Abstract: This study employed a full-scale 220 kV oil-immersed transformer fire model to conduct fire extinguishing tests using the inert gas foam system (IGFS), verifying the effectiveness of the IGFS fire suppression solution and determining its application parameters. The results indicate that the IGFS system can effectively extinguish full-scale 220 kV oil-immersed transformer fires, with a rapid fire control time and an extinguishing time of 262 s. Continuous foam supply for 10 min cooled the transformer oil temperature below 100 °C. The sprayed foam layer completely covered the fuel surface, and no re-ignition, candle burning, or flash fire occurred in the foam-covered fuel after extinguishment, with residual fuel remaining. The foam extinguishing agent used in the IGFS system is a 3% AFFF (aqueous film-forming foam) solution, classified as fire performance level IA, with an electrical conductivity of 1 100 μS/cm. Under the conditions of a foam solution flow rate of 1 747.8 L/min and a gas-to-liquid ratio of 6.5∶1.0, the measured expansion ratio was 8.5, and the 25% drainage time was 4.1 min, the spray pipe's range exceeded 7 m, and symmetrical spraying from both sides could cover a width of 14 m.

Key words: inert gas foam system, full-scale experiment, oil-immersed transformer, foam extinguishing agent