WT Load Measurements: A Comparison between Load-Based and Analytical Calibration

1. WT Load Measurements: A Comparison between Load-Based and Analytical Calibration D. J. Lekou, F. Mouzakis Centre for Renewable Energy Sources Wind Turbine Testing Laboratory

2. Load Measurements • Tower (Bending & Torsion) • Main Shaft (Bending & Torsion) • Blades (Bending) • Supporting Systems • Hydraulic pistons • Coupling axles • Bearing plates European Wind Energy Conference 2007, Milan, Italy

3. Recommended Sensors • Bending Moments Tower – type T • Bending Moments Shaft – type II • Torsion – type V • Axial Loads – type T European Wind Energy Conference 2007, Milan, Italy

4. Load-based Calibration • Apply load • Determine influence coefficient European Wind Energy Conference 2007, Milan, Italy

5. Analytical Calibration • Electrical calibration • Knowledge of material & geometry • Definition of influence coefficient European Wind Energy Conference 2007, Milan, Italy

6. Calibration uncertainty • Measured quantity: y • Normal (measured value, standard uncertainty) • Type A: analysis of repeated measurements • Type B: based on scientific judgment European Wind Energy Conference 2007, Milan, Italy

7. Load-based Calibration Uncertainty • Load • Magnitude of load • Load direction & Load introduction point • Sensors • Location of sensors • Data Acquisition System • Other parameters European Wind Energy Conference 2007, Milan, Italy

8. Analytical Calibration Uncertainty • Material properties • E-modulus, Poisson Ratio • Geometrical Data • Diameter, Thickness • Sensors • Location, orientation • Data Acquisition System • Gauge factor, Resistor, etc. • Other parameters European Wind Energy Conference 2007, Milan, Italy

9. Tension of Plate – Load based • Load Magnitude • ±0.2% full scale • Load direction • ±1° • Data Acquisition System • uV = 2.89mV European Wind Energy Conference 2007, Milan, Italy

10. Tension of Plate - Analytical • Material Properties • E-modulus • Poisson Ratio • Geometrical data • Width • Thickness • Electrical calibration (C) • S.g. factor • S.g. calibrator • Type A (linear regression) • Data Acquisition System • S.g. misalignment (neglected) European Wind Energy Conference 2007, Milan, Italy

11. Tension of Plate - Results • Influence Coefficient & uncertainty European Wind Energy Conference 2007, Milan, Italy

12. 12.12 11.93 12.34 11.75 Tension of Plate - Sensitivity • Influence of material properties on coefficient • E-modulus • Poisson ratio European Wind Energy Conference 2007, Milan, Italy

13. Wind Turbine Tower – Load based • Bending moment • Applied load • Distance measurement • Load Direction • Indication of s.g. bridge output • Nacelle position • Prevailing wind European Wind Energy Conference 2007, Milan, Italy

14. Wind Turbine Tower - Analytical • Electrical Calibration (C) • Material properties • Geometrical Properties • Data Acquisition system • Strain gauge misalignment (neglected) • Strain gauge positioning (neglected) European Wind Energy Conference 2007, Milan, Italy

15. Wind Turbine Tower - Results • Load calibration • 2.25% • Analytical calibration • 3.56% • Target (IEC) uncertainty • 3% European Wind Energy Conference 2007, Milan, Italy

16. Wind Turbine Main Shaft • Similar approach to previous • Load calibration • Blade position • Analytical calibration • Only E-modulus European Wind Energy Conference 2007, Milan, Italy

17. Wind Turbine Main Shaft - Results • Load based calibration • 1.26% • Analytical calibration • 3.15% • Target (IEC) uncertainty • 3% European Wind Energy Conference 2007, Milan, Italy

18. Conclusions - Recommendations • Both methods have limitations • Load calibration needs high loads • Load calibration not always feasible • Analytical calibration results to higher uncertainties • Combination of methods preferred European Wind Energy Conference 2007, Milan, Italy

19. Thank you for your attention European Wind Energy Conference 2007, Milan, Italy