Abstract: A full-scale cable trench model is established to analyze the temperature distribution characteristics at the cable trench top, and combining with the development process of the coupling fire source, two fire extinguishing agents, including superfine dry powder and heptafluoropropane, are employed to analyze the extinguishing effect of the distance of the fire extinguisher-fire source and the fire extinguishing agent types. The study found that the ceiling temperature attenuation induced by the coupled fire source has an exponential relationship with the increasing distance; When the distance between fire extinguishers is large, the fire extinguisher will not reach the response temperature, leading to the fire extinguishing system failure; Both superfine dry powder and heptafluoropropane extinguishing have chemical inhibition, cooling and asphyxiation effects. Because heptafluoropropane has the process of liquid transforming into gas during the fire extinguishing, it has better cooling effect. At the same time, it can rapidly discharge the air in the cable trench at the spraying moment, enhancing the asphyxiation effect in the confined space, and finally extinguishs the fire successfully. The 220 kV large cross-section cable (16 cm in diameter) is used in this study, which leads to the more significant shielding effect of the upper large cross-section cable on the lower fire source, reduces the contact area between the superfine dry powder and the combustor surface, thereby weakens the fire extinguishing effect of the superfine dry powder, and ultimately leads to fire extinguishing failure.

Key words: cable trench, coupled fire source, temperature distribution, fire extinguishing technology