The Origin and Effect of Small Discontinuities in Polyethylene Insulated URD Cables

Numerous small star-shaped discontinuities have been found in the thermoplastic polyethylene insulation of 15 kV URD cables which have never been entered into service. The discontinuities in eleven representative samples of cables manufactured fran 1968 through 1975 were analyzed by Raman spectra generated by a laser microprobe, by a Scanning Electron Microscope equipped with a secondary x-ray detector (energy dispersive x-ray analysis) and by optical microscopy. The chemical nature of the discontinuities was identified and the number and distribution of the discontinuities determined.