Water drop corona on hydrophobic epoxy

Outdoor insulation materials not only have to withstand the electric field during service; they also must be resistant against ageing phenomena by dust and humidity. Water drops from dew or rainfall play an important role. Research work has been done on the damaging effects of water drop corona to insulating materials. Earlier investigations were focussed on silicon rubber which is intrinsically hydrophobic. Now the research work was extended to epoxy resin systems. This publication reports about the onset conditions for water drop corona. Water drops are put on test specimens in special experimental set-ups and they are exposed to increasing AC field. The experimental set-ups allow to have an electric field parallel respectively perpendicular to the surface of the insulating material.