Characterization of epoxy resin surfaces exposed to partial discharges in SF6 and N2-SF6 mixtures

In order to improve our understanding of surface degradation of epoxy resin used in high-voltage gas-insulated systems (GIS), discharge-induced microstructural, morphological, and compositional changes have been investigated using Atomic Force Microscopy (AFM) and X-ray Photoelectron Spectroscopy (XPS). The AFM technique enables direct observation of any possible relationship that may exist between electrical aging and structural changes on polymer surfaces. Samples of epoxy resin aged under the effects of partial discharges (PD) were studied with the high-resolution AFM technique to explore their surface topography. PD (corona) were produced in SF₆ and in nitrogen with 1% of SF₆ in a plane-point-plane electrode configuration at 800 Torr, and these discharges were made to interact with virgin epoxy resin samples. As expected, the resin surfaces exposed to PD in pure SF₆ were found to be more readily modified than those exposed to discharges in the gas mixture, because of the higher concentration of reactive fragments resulting in the former case. Surface homogenisation and/or enhancement of nanometric surface “nodules” could be observed with increasing total surface energy deposited (“dose”). At the same time, XPS was carried out on the same samples, the results of which confirmed the dominating role of reactive neutrals; when pure SF₆ was used, results indicated that surface changes were due mainly to the effects of fluorine-containing species