A Numerical and Experimental Analysis of the Temperature Dependence of the n-Index for 2G HTS Tape Surrounding the 77 K Temperature Range

Most superconducting devices are designed for a fixed operating temperature range, however, temperature varia- tions are inevitable in some situations. For example, the temperature of a resistive-type superconducting fault current limiter becomes higher during fault cycle operation. Therefore, knowledge of the temperature dependence of the current-to-voltage characteristic is necessary for accurate simulation or design processes. This paper explores the temperature dependence of the n-index, which describes sharpness of superconductivity to normal transition, using a second-generation high-temperature superconducting tape sample under a liquid nitrogen surrounded environment. The voltage across the sample according to given current and temperature is measured by establishing a measurement system with a protection system. The average of the data from multiple measurements is calculated and compared with three different n-index models. Constant, inversely proportional, and modified inversely proportional models are analyzed. The modified inversely proportional model showed the least error when compared to the measurement data.