Dielectric Characteristics of Liquid Nitrogen According to the Electrode Material

High-voltage superconducting apparatuses, such as superconducting fault current limiters, superconducting transformers, and superconducting cables, are operated in high voltage, cryogenic conditions. A superconducting coil system may breakdown electrically not only in quench state but also in normal state (Kang et al. IEEE Trans. Appl. Supercond., 17, 1493-1496, 2007). In this paper, dielectric experiments of liquid nitrogen according to electrode material are performed with AC and lightning impulse voltages to design an electrically reliable, high voltage superconducting system. The electrical breakdown voltage of liquid nitrogen for various pressures (from 0.1 MPa to 0.4 MPa) strongly depended on the electrode material. Therefore, the design of a high-voltage superconducting apparatus should consider the kind of electrode material. The experimental results in this study can be used to design the different parts of a high-voltage superconducting apparatus according to the electrode material.