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Blade Angle Assessment. 

  • It should be clear that in any attempt to mass balance a wind turbine rotor, one can not avoid including aerodynamic characteristics. For example, one can not treat a wind turbines rotor like a solid rotor disc without the effects of aerodynamics on each individual blade.

  • Deviations around the zero mark or even twist deviations will cause an aerodynamic unbalance vector which will interact with the mass unbalance vector and render a standard balancing approach inaccurate!

  • It is unfortunately not uncommon that "TC-marks" are incorrect. A method independent of those marks is therefore deployed by us.

  • Early in providing services of this nature, especially pitch deviation AoA, was recognized as the most common issue, which could be addressed with photogrammetric methods.

  • However, it was quickly evident that standard methods applied would leave huge, almost random errors. Sometimes rendering the results simply false.

  • In a lengthy evaluation process, which included original blade segments aligned and measured on the ground, measurements on a 1:33 hub-blade assembly, as well as several equipment selection tests, a number of serious issues could be identified. 

  • As a result a number of countermeasures and corrective methods were developed. If those measures were not taken appropriately, one could get measurements of angles that are only created in the picture but are not in a relevant way physically present at the turbines. 

  • Those angles are named Ghost Angles.

  • If one adjusts for suspected ghost angles, the aerodynamic unbalance might actually be increased, as well, as potentially unsafe conditions for operation are created!

  • We also developed a critical measurement method of the torsional vibration to verify any adjustment.

  • This measurement is independent of load to the structure and axial location of the effective center of mass of the structure. It also allows comparison between turbines.

  • The craziest turbine ever found was the one shown in the slide below. After a lightning strike and delamination in tow blades, the shells got literally "glued back together" by a "professional company. As a result, the twist along the blade was now different between all three blades, as well as the tip difference to the tower. Although we did that measurement in November 2006, it still keeps happening today in 2022.

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