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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
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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
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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
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European Wind Energy Conference 2007, Milan, Italy 4 Load-based Calibration Apply load Determine influence coefficient
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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)
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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
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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
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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
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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
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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
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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 (%) 11.530.3411.663.00 12.090.3611.943.00 11.810.3611.693.00 12.180.3112.023.00
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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) 11.9012.0412.3411.7512.1211.93 12.3411.7512.1211.93
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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
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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)
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European Wind Energy Conference 2007, Milan, Italy 15 Wind Turbine Tower - Results Load calibration 2.25% Analytical calibration 3.56% Target (IEC) uncertainty 3%
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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
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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%
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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
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European Wind Energy Conference 2007, Milan, Italy 19 Thank you for your attention
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