Presentations - WindEurope Annual Event 2024

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Fibre Optic Electrical and Mechanical Condition Assessment of Subsea Cables

Chris Minto, Director, Indeximate Ltd


Fibre Optics embedded within subsea cables live within an environment largely dominated by thermal, vibration and strain signals emanating from the cable, the flow of power and the environment in which the cable is embedded. We report field experiences of monitoring from two in-service offshore wind farm cables with a mix of Distributed Temperature Sensing (DTS) and Distributed Acoustic Sensing (DAS) where we use the received broadband signals to deconvolve the status of the cable and environment at every point along the cable. One aspect that makes extracting condition information simpler is the availability of a "standard candle" to probe response; in our case we exploit the power flowing through the cable. In a three-phase cable we expect to see a sympathetic vibration at 100Hz from the individual 50Hz modulation in each phase to the current flowing through the cable. This is largely a response to the vibration of the cable itself under the radial and tangential magnetic forces. The fibre itself will experience this sympathetic vibration directly via a coupling coefficient representing the geometry and materials in the makeup of the cable. DTS and low frequency (LF) DAS is analysed to provide significant detail on the thermal response of cables and how that is affected by both construction and environment. Electro-Mechanical transforms of DAS data tell us about how the signal from the flow of power is modified by the construction of the cable, the environment and the presence of defects or issues with either the cable or the environment. When trended over time these provide a valuable indication of degrading conditions and the need for action.

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