Evaluation of diagnostic techniques for non-ceramic outdoor high voltage insulators

Compounds for high voltage insulators are mixtures of rubber, fillers and additives. Polymers are generally either silicone rubber or EPDM and the filler is mostly alumina tri-hydrate (ATH). In this work, we focused on permanent changes of the surface after natural ageing. These changes have been monitored by using some techniques such as SEM, surface roughness, contact angle, ATR-FTIR, EDAX and XPS usually used to characterise these phenomena. On the one hand, we found a strong correlation between the surface roughness and the data given by the contact angle and the ATR-FTIR methods. Moreover, we demonstrate that the use of only one of these techniques is not sufficient to yield a reliable diagnostic of the material surface after ageing and could lead to wrong interpretations. On the other hand, the comparison of XPS and EDX spectra obtained on the same samples leads to apparently conflicting results which are discussed. In any case, these observations conduct us to consider that the ATH plays an important role in ageing phenomena