On the role of water in the aging of polymers in air-insulated electrical systems

The direct interaction between coronas and insulating surfaces is examined, including the generation of water by corona oxidation of the polymer. The authors then report on recent measurements of indirect corona/polymer interaction, by corona exposure of distilled water with submerged polymer samples. It is shown that corona discharges in ambient air will form a water layer on any exposed polymer surface, both by bringing water to the surface made hydrophilic by the corona and by producing water from the polymer itself, by oxidation. Water exposed to air coronas becomes acid and oxidizing, and causes marked aging effects on polymer surfaces. Thus, any model of the action of air corona discharges on polymer surfaces must include the presence and effects of an intermediary aqueous electrolyte surface layer