The effect of interface adhesion of over-moulded polymer materials for electrical components used in power distribution equipment

The interface adhesion of two over-moulded polymer materials is critical in controlling the partial discharge occurring in an electrical component used in power distribution equipment when medium voltage is applied. Voids or delamination occur at the interface between the overlay and the substrate if the surface tension of the substrate is lower than that of the overlay. In this study we investigated silicone rubber, epoxy substrates and epoxy overlays using X-ray examination, computer tomography scanning and electrical tests such as partial discharge tests, thermal-cycle test, to identify the material combination with good and repeatable adhesion and minimal partial discharges. The results from X-rays and computer tomography scanning show obvious delamination and voids with untreated silicone rubber substrate and epoxy overlay. This is further reflected in high partial discharges from the electrical tests. An alternative material combination showed good adhesion, there were no voids nor delamination at the interfaces and the partial discharges were minimal from the electrical test results even after thermal cycle test and additional electrical stress tests. From the results, we can conclude that it is possible to choose polymer material combinations requiring minimal surface modification processes that yield good adhesion throughout with extremely low partial discharge.