Enhancement of charge transfer due to electrohydrodynamic motion in contaminated insulating liquid

Data are presented on the effect of particulate contamination on prebreakdown processes in commercially used insulating liquid. Test samples were subjected to a voltage step applied to parallel plane electrodes. The test results show that copper and iron particles (<2 mu m) have considerably greater influence on EHD (electrohydrodynamic) motion than graphite particles (<5 mu m). In addition to particle size, the shape, concentration, and especially the charge on the particle surface have an influence on EHD motion. The addition of insulating particles such as alumina did not induce any liquid motion. The dominance of dwell time over transit time of the insulating particles led to the formation of a thin insulating coating on the electrode surface, resulting in slightly reduced current.<>