ANALYSIS OF ELECTRICAL INSULATOR SURFACES BY X-RAY PHOTOELECTRON-SPECTROSCOPY

Our earlier studies centered on understanding the incipient failure me chanism in polyethylene (PE) as an insulation material. The results si mulated conditions not measured in routine manufacturing or electric u tility test procedures. These findings indicated that detectable chang es with pure PE can occur on the surface of cavities (artificially pro duced), as observed by X-ray photoelectron spectroscopy (XPS). Because the prior studies were done with pure PE and cavities that were made for easy XPS analysis, the question remained ''would the findings from the earlier inquiry be relevant to materials used by the electrical u tilities?'' To answer this question PE insulation was analysed from a series of commercial type cables that had undergone long-term testing. Occasionally oxygen was found by XPS on the interior surfaces of the more highly stressed PE cable samples. The estimated amount of oxygen was lower than that often found previously. The oxygenated carbon spec ies were similar to those found previously, i.e., alcohols and/or ethe rs and carbonyls. Some outgassing, probably hydrocarbons, of the PE wa s observed. The role, if any, of these outgassing components on the fa ilure of PE as an insulation material is unclear.