As the size of wind turbines increases, the early detection of structural instability becomes increasingly important for
safety. This paper introduces a fiber Bragg grating-based sensing system for use in multi-MW scale wind turbine health
monitoring, and describes the results of preliminary field tests of dynamic strain monitoring of the tower structure of an
onshore wind turbine. For this research, the Korea Institute of Energy Research (KIER) and the FiberPro, Inc. cooperated
on the development of a wavelength division multiplexing (WDM) Bragg grating sensing system for high-speed strain
sensing. The FBG interrogator thus developed can be used in the sensing of high-speed vibration as well as low-speed
dynamic strain. In the case of high-speed sensing, the interrogator allows a sampling ratio of over 40 kHz for six linearly
arrayed FBG sensors per channel. To monitor the dynamic strain behavior of the tower and substructure of onshore and
offshore wind turbines, 41 FBGs were installed on the supporting structures of the wind turbines. As a result, the Bragg
grating sensing system showed stable, accurate performance in the thermal chamber test and good dynamic strain
sensing performances during the strain monitoring of the tower structure at the Woljeong test-bed wind turbine in Jeju
Island.
In this study, a down-scaled wind turbine blade was designed and fabricated using glass and carbon fiber materials for
the skin and stiffener, respectively. In the course of its fabrication, an array of FBG (fiber Bragg grating) sensors was
embedded in the composite laminates. The embedded FBG sensor array was used to measure the residual strain in the
stiffener before and after the curing process, and after fabrication of the blade, the FBG array was used to monitor the
structural conditions, including structural dynamic behavior during the structural testing of the blade. The results of the
tests showed that the FBG sensor array effectively measured the residual strain distribution of the blade stiffener before
and after the curing process. And the measured natural frequencies and mode shapes by the FBG array matched the
results obtained from the FE analysis and conventional accelerometers.
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