The effect of electrical ageing on a cast epoxy insulation

An epoxy composite used as cast electrical insulation in outdoor applications is studied for property and structure changes caused by aging under intensified electric field. The dielectric loss and the dielectric strength of the material are found to be slightly changed over an aging time of 1500 hours. Dynamic mechanical properties of the material show appreciable changes. Scanning electron microscope and atomic force microscope results indicate morphological changes on the surfaces of aged samplers. It is concluded that electrical aging occurs in interconnected regions where the cross-linking density of the material decreases. The dynamic mechanical analysis is found to be more sensitive to the changes of crosslink density than are measurements of dielectric loss and dielectric strength.