Direct drive wind turbine with slip ring

A direct-drive wind turbine includes a tower with a nacelle having a direct-drive generator and a rotatable hub carrying turbine blades, wherein the direct-drive generator comprises an outer stator and an inner rotor and has a first side facing the turbine blades and a second side facing away from the turbine blades. A slip ring at the second side transfers power and/or signals from the nacelle to the rotatable hub being mounted coaxially with the centerline of the direct-drive generator. The slip ring mounts on a first arm. An end of a second arm distal to the slip ring can engages the rotor or a shaft. The assembly of the first arm, slip ring and second arm may be at a first position where the slip ring is aligned with the centerline of the direct drive generator and at a second position to provide access to the hub.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Section 371 National Stage Application of International Application PCT/EP2012/000509 filed Feb. 5, 2012 and published as WO2012/107192 A2 in English.

BACKGROUND

Aspects of the present invention relate to a direct-drive wind turbine comprising a tower with a nacelle, said nacelle being provided with a direct-drive generator and a rotatable hub carrying turbine blades, wherein the direct-drive generator comprises an outer stator and an inner rotor and has a first side facing the turbine blades and a second side facing away from the turbine blades, the nacelle further being provided with a slip ring for transferring power and/or signals from the nacelle to the rotatable hub, said slip ring being mounted coaxially with the centerline of the direct-drive generator.

A hub carrying turbine blades requires power, for example for powering pitch motors, various sensors (such as sensors measuring the pitch of a turbine blade), etc. This requires one or more electrical connections between the stationary world (the tower with the nacelle) and the rotatable hub. This function is performed by a slip ring. For direct-drive generators, access to the hub is provided via the hollow center of the generator, or via a bypass. The latter is inconvenient because it is dangerous for maintenance personal and adds significant additional cost. The first option is problematic for those direct-drive generators that have an inner rotor, as a result of which the inside wall of the direct-drive generator is not part of the stationary world. This is in particular the case for direct-drive turbines that have bearings at both the first and the second end of the direct-drive generator. More specifically the problem is that the placement of the slip ring at the second end would block the passage through the direct-drive generator, and placement of the slip ring at the first end requires a long frame extending through the hollow axis of direct-drive generator, which is a burden in view of the required co-axial placement of the slip ring. Such a frame would have to be very rigid, bulky and heavy to meet the alignment requirements.

SUMMARY

An aspect of the present invention is to provide a construction that allows passage through the hollow rotor of the direct-drive generator without increasing the design requirements for accurate co-axial alignment with the centerline of the direct-drive generator.

To this end, a direct-drive wind turbine according to the preamble is characterized in that the slip ring is provided at the second side of the direct-drive generator and is mounted on a first arm, the slip ring further being provided with a second arm, wherein an end of said second arm distal to the slip ring is capable of being engaged by an element chosen from i) a shaft connecting the rotor of the direct drive generator to the hub, and ii) the rotor of the direct drive generator, wherein the assembly of first arm, slip ring and second arm can be at a first position in which the slip ring is aligned with the centerline of the direct drive generator and at a second position in which the slip ring is not aligned with the centerline of the direct drive generator to provide access to the hub, wherein the direct-drive wind turbine is provided with a mounting support capable of guiding the assembly from a third position that is away from the first position to the first position.

Thus, in case of maintenance, the hub can be accessed by moving the assembly from the first position, thus clearing the passage through the hollow direct-drive generator. After maintenance, the assembly is moved back again, without re-alignment of the axes of the slip ring and the direct-drive generator being required thanks to the guiding of the assembly from the third position to the first position by the mounting support. The second and third position may be the same, in which case the assembly is guided over the entire distance from the second position to the first position. According to a simple embodiment, the stationary part of the generator is provided with two upright, diametrically opposed pins and the first arm is provided with holes at either end receiving said pins. The pins guide the first arm, seating the assembly in the first position. To engage the second arm, the distal end may comprise a guiding slot and the rotor may be provided with a pin capable of being received in the guiding slot. The guiding slot will accommodate for minor deviations in the coaxial alignment of the axis of rotation of the slip ring and of the rotor of the direct-drive generator.

According to one embodiment, the first arm is a swing arm that is capable of being swung clear by rotating about an axis located at an end of the first arm opposite of the slip ring.

After maintenance, the swing arm is swung back again, without re-alignment of the axes of the slip ring and the direct-drive generator being required. This guides the assembly over the entire path from the second position all the way to the first position. As an additional benefit, the maintenance worker doesn't have to lift the full weight of the assembly.

According to another embodiment, the axis of the first swing arm is affixed to a stationary part of the direct-drive generator.

The stationary part is the stator of the direct-drive generator or the housing thereof. This reduces the length of the arm and thus avoids compromising the accuracy of the co-axial alignment of the centerlines of the rotor of the direct-drive generator and the slip ring.

According to one embodiment, the axis about which the first arm can swing tilts towards the hub, allowing the first arm to move towards the hub by gravity, and the first arm is blocked by a stop.

This provides a very reliable method of keeping the slip ring at the desired first position, even in case a locking means such as a safety catch fails. The stop or the first arm may be provided with a bolt to allow adjustment of the position of the slip ring. The stop may be in the form of a short arm, that in itself does not impede a person from access to the hub. The short arm will be fixed to the stationary world, e.g. the housing of the generator.

According to one embodiment, gravity assists in keeping the slip ring away from the centerline of the generator if the slip ring has been swung clear.

This is, for example, achieved if the swing arm can swing over more than 90°.

According to another embodiment, the first arm is at an angle to a horizontal plane −30° to 30°.

That is, the arm is substantially horizontal. This reduces the effect of the weight of the combination of the first arm, the slip ring and the second arm, making it easier to swing aside, or swing back after maintenance.

According to yet another embodiment, the swing arm is provided with an electrical connector leading to the slip ring and the second arm is provided with an electrical counter connector for the electrical connector.

This allows, in case of maintenance, maintenance staff to plug the electrical counter connector of the stationary world into the electrical connector of the hub. Thus, by way of example, the turbine-blade driven section can be powered in case of maintenance, e.g. to check the operation of a pitch motor. The electrical connector may be female, in which case the electrical counter connector is male, or vice versa. By way of example, there is a data connection cable in the stationary world that has a first female connector. The first arm will have a first male counter connector that is connected, via the slip ring, with a second female connector. This second female connector will be connected to a second male counter connector of the rotating world. During maintenance, the first female connector may be connected to the second male counter connector and the swing arm can be moved out of the way. Power supplying connectors will be female, for reasons of safety.

According to another embodiment, the first arm is provided with a sensor for measuring the rotational speed of the rotor of the direct-drive generator.

The sensor, such as a revolutions counter, may be used to detect the presence or absence of the first arm, and hence the slip ring, e.g. in case the means locking the first arm fail.

According to one embodiment, the first arm is locked in a co-axially aligned state.

This helps to ensure reliable operation of the slip ring, even after long periods of vibration, as will occur in the nacelle.

According to yet another embodiment, the rotor of the direct-drive turbine is provided with a floor, and a cable towards the hub is guided below the floor.

This helps to provide a clear and safe passage for maintenance personnel.

DETAILED DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENT

FIG. 1shows a direct-drive wind turbine100comprising a tower101, a nacelle102supported by the tower101. The nacelle102carries a hub103with turbine blades104, the hub103capable of driving a generator105. As is customary, the axis of rotation of the hub103and the generator105are at an angle with a horizontal plane113, in this case 6°. The generator has a first side111, facing the hub103, and a second side112facing away from the hub103. In accordance with an aspect of the present invention, a slip ring106is provided at the second side112.

FIGS. 2aand 2bshow the slip ring106ofFIG. 1from the nacelle102. It is mounted on a first arm201capable of being swung aside (FIG. 2b). The slip ring106is provided with a second arm202that engages a pin203on the rotor204of the generator105. When the rotor204rotates, the second arm202rotates along with it. A floor210is provided allowing an even surface for the maintenance worker. Cables to the second arm202may be passed below the floor210, improving worker safety.

FIG. 3shows a detailed rear view of the slip ring106ofFIG. 2a. It shows the first arm201being mounted on a mounting support301, and rotatable about an axis320(seeFIG. 4). The first arm201is provided with connectors302of cables372for connecting power and data cables (not shown) to the slip ring106. It should be noted in the figures primes and double-primes associated with a reference number denote a first and second occurrence, respectively, of the element associated with the reference number.

There are also cables303with connectors304(FIG. 4) for passing said power and data to corresponding cables (not shown) leading into and co-rotating with the hub103.

The first arm201is provided with a sensor401capable of detecting pins203, which give an indication of the number of rotations per minute of the rotor204of the generator105.

To lock the arm201and hence the slip ring106in a first position in which the slip ring106and the axis of rotation of the rotor204are aligned, the first arm201is provided with two curved auxiliary arms410with holes411. A locking pin412is inserted into the holes411at one side of the mounting support301to lock the first arm201in the first position and at an opposite side of the mounting support301to lock the first arm201into the second position in which the slip ring106doesn't block the access through the generator105(FIG. 2b). The locking pin412has an off-center protrusion413, as a result of which rotating the locking pin412will push the curved auxiliary arm410against the mounting support301. The locking pin412is held in place by safety catch414.

To free the path to the hub103, the safety catch414is lifted, allowing rotation of the locking pin412which is subsequently taken out of the holes411. The first arm201is now rotated to the second position, the locking pin412is introduced back into the holes411, as a result of which the first arm201will remain locked in the second position. To bring the slip ring106into the first position, repeat these steps in reverse, making sure the second arm202engages one of the pins203on the rotor204of the generator105. If you do that, the slip ring106is aligned, and does not need further alignment, because the first arm201has a fixed length. That is not to say that the first arm201can't benefit from adjusting its length, or more generally, the distance between the mounting support301and the slip ring106, because this may be convenient the first time the slip ring106is aligned. The first position is determined by a stop432, which may be provided as a screw to provide first-time adjustment.

FIG. 5shows a schematic cross-sectional view of an alternative embodiment of a mounted slip ring106(in the first position), the axis320for swinging the first arm201being at an angle, β, of 80° with respect to the horizontal plane113. Thus gravity can help to maintain the slip ring106maintain its first position.

The present invention is in particular suitable for generators with bearings at opposite sides of the generator. The bearings501and502mounted on a shaft533(which is connected to the hub103) are indicated, together with generator housing534, the rotor204and stator503of the generator105.

The invention as discussed above may be varied in any of several ways within the scope of the appending claims. For example, magnets may be used to keep the assembly in the first position. The slip ring may be provided with a counter-weight or another second arm to counter-balance wobbling or vibrations.