Choices of Droplet size and measuring time on measuring hydrophobic angle of HTV silicone rubber

Hydrophobicity can reflect the operating and ageing characteristics of silicone rubber material of composite insulator. Static contact angle method can be used to judge hydrophobicity by measuring hydrophobic angle, but it is still lack of deep research on the choice of droplet size and the moment for measuring the angle's value. In this paper's study, several HTV specimens are taken as samples whose hydrophobicity are different. The titration tests are conducted on the samples' surfaces and the values of the hydrophobic angle are observed and recorded for minutes. The experimental results indicate that on the surface of worse hydrophobic sample, the value of the contact angle declines quicker and greater during the initial 30s. The droplet on the different surfaces can keep relatively steady form after different time but worse hydrophobicity makes the time of reaching this steady form longer. So the relatively proper time for measuring the hydrophobic angle should be prolonged to after about 60s to increase accuracy. Furthermore, only certain droplet size range is suitable for measuring use for the reason of reducing the error. As hydrophobicity becomes worse, the suitable droplet size range becomes narrower. Relative reasons, e.g., surface roughness, are discussed and analyzed. The regularity of the forms of droplets on the specimens' surfaces can be summarized in one figure. These results and conclusions can help standardize the methods of measuring the hydrophobic angle, which could better reflect the insulators' performance.