What are the common misconceptions concerning creepage distance vs. pollution performance?

The choice and performance of insulators for polluted environments is very often expressed solely in terms of the creepage distance necessary to withstand the polluted conditions under the system voltage.

However the use of creepage distance alone to establish orders of merit does not take into account other factors which depend on the creepage distance available per unit length of the insulator. This point is worth being borne in mind when choosing insulators, notably for applications where insulator length is a minor constraint.

Conversely, if insulator length or height is a major constraint, increasing the creepage distance in the available space may not give the full improvement in performance expected due to reduced profile efficiency.

Additionally, for polymer materials, such an increase of creepage or reduction of shed spacing may result in aggravated ageing effects.

Similarly, increasing the shed diameter to increase creepage distance may also not yield a favorable result as experience has shown that pollution performance tends to decrease with increasing diameter.

Hence, it is important that all factors that affect the pollution performance be considered and analyzed prior to specifying the type of insulator and creepage distance.