Behaviour of streamers under divergent AC fields in transformer oils at large gaps

Measurements of streamer lengths in transformer oils under various divergent AC fields and at large gaps (⩽8 cm) have been conducted. Positive streamers play a dominant role in breakdown since their propagation lengths are much larger than those of negative ones. Several configurations of electrodes have been investigated and some geometrical effects have been found. Specifically, the positive streamers stop at a length which depends not only on the initiation voltage, but also significantly on the geometry (distance and shape of electrodes)