Effect of Cooling Rate on Structure and Electrical Properties of Polypropylene-Based Cable Insulation Materials

Thermoplastic polypropylene (PP) cable insulation material represents a new generation of environmentally friendly insulation material as an alternative to traditional cross-linked polyethylene. However, PP cable insulation typically consists of composite materials blended from multiple phases, whose electrical properties are significantly influenced by cooling rates. For high-voltage (HV) cables with large thickness and high voltage ratings, extruded cable insulation inevitably faces non-uniform cooling rate distributions along the radial direction. This study investigates PP-based composite insulation materials blended with different modulus base resins and skeleton elastomers, focusing on the effects of cooling rates on phase distribution, crystallization characteristics, and electrical properties. The result indicates that cooling rates have minimal impact on composite loss factor and conductivity but significantly affect phase distribution, thereby influencing space charge characteristics. Faster cooling rates promote uniform elastomer dispersion and enhance material performance. Composites with low-modulus base resins and propylene-based elastomers show less sensitivity to cooling rates. Comprehensive analysis suggests that AC cable insulation has lower requirements for cooling rate sensitivity, while DC insulation necessitates materials with low cooling rate sensitivity.