The metallic particle contamination is the important factor to cause the flashover of the disc insulator from the practical experience. In order to understand the influence of metallic particle contamination on the flashover characteristics of disc insulators

the flashover characteristics of disc insulators under standard lightning impulse（LI）voltages is investigated on the basis of analysis of metallic particle profile

including the influence of the particle length

attached location and gas pressure. The experimental results show that the flashover voltage under positive polarity of LI is higher than that of negative polarity when the metallic particle is attached to the surface of disc insulators. With the distance between the metallic particle and the high-voltage electrode decreases

the flashover voltage under positive polarity of LI further decreases. The flashover voltage drops obviously with the extension of the metallic particle’s length. The reduction would become not obvious when the length of metallic particle exceeded a certain limit. It was also found that the U-P curve under positive polarity of LI is looked like a hump

when the metallic particle is attached to the surface of disc insulators. Due to the effect of space charge

the hump will be more obvious under negative polarity of LI than that under positive polarity. This study can provide some references for the detection of the defect in GIS.