Dielectric response analysis of real insulation systems

Real insulation systems are often heterogeneous and sometimes non-linear. In this paper we discuss the application of dielectric frequency response methods to a number of such practically important systems. Important examples of composite insulation systems are the oil/cellulose insulation of power transformers and the glass-mica-epoxy system of machine insulation. A few examples of non-linear effects and their implication for dielectric response analysis are discussed. These include narrow liquid ducts in transformer insulation, exhibiting a voltage dependent conductivity, polymer cables with water trees exhibiting non-linear behaviour that is the basis for diagnosis. The relation between partial discharges and dielectric response is elucidated and finally the special problems of measuring non-linear field grading material is discussed.