Breakdown Characteristics of Cryogenic Gaseous Nitrogen and Estimation of its Electrical Insulation Properties

Electrical properties of liquid nitrogen and its vaporized gas have become of great interest again since the discovery of high-temperature superconducting materials. This paper presents 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 non-uniform field gap, there is a remarkable difference in the effect 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.