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A novel investigation into the behavior of the interface between an insulating material and a conductor subjected to sinusoidal stimulus is presented. Both copper and aluminum wires are used in the windings of electrical machines and also as power cable conductors. During in-service operation, partial discharges (PD) may be initiated in the insulation systems. The paper presents experimental results showing the interaction of different kinds of conductors and dielectric materials on the mechanism of partial discharges in the insulation system. The dedicated test setup is designed to perform experiments with various electrodes, with special focus on copper. Two kinds of specially prepared insulation samples were tested, ethylene propylene rubber (EPR), cross-linked polyethylene (XLPE). These insulating materials were subjected to a sinusoidal stimulus at predefined time intervals and were exposed to PD action. The paper comprises the results of PD measurements and microstructural observations performed by means of scanning electron microscope (SEM) coupled with energy dispersive analysis (EDS). The morphological and elemental analysis reveals the interaction of conductor on polymeric material degradation. Two zones were distinguished, migration and erosion. The migration of atoms of electrode material into the dielectric substrate due to PD activity was observed. [ABSTRACT FROM PUBLISHER]