Experience with salt-fog and inclined-plane tests for aging polymeric insulators and materials

摘要

Aging, under contaminated conditions, manifests itself by tracking and/or erosion of polymer materials and insulators and usually leads to failure of insulators. Aging is still one of the main causes of the registered failures of polymer insulators in the field. Consequently, to improve both materials and insulator designs, it is important to understand the mechanisms of aging, as well as the factors surrounding aging, and the best way to do this is through actual field experience. However, the problem with field experience is that it often requires a very long time before any noticeable changes become evident. For this reason, several laboratory accelerated tests have been developed to evaluate aging of polymer materials and insulators. Laboratory aging tests are of 2 types: one for polymer materials and another for polymer insulators. Salt-fog and rotatingwheel tests are examples of tests for insulators, and the inclinedplane tracking and erosion of insulating materials test is an example of a test for materials. Using both tests to either design or evaluate insulators requires exhaustive work, but regardless of the aging test, the main challenge is to correlate accelerated aging in the laboratory to the natural aging process to correctly evaluate the insulator design or material. The 2 most important characteristics of polymer materials are their hydrophobicity, which prevents the development of leakage current (LC), and their resistance to the degradation process that can ensue when hydrophobicity is lost, either temporarily as in the case of silicone and silicone co-polymers or permanently as for other polymer materials. These 2 characteristics are also interrelated with the profile of the insulator. As a result, it is important to evaluate the performance of polymer insulators and materials based on these 2 characteristics using accelerated aging tests. This article briefly describes the experiences of using both the IEC 61109 salt-fog test and the IEC 60587 i-n-nnclined-plane test, with some emphasis on the practical difficulties of using these tests and what can be measured by each test.