Visualization experiment on cryogenic boiling heat transfer and recovery characteristics in the first and second quench of RSFCLs

Abstract

The resistive type superconducting fault current limiter (RSFCL) based on YBCO superconducting tape has great potential to protect the large high-voltage power grid. The rapid recovery of the YBCO superconducting tape after the 1st quench not only affects the reclosing time but also the 2nd quench response. Besides, the retention of bubbles generated from the liquid nitrogen (LN2) boiling during the 1st quench may also worsen the heat transfer and the recovery process of the 2nd quench, which is seldom revealed at present. In this work, the effects of the different initial states, i.e., the recovery stages after the 1st quench, on the 2nd quench of YBCO tapes in LN2 bath are studied. A visualization experimental setup is used to study the 1st and 2nd quench performance from the perspective of LN2 boiling bubble dynamics. Two characteristic parameters, in terms of the peak temperature Tpeak and the recovery time extension ratio ε, are adopted to describe the deterioration of quench and recovery performance. The experimental results show that the shorter the time interval between the two quenches, the greater the recovery time extension ratio ε, and the higher 2nd peak temperature Tpeak,2. Furthermore, the visualization results show that the film and the remaining bubbles after the previous quench are the main factor affecting the next quench and recovery. The maximum difference of the peak temperature between these two quenches can be as high as 46.4 K, and the extension ratio could reach 2.06. Even when the tape has recovered to about 77.3 K at the beginning of the 2nd impulse, Tpeak,2 still reaches 155.8 K due to the presence of remaining bubbles, which is 5.2 K higher than that of the 1st quench. The greatly prolonged recovery time and the sharp increase in peak temperature will further increase the risk of YBCO tape burnout. Therefore, this research can provide a more comprehensive and reliable reference for the RSFCL system to safely response repetitive current impulses.