Researches on the observation of charge distribution inside thundercloud by rocket and the protection techniques of power systems by means of triggered lightning.

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Since the first success of the experiment of triggered lightning by rocket on 22 December of 1977, the experiment in every winter in Hokuriku district was performed, and the total attained to 83 lightnings until 1987.In this research for three years from 1988, the triggered lightning experiment to a test transmission line was succeeded together with the measurement of space charge under thundercloud with the measuring device carried by rocket, The total of triggered lightning for three years was 31 including 12 of lightning to the test transmission line and tower. A new triggering method by two stages rocket was developed with three times of successful triggerings.The measurement of electric field at ground around the triggered lightning time and the measurements of electric current, thunder, and photograph of lightning discharge, etc were carried out. The measurement of characteristics of current flowing parallel through the legs of tower and over-head ground wire was also carried out as well as the measurement of over voltage appeared across the insulater of the line by the triggered lightning. The suppression effect for over voltage in the line by Zinc Oxide arrester set on the line was confirmed.In the striking test to ground wire and Zinc Oxide arrester set on the ground, the relation between the damage or breakdown of them and the lightning current was made clear. The measurement of electric field in space by rocket with electric field senser and memory was successful two times. The electric field increased with the altitude until 40-50 KV/m at about 500 m in altitude inside of thundercloud. From the data, the distribution of space charge from the ground to the inside of thundercloud was made clear.