Aging of distribution composite insulators under environmental and electrical stresses

Seven types of commercially available distribution composite insulators with sheds made of EPR (ethylene-propylene rubber) or epoxy resin were subjected to various functional aging tests recommended by the IEC or the IEEE. The influence of ultraviolet (UV) radiation on the aging of the shed materials was also evaluated. The usefulness of the various aging and diagnostic tests is discussed, and a modification of the recommended test procedures is proposed in order to improve the evaluation of the long-term performances of these insulators. The aging test methods and the acceptance criteria proposed by the IEC and the IEEE are not sufficient to discriminate between the seven insulator types tested. Extending the aging test duration to 2500 h and using the IEC water immersion test as a diagnostic tool brought out differences in the performances of the insulators. No significant synergism was found to exist between the UV radiation and the stresses caused by the salt fog test or the tracking wheel test when they are applied sequentially