Experimental investigation of fundamental combustion characteristics of transformer oil pool fires

To investigate the combustion characteristics of transformer oil pool fires beneath large-scale converter transformers, an experimental platform was established using KI25# transformer oil. The effects of pool diameter, initial oil thickness, and initial oil temperature on burning rate, plume behavior, and combustion development were systematically analyzed. The results show that transformer oil pool fires undergo four stages: initial growth, steady burning, boiling combustion, and extinction. The burning rate is mainly controlled by pool diameter and oil thickness, while initial oil temperature has a limited effect on the average burning rate during the full development phase. Oil thickness shows a nonlinear influence on burning rate; for a 40 cm diameter pool, the 5 cm oil layer gives a burning rate of 14.92 g/(m2·s), which is higher than that of the 3 cm layer but lower than that of the 9 cm layer. The burning rate increases with pool diameter and gradually approaches a stable value, indicating a clear scale effect under the investigated conditions. Based on experimental data under different oil thicknesses, thickness-dependent burning-rate correlations were developed and compared with classical pool fire models, thereby supplementing the Blinov classical model with fundamental data for transformer oil in the optically thin regime. These results provide basic data for combustion intensity prediction, fire hazard assessment, and fire protection design of oil-immersed transformers.