Superconducting current limiter guarantees electricity supply of the Boxberg power plant

Jan 13, 2012
Superconducting coils are cooled with liquid nitrogen and have zero resistance to current flow. Credit: Martin Lober, KIT

For the first time, a superconducting current limiter based on YBCO strip conductors has now been installed at a power plant. At the Boxberg power plant of Vattenfall, the current limiter protects the grid for own consumption that is designed for 12 000 volts and 800 amperes against damage due to short circuits and voltage peaks. The new technology co-developed by Karlsruhe Institute of Technology and made by Nexans SuperConductors enhances the intrinsic safety of the grid and may help reduce the investment costs of plants.

"For a long time, high-temperature superconductors were considered to be difficult to handle, too brittle, and too expensive for general ," explains project manager Wilfried Goldacker from Karlsruhe Institute of Technology. "The second generation of high-temperature superconductor wires based on YBCO ceramics is much more robust. Properties have been improved." Superconducting limiters work reversibly. In case of current peaks after short circuits in the grid, no components are destroyed. The limiter automatically returns to the normal state of operation after a few seconds only. Consequently, the is much shorter than in case of conventional current limiters, such as household fuses, whose components are destroyed and have to be replaced with a high time and cost expenditure.

"Superconducting current limiters have a number of advantages for the stability of medium- and high-voltage grids," explains Mathias Noe, Head of the Institute of Technical Physics of Karlsruhe Institute of Technology. Reliable, compact current limiters enhance the operation stability of and allow for a simplification of the grid structure. As they are protected against current peaks, decentralized energy generators, such as wind and solar systems, can be integrated much better in grids. Expensive components in the existing grid are protected efficiently, components in future grids can be designed for smaller peak currents, and transformers will no longer be necessary. Investment costs of power plants and grids will be reduced. Moreover, superconducting current limiters on the basis of YBCO can also be applied in high-voltage grids of more than 100 kilovolts for better protection against power failures in the future.

YBCO stands for the constituents of the superconductor: Yttrium, barium, copper, and oxygen. An YBCO crystal layer of about 1 micrometer in thickness is grown directly on a stainless steel strip of a few millimeters in width that gives the ceramics the necessary stability. Below a temperature of 90° Kelvin or minus 183° Celsius, the material becomes superconductive. However, superconductivity collapses abruptly when the current in the conductor exceeds the design limits. This effect is used by the current limiter. In case of current peaks in the grid, the superconductor loses its conductivity within fractions of a second and the current will flow through the stainless steel strip only, which has a much higher resistance and, thus, limits the current. The heat arising is removed by the cooling system of the superconductor. A few seconds after the short circuit, it is returned to normal operation in the superconducting state. YBCO superconducting layers on stainless steel strips are more stable and operation-friendly than first-generation superconductors based on BSCCO ceramics. Moreover, their production does not require any noble metals, such as silver, and will presumably be cheaper.

The superconducting current limiter was developed in the past two years under the ENSYSTROB project. The project partners are Karlsruhe Institute of Technology, Nexans SuperConductors, TU Dortmund, and BTU Cottbus. The field test will be carried out at the user, the Vattenfall utility company. The project was funded with about EUR 1.3 million by the Federal Ministry of Economics. The results of the project are of high relevance, as the functionality of current limitation may be integrated in superconducting transformers and energy cables in the future.

Explore further: How to maximize the superconducting critical temperature in a molecular superconductor

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User comments : 3

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4 / 5 (1) Jan 13, 2012
I see a problem if the refrigeration system fails, the device would very quickly be destroyed unless an additional cutout was in the circuit and power could not be restored until the refrigeration system was repaired or the device bypassed.
not rated yet Jan 14, 2012
@Gino, if the refrigeration system did fail, failure would not be immediate, depending on how well insulated the system is, there could be a reasonable window of time to respond with a cask of liquid nitrogen which could tide the system over until repairs could be made.
not rated yet Jan 15, 2012
I tried to post this in the comments for an article on plasma rotational change (comments closed/expired), but this article will do just fine. It will be self explanatory:

Voltage is a descriptor for 'polarity agreement' between two given particles. we don't call it 'potential' or 'differential' for nothing.

When the given differential is forced to be different across/between the given particles (change in polarity alignment) ...then the vector differential of the vortex energies shifts to a different orientation..and then we get this change in rotation... as the particle/wave polarity agreeance or 'matching' of the flow changes.

This is the exact same mechanism that causes superconductors to 'conduct' or not conduct, as we change the temperature. also causes the slipping out of superconductivity as we try to increase the current load in the given superconductor experiment in materials.

Electric Universe.

Maxwell's original equations contained 'elasticity'.

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