National Grid NSN Link Ltd and Statnett SF are building an electricity interconnector between Kvilldal in Norway and Blyth in the UK which, on completion, will be the longest subsea interconnector in the world. Fugro supported Nexans’ installation of two high-voltage power cables along a lakebed in Norway using remote solutions and adapting its proven offshore vision technology.
Cable installation is a complex task, especially along the bottom of Lake Suldalsvatnet in a remote part of Norway at the height of the Covid-19 travel restrictions!
With cable-laying vessels unable to access the land-locked site, Nexans required a modular cable work platform (CWP) to be built on the lake, which comprised a work-class remotely operated vehicle (ROV), survey equipment, and Back2Base™ remote data-processing technology. Nexans also engaged Fugro to monitor the cable as it was being laid, both with ROV imagery and survey positioning, and to monitor the cable’s departure angle in real time.
Already a challenging scope of work, the project site had restricted road access, which limited the ROV equipment that could be used onsite. Furthermore, the equipment was height-restricted due to the numerous tunnels en route to the mobilisation location. In short, this project was a great test of Fugro’s problem-solving abilities!
To ensure this project was a success, we applied our transferable skills and decades of experience in cable-laying for the oil and gas, and renewables industries. We also achieved a leaner onsite crew by using remote solutions to adhere to Covid-19 restrictions.
In preparation for this complex operation, and given the equipment dimension restrictions on the CWP, we maintained close cooperation with Nexans as we mobilised the equipment to the site.
Nexans also requested acoustic positioning via an ultra short baseline (USBL) deployment system for the CWP, for which Fugro proposed a pre-existing I-beam and trolley set-up. After Nexans had accepted a customised design developed by our specialist team in Aberdeen, Scotland, we used a local supplier to fabricate the equipment.
Due to Covid-19 restrictions, the factory acceptance test (FAT) on the ROV system was cancelled, but we adapted to this change of plan by conducting a FAT of the topside survey equipment via Microsoft Teams. This remote solution allowed Nexans to see that all their requirements were met and gave them the opportunity to ask any questions before project delivery.
Fugro’s scope of work covered the pre-lay survey, touchdown monitoring (TDM), and as-laid surveys and positioning. The pre-lay survey was conducted using a multibeam echosounder (MBES) to ensure that the cable would not be laid over any lake debris that could damage the cable. We also used the MBES to identify the three cables that were already laid in the lake.
The two new cables were subsequently laid with the ROV conducting the TDM, and Blueview Sonar and survey logging the cable position.
Next, we completed a final as-laid survey using MBES on the two power cables to make sure they were laid correctly and to provide as-built records.
Throughout the operations, no downtime was logged against any of the Fugro equipment. Once the cable lay was complete, we demobilised all our equipment 48 hours ahead of schedule.
Fugro measures the amount of cable paid out and ensures they are correctly laid
Our proprietary InclinoCam technology is designed to provide accurate and continuous verticality monitoring during offshore piling operations for installing wind turbines. However, on this project we successfully repurposed InclinoCam to monitor the cables’ departure angles – this had never been done before.
Fugro’s InclinoCam allowed Nexans to accurately measure essential cable layback for TDM. Our vision technology removed the need for a worker onsite to physically monitor and interpret angles for the most of the operations, which improved operational safety and data accuracy.
InclinoCam keeping a watchful eye on the cable angle of departure
Providing Nexans with real-time information increased efficiency and empowered them to make quick and better-informed decisions. This enabled continuous operations and reduced project risk by accurately measuring the cable’s departure angle and therefore the layback (the distance between the touchdown point on the lakebed and the offset to the end of the chute on the CWP).
Finally, our remote operations capabilities meant that the client was able to access real-time information in their office in Oslo, Norway, just as easily as the onsite installation team. All key clients were also provided with independent remote access, enabling them to log in from any computer, including at home.
Fugro performed excellent work during the challenging times of Covid-19 and in a complex technical environment.
Einar Betten, Nexans Project Manager