Thermal stress analysis of dry-type transformers under short-circuit conditions considering temperature-dependent epoxy properties

Abstract

Accurate prediction of temperature rise and hotspot formation is critical for the lifetime and safety of cast-resin dry-type transformers. Conventional thermal design methods typically assume constant thermophysical properties for epoxy insulation, neglecting their nonlinear temperature dependence - an oversimplification that can introduce significant errors under severe operating conditions such as short-circuit faults. This study applies a temperature-dependent thermal modeling approach to a 320 kVA, 22/0.4 kV amorphous-core dry-type transformer, employing coupled Finite Element Method (FEM) and Computational Fluid Dynamics (CFD) to simulate the three-dimensional transient temperature field with temperature-dependent thermal conductivity, diffusivity, and specific heat capacity of epoxy insulation. Results show that the high-voltage winding is the most thermally critical region under short-circuit conditions, and that incorporating temperature-dependent material properties yields higher predicted hotspot temperatures and stronger thermal stress concentration compared to conventional constant-property assumptions. These findings highlight the importance of temperature-dependent modeling in transformer thermal design and provide a more reliable basis for structural optimization and safety assessment.