Corona discharge characteristics of water droplets on hydrophobic polymer insulator surface

Although polymer insulators show excellent insulation characteristics, especially under contaminated conditions due to hydrophobicity on their surface, it is reported that corona discharges generated at high electric field portions such as energized end of a 500-kV polymer insulator, damaged the surface of its sheath. Due to hydrophobicity, voltage distribution along a long rod type polymer insulator is very non-uniform even under wet conditions. So water droplets deposited on hydrophobic surface of energized end of a polymer insulator for higher voltage application are subjected to high electric field, and deformed under such electric field. Corona discharges may generate from the tips of deformed water droplets. We investigated fundamental mechanism of corona discharges from water droplets on the energized end of a hydrophobic polymer insulator under AC and DC voltages. Behavior of water droplets was carefully examined by a high speed video camera and leakage currents were measured for detailed analysis