A creepage failure which may generate at the wire supporting points of the distribution lines by the invasion of a lightning surge was simulated in the laboratory. The properties of creepage discharges which develop along the wire surface have been studied using the impulse voltage with various duration of wave fronts Tf. The effects of the voltage polarity and Tf on the developing length and aspect of the creepage discharge are shown in the present paper. The properties of positive creepage discharges were not affected by Tf, but a remarkable effect of Tf was found when the negative creepage discharges developed along the wire surface. These results indicated that the lengths of discharges were closely related to the aspects of them.
