Experimental Study on the Electrical Breakdown Characteristics of Sub-Cooled Liquid Nitrogen for Designing a High Voltage Superconducting Machine

The electrical breakdown characteristics of liquid nitrogen should be investigated for developing of a high voltage superconducting machine. This paper deals with the experimental study for the verification of dielectric characteristics of sub-cooled in accordance with utilization factors. AC dielectric experiments were carried out by using sphere-plane electrode systems. The utilization factors of simulated electrode systems were controlled by gap distance between two electrodes and diameter of a sphere electrode. Also, dielectric experiments according to various pressures, 1.25, 1.5 and 2 bar, by gaseous nitrogen were carried out. In this paper, the electrical breakdown criteria of sub-cooled conditions are derived with various sphere diameters. In addition, the sub-cooled condition and saturated condition were compared with AC dielectric characteristics. Research results could be applicable to designing of high voltage superconducting applications such as superconducting fault limiters (SFCLs), cables and large-capacity transformers.