The influence of structure on water treeing in crosslinked polyethylene: accelerated aging methods

The influence of voltage and temperature on water-tree nucleation and growth in accelerated aging experiments has been evaluated for miniature cables of crosslinked polyethylene. Both as-produced cables and cables annealed at 88°C have been considered. Data from studies of crystal growth have been analyzed in order to obtain estimates of the rate of nucleation and of tree growth independently of each other. The total number of nucleation sites is influenced by annealing procedures, but the nucleation rate is not. The growth rate of bow-tie trees follows a single power law relation in which the growth rate constant is influenced by annealing, but the growth index is not. Bow-tie tree nucleation is linearly dependent on voltage, but the average length of a bow-tie tree is inversely dependent on voltage. The behavior is explained in terms of the volume fraction of the trees present (relative to the specimen volume). A major increase in bow-tie tree population occurs at the onset of the α-relaxation process (55°C). It is recommended that temperatures be used as an accelerating variable only if information is required on performance at elevated temperature