This paper presents the experimental results obtained during an investigation into the interaction at the interface between different dielectric materials and a copper conductor in an electric field during partial discharge action. The experimental setup compares the following metal-dielectric layers: cross-linked polyethylene, ethylene-propylene rubber, epoxy composite, dielectric enamel and paper insulation. The electrical mechanism of metal migration into a dielectric material is investigated through partial discharge patterns. The electric field-driven migration of the copper particles from the conductor to the insulating medium was observed. In order to understand the relationship between the electrical stress and the associated morphological changes, a microstructural analysis of the insulator surface, by means of electron microscopy and elemental analysis, was performed. The migration of metal particles into dielectric insulation systems might occur when a strong electric field is accompanied by certain thermal phenomena. It is important to recognize the role that a Cu conductor material plays in this phenomenon. Hence, the understanding of the migration mechanism and associated assessment criteria is a relevant and important research topic. Migration effects occurring at the metal/dielectric interface are presented quantitatively in the paper. A novel aspect relates to the investigation of the electrode metal concentration for different dielectric materials.