A revisit to impulse breakdown voltage of standard air gaps

The negative and positive polarity of standard impulse breakdown voltage had been taken to study for Ø5 cm and Ø10 cm sphere-gap by taking into account the influence of irradiation and humidity. Gap spacing of 0.5, 1.0, 1.5, 2.0 and 2.4 cm was selected for this investigation. In order to control the atmospheric conditions around the sphere-gap, it was enclosed in a test chamber which was designed to have a negligible effect on electric field distribution across the air gaps. Two different measuring devices were chosen according to the breakdown voltage level to ensure the measurement uncertainty. The results showed that the difference U₅₀ of this present experiment from the value given in the standard generally decrease as the gap spacing increase. And the value of U₅₀ for Ø5 cm and Ø10 cm in this experiment tend to be close to each other.