Using AIS monitoring to reduce the risk of subsea cable failures caused by external factors

By Siddharth Uppal, Product Manager Service & Installation at NKT

Subsea power cables are critical infrastructure for the transmission of renewable energy globally. Growing demand for renewable power has led to an exponential increase in the number of offshore wind farms in Europe and around the globe. The European Commission predicts having an estimated offshore wind capacity of at least 60 GW installed by 2030, with a view to expanding that capacity to up to 300 GW by 2050. This exponential growth in demand in turn means a tremendous increase in demand for subsea power cables. Another factor that will amplify the rise in demand is the increasing need for subsea interconnector cables, which are used to connect grids across borders via land or sea to ensure increased grid reliability and enable active trading of energy.

Following installation of these submarine cable systems in the renewable energy infrastructure, the key objective is to ensure power transmission remains safe and operational. Thanks to the emergence of new technologies over the years, HV submarine cable failures are now rare. Yet the high cost of repairs and the losses incurred due to outages cannot be ignored. Repairing a subsea power cable can take up to 90 days – or even longer. This is dependent on various factors, such as the availability of skilled personnel, cable-jointing equipment, a suitable repair vessel, and the weather conditions, among other things. According to export cable reliability report 2017 by Offshore Wind Programme Board (OWPB), average repair costs £12.5m, excluding transmission losses. This raises the question: are we doing everything we should to prevent subsea power cable failures?

Most new innovations in monitoring technology have focused on detecting what is happening inside a cable; however, most preventable threats to cable health are created elsewhere – the cable’s environment. Cable failures can be the result of various factors – either human error or natural. Studies have found that, at depths greater than 1000 m, faults can be caused by natural events such as underwater seismic activity, underwater landslides and current abrasion, for example. At depths of less than 200 m, faults are nearly always caused by human activities such as fishing and anchoring. Fishing is one the most commonly cited causes of power cable failures.
According to KIS-ORCA (the Kingfisher Information Service—Offshore Renewable and Cable Awareness), 70% of all cable faults are caused by fishing and anchoring activities, while roughly 14% are the result of natural hazards, such as current abrasion or earthquakes. Therefore, human activity clearly is one of the main cause of subsea power cable failure and expensive errors of this kind must be minimized.

There is a clear need for monitoring of marine activity near power cables. AIS (Automatic Identification System) monitoring technology is ideal for this. Vessels carry AIS transponders which regularly transmit AIS messages. These messages contain a wealth of data, including location, type, vessel name, navigational data, status, heading, speed and MMSI number, for example. Satellites and/or VHF antennas from multiple data providers can be used to receive signals, providing full coverage of the area to be monitored. All this data can be fed into the AIS monitoring software system to generate a live view showing the real-time movements of marine traffic on the map (Figure 1).

The system also enables the asset needing protection to be loaded in the software and protection zones to be set around it. These protection zones are set based on a detailed desktop study and risk analysis, covering parameters such as fishing, shipping and transit activities, cable burial assessment, existing subsea infrastructure, bathymetry, seabed sediments and benthic ecology (fish, shellfish, etc.). Custom rules are defined in order to monitor vessel behavior within the protection zones (such as fishing and anchoring) and an alert is triggered to warn users if a rule is violated.

Detailed analysis of these alerts helps build an accurate picture of where there is most risk and enables more effective mitigation plans to be made for the future.
Data analysis enables users to:

• Redefine rules and protection zones to more effectively protect assets
• Create database subgroups for different industry sectors or risk factors in order to target specific stakeholder groups more effectively
• Create heat maps for vessel activity and use them to refine the repair preparedness plan
• Access historic data for use as evidence in the event of cable damage (reclaiming repair costs)

NKT’s AIS Subsea Asset Protection system provides a range of benefits for submarine assets, taking external causes of failure into account.

The product offering consists of:

• AIS Software with a live vessel data feed, providing a real-time picture of what’s happening in the area around the asset.
• 24/7 Monitoring service to proactively identify key vessel threats, trends and stakeholders in the asset’s region and take necessary interventions to avoid cable damage.
• Marine Liaison service dedicated to proactively communicate with all relevant stakeholders identified by the monitoring team.
• Periodic analysis and reporting provides a historical trend comparison and an overview of all marine liaison activity beyond monitoring, and takes into consideration any changes to fishing and vessel transit patterns.

NKT’s Service and Installation division is committed to reducing the impact of cable failures by minimizing the duration of outages and keeping the systems operational with our comprehensive offshore product portfolio (Repair Preparedness Plan, Service Level Agreements and Marine Resource Plan). We also help our customers improve system productivity with our cable monitoring solutions.

For more information or a free product demo, visit: https://www.nkt.com/cable-services/cable-monitroing/AIS
Or send us an e-mail: [email protected]