부산대학교 도서관

Pre-breakdown and breakdown phenomena are investigated in liquid nitrogen (LN $_{{2}}{)}$ with a tape-plane electrode geometry. Different voltage waveforms are used: lightning and switching standard impulses, step impulse (STI), and dc ramp. The influence of temperature is also investigated, by sub-cooling LN2 down to 65 K. Breakdown voltage depends on polarity, gap distance, temperature, and high voltage (HV) waveform: the longer the waveform, the lower the breakdown voltage. Positive pre-breakdown streamers are about three decades faster than negative ones. With short-duration lightning impulses (LIs), the propagation of slow negative streamers is quenched, resulting in higher breakdown voltage. In boiling conditions, slow negative streamers may propagate for long durations. Sub-cooling LN2 induces a slight increase in streamer initiation voltage and impedes the propagation of slow streamers due to condensation.