Pyrolysis and gas evolution behavior of overloaded flame-retardant polyethylene cable insulation

In increasingly high-load energy systems, the thermal failure of electrical insulation and the release of flammable gases have become critical risk factors for electrical fires. This study investigates the thermal degradation behavior, reaction mechanisms, and volatile product evolution of flame-retardant polyethylene (FR-PE) cable insulation, widely applied in urban power grids, rail transit systems, and data centers, under varying overload current conditions. Using an integrated TG–FTIR–GC/MS system, the results demonstrate that under high overload current (80 A), the pyrolysis pathway and gas composition change significantly, characterized by earlier decomposition onset, increased char yield, and notable enrichment of aromatic and oxygenated compounds. Kinetic analysis using KAS, FWO, and Friedman methods reveals that the activation energy in the initial stage decreases with increasing current, facilitating early decomposition, while the second stage exhibits increased activation energy due to crosslinking reconstruction and enhanced charring, indicating a more complex reaction process. Mechanistic function fitting suggests a shift from diffusion-controlled to diffusion–reaction coupled mechanisms, with non-linear reaction behavior becoming dominant under severe overload. Thermodynamic parameter analysis further confirms the evolving pyrolysis pathway, indicating increased spontaneity, higher entropy, and enhanced system disorder. This work not only elucidates the thermal failure mechanism of FR-PE insulation under overload conditions but also provides a theoretical and experimental foundation for thermal fault modeling and fire risk assessment in high-power-density energy systems.