Method of mounting a blade bearing to a wind turbine rotor hub

Abstract

According to the present disclosure, there is provided a method of mounting a blade bearing to a wind turbine rotor hub to which at least one wind turbine blade is attached.

Description

[0001] METHOD OF MOUNTING A BLADE BEARING TO A WIND TURBINE ROTOR HUB

[0002] FIELD

[0003] The present invention relates to a method of mounting a blade bearing to a wind turbine rotor hub.

[0004] BACKGROUND

[0005] During the operational life of a wind turbine, components of the wind turbine are likely to experience various types of adverse weather conditions such as high-winds and changes in temperature and / or humidity.

[0006] Once a wind turbine has been operated for a given period of time (e.g., several years), it may be beneficial to replace one or more of the blade bearings of the wind turbine to enable the wind turbine to continue producing power efficiently. The mounting of such blade bearings to the rotor hub of a wind turbine should be carried out as safely, swiftly, and effectively as possible.

[0007] Various solutions are known for safely, swiftly and effectively mounting blade bearings to wind turbine rotor hubs. However, the present disclosure seeks to improve the known solutions.

[0008] SUMMARY

[0009] According to an aspect of the present disclosure, there is provided a method of mounting a blade bearing to a wind turbine rotor hub comprising the steps of: a) providing a wind turbine rotor hub to which at least one wind turbine blade is attached, said rotor hub comprising an empty blade bearing mount for receiving a blade bearing, and wherein the at least one wind turbine blade imparts a force on the rotor hub which causes the blade bearing mount to deform from its original, un-deformed shape to a deformed shape; b) providing a blade bearing for attaching to the blade bearing mount via a plurality of connectors; c) determining a shape of the deformed blade bearing mount; d) deforming the blade bearing by applying a deformation load to said blade bearing such that a shape of the deformed blade bearing matches the shape of the deformed blade bearing mount; e) mounting the blade bearing to the blade bearing mount via the plurality of connectors; and f) applying an axial load onto one or more of the plurality of connectors so as to secure the blade bearing to the wind turbine rotor hub.

[0010] Thus, an improved method of mounting a blade bearing of a wind turbine generator is provided. It may be seen that carrying out the method steps as claimed provides a more safe, swift, and effective method for mounting blade bearings than in prior art methods. It may be seen as an insight disclosed hereby that deforming the blade bearing as claimed is a manner of providing a safe, swift, and effective method for mounting a blade bearing to a wind turbine rotor hub.

[0011] In particular, the aforementioned method helps to better account for deformation of the blade bearing mount during mounting of the blade bearing thereby allowing the blade bearing to be more easily installed onto the empty blade bearing mount.

[0012] The aforementioned method also helps to better avoid significant contact stresses from being generated between the plurality of connectors and the blade bearing during mounting of the blade bearing to the rotor hub.

[0013] In some examples, a pair of wind turbine blades are attached to the wind turbine rotor hub provided in step a).

[0014] In some examples, the pair of wind turbine blades each impart a force on the rotor hub which causes the blade bearing mount to assume a substantially oval cross-sectional shape.

[0015] In some examples, the blade bearing provided in step b) has a substantially circular cross-sectional shape.

[0016] In some examples, step d) comprises applying the deformation load to the blade bearing so as to cause the blade bearing to assume a substantially oval cross-sectional shape. In some examples, the deformation load applied to the blade bearing during step d) is applied across an internal diameter of the blade bearing.

[0017] In some examples, the force imparted on the rotor hub by the at least one wind turbine blade is a gravitational force and / or a wind load.

[0018] In some examples, step c) comprises measuring the shape of the deformed blade bearing mount in-situ.

[0019] In some examples, step c) comprises predicting the shape of the deformed blade bearing mount (e.g., via a look-up table) based on a weight and / or an angular position of the at least one wind turbine blade attached to the rotor hub and / or based on a magnitude of a wind load predicted to act on the at least one wind turbine blade attached to the rotor hub during mounting of the blade bearing to the wind turbine rotor hub.

[0020] In some examples, during steps e) and f), the blade bearing mount is provided at a first angular position about the rotor hub.

[0021] In some examples, the first angular position is a 12 o’clock angular position.

[0022] In some examples, the method further comprises, after step f), attaching a wind turbine blade to the blade bearing.

[0023] In some examples, the method further comprises rotating the blade bearing about the rotor hub from the first angular position to a second angular position prior to attachment of the wind turbine blade to said blade bearing.

[0024] In some examples, the second angular position is a 3 o’clock position.

[0025] In some examples, the blade bearing provided in step b) comprises a plurality of apertures disposed about a circumference thereof, the plurality of connectors are disposed about a mounting surface of the empty blade bearing mount, and step e) comprises inserting the plurality of connectors into the plurality of apertures disposed about the circumference of the blade bearing. In some examples, the method further comprises, after step f) removing the deformation load from the blade bearing.

[0026] In some examples, the method may further comprise, prior to attachment of the wind turbine blade, measuring the shape of the blade bearing after the deformation load has been removed.

[0027] In some examples, the method further comprises, prior to step a), detaching a blade bearing from a blade bearing mount.

[0028] In some examples, steps a) to f) are performed in alphabetical order.

[0029] In the claims and description, ‘rotor hub’ and ‘wind turbine rotor hub’ is the same.

[0030] BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Examples of the present disclosure will now be described with reference to the accompanying drawings, in which:

[0032] Figure 1 is a front-view of a wind turbine according to an example of the present disclosure;

[0033] Figure 2 is a perspective view of a rotor hub of the wind turbine illustrated in Figure 1 ;

[0034] Figure 3A is a perspective view of a blade bearing for mounting onto a blade bearing mount of the rotor hub illustrated in Figure 2;

[0035] Figure 3B is a side view of the blade bearing illustrated in Figure 3a which has been “cut-away” such that the rolling elements of the blade bearing are visible;

[0036] Figures 4A to 4D are a series of schematic illustrations depicting a method of mounting a blade bearing to the rotor hub illustrated in Figure 2;

[0037] Figures 5A and 5B are a series of schematic illustrations depicting the step of deforming the blade bearing to match the shape of the deformed blade bearing mount; Figure 6A is a side-view of the rotor hub illustrated in Figure 2 depicting the step of applying an axial load onto one or more of the plurality of connectors; and

[0038] Figure 6B is a perspective view of the rotor hub illustrated in Figure 2 after the blade bearing has been mounted thereto.

[0039] DETAILED DESCRIPTION

[0040] Figure 1 shows a wind turbine 1 according to an example of the present disclosure.

[0041] The wind turbine 1 includes a nacelle 2 supported on a tower 3 that is mounted on a foundation 4. The wind turbine 1 depicted here is an onshore wind turbine such that the foundation 4 is embedded in the ground, but the wind turbine 1 could be an offshore installation in which case the foundation 4 would be provided by a suitable marine platform, such as a monopile or jacket.

[0042] The nacelle 2 supports a rotor 5 comprising a rotor hub 6 to which a plurality of blades 7a-c are attached. The blades 7a-c which make up the rotor 5 of the wind turbine 1 each comprise a tip end, which is located distal from the rotor hub 6, and a root end, which is located proximal to the rotor hub 6.

[0043] It will be noted that the wind turbine 1 illustrated in Figure 1 is the common type of horizontal axis wind turbine (HAWT) such that the rotor 5 is mounted at the nacelle 2 to rotate about a substantially horizontal axis defined at the centre at the rotor hub 6.

[0044] As is known, the blades 7a-c are acted on by the wind which causes the rotor 5 to rotate about its axis thereby operating generating equipment through a gearbox (not shown) that is housed in the nacelle 2. The generating equipment is not shown in Figure 1 since it is not central to the examples of the invention.

[0045] The rotor hub 6 of the wind turbine 1 is shown in further detail in Figure 2.

[0046] As shown in Figure 2, the rotor hub 6 has a body 10 which is roughly spheroidal in shape and comprises a hollow structure which defines an interior volume. In the illustrated example, the body 10 is provided as a single unitary cast-iron structure. However, in other examples, the body 10 of the rotor hub 6 may comprise a different material and / or may be provided in multiple sections.

[0047] A plurality of blade bearing mounts 20a-c are disposed at regular intervals about the body 10 of the rotor hub 6 with each blade bearing mount 20a-c being configured to receive a respective blade bearing 30a-c of the wind turbine 1 (shown in Figure 3A).

[0048] In the example illustrated in Figure 2, the rotor 5 comprises three wind turbine blades 7a-c and hence the rotor hub 6 comprises three blade bearing mounts 20a-c (one for each blade bearing) which are disposed about the outer circumference of the body 10 at intervals of approximately 120 degrees.

[0049] However, in other examples, the rotor 5 may comprise a different number of blades I blade bearings, such as 2, 4, 5, 6 etc., and hence, in some examples, the rotor hub 6 may comprise a different number of blade bearing mounts accordingly, such as 2, 4, 5, 6, etc, to match the number of blades I blade bearings.

[0050] It shall also be appreciated that in examples where the number of blade bearing mounts is less than or greater than three, the blade bearing mounts may be disposed about the outer circumference 10 of the rotor hub 6 at intervals of more or less than 120 degrees. For instance, in some examples, the plurality of blade bearing mounts may be disposed about the body 10 of the rotor hub 6 at intervals of 360 / N degrees, wherein N is the number of blade bearing mounts.

[0051] As shown in Figure 2, each blade bearing mount 20a-c has a substantially annular shape defining a central cavity 24a around which a generally planar mounting surface 22a-c extends, although only one mounting surface 22a is depicted in Figure 2.

[0052] Although not shown in Figure 2, each mounting surface 22a-c comprises a plurality of connectors 26a-c (e.g., studs, bolts etc.) which extend transversely away from the respective mounting surfaces 22a-c to facilitate coupling of a blade bearing 30a-c to the blade bearing mount 20a-c as shall be described in greater detail below.

[0053] A blade bearing 30 of the wind turbine 1 is depicted in Figures 3A and 3B. As shown in Figure 3A, in the illustrated example the blade bearing 30 is a ring-bearing and comprises an outer race 32 and an inner race 34 which is arranged concentrically within the outer race 32.

[0054] The outer race 32 comprises a pair of inner 32a and outer 32b circumferential surfaces, between which a body of the outer race 32 is defined. The outer race 32 also comprises a series of apertures 33 which are disposed circumferentially at regular intervals about the body of the outer race 32.

[0055] The series of apertures 33 extend through a thickness of the outer race 32 and are each configured to receive a corresponding one of the connectors 26a provided at the mounting surface 22a of the blade bearing mount 20a for coupling the blade bearing 30 to the blade bearing mount 20a accordingly.

[0056] The inner race 34 also comprises a pair of inner 34a and outer 34b circumferential surfaces, between which a body of the inner race 34 is defined. As with the outer race 32, a series of apertures 35 are also disposed circumferentially at regular intervals about the body of the inner race 34.

[0057] The series of apertures 35 extend through a thickness of the inner race 34 and are each configured to receive a corresponding connector (not shown) provided at a root end of a respective one of the wind turbines blades 7a so as to facilitate connection of said wind turbine blade 7a to the blade bearing 30.

[0058] However, it shall also be appreciated that in other examples, the series of apertures 35 disposed about the inner race 34 may each be configured for receiving a corresponding one of the connectors 26a provided at the mounting surface 22a of the blade bearing mount 20a and the series of apertures 33 disposed about the outer race 32 may each be configured for receiving a corresponding connector (not shown) provided at a root end of a respective one of the wind turbines blades 7a.

[0059] Referring now to Figure 3B, the inner surface 32a of the outer race 32 and the outer surface 34b of the inner race 34 each comprise a recessed portion which together define a raceway 31 which extends circumferentially around the blade bearing 30 between the inner 34 and outer 32 races. A plurality of rolling elements 36 (e.g., ball bearings) are housed within the raceway 31 between the inner 34 and outer 32 races which are arranged so as to enable relative axial rotation between the inner 34 and outer 32 races.

[0060] In the illustrated example, the blade bearing 30 is a one-row two-point contact bearing meaning that a single row of rolling elements 36 are provided in which each rolling element 36 has two points of contact with the raceway 31. For example, in the illustrated example, each rolling element has one point of contact with the inner surface 32a of the outer 32 race and one point of contact with the outer surface 34b of the inner race 34.

[0061] However, it shall be appreciated that in other examples, the blade bearing 30 may comprise multiple rows of rolling elements (such as 2, 3, 4 etc.) and / or may be configured so as to provide multiple points of contact (such as 4, 6, 8, 10 etc.) between each rolling element 36 and the raceway 31 .

[0062] Referring back to Figure 3A, although not shown in the illustrated example, the inner surface 34a of the inner race 34 also comprises a plurality of teeth which form a geared surface configured for interfacing with a corresponding blade pitch actuator (not shown) which is housed within the cavity 24a of the blade bearing mount 20a.

[0063] In some examples, the blade pitch actuator (not shown) may be provided as one or more hydraulic cylinders. In other examples, different types of actuators (e.g., electric actuators) may be utilised.

[0064] As alluded to above, in the illustrated example, the outer race 32 of the blade bearing 30 is fixed to the rotor hub 6 via the plurality of connectors 26a such that axial rotation of the outer race 32 is substantially constrained.

[0065] As such, when a rotational drive force is applied onto the geared surface 34a of the inner race 34, the blade pitch actuator (not shown) is able to enact pitch-wise axial rotation of the inner race 34 relative to the rotor hub 6, thereby allowing the pitch of the wind turbine blade 7a (which is mounted to the inner race 34) to be adjusted.

[0066] The blade pitch actuator (not shown) is controlled via a pitch control system (not shown) which may alter the pitch of the wind turbine blade 7a based on various factors (such as wind speed, power demand etc.) to increase or decrease the rotational speed of the rotor 5, thereby regulating the power output of the wind turbine 1.

[0067] In some circumstances, the pitch control system may also control the blade pitch actuator (not shown) to move the wind turbine blades 7a into a zero lift (or “feathered”) position when wind speeds are too high for the wind turbine 1 to safely operate.

[0068] It shall be appreciated that the means by which the pitch of the one or more wind turbine blades 7a-c are adjusted is not central to the examples of the invention and hence shall not be described in further detail.

[0069] It shall also be appreciated that in examples in which the wind turbine blade 7a is mounted to the outer race 32 of the blade bearing 30, the geared surface (not shown) may be provided at the outer surface 32b of the outer race 32.

[0070] Referring back to Figure 2, when all three blade bearings 30a-c are attached to the rotor hub 6, the blade bearing mounts 20a-c have a substantially circular (or annular) cross-sectional shape which effectively matches the “as manufactured” shapes of the annular blade bearings 30a-c.

[0071] However, as illustrated in Figure 2, when one of the wind turbine blades 7a and its associated blade bearing 30a is detached from the rotor hub 6, for example during replacement of one of the blade bearings 30a-c, the weight of the wind turbine blades 7b, c which remain attached to the rotor hub 6 and, in some instances, the wind loads acting on said wind turbine blades 7b, c can apply a stress (or load) pattern onto the rotor hub 6.

[0072] It has been found that the aforementioned stress pattern can cause the rotor hub 6, and hence the empty blade bearing mount 20a, to deform from its original, un-deformed shape in which the blade bearing mount 20a exhibits a substantially circular (or annular) cross-sectional shape to a deformed shape in which the empty blade bearing mount exhibits a non-circular cross-sectional shape.

[0073] In the illustrated example, the empty blade bearing mount 20a is located at a 12 o’clock (0 degree) angular position about the horizontal axis (Z) of the rotor hub 6. Meanwhile, a pair blade bearings 30b, c, and associated wind turbine blades 7b, c, remain mounted to the remaining two blade bearing mounts 20b, 20c, which are located at the 4 o’clock (120 degree) and 8 o’clock (240 degree) angular positions about the horizontal (Z) axis of the rotor hub 6.

[0074] As such, the weight of the two wind turbine blades 7b, 7c, depicted by the vertical arrows in Figure 2, will impart a bending moment onto the rotor hub 6 which, in turn, will compress some portions of the blade bearing mount 20a, depicted by the horizontal arrows in Figure 2, causing it to assume a roughly oval cross-sectional shape. This effect can be referred to as “ovalisation”.

[0075] This change in shape (or “ovalisation”) of the empty blade bearing mount 20a makes it extremely difficult to align the plurality of connectors 26a with the corresponding apertures 33 disposed about the substantially circular (or annular) blade bearing 30a and, even if an operator did manage to force the annular blade bearing 30a onto the empty blade bearing mount 20a, it is likely that the plurality of connectors 26a would urge against, and hence contact, the respective bearing surfaces of the plurality of apertures 33 (or vice versa) thereby generating significant contact stresses which could cause damage to the apertures 33 and / or to the threaded surfaces of the respective connectors 26a.

[0076] Previous solutions intended to address this issue have provided blade bearings having larger bolt holes to account for deformation of the blade bearing mount, thereby making it easier to locate the blade bearing onto the associated connectors provided at the blade bearing mount.

[0077] However, as the size (and hence weight) of modern wind turbine blades continues to increase, so too does the magnitude of the loads acting on the rotor hub 6 which increases the amount of deformation. Because of this, previous solutions are no longer feasible.

[0078] Furthermore, alternative solutions such as reinforcing the rotor hub 6 so as to limit the amount of deformation would add significant weight (and hence cost) to the wind turbine 1 which is also undesirable. A method of mounting a blade bearing to a wind turbine rotor hub which aims to address this issue shall now be described according to an example of the present disclosure with reference to Figures 4 to 6.

[0079] It shall be appreciated that the illustrated example depicts a method of replacing a blade bearing on an already installed wind turbine and hence in a first step of the method depicted in Figure 4A a wind turbine blade (not shown), and its associated “to be replaced” blade bearing 30x, are detached from the rotor hub 6 thereby providing a rotor hub 6 comprising an empty blade bearing mount 20a for receiving a new blade bearing 30a.

[0080] However, it shall be appreciated that in other examples, the aforementioned method may also be used during installation of a new wind turbine and hence, in some examples, the step of detaching the “to be replaced” blade bearing 30x from the rotor hub 6 may be omitted.

[0081] Before the “new” blade bearing 30a is mounted to the rotor hub 6 via the blade bearing mount 20a, a shape of the empty blade bearing mount 20a is first determined.

[0082] As set out above, in the illustrated example, a pair of wind turbine blades 7b, 7c are mounted to the rotor hub 6 at the 4 o’clock and 8 o’clock angular positions about the horizontal (Z) axis of the rotor hub 6.

[0083] As such, the respective forces (shown in Figure 2) which are imparted on the rotor hub 6 by the pair of wind turbine blades 7b, 7c apply a bending moment onto the rotor hub 6 which causes the empty blade bearing mount 20a, provided at the 12 o’clock angular position, to assume a substantially oval cross-sectional shape.

[0084] In the illustrated example, the respective forces imparted on the rotor hub 6 by the pair of wind turbine blades 7b, 7c cause the empty blade bearing mount 20a to assume a substantially elliptical cross-sectional shape.

[0085] However, it shall be appreciated that in other examples in which a different number of wind turbine blades 7a-c are mounted to the rotor hub 6 and / or in which the empty blade bearing mount 20a is provided at a different angular position about the horizontal axis (Z) of the rotor hub 6, a different load (or stress) pattern will be exerted onto the rotor hub 6 and hence, in other examples, the empty blade bearing mount 20a may assume a different cross-sectional shape.

[0086] Similarly, whilst the forces imparted on the rotor hub 6 by the pair of wind turbine blades 7b, 7c in Figure 2 are purely gravitational forces associated with the respective weights of the wind turbine blades 7b, 7c mounted to the rotor hub 6, it shall be appreciated that in some examples the force(s) imparted on the rotor hub 6 may also comprise elements of wind loading which are associated with the force of the wind acting on the one or more wind turbine blades 7b, c attached to the rotor hub 6 during mounting of the blade bearing 30a to the empty blade bearing mount 20a.

[0087] It shall be appreciated that such wind loads may further alter the load pattern exerted on the rotor hub 6 and hence may also cause the blade bearing mount 20a to assume a different shape to that which is depicted in Figure 2.

[0088] In some examples, the step of determining the shape of the empty blade bearing mount 20a may involve an operator physically (or electronically) measuring the shape of the empty blade bearing mount 20a in-situ.

[0089] Advantageously, measuring the shape of the empty blade bearing mount 20a in-situ allows the shape of the empty blade bearing mount 20a to be accurately determined with minimal error. However, it shall be appreciated that this method can also lead to longer on-site installation times since, until the shape of the empty blade bearing mount 20a has been ascertained, many preparations required for installing the new blade bearing 30a onto said blade bearing mount 20a cannot be performed.

[0090] Alternatively, in some other examples, rather than measuring the shape of the empty blade bearing mount 20a in situ, the step of determining the shape of the blade bearing mount 20a may instead involve predicting the shape of the empty blade bearing mount 20a based on the weight and / or angular position of the at least one wind turbine 7b, 7c attached to the rotor hub 6 and / or based on a magnitude of the wind load predicted to act on the at least one wind turbine blade 7b, 7c during mounting of the blade bearing 30a to the empty blade bearing mount 20a.

[0091] Advantageously, predicting (rather than measuring) the shape of the empty blade bearing mount 20a enables the shape of the empty blade bearing mount 20a to be ascertained before installation of the blade bearing 30a has begun, thereby allowing a greater number of preparations to be performed prior to installation which, in turn, will help to reduce on-site installation times.

[0092] The step of predicting the shape of the empty blade bearing mount 20a may be performed computationally (for example via Finite Element Analysis (FEA)) and / or may be performed via consulting a look-up table such as the one depicted in Table 1 below.

[0093] Ta&fe 1

[0094] It shall also be appreciated that in some examples, the step of determining the shape of the empty blade bearing mount 20a may comprise both predicting the shape of the empty blade bearing mount 20a and then physically (or electronically) measuring the shape of the empty blade bearing mount 20a once the rotor hub 6 is in-situ.

[0095] For example, the shape of the empty blade bearing mount 20a may be predicted prior to installation (e.g., via using a look-up table and / or via FEA) so that the rough shape of the empty blade bearing mount 20a can be ascertained and then may be measured once the rotor hub 6 is in-situ so that the operator can account for any errors in the aforementioned prediction.

[0096] Once the shape of the empty blade bearing mount 20a has been determined, the blade bearing 30a which is due to be mounted to the empty blade bearing mount 20a is deformed from its original, “as manufactured” un-deformed shape in which the blade bearing 30 is substantially circular (or annular) to a non-circular shape which matches that of the empty blade bearing mount 20a.

[0097] As set out above, in the illustrated example, the load pattern imparted on the empty blade bearing mount 20a due to the weight of the wind turbine blades 7b, 7c which have already been attached to the rotor hub 6 have caused the empty blade bearing mount 20a to assume a substantially oval cross-sectional shape. As such, in the illustrated example, a load is applied onto the new blade bearing 30a so as to cause it to deform from its original, “as manufactured” un-deformed shape to a substantially oval shape which matches the shape of the deformed blade bearing mount 20a.

[0098] More particularly, as shown in Figures 5A and 5B, in the illustrated example the blade bearing 30 is deformed into a substantially oval shape by applying a deformation load, illustrated by the horizontal arrows in Figure 5A, across an internal diameter of a cavity 38 of the blade bearing 30 which is defined by the inner race 34.

[0099] For example, a hydraulic blade jack 40 may be placed within the cavity 38 of the blade bearing 30a such that the respective ends of the blade jack 40 contact opposing points along the inner surface 34a of the inner race 34.

[0100] As shown in Figure 5B, as the blade jack 40 is lengthened, for example by introducing hydraulic fluid into a cylinder 41 of the jack 40, a deformation load will be applied onto the inner surface 34a of the inner race 34 at the points contacted by the blade jack 40 thereby causing the inner race 34 to displace radially outwardly and hence causing the blade bearing 30 to assume a substantially oval cross-sectional shape.

[0101] However, it shall be appreciated that in other examples, one or more deformation loads may be applied to other points about the blade bearing. For example, in some examples, the deformation load may be a clamping force which is applied onto an outer surface 32b of the outer race 32 via a suitable clamp or vice.

[0102] Furthermore, in examples in which the blade bearing mount 20a has a different noncircular shape to the blade bearing mount 20a depicted in Figure 2, one or more deformation loads may be applied at other points about the blade bearing 30 in order to cause the blade bearing 30 to deform into a non-circular shape which matches that of the deformed blade bearing mount 20a.

[0103] Referring now to Figure 4B, once the blade bearing 30a has been deformed so as to substantially match the shape of the deformed blade bearing mount 20a, the blade bearing 30a is installed onto rotor hub 6 via the blade bearing mount 20a. Advantageously, by deforming the blade bearing 30a so as to substantially match the cross-sectional shape of the blade bearing mount 20a prior to installation, the method according to the present disclosure is able to better account for deformation of the rotor hub 6 thereby enabling the plurality of apertures 33 disposed about the blade bearing 30a to be more easily aligned with the plurality of connectors 26a disposed about the empty blade bearing mount 20a.

[0104] Referring now to Figure 6A, the blade bearing 30a is installed onto the blade bearing mount 20a via inserting the plurality of connectors 26a disposed circumferentially about the mounting surface 22a of the blade bearing mount 20a into the respective apertures 33 provided about the outer race 32 of the blade bearing 30 and then lowering the blade bearing 30a towards the blade bearing mount 20a until a lower surface 30d of the blade bearing 30a abuts against the mounting surface 22a of the blade bearing mount 20a and until the respective ends of the plurality of connectors 26a protrude beyond an upper surface 30e of the blade bearing 30a.

[0105] As alluded to above, deforming the blade bearing 30a so as to substantially match the cross-sectional shape of the blade bearing mount 20a prior to installation also helps to prevent the plurality of connectors 26a from urging against the surfaces of the respective apertures 33 (or vice versa) as the blade bearing 30 is lowered onto the blade bearing mount 20a.

[0106] Once the plurality of connectors 26a have been inserted into the corresponding apertures 33 provided about the outer race 32, an axial load is applied onto one or more of the respective connectors 26a, as shown by the arrows in Figure 6A, thereby securing the new blade bearing 30a to the rotor hub 6 via blade bearing mount 20a, shown in Figure 6B.

[0107] In some examples, an axial load may be applied onto all (or each) of the plurality of connectors 26a. However, it shall be appreciated that in other examples, only some of the plurality of connectors 26a, such as 4, 8, 12, 15, 32, 48 etc, may be applied with an axial load.

[0108] As shown in Figure 4B, in the illustrated example, the steps of mounting the blade bearing 30a onto the blade bearing mount 20a and applying an axial load onto one or more of the plurality of connectors 26a are performed when the blade bearing mount 20a is at a 12 o’clock (i.e., a first) angular position about the horizontal (Z) axis of the rotor hub 6. However, it shall be appreciated that in other examples, the aforementioned steps may be performed with the blade bearing mount 20a at a different angular position.

[0109] It shall be appreciated that the axial load may be applied onto one or more of the respective connectors 26a via either “tensioning” or “torquing”.

[0110] In examples where the axial load is applied onto one or more of the respective connectors 26a via “torquing”, a series of nuts 28a are first located onto the respective ends of each connector 26a until a lower surface of the nut 28a abuts against the upper surface 30e of the blade bearing 30a. As the nuts 28a are further tightened (e.g., via a torque wrench) the connectors 26a become drawn through the respective threads provided on the inner surfaces of the nuts 28a which applies an axial load onto the respective connectors 26a.

[0111] Alternatively, in examples wherein the axial load is applied onto one or more of the respective connectors 26a via “tensioning”, the axial load is first applied onto the plurality of connectors via pulling on the ends of each connector 26a before application of the nuts 28a.

[0112] It shall also be appreciated that during the method step illustrated in Figure 4B, the one or more connectors 26a may be partially tightened or may be fully tightened such that the axial load applied onto the one or more connectors 26a is close to their maximum axial load threshold.

[0113] Once the new blade bearing 30a has been mounted to the blade bearing mount 20a and a partial or full axial load has been applied onto one or more of the plurality of connectors 26a, the deformation load applied across the internal diameter of the blade bearing 30 can be removed such that the blade bearing mount 20a and the blade bearing 30a can return back to their original, approximately circular (or annular) shapes.

[0114] It is an insight provided hereby, that the returning of the blade bearing mount and the blade bearing mount to their original, approximately circular (or annular) shapes will happen from when the blade bearing is at least partially tightened to the blade bearing mount and the deformation load is at least partly removed or fully removed, and this will happen at least due to the additional stiffness and material provided by and / or with the blade bearing.

[0115] It is also an insight disclosed hereby, that the particular non-circularly of the blade bearing mount will be gone at the latest when the deformation load is fully removed, and the blade bearing is fully tightened down and the blade is also installed and fully tightened to the blade bearing again.

[0116] Referring now to Figures 4C, once the blade bearing 30a has been mounted to the rotor hub 6, the rotor 5 is rotated about its horizontal (Z) axis such the blade bearing 30a is located at a second angular position about the horizontal axis (Z) of the rotor hub 6.

[0117] In the illustrated example, the rotor 5 is rotated by approximately 90 degrees in the clockwise direction such that the blade bearing mount 20a and the blade bearing 30a are located at a 3 o’clock (or 90 degree) angular position.

[0118] Finally, referring now to Figure 4D, once the blade bearing 30a is at the 3 o’clock position, a wind turbine blade 7a is mounted to the blade bearing 30a, thereby coupling the wind turbine blade 7a to the rotor hub 6.

[0119] More particularly, as alluded to earlier within this application, the root end of the wind turbine blade 7a is secured to the inner race 34 of the blade bearing 30a via inserting respective connectors (not shown) provided at the root end of the wind turbine blade 7a into the plurality of apertures 35 disposed about the inner race 34 which are then subsequently tightened.

[0120] However, it shall be appreciated that in other examples, the wind turbine blade 7a may be mounted to the outer race 32 of the blade bearing 30a and / or the wind turbine blade 7a may be mounted to the blade bearing 30a when the blade bearing 30a is located at other angular positions about the horizontal (Z) axis of the rotor hub 6.

[0121] It shall also be appreciated that, in some examples, prior to installing the wind turbine blade 7a to the blade bearing 30a, the nacelle 2 of the wind turbine 1 may be yawed (or rotated) about the tower 3 such that the horizontal (Z) axis of the rotor hub 6 is parallel to the wind direction to help minimise the wind loads acting on the wind turbine blade 7a during installation.

[0122] Finally, it shall also be appreciated that in some examples, the method may further comprise measuring the blade bearing 30a after the deformation load has been removed from the blade bearing 30a to determine that the blade bearing 30a has indeed returned back to its original “as manufactured” shape before the wind turbine blade 7a is attached to the blade bearing 30a. Although the invention has been described above with reference to one or more preferred embodiments, it will be appreciated that various changes or modifications may be made without departing from the scope of the invention as defined in the appended claims.

Claims

CLAIMS1. A method of mounting a blade bearing to a wind turbine rotor hub comprising the steps of: a) providing a wind turbine rotor hub (6) to which at least one wind turbine blade (7) is attached, said rotor hub comprising an empty blade bearing mount for receiving a blade bearing, and wherein the at least one wind turbine blade imparts a force on the rotor hub which causes the blade bearing mount to deform from its original, undeformed shape to a deformed shape; b) providing a blade bearing for attaching to the blade bearing mount via a plurality of connectors; c) determining a shape of the deformed blade bearing mount; d) deforming the blade bearing by applying a deformation load to said blade bearing such that a shape of the deformed blade bearing matches the shape of the deformed blade bearing mount; e) mounting the blade bearing to the blade bearing mount via the plurality of connectors; and f) applying an axial load onto one or more of the plurality of connectors so as to secure the blade bearing to the wind turbine rotor hub (6).

2. The method according to claim 1 , wherein a pair of wind turbine blades are attached to the rotor hub provided in step a), and wherein the pair of wind turbine blades each impart a force on the wind turbine rotor hub (6) which causes the blade bearing mount to assume a substantially oval cross-sectional shape.

3. The method according to claim 2, wherein the blade bearing provided in step b) has a substantially circular cross-sectional shape, and wherein step d) comprises applying the deformation load to the blade bearing so as to cause the blade bearing to assume a substantially oval cross-sectional shape.

4. The method according to claim 3, wherein the deformation load applied to the blade bearing during step d) is applied across an internal diameter of the blade bearing.

5. The method according to any preceding claim, wherein the force imparted on the rotor hub (6) by the at least one wind turbine blade (7) is a gravitational force and / or a wind load.

6. The method according to any preceding claim, wherein step c) comprises measuring the shape of the deformed blade bearing mount in-situ.

7. The method according to any preceding claim, wherein step c) comprises predicting the shape of the deformed blade bearing mount based on a weight and / or an angular position of the at least one wind turbine blade attached to the rotor hub (6) and / or based on a magnitude of a wind load predicted to act on the at least one wind turbine blade attached to the rotor hub during mounting of the blade bearing to the wind turbine rotor hub.

8. The method according to any preceding claim, wherein, during steps e) and f), the blade bearing mount is provided at a first angular position about the rotor hub, and optionally wherein said first angular position is a 12 o’clock angular position.

9. The method according to any preceding claim, wherein the method further comprises, after step f), attaching a wind turbine blade to the blade bearing.

10. The method according to claim 9, wherein the method further comprises rotating the blade bearing about the rotor hub (6) from the first angular position to a second angular position prior to attachment of the wind turbine blade to said blade bearing, and optionally wherein said second angular position is a 3 o’clock position.11 . The method according to any preceding claim, wherein the blade bearing provided in step b) comprises a plurality of apertures (33) disposed about a circumference thereof, wherein the plurality of connectors are disposed about a mounting surface of the empty blade bearing mount, and wherein step e) comprises inserting the plurality of connectors into the plurality of apertures disposed about the circumference of the blade bearing.

12. The method according to any preceding claim, wherein the method further comprises, after step f) removing the deformation load from the blade bearing.

13. The method according to claim 12, when dependent on claims 9 or 10, wherein the method further comprises, prior to attachment of the wind turbine blade, measuring the shape of the blade bearing after the deformation load has been removed.

14. The method according to any preceding claim, wherein the method further comprises, prior to step a), detaching a blade bearing from a blade bearing mount.

15. The method according to any preceding claim, wherein steps a) to f) are performed in alphabetical order.

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