Thermal relaxation of HTS cable tapes after a short circuit current pulse
IVANOV Yury, 神田 昌枝 （中部大）； 山口 作太郎 （e-Donuts）
Abstract:High-temperature superconducting (HTS) cables are designed to operate as part of bulk power transmission systems, so improving operational safety is very important. Conventional HTS cable is a concentric multilayer structure with many HTS wires (tapes) tightly sandwiched between insulation layers. Kraft or polypropylene laminated paper (PPLP) impregnated with liquid nitrogen (LN2) is used as electrical insulation. When HTS tapes overheat due to short circuit current, local cooling of the tapes is difficult due to the paper's low thermal conductivity and low liquid permeability. This causes rapid heating and subsequent transition to the normal state. To study the behavior of HTS tapes during a short circuit, a test bench was assembled that generated current pulses with a duration of about 8 ms and an amplitude of up to 4-5 kA (which is 20-25 the critical current (Ic) of HTS tapes). Measurements revealed a significant increase in the cooling time of the tape sandwiched between the papers. Analysis of the time-temperature curves suggests that cooling in the presence of insulating paper occurs in a regime close to the film one since the high hydraulic resistance in the paper's pores prevents the rapid entry of LN2 into the heated region. Therefore, improving the microcirculation conditions of LN2 can increase the recovery rate of the HTS cable after a short circuit. In addition, the surface of the HTS tapes can be modified to initiate a transition to nucleate boiling at a higher temperature.