Copper Oxide Formations under Polymer Coatings during Accelerated Thermal Aging

Enameled wires are used in solenoids, electrical actuators, and rotor and stator windings in electric machines. These wires typically comprise copper conductors, which are preferred for their balance between cost and current carrying capacity, combined with a dielectric insulating layer. This insulation is made from polymeric materials, which can provide high dielectric strength with a relatively thin coating layer. The downside of these polymers is their inherent oxygen permeability, which may have an effect on the degradation phenomena associated with the conductor material. The main focus is typically on either the conductor or the insulator, but it does not consider collective antagonistic/synergistic interactions. The results presented in this paper outline a preliminary analysis of the interaction between the conductor and the insulation layer(s), focusing primarily on the interfacial region. Thermal degradation at the copper conductor/enamel insulation interface at 250ºC for five aging time periods (100 to 500 hours) is reported. The oxidation processes of copper were studied using X-ray Photo-Electron Spectroscopy. The impact of exposure time on the type and amount of each oxide was analyzed and was related to the identified degradation phenomena.