Finite element modeling of electric field distributions around a resistive glazed post station insulator covered with ice

The main objective of this research is to study the potential and electric field distributions around a semi-conducting glazed standard post insulator for power frequency operation, in the presence of lightning impulse (LI) and switching impulse (SI) voltages under icing conditions. Those distributions are computed numerically using the finite element method (FEM). The thicknesses and conductivities of the semi-conducting glaze, the ice layer and the water film are varied and their effects are studied for the purpose of improving the electrical performance of the insulator under icing conditions. The thin semi-conducting glaze requires a very large number of elements for the FEM because of the open boundary around the insulator. To reduce the number of elements, the open boundary is simulated using a form of Kelvin transformation. The computation time is compared with that of using an artificial boundary. It is found that this time is considerably reduced by applying the Kelvin transformation to a wet ice-covered semi-conducting glazed insulator.; Simulation results are confirmed by laboratory experiments, and it is found that the switching impulse is the limiting factor in the design of a semi-conducting glazed insulator under icing conditions contrary to clean ones, i.e. ice-free conditions where the lightning impulse is the limiting factor. Any wet ice, accumulated on the insulator, has very little effect on the electric field distribution for a lightning impulse voltage, but has a major effect on the electric field distribution and hence, on the flashover performance of the insulator, for a switching impulse voltage. For the time instant of breakdown, the flashover occurs after the peak voltage for the clean as well as the wet ice-covered insulator under the lightning impulse voltage, and before the peak voltage for the clean insulator and after the peak voltage for the wet ice-covered insulator under the switching impulse voltage.