Conceptual Design of a Liquid-Nitrogen-Insulated Metal-Enclosed Switchgear

Gas-insulated metal-enclosed switchgears (GISs) are widely applied in the electrical power industry to transmit and distribute electrical energy because of the attractive dielectric and interrupting properties of sulfur hexafluoride (SF6). However, the use of SF6 may have a negative effect on the atmosphere and may contribute to global warming. This paper presents an eco-friendly switchgear: liquid-nitrogen-insulated metal-enclosed switchgear (LNIS). In LNIS, a superconducting fault current limiter can be applied to limit fault currents. Liquid nitrogen has good dielectric properties, and its low temperature helps the switchgear against thermal shocks caused by impulse currents and short-circuit currents. Power loss was compared between a 126-kV GIS and a 126-kV LNIS; at same voltage level, the power loss of LNIS is approximately 15% lower than that of GIS. This result suggests that LNIS may be a suitable replacement for GIS.