EWEC 2007 Centre for Renewable Energy Sources Wind Turbine Testing Laboratory WT Load Measurements: A Comparison between Load- Based and Analytical Calibration D. J. Lekou, F. Mouzakis

European Wind Energy Conference 2007, Milan, Italy 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 LoadTypeB Bending (tower)T2(1+ν) Bending (shaft)II4 TorsionV4 AxialT2(1+ ν)

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  u V = 2.89mV

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

European Wind Energy Conference 2007, Milan, Italy 11 Tension of Plate - Results Influence Coefficient & uncertainty Load-basedAnalytical A L (kN/V)u AL /A L (%)A A (kN/V)u AA /A A (%)

European Wind Energy Conference 2007, Milan, Italy 12 Tension of Plate - Sensitivity Influence of material properties on coefficient  E-modulus  Poisson ratio NOMINALVariation E Variation ν AL*AL* A A * E=205, ν =0.29 A (E=210)A (E=200)A (ν=0.28)A (ν=0.30)

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