Different from cross-linked polyethylene insulated cables, short-circuit current thermal shock will permanently deform the thermoplastic insulated cable’s insulation layer. To investigate the insulation eccentricity caused by short-circuit thermal shock, a numerical calculation method was established based on electromagnetic-thermal equations which simulate conductor heating; heat transfer equations which calculate the temperature distribution, and fluid control equations which simulate the melt flow. Based on the enthalpy-porosity model, the melt crystallization and rheological properties of screen and insulation materials were measured and introduced into heat transfer and fluid equations. Taking a high-voltage single-core polypropylene-based insulated cable as the object, the entire process of the cable undergoing short-circuit thermal shock under the rated operating conditions is simulated. The simulation results indicate that the insulation structure continues to eccentrically deform within 4756 s after a single thermal shock, and the eccentricity ratio eventually reaches 3.28%, which is far below the standard requirement of 10%. The insulation eccentricity ratio shows a linear accumulation relationship with the times of thermal shock. This simulation method provides a reference for the design and reliability assessment of thermoplastic insulation cables.

Space charge injection in polypropylene (PP) significantly weakens the stability of HVDC cables. Impact polypropylene copolymer (IPC) is often used as insulation material for AC cables, but in the DC field, IPC has the problem of space charge accumulation. This is because there is a multi-phase structure inside the IPC to which ethylene monomer was added in the production process, and the difference in physicochemical properties of each phase is an important reason for the accumulation of space charge inside the material. In this work, the vinyl phases and propenyl phases of two types of IPC were separated. The film samples were prepared and tested at 30 °C and 50 °C for DC electrical conductivity, and at 30 °C, 50 °C, and 80 °C for space charge. The experimental results show that the DC conductivity of vinyl phases is significantly higher than that of propenyl phases in both types of IPC. The degrees of mismatch between the DC conductivity of vinyl phase and that of propenyl phase are different in the two types of IPC, and the mismatch degree of DC conductivity is from several times to hundreds of times. The conductivity of the two vinyl samples is ohmic. The conductivity of the two propenyl phases shows nonlinearity under different electric field intensity, and the mismatch degree of the two phases increases with temperature. Compared to untreated IPC, at all test temperatures, the maximum space charge density of the propenyl samples is much lower, which can be reduced by about 1/3 at 50 °C and by about 50% at 80 °C. The density of heteropolar charge produced by impurity ionization in the samples and the depth of electrode injection both decreased. At each temperature, the distortion rate of the electric field in propenyl samples is lower than that in IPC, the distortion rate can be reduced by more than 15%, and the distortion rate can be reduced by nearly half at 80 °C. The charge dissipation characteristic of propenyl samples during depolarization is also optimized compared with IPC samples, the time required for charge dissipation to reach stability is shortened, and the residual charge density in the sample is reduced at the end of depolarization. In addition, the relevance between the variation of DC conductivity of phases and space charge characteristics was discussed according to SCLC (space charge limited current) theory. This work provides a feasible reference for the manufacture of high-reliability polypropylene-based cable material with excellent insulation performance.