Impulse flashover performance of semiconducting glazed station insulator under icing conditions based on field calculations by finite-element method

The flashover performance of a semiconducting glazed standard post insulator for lightning impulse and switching impulse stresses under icing conditions is studied. The flashover performance can be predicted by calculating the potential distribution along the station post insulator. The potential distribution is computed numerically using the finite-element method. The thickness and conductivity of the semiconducting glaze are varied and their effects on the potential distribution have been studied, to improve electrical performance under icing conditions. Thin semiconducting glaze requires a very large number of elements for finite-element analysis because of the open boundary around the ice-covered insulator. To reduce the number of elements and hence computation time, the region between the domain of interest and infinity is modelled simply by adding a circular boundary, connected to a second mesh of the same size, and boundary constraints to force equivalent boundary potentials to be identical. Infinity lies at the centre of the second mesh. Simulation results are confirmed by laboratory experiments, and it has been found that switching impulse is the limiting factor for the design of a semiconducting glazed insulator under icing conditions. This is contrary to clean conditions, where it has been found that lightning impulse is the limiting factor for the design of a semiconducting glazed insulator.