Short-Time AC Breakdown Characteristics of Polyethylene Aged Under Multistress Conditions

The effects of conditions which influence the service life of extruded insulation power cables has been a subject of great interest recently. An investigation of this topic has been made using AC short-time breakdown characteristics after aging under multistress conditions. For these tests, 2.25 mm thick extruded polyethylene samples were subjected to 27 kV and 15 kV voltage s and aged at temperature s of 20°C and 70°C. There were four groups of samples which all allowed the study of two more factors: partial discharges on the outer surface of the sample and water on the high voltage side, acting separately or simultaneously. The short-time breakdown results of each group were analyzed on the basis of the Weibull distribution. It was found that the shape parameter in the Weibull distribution exon exhibited a more regular decrease in time than the breakdown strength. This parameter may prove useful not only to discuss the influence of temperature and stress on aging of samples in the presence of water and partial discharges, but also in preparing life curves. Calculated life curves show there is no change in the slope with some conditions but a shift to shorter times.