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ENERGIX-Stort program energi

Future Design of Subsea High Voltage AC Power Cables for Offshore Renewables

Alternative title: Fremtidens HVAC sjøkabler for fornybar energiproduksjon

Awarded: NOK 7.4 mill.

Project Number:

317883

Project Period:

2021 - 2024

Funding received from:

Location:

Subject Fields:

Nexans Norway, together with research partners, aims to develop the next generation lead-free power cables. In the FutureCaRe project, we will perform testing and develop modelling tools to secure high reliability and long lifetime of lead-free (wet design) high voltage AC subsea cables. High Voltage (HV) wet design cables will support the development of renewable floating energy sources such as offshore wind, offshore solar power, wind-hydrogen, and wave power technologies. Traditionally, subsea XLPE cables rated at or above 52 kV are equipped with a metallic water barrier (extruded lead sheath) to prevent ingress of seawater to the cable core (dry design). Cables rated below 52 kV do not need a metallic barrier (wet design). The technical need for a water barrier is driven by the ageing properties of the insulation system, which are negatively affected by the presence of water. The potential EU ban on the use of lead by 2026 provides a critical driving force for the research, development, and demonstration of high voltage subsea cable designs without lead sheaths. However, there are other good reasons to use a lead free (wet design) where possible. These include environmental and health concerns caused by lead on people and environment, technical benefits such as weight and dynamic performance, and cost savings. The next generation subsea cables facilitate new cost-reducing concepts for future transportation of energy produced by offshore renewables such as floating wind- and solar farms. As demands for renewable energy increases, reliable high voltage subsea cable designs will be of crucial importance for meeting the ambitious demands and requirements to reduce the European carbon footprint. In this project, a lifetime model for wet designed HV subsea cables will be established based on long term wet ageing tests on full-scale cables. A full scale 52 kV cable has been manufactured using state of the art manufacturing line and high voltage insulation system. In addition, another full-scale cable featuring a new innovative HV insulation system will be manufactured. The full-scale cables will be used in wet ageing tests to generate test data for predicting the lifetime of HV cables. The diffusion of ions in the insulation system will also be studied in this project by utilising a measurement methodology developed in a previously funded project. The presence of ions in the insulation system has been shown to accelerate water treeing, the main degradation mechanism in wet design cables. A purpose-built test setup will be used to study the diffusion of ions through the insulation system of modern HV cables. Dynamic HV cables will experience larger mechanical strain in the insulation system during operation compared to medium voltage cables with smaller diameter. A master thesis, with the aim of studying the effect of strain on possible enhancement of water treeing will also be part of the project.

Today, high voltage (HV) subsea cables with voltage ratings from 52 to 420 kV are traditionally equipped with an extruded outer sheath of lead to avoid ingress of seawater to the cable core (dry design). There are many good reasons to abandon this "old" design. These includes e.g. the development of micro-cracks in the lead sheath over time caused by vibrations and dynamic bending, the heavy weight of cables causing significant strains in load bearing elements, and environmental considerations of using lead. Dynamic cables connected to a floating topside structure and a fixed installation at the seabed, are subjected to everlasting cyclic mechanical loads (waves) during service excluding lead sheathed cable designs. Dynamic cables must be used for connection of renewable floating energy sources such as offshore wind, the emerging offshore solar power, wind-hydrogen and wave power technologies. The potential EU ban on the use of lead by 2025 provides a critical driving force for the research, development, and demonstration of high voltage subsea cable designs without lead sheaths. This also calls for new designs for large high voltage transport cables installed at the seabed for energy transfer of e.g. floating offshore renewable energy production from offshore substations to shore, and long subsea AC interconnections. Nexans Norway will in the FutureCaRe project together with the research partners perform testing and develop modelling tools to secure high reliability and long lifetime of the next generation high voltage AC subsea cable designs. The next generation subsea cables facilitates new cost-reducing concepts for transportation of energy produced by offshore renewables such as floating wind- and solar farms in the future. As demands for renewable energy increases, reliable high voltage subsea cable designs will be of crucial importance for meeting the ambitious demands and requirements to reduce the European carbon footprint.

Funding scheme:

ENERGIX-Stort program energi