Wind turbine, a method for servicing a main bearing unit of a wind turbine and use thereof

1. A wind turbine comprising a nacelle and a rotor, said rotor being rotatably mounted on said nacelle by means of at least one main bearing unit characterized in that said main bearing unit comprises at least one outer ring, at least one centre ring being radially positioned inwardly in relation to said outer ring, a first bearing assembly disposed between said outer ring and said centre ring and having an outer race, an inner race, and rolling elements disposed between said outer and inner races, at least one inner ring being radially positioned inwardly in relation to said centre ring, a second bearing assembly disposed between said centre ring and said inner ring and having an outer race, an inner race, and rolling elements disposed between said outer and inner races, and wherein said centre ring is capable of rotation in relation to said outer ring and said inner ring, or said outer ring and said inner ring are capable of rotation in relation to said centre ring, subsequent to assembly of said wind turbine.

2. The wind turbine according to claim 1 , wherein said at least one outer ring and said at least one inner ring are rigidly connected.

3. The wind turbine according to claim 1 , wherein said at least one outer ring and said at least one inner ring are attached to a hub of said rotor.

4. The wind turbine according to claim 1 , wherein said at least one centre ring is attached to a hub of said rotor.

5. The wind turbine according to claim 1 , wherein at least one of said main bearing unit and said wind turbine comprises means for allowing said outer ring or at least a part of said outer ring to be displaced axially.

6. The wind turbine according to claim 1 , wherein at least one of said main bearing unit and said wind turbine comprises means for allowing said inner ring or at least a part of said inner ring to be displaced axially.

7. A method for servicing said main bearing unit of said wind turbine according to claim 1 , said method comprising the steps of

moving said inner ring or a part of said inner ring of said main bearing unit while said centre ring and said outer ring of said main bearing unit remains load-transmitting, or

moving said outer ring or a part of said outer ring of said main bearing unit while said centre ring and said inner ring of said main bearing unit remains load-transmitting.

8. The method according to claim 7 , wherein said method further comprise the step of disengaging said inner ring or said part of said inner ring or said outer ring or said part of said outer ring from said main bearing unit.

9. The method according to claim 7 , wherein said inner ring or said part of said inner ring is moved to gain access to internal parts between said centre ring of said main bearing unit and said inner ring.

10. The method according to claim 7 wherein said outer ring or said part of said outer ring is moved to gain access to internal parts between said centre ring of said main bearing unit and said outer ring.

11. The method according to claim 7 , wherein said method is further a method to level out wear of one or more parts of said main bearing unit.

12. The method according to claim 11 , wherein said one or more parts comprise a region of stationary bearing rings of said main bearing unit which are in direct contact with rolling elements of said main bearing unit.

13. The method according to claim 12 , wherein said stationary bearing rings are one or more rings of said main bearing unit which are fixed in relation to said nacelle during normal operation of said wind turbine.

14. The method according to claim 7 , wherein said rings or said part of said rings of said main bearing unit are reattached in a new angle-position.

15. A wind turbine comprising a nacelle and a rotor, said rotor being rotatably mounted on said nacelle by means of at least one main bearing unit characterized in that said main bearing unit comprises at least one outer ring, at least one centre ring being radially positioned inwardly in relation to said outer ring and at least one inner ring being radially positioned inwardly in relation to said centre ring and wherein said centre ring is capable of rotation in relation to said outer ring and said inner ring or said outer ring and said inner ring are capable of rotation in relation to said centre ring, wherein said at least one centre ring is formed integrally with a hub of said rotor.