Flame Spread Over Inclined Pure and Oil‐Impregnated Insulating Paperboard

To explore the fire hazards of various components in the converter transformer, experiments on flame propagation characteristics of pure insulating paperboard (PIPB) and oil‐impregnated insulating paperboard (OIIPB) were conducted at different inclined angles. The experiments collected data on flame morphology, mass loss rate, flame spread rate, flame length, and pyrolysis length (two characteristic lengths) during the combustion process. The results indicate that when spreading downward, oil‐impregnated insulating paperboard exhibits increased flame length and pyrolysis area as compared to pure paperboard burning. Additionally, the flame length and pyrolysis area of oil‐impregnated insulating paperboard gradually increase with the inclined angle's increase. When spreading upward, the flame thickness and flame pyrosis length of oil‐impregnated paperboard significantly increase as compared to pure paperboard, and the flame produced by the superposition of two fuels is larger than that of a single fuel. Overall, the flame spread rate of oil‐impregnated insulating paperboard is slightly faster than that of pure paperboard. The mass loss rate of OIIPB is generally higher than that of PIPB, and it shows a different trend, roughly divided into three stages. The mass loss rate decreases rapidly primarily within the range of −20° to 20°. Empirical correlations are developed to relate the characteristic lengths to the inclination angle. These correlations are incorporated into a simplified heat‐transfer framework to describe the mass loss rate and flame spread rate within the tested conditions.