Monitoring technologies across offshore wind have advanced significantly in recent years. Turbines, substations, and electrical systems are increasingly equipped with sophisticated condition monitoring and performance analytics. By contrast, subsea cable monitoring has historically relied on approaches that provide only intermittent insight into asset condition. Unlike many electrical assets, subsea power cables rarely fail due to electrical faults alone. Instead, degradation is typically driven by mechanical processes that occur over long periods of time. These include fatigue from repeated loading, abrasion caused by seabed interaction and cyclic strain resulting from tidal currents, waves, and gravity effects.

These stresses are not evenly distributed along a cable route. Instead, they tend to concentrate at specific high-risk locations such as touchdown points, cable protection systems, monopile interfaces, or sections where burial depth changes. Traditional monitoring approaches have relied heavily on periodic inspection campaigns, including remotely operated vehicle (ROV) surveys and targeted seabed assessments. While these methods provide valuable information about the physical condition of the cable and its surrounding environment, they effectively offer only snapshots of behaviour separated by months or years.

As a result, many of the progressive mechanical processes that ultimately lead to cable failure remain difficult to observe as they develop. Recent advances in fibre-optic sensing are beginning to offer new ways of understanding subsea cable behaviour.

The value of long-term monitoring

Modern subsea power cables typically contain optical fibres installed for communications or control. Distributed acoustic sensing (DAS) technologies can now repurpose these fibres as continuous sensing elements using a device known as an optical interrogator, typically installed at the onshore substation. The interrogator sends rapid pulses of laser light along the fibre and measures the tiny portion of light that is naturally scattered back along its length. When the cable experiences strain, vibration, or movement, these changes subtly alter the backscatter pattern detected by the interrogator. By analysing these variations, the system effectively turns fibre into a continuous line of sensing points along the cable route, capable of detecting mechanical behaviour across many kilometres.

In practice, this creates thousands of sensing points along a single cable. Rather than monitoring a small number of locations, operators can observe how the entire cable responds to environmental loading conditions. The result is a fundamentally different type of monitoring, one that captures continuous structural behaviour rather than isolated inspection observations.

While distributed sensing technologies have existed for several years, one of the key barriers to their widespread use has been the sheer volume of data generated. DAS systems produce extremely large datasets, as signals are sampled thousands of times per second across the length of a cable. Historically, this has limited monitoring campaigns to relatively short durations, often lasting only days or weeks. However, long-term datasets are precisely what is required to understand cable degradation. Data compression techniques, as well as modern connectivity methods now allow the transmission and analysis of these high data volumes.

Mechanical damage rarely occurs as a single event. Instead, it accumulates gradually through repeated loading cycles, environmental changes, and seabed interaction. By analysing behaviour over months and years rather than short monitoring windows, operators can begin to identify trends such as increasing vibration amplitudes, evolving strain responses, or changes in cable exposure. These insights allow degradation mechanisms to be tracked as progressive processes rather than isolated anomalies. This shift from short-term observation to long-duration monitoring is increasingly seen as an important step towards predictive cable management.

Continuous fibre-optic monitoring has already been applied to operational offshore wind infrastructure. At RWE’s Arkona offshore wind farm in the Baltic Sea, fibre-optic monitoring has been used to observe mechanical behaviour along subsea power cables under real operating conditions. The system analysed several months of data captured during winter storm periods, when cables experience some of their highest loading conditions.

The monitoring revealed how vibration and strain accumulated in different sections of the cable route, including areas that are traditionally difficult to inspect, such as within cable protection systems and near turbine monopiles. By correlating these measurements with environmental conditions, it became possible to identify where mechanical loading was concentrated and how it evolved over time. This type of insight helps operators understand which sections of cable may be approaching fatigue limits and where preventative intervention could be most effective.

Rather than waiting for faults to emerge, operators gain the ability to observe how degradation mechanisms develop under real environmental conditions.

Supporting a shift towards predictive maintenance

As offshore wind projects grow in scale, the importance of reliable subsea infrastructure will only increase. Multi-gigawatt developments and long-distance export cables will require monitoring approaches that can provide greater visibility of asset behaviour across entire cable networks.

Continuous fibre-optic sensing offers a way to complement existing inspection methods by providing a persistent view of mechanical conditions along the cable route. This can support more targeted inspection campaigns, improve understanding of environmental loading and allow operators to identify emerging failure risks earlier and plan their maintenance and repair at lower cost.

In practical terms, this means moving away from a reactive model, in which faults are discovered after they occur, towards a more predictive approach to cable integrity management. As offshore wind continues to expand across increasingly complex marine environments, the ability to observe cable behaviour continuously may become an essential part of ensuring the long-term reliability of the sector’s subsea infrastructure.

This article was written Chris Minto. He has been working in the application of acoustics for the last 30 years, and is currently Co-Founder and Co-Director of In-deximate, a start-up organisation dedicated to preventing failure of subsea cables. Chris and his colleagues have worked at the forefront of fibre optic sensing for the last 16 years, pioneering the use for cable failure identification.

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Energy Global’s Winter 2025 issue

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Read the article online at: https://www.energyglobal.com/special-reports/23032026/improving-subsea-power-cable-reliability-in-offshore-wind/