|Budget Amount *help
¥2,000,000 (Direct Cost : ¥2,000,000)
Fiscal Year 1993 : ¥700,000 (Direct Cost : ¥700,000)
Fiscal Year 1992 : ¥1,300,000 (Direct Cost : ¥1,300,000)
This report relates to the fundamental study on the negative lightning flashes with multiple channels to ground. As a result, we obtained conclusion as shown under.
(1)At two sets of rod to plane electrodes, when flashover occurred in gap A, the plane electrode potential of gap A dropped and then recoverd with times. Because such voltage change in gap A was applied in gap B as impulsive change of voltage, concurrent discharge occurred.
(2)To imitate the case in which difference of height exists between steel towers under thundercloud, we discussed the case in which length of gap A and gap B was different individually, As a result, as gap length of gap B was longer that is, flashover voltage was higher, a probability of concurrent discharge occurrence was higher. Besides, when distance between steel towers was different, as distance between two sets of gaps was shorter, a probability of concurrent discharge occurrence was higher. In any case, to occur concurrent discharge occurrence, at a gap B where concurrent discharge was induced, discharge charge(about 10nC in case of gap length was 3cm) to transmit leader from corona discharge was needed to supply from gap A where concurrent discharge was induced.
(3)When lightning flashes occurred between a steel tower A and the group of charge B over them, we assumed that potential between another steel tower C and the group of charge D over them changed if potential between A and B changed. In the case, we concluded that if impedance between the group of B and D depended on distribution state of negative charge between them and smaller and smaller the impedance, a probability of lightning flashes occurrence between C and D induced by lightning flashes between A and B was larger.