Dynamic Thermal Modelling for Core-Type High-Frequency Transformers Based on Air-Solid Surface Nusselt Number Calibration

Abstract

Quickly and accurately obtaining the internal temperature distribution of a transformer plays a key role in predicting its operating conditions and simplifying the maintenance process. A reasonable equivalent thermal circuit model is a relatively reliable method of obtaining the internal temperature distribution. However, thermal circuit models without targeted consideration of operating conditions and parameter corrections usually limit the accuracy of the results. This paper proposed a five-node transient thermal circuit model with the introduction of nonlinear thermal resistance, which considered the internal structure and winding layout of the core-type high-frequency transformer. The Nusselt number, a crucial variable in heat convection calculations and directly related to the accuracy of thermal resistance parameters, was calibrated on the basis of the distribution of external cooling air. After parameter calibration, the maximum computational error of the hotspot temperature is reduced by 5.48% compared with that of the uncalibrated model. Finally, an experimental platform for temperature monitoring was established to validate the five-node model and its ability to track the temperature change at each reference point after calibrating the Nusselt number.