Cables and Connectors

The 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 increasing demand; now it is upscaling its HVDC cables, typically 400kV, to 525kV. The company will be supplying at least 10 of these cable systems to European grid operator 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 determining the cost of offshore wind power is what insulation technology 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 Renewables. 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 performance, 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 operation 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 transmission grows. “We are developing a 66kV subsea wet-mate connector system, aiming to be the first in the market with this rating, surpassing our current highest-rated 45kV system.” The product is set for release later this year and targets subsea electrification and floating offshore wind energy markets. Feasibility studies have been conducted for wet-mate connectors rated at 150kV for subsea electrification projects and future floating offshore wind applications to address the requirements of longer step-outs, deeper water and higher volumes of subsea consumers. New subsea LV control connectors and HV connectors for production and processing are also under development.

Demand for greater subsea connectivity is pushing the cable and connector market forward. Hardisty says big data is being utilized subsea to improve well efficiency and economic performance. This trend requires ethernet and fiber optic products. “Recently, we completed a project that involved installing a fiber optic subsea network to facilitate communication between onshore locations and multiple offshore oil and gas production units.”

There is also a transition towards all-electric trees. Siemens Energy has introduced a high-performance fiber optic wet-mate connector for subsea networks, supporting oil and gas and future offshore wind applications.

Additionally, efforts are being made to digitalize connectivity products. Siemens Energy is collaborating with UK universities to develop first-generation digital connectivity products as it explores ways of introducing health monitoring into its products to boost asset management capabilities. This could allow a customer to get data feedback from sensors in a connector system that tells if it is working well or has performance issues such as running too hot or being subject to adverse shock.

Teledyne Impulse-PDM specializes in high-performance subsea fiber optic connectors and interconnect systems, and Andy Cackett, Teledyne Impulse-PDM European Business Development Manager, says he is seeing growing demand for solutions that can perform reliably in less-than-ideal installation conditions. Expanded beam optical connectors are an ideal solution for fiber optic cables, he says, because they use lenses to transmit light between fibers without requiring direct physical contact.

The company’s latest developments in optical expanded beam technology are designed to withstand the most extreme marine environments, offering enhanced resilience to dust and misalignment during installation. “The ability to clean the optics in the field without specialized equipment makes it an ideal choice for demanding offshore applications,” he says. “Additionally, it can be integrated with electrical contacts, providing a versatile solution for complex subsea systems.”

BIRNS has opened a new extreme depth hydrostatic pressure testing facility that allows 48 hour+ continuous precision testing of fiber optic connectors and cable assemblies at 6km in a controlled 2°C (±1°C) environment. The company’s products for these conditions include the Millennium™ underwater dry-mate subsea interconnect series that features fast data speeds and extreme cold and depth pressure resistance. Optical fibers are often used in systems that require greater bandwidth over longer distances, with a smaller footprint, smaller hull penetrations, for applications such as offshore oil and gas, towed arrays, side scan sonar systems and oceanographic instrumentation.

Frontiers in hazardous conditions are continuing to drive the cable industry forward. Space Norway, for example, has announced SubCom as the contractor for a new high-speed connection from the Norwegian mainland to Jan Mayen and Svalbard. The 2,350km subsea fiber optic Arctic Way Cable System will be located entirely within the Arctic Circle.

And in February, Meta announced its most ambitious subsea cable endeavor yet: Project Waterworth. The project will reach five major continents and span over 50,000km (longer than the Earth’s circumference), making it the world’s longest 24 fiber pair cable project. Meta is also maximizing the cable laid in deep water—at depths up to 7,000 meters—and using enhanced burial techniques in high-risk fault areas, such as shallow waters near the coast, to avoid damage.