Effects of a DC Offset on Lifetime and PD Activity During AC Aging Tests on Enameled Twisted Pairs

The insulating systems are one of the most important parts for the proper operation of the electrical devices and can be subject to deterioration due to several phenomena like partial discharges (PDs). Nowadays, due to the increasing presence of the power electronic devices, there is an interest in studies relevant to the PD activity not only in the presence of pure sinusoidal voltage waveforms but also when a dc component is added as a result of electronic ac/dc conversions or floating potential operations. This work is focused on aging tests on twisted pairs specimens applying pure ac or ac + dc waveforms. The test voltage waveforms are applied to twisted pairs specimens until the total breakdown, assumed as end life criterion, is reached defining the life curves both in ac and ac + dc cases. During the aging, PDs are acquired, and it is possible to compute derived quantities useful to define a predictive model of the residual specimen lifetime. For what it concerns the presence of an overlapped dc component, the obtained results suggest that, considering the conditions imposed in this study, no remarkable changes in the aging phenomena and in the measured PD activity are identified.