PD energy as a marker of low-voltage insulation aging

The aging of the insulation system is, in most cases, due to 4 factors known as TEAM: thermal, electrical, ambient and mechanical. In this study we focused on the first two (thermal and electrical), as often being the most severe and problematic ones. Type I electrical insulation system, widely used in low-voltage machines, is not designed to withstand the partial discharge activity, which can easily damage the polymer insulators. For this reason the partial discharge inception voltage (PDIV) is one of the key factors to be taken into consideration when designing the insulation system. This study aims to verify to what extent the repetition of partial discharge inception voltage measurements is detrimental for the turn-to-turn insulation and to determine if the PDIV can be a good marker of insulation aging. Two thermo-electrical aging tests were conducted: one at high temperature, with repeated PDIV measurements; the second at lower temperature but with significantly higher electrical stress (times the PDIV) during aging. In the first test, almost 10000 measurement cycles were done and a slight change of PDIV value was observed during aging. At the same time it was verified that repetitive PDIV measurement, to some extent, does not have a significant impact on the lifespan. The second study showed that at higher voltage, where lifespan is mostly driven by electrical aging, the number of PDs is relatively stable throughout the whole lifespan. However, PDs energy can be considered as an aging marker, because it significantly increases in the end of the sample's lifespan.