High-power medium-voltage superconducting cables for Europe’s energy transition

A particularly well-suited application for superconducting cables is high-power DC transmission at medium voltage (MVDC). The absence of electrical losses and the high currentcarrying capacity of superconductors enable a reduction in voltage while maintaining—or even increasing—the power transfer capacity. One of the key drivers for developing MVDC superconducting export cables is the potential to eliminate expensive and complex high-voltage converter stations by transitioning from high to medium voltage, resulting in significant cost savings. This is especially relevant for offshore applications and renewable energy systems, where power is often generated in DC throughout the conversion chain. The European project SCARLET is developing and demonstrating MVDC cables capable of transmitting power at the gigawatt level, using two superconducting technologies and addressing their protection requirements.

This paper focuses on high-temperature superconducting export cables operating at 50 to 100 kV DC, designed to transmit up to 2 GW over long distances to connect offshore renewable energy sources. The cable design has been validated under rated and transient conditions, including rapid current changes and short circuits. Thermo-hydraulic modelling provides estimates of 20 to 35 km depending on water depth to maintain the offshore cable in cryogenic conditions with a cooling system at one end. This allows for distances of up to 70 km without the need for an intermediate cooling system. Additionally, the system architecture and protection are introduced, together with recent results on the resistive superconducting fault current limiter (RSFCL) developed in SCARLET, which is considered an effective protection strategy.