Basic Study of Discharge Characteristics to an Open Wire and a Tree under Lightning Impulse Voltage

There are many cases where trees grow around power system equipments uch as transmission lines and distribution lines in Japan. For developing better lightning protection measures, it is essentially important o clarify influence of trees upon lightning stroke attachment manners. This paper presents results of experiment of discharge characteristics for an open wire of power distribution lines and a tree, which were placed close to each other. In this experiment, lightning impulse voltages were applied under the condition that an open wire and a tree were placed close to each other, and the rate of sparkover to the open wire or the tree was examined. Moreover, pictures of sparkover were taken by the video camera and the 50% sparkover voltages were measured for the open wire and the tree that were placed independently. As a result, sparkover to the open wire only occurs, even when the open wire is lower than the tree by about 1.5 meters. For some configuration, the rate of sparkover to the open wire tends to increase in comparison with that of sparkover to the open wire via the tree when the value of applied voltage has gradually raised. From this experimental results, it is clarified that the shielding effect of trees for power distribution lines is not expected under some conditions.