The “first superconducting cable integrated in a public electricity supply grid” has entered service (see p 29) and the Danes are declaring themselves victors in what they describe as “the first round in a global race”. It has been a close run competition between the Copenhagen installation and a project in Detroit, which, until now, had been considered the front runner. The Danes claim a great leap forward, but it is only one of many that will be needed to get high temperature superconductors into the marketplace.
Considering that the strange phenomenon of high temperature superconductivity was only discovered in 1986, the rate of progress to date has nevertheless been impressive. The attraction of these high temperature superconductors is that they take much less cooling than “conventional” low temperature superconductors, meaning, for example that liquid nitrogen (at a mere -198°C or so) can be used. One downside is that the ceramic type materials that exhibit high temperature superconductivity – for example BSCCO 2223, which is the compound of bismuth, strontium, calcium, copper and oxygen used for the wires in the Copenhagen installation – tend to be brittle and unwieldy. The process of turning this awkward material into a useable cable is extremely intricate, involving 100 or more manufacturing steps.
Copenhagen Energy’s trial installation, an internal connection between two busbars at a substation on the island of Amager, consists of three cables, 30 m long, operating at 30 kV with a 2000 A rating. The cable was manufactured by NKT Cables. The plan is to test the supercable under realistic conditions over the next 18 months to two years. Theoretically it has the capacity to supply the whole Amager district, but Copenhagen Energy is taking no chances. There is conventional technology is reserve, which will be switched out once sufficient confidence has been gained in the superconducting link. If the results are positive, says NKT Cables, the next step towards developing a commercial superconducting cable will be manufacture and testing of a much longer cable.
Meanwhile at the Frisbie substation in downtown Detroit, the world’s second utility superconducting cable installation is close to operation. This is a US DoE sponsored project led by Pirelli Cables.
The American project aims to show the potential of high temperature superconductors in retrofits. Three high temperature superconducting cables, 130 m long, are being used to replace nine old copper cables. The new superconducting cables will provide the same 100 MW capacity as the copper conductors but will only need three of the nine existing 4in diameter ducts – demonstrating a key benefit promised by superconductors: less cable, more carrying capacity.
While the Copenhagen and Detroit projects are believed to be the first instances of high temperature superconducting cables in public grids, they are by no means the first high temperature superconducting cables. A notable milestone was achieved early last year when the US company Southwire energised a 30 m high temperature superconducting cable supplying power to three of its own manufacturing plants, in Carrollton, GA. The 20 MVA Carrollton cable – also supported by US DoE – is said by Southwire to be the “first high temperature superconducting power delivery system to provide power for an industrial use.”
Developers of high temperature superconductors see huge future potential, in terms of reduced losses, removal of transmission bottlenecks, simplification of the grid, and massively increased transmission capacity on existing cable routes. “In the very long term,” says a press release put out by NKT Cables and Copenhagen Energy, “supercables offer almost infinite scope for power transmission. If we really want to, we can obtain solar energy from the Sahara by day and send back Danish wind power by night.”
So no one can accuse the Danes of lacking ambition. However, in the near term there are some formidable technical and economic hurdles to be overcome. The technology of high temperature superconducting cables is in its infancy and still has a very long way to go indeed before it can be thought of as a commercial contender in the much needed upgrading of transmission and distribution networks around the world.
Finns take the lead
Long term vision is also needed when it comes to dealing with the issue of spent fuel disposal, long portrayed as the Achilles heel of nuclear energy by its opponents and some of its supporters as well.
As reported in this month’s news the Finnish parliament has just ratified the “decision in principle” to take steps towards building a final spent fuel disposal facility at Olkiluoto. This makes Finland the first country to have such firm plans for a permanent geological repository, although its not going to happen overnight. The next step is construction of a rock characterisation facility at the proposed site. Called ONKALO, this will allow investigations at final disposal depth to start around 2006, with operation of the facility itself not envisaged before about 2020.
Another piece of reasonably positive news for nuclear energy comes from Germany, where the agreement between the federal government and the utilities on nuclear power has just been signed (see p 3). Although the agreement is basically about phasing out Germany’s nuclear reactors – perhaps not entirely an altogether sensible thing to do in view of global warming worries and Kyoto commitments – the time scales are much longer than might have been envisaged in those heady days when the current German government came to power.
Even the Deutsches Atomforum – mouthpiece of the nuclear industry – sees the agreement as “an acceptable compromise because it guarantees the undisturbed operation of the nuclear power plants for a long time to come”.
The agreement also “puts an end to a long-running ideological and fundamentalist debate” and “offers the chance to promote a pragmatic and matter-of-fact energy policy”, says the Atomforum. To say nothing of the fact that the new accord allows German nuclear capacity to remain virtually intact for the time being, with the strong likelihood that a future change of German government could see the phase-out policy reversed.
