AC Current Interruption by Liquid Nitrogen in a Superconducting Fault Current Limiting Switchgear

A new switchgear named Liquid Nitrogen Insulated metal-enclosed Switchgear (LNIS) is proposed, which uses LN2 as an insulation medium to substitute SF6in Gas Insulated metal-enclosed Switchgears (GIS). Power loss of the LNIS is only about 1/8 of the same level GIS, making the novel switchgear a fascinating technology for future power systems. To make the switchgear more compact and efficient, LN2 is also used as an arc extinguishing medium of disconnecting switches. Thus, closed-loop current that can up to thousands of amps should be interrupted by LN2. However, AC current interruption ability of LN2 is still unknown. The objective of this paper is to obtain the AC current interruption properties of LN2. Experiments are conducted with currents ranging from 700 A to 4 kA. AC current of 2950 A (Peak value) is interrupted by LN2 successfully. The maximum arc energy during the interruption is about 437 J, far less than the Joul heat generated by the rated current flow. Arc energy during interruption doesn't burn extra burden on the cooling system. Thus, AC current interruption ability of LN2could meet requirements for LNIS.