Subsea Substations as an Economical Enabler for Floating Offshore Wind

Summary This paper outlines the authors' application of their expertise in transformer and high-voltage technology from the oil and gas sector to develop Subsea Substations, 66 kV Collectors and wet mate connectors for floating offshore wind and renewable energy applications. The technical capabilities have been expanded to include 400 MVA subsea transformers, featuring 66 kV inter-array cable inputs and 220 kV transmission to shore. Subsea transformers benefit from stable seabed conditions, which mitigate risks such as partial discharges and eliminate explosion hazards. They are designed for long lifespans (30-50 years) and high reliability. Their weight and size are optimized for installation using well-established subsea construction vessels, eliminating the need for costly heavy lift operations. Utilizing a 66 kV Subsea Collector with switchgear for star-configured turbine connections, instead of the more common daisy chain method, reduces cable copper usage by 50-60 %. This approach allows for identical floating turbines with much smaller dynamic cables, thereby reducing risks and costs associated with cables and marine operations. The final large dynamic cable, which carries all current in a daisy chain configuration, is replaced with a static seabed cable in a Collector configuration. Subsea substations are significantly smaller than their topside counterparts, using 80-90 % less material. This not only reduces CO2 emissions but also results in substantial cost savings for the substation. Overall, these technologies can typically reduce costs by around 10 % for a 1 GW floating offshore wind park, making a significant contribution to revitalizing global offshore wind business cases.