dr. carsten hein westergaard: 2013 sandia national laboratoies wind plant reliability workshop
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Bladena's new simple retrofit for increased reliability an repair of the trailing edge bondsTRANSCRIPT
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Together, we make your blades stronger
Bladena’s new simple retrofit for increased reliability and repair of the trailing edge bonds
Dr. Carsten Hein WestergaardPresident, NextraTEC Inc.Board member, Bladena ApsBladena [email protected]
Sandia National LaboratoriesWind Reliability workshop 2013 August 13 – 14, 2013, Albuquerque
Bladena US based service partners
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Agenda
• Short introduction to Bladena• Trailing edge damages• Effect of D-string• Pilot projects• Installation• Recommendations• Future projects
©Bladena 2013
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Together, we make your blades stronger
• Spin out from Danish Technical University, established 2011
• Seven patents making blades stronger and more durable developed at RISØ (DTU)
• Technology based on 10+ years of research & experience at DTU
• Based in Denmark
• Two Strong Service Partners in North America
.
©Bladena 2013
D-StringSimply effective!
Bladena – the company
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Catastrophic trailing edge failures, starts small
• Repairs can be costly and does not eliminate the need for larger fleet repairs or replacement at a later stage
• Significant risk for catastrophic failure remains, when the small cracks propagate unnoticed
Unrepaired cracks lead to de-bonding Blade broken near max chord Trailing edge splitting
©Bladena 2013
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Root causes of trailing edge cracks are many
• Design system, verification system and standards applied: – Non accommodating for critical errors; for example; lack of combined loads
verification during testing– Exclusion of important failure mode combinations; for example, breathing of panels
which leads to accelerated peeling
• Manufacturing deficiencies:– Tolerances, random and/or systematic; for example, incorrect application of fibers– Quality deviations; for example, application of glue or curing of glue bond deviations
• Unforeseen blade loading events:– Systematic; for example, by failure of sensors– Random occurrence; for example, induced by extreme weather events
• Service methods– It is very difficult to detect hairline cracks, service methods can influence the root
cause of failure mode development
• Almost always, failure is a sequence or combination of these root causes
©Bladena 2013
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Blade panel deformations induced by edgewise gravity induced loads during any operation of any wind turbine makes the panels breath
©Bladena 2013
Panel breathing
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Panel breathing and peel stress
• Peel stresses at the bond lines, peels the adhesive from the shells by stress concentration
• Until peeling occurs, the stresses will create surface tension right at the trailing edge bond line eventually developing into (hairline) cracks
• Trailing edge bonds are designed for shear stress, which occurs from blade bending during wind loading.
• Peel stress is added to the shear stress
©Bladena 2013
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Panel breathing accelerates crack propagation through peeling and necessitates regular inspections and preventative repairs
Hairline crack found at inspection
Uptower repairs of trailing edge cracks
©Bladena 2013
It starts with hairline cracks
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D-String reduces breathing(Deformation Limiting String)
Typically, ten strings spaced along the trailing edge limits the panel breathing, sufficiently
©Bladena 2013
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The D-String limits the outward panels from breathing, hence reducing peel stresses in the bond lines
©Bladena 2013
Without D-Strings With D-Strings installed
Typical 10 D-Strings installed in max chord area
Typical 10 D-Strings per blade
Finite element model prepared for a specific blade sized by calibration with site measurements of the in-situ panel deformations
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First demonstration project – rope access installation
Installed in Denmark in January 2013.
©Bladena 2013
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First US Pilot Project
First pilot under installation in Texas
Platform access
Partners:
©Bladena 2013
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First step: Size string by one time measurement of panel deformationCurrently three blades are documented with D-string implantation
For other blades:A. Blade Survey to establish key dimensions of
blade, and determine needs for step B&CB. Pilot, where loads and deformation levels are
measured and installation methods are testedC. If needed: panel testing to establish panel
strengthD. Feasibility study establishes:
Suitable strength and fatigue life of panel and D-String
FEM simulation Verify the effect of the D-String Variations from a standard installation
©Bladena 2013
Step B: Measurements with temporary installed sensor from rope access, typically there are three places used to qualify D-string installation
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Estimating impact through measurements
Without D-Strings
With D-Strings installedTest on turbine, results from
temporarily installed sensors
Resulting analysis
©Bladena 2013
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Easy Installation from platform or rope access
©Bladena 2013
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Static safety against damage to blade skin from D-string
• A comprehensive test program of the D-String has been performed at DTU, demonstrating safety margins against damage to the supporting blade skin foam sandwich
• A string (fuse) is included for well defined protection at breaking point 1.5kN
• Field test has shown measured string loads are very low, with peaks up to 0.4kN during emergency stops
©Bladena 2013
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Fatigue safety against damage to blade skin from D-string
Measured extreme event
Typical normal load situation
Fuse
©Bladena 2013
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Increased reliability based on measured data• Based on the in-situ measured deformation and stress, the lifetime stress
reduction can be calculated. By using Palgren-Miners, rule the life extension can be calculated
• In the pilot projects, the measured improvement from the D-string is a 97% reduction in stress. This can be translated to: “If the blade was prone to cracks after 4 years, the life expectancy would be expanded to 40 years, i.e. a factor 10 in lifetime”
Without D-Strings
With D-Strings installed
Resulting analysis based on measurements
©Bladena 2013
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Preventive or reactive use ?Age Frequency of
damageAction Result of D-string use
ReactiveA few damagedblade(s)
1 to 4 years
One time isolated event(s)
Add D-string to blade repair
• Avoid scrap• Additional safety in repair• “New” healthy blades in
inventory• Direct savings
ProactiveMultiple damaged blades
2 to 10 years
Multiple events, more than 1/200 rotors damagedper year
Install D-string fleet wide on turbine type, preferably combined with blade inspection
• Life extension through reduced stress in hairline cracks
• Life extension far beyond 20 years for un-cracked blades
• Preventive savings by reduced (eliminated) failure rate
Preventive N/A No damage documented
Install D-string fleet wide on turbine type
• Strongly reduced sensitivity to manufacturing deficiencies or any other potential weaknesses
• Statistical mean value moved far beyond 20 year life, so “no failures” will occur
• Stronger blades
Improved new built blades
N/A Statistical variance of design
Include D-string in new blade build
©Bladena 2013
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Next project: Cross-sectional shear distortion was observed in the field
Measurements on a MW turbine showed cross-sectional shear distortion under normal operation
Cross section shear, adds loading to the leading edge bond, and possible additional failures
©Bladena 2013
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Three new combined technologies making blades stronger in the field
1) D-String2) X-Stiffener3) Floor
1) Stronger trailing edges 2) Stronger leading edges3) Strong root panels less prone to buckling
©Bladena 2013
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Together, we make your blades stronger ©Bladena 2013
Thank you
Dr. Carsten Hein Westergaard
President, NextraTEC Inc.
Board member, Bladena ApsBladena representative
Bladena US based service partners
Bladena US based service partners