Development of Heat Transfer Correlations for Outer Surface of Transformer Bushing Porcelain Shell for Thermal Network Modeling

Abstract

Bushing is the critical component of the transformer, and accurate acquirement of its temperature distribution during operation is essential to ensure its safety. The thermal network model is a widely used method for temperature distribution calculation, which has the advantages of accuracy and efficiency, but requires accurate convection heat transfer coefficients as input conditions. However, the outer surface of the porcelain shell is a complex structure composed of multiple weather-sheds of different sizes, so there is currently no equation for its convection heat transfer coefficient calculation, which hinders the application of the thermal network model in transformer bushing. This paper proposed a set of novel Nusselt number correlations for the calculation of convection heat transfer intensity of the outer surface of bushing porcelain shell based on computational fluid dynamics and genetic programming, and the model validation was performed with an experimental setup. The temperature distribution results of the conducting rod obtained from the thermal network model are consistent with the experimental values, with an average relative error of 4.081% and a maximum relative error of 6.634%. This paper promotes the application of thermal network models in transformer bushing, providing a more efficient tool for its optimal design and lifespan evaluation. © 2025 Institute of Electrical Engineers of Japan and Wiley Periodicals LLC.