Direct-drive wind turbine The invention relates to a direct driven wind turbine with a plain bearing and a service method for this bearing.

A wind turbine transfers wind energy into electrical energy. The moving air accelerates the rotor of the wind turbine. The rotation of the rotor is transferred to an electrical genera ^¬ tor. The electrical generator transforms the rotational en ^¬ ergy into electrical energy.

In the last years the concept of a direct driven wind turbine was established. In a direct driven wind turbine the rota ^¬ tional energy of the rotor is transferred to the generator directly without the use of a gearbox.

In a direct driven wind turbine the rotor of the wind turbine is directly connected to the rotor of the electrical genera ^¬ tor. The chain of mechanically connected parts leading from the rotor of the wind turbine to the rotor of the generator is called the drive train of the wind turbine. To allow the rotational movement and to provide the necessary stability of the rotating parts, the drive train is mounted with at least one bearing. This bearing allows the drive train to rotate. At the same time it provides the necessary stability by supporting the radial and axial loads and the bending moments present in the drive train.

WO 2011/003482 A2 describes a wind turbine main bearing real ^¬ ized to bear a shaft of a wind turbine. The bearing comprises a fluid bearing with a plurality of bearing pads.

The document describes a bearing with a cylindrical bearing surface and a series of trust pads. The plain bearing has to provide a large surface to withstand the forces present in the drive train. As a consequence the pads used for the cylindrical bearing surface are very large, heavy and difficult to exchange.

For the exchange of the bearing pads the shaft of the wind turbine needs to be lifted by help of a lifting arrangement.

It is the aim of the invention to provide a wind turbine with a plain bearing that enables a service of the bearing and an exchange of the bearing pads without the use of heavy equip ^¬ ment .

The aim is reached by the features of the independent claim. Preferred embodiments of the invention are described in the dependent claims.

A rotor of the wind turbine is directly connected with a ro- tatable drive train of the wind turbine. The rotatable drive train is directly connected with a rotor of an electrical generator of the wind turbine.

The rotatable drive train is connected with a stationary part of the wind turbine via at least one bearing, which allows the rotation of the drive train in relation to the stationary part.

The electrical generator provides a support structure to which the stationary side of the at least one bearing is mounted. The at least one bearing is a plain bearing and the plain bearing comprises a wear-and-tear-part , which is an ob- ject to be exchanged.

The rotatable drive train is prepared to be fastened to the stationary part of the wind turbine and at least one wear- and-tear-part of the plain bearing is exchangeable while the rotatable drive train is fastened to the stationary part.

The drive train of a wind turbine transfers the rotational energy of the rotor of the wind turbine to the electrical generator of the wind turbine. The drive train is a mechani- cal chain of parts connecting the rotor of the wind turbine and the rotor of the electrical generator. The drive train is rotating when the wind turbine is in operation. The stationary part of the wind turbine comprises the stator of the electrical generator and the nacelle construction that is prepared to transfer the loads of the drive train and the weight of the rotor of the wind turbine and the nacelle to the tower of the wind turbine.

The drive train of the wind turbine and the rotor of the gen ^¬ erator are connected to the stationary part of the wind tur ^¬ bine via at least one bearing. The bearing comprises a rotatable side that is connected to the rotatable drive train and a stationary side that is con ^¬ nected to the stationary part of the wind turbine.

The stator of the electrical generator comprises a support structure which connects the stator of the electrical genera ^¬ tor to the stationary part of the wind turbine. The station ^¬ ary side of the bearing is connected to the support structure of the electrical generator. A plain bearing is a bearing without rolling elements, like balls or rollers. A plain bearing is also known as a sliding bearing, a friction bearing or a floating bearing.

Several parts of the bearing experience a certain wear due to the operation of the wind turbine and thus the rotation of the bearing. These parts have a limited lifespan that is shorter then the expected lifespan of the bearing, and have to be exchanged regularly to continue the operation of the wind turbine. These parts are called wear-and-tear-parts and they are checked and/or exchanged during maintenance and ser ^¬ vice . To access and exchange the wear-and-tear-parts in the bearing of the wind turbine, the rotatable part of the wind turbine is fastened to the stationary part of the wind turbine. Thus the weight of the rotor of the wind turbine, the drive train and the rotor of the generator is transferred to the station ^¬ ary part of the wind turbine via the fastened connection be ^¬ tween the drive train and the stationary part.

The drive train is fixed in its position by the fastened con- nection. Thus the bearing is not needed to transfer the weight, when the drive train is fastened to the stationary part of the wind turbine. Thus the bearing is free of loads from the drive train. Thus the bearing can be opened and the wear-and-tear-parts in the bearing can be exchanged.

The bearing is opened and the wear-and-tear-parts are acces ^¬ sible and exchangeable, while the drive train is fastened to the stationary part of the wind turbine. Thus no heavy part of the wind turbine has to be lifted to access and/or ex- change the wear-and-tear-parts.

Thus no crane is needed for the exchange of wear-and-tear- parts in the bearing. Thus time is saved and no heavy machin ^¬ ery is needed during maintenance and service for the exchange of wear-and-tear-parts in the bearing.

In a preferred configuration the bearing comprises a ring that is detachable from the bearing for an exchange of at least one wear-and-tear-part of the bearing.

The bearing comprises a ring that closes the bearing. The axis of rotation of the ring is the same as the axis of rota ^¬ tion of the bearing. To open the bearing for the exchange of a wear-and-tear-part the ring can be detached from the bearing to allow mainte ^¬ nance personnel access to the wear-and-tear-parts that have to be exchanged. Preferably the ring is at least a part of the rotatable side or at least a part of the stationary side of the plain bear ^¬ ing. Thus the sliding surface is directly accessible when the ring is removed.

In another preferred configuration the ring is an additional ring mounted to the rotatable side or the stationary side of the bearing to close the bearing. Thus the alignment of the rotatable side and the stationary side of the bearing is not changed when the ring is removed and the bearing is opened for maintenance and service.

Thus only the ring has to be detached to access the wear-and- tear-parts. Thus the bearing can be opened very easily with ^¬ out the use of heavy tools. Thus time and material is saved during maintenance and service.

In a preferred configuration the ring is segmented.

Thus a segment of the ring is less heavy and smaller then the whole ring. Thus the segment of the ring is easier to handle inside the wind turbine then the whole ring. Thus fewer tools and fewer personnel are needed for the service of the bear- ing.

In a preferred configuration at least a part of the ring is detachable to open the bearing for the exchange of the wear- and-tear-part .

Thus the bearing is opened to access and exchange the wear- and-tear-parts of the bearing. Thus the exchange of the wear- and-tear-parts is possible. The bearing can be opened partially by detaching a part of the ring. Thus only the part of the bearing is opened, where wear-and-tear-parts have to be exchanged. Thus the rest of the bearing stays closed and is therefore protected from dust and particles present in the surrounding of the bearing.

Dust and particles are present in the surrounding of the bearing and they reduce the lifetime of the bearing when they come into the bearing and the bearing is in operation again.

In a preferred configuration the bearing comprises a sealing and/or a sliding surface.

In a preferred configuration the wear-and-tear-part is the sealing of the bearing and the sealing of the bearing is an object to be exchanged. The bearing comprises a sealing. This is sealing the bearing so that the lubrication stays within the bearing and dust or particles present in the surrounding of the bearing can not get into the bearing. The sealing is located between the ro- tatable side and the stationary side of the bearing. The sealing is also a wear-and-tear-part that needs to be ex ^¬ changed regularly.

Preferably the sealing is exchanged when the bearing is opened. Thus the sealing can be exchanged during maintenance and service as a wear-and-tear-part. Thus also the sealing can be exchanged without the need to exchange the whole bear ^¬ ing and/or without the use of heavy machinery.

In a preferred configuration the sliding surface of the bear- ing is segmented and the segments are arranged and connected within the plain bearing in a way that the exchange of an individual segment is permitted.

In a preferred configuration the wear-and-tear-part is the sliding surface of the bearing and at least a segment of the sliding surface is an object to be exchanged. The plain bearing comprises a sliding surface at a first side of the bearing that slides along the second side of the bear ^¬ ing when the bearing is rotating. The sliding surface experiences a certain friction that leads to wear on the sliding surface. The sliding surface therefore needs to be exchanged after a predetermined time span. So the sliding surface is a wear-and-tear-part .

The sliding surface is exchanged when the bearing is opened. Thus the sliding surface of the bearing is exchanged and the rest of the bearing stays in the wind turbine. Thus a com ^¬ plete exchange of the bearing is avoided. Thus time is saved in maintenance and service and no heavy machinery is needed to lift parts of the wind turbine.

Preferably the sliding surface is segmented and individual segments of the sliding surface are exchanged.

Thus an exchange of a part of the sliding surface is possi ^¬ ble. Thus the sliding surface doesn't have to be exchanged completely. Thus material and time is saved during mainte ^¬ nance and service.

In a preferred configuration the support structure of the generator comprises an opening, which can be used as a man hole.

Thus personnel in maintenance and service are able to access the support structure of the electrical generator and/or pass through at least a part of the structure. Thus the personnel are able to access an area, like the area where the drive train is fastened to the stationary part of the wind turbine, or an area at the bearing to allow the exchange of wear-and- tear-parts. Thus the access to areas needed for maintenance and service is provided from inside the wind turbine and without the need to detach parts of the wind turbine or the nacelle of the wind turbine. In a preferred configuration the generator comprises a cavity along the axis of rotation of the generator.

Preferably the cavity is big enough for personnel in mainte- nance to crawl through. Most preferably it is big enough for personnel in maintenance to walk through. The cavity can reach into the electrical generator. Thus personnel in main ^¬ tenance are able to access the inner part of the generator or the support structure or the bearing for the exchange of wear-and-tear-parts .

Preferably the cavity reaches through the electrical genera ^¬ tor. Thus the personnel in maintenance can cross the genera ^¬ tor to reach the other end of the generator. Thus the person- nel don't have to detach parts of the structure of the na ^¬ celle or the generator to access the other side of the gen ^¬ erator .

Thus access to the other end of the generator seen along the axis of rotation is possible. Thus the bearing can be reached easily for the exchange of wear-and-tear-parts and exchange parts can be transported to the bearing through the nacelle of the wind turbine. In a preferred configuration the opening is accessible from the cavity of the generator.

Thus personnel in maintenance move through the cavity to ac ^¬ cess the opening. The opening is located close to the connec- tion where the drive train is fastened to the stationary part of the wind turbine. Thus the connection is directly accessi ^¬ ble through the opening.

Thus the opening is located close to the bearing. Thus the wear-and-tear-parts that need to be exchanged through the opening can be exchanged directly. In a preferred configuration the generator comprises a shaft and the opening in the support structure of the generator is accessible in axial direction along the shaft. In this configuration the generator comprises a shaft. The shaft leads through the generator. The support structure con ^¬ nects the stator of the generator to the shaft. The opening is located in the support structure to allow the access into the support structure.

Thus personnel in maintenance and service can directly access the connection point, where the drive train is fastened to the stationary part of the wind turbine, and/or the bearing through the opening.

Thus the drive train can be fastened to the stationary part through that opening. Thus the access to the bearing and the exchange of the wear-and-tear-parts is possible through the opening .

The invention is shown in more detail by the help of figures. The figures show a preferred configuration and do not limit the scope of the invention. FIG 1 shows a cut through the direct driven wind turbine.

FIG 2 shows the drive train fastened to the stationary part of the wind turbine. FIG 3 shows the ring detached from the bearing.

FIG 4 shows the exchange of the wear-and-tear-parts.

FIG 5 shows another embodiment of the wind turbine. FIG 1 shows a cut through the direct driven wind turbine. FIG 1 shows a cut through a part of the electrical generator 1, the bearing 2 and a part of the hub 3. The electrical gen ^¬ erator 1 comprises a stator 4 and a rotor 5. The rotor 5 is connected to the rotatable side 6 of the bearing 2 and to the hub 3 of the wind turbine.

The stator 4 comprises the support structure 8. The support structure 8 comprises an opening 9 that can be used as a man hole and an opening 10 that allows the access to the area where the drive train is fastened to the stationary part of the wind turbine.

The generator 1 comprises a cavity 11 in the area within the support structure 8. The opening 9 is accessible from the cavity 11.

The bearing 2 comprises a rotatable side 6 and a stationary side 7. The rotatable side 6 is connected to the rotor 5 of the generator 1 and to the Hub 3. The stationary side 7 is connected to the support structure 8 of the generator of the wind turbine. The bearing 2 further comprises a sliding surface 12 that is located between the rotatable side 6 and the stationary side 7 of the bearing. FIG 2 shows the drive train fastened to the stationary part of the wind turbine.

FIG 2 shows the same construction as described under FIG 1. In addition the drive train is fastened to the stationary part of the wind turbine. Fastening means 13 are introduced that are bolted to the rotor 5 and the support structure 8 of the stator 4 of the generator 1. The fastening means 13 transfer the weight of the components of the drive train and the wind loads acting on the blades and the hub to the sta- tionary part of the wind turbine. Thus the bearing 2 is not necessary to carry the weight and the loads of the components of the drive train as long as the fastening means 13 are in place . FIG 3 shows the ring detached from the bearing.

FIG 3 shows the same construction as described under FIG 1 and FIG 2. In addition the ring 14 of the bearing 2 is detached from the bearing 2. The ring 14 is moved in the direc ^¬ tion of the arrow.

This can also be a segment of the ring that is detached from the bearing 2. When the ring 14 is detached from the bearing 2 access to the wear-and-tear-parts is provided. In this case the sliding surface 12 is accessible and can be exchanged.

FIG 4 shows the exchange of the wear-and-tear-parts.

FIG 4 shows the same construction as described under FIG 1, FIG 2 and FIG 3.

In addition it is shown how the sliding surface 12 or parts of a segmented sliding surface can be exchanged by pulling them out of the bearing 2 and introducing new parts in the same way.

FIG 5 shows another embodiment of the wind turbine. Fig 5 shows a cut through a part of the electrical generator 1, the bearing 2 and a part of the hub 3. The electrical gen ^¬ erator 1 comprises a stator 4 and a rotor 5. The rotor 5 is connected to the rotatable side 6 of the bearing 2 and to the hub 3 of the wind turbine.

The stator 4 comprises the support structure 8. The generator 1 comprises a cavity 11 in the area within the support struc ^¬ ture 8. The bearing 2 comprises a rotatable side 6 and a stationary side 7. The bearing 2 further comprises a sliding surface 12 that is located between the rotatable side 6 and the station ^¬ ary side 7. In this configuration the bearing 2 is accessible from the cavity 11 in the generator 1. After the drive train is fixed to the stationary part of the wind turbine, the bearing 2 can be opened by detaching segments of the rotatable side 6 of the bearing, or a ring of the stationary side 7 of the bearing 2. After opening the bearing 2 the wear-and-tear-parts like the sliding surface 12 or segments of the sliding sur ^¬ face can be exchanged.