridges the housing gap G1, even if the gap width varies or fluctuates as the outer rotor turns relative to the stationary housing 10S. One stage of the first lightning current path P2 is therefore given by the carbon brush 21 that electrically connects the rotor housing 10R to the stator housing 10S.

(13) The stator housing 10S may be realized to include an EMC shielding plate at the non-drive end of the generator 10. Another known feature of a brush assembly is that the body of the brush assembly is also electrically conductive, and is usually made of steel. Electrical current is therefore passed from the carbon brush to the brush holder. In the inventive wind turbine, the brush holders 20 are mounted in an annular arrangement to the stator housing 10S, so that during a lightning strike or during the build-up to a lightning strike, charge will be able to distribute itself evenly over the EMC shielding plate.

(14) Each brush assembly 2 also has a lead 22 that extends across the canopy gap G2 to electrically connect the brush holder 20 to the LPS elements of the canopy 11. The next stage of the first lightning current path P2 is therefore given by the lead 22 which electrically connects the stator housing 10R to the canopy 11. This is shown in the enlarged view given by FIG. 3. An outer terminal 220 of the lead 22 is connected to a part of the canopy's LPS arrangement. The lead 22 is realized as a flexible part, for example a ribbon cable or cable braid, that can adjust to minor alterations in width of the canopy gap G2. The length of the lead 22 exceeds the canopy gap width by at least 5%, more preferably by at least 10%, so that the leads can compensate for fluctuations in gap width.

(15) In this exemplary embodiment, the canopy 11 is realized to incorporate an LPS system LPS.sub.11 in the form of a conductive mesh 110, and the lead 22 of each brush assembly 2 is connected to a point in this conductive mesh 110.

(16) This is illustrated by FIG. 4, which shows (schematically) a plurality of brush assemblies 2 mounted on the stator housing 10S as described above to electrically connect the rotor housing 10R to the conductive mesh 110 in the canopy 11. The conductive mesh 110 in turn is connected to the LPS system LPS.sub.12 of the tower 21, and from there in the usual manner to ground.

(17) An alternative arrangement is shown in FIG. 5. Here, instead of a conductive mesh in the canopy 11, the canopy 11 is provided with a set of down conductors, one of which is arranged as an annular conductor 112 about the front end of the canopy 11, and all leads 22 of the brush assemblies 2 are connected to this front-end down conductor 112, which in turn is connected to the LPS system LPS.sub.11 of the canopy 11, leading to the LPS system LPS.sub.12 of the tower 21, and from there in the usual manner to ground.

(18) FIG. 6 shows a further embodiment of the inventive wind turbine 1. The diagram is a cross-section of the region about the main shaft 15S, 15R with its rotating part 15R and stationary part 15S, indicating the generator's axis of rotation. Here, a turner ring 16 is provided for use in the installation of the wind turbine 1. The turner ring 16 is structurally a part of the outer rotor, and remains in place after installation, even if it is no longer required. Drive units 160 anchored in a stationary front plate 140 are used to turn the ring 16 (and therefore the aerodynamic hub). Each drive unit 160 has a pinion 161 that engages with the toothed outer side of the turner ring 16.

(19) The stationary front plate 140 may be assumed to be electrically connected to a bedframe, which in turn may be assumed to be electrically connected in the usual manner to the LPS system of the wind turbine. The diagram shows a second lightning current path P3 that is provided by a plurality of brush assemblies 3 mounted on a stationary front plate 140 that supports the main bearing 14. Each of these brush assemblies 3 comprises a brush holder 30 that is mounted on the stationary front plate 140 such that the brush assembly 3 extends across a turner ring gap G3 to make electrical contact with the turner ring 16. Here also, it may be assumed that a spring-loaded mechanism acts to press the carbon brush 31 against the turner ring 16. In this way, any lightning current reaching the turner ring 16 from the hub 13 will be given a safe path P3 to the stationary front plate 140. Since this front plate 140 is mounted to the bedframe, a safe path to the down conductors of the tower 12 is ensured.

(20) Although the present invention has been disclosed in the form of preferred embodiments and variations thereon, it will be understood that numerous additional modifications and variations could be made thereto without departing from the scope of the invention.

(21) For the sake of clarity, it is to be understood that the use of “a” or “an” throughout this application does not exclude a plurality, and “comprising” does not exclude other steps or elements.