Superconducting cables: maximum transmission capacity and near-zero losses

Our market-proven superconducting cables are transforming urban power. These compact cables allow grid operators to transfer more power at medium voltage, while reducing land take, cutting the amount of capital equipment and eliminating heating and electric and magnetic fields (EMF).

What is superconductivity?

Superconductivity is the loss of electrical resistance which takes place in some materials when they are cooled to an extremely low temperature.

This phenomenon – discovered in 1911 – has major implications for the way electricity is transmitted and distributed. By incorporating superconducting wires or tapes into cables, it is possible to create near-perfect electrical conductors.

Superconducting cables for electricity transmission are manufactured using materials known as High Temperature Superconductors (HTS). The word “high” in this context is relative to absolute zero. Despite their name, High Temperature Superconductors need to be kept extremely cold (minus 200 degrees centigrade). Cooling is achieved using a cryogenic envelope – a thermally-insulated jacket that surrounds the cable. The coolant used is liquid nitrogen. This is relatively inexpensive, easy to manage and harmless to the environment.

Interview with Jacques Lewiner (physicist and inventor) on superconductivity

White paper
Superconductors for electricity grids

The future is electric. From transport to heating, almost everything that currently depends on fossil fuels will need to switch to electricity if zero carbon goals are to be achieved.

Download our white paper

Nexans is a global leader in high temperature superconductor* (HTS) technology for power grid applications. Our offer includes both HTS cables and HTS fault current limiters. Let’s take a look at these products in more details.

HTS cables – transforming urban power

Transmission system operators (TSOs), distribution system operators (DSOs) and railway operators need a way to satisfy the ever-growing demand for energy in cities and transport networks. Nexans HTS cables are designed to meet that demand.

  • Minimal land take – rights of way for HTS cables are up to ten times narrower than those for conventional cables and lines. Fewer cables are required and there is no need for space between phases. This reduces the need for permitting, minimises disruption to the public, accelerates deployment and contributes to lower costs.  
  • Energy savings – superconducting cables are ultra-efficient conductors with zero or near-zero resistance. The power saving achieved in this way is greater than the energy expended to maintain conductors at a low temperature. By contrast, conventional long-distance transmission systems using aluminium and copper conductors experience power losses of around 10%. This amounts to around 180 TWh annually in Europe alone – enough to power three cities.
  • Zero heating – superconducting cables do not emit heat, no matter how much power they carry. This has three important benefits. First, it means that HTS cables can be direct-buried in the ground, accelerating project delivery and reducing costs, and deeper than conventional cables, as heat exhaust is not an issue. Second, the absence of heating effects means that there is no reduction in transmission capacity when other cables are run in proximity. Third, there is no soil drying effect – a key consideration if HTS cables are run alongside conventional cables.
  • No need for tunnels – as noted above, HTS cables can be direct-buried. This means that tunnels and pipes for cables are not required – even in high capacity transmission projects. In cases where pipes or tunnels already exist, retrofitting HTS cables in place of conventional cables dramatically increases the transmission capacity of these assets.
  • Minimal EMF – HTS cables are fully shielded to prevent the generation of stray electromagnetic fields, minimising effects on surrounding infrastructure and allaying public concerns about EMF.

World-leading innovation: our references include the LIPA 138kV AC cable project in Long Island USA, and the Ampacity 10kV AC link in Essen in Germany – the world’s longest superconducting cable, in use for seven years.

Interview with Charles Beigbeder, CEO Audiacia, on superconducting cables

Six questions about superconducting cable systems

Can superconducting cable systems save money?

Yes. The greatest potential for savings can be found in projects where medium-voltage HTS cables are used as a replacement for either conventional medium voltage or conventional high-voltage cable systems in urban settings. Savings are achieved through reductions in land take, civil works and permitting, and also through a reduced need for HV transformers and substations in city centres.

What is the optimal length for HTS cables?

Current HTS projects are between 200m (about 600 feet) and 10km (6 miles). However, there is no technical limit to how long an HTS cable can be. Nexans manufactures superconducting cable in drum lengths of about 500m (1,640 feet) to ease handling on site.

Do I need new expertise to manage superconducting cables once installed?

An HTS cable system is managed in much the same way as a conventional cable system. The only difference is the need to manage the cryogenic system. Cooling is achieved using commercially-available equipment.

Do HTS cables have any special maintenance requirements?

Aside from the routine inspection and maintenance of the cooling system, there are no special maintenance requirements associated with HTS cables.

How durable are superconducting cables?

HTS cable systems have been used in grid applications for more than eight years, with complete success. A key point about superconducting cables is that they are less susceptible to ageing than conventional cables. This is because the extremely low temperature within the HTS cable minimises heating, extending the life of insulation within the cable. By contrast, heating is one of the main causes of insulation degradation and ageing in conventional cables. This suggests that the lifespan of HTS cables is likely to be equal to or potentially greater than that of non-HTS cables.

What happens if a cable is damaged?

The coolant used in HTS cable systems is nitrogen, which is chemically inert in both its liquid and gaseous states. It is not harmful to the environment.

Superconducting Fault Current Limiters (SFCLs)

Protecting grid assets with lightning-fast protection from fault currents

Growing demand for electricity and the rise of decentralised generation means that distribu¬tion grids are working harder than ever before. One consequence of this is the increasing risk of fault currents caused by short circuits. Fault currents can damage critical assets such as transformers and switchgear. They can also result in power outages, with serious impacts for businesses and consumers.

Superconducting Fault Current Limiters (SFCLs) are designed to tackle these challenges. In normal operation, the SFCL allows current to flow easily and with no losses.

Superconducting fault current limiters can be used in any type of distribution grid. These include private power networks for railways and industry. A key point is that SFCLs can be used in conjunction with any type of distribution cabling – not only superconducting cables, but conventional copper and aluminium cables as well.

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