Gas-filled voids and metallic particles in epoxy insulation: A lifetime comparison of model samples

Metallic impurities and voids are supposed to be two main reasons for dielectric breakdown of polymeric insulation in High-Voltage applications. In this paper we address the question which of the two defect types has more severe consequences on insulation lifetime. In the case of bisphenol A based filled epoxy samples, we find clear indication that gas-filled voids with a typical size of 0.2-0.7mm lead to a more rapid breakdown than metallic particles with an average size of 50 microns. Therefore initial Partial Discharge testing of HV components seems to play a key role in ensuring high insulation lifetime.