Superconducting Medium Voltage DC Transmission: Architecture, Protection, and Simulation Insights

To address these challenges, several manufacturers have leveraged superconductivity, bringing superconducting cable technology to an industrial level. Superconducting cables can be designed for medium or high voltage applications and can carry extremely high continuous currents, exceeding 10 kA. The SCARLET project, funded under European Union’s Horizon

Europe research and innovation program, started in September 2022, brings together industrial companies and research organizations to demonstrate the industrial feasibility of rethinking large-scale Renewable Energy (RE) transmission. Instead of relying on high voltage DC, the project explores the use of medium DC voltage enabled by superconducting (SC) cable as an alternative means of power transport. Two different SC cables technologies are considered for both offshore and onshore applications, together with their respective protection schemes. They operate at a voltage level that can potentially eliminate the need for costly offshore conversion stations. High temperature SC, specifically using Rare-earth Barium Copper oxide (ReBCo) as the conductor material and cooled with liquid nitrogen is particularly suitable for offshore application. Alternatively, low temperature Magnesium diboride (MgB2) SC cable, cooled with liquid hydrogen, could also be adopted, particularly for in-land installations. In this case, the system is proposed as a bi-energy transport solution, combining both hydrogen and electricity.

Within this scope, an electrical system architecture and its protection scheme is elaborated. As a reference case, a 1 GW system is described, operating at ± 50 kVDC, using a High Temperature

SC cable. The protection strategy is analysed with the target of protecting the cable and converter against DC short circuit faults as well as maximizing the continuity of service.

Moreover, a Resistive Superconducting Fault Current Limiter (RSFCL) used in coordination with mechanical DC Circuit Breakers is considered in the protection scheme. To analyse the interaction between the SC cable, converters, breakers and RSFCL, detailed Multiphysics models of the SC cable and the RSFCL are implemented into an EMTP software as well as an

Average Arm Model of the onshore converter.

Finally, after discussing the simulation results, an overview of the status of the two types of SC cable systems and the RSFCL demonstrators will be given.