Purpose/Aim
There is a difference in insulation requirements between indoor and outdoor electrical equipment. So far, there is no unified standard for the insulation design of indoor equipment. The purpose of this experiment is to measure the flashover voltage of silicone rubber sheet under different relative humidity conditions, so as to provide the basis for the creepage distance design of indoor equipment.
Experimental/Modeling methods
In this experiment, a certain mass of sodium chloride and diatomite were accumulated on the surface of silicone rubber sheet by artificial pollution. The test equivalent salt deposit density was about 0.35 mg/cm² and the test non-soluble deposit density was about 2.10 mg/cm², both of which were based on on-site measurement. The sample was placed in the different relative humidity conditions and the U₅₀ was measured by the up-and-down method after the pollution layer was sufficiently moistened.
Results/discussion
The research shows that with the increase of relative humidity, the U₅₀ of silicone rubber sheet decreases. This is because as relative humidity increases, the amount of dissolved pollution layer increases, releasing more free-moving ions, and the surface insulation of silicone rubber sheet decreases, resulting in the decrease in flashover voltage.
Conclusions
When the relative humidity is higher than 55%, the U₅₀ of silicone rubber sheet is negatively correlated with the relative humidity.
 

Pollution flashover,Silicone Rubber,Relative Humidity