The aim of this study was to investigate the electrical resistance of polycarbonate film and polyester film materials in new energy materials during electrothermal aging in transformer oil. Insulating paper was used as a comparative material to compare the breakdown voltage and initial
voltage of insulating paper, polycarbonate film, and polyester film in electrothermal aging at 90 °C, 110 °C, and 130 °C. The best performance in the test was achieved by polycarbonate film, followed by polyester film, while the worst performance was that of insulating paper. Polycarbonate
film can be used as an insulating material in transformers, and it has great application value and commercial prospects.