Abstract: The short sphere-sphere and rod-rod gap are taken as the research models, and the effects of water films with different water conductivity and types of electrodes on the breakdown voltage of air gap are investigated. Research has shown that,the breakdown voltage of the both electrodes coated by water film is higher than that of the dry electrodes at the sphere-sphere short air gap,however when the gap length increases from 1 cm to 6 cm, the amplification of breakdown voltage decreases from 27.2% to 4.44%,the increase in breakdown voltage is due to the presence of a water film, which leads to an increase in the energy required for the initiation of secondary electron avalanches and photoelectrons,the increase in gap leads to an increase in the ionization region and and as a result the increase in breakdown voltage decreases with the increase of gap length.At the short rod-rod gap, the water film has no effect on the breakdown voltage of air gap. The water film has different effects on the discharge of the short sphere-sphere and short rod-rod air gaps. It is due to the fact that, at the sphere-sphere gap, the streamer is negative,the starting photoelectrons of the secondary electron collapse originate from the photoionization of the cathode, and at the rod-rod gap the streamer is positive, the starting photoelectrons of the secondary electron collapse are derived from the photoionization of air molecules, the rod to rod gap is longer, and the electric field distortion rate is smaller,and the conductivity of water has no effect on the breakdown voltage of the air gap.

Key words: water film, sphere-sphere, rod-rod, power frequency, discharge characteristics, breakdown voltage