Patent Description:
Modern utility-scale wind turbines typically comprise a rotor formed of a plurality of wind turbine blades that are attached to a central hub at their root ends, the hub being coupled to a nacelle at the top of a tower. Wind turbine blades are usually designed to perform well in a wide range of conditions, as wind conditions can vary significantly between different wind turbine sites. Even within the same wind farm, different wind turbines may experience significantly different wind conditions dependent on their location within said wind farm. It follows that there is scope to optimise the design of blades and rotors for individual turbines to improve aerodynamic and structural performance over that of a standard blade.

One way of optimising a rotor for a specific location is to tailor an angle at which the wind turbine blades are oriented relative to the hub. For example, "sweep" and "coning" are known to improve loading on turbine components, regulate turbine power output or to reduce the risk of blades striking the tower in high wind conditions. Rotors having "sweep" comprise blades oriented such that the longitudinal axis of a blade is angled relative to a radial direction of the rotor in the plane of rotation. Conversely, rotors having "coning" comprise blades oriented such that the longitudinal axis of a blade is angled upwind, increasing the distance between tips of the blades and the tower.

To configure a rotor having coning or sweep, a face of the hub to which the root end of a blade is connected may be configured to orient the blades at an angle relative to a radius of the rotor. Tailoring the design of the hub, or machining surfaces of the hub, to provide a site-specific rotor is very expensive and inefficient.

Alternatively, the rotor may comprise a blade connection component connected between the root end of each blade and the hub. The blade connection component comprises a first surface for connection to the hub, and a second surface for connection to the blade which is oriented at an angle relative to the first surface, thereby effecting an angle between the blade and hub when said blade is connected to the hub via the connection component.

However, such a solution introduces additional failure modes in the connection between a blade and the hub. Further, connection components are sized according to the diameter of a blade's root end and are therefore large components. Manufacturing individual tailored connection components for site-specific blades is therefore expensive and may require considerable additional tooling.

Modern wind turbine blades are generally manufactured using a blade mould. However, due to their size and complexity, blade moulds can be very expensive, and often take up a considerable amount of floor space in a blade manufacturing facility. For at least these reasons it is unfavourable to produce individual new blade moulds to manufacture each individual wind turbine blade having a site-specific root end configuration.

A rotor according to the background art is disclosed in <CIT>. The rotor includes a hub, a rotor blade, and a bearing assembly configured to rotate the rotor blade with respect to the hub. The rotor further includes an insert, the insert including a first end, a second end, and a body extending therebetween. The first end is coupled to the hub and the second end is coupled to the bearing assembly. The second end defines a second plane oriented at a cone angle with respect to a first plane defined by the first end.

It is against this background that the present invention has been developed.

According to the invention there is provided a method of manufacturing a wind turbine blade. The method comprises providing a mould for a shell of the wind turbine blade, the mould extending in a longitudinal direction from a root end to a tip end; providing a plurality of elongated root inserts; providing a root plate with a plurality of arcuately arranged connection points; at the connection points, connecting the root inserts to the root plate, such that the connected root inserts jointly form a contour of a portion of a root section of the wind turbine blade; and positioning the root plate relative to the mould in order to place the contour formed by the root inserts at least partially into the mould. The method further comprises providing a spacer having a decreasing thickness, and the connecting of the root inserts to the root plate comprises providing the spacer between the root inserts and the root plate.

Providing the spacer with decreasing thickness between the root inserts and the root plate results in an offset in the longitudinal direction between end surfaces of root inserts of the plurality of root inserts. The end surfaces of the root inserts together form an end surface at a root end of a wind turbine blade formed by the method described above. The longitudinal offset between end surfaces of the root inserts thereby serves to form an end surface of the blade which is inclined at a non-perpendicular angle to a longitudinal axis of the blade. A plurality of such blades having an end surface oriented at a non-perpendicular angle to the longitudinal axis of the blade can be connected to a central hub to provide a rotor having sweep or coning, or a combination or sweep and coning dependent on the orientation of the end surface. Preferably the rotor comprises three wind turbine blades, the end surface of each respective wind turbine blade being equally oriented relative to a longitudinal axis of said blade. A rotor of a different wind turbine in the same wind farm may have a rotor comprising blades with end surfaces oriented at a different angle relative to their longitudinal axes, the rotor thereby having a different degree of sweep and/or coning to the previously described wind turbine.

The spacer may have a continuously decreasing thickness. Arranging a plurality of root inserts with a spacer having a continuously decreasing thickness provides the advantage that the blade formed by the method comprises a smooth end surface inclined at a non-perpendicular angle to the longitudinal axis of the blade. Such a blade comprising a smooth end surface may not require significant further processing steps such as milling to finish the blade, and may provide a surface complimentary to a surface of the hub to which the blade may be connected.

Alternatively, the spacer may have a stepwise decreasing thickness. A stepwise decreasing spacer provides the advantage that the plurality root inserts arranged with the spacer are oriented substantially parallel to the longitudinal direction of the mould, and therefore parallel to the longitudinal axis of a blade formed in said mould. Such a parallel arrangement of root inserts reduces misalignments or gaps between neighbouring root inserts, providing a blade having high rigidity and strength at the root end. Furthermore, a stepwise decreasing spacer was found to be simpler and hence cheaper and faster to manufacture. This is particularly the case when the spacer comprises multiple separate spacer sections each having one fixed thickness.

The spacer may comprise multiple separate spacer sections, each spacer section configured for being provided between the root plate and multiple ones of the plurality of elongated root inserts. Preferably each spacer section may be configured for being provided between the root plate and <NUM> to <NUM> elongated root inserts. That is to say, preferably around <NUM> to <NUM> elongated root inserts may be associated with each spacer section.

Forming the spacer of multiple spacer sections is advantageous both for transport and handling as the spacer sections are of a relatively small size in comparison to the size of the root end of the blade. Further, being smaller components, the spacer sections may be manufactured to a high dimensional accuracy and/or at a lower cost.

Each spacer section may alternatively be configured for being provided between the root plate and an individual root insert of the plurality of root inserts. However, such a configuration may have drawbacks in terms of assembly time and the number of parts required in comparison to examples wherein each spacer section is configured for being provided between the root plate and multiple ones of the plurality of elongated root inserts.

Each spacer section may have a different and gradually decreasing thickness. Such spacer sections can be arranged to form a spacer having a continuously decreasing thickness. Alternatively, the multiple spacer sections may each have one of at least two different, but substantially constant thicknesses. Such spacer sections each having a substantially constant, but different, thickness can be arranged to form a spacer having a stepwise decreasing thickness.

Positioning the root plate relative to the mould may further comprise positioning the root plate relative to the mould such that the connection points are outside of the mould and spaced apart from the root end of the mould in the longitudinal direction. One or more root inserts of the plurality of root inserts may therefore extend at least partially beyond the root end of the mould in the longitudinal direction. The spacer may be at least partially provided outside of the mould. Alternatively, where the connection points are not outside the mould, the spacer may be provided completely inside the mould.

The root plate may comprise one or more distancing features configured to set a distance between the root end of the mould and the connection points. Such distancing features may comprise protrusions extending from the root plate in the longitudinal direction. Alternatively or in addition, the method may comprise providing one or more tools to set a distance between the root end of the mould and the connection points. The distancing features of the root plate and/or tools provided serve to accurately position the root plate relative to the mould to correctly set a distance between the connection points and the root end of the mould.

The method may further comprise providing a shim plate between the root plate and the root end of the mould. The shim plate is a substantially planar member, and is configured to set a distance offsetting each of the connection points of the root plate from the root end of the mould in the longitudinal direction.

The method may further comprise forming the shell of the wind turbine blade inside the mould, an end surface of the shell being formed by end surfaces of the plurality of root inserts; removing the root plate and the spacer from the end surface of the shell; and smoothening the end surface of the shell. The smoothening may comprise using a milling machine.

Each of the plurality of root inserts may be of substantially the same length. Where the root inserts are of substantially the same length, providing the spacer between the root inserts and the root plate results in an offset in the longitudinal direction between end surfaces of root inserts of the plurality of root inserts such that, when the root plate is positioned relative to the mould, the plurality of elongated root inserts extend to different respective depths into the mould.

There may be provided a wind turbine blade obtainable by the method as described above, however not according to the claimed invention.

Such a wind turbine blade may differ from traditional wind turbine blades by having a build-in sweep and/or coning of the root end. Hence, a blade connection component between the blade root and the hub hence is not required to realize a wind turbine having sweep and/or coning. This may provide a stronger and lighter solution achieve sweep and/or coning of a wind turbine.

There may be provided a set of at least two separate spacer sections each having a different thickness, and a plurality of elongated root inserts for a wind turbine blade, each spacer section configured for being provided between arcuately arranged connection points of a root plate and multiple ones of the plurality of elongated root inserts.

At least one of the spacer sections of the set of at least two spacer sections may comprise at least two spacer section plates stacked on top of each other to form said spacer section. A wind farm may comprise at least a first wind turbine and a second wind turbine as defined above, the first wind turbine is having a first sweep angle and a first coning angle, the second wind turbine is having a second sweep angle and a second coning angle, wherein the first sweep angle is different from the second sweep angle and/or the first coning angle is different from the second coning angle. Wind turbines having sweep and/or coning were known prior to this disclosure. However, tailoring of sweep and/or coning for individual wind turbines was not feasible due to lack of a flexible and affordable manufacturing method. The present disclosure finally makes it possible to make an individual customization for sweep and/or coning by adjusting the spacers (shifting along the periphery of the blade root or replacing some of the spacers by thicker or thinner spacers or spacer sections. This enables optimization of the sweep and/or coning for the wind turbines at each the position (or type of position) in a wind farm park to optimized energy production and/or reduced wear or fatigue of the wind turbine.

There may be provided a wind farm comprising a first wind turbine and a second wind turbine, however not according to the claimed invention. The first wind turbine comprises a rotor with a first rotor blade oriented at a first angle relative to a radius of the rotor, wherein the first angle corresponds to the orientation of an end surface of the first blade relative to a longitudinal axis of said blade. The second wind turbine comprises a rotor with a second rotor blade oriented at a second angle relative to a radius of the rotor, wherein the second angle corresponds to the orientation of an end surface of the second blade relative to a longitudinal axis of said blade. The first angle is different from the second angle. The angle relative to the radius of the rotor is a result of the combination of cone and sweep angles and is hence a property of the blade for a specific arrangement of the blade. Comparison of the angle relative to the radius of the rotor for two blades should therefore be made for blades arranged the same way. Pitching of a blade during operation of a wind turbine may change the angle relative to the radius of the rotor observed for that blade, but this is due to a change in the arrangement of the blade, and if comparing two blades with different angles relative to the radius of the rotor in this new arrangement of the blade, then the two blades would also have different angles relative to the radius of the rotor in the new arrangement. Wind turbines having sweep and/or coning (and hence an angle relative to the radius of the rotor) were know prior to this disclosure. However, tailoring of sweep and/or coning for individual wind turbines was not feasible due to lack of a flexible and affordable manufacturing method. The present disclosure finally makes it possible to make an individual customization for sweep and/or coning by adjusting the spacers (shifting along the periphery of the blade root or replacing some of the spacers by thicker or thinner spacers or spacer sections. This enables optimization of the sweep and/or coning for the wind turbines at each the position (or type of position) in a wind farm park to optimized energy production and/or reduced wear or fatigue of the wind turbine.

Embodiments of the present invention will now be described by way of non-limiting example only, with reference to accompanying figures, in which:.

<FIG> shows a schematic front view of a modern utility scale wind turbine <NUM>. The wind turbine <NUM> comprises a rotor <NUM> rotatably mounted to a nacelle <NUM> which sits atop a tower <NUM>. The rotor <NUM> is formed of a plurality of wind turbine blades <NUM> which are connected at their respective root ends to <NUM> a central hub <NUM>, each blade <NUM> extending in a longitudinal direction (L) from its root end <NUM> to a respective blade tip <NUM>. The wind turbine blades <NUM> each comprise a leading edge <NUM> and a trailing edge <NUM>, and the rotor <NUM> rotates in a direction indicated by the arrow R about a rotor axis A (shown in <FIG>) extending through the centre of the hub <NUM> and perpendicularly to the page in <FIG>.

The rotor <NUM> in this example has "sweep", wherein the blades <NUM> are arranged with the hub <NUM> such that a longitudinal axis LA of each blade <NUM> is inclined at an angle α relative to a radius r of the rotor. As a consequence, the longitudinal axes LA of the three blades <NUM> of the wind turbine <NUM> do not run through a single point at the centre of the hub <NUM>, as they would do had there been no sweep. For reference, an arrangement of wind turbine blades 16i of a standard rotor not having sweep are indicated in <FIG> by the dotted outlines. A rotor <NUM> having sweep may be implemented at a wind turbine site where strong wind conditions are expected. Angled blades <NUM> of a rotor <NUM> having sweep can help to unload the rotor <NUM> in high wind conditions as the blades <NUM> bend, reducing the loading of gearbox components and bearings within the nacelle <NUM> of the turbine <NUM> for example.

<FIG> shows an exaggerated schematic view of the root end <NUM> of a wind turbine blade <NUM> of the wind turbine <NUM> in <FIG>. The blade <NUM> has an end surface <NUM> at the root end <NUM> which interfaces with a corresponding surface on the hub <NUM> when the blade <NUM> is connected thereto. The end surface <NUM> is oriented at a non-perpendicular angle to the longitudinal axis LA of the blade <NUM> to effect the angling of the blade <NUM> with respect to a radius r of the rotor <NUM> when the blade <NUM> is connected to the hub <NUM>. As such, the leading edge <NUM> extends further in the longitudinal direction L of the blade <NUM> than the trailing edge <NUM> at the root end <NUM>.

Typically, a sweep angle α of a wind turbine blade <NUM> of a rotor <NUM> having sweep is between <NUM> and <NUM> degrees with respect to a radius r of the rotor <NUM>. Such a sweep angle may for example result in a displacement of the tip end of a blade by up to <NUM>, dependent in part on the length of the blade.

<FIG> is a schematic side view of a further modern utility-scale wind turbine <NUM>. Arrow W indicates the direction of the wind incident on the wind turbine <NUM>. The wind turbine blades <NUM> comprise a windward side <NUM> facing the incident wind, and a leeward side <NUM> on the opposite side of the blade <NUM>. The wind turbine <NUM> of <FIG> is largely identical to that described with reference to <FIG>, and similar features will not be described in detail in the interest of conciseness.

The rotor <NUM> of the turbine <NUM> in <FIG> has coning, wherein the blades <NUM> are inclined at an angle β relative to a radius r of the rotor <NUM>. The blades <NUM> are angled upwind such that a distance x between the blade tips <NUM> and the tower <NUM> is increased in comparison to a rotor <NUM> which does not have coning. Typically, the blades <NUM> of a rotor <NUM> having coning are angled at between <NUM> and <NUM> degree relative to a radius r of the rotor <NUM>. Such an angle may in some examples result in an increase in distance x of between <NUM> and <NUM> greater than a distance x of a typical rotor not having coning. A rotor <NUM> having coning, such as that shown in <FIG>, may be implemented at a wind turbine site prone to high or unpredictable wind conditions where there exists a high risk of wind turbine blades <NUM> striking the tower <NUM>.

<FIG> shows an exaggerated schematic view of the root end <NUM> of a wind turbine blade <NUM> of the wind turbine <NUM> in <FIG>. The blade <NUM> has an end surface <NUM> at its root end <NUM> which is inclined relative to the longitudinal axis LA of the blade <NUM> at a non-perpendicular angle. The end surface <NUM> is inclined relative to the longitudinal axis LA such that the leeward side <NUM> of the blade <NUM> extends beyond the windward side <NUM> in the longitudinal direction L of the blade <NUM> at the root end <NUM>. When arranged with a corresponding surface of the central hub <NUM>, the inclined end surface <NUM> of the blade <NUM> serves to angle the blade <NUM> in an upwind direction.

Whilst the blades <NUM> of <FIG> have been described as having one of either sweep or coning, it will be appreciated than in many examples, a blade <NUM> may to a certain extent have both sweep and coning.

In order to optimise the amount of wind energy harvested, a wind farm may comprise wind turbines <NUM> as shown in <FIG> which are each configured to best capture energy from incident wind dependent on their specific location in the wind farm and the wind conditions at this location. The wind farm therefore comprises a first wind turbine <NUM> with a first rotor <NUM> formed of a plurality of wind turbine blades <NUM> which are connected to a central hub <NUM>. The rotor blades <NUM> of the first wind turbine <NUM> are oriented at a first angle relative to a radius r of the rotor <NUM>. That is to say, a longitudinal axis LA of each blade <NUM> of the first wind turbine <NUM> is oriented relative to a radius r of the first rotor <NUM> at a first sweep angle α<NUM> and a first coning angle β<NUM>. The orientation of a blade <NUM> of the first wind turbine <NUM>, i.e. the first angle, corresponds to the orientation of an end surface <NUM> of the first blade <NUM> relative to the longitudinal axis LA of said first blade <NUM>.

Further, the wind farm comprises a second wind turbine <NUM> with a second rotor <NUM> formed of a plurality of wind turbine blades <NUM> which are connected to a central hub <NUM>. The rotor blades <NUM> of the second wind turbine <NUM> are oriented at a second angle relative to a radius r of the rotor <NUM>. That is to say, a longitudinal axis LA of each blade <NUM> of the second wind turbine <NUM> is oriented relative to a radius r of the second rotor <NUM> at a second sweep angle α<NUM> and a second coning angle β<NUM>. The orientation of a blade <NUM> of the second wind turbine <NUM>, i.e. the second angle, corresponds to the orientation of an end surface <NUM> of the second blade <NUM> relative to the longitudinal axis LA of said second blade <NUM>.

The first and second angles of the blades <NUM> of the respective first and second wind turbines <NUM> in the wind farm are different. The orientation of a blade <NUM> of the first wind turbine <NUM> is set to best capture energy from wind at a first location in the wind farm. Similarly the orientation of a blade <NUM> of the second wind turbine <NUM> is set to most effectively capture energy from the wind at a second location in the wind farm. The blades <NUM> of the first and second wind turbines <NUM> are therefore configured differently, each with a differently oriented end surface <NUM> in comparison to the end surface of blades of the other wind turbine <NUM> in the wind farm.

Modern wind turbine blades <NUM> can exceed <NUM> in length and are typically formed of a substantially hollow shell <NUM> made of composite materials such as glass fibre reinforced plastic (GFRP). In order to manufacture such large composite structures, the shell <NUM> of a wind turbine blade <NUM> may be formed of two half shells, each individually formed in a corresponding mould of a blade mould assembly.

An improved method of manufacturing a wind turbine blade <NUM> having an end surface <NUM> oriented at a non-perpendicular angle to the longitudinal axis LA of the blade <NUM>, such as those described with reference to <FIG>, will now be described with reference to the remaining <FIG>.

The method comprises providing a mould <NUM>. <FIG> shows part of a mould assembly <NUM> for manufacturing a wind turbine blade <NUM>. The mould assembly <NUM> in this example is formed of two moulds <NUM>, each mould being configured to form a shell for one of the windward or leeward sides <NUM>, <NUM> of the blade <NUM>. For clarity only one of the moulds <NUM> is shown in <FIG>. It will be appreciated that the other mould of the mould assembly <NUM> is configured in substantially the same manner as that shown in <FIG> and will therefore not be described in further detail.

The mould <NUM> extends in a longitudinal direction LD from a root end <NUM> to a tip end <NUM>. The mould <NUM> comprises a mould surface <NUM> shaped to form an outer surface of one of the windward or leeward sides <NUM>, <NUM> of the blade <NUM>. In this example, a first edge <NUM> of the mould <NUM> is configured to form the trailing edge <NUM> of a wind turbine blade shell <NUM>, and a second edge <NUM> is configured to form the leading edge <NUM> of a wind turbine blade shell <NUM>.

The method further comprises providing a root plate <NUM>. The root plate <NUM> comprises a plurality of arcuately arranged connection points <NUM>. In this example the connection points <NUM> comprise through bores arranged in an arc in the root plate <NUM>. The connection points <NUM> are configured to enable connection of a plurality of root inserts <NUM> to the root plate <NUM>.

The root inserts <NUM> each comprise a means for connecting a finished blade <NUM> to the hub <NUM> of a wind turbine <NUM>. In this example, the root inserts <NUM> comprise a threaded bushing <NUM> (see <FIG>), provided to form one side of a compression joint between the wind turbine blade <NUM> and the hub <NUM> when mounting a finished blade <NUM> to the hub <NUM>.

In this example, the root inserts <NUM> are connected to the root plate <NUM> by arranging a bolt <NUM> (see <FIG>) at a connection point <NUM> and fastening said bolt <NUM> with the threaded bushing <NUM> of a root insert <NUM>. When connected to the root plate <NUM>, the root inserts <NUM> jointly form a contour <NUM> of a portion of a root section of the wind turbine blade <NUM>. In this example the contour <NUM> formed by the plurality of root inserts <NUM> connected to the root plate <NUM> corresponds directly to the arcuate arrangement of the connection points <NUM> of the root plate <NUM> to form a substantially semi-cylindrical convex surface.

The root plate <NUM> is positioned relative to the mould <NUM> in order to place the contour <NUM> formed by the root inserts <NUM> at least partially into the mould <NUM>. In some examples one or more root inserts <NUM> may partly extend beyond the root end <NUM> of the mould <NUM> in the longitudinal direction LD. In other examples the root inserts <NUM> may be so configured that when the root plate <NUM> is positioned relative to the mould <NUM>, the full length Lr of each of the root inserts <NUM> is in the mould <NUM>.

According to the invention, a spacer <NUM> having a decreasing thickness T is provided between the root inserts <NUM> and the root plate <NUM> when connecting said root inserts <NUM> to the root plate <NUM>. The spacer <NUM> is configured to permit the connection of each root insert <NUM> to the root plate <NUM>. In this example, the spacer <NUM> comprises a bore <NUM> corresponding to each connection point <NUM> of the root plate <NUM> such that bolts (not shown) may be arranged through the connection points <NUM>, through bores <NUM> in the spacer <NUM>, and fastened to the threaded bushings <NUM> in each of the plurality of root inserts <NUM>. End surfaces <NUM> (shown in <FIG>) of each of the root inserts <NUM> abut the spacer <NUM>.

A decreasing thickness T will be understood to mean that the spacer comprises at least one region (up to two regions in some examples) having a maximum thickness Tmax and at least one region having a minimum thickness Tmin, wherein the thickness T is a dimension of the spacer <NUM> measured in the longitudinal direction LD of the mould <NUM> when the root plate <NUM> is positioned relative to the mould <NUM>. It will be understood that whilst the thickness is described herein as decreasing from a maximum thickness Tmax to a minimum thickness Tmin, the same thickness T can be described as an increasing thickness T, increasing from a minimum thickness Tmin to a maximum thickness Tmax without departing from the scope of the invention.

In this example, the thickness T of the spacer <NUM> is greater at a first end <NUM> of the spacer <NUM> than at a second end <NUM> of the spacer <NUM>. As a result of the decreasing thickness T of the spacer <NUM>, the end surfaces <NUM> of the root inserts <NUM> are offset from the end surfaces <NUM> of other root inserts <NUM> in the longitudinal direction LD of the blade mould <NUM>. In this example, the end surface <NUM> of a root insert <NUM> arranged with the spacer <NUM> in proximity to the first end <NUM> is situated nearer the tip end <NUM> of the mould <NUM> in the longitudinal direction LD than an end surface <NUM> of a root insert <NUM> arranged with the spacer <NUM> in proximity to the second end <NUM> thereof when the root plate <NUM> is positioned relative to the mould <NUM>. In other examples, dependent on the profile of the thickness T of the spacer <NUM>, an end surface <NUM> of a root insert arranged between with the spacer <NUM> between the first and second ends <NUM>, <NUM> may be situated nearest the tip end <NUM> of the mould <NUM> in the longitudinal direction LD.

In some examples, the length Lr of each of the root inserts <NUM> may vary. However, in this example, each of the plurality of root inserts <NUM> is of substantially the same length. The decreasing thickness T of the spacer <NUM> therefore results in a longitudinal offset between the plurality of root inserts <NUM> such that, when the root plate <NUM> is positioned relative to the mould <NUM>, the plurality of elongated root inserts <NUM> extend to different respective depths into the mould <NUM>. In examples where the root inserts <NUM> are all of substantially the same length Lr, the decreasing thickness T of the spacer <NUM> therefore also results in a longitudinal offset between tip ends <NUM> of the plurality of root inserts <NUM> corresponding to the decreasing thickness T of the spacer <NUM>. This may be advantageous in some examples as the root inserts <NUM> provide structural rigidity to the root end <NUM> of the blade <NUM>, and by increasing the depth to which some of the inserts <NUM> extend into the mould <NUM>, the blade <NUM> formed in the mould <NUM> comprises increased rigidity extending further along the blade <NUM> at the root end <NUM> on one side of the blade <NUM>.

The spacer <NUM> comprises one of a stepwise decreasing thickness T, as shown in <FIG>, or a continuously decreasing thickness T. A 'stepwise decreasing thickness T' is defined as a thickness T which decreases in discrete, discontinuous steps. In such a situation, a surface <NUM> (shown in <FIG>) of the spacer <NUM> against which the end surface <NUM> of a root insert <NUM> is abutted, can be substantially perpendicular to the thickness T of the spacer <NUM>. Conversely, a 'continuously decreasing thickness T' is defined as a thickness T which decreases gradually and smoothly from a maximum thickness Tmax to a minimum thickness Tmin.

In this example, the spacer <NUM> is formed of multiple separate spacer sections <NUM> which, when arranged together, form a spacer <NUM> as shown in <FIG>. <FIG> respectively show spacer sections <NUM> forming a spacer <NUM> having a stepwise decreasing thickness T, and spacer sections <NUM> forming a spacer <NUM> having a continuously decreasing thickness T. Each spacer section <NUM> is configured for being provided between the root plate <NUM> and multiple ones of the plurality of elongated root inserts <NUM>.

In some examples, each spacer section <NUM> may be configured for being provided between the root plate <NUM> and one individual root insert <NUM> of the plurality of root inserts <NUM>. However, in such an example the time required to manufacture a blade <NUM> is significantly increased as there may be in excess of eighty individual root inserts <NUM> to connect to the root plate <NUM>, and so arranging these with in excess of eighty spacer sections <NUM> may prove inefficient. Preferably each spacer section <NUM> is configured such that it may be provided between the root plate <NUM> and about five to fifteen elongated root inserts <NUM>.

The spacer sections <NUM> shown in <FIG> form a spacer <NUM> having a stepwise decreasing thickness T. In this example each of the spacer sections <NUM> have one of at least two different, but substantially constant thicknesses t. Each individual spacer section <NUM> therefore comprises a substantially constant thickness t throughout, from a first end <NUM> of the spacer section <NUM> to a second end <NUM> thereof. Although the spacer <NUM> shown in <FIG> comprises spacer sections having one of nine different thicknesses t, it will be understood that a spacer <NUM> having a stepwise decreasing thickness T may comprise spacer sections <NUM> having any of two or more different thicknesses t, and one or more of the spacer sections <NUM> may have the same thickness t as one or more other spacer section <NUM>.

In this example, the spacer sections <NUM> are arranged such that the thickness T of the spacer <NUM> as a whole decreases from the first end <NUM> to the second end <NUM>. Each of the spacer sections <NUM> forming the spacer <NUM> therefore comprises a different thickness t. In this example, a spacer section <NUM> having the greatest thickness t is arranged to form the first end <NUM> of the spacer <NUM>, and a spacer section <NUM> having the smallest thickness t is arranged to form the second end <NUM> of the spacer <NUM>. Spacer sections <NUM> arranged between the first and second ends <NUM>, <NUM> of the spacer <NUM> each respectively comprise a decreased thickness t in relation to a neighbouring spacer section <NUM> arranged closer to the first end <NUM> of the spacer <NUM>, such that the thickness T of the spacer <NUM> as a whole decreases from the first end <NUM> to the second end <NUM>.

In other examples, each of the spacer sections <NUM> may merely have one of at least two different thicknesses t, provided an arrangement of said spacer sections <NUM> results in a spacer <NUM> having a decreasing thickness T.

A spacer <NUM> having a stepwise decreasing thickness T is advantageous as root inserts <NUM> arranged with such a spacer <NUM> are arranged such that a longitudinal axis of each root insert <NUM> can be substantially parallel to the longitudinal direction LD of the mould <NUM>. Each of the root inserts <NUM> is therefore also substantially parallel to the other root inserts <NUM> of the plurality of root inserts <NUM> connected to the root plate <NUM>, as shown in <FIG>. Gaps between neighbouring root inserts <NUM> are thereby minimized and the contour <NUM> formed by the plurality of root inserts <NUM> connected to the root plate <NUM> comprises a relatively smooth convex surface. A blade <NUM> comprising such an arrangement of parallel root inserts <NUM> at the root end <NUM> has high structural strength and rigidity. Such uniformity in the orientation of the root inserts <NUM> also minimizes the risk of manufacturing defects such as misalignments or clashes between neighbouring root inserts <NUM>. Furthermore, spacer sections <NUM> having a uniform thickness t can be manufactured at a reasonably low cost.

The spacer sections <NUM> shown in <FIG> are arranged to form a spacer <NUM> having a continuously decreasing thickness T from the first end <NUM> of the spacer <NUM> to the second end <NUM>. In this example each spacer section <NUM> has a different and gradually decreasing thickness t. The thickness t of each separate spacer section <NUM> decreases from a first end <NUM> of the spacer section <NUM> to a second end <NUM> of the spacer section <NUM>. That is to say for each spacer section <NUM> in the example shown in <FIG>, the thickness t decreases continuously from the first end <NUM> to the second end <NUM> thereof. Further, in this example an average (mean) thickness t of each separate spacer section <NUM> is different to an average (mean) thickness t of other spacer sections <NUM> forming the spacer <NUM>.

Using a spacer <NUM> having a continuously decreasing thickness T to manufacture a blade shell <NUM> can result in said blade shell <NUM> having a smoother end surface <NUM> in comparison to a blade shell <NUM> manufactured using a spacer <NUM> having a stepwise decreasing thickness T. A shell <NUM> having a smoother end surface <NUM> may provide a surface complimentary to a surface of the hub <NUM> to which the blade <NUM> is to be connected, thereby providing a better connection between blade <NUM> and hub <NUM>.

In some examples the spacer <NUM> may be a single part comprising a decreasing thickness T which is one of a stepwise or continuously decreasing thickness T. Such a spacer <NUM> may in some examples exceed <NUM> in diameter, dependent on the root diameter of the blade <NUM> being manufactured. Preferably the spacer <NUM> is formed of multiple separate spacer sections <NUM> as shown in <FIG>. A spacer <NUM> formed of multiple separate spacer sections <NUM> may have a higher dimensional accuracy, as the separate spacer sections <NUM> are relatively small components in comparison to the root diameter of a wind turbine blade <NUM>, and so they can be manufactured to a much higher tolerance. Further, ease of transport and handling are greatly increased for a set of spacer sections <NUM> in comparison to a single-piece spacer.

In each of the examples described above with reference to <FIG>, the spacer <NUM> comprises a thickness T which decreases from the first end <NUM> of the spacer <NUM> to the second end <NUM> of the spacer <NUM>. Such a spacer <NUM> may be used with the mould assembly <NUM> as described above with reference to <FIG> where the first edge <NUM> of the mould <NUM> is configured to form a trailing edge <NUM> of the blade <NUM>. Arranging the spacer <NUM> such that the first end <NUM> of the spacer <NUM> is in proximity to the first edge <NUM> of the mould <NUM> when manufacturing the shell <NUM> of a wind turbine blade <NUM> results in a shell <NUM> having a leading edge <NUM> which extends beyond the trailing edge <NUM> in the longitudinal direction L of the blade <NUM>. The above described method and apparatus may therefore be used to manufacture the shell <NUM> of a blade <NUM> for a rotor <NUM> having sweep.

It is also anticipated that the spacer <NUM> may comprise a decreasing thickness T wherein the maximum thickness Tmax and/or minimum thickness Tmin are not located at the first and second ends <NUM>, <NUM> of the spacer <NUM>. That is to say, in some examples the spacer <NUM> may comprise a maximum thickness Tmax at a point on the spacer <NUM> between the first and second ends <NUM>, <NUM> thereof. The thickness T of such a spacer <NUM> decreases from said point of maximum thickness Tmax to a minimum thickness Tmin towards the first and second ends <NUM>, <NUM> of the spacer <NUM>. Similarly, a spacer <NUM> may comprise a minimum thickness Tmin at a point between the first and second ends <NUM>, <NUM> of the spacer <NUM>, the thickness T of the spacer <NUM> decreasing from each of the first and second ends <NUM>, <NUM> to said point of minimum thickness Tmin between the first and second ends <NUM>, <NUM>.

A spacer <NUM> having a maximum or minimum thickness Tmax, Tmin at a point on the spacer <NUM> between the first and second ends <NUM>, <NUM> may be used in a mould assembly <NUM> such as that shown in <FIG>, configured to form one of the windward or leeward sides <NUM>, <NUM> of a wind turbine blade <NUM>, to form a blade <NUM> for a rotor <NUM> having coning, or a combination of sweep and coning. For example, to form a blade <NUM> for a rotor <NUM> having coning, a spacer <NUM> comprising a maximum thickness Tmax at a mid-point on the spacer <NUM> between the first and second ends <NUM>, <NUM> may be used with a mould <NUM> configured to form the leeward side <NUM> of the blade <NUM>. A spacer having a minimum thickness at a mid-point on the spacer between the first and second ends thereof may be used with a corresponding mould configured to form the windward side <NUM> of the blade. The resultant blade shell <NUM> in such an example comprises an end surface <NUM> inclined relative to the longitudinal axis LA such that the leeward side <NUM> of the blade <NUM> extends beyond the windward side <NUM> in the longitudinal direction LD at the root end <NUM>.

Using multiple separate spacer sections <NUM> to form the spacer <NUM> is further advantageous as a number of wind turbine blades <NUM> having differently oriented end surfaces <NUM> at their respective root ends <NUM> may be manufactured using the same mould assembly <NUM> and set of spacer sections <NUM>. A number of different blade shells <NUM>, with differently oriented end surfaces <NUM> may be formed using the same mould <NUM> and set of spacer sections <NUM> simply by changing the order in which the spacer sections <NUM> are arranged. For example, rather than arranging the spacer section <NUM> having the greatest thickness t to form the first end <NUM> of the spacer <NUM>, said thickest spacer section <NUM> may be arranged at a point between the first and second ends <NUM>, <NUM> with spacer sections <NUM> either side thereof having a lesser thickness t to form a spacer <NUM> having a decreasing thickness T. Various different configurations of spacer <NUM> are therefore possible using a single set of spacer sections <NUM>, without any requirement to produce new tools for various different blade root designs.

To form a spacer <NUM> having a continuously decreasing thickness T, comprising a maximum or minimum thickness Tmax, Tmin at a point on the spacer <NUM> between the first and second ends <NUM>, <NUM>, the set of spacer sections <NUM> may include an additional spacer section not previously described. The spacer section <NUM> forming said maximum thickness Tmax may comprise a decreasing thickness t which decreases continuously from a maximum thickness between the first and second ends <NUM>, <NUM> of the spacer section <NUM>. Similarly, where the spacer <NUM> comprises a minimum thickness between the first and second ends <NUM>, <NUM>, a spacer section <NUM> forming said minimum thickness may comprise a decreasing thickness t which decreases from the first and second ends <NUM>, <NUM> of the spacer section <NUM> to a minimum thickness at a point between the first and second ends <NUM>, <NUM>.

In some examples wherein the spacer is formed of multiple separate spacer sections <NUM>, one or more of the spacer sections <NUM> may in turn comprise two or more spacer section plates (not shown). Such spacer section plates may be stacked in the longitudinal direction LD of the mould <NUM> to form a spacer section <NUM>. The spacer section plates are arranged to form one or more spacer sections <NUM> such that a cumulative thickness T of the spacer <NUM> decreases between two regions of the spacer <NUM> in order to form a spacer <NUM> having the required decreasing thickness T. In particular, a spacer section <NUM> having a constant thickness t, such as those described with reference to <FIG>, may be formed by stacking two or more spacer section plates. The spacer section plates may be stacked to form spacer sections <NUM> in one or more regions of the spacer <NUM>. It is also anticipated that in some examples, spacer sections <NUM> having a decreasing thickness t, such as those shown in the example of <FIG>, may be formed of two or more spacer section plates stacked in the longitudinal direction LD of the mould <NUM>. In some examples the spacer <NUM> having a decreasing thickness T is therefore formed of spacer sections <NUM> which may in turn be formed of spacer section plates (not shown).

Whilst throughout the examples described above the spacer <NUM> has been configured to form a blade <NUM> having an end surface <NUM> inclined relative to the longitudinal axis LA of the blade <NUM>, to form a blade shell <NUM> for a rotor <NUM> having sweep or coning, it is expressly anticipated that in other examples the spacer <NUM> may be so configured to produce a blade shell <NUM> of a blade <NUM> for a rotor <NUM> having a degree of both sweep and coning. Taking the mould assembly <NUM> of <FIG> for example, wherein the mould <NUM> is configured to form a shell <NUM> for one of the windward or leeward sides <NUM>, <NUM> of the blade <NUM>, a blade shell <NUM> for a rotor <NUM> having both sweep and coning may be manufactured using a spacer <NUM> comprising a region of greatest thickness Tmax between a central point of the spacer and one of the first or second ends <NUM>, <NUM> of the spacer <NUM>.

<FIG> shows a schematic cross-sectional view in a direction transverse to the longitudinal direction LD of a mould <NUM> and root plate <NUM> following positioning of the root plate <NUM> relative to the mould <NUM>. In some examples of the method, the connection points <NUM> of the root plate <NUM> are offset from the root end <NUM> of the mould <NUM> in the longitudinal direction LD. Positioning the root plate <NUM> may therefore further comprise positioning the root plate <NUM> relative to the mould <NUM> such that the connection points <NUM> are outside of the mould <NUM> and spaced apart from the root end <NUM> of the mould <NUM> in the longitudinal direction LD.

It follows that in some examples, the spacer <NUM> provided between the root plate <NUM> and the root inserts <NUM>, may be provided at least partially outside the mould <NUM>. Dependent on the selection of spacer thickness T, one or more root inserts <NUM> of the plurality of root inserts <NUM> may extend beyond the root end <NUM> of the mould <NUM> as a result of the longitudinal offset between the connection points <NUM> and the root end <NUM> of the mould <NUM>.

In order to accurately position the root plate <NUM> relative to the mould <NUM> such that the connection points <NUM> are offset from the root end <NUM> of the mould <NUM>, the root plate <NUM> may comprise one or more distancing features configured to set a distance y between the connection points <NUM> and the root end <NUM> of the mould <NUM>. Such distancing features may comprise protrusions which extend from the root plate <NUM> in the longitudinal direction LD.

Alternatively or additionally, one or more separate tools may be provided to set the distance y between the connection points <NUM> of the root plate and root end <NUM> of the mould <NUM>. One example of such a tool is a shim plate <NUM>. Therefore, in this example the method further comprises providing a shim plate <NUM> between the root plate <NUM> and the root end <NUM> of the mould <NUM>. In this example the shim plate <NUM> is a substantially planar component, extending across the width of the root end <NUM> of the mould <NUM>. The shim plate <NUM> may alternatively consist of multiple individual shim plate sections.

To form the shell <NUM> of a wind turbine blade inside the mould <NUM>, the method further comprises arranging one or more layers of material which form the composite shell <NUM> (not shown) on the mould surface <NUM>. The root inserts <NUM>, connected to the root plate <NUM>, are arranged in the mould <NUM> on top of the one or more layers of composite material by the root plate <NUM> being positioned relative to the mould <NUM>. Further layers of material (not shown) may be arranged in the mould <NUM> on top of the root inserts <NUM> and initial layers of material. The composite shell <NUM> may then be formed by implementing a forming technique such as Vacuum Assisted Resin Transfer Moulding (VARTM) for example.

Following forming of the shell <NUM>, the method further comprises removing the root plate <NUM> and the spacer <NUM> from the end surface <NUM> of the shell <NUM>. A second shell, formed in a mould configured to form the other of the windward or leeward side <NUM>, <NUM> of a wind turbine blade <NUM>, is arranged with the composite shell <NUM> described above. The shells are bonded together to form a complete outer shell of the wind turbine blade <NUM>.

<FIG> shows a schematic perspective view of the root end <NUM> of the blade <NUM>. The end surface <NUM> of the shell <NUM>, inclined relative to the longitudinal axis LA of the blade <NUM>, is formed by the end surfaces <NUM> of the plurality of root inserts <NUM>. Root inserts <NUM> of the shell <NUM> are shown in dashed lines on <FIG>. In this example a spacer <NUM> comprising a stepwise decreasing thickness T was provided between the root inserts <NUM> and the root plate <NUM> when manufacturing the blade <NUM>, as evidenced by the stepped end surface <NUM> of the shell <NUM>. Further, as the root inserts <NUM> are each of the same length Lr , tip ends <NUM> of the root inserts <NUM> are also offset from tip ends <NUM> of other root inserts <NUM> in the shell <NUM>.

Optionally, after forming the shell <NUM> in the mould <NUM>, the end surface <NUM> of the shell <NUM> may be smoothened. Smoothening the end surface <NUM> of the shell <NUM> may be achieved for example by using a milling machine (not shown). The milling machine is oriented such that a cutting plane is inclined relative to the longitudinal axis LA. This may for example be achieved by aligning reference or mounting points of the milling machine with a plurality of root inserts <NUM> in the blade shell <NUM> which are offset from one another in the longitudinal direction L of the blade <NUM>. The end surface <NUM> is therefore smoothened to provide a surface complimentary to a surface of the hub <NUM> to which the blade <NUM> may be connected, in order to provide a constructive interface at the joint between blade <NUM> and hub <NUM>.

Many alternatives to the method described above are anticipated without departing from the scope of the invention as defined by the claims.

In some examples, the configuration and arrangement of the connection points <NUM> may be different to that described above. For example, the connection points <NUM> may comprise a protrusion, recess or other means to locate a plurality of root inserts <NUM> relative to the root plate <NUM>.

Further, the root inserts <NUM> may each comprise an embedded bolt or other threaded protrusion instead of the threaded bushing <NUM> as described with reference to <FIG>. Connecting a root insert <NUM> of the plurality of root inserts <NUM> to the root plate <NUM> may therefore comprise arranging the embedded bolt of the root insert <NUM> with a connection point <NUM>, and fastening a nut to the bolt to form a compression joint connecting the root insert <NUM> to the root plate <NUM>.

In some examples the root plate <NUM> may comprise the shim plate <NUM>, i.e. the shim plate <NUM> may be formed integrally with the root plate <NUM>.

The mould <NUM> may be configured to form one of a leading edge shell or a trailing edge shell of a wind turbine blade <NUM>. Alternatively the blade <NUM> may be manufactured using a mould assembly comprising more than two moulds, wherein each mould is configured to form a portion of the wind turbine blade shell <NUM>.

Claim 1:
A method of manufacturing a wind turbine blade (<NUM>), the method comprising:
providing a mould (<NUM>) for a shell of the wind turbine blade, the mould extending in a longitudinal direction from a root end (<NUM>) to a tip end (<NUM>);
providing a plurality of elongated root inserts (<NUM>);
providing a root plate (<NUM>) with a plurality of arcuately arranged connection points (<NUM>);
at the connection points (<NUM>), connecting the root inserts (<NUM>) to the root plate (<NUM>), such that the connected root inserts jointly form a contour of a portion of a root section of the wind turbine blade; and
positioning the root plate (<NUM>) relative to the mould (<NUM>) in order to place the contour formed by the root inserts at least partially into the mould,
wherein the method further comprises
providing a spacer (<NUM>) having a decreasing thickness, and wherein
the connecting of the root inserts (<NUM>) to the root plate (<NUM>) comprises providing the spacer between the root inserts and the root plate.