Experimental Test of Superconductor Fault-Current Switchgear Using Liquid Nitrogen as the Insulation and Arc-Quenching Medium

Abstract

With an impressive dielectric constant of 1.43 at 77.3 K, liquid nitrogen (LN2) has the potential to be used as a promising insulation medium for next-generation power switchgear protection systems. It can potentially replace the conventionally used SF6 gas. We have the privilege of having firsthand knowledge of the arc conditions in LN 2 . This paper deals with the experimental approach of first limiting the fault current using an SFCL, and then, interrupting it using the LN 2 switch and a controlled magnetic field. This is a series of totally R&D based tests to show that the limited fault currents can be interrupted using LN 2 as an arc quenching medium. The experiments were conducted on 50 Hz, 500 VAC. Nine-meter superconducting tapes were used to limit the prospective current of 15.7 kA into 800 Amps. The 800 Amps were tested to be interrupted using the LN 2 switch. The electrode gaps were taken to be 35 mm for all the cases. Pure copper and aluminum alloy (Al6061) made electrodes were employed. NdFeB (N35 type) magnets were used to control the shape, size, and direction of the arc plasma. Total circuit voltages, arc voltages, SFCL voltages, arc currents, and arcing times were measured. The optical observations were done using a high-speed camera. Some very important and preliminary results were achieved. All the interruption tests were successful. The results show that the prospective currents were limited by the SFCL within 1 ms and the LN 2 switch extinguished arcs in 2.1 ms.