WO2011051778A1

WO2011051778A1 - System for determining wind turbine blade pitch settings

Info

Publication number: WO2011051778A1
Application number: PCT/IB2010/002723
Authority: WO
Inventors: Thomas E. Nemilla; Daniel R. Charlton; Robert Pharris
Original assignee: Clipper Windpower, Inc.
Priority date: 2009-10-27
Filing date: 2010-10-26
Publication date: 2011-05-05

Abstract

A system for determining the relative and absolute blade angle settings of variable pitch wind turbine blades (12, 14, 16). The system uses a wire frame digital file and physical reference apparatus (15, 17, 19, 21) applied to the rotor hub (23) of a wind turbine (10). This results in an "absolute" pitch angle reading according to the plane of rotation. A camera (26) is placed in a fixed repeatable reference position on the ground. A reference blade is positioned facing down, a rotor lock is engaged to keep the blade from moving, and a pitch control unit (PCU) pitches the blade to reference 0. This enables the taking of a digital picture from a repeatable reference position for the other blades. Photographs are taken of each blade from the ground and the wire frame digital file is overlaid with the digital photographs. Alternatively, a total station is placed on the ground to measure angles and distance to maximum chord and to reference points of each rotor blade. Using measurements provided by the total station, computer software calculates the rotor plane swept by each blade. An error between the projected plane of rotation and the chord of the wire frame image is resolved to arrive at a new angle reference position for the reference blade. The PCU commands the blade to move to the new angle via the pitch control unit (PCU).

Description

System for determining wind turbine blade pitch settings

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to variable pitch blade devices and more particularly to a system for determining the relative and absolute blade angle settings of variable pitch wind turbine blades, and other device parameters, including the ability to measure the parameters from ground level.

2. Description of the Related Art

In variable pitch blade devices such as wind turbines, it is very important that the blades be initially calibrated at substantially identical pitch angles. The determination of blade pitch setting quality is essential for assurance of maximum energy capture in a wind turbine installation. In pitch- regulated wind power installations the angles of the rotor blades can be adjusted collectively or independently of each other. In either case, it is important that the initial blade angle for each blade be set accurately in respect of all the other blades. For collective blade operation, it is necessary that the relative angle of the rotor blades in respect of one another be equal to zero.

Rotor blade angles that are out of adjustment may result in increased loadings on the components of the installation. Rotor blade angles that are out of adjustment from manufacturing tolerances, or manufacturing errors, such as misplaced zero degree markings or displaced blade connecting bolts, can result in inefficient power output or mechanical responses resulting in unwanted oscillations and vibrations.

In the prior art, if after the wind power installation is brought into operation and a defective blade angle setting is suspected, an operation is usually implemented with blade jig templates . Jig templates are pushed over the blade tips as far as a defined position on the rotor blade and, with the blade in a horizontal position, a sensor on the jig template measures the angle of the plane of the blade to the surface of the earth. By further 180-degree rotation of the rotor and renewed

measurement, possible inclined positioning of the tower or any rotor axis angles that may be present are averaged out and the procedure gives the absolute angle of the respective rotor blade. Even with the advent of sensor systems, which permit wireless data transmission, the above method is costly and complicated, especially with regard to large rotor blades where large jig templates are needed. United States Patent 7,052,232 to obben, granted May 30,

2006, discloses a method for determining the angle of a rotor blade in a multi-blade wind turbine, which eliminates the use of the above-described jig. It allows the rotor blade angle

measurements to be taken from the ground, thereby allowing the measuring equipment to be easily disconnected and transported to other sites. A rotor blade angle of a wind turbine is determined by using a spacing-measuring device to measure the spacing between the rotor blade and the spacing-measuring device. The measurements are processed in a computer to calculate the angle between the rotor blade and the spacing-measuring device. Once this angle is ascertained, it is compared to other values to assist in further adjusting the rotor blade angle.

BRIEF SUMMARY OF THE INVENTION

Briefly, the present invention pertains to a procedure to determine the pitch angle and other parameters of a wind turbine by surveying key points of the of the wind turbine from the ground or by the use of a wire frame digital file and physical reference apparatus applied to the rotor hub of the wind turbine. Either method results in an "absolute" pitch angle reading according to the plane of rotation. The pitch axis and main shaft orientation can also be determined. A first procedure uses a wire frame digital file and physical reference apparatus applied to the rotor hub of a wind turbine. This results in an "absolute" pitch angle reading according to the plane of rotation. A camera is placed in a fixed repeatable reference position on the ground. A reference blade is positioned facing down in the 6 o'clock position, a rotor lock is engaged to keep the blade from moving, and a pitch control unit (PCU) pitches the blade to reference 0. This enables the taking of a digital picture from a repeatable reference position for the other two blades of a three-blade installation.

Photographs are taken of the blade from the ground and the wire frame digital file is overlaid with the digital

photographs. An error between the projected plane of rotation and the chord of the wire frame image is resolved to arrive at a new angle reference position for the reference blade. The PCU commands the blade to move to the new angle via the pitch motor.

A second procedure determines the pitch angle of a wind turbine rotor blade by surveying key points of the blade from the ground. This includes the implementation of reflector targets into the blade skin to allow for accurate surveying from distances exceeding 250 meters utilizing readily available surveying equipment .

This second procedure allows for a quick calculation of the blade pitch angle without using blade mounted fixtures which typically have to be installed up tower using specialized rigging and offers greater accuracy and speed than other

photographic based methods to verify pitch alignment.

The invention has the advantage of absolute blade pitch verification, which is a limitation of previous methods. According to a further aspect of the inventions, an apparatus for use in determining parameters of a wind turbine in a installation including a hub/spinner by inspecting key

reference points of said installation from at or near ground level is disclosed. A blade reference tool for projecting the wind turbine hub face outside of the hub/spinner for visual reference from at or near ground level is provided. This blade reference tool is positioned in a manner which allows for taking the picture of the reference tool and the blade from the

reference position. During the analysis the image of the

reference tool is used as a reference when it comes to

determining the blade parameters .

The blade reference tool may have any shape which allows for a projection of the hub face. In one embodiment it is a t-shaped metal frame which can be attached to the hub/spinner, wherein the portion of the t-shaped metal frame provides a horizontal machine-surface reference bar of the projection tool.

For the attachment of the tool to the hub or other parts of the wind turbine system the blade reference tool may have an angle bracket welded to a plate, which can be attached to the hub/spinner .

An additional advantage is the ability to determine the pitch angle from far distances, possibly over 1000 m away depending on conditions and allows for the pitch angle to be calculated without accessing the turbine.

This second method is estimated to save possibly 2,75 man- hrs per turbine to verify pitch angle as compared to performing a photographic based verification.

The prior art quantifies relative pitch angle readings (relative to the other blades within the rotor) exclusive of the plane of rotation therefore rendering the results less valuable .

The invention has the advantage of enabling the acquisition of blade pitch setting data with a minimum of resource expenditure, thereby lowering commissioning and quality assurance costs .

The invention has the advantage of eliminating the use of a crane to place template hardware onto the rotor blade being evaluated.

The Wobben patent 7,052,232 arrives at blade pitch angle using the low-pressure surface of the airfoil only and from the perspective of the turbine tower, not from the ground.

The prior art doesn't employ a "plane of rotation" reference tool. The prior art doesn't employ the wireframe method or the surveying method. The prior art doesn't determine the "absolute" blade pitch value relative to the plane of rotation. The prior art only results in a blade-to-blade relative measurement, which the present invention does as well as absolute measurement. The advantage of the present invention system is that it results in an absolute measurement .

The reference tool is a tool to project the hub face provides a "plane of rotation" reference by projecting it from a known machined hub surface . BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings :

FIGURE 1 shows a front view of a wind power installation having a hub and rotor, a plurality of rotor blades, a support tower, and a digital camera located on the ground;

FIGURE 2 illustrates the relative angle of attack of a wind turbine rotor blade;

FIGURE 3 is a flow diagram of calculation of the rotor blade angle ;

FIGURE 4 is diagram of a projection tool, which projects the hub face outside of the spinner for visual reference from ground level ; FIGURE 5 is an image of blade position #1 in the 6 o'clock position as viewed from the ground;

FIGURE 6 is an image of a jpeg wireframe template used as a reference;

FIGURE 7 is an image of blade position #1 (hub and nacelle shown in phantom) with the jpeg wire frame image superimposed thereon;

FIGURE 8 is an image of blade position #1 with the jpeg wire frame image superimposed upon the blade shown in FIGURE 5 ; and

FIGURE 9 is an image of blade position #1 with the jpeg wire frame image superimposed upon the blade shown in FIGURE 5 with reference line 15 added. DETAILED DESCRIPTION OF THE INVENTION

In FIGURE 1 a wind turbine 10 is shown facing the incoming wind. This wind creates lift on wind turbine blades 12, 14, 16 causing rotation of the entire rotor. Rotation of the rotor results in rotation of the low speed main shaft connected to the hub/spindle 18, which is the mechanical input to a speed

increaser. The mechanical output of the speed increaser is a high-speed shaft, which is connected to a high-speed generator within the nacelle 20. The gear ratio of the gearbox is selected to match the required speed of the low speed shaft to that of the high-speed generator and high-speed shaft. The wind turbine tower structure is identified as 22 in FIGURE 1. This structure is used to elevate the turbine and provide static and dynamic support for mechanical loads on the up tower structure . It is customary for the tower to have an entry door as shown at 24.

A camera 26 is placed in a fixed repeatable reference position on the ground 28. A reference blade 12 is positioned facing down as shown in FIGURE 1 and a rotor lock is engaged to keep the blade from moving. A pitch control unit (PCU) is activated to pitch the blade to reference 0. This enables the taking of a digital picture from a repeatable reference position for the other two blades, 14 and 16. Brief Description of Existing Blade Angle Evaluations

Blade angle evaluation is an optical process used by the wind power industry to determine the relative and absolute blade angle settings. The evaluation of the relative blade angle adjustment is important for the correction of aerodynamic imbalances . Measurements of the absolute blade angle setting are used to optimize the rotor settings and improve turbine

performance .

Aerodynamic imbalances on wind turbine blades lead to suboptimal incident wind flow on the blade. This results in different flow paths for the three rotor blades, resulting in potentially damaging force differences between the blades.

The causes of aerodynamic imbalances may be due to faulty blade twist, rotor partition error, blade cone angle error, different angles of attack, defective air stream elements, leading-edge erosion and other blade damage.

Aerodynamic imbalances may result in damage to important components due to vibrations, higher repair costs, reduced life cycle, lower operational availability and decreased energy output .

Measurement process

Using the existing methods, a blade is positioned vertically and locked into position with the rotor lock fixed. Photos of the turbine blades are analyzed using computer software capable of determining the blade angle to within one-tenth of a degree accuracy. Based on these measurement results, adjustments to the blade angle can be made to considerably reduce the vibration levels in the wind turbine . Measurement of relative blade angles on the wind turbine is conducted to identify and quantify blade angle errors since these lead to aerodynamic imbalances during operation. Deviations of the angle of attack at the blade tips of the three blades are checked comparatively to each other. The differing angles of attack of the three blades will cause unbalanced stream flows that generate additional dynamic loads during operation.

The power curve can be enhanced by blade angle corrections .

Taking blade pictures

To verify the blade angles, a series of photos of the individual blades are taken. Therefore digital cameras with adequate resolution and focal distance are used to capture blade angles. For each blade photo, the rotor is put into the 6 o'clock position and the rotor lock is engaged so that the blade is held in a fixed position.

Blade photo analysis

Every photo is evaluated individually. Thereby each angle of attack is detected and compared to a reference line called the blade chord line. For all blades a standard plus or minus deviation is given which represents an accuracy standard of evaluation within the photo series .

Refer to FIGURE 2. One blade 12 is then chosen as the reference blade and used to determine the relative deviation in the angle of attack 30 or 32 of the other blades. In this description blade #1 is the reference blade. A positive value 30 for the angular deviation means the blade is rotated from the chord blade line 36 further towards the feather position. A negative value 32 for the angular deviation means the blade is rotated from the chord blade line 36 further away from the feather position.

Rotor blades are initially pitch-adjusted to factory

reference marks. Observation of noise emissions and imbalanced relative deflections during operation may indicate a problem with the initial blade pitch settings. If a procedural error is identified with the factory application of the reference marks, small corrections of <0.2 degrees may be made. If indications of pitch imbalance according to observations still exist, further adjustment may be made on blade setting by using the following procedure in accordance with the teachings of the present invention.

FIGURE 3 summarizes the process steps involved in the measuring of the true angle of the rotor blade with respect to the hub. Processing starts with step 50 wherein a reference blade is positioned facing down, a rotor lock is engaged to keep the blade from moving, and a pitch control unit (PCU) pitches the blade to reference 0. This will enable the taking of a digital picture from a repeatable reference position. In step 52, a projection tool projects the hub face outside of the spinner for visual reference from ground. In step 54, a camera is placed in a fixed repeatable reference position on the ground. The process continues with step 56, photographing the blade and the hub/spinner. In step 58, a jpeg wire frame image is placed over the photograph. The jpeg wire frame image depicts the chordline at a particular radial position relative to the airfoil type.

Continuing with step 60, the error between the projected plane of rotation and the

chord of the wire frame image is resolved to arrive at a new angle reference position for the reference blade. In step 62, the blade is commanded to move to the new angle via the pitch control unit (PCU) .

In step 64 a digital picture is retaken from the fixed repeatable reference position to verify that the plane of rotation of the blade and the 0 degree chord representation of the jpeg image are parallel.

In step 66, the above steps are repeated for each rotor blade . In step 68, the measurement results of the individual blades are now compared to each other. In step 70, compensation is effected on the basis of the relative blade angles so that the blades are set to the same angle whereby the relative angle becomes zero for all blades.

The photographing equipment is positioned on the ground, at the base of the tower, under the blade to be measured. This permits ease of service, data collection and electrical

connection. The photographing equipment can be transported from site to site. It can be used at a first wind power installation and then disconnected and moved to another site. Refer to FIGURE 4, which is diagram of a blade reference tool attached to the rotor hub face 23. The blade reference tool projects the hub face outside of the spinner for visual

reference from the ground. The tool comprises a t-shaped metal frame 15, 17, with an angle bracket 19 welded to a plate 21, which is attached to the hub face 23. The portion 15 of the t- shaped metal frame provides a horizontal machine-surface reference bar 15 of the projection tool, which provides a fixed horizontal surface for determining blade angles and other parameters as described subsequently.

Refer to FIGURE 5, which is an image of blade position #1 in the 6 o'clock position as viewed from the ground. The image shows the blade 12, blade tip end 13 and blade base 11, which bolts to the rotor hub (not shown) .

FIGURE 6 is an image of a jpeg wireframe template. The template comprises a horizontal reference line 40 and three- blade chord shaped templates 42, 44, and 46. Refer to FIGURES 7, 8 and 9, which are depictions of blade

12 (blade position #1) in the 6 o'clock position with the jpeg wire frame image 40, 42, 44, 46 (solid lines) superimposed thereon. In FIGURE 7, the hub 18, blades 12, 14 and 16, nacelle 20 and tower 22 are shown in phantom. In FIGURES 8 and 9 only the blade 12 portion of FIGURE 7 is shown for clarity, with the jpeg wire frame image 40, 42, 44, 46 (solid lines) superimposed thereon. In FIGURE 9 the horizontal machine-surface reference bar 15 of the projection tool (shown in FIGURE 4) is added.

As illustrated in FIGURE 7, the projection tool is attached to the hub and projects the hub face outside of the spinner 18 for visual reference from ground 28. The jpeg wireframe 40, 42, 44, 46 (the solid lines) depicts the airfoil chord angle at the designed blade radial location and the airfoil shape at the optimum-viewing angle from the ground. The term "chord" refers to an imaginary straight line joining the trailing edge and the center of curvature of the leading edge of a cross-section of the blade .

The jpeg image (FIGURE 6) is like a template that is the same for all blades. The jpeg image 19 is layered over the digital picture of the blade 12 and hub/spinner 18 with the three wireframes of image 19 in alignment with the blade image 12 and the solid horizontal reference line 40 in parallel with the blade images 14 and 16. This is done with a photo program, such as Adobe Photo Shop tm, running on a computer. The software involved is angle resolving off-the-shelf software.

Registration markings on the blade, hub and/or spinner may be provided but are not necessary to ensure that the jpeg image overlay registers correctly with the blade digital photograph. This is the purpose of the wireframe. It has the airfoil shape that is viewed from the ground and the chord angle at the desired radial station. The shape is used to align the wireframe therefore making the comparison between the chord and the "plane of rotation" reference tool possible.

The blade errors that this procedure will correct are 0 reference angles for all 3 blades; blade cone-angles; angle of attack; etc. It corrects reference and angle of attack. It will not correct cone angle errors .

Refer to FIGURE 8, which is an image of blade position #1 with the jpeg wire frame image superimposed upon the blade shown in FIGURE 5.

Refer to FIGURE 9, which is an image of blade 12 (blade position #1) in the 6 o'clock orientation with the jpeg wire frame image superimposed upon the blade shown in FIGURE 5 with the blade reference tool 15 depicted and wireframe template chord reference 40 depicted. The term "chord" refers to an imaginary straight line joining the trailing edge and the center of curvature of the leading edge of a cross-section of the blade.

Surveying Total Station Embodiment of the Invention

A total station is an electronic/optical survey instrument. The total station is an electronic transit integrated with an electronic distance meter to read distances from the total station to a distant point. Internal electronic data storage is included in the total station to record distance, horizontal angle, and vertical angle and to send the measurements to an external computer. Angles and distances are measured from the total station to points under survey, and the coordinates of surveyed points relative to the total station position are calculated using trigonometry and triangulation. Data downloaded from the total station to a computer allows application software to compute results and generate an output .

Total stations can measure distances to any object that is reasonably light in color. However, the accuracy of such measurements is limited to only a few hundred meters. Therefore it is desirable to have reflector targets pre-installed on each blade during manufacturing. This simplifies the procedure and greatly increases accuracy. Field Procedure

The following describes the invention using a total station but the same procedure can be carried out using a digital theodolite (a total station without the ability to measure distance) . This requires surveying the same points from two locations, which takes much more time and is not preferred.

The total station is setup on a tripod near the base of the tower. The total station measures angles and distance to maximum chord and to reference points of each rotor blade, which are set to a consistent pitch setting, at a minimum of three locations around the rotor blade plane. Increasing the number of points around the rotor plane that are surveyed will increase the accuracy. In addition, if greater accuracy is required, the pitch setting can be varied during the preceding step to allow for calculation of the pitch axis of each blade. If absolute blade pitch verification is desired, the total station should survey reference points or targets on the machine for example the nacelle.

Post Processing

Using measurements provided by the total station, computer software calculates the rotor plane swept by each blade . For a three-blade installation, this results in three separate rotor blade planes. The software next determines the normal distance between the rotor planes swept by each blade. Using the known distance from the pitch axis to reference points, the software calculates the relative pitch angle, coning angle between the blades and orientation of the turbine main shaft. To calculate absolute pitch angle, the software determines the normal distance between the swept rotor plane and the actual rotor plane, which is based on the machine reference points. The software also determines the pitch axis for each blade and the main rotor shaft orientation.

From the foregoing it will be appreciated that, although specific embodiments of the invention have been described herein for purposes of illustration, various modifications may be made without deviating from the spirit and scope of the invention.

Claims

1. A method of determining parameters of a wind turbine in multi-blade installation comprising steps of:

A. inspecting key reference points of said multi-blade installation from ground level utilizing one or more of (1) a surveying instrument and (2) a photographic instrument

producing a wire frame image 40, 42, 22, 46;

B. calculating the rotor plane swept by each blade 12, 14, 16, of said multi-blade installation resulting in multiple separate rotor blade planes;

C. determining the normal distance between the rotor planes swept by each blade; and

D. calculating . the relative pitch angle and/or coning angle between the blades using the known distance from the pitch axis to said key reference points.

2. The method of claim 1, further comprising the step of: E. calculating absolute pitch angle, by determining the normal distance between the swept rotor plane and the actual rotor plane, which is based on machine reference points.

3. The method of claim 1, further comprising the step of: E. calculating pitch axis for said rotor blade.

4. The method of claim 1, further comprising the step of: E. calculating main shaft orientation.

5. The method of claim 1, wherein the wireframe image 19 comprises a horizontal line.40 and a plurality of chord shapes 42, 42, 46.

6. The method of any of claims 1-6, wherein at least one of said key reference points comprises a horizontal machine- surface reference bar 15 of a projection tool, which provides a fixed horizontal surface for determining one or more of said parameters of said wind turbine .

7. The method of any of claim 6, wherein said projection tool is attached to a rotor hub of said wind turbine .

8. An apparatus for use in determining parameters of a wind turbine in a installation including a hub/spinner 18 by inspecting key reference points of said installation from at or near ground level, characterized by

a blade reference tool 15, 17, 19, 21, for projecting the wind turbine hub face outside of the hub/spinner 18 for visual reference from at or near ground level.

9. The apparatus of claim 8 wherein the blade reference tool is a t-shaped metal frame 15, 17, which can be attached to the hub/spinner, wherein the portion 15 of the t- shaped metal frame provides a horizontal machine-surface reference bar 15 of the projection tool.

10. The apparatus of claim 8 or 9 wherein the blade reference tool has an angle bracket 19 welded to a plate 21, which can be attached to the hub/spinner.