Construction of a gas–liquid two-phase mass transfer model for fault-generated gas in converter transformers and analysis of gas diffusion distribution characteristics

Large oil-immersed transformers, due to their complex structure and high capacity, exhibit a significant time-delay effect when characteristic gases generated by internal faults diffuse to monitoring points. This delay is caused by the intricate gas–oil two-phase mass transfer process, severely impacting the diagnostic accuracy of dissolved gas analysis. To address this issue, this study focuses on a ±400 kV oil-immersed converter transformer. First, a coupled gas–liquid mass transfer model under fault-induced gas generation conditions was established, systematically analyzing the dynamic diffusion and distribution patterns of characteristic gases at different spatial locations. Subsequently, a fault simulation test platform for the converter transformer was constructed, and comparative tests verified the validity of the simulation model. The results demonstrate that the simulation and experimental data exhibit highly consistent trends, confirming that the proposed coupled gas–liquid flow and gas dissolution-transport model accurately characterizes the migration and diffusion behavior of characteristic gases inside the transformer. This model can predict the spatial distribution patterns of characteristic gases under actual operating conditions, providing a new theoretical foundation and technical support for the operational state assessment of oil-immersed transformers.