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 limiters in particular.

A superconductor has an intrinsic current-limiting function via its highly nonlinear electric field versus current characteristic. Nil or extremely low below a certain adjustable current, its critical current, the electric field rises 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 current limiter guarantees the absence of current above a certain value ${\hat{I}}_{lim}$ , reducing the costly oversizing of many devices otherwise calculated to withstand short-circuit currents well in excess of ${\hat{I}}_{lim}$ . 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. The 2nd generation of high-temperature-critical superconducting conductors, currently undergoing industrial development, further enhance the attractiveness of superconducting current limiters.

Several superconducting fault current limiters have been successfully commissioned, notably in the European network. What remains to be done is to demonstrate the economic viability of superconducting fault current limiters, and to increase feedback on this breakthrough technology.