Electric Performance of Interfaces in Outdoor Insulation Systems

Insufficient long term reliability of internal interfaces in polymeric outdoor insulators is considered as a potentially critical factor in the performance of modern outdoor insulation systems. In this study, aiming to elucidate this question, test objects composed of silicone rubber layers moulded onto plates of epoxy resin were tested. The epoxy substrate was incompletely covered by a bonding primer and therefore a chemically unbounded interface was formed. A thin wire electrode was inserted into the unbounded interface for ageing it by partial discharges. The samples were tested in a humid environment. In addition, one set of samples was also boiled for 100 h in deionised water. Changes of adhesion imposed by this treatment were analysed with a modified peel-test. No significant reduction of the interfacial mechanical strength could be revealed, although microscopic inspections and IR analyses of the interfaces involved identified evidences of interfacial degradation. The boiling and subsequent testing in high humidity yielded also a higher dissipation factor of the tested objects.