This paper presents the results of the basic experiments on discharge suppression depending on air pressures in simulated lightning intruding into a junction-concrete gap. The distorted waveforms by way of a junction-concrete gap more than air pressured 2 atm are smoothly conditioned approaching to positive or negative polarities, and their amplitudes are sharply attenuated by 39 and 52 %, respectively. Using the FFT analysis of discharge waveforms and the impedance vector loci, discharge impedance more than air pressured 2 atm can be obtained in frequency bands of the lightning conventional current (10/350μs). An R-L series circuit is proposed to equivalent circuits below 100 kHz corresponding to the front duration of the conventional current waveform. Their values of circuit elements from 2.0 to 5.0 atm are estimated as R≤500 Ω and L≤450 μH in positive discharges, and R≤450 Ω and L≤280 μH in negative discharges, while both values of the elements largely decrease with time exceeding the front duration.

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