Oil-filled electrical equipment is widely used in substations/converter stations and hydropower projects as key facilities for securing power supply. However, transformer oil leaks from the rupture, accumulates at the base of oil-filled equipment, and encounters an ignition source, forming an external heat source that leads to a fire in the oil-filled equipment. Notably, heat from this external source is transferred back to the equipment via conduction, convection, radiation, and other pathways. This accumulated internal heat causes oil from ruptured oil-filled equipment to be sprayed and ignited by an external heat source, forming a jet fire. The transition to a jet fire triggers nonlinear shifts in the system's original state, leading to further deterioration in the degree of fire hazard. As fire incidents involving oil-filled equipment pose a major safety hazard in the electric power industry, effective and reliable prevention and control strategies must rely on a precise understanding of their dynamics. Therefore, a comprehensive and profound understanding of the characteristics of oil-filled equipment jet fire dynamics under the influence of external heat sources is of practical importance for improving the fire prevention and control capabilities of the electric power industry and for developing major fire monitoring and early warning technologies. In essence, once internal transformer oil leaks and burns, fire development mainly experiences two typical stages: first, the instability of oil-filled equipment combustion under the influence of an external heat source to form a jet fire, and second, the formation of a jet fire, which considerably changes the typical characteristics of the fire parameters. An oil-filled-equipment fire is a combination of combustion phenomena of multiple fire modes, such as bottom pool fire, sidewall flow fire, and top jet fire.

Previous studies have focused on single-mode fire dynamics experiments. Little attention has been paid to key scientific issues, such as the evolution of typical fire characteristics and the prediction of fire behavior under combined combustion of multiple fire modes, which have posed considerable challenges for the prevention and control of fires in electric-power charging equipment and fire rescue missions. In view of oil-filled equipment jet fire accidents and their complex fire characteristics, issues in electric power fire prevention and control remain serious challenges. Fundamental scientific questions regarding these dynamics remain unresolved, necessitating further theoretical studies to address the safety challenges they pose.

In this study, we designed and constructed an experimental platform to simulate the fire dynamics of oil-filled electrical equipment. By integrating the measurement systems for the mass-loss rate, temperature, radiation heat flux, and image acquisition, we clarified the basic combustion phenomena of these fires. Furthermore, we established the typical phases and morphological characteristics and revealed the evolution laws of the characteristic parameters, such as the flame height, flame temperature, and flame radiation.

We identified the catastrophic mechanism of oil-filled equipment jet fire at its essence, further enriching the theory of fire dynamics and providing strong scientific and technological support for enhancing fire prevention and control strategies within the power industry.