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Welcome to the electricity superhighway
How can I reduce my transmission losses? Electrical engineers have puzzled over this question ever since the first power station opened nearly 140 years ago. Transmission technology has come a long way since then. But losses remain a problem.
Just over 6% of the electricity generated in Europe never makes it to the consumer. Some of it – about a quarter – is lost in transformers. But most of it vanishes on its journey through transmission and distribution systems. These systems use copper or aluminium conductors. When electricity flows, heat is generated in the conductor and energy is lost.
Six percent may not seem very much – and Europe’s grids are highly efficient by global standards. But the losses add up to a surprisingly large amount. In fact, the total amount of electricity lost in an average year is about 180TWh (Source: Eurostats). Or put another way, enough to power Paris, London and Berlin combined (Source: Eurostats)
“ Superconductors are perfect electrical conductors. There is no resistance, no heating and no loss. ”
Could superconducting systems help?
Superconductors are perfect electrical conductors. There is no resistance, no heating and no loss. Superconducting systems for the electricity industry – which include cables and fault current limiters – are built using High Temperature Superconducting (HTS) materials.
The word “high” in this context is relative to absolute zero. HTS materials are actually very cold – minus 200 degrees centigrade. HTS cables incorporate thermal insulation and the coolant used is liquid nitrogen, which is inexpensive and does not harm the environment.
Another characteristic of HTS cables is that they are surprisingly small. A single 17cm diameter cable can transmit 3.2GW, equivalent to the power of three nuclear reactors. They are also capable of carrying extremely high currents. And there is no electromagnetic field, so interference with surrounding power and telecoms cables is eliminated.
Annual electricity transmission loss in Europe (Source: Eurostats)
temperature inside a superconducting cable, achieved with liquid nitrogen
a superconducting cable of this diameter can transmit the power of 3 nuclear reactors
energy loss in a superconducting transmission system
Superconductors meet real needs
Superconducting systems solve many of the most pressing problems faced by distribution and transmission system operators. Here are some of the ways they can help.
Zero loss transmission
HTS systems turn the vision of lossless, high-capacity transmission into a reality. Grid congestion is eliminated, so system operators can make the best use of all generation resources, no matter how far away they are. This capability is becoming more important as reliance on remote offshore generation increases.
The beauty with HTS systems is that they enable grid operators to do more with medium voltage. Because superconductors offer no resistance, it is possible to boost the power transmitted by increasing the current instead of the voltage. Step-up and step-down transformers are not needed. This reduces equipment costs, as well as eliminating the need to build new substations – a key consideration when upgrading an urban grid.
Reduced land take
HTS cables save a huge amount of space. This means acquisition and permitting costs are reduced while disruption and routing problems are minimised. An additional benefit is freeing-up land for other purposes – a key benefit in today’s crowded cities. There is also scope to get more out of valuable urban infrastructure, such as cable tunnels. Beyond this, HTS cables have the potential to revolutionise cross-country transmission: the footprint for a high-capacity underground HTS cable route is just 5.5m – more than 20 times less than the width of the equivalent corridor for overhead transmission.
Kinder to the environment
HTS cables reduce the impact of electricity transmission. Visual amenity is preserved because cables run underground. This can play a critical part in winning public acceptance for new transmission projects. Habitat disruption is minimal, because route corridors are narrow. This also means there is less need for land sterilisation to protect the infrastructure.
The road ahead
Superconducting cables are still relatively expensive compared to their conventional copper cousins. Yet when considered as part of the whole transmission system, the economics look increasingly attractive. The costs of land, equipment, permitting and civil works are all lower with HTS systems.
Meanwhile, industrialisation of the manufacturing process means that the cost of HTS solutions is on a steady downward trajectory. And that will increasingly put this innovative technology within reach of transmission and distribution system operators.
Superconducting systems in action
Did you know that Nexans is a world leader in the design, development and deployment of superconducting systems?
Our references include the world’s longest superconducting cable, delivered for RWE in the city of Essen in Germany. This is a 10kV, 2300A HTS cable that does the same job as a 100kV conventional cable. This cable has now been in continuous use for six years.
We also manufacture superconducting fault current limiters (SFCLs). These are used in conjunction with conventional cabling systems to protect against fault currents. They require no human intervention.
Nexans’ HTS cables and HTS fault current limiters are commercially available in a large number of configurations for both AC and DC applications.