Examination of vented water tree microstructure using scanning transmission electron microscopy

A previous report has been given of a series of life tests on XLPE insulated cables aged in water at stress levels from the service stress to 5 times service stress(1). This work showed that vented tree growth is stress and time dependent and that even though cables had been immersed in water at stress for as long as 11,000 hours there was still an incubation period of nearly 1000 hours before vented trees formed after a stress increase. This long term nucleation of vented trees is shown in Table 1.