Temperature and pressure simulation of a 1.5-km HTS power cable cooled by Subcooled LN₂ with a fault current

Waseda University has developed computer programs to estimate the transient temperature and pressure distributions in a high-temperature superconducting (HTS) power cable cooled by a forced flow of subcooled LN₂. This simulation is crucial for realizing a practical HTS power cable to assess the effects of short-circuit accidents. When a short-circuit accident occurs, a fault current of 31.5 kA with a duration of 2 s may flow in a cable in the worst case, which is the Japanese criterion for a 66-kV transmission line. The temperature profiles of the LN₂ coolant and cable cores were analyzed by solving the heat conduction and heat transfer equations using a finite-difference method. The pressure profiles of the LN₂ coolant were calculated using Fanning's equation. For practical use, it was assumed that HTS cables that are a few kilometers long will be adopted. In this study, an evaluation of the stability of a 1.5-km HTS cable with a fault current of 31.5 kA over 2.0 s was performed using our computer program. According to the results, the temperature of the LN₂ coolant at the outlet reached the saturation temperature after the fault, and vaporization suddenly occurred. The evaporated gas was released from the outlet to the terminal.