‘Superconducting breakthrough’

Ir. Roy Zuijderduin:" Such cables wil be replaced by supercondutors". (Photo: Tomas van Dijk)

High voltage researchers last week announced a breakthrough in the development of a superconducting transmission cable.

The Delft high voltage laboratory collaborates with the German-Danish power cable producer NKT in the development of a high temperature superconducting (HTS) power cable. The superconducting cable should replace one of the existing 6 kilometre long transmission cables connecting the centre of Amsterdam with a distribution point further north.

Losses in the cable should be kept below 1 Watt per meter for each of the three phases at maximum power (3,000 Amperes at 50,000 Volt). The breakthrough that researchers Roy Zuijderduin and Dr Oleg Chevtchenko (both from the faculty Electrical Engineering, Mathematics and Computer Sciences) have achieved is that the losses are “an order of magnitude lower” than this threshold value. NKT cables do not allow chief researcher Professor Johan Smit to give an exact value for the measured losses.

Smit explains that minimising the losses is vital for a superconducting cable, since any heat production has to be cooled off in order to maintain superconductivity.
On both sides of the Amsterdam HTS cable, cooling stations will be pumping liquid nitrogen down the hollow centre of the cable in order to keep its temperature below 90 Kelvin. All included, a superconducting cable features about half the loss of normal high voltage power transmission (typically 5 percent).

The main losses are due to thermal leakage and alternating electromagnetic fields. By spiralling the thin, 3 millimetre wide superconducting strips neatly side by side along the hollow centre, the researchers succeeded in closing any gaps between the tapes, thus minimising the electromagnetic losses.
Smit foresees HTS cables taking the place of copper wires in the next decade, not only in power transmission, but also in motors and generators for wind turbines. This will be especially true when copper prices rise.