Spectroscopic and chemometrics analysis of cable condition in the Artemis program

Infrared, Raman and UV-VIS spectroscopies have been used to investigate the chemical composition and structure of cross-linked polyethylene used in a set of high-voltage polyolefin-insulated cables, both before and after electrical stressing and thermal ageing. Acrylate oligomers present in the semi-conducting screen materials, and the breakdown products of cross-linking are observed to diffuse into the insulation with a diffusion profile that is ageing time and temperature dependent - it appears that temperature, not voltage, has by far the biggest effect on migration in these materials. Multivariate statistical analysis has been used to examine the relationships between both the chemical changes in the material and the "intrinsic variables" such as radial distance, ageing time, temperature and voltage stress condition as well as the "physical properties" including AC electrical breakdown strength, charge mobility and oxidation potential. In all cases, the increase or decrease of certain chemical groups can be associated with the changes observed in these properties. Well-populated chemometrics models, based on spectroscopy, can provide sound structure-property relationships and a predictive capability for cable condition assessment that could be extended to cable performance and other insulating materials.