Laboratory test of FBG interrogators for wind turbine blade monitoring

www.ecn.nl

Load measurements of bladesFibre Optics, ready for implementation?

Theo VerbruggenWind Turbine Condition Monitoring Workshop, October 8-9, 2009

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Contents

• Applications• Principles• Suppliers• Tests• Hardware developments• Software developments• Conclusions

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Applications of blade load measurments

• Load measurements for certification

• Turbine control• Blade monitoring• Operation and

maintenance

Blade load measurements can be used for :

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Principles of FBG-based measurements

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Principles

TDM: Time Division multiplexing

WDM: Wavelength Division Multiplexing

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Suppliers

• Smart Fibres TDM

• Insensys TDM

• HBM WDM

• (Micron Optics) WDM

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User experienceWhat is demonstrated…

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User experienceOr even more...

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User experienceAnd this are the details….

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User experience

•Inaccuracies in strain•Large differences foropposite locations

•Spikes / missing data•Strain modulation on temperature measurements

•Unreliable instrumentation•Complex repair due to required skills and tools

•Long installation time Still promising!But how to proceed?

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Still promising!

But how to proceed?

• Selection of reliable interrogator which meets requirements for in house developments and on site testing

• Development of user friendly sensor assembly, suitable for on site installation

• Development of user friendly data processing and interface

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Selection of interrogator

• Accuracy / resolution / long term stability

• Thermal sensitivity• Acceleration / environmental

conditions• Stability during operation /

polarization effects• Reliability / robustness

Reference grating (AOS)

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Accuracy / resolution

Single micro strain simulator

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Thermal sensitivity

Climate room

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Acceleration

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Polarization

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Remarks interrogator • Required accuracy not ensured• Long term stability not ensured• Thermal effects found• Acceleration effects minimal• Polarization effects (Strong!)• Reliability / robustness• Strong sensitivity for Bragg grating properties• Strong effects due to attenuation

But we made our choice for our sensor development

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Sensor developments

• Complicated installation- Skilled personnel / not certified- Special tools

• Time consuming- Gluing process- Curing time and fixation

• Result- Not robust- Prone to damage

Experience:

• Inaccuracies- Strain- Temperature

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Sensors development

Requirements: • Life time > 20 years• Easy installation• No drift• Temperature compensation• No (re-)calibration• Easy replaceable• Robust

These requirements are met by the ECN sensor development

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Software development (Blade monitoring)

Purpose• Fully automatic• Very limited data to be

stored• Robust to measurement

faults• Applicable for various

platforms• Applicable for various

turbines• Auto-reporting / warning• Friendly user interface

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Conclusions

• Load measurements are essential for various wind applications

• Fibre Bragg grating is still promising and still expensive

• Users friendly components still required• Data processing / reduction essential for

monitoring applications

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Thank you for your attention!