Asymmetrical ageing of composite insulators: effect on water dripping behaviour and electrical performance

This paper presents work that was carried out to investigate the effect that asymmetrical ageing of composite insulators, including ethylene-propylene rubbers (EPDM) and silicone rubbers (SiR), has on water dripping behaviour and subsequent electrical performance. Surface features and hydrophobicity measurements of 132 kV EPDM and 400 kV SiR service aged insulators from coastal environments are examined. The examination demonstrates that surface features including surface roughness, discolouration and hydrophobicity are different along areas of the insulator string, shed and core. Possible reasons are discussed. To investigate the effect that the asymmetrical distribution of hydrophobicity along the composite insulators' surface has on their electrical characteristics; three porcelain insulators with symmetrical and asymmetrical hydrophobicity distributions were used. One of the porcelain insulators has a hydrophobic surface, the second one has a hydrophilic surface and the third one is half-hydrophilic and half-hydrophobic. The results show that the electrical performance of the hydrophilic and half-hydrophilic insulators are similar. This finding suggests that the electrical performance of an asymmetrically aged insulator is governed by the most hydrophilic surface area along its length.