ENTSO-EHigh Temperature Superconducting (HTS) Cables
Overview
Superconducting cables are capable of carrying electrical current without electrical losses. In turn, to activate the superconductivity phenomenon, which is responsible for zero resistance, the cables need to be cooled down to very low temperatures (below -160°C), which requires an additional cooling system and additional electrical energy. For this reason, the superconducting cables are used in applications where the energy needed for cooling is significantly lower comparing to the electrical losses of conventional cables.
High Temperature Superconducting cables (HTS Cables) are based on special superconducting materials that are cooled down to extremely low temperatures (above 77° K or – 213 °C) using liquid nitrogen (or liquid helium for MgB2) to activate the superconductivity phenomenon (very low resistance). The superconducting cables are placed in a pipe with vacuum (cryogen) which thermally isolates the superconductor from the remaining environment. The technology requires special cable joints and specific cable termination for extreme temperature differences and permanent cooling for keeping cryostat.
Benefits
HTS cables offer several advantages compared to conventional cables, depending on the case study:
- Easier cable routing especially for urban areas: HTS cables are compact and does not emit heat. For this reason, it can be routed through a narrower space. Examples of where it could be routed are underground through existing gas, oil, water, or electric corridors or along highway or railway rights of way or in the old mines, also there are no special requirements for the open trench approach.
- Low impact on the environment: a superconductor system does not emit heating which is beneficial if routed directly in a soil. HTS cables can be constructed in a way where they do not emit any electric and magnetic fields. Moreover, they will not require additional routing if combined with existing complex infrastructures.
- High Power carrying capacity: achieving higher levels of current density means that operational voltages can be reduced while still facilitating bulk power transfer at high capacities. Lower operating voltages reduces the size and volume of the electrical equipment required at both ends of the cable.
Current Enablers
The price of superconducting materials is high and can be lowered only by an increased demand. In total calculation including electrical losses for cooling, the superconducting cables are frequently more expensive as standard solutions.
Moreover, the superconducting materials are not widely available on the market and are a special product.
The low technology readiness level is also a barrier for application in extra high voltage grids.
R&D Needs
The on-going EC funded R&D project SCARLET (Superconducting cables for sustainable energy transition, 2022-2027) is going to develop a demonstrator for 1 GW medium voltage (± 50 kVDC and 10 kA) high-temperature superconductive cable. The project also tests a high-current superconducting fault current limiter module for grid protection [5].
Feasibility studies and, after cost-effort-environment benefits were weighted, demonstrators of superconducting cables for Alternating Current (AC) voltages above 145 kV and for Direct Current (DC) voltage 525 kV are needed, especially for longer sections where the application of conventional cables is highly restricted for example routing through industrial areas or for temporary applications to increase the flexibility of system extension or bridge the faulty components.
The technology is in line with milestone “Development of high power innovative transmission components” under Mission 1 of the ENTSO-E RDI Roadmap 2024-2034.
TSO Applications
Examples
| Location: Germany, Hungary, Norway, Belgium, Sweden, Spain, Denmark, Switzerland, France, United Kingdom and Italy | Year: 2017 |
|---|---|
| Description: BEST PATHS was a collaborative project of 40 leading European organisations from science and industry, supported by the EC FP7 (2014 – 2018). The project investigated the feasibility of technological innovations that could advance high-capacity transmission links. This included a demonstrator project dedicated to superconducting electric lines, to validate the novel MgB2 technology for GW-level HVDC power transmission. | |
| Design: Through insulated cross-arms, long-term tests with HTLS as well as dynamic line rating, existing lines are to be optimised to maximise power transmission. | |
| Results: The operation of a full-scale 320 kV MgB2 monopole cable system that can transfer up to 3.2 GW was demonstrated (demonstration nb. 5 of the project). | |
| Location: Essen, Germany | Year: 2014 |
|---|---|
| Description: The AmpaCity project is a 1 km 10 kV HTS cable installed in 2014 to replace a 110 kV underground cable system connecting two 10 kV substations in Essen Germany. | |
| Design: The three-phase, concentric cable replaces the conventional 110 kV copper line connecting two substations in central Essen and eliminates the need for a high-voltage transformer at one of the substations. | |
| Results: The cost of the energy required to cool the cable down to eliminate its resistance over its lifecycle was found to be 15% lower than the equivalent cost of compensating losses in conventional 110 kV cables. HTS are mentioned as the best technical and economically viable solution to avoid the necessary extension of the 110 kV grid in urban areas. The link has been decommissioned 2024 due to changed grid requirements. | |
| Location: Munich, Germany | Year: t.b.d. |
|---|---|
| Description: The SuperLink project (Germany) was launched in 2020: it investigates how the load centre in the south of Munich can be connected to the main feed of the transmission grid in the north by means of a 12 km long HTS cable. | |
| Design: 500 MVA, single and slim 110 kV HTS cable. The cable should fit into partially existing empty conduits with a diameter of 150 mm, thus reducing laying costs. | |
| Results: Work in progress. | |
Technology Readiness Level The TRL has been assigned to reflect the European state of the art for TSOs, following the guidelines available here.
- The following TRL is observed for high temperature super conducting cables:
- TRL 6 for high AC voltages.
- TRL 5 for extra high AC voltages.
- TRL 6 for DC voltage at 320 kV.
- TRL 5 for DC voltages at 380 kV and 525 kV.
References and further reading
M. Yazdani-Asrami et al., “High temperature superconducting cables and their performance against short circuit faults: current development, challenges, solutions, and future trends,” Supercond. Sci. Technol, vol. 35, p. 083002, Jun. 2022.
alvin C.T. Chow et al., “High temperature superconducting rotating electrical machines: An overview”, Energy Reports, vol. 9, pp. 1124–1156, Dec. 2023.