Examination of field-aged insulation for changes in molecular structure

The GPC results for samples taken from along the cable and with radius suggest that some very minor changes in the molecular weight distribution have taken place with aging. The changes are too small to affect the physical properties of the insulation and would not be normally connected either with large chemical or bulk electrical changes. This then appears to exclude the possibility of uniform molecular degradation as a necessary preliminary to the very local changes associated with dielectric breakdown, unless the aging process can vary significantly over distances of a meter or less. Further efforts will be directed at finding such “hotspots”, if they indeed exist, and at improving the precision of the techniques for detecting molecular weight changes.