Abstract
To clarify the attachment manner of direct lightning stroke on power distribution lines with nearby trees, several experiments have been conducted to examine how the discharge occurs when an open wire as an overhead ground wire is placed near a 3.5 m tree. In the next phase, our focus is placed both the characteristics of lightning impulse discharge and switching impulse discharges on an experimental distribution line and a live 13 m tree. The results showed that the status of sparkover and pre-breakdown phenomena closely coincided with the previous experimental results obtained using an open wire and a 3.5 m tree. This finding proved that a direct lightning stroke to the distribution lines could be brought about by both the rapid progress of leaders from the overhead ground wire and the effect of the tree’s discharge attraction when trees were placed close to the lines. From this study, it was found that a tree’s shielding effect for the distribution lines is not effective; thus, countermeasures against direct lightning applying overhead ground wires and arresters are necessary when the distribution lines and trees exist close together.
