SHIELDING EFFECT OF SURROUNDED SPACE CHARGE ON THE LIGHTNING STRIKING CHARACTERISTIC TO THE POWER LINE AND THE INVESTIGATION BY ARTIFICIAL TRIGGERED LIGHTNING APPROACH

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In order to make clear the shielding effect of surrounded space charge on the lightning striking characteristic to the transmission line, the measurement of the corona discharge current emitted from a transmission tower was performed, and the artificial triggered lightning tests for the transmission line were carried out in parallel. During three years since 1996, the experiments have been performed in Mt. Okushishikui near Japan sea for winter thundercloud. The experiments were continued during one month on November in each year. The results were as follows,(1) The corona discharge current measurement was performed at eight arm ends of a test transmission tower which is 60 meters high. The maximum current was more than 500 A which was measured at one arm end on the up pest level. The currents at the lower level were comparatively smaller than the upper level.(2) The average charge of the current from the whole arms of the tower was around 0.1 C/hour under the exposure of thundercloud.(3) The artificial triggered lightning experiment was performed using rocket. First the rocket carries a bobbin from which a nylon line was pulled out and a wire connected follows. The nylon line was used for insulation of wire from the ground. The length of the nylon line was 160m. Thirteen times of triggered lightning struck the transmission line and tower. It is estimated that the lightning strikes to the transmission line and tower take place in the surrounded air with such space charge.(4) Additional seventeen times of triggered lightning were obtained to strike the ground level by means of another triggering methods, and the current wave forms and the energy of lightning discharge channel were measured. And another kinds of observation were successfully performed.(5) The total triggered lightning strikes obtained in these three years were 30 times.