Nonstandard method for accelerated ageing tests of nonceramic insulators

A methodology for testing accelerated ageing of nonceramic insulators (NCI) is presented based mainly on polluting the insulators with several substances, such as kaolin, lime, fertilizer and natural field pollutants. The polluted insulators are evaluated inside a salt fog chamber by applying cycles of salt fog, clean fog, drying and constant voltage. During the tests, clear evidence of tracking, erosion, chalking and puncture was observed on the insulators. Flashover takes place on the early damaged insulators in a relatively short time with respect to the test time of 5000 h recommended by IEC 61109. Based on the results obtained it is necessary to modify the standard continuous 5000 h salt fog test to evaluate the long-term performance of NCI. The new test must consider low salinity, clean fog and drying periods and an initial pollution coating. Under these conditions, the leakage current magnitude is smaller and consequently much more discharge activity occurs over the polluted insulator surface leading to surface deterioration, since hydrophobicity recovery of the insulator surface is allowed during the drying period. Measurements show that the leakage current peak values were in a range from 50 to 120 mA