For Station Post Insulators the deciding parameter is always the applicable BIL value.
But for Suspension type insulators (Specially for polymer insulator strings) manufacturers specify various parameters such as Dry/ Wet flash over and Critical Impulse Flash Over (CIFO-Pos & Neg) values for the string for the SAME SYSTEM VOLTAGE.(BIL is not normally specified)
What is the selecting criteria for these strings for a given voltage?
Critical Impulse Flashover is the number to look at for lightning performance. It is roughly comparable to BIL of substation insulators. Creepage distance is the number to look for for insulator contamination performance.
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