Influence of thermal aging on electrical properties of inhomogeneous dielectric material

This paper deals with diagnostic of composite insulation material which are currently used in high voltage appliances e.g. in large rotating machines - turbo or hydro generators. This composite is consist of calcinated mica paper, polyethylene terephthalate (PET) foil and epoxy-novolac resin. The insulation composite material with inhomogeneous structure was subjected to accelerated thermal aging and dielectric parameters such as dissipation factor, permittivity, capacity, absorption characteristics with its related parameters and breakdown voltage were measured in predetermined time intervals. Two temperature levels (180 and 195 °C) and various times of exposure were investigated. The temperature and time of exposure dependences of individual parameters are presented in this paper.