Superconducting fault current limiter

The Fault Current Limiter is the Holy Grail for electrical network designers. This device makes it possible to design an ideal network, i.e. one with theoretically infinite short-circuit power, but with controlled fault currents thanks to the limiter. Increasing the short-circuit power of networks is a major current demand, in particular to improve voltage quality and increase the maximum share of distributed energies, including renewable energies. Today, there is no satisfactory industrial solution for high-voltage fault current limiting. One industrial limiter is the pyrotechnic fuse (ABB's Is-limiter, for example), but this is limited to around 40 kV.

A superconductor has an intrinsic current-limiting function via the highly non-linear characteristic of its electric field as a function of the current flowing through it. Nil or extremely low below a certain adjustable current, its critical current (I _c ), the electric field increases sharply above I _c . With virtually no resistance below I _c , and therefore transparent to the grid, a superconducting element automatically and naturally becomes, without any external action and virtually immediately, a high resistance above I _c , limiting the current in less than a millisecond. The Superconducting Fault Current Limiter (SFCL) ensures that no current flows above a certain value. ${\widehat{I}}_{\text{lim}}$ This reduces the costly oversizing of many devices, which are otherwise designed to withstand short-circuit currents well in excess of ${\widehat{I}}_{\text{lim}}$ . It is intrinsically safe. Its resistance disappears again after a certain time as soon as it is isolated from the fault. A superconducting fault current limiter is therefore a particularly attractive technical solution.

However, superconductivity only exists at low temperatures, introducing a technical complexity linked to the indispensable cryogenic environment. Cryogenics is the science of low temperatures. The discovery of high critical temperature superconductors (HTSC) in the late 1980s paved the way for devices operating in liquid nitrogen, a fairly common industrial fluid. SHTC conductors adapted to SFCL only recently entered a pre-industrial phase, at the end of the 2010s.

Several superconducting fault current...