Effect of Elastomer Content on Interface Discharge Behavior Between Polypropylene and Silicone Rubber Under AC Voltage

Polypropylene (PP) as a thermoplastic polymer with high breakdown strength as well as high melting point has been considered as a promising candidate for the new generation recyclable cable insulation. However, the tensile yield strength and modulus of elasticity of PP are too large, and the mechanical properties of PP can not meet the requirements of cable materials. In this paper, two kinds of elastomers, i.e. ethylene-octene copolymer (POE) and propylene-based elastomer (PBE), were used to improve the flexibility of polypropylene (PP) so as to make it proper for the main insulation of recyclable power cable. The microstructure of the blends was inspected under electron microscope, and the mechanical properties were tested and compared in this paper. It has been generally accepted that the weak point in a long cable route is cable accessory which connects each cable segment with typical length of several hundred meters. Due to the complex structure of high voltage power cable joints, the electric field is distorted, which is likely to induce interface discharge between the cable insulation and joint insulation. By simulating the electric field distribution of a cable joint, the effect of elastomer content on the interfacial breakdown of PP/SiR was investigated. The test results show that the addition of POE and PBE can greatly prolong the breakdown time of the PP/SiR interface. Discharge initiation time of (PP+POE)/SiR interface is longer than that of (PP+PBE)/SiR, while (PP+POE)/SiR discharge development time is shorter than that of (PP+PBE)/SiR. It is suggested that the decrease of elastic modulus results in the presence of smaller size of air cavities along the interface, which leads to the delay of breakdown time. In addition, the difference of microstructure and trap distribution caused by different compatibilities between the two elastomers and PP is the main factor affecting the interfacial breakdown process.