Computation and analysis of power transformer winding damage due to short circuit fault based on 3-D finite element method

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.