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According to New Energy Update, the organisers of the Offshore Wind Europe conference, the industry is at a “crucial tipping point in time”. It is facing a number of changes, from implementing the latest in turbine technology to navigating a changing financial landscape as subsidies disappear. At the same time, offshore wind projects are expanding in Europe and beyond, with over 160GW capacity to begin construction within the next decade.

The conference gave the opportunity for leaders in the industry to strategize and connect. Product Line Director, Stuart Large, was in attendance to present to delegates about how Fotech’s Distributed Acoustic Sensing (DAS) technology can be applied to offshore wind enterprises.

“It wasn’t just a regular presentation; I got the chance to ask questions and interact with the audience,” said Stuart. “At the start I asked if they were familiar with DAS technology. About two-thirds said ‘no’; the others had heard of it but didn’t know much about it.” It was the perfect opportunity to give the audience an idea of what DAS could do for them.

Briefly, DAS technology uses a single fibre optic cable to detect acoustic energy and vibrations, generated by activity around the cable. This information is then analysed by AI systems, which raise an alarm if unwanted activity is detected. This incredibly sensitive technology has the ability to pinpoint activity down to just five metres – is already used with great success in the pipeline industry.

Stuart Large, Cable monitoring, Fotech, DASStuart explained to delegates how it could be implemented in the offshore wind industry: “DAS uses one of the optical fibres already present in subsea power cables to detect the vibrations caused by threats, such as electrical arcing caused by insulation breakdown, cable exposure, and cable strikes, and then warns operators of these different threats.” His polling on the day indicated that these are the issues most important to delegates when thinking about the risks to both subsea and array cables.

The top concern was cable exposure. Because subsea power cables are buried in the seabed to protect them, they can become damaged easily by the forces of ocean currents if they are exposed. Stuart believes that DAS will able to identify the vibration patterns associated with loss of burial by detecting effects such vortex shedding, strains in the cable, and maybe even ambient noise that would not be detected were the cable buried. This would allow operators to identify the problem sooner, giving them the opportunity to cover the cable back up before damage occurs.

“Average outage time of 26.5 days resulting in loss of £120,000 per day”

Similarly, DAS can detect the vibrations caused by trawlers dragging nets or anchors being dropped to the sea bed, alerting operators who can cross-reference with ship location data to alert the vessels and avoid further damage. It can also identify the initial impulse and subsequent shock waves travelling along the cables at the speed of sound, indicative of insulation breakdown.

Preventing or quickly identifying and planning repair from this kind of damage to cables is paramount to the industry as outages cost a great deal of both time and money. “Speakers at the event made it very clear just how long it takes to repair damage to cables and the great cost that goes with it” Stuart says. “There were four array cable outages in UK waters recorded in 2017, average outage time was 26.5 days, resulting in £2.2 million in losses, or £120,000 a day on average. Meanwhile, the average repair time for the export cables is 100 days, which costs around €8,000-10,000 a day.” With operators expecting one fault per year for every 400 kilometres, the role DAS has to play on offshore networks is all more apparent – providing the means to greatly reduce costs through early warnings and targeted maintenance.

“Average repair time for the export cables is 100 days, which costs around €8,000-10,000 a day”

Cable monitoring, Fotech, DAS

Another major cost to the industry is monitoring. “Operators are obliged to monitor their cables with ROVs once every two years at a cost of up to £10,000 per kilometre,” explains Stuart. “These cables can be buried one day, unburied the next, and then reburied, because currents change. So it might just be on that day you do that schedule drive by, everything looks fine, even if it was uncovered the week before and again the following week. You’re just not getting enough warning. If the sea currents are violent, it could get damaged very quickly ”. The information provided by the DAS system can be used to direct ROVs with precision to the areas where they are needed most.
The audience were certainly convinced. “When I asked them at the end of the presentation if they thought DAS would be valuable to the industry, 73% said ‘yes’, which is encouraging. And we had at least one person interested in a proof of concept demo opportunity by the end.”

“€350 million in insurance claims”

Stuart said one of the most interesting things he did at the conference was getting to speak industry insurers. With 90 subsea cable losses over seven years totalling €350 million in insurance claims, insurers have an interest in minimising damage to cables as well. Insurers agreed these could even lead to lower premiums for operators who have the technology installed on their offshore network.

The role DAS has to play on offshore networks is all more apparent – providing the means to greatly reduce costs through early warnings and targeted maintenance

With growth in the industry set to see 20,000 km of new cable laid by 2030 and with cables going into deeper water and further offshore, the financial implications for installers, operators, and insurers in monitoring and repairing damage will only increase. Although a new technology to the world of offshore wind, Stuart is confident that the industry will find value in Fotech’s DAS technology.

Watch out for Stuart in February next year, when he will appear as part of a panel discussion at the Annual Offshore Power Cable Engineering and Reliability Forum in Amsterdam.
Offshore Cable Monitoring. DAS. Fotech