23.03.2012
Superconductivity: cost bisection up to 2017
Electricity technology: High-temperature superconductivity is technology in the electricity industry shortly before the commercial market launch. At the ZIEHL III symposium in Bonn, however, it became clear that the industry still has problems to overcome.
For Mathias Noe, head of the Institute of Technical Physics at the Karlsruhe Institute of Technology, there are four major fields of application of so-called high-temperature superconductivity (HTSC): cables and wires, rotating machines, current limiters and transformers.
The increased use of regenerative energies and the associated fluctuating feed-in make intelligent grid expansion necessary. Here, too, HTSL is increasingly coming into view, according to Noe. A popular area of application for cable is the pilot line in Essen, where two substations are connected with a HTSL-1-kV cable that is around 10 km long (see VDI messages, 27, 1, 12, S. 12).
The new connection is likely to pay off: according to Frank Merschel, coordinator at RWE Germany for New Technologies, one voltage, namely the 100 kV level, can be dispensed with, the inner-city space requirement is lower than with conventional supply, and fewer substations are required.
Many experts of the Bonn conference "Future and innovation of energy technology with high-temperature superconductors" (Ziehl III), which took place at the beginning of March, are also expecting lower costs of the HTSL of the so-called 2. Generation.
Noe himself predicts a halving of the cost per kA / m, measured by today's prices to 2017. The price in dollars will then have dropped from over 1000 $ per kA / m in 2006 to just over 50 $ per kA / m in year 2017.
"The price-to-current capacity ratio of copper can be determined by the HTSL of the 2. In just a few years, "said Noe. Instead of expensive silver, it uses nickel, chromium, iron or yttrium-barium-copper oxide (YBCO).
But if a technology like the HTSL is on the cusp of commercial use, it's still not over it. Even isolated operations such as those of a superconducting current limiter in the real operation of the lignite power plant Boxberg in Lusatia do not change anything (see VDI news, 4, 6, 10, p. 11).
But there are more and more ideas, studies and demonstrators. For example, Vision Electric, a specialist for high-current busbar systems from Schwanenmühle near Kaiserslautern, Germany, has presented a concept study for the use of superconducting high-current busbar systems. "One of the great advantages is the small footprint in the often tight factories," says Managing Director Wolfgang Reiser.
Such rail systems are transporters of large currents at rather low voltage, for example in chlorine plants, in zinc electrolysis or in aluminum smelters. Through testing, Vision Electric found that HTSL could transport up to 600 nos.
Aluminum smelters currently transport up to 350 kA over distances up to 500 m. With HTSL, the space requirement would be reduced to 5%. Elaborate protective equipment for the employees could be omitted. "Actually, we could have used HTSL long ago," enthuses Reiser. A comparison of the power losses shows him clearly that above 10 kA and at distances above 20 m HTSC technology would be more advantageous than conventional copper or aluminum technology.
Michael Bäcker, founder of the German Nanoschicht from Rheinbach, pointed out in Bonn that the LCA had to be included in the HTSL considerations. Although HTSL can do with drastically less material, it has an 100-fold power density.
For example, if you were to build generators for an 8 MW wind turbine in line with copper technology, you would need 80 t copper - with HTSL it would only be 8 t. And again the reference to the square: If the rotor measures copper 11 m for copper, then it is only 3,8 m for the HTSL. Disadvantage however: Around 20 kg of rare earths would be needed.
The most promising is the use of the HTSL in current limiters: Here it plays its inherent advantages (see box). Since 2010, the new type of current limiter has been in operation at Vattenfall's lignite-fired power plant in Boxberg, Saxony. In the meantime, according to Achim Hobl, site manager of technology supplier Nexans in Hürth, he has been further developed. "It's identical from the outside, but optimized in terms of material properties."
The areas of application are increasing. Siemens has made initial tests with current limiters in high-voltage systems. Under the project financing of the US Department of Energy, Siemens Erlangen built a demonstrator under the project management of cable manufacturer AMSC.
The task of the Erlangen was the development, construction and testing of the switching modules. The current limiter comes in stately proportions: over 5 m long, completely filled with LPG and a switching module of three 21 bifilar coils.
He was installed and tested at Southern California Edison in a substation. He has all passed the high-voltage tests for insulation testing, including the lightning impulse, switching impulse and short-time alternating voltage test and the partial discharge test.
"This resistive current limiter is suitable for high voltage systems," summarizes Wolfgang Schmidt, Magnetic Engineering Expert at Siemens Corporate Technology. The thing has only one catch: Actually, this year should start the regular test operation. "But there is currently no money for this phase to really use the device," says Schmidt. ULRICH SCHMITZ
Superconductor application current limiter
- If a critical current is exceeded - for example in the case of a short circuit or lightning strike - the conductor material leaves the superconducting state within milliseconds and acts as a high electrical resistance. It flows a defined residual current, which can be set exactly.
Superconducting current limiters need no control or spare parts after an incident, they are completely intrinsically safe. After the short circuit, the limiter only has to be de-energized for a short time, so that it returns to operational readiness through the cooling.
Source: VDI nachrichten, Bonn, 23. 3. 12, swe us
