ABSTRACT
Electrical breakdown at the edges of sessile water droplets on a horizontal, insulating surface
subject to high AC electrical stress has been studied experimentally. The behaviour of the
water droplets under these conditions has been examined using a high-speed video camera
and by detecting electrically partial discharge activity. Different modes of droplet vibration
have been observed, some of which lead to transient changes in droplet contact angle at the
insulator surface with concomitant changes in the electric field in the vicinity of the triple
junction. These field effects have been calculated and their significance on partial electrical
discharges discussed. Lateral spreading of water droplets has also been observed. It is
considered this spreading is associated with the vibration and with the partial discharge
activity.