Evaluation of high temperature capacitor dielectrics

Four candidate materials were evaluated for use as high-temperature capacitor dielectrics. The materials investigated were polybenzimidazole polymer and three aramid papers. The samples were characterized with and without heat treatment in terms of their dielectric constant and loss. These properties of the heat-treated samples were also evaluated in a temperature range of 20 to 250°C in the presence of electrical stress of 60 Hz, 50 V/mil. The AC and DC breakdown strengths of both dry and impregnated samples were determined at ambient conditions. The preliminary data indicate that heat treatment of the materials tested improves their dielectric properties and breakdown voltages. The AC and DC dielectric strengths are further improved upon impregnation with a suitable liquid