DC Breakdown Characteristics of Needle–Needle–Plane Electrodes With Insulation Barrier and Thermal-Induced Bubbles in Liquid Nitrogen

Insulation barriers are an effective way to improve the insulation strength of the resistive-type superconducting fault current limiters (R-SFCLs). The objective of this article is to obtain the dc discharge characteristics of composite insulation systems including two liquid nitrogen (LN
₂
) gaps in series, but separated by a solid insulation barrier mixed with vapor bubbles. The needle–needle–plane stainless steel electrodes with the insulation barrier and bubbles generation systems are used to simulate the electric strength under quenching conditions of the R-SFCLs. The results show that the composite systems’ breakdown characteristic switched from insulation barrier breakdown to surface flashover with the insulation barrier approaches the needle electrodes side. The breakdown voltage of the composite systems decreased due to the thermal induced bubbles. The presence of the bubbles increases the probability of the surface flashover of the insulation barrier. The results have guiding significance for the design of the high-voltage R-SFCLs.