Balancing of Wind Turbine Parts

Abstract

A wind of the type having a tower and a nacelle with a rotor rotatably connected to the nacelle for rotating about a rotor axis and having a plurality of equally spaced blades has the rotor balanced by firstly taking a measurement of torsional vibration and then by using photographic techniques to analyze dynamic imbalance caused by differences in the angle of attack of the blades. The torsional vibration is detected using two sensors at positions mirrored exactly in distance to the left and right of the rotor axis and detecting vibration in the axial direction. The angle of attack is measured by analyzing images of the tip of the blade where, during the analysis, distortion in angles at different locations in the image are corrected, in dependence upon a prior analysis of an image taken by the camera relative to a known image.

1 . A method of aerodynamic balancing a rotor of a wind turbine,
 the wind turbine comprising a tower and a nacelle mounted to the top of the tower, the rotor being rotatably connected to the nacelle for rotating about a rotor axis and having a plurality of equally spaced blades,   the method comprising:   positioning a camera below the rotor;   rotating the rotor so that each blade in turn is in a reference position in which a tip of the blade is directed toward the camera;   capturing an image of the tip of each blade in turn in the reference position;   carrying out an analysis of the image to determine a blade angle of each blade;   in the event that a blade angle of one of the blade is different from that of the other blades by a blade angle difference greater than a predetermined angle, adjusting said one of the blades to reduce the blade angle difference;   and during the analysis, correcting angles at different locations in the image, in dependence upon a prior analysis of an image taken by the camera relative to a known image.   
     
     
         2 . The method according to  claim 1  wherein different points of the image of the tip are identified in the image and the angles between the different points are corrected in dependence upon their location in the image. 
     
     
         3 . The method according to  claim 1  wherein easily recognizable contour lines or reference points of the image of the tip are used which are selected so that they are identical on every blade. 
     
     
         4 . The method according to  claim 1  wherein the accuracy of the angle of attack is in the range of ± 1/10 of a degree to ± 2/10 of a degree. 
     
     
         5 . The method according to  claim 1  wherein during the analysis, correction is made for trapezoidal distortion in the image. 
     
     
         6 . The method according to  claim 5  wherein during the analysis, correction is made for trapezoidal distortion in the image caused by the angle between the optical axis during taking the photos compared to the vertical axis of the tower. 
     
     
         7 . The method according to  claim 5  wherein during the analysis, correction is made for trapezoidal distortion in the image caused by a measurement line created on a sloping away contour line, that is sloping away from the camera. 
     
     
         8 . The method according to  claim 1  wherein for the capturing of the image of the tip of each blade in turn, one of the blades is selected to be first imaged. 
     
     
         9 . The method according to  claim 8  wherein the blade is selected to be first imaged by determining any one which has cone angle deviation and by selecting as the first one which has less cone angle deviation. 
     
     
         10 . The method according to  claim 9  wherein the blade is selected to be first imaged by applying a rotor lock to locate each blade in turn as close as possible to the vertically downward position and by taking an image of each blade in turn from a remote position to determine those that are closest in position to each other at the vertically downward position and selecting as the first to be imaged one of those which are closest. 
     
     
         11 . The method according to  claim 1  including measuring the torsional vibration of the system before and after the adjustment. 
     
     
         12 . The method according to  claim 1  wherein the torsional vibration of the system is detected using two sensors at positions mirrored exactly in distance to the left and right of the rotor axis and detecting vibration in the axial direction. 
     
     
         13 . The method according to  claim 12  wherein the use of the two axial sensors in the axial direction and at the mirrored or exactly symmetrical distance from the axis eliminates all axial vibration by subtracting both axial signals and doubling the torsional signal at the same time. 
     
     
         14 . The method according to  claim 1  wherein in a wind farm of a plurality of wind turbines, the torsional vibration of each is measured and a number of the turbines is selected for analysis of the angle of attack having a vibration beyond a predetermined set value to avoid analyzing all of the blades of all of the rotors. 
     
     
         15 . A method of aerodynamic balancing a rotor of a wind turbine,
 the wind turbine comprising a tower and a nacelle mounted to the top of the tower, the rotor being rotatably connected to the nacelle for rotating about a rotor axis and having a plurality of equally spaced blades,   the method wherein the torsional vibration of the system is detected using two sensors at positions mirrored exactly in distance to the left and right of the rotor axis and detecting vibration in the axial direction.   
     
     
         16 . The method according to  claim 15  wherein the use of the two axial sensors in the axial direction and at the mirrored or exactly symmetrical distance from the axis eliminates all axial vibration by subtracting both axial signals and doubling the torsional signal at the same time. 
     
     
         17 . A method of aerodynamic balancing a rotor of a wind turbine,
 the wind turbine comprising a tower and a nacelle mounted to the top of the tower, the rotor being rotatably connected to the nacelle for rotating about a rotor axis and having a plurality of equally spaced blades,   the method comprising:   measuring the torsional vibration of the system;   adjusting the angle of attack of the blades by:
 positioning a camera below the rotor; 
 rotating the rotor so that each blade in turn is in a reference position in which a tip of the blade is directed toward the camera; 
 capturing an image of the tip of each blade in turn in the reference position; 
 carrying out an analysis of the image to determine a blade angle of each blade; 
 in the event that a blade angle of one of the blade is different from that of the other blades by a blade angle difference greater than a predetermined angle, adjusting said one of the blades to reduce the blade angle difference; 
   and re-measuring the torsional vibration of the system to ensure that it is reduced by the adjustment.   
     
     
         18 . The method according to  claim 17  wherein the torsional vibration of the system is detected using two sensors at positions mirrored exactly in distance to the left and right of the rotor axis and detecting vibration in the axial direction. 
     
     
         19 . The method according to  claim 18  wherein the use of the two axial sensors in the axial direction and at the mirrored or exactly symmetrical distance from the axis eliminates all axial vibration by subtracting both axial signals and doubling the torsional signal at the same time. 
     
     
         20 . The method according to  claim 17  wherein in a wind farm of a plurality of wind turbines, the torsional vibration of each is measured and a number of the turbines is selected for analysis of the angle of attack having a vibration beyond a predetermined set value to avoid analyzing all of the blades of all of the rotors.