Research on the Effect of Initial Surface Temperature of Transformer Oil on Drainage Properties of Three Common Foam Extinguishing Agents

Foam extinguishing agents are widely used in large transformer fire extinguishing systems. A stability experiment platform based on the law of connected vessel was built to investigate the influence of transformer oil temperature on the stability of foam extinguishing agents. The drainage properties of aqueous film forming foam (AFF-F), fluorinated-protein foam (FP-F), and synthetic foam (S-F) on KI25X transformer oil at various temperatures were obtained. The drainage percentage and drainage rate with the various oil temperatures were investigated, and the drainage behavior of three kinds of foam extinguishing agents was compared. The resuts showed that the foam stability first increased and then decreased with the increase of oil surface temperature with a critical temperature of 60 ℃. This is due to that while the temperature is below 60 °C, the decrease in surface tension is the most important factor, and the Marangoni effect increases as the temperature rises. The dominance of high temperature caused the foam to be heated to fracture and the drainage rate to increase as the oil surface temperature further rises. The S-F has the longest longer drainage time on the surface of transformer oil at various temperatures and was less impacted by oil surface temperature, resulting in the best oil resistance and high temperature resistance. In comparison to the AFF-F and FP-F extinguishing agents, S-F has the best stability.