Relative Blade Pitch Angle Misalignment Verification

Case study: Dynamic Relative Blade Pitch Misalignment Measurements with Visual Inspection.

Campaign details
Alt Objective:
Verify that the detected relative blade pitch angle misalignment measured in a previous campaign has been successfully corrected by the service company. The type certificate indicates that the turbine should operate with a relative blade pitch misalignment ranging ± 0.3°.
Alt Wind turbine:
Senvion MM92
Rotor 92m
Alt Country:
Alt Measurement period:
August 2022
Alt Campaign outcome:
Verification of successful correction from a detected relative blade pitch angle misalignment of -0.85° to an accepted by type certification misalignment of -0.14°
General overview

Key facts regarding relative blade pitch angle misalignment:

Leads to a significant increase in loads and power production loss. It is a general assumption in the industry that, even a 1° relative pitch angle difference between the blades could lead to up to 2% of power production loss. Causes aerodynamic rotor imbalance, which leads to increased loads on different components of the wind turbine, reduces lifetime and leads to consequential damages on the wind turbine structure and main components.

Key benefits from correcting relative dynamic blade pitch angle misalignment:

Measurement principle and set-up

In order to detect relative blade pitch angle misalignment between the wind turbine blades, visual inspections of the wind turbine are performed while in operation (Dynamic) for both the detection and the verification measurements. The captured images are then filtered and analysed, using different methods. The camera set-up is placed on the ground, targeting on the wind turbine blades. In addition, the system is located at 4 o’clock rotor position, to avoid the influence of the blade-tower interaction.

Relative blade pitch angles misalignment detected
Blade 1 - Blade 3
Blade 1 - Blade 2
Blade 3 - Blade 2
Relative blade pitch angles misalignment verified after correction
Blade 1 - Blade 3
Blade 1 - Blade 2
Blade 3 - Blade 2
Conclusion and Recommendation