PD characteristics and degradation in PET insulation with vented and unvented internal voids

•PD characteristics and degradation are investigated in vented and unvented voids in PET.•More PD activity is observed in contained unvented voids.•For vented voids, reactive by-products formed during PD disperse more easily through flow of gas in the vent.•There are measurable differences in PD activity and subsequent material degradation between vented and unvented voids.

Voids in solid insulation give rise to partial discharge (PD). Factors affecting PD activity in internal voids include the type of gas contained, gas pressure and surface properties of the void. Identifying the presence of PD and understanding the measurable parameters may allow improved management of industrial assets. This paper reports on quantifiable and measurable differences in PD activity and material degradation among voids which have vented and unvented channels. To investigate changes in PD activity with void characteristics experiments are carried out using artificial voids created from layered sections of poly(ethylene terephthalate) (PET) polymer. One set of samples has a confined internal void; a second set of samples has a void with a channel having a closed end and a third set of samples has a vented channel connecting the void to the outer atmosphere. The results show measurable differences in PD activity and subsequent material degradation in the various voids.