Our client suffered a fault in one of their four subsea cables connecting the offshore substation to the onshore substation. As a result, the export cable was taken out of service, resulting in a significant reduction in transmission capacity.
N-Sea were awarded the contract to carry out a turn key fast response cable repair, in what was a very challenging and exposed nearshore location, with water depths ranging from 0m to 2m LAT.
Extensive fault finding and engineering resulted in the installation of a spare cable section between the Transition Joint Bay (TJB) onshore and KP1.0 offshore.
N-Sea, as the principal contractor and designer under CDM, were required to deliver all necessary engineering, analysis, and preparations for both onshore and offshore operations before going on to execute the following works.
Key operations included:
• Pre Surveys including MBES, SSS, SBP, magnetometer, LIDAR and onshore CPT’s delivering a viable cable route including UXO ALARP certificate.
• Spare cable loading and transportation from N-Sea’s storage facility in the Netherlands to the UK for mobilisation onto the installation spread.
• Mobilising two jack-up barges (JUB) equipped with cable lay equipment, crane, and accommodation modules, as well as the required jointing equipment including supporting tugs to position equipment.
• Mobilise an additional supporting multi-cat vessel and mooring spread to execute the cable de-burial, fault finding, subsea cutting, and the removal of the faulty cable section, followed by burial of the new cable with CFE after the repair was completed.
• Onshore and beach operations involved setting up a full site to execute a cable landing (float-in), two onshore cable crossings, removal of the old cable, burial of the new cable and thermal grouting of the Horizontal Directional Drilling (HDD). The TJB was also modified to accommodate a new onshore joint.
• Offshore universal joint installation (on-board the JUB) and deployment.
• Onshore joint installation within the TJB and full reinstatement of TJB
The scope was delivered safely and successfully allowing the client to re-energise and resume the transportation of green energy.
N-Sea’s solution was focused on delivering a repair in a safe and timely manner, for the right price, while mitigating risks to existing and to be installed cable asset(s). Our focus was on delivering a right first time repair.
Dale McDonald (Operations Manager for N-Sea Subsea Cables) states that the success of the repair was owed to the knowledge, experience, commitment and professionalism of the project team lead by Roy Schrauwen. The engineering and execution of this very complex scope within a short timeframe, clearly demonstrates N-Sea’s capabilities in all aspects of nearshore installation and repair works. Dale also extended his thanks to the trusted supply chain partners and subcontractors, who also played a big part in this success and thanked the client and its advisors for the trust and cooperation throughout.
Our client stated: “This repair was, without doubt, the most complex cable repair intervention that we have carried out to date. N-Sea actively sought out solutions for the complexity that we faced and delivered the repair safely and successfully. This is the second repair we have completed using N-Sea and we are very grateful for the support and cooperation in delivering this repair.”
The N-Sea group includes the entities N-Sea Offshore B.V., N-Sea Offshore Wind B.V., and UXO Control B.V.
N-Sea Headquarters is located in The Netherlands. N-Sea offices are geographically favorable located to benefit key clients on their operations.
