Improvements relating to wind turbine blade anti-icing systems

Abstract

A wind turbine blade comprises an anti-icing system (30) comprising an electro-thermal heating device (35) configured to provide heat to an outer surface of the blade wherein the electro-thermal heating device is connected to a power supply interface (38) of the wind turbine blade by a power supply conductor (40) and a ground conductor (44). The blade further comprises a lightning protection system (31) having a lightning protection device (56) associated with the electrically heated heating element of the heating device, said lightning protection device being connected to a lightning down conductor (50) of the lightning protection system, leading to a current transfer unit (54) configured, in use, to transfer lightning current to the rotor hub. A transient current limiting device (60) is connected in a conductive path (62) between a lightning down conductor of the lightning protection system and a ground conductor of the anti-icing system, allowing an induced parasitic current in the lightning down conductor to ground through the anti-icing system. This provides the benefit of preventing electromagnetic emissions that would otherwise interfere with electronics in the vicinity of the wind turbine. Thus, the wind turbine is allowed to comply with the established EMC standard.

Description

TECHNICAL FIELD

[0001] The present invention relates to a wind turbine blade having an anti-icing system and a lightning protection system that more effectively mitigates lightning strikes. The present invention also relates to a wind turbine comprising such a wind turbine blade. BACKGROUND OF THE INVENTION

[0002] The rate of installation of wind turbines is increasing globally, and as a result, they need to operate under a wide range of environmental conditions. Cold climates can pose particular challenges to wind turbine operation because temperatures below zero combined with a significant liquid water content in the air can cause ice to form on the wind turbine blades. Ice formation on the blades increases the mass of the blades but also reduces aerodynamic efficiency, which means that the rotor generates less torque for a given wind speed, thus affecting power generation. Another problem is that the accumulated ice may break off from the blades, which can cause damage to other equipment near the wind turbine.

[0003] Various methods are known for removing ice from wind turbine blades or preventing ice formation in the first place. For example, it is known to blow hot air into the inner cavity of the wind turbine blade to increase the blade surface temperature and thus prevent ice accumulation. However, such heating systems typically have high power consumption and in some cases may require the wind turbine to be stationary during operation, thus limiting their effectiveness.

[0004] Another known method is to incorporate one or more electrothermal heating elements beneath the surface of the wind turbine blade. WO2017 / 108064 shows an example of such a system. When power is supplied, the heating elements generate heat energy that is directly dissipated into the blade surface, which is generally a more effective way of preventing ice accumulation. One challenge with this method is that such electrothermal heating elements increase the risk of damage by lightning attachment during a lightning strike. Therefore, the electrothermal heating elements can be shielded by a metal plate in the wind turbine blade that is connected to the lightning protection system on the blade. However, the proximity between the electrothermal heating elements and the shielding panel may result in capacitive interactions, which are undesirable. Against this background, the present invention has been developed. SUMMARY OF THE INVENTION

[0005] In one aspect of the claimed invention, there is provided a wind turbine blade comprising: an anti-icing system including electrothermal heating means configured to provide heat to the outer surface of the blade, wherein the electrothermal heating means is connected to a power supply interface of the wind turbine blade via a power supply conductor and a grounding conductor; a lightning protection system having a lightning strike protection device associated with the electrothermal heating element of the heating means, the lightning strike protection device being connected to a lightning down conductor of the lightning protection system, the lightning down conductor leading to a current transfer unit configured to transfer lightning current to the rotor hub during use; and a transient current limiting device connected in the conduction path between the lightning down conductor of the lightning protection system and the grounding conductor of the anti-icing system, thereby allowing induced parasitic current in the lightning down conductor to be grounded through the anti-icing system.

[0006] This provides the benefit of preventing electromagnetic emissions that would otherwise interfere with electronic devices in the vicinity of the wind turbine. Thus, the wind turbine is allowed to comply with established EMC standards.

[0007] By connecting the lightning strike protection device to the lightning down conductor, it will be understood that the connection is in the form of an electrical connection capable of conducting lightning current from the protection device to the lightning down conductor.

[0008] In one embodiment of the invention, the lightning strike protection device may be spaced apart from the electrothermal heating element so as to form a capacitive coupling.

[0009] This provides a degree of protection for the electrothermal heating element and prevents the heating element from being damaged due to high currents caused by lightning strikes.

[0010] In another embodiment, the transient current limiting device may have a relatively low impedance value in a first electrical frequency range associated with the anti-icing system and a relatively high impedance value in a second electrical frequency range associated with lightning strikes. By way of example, the first electrical frequency range may be less than 100 Hz and the second electrical frequency may be greater than 10 kHz. In some embodiments, the ratio between the relatively low impedance value and the relatively high impedance value may be at least 1:100.

[0011] This provides the advantage of controlling the level of current transmitted to the anti-icing system and thus protecting the anti-icing system from overwhelming high currents (such as lightning) that would occur at higher frequencies.

[0012] In another embodiment, the transient current limiting device may include a resistive fuse element in the conduction path.

[0013] Advantageously, this is cost-effective to implement as it is very simple in terms of electronic components.

[0014] In another embodiment, the transient current limiting device may include a switching device in the conductive path. When the anti-icing system operates, the switching device may be operable to a closed position. Optionally, and as another example, when a lightning condition is detected and / or anticipated, the switching device may be operable to an open position.

[0015] In some embodiments, the transient current limiting device may include an inductor in the conductive path. In other embodiments, the inductor may be on the high voltage side of the switching device. Thus, the transient current limiting device may be configured to include an inductor and / or a resistive fuse element.

[0016] Thus, advantageously, the conductive path enters operation only when the anti-icing system may generate parasitic currents in the down-lead conductor. Additionally, a wind farm including several such wind turbines of the present invention may provide, for example, a detection function. If a lightning strike is detected, the protection switch may be opened to protect itself and the inductor that may deteriorate during a lightning strike.

[0017] In a further embodiment, the transient current limiting device may include a surge protection device in parallel with the switching device.

[0018] This provides an additional conductive path through which current can travel from the anti-icing system to the down-lead conductor of the lightning protection system in the event of a lightning strike on a component of the anti-icing system, and thus provides a safety function.

[0019] On the other hand, the present invention relates to a wind turbine including a wind turbine blade as described above. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Examples of the present invention will now be described with reference to the drawings, in which:

[0021] Figure 1 A wind turbine according to one aspect of the present invention is schematically shown, which includes a rotor and a plurality of variable pitch rotor blades;

[0022] Figure 2 Components of an anti-icing system and a lightning protection system integrated into the blade of the wind turbine are shown;

[0023] Figures 3a to 3c Shows connected between Figure 2 Various configurations of a transient current limiting device in the conductive path between the lightning down-lead conductor of the lightning protection system and the ground conductor of the anti-icing system. DETAILED DESCRIPTION

[0024] Specific embodiments of the present invention will now be described, in which many features will be discussed in detail in order to provide a thorough understanding of the inventive concept defined in the claims. However, it will be apparent to those skilled in the art that the present invention can be practiced without specific details, and in some cases, well-known methods, techniques, and structures have not been described in detail so as not to unnecessarily obscure the present invention.

[0025] Referring to Figure 1 , the wind turbine 10 includes a tower 12, and the top of the tower 12 supports a nacelle 13. The nacelle includes a power generation device (not shown) having a rotor 14 connected therein. The rotor 14 includes a central hub 16 and a plurality of blades 18 extending radially from the hub 16. In the example shown, the wind turbine 10 is a horizontal axis wind turbine (HAWT) having three blades 18. However, the exact architecture of the wind turbine 10 is not important for the present invention, and the present invention can be used with other wind turbine configurations. The blades 18 are connected to the hub 16 using a pitch bearing such that each blade 18 can rotate about its longitudinal axis to adjust the pitch of the blade 18.

[0026] In order for the wind turbine to operate acceptably in various weather conditions, it can be equipped with various functional systems. Two such typical functional systems in the wind turbine 10 are a blade-based anti-icing system and a lightning protection system. Generally, such systems are functionally separate. However, as described above, some electrical interactions may occur between the two systems, which are generally not desirable.

[0027] Now referring to Figure 2 , the following discussion will focus on the components of the anti-icing system 30 integrated into the blades 18 of the wind turbine 10, and also on the components of the lightning protection system 31. Figure 2 Two systems 30, 31 are shown in a schematic form with respect to an associated wind turbine blade 18 and its hub 16.

[0028] The anti-icing system 30 includes a plurality of electrical heating devices or elements 32 electrically connected to a control system 34, and the control system 34 provides control signals and power to the heating devices 32 through a power controller 33. The power controller 33 can be arranged in the blade (as Figure 2as shown), or for example arranged in the nacelle or at another location in the wind turbine 10. Arranging the controller 33 away from the blade has the advantage that only one power controller 33 can be used to control the power in all the blades 18, thus reducing costs. In the illustrated embodiment, the heating device 32 is in the form of an electric heating element. Collectively, the heating device 32 and the power controller 33 can be referred to as the blade heating device 35. Thus, the anti-icing system 30 provides a means for preventing ice from accumulating on the surface of the blade 18. To this end, the anti-icing system 30 is operable to apply heat to the blade surface using one or more heating devices 32 under various triggering conditions.

[0029] The heating device 32 can be in the form of a conductive pad, panel or liner known in the art. A suitable electric heating device is known from WO2017 / 108064, which discloses a heating device in the form of a glass fiber mat coated with conductive carbon. Although conductive, the heating device 32 has an associated resistance value. Thus, when a voltage is applied across the heating device 32, according to Ohm's law, current will flow due to the resistance of the carbon material. This results in Joule heating (also known as Ohmic heating) of the heating device, which is why they are referred to as "electrically heated" heating devices / elements. According to Joule's first law as shown in equation (1), the power generated by the heating device 32 is linearly proportional to the product of its resistance / impedance (R) value and the square of the applied current, where the resistance / impedance (R) value of the material (i.e., glass fiber and carbon) is typically a known constant.

[0030] In the illustrated embodiment, two heating devices 32 are arranged at spaced positions along the blade 18. As Figure 2 shown, the spacing of the heating devices 32 is for convenience only and does not indicate a specific spacing within the blade 18. Generally, more than two heating devices 32 can be provided, although this is not necessary, and the heating devices 32 can have an optimized spacing different from that shown here. For example, between ten and forty heating devices 32 can be incorporated in the blade 18, distributed between the windward and leeward surfaces. Certain arrangements of the heating devices 32 can be designed where less critical or vulnerable areas of the blade 18 are not provided with heating devices 32, such as the area near the blade root. However, it should be noted that at this time the positioning and spacing of the heating devices 32 are not central to the present invention, and the previous arrangements are provided only as examples. Thus, a single heating device 32 extending over a significant area of the blade 18 would also be an acceptable configuration.

[0031] Reserved Figure 2 A schematic system view for the control system 34 for the heating device 32 is coupled to the heating device 32 via the power transmission device 38 and the power controller 33. The power controller 33 can be arranged after the transmission device 38 (as Figure 2 shown) or before the transmission device 38.

[0032] It should be understood in this regard that the anti-icing system 30 is shown here only for one of the blades 18, and in practice, each blade 18 will be provided with the same or a similar arrangement. However, for clarity, a single anti-icing system 30 will be referred to in this discussion and it will be understood to cover equivalent components and functions provided in the other blades 18 of the wind turbine 10. The various electrical and electronic components mentioned above are suitably interconnected by appropriate power and control cables and / or busbars such that power and control signals can be transmitted between the respective components as required.

[0033] The power transmission device 38 is a rotational interface between the variable pitch blade 18 and the hub 16. Such a component is conventional and thus does not require a full discussion here. However, such a component typically takes the form of a slip ring arrangement that is capable of transmitting power from a nacelle- or hub-based power input and providing a power output into the structure of the blade 18 to supply power to the heating device 32. The power transmission device 38 can transmit DC and / or AC power. Typically, AC power will be transmitted as single-phase or three-phase. The control system 34 provides a positive line 40, a neutral line 42 and a ground line 44 via the power transmission device 38 and the power controller 33. The positive line 40 and the neutral line 42 are connected to the two heating devices 32 for providing an appropriate power input. The ground line 44 provides a suitable ground point for stray currents. The electrothermal heating device 35 can be connected to the power supply interface 38 of the wind turbine blade via the supply conductor 40, the neutral conductor 42 and the ground conductor 44.

[0034] The control system 34 is configured to control the power supplied to the heating device 32 to be suitable for weather conditions. The exact nature of the control method is not essential to the inventive concept. However, it can be noted that at least, the control system 34 can be configured to energize the anti-icing system 30 when it detects that icing conditions exist. This determination can be based, for example, on sensing ambient temperature conditions and the airborne liquid water content in the air, the combination of these two factors being a reliable indication of the likelihood of ice formation on the blade 18.

[0035] Continuing to refer to Figure 2 , the main components of a lightning protection system 31 for the wind turbine blade 18 are also shown. In this regard, it should be noted that lightning protection systems commonly used for wind turbine blades are known in the art, as shown in EP2282957B1, EP2770197A1 and EP3058222B1, by way of example only.

[0036] Generally speaking, the lightning protection system 31 includes a conductive cable known as the down-conductor 50, which extends generally along the span direction of the blade 18. The function of the down-conductor 50 is to provide a connection between a plurality of lightning receiver points 52 or "receivers" that penetrate the surface of the blade 18. Figure 2 Several receivers 52 are shown. The receivers 52 can take various forms depending on the desired configuration of the lightning protection system 31. For example, they can take the form of metal bolts with bolt heads flush with the blade surface. Another form of the lightning receiver 52 is a metal blade tip mounted at the outermost end of the rotor blade 18. Another example is a metal mesh embedded in the surface of the blade 18. Other receiver configurations are possible, and there can be one or more receivers 52, although typically there are several receivers 52.

[0037] The down-conductor 50 extends to the root of the blade 18 and terminates at a lightning current transfer unit 54 or LCTU. Generally, the technology associated with the LCTU is known and is disclosed, for example, in WO2013182202 A1 and WO2015051800A1, and generally relates to spark gaps or brush connections.

[0038] The lightning protection system 31 also includes a second type of receiver 52, which is a protective device or shielding device in the form of a panel 56, such as a metal mesh or a metal sheet. In the example shown, there are two protective panels 56, which cover each respective heating device 32. Thus, the protective panel 56 provides a conductive shield for the heating device 32 against the risk of lightning strikes. Thus, lightning is more likely to attach to the protective panel 56 rather than to the underlying heating device 32. Therefore, the protective panel is positioned closer to the outer surface of the blade than the heating device 32. The protective panel can be configured to cover the heating device, for example, the protective panel has dimensions in the span direction and the chord direction and is positioned such that the extensions in the chord direction and the span direction are greater than the corresponding extensions of the heating device.

[0039] The protective panel 56 can be of any suitable configuration to achieve the shielding function. However, it is envisaged that a metal mesh will be particularly suitable for the required function. Examples of suitable lightning protection meshes can be understood from EP22820571 A1 and WO2022057990 A1.

[0040] It should be understood that the proximity of the protection panel 56 to the heating device 32 at this time creates a capacitive effect. Thus, when the anti-icing system 30 is operable, the alternating current voltage that drives the heating of the heating device 32 will induce parasitic currents in the protection panel 56, which will cause current to flow through the down-conductor 50 to the LCTU 54. The sliding / moving connection at the LCTU 54 between the blade 18 and the hub 16 means that the induced current in the down-conductor 50 will create an arc at the interface, and this phenomenon can generate electromagnetic emissions that can cause interference to the electronics near the wind turbine 10. Since industrial systems such as the wind turbine 10 need to comply with established EMC standards, the electromagnetic emissions at the LCTU 54 are not desirable.

[0041] To prevent this, Figure 2 the arrangement shown in includes a conductive path or bridge 60 that extends between the down-conductor 50 of the lightning protection system 31 and the ground wire 44 of the anti-icing system 30. The conductive path 60 provides a low-impedance path for conducting parasitic currents from the down-conductor 50 to the ground wire 44 of the anti-icing system 30 in the typical frequency range of anti-icing system operation (i.e., below about 100 Hz).

[0042] To protect the anti-icing system 30 from the overwhelming high currents that occur at the higher frequencies (10 kHz and above) inherent in lightning strikes, the conductive path 60 includes a transient current limiting device 62. Advantageously, the transient current limiting device 62 has a relatively low impedance at a first electrical frequency associated with the anti-icing system 30, such as below about 100 Hz, and a relatively high impedance in a second electrical frequency range associated with lightning strikes, such as from 10 kHz and above.

[0043] The impedance established by the transient current limiting device 62 in the two frequency ranges is determined to block the current passing through the conductive path 60 at relatively high frequencies, as defined herein, but to allow the flow of relatively low-frequency currents. It is contemplated that the minimum ratio of the impedance between the above-mentioned low-frequency range and high-frequency range should be 1:100.

[0044] The transient current limiting device 62 can be configured in various ways. Some example configurations are shown in Figures 3a to 3c in.

[0045] First, referring to Figure 3a, the transient current limiting device 62 is shown to be implemented by a resistive fuse element 64. The resistive fuse element 64 can be selected to have an appropriate resistance so as to open circuit when a current at a predetermined level flows through the downlead conductor 50. Thus, in the relatively low frequency range of the parasitic current and the corresponding low current amplitude, the resistive fuse element 64 allows current to flow through the conduction path 60 to the ground wire 44 of the anti-icing system 30 because it presents a low impedance path. In contrast, at relatively high frequencies and the corresponding high currents associated with lightning strikes, the resistive fuse element 64 is configured to blow, thus opening the circuit and presenting a very high impedance to the current.

[0046] The advantage of this solution is that it is cost-effective to implement as it is simple in terms of electronic components. However, once the resistive fuse element 64 has blown, it will need to be replaced, which limits its practicality as a solution, especially for wind turbines located remotely, such as most offshore wind turbines.

[0047] Figure 3b A second example is shown in which the conduction path 60 includes an inductor 66. In this example, the conduction path 60 also includes a protection switch 70. The protection switch 70 and the inductor 66 are connected in series in the conduction path 60. It can be understood from the figure that the inductor 66 is coupled to the protection switch 70 on the high voltage side of the protection switch 70. That is, the inductor 66 is connected between the conduction path 60 and the protection switch 70. In this example, the inductor 66 is in the following position in the conduction path 60: in this position, the inductor 66 is located on the side of the switch closer to the downlead conductor 50. In other words, the inductor 66 is located on the high voltage side of the switch 70.

[0048] The protection switch 70 is controlled by the anti-icing system 30 to be configured to the closed position when the anti-icing system 30 is operating and to the open position when the anti-icing system 30 is not operating. Thus, advantageously, the conduction path 60 only enters operation when the anti-icing system 30 can generate parasitic current in the downlead conductor 50. Although there is only a small probability of lightning when there are icing conditions, disconnecting the protection switch 70 in this way provides an additional safety measure.

[0049] A simple on / off state that depends on the operating state of the anti-icing system 30 is an example of an operating logic that can be applied to protect the operation of the protection switch 70. Additional logic can be used to enhance the operation of the protection switch 70. For example, in one enhancement of the functionality, suitable logic can be provided to configure the protection switch 70 to the open position where a lightning strike has been detected or is expected near the wind turbine 10. A wind power plant that includes a number of such wind turbines 10 can provide a detection function, for example. If a lightning strike is detected in one of the wind turbines in the wind power plant, the protection switch 70 can be the wind turbine that is opened to protect the anti-icing system 30 and the inductor 66 that may deteriorate during the lightning strike. In addition to detecting lightning, the protection switch 70 can be configured to open when lightning is expected or predicted, which can be achieved in various ways, for example, based on atmospheric conditions. For example, a monitoring system can be configured to measure environmental factors such as pressure, temperature, liquid water content, and even weather forecast data to evaluate the lightning conditions.

[0050] The characteristics of the inductor 66 can be appropriately selected to provide the required functionality as specified above. Without wishing to be bound by theory, it is believed that an inductor value between 50 μH and 1000 μH provides this suitable range. In principle, a variable inductor can be used so that the function of the transient current limiting device 62 can be adjusted.

[0051] Figure 3c Another example is shown in. Figure 3c The form of the transient current limiting device 70 shown in is similar to Figure 3b the form in, because it includes a conductive path 60 that includes a protection switch 70 and an inductor 66. Therefore, the discussion above about Figure 3b is also relevant here.

[0052] However, Figure 3c the example of has a second conductive path 74 that is parallel to the first conductive path 60 mentioned. In this example, the second conductive path 74 includes a surge protection device 76. The surge protection device 76 provides an additional conductive path through which current can travel from the anti-icing system 30 to the down conductor 50 of the lightning protection system 31 in the event of a lightning strike on a component of the anti-icing system 30. Therefore, the surge protection device 74 provides a safety function.

[0053] As a further explanation, consider the case where the anti-icing system 30 is in operation such that the protection switch 70 is closed and the environmental conditions are such that a lightning strike is possible. As described above, the protection panel 56 protects the corresponding underlying heating device 32 from lightning strikes. However, in the unlikely case where lightning does attach to the heating device 32, the electronics of the anti-icing system 30 should desirably be protected from damage by the lightning current, as is the case with other electronics of the wind turbine. However, inFigure 3c In the example of, the conductive path 60 not only provides a route for the parasitic current from the down-conductor 50 to the ground wire 44 of the anti-icing system 30, but also the second conductive path 74 provides a route for the lightning current to travel to the lightning protection system 31 via the surge protection device 76.

[0054] As will be understood by those skilled in the art, known surge protection devices 76 for industrial electronic devices can conduct and divert current with a very fast response time, thus protecting sensitive electronic devices. As is known to those skilled in the art, the surge protection device 76 includes appropriately configured components, such as metal oxide varistors, resistors, and capacitors, in order to provide sufficient current handling during a lightning strike. Within the scope of those skilled in the art, the operating parameters of the surge protection device 76, such as voltage rating, current rating, and response time, are configured to suit the application. As a non-limiting example, suitable surge protection devices 76 are available from Raycap GmbH, for example, the "Strikesorb" 80 series of the device.

[0055] Figure 3b and Figure 3c The examples shown in are particularly beneficial for wind turbines located remotely because their operation is not adversely affected by lightning strikes on the lightning protection system 31.

[0056] In the above discussion, various modifications and variations of the shown examples have been introduced. However, those skilled in the art will understand that other changes can be made without departing from the inventive concept defined by the claims.

Claims

1. A wind turbine blade, comprising: An anti-icing system (30) comprising an electrothermal heating device (35) configured to provide heat to an outer surface of a blade, wherein the electrothermal heating device is connected to a power supply interface (38) of the wind turbine blade via a power supply conductor (40) and a ground conductor (44), A lightning protection system (31) having a lightning strike protection device (56) associated with the electrothermal heating element (32) of the heating device (35), the lightning strike protection device being connected to a lightning down conductor (50) of the lightning protection system, the lightning down conductor leading to a current transfer unit (54) configured to transfer a lightning current to a rotor hub (16) in use, and a transient current limiting device (62) connected in a conductive path (60) between the lightning down conductor (50) of the lightning protection system and the grounding conductor (44) of the anti-icing system, thereby allowing an induced parasitic current in the lightning down conductor (50) to be grounded through the anti-icing system (30).

2. The wind turbine blade according to claim 1, wherein: The lightning strike protection device is spaced apart from the electrothermal heating element so as to form a capacitive coupling.

3. A wind turbine blade according to claim 1 or 2, wherein: The transient current limiting device (62) has a relatively low impedance value within a first electrical frequency range associated with the anti-icing system and a relatively high impedance value within a second electrical frequency range associated with lightning strikes.

4. The wind turbine blade according to claim 3, wherein: The first electrical frequency range is less than 100 Hz.

5. A wind turbine blade according to claim 3 or 4, wherein: The second electrical frequency range is greater than 10 kHz.

6. A wind turbine blade according to any one of claims 3 to 5, wherein: The ratio between the relatively low impedance value and the relatively high impedance value is at least 1:

100.

7. A wind turbine blade according to any one of the preceding claims, wherein: The transient current limiting device (62) includes a resistive fuse element (64) in the conductive path (60).

8. A wind turbine blade according to any one of claims 1 to 6, wherein: The transient current limiting device (62) includes a switching device (70) in the conductive path (60).

9. The wind turbine blade of claim 8, wherein: The switch device (70) is operable to a closed position when the anti-icing system is in operation.

10. A wind turbine blade according to claim 8 or 9, wherein: The switch device (70) is operable to an open position when a lightning condition is detected and / or anticipated.

11. A wind turbine blade according to claims 8 to 10, wherein: The transient current limiting device (62) includes an inductor in the conductive path (60).

12. A wind turbine blade according to any one of claims 8 to 11, wherein: The inductor (66) is on the high voltage side of the switching device (70).

13. A wind turbine blade according to any one of claims 8 to 12, wherein: The transient current limiting device (62) includes a surge protection device (76) connected in parallel with the switching device (70).

14. A wind turbine comprising a rotor hub to which is attached at least one wind turbine blade according to any one of the preceding claims.

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