Formation of Hot Spots in Coated Conductors During Static and Dynamic DC Loading

High voltage DC transport at long distances represents an opportunity for wider use of superconductors. In particular, the second generation of high temperature superconductor tapes produced in form of coated conductors (CC) offers a unique solution for protecting a high-capacity connection against fault currents. In the resistive superconducting fault current limiter (R-SFCL), the CC tape would emerge as a substantial resistance in case of overcoming its critical current, I_c . Non-uniformity of I_c along the CC length is a common issue requiring attention. Because of highly nonlinear current/voltage dependence, the spot with critical current I_cmin < I_c could transform into the hot spot with rapid rise of local temperature. Due to its small dimension, it would not create an observable voltage at the device terminals, thus may escape attention of a quench detection system. We have investigated the mechanism of hot spot creation at the DC currents between I_cmin and I_c , and the analytical formulas have been derived predicting the limits of stable operation. Now we extend the analysis to the case of the limitation event, when for a fraction of second the current exceeds also the I_c . It is desirable that the temperature rise happens along all the conductor length, leading to a quick reduction of transported DC. Numerical modelling has been utilized to analyze such an event, and a simplified analytical model has been developed to predict the range of currents causing the formation of hot spots.