The IEC’s first Guide for selecting insulators with respect to pollution in was published 1986 and standardized the concept of creepage distance. Although the Guide quickly found application due to its simplicity, field experience did not always prove successful.
The butterfly insulators and pin insulators in ceramic insulator products are mainly used for high and low voltage transmission lines, and suspension insulators are used for high voltage transmission lines.
The performance of overhead line insulation in DC differs from AC due to ionization of airborne particles resulting from the unidirectional electric field.