HTS Cables
Overview
High-temperature superconducting (HTS) cables use superconducting materials that, when cooled to cryogenic temperatures (below -160°C), exhibit near-zero DC electrical resistance. In practical power applications, overall system losses still occur due to AC effects in the superconductor and the energy required for cryogenic cooling. HTS cables can therefore be attractive where the cooling energy and system losses are significantly lower than the losses of conventional cable alternatives for the same power transfer.
HTS Cables are based on special superconducting materials that are cooled down to extremely low temperatures (< 77 ° K or - 213 °C) using liquid nitrogen (or ~20 ° K for liquid helium cooled MgB2 conductor) to activate the superconductivity phenomenon (very low resistance). The superconducting phases are installed inside a vacuum-insulated cryostat to thermally isolate them from the environment. The systems require specialised joints, terminations, and warm-cold transition equipment to accommodate extreme temperature gradients, mechanical tolerances, and continuous cooling for stable operation.
In the case of DSOs, there are a limited number of use cases for implementation of HTS cables. Today, they are targeted towards dense urban areas with space constraints and for specific applications requiring high power density. Therefore, for DSOs this technology is at the demonstration stage.
Benefits
HTS cables offer several advantages compared to conventional cables, depending on the case study:
- Compact, high power-density: Very high current densities enable bulk power transfer at lower operating voltages, reducing the size and footprint of associated substation equipment while achieving high transfer capacity in constrained corridors.
- Easier routing in dense urban environments: Small outer diameters, negligible heat emission to the surrounding soil, and coaxial designs enable installation in narrow ducts or existing utility corridors with reduced clearance requirements and minimal thermal backfill constraints.
- Low external electromagnetic fields: Coaxial or concentric return configurations allow strong cancellation of external electric and magnetic fields, reducing EMF exposure and electromagnetic interference.
- Reduced environmental and urban impact: Limited thermal impact on soil, low visual footprint, and shorter, narrower trenches can reduce construction disruption and ease permitting.
- Case specific loss reduction: For selected applications, total lifecycle energy for cooling and operation can be lower than the compensation of losses in conventional high voltage cables, improving overall efficiency
Challenges
Challenges faced for HTS Cables are:
- Cryogenic cooling required
- Complex system integration
- Cost-intensive materials
- Mechanical sensitivity
- Lack of long-term experience
- Susceptibility to faults during quenches
- Limited standardisation
- Limited purchasing power
HTS cables must be cooled to temperatures of around -196 °C (77 K) using liquid nitrogen or even lower using liquid helium. A consequence of this is high energy and maintenance costs for cooling technology, risk of coolant loss.
Integration into existing networks requires special transition stations (cable terminations, transitions to conventional cables). Specialised terminations, joints, warm-cold transitions, and interfaces to conventional cable systems increase engineering complexity and cost; network compatibility and protection coordination require careful design.
HTS materials such as YBCO (yttrium barium copper oxide) or BSCCO (bismuth strontium calcium copper oxide) are expensive to manufacture and process. HTS cable systems are significantly more expensive than conventional copper or aluminium cables. In total calculation including electrical losses for cooling, the superconducting cables are frequently more expensive as standard solutions.
Superconducting materials are often brittle and sensitive to mechanical stress (e.g. bending, vibration). Protective measures increase the complexity of cable design.
There are only a few long-term demonstration projects. Uncertainty exists about service life, ageing and reliability under real operating conditions. In addition, the low technology readiness level is also a barrier for application within extra HV grids.
A quench is the transition from the superconducting to the normal state can lead to sudden resistance and heat generation, which can ultimately lead to risks of cable damage.
Very limited international standardisation for HTS cable systems exist (in contrast to conventional high-voltage cables according to IEC 62067 etc.).
Superconducting materials are not widely available on the market and are a special product. Moreover, the cost of these materials are high and could be lowered only by heightened demand.
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.
Applications
DSO
| Location: Germany | Year: 2016 |
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| Description: The SWM SuperLink projects sets new standards in energy technology by laying the foundation for the world's largest and most significant implementation of a High-Temperature Superconductor (HTS) cable system. Started in 2016 the project examined whether the use of a HTS cables would be economical, technically feasible and helpful in comparison to common technologies expanding the electricity grid in Munich. In October 2024 the SWM began testing an approximately 150-metre-long test structure in a main substation, which is integrated into the 110 kV grid of SWM network. The tests have been successfully finalised, and the project is in closure. The main objective of the project was to show evidence that a more than 10 km long HTS cable connection between two substations in the northwest and the south of Munich would fit all three necessary dimensions: economically feasible, technically feasible and useful to the grid. The demonstrator successfully showed that all objectives have been reached, and the results are applicable for the planned HTS cable. | |
| Design: Technical key points:
Urban grids are very limited in available space for cable routes and further require necessary equipment. Because of this requirement the HTS-System was designed to fit in with DN200 steel tubes. Special challenges were:
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| Result: As the tests delivered promising results: The construction of an over 10 km long connection between two substations is in planning. After commissioning, this connection would be the world's first commercial use of a superconductor cable. Advantages of the HTS solution:
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| Technology Readiness Level (TRL): TRL 7 | |
| References: | |
| Location: Essen, Germany | Year: 2014 |
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| 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. | |
| Result: 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. | |
| Technology Readiness Level (TRL): TRL 6 | |
| References: | |
TSO
| Location: Germany, Hungary, Norway, Belgium, Sweden, Spain, Denmark, Switzerland, France, United Kingdom and Italy | Year: 2017 |
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| 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. | |
| Result: The operation of a full-scale 320 kV MgB2 monopole cable system that can transfer up to 3.2 GW was demonstrated (demonstration no. 5 of the project). | |
| Technology Readiness Level (TRL): TRL 6 | |
| References: | |
| Location: France, Germany, Ireland, Italy, Portugal, Slovakia, Norway | Year: |
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| Description: The on-going EC funded R&D project SCARLET (Superconducting cables for sustainable energy transition, 2022-2027) is going to develop a demonstrator for 1GW 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]. | |
| Design: The SCARLET demonstrator focuses on high-temperature superconducting (HTS) technology for DC transmission at ±50 kV and 10 kA, enabling compact, low-loss power transfer. The design integrates:
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| Result: | |
| Technology Readiness Level (TRL): TRL 6 | |
| References: | |
R&D Needs
- Higher voltage and longer length demonstrators: AC above 145 kV and DC up to 525 kV at utility-relevant lengths, including full qualification of long-distance joints, terminations, and intermediate cooling stations under realistic load cycles.
- Standardisation and testing: Development of IEC/EN standards for HTS cable systems (type tests, routine tests, prequalification, accessories).
- Fault and quench management: Faster, more selective quench detection, coordinated protection schemes for high short-circuit duties (e.g., 40-60 kA, 1 s), and validated fault current limiter integration.
- Reliability and lifetime: Ageing models and long-term data for superconducting tapes, cryostats, and accessories under thermal cycling, mechanical loads, and transient stresses
- Cryogenic systems: Higher efficiency, modularity, and redundancy of cooling plants; safer coolant management (leak detection, venting).
- System integration: Grid modelling, protection and control for HTS links (AC and DC), interaction with converters, harmonics and reactive power (AC), space-charge and polarity reversal behaviour (DC), and earthing/transfer current studies.
- Lifecycle economics and sustainability: Transparent CAPEX/OPEX and loss accounting including cooling energy, maintainability, and end-of-life strategies; environmental and safety guidelines for urban deployment.
- Compact multi-circuit concepts: Modular, multi-phase/multi-circuit cryostats to maximise corridor utilisation in urban applications.
Demonstrators of superconducting cables for AC voltages above 145 kV and for 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.
Technology Readiness Level (TRL)
The following TRL is observed for high temperature super conducting cables:
TRL 6 for high AC voltage.
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.
To find more information on TRL definition for the Technopedia, read here.
References
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.