Distributed subsea substation for Offshore Renewable Energy collection architectures and compliance with metal-enclosed switchgear’s normative references


The deployment of Offshore Renewable Energies is essential to reach climate neutrality. The EU Strategy on Offshore Renewable Energy proposes to increase Europe’s capacities from its current 12 GW-level to at least 60 GW by 2030 and to 300 GW by 2050. In this context, the Offshore Wind Temporary Working Group, composed of representatives of relevant countries and stakeholders, ascertains the need for Europe to focus both on bottom-fixed and floating offshore wind. The latter gives access to remote locations where 80% of the world’s energy potential resides. The increase of such geographically-spread production centres contributes to a more efficient integration into the energy systems.
In current offshore wind farms, substation equipment such as metal-enclosed switchgear apparatuses are only installed at topside level on the offshore substation platform or in wind turbine towers. New studies suggest that innovative collection grids, referred to as Fishbone, would decrease costs, increase wind farms availabilities and ultimately support the floating offshore wind industry’s growth. Such optimised architectures require the installation of new High Voltage (typically 66 kV AC and higher) subsea substation equipment called Smart Hubs that are yet to be standardised.
The purpose of this publication is to introduce and assess the operations of the so-called Fishbone architectures from a switchgear point of view. First the current offshore wind farm architecture will be described to analyse the challenges they face today in floating wind applications. Then the Fishbone collection grid system will be described to explain how it can solve these challenges. Finally, the publication will delve into assessing the existing standard requirements to highlight their limitations when it comes to designing and qualifying subsea apparatuses such as Smart Hubs, be it from a cable system point of view or a high voltage equipment point of view.
There is a need for common work from the floating offshore wind industry different stakeholders to specify the procedures and requirements for the Fishbone architecture to be viable.

Isabelle Najarre, Frank JACQUIER, Leo DALMAR,

Presented at CIGRE 2022