Design of GIS insulators including small metal particle influence

Surface breakdown of post spacers in gas insulated substation was analyzed using FEM calculations of surge wave electric field and presence of small metal particles caused by imperfections in manufacture. The relative increase of electric field was considered directly related to breakdown probability. It included the length of the particle and foregoing stress on the insulator surface near to the particle ends. The computed results were in good agreement with measured breakdown voltages in a real scale GIS compartment.