Effects of water absorption on interfacial phenomena in HV insulating materials

Dielectric properties of filled epoxy resins were measured after water attack at 50°C and after HF vapors attack. The loss tangent tan δ of these composites showed tendency to increase rapidly from moisture content 0.6%. But roundish filled resin didn´t show the phenomena to increase rapidly, and this tan δ increased only a little. The filler particle size and the filler material in filled resin had a little influence on the phenomena. The same was true of the case that roundish silica filled resins were exposed in HF vapor, that is to say, this tan δ had a little increase in comparison with square silica filled resins. These results should be understood that the water entered into the bulk along the interfaces between filler and epoxy resin. We could obtain the lower loss tangent epoxy resin castings through the roundish silica filler