Abstract: In order to explore the fire dynamics of different oil-immersed transformers subject to an external fire, a full-scale transformer fire test platform is constructed to conduct the fire tests on 10 kV natural ester vegetable oil and mineral oil immersed transformers, respectively. It is found that the mineral oil-immersed transformer can form violent jet fires as subjected to the fire for about 9 min, and the ejected mineral oil results in massive pool fires and spill fires, enlarging the burning area. In contrast, the combustion of natural ester vegetable oil immersed transformer is rather gentle. Although the jet fire phenomena also occur after subjected to the fire about 24 min, the combustion area is not markedly enlarged. Meanwhile, a large amount of vegetable oil can be observed in the vicinity of the transformer. During the test, the temperature rise rate of the vegetable oil is 0.18 ℃/s, much lower than that of mineral oil, 0.24 ℃/s, which further confirms the poor combustibility of the vegetable oil. Therefore, the vegetable oil immersed transformer is much safer than the mineral oil-immersed one from the perspective of fire safety, and exhibits a better application prospect.

Key words: transformer, RAPO natural ester vegetable oil, 25# mineral oil, fire test