A study of partial discharges from water droplets on a silicone rubber insulating surface

This paper presents measurements of partial discharge (PD) from water droplets on a silicone rubber insulating surface in an ac field. Tests are done by placing droplets on the surface using a micro-pipette, and by condensing water in a controlled humidity chamber. The field enhancement factor due to droplets placed on the insulation surface is experimentally and numerically determined. Values in the range of 3.8 to 6.3 are obtained depending on the size and number of droplets. The time resolved analysis of PD from water condensation indicates a threshold field, between 3.0 and 3.5 kV/cm, above which the PD activity increases with time, and brings the insulation to a surface breakdown. The corresponding field enhancement factor obtained for the condensation experiments is between 5.8 and 6.8. The results therefore suggest that the PD activity on the hydrophobic surface can be used effectively to learn about the insulation surface conditions.