ABSTRACT

Abstract-Sessile water drop geometries on various surfaces have been studied with and without exposure to electric fields with the aim to understand the phenomena involved in the generation of the sound emission from wet high-voltage transmission lines. It has been demonstrated that noise can be reduced by the application of certain coatings to the high-voltage conductors. Various coatings and treatments have been evaluated with respect to contact angle measurements under a wide range of conditions, including discharge levels. In the experiments presented water drops of wellcontrolled volume were placed on horizontal stainless steel and aluminium surfaces which had undergone a variety of treatments, singly or in combination: sandblasting, glass-bead blasting, hydrophobic and hydrophilic coatings. The surfaces mentioned formed the lower electrode of a parallel plate discharge gap. Contact angles were determined by first producing an electronic image of the drop which was then assessed by means of the software developed in this study. It has been shown that the voltage at which instability, resulting in ejection of a fine jet of water of a few f.!m with increasing electric field, is reached depends strongly on the initial shape of the water drop and, thus, on the contact angle which, in tum, is controlled by the surface properties. This work demonstrated that the instability voltage was roughly doubled if the surface conditions changed from hydrophobic to hydrophilic.