WO2009001310A1

WO2009001310A1 - Method and apparatus for determining the angular position of the rotor on a wind turbine

Info

Publication number: WO2009001310A1
Application number: PCT/IB2008/052547
Authority: WO
Inventors: Troels Friis Pedersen
Original assignee: Danmarks Tekniske Universitet
Priority date: 2007-06-28
Filing date: 2008-06-25
Publication date: 2008-12-31

Abstract

The present invention relates to a method and apparatus for determining an angular position of a rotor of a wind turbine. The method comprises the steps of rotating at least three acceleration sensors (16), which are situated at a distance from the rotor centre axis, around the rotation axis (4) of the rotor (2) in accordance with the rotation (5) of said rotor (2), and measuring the acceleration, said at least three acceleration sensors (16) are mounted tangentially or radially or in any intermediate tilted position between tangentially and radially on the rotor in equidistant angular positions, converting the measured accelerations to input signals for computing the relationship between said inputs from said at least three acceleration sensors to determine the direction of gravity as a reference position of the rotor (2), and on basis of the measured accelerations from said acceleration sensors and said computed relationship calculating the angular position of the rotor.

Description

Method and apparatus for determining the angular position of the rotor on a wind turbine .

Modern wind turbines build within the last years have variable rotational speed that results in the best overall performance of the wind turbine. Many loads on the wind turbine depend on the rotational speed and also on the angular position of the rotor. Therefore, angular position measurements of the rotor are regularly performed on wind turbines.

Traditionally, the angular position of the rotor of a wind turbine has been determined by measuring the angular position directly on e.g. the main shaft of the wind turbine using mechanical or optical sensors. For obvious reasons, such sensors need to be in the vicinity of the main shaft or directly in line with the main shaft axis.

From European patent application EP 1 783 036 A2 is known a traditional angular measurement system where angle measurement devices are engaged to a shaft by a teethed connection, in this case for a steering wheel for a car. Although the dimensions are smaller, the same principle is used in a large variety of angle measurement systems. Such systems are restricted to be placed in the utmost vicinity of the shaft or rotor of which the angular position is sought. Furthermore, this system is to a high extend dependent on lubrication because wear and tear will render the teeth less accurate. For wind turbines, having a main shaft diameter of approximately 1 meter such a teethed system needs to be of a robust construction and may therefore be both heavy and expensive.

As it is necessary for the measurement equipment to be close to either the main shaft or the wind turbine gearbox for measuring the rotation, the system described in the above mentioned patent application has great limitations concerning the placement and positioning of these systems. Additionally, angular position is measured for other reasons than loads. The spinner anemometer disclosed in European patent EP 1 733 241 Bl uses an angular position measurement for determination of wind as seen by a wind turbine. The spinner anemometer is described i detail in three papers: "Spinner Anemometry - an Innovative Wind Measurement Concept", Troels Friis Pedersen et al . , May 2007, EWEC2007, "Aerodynamics and Characteristics of a Spinner Anemometer", Troels Friis Pedersen et al., August 2007, TWIND2007, and "Operational Experiences with a Spinner Anemometer on a MW Size Wind Turbine", Troels Friis Pedersen et al . , March 2008, EWEC2008.

From US patent application US2004/0083811 Al and International patent application WO2007/104585 Al it is evident that measurement of angular speed and rotor position parameters can be made by measurement of the acceleration due to gravity with the use of accelerometers . In both patent applications these measurements are indicated to be measured from the centre of the rotating shaft or wheel with two orthogonal measurement directions. Due to this measuring location in these known systems the centrifugal or angular accelerations do not influence on the measurements, and the direction of gravity can be determined without the influence of centrifugal or tangential accelerations. However, if the sensors were moved away from the centre of the axis of the rotation shaft or wheel, this would no longer be the case, and one or both of the sensors would be influenced by the centrifugal or tangential accelerations, and determination of the direction of gravity as a reference position for establishing the angular position of the rotor, would be disturbed. Furthermore, the mere size of the today's wind turbines is a problem because the main shaft are such large constructions of e.g. 1 meter or more in diameter, that the necessity of either teeth or reflection point for an optical sensor is an expensive feature to manufacture. A further problem of having the sensors positioned along the centre of the shaft is that many other items have this position as the preferred position, for instance hydraulic systems or controller unit items, leaving limited space for the sensors. The dimensions of todays wind turbines are considerable and the cost for wiring and fitting equipment into them are constantly increasing due to their size. Therefore, sensors must be placed at locations that are well suited for protection and easy access and such accessibility puts hard restrains on the design of the surrounding equipment.

Furthermore, more and more focus is on placing wind turbines at geographical locations which minimize the visual and audio pollution effect of the wind turbines. This means that wind turbines are often positioned in places where it may be problematic and difficult to provide access e.g. at sea, which in turn requires a high standard for robustness, durability and for backup systems for the measuring instruments used in the wind turbine.

Instruments in wind turbines placed offshore, must especially be adapted to withstand the salty environment, which may be extremely aggressive and destructive. Thus, expensive special preventive measures must be taken e.g. placing the equipment in sealed boxes of stainless steel etc. Such special arrangements are difficult to mount on existing equipment and makes it expensive, difficult and time consuming to provide service and maintenance .

Thus, there is a need for an angular positioning system that requires a minimum of space and could be located at a distance from the main shaft without direct physical or visual contact to the main shaft of the wind turbine. In this context there is a need to determine an undisturbed reference position that is not influenced by centrifugal or tangential accelerations.

It is a first aspect of the present invention to provide a method for measuring angular position and an angular measuring apparatus that is located at a distance from the rotor centre axis .

It is a second aspect of the present invention to provide a method and apparatus for measuring angular position that are capable of determination of a constant and accurate reference position for monitoring of the angular position of a wind turbine rotor.

It is a third aspect of the present invention to provide a method and an apparatus for angular measurement where the apparatus can be mounted on the spinner of a wind turbine.

It is a fourth aspect of the present invention to provide a method and apparatus for angular measurement where the apparatus can be integrated into a spinner anemometer.

It is a fifth aspect of the present invention to provide an apparatus for angular measurement that is simple to adapt and install on the spinner of an existing wind turbine already in use .

It is a sixth aspect of the present invention to provide an apparatus for angular measurement that is reliable during use.

The novel and unique way whereby this is achieved according to the present invention is a method for determining an angular position of a rotor of a wind turbine comprising the steps of rotating at least three acceleration sensors, which are situated at a distance from the rotor centre axis, around the rotation axis of the rotor in accordance with the rotation of said rotor, and measuring the acceleration, said at least three acceleration sensors are mounted tangentially or radially or in any intermediate tilted position between radially and tangentially on the rotor in equidistant angular positions, converting the measured accelerations to input signals for computing the relationship between said inputs from said at least three acceleration sensors to determine the direction of gravity as a reference position of the rotor, and - on basis of the measured accelerations from said acceleration sensors and said computed relationship calculating the angular position of the rotor.

As the method uses at least three acceleration sensors situated at a distance from the rotor centre axis, and which rotates around the rotation axis of the rotor, it is possible to compute the angular position without having to use measurement equipment that is in direct physical or visual contact with the drive shaft of the wind turbine. This eliminates mechanical wear and tear, periodical service operations such as lubrication that are unavoidable during operation of angular measurement equipment that is in mechanical communication with the drive shaft.

Furthermore, as there is no need for visual communication to the drive shaft the acceleration sensor is not restricted to be positioned or located inside the nacelle. This would make it more convenient to retrofit an acceleration sensor to an existing wind turbine, as the drive shaft is enclosed in a housing which would have to be modified to fit a mechanical or visual acceleration sensor.

The above-mentioned method is thus performed using at least three acceleration sensors and a small computer circuit computing the reference position and the angular position of the rotor. Both the sensors and the computer circuit are commonly used equipment in alternative applications and can be found in a large variety of form and arrangements in a quality that complies with the requirements of the specific location. It is possible to use the method in a large variety of wind turbines as well as other applications. Due to the fact that the method is almost non-reliant on specific constructional features of the physical equipment of a specific wind turbine, means that the method is simple and easy to use in both existing wind turbines and new wind turbines.

In a preferred embodiment of the present invention the method for determining the angular position of a rotor of a wind turbine can record the input signal for the computer circuit continuously during the rotation of the rotor thereby providing the measured accelerations as sinusoidal recordings, overlayed tangential and centrifugal accelerations, of magnitude of said measured acceleration.

The measured sinusoidal recordings, overlayed tangential and centrifugal accelerations, from the acceleration sensors enable the constant determining of the reference position, from which the angular position of the rotor is determined. It is important to understand that when a wind turbine rotor is rotating at a constant velocity the acceleration measured by the acceleration sensor is the acceleration due to gravity and not the acceleration of the sensor itself and/or the rotor.

The current invention also provides for an apparatus for determining the angular position of a rotor of a wind turbine comprising, at least three acceleration sensors situated in equidistant angular positions on the rotor at a distance from the rotor centre axis and rotating according to the rotor of said wind turbine, which acceleration sensors are mounted tangentially or radially or in any intermediate tilted position between tangentially and radially on the rotor, and a computer circuit which on basis of the measured accelerations from said acceleration sensors determines the direction of gravity as a reference position, and derives the angular position of the rotor.

Acceleration sensors are robust and reliable measurement instruments and therefore are the measurements of the acceleration very reliable. Furthermore, it is possible to construct and assemble the computer circuit in such a way that it is reliable in almost any environment.

It is further an advantage that these sensors and computer circuits could be designed and produced to the specific use with a wind turbine, where the production could be achieved at very low cost and could be easily produced by a large variety of manufacturers.

In a preferred embodiment the at least three acceleration sensors can be mounted at a distance from the rotor centre axis on a spinner or a hub of a wind turbine or on a body fixed to the rotor of the wind turbine.

The spinners on modern wind turbines are large structures and may therefore be an advantageous location on the wind turbine where the acceleration sensor is easy to install. The installation requires a minimum of special tools because the working space in the spinner is easily accessible, and at a location at a distance from the shaft or the shaft centre.

In a further preferred embodiment the at least three acceleration sensors are mounted at equidistant angles around the rotation axis of the rotor and at the same distance from the rotor centre axis or main shaft of the wind turbine.

The further away from the main shaft of the wind turbine the acceleration sensors are mounted the better the sensor is in measuring the tangential acceleration due to acceleration of the rotor and the centrifugal acceleration due to the rotational speed of the rotor, as the actual velocity of the rotor increases in a direction away from the rotational axis. The tangential acceleration and the centrifugal acceleration are important factors in determination of the exact reference position as the acceleration sensor measures the total acceleration affecting the sensor and not just the gravity acceleration. The effects of the tangential acceleration and the centrifugal acceleration in determination of the reference position have to be removed, as explained in the following. The acceleration sensors are preferably mounted at the same distance from the rotor shaft axis and at substantially equidistant angles around said rotor shaft axis. The acceleration sensors are also oriented with substantially the same tilt angle relative to the periphery at which they are mounted. This means that the centrifugal acceleration and the tangential acceleration on each acceleration sensor does influence on the measurement of the gravity acceleration in the same way. Typically, the acceleration sensors and the computer circuit are mounted to the spinner in a small housing, such as a box or similar. Such a box could be fixed to the spinner by various means, such as adhesive means, screws or similar, or it could be fixed to a spinner anemometer sensor.

In a preferred embodiment of the present invention the at least three acceleration sensors may be integrated into a spinner anemometer that during use rotates according to the rotor.

Due to the small physical size of acceleration sensors the acceleration sensor can be integrated into spinner anemometers. For obvious reasons, such anemometers need to be a rotating spinner anemometer such as the anemometer described in EP 1 733 241 Bl. The described anemometer is placed in an appropriate location and has the sufficient physical space to house the acceleration sensor and the computer circuit. Furthermore, such anemometers are fully adapted to withstand the harsh environment in and around the spinner. To simplify the acceleration measurements the at least three acceleration sensors can be at least one-dimensional accelerometers .

By using one-dimensional accelerometers it is achieved that the computation by the computer circuit is minimized. Since the result from a one-dimensional accelerometer just measures the acceleration in one direction there are no excessive results to leave out of the computing in the circuit.

When three or more accelerometers are used for measuring the acceleration it is possible to eliminate the effects that occur if the rotational velocity of the rotor is decreasing, (decelerating and thus having a negative tangential acceleration) , or increasing, (accelerating, thus having a positive tangential acceleration) . If just one accelerometer were used, the accelerometer measuring the acceleration due to gravity would register an increased positive effect if the rotor is accelerating and a decreased negative acceleration if the rotor were decelerating. This results in a less accurate determination of the reference position of the gravity, and the angular positioning measurements of the rotor if the rotor is decelerating or accelerating. However, using three accelerometers it is possible to eliminate the contribution from the tangential acceleration, simply because the sum of the contribution from total acceleration subjected to the three accelerometers mounted at equidistant angles around the rotation axis of the rotor, is zero. Thus, despite an acceleration or deceleration of the rotor it is still possible to achieve accurate measurements from the accelerometer and thereby computing an accurate angular position of the rotor.

Furthermore when three or more accelerometers are mounted radially and used for measuring the acceleration it is possible to eliminate the effects that occur from the rotational velocity, i.e. the centrifugal acceleration. If just one accelerometer were used, the accelerometer measuring the acceleration due to gravity would register an increased positive effect which would increase with increased rotational velocity. However, using at least three accelerometers it would in this case also be possible to eliminate the contribution from the radial acceleration, and to achieve an accurate determination of the reference gravity position.

When three or more accelerometers are mounted in an orientation between a tangential or a radial orientation it is also possible to eliminate the effects that occur from rotational velocity and rotational acceleration. By using three or more accelerometers it would be possible to eliminate the contributions from tangential acceleration and the centrifugal acceleration, and to achieve an accurate determination of the reference gravity position.

In yet another embodiment of the apparatus the acceleration measured by the acceleration sensors and computed by the computer circuit may be used to determine the angular position of a rotor on a wind turbine, whereby the angular position is achieved by an apparatus that requires very little space and is very robust .

The apparatus may further be used for determining the angular position of an anemometer mounted on the spinner of a wind turbine. In order to determine the angle of which the wind attacks the rotor using spinner anemometers, it is necessary to know continuously at which angular position the anemometer is located. Using the apparatus according to the present invention to do so ensures that the measurement is accurate if the distance between the apparatus of the present invention and the anemometer are known. In yet another preferred embodiment the apparatus can be mounted in an anemometer for measuring the angular position of the anemometer mounted on the spinner or hub of a wind turbine.

If the apparatus of the present invention is mounted on or inside a spinner anemometer the apparatus is in the same position as the spinner anemometer which thereby saves time for calculating the distance between the anemometer and the apparatus according to the invention, as there is no distance between the two. Furthermore, the additional time needed for attaching the apparatus according to the present invention to the spinner or rotor, is eliminated as the apparatus is attached along with the anemometer.

It should be obvious to the person skilled in the art, that the above-described embodiments are just a few of many apparatuses and methods which can be implemented within the scope of the current invention.

By the above described method and apparatus it is achieved that no visual or physical contact is necessary between the measuring device and the main shaft.

The invention will now be described in the following by way of example only with reference to the drawing, in which

Fig. 1 shows a perspective view of a wind turbine with a rotor having three acceleration sensors,

Fig. 2 shows an enlarged view of the rotor shown in figure 1 having left the wings out,

Fig. 3 shows a schematically indicated acceleration sensor mounted in a spinner anemometer, Fig. 4 shows schematically a cross sectional view of the spinner shown in figure 1 with an indication of the placement of the acceleration sensors, and

Fig. 5 shows schematically the magnitude of acceleration measured by one of the at least three acceleration sensors.

Figure 1 shows a perspective view of a wind turbine 1 having a rotor 2 with a spinner 3. The rotor 2 and the spinner 3 are rotating around the rotational axis 4. The rotational axis 4 defines the centre axis of both the spinner 3, the rotor 2 and the main shaft (not shown) . The direction of rotation is indicated by the dashed arrows 5. The wind turbine 1 further comprises three wings 6 mounted on a hub (not shown) , a nacelle 7 and a tower 8. The spinner 3 is in this case covering the hub (not shown) however the spinner could also be mounted in front of the hub (as will be shown in fig. 2) .

Figure 2 shows an enlarged view of the rotor 2 and the main shaft 8. The wings 6 of figure 1 are not shown and therefore only the hub 9 and the circular wing flanges 10 are shown. The centre of each of the circular wing flanges 10, are all located in a wing plane 11 orthogonal to the rotor rotation axis 4.

Parallel to the wing plane 11 are two of three spinner anemometers 12, which are mounted angularly spaced apart at angles of 120° on the spinner 3 in an anemometer plane 13. A third spinner anemometer is not visible in this figure.

Figure 3 shows a cross sectional view of a fraction of the spinner 3 around an anemometer 12. The anemometer 12 is mounted in the spinner 3 thereby having an outer sensor part 14 and an inner box 15. An accelerometer 16 is mounted inside the box 15 of the spinner anemometer 12. Mounting the accelerometer 16 and the computer circuit 17 (not shown) inside the box 15 ensures that they are protected against the surrounding environment.

Furthermore, the anemometer 12 is sending information to a central computer (not shown) either wireless or by wire (not shown) and therefore it is not necessary to draw additional wiring for the accelerometer 16 and the computer circuit 17. Placing the accelerometer in the box 15 further results in the advantage that a precise determination of the angular position of the accelerometer 16 as a consequence results in a precise positioning of the anemometer 12.

If the accelerometer 16 and the circuit 17 were placed outside the box 15 this would not imply any major complications.

However, in order to know the angular position of the anemometer 12 it would be necessary to determine the location of the accelerometer 16 in relation to the anemometer.

Furthermore, the accelerometer 16 could be as small as e.g. 0,5 cm² and therefore it might be beneficial for it to be mounted on or in a plate or box that would ease the orientation of the accelerometer. The anemometer 12 necessitates the same orientation but is in itself a larger structure that is more easily oriented. Therefore, placing the accelerometer 16 in the box 15 would ease the final adjustment of the accelerometer when mounting it in the spinner 3.

Figure 4 shows a schematic representation of three accelerometers 16_A1, 16_A2, 16_A2 placed in the anemometer plane 13 shown in figure 2. The three accelerometers 16 are one- dimensional accelerometers measuring the gravitational acceleration g and the tangential acceleration they are subjected to in said one dimension.

The three accelerometers will measure a signal during rotation A₁₅A₂₅A₃. These signals do not by themselves indicate the reference position of the gravity. When the components of tangential and centrifugal accelerations are taken into account the reference position of the gravity φ₀ is determined accurately and the rotor position φ is calculated without error. The accelerometer signals are assumed to have the following components with respect to the reference position of gravity (accelerations due to vibrations are not considered) :

A₁=Bcos(^₀ -β) + A_t sinβ+ A_c cosβ

A₁ = B cos(φ₀ - β + 2π / 3) + A_t sin β + A_o cos β

A₃ = B cos(φ₀ - β + 4π / 3) + A_t sin β + A_o cos β

A₁ is the tangential acceleration and A₀ is the centrifugal acceleration, which with this procedure are eliminated in determination of the reference position of the gravity by using all three accelerometers 16_A1, 16_A2, 16_A2. β is the tilt angle of the accelerometer sensors. In case the accelerometers are mounted in a tangential orientation this tilt angle is zero and in case the accelerometers are mounted in a radial orientation this tilt angle is 90°. In figure 4 the tilt angle is shown for a tangential orientation, where the tilt angle is zero.

This elimination is due to the fact that having the accelerometers 16_A1, 16_A2, 16_A2 placed at equal distances from the rotor centre the tangential acceleration component A_t is equally affecting all accelerometers 16 and therefore it is possible to determine that a tangential acceleration is present. Similarly, the centrifugal acceleration component A₀ is equally affecting all accelerometers 16 and therefore the relations between them are unaffected.

The correct reference position of the gravity acceleration <p₀ is, with this procedure, determined from the three one- dimensional acceleration measurements by:

COS(^₀ -β) = (A₂-A₃)/(V3fi) sin(φ_o - β) = (2A₁ - A₂ - A₃) /(3B)

ύn(φ_o - β) φ_o = Atan( ) + β cos(φ₀ -β)

When the correct reference position of the gravity acceleration φ₀ on the rotor is known then the rotor position, as defined relative to the fixed nacelle, can be calculated. If the rotor position is defined relative to vertical, for example, the rotor position is calculated as:

φ= φ_o+π

Figure 5a - 5f shows one accelerometer 16 during its rotation 5 around the rotation axis 4. In the following, the rotation velocity around the rotation axis 4 is considered to be constant. The arrow A indicates the direction measurement by the accelerometer. It is important to notice that the size of the arrow does not indicate the magnitude of the measurement. It is further important to notice that the accelerometer does not at least directly measure the acceleration of the rotor 2 (not shown) but measures the result of the gravity g affecting the accelerometer 16, as the rotational velocity is constant.

Figure 5a shows the accelerometer 16 in a first position in which the acceleration measured is orthogonal to the gravity g. Since the accelerometer 16 is one-dimensional the accelerometer 16 will experience no acceleration.

Figure 5b shows that the rotor is rotated to a second position and the accelerometer 16 is therefore no longer orthogonal to the gravity g. Therefore, an acceleration will be experienced by the accelerometer 16. Because the accelerometer 16 is still slanted in relation to the gravity g the magnitude of the acceleration is not maximal. Figure 5c shows a third position of the accelerometer 16 during the rotation of the rotor in which an accelerometer 16 experiences the maximal acceleration. This is due to the fact that the measurement axis of the accelerometer 16 in this position is parallel to the gravity g.

Figure 5d shows a fourth position of the accelerometer 16 in which the axis of measurement of the accelerometer 16 is slanted similar to the second position described in figure 5b. Though the accelerometer 16 in the fourth position is turned 90° compared to position two in figure 5b the magnitude of the acceleration experienced by the accelerometer 16 would be the substantially the same in both positions.

Figure 5e shows the accelerometer in a fifth position in which the measurement axis of the accelerometer is orthogonal to the gravity g. Similar to the position in figure 5a the acceleration experienced by the accelerometer 16 is zero.

Figure 5a - 5f shows the rotation of one accelerometer and it is worth noting that in order to determine whether the accelerometer is en e.g. first or second quadrant is not possible. However, if a memory or storage is built into the computer circuit (not shown) and two successive measurements are compared it is possible to determine in which quadrant the accelerometer is positioned.

It should be obvious to the person skilled in the art that within the scope of the invention the number of accelerometers can be more than three and that their distance from the rotor centre axis may be adjusted in dependency of the size of the wind mill and environmental conditions. The above description and the figures should therefore only be used as example embodiments .

Claims

Claims :

1. A method for determining an angular position (φ) of a rotor (2) of a wind turbine (1) comprising the steps of: - rotating at least three acceleration sensors (16), which are situated at a distance from the rotor centre axis, around the rotation axis (4) of the rotor (2) in accordance with the rotation (5) of said rotor (2), and measuring the acceleration, - said at least three acceleration sensors (16) are mounted tangentially or radially or in any intermediate tilted position between tangentially and radially on the rotor in equidistant angular positions, converting the measured accelerations to input signals for computing the relationship between said inputs from said at least three acceleration sensors to determine the direction of gravity as a reference position of the rotor (2 ) , and on basis of the measured accelerations from said acceleration sensors and said computed relationship calculating the angular position of the rotor.

2. A method for determining the angular position of a rotor

(2) of a wind turbine (1) according to claim 1, wherein the input signals are recorded continuously during the rotation of the rotor (2) thereby providing the measured accelerations as sinusoidal recordings of magnitude of said measured acceleration.

3. An apparatus for determining the angular position φ of a rotor (2) of a wind turbine (1) comprising, at least three acceleration sensors (16) situated in equidistant angular positions on the rotor at a distance from the rotor centre axis and rotating according to the rotor (2) of said wind turbine (1), which acceleration sensors are mounted tangentially or radially or in any intermediate tilted position between tangentially and radially on the rotor, and a computer circuit (17) which on basis of the measured accelerations from said acceleration sensors (16) determines the direction of gravity as a reference position, and derives the angular position (φ) of the rotor (2) .

4. An apparatus according to claim 3, wherein the at least three acceleration sensors (16) are mounted on a spinner

(3) or a hub (9) of the wind turbine (1) or on bodies fixed to the rotor (2) of the wind turbine (1) .

5. An apparatus according to any of the claims 3 or 4 wherein said at least three acceleration sensors (16) is integrated into a spinner anemometer (12) that during use rotates according to the rotor (2) .

6. An apparatus according to any of the preceding claims 3, 4 or 5 wherein the at least three acceleration sensors (16) are at least one-dimensional accelerometers .

7. Use of an apparatus according to any of the preceding claims 3 to 6 for determining the angular position (φ) of a rotor (2) on a wind turbine (1) .

8. Use of an apparatus according to any of the preceding claims 3 to 6 for determining the angular position (φ) of an anemometer (12) mounted on the spinner (3) of a wind turbine (1) .

9. Use of an apparatus according to any of the preceding claims 3 to 6 having at least three one-dimensional accelerometers (16) mounted in an anemometer (12) for measuring the angular position (φ) of the anemometer (12) mounted on the spinner (2) or hub (9) of a wind turbine (D •