Moisture absorption and electrical treeing in glass-fibre reinforced cast-resin

Tests with filament-wound glass-fiber-reinforced epoxy resins (GFRs) have shown that the interface is the weak point in these composite insulators. Although there is a relatively large number of microvoids in the resin matrix, they do not have a significant influence on the electrical properties. It is evident that the trees prefer the interface areas for propagation. This may be caused by long capillary voids around the fibers or by moisture which remains from the fabrication processes of the glass fibers. The application of filament-wound tubes in HV apparatus does not offer any problems provided that the electrical stress is kept below certain limits. The measurement of moisture absorption demonstrates that the water transport mechanisms in composites are different from those in epoxies. It is suggested that the interface also plays a decisive role for water transport in GFR