Electrical Breakdown Characteristics of LNG for Cryogenic Feedthrough Insulation Under Explosion-Proof Conditions

Reliable insulation design for LNG feedthroughs requires fundamental dielectric breakdown data obtained under cryogenic LNG conditions. However, such data remain scarce owing to the explosion-proof requirements imposed by the flammable nature of LNG. Furthermore, the influence of phase differences between LNG and NG on creepage dielectric breakdown behavior along insulation surfaces has received little attention. In this study, an explosion-proof cryostat and test facility compliant with the IEC 60079 series of standards were developed, and dielectric breakdown tests were conducted over a range of electrode gap distances and pressures. Two electrode configurations were employed: rod–plate electrodes for dielectric breakdown characterization in LN2 and LNG, and creepage electrodes for surface dielectric breakdown evaluation in NG and LNG. Experimental results show that LNG requires approximately 1–2 bar of additional operating pressure above that of LN2 to achieve equivalent dielectric strength. Moreover, LNG exhibited higher creepage dielectric breakdown voltages than NG under all test conditions, with the difference becoming more pronounced as pressure and creepage distance increased. Post-breakdown surface analysis revealed distinct differences in carbonization patterns between the two media. The findings of this study are expected to serve as fundamental reference data for the insulation design of LNG-based cryogenic feedthroughs.