Rolling droplets and partial discharges in AC electric field

High-voltage silicone insulators can be used in climatic conditions such as rain or fog since they are hydrophobic. However, water droplets lead to discharges, which reduces hydrophobicity of the silicone rubber which is, in turn, is a first step to failure of an insulator. To increase the resistance of the rubber to the discharges, it is necessary to study the discharges between droplets in detail. The present work is devoted to the study of the loss of hydrophobicity of silicone rubber due to rolling droplets and discharges between them on the inclined silicone rubber sample under AC voltage of 35 kV. An experimental setup used in the work has been developed based on Dynamic Drop Test (DDT) and makes it possible to study discharges only between droplets, and avoid contact of droplets with the electrodes. Simultaneous observation of droplets and discharges made it possible to distinguish characteristic events and to divide the loss of hydrophobicity into stages. Experiments showed that the behavior of the droplets changed gradually, while the discharges were observed only at the last stage. Presumably, the resistance of rubber to discharges is not the only factor that determines the time of loss of hydrophobicity. The very beginning of the process of loss of hydrophobicity should be investigated further.