Dynamic Analysis using FEM and SC-Withstand Test for Verification of Short Circuit Withstand Capability of a 600MVA, 405kV Auto-Transformer

IEC 60076-5 defines three methods for demonstrating short circuit withstand capability:

calculation based design verification, full scale short circuit testing, and design comparison with a reference transformer that has successfully passed a short circuit test. In this paper, a short circuit test was conducted on a single phase transformer to verify the short circuit withstand capability of a 600 MVA, 405 kV autotransformer. To reduce cost and time associated with retesting in the event of a short-circuit failure, the test was performed on a single phase unit having identical winding dimensions and a similar pressing structure to the full scale transformer, based on an agreement with the customer.

The electromagnetic forces acting on transformer windings during a short circuit are strongly influenced by winding arrangement and supporting structures. In the studied transformer, a regulating winding is located between the main windings to satisfy impedance and transport constraints. This regulating winding adopts a multi helical structure with a large pitch, making it susceptible to spiralling deformation. However, the conventional interpretation of spiralling failure based solely on radial force does not fully explain the observed deformation characteristics. To investigate this phenomenon, a three dimensional magnetic field–structure coupled analysis was performed. The influence of circumferential force on spiralling deformation was examined, and the stabilizing effect of axial clamping force was evaluated through axial dynamic response analysis using the finite element method.

Finally, the short circuit test was successfully completed in the presence of customer representatives, confirming the adequacy of the proposed design and manufacturing technology.