The paper reports about the role of humidity and frequency on the electrical
breakdown of air in uniform field gaps. Experiments were conducted on Rogowski-profile
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.