Electric field calculations on a high voltage insulator under wet conditions

Occurrence of water droplets on outdoor insulators either due to rain, fog, dew etc. leads to localized field enhancement causing partial discharges and dry arcs which ultimately results in complete flashover. Presence of a hydrophobic coating (e.g. RTV coating) inhibits the formation of water films and hence lead to formation of discrete water particles which are less dangerous. In this paper two cases are investigated. The first case refers to the hydrophobic case where water droplets reside as discrete droplets on silicon rubber (SIR). The second case is when water droplets coalesce and form a film due to the diminution of the hydrophobic property. The first set of simulations inquired the role of single, multiple discrete water droplets on the shed and the sheath region in enhancing the E-Field. The second set of simulations looked into effect of the water films on the shed region. A high voltage insulator (138KV) made of SIR is considered to perform the electric field calculations. The first set of results indicates that the water droplets in the sheath region greatly contribute towards enhancing the probability of initiation and progression of wet flashover on insulator surface. The second set of simulations revealed that the E-Field intensification is more when there is abatement of hydrophobic property on the SIR insulators when compared to the discrete droplets case. Simulation was done with the help of a 3D electric field analysis package called COULOMB.