Can transformer oil burn?

Of course.
We can see many cases of oil-immersed power transformers catching fire. Mineral oil is the most common transformer oil. Its density is smaller than water, about 890 kg/m3. The boiling point is about 220℃, not easy to volatilize, and the closed cup flash point is higher than 135℃. Referring to the flammable material standard value of 60°C, transformer oil is combustible, but not flammable or explosive.

Transformer oil is a mixture of hydrocarbons of different molecular weights. During operation, under the action of high temperature, electric field and arc, the C-H and C-C bonds in these compounds are broken, producing hydrogen and hydrocarbon gases such as methane, ethane, ethylene and acetylene. At the same time, the decomposition of solid insulation will also produce carbon monoxide.

These are basically flammable and explosive gases. This provides a prerequisite for the combustion of transformer oil.

Under normal circumstances, even if the content of this flammable gas inside the transformer is high, it will not cause combustion. Because there is basically no air inside the transformer, and the temperature is usually not high enough.
Transformer oil burning is generally accompanied by internal faults in the transformer. Under the action of fault arc, the transformer oil decomposes, and the combustible gas inside the transformer increases sharply. The pressure may destroy the seal of the transformer body (pressure release or structural damage of the transformer body), and a mixture of transformer oil, flammable gas and other materials will eject. If the temperature conditions are right, transformer oil will begin to burn. For example, there is a saying that the process of gas ejecting out of the transformer at high speed may itself cause high temperatures.
The high temperature when the transformer oil burns will continue to cause the decomposition of the transformer oil and replenish flammable gas, causing the combustion to continue or even intensify. And may cause the transformer oil remaining in the transformer body to continue to decompose and deflagrate.

Once transformer oil burns, it is difficult to effectively extinguish the flame. It often burns for a long time. Large power transformers may even burn for more than 10 hours, causing devastating losses to the transformer and even affecting other equipment.

Therefore, large oil-immersed power transformers must be equipped with fire-fighting measures such as nitrogen-filled and oil-draining fire extinguishing devices to limit the development of fires.