Thermal Field Analytical Modeling of Oil-Immersed Amorphous 3D Wound Core Transformer Based on Fluid–Solid Coupling

The hot-spot temperature in oil-immersed 3D wound core transformer has a significant impact on its performance. The complexity of the winding structure and the characteristics of oil flow increase the difficulty of temperature field analysis. To address this challenge, this study aims to propose a comprehensive thermal network model for oil-immersed 3D wound core transformers to accurately calculate the winding average temperature rise and local hot-spot temperature rise with high efficiency. First, based on the principle of constant thermal resistance, a detailed model of high- and low-voltage winding is calculated using 2D finite element simulation technology. An equivalent model is established to obtain the equivalent thermal conductivity. This model considers various variables, including wire diameter, external insulation dimensions, and the vertical and longitudinal spacing of the windings. Next, multiple types of thermal resistance are defined using the thermoelectric analogy method, and a global thermal network model of the oil-immersed 3D wound core transformer is constructed. Using the Gauss–Seidel method and relevant heat transfer theory, factors such as the flow of transformer cooling oil are taken into account, which allows for the calculation of the average temperature rise and local hot-spot temperature rise in the windings. This approach effectively reduces calculation time while ensuring accuracy. Finally, a 50 kVA oil-immersed amorphous alloy 3D wound core transformer is used as a case study, and temperature field experimental tests are conducted to verify the accuracy of the proposed analytical model.