The impact of electrical field stress on the volume conductivity of syntactic foam

This paper deals with the experimental investigation on the volume conductivity of syntactic foam, a new composite insulation material consisting of a epoxy resin matrix filled with hollow glass microspheres. This investigation focuses on the impact of high electrical field stress on the volume conductivity. Plate specimens of syntactic foam with a thickness of 3 mm are produced for the experiments. Hollow microspheres as well as solid microspheres are applied as filler. In addition, pure epoxy is used as a reference material during the measurements. The volume conductivities of the different specimens are determined by shield electrode configuration according to DIN IEC 60093 applying electrical fields up to 16 kV/mm dc. For each material and each voltage level a time resolved conductivity characteristic is recorded as a function of the load duration. Specimens with solid microspheres show a similar characteristic to the one of pure epoxy, while the behavior of the specimens with hollow microspheres differs. The results are discussed with regard to the filler types (hollow or solid). The impact of the cavity inside the filler on the conductivity and the time resolved measurement curve is shown. The main result of the investigations ascertains that the material behavior is not dominated by the presence of filler but by the presence of hollow filler. Finally, design recommendations for the use of syntactic foam in high voltage dc components are provided.