Study on the Influence of Ultraviolet-Absorbing Molecules on the Lightning Impulse Characteristics of Natural Ester Oil-Paper Insulation

Natural ester insulating oils are increasingly replacing mineral oils as the preferred dielectric fluid for oil-immersed power transformers. However, natural esters exhibit relatively low lightning impulse voltage withstand capabilities, which can result in surface discharge within transformer oil-paper insulation systems. Improving the lightning impulse performance of such insulation systems is therefore a critical requirement. This study selects two ultraviolet (UV) absorbing molecules based on microscopic physical property calculations and conducts lightning impulse tests on UV-absorbing molecule-modified natural ester oil-paper insulation. The lightning impulse breakdown voltage, streamer development speed, and morphology of the oil-paper insulation system before and after modification were compared and analyzed. The results show that UV-absorbing molecules can enhance the positive-polarity lightning impulse breakdown voltage and reduce the average development speed of both positive and negative streamers. Specifically, when 2 wt.% of the UV-absorbing molecule UV329 is added, the positive-polarity lightning impulse breakdown voltage increases by 17.45%, and the streamer development speed is reduced by 48.77%. Moreover, morphological analysis reveals that the modified oil-paper composite insulation system exhibits more branched streamer paths, which are longer and wider in diameter.