CFO voltage and V-t characteristic of 15 kV polymer suspension insulator under lightning and steep front short duration impulses

The CFO voltage and V-t characteristic of 15 kV polymer suspension insulators are important factors in insulation coordination designing of power distribution systems. Typical insulation designs for distribution feeders usually are based on 1.2/50 μs lightning impulse, while insulator behavior under steep front short duration (SFSD) impulse is not concerned. Comparing with lightning impulse, SFSD impulse is more severe and destructive to insulator because of its high voltage magnitude. To study the insulator behavior under different kinds of impulses, both standard lightning impulses and SFSD impulses are generated and applied on selected 15 kV polymer suspension insulators. The generated standard lightning impulse has 1.2 μs front and 50 μs on the tail to half value of the voltage impulse. The generated SFSD impulse in this study has 60 ns front and less than 200 ns of the tail. In order to measure CFO voltage under SFSD impulses, up and down method as in lightning impulses is developed and used. For each kind of impulse, the CFO voltage and V-t characteristic for 15 kV polymer suspension insulators are evaluated under dry and wet condition with both negative and positive polarity impulses. In order to study the added insulation strength by wood crossarm and to compare the results, all the above mentioned tests are performed again with the 15 kV polymer suspension insulator plus 0.5 foot and later 1 foot wood crossarm.