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Monitoring and Managing Threats to Subsea Export Cables

For both power and telecoms operators, protecting subsea cables is vital to business continuity. But, in these fast-paced, demand driven sectors, traditional cable monitoring techniques simply can’t rise to the challenge. It would be forgivable to assume that, in the case of export and array cables, their comparatively shallow shoreline locations render them less vulnerable than their deep-sea counterparts. In fact, this is not the case.

Take renewable power, for example. In November, the world’s eyes were firmly on COP26. Global leaders came together to accelerate actions towards the goals of the Paris Agreement and the UN Framework Convention on Climate Change. One of the key commitments emerging from the conference was the need to grow renewable energies, with wind power playing a significant role. Indeed, as of this year, 162 wind farms are up and running worldwide, with a further 26 under construction.

For Offshore Transmission Owners (OFTOs), though, monitoring the offshore export and array cables that transmit that energy is a costly and risky business. According to Offshore Engineer, the average repair time for export cables is 100 days, at a cost of around £6,000-£8,000 per day. Yet, these cables are jointly responsible for transmitting precious renewable energy to its landing point, and so must be safeguarded. As offshore renewable energy grows, so too will the cabling infrastructure that transmission depends on, making the challenge even more pressing.

Similar is true of the fibre optic subsea cables that drive global telecoms infrastructure. Our recent Fotech blog on monitoring subsea telecoms cables explored the power of DFOS (distributed fibre optic sensing) to monitor vast networks of subsea cables. Globally, those networks amount to more than 1.3 million kilometres of connectivity. This blog, however, focuses on the challenges associated with monitoring export and array cables, which are usually buried in waters less than 200 kilometres deep. Whether these cables are transmitting power or fibre optic connectivity into a landing point, the risks are the same since power and fibre cables are typically co-located.

The threat of trawler fishing to subsea cables

The global fish and seafood industry had an estimated value of US$ 113 billion in 2020 and is predicted to increase to US$ 138.7 billion by 2027. It’s hardly surprising, then, that fishing trawlers engage in high stake strategies to win the biggest catch. In fact, the scientific jury remains out on whether the electromagnetic fields emitting from offshore cables really attract fish. Cases of direct damage to cables from sharks, for example, are more anecdotally recognised than a proven statistical risk. Nonetheless, the European Subsea Cables Association confirms that 70% of damage to offshore cables is caused by fishing related activities.

Historically, it has been very difficult to track and prosecute perpetrators. In 2004, the IMO (International Maritime Organisation) introduced new regulations that all qualifying vessels must be fitted with AIS transponder technology. The reality, as our global customer base tells us, is that if a healthy catch is available near a subsea cable, vessels may well disable those systems to avoid detection as they trawl. So, if they cause damage (which they quite likely will) there is no way to identify the vessel and therefore no opportunity for recourse.

What’s more, because export and array cables are buried in much shallower locations, they are particularly vulnerable to trawler or anchor drag damage. So much so that underwater cable operators are now seeking injunctions to prevent fishermen trawling near their subsea cable sites. But legal action incurs significant cost and man hours, as well as being far from 100% effective.

DFOS subsea cable monitoring offers a game-changing alternative for protecting offshore power and telecoms cable networks. When this fibre enabled monitoring is combined with photonics and AI, it not only gathers but also interprets vast quantities of vibration sensing data, reporting subsea cable threats as well as the likely cause and location of the threat. Intelligent, fast action can then be taken. For example, an integrated UAV (or drone) can be flown directly to the location to warn the vessel away and capture footage of the incident. Where an incident cannot be prevented by warnings, this footage can provide the evidence needed to prosecute and recoup valuable damages.

Protecting subsea export and array cables from arcing damage

Cable arcing is particularly difficult to locate and repair in offshore cables. It can cause considerable damage – but because the damage happens internally, it is not easy for operators to spot. In both power and telecoms, the risk of an undetected offshore arcing event is considerable.

Correctly configured DFOS cable monitoring, however, can detect arcing within minutes and pinpoint the location to within metres, so that the operator can take fast, safe remedial action. Fotech recently produced a case study demonstrating that our Helios® cable monitoring system can pinpoint the location of a subsea cable fault to within less than a metre. As a result, only 3.5 metres of cable needed to be cut, minimising the cost, time and risk associated with the repair.

Read the full subsea cable monitoring case study here

Monitoring export and array cables for environmental damage

Whilst the vast majority of damage to subsea export and array cables is caused by fishing and maritime activities, natural undersea hazards also occur. Extreme weather events can cause massive shifts in the seabed, exposing buried cables and rendering them vulnerable to turbulent subsea currents - as well as seabed trawling, and anchor drag.

None of us can control nature! However, distributed acoustic cable monitoring can play a crucial role in spotting natural disturbances before they cause a serious power or telecoms outage. DFOS sends hundreds of thousands of pulses of light along a fibre optic cable every second. The DFOS interrogator observes every disturbance to those light patterns, whether caused by naturally shifting vibrations or a man-made event.

Where that acoustic cable monitoring data becomes really powerful, though, is in the enabling technology that interprets and reports on the data. Fotech Helios® interrogator deploys advanced AI algorithms that recognise the unique vibrational patterns of every event, transmitting the data to a Panoptes alarm server that interprets the data and warns on the location, nature and severity of the threat. The machine learning involved is even capable of filtering out false positives and benign events, giving operators the confidence that when the alarm is raised, a genuine disturbance needs to be dealt with.

Find out more about subsea cable monitoring

Explore Fotech’s always-on telecoms cable monitoring DFOS technology.

Find out how DFOS and machine learning can monitor onshore and offshore cable infrastructure.

Or, if you would like to discuss your cable monitoring challenges with a Fotech expert, simply contact us.

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