Transient charge deposition and electric stress in HV GIS

High voltage insulator in a typical GIS (gas insulated substation) was considered to withstand DC electrical stress that cause the ion charge transfer. The field distribution across insulator with long creepage paths and field distortion due to the deposition of charge on the insulator surface was calculated on a geometry model by finite element techniques. The applied voltage was a standard surge wave and the final charge distribution was calculated. The gas ionization and the charge transfer to insulator were dependent on the changing electric field between the busbar and the insulator concave surface. Overcritical value of electric field at busbar surface were used in calculation of electron emission at cold cathode conditions. The results of field analysis were verified by standard measurements on 110 kV insulators in real scale GIS compartment.