Operation of longest superconducting cable worldwide started

May 12, 2014 by Monika Landgraf, Karlsruhe Institute of Technology

(Phys.org) —Today, the longest superconducting energy cable in the world was integrated officially into the power grid of a German city. The cable of about 1 kilometer (0.62 miles) in length now connects two transformer stations in the city center of Essen. This marks the start of a landmark practical test for the future energy supply of inner cities by RWE, Nexans, and KIT. Compared to conventional cables, the highly efficient and space-saving superconducting cable technology transports five times more power with hardly any losses.

Today's celebration of the commissioning of the cable under the AmpaCity project took place at the Herkules transformer station in the inner city of Essen in the presence of Hannelore Kraft, Minister President of the state of North Rhine-Westphalia, Physics Nobel Prize Winner Johannes Georg Bednorz, one of the discoverers of high-temperature superconductivity, and numerous representatives of politics, industry, and science. KIT is one of the project partners of AmpaCity and contributes research and development work. In addition, it comprehensively studied the technical and economic feasibility of superconducting city grids and supports cable operation.

"This is a good day for […] the transformation of the energy system in Germany. Today, we start the first practical test of superconductor technology worldwide. The AmpaCity project is of high priority to North Rhine-Westphalia as a location of energy-producing industry," Minister President Hannelore Kraft said.

"Research has to contribute to solving problems and meeting the needs of society," emphasized Holger Hanselka, President of the Karlsruhe Institute of Technology. "The AmpaCity project is a good example of how contributions to current challenges like the energy turnaround may result from national long-term application-oriented fundamental research and close cooperation with innovative industry partners."

Peter Terium, Chief Executive Officer of RWE AG, pointed out: "AmpaCity is one of the outstanding innovative projects executed by RWE with high dedication and passion. The transformation of the energy system does not only require courage, inventive talent, and reliable partnership. The transformation of the energy system also needs healthy, competent companies that are able to cope with the associated challenges. Here in Essen, this is demonstrated in an impressive manner."

"For KIT, AmpaCity represents an important milestone in long-term research into and development of superconducting grid components. For us, the profound change to be experienced by the electricity grid as a result of the increasing integration of renewable energy sources is a motivation to continue our efforts to supply innovative superconducting solutions for a secure, stable, and efficient grid," said Joachim Knebel, Head of the Mechanical and Electrical Engineering Division of KIT.

"I am excited," admitted Physics Nobel Prize Winner Johannes Georg Bednorz in the early phase of the AmpaCity project already. "What started to be a dream in the 1980s is now becoming reality. Real operation of a […]." As regards the status of superconducting technology, he confirms "that Germany is at the top of development again."

"High-temperature superconducting energy cables are ready for commercialization. It took about 30 years for high-temperature superconductors to develop from an idea worth a Nobel Prize to an industrial application," explained Mathias Noe, Head of the KIT Institute of Technical Physics and project partner of AmpaCity. "Research has succeeded in identifying better suited materials, producing cables of enhanced mechanical robustness, and minimizing AC losses. Cable operation under the AmpaCity project is to demonstrate that technical requirements associated with the use in practice are fulfilled with a high reliability."

The three-phase, concentric 10,000 volt cable of the AmpaCity project is designed for a transmission power of 40 megawatts. Compared to a copper cable of the same size, the superconducting cable can transport five times more electricity in spite of its thick cooling jacket. Moreover, electric losses are low. As a result of the properties of the superconducting material, a special ceramic, and cooling to -200°C, the cable is turned into an ideal electric conductor. In Essen, the 10,000 volt superconducting cable replaces a conventional 100,000 volt line.

Prior to the AmpaCity project, technical feasibility and economic efficiency of a superconducting on the inner-city medium-voltage level were studied extensively under the direction of KIT. Superconducting cables are the most reasonable option to reduce the use of high-voltage cables in urban grids, to simplify the grid structure, and to dismantle transformer stations that require considerable resources and large areas. High power can be transmitted cost-effectively in inner cities by copper medium-voltage cables, but the associated ohmic losses are much higher. Upon the successful completion of the now starting field test of two years' duration, the high-voltage systems of the Essen power grid might be replaced largely by 10,000 volt superconductors in accordance with the preliminary study. In the medium term, this would lead to an enhanced efficiency, a leaner grid, lower operation and maintenance costs, and reduced area consumption.

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3 / 5 (2) May 12, 2014
And the first time it looses coolant it all goes poof in a huge spray of sparks....
5 / 5 (2) May 13, 2014
Sure, but by now there is some experience with not letting that happen (from MR scanners to supercolliders).
If you look at the cross section of the cable you notice that the cooling fluid is in the interior and that there is a vaccuum shell on the outside. Sensors in that part will detect if there is any leakage - which will give time to shut the system down before it's too late.
Also superconducting systems are constructed in sections (to reduce quenching damage). So if anything does go catastrophically wrong (e.g. due to earthquake) only a small section will be damaged. There won't be a huge spray of sparks, as this cable is underground. That section will just melt.
not rated yet May 13, 2014
Maby a cheaper Superconductor http://samuel-hei...eii-more
1 / 5 (1) May 13, 2014

I thought it new to use AC with superconductor cable, as Its generally not very efficient. As the above link explains the losses in the AmpaCity Project are about 20 %

The liquid Nitrogen (cooling fluid) is cycled through the cable in an inner an outer channel. (Illustration of the Nexus cable in link). No vacuum shell. No sensors.

The higher voltage DC superconducting cable in Long Island NY, is more efficient and used for an inter grid link. It's has successfully operated for several years and is scheduled for expansion.


Neither of these will go bang with lots of sparks or melt, due to some magic fault current limiting.

5 / 5 (1) May 13, 2014
No vacuum shell. No sensors.

The vacuum shell is labeled cryostat (which is a two walled steel constructionlaminated with highly insulating foil with vacuum in between). Due to this concept, even if the cooling pumps fail, the thing will remain suoerconductive over a period of several hours (ample time to turn off the juice). There are temeprature sensors for the nitrogen. Any leak will show up immediately in a loss of pressure and/or a change of temperature.

In summary - even though it needs some energy to keep the nitrogen at temperature an - due to the open circulation system - some a need to comtunally replenish some liquid nitrogen it saves money compared to an equivalent conventional cable of similar capacity.

You could only get a 'catastrophic' event if something were to sever the cable in one go (e.g. an inattentive bulldozer driver).

3 / 5 (2) May 13, 2014
Nitrogen is cheap. It's the 'smaller trenches and fewer transformers' that make this cost effective. The cooling system is not 'open'. The nitrogen is circulated in a closed loop. The cooling losses are minimal. The cryostat is not evacuated, it's an insulating foam. The temperature and pressure sensors are at the terminations. The cable is continuous and not constructed in sections. The fault current limiters prevent catastrophic events within seconds, not hours.

... and the experience does not come from MR scanners or supercolliders. The experience comes from other installations of superconducting cable installations.

1 / 5 (1) May 13, 2014
You could only get a 'catastrophic' event if something were to sever the cable in one go (e.g. an inattentive bulldozer driver).

For sure. Catastrophic for the dozing driver.

not rated yet May 13, 2014
@ Bluehigh

"The cable is continuous and not constructed in sections."

"The cable of about 1 kilometer (0.62 miles) in length now connects two transformer stations in the city center of Essen."

As far as power transmission lines go, that's pretty short. I'd call it a section.

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