Wind Turbine Testing And Certification

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Wind Turbine Blade WorkshopFebruary 24-35, 2004Sheraton Uptown, Albuquerque, NMWind Turbine Testing andCertificationWalt MusialNational Wind Technology CenterNational Wind Technology CenterGolden, CO USAWalter [email protected] Wind Technology Center

Presentation Outline Why test blades? Testing methods Relevant standards and practices Future outlookNational Wind Technology Center

Why test blades?Blades designs are altered inproduction. Blade strength is dependent onproduction process and facility, aswell as design. Blade properties are not knownat every location. Blade designs cannot be fullyrepresented by design analysis. Field repairs are extremelyexpensive. National Wind Technology Center

What can we learn? Design Verification Canthe blade withstand the design loads? Used in most certification testing. Strength Verification Doesthe actual blade strength match the designstrength? Used to verify blade structural design. Verify Blade Properties deflections- maximum requirements for most standards stiffness stress/strainNational Wind Technology Center

Blade Test LabsBlades Tested at NREL NREL - National WindTechnology Center –USAWMC / TU DelftNetherlandsRISO - NationalLaboratory – DenmarkNaREC – UnitedKingdomPrivate labs -- LMGlasfibers, NEG Micon,MHI, othermanufacturers.National Wind Technology Center

Static Testing Tests the blade’s ability to withstandextreme design load cases (e.g. 50year gust)Four load quadrants – worst case ineach direction.Verification of buckling stabilityLoads applied with cranes,actuators, etc.Required by all internationalcertification authorities.Failure beyond limit load isrecommended but not required.Property measurements –deflection, strain verification,frequency – performed inconjunctionNational Wind Technology Center

Types of Static LoadingDistributed LoadingWhiffle TreeHydraulic Actuators - NRELWinches – LM GlasfibersNational Wind Technology Center

Types of Static TestingProgressive Loading Portions of the blade aretested in multiple tests. Test loads can be appliedat single station. Allows rapid execution ofmultiple load cases. Shear loads are higher.Bending Moment (ft-kips)1000900GH-MDEC Design Bending Moment800Applied 55% Test Loading Bending Moment700Applied 68% Test Loading Bending MomentApplied 79% Test Loading Bending Moment600500400300200100001020304050Percent Station60708090100National Wind Technology Center

Fatigue Testing Verifies the blade’s ability towithstand the operating loads for afull design life. 30 year life 5 x 108 cycles appliedwith accelerated load history to 1 to10 million cycles. Required by IEC-61400-23, IECWT01, Danish Energy Agency Load applied on one or two axes. Load methods vary among labs.National Wind Technology CenterForced Hydraulic LoadingNational Wind Technology Center

Blade Fatigue Test SystemsForced-displacement Used at NREL, WMC/TU delft, CRES Hydraulic actuators – accurate load replication Dual axis capability – representative loading High equipment cost Large energy consumption Lower test speeds - limited by hydraulic capacity Cannot test entire blade lengthTruncated to70% LengthTurbine BladeHydraulicActuatorEccentric Mass Resonance Excitation Denmark – RISO, LM, Vestas, NEG Micon/UKElectricMotorEccentric LowMassEquipment Cost Fast test speed Can test the whole blade span.Turbine BladeAdded Masses Adds unwanted moments due to axial loads Cannot simultaneously apply flap and lead-lagNational Wind Technology Center

Forced Hydraulic LoadingScaling to Large Blades Bladefatigue resourcerequirements growcubically with bladelength Testspeed limitationson Hydraulic Flow andenergy use. Highcapital expense toexpand test hardware forcurrent method. Newfatigue methodwas developedNational Wind Technology Center

Implementation of Hybrid ResonanceBlade Fatigue Test System Largeflap actuator is replacedby a smaller hydraulic exciter. Edgeactuator uses existing bellcrank. Uses1/3 the energy and cycles2x faster. 0.35-Hz 0.70-Hz Tests Canfull-blade lengthbe scaled up to 70-m blades Usesexisting equipment andexperience at NREL. PCTGE Wind 37a Blade Fatigue Testpatent application filedNational Wind Technology Center

Small Blade Fatigue Test System New testing capability totest small turbine blades Single axis fatigue testusing resonanceexcitation. Multiple blades tested ona single rotor. 3-6 Hz cycling using baseexcitation.H-40 Rotor BladesSouth West Windpower Scalable to 3-4 meterblades.National Wind Technology Center

Equivalent Damage Calculation Blade section properties Convert load to stresses S-N data for each location Goodman diagramMandell et al, “New Fatigue Data for Wind Turbine BladeMaterials” ASME Transactions, Nov 2003 Miner’s rule Determine fatigue load for equivalent damage Load acceleration – Define Number of test cycles Define test load ratio Define phase relationship between flap and lead-lagNational Wind Technology Center

Flap Bending Test Loads - ExampleNational Wind Technology Center

Relevant Codes for theCertification of Rotor BladesIEC WT01 “IEC System for Conformity Testing and Certification of WindTurbines, Rules and Procedures”IEC 61400-1 “Wind Turbine Generator Systems – Part 1: SafetyRequirements”IEC 61400-23 “Wind Turbine Generator Systems – Part 23: Full-scaleStructural Testing of Rotor Blades”IEC 61400-24 “Wind Turbine Generator Systems – Part 24: LightningProtection”Germanischer Lloyd “Regulations for the Certification of Wind Turbines”Danish Energy Agency DS-472 – Type Approval Scheme for WindTurbines – Recommendation for Design Documentation and Test ofWind Turbine Blades.NVN 11400-0 “Wind Turbines - Part 0: Criteria for Type Certification –Technical Criteria”National Wind Technology Center

Application of IEC 61400-23Design and Test Load Factors gDesign load factors Loads provided by manufacturer Understand what factors have been applied. Design Material factors Material factors are embodied in the blade Not used again for test. Environmental factors must be considered. Test load factors (TLF) TLFs recommended by IEC 61400-23 Account for uncertainty introduced in the lab.National Wind Technology Center

IEC 61400-23 Test Load Factors Blade to Blade Variations Accounts for possible strength variations-single blade test IEC 61400-23 recommends a factor of 1.1Test Load Uncertainty Accounts for uncertainty in fatigue formulationIEC 61400-23 recommends a factor of 1.05 on fatigueloads.Environmental Accounts for more benign laboratory test conditions. No specified level - Properties vary commonly 1.05 to 1.3National Wind Technology Center

Lightning ProtectionIEC 61400-24 “Wind Turbine Generator SystemsPart 24: Lightning Protection” Rotor blades shall have atleast one receptor at eachshell. More than one receptorrecommended for largerblades (blade length greaterthan 30m) Minimum dimensions ofdown conductors given.National Wind Technology Center

Summary of Full-ScaleBlade Test Requirements Static test is required in all international standards. Fatigue test is required in IEC WT01 and DS 472 Tests in flapwise direction and in lead-lag direction Performed by a recognized testing body or supervisedby the certification body Blade shall withstand the tests without showingsignificant damage regarding safety or blade function[Requirements for the Certification of Rotor Blades – Germanischer Lloyd]National Wind Technology Center


Structural TestingFuture FacilitiesCapacity of current facilities at NREL is inadequate Stronger test stand foundation is being developed Higher strength for 45-m blades – 8x106 ft-lbs Greater stroke / larger force capacity for loading apparatusLong-term – Larger Test Facilities are planned. 70- meter capacity 3 test bays 50,000 kN-m static load capacityNational Wind Technology Center

Blade Trends Standards compliance increasing. Blades are getting longer. Offshore drivers – Transportation anderection issues are less important. Land-based turbines may not follow trend. Facilities are too small for 2MW blades. Current test facilities busy – driven byinnovations.National Wind Technology Center

IEC 61400-24 “Wind Turbine Generator Systems Part 24: Lightning Protection” • Rotor blades shall have at least one receptor at each shell. • More than one receptor recommended for larger blades (blade length greater