Droplet Behavior Under the Impact of Lightning and Switching Impulse Voltage

Sessile water droplets on insulating surfaces influence the ageing behavior of the insulating material, especially for composite insulators, which are covered by silicone rubber. The hydrophobic silicone surface causes the formation of high contact angles of sessile droplets, which leads to local enhancement of the electric field directly at the contact line. The enhanced electric field can cause partial discharges, which deteriorate the surface properties and enhance ageing of the surface. During operation, beside the constant stress by AC or DC voltage, composite insulators are exposed to different transient electrical stresses like switching or lightning impulse voltages. In this paper the impact of switching and lightning impulse voltage on multiple droplets is investigated to improve the understanding of the interaction between the droplets and the electric field, especially during operation. The behavior of multiple droplets is investigated in dependence on droplet-droplet distance, droplet volume as well as the applied voltage amplitude. Depending on the boundary conditions, three different regimes for multiple droplet interaction are identified: coalescence of droplets, vibration or movement of the individual droplets without coalescence and no interaction. Thereby, the investigation improves the understanding of the behavior of sessile droplets as well as the interaction of several droplets exposed to transient electric fields, and thus the understanding of ageing mechanisms of composite insulators.