Cables for HVDC Offshore Transmission Networks

Project Information

CABOTioN

Grant agreement ID: 101031088

DOI

10.3030/101031088

Project closed

EC signature date 15 March 2021

Start date 1 September 2021

End date 31 January 2024

Funded under

• EXCELLENT SCIENCE - Marie Skłodowska-Curie Actions

Total cost

€ 219 312,00

EU contribution

€ 219 312,00

Coordinated by

AALBORG UNIVERSITET
Denmark

Periodic Reporting for period 1 - CABOTioN (Cables for HVDC Offshore Transmission Networks)

Reporting period: 2021-09-01 to 2023-08-31

Summary of the context and overall objectives of the project

Driven by current perspectives on the potential of renewable resources, technological advances in the areas of offshore wind as well as solar and storage systems are setting the pace towards the fulfilment of sustainable strategies. In order to face such a challenge, EU countries are focusing their efforts on cost-effective solutions to enable a more effective integration of renewable energy. Energy hubs for offshore wind production and interconnections between nations form a crucial part of the European vision for a greener electricity market.
Aware of the fact that high voltage cables are quite complex and with a different electric behaviour to traditional overhead lines, there is still a gap regarding the proper modelling of submarine HVDC cables since field measurements show the lack of confidence in simulation results with regard to the voltage and current profiles on the core, sheath and armour layers.
To face the ambitious plan to develop an offshore network connecting the Nations bordering the North Sea to harness offshore wind energy efficiently, the CABOTioN project focused on the development of an innovative approach for identification of per-unit-length (p.u.l) parameters of submarine HVDC cables suitable for incorporation in third-party software in a straightforward way. The action exploited the Method of Moments with the Surface Admittance Operator (MoM-SO) and a modified version of Pollaczek's formulae to account for the effects of the cable cross-section and the external media. The proposed approach was validated against the Finite Element Method (FEM), and the impact of more accurate cable parameters on typical analysis involving submarine HVDC cables has been assessed on system-level studies for the connection of offshore wind farms to the transmission grid using HVDC technology or for an HVDC interconnection between AC grids.
The obtained outcomes have made it possible to measure the variances that occur when simplifying assumptions are implemented. This allows for a clearer understanding of the impact these assumptions have on the accuracy of the results. By quantifying these deviations, we can better assess the accuracy of simplified models in representing complex systems. The project will contribute to the development of cost-effective green projects for the integration of renewable energy and the creation of a unified electricity market.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

WP1 – Development of FEM model for submarine HVDC cable: The project developed a detailed model of a submarine HVDC cable using a FEM software (COMSOL), which served as a reference for the accuracy of the proposed approach. The model considered the cable geometry with respective materials and computed the per-unit-length (p.u.l.) parameters of the cable from low to high frequency range.
WP2 – Universal Cable Parameters (UCP): The project implemented a novel approach for the computation of p.u.l. parameters of submarine HVDC cables based on the MoM-SO method and a modified version of Pollaczek's formulae. The MoM-SO method accounted for the skin and proximity effects of the cable conductors, while the modified Pollaczek's formulae accounted for the effects of the external media (sea and seabed). The approach was implemented in a user-friendly web tool and the derived results can interfaces with third-party software like PSCAD, EMTP and ATP.
WP3 – Test cases: The assessed the impact of the proposed approach simulating various events that submarine HVDC cable systems can experience, such as electromagnetic transients originated rm switching and lighting disturbances. The results were compared with those obtained with the conventional approach of modelling the submarine cable as buried in the ground with modified data. The project found that the proposed approach can provide more accurate and reliable evaluations of submarine HVDC cable systems enabling the implementation of a reliable digital twin in a systematic way.
WP4 – Validation with measurements: Validation of the proposed approach with field measurements were impacted by the threats against the European energy infrastructure. Then, the required data could not be disclosed by cable system owners.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

The project addressed current challenges and gaps in the modelling of submarine HVDC cables, i.e. taking the detailed description of the cable cross-section into account and the sea/seabed as the outer media. The MoM-SO formulation enables a seamless representation of stranded or tubular conductors rather than an equivalent solid or tubular conductor for the core, sheath and armour layers. Such achievement is game changer in the seek for a reliable digital twin.
Some of the current challenges and gaps in the modelling of submarine HVDC cables, i.e. taking the detailed description of the cable cross-section into account and the sea/seabed as the outer media were overcome. The MoM-SO formulation enables a seamless representation of stranded and tubular conductors rather than a single equivalent conductor for the core, sheath and armour layers. Such achievement is game changer in the seek for a reliable digital twin and efficient way to compute the electrical parameters of submarine HVDC cables, allowing for more accurate evaluations of offshore energy facilities and transmission systems.
The CABOTioN project has the potential to contribute to the development of cost-effective solutions for offshore wind energy and HVDC interconnections, which are key components of European energy transition goals.. This could have significant socio-economic impact and wider societal implications, including reducing the cost of electrical infrastructure, increasing the penetration of renewable energy sources, and promoting regional cooperation for a greener and unified electricity market.