Comparison of the Impulse Breakdown Voltage of Different Glass Fiber Reinforced Epoxy Resin Based Composites

The aim of this study is to compare the impulse breakdown voltage of three different insulating composite materials based on glass fiber reinforced epoxy resin technology and thereby to evaluate the bonding characteristics between the alkoxysilane coating of the glass fibers and the epoxy resin, which determine the electric behavior of the interface between both materials. For the investigations, model coils were constructed in order to recreate the manufacturing conditions of the insulating composite based on a filament winding process. The cylindrical samples consisted of an inner electrode, which was wound on a support structure made of aramid paper. The insulation was wound over the rotating structure with epoxy impregnated glass filaments under tension. An outer electrode is wound over the insulating layer and covered with additional insulation material. After the winding process the samples were cured in an oven. The used glass fiber was the same for all the samples, whereas the epoxy resin was variated. For each combination five samples were wound. The test was performed applying 1.2/50 μs lightning impulses, for which the amplitude was stepwise increased until a breakdown occurred as defined in the standard IEC 60060-1.