CFD Analysis of Natural Oil Convection in Three Phase Transformers between Detailed and Simplified Winding Models

Accurate prediction of hot-spot temperature is essential for transformer thermal design, as it directly affects load management, performance, and service life. THNM and CFD models are widely used to study temperature distribution in windings. Although CFD offers detailed insights into natural oil convention, it is often complex, time-intensive, and computationally costly. To reduce this complexity, simplified 2D axis-symmetric CFD models are applied, especially for small distribution and medium power transformers. This study evaluates the effectiveness of SW compared to DW. Results indicate that SW is unsuitable for medium power transformers with disc windings due to significant deviations in oil flow velocity and thermal distribution. However, for small distribution transformers with layer windings, SW provides sufficiently accurate results. Overall, SW is recommended during early design stages of both transformer types, where minor variations in average winding temperature are acceptable.