Condition assessment of EPDM composite insulators using FTIR spectroscopy

Two new sampling and analysis techniques for assessing the condition of EPDM (ethylene-propylene diene monomer) composite insulators are presented. Polymer oxidation is assessed by removing small amounts of surface polymer by swabbing with xylene and analyzing this material by FTIR (Fourier transform infrared) emission spectroscopy. A measure of the amount of surface chalking is obtained by scraping a small amount of degraded surface material with a blade and analyzing by FTIR absorption spectroscopy. Numerical indices quantifying the amount of oxidation and surface chalking are obtained by calculating the ratios of absorption or emission peak heights in the infrared spectra. These indices are named the oxidation index and the chalking index. Three types of field-aged 275 kV EPDM composite insulators are investigated and the results from the new techniques compared with analyzes by XPS (X-ray photoelectron spectroscopy) with good agreement. It is found that for two types of insulator that the oxidation index is increased in regions near the HV conductor.