A superconductor conducts electric current with no resistance, hence with no loss. Superconducting cables are hence a logical application even if it is not very convenient from a cryogenic point of view, because of the high ratio between surface and volume: what is won with the absence of energy loss is lost with the price paid to cool the cable. However, one of the principal interests of superconducting cables is their stronger transportation capacity (3 to 5 factor) for a given congestion, taking into account the cooling necessities. This solution is especially attractive to solve the issue of electric power increase in some large international major cities. A superconducting cable using a present cable duct, with a 5 times higher power capacity is a more profitable alternative than building a new duct for a stronger resistant cable: this is called “retrofit”. The thermal signature being equal to zero, installing a cable becomes a more flexible matter, especially in places where it is impossible to use classical cables. As far as losses are concerned, a superconducting cable is more convenient than a classical cable only over a certain current, because of the losses of the cryostat.
However, a superconductor still presents some (minor) losses when an alternating current of 50 to 60 Hz flows through it, for instance.
With many constructions, superconducting cable technology has reached some maturity. For instance, the company Nexans [www.nexans.fr] has already built many cables over 12 years of operational experience. Since March 2008, this company has operated on 600 metres of the most powerful superconducting cable in the world (600 megawatts), in the United Stated (LIPA project).
Besides a thermal signature equal to zero, superconducting cables often have an electromagnetic signature equal to zero and very low impedance (VLI). This specific property has many advantages, especially when it comes to conducting an electric network. This kind of cable can divert power transfer and enhance the electric networks’ capacities while securing the way they work.
A superconducting cable can also present an innovative function: fault current limiters.
