Research on the Pyrolysis Mechanism and Products of Natural Ester Insulating Oil

Oil-immersed Transformers are key components of modern power grids and play a crucial role in voltage regulation and energy distribution. In recent years, natural ester insulating oil has emerged and gradually replaced traditional mineral insulating oil to play the role of insulation protection for transformers. However, at present, the research on the physicochemical properties of natural ester insulating oil is not clear. Therefore, it is of great significance to explore the thermal cracking mechanism of natural ester insulating oil and the changes of its pyrolysis characteristic gases with temperature. In this paper, a molecular model of natural ester insulating oil was established and its pyrolysis mechanism was explored based on the Reaction Force Field (ReaxFF). It was found that the initial reaction of thermal decomposition of natural ester insulating oil was the breaking of ester bond, forming C3H5 free radical and three C18H23O2 intermediates. In the secondary reaction, the free radical C18H33O2 undergoes β-scission decarboxylation to generate CO2 and long-chain hydrocarbon C17H33. Finally, the long-chain hydrocarbon C17H33 undergoes C-C bond fracture and is transformed into some small hydrocarbon molecules, such as C2H4, CH3 and C4H6, which are reorganized by free radicals to form characteristic gas products. Through the tubular furnace heating GC/MS combined technology, it is determined that the main gas components are CH4, CO, CO2, C3H8, C3H6, C4H10, C4H8, C2H4, C2H6, C2H2, H2. The change of gas products with temperature was qualitatively analyzed, which was confirmed by the results of molecular dynamics simulation.