A practical implementation of statistical principles to select insulators with respect to polluted conditions on overhead a.c. lines

A practical and simplified implementation is presented for the dimensioning of insulators with respect to contamination conditions based on a statistical analysis. This simplified statistical method entails the selection of a minimum insulator withstand severity relative to the site contamination severity by making use of a coordination factor. Evidence is presented to show that the proposed dimensioning procedure agrees well with present IEC creepage distance requirements for cap & pin overhead line insulators, based on a commonly used availability requirement and a realistic number of insulator strings on the line. Results from contamination laboratory test can be used to verify the withstand characteristic of the selected insulators. This simplified method may be used for dimensioning overhead a.c. line insulation when there is insufficient statistical information available to warrant a full risk analysis.