Breakdown Phenomena in Liquid Nitrogen Under Synchronized Transient Boiling and Impulse Voltage

Abstract

Resistive superconducting fault current limiters constitute a promising solution for high voltage networks. During the resistive current limitation, transient overvoltages and heat dissipation occur on superconducting tapes, inducing fast boiling of surrounding liquid nitrogen (LN2). An experimental system reproducing the fast transient heating of a tape electrode, synchronized with a high voltage impulse is described. Breakdown voltages measurements in both polarities are carried out versus synchronization delay, pressure (0.10 to 0.40 MPa), temperature (77 K and 65 K). Breakdown voltages show complex variations with these parameters. More insight is obtained from the recording of prebreakdown phenomena (streamer). The size of vapor bubbles has a large and counter-intuitive influence on streamer initiation: the smaller bubbles, the lower inception voltage. Subcooling LN2 (by decreasing temperature and/or increasing pressure) sometimes has a beneficial influence (quenching of negative streamer propagation), but deleterious effects can be as well observed in other circumstances (by favouring positive streamer initiation).

Electrical Breakdown in Gaseous Nitrogen at Cryogenic Temperature with a Heated Tape Electrode

“…Heating LN2 induces a very large drop of Vb (by a factor of nearly 10 in negative polarity). In such conditions, the tape becomes entirely surrounded by N2 vapor [10]. Vb then compares with that recorded with either heated GN2, or with non-heated GN2 at high temperature (293 K, Fig.…”