A wind turbine

Abstract

In a first aspect of the present invention there is provided a wind turbine comprising a rotor The rotor comprises a hub and at least three wind turbine blades which are attached to the hub and pitchable relative to the hub. Each blade extends between a root and a tip, and each blade comprises a connection point located in a mid-portion of the blade between the root and the tip. The wind turbine further comprises a plurality of blade connecting members, each blade connecting member extending between a respective pair of wind turbine blades. Each blade connecting member is connected at one end to a connection point of a wind turbine blade and at the other end to a connecting member tensioning system attached to the other blade of the pair of wind turbine blades.

Description

[0001] A wind turbine

[0002] Technical field

[0003] The present invention relates generally to wind turbines and more particularly to a wind turbine comprising a blade connecting member extending between a pair of wind turbine blades.

[0004]

[0005] Increasing the swept area of a wind turbine rotor typically means that the wind turbine can produce increased levels of power. Accordingly, there is a motivation to manufacture wind turbines with increasingly larger blades. However, increasing the length of a wind turbine blade increases the magnitude of loads, such as wind loads and weight loads, experienced by the blade and transferred to a hub of the rotor, in use.

[0006] It follows that increasing blade length typically requires an increase in blade root diameter to safely transfer the increased blade loads. However, increasing the blade root diameter introduces further challenges for manufacturing and transporting such blades. In some cases, a support frame or supporting cables may be included on the rotor to transfer some of the blade loads to the hub and / or to other blades. For example, a cable-stayed rotor may include support cables extending between the blades and / or hub of a rotor to share and transfer blade loads, such that the structural requirements for the blade root may be reduced. Reducing the structural requirements of the blade root means that the length of a blade can be increased without increasing the root diameter of the blade.

[0007] The tension in the support cables is one of the factors which dictates the proportional distribution of loads between the support cables and the root of the blade. As such, it is important to set and maintain the tension in the support cables at specific levels. An optimal tension level may be dependent on factors such as wind speed and / or direction, seasonal conditions, and turbine operating modes. The tension in the support cables may be set during assembly and initial configuration of the wind turbine. In some cases, it may be beneficial adjust the tension at a later stage after assembly, for example during operation of the turbine, in a reconfiguration phase between operational phases and / or during maintenance. Further, with particular reference to maintenance operations, in some cases it may be necessary to entirely unload blade-related tension from a support cable. Adjusting the tension and / or slackening support cables on existing cable-stayed rotors in a simple, efficient, and safe way can be challenging.It is against this background that the present invention has been developed.

[0008] In a first aspect of the present invention there is provided a wind turbine comprising a rotor. The rotor comprises a hub and at least three wind turbine blades which are attached to the hub and pitchable relative to the hub. Each blade extends between a root and a tip, and each blade comprises a connection point located in a mid-portion of the blade between the root and the tip. The wind turbine further comprises a plurality of blade connecting members, each blade connecting member extending between a respective pair of wind turbine blades. Each blade connecting member is connected at one end to a connection point of a wind turbine blade and at the other end to a connecting member tensioning system attached to the other blade of the pair of wind turbine blades.

[0009] It should be understood that the term “pitchable” refers to the ability to rotate the whole blade about its longitudinal, i.e. spanwise, axis relative to the hub and at the hub.

[0010] In some examples, the blade connecting members may be referred to as “direct blade-to-blade” connecting members, because the connecting members are connected between respective pairs of blades. Locating the connection point in the mid-portion of the blade means that the connection point is located away from the root and the tip. For example, the mid-portion of the blade may be a portion extending between a point located 15% of the length of the blade from the root and a point located 15% of the length of the blade from the tip. As such, the connection point located in the mid-portion of the blade may be located at least 15% of the length of the blade away from the root. Similarly, the connection point located in the mid-portion of the blade may be located at least 15% of the length of the blade away from the tip.

[0011] Attaching the connecting member tensioning system to the blade means that the blade connecting members can be connected directly between the blades which results in more flexibility or freedom in the design and configuration of the blade connecting members. This means that the blade connecting members can be optimized for load sharing and not compromised by constraints related to locating and packaging a connecting member tensioning system in the hub.

[0012] The rotor may be referred to as a stayed rotor such as a cable stayed rotor or such as a pitchable cable stayed rotor.In some examples the blade connecting members are arranged for transferring load from one blade to another blade. In some examples the blade connecting members are configured to transfer loads between the blades during operation of the wind turbine, whereby peak loads at the root of the blades are reduced.

[0013] In some examples the connecting member tensioning system is attached to the other blade of the pair of wind turbine blades in a mid-portion of the blade between the root and the tip and the blade connecting members are configured to transfer loads between the midportion of the blades. Attaching the connecting member tensioning system in the midportion of the blade means that the connecting member tensioning system is located away from the root and the tip. For example, the mid-portion of the blade may be a portion extending between a point located 15% of the length of the blade from the root and a point located 15% of the length of the blade from the tip. As such, the connecting member tensioning system attached in the mid-portion of the blade may be located at least 15% of the length of the blade away from the root. Similarly, the connecting member tensioning system attached in the mid-portion of the blade may be located at least 15% of the length of the blade away from the tip.

[0014] In some examples the blades are non-foldable blades. In this context non-foldable is to be understood as the blades does not comprise a hinge enabling folding or deflection of the blades substantially without elastic deformation of the blades. In some examples the blades may be non-hinged blades.

[0015] In some examples the connection point and the connecting member tensioning system are located in the same spanwise location of the blade or in substantially the same spanwise location of the blade. This provides the advantage that loads may be transferred directly between the connecting members through minimal structural elements thereby reducing the material use and weight of the blade. In some examples, each connecting member tensioning system may comprise a winch. The winch may be operable to spool the respective blade connecting member off and onto a winch reel to vary a free length of the blade connecting member. In such examples, the blade connecting member is preferably a flexible, i.e. bendable blade connecting member, such as a rope, wire, cable or belt.

[0016] The free length of a blade connecting member may refer to the length of a portion of the blade connecting member, which is not spooled onto the winch reel, i.e. the length of the portion of the blade connecting member between the winch reel and the connection point of the other blade in the pair of wind turbine blades. Varying the free length of the bladeconnecting member may vary the tension in the blade connecting member. Accordingly, the winch may be operable to vary the tension in the respective blade connecting member by spooling the blade connecting member off and onto the winch reel.

[0017] In some examples, each connecting member tensioning system may comprise a winch comprising a winch reel and a winch line wound onto the winch reel. The respective blade connecting member may be connected to the winch line, and the winch may be operable to spool the winch line off and onto the winch reel to thereby vary the tension in the connected blade connecting member.

[0018] The inclusion of a winch line means that a substantially rigid blade connecting member can be used, in some examples, whilst still facilitating tensioning the blade connecting member using a winch. A substantially rigid blade connecting member may comprise a fibre reinforced pultrusion, a metal bar or rod. The winch line may comprise a rope, wire, cable or belt.

[0019] In some examples, the winch line may be routed from the winch reel to the blade connecting member via at least one pulley. The inclusion of one or more pulleys may provide a mechanical advantage in relation to the force required to tension the blade connecting member. Further, the inclusion of one or more pulleys may provide greater flexibility for locating the connecting member tensioning system on or in the respective blade.

[0020] In some examples, the winch may comprise a motor, such as an electric motor. For example, the motor may be operable to drive the winch reel. In some examples the tension lock arrangement may be integrated as part of the winch reel or the motor.

[0021] In some examples, each connecting member tensioning system may comprise a linear actuator. In some examples the blade connecting member may be connected directly to the linear actuator. In some other examples, the blade connecting member may be connected to the linear actuator indirectly, for example via a coupling member such as a rope, wire, cable or belt.

[0022] The linear actuator may actuate in a plane orthogonal to the span of the blade. For example, the linear actuator may actuate in a plane substantially parallel to the blade connecting member, or parallel to the span of the blade. Actuating parallel to the span of the blade may provide more design freedom and space for lengthwise extension of the linear actuator.In some examples, the linear actuator may be a hydraulic or pneumatic linear actuator. Alternatively, in some other examples the linear actuator may be an electric linear actuator. As such, the electric linear actuator may comprise a screw or threaded bar which is driven into and out of a housing when actuating the linear actuator. The blade connecting member may be connected to the screw or threaded bar.

[0023] In some examples, the blade connecting member may be connected to the linear actuator via a lever arm. The lever arm may be attached to the respective blade via a pivot. The blade connecting member and linear actuator may be connected to the lever arm such that extending or retracting the linear actuator pivots the lever arm about the pivot to thereby vary the tension in the blade connecting member.

[0024] In some preferred examples, the connecting member tensioning system may be configured such that the blade connecting member can be slackened without necessarily requiring disconnection of the blade connecting member from the associated connecting point. For example, where the connecting member tensioning system comprises a winch, the winch may be configured such that the blade connecting member, or the winch line, can be unspooled far enough to substantially unload the blade connecting member. For example, the winch may be configured such that operation of winch reduces the tension in the blade connecting member by at least 75% of the operation tension, or more preferably by at least 90% of the operation tension, in some examples.

[0025] In some examples, each blade connecting member may be connected to the respective connecting member tensioning system via a tension lock arrangement. The tension lock arrangement may be configured to maintain a tension applied to the blade connecting member by the connecting member tensioning system. In some preferred examples, the tension lock arrangement may be remotely operable to allow for adjustment of tension in the blade connecting member remotely.

[0026] In some examples, the adjustable tension lock and the connecting member tensioning system may be jointly operable in a plurality of conditions. For example, in an active adjustment configuration the connecting member tensioning system may be operable to adjust the tension of the associated blade connecting member. In such an active adjustment configuration, the adjustable tension lock may be released, i.e. unlocked. In a passive tension configuration, the adjustable tension lock may be locked to maintain a tension applied to the blade connecting member by the connecting member tensioningsystem. With the tension lock locked, the connecting member tensioning system may be inactive, or even disconnected from the blade connecting member.

[0027] The tension lock arrangement is preferably attached to the wind turbine blade. That is to say, the tension lock arrangement is preferably attached to the same blade that the respective connecting member tensioning system is attached to.

[0028] The tension lock arrangement may also act as a safety system. For example, the tension lock arrangement may facilitate maintaining the tension in the blade connecting member if the connecting member tension system were to lose power, experience a technical issue, or fail in any other way.

[0029] In some examples, the tension lock arrangement may be integrated with another component of the wind turbine. For example, the tension lock arrangement may be integrated in an assembly with the connecting member tensioning system. As described in more detail later, in some examples the connecting member tensioning system may include a winch and / or a motor. The tension lock arrangement may be part of the winch and / or motor.

[0030] In some examples, each tension lock arrangement may comprise a locking bar comprising at least one hole. Each tension lock arrangement may further comprise at least one locking pin extending into the hole in the respective locking bar. The blade connecting member may be connected to the respective locking bar. The locking pin is preferably removably located in the hole in the locking bar such that the pin can be removed to thereby release the tension lock.

[0031] In some examples, each tension lock arrangement may comprise a locking bar comprising a plurality of sequential holes. Each tension lock arrangement may comprise at least one locking pin arranged to selectively extend into one of the plurality of sequential holes, and wherein the blade connecting member is connected to the locking bar. As such, the tension lock arrangement may comprise a plurality of locked positions dependent on the which hole the locking pin is engaged in. This means that the tension lock arrangement may facilitate locking the tension at a plurality of pre-defined tensions, by selectively engaging the locking pin in any one of the holes in the locking bar.

[0032] In some examples, the tension lock arrangement may comprise a plurality of locking pins arranged to extend into the same hole in the locking bar. As such, the tension lock arrangement may be referred to as a multi-pin locking system in some examples. Such anarrangement increases redundancy and safety for engaging at least one pin in the hole to lock the tension in the blade connecting member. In some examples, the tension lock arrangement may comprise at least one locking pin arranged to extend into the hole from one side, and at least one locking pin arranged to extend into the hole from an opposing side of the locking bar.

[0033] In some examples, the or each locking pin may be biased into a normally engaged arrangement in which the locking pin extends into a hole in the locking bar. For example, the or each locking pin may be biased into the hole in the locking bar by a spring or a magnet. The tension lock arrangement may comprise an actuator, a solenoid, a magnet, or other disengagement apparatus configured to selectively move the locking pin out of engagement in the hole, against the biasing force. For example, a solenoid may be engaged to pull the locking pin out of the hole in the locking bar and thereby release the tension lock arrangement to facilitate adjustment of the tension in the blade connecting member.

[0034] In some examples, the tension lock arrangement may comprise one or more clamps configured to clamp the blade connecting member, or an associated component, to thereby lock the tension in the blade connecting member. In some examples, the one or more clamps may be spring-loaded, and thereby biased into a normally-clamped configuration.

[0035] In some examples, each connecting member tensioning system may be located on or in a root portion of the respective blade to which it is attached. For example, the root portion of a blade may be considered to extend up to 10 m outboard of the root of the blade. In some examples, the mid portion of the wind turbine blade may include at least a portion of the root portion. Locating the connecting member tensioning system within 10 m from the root of the blade may be advantageous for facilitating access to the tensioning system for assembly and / or maintenance operations. Further, locating the connecting member tensioning system on or in a root portion of the respective blade means that the mass of the connecting member tensioning system is located closer to the hub, and to the rotor axis about which the rotor rotates during operation of the wind turbine. In some examples, the connecting member tensioning system may be located at substantially the same radial location as the connection point of a respective wind turbine blade, in relation to a rotor axis of the wind turbine.In some examples, the wind turbine may further comprise at least one active tension control system coupled between a blade connecting member and the hub to actively adjust the tension in the blade connecting member during operation of the wind turbine. In some examples, the active tension control system may be coupled to a midpoint, or substantially the middle of the respective blade connecting member. In some examples, the active tension control system may be coupled to the blade connecting member via a tension adjustment member such as a cable, wire, rope or belt. The active tension control system may be configured to vary the tension in the blade connecting member based on inputs such as wind speed, wind direction, operating mode, pitch angle and yaw angle. The active tension adjustment system may be operable to continuously vary the tension in the blade connecting member during operation of the wind turbine.

[0036] Notably, in examples including an active tension control system, the mechanism or apparatus for providing the active tension adjustment, such as a winch or actuator, may be relatively small, or underpowered compared to the connecting member tensioning system. This is because the connecting member tensioning system may be configured to apply the majority of the tension in the blade connecting member and optionally lock the length of the blade connecting member. Therefore, only a smaller, or lesser powered active tension control system may be required to effect small tension adjustments when actively controlling the tension during operation of the turbine.

[0037] In some examples, each blade connecting member may extend between a respective pair of wind turbine blades at an angle of between 10 to 40 degrees relative to a pitch axis of each blade in the respective pair of wind turbine blades. In some preferred examples, each blade connecting member may extend between a respective pair of wind turbine blades at an angle of between 20 to 30 degrees relative to a pitch axis of each blade in the respective pair of wind turbine blades. It should be understood that the pitch axis of wind turbine blade is the axis about which the blade pitches, i.e. rotates around the spanwise direction of the blade, relative to the hub. Configuring the wind turbine such that the blade connecting member extends at an angle of between 10 to 40 degrees, or preferably between 20 to 30 degrees, may be particularly advantageous in examples including an active tension control system coupled to the blade connecting member. In such an example the active tension control system may require less force to actively vary the tension in the blade connecting member.

[0038] In a highly preferred example, the blade connecting member may be substantially horizontal when the blades between which the blade connecting member extends arearranged in respective 4 and 8 o’clock positions, i.e. when the blades extend diagonally downwards. In such examples, it may be preferred that the angle between the pitch axis and the blade connecting member is 32 to 35 degrees by coning of the blades relative to the rotation axis of the rotor. This configuration was found to be particularly advantageous when the wind turbine does not necessarily include an active tensioning control system.

[0039] In some examples, each blade to which a respective connecting member tensioning system is attached may comprise an access opening through a surface of the blade proximal to the connecting member tensioning system. The access opening may facilitate access to an externally mounted connecting member tensioning system from inside the blade. In some other examples, the access opening may facilitate access to an internally mounted connecting member tensioning system from outside of the blade. Such access to the connecting member tensioning system may be advantageous for assembly and / or maintenance operations.

[0040] In some examples, the blade connecting member may be connected to the tension lock arrangement, such as to a locking bar of the tension lock arrangement, indirectly, for example via a coupling member such as a rope, wire, cable or belt. In some examples, the blade connecting member may be connected to the connecting member tensioning system indirectly, for example via a coupling member such as a rope, wire, cable or belt.

[0041] Brief description of the drawings

[0042] Examples of the present invention will now be described by way of non-limiting example only, with reference to the accompanying figures, in which:

[0043] Figure 1 is a schematic perspective view of a wind turbine comprising a hub, a plurality of wind turbine blades and a plurality of blade connecting members;

[0044] Figure 2 is a schematic perspective view of a connection point at which a blade connecting member is connected to a wind turbine blade;

[0045] Figure 3 is a schematic perspective view of an example of a connecting member tensioning system;

[0046] Figure 4 is a schematic perspective view of a different example of a connecting member tensioning system;Figure 5 is a schematic view of an example of a tension lock arrangement via which a blade connecting member may be connected to a respective connecting member tensioning system; and

[0047] Figure 6 is a schematic perspective view of an example of a wind turbine including an active tension control system coupled between a blade connecting member and the hub.

[0048] Detailed description

[0049] Figure 1 is a schematic perspective view of a wind turbine 10 comprising a rotor 12 which features a plurality of wind turbine blades 14 attached a hub 16. The blades 14 are pitchable, i.e. rotatable, about their respective pitch axes relative to the hub 16. Each blade 14 extends between a blade root 18 and a blade tip 20, and each blade 14 includes a connection point 22 located between the root 18 and the tip 20. Each connection point 22 is configured to facilitate attachment of a blade connecting member 24 to the respective blade14. It follows that the wind turbine 10 also includes a plurality of blade connecting members 24, and each blade connecting member 24 extends between a respective pair of wind turbine blades 14. Accordingly, the rotor 12 may be referred to as a cable-stayed pitchable rotor 12, in some examples. The blade connecting members 24 are configured to transfer loads between the blades 14 during operation of the wind turbine 10 and thereby reduce peak loads experienced at the root 18 of each blade 14.

[0050] Whilst it should be appreciated that the accompanying drawings are not drawn to scale, Figure 1 shows an example of a turbine 10 where each blade connecting member 24 extends between a respective pair of wind turbine blades 14 at an angle of between 10 to 40 degrees, such as 30 degrees, relative to a pitch axis of each blade 14. Each blade connecting member 24 is connected at one end to a connection point 22 of a wind turbine blade 14. The connection point 22 is located in a mid-portion 26 of the respective blade 14 between the root 18 and the tip 20. This facilitates an advantageous transfer of blade loads into the blade connecting member 24 such that some of the blade loads are diverted to bypass the root 18 of the respective blade 14. An example of a connection point 22 is shown more clearly in Figure 2.

[0051] As shown schematically in Figure 2, the blade connecting member 24 may be connected to the respective connection point 22 by a hinged or pivoting joint. This allows the blade connecting member 24 to move relative to the wind turbine blade 14 to facilitate optimal loading of the blade connecting member 24. Whilst one end of each blade connecting member 24 is connected to a respective connection point 22, the other end of therespective blade connecting member 24 is connected to a connecting member tensioning system 30. For reference, Figure 2 shows one end of a blade connecting member 24 and the other end of another blade connecting member 24.

[0052] The connecting member tensioning system 30 facilitates adjustment of the tension in the respective connecting member 24, and thereby facilitates adjustment of the proportion of blade loads loading taken up by the blade connecting member 24. The connecting member tensioning system 30 may be operated during operation of the wind turbine 10, this may be referred to as an active tension adjustment configuration. In some examples the connecting member tensioning system 30 may be operated during assembly of the wind turbine 10 or during an initial configuration phase, prior to operation of the wind turbine 10.

[0053] Each respective connecting member tensioning system 30 is attached to a wind turbine blade 14. As such, for a pair of wind turbine blades 14, the blade connecting member 24 extending between the pair of blades 14 is connected at one end to a connection point 22 of a wind turbine blade 14 and at the other end to a connecting member tensioning system 30 attached to the other blade 14 of the pair. A connecting member tensioning system 30 attached to a blade 14 may be located on or in the blade 14. For example, the tensioning system 30 may be located inside a blade shell 32 of the blade 14 as shown in Figure 2. In some other examples (not shown) the tensioning system 30 may be located on an exterior surface 34 of the blade shell 32.

[0054] The connecting member tensioning system 30 is preferably located on or in the root portion 28 of the respective blade 14 to which it is attached. For reference, the mid portion 26 of the blade 14 may include at least some of the root portion 28, in some examples. Locating the tensioning system 30 on or in the root portion 28 helps to keep mass associated with the tensioning system 30 close to the rotor axis of the wind turbine 10. Locating the tensioning system 30 on or in the root portion 28 may also be advantageous for installation, maintenance, inspection or operation of the tensioning system 30. Such a location may facilitate simple access to the connecting member tensioning system 30 from the hub 16 of the wind turbine 10.

[0055] With reference to access considerations, in some examples a blade 14 to which a respective connecting member tensioning system 30 is attached may feature an access opening 36. The access opening 36 may be provided through the blade shell 32 proximal to the connecting member tensioning system 30. This may be particularly advantageous in examples where the tensioning system 30 is attached to the exterior surface 34 of theblade shell 32. In such an example the access opening 36 may facilitate access to the tensioning system 30 from inside the blade 14, i.e. inside the blade shell 32, which may be easier and safer than traversing an exterior of the wind turbine 10 and blade 14 to reach the tensioning system 30.

[0056] Examples of a connecting member tensioning system 30 will now be described with reference to Figures 3 and 4.

[0057] Referring initially to Figure 3, in some examples a connecting member tensioning system 30 may include a winch 38. For example, the winch 38 may include a winch reel 40 which may be driven by an electric motor 42. In some examples (not shown), the associated blade connecting member 24 may be flexible, such as a belt, strap, rope or wire, and the blade connecting member 24 itself may be wound onto the winch reel 40. Accordingly, the winch 38 may be operable to spool the respective blade connecting member 24 off and onto the winch reel 40 to vary a free length of the blade connecting member 24. Varying the free length, i.e. the portion of the blade connecting member 24 which is not wound onto the winch reel 40, may vary the tension in the blade connecting member 24.

[0058] In some other examples, the blade connecting member 24 may be indirectly connected to the connecting member tensioning system 30. For example, the blade connecting member 24 may be connected to a winch line 44, and the winch line 44 may be wound onto the winch reel 40. Accordingly, the winch 38 may be operable to spool the winch line 44 off and onto the winch reel 40 to thereby vary the tension in the connected blade connecting member 24. Such a configuration may enable use of a greater range of blade connecting members 24, including substantially rigid blade connecting members 24 such as bars, rods or pultrusions. As shown in Figure 3, in some examples the winch line 44 may be routed from the winch reel 40 to the blade connecting member 24 via a pulley 46. Use of one or more pulleys 46 may offer greater flexibility for positioning the connecting member tensioning system 30 on or in the blade 14.

[0059] Figure 4 shows another example of a connecting member tensioning system 30 which is operable to adjust the tension in a respective blade connecting member 24. As shown in Figure 4, in some examples a connecting member tensioning system 30 may include a linear actuator 48. For example, the linear actuator 48 may be a hydraulic or pneumatic linear actuator 48. In some other examples the linear actuator 48 may be an electric linear actuator 48. Notably, where included, the linear actuator 48 may have a selectively variablelength. It follows that the tension in a blade connecting member 24 may adjusted by varying the length of the linear actuator 48 to which the blade connecting member 24 is connected.

[0060] The blade connecting member 24 may be directly connected to the linear actuator 48 in some examples (not shown). Alternatively, in some other examples the blade connecting member 48 may be indirectly connected to the linear actuator 48, for example via a lever arm 50 as shown in the example of Figure 4. The lever arm 50 may be attached to the wind turbine blade 14 via a pivot or hinge 52, such that the lever arm 50 can be pivoted relative to the wind turbine blade 14. The blade connecting member 24 and linear actuator 48 are preferably connected to the lever arm 50 such that extending or retracting the linear actuator 48 pivots the lever arm 50 about the pivot 52. Accordingly, the tension in the blade connecting member 24 may be adjusted by moving the lever arm 50 using the linear actuator 48.

[0061] As indicated schematically in Figures 3 and 4, in some examples the blade connecting member 24 may be connected to the respective connecting member tensioning system 30 via a tension lock arrangement 54. Where included, a tension lock arrangement 54 is configured to maintain a tension applied to the blade connecting member 24 by the connecting member tensioning system 30. An example of a tension lock arrangement 54 will now be described with reference to the schematic view in Figure 5.

[0062] For example, the tension lock arrangement 54 may include a locking bar 56, and the blade connecting member 24 may be connected to the locking bar 56. Where included, the locking bar 56 may have a plurality of holes 58, although in some examples only a single hole 58 may be required. As shown in Figure 5, in examples comprising a plurality of holes 58, such holes 58 may be arranged sequentially in the locking bar 56. This allows the bar 56 to be locked in a plurality of different positions such that the associated blade connecting member 24 can be maintained at a plurality of different tension levels.

[0063] The tension lock arrangement 54 includes a locking pin 60 which engages the hole 58 in the locking bar 56 to lock the position of the locking bar 56. The locking pin 60 may be actuated to selectively extend into a respective hole 58 in the locking bar 56 to maintain a desired tension in the blade connecting member 24. As shown in Figure 5, in some examples additional safety and redundancy may be achieved by providing a plurality of locking pins 60 arranged to extend into the same hole 58 in the locking bar 56. For example, the locking pins 60 may extend into the hole 58 from opposing sides of the bar 56.The locking pin(s) 60 of the tension lock arrangement 54 are preferably biased into a normally engaged arrangement meaning that without an additional motivation, the locking pin 60 remains engaged in the respective hole 58. For example, the locking pin 60 may be biased into engagement in the hole 58 by a spring 62 or a magnet, for example. Motivation for disengaging the locking pin 60 from the hole 58 may be provided by a solenoid, or electric motor, in some examples (not shown).

[0064] The wind turbine 10 described herein with reference to Figures 1 to 5 may be operable in a passive tension configuration. For example, as previously described, the connecting member tensioning system 30 may be operable to adjust the tension in the blade connecting member 24 and the tension lock arrangement 54 may be configured to maintain the adjusted tension in the blade connecting member 24. The wind turbine 10 may then be operated with the tension in the blade connecting member 24 maintained at a substantially constant level.

[0065] In some examples, as shown in Figure 6, the wind turbine 10 may additionally include an active tension control system 64. The active tension control system 64 may be coupled between a blade connecting member 24 and the hub 16. Such an active tension control system 64 may be operable to adjust the tension in the blade connecting member 24 during operation of the wind turbine 10. Notably, the active tension control system 64 may facilitate incremental adjustment of the tension without requiring operation of the connecting member tensioning system 30 or tension lock arrangement 54, which may remain in a passive tension configuration.

[0066] The description provided herein serves to demonstrate a plurality of possible examples of the present invention. It will be appreciated that features described in relation to any of the examples above may be readily combined with any other features described with reference to other examples without departing from the scope of the invention as defined in the appended claims.

Claims

Claims:

1. A wind turbine (10) comprising:a rotor (12) comprising a hub (16) and at least three wind turbine blades (14) which are attached to the hub and pitchable relative to the hub, wherein each blade extends between a root (18) and a tip (20), and wherein each blade comprises a connection point (22) located in a mid-portion (26) of the blade between the root and the tip; anda plurality of blade connecting members (24), each blade connecting member extending between a respective pair of wind turbine blades;wherein each blade connecting member is connected at one end to a connection point of a wind turbine blade and at the other end to a connecting member tensioning system (30) attached to the other blade of the pair of wind turbine blades.

2. The wind turbine (10) of claim 1 , wherein each connecting member tensioning system (30) comprises a winch (38), and wherein the winch is operable to spool the respective blade connecting member (24) off and onto a winch reel (40) to vary a free length of the blade connecting member.

3. The wind turbine (10) of claim 1 , wherein each connecting member tensioning system (30) comprises a winch (38) comprising a winch reel (40) and a winch line (44) wound onto the winch reel, wherein the respective blade connecting member (24) is connected to the winch line, and wherein the winch is operable to spool the winch line off and onto the winch reel to thereby vary the tension in the connected blade connecting member.

4. The wind turbine (10) of claim 3, wherein the winch line (44) is routed from the winch reel (40) to the blade connecting member (24) via at least one pulley (46).

5. The wind turbine (10) of claim 1 , wherein each connecting member tensioning system (30) comprises a linear actuator (48).

6. The wind turbine (10) of claim 5, wherein the linear actuator (48) is a hydraulic or pneumatic linear actuator.

7. The wind turbine (10) of claim 5, wherein the linear actuator (48) is an electric linear actuator.

8. The wind turbine (10) of any of claims 5 to 7, wherein the blade connecting member (24) is connected to the linear actuator (48) via a lever arm (50), wherein the lever arm is attached to the respective blade (14) via a pivot (52), and wherein the blade connecting member and linear actuator are connected to the lever arm such that extending or retracting the linear actuator pivots the lever arm about the pivot to thereby vary the tension in the blade connecting member.

9. The wind turbine (10) of any preceding claim, wherein each blade connecting member (24) is connected to the respective connecting member tensioning system (30) via a tension lock arrangement (54) configured to maintain a tension applied to the blade connecting member by the connecting member tensioning system.

10. The wind turbine (10) of claim 9, wherein each tension lock arrangement (54) comprises a locking bar (56) comprising at least one hole (58) and at least one locking pin (60) extending into the hole in the locking bar, and wherein the blade connecting member (24) is connected to the locking bar.

11. The wind turbine (10) of claim 9 or claim 10, wherein each tension lock arrangement (54) comprises a locking bar (56) comprising a plurality of sequential holes (58) and at least one locking pin (60) arranged to selectively extend into one of the plurality of sequential holes, and wherein the blade connecting member (24) is connected to the locking bar.

12. The wind turbine (10) of claim 10 or claim 11, wherein the tension lock arrangement (54) comprises a plurality of locking pins (60) arranged to extend into the same hole (58) in the locking bar (56).

13. The wind turbine (10) of any of claims 10 to 12, wherein the or each locking pin (60) is biased into a normally engaged arrangement in which the locking pin extends into a hole (58) in the locking bar (56).

14. The wind turbine (10) of any preceding claim, wherein each connecting member tensioning system (30) is located on or in a root portion (28) of the respective blade (14) to which it is attached.

15. The wind turbine (10) of any preceding claim, further comprising at least one active tension control system (64) coupled between a blade connecting member (24) and the hub (16) to actively adjust the tension in the blade connecting member during operation of the wind turbine.

16. The wind turbine (10) of any preceding claim wherein each blade connecting member (24) extends between a respective pair of wind turbine blades (14) at an angle of between 10 to 40 degrees relative to a pitch axis of each blade in the respective pair of wind turbine blades, preferably at an angle of between 32 to 35 degrees relative to a pitch axis of each blade in the respective pair of wind turbine blades.

17. The wind turbine (10) of any preceding claim, wherein each blade (14) to which a respective connecting member tensioning system (30) is attached comprises an access opening (36) through a surface (34) of the blade proximal to the connecting member tensioning system.

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