Improved Electrical Properties of Organic Modified Thermoplastic Insulation Material for Direct Current Cable Application.

To achieve exceptional recyclable DC cable insulation material using thermoplastic polypropylene (PP), we have introduced the organic polar molecule styrene-maleic anhydride copolymer (SMA) into PP-based insulation materials following the principles of deep trap modification. PP, PP/SMA, PP/ethylene-octene copolymer (POE), and PP/POE/SMA insulating samples were prepared, and their meso-morphology, crystalline morphology, and molecular structure were comprehensively characterized. The results indicate that SMA can be uniformly dispersed in PP with minimal impact on the crystalline morphology of PP. The DC electrical properties of the materials were tested at temperatures of 30, 50, and 70 °C. The findings demonstrate that the introduction of SMA can improve the DC properties of the material in both PP and PP/POE. The thermal stimulated depolarization current results reveal that SMA can introduce deep traps into the material, thereby improving its DC properties, which is in agreement with the quantum chemical calculation results. Subsequently, a bipolar carrier transport model was employed for coaxial cables to simulate the space charge distribution in the insulation layer of the four sets of insulation samples as well as the actual cable in service. The results highlight that SMA can significantly suppress space charge in PP and PP/POE systems, and it exhibits excellent electric field distortion resistance. In summary, the results illustrate that SMA is expected to be used as an organic deep trap modifier in PP-based cable insulation materials.