Analysis of electrical insulator surfaces by X-ray photoelectron spectroscopy

Our earlier studies centered on understanding the incipient failure mechanism in polyethylene (PE) as an insulation material. The results simulated conditions not measured in routine manufacturing or electric utility test procedures. These findings indicated that detectable changes with pure PE can occur on the surface of cavities (artificially produced), 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 utilities?" To answer this question PE insulation was analyzed 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 species were similar to those found previously, i.e., alcohols and/or ethers and carbonyls. Some outgassing, probably hydrocarbons, of the FE was observed. The role, if any, of these outgassing components on the failure of PE as an insulation material is unclear.