Influence of Current Change Rate During DC Current Limitation on the Coated Conductor Degradation

The paper explores the idea of reducing the amount of REBCO conductor in Resistive Superconducting Fault Current Limiters (R-SCFCL) by reducing the temperature of liquid Nitrogen from 77 K to 66 K. Because of lower temperature, the critical current increase approximately two times, and instead of two parallel tapes, one can use only one tape in a 1000 A class R-SCFCL. However, recent experimental results on short samples show a frequent degradation of superconductors by DC current limitation at 66 K. The paper reports our investigation of this phenomenon by experiments complemented by extensive numerical modeling. We suggest that the primary cause of conductor degradation initially appearing at 66 K should be sought in the first sub-millisecond period of the limitation pulse. We observed that a reduced initial rate of the current rise during the limitation event can prevent the conductor damage.