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.

Automated summary

Using superconductors for high voltage DC transport over long distances presents an opportunity for wider applications, with high temperature superconductor tapes serving as a unique solution for protecting high-capacity connections against fault currents. However, non-uniformity of critical current along the coated conductors length is a common issue that may lead to hot spot formation, potentially escaping detection by monitoring systems.