Methods for installing wind turbine blades

Abstract

The present disclosure relates to methods (100) for rotating an unbalanced hub (20) of a wind turbine (10), to methods (200) for mounting at least one wind turbine blade (22) to a wind turbine hub (20) and to wind turbine hubs (20). A method (100) comprises removably connecting a blade holder (29) to the hub (20), and using a weight of the blade holder (29) to rotate the hub (20).

Description

METHODS FOR INSTALLING WIND TURBINE BLADESTECHNICAL FIELD

[0001] The present disclosure relates to methods for rotating a wind turbine hub and methods for installing at least one wind turbine blade on a wind turbine hub on top of a wind turbine tower. More particularly, the present disclosure relates to rotation of unbalanced rotors during blade installation. The present disclosure further relates to wind turbine hubs and wind turbines specifically configured for such methods.BACKGROUND

[0002] Modern wind turbines are commonly used to supply electricity into the electrical grid. Wind turbines of this kind generally comprise a tower and a rotor arranged on the tower. The rotor, which typically comprises a hub and a plurality of blades, is set into rotation under the influence of the wind on the blades. Said rotation generates a torque that is normally transmitted through a rotor shaft to a generator, either directly (“directly driven” or “gearless”) or through the use of a gearbox. This way, the generator produces electricity which can be supplied to the electrical grid.

[0003] The wind turbine hub may be rotatably coupled to a front of the nacelle. The wind turbine hub may be connected to a rotor shaft, and the rotor shaft may then be rotatably mounted in the nacelle using one or more rotor shaft bearings arranged in a frame inside the nacelle. The nacelle is a housing arranged on top of a wind turbine tower that may contain and protect the gearbox (if present) and the generator (if not placed outside the nacelle) and, depending on the wind turbine, further components such as a power converter, and auxiliary systems.

[0004] During wind turbine installation, a plurality of blades is mounted on the wind turbine hub. The hub generally comprises a plurality of annular mounting flanges with holes to which the blades can be connected to, for example by pitch bearings. The blade may comprise a plurality of fasteners, such as pins or studs, at its blade root. During installation, these fasteners are fitted into the holes in the mounting flanges.

[0005] It is known to hoist a complete rotor assembly, i.e. the hub with all the blades, and mount it on e.g. the nacelle. But in order to mount a complete rotor assembly, a large surface area is required for attaching the blades to the hub before the hub with the blades is lifted, which is typically not available in the case of offshore wind turbines.

[0006] It is further known to mount an incomplete rotor assembly on the nacelle, e.g. the hub with two blades, and subsequently, mount the remaining blade. In these cases, the rotor with the two blades is normally mounted with the two blades pointing upwards, i.e. “bunny ears” configuration. The third blade can be vertically mounted from below. However, in order to be able to perform these operations, the prevailing wind speed has to be below a predetermined value for a prolonged period time. However, windows of several hours in which the wind does not reach the predetermined value may not be available very often during certain seasons. In practice, this may mean that personnel and equipment including e.g. expensive cranes and jack-up barges may be in stand-by during days or even weeks. This can represent an enormous cost and is therefore not typically used in the case of offshore wind turbines.

[0007] Individually mounting each of the blades at potentially different angles is commonly used for offshore wind farms due to the larger component sizes and offshore logistic constraints. However, such methods require rotation of the hub between the mounting of one blade and another. In order to correctly position the hub, torque is required for rotating the (incomplete) wind turbine rotor after mounting one blade in order to mount the next one. When not all blades have been mounted onto the hub, the hub is not balanced, so that the weight of one or more blades has to be carried upwards when rotating the hub. The torque required for rotor rotation may thus be very high.

[0008] The torque may be delivered using the gearbox (when present) with for example an external power supply for rotating the rotor. Such a system may be used in combination with a locking pin for maintaining the rotor in a desired position for installation. However, this is possible only if the wind farm is already connected to the grid and provided that the turbines are configured to be able to use the generator as motor. The alternative would be to install large diesel generators, which is impractical and requires too much time affecting the so-called installation critical path for offshore wind turbines.

[0009] Also, the torque to rotate the rotor may be provided by the using weight of a blade holder (and the corresponding blade) when the blade has been attached to the hub. However, this may work for certain orientations or positions at which the blade is attached to the hub and not for others. Mounting the blade for example at 302above the 3 o’clock position may enable using the weight of the blade holder connected to the blade for rotating the unbalanced rotor immediately after mounting the blade. However, a large lifting device and a large vessel may be required to be able to mount the blade at such an angle. A vessel sufficiently large may be scarce.

[0010] A way to position the hub such that the next blade may be installed when mounting individual blades includes yawing the nacelle. However, this may be complicated and time consuming as, in order to be able to yaw, the related system has to be commissioned first.Mounting of the blades thus has to be halted in such a scenario until the yaw system on the specific wind turbine has been commissioned.

[0011] The present disclosure aims to at least partially reduce one or more of the aforementioned drawbacks.SUMMARY

[0012] In an aspect of the present disclosure, a method for rotating an unbalanced hub of a wind turbine is provided. The method comprises removably connecting a blade holder to the hub, and using a weight of the blade holder to rotate the hub.

[0013] Accordingly, a blade holder, which may be used for lifting a wind turbine blade to be mounted to the hub and for approaching the blade to the hub, may also be used as counterweight for rotating the hub when the hub is unbalanced i.e. when the hub carries at least one blade, but not all blades yet.

[0014] Yawing may therefore be avoided during blade mounting. Also, excessively large lifting devices and excessively large vessels or jack-up barges may also be avoided.

[0015] Throughout this disclosure, a blade holder may be understood as a system, device or tool configured to surround at least in part a wind turbine blade and to support it or gripped when the blade holder, and therefore the tool, is lifted. In this regard, the blade holder may be connected to lifting device such as a crane. The blade holder may therefore be an interface between the lifting device and the wind turbine blade. Examples of blade holders may also commonly be referred to as “blade yokes”.

[0016] In some examples, the blade holder may comprise a frame and a plurality of slings coupled to the frame for surrounding and supporting the blade when the blade holder, and therefore the blade, are lifted. In other examples, the blade holder may comprise a frame shaped and size to surround and support the blade. The frame may include a plurality of pads or clamps to securely hold the blade. Examples of such blade holders include e.g. Blade Eagle or Blade Hawk commercialized by Liftra®, RBC yoke commercialized by ematec and C-Yoke commercialized by ENABL. Other blade holders known in the art which are able to operate as described herein may also be used.

[0017] In a further aspect, a method for mounting at least one wind turbine blade to a wind turbine hub atop a wind turbine tower is provided. The method comprises lifting a wind turbine blade by lifting a blade holder arranged with the wind turbine blade, and attaching the wind turbine blade to the hub. The method further comprises removing the blade holder from the wind turbine blade, and removably connecting the blade holder to the hub by attaching the blade holder to aninterface of the hub. The method further comprises using a weight of the blade holder to rotate the hub with the wind turbine blade, and disconnecting the blade holder from the hub.

[0018] According to this aspect, the wind turbine blade is lifted and attached to the hub by using a blade holder. The blade holder is then removably attached to an interface of the hub, and the weight of the blade holder is used for turning the hub with the blade.

[0019] The unbalanced rotor may therefore be rotated taking advantage of the weight of the blade holder, and steps such as yawing may be avoided during blade mounting. Also, excessively large lifting devices may be avoided, and excessively large vessels or jack-up barges may also be avoided.

[0020] Throughout this disclosure, an interface of the hub may be understood as an element which is removably or fixedly (i.e. non-removably) attached or connected to the hub. The interface may be configured, e.g. sized and shaped, for connecting the blade holder and the remainder of the hub when the blade holder is attached to the interface. Specifically, the interface acts as such between the blade holder and the hub such that the hub can be rotated due to the weight of the blade holder. A connection between the blade holder and a lifting device may help to control the rotation of the hub when the blade holder is attached to the interface of the hub.

[0021] Features, details and explanations of the previous aspect may be applicable to, and combined with, this aspect, and vice versa.

[0022] In a further aspect, a wind turbine hub is provided. The hub comprises an interface configured to support a blade holder for rotating the hub using a weight of the blade holder, specifically during blade installation.BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 schematically illustrates a perspective view of one example of a wind turbine;

[0024] Figure 2 illustrates an example of a hub and a nacelle of a wind turbine;

[0025] Figure 3 schematically illustrates a flowchart of an example of a method for rotating a hub of a wind turbine;

[0026] Figures 4 - 15 schematically illustrate frontal views of a wind turbine hub to which three wind turbine blades are attached according to an example of the method of figure 16. The method of the example of figure 3 may also include steps which are represented in at least some of the figures 4 - 15; and

[0027] Figure 16 schematically illustrates a flowchart of an example of a method for mounting at least a wind turbine blade to a wind turbine hub atop a wind turbine tower.DETAILED DESCRIPTION OF EXAMPLES

[0028] Reference now will be made in detail to embodiments of the disclosure, one or more examples of which are illustrated in the drawings. Each example is provided byway of explanation of the disclosure, not as a limitation. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present disclosure without departing from the scope or spirit of the teaching. For instance, features illustrated or described as part of one embodiment can be used with another embodiment to yield a still further embodiment. Thus, it is intended that the present disclosure covers such modifications and variations as come within the scope of the appended claims and their equivalents.

[0029] Figure 1 is a perspective view of an example of a wind turbine 10. In the example, the wind turbine 10 is a horizontal-axis wind turbine. Alternatively, the wind turbine 10 may be a vertical-axis wind turbine. In the example, the wind turbine 10 includes a tower 15 that extends from a support system 14 on a ground 12, a nacelle 16 mounted on tower 15, and a rotor 18 that is coupled to nacelle 16. The rotor 18 includes a rotatable hub 20 and at least one rotor blade 22 coupled to and extending outward from the hub 20. In the example, the rotor 18 has three rotor blades 22. In an alternative embodiment, the rotor 18 includes more or less than three rotor blades 22. The tower 15 may be fabricated from tubular steel to define a cavity (not shown in figure 1) between a support system 14 and the nacelle 16. In an alternative embodiment, the tower 15 is any suitable type of a tower having any suitable height. According to an alternative, the tower can be a hybrid tower comprising a portion made of concrete and a tubular steel portion. Also, the tower can be a partial or full lattice tower. A wind turbine 10 may be placed both onshore and offshore.

[0030] The rotor blades 22 are spaced about the hub 20 to facilitate rotating the rotor 18 to enable kinetic energy to be transferred from the wind into usable mechanical energy, and subsequently, electrical energy. The rotor blades 22 are mated to the hub 20 by coupling a blade root portion to the hub 20 at a plurality of load transfer regions 26. The load transfer regions 26 may have a hub load transfer region and a blade load transfer region (both not shown in figure 1 ). Loads induced to the rotor blades 22 are transferred to the hub 20 via the load transfer regions 26.

[0031] In examples, the rotor blades 22 may have a length ranging from about 15 meters (m) to about 90 m or more. Rotor blades 22 may have any suitable length that enables the wind turbine 10 to function as described herein. For example, non-limiting examples of blade lengths include 20 m or less, 37 m, 48.7 m, 50.2m, 52.2 m or a length that is greater than 91 m. As wind strikes the rotor blades 22 from a wind direction 28, the rotor 18 is rotated about a rotor axis 30.As the rotor blades 22 are rotated and subjected to centrifugal forces, the rotor blades 22 are also subjected to various forces and moments. As such, the rotor blades 22 may deflect and / or rotate from a neutral, or non-deflected, position to a deflected position.

[0032] Moreover, a pitch angle of the rotor blades 22, i.e., an angle that determines an orientation of the rotor blades 22 with respect to the wind direction, may be changed by a pitch system 32 to control the load and power generated by the wind turbine 10 by adjusting an angular position of at least one rotor blade 22 relative to wind vectors. Pitch axes 34 of rotor blades 22 are shown. During operation of the wind turbine 10, the pitch system 32 may particularly change a pitch angle of the rotor blades 22 such that the angle of attack of (portions of) the rotor blades are reduced, which facilitates reducing a rotational speed and / or facilitates a stall of the rotor 18.

[0033] In the example, a blade pitch of each rotor blade 22 is controlled individually by a wind turbine controller 36 or by a pitch control system 80. Alternatively, the blade pitch for all rotor blades 22 may be controlled simultaneously by said control systems.

[0034] Further, in the example, as the wind direction 28 changes, a yaw direction of the nacelle 16 may be rotated about a yaw axis 38 to position the rotor blades 22 with respect to wind direction 28.

[0035] In the example, the wind turbine controller 36 is shown as being centralized within the nacelle 16, however, the wind turbine controller 36 may be a distributed system throughout the wind turbine 10, on the support system 14, within a wind farm, and / or at a remote-control center. The wind turbine controller 36 includes a processor 40. Further, many of the other components described herein include a processor.

[0036] As used herein, the term “processor” is not limited to integrated circuits referred to in the art as a computer, but broadly refers to a controller, a microcontroller, a microcomputer, a programmable logic controller (PLC), an application specific, integrated circuit, and other programmable circuits, and these terms are used interchangeably herein. It should be understood that a processor and / or a control system can also include memory, input channels, and / or output channels.

[0037] Figure 2 is an enlarged sectional view of a portion of the wind turbine 10. In the example, the wind turbine 10 includes the nacelle 16 and the rotor 18 that is rotatably coupled to the nacelle 16. More specifically, the hub 20 of the rotor 18 is rotatably coupled to an electric generator 42 positioned within the nacelle 16 by the main shaft 44, a gearbox 46, a high-speed shaft 48, and a coupling 50. In the example, the main shaft 44 is disposed at least partially coaxial to a longitudinal axis (not shown) of the nacelle 16. A rotation of the main shaft 44 drives the gearbox 46 that subsequently drives the high-speed shaft 48 by translating the relatively slow rotational movement of the rotor 18 and of the main shaft 44 into a relatively fast rotationalmovement of the high-speed shaft 48. The latter is connected to the generator 42 for generating electrical energy with the help of a coupling 50. Furthermore, a transformer 90 and / or suitable electronics, switches, and / or inverters may be arranged in the nacelle 16 in order to transform electrical energy generated by the generator 42 having a voltage between e.g. 400V to 1000 V into electrical energy having medium voltage (10 - 35 KV). Offshore wind turbines may have for example generator voltages between 650 V and 3500 V, and transformer voltages may for instance be between 30 kV and 70 kV. Said electrical energy is conducted via power cables from the nacelle 16 into the tower 15.

[0038] The gearbox 46, generator 42 and transformer 90 may be supported by a main support structure frame of the nacelle 16, optionally embodied as a main frame 52. The gearbox 46 may include a gearbox housing that is connected to the main frame 52 by one or more torque arms 103. In the example, the nacelle 16 also includes a main forward support bearing 60 and a main aft support bearing 62. Furthermore, the generator 42 can be mounted to the main frame 52 by decoupling support means 54, in particular in order to prevent vibrations of the generator 42 to be introduced into the main frame 52 and thereby causing a noise emission source.

[0039] Optionally, the main frame 52 is configured to carry the entire load caused by the weight of the rotor 18 and components of the nacelle 16 and by the wind and rotational loads, and furthermore, to introduce these loads into the tower 15 of the wind turbine 10. The rotor shaft 44, generator 42, gearbox 46, high-speed shaft 48, coupling 50, and any associated fastening, support, and / or securing device including, but not limited to, support 52, and forward support bearing 60 and aft support bearing 62, are sometimes referred to as a drive train 64.

[0040] In some examples, the wind turbine may be a direct drive wind turbine without gearbox 46. Generator 42 operate at the same rotational speed as the rotor 18 in direct drive wind turbines. They therefore generally have a much larger diameter than generators used in wind turbines having a gearbox 46 for providing a similar amount of power than a wind turbine with a gearbox.

[0041] The nacelle 16 also may include a yaw drive mechanism 56 that may be used to rotate the nacelle 16 and thereby also the rotor 18 about the yaw axis 38 to control the perspective of the rotor blades 22 with respect to the wind direction 28.

[0042] For positioning the nacelle 16 appropriately with respect to the wind direction 28, the nacelle 16 may also include at least one meteorological measurement system which may include a wind vane and anemometer. The meteorological measurement system 58 can provide information to the wind turbine controller 36 that may include wind direction 28 and / or wind speed. In the example, the pitch system 32 is at least partially arranged as a pitch assembly 66 in the hub 20. The pitch assembly 66 includes one or more pitch drive systems 68 and at least one sensor 70. Each pitch drive system 68 is coupled to a respective rotor blade 22 (shown in figure1 ) for modulating the pitch angle of a rotor blade 22 along the pitch axis 34. Only one of three pitch drive systems 68 is shown in figure 2.

[0043] In the example, the pitch assembly 66 includes at least one pitch bearing 72 coupled to hub 20 and to a respective rotor blade 22 (shown in figure 1 ) for rotating the respective rotor blade 22 about the pitch axis 34. The pitch drive system 68 includes a pitch drive motor 74, a pitch drive gearbox 76, and a pitch drive pinion 78. The pitch drive motor 74 is coupled to the pitch drive gearbox 76 such that the pitch drive motor 74 imparts mechanical force to the pitch drive gearbox 76. The pitch drive gearbox 76 is coupled to the pitch drive pinion 78 such that the pitch drive pinion 78 is rotated by the pitch drive gearbox 76. The pitch bearing 72 is coupled to pitch drive pinion 78 such that the rotation of the pitch drive pinion 78 causes a rotation of the pitch bearing 72.

[0044] Pitch drive system 68 is coupled to the wind turbine controller 36 for adjusting the pitch angle of a rotor blade 22 upon receipt of one or more signals from the wind turbine controller 36. In the example, the pitch drive motor 74 is any suitable motor driven by electrical power and / or a hydraulic system that enables pitch assembly 66 to function as described herein. Alternatively, the pitch assembly 66 may include any suitable structure, configuration, arrangement, and / or components such as, but not limited to, hydraulic cylinders, springs, and / or servomechanisms. In certain embodiments, the pitch drive motor 74 is driven by energy extracted from a rotational inertia of hub 20 and / or a stored energy source (not shown) that supplies energy to components of the wind turbine 10.

[0045] The pitch assembly 66 may also include one or more pitch control systems 80 for controlling the pitch drive system 68 according to control signals from the wind turbine controller 36, in case of specific prioritized situations and / or during rotor 18 overspeed. In the example, the pitch assembly 66 includes at least one pitch control system 80 communicatively coupled to a respective pitch drive system 68 for controlling pitch drive system 68 independently from the wind turbine controller 36. In the example, the pitch control system 80 is coupled to the pitch drive system 68 and to a sensor 70. During normal operation of the wind turbine 10, the wind turbine controller 36 may control the pitch drive system 68 to adjust a pitch angle of rotor blades 22.

[0046] According to an embodiment, a power generator 84, for example comprising a battery and electric capacitors, is arranged at or within the hub 20 and is coupled to the sensor 70, the pitch control system 80, and to the pitch drive system 68 to provide a source of power to these components. In the example, the power generator 84 provides a continuing source of power to the pitch assembly 66 during operation of the wind turbine 10. In an alternative embodiment, power generator 84 provides power to the pitch assembly 66 only during an electrical power loss event of the wind turbine 10. The electrical power loss event may include power grid loss or dip,malfunctioning of an electrical system of the wind turbine 10, and / or failure of the wind turbine controller 36. During the electrical power loss event, the power generator 84 operates to provide electrical power to the pitch assembly 66 such that pitch assembly 66 can operate during the electrical power loss event.

[0047] In the example, the pitch drive system 68, the sensor 70, the pitch control system 80, cables, and the power generator 84 are each positioned in a cavity 86 defined by an inner surface 88 of hub 20. In an alternative embodiment, said components are positioned with respect to an outer surface of hub 20 and may be coupled, directly or indirectly, to the outer surface.

[0048] In an aspect of the disclosure, a method 100 for rotating an unbalanced hub of a wind turbine is provided. The hub may be atop a wind turbine tower. For example, the hub may be attached to a nacelle arranged, e.g. fixed, on top of the wind turbine tower. The wind turbine may be a direct-drive wind turbine, specifically an offshore wind turbine. A flowchart of an example of this method 100 is shown in figure 3. The method comprises, at block 110, removably connecting a blade holder to the hub. The method further comprises, at block 120, using a weight of the blade holder to rotate the hub.

[0049] In this manner, a system or tool for installing one or more wind turbine blades, namely the blade holder, is used for rotating the hub of the wind turbine. It should be noted that the blade holder supporting the blade, and the blade being attached to the hub (e.g. the situation of figures 5 and 6), may not be covered by a removable connection between the blade holder and the hub throughout this disclosure. An interface (and not a blade) may for example connect the blade holder to the hub.

[0050] A blade holder 29 connected to the hub 20 for then rotating the hub 20 is schematically illustrated in the examples of figures 7 and 8, and in the examples of figures 12 and 13. The blade holder can therefore be used for mounting wind turbine blade(s) to the hub and for rotating the hub to suitably orient the hub such that a wind turbine blade can then be mounted to the hub. In this regard, the method of rotating the wind turbine hub may be part of a method for mounting one or more wind turbine blades to the hub, or the method 100 may further comprise mounting one or more wind turbine blades to the hub.

[0051] Although not depicted in the figures, a lifting device may be connected to the blade holder 29 for controlling the rotation of the hub 20. Specifically, the blade holder 29 may be attached to a crane, and the crane is used to control the rotation of the hub 20. The speed at which the hub 20 rotates may therefore be adjusted with the help of the lifting device. For example, the lifting device may cause the speed of rotation of the hub 20 to be less than a speed of rotation in absence of the lifting device.

[0052] The blade holder 29 may move substantially in a rotor plane when the hub 20 is rotated. Rotation may therefore be efficient, and undesired forces, e.g. out of the rotor plane, may be avoided.

[0053] The hub 20 may be rotated such that a wind turbine blade can be attached to the hub 20 at a 3 or 9 o’clock position plus or minus from 02to 302, e.g. from 02to 152. For example, the hub 20 may be rotated such that a wind turbine blade may then be attached at an angular position between 752and 1052(3 o’clock position plus or minus from 02to 152). Similarly, the hub 20 may be rotated such that a wind turbine blade may be attached at an angular position between 2552and 2852(9 o’clock position plus or minus from 02to 152). The example of figures 8 - 10 show that the hub 20 has been rotated such that a wind turbine blade 222 is mounted at a 3 o’clock position.

[0054] Removably connecting the blade holder 29 to the hub 20 may comprise attaching the blade holder 29 to an interface of the hub 20. The interface may be configured to support the blade holder 29. The examples of figures 7 and 12 show the blade holder 29 attached to a first interface 21 and to a second interface 23. The interface(s) may be integrally formed with the hub in some examples. In other examples, e.g. the examples of figures 4 - 15, the interfaces are removably attached to the hub 20. An interface may be removed after rotating the hub 20, see for example figures 8 and 9, and figures 13 and 14. In these examples, the hub 20 has been rotated to a desired position and then the interface (together with the blade holder 29, or after removing the blade holder 29) has been removed.

[0055] The interface 21 , 23 may be arranged with a portion of the hub 20 where a wind turbine blade is to be attached later on, see e.g. figures 8 - 10 and figures 13 - 15.

[0056] The method may further comprise arranging the blade holder 29 with a wind turbine blade, and lifting the blade holder 29 and the wind turbine blade. The method may further comprise attaching the wind turbine blade to the hub 20; and removing the blade holder 29 from the wind turbine blade. These steps may be performed before the steps of blocks 110 and 120, e.g. if a first blade 221 is first mounted to the hub 20, see figs. 4 and 5, and then the blade holder 29 is connected to the hub 20 for rotating the hub 20, see figs. 7 and 8. Additionally or alternatively, these steps may be performed after the steps of blocks 110 and 120. For example, one or more blades may already be mounted to the hub 20 (even a hub 20 with an already attached blade may be lifted up tower in some examples), and then the blade holder 29 may be used for rotating the hub 20.

[0057] In some examples, after attaching the wind turbine blade and before removing the blade holder 29, the method may further comprise using the weight of the blade holder arranged with the wind turbine blade for rotating the hub 20. An example of this step is illustrated in theexample of figures 5 and 6: the weight of the blade holder 29 arranged with the blade 221 is used for rotating the hub 20 until the blade 221 is at a certain position, and the blade holder 29 is removably connected to an interface 21 of the hub 20 for continuing the rotation of the hub 20.

[0058] In a further aspect, a method 200 for mounting at least one wind turbine blade, e.g. a first wind turbine blade, to a wind turbine hub atop of a wind turbine tower is provided. The wind turbine may be a direct drive wind turbine, specifically an offshore wind turbine. A flowchart of the method 200 is shown in figure 16. Details and explanations of this method may be applicable to, and may be combined with, method 100 of the previous aspect, and vice versa. Method 200 (and method 100) may exclude yawing the hub, specifically for orienting or positioning the hub for installing a (next) wind turbine blade.

[0059] The method comprises, at block 210, lifting the wind turbine blade by lifting a blade holder arranged with the wind turbine blade; and at block 220, attaching the wind turbine blade to the hub. The method further comprises, at block 230, removing the blade holder from the wind turbine blade and removably connecting the blade holder to the hub by attaching the blade holder to an interface, e.g. a first interface, of the hub. The interface may be configured to support the blade holder. The method further comprises, at block 240, using a weight of the blade holder to rotate the hub with the wind turbine blade; and at block 250, disconnecting the blade holder from the hub, e.g. by removing the blade holder from the interface.

[0060] Figure 4 schematically illustrates a frontal view of an example of a wind turbine hub 20 with two interfaces: a first interface 21 and an additional or second interface 23. In this example, the first interface 21 is arranged with a portion of the hub where an additional or second wind turbine blade (see e.g. figure 10) is to be attached. The first interface 21 may for example be attached or connected to a pitch bearing to which the additional blade will be attached later on. The first interface 21 may additionally or alternatively be attached or connected to a hub portion close to the pitch bearing. The first interface 21 may for example be attached or connected to an inside portion of the hub 20 and / or to an outside portion of the hub 20.

[0061] The location of the first interface 21 may be adjusted to the blade holder, e.g. to its size and shape, which is later used to lift and approach the corresponding blade to the interface, see e.g. figure 7. In some examples, for example if the first interface 21 is integrally formed with the hub 20, at least a portion of the first interface 21 may be provided inside the hub 20. In these or the examples, at least a portion of the first interface 21 may be provided outside the hub 20.

[0062] The first interface 21 may be integrally formed with the hub 20 in some examples. An integrally formed interface 21 may reduce the time required for blade installation as no additional time is required to secure the interface 21 to the hub 20 and to remove it from the hub when it is no longer required. In other examples, as already mentioned, the interface 21 may be configuredto be removably attached to the hub 20. Removable attachment may be performed before attaching 220 the (first) wind turbine blade, and specifically before lifting 210 the (first) wind turbine blade. A removable interface 21 may allow to use the method with existing wind turbines without having to modify them.

[0063] In some examples, see for example figure 4, the first interface 21 comprises two or more arms 25, 27 extending away from the hub 20. In other examples, a single arm may be sufficient. The arm(s) may help to arrange the blade holder at a suitable position and distance from the hub 20. In the example of figure 4, the blade holder 29 is coupled, e.g. fastened, to one of the arms 27. The blade holder 29 may comprise a clamp or other feature for clamping the other arm 25. The arms, and the first interface 21 in general, may help to transfer the force exerted downwards due to the weight of the blade holder to the hub for rotating the hub 20.

[0064] The details and explanations provided with respect to the first interface 21 may also be applicable to the additional interface 23. The first 21 and the second 23 interfaces may be equal. For example, they may have a same size and shape, and they may be made of a same material.

[0065] Figure 5 schematically illustrates an example of attaching 220 the (first) blade to the hub 20. The first blade 221 has been lifted and is attached to the hub 20. For lifting the first blade 221 , the first blade 221 is first surrounded at least in part with the blade holder 29. A lifting device such as a crane (not shown) is connected to the blade holder 29 and lifts both the blade holder 29 and the first blade 221 . The first blade 221 can then be approached and secured to the hub 20.

[0066] In the illustrated example, see figures 4 and 5, the first wind turbine blade 221 is attached at a substantially horizontal position, for example at a 3 o’clock (or equivalently at a 9 o’clock) position. In general, the blade 221 may be mounted at a horizontal position plus or minus from 02to 302, e.g. from 02to 152, e.g. between 752and 1052for the 3 o’clock position. Mounting at this position may facilitate to control the lifting device and the installation direction. In other examples, the first wind turbine blade 221 may be attached in a different position, e.g. the first blade 221 being oriented at a certain other (non-zero) angle with respect to the horizontal direction.

[0067] Figure 6 schematically illustrates an optional step of method 200 between attaching 220 and removing 230. The optional step comprises using the weight of the blade holder 29 arranged with the first wind turbine blade 221 for rotating the hub 20. The lifting device to which the blade holder 29 is connected may help to control the rotation of the hub with the first blade 221 , e.g. the speed at which the hub-first blade assembly rotates. The rotation may specifically be such that the tip of the first blade 221 descends due to the gravity force. The hub 20 may thenbe locked. In some examples, the first blade 221 may be rotated until reaching 60° below the 3 o’clock position.

[0068] Depending on the position at which the first blade 221 is installed, performing this step may be advantageous. For example, if the first blade 221 is installed horizontally (or close to this position), see figure 5, moving the blade holder 29 to the first interface 21 from the beginning may not be very efficient in terms of applying a rotating force as the blade holder 29 may be at or close to a vertical position when connected to the first interface 21. Also, as the rotor (i.e. hub 20 and first blade 221 assembly) is unbalanced, the weight of the first blade 221 and the blade holder 29 are sufficient for starting to rotate the hub 20.

[0069] The angular position of the first blade 221 at which the blade holder 29 is moved from the first blade 221 to the interface 21 may for example be selected depending on the angular position at which the second blade 222 is to be installed (e.g. horizontally or with an angle with respect to the horizontal).

[0070] Figure 7 schematically illustrates an example of removably connecting the blade holder 29 to the hub, specifically to the first interface 21. In some examples, connection may be performed without direct human intervention. The interface 21 may be configured to this end. For example, the interface 21 may comprise one or more “quick connect” mechanisms. In this figure, the blade holder 29 has been removed from the first blade 221 and has been removably attached to the first interface 21 . The lifting device helps to move the blade holder 29 from the first blade 221 to the first interface 21 . Before the blade holder 29 is removed from the first blade 221 , the hub 20 has been locked such that the hub 20 no longer rotates.

[0071] Figure 8 schematically illustrates an example of using 240 a weight of the blade holder 29 for rotating the hub 20. The blade holder 29 acts as a counterweight, and the hub-first blade assembly is rotated. The lifting device, for example a crane, may help to control the speed of rotation of the assembly. The hub 20 (and the first blade 221 ) may specifically be rotated until an additional, e.g. second, wind turbine blade may be attached to the hub at a desired position, for example a horizontal position.

[0072] Rotation of the hub 20 (and the first blade 221 ) occurs in the rotor plane, i.e. the plane defined by the hub 20 and the first blade 221 when the blade holder 29 is used as a counterweight (also at the optional step illustrated in figure 6). Specifically, the blade holder 29 may move in the rotor plane at these steps. The rotation of the hub 20 may be performed effectively, and additional forces in other directions, e.g. out of the rotor plane, may be avoided or at least reduced.

[0073] Once the hub 20 with the first blade 221 has been rotated to a desired position, the hub 20 may be locked and the blade holder 29 may be removed. Figure 9 schematically illustrates a frontal view of a hub where the blade holder 29 has been removed from the hub 20, specificallyfrom the first interface 21 . Also, as in this example the interface 21 is removable from the hub 20, the interface 21 has also been removed from the hub 20. In some examples it may be possible to remove the blade holder 29 and the interface 21 together. If removable, the interface 21 may be removed when or after disconnecting the blade holder 29 from the hub 20. For example, the first blade 221 may be removed first, and the interface 21 may be removed afterwards. The blade holder 29 and the interface 21 may e.g. be moved to a vessel deck.

[0074] The method 200 may comprise repeating the steps of blocks 210 to 250 for mounting an additional wind turbine blade to the wind turbine hub 20. An additional interface 23 is used at block 230 for supporting the corresponding blade holder 29. Specifically, the blade holder 29 may be arranged with the additional wind turbine blade before lifting the wind turbine blade at block 210. I.e., the same blade holder 29 is used for lifting the first blade 221 and the additional, e.g. second, blade.

[0075] Figure 10 schematically illustrates block 220 of method 200 being repeated. A second blade 221 has been lifted and attached to the wind turbine hub 20. The second blade 222 has been attached horizontally (or close to a horizontal position). The second interface 23 is also seen in figure 10. In these examples, see also figure 4, the first 21 and second 23 interfaces were removably attached to the hub 20 before the first wind turbine blade 221 has been lifted and attached to the hub 20.

[0076] Figure 11 schematically illustrates the repetition of the optional step of turning the hub 20, now with two blades 221 , 222 attached, using the weight of the blade holder 29. The details and explanations regarding figure 6 apply to figure 11 , the difference being that now the second blade 222 is also present (and the first interface 21 is not).

[0077] Figure 12 schematically illustrates the step of connecting the blade holder to the hub of method 200 being repeated. The blade holder 29 has been removed from the second blade 222 and has been removably attached to the second interface 23. Figure 13 schematically illustrates the step of rotating the hub by using the weight of the blade holder of method 200 being repeated. The weight of the blade holder 29 is used for turning the hub 20 with the first 221 and second 222 blades. The weight of the blade holder 29 may be sufficiently high for being able to move the hub with the two blades due to the force of gravity. The lifting device may help to control the rotation of the hub. For example, if rotation due to the weight of the blade holder 29 is too fast, the lifting device may reduce the speed of rotation by pulling the blade holder 29 upwardly. The hub 20 may be rotated until it has been positioned at a desired orientation for installing a third blade. The hub 20 may be locked.

[0078] Figure 14 schematically illustrates a frontal view of a hub 20 where the blade holder 29 has been removed from the hub 20, specifically from the second interface 23. As previouslyindicated, as in this example the second interface 23 is removable from the hub 20, the second interface 23 has also been removed from the hub 20. In some examples it may be possible to remove the blade holder 29 and the second interface 23 together. If removable, the second interface 23 may be removed while or after disconnecting the blade holder from the hub. For example, the blade holder 29 may be removed first, and the second interface 23 may be removed afterwards.

[0079] As the wind turbine of the example of figures 4 - 15 has three blades 22, for finishing blade installation, the steps of blocks 210 and 220 are repeated for the third and last blade 223, see figure 15. In figure 15, the blade holder 29 and the lifting device have been used to lift the third blade 223 and attach it to the hub 20. After installing the third and last blade 223, the blade holder 29 may be removed. The third blade 223 has been attached at a horizontal position, like the first 221 and second 222 blades. The blades 221 , 222, 223 may be attached at a different angular position in other examples.

[0080] As illustrated in the example of figures 4 - 15, if a number X of blades 221 , 222, 223 (e.g. three blades) are to be mounted, a number of X-1 interfaces 21 , 23 (e.g. two interfaces) may be provided. It may also be possible to provide a same number of blades to be mounted and interfaces. For example, if the hub is already installed with the first blade attached to the hub, two interfaces and two blades to be mounted may be provided.

[0081] In examples where interfaces 21 , 23 removable from the hub 20 are provided, they may be mounted to the hub before the hub is installed on the wind turbine tower. For example, for an offshore wind turbine, the interfaces may be installed while the hub, e.g. connected to the nacelle, is on a vessel.

[0082] As previously indicated, the features and explanations of this method 200, e.g. with respect to figures 4 - 15, may also apply to, and combined with, the features and explanations of previous method 100, and vice versa.

[0083] According to a further aspect, a wind turbine hub 20 is provided. The hub 20 comprises an interface 21 , 23 configured to support a blade holder 29 for rotating the hub 20 using a weight of the blade holder 29. The interface 21 , 23 may be removable from the hub 20, or the interface may be integrally formed with the hub. An example of such a hub 20 is provide in figure 4, which as explained previously, comprises two interfaces 21 , 23.

[0084] This written description uses examples to disclose a teaching, including the preferred embodiments, and also to enable any person skilled in the art to put the teaching into practice, including making and using any devices or systems and performing any incorporated methods. The patentable scope is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims ifthey have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims. Aspects from the various embodiments described, as well as other known equivalents for each such aspects, can be mixed and matched by one of ordinary skill in the art to construct additional embodiments and techniques in accordance with principles of this application. If reference signs related to drawings are placed in parentheses in a claim, they are solely for attempting to increase the intelligibility of the claim, and shall not be construed as limiting the scope of the claim.

Claims

CLAIMS1. A method (100) for rotating an unbalanced hub (20) of a wind turbine (10), the method (100) comprising: removably connecting (110) a blade holder (29) to the hub (20); and using a weight of the blade holder (29) to rotate (120) the hub (20).

2. The method of claim 1 , wherein the blade holder (29) is attached to a crane, and wherein the crane is used to control the rotation of the hub (20).

3. The method of claim 1 or claim 2, wherein the blade holder (29) moves substantially in a rotor plane when the hub (20) is rotated.

4. The method of any of claims 1 - 3, wherein the hub (20) is rotated such that a wind turbine blade (22) can be attached to the hub (20) at a 3 or 9 o’clock position plus or minus from 02to 302.

5. The method of any of claims 1 - 4, wherein removably connecting (110) the blade holder (29) to the hub (20) comprises attaching the blade holder (29) to an interface (21 , 23) of the hub (20).

6. The method of claim 5, wherein the interface (21 , 23) comprises one or more arms (25, 27) extending away from the hub (20).

7. The method of claim 5 or claim 6, wherein the interface (21 , 23) is arranged with a portion of the hub (20) where a wind turbine blade (22) is to be attached.

8. The method of any of claims 5 - 7, further comprising removing the interface (21 , 23) after rotating (120) the hub (20).

9. The method of any of claims 5 - 7, wherein the interface (21 , 23) is integrally formed with the hub (20).

10. The method of any of claims 1 - 9, wherein the wind turbine (10) is a direct-drive wind turbine, specifically an offshore wind turbine.11 . The method of any of claims 1 - 8 and 10, further comprising: arranging the blade holder (29) with a wind turbine blade (22) and lifting the blade holder (29) and the wind turbine blade (22); attaching the wind turbine blade (22) to the hub (20); and removing the blade holder (29) from the wind turbine blade (22).

12. The method of claim 11 , wherein the wind turbine blade (22) is attached at a 3 or 9 o’clock position plus or minus from 02to 302.

13. The method of claim 11 or claim 12, further comprising, after attaching the wind turbine blade (22) and before removing the blade holder (29), using the weight of the wind turbine blade (22) and the blade holder (29) arranged with the wind turbine blade (22) for rotating the hub (20).

14. A wind turbine hub (20) comprising an interface (21 , 23) configured to mount and support a blade holder (29) for rotating the hub (20) using a weight of the blade holder (29).

15. The hub of claim 14, wherein the interface (21 , 23) is removable from the hub (20).

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