Influence of fog parameters on the aging of HTV silicone rubber

Testing of outdoor insulators in a fog chamber is universally used. Many fa ctors affect the generation of fog. Fog parameters such as the pressure of the compressed air and the water now rate feeding the nozzles to form the f og, as well as the size and the speed of the fog droplets impinging on the surface of the insulators, play a major role in the outcome of electrical p erformance tests. In order to be able to compare test results from differen t laboratories, the conditions of fog generation should be defined unambigu ously and clearly. In the present paper relationships between air pressure, water now rate and air speed which are related to the distribution and the speed of the fog droplets, are determined as a function of distance from t he IEEE-IEC standard nozzles forming the fog. The distribution of different fog droplet sizes is measured. The influence of the fog parameters on the aging characteristics of surface resistance, surface roughness, leakage cur rent and surface hydrophobicity of high temperature vulcanized (HTV) silico ne rubber are presented.