Repression properties of lightning impulse discharge in short composite gap consisting of air and concrete material invaded by salt water at high air pressures

For consideration of internal protection measures, the repression property on amplitudes and higher harmonic components in the lightning impulse discharges have been examined by increasing the high air pressure using a short composite gap consisting of air and concrete soaked in salt water. It is reported that First, the voltage waveform was distorted for all air pressures and involved two-stage discharge through the air and concrete gap, Second, all the discharge waveforms changed from unipolar to bipolar modes with increasing amplitudes for an air pressure larger than 5.0 atm. Third, the higher harmonics of the positive and negative discharge currents at an air pressure of 5.0 atm and the harmonic frequencies greater than 200 kHz were reduced by 12 dB and 6 dB, respectively, compared with the case at 1.0 atm.