Abstract: Based on literature review and analysis of accident data,the structural characteristics and accident conditions of UHV converter transformer were elaborated. By means of CFD numerical simulation, according to the oil states, boundary conditions and environmental conditions of typical accident conditions, the occurrence and development process of transformer fire in typical UHV converter station were studied based on 5 scenarios. The combustion form, heat release rate and temperature around fire source of typical transformer fire were analyzed. The influence of the temperature of the outer wall of the valve chamber on the valve chamber were obtained. The characteristics of slow temperature rise and low temperature in the early stage of fire should be considered during the design of the detachable Box- in roof. In order to create favorable conditions for the extinction of the converter fire source,the sealing of the valve hall and the Box- in noise reduction plate should not be damaged at fire, and the lower 3 rows of cooling fans should be closed actively to prevent air from flowing in. The front cooling fan hole of the converter should be completely closed to prevent air from entering when the valve hall plugging is damaged.

Key words: converter transformer, numerical simulation, UHV, fire