Overhead line transmission composite insulators. Evaluation of their technical condition in the laboratory after their removal from service

A sequence of tests accomplished in the laboratory on composite insulators removed from service is presented. The object of the tests was to evaluate the technical condition of the insulators in order to provide an indication of population health or life expectancy and therefore determine whether to leave the population or individual units in-service or to take any countermeasures such as removal of the units. The tests and their results analysis were performed under the methods, philosophies and tools described and/or suggested by CIGRE Technical Brochure 481. The tests involved in this research were, in the following sequence: visual inspection, hydrophobicity classification, measuring of leakage current under both dry and wet conditions, equivalent salt deposit density (ESDD) and non-soluble deposit density (NSDD) measuring, sheds hardness measuring. Samples of suspension and line post composite insulators removed from several 132 kV overhead transmission lines were used in this study. As a result of this evaluation it was possible to determine which model/brand had overcome its life-time limit and which has still a residual life expectancy.