Mechanism of Mechanical Failure in Multiphase Polypropylene and Design of Allowable Stress for Cables

Power cables are subject to various mechanical stresses during manufacturing, installation, and service. In extreme cases, defects may occur in the internal structure of cable insulation, causing electrical treeing even under relatively low electric field strength, which leads to insulation damage. For the new polypropylene insulation characterized by high modulus and low toughness, its mechanical performance requirements basically refer to the specifications for XLPE insulated cables. However, whether the insulation performance can remain reliable under external mechanical stresses is an important issue worthy of attention. Based on test data such as the tensile process and impact stress of polypropylene insulation materials, this paper explores the structural evolution and failure mechanism of polypropylene insulation during elastic and yield deformation, and conducts a correlation analysis on the allowable stress of power cables. The results show that for polypropylene insulation materials with multiphase structures, crystalline slip and multiple strain processes occur during tension and impact. Therefore, the index determining the minimum bending strength of power cables is the elastic limit strain; exceeding this limit will cause irreversible damage to cable insulation. This can provide guidance for material selection, structural design, and standard formulation of polypropylene insulated power cables.