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Transformers, being the largest oil-bearing equipment, are susceptible to high-temperature hot oil fires and large-area flowing fires that can be challenging to extinguish. To investigate the effectiveness of compressed air foams (CAFs) agents in extinguishing fires in ultra-high voltage (UHV) converter transformers, this work examines the fire suppression capabilities of three typical CAFs agents. A test model of a hot oil fire in a transformer with a burning area of 1 m2 was constructed for this purpose. The fire test was conducted by heating the transformer oil using an electric heating system, and the test process was monitored using an unmanned aerial vehicle. The results indicate that three CAFs agents used in the tests are capable of extinguishing a 1 m2 transformer hot oil fire without causing boiling over phenomenon. 1% MJBP CAFs is the fastest with a fire extinguishing time of 168 s, and is even more efficient when the gas to liquid ratio is 9:1. CAFs have the advantage of uniformity and stability, making it suitable for extinguishing hot oil fires in extra high voltage transformers as it does not cause boiling fires during firefighting.

To have a deep understanding of influence of woodgrain orientation on the upward flame spread performance, a series of tests were conducted to obtain the profile of mass loss rate (MLR), flame spread rate (FSR), total burning duration (TBD), and the maximum flame characteristic length (MFL) by using a traditional flame spreading measurement facility. The woodgrain orientation of samples tested in the current work are horizontal (H), vertical (V), and slanting (S). During the tests, a series of six 2 cm-long 10 cm-wide wood chips were uniformly installed on a vertical sample holder. The distance of air-gap differed from 1.0 cm to 3.0 cm and the thickness of wood chips varied from 1 mm to 4 mm. It is found that flame spread over discrete solid fuels depends on the generation rate of pyrolysis gas and direction of gas-flow, which is highly differed by the woodgrain orientation with respect to the wooden chips. The charring rate of samples imposed a strong effect on the flame spread performance. The a-MLR of three kinds of woodgrain are ranked as V > S > H. The FSR are ranked in general as H > V > S. The thickness of the samples imposed a larger effect on the TBD comparing with wood grains orientation. The TBD are ranked as S > V > H. The results of MFL indicate that as the thickness of the sample increases, MFL of samples performed with the H woodgrain is reduced greatly. However, both S and V woodgrain show a small effect on the MFL. It hopes to provide a deep understanding of flame spreading performance over wooden structures.