Fiber optic cables, it turns out, can be incredibly useful scientific sensors. Researchers at Lawrence Berkeley National Laboratory (Berkeley Lab) have studied them for use in carbon sequestration, groundwater mapping, earthquake detection, and monitoring of Arctic permafrost thaw. Now they have been awarded new grants to develop fiber optics for two novel uses: monitoring offshore wind operations and underground natural gas storage.
“One of the most expensive components of a wind turbine is the gearbox; they also tend to be the part that’s most vulnerable to failure,” said Wu, who is also head of Berkeley Lab’s Geophysics Department. “Often before they fail they produce abnormal vibrations or excessive heat due to increased or irregular friction. We intend to use fiber optic cables to monitor the vibrational, strain, and temperature signal of the gearbox, in order to pinpoint where problems are happening.” Wrapping fiber optic cables around the entire gearbox can provide a 3D map of changes with resolution at the millimeter scale. “It could help identify problems with the gearbox at an early stage, which would trigger emergency management, before a catastrophic failure causing loss of the whole turbine,” Wu said.
EM-TDR (or electromagnetic time domain reflectometry) is similar to the fiber optic technology except that it uses longer wavelength electromagnetic waves instead of visible light (also an electromagnetic wave but at much short wavelength) as signals. “EM-TDR sends electromagnetic waves into an electronically conductive material, and when there is a change due to damage, such as corrosion, you get an EM signal back which can help you identify corrosion or other degradations,” Wu said. And because the borehole is made of steel, which is electrically conductive, no downhole equipment will need to be installed. Thus, EM-TDR is very easy to deploy and can be used under many circumstances that prevent the use of other types of sensors. On the other hand, EM-TDR is still an early-stage technology; this new project will allow further testing and development.