Breakdown characteristics of cryogenic gaseous nitrogen and estimation of its electrical insulation properties

The electrical properties of liquid nitrogen and its vaporized gas have become of great interest since the discovery of high-temperature superconducting materials. The authors present the breakdown characteristics of gaseous nitrogen from room temperature down to 74 K. With uniform field gap geometry, the validity of Paschen´s law is confirmed even under the saturated gas condition at 74 K. In the case of a nonuniform field gap, there is a remarkable a difference in the effects of positive and negative polarities on corona stabilization. A wider gap length is necessary for stable negative corona formation than for positive corona at temperatures <100 K. Breakdown criteria are proposed, on the basis of experimental results, to give a practical and reliable procedure for the design of cryogenic insulating systems which use liquid nitrogen and the vaporized gas as the coolant