Abstract
Developing offshore wind, particularly floating wind, presents significant cost challenges. A major portion of these costs, both CAPEX and OPEX, is attributed to the offshore substation within the power transmission infrastructure. By positioning the substation on the seabed and leveraging the low and stable ambient temperature, a maintenance-free convection cooling system can be achieved, significantly reducing costs.
Subsea power transformers and distribution systems have a proven track record in subsea pumping and compression systems. Since the first installation in 1997, over 20 subsea transformers with wet-mate subsea high voltage power connectors have been deployed, showing a steady increase in power ratings over the years. However, power and voltage requirements for offshore wind farm systems are significantly higher than those of previous subsea solutions for the oil and gas (O&G) sector.
Recently, a technology development program was initiated aimed at creating a 400 MVA subsea substation to simplify and reduce the cost of offshore wind developments. The world’s most powerful subsea transformer, rated at 24 MVA and equipped with 45 kV wet-mate connectors, is currently installed at the Ormen Lange field on the west coast of Norway. By integrating lessons learned from this project and previous relevant experiences from the subsea O&G industry, a 400 MVA subsea substation has been developed. This solution includes a passively cooled subsea transformer with a 230 kV dry-mate connection on the high voltage side and 66 kV wet-mate connections on the low voltage side, all integrated into a scalable connection chamber. Additionally, an advanced monitoring system has been developed to oversee performance and facilitate fault detection.
A comprehensive technology maturity assessment evaluated the various components and systems, leading to the initiation of detailed gap-closing programs and qualification activities. Our conclusion is that qualifying a 400 MVA subsea substation with a passively cooled transformer is entirely feasible and will provide a cost-efficient solution for offshore substations in offshore wind energy.
This paper will provide insights into the state-of-the-art subsea transformers and connection systems and describe the 400 MVA subsea substation technology designed for offshore wind. Compared to a similarly rated topside substation, the subsea alternative reduces overall weight by up to 85%, lowers maintenance costs, and eliminates the need for human presence, thereby reducing exposure to conventional substation hazard
