Abstract: The UHV (Ultra High Voltage) transformer has a high risk of fire and explosion due to its large volume, large amount of oil and high voltage. In this paper, the explosion accident of an UHV transformer is analyzed. According to the fact that the site of the accident is located in the HV casing, a fullsize UHV transformer model is established by FLACS to simulate the two working conditions of the HV casing leaking first and exploding and the casing exploding first and causing a secondary explosion. Through the study, it is found that under the condition of first leakage and then explosion, there is a big difference between the simulated explosion pressure and the explosion pressure estimated according to the accident monitoring, which can be eliminated from the cause. As for the internal explosion of the transformer bushing causes a secondary explosion, the simulated internal explosion pressure and the flame shape of the secondary explosion are in good agreement with the accident monitoring, indicating that the high probability of the accident is the direct explosion inside the bushing. According to the above process, the simulated method can be used to reconstruct the transformer explosion accident scene, which provides reference for accident investigation.

Key words: explosion of transformer bushing, FLACS simulation, flame shape, explosion pressure