Modeling for Short-Circuit Process in Polypropylene-Based Cable Insulation Considering Phase Change and Melt Flow

Different from cross-linked polyethylene (XLPE) 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 is established based on electromagnetic-thermal equations that simulate conductor heating, heat transfer equations that calculate the temperature distribution, and fluid control equations that simulate the melt flow. Based on the enthalpy-porosity model, the melt crystallization and rheological properties of screen and insulation materials are measured and introduced into heat transfer and fluid equations. Taking a high-voltage (HV) single-core polypropylene (PP)-based insulated cable as the object, the entire process of the cable undergoing short-circuit thermal shock under 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 remains 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.