Ground/sea return with electrode systems for HVDC transmission

HVDC transmission is booming worldwide. Despite electrode systems are one of the frontiers of DC technology, being a key component of HVDC links, in the experience of the Authors many aspects of their manufacturing, design and operations are less known among the HVDC community with respect to other components, like cables and converters. Aiming at filling this gap, this paper is a survey on ground/sea return with electrode systems for HVDC links, particularly focused on the preliminary design. The configurations of HVDC systems (monopolar, homopolar, bipolar) are recalled first, highlighting the advantages of ground/sea return. Then, ground electrodes are treated, illustrating the basic parameters and geometrical arrangements for the design of ground electrodes. Later, shore and sea electrodes are illustrated. Considerations relevant to ground current close the paper.