Effect on 50% flashover voltage due to accumulated charges on the surface of polymer insulators

The influence of accumulated charges on a polymer insulated surface on the 50% lightning impulse (1.2-50 mu s) has been investigated. The 50% flashover voltage was measured for three different conditions: under dry environment, immediately after immersing the upper shed and body of the insulator in saline water, and immediately after completely immersing the insulator in saline water. The negative polarity 50% flashover voltage under the dry condition is the highest. This shows that negative charges accumulated on the air-insulator interface under the triple junction and in voids near the triple junction suppress the progress of the streamer. The 50% flashover voltage for the positive polarity case under dry conditions is lower than that for the negative case. This shows that the amount of positive charges accumulated on the insulator surface under the triple junction and in voids near the triple junction is less than that under negative polarity. It also suggests that positive charges generated around the stripped cable-insulator interface diffuse onto the shed surface more extensively.<>