Influence of moisture on the dielectric strength of insulators in GIS

Excess moisture in GIS will condense on solid insulating materials under certain environmental conditions and cause the reduction of flashover voltage, thus threatening its normal operation. To formulate proper standard of moisture content in GIS, it's necessary to study the influence of moisture on the dielectric strength of insulators. In this paper, the influence of moisture on the flashover voltage of insulators in SF
₆
is studied with consideration of ambient temperature. The results show that flashover voltage of insulators is almost unaffected by moisture at constant ambient temperature. After a sharp change of ambient temperature, moisture within a certain amount doesn't influence flashover voltage of insulators; when the moisture content becomes larger, flashover voltage begins to decrease. The larger the moisture content is, the lower flashover voltage becomes. And moisture has a bigger influence after a sharp rise of ambient temperature than after a sharp decrease. The range of temperature plays an important role in the threat caused by moisture. In addition, the experimental results show that current standard of moisture content cannot guarantee the normal operation of GIS and some advice is given for modification of the standard.