Diagnosis of hydrophobic condition of polymer materials using dielectric measurement and image analysis [insulator applications]

Dielectric measurement and image analysis are used to evaluate the hydrophobic condition of a polymer surface. Silicone rubber sheets were used as the experimental material, which had different concentrations of alumina tri-hydrate and with or without surface treatment of fillers. The hydrophobicity of the sample surface was studied by using image data analysis of a water droplet between a pair of inter-digital electrodes on the sample surface. The motion of the water droplet on the sample under ac high field application was captured. The video image was divided into each image frame and the FFT data of image indices such as size and shape factor of the droplet were evaluated. The hydrophobic condition of the sample surface was also determined by measuring the dielectric property of silicone rubber by using parallel plane electrodes. The properties were detected by using unbalance operation of a current comparator type capacitance bridge. The changes in dielectric loss current and the capacitive current by the change in hydrophobic condition were measured for every cycle of applied ac field. Comparison of these results can define the degradation of hydrophobicity of polymer insulators more accurately.