The cap which represents the HV electrode was energised with an AC voltage of 6.3 kV at 50 Hz. This was the rms potential to which the insulator was subjected to under heavy pollution conditions, according to the IEC 60507 standard. The bottom electrode was connected to ground at 0 V. The air space surrounding the insulator in the fog chamber was simulated large enough to minimise it’s effect on the distribution of potential near the electrodes and along the insulator profile, and also to simulate the air surrounding the insulator in the fog chamber. The outer edges of the air background region are assigned with a boundary that assumed zero external current and electromagnetic sources, hence representing a physical system that is in an isolated open space. The symmetry line of the insulator was set to be the axi-symmetric along the axis on the r-z plane.