Evaluation of the aging process of composite insulator based on surface charaterisation techniques and electrical method

Long term reliability is one of the most important performance measures for high voltage insulators in the power transmission and distribution networks. To evaluate the long-term performance of insulators, properties such as hydrophobicity, surface roughness, images from Scanning Electron Microscopy and dielectric breakdown measurements are often studied. In this paper, a new evaluation method based on the oscillating period of water droplet, namely Oscillating Water Droplet (OWD) method is proposed. Using a high-speed camera, the full sequence of the water droplet making contact with the composite surface was recorded and analyzed. The OWD was performed on specimens of different ageing levels. Further investigation on hydrophobicity using the optical contact angle device is performed to study the relationship between the oscillating water droplet over the surface and the contact angle. To study the loss of hydrophobicity, surface roughness tests were conducted using BRUKER ContourGT Optical Profiler with eight different roughness spots per specimen. Our results show that more time is needed for the water droplet to settle over the surface when the hydrophobicity is decreased due to aging. Scanning Electron Microscopy (SEM) images showing the level of degradation on the surface of the specimens are included. The results obtained are closely correlated to the decrease in dielectric breakdown voltage over the insulator surface as the period of aging cycle increases. This work also indicates that the OWD method can be applied as a new method for evaluating the hydrophobicity of polymeric insulators.