Partial discharge investigation and electric field analysis of different oscillation modes of water droplets on the surface of polymeric insulator under tangential AC electric field stress

For this contribution, different oscillation modes of a 20 microliter water droplet on the hydrophobic surface of a silicone rubber insulator under tangential AC electric field stress were investigated, using a high speed camera. Since the deformation of water droplet increases the local electric field stress at the triple zones, an electric field analysis at the triple zone is performed to find the worst case of water droplet oscillation modes. Different kinds of water droplet deformation at four dominant oscillation modes, namely mode No. 1 to mode No. 4, which were found experimentally, are simulated and compared. These results show that mode Nos. 1 and 3 provide higher electric field values at the triple zone in comparison to mode Nos. 2 and 4. In parallel, partial discharge inception voltages of a 20 microliter water droplet located on the hydrophobic surface of a silicone rubber insulator under tangential AC electric field stress are measured in the frequency range of 20 Hz to 100 Hz. With the aid of frame analysis of the captured videos, the mode number of water droplet oscillation at each frequency is obtained, and the measured partial discharge inception voltages at each oscillation mode are compared with electric field simulation results. Partial discharge investigations confirmed that the water droplets oscillating at mode Nos. 1 and 3 have lower inception voltages compared to PD inception voltages of water droplets that oscillate at mode Nos. 2 and 4. These measurements also show that inception voltage makes a step whenever the oscillation mode of water droplet changes.