Impedance property of lightning impulse discharge in short composite gap consisting of air and water

From the viewpoint of internal protection measures using surge protective devices (SPDs) against lightning surges invading the green power generation systems, it is important to investigate the discharge waveform and impedance for lightning surges via multiple media. We demonstrate a simple method for determining the discharge impedance in a short composite gap consisting of atmospheric air and tap water. We report experimental results related to the discharge waveforms and impedance to lightning impulse discharges in a short composite gap consisting of air and tap water: (1) the discharge waveforms indicate periodic, attenuated waveforms for more than one period, and the voltage waveforms indicate amplitude distortions; (2) the impedance depending on the time for discharging is in the ranges of Z= 1.4-22 Ω and Z= 1.3-35 Ω for positive and negative discharges, respectively; (3) the typical resistance property may indicate how to effectively apply an SPD system for internal lightning protection measures because the discharge is characterized by the type of media included in the discharge path.