Breakdown characteristics of gaseous and liquid nitrogen in parallel plane electrodes system with small gap spacer

To design the electrical insulation for a superconducting magnet cooled by liquid nitrogen or liquid helium measurements were carried out on the DC breakdown voltage of gas or liquid nitrogen with and without a GFRP spacer. The results are summarized as follows: Breakdown voltages are determined by the product of the cryogenic nitrogen gas density and electrode distance when a spacer is inserted between the electrodes tightly without apparent gap. When a small gap is introduced, the breakdown occurs along the surface of the spacer or in the vicinity of the spacer. The surface breakdown occurs below the gap breakdown voltage. In liquid nitrogen, bubbles stagnate on the spacer surface and surface breakdown occurs below the breakdown voltage of liquid nitrogen at the presence of the spacer between electrodes.