Relative Blade Pitch Misalignment Detection

Case study: Dynamic and Static Visual Inspection Measurements.

Campaign details
Alt Objective:
Verify that the detected relative blade pitch misalignment between the wind turbine blades has been corrected successfully, inside the acceptable by type certification threshold of ± 0.3°
Alt Wind turbine:
ENERCON E101
3.05MW
Rotor 101m
Alt Commissioning year:
2015
Alt Measurements date:
January 2020
Alt Campaign outcome:
Verification of successful correction from a detected relative blade pitch misalignment of -2.71° to an accepted by type certification misalignmentof -0.29°
General overview

Key facts regarding relative blade pitch misalignment:

  • Leads to a significant power production loss. It is a general assumption in the industry that, even a 1° pitching angle difference between two blades could lead to up to 5% 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 misalignment:

  • Increase energy production
  • Avoid premature wear due to excessive stress and loads
  • Prevent critical component failures and extend turbine lifetime
Measurement principle and set-up

In order to detect relative blade pitch misalignment between the wind turbine blades, visual inspections of the wind turbine are performed while in operation (Dynamic) foor 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, it is located at 4 o’ clock rotor position, in order to avoid the tower influence while the blade is passing from it.

Results

Detection dynamic measurement

Alt
Fig. 1: Blade A
Alt
Fig. 2: Blade B
Alt
Fig. 3: Blade C
Static results
Blade A - Blade B
-0.69°
Blade B - Blade C
-2.71°
Blade A - Blade C
-2.02°

Verification dynamic measurement

Alt
Fig. 4: Blade A
Alt
Fig. 5: Blade B
Alt
Fig. 6: Blade C
Dynamic results
Blade A - Blade B
-0.15°
Blade B - Blade C
-0.29°
Blade A - Blade C
-0.14°
Conclusion and Recommendation
  • From the above presented results, it can be noted that there has been a successful correction from a detected maximum relative blade pitch misalignment of -2.71° to an accepted by type certification maximum misalignment of -0.29°.
  • Another important observation from the comparison of the detection and verification dynamic measurement images, is the blade bending differences between the three blades before and after correction. It can be clearly seen that the bending differences between the three blades, that are observed during the detection dynamic measurement, are not present after the successful correction on the verification dynamic measurement images.

This is visual confirmation of the significant importance of relative blade pitch misalignment detection & successful correction for
achieving the desired aerodynamic rotor balance.

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