Use cases
UC1 HV AC/DC hybrid transmission systems
Nowadays, planning and designing high voltage (HV) hybrid AC/DC transnational corridors poses several challenges, particularly when incorporating multi-terminal HVDC configurations. These challenges are amplified when integrating fluctuating energy sources, such as offshore wind, which introduce operational complexities that are not well addressed by current planning tools. Coming to the design stage, there is an increasing need for advanced predictive models and simulation tools. A major hurdle in the design of such hybrid systems lies in fault detection and isolation, which are crucial to maintaining system integrity and minimizing downtime. Furthermore, the economic and regulatory landscape adds another layer of complexity, as such large-scale projects involve significant investment and require harmonization of policies and standards across different countries. This highlights the importance of coordinating national grid regulations, grid codes, and standards during the planning phase to ensure smooth cross-border integration.
Depending on the different applications and goals to support the transnational transmission expansion planning, design and evaluation of hybrid HVAC/HVDC grids in the European context, different portions of the existing, planned and prospective Greek onshore and offshore network have been targeted for test benches in UC.1 of THEUS. Specifically, this UC is focused on utilizing advanced methodologies and tools for transnational HVAC/HVDC system expansion planning (P1) and for evaluating the reliability and resilience of transmission systems (P2).
On the one hand, P1, upon the set-up of a provisional model of a portion of the European system, is used for the evaluation of the selected candidates for transnational transmission expansion planning with particular attention on potential embedded HVDC link/corridor(s) interconnecting continental Greece with bordering zones/islands/countries. Additionally, it considers the integration of planned RES plants, especially offshore wind farms in the Aegean Sea. This activity is based on a close collaboration of RSE and IPTO in the different stages, with the application of combined methodology and tool developed and extended by RSE. It is worth noting that the ENTSO-E CBA Implementation Guidelines will be considered as reference for the scenarios studied. In addition, RSE, together with IPTO, will use P2 to investigate the impact of key HVDC links, such as the Great Sea HVDC corridor, on the Greek network and its associated interconnections from resilience, reliability, and techno-economic perspectives. This analysis will be carried out on an annual hour-by-hour basis optimisation process, considering different architectural scenarios, including potential additional DC links and related offshore projects.
Finally, within UC1, CIRCE will develop a new methodology for standardisation of HV AC/DC smart substations (P3) to standardize and digitize the Building Information Model (BIM) of the HV hybrid AC/DC substation at Arachthos, utilizing data provided by IPTO. The digital model will serve as a crucial tool for simulating various scenarios, thereby improving the reliability and resilience of the system, as well as its resilience towards possible failures.