Aging of polymeric housing for HV insulators: comparison between natural and artificial testing

Polymeric housings for high voltage insulators are usually made with compounds of rubbers (silicone and EPDM) filled with alumina tri-hydrate. In order to test these materials, a 5000 hours multistress aging test was achieved together with a two year exposure at Martigues natural site on the French Riviera. The test specimens were slabs and insulators. In order to compare the modes of degradation, a few physical and chemical diagnostics were performed such as XPS, surface roughness, hardness and evaluation of hydrophobicity. The results showed that aging is, in each case, characterized by irreversible changes such as an increase of surface roughness and hardness. We measured a change in the surface chemistry mainly characterized by an increase of oxygen rate, which could be involved in a partial but definitive loss of hydrophobicity. Comparison between the effects of artificial and natural aging shows that the modes of degradation are the same and that the acceleration depends on the material itself and on the technique used