Study on heterogeneous diffusion of fault gas in converter transformer driven by thermal-fluid coupled field and optimization of monitoring points layout

In the converter transformer, the thermal-fluid coupled field of the transformer oil drives the spatial diffusion of fault characteristic gases. Due to the unclear heterogeneous distribution of fault gases, existing oil chromatography monitoring scheme suffers from significant spatial deviations errors and monitoring blind spots. To elucidate the heterogeneous distribution of characteristic gases, a multi-physics computational fluid dynamics(CFD) model coupling oil flow, heat transfer, and gas diffusion was established. By integrating turbulence equation, energy equation, and component transport equation, the study innovatively employed energy decomposition and frozen flow field method to simulate the spatial diffusion of characteristic gas C₂H₂. Simulation results reveal that the transformer oil flow is governed by the coupled effects of forced oil circulation and thermal buoyancy. The oil flows out from the bottom duct, converges into distinct “upward flow columns” at the winding pillars, and diffuse along the tank cover, exhibiting pronounced spatial heterogeneity. Driven by the oil flow, the spatial diffusion of C 2 H 2 component also exhibits significant spatial heterogeneity. The dilution ratio of C 2 H 2 component between monitoring point and gas generation point range from 0.0143% to 0.353%, and its diffusion volume ratios for monitoring threshold value of 0.3 μL/L under four operational scenarios are 22.67%, 82.89%, 24.26%, and 23.24%, respectively. Based on the heterogeneous diffusion of C₂H₂ component, we designed three optimized monitoring points layouts for oil chromatography, whose trigger probability for threshold value 0.3 μL/L were improved from 42.5% of existing layout to 82.5%, 72.5% and 90% respectively. The study provided technical support for improving oil chromatography monitoring performance for the converter transformer.