Air Humidity: An Important Factor for UHV Design

The switching-surge performance of long air gaps has been studied with regard to humidity. It has been found that humidity affects the flashover characteristics more than what could be expected from the present knowledge for large gap spacings . Based on physical observations of the discharge development, it has been shown that the position of the minimum of the U-curve changes: the minimum flashover voltage increases while the critical time-to-crest decreases with humidity. This results in important consequences for UHV insulation design.