Electric field analysis at the triple junction of a optimum profile disc type spacer in SF6 gas insulated system with abnormalities under DC voltages

In Gas Insulated Systems the breakdown strength of SF₆ gas is badly affected by locally enhanced electric fields due to protrusions and delamination. Metal insert electrodes, which are used in GIS, reduces stresses near the triple junctions with simultaneous rise in the stresses elsewhere along spacer surface. AC-GIS are in operation for a long time but there is a limited knowledge for DC application. In the case of DC-GIS, charges invariably accumulate over a period of time along the spacer surface. The electric field distribution around solid spacer is greatly altered by the accumulated surface charges. In this work, the electric field distribution with DC as applied voltage is studied at the triple junction for a cone type spacer with and without metal insert along with the effect of delamination and protrusions on the surface of the insulator. Finite Element Method (FEM), one of the proven numerical method, is used for computing the electric fields at various points under consideration.