Lightning transient impedance analysis of a junction concrete gap soaked in salt water under varying air pressure conditions

This paper presents our investigation of the properties of lightning impulse discharges and the extent to which they depend on the pressure of air entering concrete material soaked in salt water. The experimental results determined that 1) the discharge through a concrete wall including a junction structure displays distorted voltage waveforms in the first half cycle; 2) these distorted waveforms also cause high-frequency noise exceeding 100 kHz; 3) a gap in which the air pressure exceeds 2 atm is capable of suppressing the amount of high-frequency noise above 100 kHz by one third; 4) for air pressures exceeding 2 atm, subjecting the discharge waveforms to Fourier transform makes it possible to specify the dependency of the impedance on the frequency, and to estimate the impedance elements and their circuit in the frequency bands of conventional lightning currents.