Accumulative effect on streamer propagation of lightning impulses on oil/pressboard interface

This paper reports the accumulative effect of multiple negative lightning impulse shots on streamer propagation along liquid/pressboard surface. Pressboards impregnated with the insulating liquids including a mineral oil, a natural ester and a synthetic ester were tested under a point-plane divergent field. Streamer propagation was recorded by a high speed intensified CCD camera. In addition, current and light signals were monitored by non-inductive current shunt and photo multiplier tube (PMT) respectively. It was found that with 60 s time interval between consecutive shots a streamer along mineral oil/pressboard interface advances itself following each shot and could eventually lead to flashover in a multiple-shot test, while streamers on ester/pressboard interface seem uninfluenced by the accumulative stresses.