Numerical and experimental validation of variation of power transformers’ thermal time constants with load factor

Thermal time constants (TTC) of a thermal dynamic model reflect the change rate of temperature, which are affected by many factors such as load current, oil temperature, etc. In this study, relative thermal time constants (RTTC) are introduced and formulated to describe the variation of thermal time constants with load current. It is verified through extensive case studies based on computational fluid dynamic (CFD) simulation and field measurements. Specific for CFD simulation, the polyhedral meshing was applied to mesh division of 3D model due to narrow part such as discs in transformer. The proposed relative thermal time constants can be integrated with dynamic thermal model to estimate the hot-spot temperature of transformers, especially in overload situations. Accuracy and adequacy metrics are used to quantify the accuracy of presented thermal model with proven thermal model.