Experimental Research and Theoretical Analysis on Flame Spreading Behaviors of Transformer Insulating Paperboard Under Different Inclined Angles

In recent years, with the development of DC transmission projects in China, the number of converter stations has increased. Fire accidents in converter stations have also become more frequent. Transformer insulating paperboard, as a typical combustible material in converter station equipment, poses a greater fire risk. So in this paper, flame spreading behaviors, including experimental visual characteristics, fire spreading rate, mass loss with time and mass loss rate, of transformer insulating paperboard with different thickness and different inclined angles are investigated. The results show that: (1) In downwards flame spread, that is, in the case of positive angle, the flame height and width gradually decrease with the increase of angle; in the case of negatively inclined angles, the flame length shows an increasing trend with the decrease of inclined angles, and the flame thickness gradually becomes thinner. (2) In upwards flame spread, that is, in the case of negative angle, the fire spreading rate of the insulating paperboard decreases sharply with the increase of the angle; In the case of a positively inclined angle, the change of flame spreading rate is not obvious with the increase of inclined angles as compared with the conditions in negative angles. The paperboard thickness also has a significant impact on the flame spreading rate, and the flame spreading rate will decrease significantly with the increase of paperboard thickness. (3) In upwards flame spread, the mass loss rate of insulating paperboard will decrease significantly with the increase of inclined angles; in downwards flame spread, the change of mass loss rate is not obvious with the increase of inclined angles as compared with those in condition of negative angles. At the same time, the mass loss rate will increase significantly with the increase of paperboard thickness. (4) The mass loss rate and fire spread rate of the insulating paperboard have a strong correlation with the flame length and the length of the pyrolysis zone. A heat transfer process model about characteristic length scale and mass loss rate is established. In order to simplify the model, a dimensionless relation about angle is defined to replace the feature length and to explore the relationship between angle and mass loss rate. Based on the inherent relationship between fire spread rate and mass loss rate, the relationship between fire spread rate and angle is found. And the result shows satisfactory agreement bet