Simulation of transformer windings mechanical characteristics during the external short-circuit fault

With the development of voltage level and capacity in recent years, the impact of external short circuit has a growing threat to the stability of transformer windings than ever before. Because of the weakness of anti-short-circuit capacity, around 40% of the transformer faults are caused by the huge impact of short circuit every year. In view of this, it is of great significance to study the mechanical behavior of transformer winding structures during external short-circuit faults. This paper represents investigations of short-circuit current, the transient leakage magnetic field, electromagnetic forces and the von Mises stress of a real full-scale 500kV single-phase two windings transformer during the external short-circuit transient process. The worst case of short-circuit fault with three-phase short-circuit happening simultaneously has been simulated. A circuit model has been built up to get the short-circuit current. The 3D geometric model has been established based on real size parameters of the DFP334000/500kV single-phase two windings oil-immersed power transformer. The 3D finite-element method (FEM) has been employed to calculate the leakage magnetic fields excited by the short-circuit current. Henceforth, the electromagnetic forces acting on windings have been obtained and analyzed according to the short-circuit current and magnetic fields calculation results, and both axial and radial dynamical responses are considered and analyzed. The mechanical characteristics of the winding disks and the insulation structures have been calculated in this paper. The von Mises stress is the crucial factor to determine whether or not the transformer windings can withstand the impact of external short-circuit current, and its distribution has been simulated and analyzed.