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 (LN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ). 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 pre-breakdown 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 LN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> (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).