Affiliations: [a] State Key Laboratory of Electrical Insulation and Power Equipment, Xi'an Jiaotong University, Xi'an, Shaanxi, China | [b] Department of Electrical and Computer Engineering, The Ohio State University, Columbus, OH, USA | [c] Alstom Grid, Redmond, WA, USA
Correspondence:
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Corresponding author: Chenguang Yan, School of Electrical Engineering, Xi'an Jiaotong University, Xi'an 710048, Shaanxi, China. E-mail:chg.yan@stu.xjtu.edu.cn
Abstract: Being aware of the great hazard of transformer winding
deformation and insulation damage under the impact of huge electromagnetic
forces caused by short circuit faults, this paper presented an analysis
method based on explicit dynamic 3-D finite element method, enabling
detailed and representative investigations of the mechanical effects of
external short circuit faults in power transformers. Considering the
displacements and deformations of windings could change the leakage flux
distribution and further influence the remaining computation, an
electromagnetic-mechanical field coupling model was proposed. To accurately
calculate the windings transient deformation, both the disks and spacers
were considered as the elastic-plastic body. Meanwhile, the high-voltage and
low-voltage windings were modeled into 21 disks and 18 spacers are evenly
arranged between the adjacent copper disks. For illustrating the
effectiveness of the proposed method, a real full-scale 120 MVA/220 kV
oil-immersed transformer model was built to suffer the serious three-phase
short circuit fault as the case study. A comparison of the von-Mises stress
distribution in healthy, pre-strain and dislocation windings under the same
short circuit fault confirmed that the healthy winding can withstand the
impact of short circuit fault without any unrecoverable deformation;
insufficient mechanical strength, pre-strain and local dislocation
are the key factors to winding deformation, rupture even collapse. Additionally, the theoretical model and simulation method can
be used as a substitute for costly and cumbersome field tests in faults
characteristics analysis of transformer windings.
Keywords: Power transformer, short circuit fault, winding deformation, electromagnetic-mechanical field coupling, finite element method
