A Statistical Approach For Insulator Design In Polluted Areas

The paper describes the statistical approach used by ENEL in the design of insulators to be used in polluted areas. This approach includes determination, on a statistical basis, of the type and level of the pollution of the site, choice of the artificial laboratory test method suitable for that site, determination of the withstand severity of an insulator set which assures a pre-established risk of failure of the line or substation to be designed, and eventually, choice of the insulator set (insulator type, insulator set length and arrangement) on the basis of the results of labora tory tests. In particular, the problem of determining site severity is amply discussed in the paper and the relevant method developed by ENEL, based on surface conductance measurements on sample insulators, is fully described. The results of systematic long-term recording performed by this method in several localities in Italy are reported on and analyzed. Examples of application of the statistical approach, using these results, are given and the problem of standardization of insulators for polluted areas is discussed.