Compact High Temperature Superconducting Cables: Super Cables of the Era?

Maximum losses occurring today in our electrical systems are the transmission losses. India has 33% transmission losses. This is because of the gigantic expanse of the country and the inevitable losses in the wires used for transmission. This problem can now be dealt with because we have the compact high temperature superconducting cable technology.

Lets take a look at these CABLES. The conductors of the cables are formed by arranging the bi-based superconducting wires in a spiral mannes around the former. The material used for insulation is polypropylene laminated paper. This is because it has got a good insulation strength and low dielectric losses. Liquid nitrogen serves as a compound insulation in addition to a coolant. A superconducting wire of the same material is wound spirally on the outer side of the insulation layer to provide a shielding effect. Three cores are stranded together and the assembly is placed in SUS corrugated piping. A vacuum state is maintained between the two layers of the SUS pipings to improve the thermal insulation.



National Institute of Standards and Technology has developed a method of making high temperature superconducting cable (HTS) through intense research. These cables are thinner and more flexible than the ones currently installed in the grid. It can be used in the grid as well as the medical and scientific equipments. There are 2 prototype cables of which one is 6.5 mm in outer diameter and carries a current of 1200 Amp. Second is 7.5 mm and carries 2800 Amp current. These cables are one-tenth in diameter of an normal HTS cable. To boost the efficiency in power grids, the HTS material is cooled below 77K or -196C  with liquid nitrogen or helium gas. The most important property of the HTS cable is it is resistant to compressive strain. A test has been carried out on the 2.25 MVA single phase system at 7.5kV which employed these wires by Siemens. The test has demonstrated all the key features required for cost effective commercial system. The fault current limiting functionality has been given a new approach in HTS cables.

Some advantages of this system are as listed below:

[*]Compact and high capacity: it can transfer power at a current density of 100A/ sq mm. this is 100 times as that of a copper cable. This allows high capacity power transmission in compact size thereby reducing the costs.
[*]Low transmission loss and eco friendly: at temperatures below the critical temperature electrical resistance offered by the wire is zero. Hence the losses are very less. Also provision has been made so that there is no electromagnetic field leakage outside the cable.Comparing 66 kV, 3 kA, 350 MVA class cables, the loss of the superconducting cable is approximately half that of a conventional cable.
[*]Low impedance: as per the size of the cable, the reactance can be lowered to one third as compared to conventional cables.

These cables should be used globally so as to bring a revolution the power sector. This would help us secure the future energy needs across the globe.

(Source: global-sei.com, physorg.com)