Excess moisture in SF

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gas will condense on solid insulating materials under certain conditions and cause the reduction of flashover voltage. Therefore research on the influence of moisture on flashover voltage of solid insulating materials in SF

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will help formulate proper standards of moisture content in SF

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gas. We studied the variation of moisture content with of temperature and its influence on flashover voltages of insulating materials. The results show that moisture hardly affects the flashover voltage of insulating materials at constant ambient temperature. When the ambient temperature changes rapidly

relative humidity in SF

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gas will increase and can

even reach 100%. After a sharp change of ambient temperature

moisture within a certain amount have no effect on flashover voltage of insulating materials. When the moisture content reaches a certain value

flashover voltages begin to decrease. The larger the moisture content is

the lower the flashover voltage becomes. And moisture has a more remarkabler influence after a sharp rise of ambient temperature than after a sharp decrease. The range of temperature also has a remarkable influence on the threat caused by moisture

for water vapor is more likely to condense at low temperatures. Moreover

the experimental results show that current standard of moisture content cannot guarantee the normal operation of SF

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electrical equipment. It is suggested that different controlling limits should be used for regions with different climate conditions.