Breakdown Characteristics and Mechanisms of Liquid Nitrogen Under Transient Thermal Stress for Superconducting Fault Current Limiters

We have been investigating the electrical breakdown (BD) characteristics of liquid nitrogen (LN2) with a transient thermal stresses to simulate the quench conditions of resistive-type superconducting fault current limiters (SFCL). We call such BD of LN2with the transient thermal stress as “dynamic BD,” and discriminate it from that with a continuous thermal stress. In this paper, we investigated the dynamic BD characteristics of LN2for different LN2pressures, electrode sizes, and terms of transient thermal stress input. In addition, we obtained the BD characteristics of LN2with the continuous thermal stress, and compared them with the dynamic BD characteristics. Furthermore, we analyzed the statistical scattering of the time from the thermal stress input to the dynamic BD occurrence and discussed the dynamic BD mechanisms of LN2. We also proposed a flowchart of rational and reliable electrical insulation design of resistive-type SFCL based on the dynamic BD characteristics of LN2.