Effect of a PTFE film on bubble triggered DC breakdown characteristics in liquid nitrogen

Abstract

Abstract In the resistive type DC superconducting fault limiter (R-SFCL), the insulation strength will be decreased seriously when the R-SFCL quenched. Insulation barriers are used inside of the R-SFCL to enhance the electrical breakdown strength of the SFCLs. The objective of this paper is to study the barrier effect on the DC breakdown characteristics of the liquid nitrogen (LN2)/insulation barrier composite system with and without bubbles. In the experiment, the DC breakdown voltage of a pair of rod-plane electrodes with an insulation barrier was measured in the presence of thermal bubbles. The results show that for both the positive and negative polarities, the breakdown voltage of the LN2/insulation barrier composite system is higher than that without the barrier. In the presence of the bubbles, the breakdown voltage of the LWinsulation barrier composite system is about 1.5 times higher than without the barrier. Furthermore, the breakdown voltage of the LN2/insulation barrier composite system with 0.04 mm PTFE is higher than with 0.1 mm PTFE. The results suggested that the barrier effect could not only improve the insulation strength of the normal state but also the quench state of the R-SFCLs.