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Protecting Subsea Cabling

Dec. 19, 2019

The energy industry is changing. Renewables are on the rise and wind energy is becoming increasingly prevalent. In fact, Britain is set to increase the amount of energy produced from offshore wind farms from 7% to 30% over the next decade.

However, offshore wind energy is completely reliant on subsea cabling to deliver power back to land and allow transmission between turbines. If these essential cables become damaged or start to malfunction, it could completely cease production — requiring expensive repair work.

Threats to subsea cables are a huge risk to offshore wind farms, one that the renewables market needs to take seriously if they’re to remain viable in the long-term.

Damage and Dangers
A significant danger to subsea cables is through shipping activity. 70% of cable faults are due to anchoring, fishing and boating. Cables can be struck by fishing trawlers and nets, or anchors may be dragged across the sea bed causing severe damage.

Cable burial is currently the predominant technique for protecting offshore cables. But, in many subsea areas, burying the cables is simply not viable. Even when they are buried successfully, strong seabed currents can still root them out, cause them to drift, or vibrate and cause faults.

When exposed to the elements, cables are under a huge amount of additional stress, which means they’re far more likely to become damaged by fatigue or suffer a harmful strike. These issues have the potential to completely shut down energy production on offshore wind farms.

Pinpointing the exact location of a fault can be like trying to find a needle in a haystack, leading to increased costs and time losses associated with painstaking searches for the source of the issues.

Current monitoring methods are proving insufficient, with cable route surveying the only option — but this does not provide the real-time monitoring wind farms need to be truly secure.

There were four array cable outages recorded in UK waters during 2017. With an average outage time of 26.5 days, this resulted in £2.2 million in losses — or approximately £85,000 a day.

The average repair time for export cables is 100 days, at a cost of around £6,000-£8,000 per day. Operators anticipate one fault per year for every 400 kilometers of cabling, demonstrating how expensive these issues can prove.

Fortunately, ‘Distributed Acoustic Sensing’ (DAS) technology provides a ready-made solution for the offshore wind industry to monitor and protect these crucial cables.

Clarity and Confidence
By harnessing cutting-edge photonics, advanced artificial intelligence and edge computing, DAS converts subsea cables into an ecosystem of highly-sensitive, individual vibrational sensors, enabling the successful detection and classification of a wide range of threats.

DAS identifies, with clarity and confidence, the different disturbances that impact cabling in offshore wind farms, providing operators with specific alarms to enable them to resolve the issue efficiently.

Fully-integrated DAS covers the entire length of subsea cables — giving a complete real-time overview of hundreds of kilometers of cabling and allowing operators access to unique insights that accelerate the decision-making process.

DAS detects the vibrations caused by fishing trawlers dragging nets along the seabed or a boat anchor impacting and dragging across the seabed. Alerts can be sent to operators who can then cross-reference with ship location data to notify the vessels and stop them from causing damage.

To safeguard against the effects of loss of burial, DAS recognizes the acoustic and vibration signatures of effects such as vortex shedding where a cable is in free span, strains in the cable, and ambient noise that would not be detected if the cable were still buried. This enables operators to find the problem sooner, giving them the opportunity to cover the cable back up before significant damage occurs.

DAS: The future
The Global Wind Energy Council estimates that there’s nearly 19 gigawatts (GW) of offshore wind turbines installed around the world, with Bloomberg New Energy Finance forecasting that capacity will grow hugely to 115 GW by 2030.

Although subsea cable networks are not a particularly visible part of offshore wind farms, they’re the most vulnerable. Without monitoring technologies such as DAS, it’s difficult for operators to assess the integrity of these crucial cables.

As demand for offshore wind energy continues to grow, solutions like DAS need to become an integral part of operations. The energy industry must take a comprehensive view of the systems necessary to successfully operate offshore wind farms, or risk costly outages that impact confidence in this renewable energy source.


The author
Stuart Large has combined technical, commercial and managerial expertise gained over 16 years in the oil an gas industry, working at two small engineering firms and two large multinationals. He is now product line director at Fotech Solutions and maintained the role for almost five years.

-----The news is quoted from Offshore Engineer written by Stuart Large

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