Page 33: of Marine Technology Magazine (May 2025)

he export cables that bring offshore wind power to shore are already so massive that one meter of cable can weigh 300kg. Nexans had previously upscaled its production facilities to cater for in-

T creasing demand; now it is upscaling its HVDC cables, typically 400kV, to 525kV. The company will be sup- plying at least 10 of these cable systems to European grid op-

POWER erator TenneT for multiple 2GW projects.

The cables will be heavier, and they have the potential to get hotter, necessitating deeper burial in the seabed. The potential risks can be a determining factor in the design of the cable. If a live cable were to be damaged, says Pascal Radue, EVP for

Power Transmission at Nexans, the power released would be like that of bringing a French high-speed train travelling at 350 kilometers an hour to a standstill in 50 meters.

Therefore, part of the calculation that goes into determin- ing the cost of offshore wind power is what insulation tech- nology is suitable and what scope there is for standardizing cable layout across the geographic range of the project. Most of these cables are tailor made for an application, says Radue, so there’s not a lot of repeatability.

Tidal energy systems face similar challenges to offshore wind, with the harsh constant motion of tidal areas a key challenge. SMI recently took part in the upscaling of a tidal system in Japan led by system integrator Proteus Marine Re- newables. Here the durability, longevity and reliability of the cabling system was critical to success.

Glen Richardson, Engineering Director at SMI, says water resistance is also a top priority. Polyethylene-based polymer cables have demonstrated exceptional subsea perfor- mance, maintaining durability for over 25 years with minimal degradation. “SMI’s traditional design philosophy prioritizes using thermoplastic over-molding to seal cable terminations to connectors, especially with polyethylene-based polymer cable sheaths,” says Richardson.

However, due to budget limitations and the need to perform terminations locally in Japan, SMI’s linear seal technology was chosen. The linear seal provides a durable and consistent seal between the polyethylene cable sheath and the connector. “It applies a measured level of compression akin to traditional

O-seal technology, ensuring the seal remains intact during op- eration and exposure to the challenging turbine environment,” says Richardson.

Jonathan Hardisty, Head of Product Development for

Subsea Products, Siemens Energy, sees upscaling in the subsea connector business as the need for higher power trans- mission grows. “We are developing a 66kV subsea wet-mate connector system, aiming to be the