Dielectric spectroscopy of composite insulating materials

Recently, methods based on dielectric relaxation phenomenon have been more and more frequently applied for diagnosing electric equipment insulation and its aging during operation. However, it has appeared that in the case that dielectric spectroscopy is used for diagnosing insulation materials most often produced on base of epoxy resins reinforced with mats, fabrics or fibers, difficulties of interpretation can occur. The problems are related to the complex material structure and numerous dielectric polarization processes involved, in particular in the case of using a multi-component polymer matrix hardened with a set of latent hardeners of diversified initial hardening temperatures. In most cases the insulation produced is an anisotropic material when speaking of its dielectric properties. Considering the spatial morphology of the composite insulation materials (CIM) they can be described as a crystalline phase composite immersed in a viscid-elastic medium. For a certain class of CIMs, e.g. in case of a matrix where the hardening process is unfinished, such an environment may show solid electrolyte properties. This paper presents the results of measurements of the complex dielectric constant of new or aged composite insulation within the frequency range 10^-4 10⁶ Hz where among other methods a method based on the phase shift angle approach was used