The paper reports about the role of humidity and frequency on the electrical
breakdown of air in uniform field gaps. Experiments were conducted on Rogowskiprofile
electrodes with gap lengths ranging from 5 to 53 mm at power frequency (60
Hz) and frequencies in the range of 18-50 kHz, corresponding to the VLF/LF bands
used for long-range communication. The results show that breakdown voltage at VLF
decreases with humidity, opposite to that observed at 60 Hz. Breakdown mechanisms
for explaining this important phenomenon are proposed. A correction factor to
calculate breakdown voltage as a function of humidity for VLF is presented.