Improving thermal simulation accuracy of dry-type transformers using experimentally identified temperature-dependent epoxy properties

Hai Pham Hong; Tung Le Duc; Minh Tran Anh; Hai Pham Hong; Tung Le Duc; Minh Tran Anh

doi:10.3934/electreng.2026024

AIMS Electronics and Electrical Engineering

2026, Volume 10, Issue 4: 585-604. doi: 10.3934/electreng.2026024

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Improving thermal simulation accuracy of dry-type transformers using experimentally identified temperature-dependent epoxy properties

School of Electrical and Electronic Engineering, Hanoi University of Science and Technology, Hanoi, Vietnam

Received: 06 March 2026 Revised: 21 July 2026 Accepted: 20 August 2026 Published: 07 September 2026

This study presents an enhanced three-dimensional conjugate heat transfer (CHT) model designed to improve the thermal simulation accuracy of a 320 kVA, 22/0.4 kV cast-resin dry-type transformer (CRDT). While conventional thermal modeling commonly assumes constant thermophysical properties for epoxy encapsulation, this research dynamically incorporates temperature-dependent functions for thermal conductivity (λ) and specific heat capacity ($ {C}_{p} $). These parameters, previously identified through experimental measurements (ASTM D5334) on the specific 8055A/8055B epoxy system, are continuously updated at every solver iteration according to the local temperature field. By utilizing a one-way multiphysics coupling strategy, the non-uniform electromagnetic losses computed via ANSYS Maxwell are explicitly mapped as volumetric heat sources into the ANSYS Fluent CHT model. The proposed framework was rigorously validated against empirical data collected from 27 thermocouples installed on an actual industrial prototype operating under rated load conditions. The integration of temperature-dependent material properties significantly reduced the maximum relative prediction error from 10.9% (using conventional constant properties) to 4.59% along the axial profile of the high-voltage winding. Furthermore, the error margin remained below 5.1% across all 27 validated locations, successfully pinpointing the hotspot temperature of 75.0℃ at the upper section of the phase-B low-voltage winding. Given that the thermal aging of epoxy insulation accelerates exponentially with rising temperatures, this substantial improvement in prediction accuracy provides a highly credible foundation for estimating insulation service life and establishing safer, better-founded design margins for CRDTs.
- dry-type transformer,
- cast resin,
- epoxy resin,
- temperature-dependent properties,
- conjugate heat transfer,
- hotspot temperature,
- finite element method
Citation: Hai Pham Hong, Tung Le Duc, Minh Tran Anh. Improving thermal simulation accuracy of dry-type transformers using experimentally identified temperature-dependent epoxy properties[J]. AIMS Electronics and Electrical Engineering, 2026, 10(4): 585-604. doi: 10.3934/electreng.2026024

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Abstract

This study presents an enhanced three-dimensional conjugate heat transfer (CHT) model designed to improve the thermal simulation accuracy of a 320 kVA, 22/0.4 kV cast-resin dry-type transformer (CRDT). While conventional thermal modeling commonly assumes constant thermophysical properties for epoxy encapsulation, this research dynamically incorporates temperature-dependent functions for thermal conductivity (λ) and specific heat capacity ($ {C}_{p} $). These parameters, previously identified through experimental measurements (ASTM D5334) on the specific 8055A/8055B epoxy system, are continuously updated at every solver iteration according to the local temperature field. By utilizing a one-way multiphysics coupling strategy, the non-uniform electromagnetic losses computed via ANSYS Maxwell are explicitly mapped as volumetric heat sources into the ANSYS Fluent CHT model. The proposed framework was rigorously validated against empirical data collected from 27 thermocouples installed on an actual industrial prototype operating under rated load conditions. The integration of temperature-dependent material properties significantly reduced the maximum relative prediction error from 10.9% (using conventional constant properties) to 4.59% along the axial profile of the high-voltage winding. Furthermore, the error margin remained below 5.1% across all 27 validated locations, successfully pinpointing the hotspot temperature of 75.0℃ at the upper section of the phase-B low-voltage winding. Given that the thermal aging of epoxy insulation accelerates exponentially with rising temperatures, this substantial improvement in prediction accuracy provides a highly credible foundation for estimating insulation service life and establishing safer, better-founded design margins for CRDTs.

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