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EIC guest editorial Subsea power cables
Critical infrastructure and mitigating risks during installation
Lying across the global seabed is a network of subsea power cables running thousands of kilometres, transporting power to industry and millions of households. Most people are probably not aware of the critical role subsea cables play in our lives, being ‘out of sight, out of mind’.
They are normally buried under the seabed and are not as visible in the same way as a power station or the huge offshore wind turbines you can see dancing offshore, such as those in the Moray Firth. According to a 2019 report published by Wind Europe, offshore wind renewable energy accounted for 15% of power generation across Europe with an increased capacity of 15.2GW. This is a significant increase of clean energy generation over the last 10 years which would not be possible without subsea power cables. The construction of an offshore wind farm is a complex and expensive process. It requires high value assets such as the wind turbines, foundations, sub-stations and subsea cables to be transported offshore using large vessels and barges. These assets can be owned and insured by multiple parties, whose understandable concern is to manage and mitigate the risks involved in the construction. Incidents can be very costly, and a faulty power cable presents significant problems to the owners, contractors and insurers, due to the costs and time to repair or replace the cable and the consequential delays in the project. The mechanical, structural and high voltage integrity of a cable design is confirmed by a type-test process. This is a range of physical tests performed prior to the full manufacturing of the cable. Type-testing is used to confirm the limits for the cable, with respect to its handling, installation and the environment that it can withstand. Cables can experience a wide spectrum of motions and accelerations on a vessel during installation and are handled several times prior to that. It is essential that the handling, transport and installation of the cable does not cause any exceedance of the permissible limits identified in the typetest or any other limits specified by the manufacturer. For owners and insurers, this is where the concern lies; ensuring that all handling and installation operations are done in a manner that respects these limits. Subsea power cables are installed using a specialised Cable Lay Vessel (CLV). It is critical that the compatibility of the CLV and the cable is confirmed before the cable is loaded onto the vessel and installed. Parameters such as carousel bend radii, instances of multi-plane bending and other vessel specific characteristics must be checked with respect to the permissible limits for the cable, as defined by the type-tests.
Subsea cable being pulled-in and laid onshore
During the cable installation process itself, the CLV is operating offshore in a hostile and dynamic environment. There are many variables, but among the most significant of these is the weather. The motion of the vessel at sea, during the voyage to site and critically, at the installation stage directly affect the forces that act on the cable. With a cable, suspended from the vessel during the laying process, installation is a critical operation and one that requires detailed analysis and risk mitigation. Owners and insurers therefore seek to protect their interests (that is manage their risk) and to ensure that the cable is installed using industry best practices. One of the main methods to help reduce incidents and damage to cables, is to identify best practice for the specific project, this is where the engagement of a Marine Warranty Surveyor (MWS) for the planning and execution of installation operations will yield the greatest benefit. The question is often asked ‘who or what is an MWS’? The MWS is an independent body appointed to satisfy the requirements of the Marine Warranty Clause in the Construction All Risks (CAR) insurance policy. Their scope typically includes independent review and approval of all procedures and related engineering, confirmation of the suitability of vessels and equipment, witnessing and approval of site preparations and critical operations, onshore and offshore.
be profiled in thisand section please contact Lucy Chakaodza, EIC Editor, Media and Communications Manager... Get in in touch touchTo Share your news views... Email lucy.chakaodza@the-eic.com newsdesk@the-eic.com • Phone +44 (0)20 7091 8600
