An optical study of prebreakdown events in AC-stressed n-hexane

For a point-to-plane gap immersed in n-hexane it is shown that discrete prebreakdown streamers can be generated and recorded when 60 Hz AC is applied. The streamers are shown to be similar to those seen under impulse conditions. Simultaneous optical and electrical measurements indicate the existence of a correlation between conduction current pulse activity and streamer development. Two distinct types of streamer are observed. Bush-like events appear at the needle tip when a discharge is initiated on the negative half cycle of the applied voltage, whereas a thin filamentary streamer can be seen during the positive half cycle. Inception and breakdown resulting from the two different types of event appear to be independent. For the chosen geometry, negative events are dominant at low voltages, with the positive streamers appearing only at higher potentials. For most conditions it is the positive streamers that are responsible for breakdown