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Cast Iron Ballast for Dynamic Cables Stabilisation

FMGC has also developed a wide range of cable protection systems which ensure the protection and the stabilisation of the cables thanks to cast iron shells. These split pipes, positioned on the touchdown point section of a cable will ensure a reliable protection and stabilisation solution.

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2019-07-11
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The conventional transmission cables are static and they have been designed to operate in conditions that differ a lot from those experienced by cables for floating offshore structures, either in the Oil and Gas or the Marine Renewable Energy Industries.

Floating platforms moving with the waves, wind and currents require dynamic cables that can adjust to the platform’s motion. As running through the water column and thus experiencing greater levels of mechanical stress due to the dynamic environment, new floating structures request innovations in dynamic power cabling.

Cast iron ballast is a versatile solution that can be adapted to the needs of various offshore installations and improve their efficiency and reliability. Indeed, cast iron ballast offers a cost-efficient and highly versatile solution for the stabilization and protection of offshore dynamic cables, resulting in optimal connection system.

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FMGC Protecting and Stabilizing Cast Iron Shells

 

Offshore Dynamic Cables: Basics and Importance

Floating structures are deployed in deep waters where bottom- fixed platforms are economically unfeasible. The shift in the platform’s design from fixed to floating requires as well a change in the accompanying subsea cables. Static cables can no longer support the loads applied by the floating platform movements. Dynamic cables are the only solution that can resist these solicitations. However they remain exposed to significant constraints induced both by the platform movements, but also by the environment itself, such as the waves for example. Due to these constraints significant damages can occur on dynamic cables, leading to complex and expensive maintenance operations.

The rapid development of the floating wind industry requires a next-generation of dynamic cables, robust enough to resist to the larger stresses acting on them.

Challenges For Offshore Dynamic Cables

Subsea cables are the vital element of an offshore project, delivering the produced electricity to the mainland grid and thus ensuring that all the efforts invested in the development and installation of a floating wind turbine have been worth it.

There are certain considerations that need to be taken into account when designing dynamic cables or looking for solutions to improve their performance.

Moreover, weather conditions in deep waters can be quite severe and unpredictable, which on the one hand can cause a malfunction and on another hand prevent technicians of reaching the damage and fixing it. Thermodynamics due to the contrasting temperatures can lead as well to breakages and performance degradation. The marine growth can also damage the cable by increasing its diameter and weight, inducing additional loads which can also lead to serious damages.

Considering the main cabling issues the offshore wind industry is facing, there is a high demand for efficient solutions, minimizing the great expenses associated with the maintenance and repairs of offshore dynamic cables.

Cast Iron Ballast Contributes to Solving the Most Dynamic Cables’s Problems  

Whether a wind, wave, tidal or an oil and gas production system is used to extract energy, subsea cables are needed to provide this energy back to land. Therefore ensuring the protection and stabilization of these cables is of critical importance to any offshore project.

In order to limit as much as possible the fatigue and damages on the dynamic cable the most used configuration applied to ensure the connection of the turbine is the S wave with buoyancy modules, allowing to reduce the loads.

However, in several cases due to marine growth, but also because of shallow waters and huge waves, the buoyancy is not sufficient to ensure the stability and reliability of the dynamic cables. On configurations such as the Steep wave / Steep S the addition of an anchoring point is considered and improves significantly the performance and stability in severe environment.

         

Example of a dynamic cable with an anchoring point

This anchoring point needs to be carefully designed in order to meet the exact stabilisation needs in accordance with the specifications of the site and the cables.

For this purpose a compact solution is highly recommended because of its limited footprint on the seabed; but also because of its easier deployment with resort to limited offshore installation means.

As an example the cast Iron, with it density of 7.1 in air (6.07 in water) can easily meets these requirements. Moreover, the wide range of shapes, and connection systems, which can be designed and manufactured allow it to fit to a wide range of site specifications and project requirements.

Another critical aspect of the dynamic cable is its ability to resist abrasion and repeated friction with the seabed on the touchdown point. To avoid the risk of important damages this section needs to be protected.

A cable protection system based on cast iron shells is in this case perfectly adapted. Indeed this system will provide both the protection, but also the stabilisation of the cable at the touchdown point.

           

FMGC Cable Protection System - Cast Iron Shells

Subsea cables are a vital part of any offshore project. They have to be secured in the most reliable way in order to ensure the transmission of power, data and control signals across wide expanses.

Thanks to its different partnerships and collaborations with the offshore and MRE industries, FMGC has acquired a deep understanding of the challenges and technical solutions required by the actors of the industry.

Through different collaborations with leading companies such as Principle Power, Ideol, Bourbon in the floating wind industry FMGC has developed a solid expertise in Cast Iron solutions for stabilisation and ballasting purposes.

In addition to the various solutions designed for mooring applications, FMGC has developed as well numerous gravity base structures and gravity anchors which can perfectly meet the needs of the dynamic cable stabilisation.

From several tons to assemblies up to tens of tons, FMGC solutions can be designed in accordance with customer requirements in terms of shapes, weights but also connection specifications (shackle dimensions & specs, applied loads…)

These elements have already convinced Bourbon which has awarded FMGC with the design, manufacturing and procurement of cast iron anchoring point for dynamic cables on an offshore floating wind project.

FMGC has also developed a wide range of cable protection systems which ensure the protection and the stabilisation of the cables thanks to cast iron shells. These split pipes, positioned on the touchdown point section of a cable will ensure a reliable protection and stabilisation solution. Moreover, the design developed by FMGC allows an installation directly on the laying vessel, avoiding the needs for additional marine operations.