Steep-fronted, single impulse breakdown in epoxy composites with powdered fillers

Steep-fronted, single impulse breakdown tests have been performed on casting composites having three different compositions, using a uniform field geometry with embedded bruce contour electrodes and gaps of 0.3, 0.6 and 2.2 cm. The binder for each composition contained diglycidyl ether of bisphenol A as the epoxy resin, nadic methyl anhydride as a hardener, and benzyldimethylamine as an accelerator, in the relative proportions by mass of 100:85:0.5. The filler materials are Mg_1-xFe_xSiO₃ with x< 0.1, MgTiO₃, and BaTi₅O₁₁, with dielectric constants of 6, 16, and 50, respectively. The phenomenology of breakdown was similar for the three compositions over the thickness range and conditions of excitation of these tests. Breakdown strength decreased with increasing dielectric constant of the composite and its filler and with increasing gap width