Review of global HVDC subsea cable projects and the application of sea electrodes

Sea electrodes have been used since the first HVDC subsea links were installed in the 1950s and provide a simple proven solution for the return current path. Today around 30% of the approximately 40 HVDC subsea links in service use sea electrodes as the return current path under normal or emergency operation conditions. This paper reviews the evolution of interconnectors with sea electrodes and the factors, such as location, environmental impact, current capacity and financial factors (cost, flexibility, losses) which need to be assessed before adopting a sea electrode. In particular findings from environmental studies undertaken on existing sea electrodes are reviewed, as well as, the detailed content of recent Environmental Impact Statements for HVDC projects with proposed sea returns. Finally, the reasons for a change in design on links with a proposed sea return to a metallic return are also considered.