Progress updates – Subsea substation

Updates from the “Subsea substation” subproject (SP3)

September 2022

SP3 Wet design cable
SP3 Lead Marius Asak (Aker Solutions)

The goal of sub project 3 is to establish requirements for subsea substations to connect to floating wind farms, and qualify a 66kV subsea connection system consisting of a wet mate connector, dry mate connector and penetrator. The base case system for Ocean Grid has been established and details can be found in picture below.

The existing field-proven subsea transformer unit from ABB is scalable up to 300 MVA with its current design. This is validated through advanced simulations of thermal and electrical performance of the transformer, built on years of experience from full-scale system testing and operation.

The new Benestad 66kV power string will be built on the existing 36 kV power string, which is currently going through qualification testing. The illustration above shows dry mate and wet mate connectors.

Testing of critical components has started, and the system design will be frozen in December 2022.

The battery limits for the subsea substation in the Ocean Grid program have been established and agreed between the partners, see the picture below for details.

Root cables from the turbines are for the base case system rated to 75 MVA. This corresponds to five 15 MW wind turbines.  The root cables are terminated in the subsea termination assembly (STA), and the base case system features 4 STA connected to the subsea transformer, resulting in a transformer size of approximately 300 MVA.