Temperature Rise Test and Thermal-Fluid Coupling Simulation of an Oil-Immersed Autotransformer Under DC Bias

Mingyang Li,Ruijuan Tan,Zezhong Wang,Zhengze Ni,Junshuang Zhang

doi:10.1109/access.2021.3060632

Abstract

Loss and temperature increase due to DC bias occurring in power transformers may lead to damage and reduced lifespan. To study the influence of different levels of DC bias on the temperature rise in transformer structural components, 0, 8, and 16 A DC were introduced into the MV side of a test transformer. A 2D axisymmetric finite element model was also established to calculate and analyze the distribution of winding loss under DC bias. Combined with the 3D field-circuit coupling model, the core loss under DC bias was calculated on the basis of the half-wave average algorithm. The eddy loss of the steel structure was also obtained using a 3D field-circuit coupling model. On the basis of the thermal-fluid coupling model, the transient temperature changes of typical points were simulated. Results showed that the calculation error of loss and temperature are small when the DC current is 0 A. Moreover, the error of loss and temperature increases when the DC current is 8 or 16 A. The methods used in this study lay the foundation for subsequent research on the temperature rise of large-capacity power transformers under DC bias, especially for the single phase transformers with ONAN cooling mode.

Highlights

Geomagnetic storms, unipolar asymmetric operation of high voltage direct current (HVDC) transmission projects, and nonlinear power electronic components in the power grid will lead to the flow of DC through the transformer in the power grid, which will cause the DC bias of the transformer
After DC bias, half-wave saturation occurs in the core, and magnetic flux leakage and structural loss increase, which can lead to local hotspots on the structure
For special cases, such as DC bias, the core model in the finite element method (FEM) model has an influence on the magnetic field distribution in the winding area, and more accurate results can be obtained by using the FEM method

Summary

INTRODUCTION

Geomagnetic storms, unipolar asymmetric operation of high voltage direct current (HVDC) transmission projects, and nonlinear power electronic components in the power grid will lead to the flow of DC through the transformer in the power grid, which will cause the DC bias of the transformer. In the area seriously affected by magnetic leakage, non-magnetic materials or electromagnetic shielding is used to reduce local loss, and a large margin is reserved in the temperature design to ensure safe and stable operation of the transformer under abnormal conditions such as DC bias. For special cases, such as DC bias, the core model in the FEM model has an influence on the magnetic field distribution in the winding area, and more accurate results can be obtained by using the FEM method. For calculating hotspot temperature of structural parts under normal operation of transformers, magnetic-thermalfluid-coupling method[8,9,10] or heat dissipation coefficient[11] is used. The calculation model of loss and temperature rise of the test transformer was established, and the correctness of the calculation model was verified by comparison with the test results

TEST PLATFORM

SIMULATION AND ANALYSIS OF TEMPERATURE DISTRIBUTION UNDER DC BIAS

OF RESULTS

CONCLUSION