Effect of Stretching Ratio on Dielectric Properties of Polypropylene Film for Capacitor in SMES

In this paper, polypropylene (PP) film samples were obtained at different stretching ratios. The dielectric properties of PP samples were studied. The crystal morphology and orientation degree of the materials were characterized. The findings indicate that the PP film sample with the stretching ratio 5 × 5 has the lowest conductivity and the highest breakdown strength. Moreover, the effect mechanism of the stretching ratio on the dielectric properties of PP films was explored. A reasonable stretching ratio can make the molecular chains of PP aligned, form an orderly crystalline morphology, and improve the crystallinity. When the stretching ratio is too high, the orientation degree of PP will decrease and the spherulite structure will be destroyed, leading to a decrease in dielectric properties. The research results can serve as a reference for improving the dielectric properties of PP films.