Barrier Effect on the Dynamic Breakdown Characteristics in Liquid Nitrogen under Transient Bubble Disturbance for R-SFCL

The objective of this study is to investigate the barrier effect on dynamic breakdown characteristics in LN₂ under transient bubble disturbance for resistive-type superconducting fault current limiters (R-SFCLs). A R-SFCL model with superconducting coils immersed in LN₂ is tested under static and dynamic conditions, with and without an insulation barrier for both DC polarities. Breakdown voltage and time delay <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</i><sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</sub> are measured across varying energy densities (0.29, 0.49 and 0.62 J/cm). The results show that the insulation barrier enhances the breakdown voltage of the R-SFCL model in the quenching state. The presence of the insulation barrier reduces <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</i><sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</sub> to a certain value when the energy density of the superconducting tapes exceeds a critical threshold, achieving a minimum delay of 7 ms. Polarity effects reveal superior insulation strength under negative polarity than that of the positive one in the R-SFCL model. These findings provide critical insights for optimizing R-SFCL insulation design and guiding DC circuit breakers (DCCB) interruption timing, ensuring reliable fault current management in high voltage DC (HVDC) systems.