Effect of ageing on space charge distribution in homogeneous and composite dielectrics

Homogeneous and composite polymeric insulating systems under operation are subjected to various stresses, including thermal, causing degradation and deterioration to the material. Ageing increases charge accumulation within the volume of the material. In this paper, charge trapping and transport phenomena in thermally aged homogeneous epoxy resin and polyethylene are studied. Pulsed Electro-Acoustic (PEA) measurements are performed to obtain the spatial distribution of charge within the volume of a dielectric. Apart from the space charge behaviour at dielectric - electrode interfaces, the behaviour of interfacial charge at dielectric - dielectric interfaces is also investigated. To this end, composite dielectrics are created with epoxy and polyethylene as constituents. The effect of thermal ageing on the interfacial charge evolution and accumulation in dielectrics with interfaces is investigated. Due to thermal ageing of homogeneous materials, charge is seen to accumulate within the bulk of the material, and not only at the interfaces. In aged composites, interfacial charge evolves at the interfaces, as well as within the bulk of the material. However, space charge measurements in aged materials with interfaces require special care, as signals reflected from space charge sites within the volume of the aged dielectrics tend to distort the real signal.