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

Resistive superconducting fault current limiters constitute a promising solution for high voltage (HV) networks. During the resistive current limitation, transient overvoltages and heat dissipation occur on superconducting tapes, inducing fast boiling of surrounding liquid nitrogen (LN
$_{{2}}{)}$
. 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 (0.10–0.40 MPa), and temperature (77 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 counterintuitive 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 favoring positive streamer initiation).