SUPERPOLI fault-current limiters based on YBCO-coated stainless steel tapes

Tubular modules of fault-current limiter (FCL) have been developed, manufactured and industrially tested in the framework of the European SUPERPOLI Project. The modules of φ55 mm × 500 mm are based on YBCO-coated stainless steel tapes exhibiting an excellent critical current of >150 A per cm-width at 77 K. A specific FCL architecture enables i) a "soft" current transfer from the YBCO film to the steel tape at over-critical currents, ii) double-sided cooling of the tape, and iii) protection against temperature shocks. The tubular configuration of the modules allows suppression of the normal component of the self magnetic field, and, as a result, gain of total critical current. Critical currents above 3000 A (78 K) have been realized in these modules in the course of industrial tests. A limitation of the fault current with an amplitude of 50 kA lead to a limited current of 3-4 kA, a voltage drop of 50 V (per module) and a power dissipation of about 100 kW. At sub-critical currents, the module introduces a negligible power loss. A quenching time of only 0.1-0.4 ms was observed.