Hydrophobicity transfer mechanism evaluation of field aged composite insulators

Surface hydrophobicity is a critical property of silicone rubber composite insulators. It is the primary advantage in comparison to ceramic and therefore is the first to be investigated when field aged insulators are examined. Initially hydrophobicity was evaluated by static contact angle measurements. However field and laboratory investigations have revealed that in the case of outdoor high voltage insulation, it is the dynamic performance that is critical and especially the capability of hydrophobicity recovery, available due to a low molecular weight molecules migration mechanism. This mechanism efficiency is related to the material formulation but also to the experienced service conditions and the ageing degree of the insulator. Therefore laboratory evaluation of field aged insulators can be considerably beneficial for both researchers and utilities. In this direction the hydrophobicity recovery efficiency of three field aged insulators, with two different base polymers is investigated in this paper. Both static and dynamic measurements are performed, according to the CIGRE guidelines. The results verify the superiority of silicone rubber polymer and reveal a recovery time exceeding 10 hours. Not considerable differences have been observed due to aging in this case. Further investigation is required, in order to be able to correlate this behavior to the insulator efficiency.