SOURCES OF INSULATOR CHARGING AND THE INDUCED ELECTRIC FIELD ENHANCEMENT IN GAS INSULATED SUBSTATIONS

摘要

Insulators used in power transmission plants can accumulate electric charges and this needs to be taken into account at the design stage. In the case of GIS, the route of the charging process is via SF_6. Therefore surface charges accumulate until the normal electric field is cancelled to zero by the surface charge induced field itself. To see the effect of electric field enhancement due to surface charges, a new boundary condition needs to be imposed for calculations, viz, zero normal potential gradient along the gas side of gas-insulator interface. The finite element method needs to be adapted by dividing the region of interest into several sub-regions and calculations carried out first in regions where charge transportation takes place. The potentials along these interfaces needs to be saved and then recalled as fixed boundary conditions for subsequent calculations in other sub-regions. A calculation for a real geometry indicates that when the surface charging has reached the equilibrium state, the electric field at a critical location can be more than doubled in comparison with no surface charging. It has also been shown that surface charging on one side of an insulator can cause flashover along the surface on the opposite side.