Underground AC cables are seen as a preferable solution to avoid overhead lines that are visible and have a widely dispersed electromagnetic field. However, underground transmission has different technical limitations and they impose additional technical risks to the system operator. While there is wide agreement on the complexity of putting transmission underground, the exact limitations of remain uncertain. For underground cables in the transmission grid, our research objectives encompass the development of optimization-based methods to increase the Cable Hosting Capacities (CHC) in grids, by improving reactive power management, power system harmonics and resonances. For that purpose, it is imperative to explore new operational concepts in systems characterized by a high penetration of underground cables, such as dynamic reactive power management and topological actions considering resonance risk. Finally, new planning guidelines for Extra High Voltage (EHV) underground cables need to be derived based on the improved operational concepts.
