Audible Noise and Corona Discharge from Water Droplets on Superhydrophobic HVAC Conductors

Audible noise from transmission lines is mainly generated by corona discharge from defects and water droplets on the conductors' surface. Applying a superhydrophobic coating to the conductors can reduce corona discharge, thereby reducing the level of audible noise produced. In this paper, corona discharge and noise measurements from an untreated conductor and a conductor coated with superhydrophobic coatings were carried out in AC electric fields and continuous water spray. The coated conductors show higher partial discharge inception voltages (PDIV) than uncoated ones. PD magnitude and PD per cycle of the coated conductors are lower compared with uncoated conductors, especially at electric fields above 14 kV/cm. A linear correlation between overall sound pressure and total PD magnitude is established. The behavior of corona discharges from single droplets with various sizes and positions and associated droplet vibration were investigated and the local electric field enhancement was analyzed by finite element analysis to examine the influence of droplet size and position on electric field distribution. Superhydrophobic coatings result in reduced PD magnitude and number and therefore reduce audible noise generated. This is attributed to small sessile droplets forming rather than large pendant droplets.