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Multi-Physics Numerical Research in Oil-Immersed Three-Phase Transformer Under Load Unbalance

Author

Listed:
  • Guanxun Diao

    (State Grid Shanghai Municipal Electrical Power Company, Shanghai 200122, China)

  • Heli Ni

    (State Grid Shanghai Municipal Electrical Power Company, Shanghai 200122, China)

  • Wenrong Si

    (State Grid Shanghai Municipal Electrical Power Company, Shanghai 200122, China)

  • Yingjie Gu

    (MOE Key Laboratory of Thermo-Fluid Science and Engineering, Xi’an Jiaotong University, Xi’an 710049, China)

  • Jian Yang

    (MOE Key Laboratory of Thermo-Fluid Science and Engineering, Xi’an Jiaotong University, Xi’an 710049, China)

Abstract

Transformers are susceptible to the influences of complex power grid systems, which may induce three-phase unbalance in transformers, thereby threatening their safety and stable operation. To better understand multiphysics interactions within a transformer under a three-phase load unbalance, a coupled multiphysics model is established and validated for an oil-immersed transformer based on the finite element method. The electromagnetic characteristics, conjugate heat transfer, and thermal stress of the transformer under three-phase load unbalance are analyzed, and the impact on the transformer’s relative aging rate is further assessed. The results show that under three-phase load unbalance, winding losses are significantly influenced by the degree of unbalance, while core losses remain almost unaffected. The maximum difference in winding losses between phases can reach 9.6 times, with a total loss increase of approximately 17.31% at a 30% unbalance degree for Case 3. The mutual heating effect between adjacent windings intensifies with the degree of unbalance, leading to higher temperatures in low-loss windings and sustaining high thermal stress and expansion. Severe three-phase unbalance (e.g., 30% unbalance degree in Case 3) can be mitigated by reducing the transformer load rate to 90%, thereby reducing the relative aging rate to about 20% of that under full load and significantly extending the transformer’s insulation life.

Suggested Citation

  • Guanxun Diao & Heli Ni & Wenrong Si & Yingjie Gu & Jian Yang, 2025. "Multi-Physics Numerical Research in Oil-Immersed Three-Phase Transformer Under Load Unbalance," Energies, MDPI, vol. 18(5), pages 1-34, March.
    • Handle: RePEc:gam:jeners:v:18:y:2025:i:5:p:1217-:d:1603752
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    References listed on IDEAS

    as
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    3. Zikuo Dai & Kejian Shi & Yidong Zhu & Xinyu Zhang & Yanhong Luo, 2023. "Intelligent Prediction of Transformer Loss for Low Voltage Recovery in Distribution Network with Unbalanced Load," Energies, MDPI, vol. 16(11), pages 1-19, May.
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    5. Jia, Xiaoyu & Lin, Mei & Su, Shiwei & Wang, Qiuwang & Yang, Jian, 2022. "Numerical study on temperature rise and mechanical properties of winding in oil-immersed transformer," Energy, Elsevier, vol. 239(PA).
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